SOUTH AUSTRALIAN MATRICULATION
2CME20 – CHEMISTRY
Should Bioplastic be Used to Replace Petroleum Based Plastic in packaging?
Chang Wei Yang
Plastics, which are utilized heavily in packaging from areas such as product wrappers to food wrapping illustrate that versatile plastic is an essential part of our lives. However, with the threat of global warming on the horizon, as well as the depletion of fossil fuels used in the production of these plastics, there has been an outcry for a greener alternative to plastic. Hence, bioplastics have emerged as a promising option to replace conventional plastic packaging to mitigate our addiction to oil and lessen our environmental impact.
Unlike typical plastics, bioplastics are derived from 100% natural materials such as corn, potato and sugarcane. Often referred to by their chemical constituent such as polylactide(PLA) or polyhydroxylalkanoate(PHA/PHB), (Vidal,2008) the bioplastics industry uses words such as ‘sustainable’, biodegradable, and compostable to depict their products, stating that bioplastics create carbon savings of 30%-80% compared to traditional oil-based plastics. Recently, there has been a great advancement in development of bioplastics and biodegradable and compostable packaging. (Thomas White Global Investing, 2010)Also, the bioplastics industry which just produced 200,000 tons in 2006 will expand to about 5 million tons in 2015 affirms the Germany-based Helmut Kaiser Consultancy.
By definition, plastics are polymers, large molecules consisting of chains or rings of connected monomer units. Bioplastics are biopolymers derived from renewable biomass sources rather petroleum and can also be designed to be biodegradable although not all are. No variety of bioplastic possesses a particular molecular formula, since each class of bioplastic consists of a combination of polymers, plasticizer and additives in varying possible ratios.
One prominent bioplastic is (Vidal, 2008) polylactic acid(PLA) which can be synthesized from corn. The melting point of PLA could range from 140 – 185 C, while a blend of Pure PLLA and PDLA could reach as high as 230 C. Molecular weight, molecular architecture along with the degree of crystallinity determines the mechanical properties of PLA. PLA bears a resemblance to most of the properties of conventional thermoplastics such as PET, and polystyrene(PS), opening possibilities to substitute petroleum based thermoplastics in various aspects.
Ring Opening Polymerization Scheme for Lactide
Image Source: http://bioplasticsonline.net/2010/06/polylactic-acid-synthesis-%E2%80%93-ring-opening-polymerization-of-lactide/
(http://bioplasticsonline.net, 2010) Another popular bioplastic is Polyhydroxyalkanoates (PHA) also known as microbial polyesters being produced via bacterial fermentation. Varieties produced are reliant on the species of microorganisms, carbon source the cells are cultivated on, fermentation conditions counting the types of enzymes utilised. The absolute properties of the PHAs chiefly hinge on on the monomer composition, and monomer with C3-C5 characteristically yields thermoplastics, while C6-C14 chain length monomers yield elastomeric polymers.
Figure: General structure of Polyhydroxyalkanoates (PHA)s.
Image Source: http://bioplasticsonline.net
(http://bioplasticsonline.net, 2010) Poly-b-hydroxybutyrate (PHB) and poly(hydroxybutyrate-co-hydroxyvalerate), both PHA isomers, are highly researched polymers because of their ideal characteristics. PHB is a melt processable, hydrophobic, semi-crystalline polyester that bears a resemblance to characteristics of typical thermoplastics for instance polypropylene and polyethylene. As PHB is approximately 80% crystalline, it retains a high melting point. It has excellent resistance towards organic solvents, though its applications are constricted attributable to its high stiffness...
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