Mechanical and chemical recycling of solid plastic waste

Abstract

This review presents a comprehensive description of the current pathways for recycling of polymers, via both mechanical and chemical recycling. The principles of these recycling pathways are framed against current-day industrial reality, by discussing predominant industrial technologies, design strategies and recycling examples of specific waste streams. Starting with an overview on types of solid plastic waste (SPW) and their origins, the manuscript continues with a discussion on the different valorisation options for SPW. The section on mechanical recycling contains an overview of current sorting technologies, specific challenges for mechanical recycling such as thermo-mechanical or lifetime degradation and the immiscibility of polymer blends. It also includes some industrial examples such as polyethylene terephthalate (PET) recycling, and SPW from post-consumer packaging, end-of-life vehicles or electr(on)ic devices. A separate section is dedicated to the relationship between design and recycling, emphasizing the role of concepts such as Design from Recycling. The section on chemical recycling collects a state-of-the-art on techniques such as chemolysis, pyrolysis, fluid catalytic cracking, hydrogen techniques and gasification. Additionally, this review discusses the main challenges (and some potential remedies) to these recycling strategies and ground them in the relevant polymer science, thus providing an academic angle as well as an applied one.

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Mechanical!and!Chemical!Recycling!of!Solid!Plastic!Waste"
Kim"Ragaert*1,"Laurens"Delva1,"Kevin"van"Geem2""
"
1"Center" for" Polymer" &" Material" Technologies," Department" of" Materials," Textiles" and"
Chemical" Engineering," Faculty" of" Engineering" &" Architecture," Ghent" University,"
Technologiepark"915,"B-9052"Zwijnaarde,"Belgium"
2"Laboratory"for"Chemical"Technology,"Department"of"Materials,"Textiles"and"Chemical"
Engineering,"Faculty"of"Engineering"&"Architecture,"Ghent"University,"Technologiepark"
914,"B-9052"Zwijnaarde,"Belgium"
"
!
*"corresponding"author:"
"
Kim.Ragaert@ugent.be"
+32"(0)9"3310392"
Tech"Lane"Ghent"Science"Park"–"Campus"A,"Technologiepark"915,"B-9052"Zwijnaarde,"
Belgium""
"
Co-authors"e-mail:"
Laurens.delva@ugent.be"
Kevin.VanGeem@ugent.be"
! !

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"
Abstract!!
This"review"presents"a"comprehensive"description"of"the"current"pathways"for"recycling"
of" polymers," via" both" mechanical" and" chemical" recycling." The" principles" of" these"
recycling" pathways" are" framed" against" current-day" industrial" reality," by" discussing"
predominant" industrial" technologies," design" strategies" and" recycling" examples" of"
specific"waste"streams."Starting"with"an"overview"on"types"of"solid"plastic"waste"(SPW)"
and" their" origins," the" manuscript" continues" with" a" discussion" on" the" different"
valorisation"options"for"SPW."The"section"on"mechanical"recycling"contains"an"overview"
of" current"sorting" technologies," specific" challenges" for" mechanical" recycling" such" as"
thermo-mechanical"or"lifetime" degradation" and" the"immiscibility"of" polymer" blends." It"
also" includes" some" industrial" examples" such" as" polyethylene" terephthalate" (PET)"
recycling," and" SPW" from" post-consumer" packaging," end-of-life" vehicles" or" electr(on)ic"
devices." A" separate" section" is" dedicated" to" the" relationship" between" design" and"
recycling,"emphasizing"the"role"of" concepts" such"as"Design"from"Recycling."The"section"
on" chemical" recycling" collects" a" state-of-the-art" on" techniques" such" as" chemolysis,"
pyrolysis," fluid" catalytic" cracking," hydrogen" techniques" and" gasification." Additionally,"
this" review" discusses" the" main" challenges" (and" some" potential" remedies)" to" these"
recycling"strategies"and"ground"them"in"the"relevant"polymer"science,"thus"providing"an"
academic"angle"as"well"as"an"applied"one.""
"
Mechanical"recycling,"chemical"recycling,"polymers,"solid"plastic"waste"
!
! !

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1. Introduction!
1.1. The!lifecycle!of!polymers!
The"lifecycle"of"polymer"materials"can"be"described"by" the"scheme"in"Figure"1:"raw"
materials"–"be"they"virgin"or"recycled"–"are"transformed"into"products"via"the"various"
converting" techniques" (injection" moulding," extrusion," etc.)." This" is" the" start-of-life"
phase"for"the"(consumer)"product."During"the"manufacturing"process,"a"first"type"of"
solid" plastic" waste" (SPW)"is" generated:"post-industrial" (PI)" waste," which" never"
makes"it"to"the"consumer."This"could"include"runners"from"injection"moulding,"waste"
from"production"changeovers,"fall-out"products,"cuttings"and"trimmings."Typically"PI"
waste"has"the"distinct"advantages"that"it"is"clean"and"the"composition"of"the"polymer"
is" known"(Ignatyev" et" al.," 2014)." Quite" often," these" waste" streams" are" also" mono-
streams,"meaning"they"are"uncontaminated"by" other" polymers" or" non-polymers." In"
terms"of"recycling,"these"are"often"the"higher-quality"grades"of"polymer"waste.""
"
"
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&',/<'&-!/&! .278+#..5!=,/74!28203'8!+&/1!>?.243#,4@%&/0'!'3!2.5:!AB(CD5!
At" end-of-life," the" product" is" disposed" and" becomes" post-consumer" (PC)" waste."
Depending"on"the"country,"PC"plastic"waste"is"collected"separately"or"not."If"it"is,"the"
different"regional"collection"schemes"vary"from"very"strict"(such"as"the"PMD1"scheme"
in"Belgium)"to" very" open" (such"as"the" orange" bags" allowing" all"packaging"waste" in"
the"Netherlands)."Typically,"PC"plastic"waste"consists"of"mixed" plastics" of" unknown"
composition" and" is" potentially" contaminated" by" organic" fractions" (such" as" food"
remains)" or" non-polymer" inorganic" fractions" (such" as" paper)"(Hubo" et" al.," 2014),"
which"makes"it"a"more"complex"stream"to"recycle"than"PI"waste.""
From"an"environmental"point"of"view,"it"remains"preferable"to"avoid"the"creation"of"
SPW" altogether," by" avoiding" production" in" the" first" place" (smarter" packaging,"
alternative" materials)" or" promoting" re-use" of" plastics" products," both" of" which" are"
""""""""""""""""""""""""""""""""""""""""""""""""""""""""
1"PMD" =" Plastics" (bottles" and" fluid" containers)," Metals" (cans)" and" ‘Drinkkarton’"
(TetraPak)"

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strongly" related" to" raising" the" awareness"of" the" consumer" (EuropeanCommision,"
2013)."Such"efforts"run"parallel"to"those"on"effective"and"efficient"valorisation"of"the"
large"amounts"of"SPW"that"inevitably"continue"to"come"into"existence."
Once"it"does,"the"further"processing"options"are"similar"for"both"PI"and"PC"waste."The"
preferred"option," which" in" fact"closes" the" loop"back" to" the" –"now" secondary"–"raw"
materials,"is"recycling."In"recycling,"new"raw"materials"are"obtained"via"a"mechanical"
(typically"leading"to"regranulate)"or"chemical"(typically"leading"to"monomer"building"
blocks)" pathway." If" polymer" waste" cannot" be" recycled," energy" recovery" is" the"
preferred"option."Landfill,"the"least-preferred"option,"should"be"avoided"at"all"cost.""
"
"
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1.2. Material/Product-to-waste:!Polymer!waste!in!the!EU!
Even"within" the" two" broad" categories" of" PI"and" PC" plastic" waste," large"differences"
can" occur," based" on" the" source" of" the" waste," or" (for" PC" waste)" the" locally"
implemented"collection"schemes."Figure"2"presents"an"(non-restrictive)"overview"of"
the"different"possible"origins"of"plastic"waste,"with"examples"and"their"typical"further"
use."Some" important" properties" will"strongly" affect" the" degree"to"which" this" waste"
can"be"effectively"recycled."These"include:"
• Is" the" waste" a" mono-plastic" (only" one" component)" or" a" mixed" plastic?" As"
discussed"further"in"this"review,"reprocessing"of"mixed"polymer"waste"poses"
quite"a"few"challenges."Therefore,"mono-streams"are"always"preferred.""
• Is" the" plastic" clean" or" contaminated" with" inorganic" components," (small"
fractions"of)" other" polymers" or"organic" waste?" In" other"words:" are" washing"
and"purifying"steps"required?"
• Are" the" composing" polymers" and" their" respective" ratios" in" the" mix" known?"
This" is" always" the" case" for" mono-streams," but" can" also" occur" for" mixed"
streams." It" is" an" advantage" to" know" the" (pro" rata)" composition" of" a" mixed"
plastic"waste."Sadly,"for"mixed"PC"waste,"this"is"seldom"the"case"and"‘average"
bulk"compositions’"are"used"as"a"rule-of-thumb"instead.""
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"#$%&'!A)!E&#$#74!/+!F?G5!!
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Quantitative"information"about"PI"plastic"waste"is"not"publicly"available,"as"this"often"
remains"in-company"or"is"handled"business-to-business."PC"waste,"on"the"other"hand,"
is"handled"by"municipalities"and"well"tracked"throughout"Europe."
On" average," 25" million" tonnes" of" PC" plastic" waste" (PlasticsEurope" et" al.," 2015)"is"
generated"in"Europe"per"year."In"2014,"29.7%"of"this"was"effectively"recycled,"39.5%"
was"sent"to"energy"recovery"and"the"remaining"amount"of"30.8%"was"landfilled."Over"
the"past"decade,"recycling"and"energy"recovery"rates"have"steadily"increased,"which"
has"significantly"reduced"landfilling."This"evolution"is"shown"in"Figure"3.""
"
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"#$%&'!H)!@</.%3#/7!/+!.278+#..#7$!:!&',/<'&-!278!&',-,.#7$!/+!F?G!#7!@I!>?.243#,4@%&/0'!'3!2.5:!AB(CD5!
"
Landfilling"rates"are"very"uneven"across"Europe."In"countries"where"landfill"bans"are"
in" effect" (Belgium," Luxembourg," Netherlands," Germany," Denmark," Switzerland,"
Austria,"Norway"and"Sweden),"less"than"10%"of"plastic"waste"is"landfilled."In"other"

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countries,"such"as"Spain"and"Greece," a" staggering"amount"of"over"50%"of"all"plastic"
waste"still"finds"its"way"to"landfill"(PlasticsEurope"et"al.,"2015).""
"
Considering" the" types" of" polymer" that" make" up" the" bulk" of" the" collected" plastic"
waste," a" fair" idea" can" be" obtained" by" looking" at" the" plastics" demand" for" new"
products." This" is" shown" in" Figure" 4," which" includes" the" dominant" polymers" listed"
with" their" respective" shares" in" those" sectors" that" use" the" most" plastics" in" their"
products"(PlasticsEurope"et"al.,"2015).""
"
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"#$%&'!J)!?.243#,4!8'1278!0'&!4',3/&!278!0'&!0/.-1'&!3-0'!>?.243#,4@%&/0'!'3!2.5:!AB(CD5!
By" far" the" largest" share" of" all" PC" plastic" waste" is" packaging" waste." Packaging"
products"are"ubiquitous"and"tend"to"have"short"life"times,"especially"when"compared"
to"other"sectors"such"as"building"&"construction,"automotive"and"consumer"products"
such"as"toys,"which" typically"have"a"longer"lifetime."With"the"exception"of"polyvinyl"
chloride"(PVC),"all"of"the"other"‘big"five’"polymers"(high"density"polyethylene"(HDPE),"
low" density" polyethylene" (LDPE)," polypropylene" (PP)" and"polyethylene" tereftalate"
(PET))" have" their" most" sizeable" application" shares" within" packaging," so" these" will"
also"dominate"the"composition"of"plastic"waste.""
"
Circular" economy" and" reduction" of" (plastic)" waste" are" high" priorities" for" the"
European"Union,"resulting"in"ever"stricter"legislation"such"as"complete"landfill"bans,"
extended" producer" responsibility" (EPR)"and" specific" recycling" targets"
(EuropeanCommision," 2013)." In" the" latest" Circular" Economy" Package" (CEP)"
(EuropeanCommission,"2015),"released"December"2015,"the"European"Commission"
announces" that" it" has" ‘developed" and" will" propose" shortly" to" Member" States"
127823/&-"product"design"and"marking"requirements"to"make"it"easier"and"safer"to"
dismantle," reuse" and" recycle" electronic" displays’." The" new" CEP" also" includes" an"
announcement"of"the"revisal"of"the"Proposal"on"Waste,"meant"to"promote"industrial"
symbiosis"(waste" or" by-products" of" one" industry" become"inputs" for" another)." This"
revision"will" include" (the" approach" of)" landfill" bans," higher" recycling" targets" –"

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specifically" for" packaging" industry" –" and" more" (or" fiercer)" EPR" schemes"
(EuropeanCommission," 2015;" World" Economic" Forum" et" al.," 2016). In" many" EU"
member" states," public" procurement" (representing" 20%" of" the" EU’s" GDP)" will" (or"
already" does)" include" an" important" ‘green’" aspect," e.g." the" amount" of" recycled"
content"in"purchased"products."
Additionally," the" market" in" itself" can" be" an" excellent" driver" for" more" recycling" as"
well." In"their" recently" released" report‚" ’the" new" plastics" economy" –" rethinking" the"
future" of" plastics’" (World" Economic" Forum" et" al.," 2016)," the" Ellen" MacArthur"
Foundation" proposes" the" creation" of" an" effective" after-use" plastics" economy" as" a"
main" strategy" to" promote" increased" recycling" rates" of" (packaging)" polymers." They"
argue" that" by" creating" this" market," more" materials" will" be" captured," resource"
productivity" will" increase" and" an" economical" incentive" will" be" provided" to" avoid"
‘leakage’"of"PC"plastics"into"the" environment."Additionally,"increased"recycling"rates"
will" contribute" to" the" decoupling" of" the" plastics" industry" from" fossil" feedstock."
Recent"studies"indicate"that"in"Europe"alone,"over"50%"of"plastic"packaging"could"be"
recycled"eco-efficiently"with"today’s"available"technologies"(Denkstatt,"2015).
"
1.3. Waste-to-material:!Pathways!for!the!recycling!of!polymers!
The"most"common"method"for"the"recycling"of"plastic"waste"is"mechanical!recycling"
(Al-Salem"et"al.," 2009c)." This" process" typically"includes"collection," sorting," washing"
and"grinding"of"the"material."Steps"may"occur"in"a"different"order,"multiple"times"or"
not"at"all,"depending"on"the"origins"and"composition"of"the"waste.""
Some"examples"from"Figure"2"include:"
• Runners" from" injection" moulding:" this" is" clean" PI" waste" of" a" well-known"
composition."It"does"not"require"collection"(can"be"re-used"in"same"company),"
sorting"(it"is"a"mono-stream)"or"washing"(the"material"is"clean);"
• PC" mixed" plastics" packaging" waste:" the" broadest" allowance" of" PC" plastics"
waste," this" stream" requires" collecting" (from" the" consumer)," sorting" (for"
example" select" out" the" PET" bottles)," washing" (removal" of" food" and" paper"
contaminants)"and"then"grinding,"often"followed"by"regranulation;"
Alternatively,"the"reuse" of" SPW"in" the" construction"industry"can" be" considered" for"the"
disposal"of"plastic"waste."The"recycled"plastics"are"used"to"substitute"virgin"construction"
materials"in"mortars"and"concrete"(Gu"and"Ozbakkaloglu,"2016;"Safi"et"al.,"2013;"Sharma"
and"Bansal,"2016;"Siddique"et"al.,"2008)."
Although"a"broad"variation"in"recycling"and"recovery"rate"of"waste"plastics"exists"within"
Europe," almost" 8" Mt"of" plastics" waste" were" still" landfilled" in" Europe" in" 2014"
(PlasticsEurope," 2015)." This" amount" of" plastics" corresponds" to" almost" 100" million"
barrels" of" oil"(PlasticsEurope," 2015)." Worldwide," the" amount" of" plastics" ending" up" in"
landfill"is"almost" half" of" the"produced" amount," being" 150"Mt"annually." This" amount" of"
plastics"is"quite"considerable;"hence"it"has"high"potential"to"be"used"as"feedstock"for"the"
production"of"valuable"products"or"to"be"used"for"energy!recovery."The"latter"being"less"

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favourable" from" an" environmental" point" of" view," the" energy" content" of" plastic" is"
nonetheless"comparable"with"heating"oil"(Kumar"et"al.,"2011),"respectively"42.6"MJ/l"and"
443.5"MJ/kg."Hence,"a"cheap"source"of"energy"can"be"found"in"using"them"as"secondary"
fuel."However,"incineration"of"plastics"introduces"the"need"of"advanced"pollution"control"
measures,"highly"regulated"by"the"EU"Hazardous"Waste"Incineration"Directive"(Brems"et"
al.,"2012)."Energy"recovery"of"plastic"waste"yields"toxic"and"noxious"dioxins"that"should"
be" carefully" monitored." Processing" difficulties" such" as" those" caused" by" the" use" of"
coatings"and"paints" complicate"the"process"of"mechanical"recycling."Also,"contaminants"
can"be"not"completely"soluble"and"can"induce"phase"separation,"with"a"negative"impact"
on"the"mechanical"properties"(Al-Salem"et"al.,"2009a)"as"a"result." This" makes" retaining"
high"product"quality"very"tough."Furthermore"the"market"of"recycled"products"is"limited"
and"the" price" is" subjected" to"high" fluctuations" (as" shown" in" Figure" 5),"because" of" this"
establishing"a"profitable"process"is"not"straightforward.""
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All" these" drawbacks" have" led" to" the" growing" interest" in" a" less" frequent" use" type" of"
recycling,"namely"chemical! recycling"(Angyal"et"al.,"2007;"Garforth"et"al.,"2004;"Kumar"
et"al.,"2011;"Okuwaki,"2004)."This"type"of"recycling"has"high"potential"for"heterogeneous"
and" contaminated" plastic" waste" material" if" separation" is" neither" economical" nor"
completely" technically" feasible." It" is" based" on" converting" the" polymers" into" smaller"
molecules," which" can" be" subsequently" be" seen" as" sustainable" as" it" also" reduces" the"
amount"of"chemicals"used"for"the"production"of"fuels"and"virgin"plastics"(Al-Salem"et"al.,"
2009a;"Garforth"et"al.,"2004;"Kaminsky"et"al.,"2004;"Lin"and"Yang,"2009;"Okuwaki,"2004;"
Scheirs" and" Kaminsky," 2006)." Recycling" plastics" is" important" to" conserve" natural"
resources"and"protect"the"environment,"as"this"type"of"recycling"can"reduce"the"amount"
of"fossil"fuels"needed"to"produce"commodity"plastics." Chemical" recycling" routes"can"be"

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roughly"divided"into"thermochemical"and" catalytic" conversion"processes."These"will"be"
discussed"more"extensively"in"one"of"the"following"sections.""
"
An" overview" of" the" different" pathways" for" recycling" is" shown" in" Figure" 6," including"
where"their"respective"end"products"re-enter"the"lifecycle"of"plastics."
"
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278!P2&.44/7:!ABBLD5!
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1.4. Material-to-product:!from!closed!to!open!loop!!
Within" circular" economy" thinking," the" recycling" of" materials" is" often" categorized"
based"on"the"product"which"is"manufactured"from"the"secondary"raw"materials:"
• In"closed-loop! recycling,"the"recycled"plastics"are"used"to"produce"the"same"
product"they"were"originally"recovered"from." The" new" product"can"be"made"
up" entirely" of" recycled" plastics," or" a" mixture" of" the" recycled" plastic" can" be"
made" with" its" virgin" counterpart." This" form" of" dilution" ensures" that" the"
product"can"continue"to"be"recycled" and" its" recovered"material"added"at"the"
same" rate." This" is" common" practice" for" many" PET" packaging" products," for"
example;"
• In"open-loop!recycling,"the"recycled"plastics"are"used"for"a"different"product"
than"the"one"they"were"originally" recovered" from." This"does" not" necessarily"
imply" that" the" new" application" is" of" lower" ‘value’." Examples" include"
manufacture" of" textile" fibres" from" bottle-PET" or" printer" components" from"
water"bottle"polycarbonate"(Kunststofindustrie,"2015)."
"
These"two"terms"are"essentially"neutral,"as"they"make"an"objective"division"based"on"
the"newly"manufactured"product."Therefore,"they" should" be"preferred"to"subjective"
labels" such" as" ‘up-cycling’" and" ‘down-cycling’," which" immediately" imply" an"
appreciation" of" the" added" value" of" the" recycling" process." It" is" a" known" pitfall" for"

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those"outside"of"plastics"converting"industry"to"consider"open-loop"recycling"as"some"
form"of"cascading"into"ever"lower-valued"applications.""
"
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2."Mechanical!Recycling!
2.1!Steps!in!the!mechanical!recycling!process!
Prior"to"the"actual"reprocessing"of"recycled"materials"into"new"products,"the"conversion"
from" waste" to" new" raw" materials" needs" to" occur." This" phase" is" generally" termed" the"
‘End-of-Waste’"and"begins"after"the"collection"step."For"SPW,"this"process"can"include"the"
following"steps,"each"of"which"can"occur"anywhere"between"not"at"all"and"multiple"times"
throughout"the"sequence:"
• Separation"and"sorting:"this"occurs"based"on"shape,"density,"size,"colour"or"
chemical"composition;"
• Baling:"if"the"plastic"is"not"processed"where"it"is"sorted,"it"is"often"baled"in"
between"for"transport"purposes;"
• Washing:"removal"of"(often"organic)"contaminants;"
• Grinding:"size"reduction"from"products"to"flakes;"
• Compounding"&"pelletizing:"optional"reprocessing"of"the"flakes"into"a"granulate,"
which"is"easier"to"use"for"converters"than"flakes."
"
PI"waste"tends"to"be"better"separated"in"advance"according"to"composition,"so"sorting"is"
applied"to"PC"waste"much"more"often"than"to"PI"waste."The"same"goes"for"washing,"as"PC"
waste"is"usually"more"contaminated.""
"
Some" of" the" most" common" sorting" and" washing" techniques" will" be" discussed" by"
following"the"flow"of"two"different"plastic"waste"streams"from"Figure"2:"
i. PMD"(BE):"A"curbside"collected"mix"with"limited"allowance"
ii. All"plastics"packaging"waste"bag"(DE"or"NL):"A"curbside"collected"mix"with"broad"
allowance"
"
"
2.1.1$Example$of$industrial$sorting:$PMD$
"
PMD"is" a" separate" collection" scheme" in" Belgium"for" ‘Plastics," Metalen" en" Drinkkarton’"
(plastics,"metals"and"carton"drink"packages)."This"selected"packaging"waste"is"collected"
curbside" by" municipalities" in" a" separate" waste" bag," for" which" the" collection" is" made"
cheaper" to" the" citizen" than" household" waste." The" bag" allows" for" all" ‘solid" bottle’"
packaging"waste"(water,"lemonades,"milk,"soap"and"detergent"bottles),"metal"cans"(drink"
cans,"canned"goods"and"cosmetics"such"as"deodorants)"and"carton"drink"packaging."For"
the"plastics"fraction"this"results"in"a"majority"of"PET,"followed"by"HDPE"and"a"minority"of"
PP"(mostly"caps)."LDPE"is"included"by"ways"of"the"attached"labels.""

11"
"
The" collected" bags" are" delivered" to" sorting" facilities," which" sort" out" the" different"
materials."For"the"plastics,"this"is"into"baled"PET"(clear,"blue"and"green),"HDPE"and"a"rest"
fraction."Optionally,"the"PP"fraction"can"be"sorted"out"as"well."A"schematic"of"the"sorting"
process"is"shown"in"Figure"7.""
"
"&/1!?Q6!3/!>1#R'8D!0.243#,4!/7.-!
The"(LDPE)"bags"are"cut"open"in"an"automated"sack"opener"and"then" the" contents" are"
passed" through" a" progressive$ rotating$ sieve!(=" sorting" by" size)." Both" really" small"
(bottle"caps)"and"overly"large"objects" (the"bags"themselves)"are"removed"and"go" to"the"
residue"fraction.""
A"medium"(40-120"mm)"and"large"(120-220"mm)"fraction"continues,"with"an"extra"wind$
sifter"in" place" to" ensure" that" loose" paper" etiquettes" and" plastic" bags" are" blown" out."
Plastic"bags"are"not"formally"allowed"in"the"PMD"bag,"but"often"end"up"in"there"anyway,"
due" to" bad" sorting" at" the" level" of" the" consumer." Next," the" mixed" waste" passes" an"
overhead"magnet"for"the"removal"of"ferrous"metals,"an"optical"sorter"for"the"removal"of"
the"carton"and"an"eddy$current"for"the"removal"of"non-ferrous"metals,"which" is"mostly"
aluminium." The" large" fraction" passes" another" ballistic$ separator," which" removes" all"
‘soft’"plastics,"meaning"the"foils."Only"the"‘hard’"plastics,"the"bottles"themselves,"remain."
"
"
"#$%&'!S)!F/&3#7$!/+!?Q6!;243'!>,/%&3'4-!/+!=782<'&:!T@D5!!
"
"&/1!1#R'8!0.243#,4!3/!4/&3'8!0.243#,4!
The"remaining" mixed" plastics" are" separated," first" by" FT-NIR" (Fourier" Transform" Near"
Infrared)"into"PET"and"HDPE." Optical! colour! recognition"sorters" divide" the" PET"into"
clear," blue" and" green." Finally," all" these" sorted" streams" pass" through" a" sorting" cabin,"

12"
"
where" trained" operators" check" for" false" positives" or" negatives" and" correct" any"
automated" mistakes" by" manual! sorting." After" this" final" sorting" step," the" separated"
HDPE,"blue"PET,"green"PET"and"clear"PET"are"baled"for"transport"off-site.""
"
FT-NIR"is"by"far"the" most" widely" used" technique"for"the"automated" sorting" of" plastics"
(Hopewell"et"al.,"2009)."It"does"have"a"few"limitations,"though,"which"are:""
• It"is"an"optical"surface"technique."Anything"which"leads"to"a"false"reading"(the"
sensor"‘sees’"a"label"instead"of"the"bottle"underneath,"products"are"inside"one"
another,"the"light"cannot"reflect"due"to"dirt)"will"give"a"false"result;"
• Products"made"up"of"more"than"one"polymer"(for"example"multilayer"packaging),"
will"be"detected"as"the"one"that"is"presented"towards"the"sensor"at"time"of"
sensing;"
• NIR"cannot"identify"black"or"dark"products."
"
Manual! sorting"by" a" trained" operator" is" expensive" but" can" be" highly" efficient." The"
operator" is" taught" to" sort" based" on" product," which" is" coherent" with" certain" material"
types."Within"PMD"recycling,"the"operator"could"sort"out"milk"bottles"(HDPE)"or"certain"
colours" of" soda" bottles" (green," blue," white" PET)." Manual" sorting" is" also" used" in" the"
sorting" of" other" waste" fractions," mostly" for" a" mix" of" hard" plastic" products." Sorting"
examples"would"include"garden"furniture"(talc"filled"PP),"cable"sleeves"(HDPE),"window"
profiles"(PVC),"children’s"swimming"pools"(PVC),"plexi-glass"(PMMA),"etc."
"
While" the" PMD" case" has" served" well" to" highlight" some" leading" sorting" techniques" at"
product"level,"it"does"not"comprise"the"entire"recycling"process."The"next"example"will"
demonstrate" a" more" complete" chain," where" the" separation" of" the" mixed" polymers" is"
done"at"the"level"of"grinded"flakes.""
"
"
"
2.1.2$Example$of$sorting:$mixed$packaging$waste$
Let"us"consider"a"broader"format"of"curbside"collected"waste:"the"bag"collection"systems"
that" allow" for" all" plastic" packaging" waste" (NL" and" DE)." The" resulting" polymer" mix" is"
much" more" diverse" and" will" contain" PET," HDPE" and" PP" as" the" example" above."
Additionally"it"will"include"fair"amounts"of"L(L)DPE"(tray"packaging),"polystyrene"(PS)"
(yoghurt"pots" and" trays)"and" –" depending"on" the" region"–" PVC" (medical"and" cosmetic"
packaging)." Furthermore" non-packaging" polymers" such" as" acrylonitrile" butadiene"
styrene"(ABS),"polyamide"(PA),"polycarbonate"(PC)"will"contaminate"the"mix,"as"well"as"
organic"(food)"remnants.""
"
This"challenging"mixture"of"polymers"can"be"sorted"by"a"series"of"washing,"grinding"and"
separating." We" discuss" the" operational" flow" of" a" small" and" medium-sized" enterprise"
(SME)"which" takes" in" this" waste" (Eco-oh!," BE)" to" highlight" the" remaining" dominant"

13"
"
separation" techniques."
"
"#$%&'!L)!"./;!/+!39'!?U!;243'!;#39#7!@,/K/9V!>,/%&3'4-!/+!@,/K/9V:!T@D5!!
The" waste" polymers," when" delivered," are" stored" in" a" large" hall." The" sorting" process"
starts" by" loading" the" material" onto" a" belt" system," which" brings" the" mix" to" a" crude"
shredder," which" reduces" the" products" to" fist-sized" particles" (1st"grinding)." These" are"
transported"into"a"feed"silo,"from"where"the"waste"is"led"to"the"first" washing." This" is" a"
rotating! drum! washer"where"rocks,"metals"and" glass" are" separated" gravitationally;" a"
water" flow"provides" the"washing." Immediately" after," friction! washers"(2nd"washing)"
will"remove" the" organic" waste"sticking" to" the" plastics."The" large" particles" are"now"fed"
into" another" shredder"(2nd"grinding)" where" they" are" further" reduced" to" flakes" sized"
roughly"1-12"mm." Immediately" after," the" flakes"are"washed"again" in" friction! washers"
(3rd" washing)." From" there," they" are" led" to" the" float-sink! separation"installation" (1st"
separation," density" based)." In" the" water" bath," PP" and" PE" will" float" and" the" other"
polymers" such" as" PET," PS," and" PVC" will" sink." As" this" is" a" water-based" technique," the"
flakes"simultaneously"undergo"a"4th"washing."We" now" have"the"float"fraction"(PP"+"PE,"
also"known"as"mixed"polyolefins"or"MPO)"and"the"sink"fraction."The"sink"fraction"passes"
a"strong"overhead"magnet"(removal" of" ferrous" remains)" to" a" mechanical! drier"and" is"
ready"as"secondary"raw"material," being" a"mix"of"technical"plastics."The"float"fraction"is"
also" dried," but" continues" into" a" wind! sifter"(2nd" separation," mass-based)." Here" the"
upward"airflow"will"remove" all" ‘soft’" particles," i.e." the"foils"(mostly"LDPE" and" PP)." The"
heavier"‘hard’"particles"will"fall"down"against"the"airstream."The"hard"fraction"MPO"(PP"

14"
"
and"HDPE" remaining)" is"now" ready" as"secondary" raw" material." The" soft" fraction" MPO"
(LDPE"and"some"PP)"is"too"low"in"bulk"density"to"be"used"directly"by"converters,"so"it"
also"undergoes"a"final"regranulation"(with"melt!filtration)"step"by"extrusion."Now"also"
this"fraction"is"ready"as"a"secondary"raw"material.""
"
Flotation," also" called" float-sink" separation," is" a" straightforward" density-based"
separation" technique." It" is" the" dominant" method" for" the" sorting" of" shredded" flakes,"
usually" with" water" as" a" flotation" agent" (Wang" et" al.," 2015a)." In" this" relatively" cheap"
sorting"step,"polymers"with"densities"below"1"g/cm3"(unfilled"PP"and"PE)"will"float"and"
all"other"common"polymers"(PS,"PET,"PVC,"ABS,"…)"will"sink.""
Flotation"could"(and"is)"equally"be"performed"with"denser"media"than"water,"to"further"
separate"the"sink"fraction."However,"many"polymers"in"PC"waste"have"a"‘density"range’"
rather" than" a" single" density" value" and" these" ranges" often" overlap," thus" making" it"
impossible" to" completely" separate" these" polymers" effectively" into" mono-streams."
Typical"density"ranges"of"packaging"polymers"are"shown"in"Figure"9.""
"
!
"
"#$%&'!W)!6'74#3-!&27$'4!/+!4/1'!/+!39'!1/43!,/11/7!0/.-1'&4!#7!F?G!><2.%'4!X24'8!/7!>U2..#43'&!278!N'39;#4,9:!AB(BY!
P2#4'&!'3!2.5:!AB(CDD5!
"
During" regranulation"or!subsequent" reprocessing" of" the" recycled" materials," melt!
filtration"is"a"useful"technique"to!remove"non-melting"contaminations"from"the"melt,"as"
these"would"inevitably"reduce"the"quality"and"properties"of"the"extrudate"(Stenvall"and"
Boldizar,"2016)."Typical"removed" fractions" include" wood," paper,"aged"rubber" particles"
and"higher-melting"polymers"(e.g."PET"in"PP"processed"at"220"°C)"(Stenvall"et"al.,"2013)."
Melt" filters" come" in" different" mesh" sizes." A" smaller" mesh" size" takes" out" more"
contaminations;"it"is"more"complex"in"production"but"will"also"lead"to"improved"process"
stability"and"polymer"quality"(Luijsterburg"et"al.,"2016).""

15"
"
Different" options" for" melt" filtration" are" listed" here," in" ascending" order" of" installation"
cost:"
• a"127%2..-!'R,927$'2X.'!4#'<',"which"is"mechanically"exchanged"once"it"is"
sufficiently"polluted"(usually"observed"via"pressure"drop"over"the"sieve)."A"clean"
sieve"is"levered"into"place,"while"the"polluted"sieve"is"rotated"out"so"that"it"can"be"
cleaned"while"the"other"sieve"is"active."This"discontinuous"method"requires"that"
the"extrusion"process"be"interrupted"while"the"sieves"are"exchanged.""
• A"4'1#K,/73#7%/%4!4.#8#7$!4,&''7!,927$'&"utilizes"a"fast-acting"hydraulic"cylinder"
to"move"the"screen"packs"in"and"out"of"the"melt"flow"without"interrupting"the"
processing."However,"during"the"exchange"some"off-specification"material"can"
(and"will)"be"produced."
• The"fully"automated"solution"of",/73#7%/%4!1'.3!+#.3&23#/7"ensures"that"a"relatively"
equal"amount"of"filtration"area"is"exposed"to"the"polymer"flow"at"all"times,"
minimizing"processing"effects"due"to"screen"changeover."Such"continuous"melt"
filtration"is"typically"achieved"either"by"an"automated"rotating"sieve"(a"moving"
circular"disk"containing"multiple"screen"packs)"or"a"continuous"belt"screens"
exchangers."In"advanced"systems,"there"is"no"external"power"source,"but"the"force"
of"the"extruder"head"pressure"is"used"to"move"the"filter"screen.!
"
2.1.2!Other!sorting!techniques!
Other" sorting" techniques" that" are" used" (or" developed)" for" the" separating" of" mixed"
polymers"include:"
• Tribo-electric!(electrostatic)!separation:"while"this"technique"is"theoretically"
applicable"for"complex"mixes,"the"best"results"have"been"reported"for"separation"
of"a"binary"mix"(only"two"polymers)"like"ABS/PC,"PET/PVC"and"PP/PE"(Reinsch"
et"al.,"2014)."In"electrostatic"separation,"letting"the"polymer"flakes"collide"in"a"
charging"unit"causes"one"to"be"charged"positively"and"the"other"to"be"charged"
negatively"(or"remain"neutral)"at"the"surface"(Al-Salem"et"al.,"2009c)."They"are"
then"separated"by"their"different"deflection"in"an"electric"field."Some"mixes,"like"
PP"+"PE"require"an"additional"pre-treatment"(e.g."electron-beam"irradiation)"to"
permit"separation"into"homogeneous"material"fractions"(Albrecht"et"al.,"2011)."
• Froth!flotation:"also"called"selective"flotation"separation,"froth"flotation"is"
another"method"to"separate"polymers"with"similar"densities"(Censori"et"al.,"
2016)."The"basic"principle"of"froth"flotation"is"to"have"air"bubbles"adhere"(or"not)"
to"a"selected"polymer"surface,"thus"causing"it"to"float"(or"sink)."A"precursor"step"is"
required"wherein"the"surface"characteristics"of"selected"polymers"are"changed"
from"hydrophobic"to"hydrophilic"(="‘selective"wetting’,"for"a"mixture"of"
hydrophobic"polymers)"or"the"hydrophilicity"of"one"of"the"polymers"is"increased"
(="‘selective"hydrophobization’,"for"partly"wettable"polymers)"(Fraunholcz,"
2004)."The"technique"is"currently"researched"at"lab-scale"rather"than"widely"used"
in"industry."It"is"mostly"used"for"the"separation"of"mixed"plastics"with"densities"
higher"than"water,"primarily"to"separate"binary"mixes"of"a"combination"of"mostly"
PS,"PVC,"PET,"PC"or"POM"(Wang"et"al.,"2015a).""

16"
"
• Magnetic!density!separation"(MDS):"MDS"is"a"refined"density-based"technique,"
with"its"origins"in"the"mineral"processing"industry."By"using"a"magnetic"liquid"
(containing"iron"oxide)"as"the"separation"medium,"the"density"of"the"liquid"can"be"
varied"by"use"of"a"special"magnetic"field"(Rem"et"al.,"2013)."Therefore,"MDS"can"be"
applied"to"separate"multiple"polymer"fractions"in"a"single"step."However,"this"is"
still"a"density-based"technique"and"polymer"fractions"with"overlapping"densities"
will"still"contaminate"one"another."MDS"has"been"successfully"applied"for"the"
separation"of"PP"and"PE"from"MPO"(Serranti"et"al.,"2015)"and"PVC"as"well"as"
rubbers"from"building"&"construction"waste"(Luciani"et"al.,"2015).""
• X-ray!detection:"useful"for"the"separation"of"PVC"containers,"their"high"chlorine"
content"makes"them"easy"to"distinguish"(Arvanitoyannis"and"Bosnea,"2001).""
"
2.2 !Main!challenges!related!to!mechanical!recycling!
Different"challenges"arise"when"recycling"both"mono-"and"mixed"plastics."The"principal"
issue"is"the"fact"that"polymers"will"degrade"under"certain"conditions."These"conditions"
are" amongst" others" heat," oxidation," light," ionic" radiation," hydrolysis" and" mechanical"
shear"(Ravve,"2000)."During"mechanical"recycling"of"polymers,"two"types"of"degradation"
prevail:" degradation" caused" by" reprocessing" (thermal-mechanical" degradation)" and"
degradation"during"lifetime"(La"Mantia,"1996b).""
"
Foremost"is"the"thermal-mechanical"degradation"of"polymers"during"reprocessing."Both"
PI"as"PC"plastics"recycling"suffer"from"this"type"of"degradation"caused"by"a"combination"
of" heat" and" mechanical" shear." The" other" type" of" degradation" is" the" degradation"
occurring" during" lifetime" by" the" long-time" exposure" to" all" sorts" of" factors" in" the"
environment"(heat,"oxygen,"light," moisture," etc.)." This" type"of"degradation,"however," is"
only"important"in"the"case"of"PC"plastics"recycling.""
"
2.2.1 Thermal-mechanical!degradation!
Thermal-mechanical" degradation" is" caused" by" the" heating" and" mechanical" shearing" of"
the" polymer" during" the" melt" processing." Different" processes" will" be" initiated" in" the"
polymer" when" it" is" subjected" to" a" combination" of" temperature" and" shear" (Beyler" and"
Hirschler,"2002)."The"most"common"mechanisms"occurring"in"commercial"polymers"are"
chain"scission"and" chain"branching."Depending"on"the"type"of"polymer"and"aspects"like"
initial" molecular" weight" (Mw)" and" temperature," one" or" the" other" of" these" competing"
radical"mechanisms"becomes"more"dominant." Thermal-mechanical"degradation"begins,"
generally," with" a" hemolytic" scission" of" a" carbon-carbon"covalent" bond" in" the" polymer"
backbone," generating" free" radicals." These" free" radicals" may" undergo" some" chemical"
reactions"such"as"disproportionation,"causing"chain"scission,"or"crosslinking"also"known"
as"branching"(Beyler"and"Hirschler,"2002).""
"

17"
"
"
"#$%&'!(B)!N278/1!,92#7!4,#44#/7!>2D!278!,&/44.#7Z#7$!>XD!
"
Chain" scission" mostly" occurs" in" terminal" pendent" groups" or" in" the" polymer" backbone"
and"reduces"the"molecular"weight"of" the" polymer" and"hence"also"the"properties."Chain"
branching"results"in"crosslinking"and"increases"the"molecular"weight."A"typical"example"
of"chain"scission"occurs"in" PP"(González-González" et"al.,"1998),"while"some"types"of"PE"
are" more" prone" in" displaying" chain" branching" (Pinheiro" et" al.," 2004)." Both" reactions"
result"in"a"degree"of"unsaturation"and"the"release"of"low-molecular"volatile"components."
"
Figure" 11" shows" a" typical" example" of" molecular" weight" reduction" due" to" thermal-
mechanical"degradation" of" a" polypropylene" sample"during" a" certain" degradation" time."
Next"to"a"decrease"in"Mw"over"time,"also"an"increase"in"polydispersity"and"a"shift"in"Mw"
distribution" is" often" seen," which" indicates"the" occurrence" of" different" chain"lengths" in"
the"polymer."An"increasing"MFI,"as"shown"in"Figure"11b,"is"symptomatic"of"the"decrease"
in"Mw."
"
"
"
a"
b"
!"#$%&'!((!)!>2D!Q/.',%.2&!;'#$93!278!0/.-8#40'&4#3-!'</.%3#/7!/+!2!??!4210.'!>[#27!'3!2.5:!AB((D5!>XD!Q"=!'</.%3#/7!/+!2!
1%.3#0.'!&'0&/,'44'8!??!4210.'!>6'.<2!'3!2.5:!AB(JD5!
The"change"in"Mw"has"a"strong"influence"on"the"rheological"and"mechanical"behaviour"of"
polymers." Figure" 12a" shows" an" example" of" the" elongation" at" break" of" a" PET" sample,"
subjected"to"different"extrusion"steps"mimicking"a"recycling"process."A"severe"reduction"
in" Mw"already" takes" place" in" the" first" few" extrusions," accompanied" by" the" same"
decreasing"trend"in"the"elongation"at"break."Besides"elongation"at"break,"all"mechanical"
properties"will"suffer"changes"depending"on"the"change"in"Mw."In"general,"elongation"at"
break" and" impact" properties" are" the" mechanical" parameters" which" are" immediately"
0
1
2
3
4
5
1 3 5 7 9 11
MFI [g/10min]
Extrusion cycles

18"
"
affected" by" thermal-mechanical" degradation" (La" Mantia" and" Vinci," 1994)." Figure" 12b"
shows" the" effect" on" the" impact" strength" of" a" PA6" sample." The" evolution" of" strength"
properties"are"very"polymer" dependent" and" can" for" some"polymer"even"increase" after"
recycling"(Braun,"2002)."Besides"the"variation"in"mechanical"and"rheological"properties,"
also" thermal" properties" (melting" temperature," crystallization," etc.)" and"physical"
properties" (surface" properties," colour," etc.)" are" affected" by" thermal-mechanical"
degradation."
These" effects" of" thermal-mechanical" degradation" can" be" compensated" by" adding"
different"additives."A"huge" range"of"additives"for"increasing"the" recyclability" of"plastics"
can" be" found." Usually," heat" stabilizers" are" re-added" during" the" recycling" because" they"
have" mostly" been" consumed" during" the" first" lifetime" and" processing" of" the" plastic"
(Ulutan," 2003)." Next" to" heat" stabilizers," also" impact" modifiers," crosslinkers,"
compatibilizers,"pigments"and"fillers"can"be"added"(Murphy,"2001)."A"special"case"is"the"
recycling" of" PET" where" postcondensation" techniques" are" applied" to" improve" the" melt"
strength" and" mechanical" properties" (Dimonie," 2012)." This" will" be" discussed" more" in"
detail"further"on.""
"
"
a"
b"
"
"#$%&'!(A)!>2D!Q/.',%.2&!;'#$93!278!'./7$23#/7!23!X&'2Z!24!+%7,3#/7!/+!7%1X'&!/+!'R3&%4#/74!+/&!2!?@\!4210.'!>*2!
Q273#2:!(WWMXD!278!>XD!=102,3!43&'7$39!+/&!2!7%1X'&!/+!0&/,'44#7$!,-,.'4!/+!2!?]M!4210.'!>F%!'3!2.5:!ABBSD5!
2.2.2 Degradation!during!lifetime!
Plastic" products" are" subjected" to" a" combination" of" heat," oxygen," light," radiation,"
moisture" and" mechanical" stress" during" their" lifetime." The" resulting" degradation" is"
mainly"caused"by"photo-oxidation"processes"(La"Mantia,"1996a)."The"structural"changes"
in" the" polymer" are" very" similar" to" the" ones" introduced" by" thermal-mechanical"
degradation." The" main" difference" here" is" the" presence" of" oxygen" in" the" atmosphere"
(generally" not" present" in" processing" machines)." This" leads" to" the" formation" of"
oxygenated"groups"on"the"polymer"chain"and"will"as"such"affect"the"final"properties"of"
the"material.""
"
Both" degradation" during" lifetime" and"thermal-mechanical" degradation" yield" low-
molecular"volatile"compounds"that"are"mostly"trapped"in"the"polymer"when"in"the"solid"
state."During"reprocessing,"however,"these"contaminants" may" diffuse" through" the" melt"

19"
"
and"hinder"the"effective"reprocessing."These"contaminants"cannot"only"compromise"the"
product" properties," but" also" the" processing" itself," since" some" may" corrode" the"
processing"equipment." Proper" degassing" on" recycling"machinery" is" required" to"reduce"
this"problem."These"volatiles" are"small"(oxygenated)"fragments"of"the"original" polymer"
and"can"be"identified"by"different"analytical"techniques"like"mass"spectroscopy"(Xiang"et"
al.,"2002).""
"
2.2.3 Processing!of!complex!mixtures!
An" additional" challenge" for" the" recycling" of" mixed" plastic" waste" is" the" differences" in"
melting" points" and" processing" temperatures" between" the" polymers" in" the" mixed"
plastics,"as"shown"in"Figure"13."When"reprocessing"these"mixtures,"the"recycler"is"often"
forced" to" reprocess" them" at" the" processing" temperature" of" the" highest" melting"
component." This" often" leads" to" overheating" and" degradation" of" some" lower" melting"
components,"which" in" turn"reduces" the" final" properties."This" is" especially"relevant" for"
mixtures"containing"both"PVC"and"PET,"wherein"the"elevated"processing"temperatures"
used" for" PET" will" accelerate" the" dehydrochlorination" of" the" PVC" (Moller" and" Jeske,"
1995).""
"
"
"#$%&'!(H)!N27$'!/+!0&/,'44#7$!3'10'&23%&'4!+/&!,/11/7!0.243#,4!>Q/..'&!278!^'4Z':!(WWCD5!!
"
"
2.3 Mechanical!recycling!of!mixed!polymers!
The"mechanical"recycling"of"mixed"polymers"ultimately"always"leads"to"the"formation"of"
polymer" blends." A" polymer" blend" consists" of" a" mixture" of" two" or" more" polymers" (>2"
wt%)"(Utracki," 2002)." The"miscibility" of" blends"is" governed" by"their" thermodynamics."
The"full"thermodynamics"of"polymer"blends"is"a"complex"matter,"outside"the"scope"of"the"
current"manuscript."A"broad"review" concerning"this"topic"can"be"found"in"the" Polymer"
Blends"handbook"(Manias"and"Utracki,"2014)."The"following"paragraph"summarizes"the"
most"important"parameters"governing"the"(im)miscibility"of"blends." "
"
2.3.1 (Im)miscibility!of!polymer!blends!

20"
"
The"simplest"way"of"predicting"the"miscibility"of"polymers"is"by"the"Gibbs"free"energy"of"
mixing" (Manias" and" Utracki," 2014)." The" fundamental" thermodynamic" relationship"
between"mixtures"is"shown"in"equation"1."
"
𝛥𝐺!"# =𝛥𝐺!" −𝐺!+𝐺!≤0"
[Eq.1]"
"""""""""""""""""""""""""""""""""""""""""
In"this"equation,"the"Gibbs"free"energy"of"the"polymer"mixture"𝛥𝐺!""has"to"be"lower"than"
the"summation"of"the"Gibbs"free"energy"of"the"different"polymeric"constituents"A"and"B."
This"can"be"rewritten"to"equation"2,"showing"that"the"Gibbs"free"energy"consists"of"two"
terms,"namely"the"enthalpy"of"mixing"(𝛥𝐻!"#)"and"the"entropy"of"mixing"(𝛥𝑆!"#)."T"is"the"
absolute"temperature."
"
𝛥𝐺!"# =𝛥𝐻!"# −𝑇𝛥𝑆!"# ≤0"
[Eq.2]"
"
Mixtures"of" different" polymers" can"be"(partially)" miscible" or"immiscible"depending" on"
the"thermodynamic"equilibrium."A"completely"miscible"blend"will"be"formed"if"the"Gibbs"
free" energy" is" negative" and" moreover" if" the" criterion" in" equation" 3" is" also" fulfilled."
φ is the volume fraction of component B."
"
(∂!𝐺/∂φ²)>0"
[Eq.3]"
"
Favourable" mixing" requires" a" negative" Gibbs" free" energy." The" increase" in" entropy" for"
mixing" of" polymers" (in" contrast" to" smaller" molecules)" is" however" negligible," meaning"
that" the" enthalpy" of" mixing" should" be" negative" for" most" common" polymeric" systems."
This"is"dependent"on"the"specific"interaction"between"both"blend"components"(hydrogen"
bonding,"ion-dipole,"dipole-dipole,"donor-acceptor"and"Van"der"Waals"interactions)."The"
more"‘chemically"alike’"the"two"polymers"are,"the"more"compatible"they"will"be"(Koning"
et"al.,"1998)."The"basic" theory"for"the"calculation"of"the"Gibbs"free" energy"was"done"by"
Flory" and" Huggins" (Flory," 1942)." By" rewriting" both" the" enthalpy" and" the" entropy" of"
mixing"in"equation"2,"equation"4"is"called"the"Flory-Huggins"equation."
"
𝛥𝐺!"# =𝑘𝑇𝑁(𝜒!" φ! φ!+φ!ln φ!+φ!𝑙𝑛(φ!))"
[Eq.4]"
"
In"this" equation," k" is"the" Boltzmann" constant," N"is" the" mole" fraction,"T" is" the"absolute"
temperature,"φ!"is" the" volume" fraction" of" component" i" and"χ!" "is" the" Flory-Huggins"
interaction"parameter,"which"has"to"be"negative"before"spontaneous"mixing"occurs."𝜒!""
is" a" dimensionless" parameter" and" is" considered" a" measure" for" the" interaction-energy"
between" polymer" A" and" polymer" B" in" a" blend." In" the" Flory-Huggins" theory,"𝜒!""is" a"
constant." In" reality" however," this" parameter" is" strongly" dependent" on" temperature,"
pressure"and"concentration."The" exact"calculation"of"this"parameter"is"therefore" rather"
complicated" (Manias" and" Utracki," 2014)." By"using" the" Hildebrand" solubility" concept"
however,"𝜒!""can" be" calculated" using" equation" 5." In" this" equation,"𝑉
!"represents"the"
mixing" volume," R" the" gas" constant," T" the" absolute" temperature" and"𝛿!"the" solubility"

21"
"
parameter" of" polymer" i." The" solubility" of" the" polymers" is" governed" by" the" possible"
interactions"between"both"components."The"interactions"are"divided"in"dispersive"(Van"
der"Waals)"forces"(𝛿!"),"polar"forces"(𝛿!" )"and"hydrogen"bonds"(𝛿!!)"(equation"6)."
"
𝜒!" =
𝑉
!
𝑅𝑇 [𝛿!−𝛿!
!]"
[Eq.5]"
"
"
"
𝛿!
!=𝛿!"
!+𝛿!"
!+𝛿!!²"
[Eq.6]"
"
Completely" miscible" blends" are" called" homogeneous" blends" and" display" a" one-phase"
morphology." Immiscible" blends" on" the" other" hand" can" have" different" kinds" of"
morphologies"(Utracki,"2002):"spherical"drops,"cylinders,"fibres,"sheets"or"co-continuous"
phases"(Figure"14).""
"
"
"#$%&'!(J)!Q/&09/./$#'4!/+!#11#4,#X.'!0/.-1'&!X.'784)!>2D!8&/0.'34!>XD!,-.#78'&!>,D!.21#72&!278!>8D!,/K,/73#7%/%4!>Q2#'&!
278!U2.2+%3:!ABBLD5!
The"resulting"morphology"of"the"blends"depends"on"different"parameters:"the"nature"of"
the"polymers"(structure" and"molecular"weight),"their"concentration" and"the"processing"
parameters"(equipment,"temperature"and"viscosity"ratio)."
"
In" typical" polymer" waste," the" dominant" polymers" in" quantity" are" the" polyolefins" (PP,"
PE)," PET" and" PVC" (PlasticsEurope" et" al.," 2015)." Blending" a" combination" of" these"
polymers" always" yields" immiscible" blends." A" typical" SEM" (scanning" electron"
microscopy)" image" of" an" incompatible" PP/PET" 85/15" blend" is" shown" in" Figure" 15."
Within"the"PP"matrix,"spherical"micron-sized"PET"droplets"are"dispersed.""
"

22"
"
"
"#$%&'!(C)!=7,/1023#X.'!??_?@\!LC_(C!X.'78!><27!T&%$$'7!'3!2.5:!AB(MD5!
"
2.3.2 Properties!of!polymer!blends!
Depending" on" the" miscibility" and" the" compatibility" between" the" polymers," polymer"
blends" can" display" synergistic," antagonistic" or" additive" behaviour" (Figure" 16)." Most"
properties"do"not" simply"follow"the"additive"law." However"not"every"property"behaves"
in" the" same" way" for" the" same" polymer" pair." For" example," the" tensile" strength" for" an"
MPO-PP"system"follows" the" additive" law," while" the" elongation" at" break" displays" the"
curve"of"a"typical" incompatible" blend" (Hubo" et"al.,"2015)."The" elongation" at" break"and"
impact" properties" are" usually" very" sensitive" to" the" distribution" and" dispersion" of" the"
second"phase."Even" the"mixing"of"two"types"of"PP"(low"and"high"molecular"weight"e.g.)"
can"lead"to"a"loss"in"properties"due"to"differences"in"crystallization."
"
"
"
"#$%&'!(M)!?&/0'&3-!K!,/10/4#3#/7!,%&<'!/+!X.'784Y!$&''7!`!4-7'&$#43#,Y!&'8!`!2732$/7#43#,!278!X.2,Z!`!288#3#<'5!
"
2.3.3 Use!of!compatibilizers!!
This"immiscibility"of"polymer"blends"can"be"mitigated"by"different"techniques."The"go-to"
strategy"is" often" the" introduction" of" compatibilizers" (Koning" et" al.," 1998)." A"
compatibilizing"agent" is" a" third" component," which" is" introduced" in" the" polymer" blend"
and"lowers"the"interfacial"tension,"thus"promoting"the"interfacial"adhesion"between"the"
immiscible"polymers."This"results"in"a"uniform"(and"small)"distribution"of"the"dispersed"
phase" and" a" stable" morphology." The" mechanism" of" compatibilization" has" to" fulfil" the"
following"requirements"in"order"to"be"effective"(Utracki,"2002):"

23"
"
"
1. Lowering"of"the"interfacial"tension,"resulting"in"a"finer"dispersion;"
2. Stabilization" of" the" resulting" morphology" against" the" effect" of" shear" and"
temperature"during"processing;"
3. Improving"the"adhesion"between"the"different"phases"in"the"solid"state."
"
Three" main" compatibilizer" groups" can" be" distinguished" based" on" the" interactions"
between"the"compatibilizer"and"the"blend:"
- Block" or" graft" copolymers:" these" compatibilizers" are" built" out" of" different"
polymer"segments,"and"one"of"the"polymer"segment"will"be"more"compatible"with"
the"matrix"phase"and"the"other"one"with"the"dispersed"phase."The"compatibilizer"
will"migrate"towards"the"interface"and"reduce"the"interfacial"tension."An"example"
of"this"type"is"a"block"copolymer"of"PE"and"PP,"used"in"mixed"PE/PP"blends;
- Non-reactive"polymers"containing"polar"groups:"the"interfacial"tension"is"reduced"
by"the"secondary"intermolecular"interactions"between"these"polymers."The"non-
reactive"polymer"will"be"compatible" with" the" matrix." The" compatibilization"will"
be" influenced" by" the" type" of" secondary" interaction" (Van" der" Waals" <" dipoles" <"
hydrogen"bonding)."PMMA"and"polycaprolactone"(PCL)"are"example" of"this"type"
of"compatibilizers;
- Reactive"functionalized"polymers:"the"reactive"group"will"covalently"bond"to"the"
dispersed" phase" and" the" polymer" backbone" is" compatible" with" the" matrix." The"
adhesion" between" phases" will" be" the" highest" for" these" types." Examples" of" this"
type" of" compatibilizer" are" PP" grafted" with" maleic" anhydride" (PP-g-MA)" or" PP"
grated"with"glycidyl"methacrylate"(PP-g-GMA).
"
"#$%&'!(S)!=73'&2,3#/74!X'3;''7!F@TFK$KaQ]!>&'8D!278!??!>-'../;D!K!?@\!>X.%':!12&Z'8!24!0/.-'43'&D5!
"
An" example" of" the" different" compatibilization" mechanisms" of" SEBS-g-GMA" (triblock"
copolymer"styrene/ethylene"butylene/styrene"grafted" with"GMA)"on"a"blend"of" PP"and"
PET"is"showed"in"Figure"17."Different"types"of"interactions"simultaneously"occur"and"all"
contribute"to"the"reduced"interfacial"tension"and" the" improved" adhesion."This"can"also"
be"seen"on" the" SEM" micrographs"in"Figure" 18." Figure" 18a"is"the" incompatible" PP/PET"
blend" with" PET" dispersions" in" a" range" between" 1" and" 3" µm." Adding" 2.5" wt%" SEBS-g-
GMA" (Figure" 18b)" to" this" blend" reduces" the" PET" dispersions" size" below" 1" µm." The"

24"
"
change"in"morphology"also"increases"the"final"mechanical"properties"(van"Bruggen"et"al.,"
2016).
"
"#$%&'!(L)!2D!=7,/1023#X.'!??_?@\!LC_(C!X.'78!278!>XD!??_?@\!LC_(C!X.'78!,/1023#X#.#b'8!;#39!A5C!;3c!F@TFK$KaQ]!
><27!T&%$$'7!'3!2.5:!AB(MD5!
Quite"a"lot"of"research"has"been"done"on" selecting"the"most"appropriate"compatibilizer"
for" a" certain" polymeric" system." Table" 1" shows" commonly" used" compatibilizers" for"
different"polymeric"systems."
"
"
"
"
\2X.'!()!U/11/7.-!%4'8!,/1023#X#.#b'&4!+/&!8#++'&'73!0/.-1'&#,!4-43'145!
Polymeric!system!
Commonly! used!
compatibilizer!
Reference!
PE-PET"
PE-g-AA," PE-g-IA," PE-g-
GMA," SEBS," SEBS-g-GMA,"
SEBS-g-MA"
(El-Nashar" et" al.," 2008;"
Jeon"et"al.,"2005;"Koning"et"
al.,"1998;"Pluta"et"al.,"2001;"
Sanchez-Valdes" et" al.,"
2013;"Zhang"et"al.,"2011)"
PP-PET"
PP-g-AA," PP-g-MA," SEBS,"
SEBS-g-MA," SEBS-g-GMA,"
EVA,"EVA-g-MA"
(Champagne" et" al.," 1999;"
Koning"et"al.,"1998;"Lepers"
et" al.,"1997;" Pang" et" al.,"
2000;" Papadopoulou" and"
Kalfoglou," 2000;" van"
Bruggen" et" al.," 2016;"
Xanthos"et"al.,"1990)"
PP-PE"
EVA,"EPDM,"SEBS"
(Blom"et"al.,"1998;"Kallel"et"
al.," 2003;" Koning" et" al.,"
1998;" Souza" and"
Demarquette,"2002)"
PP-PA"
PP-g-GMA,"PP-g-MA,"SEBS-
(Holsti-Miettinen" et" al.,"

25"
"
g-MA"
1994;" Koning" et" al.," 1998;"
Lin"et"al.,"2013)"
PE-PA"
PE-g-MA,"PE-g-GMA"
(Chiono" et" al.," 2003;"
Dasdemir" et" al.," 2015;"
Jiang"et"al.,"2003;"Yao"et"al.,"
2000)"
PP-PS"
SBS,"SEBS,"EVA"
(Hlavatá" et" al.," 2001;"
Ismail"and"Nasir,"2002)"
ABS-PC"
ABS-g-MA,"PP-g-MA,"epoxy"
resins,"PMMA"
(Elmaghor"et" al.," 2004;" Jin"
et" al.," 1998;" Tjong" and"
Meng," 2000;" Zhang" et" al.,"
2001)"
PC-PS"
PC-g-PS," PS–Par," SEBS-g-
PC"
(Chevallier" et" al.," 2013;"
Ohishi" et" al.," 2001;" Pu" et"
al.,"1998)"
"
"
2.4 !Typical!examples!of!mechanical!recycling!
2.4.1 PET!
The"recycling"of"PET"is"a"typical"example"of"a"broadly"implemented"PC"recycling"process."
According" to" Petcore," the" PET" recycling" rate" in" 2014" for" bottles" and" containers" in"
Europe" was" at" 57%" (Petcore)." This" recycling" rate" is" very" high" compared" to" other"
disposed"plastics."The"process"of"PC"PET"recycling"consists"of"different"parts:"collection,"
sorting"and"reprocessing"into"a"product."Collection"of"PET"in"Europe"is"governed"by"the"
European" Union" directive" on"Packaging" and" Packaging" Waste" (2004/12/EC)." This"
directive"states"that"each"member"state"must"set"up"a"collection"scheme,"but"is" free" to"
choose"the"most"suitable"method"themselves."Existing"collection"methods"are"curbside"
collection,"drop-off"locations"or"the"refill"and"deposit"system."The"important"factors"here"
are"the"overall"collection"quantities"and" the"amount"of"contamination."Each"system"has"
its" advantages" and" drawbacks." Between" the" different" member" states," collected"
quantities"differ"quite"a"lot.""
"
After" collection," the" PET" is" sorted" from" the" other" contaminating" plastic" waste" (HDPE,"
PVC,"etc.)"through"hand"sorting"or"automated"systems"and"afterwards"compressed"into"
bales" for" easier" transportation." Finally," these" PET" streams" are" reprocessed" into" new"
products," mostly" packaging" applications" (bottles" and" containers)," but" also" turned" into"
fibres" or" new" applications." These" PET" streams" must" be" as" clean" as" possible" to" avoid"
contaminations,"which"inevitably" lead"to"a"decrease"in"final"properties"or"difficulties"in"
reprocessing"(Awaja"and"Pavel,"2005)."
"
Different" techniques" are" used" to" counter" the" thermal-mechanical" degradation" and"
accompanied" Mw"reduction" of" recycled" PET." This" is" mostly" done" to" increase" the" melt"
strength"and"facilitate"further"processing."The"most"common"techniques"are:"

26"
"
- Solid-state" post-condensation:" this"process" involves" heating" of" the" PET" at" a"
temperature" between" the" glass" transition" temperature" and" the" melting"
temperature" in" a" reactor." Condensation" reactions" occur" between" the" chains"
terminal"groups"in"the"amorphous"phase"of"the"polymer,"in"a"temperature"range"
of" 200-240"°C." The" reaction" proceeds" under" vacuum" to" remove" by-products"
(Welle,"2011);"
- Addition"of"chain" extenders" (Awaja" and"Pavel," 2005):" in" this"process,"a" low" (or"
moderate)" molar" mass" compound" with" different" functional" groups" reacts" with"
the"hydroxyl"PET" end-groups"to"crosslink"the"affected"polymer"chains," resulting"
in" chain" extension" and/or" branching" and" an" increase" of" Mw." A" commercial"
example" of" a" chain" extender" is" Joncryl" from" BASF" (Baden" Aniline" and" Soda"
Factory),"which"is"a"multifunctional"epoxy-based"oligomer"(Figure"19)."
"
"
"#$%&'!(W)!U9'1#,2.!0&#7,#0.'!/+!2!?@\!,92#7!'R3'78'&5!
"
!
2.4.2!SPW!from!WEEE!and!ELV!
Both"WEEE"(Waste"of"Electric"and"Electronic"Equipment)"and"ELV"(End-of-Life"Vehicles)"
provide" an" abundant" source" for" the" more" technical" (non-polyolefin)" thermoplastic"
polymers" like" ABS," PC," (High" Impact)PS" and" ABS-PC" blends" (Beigbeder" et" al.," 2013;"
Buekens"and"Yang,"2014;"Guo"et"al.,"2009;"Stenvall"et"al.,"2013;"Tarantili"et"al.,"2010)."A"
sample"composition"of"WEEE"plastics"per"product"type"is"shown"in"Figure"20."This"mix"is"
often"further"separated"into"the"individual"polymers"with" heavy-medium" flotation" (Al-
Salem"et"al.,"2009c).""
"

27"
"
"
"#$%&'!AB)!?.243#,!,/10/4#3#/7!+/&!G@@@!200.#27,'4!>Q2&3#79/!'3!2.5:!AB(AD5!
""
Of" these" polymers," the" most" effectively" recycled" is" ABS." However," ABS" is" sensitive" to"
degradation" both" during" its" lifetime" (UV" and" oxygen" induced)" and" during" processing"
(thermo-mechanically"induced)."The" mechanisms" involved" are" both"chain"scission" and"
crosslinking"(Arostegui"et"al.,"2006;"Peydro"et"al.,"2013;"Scaffaro"et"al.,"2012),"as"shown"
in"Figure"21."Additionally,"volatile"components"(mainly"styrene"derivates)"may"develop"
during"the" product" lifetime" due" to"environmental" degradation." These" are"freed" during"
the"reprocessing" of" the" ABS," potentially" leading" to"void" formation" in"the" recycled" ABS"
extrudate"(Arnold"et"al.,"2009)"and"reduction"of"impact"strength"(Bai"et"al.,"2007)."
"
"
"#$%&'!A()!6'$&2823#/7!1',927#414!#7! ]TF:! >2D! #7!39'!0/.-KX%328#'7'!>?TD!0924'! 278!>XD!23! 39'!?TKF]d!$&2+3#7$!4#3'4!
>F,2++2&/!'3!2.5:!AB(AD5!!
This" degradation" will" inevitably" lead" to" inferior" mechanical" properties" of" rABS," when"
compared"to"virgin"ABS."Impact"strength"and"ductility"are"foremost"among"these"(Bai"et"
al.,"2007;"Boldizar"and"Moller,"2003;"Brennan"et"al.,"2002;"Peydro"et"al.,"2013)."

28"
"
Routes"for"upgrading"recycled"ABS"primarily"include"blending"with"virgin"ABS"(Scaffaro"
et" al.," 2012;" Van" Damme" et" al.," 2016)," and" the" addition" of" impact" modifiers" like" SEBS"
rubber"(Peydro" et" al.," 2013;" Van"Damme" et" al.," 2016)"or"chain" extenders" (Wang" et"al.,"
2015b).""
"
Some" specific" WEEE" products" like" printed" circuit" boards" contain" mostly" (thermoset)"
phenolic"resins"as"polymer"component,"up"to"40"wt%"(Mou" et"al.,"2007)."Currently,"the"
only" viably" pathway" for" mechanical" recycling" of" these" waste" streams" is" pulverization"
and"subsequent"use"as"a"filler"in"both"thermosetting"and"thermoplastic"resins"(Guo"et"al.,"
2009)."Similar"to"the"use"of"talc"(Leong"et"al.,"2004),"it"is"possible"to"use"pulverised"epoxy"
waste"from"circuit"boards"as"strengthening" filler" in" PP."With"a"loading"of"up"to"30%,"it"
has" been" found" that" (both" tensile" and" flexural)" strength" and" modulus" increase"
proportionally" for" a" PP" matrix," as" does" temperature" resistance" (expressed" by" an"
increase"in"Vicat"softening"temperatures)"(Zheng"et"al.,"2009)."
"
The"mechanical"recycling"of"polymers"from"WEEE" and"ELV"is"currently"complicated"by"
the" presence" of" certain" brominated" flame" retardants" (BFR)" like" pentabrominated"
diphenyl"ethers"(PBDE)"and"decabrominated"diphenyl"ethers"(DBDE),"which"have"been"
banned"as" an" additive" for"new" products" (Stenvall" et" al.," 2013;" Vilaplana" and" Karlsson,"
2008)."However,"methods"for"detection"of"BFR-holding"polymers"do"exist"(Vilaplana"and"
Karlsson," 2008)" and" even" the" extraction" of" BFR" from" the" melt" is" possible" with"
techniques" like" supercritical-fluid" extraction" (Altwaiq" et" al.," 2003)" or" ultrasonic"
extraction"(Pohlein"et"al.,"2005).""
"
"
2.4.3!SPW!from!post-consumer!packaging!waste!
In"several"EU"countries"(e.g."NL,"DE,"IT),"PC"packaging"waste"(PC-PPW)"is"collected"and"
processed"separately."In"some"countries," like"BE,"pilot"projects"are"running"to"evaluate"
the"feasibility"(FostPlus,"2014)."Typically,"such"countries"also"have"a"separate"collection"
system"(often"based"on"a"deposit"system)"in"place"for"PET"bottles."Therefore,"PET"bottles"
are"considered"exclusive"to" this" waste" stream."The"dominant"polymers"in" PC-PPW" are"
PET"(from"thermoformed"food"trays),"PP"(trays),"LDPE"(foils),"PVC"(flexible"packaging),"
ABS" and" (E)PS" (yoghurt" pots," food" trays)"(Bonifazi" et" al.," 2016)." A" detail" of" a" typical"
composition"for"such"waste"is"given"in"Table"2.""
"
"
"
"
\2X.'!A)!\-0#,2.!,/10/4#3#/7!/+!2!4210.'!?UK??G!>T/7#+2b#!'3!2.5:!AB(MD5!!
Waste!
%!Weight!
PET"
26.80"
PVC"
24.90"

29"
"
Rubber"
3.10"
PS/ABS"
9.60"
PA/PBT"and"other"polymers"
5.40"
PE/PP"(added)"
11.90"
PE/PP"
5.50"
PAPER/FIBRE"
4.20"
METAL/INERTS"
8.60"
"
An" important" fraction" of" PC-PPW" materials" is" made" up" of" multilayer" products"
(Luijsterburg" and" Goossens," 2014)." These" include" PET/PE," PET/PE/EVOH" or" PA/PE."
Typically,"initial"sorting"of"PC-PPW"is"done"by"flotation"in"water:"the"polyolefins"(PP"and"
PE)"will"float"and"the"sink" fraction" will" contain"mostly"PET"(around"50%),"multilayers,"
PP"(talc-filled),"PS"and"PVC"(Bonifazi"et"al.,"2016)."Small"amounts"of"ABS,"PMMA,"PC"and"
PA"might"occur.""
"
This"complex" sink" fraction" is"currently" sent" to"energy" recovery" (Bonifazi" et"al.," 2016)."
The" MPO" fraction," however," is" usually" valorised" through" mechanical" recycling." MPO"
fractions"are"commonly"a"combination"of"PP"and"(mostly)"HDPE"from"‘hard"plastics’"or"a"
combination"of"PP" and" (mostly)" LDPE" from"‘soft"plastics’," i.e." foils." This" equates"to"the"
hard" MPO" and" soft" MPO" fractions" discussed" in" the" sorting" scheme" of" Figure" 8." By"
experimental"estimation,"the"composition"of"a" hard" MPO"fraction"is"about"60%"PP"and"
30%"PE"(Hubo"et"al.,"2014)."The"rest"is"a"mixture"of"non-polyolefin"plastics"and"floating"
contaminations"like"wood"or"cork.""
Mechanical" properties" for" these" unmodified" industrial" MPO’s" have" been" reported" as"
shown" in" Table" 3."Typically," the" hard" MPO" will" have" higher" strength" properties" but"
lower"toughness"and"the"soft"MPO,"with"its"large"amount"of"LDPE,"will"have"high"impact"
strength"but"inferior"stiffness.""
"
\2X.'!H)!3-0#,2.!0&/0'&3#'4!+/&!92&8!278!4/+3!Q?E!+&2,3#/74! >e%X/! '3!2.5:!AB(JD!<2.%'4!2&'!49/;7!24!1'27! f! 432782&8!
8'<#23#/7!5!!
material!
Notched!Charpy!
impact!(23!°C)!!
[kJ/m2]!
Young’s!
modulus!!
[MPa]!
Tensile!
strength!
[MPa]!
Hard!MPO!
3.22"±"0.15"
1095"±"95"
14"±"0.5"
Soft!MPO!
9.88"±"1.12"
569"±"31"
14"±"0.6"
"
"
Even"these"similar"polymers"like"PP"and"PE"turn"out"to"be"immiscible"in"the" melt" (Liu"
and" Truss," 1996;" Teh" et" al.," 1994;" Utracki" and" Dumoulin," 1995)." Furthermore," it" has"
been"shown"that"the"properties"of"the"MPO"blends"strongly"depend"on"(i)"the"individual"
polyolefin"characteristics" and" (ii)" the"mixture"composition."The"latter" will" affect"blend"
morphology," which" will" in" turn" determine" whether" or" not" the" resulting" mechanical"

30"
"
properties"like"modulus"and"elongation"at"break"follow"a"proportional"law-of-mixtures."
Impact"strength,"which"is"strongly"dependent"on"interfacial"adhesion,"usually"does"not"
follow"any"law-of-mixtures"and"will"display"the"antagonistic"behaviour"from"Figure"16"
(Delva"et"al.,"2015;"Hubo"et"al.,"2015).""
"
Typical" products" for" mechanical" recycling" of" MPO" include" garden" furniture," outdoor"
flooring"and"boards"for"stables"or"water"edges."Industry"would"like"to"move"into"higher-
level"products"as"well."Therefore,"much"research"is"conducted"on"improving"either"the"
stiffness"or"the"impact"toughness"of"the"MPO"materials.""
!
Common" low-cost" strategies" to" improve" the" toughness" of" recycled" MPO," through" a"
combination"of" impact" modification" and"compatibilization"effects,"include" the" addition"
of"EPDM"(ethylene"propylene"diene" monomer)"rubbers"(Banerjee"et"al.,"2016;"Delva"et"
al.,"2013)"or"ethylene/propylene"block"copolymers"(EPR)"(Radonjic"and"Gubeljak,"2002)."
Results" strongly" depend" on" the" quality" of" the" recycled" MPO," as" contaminations" are"
known" to" adversely" affect" the" effectiveness" of" the" compatibilization" (Kazemi" et" al.,"
2015)." For" improvement" of" strength," additives" like" inorganic"(ceramic" or" glass)" fibres"
(Borovanska"et"al.,"2016;"Kuram"et"al.,"2014)"or"natural"fibres"(Akesson"et"al.,"2016;"Ares"
et"al.,"2010;"Twite-Kabamba"et"al.,"2011)"have"been"used."Other"efforts"to"upgrade"the"
properties"of"recycled"MPO"include"blending"with"virgin"LDPE"(Delva"et"al.,"2015;"Guerfi"
and"Belhaneche-Bensemra,"2014)"or"high-quality"recycled"mono-PP"(Hubo"et"al.,"2015)."
It" has" also" been" shown" that" MPO" could" be" considered" for" specialty" applications" like"
mirror"welding,"where"the"can"replace"high-purity"recycled"PP."It"was"found"that"HDPE"
‘contaminations’"up"to"20"wt%"do"not"adversely"affect"the"mirror"welding"process"(Hubo"
and"Ragaert,"2016)."
"
!
!
!
!
2.5!Design!and!Recycling!
"
The"design"of"plastic"products"has"a" large"impact"on"both"their"recyclability"(at"end-of-
life,"EoL)"and"the"degree"to" which" they" can" incorporate" recycled"materials"(at"start-of-
life,"SoL).""
"
Design!+/&" Recycling" is," via" the" Ecodesign" Directive" (EuropeanCommission," 2009),"
heavily"promoted"by"the"EU"within"the"framework"of"the"Circular"Economy,"a"schematic"
of" which" is" shown" in" Figure" 22." It" is" a" well-known" product" development" strategy" in"
which"new"products"are"developed"so"that"they"can"be" recycled" at" their" EoL." It" entails"
easy"separation" of" different"materials" and" an" all-round"efficient" material" use"(Rodrigo"
and"Castells,"2002)."The"strategy"is"part"of"a"virgin"material’s"SoL.""
"

31"
"
"
"#$%&'!AA)!F,9'123#,!/+!39'!0&#7,#0.'4!/+!39'!U#&,%.2&!@,/7/1-!>@IK?2&.#21'73:!AB(CD5!!
"
In"the"European"Commission’s"latest"Circular"Economy"Package"(CEP),"it"was"proposed"
to"make" mandatory" a" ‘product"design…to" make" it"easier" and" safer" to"dismantle," reuse"
and"recycle"electronic"displays’"(EuropeanCommission,"2015)." It" is"expected"that"other"
product"categories"will"follow."Additionally,"Design"for"Recycling" is" encouraged" via" the"
implementation"of" Extended" Producer" Responsibility"(EPR)" schemes," wherein" the"EoL"
costs"will" factor" as" an" economic" incentive" to" producers" (EuropeanCommission," 2015)."
Design"for"Recycling,"as"such,"only"covers"the"EoL"in"terms"of"recycling/recyclability.""
"
The"authors"would"like"to"advocate"also"considering"design"at"the"product’s"SoL"and"this"
is"where"Design"from"Recycling"comes"in"(Ragaert,"2016;"Ragaert"et"al.,"2016)."In"Design"
from"Recycling,"the"secondary"raw"material"originating"from"the"recycled"polymer"waste"
of"a"previous"product’s"EoL"is"the"starting"point"of"a"new"product"development."Design"
from"Recycling"involves"the"following"key"aspects"(Ragaert,"2016):"
• Identifying"the"recycled"polymer’s" strengths" and" weaknesses"through"extensive"
characterization;"
• Matchmaking"between"the"recycled"material’s"characteristics"and"potential"(new"
or"existing)"products;""
• Adapted" product" (and" mould)" design" for" manufacturing" of" the" products" in"
recycled"polymers;"
• If"needed," identifying" acceptable" (cost-effective)" strategies" for" the"upgrading"of"
the" material" quality" (to" product" requirements)" where" necessary." This" usually"
involves"small"amounts"of"additives"like"stabilizers"or"compatibilizers;"
• Through"life"cycle"analysis"(LCA),"life"cycle"costing"(LCC)"and"Resource"Efficiency"
calculations,"quantifying"the"overall"resource"efficiency"of"the"whole"process,"thus"
ensuring"the"best"possible"use"of"the"recycled"polymers"as"well"as"demonstrating"

32"
"
to"the"broader"public"the"gain"that"is"to"be"had"by"using"these"secondary"material"
sources.""
"
Design"from"Recycling"needn’t"be"closed-loop."It"is"perfectly"valid"–"and"often"necessary"
–"to" valorise" a"recycled" material" outside"its" original" product"application." For" example,"
this"could"be"because"a"packaging"material"cannot"(legally)"be"re-used"in"a"food-contact"
application"or"because"the"recycled"material"has"an" entirely" different" composition" and"
properties"set"compared"to"the"virgin"(recycling"of"multilayers,"which"become"blends).""
"
Design"from"Recycling," being" a" relatively"new"concept,"is"not"without" its" challenges." It"
requires" a" close" collaboration" between" (materials)" engineers" and" product" designers,"
two" classes" of" professionals" that" typically" think" and" speak" in" a" different" ‘language’." A"
tool"for"harmonisation"between"the"two"is"required"(Veelaert"et"al.,"2016)."Furthermore,"
the" volatile" feedstock" prices" of" virgin" materials" steadily" undermine" the" economic"
incentive"for"industry"to"take"up"recycled"materials"in"production.""
"
Design"for"and"from" Recycling"are"in"fact"complementary"strategies" that,"when"applied"
together,"can"truly"bring"a"material"full-circle."Simplifying"the"schematic"from"Figure"22,"
this"principle"is"illustrated"in"Figure"23.""
"
"
"
"#$%&'! AH)! \9'! ,/10.'1'732&#3-!/+! 6'4#$7! +/&! 278! +&/1! N',-,.#7$! #7! 39'! U#&,%.2&! @,/7/1-! >#,/74! 28203'8! +&/1! >@IK
?2&.#21'73:!AB(CDD5!
3 Chemical!recycling!
"
Plastic"waste"seems"to"be"a"very"promising"feed"in"the"production"of"valuable"chemicals"
and" fuels." The" current" interest" is" not" only" in" recovering" energy" or" in" mechanical"
recycling" but" also" in" the" production" of" valuable" products" such" as" monomers" or"
petrochemical"feedstocks.""
For"some"feedstocks"such"as"PET,"PUR"and"nylon,"chemical"recycling"options"exist."The"
interest" in" using"them"as" feedstock" has" been" growing" steadily," as" these" are" closely"

33"
"
related" to" the" conventional" petroleum" fractions" and" have" high" hydrocarbon" content."
Unlike" biomass," plastic" waste" and" in" particular" polyolefin" waste," do" not" contain"
significant"amounts"of"oxygen."Therefore,"higher"carbon"efficiency"can"be"expected"and"
hence,"higher"gross"margins."In"the"following"section,"different"types"of"technologies"for"
processing"these" SPW" streams" are"reviewed." Known" processes" to" handle" this" feed"
stream"are"gasification,"pyrolysis,"fluid-catalysed"cracking"and"hydrocracking."The"main"
focus" of" this" section" will" be" those" types" of" chemical" recycling" that" consist" of" either"
monomer" recycling" or" feedstock" recycling." Both" paths" have" been" recognized" as" ideal"
methods" for" the" preservation" of" limited" resources" and" for" the" protection" of"the"
environment"by"decreasing"the"volume"of"non-degradable"waste"(Al-Salem"et"al.,"2009a,"
2010)."
"
3.1!Chemolysis!
Chemical" recycling" is" an" accepted" recycling" method" that" follows" the" principles" of"
“sustainable"development”."The"fact"that"chemically"recycled"plastics"can"be"well-suited"
for" food"applications" has" steadily" increased" an" interest"in" the" various" chemolysis"
possibilities."Chemical"recycling"methods"are"opening"newer" pathways" for" using" waste"
as" a" precursor" in" generating" pure" value-added" products"for" various" industrial" and"
commercial" applications." However,"it" has" to" be" stressed" that" chemically" recycled"
polymers"are"more"expensive"than"the"virgin"material"because"of"the"raw"material"cost,"
capital"investment,"and"scale"of"operation."For"example,"it"has"been"calculated"that"for"a"
PET" chemolysis" facility" to" be" economically" viable," a" minimum" throughput" of" 1.5×104"
tonnes"per"annum"is"required"(George"and"Kurian,"2014)."
"
3.1.1!Chemical!recycling!of!PET!
Chemical" recycling" of" PET" can" completely" depolymerize" it" into" its" monomers"
terephthalic" acid" (TPA)," dimethyl" terephthalate" (DMT)," bis(hydroxylethylene)"
terephthalate" (BHET)," and" ethylene" glycol" (EG)." In" this" case," depolymerization" is" the"
reverse" reaction" of" the" polymer" formation" route." PET" can" also" be"partially"
depolymerised" to" oligomers" or" other" chemical" substances." There" are" different"
depolymerization" routes" such" as" methanolysis," glycolysis," hydrolysis," ammonolysis,"
aminolysis,"and"hydrogenation,"depending"on"the"chemical"agent"used"for"the"PET"chain"
scission."Figure"24"summarizes"the"different"options" for"PET"chemolysis,"as" well"as"the"
type"of"products"that"can"be"derived"from"PET"depolymerisation.""
"

34"
"
"
"#$%&'!AJ)!6#++'&'73!1'39/84!/+!?@\!,9'1/.-4#4!278!39'!<2.%'K288'8!0&/8%,34!8'&#<'8!39'&'/+!>]$%28/:!(WWWD5!
PET" methanolysis" is" based" on" the" treatment" of" PET" with" methanol" at" relatively" high"
temperatures"(180−280"°C)"and"pressures"(20−40"atm),"which"leads"to"the"formation"of"
DMT"and"EG"as"the"main"products."The"degradation"products"of"PET"after"glycolysis"and"
aminolysis" find" potential" applications" as" plasticizers," cross-linking" agents," chain"
extenders," corrosion" inhibitors," and" precursors"in" the" generation" of" value-added"
products" such" as" UP" resins," polyurethanes," textile" dyes," antibacterial" drugs," epoxy"
resins,"and"vinyl"esters.""
"
Hydrolysis,"i.e."the"reaction"of"PET"with"water"under"neutral,"acidic,"or"basic"conditions"
at" high" temperature" and" pressure," breaks" the" polyester" chains" into" TPA" and" EG." The"
main"drawbacks"are"the"low"purity"of"TPA"and"the"fact"that"this"is"a"comparatively"slow"
option"because"water"is"a"weak"nucleophile."
"
Glycolysis" is" the" simplest" and" oldest" method" of" PET" depolymerization." It" is" even" a"
commercial"PET"recycling"method"practiced"by"renowned"companies"worldwide"such"as"
DuPont/DOW,"Goodyear,"Shell"Polyester,"Zimmer,"Eastman" Kodak," etc." (Scheirs," 1998)."
It" is" a" versatile" recycling" method" because," besides" the" formation" of" monomers,"
specialized" oligomeric" products" such" as" α,ω-dihydroxy" materials" (polyols)" are" also"
produced." The" latter" can" be" further" utilized" for" the" synthesis" of" polymers" such" as"
unsaturated"polyesters," polyurethanes," vinyl"esters," epoxy" resins,"etc." Glycolysis" is"the"
preferred"recycling"option"when"the"incoming"PET"feed"is"of"high"quality."It"is"absolutely"
not"suited"for"the"removal"of"low"levels"of"copolymers,"colorants"or"dyes."It"is"best"suited"
to"the"recovery"of"PI"scrap"(Scheirs,"1998)."Glycolysis"involves"the"transesterification"of"
PET"with"an"excess"of"glycol"at"temperatures"in"the"range"of"180−"250"°C,"promoting"the"
formation" of" BHET." Different" glycols," such" as" EG," diethylene" glycol" (DEG)," propylene"
glycol"(PG),"polyethylene"glycol" (PEG)," 1,4-butanediol"and"hexylene"glycol,"can"be"used"
for"the"glycolysis"of"PET."Because"the"process"is"sluggish"in"the"absence"of"any"catalyst,"

35"
"
transesterification"catalysts"are"usually"employed"(George"and"Kurian,"2014)."Glycolysis"
of" waste" PET" proceeds" through" three" stages:" oligomers," dimers," and" monomers." The"
glycol" diffuses" into" the" polymer," causing" the" polymer" to" swell," thus" increasing" the"
diffusion."The"glycol"subsequently"reacts" with"an"ester"bond"in"the"chain" and" degrades"
the"PET" into" lower" fractions."George" and" Kurian" showed"that" the" reaction" parameters"
such"as"reaction"time,"temperature,"catalyst"concentration,"and"PET:reagent"ratio"have"
great" significance" on" the" efficient" depolymerization" of" PET." These"reaction" conditions"
can"be"ranked"according"to"decreasing"importance"as:"catalyst"concentration">"reaction"
temperature">"reaction"time"(George"and"Kurian,"2014)."
"
"
3.1.2!Other!chemical!recycling!processes!
Sub-"and"supercritical"fluids"such"as"water"and"alcohol"are"excellent"reaction"media"for"
depolymerization" or" decomposition" of" plastics." By" using" sub-" and" supercritical" fluids,"
polymer"decomposition"can"in"some"cases"proceed"rapidly"and"selectively."In"this"way"it"
is"possible"to"convert"condensation"polymers"with"ether,"ester,"or"acid"amide"linkages"by"
solvolysis"back"to"their"monomers."Indeed,"these"condensation"polymers"are" relatively"
easily"depolymerized"into"their"monomers"without"using"a"catalyst"in"water"or"alcohol,"
which" act" as" reactant" as" well" as" solvent." Also," addition" polymers" can" be" decomposed"
with" or" without" catalysts" in" sub-" and" supercritical" fluids." Composite" plastics" such" as"
fibre-reinforced"plastics"are"decomposed"into"smaller"molecular"components"and"fibre"
materials"(Goto,"2009;"Oliveux"et"al.,"2012)."
"
PA6,"which"is"a"polymer"synthesized"by" ring-opening" polymerization" of"ɛ-caprolactam,"
can"be"depolymerized"by"hydrolysis"in"sub-"and"supercritical"water."ɛ-Caprolactam"and"
ɛ-aminocaproic" acid" can" be" collected" in" the"liquid" phase." The" total" yield" of" these"
monomers"was"about"100%"for"reactions"at"573"K"in"60"min"and"at"603"K"in"30"min.""
"
Matsushita" Electric" Works," Ltd.," Japan" has" been" developing" a" technology" for" the"
depolymerisation" of" flame" retardant" polymers" (FRP)" using"hydrolysis" in" subcritical"
water." In" their" technology," thermosetting" resin" in" FRP" can" be" recycled" into" basic"
materials"with"a"material"recycling"rate"of"70%."The" concept" of" their" subcritical" water"
recycling"process"is"illustrated"in"Figure"25."After"subcritical"water"hydrolysis,"the"resin"
is"dissolved" into" a"liquid." The" recovered"components" such" as" glycols" and" fumaric" acid"
can"then"be"separated"from"the" aqueous" solution" and" polymerized" into" polyester"with"
fresh"resin" material" to" produce"recycled"resin." Also," a" styrene-fumaric"acid" copolymer"
(SFC)"could"be"separated"from"the"aqueous"phase."
"
"

36"
"
"
"#$%&'!AC)!U/7,'03!/+!"N?!&',-,.#7$!8'<'./0'8!23!Q234%49#32!@.',3&#,!G/&Z4:!*38!
"
3.2 Pyrolysis!
Pyrolysis" is" an" interesting" technology" for" plastic" waste" feeds" that" are" difficult" to"
depolymerize"and"that"are"currently"not"(mechanically)"recycled"but"incinerated"and/or"
dumped" to" landfill" such" as" mixed" PE/PP/PS," multilayer" packaging," fibre-reinforced"
composites,"polyurethane"construction" and" demolishing" waste." Especially"these"newer"
multilayered"films"seem"to"be"much"harder"to"recycle"than"the"simpler"metal,"paper,"and"
glass" containers" they" replace."Figure" 26" shows"such" a" typical" structure" of" a" highly"
engineered" multilayer" package" material." The" workhorse" is" PE," because" it"will" be" the"
least" expensive." PE" gives" the" packaging" its" bulk" and" structural" integrity." If" more"
toughness" is" needed," a" packaging" company" might" opt" for" PET," the" resin" of" choice" for"
beverage"containers."Most"food"packages"need"a"barrier"layer"to"protect"against"oxygen."
Ethylene-vinyl"alcohol"(EVOH)"is"popular"because"it"is"more"effective"in"blocking"oxygen"
than" PE," PET," or" nylon." If" even" more" barrier" is" needed," a" package" might" incorporate"
metallized"film."One"can"immediately"see"that"depolymerization"or"mechanical"recycling"
is"no"longer"an"option"and"tougher"methods"are"needed,"and"here"pyrolysis"comes"in"to"
play."Unlike"mechanical"recycling," this" option" can" handle"highly"contaminated,"such" as"
automotive"shredder"residue," and"highly"heterogeneous"mixtures"of"plastics"increasing"
the"flexibility"of"the"process" with"respect"to"feedstock"(Vermeulen"et"al.,"2011)."This"is"
the"main" advantage" as"economic" viable" and" satisfactory" separation" of"all" the" different"
types"of"plastic"is"hardly"achievable"(Al-Salem"et"al.,"2010)."
"
"

37"
"
"
"#$%&'!AM)!]&,9#3',3%&'!/+!1/8'&7!1%.3#.2-'&!02,Z2$#7$!123'&#2.4!>\%../:!AB(MD!
The"pyrolysis"process"takes"place"at"moderate"to"high"temperatures"(500"°C,"1-2"atm)"in"
absence"of"oxygen."The"high" temperatures" allow" to" break"down"the"macrostructure"of"
the"polymer"to"form"smaller"molecules"(Angyal"et"al.,"2007)."Depending"on"the"nature"of"
the" polymer," either" depolymerisation" or" random" fragmentation" will" dominate." The"
pyrolysis"products"of"SPW"can"be"decomposed"into"three"fractions:"gas,"liquid"and"solid"
residue"(Al-Salem"et"al.,"2009a,"b,"2010)."As"an"example,"the"process"scheme"in"Figure"27"
shows" the" implementation" of" a" novel" vortex" reactor" technology" in" a" classical" plastic"
waste"pyrolysis"plant" design"equipped" with" a"conventional" separation" section." Several"
demonstration"plants"have"been"built"and"are"operational"as"summarized"in"Table"4."
"
"
!
"#$%&'!AS)!?&/,'44!"./;!6#2$&21!/+!2!,.244#,2.!0-&/.-4#4!0.273!;#39!2!7/<'.!</&3'R!&'2,3/&!3',97/./$-!!
"
\2X.'!J)!E<'&<#';!/+!,/11'&,#2.!/&!0#./3!0.273!/+!0.243#,!0-&/.-4#4!0&/,'44'4!>T%3.'&!'3!2.5:!AB((D5!
Process!
Location!
Capacity!
Status!
Mogami-Kiko!!
Japan"
3"t/d"
"operational"

38"
"
Royco!Beijing!
China"
6"kt/d"
"unknown"status"
Sappro/Toshiba!!
Japan"
14.8"kt/a""
"operational"
ALTIS!!
Japan"
Unknown"
"Commercially"applied"
Gossler!Evitec!!
Germany"
1"kt/a"
"status"unknown"
Changing!World!
Technologies!
USA"
10"Mgal/year""
"demo"
A" key" difficulty" of" the" pyrolysis" process" is" the" complexity" of" reactions" that" occur,"
especially" when" mixed" streams" are" processed." Different" polymers" give" rise" to"
completely" different" product"spectra," according" to" their" dominant" decomposition"
pathway." Even"the" presence" of" certain" impurities" can" substantially" affect" the" product"
distribution"and"make"that"the"obtained"product"lose"a"substantial"part"of"its"value,"for"
example"certain"oxygenates"that"lead"to"the"formation"of"methanol"or"formaldehyde."To"
make"it"even"more"difficult,"PE"and"PP"have"the"tendency"to"randomly"fragmentize"while"
polytetrafluoroethylene"(PTFE)," PA," PS" and" PMMA" can" be" pyrolysed" into"products"
containing" mostly" their" respective" monomers." For" example" PMMA" pyrolysis" has" a"
remarkable"monomer"yield"of"near"98%"(Garforth"et"al.,"2004)."These"polymers"can"be"
depolymerized" and" hence" both" from" an" economical" and" environmental" point" of" view,"
this"is"the"most"interesting"route"to"valorised"these"waste"streams."On"the"other"hand,"
the" product" spectrum" of" PE" and" PP" is" very" broad" and" is" characterized" by" a" skewed"
distribution."This"is"due"to"the"random"fragmentation"mechanism"of"these"resins"(Ranzi"
et" al.," 1997)." Hence,"further" processing" is" needed," resulting" finally" in" petrochemical"
feedstock"such"as"naphtha"or"diesel.""
"
Although"pyrolysis"is"a"simple"technology"it"is"only"economically"viable"when"carried"out"
in" large" volumes" at" present." The" latter" implies" that" today" only" the" most" common"
polymers"and" their" mixtures" are"suitable" for" conversion" to"either"monomers" or" liquid"
energy" carriers/petrochemical" streams." These" are" PE," PP," PS" and" PVC" and" they"
represent"approximately"80%"of"the"polymers"being"produced"in"Europe,"see"Figure"28."
Other" waste" plastics" have" a" marginal" contribution" to" the" waste" stream" and" hence"
specific" valorisation" of" these" streams" cannot" significantly" contribute" to" a" commercial"
high"scale"production"facility"such"as"a"pyrolysis"plant."This"is" primarily" related" to" the"
complexity" of" the" separation" section" if" complex" mixtures" are" used." At" present,"
distillation"is"the"only"technique"that"can"be"used"to"purify"the"obtained"monomers"and"
the"formed"liquids."In"some"cases,"even" complex"extractive"separation"technologies"are"
needed,"such"as"for"the"recovery"of"certain"aromatics."Moreover,"the"strict"specifications"
on" the" monomers’" purity" implies" that" large" distillation" towers" are"needed," with" high"
cooling" duties." However," by" integrating" pyrolysis" in" an" existing" olefin" complex,"
investment"costs"could"be"drastically"reduced.""
"

39"
"
"
"#$%&'!AL)!]<'&2$'!0.243#,!,/74%103#/7!X-!0/.-1'&!3-0'!#7!27!@%&/0'27!,/73'R3!>T&'14!'3!2.5:!AB(AD5!
One"of"the"other"main"issues"with"pyrolysis"of"SPW"is"the"presence"of"PVC"in"the"stream"
(Bhaskar"et"al.,"2003;" Okuwaki," 2004;" Rijpkema," 1999;"Sadat-Shojai"and"Bakhshandeh,"
2011)." Notwithstanding" the" significant" difference" in" density" to" other" types" of"plastics,"
there"will"always"remain"a"small"fraction"of"PVC"in"the"mixture,"as"a"result"of"imperfect"
separation."This"requires"special"attention,"as"the"formed"HCl"will"have" to" be" removed"
from"the"products."Furthermore,"the"presence"of"this"acid"will"impose"severe"metallurgic"
constrains"on"the"equipment"material."Note"that"the"presence"of"even"small"amounts"of"
halogens" in" the" oil/waxes" prevents" the" use" of" it" as" fuel" or" petrochemical" feedstock." A"
typically"used"specification"indicates" that" the"amount"of"chlorine"should"not"exceed"10"
ppm"(Bhaskar" et" al.," 2003)." To" tackle" the" challenge" of" PVC" contaminants" in" the" SPW"
stream," pyrolysis" at" lower" temperature" (300" °C)" has" been" suggested"(Bhaskar" et" al.,"
2003;"Okuwaki,"2004;"Sadat-Shojai"and"Bakhshandeh,"2011)."In"a"pre-pyrolysis"reactor"
the"plastics"are"melted"and"degradation"of"PVC"takes"place"while"other"types"of"plastics"
remain" almost" unaffected." Chlorine" removal" of" 98"wt%" has" been" reported"(Okuwaki,"
2004)."The"remaining"chloride"in"the"effluent"can"be"neutralized"via"reaction"by"addition"
of"CaCO3," CaO," NaHCO3," Na2(CO3)2"or" NH3." Nevertheless," proper"sorting" of" the"starting"
material"is"paramount,"as"these"last"techniques"will" lead"to"waste"streams"that"need"to"
be"processed,"increasing"the"overall" operating" cost" of" the"plant."In"addition,"the"use"of"
these"neutralization" agents" is" less"favoured"from" an" environmental"point" of" view." The"
formed"HCl"will"be"contaminated"by" some" light" hydrocarbons" and" economically" viable"
valorisation"is"not"possible"today."Last"but"not"least,"the"different"product"fractions"will"
also" contain" some" traces" of" sulphur" or" other" elements" as" most" plastics" contain" anti-
flame"or"antioxidant"additives"(Miskolczi"et"al.,"2004).""
"
The"primary"pyrolysis"reactor"can"be"of"several"design"types,"as"schematically"depicted"
in"Figure"29."Bubbling"fluidized"bed,"stirred"tank"reactors"and"screw/auger"reactors"are"
the"main"designs"and"have"been"extensively"reviewed"(Butler"et"al.,"2011)."Most"authors"
conclude"that"fluidized"bed"reactors"are"the"most"favourable"option"for"plastic"pyrolysis,"
due"to" a" vast" number" of" advantages" such" as" uniform" product" and" higher" conversion"
rates"(Westerhout"et"al.,"1998)."However,"recently"a"new,"disruptive"reactor"concept"has"
been" introduced," that" makes" use" of" a" rotating" bed," the" so-called" the" gas-solid" vortex"
reactor"in" a" static" geometry" (GSVR−SG)"or" vortex" reactor," as" shown" in" Figure" 26." The"

40"
"
unique"attributes"of"the"vortex"reactor"allow"it"to"significantly"improve"certain"processes"
that" suffer" from" convective" heat" or" mass" transfer" limitations" between" phases." Other"
advantages"may"arise"from"the"ability"to"work"with"different"fluidisation"agents"such"as"
steam" or" hydrogen" (de" Broqueville," 2009)." The" high" centrifugal" acceleration" (greater"
than" 30"g’s)" generates" much" higher" slip" velocities" and" more" intense" heat" and" mass"
transfer"between" phases." Since" the" GSVR−SG" technology" is"relatively" new," the"state" of"
the" art" is" still" at" the" level" of" cold" flow" assessment" analyses," experimentation" and"
modeling," with" valuable" experimental" studies" carried" out" for" different" applications"
(Ashcraft" et" al.," 2012;" Ashcraft" et" al.," 2013;" De" Wilde" and" de" Broqueville," 2007," 2008;"
Dutta"et"al.,"2010;"Ekatpure"et"al.,"2011;"Kovacevic"et"al.,"2014;"Kovacevic"et"al.,"2015)."
"
For"the"fluidized"bed"reactor,"the"molten"plastic"stream"coming"from"the"pre-treatment"
step"in"which"removal"of"the"chlorine"takes"place"is"fed"to"the"reactor."The"formed"gasses"
are" rapidly" cooled" to" prevent" undesired" secondary" gas" phase" reactions." In" order" to"
fluidize"the"bed,"a"fluidizing"gas"is"needed."Theoretically,"nitrogen,"steam"or"a"recycle"gas"
can" be" used." When" targeting" high" small" olefins" yields," recycle" gas" is" a" questionable"
option"as"secondary" reactions" will" dominate"and"hence" will" decrease" the" small"olefins"
yields." Nitrogen" is"not" a" good" option" either" as" separation" of" the" products" nor" is" it"
economically"feasible"from"an"industrial" point"of"view."Steam"has"been" found"to"be"the"
best"option"in"that"respect"(Westerhout"et"al.,"1998).""
"
As" stated" previously," the" products" of" the"reaction" can" mainly" be" divided" into" three"
generic" fractions:" gas," liquids" and" char." The" temperature" of" the" reactor" has" a" big"
influence"on"the"mass"distribution"among"these"fractions."

41"
"
"
"
"#$%&'! AW)! 6#++'&'73! 8'4#$74! +/&! 0.243#,! 4/.#8! ;243'! 0 -&/.-4#4>T%3.'&! '3! 2.5:! AB((D)! >2D!T%XX.#7$! ".%#8#b'8!T'8:! >XD ! +.%#8!
,232.-3#,!,&2,Z'&:!>,D!43#&&'8!327Z!&'2,3/&!278!>8D!4,&';_2%$'&!&'2,3/&5!
Beside"the"temperature,"a"vast"number"of"parameters"influence"the"product"spectra"of"
the"plastic"pyrolysis"process:"composition,"macrostructure"of"the"polymer,"level"of"micro"
mixing,"residence"time"of"the"gas,"temperature"and"fluidizing"gas"(Al-Salem"et"al.,"2009b;"
Faravelli" et" al.," 2003;" Faravelli" et" al.," 1999;" Marongiu" et" al.," 2007;" Ranzi" et" al.," 1997;"
Walendziewski"and"Steininger,"2001;" Yan"et"al.,"2015)."Therefore,"detailed"modeling"of"
the"process"is"necessary"to"raise"the"performance"of"the"process"to"unprecedented"levels"
of"efficiency" and" maximize" profit."Although" the" kinetics" are"highly" complex" due" to"the"
condensed"phase,"the"free"radical"mechanism"and"the"vast"number"of"species,"detailed"
models"are"an" indispensable" tool," allowing" to" reduce"the"uncertainty,"while" increasing"
the" credibility" and" hence" proving" the" economic" viability" of" the" process." Many" groups"
have" been" conducting" experiments" and" developing" kinetic" models" for" the" pyrolysis" of"
SPW."In"particular,"this"has"been"done"for"the"polyvinyl"polymers"such"as"PE,"PP"and"PS,"
as" these" give" rise" to" products" with" favorable" properties"for" further" applications."
Thermogravimetric" analyses" have" been" mainly" used" to" understand" the" mechanism" of"
pyrolysis"of"virgin"plastics"and"to"determine"kinetic"parameters"of"rather"simple"kinetic"
models"consisting"of"several"lumped"fractions"and"power"law"equations,"i.e."the"so-called"
Coats−Redfern"method."These"models"have"focused"on"describing"isothermal"of"dynamic"
thermogravimetric" data." One" disadvantage" is" that" these" thermogravimetric" data" have"
been"measured"at"quite"low"temperatures"and"hence,"extrapolation"towards"industrially"
relevant" temperatures" might" be" error-prone." Differences" in" thermal" decomposition"
were"noticed,"most"likely"related"to"the"presence"of"contaminants" and" additives" in" the"

42"
"
plastics." For" example," it" has" been" observed" that"waste" plastics" have" a"lower" initial"
decomposition"temperature"(Yan"et"al.,"2015)."
Ranzi"et"al."have"published"models"for"the"pyrolysis"of"polyolefins"by"assuming"a"typical"
radical" chain" mechanism" consisting" of" initiation," H-abstraction," β-scission" and" radical"
recombination"(Ranzi"et"al.,"1997)."Further"extension"has"been"done"in"the"modeling"of"
the" process." Faravelli" et" al."(Faravelli" et" al.," 2003;" Faravelli" et" al.," 1999)" paid" more"
attention"to"the"product"distribution"and"later"the"thermal"decomposition"of"PE"and"PS"
mixtures" where" the" amount" of" macromixing" was" taken" into" account" (Faravelli" et" al.,"
2003;"Faravelli"et"al.,"1999)."More"recent"developments"were"accomplished"by"extending"
the" number" of" reaction" possibilities" by" Marongiu" et" al."(Marongiu" et" al.," 2007)." The"
amount" of" ordinary" differential" equations" which" has" to" be" solved" is" very" high" and"
different"solution"methods"have"been"compared"(Marongiu"et"al.,"2003;"Marongiu"et"al.,"
2007)."Compact," yet" sufficiently" detailed" kinetic" models" that"have" been" validated"with"
reliable"experimental"data"are"still"lacking,"and"this"leads"to"scale-up"problems,"which"is"
therefore"one"of"the"key"difficulties"to"improve"the"flexibility"of"plastic"waste"pyrolysis.""
"
Another"major"challenge"is"stable"waste"supply,"with"the"focus"on"quantity,"composition"
and"quality."For"example" the"BASF"feedstock"recycling"process"was"designed" to"handle"
the" recycling" of" mixed" plastic" waste" supplied" by" the" DSD" (Dual" System" Germany" Ltd)"
collection"system."A"pilot"plant"was"started"in"1994"in"Ludwigshafen,"with"a"capacity"of"
15,000"ton/yr."Uncertainties"in"the"feedstock"supply"caused"that"no"agreement"could"be"
reached" on" a" waste" supply" guaranteed" in" the" long" term" for" a" gate" fee" that" would" be"
sufficient"to"cover"the"costs"of"a"full-scale"plant."Particularly"due"to"the"long"mortgaging"
periods"of"such"industrial"installations,"long-term"commitments" are"essential"to"reduce"
the" financial" risks" for" the" investor" to" reasonable" levels." The" pilot" plant" was" closed" in"
1996.""
"
3.3 Fluid!Catalytic!cracking!(FCC)!
Thermal" decomposition" of" SPW"yields" a" skewed" carbon" distribution" of" the" reactor"
effluent,"as"shown"in"Figure"30."Therefore"catalytic"decomposition"of"SPW"seems"to"be"a"
better" alternative" as" the" product" spectra" will" be" narrower" by" the" intrinsic" shape"
selectivity"that"a"catalyst"exhibits,"as"shown"in"Figure"30.""
!
!

43"
"
!
"#$%&'!HB)!?&/8%,34!8#43&#X%3#/7!/+!39'!.#g%#8!0&/8%,34!/+!39'!0-&/.-4#4!X-!F,9#&1'&!'3!2.5!>F,9#&1'&!'3!2.5:!ABB(XD5!
Another"advantage"is"that"the"product"spectra"can"be"directed"towards"fuel,"commodity"
chemicals" and" fine" chemicals," depending" on" the" process" conditions." Also," the" use" of"
catalyst"allows"to"use"less"stringent"reaction"conditions,"lowering"energy"consumption"of"
the"overall"process"and"as"such"affecting"the" total" operating" cost" (Lin" and" Yang,"2009;"
Passamonti" and" Sedran," 2012;" Thegarid" et" al.," 2014)." In" Figure" 30" a" comparison" has"
been"made"between"the"reactor"effluent"of"the"thermal"and"catalytically"cracked"plastics."
As"can"be"seen,"the"product"spectrum"has"been"shifted"towards"smaller"carbon"numbers"
and" has" a" smaller" tail." Furthermore," the" aromatic" and" naphthenic" compounds" are"
selectively"formed"in"presence"of"a"classical"FCC-catalyst"(Buekens"and"Huang,"1998;"Li"
et"al.,"2014)."Catalytic"cracking"increases"the"gasoline"yield"as"shown"in"Figure"31.""
"
Two"different"types" of"catalytic"cracking"can"be"distinguished:"liquid"phase"and"vapour"
phase" (Buekens" and" Huang," 1998)." In" the" liquid" phase" process" the" catalyst" comes" in"
direct" contact" with" the" molten" polymer" phase." In" this" mode" the" catalyst" aids" with"
converting"the" partially" degraded" oligomers." In" vapour"phase" contact"processes," the"
vapours"formed"during"cracking" are" brought" into" contact" with"the"catalyst."The"use"of"
solid" catalysts" such" as" silica-alumina," ZSM-5," zeolites," and" mesoporous" materials" for"
these"purposes"are"all"possible"and"have"been"tested."The"reactor"design"is"very"similar"
to"the"FCC-unit"shown"in"Figure"29."
"

44"
"
"
"#$%&'!H()!?&/8%,34!-#'.84!/+!<2&#/%4!,232.-434!23!JJB!hU!X-!F,9#&1'&!'3!2.5!>F,9#&1'&!'3!2.5:!ABB(2D5!!
"
As"stated"previously,"one"of"the"main"advantages"over"SPW"pyrolysis"is"that"conversion"
can" be" achieved" at" lower" temperatures," having" a" positive" effect" on" the" overall" heat"
requirement"and"hence"on"the" economics" of" the" process." The"required"temperature"to"
achieve"reasonable"conversion"for"pyrolysis"is"above"450"°C,"while"the"temperature"can"
be"lowered"to"300-350"°C"when"using"a"catalyst"(Buekens"and"Huang,"1998)."Moreover,"
the"yields"towards"iso-alkanes"and"aromatics"in"the"range"of"C5-C15"are"increased,"which"
are"the"higher"valued"gasoline"components,"as"can"be"seen"in"Figure"31.""
"
Nevertheless" catalytic" cracking" also" suffers" from" several" drawbacks." Carbonaceous"
deposits,"being"Cl"and"N"components"present"in"the"raw"waste"stream,"rapidly"deactivate"
the" catalyst." Furthermore," inorganic" materials" tend" to" block" the" pores" of"the" catalyst,"
which"sometimes"results" in"a"permanent"deactivation"of"a"large"number"of" active"sites."
Therefore," harsh"pre-treatment" steps"are" quite" often" required" to" protect" the" catalyst."
Sometimes" light" pyrolysis" of" the" feed" as" pre-treatment" allows" dealing"with" highly"
contaminated" feeds" or" feeds" containing" significant" amounts" of" heteroatoms." The"
presence" of" these" contaminants" can" also" deteriorate" the" quality" of" the" products," and"
hence"special"care"is"needed"(Miskolczi"et"al.,"2009)."
"
Several"commercial"catalytic"processes"are"available."Their"main"goal"is"to"produce"high"
yields"of"transport"grade"fuels"such"as"gasoline"and"diesel."An"overview"of"current"pilot"
and"commercial"processes"is"given"in"Table"5."
"
"

45"
"
\2X.'!C)!E<'&<#';!/+!,%&&'73!,232.-3#,!,&2,Z#7$!0.2734!+/&!0.243#,4!>T%3.'&!'3!2.5:!AB((D5!
Process!
Temperature!
Catalyst!
Feedstock!
Capacity!
Yield!
Zadgaonkar"
Process"
400"°C"
unknown"
catalyst"
PE,"PP,"PS"
PVC,"PET"
5"Mt"
(India)"
10-20%"gas,"
60-80%"liquid,"
7-10%"residue"
Smuda"Process"
300-450"°C"
Ni-silicate,"
Fe-silicate"
PE,"PP,"PS,"
PVC,"PET"
10"kt/a""
(Poland)"
32.3"vol%"
gasoline,"43"
vol%"diesel,"
29.7"vol%"
residue"
T-Technology"
390-420"°C"
unknown"
PE,"PP,"PS"
10kt/a""
(USA)"
15-20%"
gasoline,"60-
70%"light"oil,"
fuel"oil"and"
diesel"
"
Note" that" the" results" presented" in" Table" 5" should" be" evaluated" with" a" certain" level" of"
scepticism." This" is" for" example" illustrated"in" the" work" of" Pinto" and" co-workers." They"
studied" plastic"waste" pyrolysis," originating" from" Portuguese" MSW," in" an" autoclave"
reactor"using"several"zeolite"and"several"metallic"catalysts"at"415"°C"and"33"atm"(Pinto"et"
al.,"1999)."The" waste" feedstock" was" a"mixture"of"PC"plastics" and" consisted"of" 68%" PE,"
16%" PP" and" 16%" PS." All" catalysts" gave" an" oil" yield" of" approximately" 90" wt%." The" oil"
fraction"consists"of"alkanes"(55%),"aromatics"(35%)"and"alkenes"(10%)."However,"when"
evaluating" the" research" of" the" octane" numbers" (RON)" of" the" produced" gasoline," Pinto"
and"co-workers"measured"values"in"the"range" between" 15" and" 30." This" is" much" lower"
than"conventional"gasoline"because"of"the"presence"of"large"amounts"of"n-paraffins"and"
the"low"amounts"of"iso-paraffins"and"aromatics."Therefore,"the"liquid"fraction"should"be"
further" treated" or" blended" in" order" to" be" used" as" fuel"(Pinto" et" al.," 1999)," which" is" a"
substantial"additional"cost.""
"
Major" challenges" that" need" to" be" overcome" are" related" to" the" bulky" nature" of" the"
polymers."This"makes"the"activity"too""limited"and"deactivation"by"coking"to"be"severe"
(Serrano"et"al.,"2012),"as"also"indicated"by"the"Ellen"MacArthur"Foundation."The"absence"
of"a"suitable" reactor" technology," in" which"catalytic"fast"pyrolysis"can"be" carried" out," is"
considered"as"the"second"major"bottleneck"(Ellen"Macarthur"Foundation,"2017).""
"
3.4 Hydrogen!technologies!
3.4.1 Hydrocracking!
The"main"difference"with"catalytic" cracking" of"plastics"is"the"addition"of"hydrogen." The"
process"takes"place"at"elevated"hydrogen"pressures,"roughly"70"atm"and"temperatures"in"
the"range"of"375-400"°C."The"catalyst"can"be"a"Ni/S"or"NiMo/S"supported"catalyst."Due"to"
the"presence"of"inorganic"matter"in"the"raw"SPW," the"plastics"are"initially"liquefied"and"

46"
"
filtered"to"remove"non-distillable"material."This"happens"via"low"temperature"pyrolysis."
The" liquid" is" then" sent" over" the" catalyst" bed." The" presence" of" hydrogen" improves"
significantly" the" product" quality," i.e." a" higher" H/C" ratio" and" lower" aromatic" content."
Experiments"for"different"types"of"catalysts" revealed" high" yield" of" paraffin" (Ding" et"al.,"
1997)."Other" main" advantages" to" upgrade"the" liquid" yield" of" plastic"pyrolysis" are" that"
heteroatoms"are"handled"excellently"and"no"toxic"products"such"as"dioxins"are"produced"
or"survive" the" process." On" the" other" hand," a" hydrogen" stream" is" necessary" which" is"
known" to" be" an" expensive" utility." For" example," electrically" produced" hydrogen" costs"
about"€"2500"per"tonne.""
!
Some"advantages"of"hydrocracking"are"that"good"quality"naphtha"feed"can"be"produced"
and"that"mixtures"of" plastics" can"be"used."This"comes"at"the" high" cost"of"hydrogen"and"
the"high"operating"pressures"and"related"investment/operational"costs.""
!
3.4.2 Integrated!hydropyrolysis!and!hydroconversion!(IH2)!
Integrated" hydropyrolysis" and" hydroconversion," also" known" as" IH2," is" a" catalytic"
thermochemical" conversion" process" able" to" convert" organic" material" into" a" range" of"
hydrocarbon"fuels."The"process"can"deal"with"virtually"all"types" of" feedstock," including"
cellulosic" fractions," wood" and" agriculture" residues," municipal" waste" and" mixtures"
thereof"(Marker"et"al.,"2013;"Marker"et"al.,"2012)."The"technology"has"been"developed"by"
Gas"Technology"Institute"(GTI)"of"Des"Plaines."A"simplified"process"scheme"is"presented"
in" Figure" 32." The" process" consists" of" three" reactors," being"hydropyrolysis,"
hydroconversion"and"reforming."
"
The"hydropyrolysis"reactor"is"a"fluidized" bed" reactor" containing" catalyst" particles."The"
catalyst" is" exclusively" licensed" by" CRI" (Criterion" Catalyst" Company)." The" inlet" of" the"
reactor"consists"of"the"renewable"feedstock"and"hydrogen."Operating"temperatures"and"
pressures" are" respectively" between" 400-500"°C" and" 15-35" atm." Note" that" the"
temperature"range"corresponds"to"typical"fast"pyrolysis"temperatures."Hence,"similar"to"
fast"pyrolysis,"volatile"components"are"released"from"the"biomass"in"the"hydropyrolysis"
reactor." In" the" gas-phase," the" formed" molecules" react" with" hydrogen" and" catalyst."
Deoxygenation" takes" place" and" the" oxygen" atoms" end" up" in" water" (dehydration)," CO"
(decarbonylation)"and"CO2"(decarboxylation)."These"reactions"are"exothermic"and"offset"
the" endothermicity" of" pyrolysis." The" effluent" of" the" hydropyrolysis" reactor" has" a" low"
oxygen"content"and"an"acid"number"of"less"than"1,"compared"to"200"for"fast"pyrolysis"oil"
(Marker" et" al.," 2013;" Marker" et" al.," 2012;" Marker" et" al.," 2014)." Acid" catalyzed"
polymerization,"aromatization,"and"coking" reactions" are" suppressed" in"hydropyrolysis,"
compared"to"thermal"pyrolysis"and"catalytic"cracking."The"remaining"solid"residue"can"
be"removed"through"cyclones"while"the"catalyst,"which"has"a"higher"density,"remains"in"
the"fluidized"bed."

47"
"
"
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AB(JD!
Subsequently," the" gaseous" stream" enters" the" hydroconversion" reactor." The" second"
reactor"is"a"fixed"bed"reactor,"again"using"a"CRI"proprietary"catalyst."Operating"pressure"
is" similar" to" the" first" reactor." The" amount" of" heteroatoms" are" further" reduced" in" this"
stage,"the"oxygen"content"goes"from"approximately"2.7"wt%"to"less"than"1"wt%"(Marker"
et"al.,"2014).""
The"product"stream"is" condensed" and"gas"and"liquid"streams"are"separated." The" liquid"
consists"of"two"phases,"an"organic"phase"with"very"low"oxygen"content"and"an"aqueous"
phase."The"gas"stream"consists"of"small"molecules"such"as"methane,"ethane,"propane,"CO"
and"CO2." The" gas" is" sent" to" a" steam" reformer" together" with" the" produced" water." The"
steam"reformer"can" produce" the" required" amount"of"hydrogen"for"hydropyrolysis"and"
hydroconversion." This" does" require" a" proper" hydropyrolysis" catalyst" and" selection" of"
operating"conditions"in"the"hydropyrolysis"reactor"that"balances"dehydration"reactions,"
which"consumes"hydrogen,"as"well"as"decarboxylation"reactions,"which"do"not"consume"
hydrogen."
"
Similar"to"pyrolysis"followed"by"hydrotreatment,"the"IH2"process"enables"the"production"
of" liquid" hydrocarbons" directly" starting" from" plastic" waste." The" IH2"process," however,"
does"not" require" an" external" import" of" hydrogen,"making" the" process"more" attractive."
Furthermore,"the"IH2"process"omits"treatment"of"the"pyrolysis"oil,"which"has"high"acidity"
and" hence" imposes"higher" constraints" on" the" construction" material" of" reactor" and"
storage"vessels." Because" of" its"efficiency," simplicity," moderate" pressures"(compared" to"
ex"situ"hydrotreatment"of"fast"pyrolysis"oil),"and"integrated"nature,"this"technology"has"
been"shown"to"have"good"overall"economic"potential."All"different"individual"elements"of"
the"IH2"process"are"all"already"commercialized,"minimizing"investment"risk"and"allowing"
fast"implementation"of"the"technology.""
The"IH2"process,"which"is"based"on"an"integrated"hydropyrolysis"and"hydroconversion"
mechanism,"is"shown"to"be"a"promising"technology"for"the"production"of"liquid"fuels"out"
of"biomass."The"creators" of" the" IH²" technology"claim"that" the" process" can" be" operated"

48"
"
based" on" a" solid" recovered" fuel" feedstock" including" plastics" from" SPW," but" further"
investigation"is" required" on" this" statement" (Narasimhan" and" Del"Paggion," 2017;" Shell,"
2017)."""
"
3.5 KDV!process!
KDV,"a"German"acronym" for"Katalytische"Drucklose"Verölung!or"the"catalytic" pressure-
less"depolymerization"process,"was"developed"by"the"German"company"Alphakat"GmbH"
and"claims"the"catalytic"conversion"of"biomass"and"plastic"waste"towards"liquid"fuels"at"
nearly"atmospheric"pressure."The"advantage"of"the"products"of"this"process"is"the"almost"
complete" removal" of" oxygen" atoms," making" the" final" liquid" fuel"directly" applicable" in"
conventional" combustion" engines." As" such," this" technology" would" make" it" possible" to"
obtain" diesel" oil," kerosene" and" petroleum" from" all" substrate" types" that" contain"
hydrocarbons"of"both"organic"and"mineral"origin."In"this"way,"the"possible"feedstock"of"
the"process"can"range"from" polymer" plastics"such"as"PET"and"PP"to"lignocellulose."The"
oxygen"will"generally"be"removed"as"CO2."A"second"advantage"of"the"process"is"the"mild"
reaction" conditions" at" which" the" reaction" takes" place" in" comparison" to" alternative"
processes" such" as"pyrolysis" (Reza" and" Bahram," 2015)." According" to" the" licensors," the"
technology"is"ready"for"industrial"use"and"many"demonstration"and"full-scale"facilities"of"
the"KDV"process"have"been"built"in"various"countries"with"outputs"ranging"from"150"to"
5000"l/hr"of"diesel"fuels"proving"feasibility"and"scale"up"possibilities."In"Table"6"different"
installed"KDV-plants"are"summarized."
\2X.'!M)!*/,23#/7:!4#b'!278!-'2&!/+!#7432..23#/7!/+!P6O!0.2734!2&/%78!39'!;/&.8!>a1XeD5!
Location!
! !Size!
Year!of!installation!
Remarks!
Monterey,"Mexico"
KDV500"
2004"
"
Bulgaria"
KDV500"
2007"
"
Ontario,"Canada"
KDV500"
2007"
1st"generation"plant"
Hoyerswerda,"
Germany"
KDV500"
2008"
1st"generation"plant"
Tarragona,"Spain"
KDV1000"
2009"
1st"generation"plant"
Massachusetts,"USA"
KDV500"
2010"
Installed"by"Covanta"Energy"
Corp"
1st"generation"plant"
Eppendorf,"
Germany"
KDV150"
2010"
"
Bary,"Italy"
KDV150"
2012"
"
Ethiopia"
KDV150"
2012"
"
Lesmierz,"Poland"
KDV1000"
2012"
First"compact"KDV1000"
Tekirdag,"Turkey"
KDV1000"
/"
Compact"KDV1000"
Schwyz,"
Switzerland"
KDV150"
/"
"

49"
"
Before"sending"the"feedstock"to"the"reactor,"a"pre-treatment"is"necessary"to"reduce"the"
water" content" to" around"5" wt%," and" the" particle" diameter" to" less" than" 3" mm." The"
shredded" feedstock," catalyst" and" lime" are" subsequently" mixed" with" carrier" oil" and"
heated" to" a" temperature" of" 180" °C." The" catalyst" applied" in" this" process" is" a" 100%"
crystalline" alkali-doped" aluminium" silicate," such" as" a" sodium" doped" zeolite" of" type" Y"
with"faujasite"structure"(Broach"et"al.,"2012)."By"using"this"catalyst"of"natural"origin,"the"
inventors" claim" to" imitate" the" natural" process" of" oil" creation" on" an" accelerated" basis"
(GmbH;"Koch,"2011)."The"lime,"Ca(OH)2,"is"added"to"control"the"pH"at"a"value"of"around"
9,"which"is"the"optimal"environment"for"the"catalytic"reaction."
"
"#$%&'!HH)!F,9'123#,2..-!/<'&<#';!/+!39'!P6OK0&/,'445!
The"oil"mixture"is"subsequently"sent"to"the"turbine"reactor"in"which"the"temperature"is"
raised"to"250"°C."This"increase"in"temperature"will"be"the"result"of"in"a"high-shear"inline"
mixer"connected"in"circuit" to" the"reactor."Liquid"and"solid"material" is" dragged"by"high-
speed"rotation" of" the" turbine" blades." Due" to" the" centrifugal" forces," the" preheated" and"
dewatered" material" is" forced" towards" the" periphery" and" the" hydrocarbons" are"
separated" from" the" residues." At" the" same" time," the" mixing" and" frictional" energy" will"
increase" the" temperature" leading" to" depolymerisation" and" deoxygenation" of" the"
extracted" hydrocarbons." A" reaction" temperature" between" 250" and" 320" °C" results" in" a"
product"distribution"in"the"middle"distillate"range,"i.e."diesel"fuel."Both"the"initial"mixer"
and"turbine"reactor"will"operate"at"pressures"slightly"beneath"atmospheric"pressure"(90"
kPa)."
"
The"reactions"in"the"KDV"reactor"are"not"studied"intensively."It"is"argued"that"before"the"
hydrocarbon" plastics" are" thermally" cracked," they" are" first" dechlorinated" and"
dehalogenated"by"neutralization"of"the"ion"exchanging"catalyst" (Scheirs" and" Kaminsky,"
2006)." As" such," issues" are" avoided" with" HCl" generation" and" chlorine" contamination,"

50"
"
which"are"encountered"in"other"waste-to-fuel"processes."Furthermore,"this"ion"exchange"
capability" of" the" catalyst" will" enable" using" considerably" lower" cracking" temperatures"
compared" to" conventional" catalysts." Furthermore," in" a" study" conducted" by" Kemi-
information" AB," a" theoretical" evaluation" of" the" process" based" on" a" claimed" energy"
efficiency"of"70%"was"performed."This"study"pointed"out"some"discrepancies"in"the"mass"
and"energy"balances"presented"by"Alphakat"(Reza"and"Bahram,"2015)."
"
Thermal"cracking"will"occur"in"the"turbine"reactor"where"the"temperature"is"raised"by"
friction."In"this"way"coke"deposition"on"the"wall" can" be" omitted" instead" of"using"direct"
heating" via" the" wall"(Koch," 2011)." The" acid" cracking" catalyst" will" produce" carbonium"
ions" by" the" abstraction" of" hydride" ions" from" the" hydrocarbon" molecules." This" is"
subsequently" followed" by" chain" scission" yielding" C30" –" C50" oligomeric" hydrocarbons."
Secondary" cracking" by" β-scission" of" these" hydrocarbons" will" then" give" rise" to" liquid"
hydrocarbon"fuel"located"in"the"middle"distillate"range"(C10"–"C25)"(Scheirs"and"Kaminsky"
2006)."
"
A"part" of" the" reaction"product"is" returned" to" the"mixer" to" maintain" the"oil"circulation."
Since"not"only"diesel"is"recycled"but"also"water"and"gaseous"products,"the"presence"of"a"
distillation"column"is"required"for"the"removal"of"these"products."Also,"the"water"present"
in" the" reactor" feed" will" be" separated" as" such," as" it" evaporates" at" the" operation"
temperature"of"the" mixer."The"other"part"of"the"reaction"product"is" separated"from"the"
turbine"reactor"by"distillation."By"running"through"condensers"at"different"temperatures"
the"water"and"gaseous"products"will"be" parted"from"the"KDV" fuel."The"temperatures"of"
these"condensers"will"be"determined"by"closed"cooling"water"and"oil"cycles."Afterwards,"
the"KDV"fuel"is"sent"to"a"distillation"column"where"it"is"separated"in"the"actual"diesel"oil"
and" bitumen." This" latter" could"be" used" as" asphalt" for" road" construction"or" as" fuel" for"
combustion."Van"Geem"and"co-workers"compared"the"most"important"properties"of"two"
of" these" KVD" fuels" with" conventional" petroleum" diesel" and" showed" that," with" minor"
upgrading," direct" use" in" refineries" is" possible," see" Table" 6" (Gonzalez-Quiroga" et" al.,"
2016)." More" specifically," the" organic" fractions" recovered" from" demolition" waste" and"
municipal"solid"waste"were"liquefied"and"deoxygenated"in"a"CPD"pilot"plant"with"150"L"
h-1"(4.2" x" 10-5" m3" s-1)" liquid" fuel" capacity." The" produced" fuels" were" characterized" by"
elemental" analysis," comprehensive" two-dimensional" gas" chromatography," and" the" ISO"
tests"for"automotive"diesel"established"by"the"EN"590:2009"Standard."The"studied"fuels"
showed"very"low"oxygen"contents"(<0.4"wt%)"and"a"high"share"of"paraffins"(>40"wt%)."
The"carbon"range"of"the"fuel"obtained"from"demolition"wood"was"wider"than"that"of"the"
fuel"obtained"from"municipal"solid"waste" (C-5-C-29" vs."C-6-C-22)."The"flash"points"(54,"
46" °C)," the" sulfur" contents" (40," 80" ppmw)," and" the" cetane" numbers" (43," 33)" did" not"
comply"with"the"respective"requirements"for"automotive"diesel"(i.e.,"≥"55"degrees"C,"<10"
ppmw,"and"≥51)."Nevertheless,"both"fuels"showed"salient"cold"filter"plugging"points"(-14,"
-15"°C)"and"cloud"points"(-15,"-44"°C),"which"are"indicative"of"good"fuel"performance"at"
extreme"winter"conditions."The"wide"carbon"number"distribution,"especially"toward"the"
lower"range"(i.e.,"carbon"number"<"C,),"suggests"that"the"studied"fuels"can"be"split"into"a"

51"
"
kerosene-like"and"a"diesel-like"cut."Overall,"the"fuels"from"the"CPD"process"exhibit"great"
potential" as" alternative" transportation" fuel." However," properly" selecting" the" starting"
material"is"crucial"for"minimizing"costly"hydrotreating."
"
\2X.'!S)! F32782&8#b'8! +%'.! 0&/0'&3#'4!/+!39'!U?6! +%'.4!,/102&'8!3/!39/4'!/+! 0'3&/.'%1! 8#'4'.!278!39'!&'g%#&'1'734! +/&!
8#'4'.!'432X.#49'8!X-!39'!@d!CWB)ABBW!F32782&8!>a/7b2.'bK[%#&/$2!'3!2.5:!AB(MD5!
Property!(Standard)!
CPD!fuel!
from!SRF-
DW!
CPD!fuel!
from!SRF-
MW!
Petroleum!
diesel!
(Labeckas!
and!
Slavinskas
,!2013a)!
EN!590:2009!
requirement!
Density"at"15"°C"(ISO"
12185),"kg"m-3"
840"
807"
842"
820-845"
Kinematic"viscosity"at"40"°C"
(ISO"3104)"mm2"s-1"
2.52"
1.49"
2.94"
2.0-4.5"
Flash"Point"(ISO"2719),"°C"
53.5"
46.0"
68"
≥55"
Cold"Filter"Plugging"Point"
(EN"116),"°C"
-14"
-47"
-5"
n.s.a"
Cloud"Point"(EN"23015),"°C"
-15"
-44"
6"
n.s."
Content"of"ashes"(ISO"
6245),"ppmw"
350"
<10"
n.r.b"
≤100"
Sulfur"content,"ppmv"
40"
80"
9.0"
<10"
Ash"content"(ISO"6245),"
ppmw"
350"
<10"
n.r."
≤100"
Nitrogen"content,"ppmv"
<100"
150"
n.r."
n.s."
High"Heating"Value"(ISO"
8217),"MJ"kg-1"
42.9"
43.2"
43.0"
n.s."
Iodine"number"(EN"14111),"
g"I2"(100g)-1"
8.8"
12.2"
12"
n.s."
Water"content"(ISO"12937),"
ppmw"
118"
96"
21"
≤200"
Cetane"number"(ISO"5165)"
43.0"
33.1"
51.6"
≥51"
an.s. non-specified. bn.r. non-reported.
An" additional" expansion" of" the" KDV" process" is" the" off-line" removal" of" ashes" from"the"
turbine"reactor."These"residuals"still"contain"a"significant"amount"of"KDV"fuel."The"ashes"

52"
"
are"therefore"heated"to"500"°C"at"which"the"remaining"fuel"is"removed"and"separated"via"
a" distillation" column." The" residual" ashes," which" contain" a" considerable" amount" of"
minerals,"could"be"applied"as"fertilizer"for"agricultural"usage"(Koch,"2011)."
"
KDV"diesel"suffers"from" a" high" sulphur" content,"see"Table"6" (Labeckas" and" Slavinskas,"
2013b)."Due"to"emission"regulations"in"the"EN"590:2009"norm,"the"sulphur"content"has"
become"one"of"the"most"important"fuel"properties"and"this"is"problematic"for"the"KDV"
fuel."Although"the"sulphur"content"strongly"depends"on"the"feedstock"composition,"it"is"
consistently" found" to" be" high." Another" issue" is" that" the" cetane" number" is"in" general"
slightly" lower" than" what" is" required" by" the" European" Standards"(Labeckas" and"
Slavinskas," 2013b)." In" addition," increased" NOx," CO" and" HC" emissions" as" compared" to"
regular" diesel" were" reported." Although" these" emissions" would" be" within" the" limits"
permitted"by"the"Emission"Standards"(Labeckas"and"Slavinskas,"2013b)."
"
The"KDV"process"has"been"demonstrated"to"be"able"to"convert"SRF"into"synthetic"fuel."In"
contrast"to"other"WtE"processes,"KDV"offers"the"opportunity"of"processing"oxygen"and"
halogenated"compounds."The"chemistry"behind"this"process,"however,"is"still"unknown."
However,"it"shows"many"similarities"with"deoxy-liquefaction"process."In"addition"to"the"
lack"of"chemical"information,"there"is"also"a"lack"of"technical"information"about"the"KDV"
process"and"hence"further"investigation"is"required"(Gonzalez-Quiroga"et"al.,"2016).""
"
3.6 !Gasification!combined!with!methanol!production!
In" the" Netherlands," a" partnership" comprised" of" AkzoNobel," Van" Gansewinkel," Air"
Liquide,"AVR"and"Enerkem"is"looking"to"build"its"waste-to-chemicals"plant"in"Rotterdam."
The" new" chemical" plant" will" use" Enerkem’s" innovative" technology" to" convert" residual"
waste"into" methanol," a" raw"material" used" in" the"chemical" industry." The" methanol"will"
then" be" converted" into" chemicals" such" as" acetic" acid" (e.g.," for" fibres" and" adhesives),"
thickening" agents" and" dimethyl" ether" (clean" propellant" gases)." These" chemicals" are"
currently"produced"almost" entirely"from"fossil"fuels."The" planned"facility"will"therefore"
provide"a"sustainable"alternative"by"producing"a"renewable"chemical"and"will"represent"
a"significant"step"toward"a"sustainable"and"circular"approach"to"waste"management" in"
Rotterdam."
Syngas"is" a" valuable" intermediate" in" the" chemical"industry" and" can" be" produced"from"
any" carbonaceous" source" such" as" natural" gas," coal," biomass" or" even" organic" wastes"
(Wender,"1996)."The"lowest" production"cost"of"syngas"so"far" is"based"on"methane"and,"
hence,"the"main"focus"has"been"on"using"associated"gas"(Dry,"2002)."Associated"gas"is"a"
byproduct"during"the"exploitation"of"crude"oil"and"comes"at"low"or"even"negative"value."
Syngas"can"be"produced"from"any"organic"source"and" it"has"profiled"itself"as"important"
intermediate"to"the"production"of"petroleum"like"products"through"FTS"or"via"methanol"
and" DME" synthesis" followed" by" MTG/MTO"(Wender," 1996)." Syngas" is" a" mixture" of"
carbon"monoxide"and"hydrogen."The"quality"of"syngas"is"measured"via"the"H2/CO"ratio."
This"is"an"important"specification"as"different"downstream"process"steps"have"different"

53"
"
optimal" ratios." At" present," these" process" steps" are" applied" at" industrial" scale" if" fossil"
feedstocks,"mainly"gas"and"coal,"are"used"and"can"be"considered"as"proven"and" mature"
technologies.""
"
3.6