Poly , composting

The new biodegradable cheese coatings (Fig. 5) are produced from poly (HAmcl) latex based on saturated fatty acids and are easily composted. 

Copolymers of polyethylene terephthalate (PET) with nonaromatic acids, poly(ethylene ethers) or hydroxy acids have been blended with starch to produce compostable products such as fibers and films.60 Starch contents up to 80% by weight are claimed. 

Polymer films prepared by Hayes [3] consisting of bis(2-hydroxyethyl)tere-phthalate, lactic acid, tris(2-hydroxyethyl)trimellitate, ethylene glycol, poly (ethylene glycol), and the colorant titanium dioxide were both biodegradable and compostable. 

PLA may be fabricated into film for packaging and is also made into fibers useful for carpeting (24). PLA is indeed biodegradable, but only under controlled composting conditions. Biodegradation of poly (lactic acid) requires temperatures of about 140 °F for many days to insure decomposition, ultimately into CO and water. Unfortunately, such conditions are not typical of landfills (3) or of most backyard compost heaps. Hence, even plastic bags made from PLA will not quickly disappear from the natural environment. Anaerobic decomposition of PLA results in liberation of methane, an even more potent greenhouse gas than CO (25-28). 

Biodegradable plates, knives, forks, and leaf bags can be made by molding or extrusion of starch plasticized with 10% water.66 After use, the materials could be composted. A mixture of benzylated wood and polystyrene can be extruded easily.67 The properties of the product are comparable with those of poly(styrene). 

V., Dow Chem. Co., Mitsui Toatsu Chem., Ltd., Neste Oy) Poly-lactic acid (PLA) for thermoforming, blow molding, extrusion of fibers and films. The available products include compostable bags, food containers, cafeteria plates, cutlery, medical and pharmaceutical articles,... 

Figure 9.4 and Table 9.1 respectively show the chemical structure and the properties of these materials. Most commonly used is poly(butylene adipate-co-terephtalate) (PBAT). BASF, DuPont and Zhejiang Hangzhou Xinfu (China) manufacture and market these aromatic polyesters, under the respective brands Ecoflex , Biomax and Biocosafe . Biomax has a high terephthalic acid content, which modifies some of its properties such as the melting temperature (200°C). According to Muller et al., an increase in terephthalic acid content tends to decrease the rate of biodegradation into compost [MUL 97]. 

GAT 02] Gattin R., Copinet A., Bertrand C., et al, Biodegradation study of a starch and poly(lactic acid) co-extruded material in liquid, composting and inert mineral media . International Biodeterioration and Biodegradation, vol. 50, no. 1, pp. 25-31,2002. 

Commercial poly(butadiene), which is mainly the 1,4 isomer, is also used to improve the impact resistance of polystyrene (Chapter 1). Polydienes also increase the rate of physical disintegration of polyblend containing them. The addition of a styrene-butadiene block copolymer e.g. SBS, page 9 et seq.) to polyethylene also accelerates the peroxidation of the latter. However, this system also requires a polymer-soluble transition metal ion catalyst e.g. an iron or manganese carboxylate) to increase the rate of photooxidation in the environment by the reactions shown in Scheme 5.3. The products formed by breakdown of alkoxyl radicals (PO ) (Scheme 3.4) are then rapidly biodegradable in compost (page 107 et seq.). 

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