polymers

Review
A Review of Bioplastics and Their Adoption in the
Circular Economy
Alberto Di Bartolo , Giulia Infurna and Nadka Tzankova Dintcheva *

Dipartimento di Ingegneria, Università degli Studi di Palermo, Viale delle Scienze, Ed. 6, 90128 Palermo, Italy;
alberto.dibartolo@gmail.com (A.D.B.); giulia.infurna@unipa.it (G.I.)
* Correspondence: nadka.dintcheva@unipa.it

Abstract: The European Union is working towards the 2050 net-zero emissions goal and tackling
the ever-growing environmental and sustainability crisis by implementing the European Green Deal.
The shift towards a more sustainable society is intertwined with the production, use, and disposal of
plastic in the European economy. Emissions generated by plastic production, plastic waste, littering
and leakage in nature, insufficient recycling, are some of the issues addressed by the European
Commission. Adoption of bioplastics–plastics that are biodegradable, bio-based, or both–is under
assessment as one way to decouple society from the use of fossil resources, and to mitigate specific
environmental risks related to plastic waste. In this work, we aim at reviewing the field of bioplastics,
including standards and life cycle assessment studies, and discuss some of the challenges that can be
currently identified with the adoption of these materials.

Keywords: bioplastic; bio-based plastic; biodegradable plastic; bioeconomy; life cycle assessment;
sustainability







Citation: Di Bartolo, A.; Infurna, G.;

Dintcheva, N.T. A Review of 1. Introduction
Bioplastics and Their Adoption in the The European Green Deal [1] is the action plan outlined by the European Commission
Circular Economy. Polymers 2021, 13,
(EC) to tackle the ever-growing environment and climate-related challenges our society
1229. https://doi.org/10.3390/
faces. The plan aims at transforming “the EU into a fair and prosperous society, with a
polym13081229
modern, resource-efficient and competitive economy where there are no net emissions of greenhouse
gases in 2050 and where economic growth is decoupled from resource use” [1] (p. 2). As also
Academic Editor: Cristina Cazan
stated in its communication “A new Circular Economy Action Plan for a Cleaner and More
Competitive Europe” [2], the EC underlines the utmost importance of shifting towards a
Received: 22 March 2021
Accepted: 7 April 2021
circular economy, with a framework of policies that make sustainable products, services,
Published: 10 April 2021
and business models the norm. On the global scale, The United Nations Development
Program (UNDP) also stressed the importance of working towards a sustainable economy,
Publisher’s Note: MDPI stays neutral
with efficient use of natural resources, little to none waste and pollution [3]. In this context,
with regard to jurisdictional claims in
the EC identifies a series of pressing challenges relating to plastic production, (mis-)use and
published maps and institutional affil- pollution, spanning from single-use items, over-packaging, and littering, to microplastics,
iations. high-carbon footprints, and lack of appropriate labeling. The strategy outlined to tackle
these challenges includes supporting the bio-based industry and developing a framework
for the use of bio-based plastics, “based on assessing where the use of bio-based feedstock results
in genuine environmental benefits”, and for the use of biodegradable or compostable plastics,
Copyright: © 2021 by the authors.
“based on an assessment of the applications where such use can be beneficial to the environment” [2]
Licensee MDPI, Basel, Switzerland.
(p. 9). These plastics, which are either bio-based or biodegradable (or both), are referred
This article is an open access article
to as “bioplastics” and have been the topic of much work and discussion at a global
distributed under the terms and level for some time now. The dwindling of fossil resources provides a strong drive to
conditions of the Creative Commons the development of bio-based products, while the possibility to mitigate environmental
Attribution (CC BY) license (https:// pollution or simplify organic waste collection are big motivations behind the development
creativecommons.org/licenses/by/ of biodegradable and compostable plastic products. Bioplastics already find applications
4.0/). on the market, particularly as packaging [4–7], carrier and compost bags [5,6]; they are

Polymers 2021, 13, 1229. https://doi.org/10.3390/polym13081229 https://www.mdpi.com/journal/polymers

Polymers 2021, 13, 1229 2 of 26

also applied in the agriculture and horticulture sector [6,8], and in the automotive and
electronic industry [6,9]. Furthermore, biodegradable polymers have been long applied in
biomedicine [5,10,11]. Still, the production of bio-based plastics is limited to one percent
of the worldwide plastic production [7,12] and their adoption comes with uncertainties,
as acknowledged in the EC Communication “A European Strategy for Plastics in a Circular
Economy” [13]. This is exemplified by the research focused on bioplastics sustainability
and [8,14–25] biodegradability [26–30], as well as the attention of media to the subject.
Excluding the ample literature on biomedical applications, academic research has been
focusing on the synthesis of bio-based polymers [31,32], on the life cycle assessment
(LCA) of the production and end-of-life (EOL) [20,24,33,34] of different bioplastics, and
biodegradation under different conditions [10,14,35].
In this paper, we present the reader with an overview of the bioplastics field, including
definitions, polymers on the market, and applications. We discuss biotic and abiotic
degradation mechanisms and present standards and certifications that are in place to
evaluate the compostability and biodegradability of bioplastics. Recent works on the
biodegradability of bioplastics are also reviewed. We report on the standards in place
for the LCA of bioplastics and review recent studies on the subject, with particular focus
on studies that consider the EOL assessment. Finally, given the material reviewed, we
concisely discuss the challenges that can be identified with the adoption of bioplastics, as
well as possible solutions, and we draw our conclusions on the topic.

1.1. Environmental Impact of Plastics

The generation of plastic waste and subsequent uncontrolled plastic pollution is one
of the major environmental problems governments and agencies must face today.
The global production of plastic reached almost 370 million metric tons (Mt) in
2019 [36], almost 60 million of which are produced in Europe. The vast majority of the
plastic products that enter the global market are durable materials, in particular, polypropy-
lene and polyethylene are the leading polyolefins on the market, with the production of
packaging being the main use of such plastics [36]. As of 2017, it was estimated that 8300 Mt
of plastics were produced worldwide while, as of 2015, 79% of all plastic produced had
been accumulating in landfills or the environment [37]. The UNEP reports that only 9% of
all plastic ever made has been recycled, 12% has been incinerated and the rest accumulates
in landfills or nature [38]. Today, 300 Mt of plastic waste are produced every year and
around 80% of marine litter is due to plastic debris, with the infamous “Great Pacific Garbage
Patch” being a dreadful testament to these numbers and with an estimate of 75,000 to
300,000 tons of microplastics entering EU habitats every year [38–41].
Plastic debris in the natural environment is extremely persistent, with degradation
in seawater being estimated from hundreds to thousands of years [42,43]. Plastic marine
debris results in severe, harmful, impact on the ecosystem [44]. Because of its long half-life
and hydrophobic nature, plastic debris provides excellent conditions for the proliferation
of diverse microbial communities, forming an ecosystem referred to as “plastisphere” [45].
The microbial action, together with mechanical stress, thermal and UV-light degradation,
results in the fragmentation of the debris into microplastics, to the point that plastic residues
can be found in many aquatic species, as well as birds and other wildlife [46]. In turn, this
poses a risk to human health by entering the food chain [47–49].
A great part of the answer to plastic pollution comes from increasing recycling and
repurposing of already produced plastics, as well as replacing several classes of plastic
items, particularly single-use products, with recyclable alternatives, and from a change
in mentality and habits in our society. At the same time, fossil resources are finite and
their use results in greenhouse gas (GHG) emissions. As reported by the Ellen MacArthur
Foundation in 2016 [50], it can be estimated that by 2050 the plastics sector “will account
for 20% of total oil consumption and 15% of the global annual carbon budget by 2050 (this is the
budget that must be adhered to in order to achieve the internationally accepted goal to remain below
a 2 ◦ C increase in global warming)” [50] (p. 7). The production of plastics from renewable
Polymers 2021, 13, 1229 3 of 26

sources has been suggested to achieve a lower carbon footprint, since the raw materials
uptake carbon dioxide during their growth, and to alleviate the economy’s dependence on
fossil fuel [13,41,50]. The application of biodegradable plastics in specific fields, such as soil
cover films, carrier bags, and single-use packaging is also suggested as part of technological
advancement in the bioeconomy [7,13].

1.2. Circular Economy and Bioplastics

Broadly speaking, a circular economy is an economic system and production model
aimed at maximizing the reuse and recycling of resources, therefore extending the life
cycle of products while minimizing waste. The model was thought of as a response to
the traditional economy, the linear economy, where resources are used to manufacture
products which are then used and discarded as waste. The Circular Economy Action Plan
presented by the EC in 2020 [2] outlines the main directions towards which the economic
model is being developed. We briefly summarize some of the main points made in the
document.
Products should be designed with reusability and recyclability in mind, i.e., they need
to be more durable, repairable, recyclable. Packaging is to be reduced, restricted to certain
applications, and designed for recyclability. The production of single-use items is to be
restricted and the destruction of unsold items is to be banned. Finally, more support to
the bio-based sector is also considered as one way to enable greater circularity in industry,
though it is also noted that the sourcing, labeling and use of bio-based, biodegradable
and compostable plastics, are emerging challenges for which the EC will develop a policy
framework [2] (p. 9). The topic of bioplastics is more extensively discussed in a 2018 EC
action plan [51] focused on bioeconomy.
Overall, the EC communications suggest that the policy will be to support, e.g., via
financial and regulatory incentives, the growth of the bioplastics industry, as one way
to move towards a low-carbon economy [41,52,53]. For example, more than 100 million
euros have been provided to finance R&D focused on alternative feedstocks, as part of
the Horizon 2020 Research Programme [52]. The European Committee for Standardization
(CEN) has also produced several harmonized standards in the past five years, covering
methodologies to claim biodegradability and compostability, and to measure the bio-based
content of plastics, to better regulate the bioplastic field. Still, it is acknowledged that more
standards are required and that applications of biodegradable plastics can come with both
positive and negative implications [53].

2. Bioplastics: Definitions and Market

The term bioplastic is often used loosely and synonymously to biodegradable. While
some bioplastics are indeed biodegradable, not all are. Bioplastics should be intended
as polymers that meet any of two criteria: the polymer is bio-based, the polymer is
biodegradable [28,54]. Bio-based means that the polymer is either entirely or partially
obtained from biomass, i.e., from any kind of organic renewable material of biological
origin as well as organic waste. Biodegradable means that the material can break down
into natural substances such as carbon dioxide, water and biomass, due to the action of
microorganisms. In a more specific sense, a biodegradable plastic is a plastic material that
complies with certain official standards of biodegradability, where a certain amount of
degradation needs to be scientifically observed within a certain amount of time and under
specific conditions. Similarly, a compostable plastic undergoes biodegradation in industrial
composting facilities and has to comply with specific standards.
Bioplastics therefore form three broad groups of polymers: those that are both bio-
based and biodegradable, those that are only bio-based and those that are only biodegrad-
able. Some main examples of bioplastics that are both bio-based and biodegradable are
polylactic acid (PLA) [55,56], polyhydroxyalkanoates (PHAs) [57] and bio-based poly-
butylene succinate (bio-PBS) [58], as well as plastics based on starch, cellulose, lignin and
chitosan. Examples of bioplastics that are bio-based but not biodegradable are bio-based
Polymers 2021, 13, 1229 4 of 26

polyamides (bio-PP), polyethylene (bio-PE), polyethylene terephthalate (bio-PET) [59].

Finally, examples of biodegradable bioplastics that are based on fossil resources are PBS,
polycaprolactone (PCL) [60], polyvinyl alcohol (PVA) [61] and polybutylene adipate tereph-
thalate (PBAT) [62]. Furthermore, polymers like bio-PE, which are bio-based and chemically
identical to their fossil-based counterparts, are typically referred to as drop-in polymers.
Table 1 lists some bioplastics that are frequently encountered on the market or in research,
classified on the basis of the origin of the raw materials and their biodegradability.

Table 1. Lists of bioplastics and indication of bio-based origin and biodegradability. In the table, “y”
means yes, “n” means no, and “y/n” refers to both statements being valid.

Polymer Bio-Based Biodegradable

Polylactic acid (PLA) y y
Starch blends, thermoplastic starch (TS) y y
Polyhydroxyalkanoates (PHAs) y y
Polybutylene succinate (PBS) y/n y
Polyurethanes (PURs) y/n y/n
Polycaprolactone (PCL) n y
Polyvinyl alcohol (PVA) n y
Polybutylene adipate terephthalate (PBAT) n y
Polyethylene Furanoate (PEF) y n
Bio-polypropylene (bio-PP) y n
Polytrimethylene terephthalate (PTT) y n
Bio-polyethylene terephthalate (bio-PET) y n
Bio-polyethylene (bio-PE) y n
Bio-polyamides (bio-PAs) y n

Today’s production volume of bioplastics is relatively small when compared to the

numbers of the common plastic industry. According to European Bioplastics, the global
production of bioplastics in 2018 was around 2 Mt [12], while the global production for
plastics was around 360 Mt. At the same time it is anticipated that the global market for bio-
plastics will grow steadily for the next five year, increasing in volume by around 40% [12].
Different examples of bioplastics already exist on the market and are produced by compa-
nies both in Europe, the USA and Asia, with some of the most important manufacturer
being BASF (Germany), Corbion N.V. (Netherlands), NatureWorks LLC (USA), CJ Cheil-
Jedang (Korea), Novamont (Italy), Tianjin Guoyun (China). Two historically successful
examples are CellophaneTM , produced from regenerated cellulose by Futamura Chemical
Company (UK), and Nylon-11 produced from castor oil by different manufacturers. More
examples are the PLA branded IngeoTM produced by NatureWorks LLC, as well as the
Luminy® series of PLA resins produced by Total Corbion (fifty-fifty joint venture between
Total and Corbion), which is also working on the production of bio-based PEF; Corbion
distributes its PURASORB® grades of bioresorbable polymers, which include PLA, PCL
and copolymers; Danimer Scientific produces the PHA-based bioplastic NodaxTM ; several
compostable polymers are produced by BASF (ecoflex® , ecovio® ); Novamont produces
its biodegradable, starch-based, Mater-BiTM ; Arkema produces a series of bio-PA (Nylon)
under the name Rilsan® .

2.1. Production Routes of Bio-Based Plastics and Main Examples

As already introduced, bio-based plastics are entirely or partially obtained from some
type of biological source, this includes plants, microorganisms, algae, as well as food waste.
Some bio-based plastics are obtained from polymers that form directly in nature, within
microorganisms and plants. Notably, cellulose—the most abundant organic compound
and the main constituent in plant fibers—has been used ever since the 19th century. Other
bio-based plastics are relatively novel and are obtained through synthetic routes making
use of natural resources to formulate monomers which are then polymerized. In general,
we can identify three main routes to produce bio-based plastics: (1) polymerization of
Polymers 2021, 13, 1229 5 of 26

bio-based monomers; (2) modification of naturally occurring polymers; (3) extraction of

polymers from microorganisms. Table 2 lists some of the main bio-based polymers grouped
by their production route and followed by a brief description of their synthesis.

Table 2. List of common bio-based polymers and overview of their production.

Polymer Technology Overview Route

Fermentation of carbohydrates (e.g., starch)
yields lactic acid which polymerizes to low Mn
Polylactic acid
PLA. This depolymerizes to lactide, which
polymerizes to high Mn PLA.
Bacterial fermentation of carbohydrates yields
succinic acid, which is esterified to also obtain
Polybutylene succinate
1,4-butanediol. The two chemicals polymerize to
PBS.
Polyols obtained from plant oils are reacted with 1
Polyurethanes
isocyanates or bio-isocyanates to yield PURs.
Diacids derived from castor oil are reacted with
a diamine to yield PAs. A typical pair is sebacic
Polyamides
acid and decamethylenediamine (obtained from
the acid).
Fermentation of saccharides yields bioethanol,
Polyethylene then dehydrated to ethylene. Polymerization
yields bio-PE.
Typically obtained by gelatinization of starch
Thermoplastic starch (from corn, cassava, etc.) followed by casting or
by extrusion of starch pellets and plasticizers.
Cellulose from wood pulp is converted to a
Cellulose acetate triacetate form which is then hydrolyzed to 2
cellulose acetate.
Cellulose is converted to a soluble form, then
Regenerated cellulose regenerated to obtain a film (cellophane) or a
fiber (rayon).
Intracellularly accumulated by different bacteria.
Polyhydroxyalkanoates Polyhydroxybutyrate was the first to be 3
discovered.

Today, several bio-based polymers are produced through the polymerization of

monomers obtained from natural sources, PLA being the primary example. Polylactic
acid is a thermoplastic aliphatic polyester obtained from the fermentation of plant-derived
carbohydrates, e.g., sugars obtained from sugarcane or sugar beet, or starch obtained from
corn or potato. The fermentation process makes use of various microorganisms, typically
Lactobacilli strains, which convert sugars to lactic acid [55,63]. If starch is used as feedstock,
this is first enzymatically converted to sugars (glucose). Most commonly, the lactic acid is
then polymerized to low molecular weight (Mn) PLA oligomers, which are in turn depoly-
merized to yield lactide, the cyclic dimer of PLA. The ring-opening polymerization (ROP)
of lactide will then yield high Mn PLA [55,64,65]. Due to the chiral nature of the monomers,
L(-) and D(+), in use during the polymerization process, three stereochemical forms of PLA
can be obtained. Depending on the ratio of L- to D-isomers, the resulting polymer can be
amorphous or show different degree of crystallinity, with influence on degradation [66]
and mechanical properties [67]. PLA processability is comparable to many commodity
thermoplastics, which leads to its use as packaging material [56,68]. PLA is also recognized
as biodegradable and compostable [55,64,65], it is therefore used in the production of
compost bags and disposable tableware, and other applications where recovery of the used
product is not feasible. Furthermore, PLA biocompatibility has made it into one of the
Polymers 2021, 13, 1229 6 of 26

most important polymers in biomedicine and tissue engineering [55,64,65,69]. Finally, PLA
is one of the main materials in use to produce filaments for fused deposition modeling, a
common 3D printing manufacturing process [70].
PBS is another thermoplastic polyester that can be produced from the microbial fer-
mentation of sugars derived from natural feedstocks. The typical route of production for
PBS is the esterification of succinic acid with 1,4-butanediol [71], where the succinic acid
can be obtained from the anaerobic fermentation of bacteria or yeast and subsequently re-
duced to 1,4-butanediol. Several microorganisms have been studied for the biosynthesis of
succinic acid, e.g., Anaerobiospirillum succiniciproducens and Actinobacillus succinogenes [72].
The polymerization process proceeds through a first step during which the 1,4-butanediol
is reacted with the succinic acid to yield oligomers of PBS, and a second step of poly-
condensation of the oligomers to yield semicrystalline, high Mn PBS [58]. PBS shows
similar properties to polyethylene terephthalate and polypropylene and finds applications
as compostable packaging and bags, as mulch film and hygiene products [58,73]. The use
of PBS in biomedical applications has also been attracting significant attention, thanks to its
biodegradability and low toxicity profile, though its low flexibility and slow degradability
rate need to be circumvented by blending or copolymerization with other polymers, such
as PLA [71,73].
Bio-based polyethylene is an aliphatic thermoplastic synthesized from the polymer-
ization of bioethanol. The bioethanol is obtained through the fermentation of sugars from
the aforementioned feedstocks (sugarcane, sugar beet, and starch from corn, wheat or
potato) [59], yeast or bacteria being used as fermentation agents [74]. The bioethanol is
distilled and dehydrated to obtain ethylene which is then polymerized to bio-PE. The
polymer is equivalent to fossil-derived polyethylene and the same different types (low and
high density, linear and branched) can be obtained, consequently, bio-PE can be used for
any of the many applications of PE. It should also be noted that bioethanol can also be used
in the synthesis of other important plastics such as polyvinyl chloride, polystyrene and
polyethylene terephthalate [59].
Several naturally occurring polymers can be used to produce bio-based and biodegrad-
able plastics, in particular the polysaccharides starch and cellulose.
Among naturally occurring polymers, cellulose is the most abundant one, being
ubiquitous in plants. It is a structural polysaccharide based on repeating units of D-glucose.
Cellulose has attracted great attention from research and industry due to its abundance,
low-cost, biocompatibility and biodegradability. Cellulose is typically obtained from
wood through a pulping process and can be converted to different materials, in particular
two main cellulose-based plastics (or cellulosics) are regenerated cellulose and cellulose
diacetates [75]. In the production of cellulose diacetates, the cellulose is first converted to
cellulose triacetate by reaction with acetic anhydride, this is then partially hydrolyzed to
obtain a lower degree of substitution. Most typically cellulose diacetates are produced with
degree of substitution around 2.5. Cellulose acetates find several applications in the textile
industry [76], as fibers in cigarette filters [77], films (e.g., photography) and membranes
in separation technologies (e.g., hemodialysis) [78]; manufactured as porous beads they
have potential applications in biomedicine and biotechnology [79]. Cellulose diacetate is
also biodegradable under different natural conditions with the process being accelerated
by hydrolysis [80].
Regenerated cellulose is typically prepared following the viscose process (though
other industrial methods exist), in which cellulose is converted to cellulose xanthogenate by
reaction with alkali and carbon disulfide. The intermediate is dissolved in NaOH solutions,
resulting in a mixture called viscose, which can be processed as films and fibers and treated
in acidic solutions to yield regenerated cellulose [81,82]. Regenerated cellulose materials
are either already applied or could find applications, in different fields, from textile and
packaging, to biotechnology and biomedicine [82]. Rayon and cellophane, which are
generic trademarks for regenerated cellulose fibers and films respectively, are materials
with great commercial importance. Rayon finds many applications in the textile industry,
Polymers 2021, 13, 1229 7 of 26

from the manufacture of clothing to the production of wound dressings [83]. Cellophane is
almost ubiquitous in the food packaging market, but also in the cosmetic (casing, boxes,
etc.) and pharmaceutical industry [82].
Starch-based polymers form an important family of bioplastics on the market. Starch
is a polysaccharide consisting of two main macromolecules, amylose and amylopectin,
and is obtained from feedstocks such as corn, rice, wheat or potato [84,85]. Thermoplas-
tic starch (TPS) is the material obtained from a granular form of native starch, through
thermomechanical processing (extrusion) with the addition of gelatinization agents or
plasticizers [84–87]. Typical plasticizers in use to improve the processability of TPS are
glycerol and other polyols, sugars, amides and amines, and citric acid [84]. TPS can be
used on its own, though very often it is used as part of polymeric blends with polymers
such as PLA and other polyesters, to improve its properties. Starch-based plastics find
different applications in the packaging, food, textile and pharmaceutical industry [88–90].
Bacteria can synthesize and accumulate a large number of biopolymers, many of
which can be potentially exploited for industrial applications or as high-value products
in the medical field [91]. Polyhydroxyalkanoates are a family of polyesters synthesized
by the activity of several types of bacteria, where they accumulate serving the purpose of
carbon reserve material. The intracellular accumulation of PHAs is typically promoted by
particular culturing conditions and nutrients starvation, which can lead to high concentra-
tion of accumulated polymer [71,91–94]. Several renewable feedstocks, as well as carbon
dioxide, chemicals and fossil resources, can be used as substrate for the production of
PHAs [94]. In a typical process a seed culture containing the chosen bacteria is inoculated
in a fermentation vessel containing the fermentation medium. At the end of the culturing
period, the polymers can be obtained by solvent extraction, separated from the residual
biomass and reprecipitated by mixing with a non-solvent, typically an alcohol [31,71,95]. To
this day, more than 150 monomeric units have been identified, which can lead to different
polymers with different properties. Polyhydroxybutyrate (PHB) is the simplest PHA and
the first one to be discovered in the bacterium Bacillus megaterium. PHAs find applications
in the packaging, food and chemical industry, though most recently attention has been
shifting towards possible agricultural and medical applications [96–98].

2.2. Biodegradability and Compostability Standards

As introduced, biodegradable polymers are susceptible to be broken down into simple
compounds because of microbial action. Many plastics have been known to undergo
this process in a reasonably short time (e.g., six months), and are commonly identified
as biodegradable, though to substantiate biodegradability claims, certain standards have
been put into place in the past twenty years. These standards present methodologies to
evaluate the biodegradability and compostability of a plastic, where compostable refers
to the material being degraded under specifically designed conditions and by specific
microorganisms, typically in industrial composting facilities. The main standardization
bodies involved are the International Organization for Standardization (ISO), European
Committee for Standardisation (CEN) and the American Society for Testing and Materials
(ASTM). Table 3 reports the main ISO [99] and CEN [100] standards in place, many of
which are shared as the CEN standards are often based on the ISO ones. In particular,
for a polymer to be marketed as biodegradable or compostable the main standards to
conform to are the European EN 13432 or EN 14995 or the international ISO 17088 (other
equivalents would be the USA ASTM 6400 or the Australian AS4736). As part of the
requirements to pass the standards, the testing methodologies in use to evaluate biodegrad-
ability need to be the ones outlined by other official standards, for example EN ISO 14855.
The simulated environment, the biodegradability indicator in use, the inoculum in use, test
duration, number of replicates required and percentage of evaluated biodegradability to
pass the test, are focus points for biodegradability testing standards. It can be noticed that
the biodegradability evaluation is carried out by different experimental methodologies,
such as release of carbon dioxide and oxygen demand measurements. Indeed, the main
Polymers 2021, 13, 1229 8 of 26

indicators of biodegradation adopted by these standards are the measurement of BOD

(the biological oxygen demand) or the measurement of evolved CO2 , though also mass
loss measurements, measurements of CH4 evolution, as well as surface morphology and
spectroscopy analysis are methodologies in use [101]. Biodegradability standards describe
a series of well-defined conditions under which biodegradability or compostability tests
are to be carried out, for example temperature, microbial activity and humidity. While
this is required for reproducibility and repeatability of results, researchers have pointed
out the difficulty in encompassing the variability of conditions encountered in natural,
open environments [10,14]. In particular, the more environmentally harmful perspective
of plastic waste leaking into the natural environment leads to a series of possible environ-
mental conditions that are hard to accurately predict and simulate. For example, plastic
debris leaked in the sea is exposed to a wide range of temperatures, depending on climate,
biomes, buoyancy, and other characteristics that might very well change over time. Given
that the appeal of biodegradable plastics in several applications is their supposed ability
to degrade in the environment, completely and harmlessly, it is of utmost importance to
understand the validity of these standards outside of laboratory conditions. In a 2018
review of biodegradability standards, Harrison et al. [35] found that the international
standards in use would be insufficient to predict the biodegradability of carrier bags in
aqueous environments (wastewater, marine and inland waters). They concluded that
the standards in use would typically underestimate the time required for polymers to
undergo biodegradation in a natural, uncontrolled environment, particularly because of
the methods in use relying on artificially modified media and inocula and relatively high
temperatures, that do not reflect what is commonly expected in a natural environment. In
2017, Briassoulis et al. [102] come to similar conclusions when reviewing the standards
relevant to the biodegradability of plastics in soil, particularly for the agriculture and
horticulture environment. They observe that the standard methodologies enhance the
conditions for biodegradation of the specimens in a way that may not be representative
of the natural environment, where temperature, water content and soil properties can
vary considerably. The standards caution the users about the potential difference between
laboratory and natural environment results, though it is not clear how the methodologies
should be modified to obtain more representative conclusions. In a 2017 work, Emadian
et al. [103] reviewed a series of studies on the biodegradation of bioplastics in different
conditions. For the same biopolymers, they reported extremely different results across the
studies taken into consideration. For example, testing the biodegradability of PLA in com-
post researchers reported biodegradation values as low as 13% over 60 days [104] and as
high as 70% over 28 days [105]. This difference in results is due to different methodologies,
conditions and sample geometry and size being in use, and therefore stresses the need for
standard procedures being followed during laboratory tests. Though, at the same time,
the kind of differences that create this discrepancy, can also be encountered in a natural
environment, and further stress the problem of how well biodegradability can be predicted
outside of a laboratory. Further problematics can be encountered when considering the
biodegradation of polymeric blends instead of homopolymers. In a 2018 paper Narancic
et al. [14] reported on the biodegradability of several biopolymers and their blends in
different environments, following the relative standards. The paper is extremely thorough,
and its full analysis goes beyond the scope of this review, though one conclusion was
that the polymeric blends would generally biodegrade well under industrial composting
conditions, but they would show poor biodegradation in aquatic environment and soil.
Interestingly, the authors observed that, while PLA is generally not home-compostable,
when blended with PCL it would result in a material that could undergo biodegradation
under home-composting conditions (though not in soil). At the same time, this was not the
case for blends of PLA and PHB, which remained not home-compostable.
Polymers 2021, 13, 1229 9 of 26

Table 3. Main ISO and CEN standards relating to biodegradability and compostability of plastics.

Standard Title
EN ISO 10210:2017 Plastics—Methods for the preparation of samples for biodegradation testing of plastic materials (ISO 10210:2012)
EN 14995:2006 Plastics—Evaluation of compostability—Test scheme and specifications
Packaging—Requirements for packaging recoverable through composting and biodegradation—Test scheme and
EN 13432:2000
evaluation criteria for the final acceptance of packaging
Packaging—Evaluation of the ultimate aerobic biodegradability of packaging materials under controlled
EN 14046:2003
composting conditions—Method by analysis of released carbon dioxide
EN 17033:2018 Plastics—Biodegradable mulch films for use in agriculture and horticulture—Requirements and test methods
ISO 17088:2012 Specifications for compostable plastics
Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting
EN ISO 14855-1:2012
conditions—Method by analysis of evolved carbon dioxide—Part 1: General method (ISO 14855-1:2012)—Part 2:
EN ISO 14855-2:2018
Gravimetric measurement of carbon dioxide evolved in a laboratory-scale test (ISO 14855-2:2018)
Plastics—Determination of the degree of disintegration of plastic materials under defined composting conditions
EN ISO 16929:2019
in a pilot-scale test (ISO 16929:2019)
Plastics—Determination of the degree of disintegration of plastic materials under simulated composting
EN ISO 20200:2015
conditions in a laboratory-scale test (ISO 20200:2015)
ISO 23977-1:2020 Plastics—Determination of the aerobic biodegradation of plastic materials exposed to seawater—Part 1: Method
ISO 23977-2:2020 by analysis of evolved carbon dioxide—Part 2: Method by measuring the oxygen demand in closed respirometer
Plastics—Determination of the ultimate anaerobic biodegradation of plastic materials in an aqueous
EN ISO 14853:2017
system—Method by measurement of biogas production (ISO 14853:2016)
Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium—Method by
EN ISO 14851:2019
measuring the oxygen demand in a closed respirometer (ISO 14851:2019)
Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium—Method by
EN ISO 14852:2018
analysis of evolved carbon dioxide (ISO 14852:2018)
Determination of the ultimate biodegradation of plastics materials in an aqueous system under anoxic
EN 17417:2020
(denitrifying) conditions—Method by measurement of pressure increase
Water quality—Preparation and treatment of poorly water-soluble organic compounds for the subsequent
EN ISO 10634:2018
evaluation of their biodegradability in an aqueous medium (ISO 10634:2018)
Water quality—Evaluation of ultimate aerobic biodegradability of organic compounds in aqueous
EN ISO 14593:2005
medium—Method by analysis of inorganic carbon in sealed vessels (CO2 headspace test) (ISO 14593:1999)
Water quality—Determination of the elimination and biodegradability of organic compounds in an aqueous
EN ISO 11733:2004
medium—Activated sludge simulation test (ISO 11733:2004)
Plastics—Determination of the ultimate aerobic biodegradability of plastic materials in soil by measuring the
EN ISO 17556:2019
oxygen demand in a respirometer or the amount of carbon dioxide evolved (ISO 17556:2019)
Soil quality—Guidance on laboratory testing for biodegradation of organic chemicals in soil under aerobic
EN ISO 11266:2020
conditions (ISO 11266:1994)
Plastics—Determination of the ultimate anaerobic biodegradation under high-solids anaerobic-digestion
EN ISO 15985:2017
conditions—Method by analysis of released biogas (ISO 15985:2014)
Plastics—Determination of aerobic biodegradation of non-floating plastic materials in a seawater/sandy sediment
EN ISO 18830:2017
interface—Method by measuring the oxygen demand in closed respirometer (ISO 18830:2016)
Plastics—Determination of aerobic biodegradation of non-floating plastic materials in a seawater/sediment
EN ISO 19679:2020
interface—Method by analysis of evolved carbon dioxide (ISO 19679:2020)
Plastics—Determination of the ultimate anaerobic biodegradation of plastic materials in controlled slurry
ISO 13975:2019
digestion systems—Method by measurement of biogas production
Plastics—Determination of the aerobic biodegradation of non-floating materials exposed to marine
ISO 22404:2019
sediment—Method by analysis of evolved carbon dioxide
ISO/DIS 23517-1 Plastics—Biodegradable mulch films for use in agriculture and horticulture
(under development) Part 1: Requirements and test methods regarding biodegradation, ecotoxicity and control of constituents

Several companies in Europe market their products with labels specifying their
biodegradability. Figure 1 summarizes the main certifications in use in Europe, which are
released by the Belgian certifier TÜV Austria and German certifier DIN CERTCO. It should
be noted that home compostability is yet to be specifically described by EN harmonized
standards, though standard prEN 17427:2020 “Packaging-Requirements and test scheme
for carrier bags suitable for treatment in well-managed home composting installations” is
Polymers 2021, 13, 1229 10 of 26

pending. Industrial compostability is covered by the standards EN 14995 and EN 13432,

and these are used during the certification. Soil biodegradability is also certified by two of
the labels through EN 17033, which therefore limits the certification to mulch film. Two
labels for biodegradability in water are offered by TÜV but they are independent from
EN standards.

Figure 1. Certification labels relating to biodegradability and compostability: (a) seedling logo by Eu-
ropean Bioplastics, indicates that the product is industrially compostable and complies with EN 13432;
(b–d) DIN CERTCO labels for industrial compostability, biodegradability in soil and home composta-
bility, respectively; (e–i) TÜV Austria labels for industrial compostability, marine biodegradability,
home compostability, soil biodegradability and freshwater biodegradability, respectively.

2.3. Overview of Abiotic and Biotic Degradation Mechanisms

While the official definition of biodegradation is exclusively focused on the biotic
phenomena, it is important to remember that abiotic phenomena take place during the
biodegradation of a polymeric material, and these can have a strong influence on the
overall degradation rate. We can identify three main steps through which biodegradation
proceeds, with the process being susceptible to stop at each step [103,106–108].
During a first step referred to as biodeterioration, the material is broken down into
smaller fractions due to biotic and abiotic activity. During this step a biofilm is formed on
the surface of the material, consisting of a variety of microorganisms embedded in a matrix
of water, proteins and polysaccharides produced by the same microorganisms [109,110].
The process of colonization of a polymeric surface by a microbial biofilm is referred to as
fouling and follows different steps that lead to the settlement of bacteria and other microor-
ganisms (microfouling) as well as larger organisms (macrofouling) such as larvae [110,111].
During and subsequently the biofilm formation, the microorganisms can infiltrate the
surface porosity of the polymer which results in a change of the porous volume and poten-
tially in cracks, furthermore this process facilitates water infiltration and consequentially
hydrolysis. Additives and plasticizers can also leach out of the polymer during this step,
resulting in embrittlement and rupture.
The microorganisms inhabiting the biofilm secrete enzymes that can be broadly de-
fined as intracellular and extracellular depolymerase [28,101,103,106,110]. These enzymes
are responsible for the second step in biodegradation, the depolymerization step, dur-
ing which the polymer chains are broken down into shorter oligomers and eventually
monomers, though this process can also result from abiotic phenomena which are covered
later in this section.
Polymers 2021, 13, 1229 11 of 26

The third step of biodegradation comprises of the assimilation and mineralization pro-
cesses during which monomers and oligomers from the broken-down polymer can reach
the cytoplasm and enter the metabolism of the microorganisms, therefore being converted
to metabolites, energy and biomass, with the release in the environment gases, organic com-
pounds and salts [106]. This step is of particular importance given that several standardized
methodologies rely on the analysis of evolved CO2 to evaluate biodegradability.
Abiotic degradation phenomena are involved either before or in concomitance with
biotic degradation. Typical abiotic degradation phenomena are mechanical, thermal, UV,
and chemical degradation.
Mechanical damage, both at macro and microscopical scale, can facilitate and acceler-
ate other types of abiotic and biotic degradation, for example by increasing the available
contact surface or creating defects that are easily attacked by chemical infiltration and more
susceptible to heat damage.
Heat can further increase mechanical damage by lowering the mechanical properties
of the polymer, e.g., if the plastic were to experience temperatures higher than its glass
transition or melting temperature, its structural integrity would be quickly compromised
under relatively low forces. Conversely, temperatures much lower than the glass transition
might result in brittleness and rupture of the polymer. The loss of crystallinity, as well as the
transition to the rubbery state, can also increase the permeability of biotic and abiotic agents
in the polymeric matrix, therefore accelerating the degradation process. This is particularly
important for polyesters, such as PLA, where the degradation process is strongly governed
by hydrolysis reactions and therefore will proceed at a much faster rate when water can
easily penetrate the polymeric network.
Chemical degradation includes oxidative phenomena due to molecular oxygen and
is, therefore, one of the main factors in abiotic degradation. Oxidation often proceeds
concomitantly with light degradation phenomena, leading to the formation of free rad-
icals, ultimately decreasing the molecular weight by chain scission as well as causing
crosslinking of the polymeric network which often leads to high brittleness. Hydrolysis
is the other main factor acting during chemical degradation. Several bioplastics contain
hydrolyzable covalent bonds, e.g., ester, ether, carbamide groups. Chemical degradation
acts synergistically with all other degradation mechanisms. For example, oxidation and
hydrolysis are facilitated by the polymer transitioning to the rubbery state and additionally
losing its crystallinity due to exposure to relatively high temperatures.
UV-light degradation, or photodegradation, is also a very common occurrence in
everyday life plastics. Photodegradation can typically lead to radicalization, resulting in
chain scission and/or crosslinking, as already discussed these phenomena can be concomi-
tant to oxidative degradation. Typically, photodegradation will result in the plastic material
break down, which in turn increases the surface area available for biotic degradation to
occur, and ultimately speeding up the biodegradation process. It can therefore be expected
a large difference in biodegradation times depending on the plastic debris being exposed
to sunlight or less; this could be the difference between a plastic bag floating at the sea
surface against dense plastic debris sinking to deep-sea level.

3. Life Cycle Assessment of Bioplastics

The topic of bioplastics sustainability is very much debated in our society, both at
the academic and institutional level. Life cycle assessment (LCA) is the main approach
through which researchers and policymakers can investigate the benefits and drawbacks
of using bioplastics in place of common plastics. LCA is a standardized methodology, with
the prevalent standards being ISO 14,040 and ISO 14044, through which it is possible to
analyze the environmental and socio-economic impacts related to the production and use
of a certain good. There exist several LCA standards in use at the international level, as well
as guidelines that are valid in the EU. The Product Environmental Footprint (PEF) and the
Organisation Environmental Footprint (OEF) [112] are two methodologies compiled by the
Joint Research Centre (JRC), the department of the EC focusing on scientific research. The
Polymers 2021, 13, 1229 12 of 26

JRC also authored the technical report Comparative Life Cycle Assessment (LCA) of Alternative
Feedstock for Plastics Production [113] which builds on the PEF providing scientific guidelines
and modeling methodologies for an audience already expert in LCA. These guidelines are
themselves based on ISO 14040 and ISO 14044. The two standards describe the various
aspects of performing an LCA, from definitions and goals to its main phases of life cycle
inventory analysis (LCI) and life cycle impact assessment (LCIA), respectively, the “data
collection and calculation procedures to quantify relevant inputs and outputs of a product
system” and the process through which the inventory data is associated with specific
environmental impact categories [114]. Table 4 reports some of the main ISO and CEN
standards relevant to the life cycle assessment of plastics and bioplastics, some of the
standards are shared as the EN version is based on the ISO one. Among these standards,
ISO 14040 and ISO 14044 are the main ones that define the principles and practices for
LCA, providing the basic framework for the assessment but leaving a range of choices to
the practitioners. Further guidance is provided by the International Reference Life Cycle
Data System (ILCD) which consists of technical documents and a data network aimed at
ensuring the validity and consistency of LCA. General definitions and aspects of bio-based
plastics are also discussed by the CEN standard EN 17228, as well as in EN 16575 which
represents a vocabulary for bio-based products.
The complete LCA of bioplastics needs to take into consideration several impact
categories, of environmental, social and economic nature, as well as different options for
the product EOL. Typically, this is not the case with most LCA research, as data on the
entirety of a certain product’s life might be lacking or because of the intended motivation of
the study not requiring assessing the whole life cycle. Depending on the system boundaries,
we can identify two main approaches to the LCA of a product: the cradle-to-gate and the
cradle-to-grave assessment [113,115,116]. Cradle-to-gate refers to an assessment from the
resource extraction stage (cradle) to the factory gate, meaning at the end of production.
For bio-based products this includes crops cultivation and biomass pre-processing, and
in general, any transportation involved should be included. Additionally, eco-profile is
a name in use to describe the cradle to factory gate life cycle inventory assessment of
polymers and chemicals. Eco-profiles are used as building blocks in cradle-to-gate LCA
studies and many can be found available on PlasticsEurope website [117] as well as on
other databases (Sphera, GaBi, openLCA Nexus, SimaPro Industrial Database, Life Cycle
Initiative).
The cradle-to-grave assessment takes into consideration the entire life cycle of the
product, from the raw material extraction to the EOL management. This includes all aspects
taken into consideration by the cradle-to-gate assessment and also the product’s retail,
storage, its use by consumers and its disposal.
LCA needs to consider several impact categories and put them into comparable num-
bers depicting the potential influence on the environment, these categories are therefore
standardized in their definitions and units in use [113,115,118,119]. Table 5 reports the
main indicators in use for the different impact categories [118]. The global warming po-
tential (GWP100 ) is the main parameter reported by LCA academic studies, it gives an
indication of the amount of GHGs produced by the system under assessment and the effect
on global warming. Several GHGs are released during the production and distribution
of a certain good, each having a different potential for global warming, which is defined
by the specific amount of infrared radiation the gas can absorb in the atmosphere. The
GWP100 considers the overall global warming potential by converting each mass of gas
emitted to the atmosphere, in the mass of equivalent CO2 that would absorb the same
amount of energy. Furthermore, the GWP depends on the number of years over which the
energy absorption is calculated. Typically, 100 years are considered, hence the subscript in
GWP100 .
Polymers 2021, 13, 1229 13 of 26

Table 4. List of CEN and ISO standards, technical reports and specifications, relevant to the life cycle
assessment of bioplastics.

Standard Title
Plastics—Bio-based polymers, plastics, and plastics
EN 17228:2019
products—Terminology, characteristics and communication
EN 16760:2015 Bio-based products—Life Cycle Assessment
EN 16751:2016 Bio-based products—Sustainability criteria
EN 16575:2014 Bio-based products–Vocabulary
Bio-based products—Bio-based carbon content—Determination of
EN 16640:2017
the bio-based carbon content using the radiocarbon method
Bio-based products—Determination of the oxygen content using an
EN 17351:2020
elemental analyser
Bio-based products—Guidelines for Life Cycle Inventory (LCI) for
CEN/TR 16957:2016
the End-of-life phase
Bio-based products—Overview of methods to determine the
CEN/TR 16721:2014
bio-based content
CEN/TR 17341:2019 Bio-based products—Examples of reporting on sustainability criteria
CEN/TR 16208:2011 Biobased products—Overview of standards
Environmental management—Life cycle assessment—Principles and
EN ISO 14040:2006
framework (ISO 14040:2006)
Environmental management—Life cycle assessment—Requirements
EN ISO 14044:2006
and guidelines (ISO 14044:2006)
Environmental management—Water footprint—Principles,
EN ISO 14046:2016
requirements and guidelines (ISO 14046:2014)
Greenhouse gases—Carbon footprint of products—Requirements
EN ISO 14067:2018
and guidelines for quantification (ISO 14067:2018)
Environmental management—Life cycle assessment—Requirements
ISO/TS 14072:2014
and guidelines for organizational life cycle assessment
Environmental management—Life cycle assessment—Data
ISO/TS 14048:2002
documentation format
Environmental management—Life cycle assessment—Critical review
ISO/TS 14071:2014 processes and reviewer competencies: Additional requirements and
guidelines to ISO 14044:2006
Environmental management—Eco-efficiency assessment of product
ISO 14045:2012
systems—Principles, requirements and guidelines
Greenhouse gases—Quantification and reporting of greenhouse gas
ISO/TR 14069:2013 emissions for organizations—Guidance for the application of ISO
14064-1
Plastics—Carbon and environmental footprint of biobased
ISO 22526-1:2020 plastics—Part 1: General principles—Part 2: Material carbon
ISO 22526-2:2020 footprint, amount (mass) of CO2 removed from the air and
ISO 22526-3:2020 incorporated into polymer molecule—Part 3: Process carbon
footprint, requirements and guidelines for quantification
Plastics—Biobased content—Part 1: General principles—Part 2:
ISO 16620-1:2015
Determination of biobased carbon content—Part 3: Determination of
ISO 16620-2:2019
biobased synthetic polymer content—Part 4: Determination of
ISO 16620-3:2015
biobased mass content—Part 5: Declaration of biobased carbon
ISO 16620-4:2016
content, biobased synthetic polymer content and biobased mass
ISO 16620-5:2017
content
Polymers 2021, 13, 1229 14 of 26

Table 5. Impact category indicators in use in life cycle assessment.

Indicator Units Description

Indicator of the potential global warming
Global Warming Potential,
kg CO2 eq due to all greenhouse gas emissions over a
GWP100
period of 100 years; CO2 as reference
Indicator of the potential destruction of the
Ozone Depletion Potential,
kg CFC-11 eq stratospheric ozone layer due to emissions;
ODP
freon-11 as reference
Indicator of the photochemical ozone
Photochemical Ozone
kg ethene eq creation potential due to emission of gases;
Creation Potential, POCP
ethene as reference
Indicator of the potential acidification of
Acidification Potential, AP kg SO2 eq water and soil due to emissions causing acid
rain; sulphur dioxide as reference
Eutrophication, EU kg PO4 eq Indicator of the over-supply of nutrients to
the ecosystem due to the release of nitrogen
and phosphorous containing compounds
which leads to algae bloom; phosphate as
reference
Human Toxicity, HT kg DCB eq Indicator of the impact on human health
due to toxic substances release;
1,4-dichlorobenzene as reference
Ecotoxicity, ET kg DCB eq Indicator of the impact on the ecosystem
due to toxic substances release;
1,4-dichlorobenzene as reference
Land Use, LU m2 Indicator of the land in use by the system
under assessment
Water Use, WU m3 Indicator of the water in use by the system
under assessment
Abiotic Resource Depletion,
kg Sb eq Indicator of the depletion of non-living
ADP
primary resources such as minerals and
metals; antimony as reference
Abiotic Resource
Depletion–Fossil fuels, MJ Indicator of the fossil energy consumed by
ADP-fossil the system under assessment

LCA studies typically take into consideration environmental impact categories, though
also social and economic aspects are of great importance. Social life cycle assessment (S-
LCA) looks at how the extraction or production of raw materials, and manufacturing,
distribution, use and disposal of goods, can bring negative effects from a social point of
view [20]. Life cycle costing (LCC) is also referred to as environmental LCC (E-LCC) [20]
when applied in conjunction with LCA. E-LCC takes into account all costs that are in-
volved with the product’s life cycle, independently from the party incurring such costs.
Environment-relate cost factors are taken into consideration, such as ecological taxes and
expenses for emissions control.

3.1. Life Cycle Assessment Research on Bioplastics

LCA research has already been reviewed in the past years, here we discuss some of
the main findings.
In 2018 Spierling et al. [20] presented a review of cradle-to-gate LCA, S-LCA and
LCC studies on different bioplastics, and focused their attention not only on the environ-
mental impacts but also on the social and economic impact assessments. Assessing CO2
emissions related to bio-sourced plastics, the authors underline that since bioplastics are
often considered carbon-neutral, the data about carbon content and CO2 uptake are often
omitted. This lack of information leads to an imbalance in modeling, especially if the EOL
stage is such that methane or GHGs other than CO2 are released. The authors observed
that many LCA studies did not provide information on important impact categories, such
Polymers 2021, 13, 1229 15 of 26

as acidification, while mostly focusing on GWP and energy depletion. Land use is also
reported by different studies, but other than reporting the square meters occupied no
related impacts are considered. Overall, the authors could only compare the LCA studies
on the GWP basis and estimate potential savings of 241–316 million tons of CO2 -eq per
year by replacing 65.8% of conventional plastics with bio-based ones. Still, the authors
acknowledged several limitations and uncertainties and noted that the assessment of the
use phase and EOL phase could strongly impact the results. Regarding S-LCA and LCC,
the authors report the lack of studies and available data, though the authors could infer a
high social risk potential when bioplastics’ raw materials are produced in countries with
weak legal standards.
In a 2020 review, Walker and Rothman [33] assess the comparative LCA of bio-based
and fossil-based plastics, focusing on environmental LCA, cradle-to-grave, studies. The
reviewed studies were checked for compliance with the EU PEF, though none of the studies
completely met the document requirements. Partially complying papers were therefore
selected; seven bio-based polymers and seven fossil-based polymers were compared across
seven impact categories for which sufficient data were available. The authors report a
lack of agreement between different studies, both for bio-based and fossil-based polymer
assessments, with variations as high as 400% for the same impact category and same
polymer. Negative values of CO2 emissions were noted for bio-based systems due to the
gas being absorbed during biomass growth. Like in Spierling et al., the authors note that
this a controversial point as potential CO2 or methane emissions during EOL are often not
considered. Indeed, the authors underline that in cradle-to-grave studies several impact
categories show far worse values than the ones in cradle-to-gate studies, which is due to the
emissions and energy consumption during several EOL options. Furthermore, the authors
notice that many studies on biodegradable polymers assumed composting as the EOL
phase, though assuming incineration would significantly increase particulate emissions.
Generally, the authors report similar values for most impact categories across fossil-based
and bio-based systems. Finally, they conclude by commenting on the lack of comparability
and standard methodologies in the field, stating that “without the ability to compare across
studies, LCA has much lower relevance than it could or should have”.
In a recent review, Bishop et al. [34] also compared results from bio-based and fossil-
based polymers LCA studies. Similar to the other works discussed, the authors found
a lack of impact categories being covered as well as a lack of uncertainty analysis being
carried out. Additionally, they noted that most studies did not account for the use of
additives and their potential leakage in the environment and suggested that LCI should
always include additives in use even if used in small quantities. In line with the other
review already discussed, Bishop et al. note that the assumption of bio-based plastics being
carbon-neutral can be misleading. In addition to the previous studies, they observe that
biogenic CO2 will spend a period of time in the atmosphere depending on the growth
cycles of the biomass. While this might be negligible for fast-growing crops, it can become
relevant with an increasing use of lignocellulosic-derived biomass which has long growth
cycles. The authors underline that the worst approach to the assessment of bioplastics is to
imply a large and permanent CO2 uptake since most certainly this amount of gas will be
released once again to the environment in the 100-year time horizon for which the GWP is
typically calculated.
An important issue for bioplastics is their durability in service conditions, i.e., the
ability of biopolymers to maintain unchanged the properties and performance in service.
To be ensured unchanged properties, the biopolymers are usually added with appropriate
stabilizing systems, such as synthetic antioxidants, UV-absorbers, quenchers [120] or natu-
rally occurring molecules having protection actions [121–123]. All stabilizers can protect
the biopolymers and improve the oxidative resistance in service conditions, making these
materials suitable and durable. Interestingly, as documented, some natural antioxidants
can exert concentration dependent anti-/pro- oxidant activity and, if they added at high
concentrations, can exert pro-oxidant activity rather than protection action [124–126].
Polymers 2021, 13, 1229 16 of 26

From what already discussed, one very important, though unfortunately overlooked,
aspect of LCA is the assessment of the EOL phase. In the following section we report on
research focused on the EOL of bioplastics.

3.2. End-of-Life Options for Bioplastics

The analysis of the EOL of a product is one of the most important parts of LCA, here
we report some of the main research works focused on the topic.
In a 2013 review, Soroudi and Jakubowicz investigated the mechanical recycling of
bioplastics and their blends [127]. The authors concluded that the performance and sus-
tainability of recycled bioplastics could not be thoroughly understood given that research
in the field was at a preliminary stage. They noticed that additives, such as compatibi-
lizers, would need to be considered for the mechanical recycling of blends of bioplastics,
because of the immiscibility of polymeric mixtures. They also noticed that biocomposites’
mechanical properties often depend on the microstructure obtained during processing, for
example, alignment of fiber fillers, which can be lost after recycling resulting in the loss of
mechanical performance. They observe that chemical recycling, as an alternative to me-
chanical recycling, can be very costly, for example, the depolymerization of PLA requires
high temperatures and therefore high energy expenditure. The authors observed that
mechanical recycling of plastics with bioplastics might result in increased contamination,
therefore affecting the performance of the recycled material.
In a 2016 paper, Cosate de Andrade et al. [128] presented an LCA of PLA compar-
ing chemical recycling, mechanical recycling, and composting. The authors found that
mechanical recycling had the least environmental impact, followed by chemical recycling
and lastly composting when considering the climate change, human toxicity, and fossil
depletion categories. In particular, it was observed that composting was outperformed as
EOL option since it does not produce PLA or starting blocks for PLA, and therefore it will
cause all the impact associated with producing virgin polymer again.
In a 2017 paper, Hottle et al. [24] investigate the EOL phase of several biopolymers
and fossil-based polymers. The three EOL options taken into consideration are recycling,
composting, and landfilling. As an important note, the paper takes into consideration the
waste collection and transport stages. The two stages are required independently from
the EOL option and can strongly influence the overall impact. The authors observed that
the EOL stage greatly influences the overall sustainability assessment of a polymer life
cycle. Recycling was found to be the most effective way to reduce environmental impacts
for the drop-in plastics under assessment. Large, negative, values of GWP, ADP-fossil,
and other impact categories are achieved through recycling of these polymers since the
original raw material is bio-based (bioethanol) and because it is assumed that the recycled
material offsets the fossil-based production of virgin polymers. A worst-case scenario for
compostable polymers being landfilled is the uncontrolled release of methane following
their biodegradation. In this case, the authors found that the GWP would drastically
increase, particularly for PLA. On the other hand, composting would drastically reduce
ODP, GWP, as well as eutrophication. Transportation, including international shipping,
waste collection, intermediate handling, all largely contributed to higher GWP and ODP.
Port-to-port shipping from California to recycling facilities in Hong Kong was considered
and resulted in large increases in several impact categories.
In a 2020 review, Lamberti et al. [129] cover the recycling routes of several bio-based
polymers. The authors observe that, generally, the best practice is to reuse any plastic as
much as possible before recycling, then the plastic should be mechanically recycled until
the resulting material is of commercially acceptable grade, finally, the plastic should be
chemically recycled to recover part of the original monomers. For example, they observe
that mechanical recycling of PLA results in a lower grade polymer that can be reused,
though further recycling should be chemical. The authors report that chemical recycling
of PLA through alcoholysis generates value-added products (different lactates depending
on the alcohol), which can also be converted to lactide which can be directly polymerized
Polymers 2021, 13, 1229 17 of 26

to high Mn PLA. Furthermore, bio-PET and bio-PE can be mechanically recycled multiple
times before being chemically recycled. They identified glycolysis as the best chemical
recycling option for bio-PET and pyrolysis as the one for bio-PE. The former results in
value-added chemicals and in the least number of steps to polymerize back to PET, while
the latter is the only route able to degrade PE resulting in valuable aromatics and fuel
(gas and char). The authors conclude that biopolymers’ mechanical performance needs
to be improved and that better schemes for recycling and waste collection need to be put
into place.
Anaerobic digestion is an appealing waste management route for compostable bio-
plastics. The process converts municipal organic waste to biogas (methane) and can incur
the problem of plastic bags contamination. The use of bioplastic bags for municipal or-
ganic waste could therefore prove to solve the contamination problems while converting
unavoidable plastic waste into energy.
In a 2018 review, Batori et al. [130] reported on the conditions needed for the effective
anaerobic degradation of bioplastics. They noted that typical biogas plants operate with
a solid retention time of 15 to 30 days and, therefore, bioplastic bags should be able to
degrade in this time length. The authors found PBS to be not suitable for the application
because the polymer does not degrade under the conditions in use at the plants, they
reported that PLA, PCL and PVA do not sufficiently degrade in the time range, but they
found PHB to be suitable. It was observed that more standardization for biodegradable
bags suitable for organic waste collection is needed, and the authors suggest that the
standards should require biodegradation greater than 50% over 1 month. It was pointed
out that the plastic bags should also be able to withstand moisture until they reach the
fermenter, a property that might not be common in many biodegradable plastics due to the
presence of hydrophilic moieties. The authors observe that less resistant bioplastics might
be still used and coated in a layer of water-resistant ones.
In the previously referenced work, Narancic et al. [14] tested several bioplastics and
blends, observing that the majority would degrade by thermophilic anaerobic digestion
with high biogas output. Still, the authors reported that the degradation times were 3 to
6 times longer than the retention times of commercial plants.
In 2018 Zhang et al. [131] reported on the anaerobic biodegradation of 9 bioplastics
compliant with standard EN 13432. The plastics, together with organic waste, were fed
daily to a digester for 177 days with a retention time of 50 days. The authors found that
the digestion process was not inhibited but they also observed that only 4 cellulose-based
materials showed substantial biodegradation.
Researchers have also taken into consideration the result of biodegradable plastics
entering the recycling process of common plastics. Different research groups investi-
gated the effect of small (5 wt%) amounts of PLA being mixed in the recycling process of
PET [132–136]. The results showed that even small quantities of PLA will negatively affect
the mechanical and thermal properties of recycled PET, which can cause technological and
economic burdens. The main problems are due to the difference in thermal degradation
temperatures, with PLA already degrading at the processing temperature of PET and
causing yellowing of the product. The polymers are also immiscible, which can cause a lack
of homogeneous surfaces, undesired opaqueness, and defects or failure during injection
molding.
Currently published study deals about that the oxidation during burning of biopoly-
mers and synthetic polymers can produce similar amount of CO2 . Therefore, a correct
waste collection and management is required to solve the environmental troubles arising
from the uncontrolled plastic use, release and accumulation of both petroleum-based poly-
mers and bio-based polymers. The sustainable live vs. waste management of polymers and
biopolymers depends on accurate end-of-life disposal of these materials and reduction of
volumes of used plastics and bioplastics, maybe just articles having short service-life [137].
Polymers 2021, 13, 1229 18 of 26

4. Bioplastics: Summary of Opportunities and Possible Challenges

Table 6 presents a summary of possible advantages and disadvantages related to the
adoption of bioplastics, as discussed in the available literature.

Table 6. Summary of potential advantages and disadvantages related to the adoption of bioplastics.

Category Description
Reducing fossil fuel dependency by using renewable resources, replacing
existing plastics with bio-based counterparts (e.g., drop-in plastics)
Advantages of Potential environmental benefits in terms of GWP reduction
bioplastics The use of compostable plastics, in applications where organic
contamination is expected, simplifies waste management and returns
carbon to soil as compost
Anaerobic digestion of biodegradable plastics can produce large specific
energy and contribute to achieve an optimal ratio of carbon to nitrogen in
the process
Biodegradable plastics could replace non-degradable plastics in products
that are likely to leak in the environment, potentially mitigating
plastic pollution
High production costs and, possibly, lower performance than
common plastics
Lack of processability with common technologies or lack of know-how
Small market volume does not justify major investments nor redesign of
Disadvantages of
production frameworks and waste manager infrastructure
bioplastics
Possible feedstock competition with biofuel and food industry
Risk of fouling of recycling streams with biodegradable plastics
Risk of landfilling biodegradable plastics resulting in GHG emissions
Lack of dedicated composting and recycling infrastructure and logistics
Uncertainty regarding biodegradability in different open environments

While it should be kept in mind that the volume of bioplastics in our economy is
still too small to accurately predict all implications resulting from large-scale adoption,
one point in favor of their adoption is that fossil resources are limited. The adoption of
bio-based plastics can, therefore, prove to be an important way to decouple our economy
from an unsustainable model.
Biodegradable plastics might also prove to be beneficial in mitigating some environ-
mental risk scenarios where the leakage of plastics is not easily avoided, nor the use of
plastic items can be effectively discontinued. For example, mulch films need to be collected
and recycled at the end of their life-cycle. However, they are contaminated with soil and
organic material which makes recycling procedures economically unviable. Furthermore,
film fragments can accumulate in the soil, causing an environmental risk. Biodegradable
mulch films have been on the market since the early 2000s, offering the same performance
as common plastic ones, while being biodegradable in soil [138].
Compostable plastic bags for organic waste collection are already in use, which
eliminates the need to separate the bag from the waste. Their use in anaerobic digestion
facilities–if the material is designed to degrade within the retention time–can also lead to
the production of renewable energy.
Figure 2 presents a simplified infographic representing the main steps in plastics
linear economy and what the authors consider some important additional steps introduced
by bioplastics in the circular economy. The linear economy route proceeds through the
collection of resources, the production of plastic goods, their use, and their disposal. The
circular economy route adds two important steps of repurposing of goods and recycling
(mainly mechanical) to extend the life of the material as much as possible. Durable bio-
based plastics, like drop-in plastics, can be recycled and their goods can be repurposed like
common plastics. Compostable plastics would be used primarily as food waste collection
bags and contribute to the production of biogas and compost in appropriate industrial
Polymers 2021, 13, 1229 19 of 26

facilities. The compost would be used for agricultural purposes, including growing the
raw materials for bioplastic production, and the biogas would provide energy, including
energy for manufacturing processes. Bioplastic goods that are no longer recyclable would
be incinerated to produce energy.

Figure 2. A simplified infographic representing the main steps in linear economy (straight arrows) and the additional steps
introduced by circular economy with a focus on bioplastics (green arrows), considering anaerobic digestion as EOL option
for compostable plastics, reuse and recycling for durable bio-based plastics and incineration as final disposal of any plastic
that is no longer recyclable nor reusable.

The bioplastic industry is still very small in volume and relatively new, when com-
pared to the common plastic industry, furthermore regulations about bioplastics have been
changing in recent years. Therefore, it is understandable that several present and future
challenges related to the adoption of bioplastics can be identified. In the following sections
we review the challenges that can be identified from what discussed so far.

4.1. Lack of Comparable LCA Studies

The use of different approaches and methodologies, as well as different reference units
and data sources, strongly hinders the comparability of LCA studies. As already discussed,
the use and EOL phases are often not taken into consideration, most assessments being
cradle-to-gate. Yet, the EOL phase is shown to drastically influence the overall values
of most impact categories. Studies that do not consider this stage can also come to the
misleading conclusion that the production of a certain bio-based plastic completely removes
GHGs from the atmosphere by converting CO2 to biogenic carbon, while, depending on
the EOL, stronger GHGs might be produced. The use of the same reference units is also
important to compare different studies. LCA studies of specific products should consider a
reference number of items produced. This approach is more comparable across different
studies than using mass as reference, because not all polymers are converted to the same
number of items per unit of mass.
Moving forward, studies should be thought-out to be comparable so that the overall
significance of LCA could be ensured.
Polymers 2021, 13, 1229 20 of 26

4.2. Issues Relating to Standards and Regulations

In the last ten years, a lot of efforts have gone into the production of standards to define
and evaluate compostability and biodegradability. While standards on industrial compost-
ing can reproduce the designed conditions of these facilities, standards for biodegradation
in less controlled or uncontrolled conditions need more development. This is certainly
the case for natural environments. Furthermore, home-composting conditions can be
expected to vary greatly [139], even on a household-to-household basis. Since this is not
an industrially regulated process, there is no confidence about the process conditions
and the quality, concentration, and type of microorganisms in use. Additionally, inde-
pendently from the adoption of bioplastics, home-composting also presents the risk of
GHGs emissions [140,141] and therefore its sustainability might need a more thorough
assessment.
One problem underlined in literature [35] is that many biodegradability standards
require duplicates or at best triplicates of results. Triplicates are generally accepted in
academia, where time and resources are often limited, and studies might be of a proof-of-
concept nature. Still, the lack of reproducibility in academic studies is a serious topic of
discussion [142]. Harmonized standards and official certifications have a great impact at
international level and should represent the most reliable piece of information on a certain
technical subject. Taking these considerations into account, the use of triplicates to assess
statistical significance does not seem acceptable.
Finally, the scientific community, as well as regulatory agencies and certification com-
panies, should consider the possibility that no standards will ever be able to encompass the
diverse and dynamic conditions that are found in natural environments, and that produc-
ing standards claiming the opposite might mislead consumers on the actual environmental
risks associated with plastic products.

4.3. Land and Water Use

One concern that has been expressed is the possible competition between the produc-
tion of raw materials for the bio-based industry and agricultural production. European
Bioplastics reports that, in the foreseeable future, bioplastics production will account for
less than 0.02% of global agricultural area usage and therefore does not compete with the
production of food. On the other hand, a Greenpeace report noted that it is important to
consider where the land is situated and if it is concentrated within a few regions [143].
Furthermore, the report offered its own calculation on the effect of replacing plastic pack-
aging with PLA packaging. The calculation suggests that in doing so, 32% of global annual
corn production would be needed to be diverted to PLA, accounting for 1% of available
agricultural land.
Furthermore, the production of bioplastics requires considerable use of fresh water,
due to crop cultivation, e.g., corn farming intended for PLA production [144]. Water
footprint analysis of bio-based plastics production is not often carried out in LCA studies,
though some alarming results suggest that replacing European packaging production with
bioplastics, would increase the related use of water to almost one fifth of the EU’s total
freshwater withdrawal [18].

4.4. Issues Related to the Waste Disposal System

Europe has been greatly developing its composting capacity ever since the Landfill
Directive 1999/31/EC. Still, the distribution of composting facilities at the national level
needs to be considered. Looking at the Italian case, there are more than 330 composting
facilities at the national level, but most are concentrated in the North of Italy [145]. The
result is that compostable waste from the Center and the South needs to be transferred
to the North, with additional costs and fuel consumption. Furthermore, if the resulting
compost were to be sold in the South the opposite process would need to take place. If we
are to adopt larger and larger volumes of compostable plastics, we need to be sure that
composting facilities can cover this increase in volume at the regional level.
Polymers 2021, 13, 1229 21 of 26

Biodegradable plastics are designed to completely break down due to microbial

action but are also susceptible to degradation phenomena such as hydrolysis and thermal
degradation, which generally play an important role in the biodegradation rate. As
discussed, contamination of biodegradable plastics in common plastic recycling streams
would be detrimental to the properties of the recyclates. The separation and sorting of this
additional stream can also be complex and expensive [135]. Therefore, with an increasing
use of biodegradable plastics, a reorganization in the recycling framework will be required,
as well as informing consumers on the correct way to dispose of such products.

5. Conclusions
European governments are working towards a zero-emission economy, decoupled
from fossil resources, and focused on sustainability and circularity. Reforming the way
plastic products are produced, handled, and disposed of, is an important part of this
process. The adoption of bio-based plastics might surely come with risks (use of fertilizers,
social risks, etc.) as well as advantages, what seems certain is that it offers an alternative to
fossil-based production and might therefore become a necessity in the future. Compostable
or biodegradable plastics might result in problems if not sorted out from recycling streams.
Still, applications like compost bags offer benefits since bag and content can be co-digested
eliminating the need for separation and producing energy and compost. Materials should
be designed to ensure effective degradation without causing technological issues while
retaining their mechanical properties during the “use” phase. The use of biodegradable
plastics to mitigate environmental pollution due to leakage in open environments is an-
other discussed advantage, currently, this seems overly optimistic. Conditions in natural
environments are dynamic, they greatly change within geographic regions and seasons,
furthermore, the size and density of the plastic debris, as well as agglomeration with other
materials, can influence the outcome. Additionally, the economic loss from this plastic
waste is not solved by using biodegradable alternatives. In this sense, stricter regulations,
promoting an environmental-friendly mentality, and investing in sustainability-focused
education at an early age could prove to be a more effective use of resources.
To conclude, it can be expected that the bioplastics industry will receive incentives
to grow, develop new technologies and materials, and scale-up its production to greater
volumes. Once larger productions are achieved and larger volumes of bioplastics are
circulated, more assessment will be undoubtedly required to understand the sustainability
of these materials. However, one thing to keep in mind moving forward is that most of
the issue lies in our throw-away mentality. Replacing one plastic with another, without
replacing the mentality, is not a solution.

Author Contributions: All authors listed have made substantial, direct, and intellectual contributions
to this work and approved it for publication. All authors have read and agreed to the published
version of the manuscript.
Funding: This work has been financially supported by MIUR—Italy (Ministry of Education, Univer-
sity and Research of Italy), Grant: CLEAN—PRIN-20174FSRZS_002.
Conflicts of Interest: The authors declare no conflict of interest.

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