BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE AND/OR BIODEGRADABLE ALTERNATIVES TO PETROPLASTICS
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BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
AND/OR BIODEGRADABLE ALTERNATIVES TO
PETROPLASTICS
1. Introduction
‘‘Plastics’’ were introduced approximately 100 years ago, and today are one of the
most used and most versatile materials. Yet society is fundamentally ambivalent
toward plastics, due to their environmental implications, so interest in bioplastics
has sparked.
According to the petrochemical market information provider ICIS, ‘‘The
emergence of bio-feedstocks and bio-based commodity polymers production, in
tandem with increasing oil prices, rising consumer consciousness and improving
economics, has ushered in a new and exciting era of bioplastics commercialization.
However, factors such as economic viability, product quality and scale of operation
will still play important roles in determining a bioplastic’s place on the commer-
cialization spectrum’’ (1).
The annual production of synthetic polymers (‘‘plastics’’), most of which are
derived from petrochemicals, exceeds 300 million tons (2), having replaced
traditional materials such as wood, stone, horn, ceramics, glass, leather, steel,
concrete, and others. They are multitalented, durable, cost effective, easy to
process, impervious to water, and have enabled applications that were not
possible before the materials’ availability.
Plastics, which consist of polymers and additives, are defined by their set of
properties such as hardness, density, thermal insulation, electrical isolation, and
primarily their resistance to heat, organic solvents, oxidation, and microorgan-
isms. There are hundreds of different plastics; even within one type, various
grades exist (eg, low viscosity polypropylene (PP) for injection molding, high
viscosity PP for extrusion, and mineral-filled grades).
Applications for polymeric materials are virtually endless; they are used as
construction and building material, for packaging, appliances, toys, and furniture,
in cars, as colloids in paints, and in medical applications, to name but a few.
Plastics can be shaped into films, fibers, tubes, plates, and objects such as bottles
or boxes. They are sometimes the best available technology. Many plastic products
are intended for a short-term use, and others have long-term applications (eg,
plastic pipes, which are designed for lifetimes in excess of 100 yr).
On the other hand, there is a growing debate about crude oil depletion and
price volatility, and environmental concerns with plastics are becoming more
serious. Approximately half of all synthetic polymers end up in short-lived
products, which are partly thermally recycled (burnt), but to some extent end
up on landfills or, worse, in the oceans, where large plastic objects are washed
ashore, sink or float (eg, the ‘‘North Pacific Garbage Patch,’’ which has continental
dimensions), and get fragmented to ‘‘microplastics’’ (particles between a few mm
and
1 Kirk-Othmer Encyclopedia of Chemical Technology. Copyright # 2015 John Wiley & Sons, Inc. All rights reserved. DOI: 10.1002/0471238961.koe00006
2 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
It is estimated that since the 1950s, approximately 1 billion tons of plastics
have been discarded and some of that material might persist for centuries or even
significantly longer, as it is demonstrated by the persistence of natural materials
such as amber (4).
One of the biggest advantages of plastics, their durability, is likewise one of
their biggest problems: The rate of degradation (biodegradation) does not match
their intended service life, and buildup in the environment occurs.
Recycling of waste plastics, in principle, a meaningful approach, can follow
different routes:
1. Reuse of the product (eg, a bag).
2. Material recycling (collection, sorting, and reprocessing).
3. Feedstock recycling (depolymerization to capture the monomers).
4. Thermal recycling (use of the energy content in waste incineration, steel
works, or cement kilns).
Recycling plastics is not always feasible, and it can have a negative eco-
balance due to the efforts for collecting, sorting, and processing them. In most
cases, they need to be washed, and waste grinding and processing are energy
consuming. The recycling rate of plastics differs from country to country; there are
also differences in the plastics concerned. In the United States, the recycling rate
for polyethylene terephthalate (PET) packaging (bottles) was 31.2% in 2013 (5).
PET has the highest value of commodity plastics and is used mainly for drinking
bottles; hence, efforts are made to collect it. Recycled plastics go through different
processing steps such as sorting and melt filtration. They can often only be used in
lower grade products, typically not with direct food contact or high performance
applications. A ‘‘usage cascade’’ can be created, ending in thermal recycling
(combustion: incineration or pyrolysis).
To summarize, the extensive use of plastics has become a problem in many
aspects. Therefore, growing interest in ‘‘bioplastics’’ is observed (for reuse and
recycling of bioplastics, an unsolved issue, see Reference 6 and Section 9).
The term ‘‘bioplastics’’ stands for ‘‘biobased polymers.’’ According to IUPAC,
a bioplastic is derived from ‘‘biomass or . . . monomers derived from the biomass
and which, at some stage in its processing into finished products, can be shaped by
flow’’ (7).
In the area of bioplastics, several terms are used vaguely, ambiguously, or
wrongly. Hence, some important definitions are provided as follows (see also
Reference 7).
Plastics (plastic materials) in general are a huge range of organic solids
that are malleable (pliable, moldable). Malleability is a material’s ability to
deform under compressive stress. Plastics usually consist of organic polymers
with high molecular weight and other substances (fillers, colors, and additives).
They are typically synthetically produced. The term ‘‘natural plastics’’ is some-
times used in the industry for unfilled and uncolored plastics, as opposed to
compounds.
BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE 3
Often, the expression bioplastics is used to make a distinction from polymers
derived from fossil resources (monomers). The term is, to some extent, misleading,
4 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
as the prefix ‘‘bio’’ suggests that any polymer derived from biomass is environ-
ment-friendly.
Biobased polymers are neither necessarily biocompatible nor biodegradable.
According to industry association European Bioplastics, bioplastics are
‘‘polymers that are biobased, biodegradable, or both’’ (8). So the industry has
adopted a rather large definition. An alternative expression could be ‘‘technical
biopolymers.’’
In case polymers are obtained from agro-resources such as polysaccharides
(eg, starch) (9), one can talk about ‘‘agro-polymers.’’
‘‘Biomaterials’’ denote materials that are exploited in contact with living
tissues, organisms, or microorganisms. Hence, ‘‘polymeric biomaterials’’ are
used in applications such as medicine (catheters, bone cements, and contact
lenses) (10). Many of them are conventionally produced polymers. Implantable
biomaterials are PET, PP, PEEK (polyetheretherketone), UHMWPE (ultrahigh
molecular weight polyethylene), and PTFE (polytetrafluoroethylene) (11,12), on
the one hand, and (bio-)resorbable polymersPGA (polyglycolide), PLA (polylac-
tide), PCL (polycaprolactone), and PGS (poly(glycerol sebacate)), on the other
hand (12,13).
Generally, a polymer is a substance composed of macromolecules.
A macromolecule is a very large molecule commonly made by polymerization
of smaller subunits. In biochemistry, the term is applied to the main biopolymers
such as nucleic acids (eg, DNA), proteins, and carbohydrates (natural polymers),
plus other large, nonpolymeric molecules such as lipids and polyphenols. Natural
polymers (‘‘biopolymers’’) can be organic or inorganic (14), the latter having a
skeleton devoid of carbon (15). Examples for the former include cellulose, starch,
latex, and chitin; examples for the latter include polyphosphazenes, polysilicates,
polysiloxanes, polysilanes, polysilazanes, polygermanes, and polysulfides. In
between, one can find so-called hybrid polymers, ie, polymers containing inorganic
and organic components such as polydimethylsiloxane (silicone rubber: - -[O--Si
(CH3)2]n --).
Synthetic polymers (artificial polymers) are man-made polymers. They are
built from monomers by polymerization, polycondensation, or polyaddition. Most
synthetic polymers have significantly simpler and more random (stochastic)
structures than natural ones. They show a molecular mass distribution, which
does not exist in biopolymers (polydispersity vs monodispersity). They are sub-
stances that are not produced by nature (xenobiotics). Due to their high molecular
weight, they are not mobile. From a practical processing point of view, synthetic
polymers can be classified into the four main categories: thermoplastics (thermo-
softening plastics), thermosets (duromers), elastomers, and synthetic fibers. The
most common synthetic polymers are
• polyethylene (PE: PE-HD and PE-LD, with HD being high density and LD
being low density);
• polypropylene;
• acrylonitrile–butadiene–styrene (ABS);
• polyethylene terephthalate;
BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE 5 • polycarbonate (PC);
6 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
Fig. 1. Typical applications of polymers. The sizes of the bubbles show the relative
importance. PS-E ¼ expanded PS; ASA ¼ acrylonitrile–styrene–acrylate; SAN ¼ styrene–
acrylonitrile; other eng. ¼ other engineering plastics. (Source: Reference 2.)
• polyvinyl chloride (PVC);
• polystyrene (PS);
• polyamides (PAs, eg, Nylon 6 and Nylon 66);
• Teflon (polytetrafluoroethylene);
• polyurethane (PU, PUR);
• poly(methyl methacrylate) (PMMA, acrylic).
They are nonbiodegradable. Note: Technically, all conventional plastics are
degradable. However, due to their slow breakdown, they are considered practi-
cally non(bio)degradable.
Typical applications of polymers are shown in Figure 1.
Semi-synthetic polymers are chemically treated polymers of natural origin.
An example is rubber. It is made from latex, the ‘‘milk’’ of Hevea brasiliensis
(rubberwood), by vulcanizing it (cross-linking the polymer chains to a certain
extent) using sulfur or S2Cl2. Another example is cellulose. Cellulose can be
modified in two different ways:
• It can be dissolved and precipitated again in a different physical shape, eg, to
produce viscose silk (rayon), using CS2.
• It can be chemically modified, using the three remaining OH groups of the
glucose monomers, eg, to cellulose acetate (CA) with acetic acid, cellulose
BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE 7 methyl ethers with methanol, and cellulose nitrate with nitric acid.
8 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
Table 1. Typical Bonds in Polymers
Type of bond Natural examples Synthetic examples
carbon–carbon (-
- C-
- C-- ) polyolefins (eg, rubber) polyolefins (eg, polyethylene,
polypropylene)
ester (-
- O-- C-
- O-
- -) nucleic acids (eg, DNA, RNA) polyesters (eg, Diolen, a
polyester fiber)
amide (- -O--NH-
-C-
-
- -) polypeptides (eg, wool, silk, polyamides (eg, Nylon, a
enzymes) polyamide)
ether (-
-O--) polysaccharides (eg, starch, special plastics (eg, DuPont’s
cellulose) Delrin, a POM)
Modified from Ref. 16. POM ¼ polyoxymethylene.
Thus, a ‘‘synthetic biopolymer’’ refers to a man-made biopolymer that is
prepared using abiotic chemical routes. Table 1 shows the bonds in polymers.
Two common processing technologies for the economically important ther-
moplastics are extrusion (continuous process, yielding, eg, window profiles or
pipes) and injection molding (batch process, yielding, eg, dishes and cups).
Polymers (‘‘plastics’’) can be blended (17) and further processed to com-
pounds and composite materials with different properties. Examples include
flame-retardant or colored polypropylene, talc-filled polypropylene (eg, for
reduced thermal expansion in bumpers), NFRPs (natural fiber-reinforced plas-
tics), and WPCs (wood plastic composites or wood polymer composites, ie, wood
fibers in a polymer such as PE or PVC). NFRPs are used in automobiles,
construction and furniture, and industrial and consumer products. Applications
of WPCs are deckings, railings, window and door frames, and furniture; the main
market is currently in the United States. For composites and nanocomposites
based on cellulose, see, eg, Reference 18.
2. Motivation for and Types of Bioplastics
After food and textiles, the ‘‘organic trend’’ is continuing to spread into materials;
bioplastics have come en vogue and receive extensive media attention, although
current production volumes are only on the order of 1% of annual plastics
manufacturing.
Increasing oil prices, rising consumer consciousness and environmental
awareness, improving feedstock and process economics, better product quality,
and scale of operation have helped ‘‘revive’’ bioplastics (see Section 5).
Other factors that motivate R&D in bioplastics are as follows:
• Rural development: added value and jobs (bioplastics feedstock is typically
grown in rural areas, where farmers can benefit).
• Interesting new properties or mix of properties (degradability, haptics,
weight, etc).
• Feedstock diversification (less dependence on crude oil, which is finite).Growth rates of bioplasticsBIOBASED
BIOPLASTICS: in excess ofPLASTICS
20–30% have been witnessed for
AS RENEWABLE 9
several years and several materials. These are expected to continue. There is a1 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
Table 2. Bioplastics Intermaterial Substitution Opportunities
Polyolefins Other polymers
LDPE LLDPE HDPE PP PS PVC PUR PET
starch polymers þþ þþ þþ þþ þ - þþ -
PLA þ þ þþ þþ þþ - - þþ
PHA
þþ
- þþ
- þþþ
- þþþ
- þþ
- þ
- þþ
- þþ
þþþ
other polyesters þþþ
biobased-PE þþ þþþ - - - - -
Source: Chemical Market Resources, Inc. (20). LDPE, HDPE: low-, high-density PE; PUR: poly-
urethane; PLA: polylactic acid; PHA: polyhydroxyalkanoates; substitution potential: (þþþ) high,
(þþ) medium, (þ) low, and (-) not foreseen.
substitution potential of up to 90% of the total consumption of plastics by biobased
polymers (19). This concerns standard polymers such as PE, PP, PVC, and PET, as
well as high performance polymers such as PAs (see Table 2).
Bioplastics have two aspects: ‘‘green’’ educt and/or ‘‘green’’ product (where
‘‘green’’ stands for ‘‘sustainable’’):
• Use of a ‘‘green’’ feedstock for the production of conventional polymers (so-
called drop-in polymers): renewability.
• Synthesis of ‘‘green’’ polymers: biodegradability.
This is illustrated in Figure 2. As Figure 2 shows, a material that is either
renewable or biodegradable qualifies as biopolymer. There are also ‘‘partly bio-
based’’ biodegradable and nonbiodegradable biopolymers, if, for instance, only one
blending partner or only part of the feedstock is derived from renewable resources
(see Table 3).
The content of biobased carbon can be determined by radiocarbon analysis
according to ISO 16620 and ASTM D6866-05 (22,23). The measurement has a high
accuracy. In this context, one can also talk about ‘‘hybrid’’ plastics (not to be
confused with those plastics that contain inorganic and organic components).
As can be seen from Figure 2 and Table 3, bioplastics can be renewable and/or
degradable. They can contribute to sustainability (24) at ‘‘the cradle,’’ at ‘‘the
grave,’’ or both. The box in the bottom left of Figure 2 is ‘‘conventional plastics,’’
whereas the other three boxes can be considered biobased polymers. The distinc-
tion, due to the two dimensions, is somewhat blurred, since many plastics on the
market contain bioplastics to a certain extent in blends with conventional
polymers.
Degradable bioplastics are intended for short-lived, disposable products.
Biobased durable plastics are to replace conventionally produced plastic goods.
A bioplastic material can also fulfill both criteria. Polylactic acid, thermo-
plastic starches (TPS), and polyhydroxyalkanoates (PHAs) are based on natural/
renewable feedstock and exhibit biodegradation under various conditions. Prod-
ucts such as biobased polyamides and biopolyethylene are fabricated from bio-
derived feedstocks but are not degradable. On the other hand, polybutyleneBIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE 1 terephthalate (PBT) and polybutylene succinate (PBS) are typically manufac- tured from petrochemical feedstocks but are biodegradable.
1 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
Fig. 2. Types of bioplastics, both biodegradable and nonbiodegradable, and examples.
(Reprinted with permission from Reference 21. # 2013, Elsevier.)
Table 3. Biodegradable vs Biobased Polymers
Biodegradable Nonbiodegradable
biobased CA, CAB, CAP, CN, PHB, PHBV, PE (LDPE), PA 11, PA 12, PET,
PLA, starch, chitosan PTT
partially biobased PBS, PBAT, PLA blends, starch PBT, PET, PTT, PVC, SBR, ABS,
blends PU, epoxy resin
fossil fuel-based PBS, PBSA, PBSL, PBST, PCL, PE (LDPE, HDPE), PP, PS, PVC,
PGA, PTMAT, PVOH ABS, PBT, PET, PS, PA 6, PA
6.6, PU, epoxy resin, synthetic
rubber
Source: Ref. 6. Abbreviations: ABS, acrylonitrile–butadiene–styrene; CA, cellulose acetate; CAB,
cellulose acetate butyrate; CAP, cellulose acetate propionate; CN, cellulose nitrate; HDPE, high
density polyethylene; LDPE, low density polyethylene; PA 6, polyamide 6; PA 6.6, polyamide 6.6; PA
11, aminoundecanoic acid-derived polyamide; PA 12, laurolactam-derived polyamide; PBAT, poly
(butylene adipate-co-terephthalate); PBS, polybutylene succinate; PBSA, poly(butylene succinate-co-
adipate); PBSL, poly(butylene succinate-co-lactide); PBST, poly(butylene succinate-co-terephthal-
ate); PBT, polybutylene terephthalate; PCL, poly(e-caprolactone); PE, polyethylene; PET, poly-
ethylene terephthalate; PGA, polyglycolide; PHB, polyhydroxybutyrate; PHBV, poly(3-
hydroxybutyrate-co-3-hydroxyvalerate); PLA, polylactide; PP, polypropylene; PS, polystyrene;PTMAT, poly(methylene adipate-co-terephthalate);
BIOPLASTICS: BIOBASED PTT, polytrimethylene
PLASTICS terephthalate; PVOH, 1
AS RENEWABLE
polyvinyl alcohol; PVC, polyvinyl chloride; PU, polyurethane; SBR, styrene–butadiene rubber.1 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
Bioplastics can reduce carbon dioxide emissions by 30–70% compared with
conventional plastics (19).
‘‘Green chemistry’’ (or sustainable chemistry) can be understood as the
design of chemical products and processes that reduce or eliminate the use or
generation of substances that are hazardous to humans, animals, plants, and the
environment, where energy efficiency should be high and the waste target is zero;
as a consequence, costs should also be low. A ‘‘green polymer’’ is one that conforms
to the concept of green chemistry. Note, however, that a green polymer does not
necessarily mean ‘‘environment-friendly polymer’’ or ‘‘biobased polymer.’’
So the motivation for bioplastics is sustainability. The principle for sustain-
ability is simply explained: Whatever man needs for survival and well-being
directly and indirectly comes from our natural environment. Sustainable action is
one that maintains conditions under which humans and nature coexist harmoni-
ously and where social, economic, and environmental requirements of present and
future generations are met.
3. Sustainability of Plastics and Bioplastics
A discussion of sustainability of plastics has to consider two main aspects: life
cycle assessment (LCA) and ecotoxicity. LCA, also referred to as eco-balance and
cradle-to-grave analysis, is the investigation and valuation of the environmental
impacts of a given product or service over its entire existence (input, life, and
output), considering raw material sourcing, production process, packaging, dis-
tribution, usage, and waste management including transport (25). For details, see,
eg, the standards ISO 14040 and ISO 14044.
Ecotoxicity subsumes the consequence of adverse effects caused by a sub-
stance on the environment and on living organisms. The environment encom-
passes water, air, and soil. When only living organisms such as animals, plants,
and microorganisms are affected, the term ‘‘toxicity’’ should be used.
Pure plastics generally show low toxicity due to their insolubility in water
and since they are biochemically inert (because of a large molecular weight).
Plastic products, in contrast, contain a variety of additives, some of which can be
toxic (eg, phthalates as plasticizers). Also, residues of toxic monomers can still
exist in the product (eg, vinyl chloride, the precursor of PVC, a human carcinogen),
or it can release such monomers or oligomers upon excessive heating (eg, PTFE).
Toxic substances can further be produced during incineration, particularly
when it is carried out in an uncontrolled way (at low temperatures, dioxins, PAHs
(polycyclic aromatic hydrocarbons), and other noxious fumes can be formed).
An increasing presence of microplastics was found in the marine food chain.
Microplastics (debrisBIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE 1 tion, it was found that the two species investigated contained on average 0.36 and 0.47 particles/g, which exposes the European shell fish consumer to an estimated
1 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
Table 4. Spatial Distribution and Abundance of Microplastics from Selected References
Location Maximum concentration observed, particles/km2
Italy, Lake Garda 1,108,000,000
Portugal, beach 218,000,000
northwestern Mediterranean Sea 1,000,000
USA, Laurentian Great Lakes 466,000
waters around Australia 839
Modified with permission from Ref. 26. # 2015, Elsevier.
11,000 microplastic particles per year (27). For images of microplastics ingested by
various animals, see, eg, the Swiss exhibition ‘‘Plastics Garbage Project’’ (28).
3.1. Environmental Aspects of Plastics. Major environmental
aspects of plastics include raw material consumption, energy use (29), and
pollution. Before the ban of CFCs (chlorofluorocarbons), the production of foamed
polystyrene (expanded polystyrene (EPS) and extruded polystyrene (XPS)) has
contributed to the destruction of the ozone layer. The production of plastics is a
rather energy-intensive process (29,30). Recycling of plastics is mostly impeded by
the lack of efficient sorting techniques. Apart from combustion, pyrolysis into
hydrocarbon fuels is feasible, but not yet carried out on an industrial level. As for
the effect of plastics on climate change (31), there is a mixed contribution;
petroplastics that are burnt (‘‘thermal recycling’’ into electricity and heat at
waste-to-energy plants) release CO2 into the atmosphere. In long-term applica-
tions and on landfills (which is increasingly banned, though), they become carbon
sinks. Over their useful life, lightweight plastics can help reduce transportation
emissions, eg, when used in cars instead of heavier materials, or when being
deployed as packaging material as opposed to glass or metal. For instance, it was
estimated that packaging beverages in PET bottles rather than glass bottles or
metal cans will save 52% of transportation energy (32). According to industry
association Plastics Europe, 5% less weight in a car translates on average into fuel
savings of 3%. Life cycle assessments are necessary to find the net contribution.
Plastics are generally perceived less environment-friendly than other mate-
rials such as paper, concrete, steel, and aluminum, partly due to lobbying
activities (33,34).
3.2. Plastics: Pros and Cons. Plastics and bioplastics in particular do
have several advantages. Table 5 provides a list of major pros and cons.
An environmental preference spectrum for plastics, exemplarily worked out
for the healthcare industry, is shown in Figure 3.
One can see from Figure 3 that bioplastics are assessed as most preferential
from an environmental point of view. The sustainability enhancement of bio-
plastics over conventional petrochemical-based plastics is depicted in Table 6.
Main sustainability drivers are energy savings and greenhouse gas emis-
sion cuts, apart from biodegradability and compostability. The environmental
and occupational health and safety hazards of biobased plastics are discussed in
Table 7.
The environmental impacts of biobased plastics are discussed in Table 8.BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE 1
Table 9 presents a comparison of a bioplastic (polyhydroxybutyrate (PHB))
with a conventional commodity polymer (PP) in 10 categories (see also Table 8).10 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
Table 5. Pros and Cons of Petrobased and Biobased Plastics
Pros Cons
conventional • low cost • based on petrochemicals
plastics • good and excellent technical • difficult to recycle
properties • mostly not biodegradable
• easy processability • uncontrolled combustion can
• can save energy and resources release toxic substances
compared with other materials, • ecotoxicity, particularly
depending on application microplastics in the marine
• thermal recycling possible environment
(cascade use) • partly toxic raw materials and
additives
bioplastics • (partly) biodegradable • costly
(compared with • (partly) based on natural • (partly) use of genetically
conventional feedstock, hence reducing the modified organisms
plastics) emission of GHG and the • use of land, fertilizers, and
dependence on crude oil pesticides for crops, potential
• interesting properties food competition
• generally, standard • narrow processing window
manufacturing processes and (lower melting temperature)
plants can be used for biobased • brittleness
feedstock, and standard • thermal degradation
processing machines can be used
for biobased plastics
• positive image among consumers
‘‘CML 2 Baseline 2000 V2.03’’ mentioned in Table 9 is a database that
contains characterization factors for life cycle impact assessment (LCIA). It is
available at the University of Leiden (37).
It is found in this study that, in all of the life cycle categories, PHB is
superior to PP. Energy requirements are slightly lower than those for polyolefin
production. PE impacts are lower than PHB values in acidification and eutro-
phication (36).Fig. 3. Environmental preference
BIOPLASTICS: spectrum
BIOBASED for the healthcare
PLASTICS industry. (Reprinted
AS RENEWABLE 11 with
permission from Reference 35. # 2012, Elsevier.)10 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
Table 6. Sustainability Improvements of Biobased Plastics Relative to Petroleum-Based
Plastics (PBP)
Bioplastic Sustainability improvement
polyhydroxyalkanoates highly biodegradable
polylactic acid production uses 30–50% less fossil energy and
generates 50–70% less CO2 emissions than PBP;
competitive use of water with the best performing
PBP, recyclable, compostable at temperatures above
600C
thermoplastic starch production requires 68% less energy than its PBP
counterpart; lower CO2 emissions than PBP;
biodegradable and compostable
biourethanes production requires 23% less energy and 36% less
GGH, compared with PBP
cellulose and lignin the biological degradation of lignin is lower than
cellulose, compostable
polytrimethylene terephthalate production requires 26–50% less energy and 44% lower
GHG than its PBP counterpart; no chemicals
additives are used; biodegradable; potentially
recyclable
Corn zein and soy protein biodegradable and compostable
Source: Ref. 35. GMOs: genetically modified organisms; GHG: greenhouse gases.
Table 7. Environmental and Occupational Health and Safety Hazards of Biobased Plastics
Bioplastic Environmental hazards Occupational health and safety
hazards
polyhydroxyalkanoates feedstock is grown using requ
methods of industrial irem
agricultural production, ents;
including GMOs; data on emis
energy requirements are sions
controversial of
polylactic acid feedstock is grown using
methods of industrial
agricultural production,
including GMOs; 1-octanol is
ecotoxic and organic tin can
build up in living organisms
thermoplastic starch feedstock is grown using
methods of industrial
agricultural production,
including GMOs
biourethanes (BURs) feedstock is grown using
methods of industrial
agricultural production,
including GMOs
cellulose and lignin the process has relatively high
energy and waterexposure to pesticides; physical extraction
BIOPLASTICS: of PHAs
BIOBASED PLASTICS AS RENEWABLE 11
uses pyridine, methanol, hexane, or diethyl ether;
chemical digestion uses sodium hypochlorite,
methanol, and diethyl ether
exposure to pesticides, sulfuric acid, tin octoate, 1-
octanol, and urea; finely pulverized starch can cause
powerful explosions
exposure to pesticides, glycerol, and urea; finely
pulverized starch can cause powerful explosions
exposure to pesticides, toluene diisocyanate (TDI),
methylene diphenyl isocyanate (MDI), tin
derivatives
exposure to elevated temperature and pressure;
exposure to disulfide, sodium
(continued)12 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
Table 7. (Continued)
Bioplastic Environmental hazards Occupational health and safety
hazards
pollutants to air and water hydroxide, volatile toxic,
during kraft process need to flammable, and malodorous
be addressed emissions of sulfur; exposure
to propionic, acetic, sulfuric,
and nitric acids
polytrimethylene feedstock is grown using exposure to pesticides,
terephthalate methods of industrial terephthalic acid, dimethyl
agricultural production, terephthalate, and methanol;
including GMOs; only 37% finely pulverized starch can
(by weight) from renewably cause powerful explosions
sourced material GMOs are
used in fermentation of
glucose to bio-PDO
corn zein and soy feedstock is grown using exposure to pesticides, alcohol
protein methods of industrial or volatile solvents, alkaline
agricultural production, and acid substances, and
including GMOs formaldehyde or
glutaraldehyde
nanobiocomposites the process has relatively high exposure to elevated
(cellulose and lignin) energy and water temperature and pressure;
requirements; emissions of exposure to disulfide, sodium
pollutants to air and water hydroxide, isocyanates,
during kraft process need to volatile toxic, flammable, and
be addressed; potential malodorous emissions of
toxicity issues of sulfur, as well as to
nanoparticles regarding nanoparticles
incineration, composting, or
recycling are unknown
Reprinted with permission from Ref. 35. # 2012, Elsevier. GMOs: genetically modified organisms;
GHG: greenhouse gases.
4. Degradation of Plastics
Biodegradable plastics had a difficult start, as marketing claims exceeded per-
formance. ‘‘The U.S. biodegradables industry fumbled at the beginning by intro-
ducing starch filled (6–15%) polyolefins as true biodegradable materials. These at
best were only biodisintegradable and not completely biodegradable. Data showed
that only the surface starch biodegraded, leaving behind a recalcitrant poly-
ethylene material.’’ (38). This situation questioned the entire biodegradable
plastics industry, and has kept consumers and regulators confused for the under-
standing of biodegradability and compostability. There are currently 23 active
standards for testing the biodegradability or biobased content of plastics according
to ASTM protocols (39). One has to discern between degradability in general and
biodegradability in specific. Biodegradability is the capability of being degraded
by biological activity (note that the in vitro activity of enzymes cannot be
considered as biological activity). Degradation is the lowering of the molar masses
of macromolecules that form the substances by chain scissions. All biodegradablepolymers BIOPLASTICS:
are degradable BIOBASED
polymers, but not necessarily
PLASTICS vice versa (note
AS RENEWABLE 13 that14 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
Q1 Table 8. Environmental Impacts of Bioplastics
Production stage Environmental impacts
feedstock new demand for biomass inputs can expand uses of
land, fossil fuels, chemical inputs, and water
feedstock choices can reinforce existing problems
associated with corn and sugarcane; converting
forests or glasslands to expand agricultural
production can offset the CO2 sequestered by
plants before harvest (Searchinger et al., 2008)
manufacturing and processing bioconversion is energy intensive (Gallezot, 2010)
bioconversion may require the use of potentially
toxic petroleum-based solvents (Ahman and
Dorgan, 2007) bioconversion produces significant
water effluent needing treatment (Ahman and
Dorgan, 2007)
bioconversion consumes water resources for
fermentation, cooling, and heating
end-of-life fate compostable bioplastics may contaminate recycled
plastic streams unless they are properly separated
and managed (Song et al., 2009)
compostable plastics require high temperatures to
decompose in a landfill and special industrial
equipment to be composted (Song et al., 2009)
unless a landfill is managed well and kept dry,
degrading bioplastics will release methane gas
life cycle assessments significant reductions of energy consumption and
GHG emissions are possible (McKone et al.,
20111; Akiyama et al., 2003); conversely, PHAs
and PHBs have higher GHG emissions because of
fossil fuel use for fertilizer production,
agricultural production, corn wet milling,
fermentation, polymer purification, and other
production processes (Kurdikar et al., 2001)
Reprinted with permission from Ref. 24. # 2013, Elsevier.
Table 9. Comparison of a Bioplastic (PHB) with a Conventional Commodity Polymer (PP)
Impact category Unit PHB PP
abiotic depletion kg Sbeq 21.8 41.4
global warming (GWP100) kg CO2eq 1960 3530
ozone layer depletion (ODP) kg CFC-11eq 0.00017 0.000862
human toxicity kg 1,4-DBeq 857 1870
fresh water aquatic ecotoxicity kg 1,4-DBeq 106 234
marine aquatic ecotoxicity kg 1,4-DBeq 1,290,000 1,850,000
terrestrial ecotoxicity kg 1,4-DBeq 8.98 44
photochemical oxidation kg C2H2 0.78 1.7
acidification kg SO2eq 24.9 48.8
eutrophication kg PO43-eq 5.19 5.84
Source: Ref. 36. LCIA of polymer production for 1000 kg of polymer product—CML 2 Baseline 2000BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE 15 V2.03. Key: Underlined bold values are the lowest values in each category. Values in bold print are within 50% of the lowest value in each category.
16 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
compounds can contain nondegradable additives, and copolymers nondegradable
moieties). Biomineralization is a process generally concomitant to biodegradation,
biofragmentation, and bioerosion. Specific modes are ‘‘hydrodegradation’’ or
hydrolysis (by the action of water), photodegradation (by visible or ultraviolet
light), oxidative degradation (by the action of oxygen) or photooxidative degrada-
tion (by the combined action of light and oxygen), thermal degradation (by the
action of heat), thermochemical degradation (by the combined effect of heat and
chemical agents), and thermooxidative degradation (by the combined action of
heat and oxygen). One can distinguish between physical and chemical degrada-
tion. Biodegradation is cell mediated (eg, bacteria). Enzymatic degradation is a
result from the action of enzymes.
An environmentally degradable polymer is a polymer that can be degraded
by the action of the environment, through, for example, air, light, heat, or
microorganisms.
Depolymerization can be caused by the enzyme depolymerase. This term is to
be used when monomers are recovered ( ! feedstock recycling).
Deterioration, which can stem from physical and/or chemical influences, is
the deleterious alteration of a plastic material in quality.
Erosion is a degradation process that occurs at the surface and progresses
from there into the bulk.
Fragmentation is the breakdown of a polymeric material into particles
irrespective of the mechanism and the size of fragments.
Mineralization is the process through which an organic substance is con-
verted into inorganic substances (CO2, H2O, and other inorganics).
Composting is the decomposition of organic wastes by fermentation. It can be
performed industrially under aerobic or anaerobic conditions.
Biodegradable plastics must undergo degradation resulting from the action
of naturally occurring microorganisms such as bacteria.
Compostable plastics must further meet the following two requirements:
• They must biodegrade at a rate comparable to common compostable organic
materials.
• They must disintegrate fully and leave no large fragments or toxic residue.
In short, a biodegradable plastic cannot be called compostable if it breaks
down too slowly, or if it leaves toxic residue or distinguishable fragments. In
general, an increase in the hydrophobic character, the macromolecular weight,
the crystallinity, or the size of spherulites decreases biodegradability (40). The
higher the amount of natural polymers such as polysaccharides in blends, the
faster the degradation progresses. Such blends are, however, not completely
degraded; the bulk material will be rendered into minute particles of conventional
polymer, which are no longer visible to the naked eye like litter, but are still
present. An example is mulch film made from PE with starch as filler. Such
materials are generally no longer used (41).
Ideally, plastics are mineralized, ie, broken down and converted to water and
carbon dioxide after their use, which is mostly time limited. When a mineraliza-BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE 17 tion product is CH4, which has a high greenhouse warming potential (31), the environmental impact is significantly aggravated.
18 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
Table 10. Biodegradable Polymers
Biodegradable polymers from renewable Biodegradable polymers from petroleum
resources sources
polylactide aliphatic polyesters and copolyesters (eg,
polyhydroxyalkanoates, eg, poly(3- polybutylene succinate and poly(butylene
hydroxybutyrate) succinate-co-adipate))
thermoplastic starch aromatic copolyesters (eg, poly(butylene
cellulose adipate-co-terephthalate))
chitosan poly(3-caprolactone)
proteins polyesteramides
polyvinyl alcohol
Source: Ref. 45. For details on compostability of plastics, see Ref. 45.
Degradation can occur by physical, chemical, and biological means. However,
plastics were initially selected for their resistance to degradation in the environ-
ment (bioresistant polymers). They withstand attack by microorganisms. Their
biostability is associated with the following problems:
• Littering (visible contamination).
• Release of water-soluble and water-dispersed macromolecular compounds
and additives contained in the plastic products.
Some modes of degradation require that the plastic be exposed at the surface
(UV light, O2), whereas other modes are only effective under special conditions of,
eg, industrial composting systems. There are also additives for polymers intended
to enhance their degradability (42,43).
For instance, BASF has been on the market for a decade with a compostable
bioplastic made from fossil sources (Ecoflex) and one made from renewable
sources (Ecovio). An overview of commercial compostable bioplastics is given,
eg, in the UL database (44).
Table 10 lists several biodegradable polymers from renewable and petro-
chemical resources.
For details on compostability of plastics, see Reference 45.
5. History of Bioplastics
Natural plastic materials (chewing gum, shellac) have been used for thousands of
years. In ancient times, natural plant gum was deployed to join pieces of wood in
house building, and natural plant gum was applied as a waterproof coating to
boats (46). Natural rubber came to the attention of Christopher Columbus in 1495,
when he had landed on the island of Haiti and saw people playing with an elastic
ball. Starch has been used for centuries as glue for paper and wood and as gum forthe textile industry (47).
BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE 1920 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
The first plastics in the modern sense were produced in the end of 19th and
beginning of 20th century. Celluloid and cellophane were the first ones, and they
were biobased.
Natural rubber was originally derived from latex, a milky colloidal suspen-
sion found in special trees. Its first use was cloth waterproofed with unvulcanized
latex from Brazilian rubber trees.
In 1839, Charles Goodyear discovered vulcanization of natural rubber
materials with sulfur for improving elasticity and durability. He also invented
Ebonite (1852), a very hard rubber.
The first man-made plastic was Parkesine (1856), which was obtained from
cellulose treated with nitric acid. Bakelite, the first fully synthetic thermoset, was
invented in 1907. The material, polyoxybenzylmethylenglycolanhydride, is
obtained in an elimination reaction of phenol with formaldehyde. Another early
bioplastic, casein, was produced from milk proteins and lye. Casein, a family of
related phosphoproteins, is still used today for paints, glues, and in cheesemaking.
Galalith (invented around 1897) is a synthetic plastic material manufactured
from casein and formaldehyde. Galalith was used for buttons around 1930.
In 1941, Henry Ford presented the ‘‘soybean car,’’ a plastic-bodied car shown
at Dearborn Days, an annual community festival. It was 1000 lb lighter than a
steel car; probably, the composition was ‘‘soybean fiber in a phenolic resin with
formaldehyde used in the impregnation’’ (48).
Mass production of ‘‘conventional’’ petrochemical mass polymers such as PE,
PP, PVC, PET, and PVC started around 1940–1950. Cheap crude oil has made
possible the mass production of these petrochemical polymers, and bioplastics
virtually disappeared (compare the case of fuels, where biobased fuels that were
initially used for combustion were replaced by petrol and diesel).
Modern bioplastics started emerging in the 1980s, when people wanted to
reduce the volume of waste in landfills. They hoped that degradable plastics
discarded into landfills would take up less space once decomposed. This concept,
however, failed, because landfills are sealed and oxygen, water, and sunlight are
hardly available to break down the material.
Another concept that helped revive the interest in bioplastics was to reduce
the use of petrochemicals for plastics production, as the price of crude oil became
unstable and started to rise (see oil crises of the 1970s). The first biopolymers were
blends of starch with conventional polymers, so that a certain biodegradability
and use of natural feedstock were partly achieved.
Packaging, an area where plastic products have a short useful life, is
currently one of the biggest markets for biopolymers, such as biodegradable
plastic bags, compostable waste collection bags, and biodegradable or compostable
food packaging.
Cheap oil and performance issues have retarded progress in biopolymers,
despite growing customer concern about the environment.
In 2005, the chemical company Dow decided to pull out of bioplastics ‘‘due to
slow sector maturation’’ after having invested an estimated $750 million (49). In
2012, bioplastics company Metabolix reduced its production capacity of PHA from
50,000 to 10,000 ton/yr (1), as sales volumes were too low at that time. OtherBIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE 21 manufacturers have been successful in mass producing bioplastics, eg, Brazil’s Braskem (biobased PE made from sugarcane) or US NatureWorks (PLA).
22 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
6. Bioplastics by Genetic Engineering
Genetically modified organisms (GMOs) are extensively used in biotechnology.
For instance, 80% of the >255 million tons of soybeans harvested annually are
genetically modified (50). Genetically engineered plants (51) and bacteria (52) also
show a good potential for bioplastics. Table 11 depicts several ‘‘phytofactories’’ for
biopolymers.
Transgenic means that the organism has received an exogenous gene, a so-
called transgene, so that it exhibits and transmits to its offspring new properties.
Apart from bacteria, also (transgenic) plants can be used to produce bio-
polymers such as PHA (53) (see Fig. 4).
7. Description of Important Bioplastics
At present, the biggest market share among biodegradable bioplastics is held by
TPS and blends made thereof, accounting for approximately 60% of consumption
(54). Next in line is PLA with approximately 20% market share, followed by CA
with 15% market share. Other bioplastics such as PHAs are at a market share
below 5%, at present. It is assumed that PLA is growing fastest (54).
Figure 5 shows an overview of biodegradable plastics in four families. An
extensive list of bioplastics is provided in Reference 6.
Biobased polyethylene is the most common nondegradable biopolymer.
Below, important biobased plastics are described. First, drop-in replacements
(PE, PP, PVC, and PC) will be discussed, followed by biodegradable biopolymers.
Note that also blends containing biobased plastics are manufactured. Drop-in
bioplastics are chemically identical to their petrochemical counterparts, but they
are at least partially derived from biomass. Generally, one can see a trend toward
the replacement of conventional petroplastics by these drop-in solutions, with
biodegradable bioplastics receiving comparatively less attention (55). Statistics
from European Bioplastics show that durables accounted for almost 40% of
bioplastics in 2011, up from around 12% in 2010 (19). This trend is in line
with improving properties of bioplastic formulations.
7.1. Biobased PE. PE is one of the most widely used commodity thermo-
plastics, eg, for packaging (plastic bags, plastic films, geomembranes, and con-
tainers including bottles). Variants are HDPE, LLDPE, and LDPE (high density
PE, linear low density PE, and low density PE, respectively). The monomer,
ethylene, is commonly made from crude oil (via cracking), natural gas, or shale gas
(from NGLs (natural gas liquids) (56) or methane after dimerization (57)). Bio-
based PE was first commercialized by Brazilian company Braskem utilizing local
sugarcane-derived ethanol/ethylene as feedstock. In September 2010, Braskem
started commercial production of biobased HDPE with a capacity of 200,000 ton/
yr. The material’s composition and performance are comparable to those of
petroleum-based PE. According to ICIS (1), the ‘‘green PE’’ has a price premium
of around 15–20%, which is possible in selected markets and covers the higher cost
of production compared with petrochemical-based plastics. Another bio-PE plantBIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE 23 was built in Brazil by Dow Chemical and Mitsui. That plant has a capacity of 350,000 ton/yr with main target markets in flexible packaging, hygiene, and
Table 11. Novel Biopolymers Produced in Transgenic Plants
Polymer Native production host Structure Plant metabolite used for Properties/applications
synthesis
PHAs bacteria; produced as a • homopolymers and depends on polymer • depends on polymer
carbon and energy copolymers of composition composition
storage polymer under polymerized hydroxy • applications in plastics,
nutrient limiting • PHB: acetyl-CoA or
acids chemicals, and feed
growth conditions (55) acetoacetyl-CoA
• PHB most common supplements
• PHAMCL: fatty acids
target in plants
• PHBV: acetyl-CoA and
threonine
spider silk spiders; produced for fibrous proteins with amino acids •multiple types of protein silk
webs and wrapping of repetitive sequences fibers exist that possess
prey possessing many different properties (41,56)
nonpolar and • good elasticity and tensile
hydrophobic amino strength
acids • clothing, textiles, medical uses
elastin mammals; extracellular fibrous proteins with amino acids • tissue engineering, gels, fibers,
matrix protein repetitive amino scaffolds (57); soluble
providing mechanical acid sequences derivatives of elastin (ie,
integrity to tissues tropoelastin and elastin
peptides(ELPs)) have more
useful properties and thus
broader applications (57)
• fusion of ELPs to other proteins
can increase protein production
(44)
collagen animals; protein found in fibrous proteins amino acids medical applications including
connective tissue tissue engineering, surgical
implants, and drug delivery
(58)
cyanophycin cyanobacteria and other nitr a compound
photosynthetic and oge g
nonphotosynthetic n e
bacteria; produced as stornonribosomally produced amino
BIOPLASTICS: acid
BIOBASED aspartic acid
PLASTICS ASand • production
RENEWABLE 25 of
polymer of aspartic acid backbone arginine polyaspartat
and arginine side groups e, a polymer
with
applications
in
superadsorbe
nts, after
chemical
hydrolysis of
arginine
• precursor for
the
production of
chemicals (2)
Source: Ref. 53. PHB, poly[(R)-3-hydroxybutyrate]; PHAMCL, medium chain length PHA; PHBV, copolymer of (R)-3-hydroxybutyrate and (R)-3-
hydroxyvalerate.
18BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE 19 Fig. 4. Metabolic engineering of high yielding biomass and oilseed crops for the copro- duction of PHB and lignocellulosic biomass or seed oil. Large-scale production of PHB in plants has the potential to provide a renewable cheap source of polymeric material that can be used for the production of plastics, chemicals, and feed supplements with lignocellulosic or seed oil coproducts that can be used to produce energy. Transmission electron micro- graphs from thin sections of switchgrass leaf tissue and Camelina mature seeds are shown in the insets and illustrate the accumulation of PHB in the form of granules in a bundle sheath leaf chloroplast (switchgrass, top inset) and a seed plastid (Camelina, bottom inset), respectively. (Reprinted with permission from Reference 53. # 2015, Elsevier.) Fig. 5. Different families of biodegradable polymers and their raw materials. (Source: Reference 41.)
20 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
medical applications. Since the project covers the entire value chain from growing
sugarcane to producing the biopolymer (1), it is competitive to conventional
polymer production.
7.2. Biobased PP. Polypropylene, the second most common commodity
plastic, can likewise be made from renewably sourced feedstock. Propylene is
accessible from methane via ethylene dimerization followed by metathesis (58).
Braskem has announced plans to build a 30,000–50,000 ton/yr biobased PP
production plant (1). A major market for biobased PP is the automotive industry,
as approximately 50% of plastic in cars is PP. For details, see, eg, Reference 59.
7.3. Biobased PET. The third most common thermoplastic is PET. It is a
thermoplastic polymer resin of the polyester family. It is mainly used for synthetic
fibers (then called ‘‘polyester’’) and for packaging, primarily bottles. The monomer
ethylene terephthalate (bis(2-hydroxyethyl) terephthalate) can be synthesized by
esterification between terephthalic acid and ethylene glycol, or by transesterifi-
cation between dimethyl terephthalate with ethylene glycol. Polymerization is
done through a polycondensation reaction of the monomers, carried out immedi-
ately after esterification/transesterification. Biobased PET can contain renewable
monoethylene glycol (MEG), produced, eg, from sugarcane-derived ethylene, as
being promoted by Coca Cola under the name Plantbottle (60,61). Its competitor
Pepsi has announced a 100% renewable PET material (62). Scale-up to commer-
cial production has been a hurdle so far (1) to replace conventional PET by a fully
biobased alternative. Plantbottle PET is produced from terephthalic acid (70% by
mass) and ethylene glycol (30% by mass), the latter coming from renewable
ethanol. The formulation is also termed Bio-PET 30. An alternative to PET is
the bioplastic polyethylene furanoate (PEF), which is expected to become com-
mercially available as of 2016 (63). The bacteria Nocardia can degrade PET with
its esterase enzyme (64).
7.4. Biobased PVC. PVC has been envisaged as one of the least environ-
ment-friendly synthetic polymers, setting free HCl and supporting dioxin forma-
tion in combustion. On top, soft PVC contains plasticizers with special
environmental challenges, eg, phthalates, so the material’s reputation is not so
high. Company Solvay from Belgium has announced the production of 60,000 ton/
yr of biobased ethylene for the production of PVC (1). Also, efforts are underway to
create biobased plasticizers for the replacement of phthalates. There are over 300
known plasticizers, with 50–100 being used commercially (65).
7.5. Biobased PC. Polycarbonates are situated between commodity
plastics and engineering plastics, as they exhibit an interesting combination of
temperature resistance, impact resistance, and optical properties. Conventional
polycarbonate is made from toxic monomers, bisphenol A (BPA), and phosgene
(COCl2).
An alternative polycarbonate can partly be made from isosorbide (derived
from glucose: hydrogenation of glucose gives sorbitol, and isosorbide is obtained by
double dehydration of sorbitol): Companies Mitsubishi and Roquette have
announced pilot plants for making isosorbide and incorporating it into PC (66).
Manufacturing PC from isosorbide and a diaryl carbonate removes the need to use
phosgene and bisphenol A in the process (1). The biobased PC is seen as still farBIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE 21 from commercialization (1). In Reference 67, the potential of a derivative of cashew nutshell liquid (CNSL) as an alternative to BPA is discussed.
22 BIOPLASTICS: BIOBASED PLASTICS AS RENEWABLE
7.6. Biobased PU. Polyurethanes (PU, RPUR, and BUR) are thermo-
setting polymers commonly formed by reacting a di- or polyisocyanate with a
polyol. Applications are rigid foams. The polyols can be obtained from plant oil to
make a biobased PU. Natural oil polyols (NOPs, biopolyols) (68) are derived from
vegetable oils. Castor oil is suited best, as it consists mainly of ricinoleic acid,
which has hydroxyl groups. Other vegetable oils such as canola oil, peanut oil, or
soybean oil need to be treated to introduce--OH groups, mainly by double bond
oxidation.
7.7. Cellulose Acetate. Cellulose esters are another important group of
bioplastics. The most common cellulose esters comprise CA, cellulose acetate
propionate (CAP), and cellulose acetate butyrate (CAB). They are thermoplastic
materials produced through esterification of cellulose (45). Applications are
synthetic fibers, cigarette filters, and formerly photography film.
7.8. Polylactic Acid. Polylactic acid or polylactate is obtained from the
monomer lactic acid, which is produced from the microorganism-catalyzed
fermentation of sugar or starch. It is similar in properties to PET and has
FDA approval for food contact. Common raw materials are corn starch, sugar-
cane, and tapioca (starch extracted from cassava root). Chemically, PLA is not a
polyacid (polyelectrolyte), but rather a polyester. Companies active in the field
are, eg, NatureWorks, Purac, and Teijin (1). PLA is used for yogurt cups, where
it replaces polystyrene. Due to inferior material properties (heat resistance,
impact resistance, and low glass transition temperature), PLA is often blended
with conventional petroplastics. Costs of PLA have improved over the last
decade and are expected to go down further as capacity is added, eg, by
NatureWorks (140,000 ton/yr) and Purac (750,000 ton/yr) (1). NatureWorks’
Ingeo is manufactured in a two-step process that starts with fermenting the
dextrose derived from hydrolysis of corn starch. The product of the dextrose
fermentation, lactic acid, is further treated to create the intermediary monomer
lactide (the cyclic diester of lactic acid), which is then polymerized through
opening polymerization (39).
Polylactic acid and its copolymers can also be obtained from engineered
Escherichia coli (69).
Composite materials of PLA, eg, with woven bamboo fabric, have been
reported (70).
PLA is subject to abiotic degradation (ie, simple hydrolysis of the ester bonds
without requiring the presence of enzymes). It is also biocompatible.
Monomer stereochemistry (D- and L-lactic acid) can be controlled to impart
targeted utility in the final polymers (71), by the relative contents of both
homopolymers (D, L) and copolymers. Polymerization of a racemic mixture of L-
and D-lactides usually yields poly-DL-lactide (PDLLA), which is amorphous.
Recycling of PLA, eg, to repolymerizable oligomer (72), is challenging. PLA
has a strong potential for future use, spearheading bioplastics proliferation, since
it is comparatively cheap and available on the market.
PLA contamination in PET recycling is a topic of concern. The bio-
degradation of a PLA cup over 2 months is shown in Figure 6.
Thermoreversible cross-linked PLA (TCP) for rewritable shape memory isYou can also read
