Biodegradability, commercial polymers

The first strategy, based on the use of starch for the production of other chemicals was recently reviewed by Robertson et al. [58], Koutinas et al. [59], Kennedy et al. [60] and Otey and Doane [61]. Three different approaches are applied in this context (i) starch as a raw matraial for the production of monomers used in the synthesis of polymers which can be non-biodegradable, such as polyethylene, or biodegradable, such as PLA (the main biodegradable commercial polymer whose monomer, lactic acid, can be obtained from the fermentation of starch [62]) (ii) as a raw material for the production of biopolymCTs like polyhydroxyalkanoates (of which PHB is the main member) (iii) as a raw material for the production of glucose, dextrin and other hydroxyl-containing monomers used in the production of mixed compositions based on starch and other monomers. 

It is evident that the area of water-soluble polymer covets a multitude of appHcations and encompasses a broad spectmm of compositions. Proteins (qv) and other biological materials ate coveted elsewhere in the Eniyclopedia. One of the products of this type, poly(aspartic acid), may be developed into interesting biodegradable commercial appHcations (70,71). 

Water-soluble biodegradable polycarboxylates with an acetal or ketal weak link were inventions of Monsanto scientists in the course of their search for biodegradable deteigent polymers. However, the polymers were prevented by economics from reaching commercial status. The polymers are based on the anionic or cationic polymerization of glyoxylic esters at low temperature (molecular weight is inversely proportional to the polymerization temperature) and subsequent hydrolysis to the salt form of the polyacid, which is a hemiacetal (R = H) or ketal (R = CH3) if methylglyoxylic acid is used, and stable under basic conditions. 

During the same period, commercialization of thermoplastic starch polymer blends was pursued by Novamont, a division of the Ferruzzi Group of Italy.162-172 Their products, marketed under the trade name Mater-Bi, are typically comprised of at least 60% starch or natural additive and hydrophilic, biodegradable synthetic polymers.64,165 It is stated that these blends form interpenetrated or semi-interpenetrated structures at the molecular level. Properties of typical commercial formulations have properties similar to those in the range of low- and high-density PE. Blends of Mater-Bi products with biodegradable polyesters have been claimed for use as water impervious films.173... 

The recognized lack of biodegradability of most commercial polymers, in particular those used for food packaging, focused public attention on the potential global environmental problem associated with plastic waste build-up in the countryside and on the seashore. Therefore, there is a growing demand for sea-biodegradable polymers. 

SEC, which allows high-speed separations, is used for control analysis of samples with unknown compositions. These samples usually contain polymers and small molecules, which is often the case for numerous commercial or industrial products, such as in the biodegradation of polymers. 

Cargill Dow LLC has developed a patented, low-cost continuous process for the production of lactic acid-based polymers. The process combines the substantial environmental and economic benefits of synthesizing both lactide and PLA in the melt rather than in solution and, for the first time, provides a commercially viable biodegradable commodity polymer made from renewable... 

One of the most studied blends has been the one composed of P(3HB) and polylactide, both commercially available polymers with superior thermal and mechanical properties than other commercial polymers. Polylactide is a chemically synthesized, biodegradable thermoplastic and derived from renewable resources. It has been shown that this blend exhibited greater flexibility and hydrolytic biodegradation than the Polylactide or P(3HB) alone [75]. 

Table 1. Commercially available biodegradable synthetic polymers...

Day, M., Shaw, K., and Cooney, J.D., 1994, Biodegradability an assessment of commercial polymers according to the Canadian method for anaerobic conditions. J. Environ. Polym. Degrad. 2 121-127. 

PLA [e.g., see Sodergi d and Stolt [26]] is raie of the most important bio-based and biodegradable thermoplastic polymers commercially available today with some molecular weights and optical purities. First attempts to reinforce PLA with manmade cellulose fibers have been reported in [12], followed by papers of other groups [27-29]. Results are in full agreement with each other and will be reported on the basis of own work in this field [30, 31]. 

Another approach to biodegradability is to blend a biodegradable natural polymer with a thermoplastic synthetic pol5nner. Blends of starch with PE or with poly(vinyl alcohol) have been commercialized as packaging materials (176), although they have mainly been used in niche markets. Early materials were rather poor because the encapsulating effect of the PE on the starch protected it from water access, and, even if the starch was biodegraded, the PE was left... 

M. H. Naitove, Push is on to commercialize biodegradable lactide polymers. Plast. Technol. 1995, March 15-17. 

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