Tailoring new materials within a perspective of eco-design or sustainable development is a philosophy that is applied to more and more materials. It is the reason why material components such as biodegradable polymers can be considered as ‘interesting’ alternatives. Besides, ecological concerns have resulted in a resumed interest in renewable resources-based products.
We can classify the biodegradable polymers into two groups and four different families. The main groups are (i) the agro-polymers (polysaccharides, proteins, etc.) and (ii) the biopolyesters (biodegradable polyesters) such as polylactic acid (PLA), polyhydroxyalkanoate (PHA) and copolyesters.
Biodegradable polymers show a large range of properties and can now compete with non-biodegradable thermoplastics in different fields (packaging, textile, biomedical, etc.). Among these biopolyesters, PLA is at present one of the most promising biopolymer. PLA is commercially and largely available (large-scale production) in a wide range of grades. It has a reasonable price and some remarkable properties to fulfill different applications. For instance, the PLA production capacity of Cargill (USA) or NatureWorks in 2007 was 140 kT per year at 2–5 Euros per kg. Other companies, such as Mitsui Chemical (Lacea-Japan), Treofan (Netherland), Galactic (Belgium), Shimadzu Corporation (Japan), produce smaller quantities. Some of them are only focused on the biomedical market like Boeringher Ingelheim (Germany), Purac (Netherland) or Phusis (France), because the constraints of this market are very specific. However, according to different sources, PLA consumption in 2007 was only about 60 000 tons per year and, at present, only 30 per cent of lactic acid is used for PLA production. Thus, this biopolymer presents a high potential for development.
PLA belongs to the family of aliphatic polyesters commonly made from -hydroxy acids, which also includes, for example, polyglycolic acid (PGA). It is one of the few polymers in which the stereochemical structure can easily be modified by polymerizing a controlled mixture of l and d isomers to yield high molecular weight and amorphous or semi-crystalline polymers. Properties can be both modied through the variation of isomers (l/d ratio) and the homo and (d,l) copolymers relative contents. Besides, PLA can be tailored by formulation involving adding plasticizers, other biopolymers, fillers, etc.
PLA is considered both as biodegradable in the environment and as biocompatible in contact with living tissues (e.g. for biomedical applications). PLA can be degraded by abiotic degradation (i.e. simple hydrolysis of the ester bond without requiring the presence of enzymes to catalyze it). During the biodegradation process, and only in a second step, the enzymes degrade the residual oligomers till final mineralization (biotic degradation).
As long as the basic monomers (lactic acid) are produced from renewable resources (carbohydrates) by fermentation, PLA complies with the rising worldwide concept of sustainable development and is classied as an environmentally friendly material.
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