S

3.l

a ND Not determined.

a ND Not determined.

Scheme 2. Oxidation of polyvinyl alcohol.

Scheme 2. Oxidation of polyvinyl alcohol.

which the products were identified as an alcohol and a carboxylic acid. This was subsequently proved in error and the Suzuki mechanism is now widely accepted for those microbes evaluated in his work.

The proposed biodegradation mechanism is supported by the rapid biodegradation of the polyketone obtained by the chemical oxidation of polyvinyl alcohol [47-49] shown in Scheme 2.

Other bacterial strains identified as biodegrading polyvinyl alcohol include Flavobacterium [50], Acinetobacter [51], and many others as well as fungi, molds, and yeasts [52]. Industrial evaluations at DuPont [53] and Air Products [54] indicate that over 90% of polyvinyl alcohol entering wastewater treatment plants is removed in those locations and hence no environmental pollution is likely.

Polyvinyl acetate, the precursor for poly(vinyl alcohol), hydrolyzed to less than 70%, is claimed to be nonbiodegradable under conditions similar to those that biodegrade the fully hydrolyzed polymer [55]. There are several packaging applications of partially hydrolyzed polyvinyl acetate whereby the rate of biodegradation is retarded deliberately to give an acceptable use life for the package. These include hot water disposable films and fabrics [56], body wrappings for mortuary use [57], moldings [58], and microfibrils for synthetic paper pulp [59].

Blends of poly(vinyl alcohol) with polycaprolactone [60] and ethylene-maleic anhydride copolymers [61] are also used in biodegradable packaging, though the latter blend is unlikely to be biodegradable.

Other interesting articles and reviews include polyvinyl alcohol composites, generally [62], with proteins [63-65], starch [66], chitosan [67], simple sugars [68], and a Baeyer Villiger oxidation [95] (Scheme 3) of a an ethylene-vinyl alcohol copolymer to produce a biodegradable polyhydroxypolyester.

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