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The American Society for Testing and Materials (ASTM) defines bioplastics as “degradable plastics in which the degradation results from the action of naturally occurring microorganisms such as bacteria, fungi, and algae”. Examples are polylactic acid (PLA), polycaprolactone (PCL and polyhydroxyalkanoate (PHA).
Bio-based, biodegradable plastics have to compete with the highly efficient, controlled large-scale production of fossil-based plastics. They also have to catch up on decades of technological advancement and development that fossil-derived plastics have enjoyed before the 1950s to date.
Bioplastics can vary based on their chemistry. Most of the more common biodegradable bioplastics are aliphatic polyesters, thermoplastic starch, or cellulose-based bioplastics. Bioplastics currently only make up around 1% of the global plastic market at around 912 thousand tonnes annual production. Compared to non biodegradable plastic production at around 390 million tonnes annually. The three main bioplastics being produced at a commercial scale are PLA, PBS, and PHA. They have estimated annual production rates of 218, 97, and 30 thousand tonnes respectively.
Biodegradable plastics can also vary based on the sources of their raw materials. These are mainly categorized as fossil-based bioplastics and bio-based bioplastics. Fossil-based bioplastics include PBS, PVA, PBAT, PCL, and PGA. There are possibilities of producing these plastics from bio-based sources however they are largely produced using fossil-based raw materials. PLA, PHA, and thermoplastic starch are examples of biobased biodegradable plastics.
Over the years bioplastics have been produced from various raw materials using a wide range of processes. Vinyl monomers, carboxylic acids, amides, and alcohols which serve as raw materials for bioplastics production can be obtained from biomass. Bioplastics can also be obtained directly from biomass using the help of specially selected bacteria.
Table 1 lists some bioplastics, their raw materials, and production processes.
Raw materials/ feedstock
|– Sugars from fermented starch||– Polycondensation of lactic acid obtained from the fermentation of sugars Or Ring-opening polymerization of lactide|
|– Carbon-rich feedstock such as organic waste, liquefied plastic waste, and activated sewage sludge, and wastewater||– Produced by bacteria such as Pseudomonas oleovorans, rhizobium meliloti and alcaligene eutrophus and some algae.|
– Extraction from cells using solvents. Potential development in extracellularly produced PHA can eliminate the need for extraction processes requiring cell lysis
Thermoplastic starch (Bio-based)
|– Food waste||– Starch extraction, gelatinization, plasticization, and blending|
|– Succinic acid and butanediol||– Copolymerization of succinic acid and butanediol.|
– Butanediol obtainable from the hydrocracking of starch and sugars
– Succinic acid potentially obtainable from fermenting of lignocellulosic sugars however existing technology is based on nonrenewable sources
|– Vinyl acetate||– Emulsion polymerization of vinyl acetate|
PBAT Polybutylene adipate-co-terephthalate (Fossil-based)
|– 1,4 butanediol, adipic acid and dimethylterephthalate||– Copolymerization of 1, 4 butanediol, adipic acid, and dimethyl terephthalate |
|– Caprolactone||– Ring-opening polymerization|
Polyglycolic acid (PGA)(Fossil-based)
|– Glycolic acid, halogenoacetates, or glycolide||– Polycondensation, of glycolic acid, solid-state polycondensation of halogenoacetates or ring-opening polymerization of glycolide |
Polylactide-co-glycolide (PLGA) (Fossil-based)
|– Glycolic acid and lactic acid/ lactide||– Polycondensation or ring-opening polymerization |
Bioplastics themselves have a benign impact on the environment, are nontoxic and biocompatible. Some bioplastics may even have added benefits such as adding nutrients to soil at the end of their usage life. The overall sustainability and ecological friendliness of plastics depend on other factors not intrinsic to the material. Factors to be considered in making bioplastic production ecofriendly include:
The following technologies are applied in bioplastic production to improve efficiency.
Gene editing technology offers the potential for more precise tuning of PHA properties through editing the gene for PHA production in the bacteria. An example of such is the recombinant Capriavidus necator that was modified to produce PHA from whey. The same technology can also be used to improve the size of the bacteria, PHA yield, and the efficiency of production. The genetic modification of plants to enhance PHA production has also been explored. Genetically modified strains of E coli have been used for commercial PHA production.
Culturing of highly efficient bacteria, identification and isolation of highly efficient microbes strains are key in achieving high yields in microorganism-dependent processes. These include the fermentation of starch or lignocellulosic biomass to sugars and PHA production by PHA-producing bacteria. Recent developments in microbe culturing include the use of mixed cultures and the production of bioplastics in nonsterile conditions to reduce cost. There is also potential to produce PHAs from photosynthetic organisms such as algae and plants.
Having the optimal conditions for these microbes to thrive relies on the use of highly efficient technologies to achieve precise control over the conditions in the bioreactor and the production environment. This also includes systems to prevent contaminations. Some systems require changing conditions at certain points of the microbe’s metabolic process. For example, switching from aerobic to anaerobic or varying temperature or nutrient media composition. These rely on efficient feedback and control systems.
For bioplastics like PLA, the purity of the monomer can affect the chain length achieved in the polymerization process. This determines the properties of the polymer. High-efficiency filters and membranes are used to achieve high purity from the extraction of the starch to the fermented sugar.
Highly efficient separation techniques are also required to separate bacteria-produced bioplastics from the bacteria and media after extraction. This is important to ensure all traces of residues are eliminated from the bioplastic for further use and processing.
Often halogenated organic solvents are required for cell lysis and extraction of PHA from the bacteria cell. More eco-friendly solvents are in development. There is also potential for culturing bacteria strains that produce PHA extracellularly thereby eliminating the need for harsh solvents for cell lysis and extraction.
The properties of bioplastics can be significantly improved by blending different bioplastics and/or creating composites of bioplastics with fibers and minerals. These can include use of nanomaterials such as nanocellulose and nanofibers.
For improved ecological impact VEnvirotech produces bioplastic formulations using minerals and fibers extracted from organic wastes. These include eggshells, oyster shells, paper waste, brewery waste among others.
VEnvirotech’s contribution to the field of bioplastics includes:
Contact VEnvirotech for our range of bioplastic products or to explore ways your business can upcycle your waste into raw materials for bioplastics.