Polymers composting systems

A polymer s compostability is a function of many factors such as pH, temperature, humidity, microorganisms population, and osmotic pressure. Simulated laboratory conditions as described by ASTM D6400 (//), D5338 (7) and ISO 14855 (6) may be an oversimplification of commercial composting systems which do not completely reflect the conditions in the commercial composting facilities. Therefore, further studies are necessary to assure that laboratory studies can duplicate commercial systems. 

Compostable biodegradable plastics must be demonstrated to biodegrade and to disintegrate in a compost system during the composting process (typically around 12 weeks at temperatures over 50 °C). The compost must meet quality criteria such as heavy metal content, ecotoxicity, and the absence of obvious distinguishable residues caused by the breakdown of the polymers. Compostable plastics are a subset of biodegradable plastics. 

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.). 

Labelling systems for compostable polymer materials exist in Europe, the LISA and Japan. 

The composting test method based on activated vermicuUte was proposed as a comprehensive system for the assessment of the environmental impact of compostable polymers [1, 2]. Vermicnlite, a clay mineral, can be activated (by an inoculation with an appropriate microbial population and fermentation) and used as a sohd matrix in place of mature compost in the controlled composting test. The formula of vermicnlite is (MgJ e,Al)3(Al,Si)40io(OH)2.4H20. The results obtained with two materials (cellulose and a starch-based blend) indicated that activated vermicnlite affected neither the biodegradation rate nor the final biodegradation level. 

Recently, compostable packaging materials were introduced into the market to reduce the amounts of conventional packaging materials and at the same time be recovered by the municipal organic waste collection system. An example of commercial implementation of compostable polymers includes Cargill Dow Nature Works polylactic acid (PLA), which is produced at a rate of 140000 tonnes/year at Blair, Nebraska (USA), via carbohydrate fermentation. Other... 

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