Petroleum-derived products, biodegradable

BIODEGRADABLE POLYMERS FROM PETROLEUM-DERIVED PRODUCTS... 

The reactivity of MPa and BaP seems to have resulted in the alteration of their source compositional ratios during transportation/deposition, and thus may not be a reliable source indicator. In addition to the compositional attributes of the parental PAHs, the presence of methylated compounds and a UCM in the surface sediments indicates possible petrogenic inputs of PAHs to the Harbor. The UCM is generally indicative of petroleum and petroleum products, and is a widely used indicator of petrogenic contamination in sediments (Prahl and Carpenter, 1979 Volkman et al., 1992, 1997 Simoneit, 1998). It is commonly assumed that a UCM consists primarily of an accumulation of multibranched structures that are formed as a result of biodegradation reactions of petroleum (Volkman et al., 1992). Since no clear indication of petroleum-derived inputs can be discerned from the compositional ratios of the prominent PAHs in the sediments, it is apparent that the isomeric ratios of the prominent petrogenic PAHs are masked by pyrogenic-derived components. 

Polyhydroxyalkanoate(s) (PHA) are one of the potential environmentally friendly alternatives to petroleum-derived synthetic plastic. Their biodegradahility and production from renewable resources make them extremely desirable substitutes for synthetic plastics. However, the use of PHA as a substitute is hindered by the overall manufacturing cost, which is far more expensive than the manufacture of non-biodegradable synthetic plastics. 

Recently, the possibility of replacing petroleum-derived synthetic polymers with natural, abundant and low-cost biodegradable products has gained much interest in both academic and industrial fields. " For instance, the production of plastics in Europe reached 57 million tons in 2012, mostly divided between polyethylene, polypropylene, poly(vinyl chloride), polystyrene and poly(ethylene terephthalate) production. These fossil-based plastics were consumed and discarded into the environment, generating 10.4 million tons of plastic waste, most of which ended up in landfills (Figure 1). 

PHAs can substitute petroleum-derived polymers, can be produced from renewable resources and are harmless to the environment due to their biodegradability. However, the major hurdle facing commercial production and application of PHA in consumer products is the high cost of bacterial fermentation. It makes bacterial PHA production 5 10 times more expensive than the petroleum-derived polymers such polyethylene and polypropylene. The significant factor of the production cost of PHA is the cost of substrate (mainly carbon source). In order to decrease this cost, the use of cheap carbon sources as substrates have been developed. The researches have been carried out to develop recombinant strains utilizing a cheap carbon source, while corresponding fermentation strategies have been developed and optimized. 

Most of the plastics and synthetic polymers that are used worldwide are produced from petrochemicals. Replacing petroleum-based feedstocks with materials derived from renewable resources is an attractive prospect for manufacturers of polymers and plastics, since the production of such polymers does not depend on the limited supply of fossil fuels [16]. Furthermore, synthetic materials are very persistent in the environment long after their intended use, and as a result their total volume in landfills is giving rise to serious waste management problems. In 1992,20% of the volume and 8% of the weight of landfills in the US were plastic materials, while the annual disposal of plastics both in the US and EC has risen to over 10 million tons [17]. Because of the biodegradability of PHAs, they would be mostly composted and as such would be very valuable in reducing the amount of plastic waste. 

Renewable raw materials are made or derived from short-term renewable sources (one to a few years or a few tens of years) such as plants, trees, wood wastes and other agricultural products. Not all these materials are necessarily biodegradable. Natural rubber, for example, comes from the latex of a tree (Hevea brasiliensis) and is not biodegradable. Renewable materials are often considered as opposites to fossil sources such as petroleum that are not renewable on a human timescale. On the other hand, some synthesized plastics such as certain polyesters are biodegradable. 

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