Biodegradable polymers from petrochemical resources

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. 

PHAs can consist of a diverse set of repeating unit structures and have been studied intensely because the physical properties of these biopolyesters can be similar to petrochemical-derived plastics such as polypropylene (see Table 1). These biologically produced polyesters have already found application as bulk commodity plastics, fishing lines, and for medical use. PHAs have also attracted much attention as biodegradable polymers that can be produced from biorenewable resources. Many excellent reviews on the in vivo or in vitro synthesis of PHAs and their properties and applications exist, underlining the importance of this class of polymers [2, 6, 7, 12, 26-32]. 

Fig. 3 shows the molecular structure of PLA. PLA polymer is made up of many long chains consisting of the repeat unit shown in the figure. PLA is derived from renewable resources, such as corn starch via fermentation and it is biodegradable under the right conditions, such as the presence of oxygen (Tsuji et ah, 2010). Thus, PLA is a possible candidate of a new class of renewable polymers as a substitute for the petrochemical polymers. However, the physical properties of PLA are inadequate for the replacement of conventional commodity plastics in many applications. 

Abstract The development and production of biodegradable starch-based materials has attracted more and more attention in recent years due to the depletion in the world s oil resources and the growing interest in easing the environmental burden from petrochemically derived polymers. Furthermore, the unique microstructures of different starches can be used as an outstanding model system to illustrate the conceptual approach to understanding the relationship between the structures and properties in polymers. 

All of the biodegradable polymers covered by this review are manufactured from renewable resources. It is important to keep this in mind since some of the findings would probably differ for biodegradable polymers based on petrochemical polymers. 

The increasing amounts of plastic products from petrochemical-based polymers in a landfill have led to serious environmental concerns over the past decade. In recent years, various biodegradable plasties have been developed as a sustainable alternative to replace commodity synthetic plastics. Polylactic add is typical biodegradable polyester produced from renewable resources and a versatile polymer that has been used for many applications in the biomedical industry [1] as well as the packaging industry [2,3]. PLA has been blended with other biodegradable and synthetic polymers for the development of improved properties, such as poly (e-caprolactone)[4], poly (vinyl butyral)[5], poly(3-hydroxy butyrate)[6], poly (ethylene oxide)[7], and poly(p-vinyl phenol) [8]. 

PHAs have frequently been championed as a solution to sustainable polymer production. This is because they can be produced from renewable raw materials and are biodegradable upon disposal. However, an inventory of materials and energy required to produce these polymers reveals a rather discouraging picture. In most categories quantifying environmental impact (land use, resource depletion and emissions to air and water) PHA production by fermentation scores worse than conventional petrochemical polymer production. 

A promising line for future R D - even though somewhat outside the scope of the biodegradability concept - could be the development of biomass-derived polymers that can be recycled mechanically, preferably also in blends with petrochemical polymers. Such recyclable polymers made from renewable raw materials are likely to be unrivalled in environmental terms provided that their manufacture is not too resource-intensive in the first place. This may offer longer term prospects to PHA, PEA and other bio-based polymers while post-consumer recycling of starch polymers seems hardly viable due to the sensitivity of these products to water. 

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