Recycling biodegradable plastics

As shown in Table I, the plastic component of MSW has increased dramatically. Past development of synthetic plastic formulations has focused on reducing the photo, chemical, and biological degradation of the plastic polymers. However, the persistence of plastics in the environment as litter, potential marine hazard, and with concern for global carbon cycling 1,6) has focused recent attention on the recycling of plastics or development of new biodegradable plastic formulations. 

This change is signihcant in that most components of MSW are either biodegradable or recyclable with relatively modest effort. For example, glass, paper, and metals have been recycled for decades. By contrast, the recycling of plastics is more difficult partly because there are so many different kinds of plastic and partly because some plastics (thermosetting plastics) cannot he remelted, an important hrst step in any recycling process. 

Biodegradable materials are created specifically with recyclability or disposal in mind. Recycling techniques for post-consumer biodegradable plastic products have two important features, which distinguish them from conventional polymers their biodegradability or compostability and the use of renewable resources in their manufacture. 

The certification programme for compostable biodegradable plastic products has been set up by experts responsible for waste recycling and compost quality assurance. The members are as follows ... 

Plastic bags have a high profile in the land waste stream as these materials are not currently accepted in the kerbside collection and recycling systems. Biodegradable plastics present an attractive alternative to polyethylene in these applications. 

Renewable raw materials can contribute to the sustainability of chemical products in two ways (i) by developing greener, biomass-derived products which replace existing oil-based products, e.g. a biodegradable plastic, and (ii) greener processes for the manufacture of existing chemicals from biomass instead of from fossil feedstocks. These conversion processes should, of course, be catalytic in order to maximize atom efficiencies and minimize waste (E factors) but they could be chemo- or biocatalytic, e.g. fermentation [3-5]. Even the chemocatalysts themselves can be derived from biomass, e.g. expanded com starches modified with surface S03H or amine moieties can be used as recyclable solid acid or base catalysts, respectively [6]. 

Mater-Bi . [Novamont N. Am.] Thermoplastic horn natural, renewable raw materials recyclable, combustible, and biodegradable plastic for pkg. films, bags, 6-pack yokes, disposable diapers, hospital and sanitary prods. 

Selke, S. Plastics Recycling and Biodegradable Plastics, In Modern Plastics Handbook, Harper, C., Ed., McGraw-Hill, New York (2006) pp. 8.1-8.109... 

In 1977, Tokiwa and Suzuki reported that some lipases, which are extracellular enzymes that usually cleave esters in oils and fats, are also able to attack ester bonds in some aliphatic polyesters and can depolymerize such materials [38]. Aliphatic polyesters, however, exhibit only limited useful properties for many applications. Aromatic polyesters, such as PET and PBT, which are widely applied because of their excellent properties, are not attacked by hydrolytic enzymes. This led to the development of aliphatic-aromatic polyesters as biodegradable plastics that present a compromise between biodegradability and material properties [39]. Recently, however, Muller et al. [40] have isolated a hydrolase (TfH) from Thermofibida fusca which is able to depolymerize the aromatic polyester PET at a high rate in contrast to other hydrolases such as lipases. They have demonstrated for the first time that commercial PET can be effectively hydrolyzed by an enzyme at a rate that does not exclude a biological recycling of PET. The effective depolymerization of PET with the enzyme TfH will result in water... 

Coal slurry feeding into pressurized gasification reactors Optimisation of rotor geometries in mbber mixers Extrasion cooking of food and feed Closed loop quality control in extrasion Twin-screw extmders for recycling Compounding of biodegradable plastics... 

Torikai A, Kato H, Fueki K, Suzuki Y, Okizaki A, Nagata M (1993) J AppI Polym Sci 50 2185 Andrady AL, Accelerated environmental exposure. Laboratory testing, and recyclability study of photo/biodegradable plastics . Final Report to USEPA under Contact 68-02-4544 Task 11-60. January 1991. 

Roediger Agencies cc. Polymer Science Building Analytical Laboratory De Beer Street, Stellenbosch 7600 6th March 2012 Recycling Report on d2w oxo-biodegradable Plastics ... 

Why are biodegradable plastics only a partial solution to our recycling problem ... 

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