J. Lemaire

Environmental biodegradation of polyethylene

The degradation of a commercial environmentally degradable polyethylene was investigated in two stages. Firstly by abiotic oxidation in an air oven to simulate the effect of the compost environment and secondly in the presence of selected microorganisms. Initial biofilm formation was followed by fluorescence microscopy and the subsequent growth of bacteria on the surface of the plastic was observed by scanning electron microscopy (SEM). It was observed that microbial growth occurred on the presence of PE samples that had been compression moulded to thick sections but had not been deliberately pre-oxidised. Molecular enlargement and broadening of molecular weight distribution occurred after preheating in air at 60 C but not at ambient temperatures but colonisation of microorganisms occurred on all samples. Erosion of the film surface was observed in the vicinity of the microorganisms and the decay of oxidation products in the surface of the polymer film was measured by FTIR measurements and was found to be associated with the formation of protein and polysaccharides, attributable to the growth of the microorganisms. # 2003 Elsevier Ltd. All rights reserved.

Photooxidation and biodegradation of commercial photodegradable polyethylenes

Abstract Representative samples of commercial photodegradable polyethylenes have been examined with respect to rate and extent of oxidation as measured by carbonyl (carboxylic acid and ester) formation, molar mass reduction and ability to support microbial growth when used as the only source of carbon. An ethylene-carbon monoxide (E/CO) copolymer was found to photodegrade most rapidly but to biodegrade most slowly. An antioxidant iron dithiocarbamate photodegradable polyethylene (Scott-Gilead) and a starch filled iron catalysed polyethylene were shown to produce more carboxylic acids during photooxidation than did the E/CO polymer, resulting in more rapid microbial growth. After removing the microorganisms, the surface of the oxidised polyethylene was found to be eroded with substantial reduction in sample thickness, while the molar mass of the polymer remained unchanged. It is shown that the microbial exo enzymes are able to recognise relatively high molar mass carboxylic acids and remove them from the surface of the polymer under conditions where water is not able to remove them by leaching. From this it is concluded that the oxidation products of oxidised polyethylene are unlikely to present a threat to the environment and that by conversion to biomass they contribute to the fertility of the soil. Abiotic iron catalysed photo- or thermooxidation is the rate-limiting step in the bioassimilation process. It is concluded that abiotic oxidation must precede the onset of biotic degradation, which is shown to occur readily at Mw as high as 40 000. Bioassimilation involves further oxidation catalysed by transition metal ions and probably by exo enzymes from the microorganisms.

Photo-, thermal and natural ageing of ethylene-propylene-diene monomer (EPDM) rubber used in automotive applications. Influence of carbon black, crosslinking and stabilizing agents

Abstract Photoageing at λ>300 nm (SEPAP, WOM, Xenotest), natural ageing (Bandol) and thermal ageing (100 and 150°C) were performed on ethylene–propylene–diene monomer (EPDM) rubber designed for automotive applications. The thermal ageing study was concentrated on a formulation designed for engine applications (peroxide crosslinked) and photoageing concerned a formulation for outdoor applications (sulfur vulcanized). Analyses were based both on infrared spectroscopy (surface analysis and profile by successive abrasion) and on physical properties analysis (dynamic mechanical thermal analysis (DMTA) and tensile tests). Both methods were complementary to describe the two competitive phenomena involved in ageing of elastomers (oxidation and crosslinking).

Photo and thermal decomposition of iPP hydroperoxides

Products resulting from the photo and thermal decomposition under vacuum of a pre-oxidized isotactic polypropylene (iPP) containing a known content of hydroperoxide have been examined. In contrast to the case of polyethylene, few products were retained in the polymer matrix. Detailed analysis of the gas phase was performed by gas chromatography, Fourier transform infra-red spectroscopy and mass spectrometry. It was revealed that about 70% of the hydroperoxides were converted into gaseous products such as acetone, acetic acid and methanol. Mechanisms for their formation are suggested, and the consequences of such a phenomenon for the evaluation of ageing in PP are discussed.

Oxidation of rubbers analysed by HATR/IR spectroscopy

Abstract The presence of large amounts of carbon black in number of industrial applications of rubbers makes their analytical study by infrared spectroscopy difficult, particularly their chemical evolution upon ageing . The present paper reports the use of a Horizontal Attenuated Total Reflectance accessory equipped with a germanium crystal. HATR (Ge) /FTIR analysis of both thermal-and photo-oxidations of EPDM, CR and NBR were first validated by conventional transmission spectroscopy in the absence of carbon black. Then, HATR (Ge) was used with fully formulated rubbers with the aim of studying their long term behaviour. Influence of temperature, UV exposure, carbon black or stress as well as the oxidation profile across the materials or the identification of carboxylic acids/carboxylates groups have been examined.

Photo-oxidation of polydimethylsiloxane oils: Part I—Effect of silicon hydride groups

Abstract Photo-oxidations at wavelengths longer than 300 nm of polydimethylsiloxane (PDMS) oil with various contents of SiH and different configurations (H inside the chain (2·2 H equivalent kg−1) or at the end of the chain (1·2–4 and 15 H equivalent kg−1)) have been examined. Hydroperoxides groups are primarily formed on photo-oxidation and result from radical attack on the SiH bond. These photo-unstable and thermally unstable hydroperoxides are transformed essentially into silanols, absorbing at 3300 cm−1. Oxygen consumption measurements suggest a 1 1 stoichiometry between SiH and oxygen consumed, whereas the quantitative determination of SiOH reveals a deficit, mainly as a result of a condensation reaction which leads to a significant increase in viscosity.

Long-term behaviour of oil-based varnishes and paints 4. Influence of film thickness on the photooxidation

Photooxidation of dried linseed oil films with various thicknesses is analysed. Distributions of the photoproducts resulting from photooxidation are determined by photoacoustic IR spectrometry and by micro-IR spectrometry. Oxidation profiles are observed and it is shown that oxidation can extend up to 300 μm. This result is confirmed by micro-fluorescence analysis of the photo-oxidized sample. On the other hand, the cross-sectional analysis of the exposed films suggest that crosslinking occurs in the oxidized layers, which could prevent some of the low molecular weight products formed from migrating from the solid film towards the surrounding atmosphere.

A Comparative Study of the Degradability and Recyclability of Different Classes of Degradable Polyethylene

Abstract Abiotic degradation of representative samples from available commercial photo(bio)degradable polyethylene films was examined with respect to the rate and extent of degradation, oxidation products, and changes in molecular weight both during outdoor exposure and in laboratory photoaging devices with different accelerating factors. Although the rate of photoxidation was found to depend on the type of degradation system used, all the samples showed rapid rate of carbonyl formation with concomitant reduction in molecular weight and mechanical properties on exposure to UV light. The photofragmented polymers were shown to be much more hydrophilic in nature compared to the unoxidized analogues, and photofragments of all samples were found to contain high levels of low molecular weight (bioassimilable) carboxylic acids and esters. Recycling behavior of virgin polyolefins, both as homopolymers and heterogenous polymer blends, which contained 10% of nonoxidized and photooxidized photo(bio)degradable plasti...

Photooxidation of polydimethylsiloxane oils and resins. IV—effect of phenyl groups

Abstract Photooxidations at wavelengths longer than 300 nm of polydimethylsiloxane (PDMS) containing various contents of MePh and Ph 2 groups have been examined, both in the case of linear and crosslinked silicones. FTIR, UV and fluorescence spectroscopies reveal a slow photooxidation involving both scission and oxidation of the phenyl ring. No significant yellowing can be associated with the presence of the phenyl ring except in the case of short wavelength irradiation.

Effect of absorbing pigments on the photo-oxidation and mechanical property changes in ethylene-propylene copolymers

Abstract The present paper reports observations on the ZnO and TiO 2 photo-catalyzed oxidations of an amorphous ethylene-propylene copolymer containing 75% w/w of ethylene. Hydroperoxide and carbonyl group formation occurs with subsequent changes in the mechanical properties. Differences between ZnO and TiO 2 are observed particularly in the hydroperoxidation processes. A reinforcing effect due to the photo-active pigments can account for the differences in mechanical properties, even at high carbonyl content.