Polymer biodegradability costs

The PHA family generally has better properties than PLA, in terms of both strength and barrier. These polymers biodegrade rapidly In a variety of environments. However, cost and availability remain significant issues. As of the time of this writing, there does not appear to be any significant use of PHAs in packaging, but they are a family of polymers to watch for the future. 

Biodegradation is the most acceptable means of solving these problems, as it is cost effective and eco-friendly. In many specific applications such as agriculture and biomedical use, biodegradation is the only means of degrading used polymers. Biodegradable polymers are therefore the only solution to the problem of landfill. 

Lactic acid and levulinic acid are two key intermediates prepared from carbohydrates [7]. Lipinsky [7] compared the properties of the lactide copolymers [130] obtained from lactic acid with those of polystyrene and polyvinyl chloride (see Scheme 4 and Table 5) and showed that the lactide polymer can effectively replace the synthetics if the cost of production of lactic acid is made viable. Poly(lactic acid) and poly(l-lactide) have been shown to be good candidates for biodegradeable biomaterials. Tsuji [131] and Kaspercejk [132] have recently reported studies concerning their microstructure and morphology. 

Biodegradable polymers are likely to be increasingly important materials in the future, finding use in applications as diverse as medicine, agriculture, and pharmacy. For applications such as packaging, they remain expensive. However, with changing public attitudes towards enviromnental pollution, it is likely that objections based purely on cost will dimiiush, and that such applications will also grow in the years ahead. 

Polylactic acid (PLA) has been produced for many years as a high-value material for use in medical applications such as dissolvable stitches and controlled release devices, because of the high production costs. The very low toxicity and biodegradability within the body made PLA the polymer of choice for such applications. In theory PLA should be relatively simple to produce by simple condensation polymerization of lactic acid. Unfortunately, in practice, a competing depolymerization process takes place to produce the cyclic lactide (Scheme 6.10). As the degree of polymerization increases the rate slows down until the rates of depolymerization and polymerization are the same. This equilibrium is achieved before commercially useful molecular weights of PLA have been formed. 

Biotechnological syntheses of PHB are still in their infancy and some problems may be overcome in near future. However, the synthesis of biodegradable polymers in a catalytic manner offers so many advantages, not only with regards to costs, that future development of such research is worthwhile. 

To define the value of biodegradable polymers, the overall system costs and the environmental impact of individual products in their respective target applications have to be considered. To this end, comprehensive life-cycle assessments (EGAs) are an appropriate tool, especially when accompanied by costs evaluations that cover all phases from cradle to grave. 

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