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Biodegradation of polyethylene and polypropylene

Authors:
  • Distinguished Prof Saveetha Dental College Chennai; Director Theevanam Additives & Neutraceuts p ltd(IIT M research park) Madras

Abstract and Figures

Polyethylene and polypropylene are the two polyolefins with wide ranging applications. They are recalcitrant and hence remain inert to degradation and deterioration leading to their accumulation in the environment, and, therefore creating serious environmental problems. In this review, biodegradation of these two polymers under in vitro conditions is reported. An attempt has been made to cover the mechanism of biodegradation, the various bacterial and fungal organisms that have been reported for the same, methods adopted for the studies and different characterization techniques followed to measure the extent of degradation.
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Indian Journal of Biotechnology
Vol. 7, January 2008, pp 9-22
Biodegradation of polyethylene and polypropylene
J Arutchelvi, M Sudhakar, Ambika Arkatkar, Mukesh Doble*, Sumit Bhaduri1 and Parasu Veera Uppara1
Department of Biotechnology, Indian Institute of Technology, Madras, Chennai 600 036, India
1Polymer Research and Technology Center, Reliance Industries Limited, Swastik Mills Compound,
Chembur, Mumbai 400 071, India
Received 26 May 2006; revised 21 February 2007; accepted 22 May 2007
Polyethylene and polypropylene are the two polyolefins with wide ranging applications. They are recalcitrant and
hence remain inert to degradation and deterioration leading to their accumulation in the environment, and, therefore creating
serious environmental problems. In this review, biodegradation of these two polymers under in vitro conditions is reported.
An attempt has been made to cover the mechanism of biodegradation, the various bacterial and fungal organisms that have
been reported for the same, methods adopted for the studies and different characterization techniques followed to measure
the extent of degradation
Keywords: polyethylene, polypropylene, biodegradation, in vitro
Introduction
The myriad applications of polymers in almost all
the fields ranging from sophisticated articles such as,
prosthetic hips and knee joints to disposable food
utensils implies their significance and importance in
our day to day life. Thus, enormous production and
utilisation of polymers lead to their accumulation in
the environment. Since not easily degraded by
microorganisms, today they have become a serious
source of pollution affecting both flora and fauna.
Polyolefins or saturated polymers have a broad
range of applications. Polypropylene (PP) and
polyethylene (PE), expressed as CnH2n, are most
widely used linear hydrocarbon polymers. The
versatility of these polymers arises from the fact that
they are made from cheap petrochemical feed stocks
through efficient catalytic polymerisation process and
their ease of processing to various products. The
range of their applications include, food packaging,
textiles, lab equipments, and automotive components.
PP has a methyl group instead of one of the
hydrogens present in PE, on every other carbon,
which gives rise to the existence of three
stereoisomeric forms namely, atactic, isotactic, and
syndiotactic1. This stereoregular polymer was first
synthesised by Ziegler and Natta with propylene as
the monomer. Metallocene catalysts can also be used
for its synthesis. Industrially applicable PE was first
synthesised in 1933 by Eric Fawcett and Reginald
Gibson at ICI chemicals2. PE is totally linear and
available with varying range of densities from 0.91 to
0.97 g/cm3. Low density PE has branching at random
places leading to low packing of the polymer chains,
whereas the high density PE is more linear with
minimal branching leading to high packing density1.
As reported by American Plastic Association,
percentage distribution of PP, high density
polyethylene (HDPE), linear low density
polyethylene (LLDPE) and low density polyethylene
(LDPE) are 18.4%, 17.4%, 12.1% and 8.2%,
respectively in terms of sales and use in the year
2004 in the United States, Canada, and Mexico3.
Non-degradable plastics accumulate in the
environment at a rate of 25 million tonnes per year4.
Extensive use of non-biodegradable thermoplastics
and the rate at which they accumulate in the
environment, makes the humankind to realise the
necessity to find its environmental impact. As the
polymer usage is unavoidable, ways have to be
found to (1) Enhance the biodegradability of the
polymers by blending them with biodegradable
natural polymers such as starch5-19 or cellulose20 etc;
(2) Mixing with prooxidants5,21,22 so that they are
easily degraded and (3) Isolate23 and improve
microorganisms that can efficiently degrade these
polymers. In order to attempt the third option the
mechanism of biodegradation should be understood.
_
________________
*Author for correspondence:
Tel: 91-44-2257407
E-mail: mukeshd@iitm.ac.in
INDIAN J BIOTECHNOL, JANUARY 2008
10
Overview of Biodegradation of Polymers
A general overview of biodegradation of polymers
over a period of time is schematically represented in
Fig. 1. Polymeric materials released into the
environment can undergo physical, chemical and
biological degradation or combination of all these due
to the presence of moisture, air, temperature, light
(photo-degradation), high energy radiation (UV, γ-
radiation) or microorganisms (bacteria or fungi). The
rates of chemical and physical degradation are higher
when compared to that of biodegradation. Also,
physical and chemical degradation facilitates
microbial degradation and complete mineralisation of
the polymer happens due to biodegradation, which is
generally the final step24,25.
Mechanism of Biodegradation
Biodegradation of polymers involves following steps:
1. Attachment of microorganism to the surface of
the polymer
2. Growth of microorganism utilising the polymer
as the carbon source
3. Primary degradation of the polymer and
4. Ultimate degradation
Microorganisms can attach to the surface, if the
polymer surface is hydrophilic. Since PP and PE have
only CH2 groups, the surfaces are hydrophobic. Initial
physical or chemical degradation leads to the insertion
of hydrophilic groups on the polymer surface making it
more hydrophilic (insertion of hydrophilic groups also
decreases the surface energy). Once the organism gets
attached to the surface, it start growing by using the
polymer as the carbon source. In the primary
degradation, the main chain cleaves, leading to the
formation of low-molecular weight fragments
(oligomers), dimers or monomers24. The degradation is
due to the extra cellular enzymes secreted by the
organism. These low molecular weight compounds are
further utilised by the microbes as carbon and energy
sources. Small oligomers may also diffuse into the
organism and get assimilated. The ultimate products of
degradation are CO2, H2O and biomass under aerobic
conditions. Anaerobic microorganisms can also degrade
these polymers under anoxic conditions. The primary
products then are CO2, H2O, CH4 and biomass under
methanogenic condition or H2S, CO2 and H2O under
sulfidogenic condition. The environmental conditions
decide the group of microorganisms and the degradative
pathway involved. Ultimate degradation of recalcitrant
synthetic polymers may take several hundred years24-28.
Additives, antioxidants and other stabilisers added to
commercial polymers may be toxic to the organisms or
may slow down the rate of biodegradation.
Strategies used to Characterize Biodegradability of Polymers
As mentioned before, the high molecular weight
polymers are degraded first into oligomers, some of
which might be water soluble and then they are
further broken down into organic intermediates. The
intermediate products may be acids, alcohols, ketones,
etc. The following strategies are used to assess and
monitor the biodegradation of the polymers:
1. Accumulation of biomass (experimentally
determine the growth rate of microorganisms
with the polymer as the sole carbon source)
2. Oxygen uptake rate
3. Carbon dioxide evolution rate
4. Products of reaction using chemical analysis
5. Surface changes
6. Changes in the mechanical and physical
properties of the polymer8
Analytical Techniques
Several analytical techniques have been used to
monitor the extent and nature of biodegradation
(Fig. 2). These characterisation techniques are meant
to study the mechanical, chemical, and physical
properties of the polymer before and after
degradation, which will help in understanding the
extent as well as the mechanism of degradation. The
study of mechanical properties comprises measuring
of the tensile strength, elongation at fail and modulus
of the polymer by using Instron. The physical
properties of the polymers monitored are: morphology
(microcracks, embrittlement using SEM, transmission
optical microscopy), density, contact angle, viscosity,
Fig. 1—Overview of degradation of polymers (Adapted from
Vasile).
ARUTCHELVI et al: BIODEGRADATION OF POLYETHYENE & POLYPROPYLENE
11
molecular weight distribution (using GPC), melting
temperature (Tm), glass transition temperature (Tg)
(doing TGA and DSC) and changes in the crystalline
and amorphous regions (X-ray diffraction, SAXS and
WAXS). The changes in the chemical properties that
could be measured include formation or disappearance
of functional groups as determined by FTIR. The
molecular weight and molecular weight distribution of
the degraded products or intermediates are characterised
by techniques such as TLC, GC, GCMS, CL, MALDI-
TOF, NMR (Fig. 3)5,23. The level of information derived
from each technique, as shown in Fig. 2, increases as
one moves downwards thereby understanding the
mechanism of biodegradation. CO2 evolution is
measured by using GC50, titrating with barium
hydroxide41. Biofilm studies can be carried out using the
acridine orange or BacLight bacterial viability kit57. The
metabolic activity of the cells in the culture as well as in
the biofilm can be done by ATP assays22, protein
analysis and FDA analysis28. Thermally stimulated
current spectra obtained from electret-thermal analysis
reveals the electric polarization properties of polymer
which is used for investigating biodegradation. Corona
discharge pretreatment of polymers showed better
results compared to UV treatment13,27.
Factors Affecting Biodegradability
Biodegradability of the polymer is essentially
determined by the following important physical and
chemical characteristics:
1. Availability of functional groups that
increases hydrophilicity
2. Size, molecular weight and density of the
polymer
3. Amount of crystalline and amorphous regions
4. Structural complexity such as linearity or
presence of branching in the polymer
5. Presence of easily breakable bonds such as ester
or amide bonds as against carbon-carbon bonds
6. Molecular composition (blend) and
7. Nature and physical form of the polymer such
as whether it is in the form of films, pellets,
powder or fibres8,27
Mechanism of Biodegradation of Polyolefins
In general, polyolefins are inert materials not
susceptible to microbial attack because of the
following reasons:
1. Hydrophobic backbones consisting of long
carbon chains that give high resistivity
against hydrolysis3
2. Addition of antioxidants and stabilisers
during their manufacture which keeps
polyolefins from atmospheric oxidation3
3. High molecular weight (from 10,000 to 40,000)
4. High packing density8
Even though PP is a polyolefin and prone to
oxidative degradation similar to PE, the substitution
of methyl in the place of hydrogen in the β position
makes it more resistant to microbial attack, as already
discussed in the factors affecting biodegradability
(namely structural complexity)8.
The decreasing order of susceptibility of polymers
to degradation in soil mixed with municipal refuse
was PE>>>>LDPE>HDPE as revealed by analysing
the weight loss of samples, CO2 evolution, changes in
tensile strength, changes in FTIR and bacterial
activity in the soil12.
Studies reported on biodegradation of PP are given
in Table 1. As evident from the table, the work carried
out in this area is scarce. Apart from fungal species
(Aspergillus niger), microbial communities such as the
species of Pseudomonas and Vibrio have been reported
to biodegrade PP23. A decrease in viscosity and
Fig. 2—Different levels of investigations on polyme
r
biodegradation.
Fig. 3—Techniques used to characterize the degraded products.
INDIAN J BIOTECHNOL, JANUARY 2008
12
Table 1—Various literature reports on biodegradation of polypropylene and its blends
Title of the paper
Polymer
Organism
Conditions
Analytical
techniques
Observation
Reference
Isotactic polypropylene
biodegradation by
microbial community
Isotactic
polypropylene
Microaerophilic
microbial
community
Mineral medium
containing
sodiumlactate &
glucose
IR, NMR,
GC-MS
Organism & mycelia
with known adaptability
& metabolic flexibility
can degrade isotactic PP
23
UV-Irradiated
biodegradability of
ethylene-propylene
copolymers
Ethylene-
propylene
copolymers
Fungal species Composting &
culture
environments
FTIR, SEM,
VISCOSITY
Viscosity decrease &
increase in
carbonyl/hydroxyl region
in FTIR
31
Biodegradation of γ-
sterilised biomedical
polyolefins
Isotactic
polypropylene
Fungal species Composting &
culture
environments
FTIR, SEM,
VISCOSITY
Viscosity decrease &
increase in chain scission
32
Blends
Calorimetric &
thermogravimetric
studies of UV-irradiated
polypropylene/starch-
based materials aged in
soil
Polypropylene/
starch
Soil Soil burial tests DSC and TGA Biodegradation not
affects the thermal
stability, photooxidation
decrease the thermal
stability of the mixture
18
Effect of short
wavelength UV-
irradiation on ageing of
polypropylene/cellulose
compositions
polypropylene/
cellulose
Soil Composted in
garden soil
ATR-FTIR,
TENSILE &
SEM
Significant mechanical
and surface changes
found
20
Mechanical behavior of
biodegradable
polyolefins
(HDPE)/
polypropylene
(PP)
Soil Soil burial tests DMM,
VISCOELASTI
C & DSC
A significant change in
mechanical behaviour
observed
36
Structure & properties
of degradable polyolefin-
starch blends
polyolefin-
starch
Phanerochaete
chrsosporium Liquid fungus
culture & soil
burial test
Tensile DMTA,
GPC, intrinsic
viscosity, FTIR,
& optical
microscopy
Increased susceptibility
to biodegradation
6
Enzymatic degradation o
f
plastics containing
polycaprolactone
PCL/PP Rhizopus
arrhizus lipase
Enzymatic
condition
SEM &
SPECTRO-
METRIC
Blends of PCL and LDPE
or PP retained high
biodegradability of PCL
33
Thermal degradation of
polypropylene/starch
based materials with
enhanced biodegradation
Polypropylene/
starch based
materials
Soil Soil burial tests TGA, FTIR Biodegradability
observed more in starch
b
ased material rather than
PP matters
15
Characterization by
thermal analysis of
HDPE/PP blends with
enhanced biodegradation
Blends of
HDPE/PP with
different
biodegradable
additives
Soil Soil burial tests TG, DSC and
dynamic-
mechanical
spectroscopy
Additive more affected
by degradation than the
polymeric matrix.
Changes both in the
crystalline morphology
and activation energies o
f
relaxation processes
happens at different time
& depends on the
additives used
52
ARUTCHELVI et al: BIODEGRADATION OF POLYETHYENE & POLYPROPYLENE
13
formation of new groups namely carbonyl and hydroxyl
were observed during the degradation process32,33.
Except for one report23, all the studies deal with
degradation of pretreated PP. The pretreatment
techniques reported range from UV-irradiation17,20,32, γ-
sterilization33 and thermal treatment14. These
pretreatments either decrease the hydrophobicity of the
polymer thereby making it more compatible with the
organism or introduces groups such as C=O or –OH,
which are more prone to degradation. It is reported that
UV-treated PP sample is more susceptible to
degradation than LDPE32. Biodegradation of
polypropylene/starch or polypropylene/cellulose blends
has been reported using soil organisms. It is observed
that the organisms easily degrade starch or cellulose
leaving behind the polymer. These carbohydrates or
fillers also increase the adhesion of the organisms to the
surface of the polymer5-20. Polycaprolactone (PCL)
blended PP has also been reported to degrade in the
presence of lipase34. PCL is an ester and since lipase is
well known to degrade ester linkages, degradation of
this polymer is facile. Lipase cannot affect the carbon-
carbon present in PP. There are no reports available on
the effect of tacticity on the nature and rates of
biodegradation as well as on the use of marine
organisms to achieve biodegradation.
Biodegradation of isotactic polypropylene without
any pretreatment is reported with one of the
community designated as 3S among the four
microbial communities (designated as 1S, 2S, 3S and
6S) adapted to grow on starch containing
polyethylene obtained from enrichment culture.
Pseudomonas chlororaphis, P. stutzeri, and Vibrio
species were identified in the community 3S. TLC,
GC-MS, FTIR and NMR analysis of dichloro
methane extracted products confirmed the mixtures of
hydrocarbons with different degrees of
functionalisation along with aromatic esters, which
are added to the PP as a plasticiser. Sodium lactate
and glucose had a co-metabolic effect. Starch
enhances the adhesion of the microorganisms and also
acts as a co-metabolite23.
The degradability of PCL blends such as PCL with
polystyrene (PS), poly-ethylenetelephthalate (PET),
and polyhydroxybutyrate (PHB) were less when
compared to the degradability of PCL blended with
LDPE or PP. This was due to the miscibility of PCL
with conventional plastics such as polyolefins. High
biodegradability of PCL was observed with PCL-
LDPE and PCL-PP blends33.
Outdoor soil burial tests were done on the samples
of a HDPE and PP blend with different biodegradable
additives. DSC analysis of these polymers with
different additives after a year showed no change in
melting temperature and fraction of crystalline region.
Therefore, it was concluded that the biodegradation
begins at the amorphous region rather than at the
crystalline region. Biodegraded HDPE/PP blends were
more brittle in nature compared to non-degraded36.
Mechanical, rheological and susceptibility for
natural degradation of polymer starch blends mainly
depends upon the content, properties of starch, kind
and concentration of additives added with the plastics.
LDPE demonstrated lower degradability as compared
with polypropylene in the presence of epoxidised
rubber. The biodegradation of polymer along with the
starch phase was observed in few cases6.
The biodegradability of the UV-irradiated films of
isotactic polypropylene (i-PP), ethylene-propylene
copolymer and LDPE was studied in composting and A.
niger culture. Increase in the rate of carbonyl and
hydroxyl groups, decrease in the intrinsic viscosity and
increase in chain scission after UV-irradiation has been
reported. Decrease in the carbonyl region in FTIR was
confirmed by the utilization of oxidized polymers by the
microorganisms. The copolymer EPF-30R (having 7.7%
ethylene) degraded faster than EPQ-30R (having 15.1%
ethylene) demonstrating the effect of the composition of
copolymer on biodegradability. PP was found to be
more susceptible to microbial attack than LDPE. Weight
loss and surface erosion were also reported.31 Additives
are more susceptible to degradation rather than the
HDPE and PP in HDPE/PP blends in outdoor soil burial
test. Changes in the crystalline morphologies and
activation energies of the relaxation process were
confirmed by thermal analysis52.
Accelerated photo- and bio-degradations were
reported with PP/cellulose blends when compared with
pure PP in garden soil compost20. γ-Sterilization of PP,
LDPE and E-P copolymers were reported to have the
same kind of effects as mentioned for UV-irradiated
films32. Colorimetric and thermogravimetric studies on
photo-degradation of polypropylene and a starch
biodegradable additive mixture showed decrease in the
crystallinity content due to free radical assisted chain
scission, followed by biodegradation in soil, which
later increased crystallinity due to the break down of
chains in the amorphous region of the starch18.
Studies carried out on polyethylene bio-
degradation have been mentioned in Table 2. Unlike
INDIAN
J
BIOTECHNOL,
JANUARY
2008
-
Table 2-Various reports on biodegradation of polyethylene and its blends
Title of the paper
Biodegradation of
thermally oxidized
polyethylene
Polymer Organism Analytical techniques Observation
LDPE
Degradation product LDPW
pattern and morphology starch
changes as means to
differentiate abiotically
and biotically aged
degradable polyethylene
Fungi
Aspergillus niger,
Penicillium
funiculosum,
Paecilomyces variotii,
&
Cliocladium virens
Bacte~
Streptomyces badius, S.
setnii
&
S. viridosporous
used Reference
DSC,
FTIR,
GPC
&
Molecular weight reduction, 34
SEM increase in carbonyl double
bond groups, erosion on the
ria surface of polyethylene is due
to the microorganism
Arthrobacter parafineus
Gas chromatography- Decrease in value of
J
mass spectrometry, crystallinity, microorganism
X-ray diffraction, size consumes carboxylic acids
exclusion (carbon) evidenced by gas-
chromatography, mass spectrometry product
FTIR, UV-Vis
spectroscopy, DSC
and SEM
Biodegradation of LDPW Soil microorganisms, sludge Tensile strength, 85% percentage of elongation 7
octanoated starch and its starch blends microorganisms elongation, weight and 50% weight loss in
6
blends.with LDPE loss
&
SEM months
Biodegradation of Polyethylene Fungi
Mucor rouxii
&
Tensile strength
disposable polyethylene
.
Bacterium
Streptomyces
spp.
by fungi and
Streptomyces
species
Mechanical behavior of HDPEPPI Soil microorganisms
biodegradable blends
polyolefins
Physical structure of LDPE blends Soil organisms
polyolefin-starch blends
after ageing
Surface changes brought LDPE
about by corona
discharge treatment of
polyethylene film and the
effect on subsequent
microbial colonization
Fungus
DSC, viscoelastic
properties
DSC
Contact angle and
FTIR
Heat treatment 70°C for 10 d
40
samples showed
60%
elongation reduction in
Streptomyces
sp
&
46.5%
in
fungi
Under soil burial conditions
36
HDPWP blends
altered
mechanical behaviours
48% increase in crystallinity 8
index
Formation of carbonyl groups 27
by oxidative process
Enhancement of LDPE/l2% Fungus
Phanerocheate
Viscosity, percentage Molecular weight reduced 41
biodegradability of starch blend
chtysoporium
of elongation, Cq2 from
90,000
to
50,000 in 6
disposable polyethylene LDPE evolution,
FT-IR
months. FT-IR showed strong
in controlled biological absorbance in the region
soil 1650-1860 cm-I, 56%
percentage of elongation in
3
months, increases COz
evolution after 45 d of
incubation
Thermally
treated
low LDPE
density polyethylene
biodegradation
Penicillium pinophilium
and
Aspergillus niger
Penicillium pinophilium
&
DSC, X-ray Mineralization was evaluated
Aspergillus niger
diffraction, FTIR
&
and observed as 0.64% for
P.
SEM
pinophilium
and 0.57% for
A.
-
niger.
Decreases crystallinity,
crystalline lamellar thickness.
Increases carbonyl index
incubation of 3 1 months
samples
ARUTCHELVI
et al:
BIODEGRADATION OF POLYETHYENE
&
POLYPROPYLENE
Table 2-Various reports on biodegradation of polyethylene and its blends:
Contd:
Title of the paper Polymer Organism
Studies on LDPWstarch Soil organisms
biodegradability, blendsJstarch
morphology and thermo phthalate
mechanical properties of
LDPEJmodified starch
blends
Degradation of LDPE
polyethylene by a fungus
Penicillum simssimum
Fungus
Penicillum
simssimum
Analytical techniques Observation
used Reference
Mechanical Tensile strength
&
elongation 11
properties, DSC, melt at break increased in
flow index
&
SEM LDPWstarch phthalate blends
compared to the LDPWstarch
blends
HT-GPC,
FT-IR
Experimental analysis Polyethylene/ Microbial consortium
GPC
and numerical simulation wax
for biodegradability of
polyethylene
Evaluation of
degradability of
biodegradable
polyethylene (PE)
Polyethylene Soil microorganisms
Biodegradation of LDPE pro- Soil dcroorganisms
thermally-oxidized, oxidant
fragmented low density additives
polyethylenes
Environmental
Biodegradation of
Polyethylene
HT-GPC
&
FT-IR
results
44
showed double bonds of PE
cut by Fungus
P.
simssimum
Weight loss was 3 1.5%
Bioassmilations of
60%
bioassimilation after
product was evaluated 180 d
CO.L Evolutioh,
NMR,
Increased 60% C02 evolution 38
FTIR and SEM.
in
18 months, carbonyl
&
double bond relative
intensities of the carbonyl
bond at 17 15 cm-
1
&
double
bond
at
1650 cm-1
Degradable Bacteria
Rhodococcus
Epiflurocent Increased absorbance of 39
polyethylene
rhodochrous, Cladosporium
microscopy, SEM, carbonyl groups
&
double
(EPI TAPA)
cladosporoides, Nocardia
FT-IR
bond formation in 6 months.
asteroides
60% mineralization produced
in 6 months
Biodegradation of Polyethylene Unidentified
three
white rot COz Evolution
synthetic polymers.
II.
A fungi
&
Fusarium redolens
limited microbial
conversion of
14c
in
polyethylene to
14c02
by
some soil fungi
Biodegradation of HDPE
synthetic polymers.III.
The liberation of
l4
Cop
by molds like
Fusurium
redolens
from
l4
C
labeled pulverized high
density polyethylene
Fusurium redolens,
Acremonium kiliense,
Aspergillus vesicolor
&
Verticilliwn Iecanii
C02 Evolution
Increases 0.5% COz evolution
45
in 2 years of incubation
Mixed culture of organism
showed more degradation
compared
to
single pure
culture by estimation of C02
-
Biodegradation of plastic HDPELPPE Heterotrophic bacteria Weight loss, tensile Starch PE
-
82.76% loss of 12
compost bags under and 9% strength, carbon tensile strength, HDPE-5.33%
controlled soil conditions starch dioxide production
&
and LDPE 13.04%. 36%
.
polyethylene IR weight loss in starch blend PE
Biodegradation of
physicochemically
treated
by a consortium
of filamentous fungi
LDPE
P.
pinophilium, A. niger,
DSC,
FTIR
&
SEM Thermal treated PE samples
47
Gliocladium virens
&
P.
decreasing melting point and
chrysosporium
relative crystallinity.
Degradation products were
carbonyl
&
double bonds
POUPS
Contd
:
ARUTCHELVI et al: BIODEGRADATION OF POLYETHYENE & POLYPROPYLENE
16
Table 2—Various reports on biodegradation of polyethylene and its blends: Contd.:
Title of the paper Polymer Organism Analytical techniques
used
Observation Reference
Electret-thermal analysis
to assess biodegradation
of polymer composites
LDPE/starch Bacteria Baccilus,
Clostridium &
micrococcus Fungi
Aspergillus, Penicillum &
Mucor
DSC, FTIR, SEM &
Physico-Mechanical
testing
Biological erosion of
polyethylene by oxidative
process
13
DSC, FTIR
characterization of
biodegradation of
polyethylene
Polyethylene Fungi A. niger DSC & FTIR Decreased amorphosity of the
sample and relative intensity
of carbonyl bond formation
48
Colonization, biofilm
formation and
biodegradation of
polyethylene by a strain
of Rhodococus rubber
LDPE blends Rhodococus rubber FTIR, SEM & weight
loss
Carbonyl index reduced 66%,
enrichment medium
supplement with 2% mineral
oil showed 50% degradation
after 30 d incubation
28
Synergistic effect of
combining UV sunlight-
soil burial treatment on
the biodegradation rate of
LDPE/starch blends
LDPE/starch
blends
Soil organisms DSC, FT-IR, tensile
strength & SEM
Starch blend PE exposed UV
radiation & soil burial samples
showed 66% degradation
14
Biodegradation of
polyethylene by the
thermophilic bacterium
Brevibacillus borstelensis
LDPE Brevibacillus borstelen DSC, FT-IR 31% Molecular weight
reduction in 30 d
51
Study and development
of LDPE/starch partially
biodegradable
compounds
LDPE/starch
blends
Sludge microorganisms Tensile strength &
SEM
Reduction in tensile strength
& elongation properties,
LDPE degraded in the
amorphous region responsible
for oxidative process
16
Acquired
biodegradability of
polyethylene containing
pro-oxidant additives
LDPE
HDPE/blends
R. rhodochrous, N.
asteroids, Aspergillus flavis,
C. cladospoides
ATP, ADP assays,
Size exclusion
chromatography,Micr
oscopy techniques &
NMR
R. rhodochrous & N. astroides
found to be most active for
molecular weight reduction
22
Effect of compatibiliser
on the biodegradation
and mechanical
properties of high content
starch/low density
polyethylene blends
LDPE/starch
blends
Soil organisms Mechanical
properties, weight
loss, melt flow index
& SEM
65% weight loss increase in
14 d
17
Polyethylene
biodegradation by
developed Penicillium-
Bacillus biofilm
Polyethylene P. frequentans B. mycoides Microscopy, weight
loss, gas
chromatography
Weight loss of preheated
polyethylene treated with
fungi showed 7.150% &
without preheating treated
with showed 6.657%
50
Photo biodegradation of
low density
polyethylene/banana
starch films
LDPE/starch
blends
Soil microorganisms FTIR, tensile strength,
elongation & weight
loss
Increased carbonyl index &
Tensile strength & elongation
at break increased in
LDPE/starch blends
19
Biodegradation potential
of some barrier-coated
boards in different soil
environments
Polyethylene
& Polyester
Soil microorganisms DSC & FTIR Under soil burial condition
PE/Polyester blends affect
mechanical behaviors
49
Contd.:
ARUTCHELVI
et al:
BIODEGRADATION OF POLYETHYENE
&
POLYPROPYLENE
Table 2-Various reports on biodegradation of polyethylene and its blends:
Contd.:
-
Title of the paper Polymer Organism Analytical techniques Observation
used Reference
Modification of polymers rnLLDPE
Aspergillus oryzae
by protein hydrolysate-A blend with
way to biodegradable
HP
materials
Mechanical strength Polymer blend with 20%
HP
40
properties (Protein hydrolysate) shows
35%
biodegradation with
acceptable range of
mechanical strength whereas
polymer with
40%
HP
shows
50% biodegradation with poor
mechanical strength properties
polypropylene, more research articles are published
on studies relating to biodegradation of PE. Fungi that
include
A.
niger, Penicillium finiculosum, Fusarium
redolens,
and
A.
vesicolor,
and soil microorganisms
(mixed culture as well as
Rhodococcus rhodochrous,
Cladosporium cladosporoides)
have been reported to
degrade neat
PE~,",~~,~~~~
.
DSC or
FTIR
and other
mechanical and physical techniques such as weight
loss, changes in tensile strength have been the
commonly used analytical techniqua to monitor the
nature of biodegradation. Thermal,
W,
photo and
corona treated PE has been found to degrade faster
than the untreated polymer. Biodegradation of starch
blended and modified PE with protein hydrolysate has
also been studied4'
Photooxidation is the triggering step in the
oxidative degradation of polyethylene.
W
radiation
leads to radical formation, followed by the absorption
of oxygen resulting in end products with carbonyl
groups. Additional
W
exposure causes the carbonyl
group to undergo Norrish type
I
andhrjNorrish type
I1
degradation which leads to the cleavage of C-C bond
and thus leading to the formation of oxidised low
molecular weight fragments. Ultimately,
photooxidation leads to the formation of low
molecular weight fragments and thus increases the
hydrophilicity of the
polymer'4~'8-20~25a~29-31
.
The
photooxidation mechanism shown in Fig. 4,
comprises both the formation of carbonyl group as
well
as
Norrish type
I
and type
11.
Thus,
photooxidation enhances
.
the susceptibility of the
polymer to microbes. The resulting carboxylic acid
from the photooxidation and o-oxidation of .long
chain hydrocarbons (similar to the biotic degradation
of paraffin-Clo-zo) enters the poxidation pathway as
shown in Fig. 4. Later, the two carbon acetyl CoA,
enters the TCA cycle and gets com letely converted
9
into carbon dioxide and ~ateJ~~~~"'~'-
'
Cell homogenates from
P. putida
and
Bacillus
brevis
were found to degrade PE films by oxidative
degradation resulting in the formation of terminal
hydroxyl, ketone and ester groups. The presence of
alcohol dehydrogenase was confirmed indirectly in
the degradation reaction by inhibition studiess5. The
known lignin degrading bacteria
S. virdosporos
Ti'A,
S. badius
252, and
S. setonni
75vi2 and the fungus
Phanerochaete chrysosporium
were used to assess
their ability to degrade biodegradable polyethylene
(polyethylene with 6% starch and pro-oxidant). The
authors observed the accelerated pro-oxidant activity
by heat treatment and UV treatment with different
time period. Reduction in polydispersity and tensile
strength were observed in biodegradable PE with
bacterial treatment and not with the fungus53. The
veratryl alcohol lignin peroxidase activity was
A.
niger
has been reported to degrade
commercially available PE. DSC analysis showed
reduction in the amorphous region of the polymer48.
Biodegradation of LDPE was enhanced with Tween
80 in the presence of
P. aeuroginosa.
This study
explains the role of nonionic surfactant in biofilm
formation, as explained before it is a prerequisite for
biodegradation process56. Biodegradation of
thermally oxidized LDPE with fungal cultures of
A.
niger, Pencillium finicalosum, Paecilomyces variotii
and
Gliocladium virens
was marked by the gradual
decrease in cxbonyl region (1715 cm-') in
FTIR~~.
Disposable polyethylene bags with 6% starch were
subjected to biodegradation for a period of four
weeks by eight different species of
Streptomyces
and
the fungi,
Mucor rouxii
and
A.
flavus.
Weight gain
was seen after degradation with few
Streptomyces
species, whereas a slight loss of weight was
observed with
S. aburaviensis, S. parvullus,
S.
nigellus
and
A.
pavus.
Reduction in percentage
elongation with
Streptomyces
and fungal cultures
were 28.5% and 46.5%, respectively. Thermally
treated film incubated with
Mucor
had 60%
reduction in tensile strength4'.
ARUTCHELVI et al: BIODEGRADATION OF POLYETHYENE & POLYPROPYLENE
18
Fig. 4—Mechanism of biodegradation of polyethylene (Adapted from Vasile).
INDIAN J BIOTECHNOL, JANUARY 2008
19
The bacteria, Arthobacter parraffineus was found
to degrade LDPE in three years by utilising
carboxylic acid formed during thermal oxidation. The
utilization was through the β-oxidation mechanism
that yields the degradation products like acetyl coA
and propionyl CoA. 3- methyl-3-octanol and 1-
hexadecanol were detected in biotic environment with
series of n-alkanes such as C21-26. These were
microbiologically metabolised by the oxidation of
carboxylic acid through β-oxidation5.
Rate of degradation of octonated starch is slower
than pure starch. OCST-LDPE blend and octonated
starch was subjected for six month soil burial test,
which showed weight loss and reduction in
mechanical properties. SEM analysis of OCST-LDPE
blend showed the presence of holes on the surface,
which confirmed the degradation of OCST region in
blend7.
Corona discharge treatment was found to be more
effective towards colonisation of microorganisms on
food packaging grade LDPE films with little effect on
the mechanical properties as compared to UV
treatment. This suggests that corona discharge
treatment is affecting the hydrophobicity of the
surface of the polymer and not penetrating it. A
reduction in hydrophobicity of the LDPE from (92° to
66.6°) was also reported27. The pH of Phanerochaete
chrysosporium inoculated soil with polyethylene
decreased at a faster rate. Biomass, biological activity
and CO2 evolution was higher in inoculated soil.
Analysis of the mechanical properties showed that
decrease in the percentage elongation is faster in the
inoculated soil compared to the uninoculated soil.
Viscosity analysis of the polymers with regular
intervals also showed the same trend41. A similar
study was performed by Yamada-Onodera et al using
Triton X-100. Improvement was observed in the
growth of Penicillium simplicissimum YK, however,
there was no utilisation of Triton X-100. FTIR
analysis confirmed the utilisation of polyethylene by
the fungus44.
Thermal treatment of LDPE-TDPA (Pro-oxidant
additive) in aerobic conditions showed substantial
polymer fragmentation with loss of mechanical
properties in 11 d. 26% of biodegradable and solvent
extractable fraction was obtained after thermal
oxidation for 20 d. 50-60% carbon dioxide evolution
was observed in 18 months of further treatment with
soil microorganisms38. Temperature is the crucial
factor in determining the rate of thermo-oxidation
whereas the effect of concentration of oxygen on the
rate of thermo-oxidation is insignificant37. A. niger, G.
virens, Penicillium pinophilum, Phanerochaete
chrysosporium showed biodegradation on thermally
treated or accelerated ageing treated (AAT) LDPE in
9 months. The biodegradation was evaluated by
observing decrease in the onset of melting
temperature (T0) and melting temperature Tm and
relative crystallinity. Highest mineralization (3.26%)
values were obtained with AAT. Superficial growth
of microorganisms occurred and penetration of
hyphae was observed in the oxidised sample47.
Synergistic effect of combining UV treatment and soil
burial test was reported by Abd El-Rehim et al14.
Electret-thermal analysis used in the electric
polarization of dielectrics was used to investigate
biodegradation of LDPE- starch blended polymer in 6
months. These studies were based on the assumption
that biodegradation process of polymer material can
cause transformation in their electrically non-
equilibrium structure. Thermally stimulated current
spectra (TSC) of PE films exposed to various ageing
conditions in soil were reported. After ageing, new
peaks were detected on spectra. FTIR results showed
formation of functional groups. Reduction in melting
was reported in DSC analysis. The degree of
biological damage of the films was a function of
starch content of the composites. The predominant
microbial taxa in composites were Bacillus,
Clostridium, Micrococcus, Aspergillus, Penicillum
and Mucor13.
Rhodococcus ruber C208 was isolated from the
surface of the PE in polyethylene waste burial site by
two step culture-enrichment protocol. Weight loss of
8% of photo-oxidised PE was observed in four weeks.
This is higher than the rates already reported (3.5% to
8.4% after 10 years)30. In contrast to Albertsson’s
report, increase in the terminal double bond after
photooxidation was observed. This could be explained
by Norrish type I degradation of the carbonyl
residues. They have reported that the double bonds
were observed after the biodegradation of short PE
oligomers produced during photooxidation. The
analysis of extracellular polysaccharides in the
biofilm of C208 was 2.5 folds higher than protein,
suggesting its role in biofilm formation. Biofilm
showed higher viability even after 60 d of incubation.
Cell surface hydrophobicity of R. ruber was studied
by SAT (salt aggregation test) and BATH (bacterial
adhesion to hydrocarbon) tests. Addition of mineral
ARUTCHELVI et al: BIODEGRADATION OF POLYETHYENE & POLYPROPYLENE
20
oil to this culture enhanced the degradation of the PE
film by about 50% after four weeks of incubation.
SEM photomicrographs of the bacterial biofilm
showed some localized degradation of the PE around
the bacteria. Protein assay and FDA hydrolysis by
extracellular esterases showed increase in the biofilm
formation for the first 2 d of assays followed by a
sharp decrease in biomass density. The authors have
hypothesised a low cell population with a low growth
rate consisting of cells that are able to utilise PE as a
carbon source28,57.
Brevibacillus borstelensis, a thermophillic
bacterium, was found to degrade polyethylene better
than R. rubber, although the biofilm forming capacity
of the former was not found to be as good as of the
latter. Still it was able to show reduction in mass and
molecular weight by 11 and 30%, respectively for UV
irradiated polyethylene51. The LDPE and HDPE films
after photo-oxidation and thermal oxidation
corresponding to three years of outdoor weathering
were incubated with R. rhodochrous and Nocardia
asteroids. ATP assay was done to see the metabolic
activity of the cells in culture and those adhered to the
surface of the polymer. There was fast growth of
microorganisms in the initial phase due to the
availability of the low molecular weight oxidised
products, which was followed by stabile metabolic
activity. This was maintained for several months by
the organisms utilising the polymer. The NMR
analysis of the photo- and thermo-oxidized
LDPE/HDPE aqueous extract revealed the presence
of ethanol and formate, which are the end products of
PE oxidation. This evidence supports the initial fast
growth of microorganisms observed by ATP analysis.
Nocardia formed dense filamentous mycelium on the
surface. The size exclusion chromatographic analysis
of the LDPE/HDPE after biotic and abiotic treatment
showed no change in the molecular weight
distribution indicating that the microbial attack was
only on the surface of the polymer. The degradation
due to both biotic and abiotic factors depended on the
thickness of the polymer22.
Studies on biofilm formation by Penicillium
frequentans and Bacillus mycoides showed that P.
frequentans formed a network of mycelia on
degradable polyethylene (DPE–chemical or
photoinitiator added polyethylene), which was
colonised by B. mycoides. The biofilm formation
increased the biodegradability of P. frequentans by 14
folds. In general, homologous gene has been found in
the genome of some Bacillus species that produce
alkane monooxygenase. The degradation was checked
with weight loss, microscopic studies to visualise
biofilm formation and CO2 production using GC50.
Conclusions
This review discusses the literature on
biodegradation of PE and PP. Most of the examples
deal with fungi and bacterial based degradation. Pre-
treated polymers degrade more easily than the
untreated polymers. Also, degradation is more facile
with starch and cellulose blended polymers. Cell
surface hydrophobicity and addition of surfactants
showed an important role in biofilm formation, which
is prerequisite for biodegradation. Degradation leads
to decrease in molecular weight, tensile strength and
viscosity, formation of new functional groups such as
carbonyl, hydroxyl, etc. Based on the literature one
could conclude that in order to enhance
biodegradation of PP or PE the following approaches
could be adopted:
I. Modify the polymer for microbial utility by the
(i)Addition of natural polymers and/or
prooxidants to PP; (ii) Modification of
polymers by protein hydrolysates; and (iii)
Pretreatment of the polymer.
II. Modify the microbes to utilise the polymer by
(i) Modifying medium composition, and thus
enhancing the utilisation of polymer; and (ii)
genetically modify the microorganism to
utilise the polymer.
III. Overexpress the enzyme, which is
responsible for degradation and purify it
and utilise for this purpose. Strategies II
and III require the understanding of
mechanism of microbial degradation of
these polymers.
APPENDIX – ABBREIVIATIONS
AAT -Accelerated ageing treatment
ATP -Adenosine TriPhosphate
ATR-FTIR -Attenuated total reflectance -
Fourier Transform Infrared
Spectroscopy
CL -Chemilluminesence
DMA -Dynamic Mechanical Analysis
DPE -Degradable Polyehtylene
DSC -Differential Scanning Calorimetry
ESCA -Electron Spectroscopy for Chemical
Analysis
INDIAN J BIOTECHNOL, JANUARY 2008
21
ESR -Electron Spin Resonance
FDA -Fluorescien DiAcetate
FTIR -Fourier Transform Infrared
Spectroscopy
GC-MS -Gas Chromatography - Mass
Spectrometry
HDPE -High Density Polyethylene
HTGPC -High temperature gel permeation
chromatography
i-PP -Isotactic Polypropylene
LDPE -Low Density Polyethylene
MALDI-TOF-Matrix Assisted Laser
Desorption/Ionisation - Time of flight
MFI -Melt Flow Index
NMR -Nuclear Magnetic Resonance
Spectroscopy
NY -Nylon
OCST -Octonated starch
PCL -Polycaprolactone
PET -Polyethylenetelephthalate
PHB -Polyhydroxy butyrate
PS -Polystyrene
SAXS -Small Angle X-ray Scattering
SEM -Scanning Electron Microscopy
Tg -Glass Transition temperature
TGA -Thermogravimetric analysis
TLC -Thin Layer Chromatography
Tm - Melting temperature
TSC -Thermally Stimulated Current
Spectra
UV -Ultra Violet Spectroscopy
WAXS -Wide Angle X-ray Scattering
XPS -X-ray Photoelectron Spectroscopy
XRD -X-Ray Diffraction
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... There has been a recent trend within the scientific community to move towards the incorporation of "mixed consortia" to aid with the breakdown of difficult and highly stable waste material. Four bacterial isolates, from various waste landfills and sewage treatment plants, were used over 140 days to biodegrade PP with a weight loss of 44 to 56% [15,35]. The microbe Stenotrophomonas panacihumi PA3-2 was discovered to have the ability to degrade PP samples of lower molecular weights, 2800 and 3600 Da, and of higher mass, 44,000 Da [29,35]. ...
... Four bacterial isolates, from various waste landfills and sewage treatment plants, were used over 140 days to biodegrade PP with a weight loss of 44 to 56% [15,35]. The microbe Stenotrophomonas panacihumi PA3-2 was discovered to have the ability to degrade PP samples of lower molecular weights, 2800 and 3600 Da, and of higher mass, 44,000 Da [29,35]. So far, despite some reports of PP breakdown, there are some doubters that PP enzymes exist, or at least believers that the evidence provided is not convincing, and there is not much understanding of the mechanisms involved [35][36][37]. ...
... The microbe Stenotrophomonas panacihumi PA3-2 was discovered to have the ability to degrade PP samples of lower molecular weights, 2800 and 3600 Da, and of higher mass, 44,000 Da [29,35]. So far, despite some reports of PP breakdown, there are some doubters that PP enzymes exist, or at least believers that the evidence provided is not convincing, and there is not much understanding of the mechanisms involved [35][36][37]. It is certainly likely that some reports of untreated PP degradation by enzymes and microbes were partially deceived by the breakdown of chemical additives, rather than the polymer itself [33,38,39]. ...
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This review article will discuss the ways in which various polymeric materials, such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and poly(ethylene terephthalate) (PET) can potentially be used to produce bioplastics, such as polyhydroxyalkanoates (PHAs) through microbial cultivation. We will present up-to-date information regarding notable microbial strains that are actively used in the biodegradation of polyolefins. We will also review some of the metabolic pathways involved in the process of plastic depolymerization and discuss challenges relevant to the valorization of plastic waste. The aim of this review is also to showcase the importance of methods, including oxidative degradation and microbial-based processes, that are currently being used in the fields of microbiology and biotechnology to limit the environmental burden of waste plastics. It is our hope that this article will contribute to the concept of bio-upcycling plastic waste to value-added products via microbial routes for a more sustainable future.
... Polyethylene (PE) is a linear hydrocarbon polymer composed of long chains of ethylene monomer (Tokiwa et al. 2009;Usha et al.). Polyethylene is difficult to decompose due to its very stable C-C and C-H covalent bonds, the addition of oxidants and stabilizers, and its high molecular weight and density (Arutchelvi et al. 2008;Leja and Lewandowicz 2010). Polyethylene fragments that infiltrate the soil may last for hundreds or even thousands of years without being digested (Wang et al. 2016). ...
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Low-density polyethylene (LDPE) is a major cause of persistent and long-term environmental pollution. In this study, we report the successful isolation of an efficient LDPE degrading bacterial strain from the wastewater sediment of an agricultural land film recycling plant and identified and designated it as Acinetobacter sp. LW-1, respectively. The surface analyses including scanning electron microscopy (SEM) and atomic force microscopy (AFM) of LW-1-treated samples revealed the existence of appreciable pits and cavities on the facet of PE film, while the formation of carbonyl group was also verified by XPS and FTIR. Moreover, water contact angle assay substantiated the chemical transformation of the LDPE film from hydrophobic to hydrophilic transition after treatment with LW-1. In addition, co-incubation of LDPE film and Acinetobacter sp. LW-1 at 35 °C for 90 days significantly decreased the weight of LDPE film with an optimal weight loss of 15 ± 0.85%. This work enriches the LDPE degradation bacterial library and shows the tremendous potential of Acinetobacter sp. LW-1 to be used in the degradation of LDPE waste.
... e resulting saline solution was serially diluted up to 10 −7 , and aliquots were disseminated on nutrient agar, with the number of colonies calculated as CFU/µL [25]. ...
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The COVID-19 outbreak again underlined plastic items’ importance in our daily lives. The public has widely utilized disposable face masks constructed of polypropylene polymer materials as effective and inexpensive personal protective equipment (PPE) to inhibit virus transmission. The consequences of this have resulted in millions of tons of plastic garbage littering the environment due to inappropriate disposal and mismanagement. Surgical masks are among them, and this study aimed to assess the biodegrading efficiency of disposable face masks using Pseudomonas aeruginosa VJ 1. This work used a bacterial strain, Pseudomonas aeruginosa VJ 1, obtained from sewage water-contaminated surface soil in Tiruchirappalli, India, to investigate the biodegradation of polypropylene (PP) face masks. The mask pieces were incubated with Pseudomonas aeruginosa VJ 1 culture in three different solid and liquid media for 30 days at 37°C. Surface changes and variations in the intensity of functional groups and carbonyl index variations were confirmed using Field Emission Scanning Electron Microscopy (FE-SEM) and Fourier Transform Infrared Spectroscopy (FTIR) analysis to ensure microbial degradation (up to 5.37% weight reduction of PP films within 30 days). These findings show that Pseudomonas aeruginosa VJ 1 could be a good choice for biodegrading PP masks without harming our health or the environment. There is a need for a novel solution for the degradation of PP. The methods and strain presented here reveal the potential biodegrading agents of PP masks.
... Polymer biodegradation by microbes is responsible for changes in peak intensity, integration value, and chemical shifts in NMR spectra [88] . NMR study of thermo-and photo-oxidized polymers during bioremediation studies can reveal the presence of degraded products [5] . This technology allows for the visualization of soluble substrates derived from oxidized polymers that can be utilized by microbial cells as a source of energy and carbon [32] . ...
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In everyday life, plastic plays a big role in people's daily lives as well as in society's life as a whole. In the environment, plastics are accumulating, and their biodegradability is very low, so this problem will likely persist for decades. Research on the degradation of synthetic plastics by enzymes or microorganisms has become a prominent topic, which paves the way for the development of biological waste treatment technologies. There are five types of biodegradation processes: (1) colonization, (2) conditional film formation, (3) assimilation, (4) bio-fragmentation, and (5) mineralization. The biodegradation of a variety of polymers has been demonstrated recently by bacteria, bacteria consortia, biofilm-forming bacteria, and fungi. Biodegradation is the microbes-assisted transformation that decomposes the plastic wastes into CO2, methane, biomass, inorganic compounds, water, organisms, the molecular weight of plastics, depending on the polymer type, and environmental conditions. Several factors influence biodegradation, such as polymer type, physico-chemical parameters, and environmental circumstances such as temperature, and ultraviolet exposure. Microplastics (MPs) cause inflammation, oxidative stress, and enhanced translocation or absorption in humans, plants, and animals. Humans are susceptible to cancer, neurotoxicity, and metabolic abnormalities, according to various studies. Additionally, we have discussed the metabolic pathways of microbes and our ongoing efforts to use them to reduce microplastic pollution in soil and water.
... Comparing HDPE FTIR spectrum of microplastics ( Fig. 7 as part of supplementary material) with the one for HDPE plastic from the FTIR reference library, all peaks of the HDPE plastic appear in the FTIR spectrum of the microplastics, except for one additional weak band at 1713 cm −1 for carbonyl groups. Because of the absence of the peak at 2700 cm −1 showing the presence of aldehydes, it can be concluded that the microplastics had undergone weathering to an extent with the formation of a ketone (Arutchelvi et al., 2008). ...
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Microplastics had been collected at two sites namely Trou d’eau Douce (TD) and La Cambuse (LC) public beaches, lying in the east coast and south-east coast of Mauritius, respectively, over 6 months from September 2019 to February 2020. The sizes of the latter varied from 180 µm to 4 mm. A higher amount of microplastics collected/6-kg sand sample was recorded at LC. Two-way ANOVA revealed that (1) there was a considerable gap in the variability regarding quantity and size distribution of microplastics on the two beaches. The post-hoc analysis showed that the majority of the microplastics at LC were > 1.40 mm, whereas the smaller plastic fragments < 1.40 mm were more dominant at TD. (2) There was a significant interaction between location and event (p value = 0.025). The post-hoc analysis showed that the torrential rain hitting the island prior to sampling week 7 had decreased the microplastic counts at both TD and LC, but not significantly. Interestingly, the two hurricanes, prior to weeks 8 and 9, had appreciably reduced the microplastic counts at TD and, on the other hand, there was an increase in the amount of microplastics at LC, but not to a significant effect. The chemical nature (qualitative analysis) of microplastics was determined by density flotation and FTIR spectroscopy. Microplastics at TD were exclusively high-density polyethylene (HDPE) in origin, whereas, at LC, microplastics were both HDPE and polypropylene (PP) in origin.
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Environmentally sustainable composite films were synthesized using polyvinyl alcohol (PVA) and cellulose. Cellulose was extracted from the Agro‐waste (sugarcane bagasse) using chemical pre‐treatment followed by the acid‐hydrolysis process. The composites were also used for the treatment of dye (Methylene blue; MB and Crystal violet dye; CV) and it was observed that the removal capacity of PVA/C was 70% for CV and 64.5% for MB dye. The biodegradation study of these composite films was also carried out using bacterial strains isolated from the marine waters of south Bengal. The biodegradation study of these polymer composites was characterized by FTIR, SEM, XRD, TGA, swelling properties, and weight loss. The results indicated that the PVA/C polymer showed a better rate of degradation (43%) than PVA (35%). Different loading parameters like pH, temperature, and inoculum dosage were studied to assess the degradation of the composite materials. Thus, biodegradable composite films were synthesized utilizing Agro‐waste and had dye removal properties. Developing a way of waste management from Sugarcane bagasse for water treatment. Extraction of cellulose from sugarcane bagasse and impregnation into PVA polymer. Biodegradation of polymer composites by marine bacterial strains. Utilization of composites in removal of crystal violet and methylene blue dye.
Chapter
Large‐scale production and use of plastics began around 1950, and since then they have become increasingly ubiquitous materials due to their combination of useful properties, including cost‐effectiveness, low density, ease of processing, water‐resistance, and durability. Microplastics in environmental samples are frequently categorized in terms of their chemical identity, color, and morphology. Despite improvements in recycling technology, the plastics economy is largely linear; some plastics are unsuitable for recycling, many plastic items are improperly disposed of by users, either as litter or into incorrect waste streams, and potentially recyclable plastic waste is sent to landfill or discharged to rivers and oceans on enormous scales. water treatment plants are significant point sources of microplastic contamination into the aquatic environment, deriving from sources including fibers and fragments of artificial textiles in washing machine run‐off, and particles from tire wear and other plastic fragments on urban surfaces.
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Fungal involvement in biodeterioration of Low Density Polyethylene (LDPE) has received a great attention in recent years. Among diverse groups of fungi, Endolichenic Fungi (ELF) are adapted to thrive in resource limited conditions. Present study was designed to investigate the potential of mangrove associated ELF, in biodeterioration of LDPE and to quantify key‐depolymerizing enzymes. A total of 31 ELF species, isolated from 22 lichens of mangrove ecosystems in Negombo lagoon, Sri Lanka were identified using DNA barcoding techniques. ELF were inoculated into mineral salt medium, containing LDPE strips and incubated at 28±2°C, for 21 days, under laboratory conditions. After incubation, biodeterioration was monitored based on percent reductions in weights and tensile properties, increments in degree of water absorption, changes in peaks of Infrared spectra and surface erosions using Scanning Electron Microscopy. Out of 31 species, Chaetomium globosum, Daldinia eschscholtzii, Neofusicoccum occulatum, Phanerochaete chrysosporium, Schizophyllum commune and Xylaria feejeensis showed significant changes. Production of depolymerizing enzymes by these species, were assayed qualitatively using plate‐based methods and quantitatively by mass level enzyme production. Among them Phanerochaete chrysosporium showed the highest enzyme activities as (9.69±0.04)x10‐3, (1.96±0.01)x10‐3, (5.73±0.03)x10‐3, (0.88±0.01), (0.64±0.06), (1.43±0.01) U ml‐1 for laccase, lignin peroxidase, manganese peroxidase, amylase, lipase and esterase, respectively.
Chapter
Though several microorganisms degrade plastics in diverse ecosystems, the degradation rate is remarkably slow; however, this process can be accelerated comparatively within an insect host. Available information on the plastic degradation ability of insects and the mechanisms underlying this process is still limited; therefore, many questions about insect-mediated plastic degradation remain unanswered. Generally, the mandibulate insects transform plastics into subtle fragmented forms by their collective chewing actions after being ingested into the guts. The gut microorganisms convert plastic polymers into assimilable simpler forms through microbial enzymes. Insect ability to degrade plastic is widespread; some insects degrade specific types of plastic, while others can degrade multiple types. Therefore, insect species greatly vary according to the biodegradation processes and based on chemical orientation and structure of plastics. This review focuses on the diversity of insect fauna responsible for plastic degradation, the types of plastics degraded by insect species, and how the degradation mechanism occurs within their gut microbial environment. Since waste plastics are causing significant annoyance, this review will further discuss how insects can benefit waste management by degrading plastics without causing any environmental hazards.
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Biodegradability of polyethylene wax (PEwax) was studied both experimentally and analytically. The weight loss of PEwax (0.5%) by a microbial consortium in approximately 3 weeks was 31.5% and the top molecular weights shifted to higher values. One of the features observed experimentally was fast consumption of low molecular weight-PEwax. On the other hand, one may speculate, theoretically, that hydrocarbons such as PE should be subject to an initial oxidation to yield carboxylated compounds at their terminals, which are then depolymerized via β-oxidation process. A mathematical model based on these theoretical and experimental aspects is proposed and a method of analysis is illustrated. β-Oxidation rates and consumption rates of low molecular weight-PEwax are determined numerically, and the temporal change of weight distribution is simulated. Numerical results are compared with experimental results, and the governing mechanism of biodegradation is interpreted. We conclude that the primary factors in biodegradation of polyethylene are an initial oxidation at the terminals of molecules followed by β-oxidation and consumption of low molecular weight-PEwax. The most reliable biodegradation limit was approx. 2000.
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Biodegrability of high density polyethylene film (HDPE) and low density polyethylene film (LDPE) both containing a balance of antioxidants and pro-oxidants was studied with defined microbial strains particularly with Rhodococcus rhodochrous and Nocardia asteroides in mineral medium. After an abiotic pre-treatment consisting of photooxidation and thermo-oxidation corresponding to about 3 years of outdoor weathering the samples were inoculated, incubated up to 200 days and during the period their metabolic activities were followed by measuring adenosine triphosphate content. Simultaneously the cultures were also monitored by optical microscopy and FTIR spectroscopy. The first initial phase of fast growth caused by the presence of low molecular extractable compounds was followed by a long period of stabilized metabolic activity suggesting that microorganisms continued to gain energy from the substrate but evidently at a much slower rate. Complementary analysis performed at the end of incubation revealed that during the experiment time biodegradation processes probably affected surface layer of materials only.
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Polypropylene compositions containing 5–30% cellulose were pre-irradiated (λ=254 nm) and then composted in garden soil in laboratory conditions. The effect of photochemical reactions on the course of further degradation during composting was investigated. Photo- and bio-induced changes in samples were studied using reflectance infrared spectroscopy (ATR-FTIR) and tensile tests. Destruction of surface morphology were also observed by scanning electron microscopy (SEM). It was found that photo- and bio-induced changes in PP/cellulose compositions are accelerated compared to these processes occurring in pure components. The mechanical properties of sample tested are lower than those for PP alone but the influence of cellulose amount on the mechanical strength of compositions is insignificant. ATR-FTIR spectroscopy combined with SEM is very useful for fast estimation of polymer surface changes during environmental degradation.
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The structure, mechanical properties and susceptibility to degradation of blends of low density polyethylene (PE) or isotactic polypropylene (PP) and glycerol plasticized starch (GS) was investigated. Monoethers of glycerol and fatty alcohols (GA) and in some cases epoxidized rubbers (ER) were used as compatibilizers for the investigated systems. It was found that mechanical properties and ageing susceptibility of blends depend strongly on their composition, i.e. the content of plasticized starch in the blend and the content of glycerol in the starch. In some cases an increased susceptibility to biodegradation during soil or fungus ageing not only of the starch phase but also of the polymer phase was observed. The susceptibility of these systems to accelerated artificial weathering was also investigated.
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We isolated a strain of Penicillium simplicissimum, YK, for use in the biodegradation of polyethylene, characterizing the fungus and examining how to treat the polyethylene before cultivation to make degradation more complete. Degradation was monitored by high-temperature gel-permeation chromatography of the molecular weight distribution of polyethylene before and after the fungus was cultivated with it. Polyethylene with starting molecular weights of 4000 to 28,000 had lower molecular weights after 3 months of liquid cultivation with hyphae of the fungus. UV irradiation of polyethylene or its incubation with nitric acid at 80°C for 6 days before cultivation caused functional groups to be inserted into the polyethylene. The strain grew better on a solid medium with 0.5% polyethylene when it was irradiated for 500 h than when it was not irradiated. Polyethylene with a molecular weight of 100,000 or higher after nitric acid treatment had lower molecular weight after 3 months of liquid cultivation with hyphae of the fungus. The efficiency of polyethylene degradation depended on the growth phase in pure cultivation of the fungus. Functional groups inserted into polyethylene aided biodegradation. Bioremediation of polyethylene may become possible.
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Octanoated starch (OCST) with a high degree of substitution (DS = 2.1) is a fully amorphous and hydrophobic thermoplastic material. Its biodegradation was followed in activated sludge from a waste water treatment plant. Its blends with low-density polyethylene (LDPE) were also studied during soil burial for 6 months. From weight loss during the biodegradation period, it was found that OCST, even with such a high degree of substitution, is biodegradable. This was also verified with scanning electron microscopy. Holes were detected on the surface of the films as a consequence of starch consumption by microorganisms. Nevertheless, the rate of biodegradation is very small and depends on the amount of OCST in the blends. The mechanical properties such as tensile strength and elongation at break were measured. A reduction in both was found during the biodegradation period, mainly in blends with a higher amount of OCST.
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The ability of fungi and Streptomyces species to attack degradable plastics was investigated in pure shake-flask culture studies. The degradable plastic used in this study was disposable polyethylene bags containing 6% starch. Eight different isolated Streptomyces strains and two fungi Mucor rouxii NRRL 1835 and Aspergillus flavus were used. Ten-day heat-treated (70°C) polyethylene films were chemically disinfected and incubated shaken at 125rpm at 30°C in 0.6% yeast extract medium (pH 7.5) for Streptomyces spp. and for the fungi in 3% yeast extract medium (pH 5.5) for 1, 2 and 4 weeks along with an uninoculated control for each treatment. Active enzymes caused changes in the films’ mechanical properties and weight.
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The biodegradability of thermally oxidized polyethylene (PE) has been studied in various conditions: (1) on solid agar in the presence of a suspension of mixed spores of four fungi (Aspergillus niger, Penicillium funiculosum, Paecilomyces variotii and Gliocladium virens); (2) in three composting units differing in temperature, moisture content and the nature of the composted materials; and (3) in liquid medium (respirometric flasks) in the presence of three Streptomyces strains (badius, setonii, viridosporus) or of a suspension of microorganisms from compost. Qualitative evidence of bioassimilation of the oxidized PE films was obtained with fungi and in composts. Coverage of the film surface by fungi increases as the molecular weight of the PE is decreased and attains 60% when the initial Mn lies between 1500 and 600. With fungi and in compost, important surface erosion was detected by SEM for samples with initial Mn around 1000. Important changes were also observed by FTIR, DSC and GPC. This last method revealed in all cases the formation of a high molecular weight fraction that was not present before incubation with microorganisms and a shift of the whole curve toward higher molecular weight. This is evidence of chain condensation probably due to purely thermal reaction at the low partial pressure of O2 prevailing in the industrial composting units used in this work. It is probably accompanied by bioassimilation of the low molecular weight fraction. Quantitative information can be obtained by a respirometric method. For incubations performed in liquid medium in the presence of a suspension of microorganisms from compost, biodegradation was important when substrate concentration was very low (≈ 0.006%). Despite the presence of unavoidable large errors in these conditions, oxygen uptake was evident and biodegradation of the low molecular weight fraction of the sample was clearly demonstrated.