Polymer Degradation

A series of highly cross-linked polysiloxane was synthesised via hydrosilylation and condensation reaction. Structural identification using Fourier Transform Infrared (FTIR) and 1 H-NMR confirmed their chemical structures. Their thermal and, mechanical properties, and crystallinity, were analysed and related to the level of cross-link density. These systems displayed elevated thermal and hardness properties at an increased cross-link density. Furthermore, the level of crystallinity was reduced as displayed by XRD analysis. Along with this observation, the calculated fractional free volume (FFV) showed a decreasing trend leading to the 'densification' effect. It was envisaged that the linear polysiloxane chain segments aligned parallel to each other in a triclinic crystal system to generate a crystalline domain. The spacing between these stacking chains was found to be about 7.2 Å as measured from simulated XRD pattern.

Degradation of polypropylene (PP) during melt processing was studied using a novel profluorescence technique. The profluorescent nitroxide probe, 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO) was added to PP during melt processing to act as a sensor for carbon-centred radicals. Trapping of carboncentred radicals, formed during degradation of PP, led to an increase in fluorescence emission from TMDBIO adducts. Through analysis of viscosity changes during processing cumulative chain scission degradation was estimated. At processing temperatures of 210 C or below, fluorescence emission from TMDBIO adducts could be correlated with cumulative chain scissions when the number of chain scissions was small. At higher temperatures, a correlation was not observed most probably due to radical-trap instability rather than decomposition of the TMDBIO. Thus, TMDBIO may be used as a profluorescent sensor for degradation of PP during melt processing when the processing temperature is 210 C or below.

Scorching of water-blown polyurethane foams is a general phenomenon usually attributed to the thermal degradation and oxidation of the foam. Scorch is more visible in the presence of some phosphorus-or halogen-containing fire retardants. In the present study four phosphorus-containing fire retardant foams and one non-fire-retardant foam have been tested for scorching. The results showed that some fire retardants are able to accelerate the scorching process by forming new easily oxidisable structures via interaction with polyurethane degradation products. #

The thermoxidative (oven ageing) and photooxidative degradation of polypropylene films (2OOpm thick) containing a range of antioxidants and light stabilisers, together with anatase and rutile titanium dioxide pigments are studied by Fourier Transform infra-red (FTIR) spectroscopy. Rates of thermal and photooxidative degradation are determined by measuring the formation of non-volatile carbonyl and hydroperoxide oxidation products which absorb in the infra-red region of the spectrum with maxima at 1710 and 3410 cm-', respectively. During photooxidation the rutile pigment is synergistic in stabilisation with phenolic antioxidants and hindered piperidine stabilisers (HAS) but antagonistic with benzotriazole and benzophenone absorbers. In the case of anatase marked autocatalytic oxidation is observed giving strong antagonistic effects. With mixed antioxidant/stabiliser combinations, synergistic stabilisation is not significantly influenced by rutile but markedly antagonised by the presence of the anatase pigment. The most effective light stabiliser in retarding the catalytic oxidative effect of anatase is the polymeric HAS, Chimassorb 944. During thermal oxidation the polymeric HAS exhibit strong thermal antioxidant activity compared with the non-polymeric HAS. Both antioxidants and the benzophenone absorber are strongly antagonistic with rutile while the HAS and benzotriazole stabilisers display weak synergism. The anatase strongly accelerated and catalysed the thermal stabilisation effects with all the stabilisers and antioxidants. For the stabiliser combinations, the HAS are more effective at inhibiting oxidative degradation than the absorbers in the presence of both pigment types. The thermal catalytic effects of anatase are strongly suppressed by antioxidant/stabiliser combinations. 0 1998 Elsevier Science Limited. All rights reserved

Maleiyl phenylene amide polymers were prepared by the condensation of maleic acid with phenylene diamine (meta and para) in boiling o-xylene using a Dean & Stark apparatus. The prepared polymers were investigated using IR spectroscopy and microanalysis. The compounds were incorporated into natural rubber (NR) and styrene butadiene rubber (SBR) mixes and the rheometric characteristics were determined using an oscillating disc rheometer. The prepared polymers were evaluated as antioxidants in NR and SBR vulcanizates. The physico-mechanical properties of the rubber vulcanizates were measured before and after exposure to accelerated thermo-oxidative aging. The results revealed that the prepared amide polymers were good antioxidants for rubber vulcanizates exceeding the commercial antioxidant phenyl -naphthylamine (PBN). In addition, the p-maleiyl phenylene amide polymer has better efficiency as an antioxidant than the m-maleiyl polymer adduct. The vulcanizates containing the maleiyl polymer adducts subjected to UV irradiation for 200 h exposure, showed significant stabilization against UV radiation. The importance of these polymers is due to the very low volatility and having no health hazards when incorporated in rubber. #

The thermal and photo-oxidation of various formulations of polychloroprene have been studied. The ATR-FUR technique has been especially used. The first step in oxidation is an allylic hydrogen abstraction leading to different radicals. Some hydroperoxides are formed and then decomposed into alcohols, ketones, acid chlorides and acids. The influence of crosslinking and carbon black on the oxidative degradation is also reported. 0 1996 Elsevier Science Limited

The results of ultrasonic irradiation of polystyrene solutions in toluene, benzene and carbon tetrachloride are described. The effect of a range of conditions such as ultrasonic intensity, solution concentration and varying solvents were investigated. The non-random nature of the degradation process was clearly demonstrated and the effect of different solvents was interpreted in terms of their thermodynamic properties.

The surface compositions of non-aging chemically synthesized polypyrrole samples doped with a-naphthalene sulfonate (PPy/ a-NS À ) were investigated by X-ray photoelectron spectroscopy (XPS). The power of the X-ray source used was 300 W. Employing liquid nitrogen cooling of the sample holder, the spectra in the regions of C 1s, O 1s, N 1s and S 2p were found to be reproducible with a gradual change in S 2p spectrum when the accumulated X-ray exposure time was less than 1050 min. Beyond this accumulated X-ray exposure time, dramatic changes were observed in all spectral regions. The decreases in the amount of dopant and HSO 4 À or SO 4 2À co-dopant species correspond to the decrease in the amount of polaron charge carrier species of PPy (-NH þ -). We found increases in the amount of the imine-like nitrogen (=N-) and hydrocarbon, and the presence of new sulfurcontaining species. These results suggested the deprotonation of the polaron by the dopant and the desulfonation of the protonated dopant. After desulfonation, these new sulfur-containing species were removed whereas the carbons of the naphthalene rings were still adhering to the surface of the PPy pellet. This degradation became more severe when the liquid nitrogen cooling system of the spectrometer was not used. The results indicate that the degradation was mainly induced by heat from the X-ray beam. #

Polymer mixtures containing 8 g of high density polyethylene (PE) or polystyrene (PS) and 2 g of acrylonitrileebutadieneestyrene copolymer containing a polybrominated epoxy type flame retardant (ABS-Br) were thermally degraded at 450 (C. FeOOH and two carbon composites based on iron (Fe-C) and calcium (Ca-C) were used for catalytic decomposition and their effect on the bromine and nitrogen amount and distribution in pyrolysis oil was determined by GC-AED analysis. It was found that iron-based catalysts removed bromine from pyrolysis oil and decreased the nitrogen amount converting nitrile compounds into ammonia. Calcium carbon composite had lower effect especially on the pyrolysis of PS/ABS-Br mixture. These liquid products can be used as fuel oil or feedstock in petroleum refinery.

Two kinds of composites, namely single-filler polypropylene (PP) composites (containing either talc or calcium carbonate) and hybrid-filler PP composites (consist of a mixture of talc and calcium carbonate) were injection moulded into dumbbells. These specimens were subjected to natural weathering i.e. tropical climate in Penang, Malaysia for 6 months. After 6 months of exposure, the mechanical properties of single-filler PP composites deteriorated due to severe physical and chemical degradation. However, the hybrid-filler PP composites were found to show better retention in mechanical properties albeit having undergone some degree of surface-degradation as well. It is believed that the 'hybridization' effect has successfully increased the resistance of the hybrid composite to severe environmental degradation to the extent that it protects the internal structure of the composite from environmental damage, even though the surface of the composite gets severely degraded. Surface treatment of fillers was also found to be able to aid in the retention of the composites' mechanical properties. #

TGA investigations on the thermal degradation of isotactic polypropyleneevapor grown carbon nanofibers composites in nitrogen are reported. The mass evolution as a function of temperature is a single sigmoid for both polypropylene and polypropylene loaded with carbon nanofibers. The inflection temperature of these sigmoids increases as the concentration of carbon nanofibers is increased. The width of the degradation process narrows as the concentration of carbon nanofibers is increased due to a better homogenization of the local temperature provided by the high thermal conductivity of carbon nanofibers. Thermogravimetric analysis data indicate the formation of polymerecarbon nanofiber interface. Based on TGA data, a two-layer structure is proposed for carbon nanofibersepolypropylene interface. The external layer is soft and has a thickness of about 10 2 nm that confines most polymer molecules in interaction with nanofibers. The core layer is rigid and has a thickness of the order of few nanometers.

The catalytic degradation of polyolefinic polymers such as polyethylene (PE) and polypropylene (PP) was carried out at atmospheric pressure by batch operation at 43O'C and 380°C using non-acidic mesoporous silica cataly:..t (FSM). A comparison with non-catalytic thermal degradation and catalytic degradation using solid acid catalysrs (silica--alumina, zeolite ZSM-5), silicalite, and silica-gel was made. Compared with thermal degradation, non-acidic FSM catalyst accelerated the initial rate of degradation, increased the liquid product yield and promoted degradation into lower molecular weight products. Silicalite and silica-gel had very negligible effects on polymer degradation. When the batch reaction was repeated four times using the same FSM catalyst, the extent of the decline in the degradation rate was lower for PE than PP. Compared with the solid acid catalyst, which turned completely black in the cases of both PE and PP, the deposition of coke on the used FSM catalyst was extremely slight. It seems likely that the catalytic effect of FSM for polyolefinic polymer degradation is related more to the hexagonal pore structure system of FSM. G

The cosmetic market for hyaluronic acid (HA)-based dermal fillers is in continuous and rapid growth and, simultaneously, the development of more effective and safer products is strongly intensifying. In order to highlight the differences among the currently available fillers, in terms of their physical characteristics and on the relation of such properties with product effectiveness, an in vitro evaluation of eight marketed HA-based gels was performed.

Polylactic acid (PLA) has now become an economically viable commodity plastic in many industries. This raises the question of recyclability of industrial production waste and some packaging wastes as well. The evolution of rheological and mechanical properties of polymer with the number of recycling cycles up to seven was investigated. For PLA, only the tensile modulus remains constant with the thermo-mechanical cycles. In contrast, stress and strain at break, rheological factors and the modulus and hardness probed by nanoindentation decrease for PLA. This dramatic effect is ascribed to a large decrease in the molecular weight due to several different complex degradation processes which are discussed. The effect of two stabilizers is also assessed.

Elucidation of the chemical changes that take place during the aging of polyethylene sheared electrical cables, and the correlation of these changes with physical properties need experiments with accelerated aging assays. These were carried out using the most representative polyethylene grades found in today's market: low density (LDPE), linear low density (LLDPE) and high density (HDPE). The samples were exposed to UV-and xenon arc radiation using a varying exposure time and different temperature cycles. The changes in the material structure and properties were analyzed by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), FTIR-spectroscopy, density and hardness measurements. During degradation polar groups in the polyethylene are generated, as well as chain scission and cross-linking. As net effects of these processes respective increases in crystallinity, density and hardness and surface cracking at late stages of degradation are observed. By varying the angle of incidence in attenuated total reflection (ATR) experiments using FTIR-spectroscopy it was possible to detect variations in composition of distinct layers from the surface down to a depth of 1.2 mm. Deeper layers were reached by microtoming the samples in layers down to 60 mm. The main chemical modifications were carbonyl formation of various kinds which were identified in the FTIR-ATR spectra of degraded polyethylene samples. #

Besides casting from water solutions, PVA processing from the melt seems to be more suitable, particularly for water-soluble films. Processing at high temperatures is very sensitive to PVA degradation and problems with stability of the melt result in a search for suitable additives. Silica is frequently used as an antiblock agent and only a little is known about its effect on PVA melt stability. The study was focused on PVA thermal and processing stability. and an evaluation of low molecular products released as by-products of PVA degradation. It was found that the thermal stability of PVA is strongly influenced by the pH of the environment before drying in the production process. Processing stability of PVA blends with and without glycerol used as plasticiser were evaluated from the torque increase during processing. Regarding the effect of the antiblock agents, silica had a strong negative effect on processing stability of PVA. In contrast, talc did not accelerate degradation up to a relatively high concentration level. To explain these effects, the changes in chemical structure of PVA blown films during thermal loading were studied using IR spectroscopy. It was confirmed that silica accelerates thermal degradation of PVA films due to its acidic character. #

ii Je dédie ce mémoire à Mays, ma femme, mon âme soeur qui m'a inspiré et accompagné tout au long de ce périple à Samir et Nadimah, mes parents qui m'ont toujours donné la chance de réaliser les rêves iv i REMERCIEMENTS Le travail exposé dans ce manuscrit a été réalisé au

Agro-wastes are derived from diverse sources including grape pomace, tomato pomace, pineapple, orange, and lemon peels, sugarcane bagasse, rice husks, wheat straw, and palm oil fibers, among other affordable and commonly available materials. The carbon-rich precursors are used in the production bio-based polymers through microbial, biopolymer blending, and chemical methods. The Food and Agriculture Organization (FAO) estimates that 20%-30% of fruits and vegetables are discarded as waste during post-harvest handling. The development of bio-based polymers is essential, considering the scale of global environmental pollution that is directly linked to the production of synthetic plastics such as polypropylene (PP) and polyethylene (PET). Globally, 400 million tons of synthetic plastics are produced each year, and less than 9% are recycled. The optical, mechanical, and chemical properties such as ultraviolet (UV) absorbance, tensile strength, and water permeability are influenced by the synthetic route. The production of bio-based polymers from renewable sources and microbial synthesis are scalable, facile, and pose a minimal impact on the environment compared to chemical synthesis methods that rely on alkali and acid treatment or co-polymer blending. Despite the development of advanced synthetic methods and the application of biofilms in smart/intelligent food packaging, construction, exclusion nets, and medicine, commercial production is limited by cost, the economics of production, useful life, and biodegradation concerns, and the availability of adequate agro-wastes. New and cost-effective production techniques are critical to facilitate the commercial production of bio-based polymers and the replacement of synthetic polymers.

The commercial importance of polymer blends implies interest in knowledge of their degradation behaviour under environmental stresses. Processes accompanying thermomechanical and thermal degradation of blends of commodity polymers are reviewed. Thermomechanical degradation, characteristic of melt processing, includes reactions between component macromolecules and relevant macroradicals. Cross-reactions giving grafted copolymers occur in some blends. Thermal degradation in an inert environment includes cross-reactions between macromolecules and low-molecular weight molecules or free radicals migrating over phase boundaries. As a consequence, thermal stability of the component polymers is either reduced or increased, according to the reactivity of involved species. #

The fire retardancy mechanisms of aluminium diethylphosphinate in combination with melamine polyphosphate and zinc borate was analysed in glass-fibre reinforced polyamide 6,6. The influence of phosphorus compounds on the polyamide decomposition pathways was characterized using thermal analysis (TG), evolved gas analysis (TGeFTIR), and FTIReATR analysis of the residue. The Lewis acidebase interactions between the flame retardants, the amide unit, and the metal ions control the decomposition. The flammability (LOI, UL 94) and performance under forced-flaming conditions (cone calorimeter using different irradiations) were investigated. Fire residues were analysed with FTIReATR, SEMeEDX, and NMR. Aluminium phosphinate in polyamide 6,6 acts mainly by flame inhibition. Melamine polyphosphate shows some fuel dilution and a significant barrier effect. Using a combination of aluminium phosphinate and melamine polyphosphate results in some charring and a dominant barrier effect. These effects are improved in the presence of zinc borate due to the formation of boronealuminium phosphates instead of aluminium phosphates.

Ethylene-vinyl acetate copolymer (EVA) is a widely used material, particularly as a zero-halogen material in the cable industry. It is frequently formulated with large quantities of inorganic filler material, such as aluminium trihydroxide (ATH). Used alone, EVA is known to form a protective layer which can inhibit combustion under well ventilated conditions, though this effect is not observed when used in formulations with ATH. The incorporation of nanoscale clay fillers into EVA appears to reinforce the protective layer. The stages of the decomposition under different conditions is described both for the 10 mg (TGA) and 200 mg (small tube furnace) scales. The latter allows the residues formed to be subjected to further analysis, to elucidate the mechanism of the reduction of decomposition and flammability. Enhancements in the thermo-oxidative stability of the EVA clay material were evident from both tube furnace and TGA experiments. The polymer-organoclay materials, prepared on a two-roll mill, showed poor dispersion when studied by SEM, suggesting that a significant portion was present as a microcomposite. However, when the char was analysed by SEM, layers of protective material were clearly evident on the char surface. From XRD spectra, there was no evidence of order within the polymer-organoclay, but ordering of the outer layer of char was demonstrated. This suggests that for EVA, which melts before burning, organoclay layers become nanodisperse at the surface of the burning polymer. These materials have also been studied in the Purser furnace, designed to replicate the conditions found in fully developed fires. This allows effluent yields, such as O 2, CO 2 and CO to be determined as a function of fire condition, by controlling the rate of burning and the ventilation rate. The effect of both the nanofillers and the protective layers are reported and discussed, under different ventilation conditions. Specifically, the relationship between equivalence ratio and hydrocarbon and carbon monoxide yield is focussed upon. #

A recently described bottle test method was used to evaluate the dependence of stress crack failure of poly(ethylene terephthalate) (PET) carbonated soft drink bottles on water hardness. Although the industry belief is that water hardness is irrelevant to stress cracking, it was found that hardness ions exert a tremendous positive impact by deactivating water alkalinity through precipitation as harmless carbonate minerals. This mitigating effect of hardness means that no complete understanding of stress cracking as a function of alkalinity is possible without also considering water hardness. A useful concept is that of excess alkalinity, which is defined as alkalinity that is not precipitated during solution evaporation. Limiting excess alkalinity by using water with sufficient hardness is an effective means of stress crack prevention in PET soft drink bottles. Evaluation of compositions which are typical of those used for lubricating PET bottles on production conveyors showed that the role of these compositions in stress cracking was that of spectators, that is, they neither cause failure if water does not otherwise cause it, nor stop failure if water otherwise causes it.

Thermal degradation process for fuel production from 10 gm polyethylene terephthalate (PET) and 50 gm of low density polyethylene waste plastics was heated up in an atmospheric Pyrex glass reactor of laboratory-scale. PET waste plastic is combination of hydrocarbon, benzene, and oxygen group. PET plastic has high percentage of oxygen content. For experimental temperature range was 250 -400 ºC and product fuel density was 0.76 gm/ml. Fuel production liquid conversion rate was 53. 5%, gas generated 11.83%, and wax and residue was 34.67%. Fuel was analysis by GC/MS, and GC/MS chromatogram compounds chain showed C 3 to C 22 . Residue percentage is higher because PET has oxygen content. Light gases are combination of methane, ethane, propane and butane. Fuel can use for refinery process further modification and power plant for electricity generation. MS PET may proceed at elevated temperatures by a random scission of ester linkages, resulting in the formation of a vinyl-ester end-group and a carboxyl end-group. Because end-groups in PET are predominantly hydroxyl-esters, International

High density polyethylene (HDPE), linear low density polyethylene (LLDPE), and isotactic polypropylene (PP) containing antioxidant additives at low or zero levels were extruded and blown moulded as films. An HDPE/LLDPE commercial blend containing a pro-oxidant additive (i.e., an oxo-biodegradable blend) was taken from the market as supermarket bag. These four polyolefin samples were exposed to natural weathering for one year during which their structure and thermal and mechanical properties were monitored. This study shows that the real durability of olefin polymers may be much shorter than centuries, as in less than one year the mechanical properties of all samples decreased virtually to zero, as a consequence of severe oxidative degradation, that resulted in substantial reduction in molar mass accompanied by a significant increase in content of carbonyl groups. PP and the oxo-bio HDPE/LLDPE blend degraded very rapidly, whereas HDPE and LLDPE degraded more slowly, but significantly in a few months. The main factors influencing the degradability were the frequency of tertiary carbon atoms in the chain and the presence of a pro-oxidant additive. The primary (sterically hindered phenol) and secondary (phosphite) antioxidant additives added to PP slowed but did not prevent rapid photooxidative degradation, and in HDPE and LLDPE the secondary antioxidant additive had little influence on the rate of abiotic degradation at the concentrations used here.

The thermal behaviour of a series of solution-cast blends of polyvinyl chloride/epoxidised liquid natural rubber (ELNR) of different mole percentage of epoxidation has been examined using thermogravimetric analysis. Thermal degradation is found to occur through a two-step ...

The commercial acrylic polymers, Paraloid B72 and Paraloid B67, and a silicon-based product, Dri-Film 104, commonly used as water repellents/consolidants in the restoration of stone artefacts, have been tested to evaluate their performances when submitted to ageing, simulating the outdoor conditions of treated stone. After full characterization, the three polymers were applied as thin films on slides, as thick film on petri dishes and on marble by brush or by imbibition and the resulting samples were submitted to photo-oxidative weathering (l ¼ 340 nm). The weathering evolution was checked by ultrasonic and colorimetric measurements and by FT-IR, NMR and SEC determinations. Removability tests were also performed. All the polymers underwent irreversible modifications with reduction of their conservative properties, colour change and, above all, impossibility of their complete removal.

Old PVC flooring materials obtained from three apartment blocks built in 1964, 1971, and 1974, respectively, have been examined in parallel with newly manufactured PVC floorings. The focus of this study was to investigate how the important properties of PVC floorings change during their service life owing to ageing processes, and how these can influence their suitability as post-consumer products for recycling methods such as mechanical recycling and energy recovery. One important objective was to obtain general information regarding the degradation processes in PVC floorings that could influence these recycling methods. Our study has shown that PVC floorings as plastic waste can be mechanically recycled in the form in which they were recovered without upgrading, and without the addition of new plasticizer. It is also shows that the high alkalinity of moist concrete can lead to the decomposition of the plasticizer when PVC flooring is glued onto it. However, the degree of decomposition of plasticizer is very small relative to the mass loss by evaporation, and consequently should not cause any problems for mechanical recycling. Nevertheless, decomposition products such as butanol and octanol can cause indoor environmental problems sometimes designated as ''sick building syndrome''. For this reason, gluing directly onto fresh concrete should be avoided. Gluing also makes mechanical recycling less favourable owing to troublesome dismantling, and the high degree of contamination from the glue. The heat content in PVC floorings is dependent on the proportions of PVC and plasticizer used. Consequently, changes in the heat content caused by long-term use of PVC floorings should be insignificant. #

A comparative study was conducted into the thermo-oxidative degradation of poly(ethylene terephthalate) (PET) and poly (butylene terephthalate) (PBT). Degradation of the polymer films and model compounds, ethylene dibenzoate (EDB) and butylene dibenzoate (BDB), was carried out in an oxygen atmosphere at 160 C. On the basis of the compounds identified by GC-MS a mechanism is proposed for the degradation of the model compounds that involves the oxidation at the a-methylene carbon with formation of unstable peroxides and carboxylic acids. From the studies performed under N 2 at 160 C it could be concluded that benzoic acid and esters are products of the thermal degradation, while benzoic and aliphatic acids, anhydride and alcohols are due to thermo-oxidative degradation. In contrast to the thermo-oxidative degradation of other polymers, for PET and PBT, especially at the beginning, thermal degradation plays an important role. The results clearly showed that PET is more stable towards degradation than PBT. #

Synergistic effects of sunlight exposure, thermal aging and fungal biodegradation on the oxidation and biodegradation of linear low density poly(ethylene) PE-LLD films containing pro-oxidant were examined. To achieve oxidation and degradation, films were first exposed to the sunlight for 93 days during the summer months followed by their incubation with fungal strains previously isolated from the soil based on the ability to grow on the oxidized PE-LLD as a sole carbon source. Some films were also thermally aged at temperatures ranging between 45 C and 65 C, either before or after fungal degradation. Films with prooxidant additives exhibited a higher level of oxidation as revealed by increase in their carbonyl index (COi). In addition to increase in the COi, films showed a slight increase in crystallinity and melting temperature (T m ), considerably lower onset degradation temperatures, and a concomitant increase in the % weight of the residues. The level of oxidation observed in thermally aged films was directly proportional to the aging temperature. The PE-LLD films with pro-oxidant exposed to sunlight followed by thermal aging showed even higher rate and extent of oxidation when subsequently subjected to fungal biodegradation. The higher oxidation rate also correlated well with the CO 2 production in the fungal biodegradation tests. Similar films oxidized and aged but not exposed to fungal biodegradation showed much less degradation. Microscopic examination showed a profuse growth and colonization of fungal mycelia on the oxidized films by one strain, while another spore-producing strain grew around the film edges. Data presented here suggest that abiotic oxidation of polymer's carbon backbone produced metabolites which supported metabolic activities in fungal cells leading to further biotically-mediated polymer degradation. Thus, a combined impact of abiotic and biotic factors promoted the oxidation/biodegradation of PE-LLD films containing pro-oxidants.

Agro-wastes are derived from diverse sources including grape pomace, tomato pomace, pineapple, orange, and lemon peels, sugarcane bagasse, rice husks, wheat straw, and palm oil fibers, among other affordable and commonly available materials. The carbon-rich precursors are used in the production bio-based polymers through microbial, biopolymer blending, and chemical methods. The Food and Agriculture Organization (FAO) estimates that 20–30% of fruits and vegetables are discarded as waste during post-harvest handling. The development of bio-based polymers is essential, considering the scale of global environmental pollution that is directly linked to the production of synthetic plastics such as polypropylene (PP) and polyethylene (PET). Globally, 400 million tons of synthetic plastics are produced each year, and less than 9% are recycled. The optical, mechanical, and chemical properties such as ultraviolet (UV) absorbance, tensile strength, and water permeability are influenced by the ...

Ultra-high molecular weight polyethylene (UHMWPE) has been the material of choice for load-bearing articular components used in total joint arthroplasty in the past 30 years. However, the durability of the whole implant has often been compromised by oxidation of UHMWPE components. Since the use of a suitable, biocompatible stabilizer would minimize this inconvenience, the possibility of adding synthetic Vitamin E to medical grade UHMWPE is currently under investigation.

Sub-and supercritical glycolysis of polyethylene terephthalate (PET) with ethylene glycol (EG) to bis(2hydroxyethyl) terephthalate (BHET) was investigated for the purpose of developing a PET recycling process. Supercritical glycolysis was carried out at 450 C and 15.3 MPa while subcritical glycolysis was carried out at 350 C and 2.49 MPa or at 300 C and 1.1 MPa. High yields (gt; 90%) of the monomer BHET were obtained in both super-and subcritical cases. For the same PET/EG weight ratio of about 0.06, the optimum reaction time was 30 min for supercritical glycolysis and 75 and 120 min for two cases of subcritical glycolysis. GPC, RP-HPLC, 1 H NMR and 13 C NMR, and DSC were used to characterize the polymer and reaction products. Supercritical glycolysis will be suitable to a process requiring a high throughput due to its short reaction time.

In an effort to shed additional light on the chemical mechanisms underlying the radiation-oxidation of polypropylene (PP), we are using samples having selective 13C isotopic labeling at the three unique sites within the macromolecular structure. After radiation exposure, we applied GC/MS, solid-state 13C NMR, and FTIR to evaluate the applicability of each technique in identifying the molecular labeling of the oxidation products, with the goal of determining the site of origin of the products with respect to the macromolecule. Using GC/MS, we have identified the position of origin of CO 2 and CO from the polymer. Most of the CO 2 (60%) and CO (>90%) come from the C(1) (methylene) position of PP, with (30%) of the CO 2 originating from the C(3) (methyl) position, and 10% coming from the C(2) (tertiary) position. By GC/MS we have also identified the labeling patterns in four volatile oxidation products (acetone, methylisobutylketone, isobutane, and methyl acetate), and have used this information to map each compound onto the macromolecular framework. Using NMR we have quantified the time-dependent formation of solid-phase degradation products occurring from post-irradiation aging of PP samples held for 28 months at room temperature in air. Most of the solid oxidation products occur at the C(2) (tertiary) site; the predominant species, C(2) peroxides, increase linearly during the first 2 years, after which they plateau at a relatively high concentration.

The effect of iron and calcium stearates on the degradation of polyethylene (LDPE and LLDPE), under natural and artificial exposure, has been studied. The activity of stearates has been evaluated by chemiluminescence and FTIR of polyethylenes. The analysis of the molecular weight changes and content of degradation products identified by GCeMS during ageing process confirmed their pro-degrading activity. Films containing stearates exhibited lower CL emission, and revealed the higher efficiency of Fe-Stearate compared to Ca-Stearate in decomposing hydroperoxides, leading to higher degradation during processing. The results were confirmed by TGA analysis, where the weight loss onset and T max shifted to lower temperatures in polyethylenes with incorporation of Fe-and Ca-stearates compared to pure polymers.