UV-Irradiated Biodegradability of Ethylene-Propylene Copolymers, LDPE, and I-PP in Composting and Culture Environments Jitendra K. Pandey and R. P. Singh* ,² Polymer Chemistry Division, National Chemical Laboratory, Pune-411008, India Received March 5, 2001 The biodegradability of UV-irradiated films of ethylene-propylene copolymers (E-P copolymer), isotactic polypropylene (i-PP), and low-density polyethylene (LDPE), was measured in composting and culture environments by monitoring the variations in intrinsic viscosity [η], weight loss per surface area, surface changes by SEM, colonization of fungus, chain scission, and evolution of hydroxyl and carbonyl groups by FT-IR spectroscopy. Photooxidation was used as a pretreatment for biodegradation of polymers. A systematic decrease in intrinsic viscosity [η] and increase in carbonyl/hydroxyl regions in FT-IR spectra was found from 0 to 100-h irradiated samples. The degradation rate was strongly dependent on the composition of copolymers and markedly increased with decrease in ethylene content. Important surface erosion was detected after composting by SEM for longer UV-irradiated samples. It was estimated that chain-scission was directly related to photoirradiation. Introduction Synthetic carbon-based polymers are mostly inert toward microorganism in the initially produced form. The long-term properties in the synthetic and natural polymers have attracted more interest during the past decades as environmental concerns have been increased, due to the accumulation of municipal solid waste, generated by the commodity polymers. It is well-known that some traditional polymers such as polyethylene and polystyrene undergo very slow biodegrada- tion, 1,2 and it is also known that extremely useful polyolefins also can be degraded through the introduction of keto/ carbonyl species in both the stabilized 3 and unstabilized samples. 4 Although several kinds of formulations filled with starch as biodegradable natural fillers 5-7 and starch with pro- oxidants 8-10 have been well documented in order to achieve biodegradability in synthetic polymers, there has been no real significant discussion on short term UV-irradiated biodegradability of “additive-free” E-P copolymers whereas E-P copolymers have a range of useful properties from thermoplastics to soft elastomers, depending upon the relative composition of the two monomers and manner of their entanglement. Photooxidation of these copolymers has already been well reported. 11,12 Scott et al. 13,14 have concluded that microbial action on the polymers is a secondary process and bioassimilation is related to oxygenated products. Albertsson et al. 15,16 investigated that biodegradation can be initiated by photooxidation where carboxylic acid parts, generated through Norrish type-I and II mechanisms during the oxidation process, can be consumed by microbial attack. The present investigation is intended to study the extent and effect of short-term photoirradiation on the biodegradability of i-PP, LDPE, and E-P copolymers. Experimental Section Materials. Commercial samples of isotactic polypropylene (i-PP, Koylene S 30330) and low-density polyethylene (LDPE, Indothene 16 MA 400) were obtained from M/s Indian Petrochemicals Corp., Baroda, India, and heterophasic ethylene propylene copolymers (EPF 30R, EPQ 30R) were obtained from M/s Himont Italia. The molar percentages of ethylene content in copolymer samples were 7.7 and 15.1, for EPF-30R and EPQ-30R, respectively. These polymer pallets were purified by dissolving in refluxing xylene under nitrogen atmosphere. The solution was precipitated with methanol, filtered, and dried at 50 °C in a vacuum oven. These samples were assumed to be additive free and were designated as purified samples. Preparation of Films and UV Irradiation. The method of sample preparation (∼100 μm thickness) has already been reported. 17 The photoirradiation of the films was carried out in a accelerated weathering chamber (SEPAP 12/24) at 60 °C. The chamber consists of (4 × 400 W) medium-pressure mercury vapor lamps supplying radiation longer than 290 nm. The details of the equipment are described elsewhere. 18 Viscosity Measurements. The method of viscosity mea- surement has already been described 19 where the intrinsic viscosity [η], dL/g, was measured by using successive dilution of only one solution (concentration 0.2 wt %) at 135 ( 5 °C in Decaline. The error due to expansion of flask is negligible as preheated flask and pipet (140 °C) were used to mix the solvent into an Ubbelohde viscometer. Incubation in Compost. The biodegradability tests were performed in a laboratory scale composter, and the size of films was 5 × 5 cm. The constitution 20 of solid waste mixture (compost) used for biodegradability testing of photooxidized samples was as follows (dry weight): 40.8% shredded leaves, 11.4% cow manure/dung, 15.8% newspaper and computer ² E-mail: singh@poly.ncl.res.in. 880 Biomacromolecules 2001, 2, 880-885 10.1021/bm010047s CCC: $20.00 © 2001 American Chemical Society Published on Web 06/26/2001