Arlette Daro

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.

Photodegradation of polyethylene: comparison of various photoinitiators in natural weathering conditions

Thin polyethylene films containing various additives as photoinitiators have been photooxidized in natural weathering conditions and under accelerated conditions using xenon radiation. The photoinitiators include iron carboxylate, allyl ether and ester and various aryl- and aralkylketones. Main chain scission is the dominant process in natural weathering conditions. The formation of cross-links is nevertheless detected by GPC in all cases except with iron carboxylate. Fragmentation of the films is observed at high doses in all cases. When xenon radiation is used, cross-linking is much more important, as indicated by the broadening of the MWD and the lowering of the OD at 1715 cm−1. The difference between photodegradation by solar light and by xenon irradiation was assigned to a temperature effect and interpreted using the classical spontaneous mechanism of polyethylene degradation.

Formation of polymeric pigments in the presence of bacteria and comparison with chemical oxidative coupling - II. Catabolism of tyrosine and hydroxyphenylacetic acid by Alcaligenes eutrophus CH34 and mutants

Abstract The formation of polymeric pigments using bacteria was investigated to produce new polymers. Polymeric pigments are formed from mutant strains of Alcaligenes eutrophus which are not able to open the aromatic ring (tyu − ) but transform tyrosine into p -hydroxyphenylacetic acid. This compound is then hydroxylated into homogentisic acid which undergoes oxidative coupling into polymeric pigments. Another carbon source is required to allow bacterial growth. The rate of disappearance of the initial product (either tyrosine or p -hydroxyphenylacetic acid) and the rate of formation and disappearance of intermediates were studied by ultraviolet (UV) absorption spectroscopy and high-performance liquid chromatography (HPLC). Pigment formation was monitored by gel permeation chromatography (GPC). The pigment was isolated and characterized by UV and infrared (IR) absorption spectroscopy, nuclear magnetic resonance (NMR) and elemental analysis. It was shown to have a complex structure involving aromatic and aliphatic saturated and unsaturated structures. Nitrogen is incorporated by condensation with amino acids and other nitrogen-containing molecules excreted by the bacteria. For comparative purposes, chemical oxidative coupling of homogentisic acid in the absence of bacteria was performed at pH 8.5 and 11.5 in the presence of oxygen. A badly defined but different mixed aliphatic-aromatic structure was isolated. The role of the bacteria in the different steps of transformation of the initial product is discussed.

Water vapour transport in polyethylene oxide/polymethyl methacrylate blends

Abstract 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

Degradation of polymer blends: Part V—Compatibility and photo-oxidation of LDPE-LLDPE blends in natural weathering conditions: A differential scanning calorimetry study

Abstract Thin films of extruded-blown LDPE-LLDPE blends have been photo-oxidized in natural weathering conditions in the absence and in the presence of a photo-initiator. DSC has been used to study the compatibility of the components of the blend and the changes of morphology induced by the degradation processes. Changes in the shape of the curves, increase in the heat of fusion and shift of T max have been observed and attributed to a reorganization of the oriented amorphous-crystalline structure due to physical ageing and to the decrease of molecular weight and branching.

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

Abstract 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.

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

Abstract 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 industial 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.

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

Abstract 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 CO 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.

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

Abstract 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% H 2 SO 4 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.

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

Abstract 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.