Biodegradation of thermally oxidized polyethylene

The biodegradability of thermally oxidized polyethylene (PE) has been studied in various conditions: (1) on solid agar in the presence of a suspension of mixed spores of four fungi (Aspergillus niger, Penicillium funiculosum, Paecilomyces variotii and Gliocladium virens); (2) in three composting units differing in temperature, moisture content and the nature of the composted materials; and (3) in liquid medium (respirometric flasks) in the presence of three Streptomyces strains (badius, setonii, viridosporus) or of a suspension of microorganisms from compost. Qualitative evidence of bioassimilation of the oxidized PE films was obtained with fungi and in composts. Coverage of the film surface by fungi increases as the molecular weight of the PE is decreased and attains 60% when the initial Mn lies between 1500 and 600. With fungi and in compost, important surface erosion was detected by SEM for samples with initial Mn around 1000. Important changes were also observed by FTIR, DSC and GPC. This last method revealed in all cases the formation of a high molecular weight fraction that was not present before incubation with microorganisms and a shift of the whole curve toward higher molecular weight. This is evidence of chain condensation probably due to purely thermal reaction at the low partial pressure of O2 prevailing in the industrial composting units used in this work. It is probably accompanied by bioassimilation of the low molecular weight fraction. Quantitative information can be obtained by a respirometric method. For incubations performed in liquid medium in the presence of a suspension of microorganisms from compost, biodegradation was important when substrate concentration was very low (≈ 0.006%). Despite the presence of unavoidable large errors in these conditions, oxygen uptake was evident and biodegradation of the low molecular weight fraction of the sample was clearly demonstrated. © 1995.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Water vapour transport in polyethylene oxide/polymethyl methacrylate blends

Polyethylene oxide/polymethylmethacrylate (PEO/PMMA) blend films have been obtained by evaporation of CHCl3 solutions. The miscibility of the components has been studied by optical microscopy and by differential scanning calorimetry (DSC). The 10/90 blend is miscible while the other compositions are biphasic in the amorphous part of the film, the components being either immiscible or partly miscible. The permeability to water vapour could be interpreted using the conventional series and parallel models for non miscible blends and the logarithmic mixing rule for miscible blends on the condition that only the amorphous phase is considered to be effective in the transport properties. In the 90/10 and 80/20 blends and in the pure components, the sorption isotherms are of the Flory-Huggins type. Sorption kinetics indicates that the permeant mobility and polymer segment relaxation rate are of the same order of magnitude (0.5 < n < 1). Zimm and Lundberg clustering functions were tentatively evaluated and the engaged species induced clustering (ENSIC) model applied to PEO, PMMA, their 80/20 blend and other polymers for comparative purposes. © 1999 Elsevier Science Ltd. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Degradation of polymer blends-III. Radiolysis of blends of poly(methyl methacrylate) with styrene-acrylonitrile copolymers

The radiolysis at low dose of poly(methyl methacrylate) (PMMA), styrene-acrylonitrile copolymers (SAN) containing 36 wt% acrylonitrile and their blends, have been studied in vacuo and in air. Study of the molecular weight distributions of PMMA and SAN by gel permeation chromatography indicates that the mechanisms of degradation of both components are modified in the blend. The G-value for main chain scission of PMMA is lower in the blend than in pure PMMA and decreases with increasing SAN content. Main chain scission and crosslinking occur simultaneously in pure SAN and in the blends. The latter process is predominant in pure SAN irradiated in vacuo while the former dominates in the other cases. The G-value for chain scission of SAN increases with increasing PMMA content. This interactive degradation process is discussed in relation to the mechanism previously proposed for the radiolysis of PMMA. © 1989.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Biodegradation of polyester-amides using a pure strain of micro-organisms or papain. II. Polymer

Two quantitative methods have been used to follow the biodegradation of a polyester-amide containing L-phenylalanine units in the presence of a pure strain of micro-organisms isolated from an industrial compost for household refuse. Weight loss and oxygen consumption have been measured as a function of time. They respectively monitor the main chain hydrolysis into small soluble fragments and the mineralization of these fragments. The residual solid and the soluble fractions have been characterized by GPC, FTIR and NMR. Specific hydrolysis has been observed at the ester site. It has also been shown that the rate of mineralization of the polymer is limited by the rate of assimilation of the fragments. When pure enzymes are the biological agents, the hydrolysis step only occurs. The hydrolysis products identified in the presence of papain are the same as those released in the presence of the micro-organisms used in this work.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Degradation of polymer blends: Part VII. Photo-oxidation in natural weathering conditions of polyethylene containing styrene-butadiene or styrene-isoprene copolymers

The photo-oxidation of a polyethylene (PE) matrix can be initiated by a dispersed unsaturated phase. Photo-initiation of PE degradation is related to the diffusion of small fragments of the easily degraded dispersed phase into the continuous phase; the rate of chain scission of the dispersed phase is thus rate determining. As a consequence, unsaturated polymers which crosslink are very poor photoinitiators of PE degradation. In contrast, polyisoprene blocks which do not crosslink but degrade with high efficiency are very good photo-initiators. Diffusion of these small fragments implies that the continuous phase of the phase separated copolymer is rubbery. Copolymers with a high styrene content are thus disadvantageous even if chain scission of the unsaturated part is efficient. The concentration of antioxidant in the unsaturated phase must also be minimal. Indeed, the anti-oxidants inhibit the formation of hydroperoxides in the PE phase during processing even if they have a low molecular weight and rapidly diffuse out of the exposed films. The type of fragmentation of the film, which occurs at high dose for some of them, is governed by the morphology of the blend. The heavily degraded dispersed phase has then completely lost its mechanical properties. If elongated co-continuous phase or long fibrils are present, they can be considered as elongated voids where fracture is initiated and propagated giving long narrow ribbons. Isotropic fragmentation can only be obtained if the photo-initiating dispersed polymer is present as small spheres and if the previously cited conditions are present. © 1994.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Biodegradation of polyester-amides using a pure strain of micro-organisms or papain. I. Model compounds

Various amides and model compounds derived from phenylalanine and succinic acid have been degraded in abiotic and biotic conditions as a first step in the study of the mechanism, rate and extend of mineralization of polyesteramides. These compounds have been incubated in the presence of pure strains of micro-organisms isolated from an industrial compost for household refuse. The rate of substrate disappearance has been measured by UV absorption spectroscopy or determined from oxygen consumption data as a function of time. Attention has been paid to the configuration of the amino-acid and to the nature of the terminal groups. It has been shown that the decay of such compounds is due to the presence of amino-acid and not to the nature of the end groups. N-Succinyl-L-phenylalanine HOOC-CH(CH2-Ph)-NH-CO-(CH2)2-COOH has been demonstrated to be very rapidly mineralized while the corresponding dimeric compound N,N′-Succinyl-L,L-phenylalanine HOOC-CH(CH2-Ph)-NH-CO-(CH2)2-CO-NH-CH(CH2-Ph)-COOH was much more slowly degraded, most probably because of its larger size. The difference between the biodegradation processes mediated by micro-organisms and by isolated enzymes is emphasized.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Utilization of waste cellulose-I. Gamma irradiation and hydrolysis with dilute sulphuric acid

The yield of glucose, levulinic acid and furaldehyde derivatives as a function of the time of hydrolysis have been determined at 190° in 1 or 0.1% H2SO4 for non-irradiated and irradiated cellulose samples. Various additives, swelling agents and decrystallization techniques were used to improve either the accessibility or the yield of irradiation-induced chain scission. Results at lower temperatures of hydrolysis and with phosphoric acid as hydrolysing medium are also reported. © 1980.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Formation of polymeric pigments from syringaldehyde in the presence of bacteria. Comparison with chemical oxidative coupling

The formation of polymeric pigments from hydroxy-substituted benzoïc acid in the presence of some strains of Pseudomonas putida was investigated as a possible route to new aromatic polymers. The rate of disappearance of aromatic compounds such as syringaldehyde and its degradation products syringic acid and 3-O-methylgallic acid have been measured. The structure of the pigment has been investigated by GPC, u.v. and FTIR spectroscopy, NMR and elemental analysis. It has been compared with that of the polymeric pigments obtained by chemical oxidative coupling in the absence of bacteria. The bacterial pigments were found to be of badly defined structure different from that of the chemical pigments, and probably similar to humic acids; indeed amino acids are incorporated in the polymer chain. The role of the bacteria at the various steps of the metabolization of the initial aromatic compounds and of pigment formation is discussed. © 1991.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Degradation of polymer blends. Part VI: Photo-oxidation of polyethylene containing SIS triblock copolymers

Two aspects of the problem have been investigated: the initiation of the degradation of the polyethylene phase by the very rapidly oxidized unsaturated block, and the deterioration of the mechanical properties of the blend which finally leads to the spontaneous fragmentation of the film. The first aspect involves the identification and the quantitative determination of the functional CO and OH groups formed in each phase as a function of the irradiation time. The molecular weight of the polyethylene phase was found to decay and to be accompanied by a narrowing of the molecular weight distribution which indicates that its degradation is initiated homogeneously. Concerning the second aspect, two types of spontaneous fragmentation of the films have been identified and related to the morphology of the blend. The first involves initiation and growth of cracks parallel to the direction of extrusion in the SIS phase when SIS is dispersed as a continuous fibrillar structure. The second concerns blends with a low SIS content dispersed as small spheres. Cracks are then initiated at the heavily degraded SIS sites but propagate isotropically in all directions through the polyethylene phase. Such isotropic fragmentation is also observed when low molecular weight photo-initiators are used instead of the unsaturated copolymer. © 1992.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Degradation of polymer blends-IV. Natural weathering of blends of low density with linear low density polyethylene

The molecular weight distribution of low density polyethylene-linear low density polyethylene blends, photo-oxidized in natural weathering conditions, has been studied. The exposure conditions cover different periods of the year from May to December, and so a broad range of intensities, total incident energy and weather. A good correlation between the results corresponding to these different conditions has been obtained using the global incident energy and a simple model for its spectral distribution. Main chain scission is the main process but some crosslinking has also been detected. Preferential degradation of LLDPE could not be observed. © 1990.SCOPUS: ar.jinfo:eu-repo/semantics/publishe