Abiotic degradation products from LDPE with starch + pro-oxidant, LDPE with starch only and pure LDPE were determined as a step towards establishing products resulting from environmental degradation. The samples were subjected to thermal ageing in water at 95°C for 6 weeks or alternatively pre-heated and subsequently immersed in aqueous environments at ambient temperature for 10 months whereafter the water phase was analyzed for degradation products. Altogether over 50 degradation products were identified by GC-MS, mainly ketones, alcohols, aldehydes, lactones and carboxylic acids, the last being most represented. The amount of degradation products formed from the different samples correlated to their molecular weight reductions as measured by SEC but was also dependent on the permeability of the sample, i.e. its ability to allow formed degradation products to diffuse out to the surrounding environment. The addition of both starch and pro-oxidant significantly increased the susceptibility to degradation, while the addition of starch alone gave a noticeable but smaller increase.
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...
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