Degradation of enhanced environmentally degradable polyethylene in biological aqueous media: Mechanisms during the first stages

Abstract

SYNOPSISDegradation of LDPE films containing a biodegradable starch filler and a pro-oxidant formulation was performed in aqueous media inoculated with bacteria or fungi at ambient temperatures for 1 year. The samples were characterized with the aim of elucidating the mechanisms that occur during the first stages and that are responsible for initiating the degradation of the LDPE matrix. Two interactive mechanisms were observed The basal salt medium (water containing trace elements ) triggered autoxidation of the pro-oxidant through decomposition of trace hydroperoxides, which, in synergistic combination with biodegradation of the starch, eventually initiated autoxidation of the LDPE matrix as monitored by chemiluminescence (CL) , differential scanning calorimetry (DSC) , and confocal scanning laser microscopy (CSLM) . The length of the induction period was dependent on the sample thickness and on the activity of the microbiological system. Up to 48% of the starch was consumed during the first year as revealed by polarized-light microscopy. I NTRO DU CTlO NRelatively inert synthetic polymers, e.g., polyethylene, can be rendered enhanced degradable by introducing prodegradant additives into the matrix. These additives provide the plastic materials with different potential degradation mechanisms that can be triggered upon environmental exposure. Several techniques in which starch is used as a biodegradable additive have been patented since the 1970s. The main problem associated with the use of starch as a filler is its hydrophilic nature and the generally hydrophobic nature of the polymer matrix. The starch particle size limits the amount to be incorporated if the composition is to be blown to a thin film, but this is not such a limitation for sheets or injection-molded articles. The starch can be used in * To whom correspondence should be addressed. its natural granular form, in the gelatinized form, or in the destructurized form. Griffin has invented formulations based on granular starch. In his early patents,lS2 the starch was surface-treated in order to improve the compatibility between the starch and the synthetic polymer matrix, whereas in a later patent,3 the starch is used together with a thermoplastic elastomer that functions both as a compatibilizer and as a n autoxidant.Willett4 presented in a recent patent a composition that includes granular starch and a copolymer carrier resin. Starch in its gelatinized form is utilized in formulations developed by Otey and W e~t h o f f .~'~ Together with the complexing agent, ethylene acrylic acid copolymer (EAA) and ammonia, it is possible to incorporate up to about 60% gelatinized starch in blown films. Bastioli et al.7 patented a technology based on destructurized starch. By combining synthetic thermoplastic polymers and copolymers and destructurized starch to which a boron compound has been added, a material is obtained that can be used as film, sheet, or fiber. We have studied polyethylene (LDPE) in which corn starch and pro-oxidants have been included in the...

Rapid test methods for analyzing degradable polyolefins with a pro-oxidant system

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Effects of synthesis conditions on chemical structures and physical properties of copolyesters from lactic acid, ethylene glycol and dimethyl terephthalate

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