Sigbritt Karlsson

The mechanism of biodegradation of polyethylene

LDPE films have been exposed to abiotic and biotic environments. The films were UV irradiated for periods of 0, 7, 14, 26 and 42 days before being mixed with water and soil. Degraded LDPE films were examined by infra-red spectroscopy. The carbonyl peak increased with time in the abiotic environment and the oxidative degradation reported in our earlier works was confirmed. In the presence of a biotic atmosphere, however, this peak decreased. At the same time there was an increase in double bonds which was related to weight loss. An explanation of this behavior is presented as a proposed mechanism for the biodegradation of polyethylene. This mechanism is compared, on the one hand, with abiotic photooxidation, Norrish type I and II degradation, and, on the other, with the biotic paraffin degradation. Abiotic, as well as biotic, ester formation mechanisms are also presented. An ESR spectrum confirms the presence of radicals on the polyethylene samples. At the beginning of the degradation the main agents seem to be UV light and/or oxidizing agents. When carbonyl groups have been produced, these are attacked by microorganisms which degrade the shorter segments of polyethylene chains and form carbon dioxide and water as end products. There is a synergistic effect between photooxidative degradation and biodegradation. The biodegradation of polyethylene can be compared with the biodegradation of paraffin.

Weight losses and molecular weight changes correlated with the evolution of hydroxyacids in simulated in vivo degradation of homo- and copolymers of PLA and PGA

Abstract Homo- and copolymers of poly(lactide)s (PLA) and poly(glycolide)s (PGA) were hydrolysed at 37 and 60 °C for periods up to 80 days. We propose that the hydrolyses of PLA100 (100% L-lactide), PLA37.5GA25 (75% D,L-lactide and 25% glycolide) and PLA25GA50 (50% D,L-lactide and 50% glycolide) in buffer solutions at 37 and 60 °C proceed in three stages. During the first stage the molecular weights decrease rapidly with little weight loss. In stage two, the decrease in molecular weight slows down and severe weight loss starts in parallel with which monomer formation is initiated. During the final third stage, when total weight loss is observed, about 50% of the polymer is converted to monomer. The hydrolyses of the soluble oligomers continues until all are transferred to lactic acid and glycolic acid.

Chemical and morphological changes of environmentally degradable polyethylene films exposed to thermo-oxidation

Abstract Thermo-oxidation of blown low density polyethylene (LDPE) films modified with different combination of biodegradable filler, prooxidant and photosensitizers was conducted in oven at 60 and 100°C for a period of 14 days. Volatile and semivolatile degradation products were extracted by solid phase micro extraction (SPME) technique and identified utilizing gas chromatography–mass spectrometry (GC–MS). Chemical and morphological changes were monitored and these are given as carbonyl index, crystallinity and melting behavior, molecular weight and molecular weight distribution. The samples containing solely prooxidant showed the highest susceptibility to thermal degradation during the test period. The second most degradable samples were LDPE modified with 20% masterbatch (containing starch and a prooxidant). LDPE containing only starch did not show any degradation during the test period. The major degradation products were homologous series of carboxylic acids, ketones, hydrocarbons and lactones. 4-Oxopentanoic acid, 5-oxohexanoic acid and benzoic acid were identified only in LDPE containing prooxidant (LDPE-PO) and LDPE modified with 20% masterbatch (LDPE-MB). A small number of aldehydes (3-methyl pentanal, benzaldehyd and 2-propyl 5-oxohexanal) were identified solely in LDPE-MB. Esters could be identified only from LDPE-Starch and pure-LDPE samples. The crystallinity of all the samples increased after aging at 60°C except for LDPE-Starch which showed no significant change in crystallinity. The melting thermograms of LDPE-PO and LDPE-MB (first heating) exhibited low temperature shoulders around 75°C (after treatment at 60°C) and appears to move downward with increasing exposure temperature (treatment at 100°C). The shoulders near 115°C (second heating) increase with increasing exposure temperature which is due to a preferential scission at the tertiary carbon atom as observed by increased crystalline melting point. ATR and transmission FTIR show that the absorbance of carbonyl containing groups is almost the same on the surface as in the bulk for virgin samples and samples aged at 60°C. Opposite to the other materials, LDPE-MB samples aged at 100°C show a much faster increase in the absorbance of carbonyl containing groups in the bulk of the film than on the surface layer. This indicates that the bulk of the latter films are more labile than the surface which could be a consequence of higher starch concentration on the surface than in the bulk.

Degradation product pattern and morphology changes as means to differentiate abiotically and biotically aged degradable polyethylene

Degradation product pattern and morphology changes as means to differentiate abiotically and biotically aged degradable polyethylene

The biodegradation of amorphous and crystalline regions in film-blown poly(ε-caprolactone)

The surface erosion of films of poly(ϵ-caprolactone) (PCL) in compost, in anaerobic sewage sludge and by Aspergillus fumigatus was compared with chemical hydrolysis (23 and 50°C). Biodegraded samples displayed grooves or cracks arranged in parallel, whereas samples exposed to an abiotic environment showed no surface changes. Differences in micro-flora together with the initial morphology of the sample resulted in different mechanisms of erosion. The degradation in compost resulted in parallel grooves or cracks, while A. fumigatus produced a spherulitic erosion pattern. A preferential degradation in the amorphous parts produced low-molar mass fractions with lengths corresponding to one, two or several times the thickness of the crystal lamellae.

Polymers from Renewable Resources

From the point of view of making novel polymers with inherent environment-favorable properties such as renewability and degradability, a series of interesting monomers are found in the metabolisms and cycles of nature. This review presents and discusses a number of aliphatic polyesters which show interesting applications as biomedical materials and degradable packages. Available from nature are amino acids, microbial metabolites from the conversion of glucose and other monosaccharides (e.g., acetic acid, acetone, 2,3-butanediol, butyric acid, isopropanol, propionic acid), lactic acid, ethanol and fatty acids. A series of biodegradable polymers with different properties and different potential industrial uses were made starting with succinic acid and/or 1,3-propanediol. There were two routes for making the polyester-based materials; the direct ring-opening polymerization of lactones (cyclic esters) synthesized from 1,3-propanediol, and the chain-extension of α,ω-dihydroxy-terminated oligomeric polyesters produced by thermal polycondensation of 1,3-propanediol and succinic acid (oligo(propylene succinate)s).

Solid waste treatment within the framework of life-cycle assessment

Abstract Traditionally, treatment of solid waste has been given limited attention in connection with life-cycle assessments (LCAs). Often, only the amounts of solid wastes have been noted. This is unsatisfactory since treatment of solid waste, e.g. by landfilling or incineration, is an operation, requiring inputs and producing outputs, which should be described in the inventory of an LCA, in parallel to other operations. However, there are difficulties in describing emissions from solid waste treatments and there is a need for development of such methods. In this paper an approach for describing emissions from incineration and landfilling is outlined. Methodological questions concerning the time-frame and allocation principles are discussed. Methods for estimating potential emissions from landfilling of municipal solid waste and industrial wastes are suggested. The methods are used for calculating potential emissions from landfilling of some typical wastes. These emissions are compared with the emissions from other stages in the life cycle for some materials and wastes. it is shown that the potential emissions from landfilling are, for some products, of importance for the final results. Hence, if emissions from landfilling are neglected, or underestimated, results and conclusions in an LCA may be misleading.

Rapid (bio)degradation of polylactide by mixed culture of compost microorganisms—low molecular weight products and matrix changes

Poly(L-lactide) (PLLA) was rapidly (bio)degraded by a mixed culture of compost microorganisms. After 5 weeks in biotic environment, the films had fragmented to fine powder, while the films in corresponding abiotic medium still looked intact. Analysis of the low molecular weight products by GC-MS showed that microorganisms rapidly assimilated lactic acid and lactoyl lactic acid from the films. At the same time, a new degradation product, ethyl ester of lactoyl lactic acid was formed in the biotic environment. This product cannot be formed by abiotic hydrolysis and it was not detected in the abiotic medium. The degradation of the PLLA matrix was monitored by differential scanning calorimetry (DSC), size exclusion chromatography (SEC) and scanning electron microscopy (SEM). A rapid molecular weight decrease and increasing polydispersity was observed in the biotic environment. In the abiotic environment only a slight molecular weight decrease was seen and the polydispersity started decreasing towards 2.0. This indicates different degradation mechanisms, i.e. preferred degradation near the chain ends in the biotic environment and a random hydrolysis of the ester bonds in the abiotic environment. SEM micrographs showed the formation of patterns and cracks on the surface of the films aged in biotic medium, while the surface of the sterile films remained smooth. The SEM micrographs showed a large number of bacteria and mycelium of fungi growing on the surface of the biotically aged films.

Susceptibility of enhanced environmentally degradable polyethylene to thermal and photo-oxidation

Susceptibility of enhanced environmentally degradable polyethylene to thermal and photo-oxidation

Aging of silicone rubber under ac or dc voltages in a coastal environment

Material samples of silicone rubber with known differences in their composition, i.e. different filler content and extra silicone oil added, have been aged at the Anneberg field station on the west coast of Sweden. ac or dc voltage supplied to cylindrical samples at stress levels of 50 or 100 V/mm. The work includes laboratory examination of material changes together with on-site, visual observations and leakage current measurements. Material samplings for the laboratory tests were made after 18 months of electrical aging, which went on for one more year in order to gather further information on the long-term electrical performance of the material. The dominant aging factor was the level of the applied stress, independent of ac or dc voltage. The dc stressed samples showed a higher leakage current and exhibited larger surface degradation compared with samples exposed to ac voltage. The material parameter, an addition of extra silicone oil, initially led to an increase in adhesion of pollutants, whereas the overall performance was improved by the higher suppression of the leakage current related to oligomer diffusion. Samples with lower levels of alumina trihydrate (ATH) exhibited a delayed onset of degradation, but once damaged they degraded more rapidly than the specimens with a higher ATH content. Infrared spectroscopy showed that the ATH was completely consumed at the eroded surface regions. The aging of the surfaces was further assessed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The low molar mass siloxanes present in the pollution layer were extracted and analyzed by size exclusion chromatography and gas chromatography-mass spectroscopy. The results indicated that the main degradation factor was thermal depolymerization activated by electrical discharges. Oxidative crosslinking of the silicone rubber, usually attributed to surface close corona discharges, appeared to have played a minor role.