Introduction to Recycling
Bupe G. Mwanza
Abstract Recycling continues to contribute to the sustainable management of
plastic solid wastes (PSWs) and it’s among the important approaches currently
used for reducing the impacts of PSWs in the plastic industry. It provides oppor-
tunities for reducing quantities of wastes disposed, oil usage and carbon dioxide
emissions. Further, opportunities in form of job creation, global warming reduc-
tion, reduction of virgin material consumption, reduction in landﬁll contamination
etc. It also presents demerits such as being costly, contamination, littering, pollu-
tion etc. The chapter outlines the concept of recycling with particular attention to
plastics. It discusses the two strategies of recycling: open-loop recycling and closed-
loop recycling. These strategies are compared and the difference is that, open-loop
recycling provides an opportunity for new product development while closed-loop
is conﬁned to the original products. Different recycling processes such as primary
recycling, secondary (mechanical) recycling, tertiary recycling and energy recovery
are discussed by focussing on the processes, merits and demerits. Recycling is
contributing to the sustainable management of wastes and, because of advances in
technologies and systems for segregating, collecting and reprocessing of recyclable
wastes, it is rapidly expanding. It is creating new opportunities for integration with
industries, communities and the governments.
Keywords Recycling ·Plastics ·Strategies ·Processes ·Merits ·Demerits
B. G. Mwanza (B
Graduate School of Business, University of Zambia, P. O. Box 32379, Lusaka, Zambia
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
J. Parameswaranpillai et al. (eds.), Recent Developments in Plastic Recycling,
Composites Science and Technology,
2B. G. Mwanza
1 Understanding Recycling
To support the survival and wellbeing of mankind, various technologies and systems
have been invented. These technologies and systems have focused on several aspects
of survival. One sector in which these technologies and systems, have contributed
massively is the manufacturing sector. This sector has produced many products that
continue to excite mankind as well as present opportunities for innovation. Never-
theless, among the many industries that exist in the manufacturing sector is the
recycling industry. This industry continues to contribute to many goals for achieving
sustainability and circular economy. As a result of numerous beneﬁts and challenges
associated with recycling, it is important to provide a detailed overview on recycling
with particular interest to the plastic industry.
Recycling involves activities in which unwanted/or waste materials are reused for
the reproduction of new products. Coelho (2011) afﬁrms that, recycling reintroduces
unwanted materials and/or energy back into the production system. The unwanted
materials reintroduced into the production system can be plastics, metals, papers etc.
The materials used in the recycling activities are substitutes for virgin materials that
would have been obtained from scarce natural resources such as petroleum, trees, coal
and many others. From the sustainability angle, there are many beneﬁts associated
to recycling other than virgin material substitution. Al-Salem et al. (2009) adds that,
recycling is important for various causes including oil preservation, minimization of
greenhouse gas (GHG) emissions, energy preservation etc. Recycling is a cardinal
element in the waste management (WM) hierarchy where it sits as the third strategy
on the 3Rs “Reduce, Reuse and Recycle.”
1.1 Recycling Strategies
Many studies on recycling processes have been conducted. Ragaert et al. (2017)
conducted an extensive review on the recent strategies for polymer recycling through
chemical and mechanical processes. The study also established the relationship
between recycling and design while emphasizing the function of design from recy-
cling perspective. Maris et al. (2018) reviewed the strategies for compatibilizing
blends of mixed thermoplastic wastes. The study conﬁrmed mechanical recycling as
the most economical, ecological and energetic option for managing plastic wastes.
Al-Salem et al. (2009a) afﬁrms mechanical recycling as the most common process
for recycling plastic wastes and it includes collecting, sorting, washing and grinding.
It is worth noting that, mechanical recycling is not the only recycling process in the
plastic industry. A number of processes including chemical recycling has emerged
as a result of the drawbacks experienced in mechanical recycling (Kumar et al. 2011;
Angyal et al. 2007). These recycling processes are discussed in more detail later.
From the circular economy perspective, categorization of recycled materials is
based on the product manufactured from the secondary raw materials (Ragaert et al.
Introduction to Recycling 3
2017). The two terms that focus on material to product processes are “closed-loop”
and “open-loop” recycling. These two terms are most important for making an objec-
tive division on the new product manufactured. Thus, the terms are subjected to labels
such as “up-cycling” and “down-cycling,” indicating an added value to the process
of recycling (Ragaert et al. 2017).
1.1.1 Closed-Loop Recycling
This term is most applicable to many PET packaging products such as water bottles.
Under this process, recycled plastics are utilized to manufacture similar products
they were originally recovered from. The new product is manufactured entirely from
recycled plastics or in some cases a mixture of recycled plastic is produced with
its virgin counterpart. The type of dilution allows continuation of the recycling and
1.1.2 Open-Loop Recycling
Examples of products recycled using this process include textile ﬁbers from manu-
factured bottle-PET. Recycled plastics are utilized to manufacture a different product
from the originally recovered one. The application does not imply the new product
is of less value than the original one.
1.2 Types of Recycling Processes
The disposal of plastic solid wastes (PSWs) has become a critical global environ-
mental problem (Environmental Impact of Polymers 2014). Despite this, large quan-
tities of PSWs continue to be generated and introduced into the environment through
disposal and production processes and this has continued the accumulation in the
ecosystems across the oceans and globe (Ivleva et al. 2017). Given the serious envi-
ronmental, economic and social challenges caused by PSWs, several decrees and
regulatory guidelines focusing on the recovery of PSWs have been imposed by
many authorities of different countries. Coupled with these guidelines and decrees,
many methods of recycling PSWs that depend on sources of plastics, polymer type
and package design have been developed. The difference in the recycling processes
presents some challenges and hence some studies have been conducted to explain the
sequential steps involved (Hopewell et al. 2009). However, the ﬁrst study concerning
the classiﬁcation of recycling techniques was conducted by Clift (1997). Further, the
classiﬁcation has been standardized into four categories by the International Organi-
zation for Standardization (ISO) and the American Society for Testing and Materials
(ASTM). Many studies have applied this classiﬁcation (Al-Salem et al. 2010; Saiter
et al. 2011; Brems et al. 2012; Ignatyey et al. 2014).
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1.2.1 Primary Recycling
This recycling process reintroduces pre-consumer residues i.e. (scrap, single polymer
edges, parts etc.) into the extrusion cycle in order to manufacture products of the same
material (Maris et al. 2018). This is the best recycling method for plastics because
of its merits on less energy consumption and fewer resources while more retain on
fossil fuels. This recycling method is referred to as the closed-loop recycling strategy
because of its ability to reuse products in their original structure (Grigore 2017).
Primary recycling presents advantages such as; simplicity and low cost. Nevertheless,
scraps of PSWs must be from a single waste source and pure (Bartolome et al. 2012).
The existence of low number of cycles for each material is a major disadvantage of
primary recycling (Singh et al. 2017; Francis 2016). Further, different materials and
polymers cannot be recycled (Park and Kim 2014).
1.2.2 Secondary Recycling
Secondary recycling also referred to as mechanical recycling involves operations
that recover PSWs through mechanical processes. This process substitutes recycled
materials for virgin polymers or a portion of virgin polymers in the new manufactured
plastic products. However, mechanical recycling has a demerit of deteriorating the
properties of recyclable materials and hence degrading the polymers. Occurrence
of low molecular weight compounds and heterogeneity of plastic wastes is another
Grigore (2017) asserts that, secondary recycling represents a physical method-
ology in which recovered PSWs are transformed through cleaning and drying, sizing,
agglomeration, extrusion and manufacturing. Transformed PSWs can be combined
with virgin materials for excellent results. However, it is challenging to recycle
PSWs or wastes that are complex and contaminated. Therefore, wastes are cleaned
to remove contaminates and it is a ﬁrst process.
Mechanical recycling is utilised as a proﬁt oriented process (Al-Salem et al.
2009) with products of different shapes being manufactured. Examples of products
manufactured through mechanical recycling include; grocery bags, windows and
pipes (Al-Salem et al. 2009). Companies in developing continue to utilise this
process because of the merits it presents (Mwanza 2018). Nevertheless, drawbacks
to mechanical recycling can be, the presence of impurities, complexity of PSWs,
mechanical stress and poor quality of recycled wastes (Tshifularo and Patnaik
2020). The quality of the manufactured product is compromised through processes
of waste preparation, cleaning and separation (Park and Kim 2014). Waste dete-
rioration, unbalanced shapes and sizes of PSWs and dissimilar colours inﬂuence
the complexity of mechanical recycling. Upasani et al. (2012) adds that, products
stored in PET bottles speed contamination and deterioration. In addition, life cycle
of recycled polymers inﬂuence the quality.
Introduction to Recycling 5
1.2.3 Tertiary Recycling
This process is also referred to as chemical recycling and involves processes that
chemically produce small molecules from polymer chains that are later used as
feedstock in the manufacture of fuels (Kunwar et al. 2016; Lopez et al. 2017;
Mohanraj et al. 2017); other chemicals (Serrano et al. 2012) and new polymers
(Kwan and Takada 2017). Globally, many chemical processes exist, gasiﬁcation,
hydrocracking, pyrolysis, depolymerisation, methanolysis and aminolysis (Nikles
and Farahat 2005; Genta et al. 2005; Pingale et al. 2010; López-Fonseca et al. 2010;
Fukushima et al. 2013). It is a paramount process for manufacturing food packaging
products (Patterson 2000).
Chemical recycling is a sustainable recycling method (Tshifularo and Patnaik
2020) and will continue to be used without difﬁculties in the future (Wang et al.
2009). Its purpose is to achieve higher rates of the monomer with reduced reaction
time (Al-Sabagh et al. 2016). The presence of depolymerizing agents, monomers
and resin synthesis are some of the advantages presented in chemical recycling. The
process of recycling PET is grouped into methanolysis, glycolysis and hydrolysis.
PET producers recycle using Methanolysis and PET is reduced using methanol at
higher pressure and temperature. The pressure is between 2 and 4 MPa and tempera-
ture between 180 and 280° (Paszum and Spychaj 1997). Its drawbacks include; high
cost, high temperature and pressure (Shukla et al. 2009).
Glycolysis begins by crushing the PSWs into ﬂakes and these are cleaned to
remove contaminants. The dried ﬂakes are then extruded into desired products. In
other cases, virgin PET is blended with the ﬂakes for quality improvement (Tshifu-
laro and Patnaik 2020). Glycolysis is also used to recycle PET bottle wastes under
pressurised reactor kept between 238 and 242°.
Hydrolysis process involves the reaction of PET with water in an alkaline, acid or
neutral environment resulting into total depolymerisation into its monomers (Grigore
2017). It is not a preferred method for manufacturing virgin PET for packaging food
because of high cost. High temperatures of between 200 and 250° and pressures of
between 1.4 and 2 MPa are the major disadvantage of hydrolysis recycling. Ghaemy
and Mossaddegh (2005) adds that, pollution and corrosion related problems are
another set of disadvantage. Compared to glycolysis and methanolysis, it is slow.
1.2.4 Quaternary Recycling
This term is also referred to as energy recovery. It involves the incineration of PSWs
and recovery of energy via the generation of heat and/or electricity. In developed
economies such as the European Union (EU), energy recovery is the most used
recovery method for post-user PSWs (Plastics Europe 2016). It is an appropriate
process for application in instances where mechanical recycling cannot be applied as
a result of separation difﬁculties, excessive contamination or deterioration of polymer
properties. The high caloric value in PSWs makes them a suitable source for energy
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In a report by Bartolome et al. (2012), the amount of chemical energy present
in PSWs is recovered through incineration. This shows that, in any burning process
of PSWs, energy is present and can be recovered. However, the amount present in
burning is much lower compared to an incineration process. Quaternary is the best
recycling option for complex to collect and segregate waste as well as harmful and
The drawbacks of quaternary process is the poisonous air generated that is harmful
to human health (Park and Kim 2014). As a result of the inability to produce another
product from a recycled materials, quaternary does not fully ﬁt in the recycling
deﬁnition (Tshifularo and Patnaik 2020).
1.3 Merits and Demerits of Recycling
Recycling as a strategy of waste management and number 3 in ranking on the waste
management hierarchy has changed the ways in which humanity deals with wastes.
It is interesting to indicate that, recycling has existed as far as the 1800 (Bradbury
2017) and the process has continued to grow globally. The growth and innovations
in recycling has come with advantages and disadvantages. A study by Hopewell
et al. (2009) discusses the opportunities and challenges found in plastic recycling but
still points out that, recycling is one of the vital options available for minimising the
environmental impacts caused by plastics. Further, the plastic industry is represented
dynamically by recycling.
1.3.1 Merits of Recycling
Recycling has enabled producers to create a wide range of products from clothing
to furniture to kitchen utensils. It provides a platform for giving new life to valuable
materials and hence closing the loop. It has expanded rapidly and provides several
merits to the recycling industry and the society at large. The following are some of
the beneﬁts of recycling.
Reduction of landﬁll contamination
Majority of the manufactured plastics are non-biodegradable and cause a lot of harm
to the environment. Recycling of plastics and other materials enables to reduce the
contamination to the environment. The contamination takes long but its effects have
lasting implications to the environment and all the living things.
Diversion of waste materials into other recovery streams
It is not certain that the operation efﬁciency of a recycling program will be at 100%
for society to beneﬁt. Major metropolitan cities continue to generate huge tonnes
of wastes per annual and with diversion of 50% by least recycling technologies, an
extensive amount would be reusable and return to the markets.
Introduction to Recycling 7
Reduction of raw material consumption
Establishment of recycling programs costs more but it contributes to less consump-
tion of virgin materials. For example, plastics are manufactured from petrochemicals
which are produced from fossil gas and oil and 4% of annual petroleum is converted
into plastics (British Plastics Federation 2008). This is not sustainable consumption
considering that, majority of the plastics are manufactured into post-consumer prod-
ucts with a short life cycle. Hopewell et al. (2009) mentions that recycling provides
opportunities to reduce oil usage hence virgin material consumption reduction.
Ability to work as an open and a closed loop system
Recycling can be implemented as a closed and open loop system. Products can be
transformed into different products. For example, transforming a plastic bottle into
a refuse bag (open-loop system). For closed loop systems, products are transformed
into the same products. For example, aluminium cans transformed into aluminium
Reduction of pollution levels
It is possible to reduce the amount of air pollution by 70% through a recycling
program. For example, 1.5 tons of CO2-e per ton of recycled PET is given as a net
beneﬁt in greenhouse gas emissions (Department of environment and Conservation
2005). LCA studies have also shown that, recycling contributes to the reduction in
emissions (Patel et al. 2000). 100% recycled PET has the ability to reduce life-cycle
emissions from 446 to 327 g CO2per bottle compared to 100% virgin PET (WRAP
2008). This shows that, recycling reduces the threat of environment impacts.
Creation of educational opportunities
Availability of knowledge on recycling is a driver to community participation in
recycling programs. Mwanza (2018) shows that, lack of information on recycling
prevents communities from participating. Therefore, creation of recycling programs
is an opportunity to provide knowledge and education. Informing communities on
waste recycling contributes to sustainable management of waste and households can
be taught how to reduce disposal and focus on recovery.
Proﬁtability of recycling programs
Depending on the size of a city, signiﬁcant proﬁts can be obtained from a recycling
program. For example, $90 per bin per year can be created and this depends on the
effectiveness of the recycling program.
Creation of jobs
In developing economies, majority of the PSWs is recovered by the informal waste
sector. The livelihood the informal waste sector get from recovering has contributed to
sustainable recovery and management of PSWs. Therefore, the existing of recycling
processes has contributed to job creation in the recycling industry.
8B. G. Mwanza
Minimization of global warming
When the wastes disposed at landﬁlls are combusted, emissions in the form of green-
house gases are generated and these contribute to climate change and global warming.
Therefore, the diversion of wastes for recycling minimizes the environment impacts
caused by wastes. The process of recycling generates less greenhouses compared to
landﬁlling since the amount of fossil fuels burnt less.
1.3.2 Demerits of Recycling
According to (Tshifularo and Patnaik 2020), the demerits presented in new products
manufactured from recycled plastics have poor thermal and mechanical properties
and lower melting viscosity. The presence of contaminants and reduced molecular
weight of the recycled wastes is caused by degenerated mechanical and physical
properties of the recycled wastes and this is another demerit of recycling. Besides
these demerits presented in recycled plastics, a number of demerits on recycling exist
Recycling is costly compared to landﬁlling
Other than the costs of constructing recycling plants, purchasing of required recycling
equipment and machinery, and educating locals on available recycling programs and
seminars, it is costly to recycle compared to landﬁll. Statistics published on Credit
Donkey show that the cost of recycling prevent communities to recycle. Mwanza
(2018) shows that, costs associated with waste recovery, logistics, and production and
labour are obstacles to recycling in developing economies. However, Mwanza (2018)
also shows that, comparative of recycling cost to landﬁlling is slowly promoting
recycling. The cost of landﬁlling a ton is around $28 compared to $147 a ton to
recycle. Further, landﬁll management is less costly than managing a recycling facility.
Communities lack of compliance to recycling programs
Lack of compliance by communities presents demerits of recycling. Communities
desire to recycle but lack the understanding of rules for wastes to include in the
curb. This creates a lot of problems for recycling programs. Mwanza (2018)shows
that, lack of information on PSWs recycling prevents communities to participate in
recycling. Despite most recyclable products having recycling symbols, compliance
from communities is still very low because most of them do not understand these
symbols and therefore end up mixing these recyclable wastes.
Unhygienic and unsafe recycling sites
Majority of recycling sites are unhygienic and unsafe because a location where waste
piles is a conductive environment for debris to form. Workers and waste collectors
face several toxins at collection points and landﬁlls. Workers are exposure to chemi-
cals, ﬂuids, and microbial agents and every collection point creates a possible health
Introduction to Recycling 9
Problems created by contaminants
The presence of any contaminant has high possibilities of damaging the entire batch
prepared for recycling. It is a big challenge in the recycling industry despite speciﬁc
rules been established for wastes.
Litter creation by waste collectors
In developing economies, major of waste collectors are in the informal sector. This
sector does not have adequate capacity in terms of waste collection equipment and
vehicles. This challenge has continued to create problems of littering after waste
recovery. Scenes of this kind are observed neighborhoods despite waste management
trucks with hydraulic arm to lift the container been used.
Non-durability of recycled products
The durability is always questioned and majority of the products manufactured prod-
ucts cannot be compared to those manufactured from virgin materials. Quality is
always an issue in recycled products.
Energy Consumption and Pollution
Throughout the life of a product, energy is required. During recycling, energy
is consumed from transportation of waste from collection points, during sorting,
cleaning and manufacturing. In all these processes energy is consumed. Further,
wastes in form of pollutants are created. The vehicles used in the transportation
processes create pollution. Chemicals pollutants from the waste materials are harmful
to the environment.
1.4 Recent Developments
Globally, the innovations, manufacturing and usage of plastics continues to increase
exponentially annually, resulting in continuous increase in disposed end-of-life plas-
tics in dumpsites, landﬁlls and natural environments. Although recycling is ranked
third on the waste management hierarchy, it has become an extremely important
ecological and economic issue because of the merits it presents such as; low cost
of energy, reduction of pollution and preservation of virgin materials. The desire
to reduce the amount of plastics on the environment is growing from developed
to developing economies and this has seen many legislations on plastics coming
up. However, the relatively low costs of landﬁlling is proving to be an obstacle to
the expansion of recycling especially in developing economies. Nevertheless, the
drive for circular economy and political pressure has resulted in the creation of strict
legislations focused on reduction of PSWs landﬁlling.
The majority of PSWs generated comes from post-consumer products because of
their short life-cycle compared to pre-consumer products. Majority of plastic mate-
rials is manufactured as post-consumer products such as packaging products. The
10 B. G. Mwanza
short life-cycle of plastic packaging products entails continuous demand for virgin
materials. However, with the efforts to educate the public on sustainable resource
utilisation, several legislations and systems have been devised to make inappropriate
disposal costly and recycling more feasible, if possible mandatory. More and more
wastes are been channelled into sustainable routes either through buy-back strate-
gies or reduced recycling quotas. From these changes, recycling has increased and
continues to increase globally.
Recycling approaches focus on; mechanical recycling, chemical recycling and
energy recovery. Mechanical recycling is the most promising strategy from the envi-
ronmental and economic aspects. However, if sorting is not conducted because of
economic or technical constraints, recovered PSWs will constitute of different poly-
mers and this presents a challenge to mechanically recycle. Thus, the drive for waste
segregation is growing because for any recycling strategy to sustainably work, wastes
should be segregated appropriately. Segregation of wastes results in reduced process
time and hence reduced production costs. Chemical recycling through monomer
recycling and pyrolysis are technologies that are showing a lot of potential in the
recycling industry. Therefore, the recycling industry should invest in research that
can provide feasible implementation plans for these technologies. Mechanical recy-
cling as an established business in many developed economies is proﬁtable and can
generate new polymer with minimum investment. It is a comparatively an advanta-
geous route to polymer manufacturing and can be used to recycle many polymers.
For example, mechanically recycling LDPE and HDPE has the potential to generate
the largest proﬁt by 2030 (Hydrocarbon processing 2019). As a result of the demerits
found in mechanical recycling such as quality deterioration and residue build-ups,
chemical recycling through pyrolysis provides an optimal value treatment option
while monomer recycling provides the highest recycling proﬁtability levels.
Contextual development of recycling systems has the potential to improve recy-
cling rates. The focus should be to design systems and deploy appropriate technolo-
gies that ﬁt contexts. For example, most emerging economies lack waste sorting
infrastructure and therefore, the wastes recovered is a small percent of the waste
ﬂow. An assessment of wastes generated and collected should be the starting point.
Once these waste management capabilities are established, waste segregation strate-
gies should follow. When this is achieved, pyrolysis of mixed PSWs can be the most
By 2030, plastics reuse could increase to 50% of its production (Hydrocarbon
processing 2019) assuming enforcement of regulatory frameworks and adjustments
in the oil prices. The regulatory frameworks should be supported by industry stake-
holders and consumers. To achieve a 50% reuse in plastics, capital investments is
The demand for plastics will continue to grow worldwide and it is imperative to
establish effective systems for managing PSWs. Development of sustainable paths
for quadrupling the amount of PSWs being reused and recycled should be focused on.
The pathways will demand alignment of regulators and behaviors from major stake-
holders such as consumer goods and society. Establishing partnerships will enable
Introduction to Recycling 11
players to access the required technologies or secure access to the feedstock supply-
chains. Collaborating with research institutions and creating long term agreements
with private waste companies, landﬁll sites, municipalities and the communities will
improve the supply-chain management of feedstock. For contextual supply-chain
management of feedstock, integration of the informal sector into formalized systems
will work for most developing economies.
Based on the reviewed literature, recycling is a vital element within the wastemanage-
ment hierarchy and will continue to contribute to sustainable development of the
global. The different recycling strategies present a number of merits and demerits.
These merits and demerits have enabled the recycling of different types of PSWs.
As innovations and technological advancement continue to emerge, improvements
within the recycling space continue to advance. This advancement in technology
through research is needed by the recycling companies because the plastic manufac-
turing industry is not waiting for recycling technology to advance before they design
and manufacture new products.
Integration of the required stakeholders, regulation enforcement, knowledge and
awareness on recycling and systems development are needed for successful imple-
mentation of recycling programs but should be contextually aligned. Societal inte-
gration in the recycling process is necessary because waste is generated from all
aspects of life i.e. workplaces and households. Lastly, the different strategies for
recycling PSWs are not 100% sustainable but are contributing to resolving the PSWs
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