Christiane David

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.

Biodegradation of polycaprolactone and its blends with poly(vinylalcohol) by micro-organisms from a compost of house-hold refuse

Abstract Polycaprolactone (PCL), poly(vinylalcohol) (PVAl) and their blends have been incubated in the presence of a pure strain of micro-organisms isolated from an industrial compost for house-hold refuse. In the conditions used in this work, pure polycaprolactone (PCL) films are completely assimilated over periods of 600–800 h. Pure PVAl is not degraded even for much longer exposure times. Unexpectedly, the blends, even PCL rich, are not altered (neither weight loss, oxygen uptake nor micro-organism growth) in the presence of these micro-organisms. It has been shown that inactivation of the strain by PVAl does not occur and is not responsible for this. PVAl, even when present in small amounts in the incubation medium, adsorbs on the surface of PCL or blend films; PCL is then inaccessible to micro-organisms.

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.

Energy transfer in polymers—V. Singlet and triplet energy transfer in polyacenaphthylene☆

Abstract The emission spectra of polyacenaphthylene (PAcN) and polyvinylnaphthalene (PVN) films and solutions have been compared at room temperature and 77°K. In organic glasses at 77°K, normal fluorescence and phosphorescence are observed for both polymers. Quenching of PAcN phosphorescence by piperylene in a glass obeys a Stem-Volmer type equation; the slope of the straight line is identical to that reported for PVN in the same conditions. In solution at room temperature, the ratio of excimer to normal fluorescence yields is 1 · 3 for PAcN whereas it is 12 · 6 for PVN. No luminescence other than excimer fluorescence is emitted by polymer films at room temperature and 77°K. The intensity of that emission decreases in the presence of benzophenone because of singlet energy transfer to the additive. The efficiency of the transfer is identical for PAcN and PVN (Forsters R o = 15 A ). The results are discussed according to a general kinetic treatment and in terms of the mobility of the chromophore side groups.

Biodegradation of polycaprolactone by micro-organisms from an industrial compost of household refuse

Abstract The rate of biodegradation of polycaprolactone samples, hydroxy- ( M n = 4000 and 37 000) and methoxy- ( M n = 4000) terminated, by mixed cultures of micro-organisms from a suspension of compost, and by a pure culture of an actinomycete isolated from compost, has been monitored by the measurement of oxygen consumption. The dependence on the molecular weight of the polymer suggests that initiation of the degradation occurs in the vicinity of chain ends. The effect of the sample crystallinity and of the methoxy termination is discussed.

Intermolecular interactions in blends of poly(vinyl alcohol) with poly(acrylic acid)-1. FTIR and DSC studies

Abstract The i.r. spectra and the melting behaviour of blends of poly(vinyl alcohol) (PVAI) and poly(acrylic acid) (PAA) have been studied as a function of blend composition. Replacement of H-bonding interactions in pure PAA and PVAI by intermolecular interactions has been proved by analysis of the OH and CO stretching region in the i.r. spectra. The efficiency of these intermolecular interactions results in a rapid decrease of the crystallinity of PVAI when the PAA content increases and its complete supression when the PAA content equals or exceeds 50 wt%. A very high negative value has been obtained for the interaction parameter by measurement of the melting point depression.

Intermolecular interactions in blends of poly(vinyl alcohol) with poly(acrylic acid): 2. Correlation between the states of sorbed water and the interactions in homopolymers and their blends

Abstract Water-polymer interactions have been studied by d.s.c. and FT i.r. in water vapour-saturated poly(vinyl alcohol), poly(acrylic acid) and their blends before and after thermal treatment (0.5 h at 180°C). The 3600-3000 cm −1 (OH stretching), 1800-1700 cm −1 (CO stretching) and 1700-1600 cm −1 (HOH bending) regions have been used. Water-polymer and polymer-polymer interactions which are respectively formed and destroyed in the presence of water have been identified. For this purpose, subtraction of the spectrum of dry samples from the spectrum of water-saturated films has been performed. Changes in crystallinity of poly(vinyl alcohol) were also measured by FT i.r. D.s.c. has been used to confirm the strength of water-polymer interactions and to demonstrate changes in the miscibility of polymer components.

Energy transfer in polymers—I. Triplet-triplet transfer in solid polyvinylbenzophenone-naphthalene system

Abstract Energy transfer has been shown to occur from triplet polyvinylbenzophenone to naphthalene by an exchange mechanism at liquid nitrogen temperature. The radius of the Terenin “critical sphere” is much larger for the polymer containing naphthalene (29A) than for mixtures benzophenonenaphthalene in organic glasses (11 A). The results are interpreted in terms of energy migration in the polymer according to Voltz theory.

THE PHOTO-OXIDATION OF POLYMERS. A COMPARISON WITH LOW MOLECULAR WEIGHT COMPOUNDS

Abstract The photo-oxidation of polymers involves different steps in which their reactivity is different from that of low molecular weight compounds. This is mainly due to the close vicinity of reactive groups in polymers and to the rigidity of the matrix. As a consequence, transfer of energy has a major role in the initiation of the photo-oxidation of most polymers on exposure to sunlight. It results in the sensitized decomposition of neighbouring hydroperoxide groups which, however, produce free radicals and thus initiate the oxidation less efficiently than model compounds in fluid solution. Scission of the polymer backbone, responsible for the alteration of the physical and mechanical properties, involves the decomposition of isolated hydroperoxide groups by two different mechanisms the relative importance of which changes with temperature.

Luminescence studies in polymers-I. Temperature effect on polyvinylnaphthalene and polyacenaphthylene fluorescence

Abstract The fluorescence spectra of polyacenaphthylene and poly-1-vinylnaphthalene films and solutions have been studied between 77 and 450°K. Excimer fluorescence only is observed in films. The ratio of monomer to excimer fluorescence intensities is a function of temperature for solutions. The influence of temperature on the intensity of monomer and excimer fluorescence has been analysed according to a general kinetic treatment. Activation energies for excimer formation and dissociation have been measured.