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Porcine and recombinant human atelocollagen I solutions were cross-linked with a water soluble carbodiimide at various stoichiometries and collagen concentrations (5-20 w/w %). The resulting hydrogels were clear and, when used as cell growth matrices, allowed cell and nerve visualization in vitro and in vivo. We have previously reported that, after six months of implantation in pigs' and rabbits' corneas, these robust hydrogels allowed regeneration of host cells and nerves to give optically clear corneas with no detected loss in thickness, indicating stable engraftment. Here, the biocompatible hydrogel formulations leading to this novel in vivo performance were characterized for amine consumption, gel hydration, thermal properties, optical clarity, refractive index, nutrient diffusion, biodegradation, tensile measurements, and average pore diameters. Gels with excellent in vitro (epithelial overgrowth, neurite penetration) and in vivo performance (clarity, touch sensitivity regeneration) had 4-11 nm pores, yet had glucose and albumin diffusive coefficients similar to mammalian corneas and allowed neurite extension through the gels.

The oxidation of high density polyethylene (HDPE), both unstabilised and vitamin E stabilised, has been studied by infrared (IR) and electron paramagnetic resonance (EPR) spectroscopies in the period following γ-irradiation at doses from 1 to 60 kGy (range of food sterilisation). Derivatisation by reaction with sulphur tetrafluoride was used to identify macro-ketone and carboxylic acid components of the overlapped IR carbonyl region. Oxidation continued for several hundred hours after the cessation of irradiation as shown by the increase in hydroxyl, ketone and acid groups. Carboxylic acid groups are particularly important as a direct indication of backbone scission. Vitamin E, although an effective antioxidant during γ-irradiation, was less effective in reducing the post-irradiation changes, which are probably driven by migration of radical sites along the polymer backbone from within the crystalline phase to the amorphous/crystalline inter-phase, where they become oxygen accessible.

Vitamin E was found to be a very effective antioxidant both in a model, liquid alkane, (teradecane) and in HDPE when oxidations at close to room temperature were initiated with γ-radiation. FTIR was used to follow changes in vitamin E in oxidising tetradecane and HDPE, even at very low concentrations of the antioxidant. Formation of isolated hydroperoxide groups as a direct result of the vitamin E–peroxyl radical reaction were clearly visible. Quinone products from vitamin E were formed during γ-irradiation, but different quinones were formed depending on the vitamin E concentrations. Vitamin E quite effectively retarded the oxidation of HDPE during γ-irradiation and so should be useful in polyethylene intended for radiation sterilisation, as packaging materials or medical devices.

The effects of several phenolic antioxidants on the thermal and γ-initiated oxidation of HDPE has been studied. Antioxidants included both di-tert.butyl hindered phenols and vitamin E. For equivalent concentrations of phenol groups, vitamin E was comparable to or better than the hindered phenols in limiting the oxidation of HDPE exposed to γ-rays. The poorer antioxidant activity in γ-irradiated HDPE at ∼32°C of a clustered, quadri-functional phenol, may stem from one group grafting through a peroxide link to the HDPE backbone. The activity of the three remaining phenolic groups will then be impaired because of restricted mobility. In thermo-oxidation at 80°C, vitamin E showed quite good performance at 80°C at low concentration, but clearly inferior to the clustered hindered phenol, present at a somewhat higher molar equivalent level. A small hindered phenol had poor performance because of its facile volatilisation from the polymer.

Infrared internal reflection spectroscopy (IR-IRS) and flux decline has been used to examine the build-up of adsorbed foulants on the surfaces of membranes during the treatment of the plug screw feed pressate (PSFP) from the sulfite digestion of wood chips. Of the four commercial membranes studied, hydrophillic cellulose and thin film composite membranes resisted fouling as shown by no drop in flux during in-plant trials and absence of foulants by IR-IRS. In contrast both hydrophobic polyvinylidene fluoride (PVdF) and polysulfone membranes showed rapid flux decline and were found by IR-IRS to be coated with essentially all of the pressate constituents after exposure to the mill effluent. PVdF membranes were examined in detail by IR-IRS to monitor membrane fouling as a function of exposure time in a laboratory permeation test cell and exposure to PSFP in a static contact test. Hydrated lignin sulfonates, as free acid or salts, were found to be the initially absorbed species, with cellulosic oligomers depositing later on the initial foulant layer.

Products resulting from the photo and thermal decomposition under vacuum of a pre-oxidized isotactic polypropylene (iPP) containing a known content of hydroperoxide have been examined. In contrast to the case of polyethylene, few products were retained in the polymer matrix. Detailed analysis of the gas phase was performed by gas chromatography, Fourier transform infra-red spectroscopy and mass spectrometry. It was revealed that about 70% of the hydroperoxides were converted into gaseous products such as acetone, acetic acid and methanol. Mechanisms for their formation are suggested, and the consequences of such a phenomenon for the evaluation of ageing in PP are discussed.

Volatile organic compounds and organochlorine species liberated by UV exposure of poly(vinyl chloride) (PVC) siding samples have been identified and preliminary quantification made. These volatiles included those remaining in a PVC sample after weathering or laboratory UV exposure and which could be released by thermal desorption. In addition, by using a flow-through cell and granular carbon adsorbents, volatile species directly desorbed during laboratory UV exposure were measured. Total directly desorbed organochlorine compounds were about 1/20 of the weight of hydrogen chloride as measured by conductometric analysis, Quite similar products were observed from old (∼1984) and current (1995) commercial siding formulations. Observed volatile compounds are proposed to come from the TiO2-controlled photo-oxidation of both PVC and its additives such as impact modifiers.

Hydroperoxide groups are widely believed to be critical intermediates in the oxidative degradation of many polymers, especially commodity polyolefins [34, 5 1-53]. Trace amounts of hydroperoxides in polyolefins such as polyethylene (PE) may be formed inadvertently during polymerization and processing. It is found that hydroperoxides are formed almost quantitatively from the oxygen absorbed by the polymer during its induction period [26,27,44]. Moreover, it has baeen suggested that the stability of articles made from polyolefins depends largely on the concentration of hydroperoxides formed during storage of the nascent polymer before any stabilizer is added 1701.

The effects of sec. and ter. piperidinyl additives on oxidative resistance of γ-irradiated polypropylene have been studied over a quite wide range of additive concentrations. Tert. amines were the more effective in suppressing oxidation during the γ-irradiation step. All piperidinyl compounds gave a product identified by IR as a ring-opened nitro compound as well as nitroxides. From the dependence of nitroxide and nitro-compound on the initial concentration of the tert. piperidinyl compounds, an amine oxide is proposed as the transient intermediate leading to nitro-formation from the tert.-piperidinyl additives.

The detailed oxidation products have been identified and compared from the γ-, photo-, and thermally-initiated oxidation of unstabilized polypropylene films. Products were identified and quantified by a combination of iodometric analysis and infrared spectroscopy. Spectral resolution was enhanced by derivatization reactions which allow the quantification of primary, secondary, and tertiary hydroperoxide and alcohol groups as well as more reliable analysis of carbonyl species. In contrast to polyethylene oxidation which yields predominantly ketone with lesser amounts of secondary hydroperoxide and carboxylic acid, polypropylene oxidizes to give predominantly tertiary hydroperoxide and lesser quantities of secondary hydroperoxide and ketone. In addition carboxylic acid groups are a minor product except at high degrees of thermal and photoinitiated oxidation. © 1993 John Wiley & Sons, Inc.

It was found that all types of initiation gave very similar products but in varying quantities. In photooxidation, hydroperoxide was clearly shown to approach a photostationary concentration either from below for fresh film or from above for samples that had been pre-oxidized by γ-irradiation, prior to UV exposure. Carboxylic acid groups, the main backbone scission product, dominated in photooxidations, possibly as the result of the further oxidation of sec-hydroperoxide sites.

The nature of AC field aging of cross-linked polyethylene (XLPE) using NaCl and CuSO/sub 4/ (0.1 M) electrodes was studied with Fourier transform infrared absorption (FTIR), thermally stimulated discharge current (TSDC), and thermal transient current (TTC) measurements. FTIR measurements show that oxidation of stabilized XLPE is significantly lower than that of the unstabilized materials. No noticeable increase in bound water content in the polymer was observed as measured by IR absorbance at 3370 cm/sup -1/. Progressive enhancements of absorbance at approximately 1715 cm/sup -1/ and the TSDC peak at 70 degrees C with increasing field aging time appear to have the same origin. Thermal transient current magnitude is related to that of the integrated charge released in a TSDC thermogram. >

The oxidative behavior of ethylene/vinyl alcohol copolymers has been examined after initiation by γ-irradiation. Oxidation products were identified and quantified by infrared spectroscopy after the use of selective derivatization reactions which allowed the resolution of the various alcohol, hydroperoxide and carbonyl species produced. Extensive preferential attack at the sites was observed to give backbone ketone and probably hydrogen peroxide. The latter was not unambiguously identified or quantified because of its volatility. The derivatization techniques failed at vinyl alcohol levels above 20 wt%, probably because of the low gas permeability of these films. Implications of the observed products to the oxidation of polyethylene are discussed.

Hydroperoxide products in solid oxidized polyolefins have been measured by iodometry, Fe2+ reaction and by derivatization infrared spectroscopy methods. Polyethylene, polypropylene and elastomers were oxidized by photo, thermal and γ-initiation. The traditional iodometric method appears to be highly reliable within certain constraints of reaction time imposed by sample crosslinking. The Fe2+ reaction was found to give values consistently one order of magnitude below the true level because of failure of the reagents to penetrate into the oxidized polymers even after a prior swelling step. Derivatization of hydroperoxides by reaction with nitric oxide produced nitrates which could be measured by infrared spectroscopy with high sensitivity. Total nitrate yields agreed well with iodometric determination of hydroperoxide for reaction conditions under which the nitrates were stable. Different nitrates, and hence hydroperoxides, could be identified and quantified by this method.

Identification et quantification par RPE et IR des radicaux formes par irradiation de polyethylene (HDPE) et de polypropenes atactique et isotactique Pour le HDPE le radical dominant serait ∼CH 2 CH(O 2 . ) CH 2 ∼ alors que pour les polypropenes les radicaux peroxyl secondaires dominent les radicaux tertiaires

The detection and quantification of polyvinylpyrrolidone (PVP) polymer in the top skin layer of the poly(ether p-phenylenesulfone) (PES, Victrex) ultrafiltration membrane was attempted by applying the technique of internal reflection Fourier transform infrared spectroscopy (FTIR-IRS). The effects of the PVP concentration in the casting solution and that of the PVP molecular weight on the residual quantity of PVP were investigated in detail. The PVP content in the membrane was further correlated to the ultrafiltration performance data of PES membranes.

Polysulfone (Udel P1800) ultrafiltration membranes were surface modified using potassium persulfate (K2S2O8) as a free radical source in the aqueous phase. The expected modification was hydrogen abstraction leading to hydroxylation at one or two sites on the isopropylidene linkage. Reaction time, K2S2O8 concentration, and temperature were optimized based on two criteria: (1) minimal change in pure water fluxes after surface modification and (2) reduction of adsorptive fouling with a pulp mill effluent. The pure water flux retention for an unmodified membrane was ∼20% after adsorptive fouling with the pulp mill effluent and was increased to 70% after reaction with K2S2O8. Angle-resolved XPS indicated increased oxygen and a new carbon peak consistent with an aldehyde reaction occurring in the top 3.5 nm. NMR solution analysis was inconclusive because of the low sensitivity of the experiment. Further analysis of oxidation products was carried out on finely dispersed polymer. Fourier transform infrared, internal reflection spectroscopy suggested oxidation by the formation of an aldehyde which was further oxidized to carboxylic acid. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1723–1730, 2006

Thermal desorption, followed by gas chromatography (GC) with mass spectrometry (MS) detection, has been found to allow the rapid identification of volatile products resulting from the gamma-irradiation of stabilized, high density polyethylene packaging and pure stabilizers. The stabilizers were tris(2,4-di-tert.butylphenyl) phosphite, octadecyl beta-(2,6-di-tert.butylphenol)-propionate and 2,4-di-tert.butylphenol, the latter resulting from phosphite hydrolysis. Thermal desorption indicated the formation and release of tert.butylbenzenes, such as 1,3-di-tert.butylbenzene upon gamma-irradiation of the HDPE. From a comparison of the products from gamma-irradiation of additive-free polyethylene, of various pure stabilizers and of related compounds, the tert.butylbenzenes were confirmed to result from the irradiation of the phosphite stabilizer and its phosphate conversion product. Thermal desorption off-line, in which volatiles released by a sample are trapped in sorbents for subsequent desorption in the heated GC inlet, is found to be a fast, extremely sensitive method that can be used to guide and supplement analyses of compounds extracted by foodstuffs.

Infrared (IR) spectroscopy has been used to identify and quantify the phosphite antioxidant, tris(2,4-di-tert.butylphenyl) phosphite, and its corresponding phosphate in high density polyethylene (HDPE) food trays, both in the original, commercial trays and also as a function of gamma-irradiation and post-irradiation, storage conditions. This direct method of inhibitor analysis complements time-consuming (some times non-quantitative) extraction methods, which for organo-phosphites are complicated by their facile conversion to phosphates by peroxidic impurities in the solvent. Because of the complete destruction of phosphite to give mainly phosphate at quite low gamma-irradiation doses (approximately 5 kGy) and phosphate formation during melt processing and radiation sterilization of these HDPE trays must take into account products from the irradiation of phosphate. Any residual phosphite is lost progressively in post-irradiation reactions, which are complex, producing a less than-quantitative yield of phosphate.

Volatile species produced during the ultraviolet irradiation of a rigid, poly(vinyl chloride) construction panel have been established as a function of irradiation time. Residual organic and chloroorganic compounds were detected in the polymer surface after irradiation. Similar species are also directly released during irradiation. In both cases, these were identifed and quantifed by gas chromatography, with mass spectrometry detection. Rates of volatilisation of organic and chloroorganic compounds were measured directly during accelerated exposure conditions and dropped sharply with irradiation time. This drop may be attribu- table to the cross-linking of the irradiated surface which becomes chlorine def- cient and rich in titanium dioxide pigment (rutile). In contrast, samples exposed to sunlight did not undergo surface cross-linking but did thermally desorb vola- tiles similar to laboratory exposed samples.

The effects of various phenols and some hindered amines have been compared both during the γ-irradiation process and during the post-irradiation oxidations of polypropylene films and test strips. Oxidation product formation, yellowing and embrittlement (as measured in an instrumented bend test) have been compared with product formation. A partial correlation between suppression of oxidation during the irradiation step with long term, post-irraidation oven aging at 60°C was found, but complicated by extensive destruction during irradiation of the active phenolic functionality in some additives, essential for peroxyl radical scavenging. Very long lifetimes with barely detectable yellowing were found for combinations of the amines with completely unhindered or only partially hindered phenols.

The destruction of additives in γ-irradiated polypropylene films has been measured by infrared and electron spin resonance spectroscopy immediately after irradiation. Hindered amine or hindered phenol additives containing the ester group [>CH---O---C(=O)---CH₂~] were found to undergo ester destruction. Hindered amines containing the >CH~O---C(=O)---C--- group were not attacked. Phenols showed extensive loss of the phenolic ---OH group, presumably by peroxyl radical attack. Irradiation under conditions where peroxyl radicals were not formed or were scavenged competitively by the presence of a phenol prevented or reduced attack on the reactive ester linkage in hindered amines. It is possible that peroxyl radical attack is occurring at the ---CH₂--- group α to the carbonyl, which is known to be activated towards oxidation.

The nature of AC field (6 kV mm-1 and 1 kHz) aging of cross-linked polyethylene (XLPE) with (i) NaCl and (ii) CuSO4 (0.1 M) liquid electrodes has been studied with thermally stimulated discharge current (TSDC), thermal transient current (TTC) and Fourier transform infrared spectroscopic (FTIR) techniques. The behaviour of thermal transient current appears to be related to the electrical aging time and consists primarily of two components, i.e. dipolar and space-charge contributions. The magnitude of the TTC is related to that of the integrated charge released in a TSDC thermogram. FTIR measurements show that oxidation of stabilized XLPE is significantly lower than that of the unstabilized polymer. No noticeable increase in bound water content in the polymer was observed as measured by IR absorbance at approximately 3370 cm-1. Progressive enhancement of absorbance at approximately 1715 cm-1 and the TSDC peak at 70 degrees C with increasing field aging time appear to have the same origin.

The primary and secondary events which occur in polymers exposed to high-energy radiation are briefly surveyed with emphasis on the role of oxygen in causing polymer degradation. In addition slow, post-irradiation reactions are discussed as they relate to deterioration during storage. Potential methods of polymer stabilization against high-energy radiation are then reviewed from the viewpoints of electron and ion scavenging, energy transfer processes, radical scavenging (both carbon-centred and peroxyl) and also acceleration of radical decay. Some recently developed additive combinations, based on hindered amines, are discussed in detail and shown to operate by suppressing the formation of hydroperoxides during the free-radical oxidative chain process which immediately follows exposure to high-energy irradiation. The absence of these thermally labile groups improves post-irradiation storage stability. Finally, the effects of the radiation and radiation-induced events on stabilizers themselves are considered.

Poly(ethylene terephthalate) fabric was degraded under rapid heating conditions and the solid residue characterized by diffuse reflectance infrared spectroscopy. Fabric samples with and without flame retardant were pyrolyzed in air or nitrogen and spectra-recorded after various percentage weight changes. Dominant species included carboxylic acid end groups and linear anhydrides, based on infrared absorbances before and after chemical treatments of the residues. Vinyl benzoate end groups were clearly precluded, as were cyclic anhydrides. Diffuse reflectance spectra were also compared with spectra obtained by transmission infrared on conventional KBr discs prepared from the same residue. The former technique was shown to be superior to the pressed disc method for the tough residues obtained by thermolysis.

The effects of various polyolefin photostabilizers on the thermal and photodecomposition of model and polymeric hydroperoxides have been investigated, both in the liquid and solid phases. Several extremely effective ultraviolet stabilizers belonging to the metal chelate class can cause the rapid thermal decomposition of model and polymeric hydroperoxides. Although stabilizers did not reduce the quantum yield for polypropylene hydroperoxide photolysis, several additives can scavenge hydroxyl and macroalkoxy radical products which result from hydroperoxide photolytic cleavage. Ultraviolet stabilizers which were found to trap radicals were able to prevent the photodegradation of polypropylene which already contained a significant concentration of hydroperoxide groups. Highly effective polypropylene ultraviolet stabilizers probably operate by a range of mechanisms including hydroperoxide decomposition, radical scavenging and singlet oxygen quenching.

The thermal decomposition of 1-(2-cyano-2′-propoxy)-4-oxo-2,2,6,6-tetramethylpiperidine in solution has been studied as a function of solvent, temperature, and the presence of radical scavengers. In the absence of a scavenger, decomposition produces a hydroxylamine and methacrylonitrile, whereas in the presence of a scavenger such as oxygen, a nitroxide and 2-cyano-2-propyl radicals result. Decomposition in the presence of a scavenger is ∼50 times more rapid than decomposition in its absence. By using various free radical scavengers, scission of the NO—C bond is confirmed, that is the reverse of the normal nitroxide–alkyl radical reaction. Increasing solvent polarity causes a marked decrease in thermal stability, both in the presence or absence of radical traps. The importance of the thermal decomposition reactions in the interpretation of nitroxide scavenging of radicals is discussed.

The small-angle light-scattering (SALS) patterns of a wide range of polypropylene, nylon 6, and polyethylene ter ephthalate (PET) fibers have been examined so as to investigate the level of superstructural (>500 nm) ordering present within them. Many samples that were highly-disordered at a microstructural level, as evidenced by their wide-angle x-ray scattering (WAXS) patterns, showed evidence of extensive superstructural ordering. For example, a rapidly- quenched polypropylene fiber, which exhibited a "smectic" WAXS pattern, had a SALS pattern characteristic of spheru lites about 6 μm in diameter. Brief annealing of this sample produced the conventional monoclinic polypropylene WAXS pattern but did not noticeably change the size or shape of the SALS pattern. The usefulness and limitations of SALS for examining sheath-core effects and for demonstrating the existence of distorted spherulites is also discussed.

A series of isomeric fully aromatic polyamides (aramids) were photodegraded in the presence of oxygen. Films and fibers of these aramids gave carboxylic acids as the major products when measured by infrared spectroscopy and potentiometric titration. These acids probably resulted from the oxygen interception of the radicals generated by photocleavage of the amide bonds. In contrast to results found upon irradiation in the absence of oxygen, carboxylic acid formation was accompanied by a rapid loss in molecular weight, and a decrease in useful mechanical properties. Quantum yields for carboxylic acid formation were ≤5.5 × 10−5 mole/einstein and decreased along the aramid series roughly in agreement with increases in Tg. The photo-Fries rearrangement product was observed in aramid fibers irradiated in air, whereas no rearrangement product was seen in films irradiated in air.

The polarized and unpolarized far-infrared (460-30 cm−1) spectra of poly(p-phenylene terephthalamide) (PPTA) fabric and fiber arrays are reported. These spectra are discussed and tentatively analyzed on the basis of the internal and external modes of the repeat unit of PPTA. To assist in band assignments, the spectra of potassium triiodide-treated PPTA fibers and of benzanilide and its benzene solution are also reported.

The data manipulation ability of a Fourier transform IR spectrometer is exploited to characterize molecular orientation in polymers. In particular, the application of spectral subtraction to dichroic ratio determination and to the measurement of three-dimensional orientation via sample tilting and internal reflection spectroscopy is explored for nylon film samples.

From a comparison of the photo-and ..gamma..-irradiation-initiated oxidations of monofilaments and films, polypropylene oxidation rates and product ratios were found to be independent of sample morphology and orientation. Filament sensitivity to photo-oxidation was, however, drastically affected by extrusion and draw conditions, photosensitivity increasing with increasing draw speed and decreasing draw temperature. Draw effects were minimized by the exclusion of oxygen, indicating that free radicals produced by backbone cleavage during draw react with oxygen to give chromophoric oxidation products. The most important product detectable after drawing was probably the polypropylene hydroperoxide. A phenolic antioxidant reduced hydroperoxide formation, although sufficient hydroperoxide was still produced to accelerate photodegradation as compared with a similarly stabilized undrawn filament. Melt oxidation within the extruder was concluded to be much more important than thermal oxidation of the extruded filament as it cooled on the spinline.

Influence de la formation de sel sur l'efficacite ulterieure de ces composes comme photostabilisant

The effect of certain metal chelates on the yield of acetone from the photodecomposition of 2-pentanone in n-hexane solution has been studied. The chelates act as quenchers but the slopes of the Stern–Volmer plots are lower than the slope observed for cis-1,3-pentadiene. These additives protect solid polyolefins against photodegradation but it is unlikely that the mechanism primarily involves quenching of carbonyl triplets.The quantum yield of acetone production in the type II decomposition of 2-pentanone in n-hexane solution is 0.20 ± 0.01; the triplet state lifetime of 2-pentanone is 2.3 × 10−8 s.

All polymeric materials photodegrade to a greater or lesser extent on exposure to terrestrial sunlight in the presence of oxygen. For most commercially important polymers, some form of photo-stabilization is essential if adequate outdoor lifetimes are to be achieved. This has led to the development of many UV stabilizers for general use in films, fibers, and moldings. Comprehensive lists of UV-stabilizers and stabilizer structures have appeared in the recent literature [1–4].

Various transition metal chelates were found to quench 1O2 in the liquid phase. 1O2 was generated either photochemically, from an ozonide, or with a microwave source and reacted with rubrene or 3-methyl-2-pentene. Rate constants for 1O2 quenching by the chelates were measured in various solvents using the three 1O2 sources, and compared with the constants of previously known 1O2 quenchers. The most efficient chelates quenched 1O2 at close to the diffusion controlled rate, as did β-carotene. Some quenchers of 1O2 in the liquid phase were qualitatively shown to quench in the solid state. The possible 1O2 quenching mechanisms of the chelates are discussed.

Some volatile acids were found to dramatically reduce the effectiveness of additives based on 2,2,6,6-tetramethylpiperidine as photostabilizers for polypropylene films. Strong acids such as HCl, HBr, and HNO3 had the largest effect with sulfurous acid somewhat less detrimental. Weak organic acids did not impair the effectiveness of the hindered amine light stabilizers. The role of acid concentration and contact time were explored for the HCl–piperidyl additive system. Secondary and tertiary amines were included in the study as well as oligomeric additives and an N-oxyl derivative. The latter is less basic than the free amines, and it was correspondingly less effected by acid exposures. The possibilities for acid exposure during the compounding, fabrication, and use of stabilized polyolefin articles is discussed as well as the effects of acids in terms of proposed stabilization mechanisms for the hindered amines.

The destruction of various UV stabilizers in polypropylene films during irradiation has been examined both in the presence and absence of air and oxidation products. Although some stabilizers were destroyed in the absence of oxygen, all were more sensitive when irradiated in the presence of air. Several stabilizers were highly effective but were destroyed so rapidly that photoprotection of the polymer must have resulted from stabilizer products. Work with preoxidized polymer and with model hydroperoxides and peroxides indicated that most stabilizers were destroyed by the attack of oxygen-centered radicals, with peroxy radical attack appearing to dominate.

Commercial geotechnical fabrics have been exposed to accelerated soil burial testing for up to 7 years and the recovered nonwovens then examined for changes using burst strength testing, optical microscopy and infrared spectroscopy. By analytical testing the test specimens were shown to be based on monofilaments of polypropylene, polyethylene terephthalate (three samples) and a mixture of polypropylene and bicomponent fibres (polyamide-coated polypropylene filaments) respectively. None of the samples showed a significant decrease in burst strength outside of the deviation of the experimental data. The polypropylene-monofilament geotextile showed a slight trend of decreasing burst strength with increasing burial time, but no detectable oxidation products by infrared spectroscopy. The polyamide coating on the bicomponent filaments showed distinct signs of delamination after seven years' exposure.

Polypropylene (PP) and polyethylene (PE) peroxy radicals undergo photoreactions, but under commonly encountered photodegradation conditions these reaction rates are much lower than those of conventional radical reactions; for example, for PP peroxy radicals in noon summer sunlight at 25°C their rate of photolysis to alkyl radicals is less than one-tenth of their rate of hydrogen abstraction from the polymer. At lower temperatures( < −10°C) or when more intense radiation is used, however, peroxy radical photolysis becomes a proportionately more important source of alkyl radicals. In addition, occurrence of photoinduced radical combination is confirmed but is shown to be important only when photolysis generates an alkyl radical sufficiently close to a peroxy radical that termination can occur before oxygen reconverts the alkyl radical to a peroxy radical. This termination mechanism therefore becomes more important for radicals generated at lower temperatures when the average separation of a radical pair is lower.

The photo-oxidative degradation of polypropylene monofilaments with xenon-arc irradiation results initially in a drop in elongation-to-break, followed by a decrease in tensile strength on prolonged irradiation. A microscopic examination of fibers that were first peeled to reveal the interior of the filament and then uv-irradiated showed that the interior is partially fibrillar, and that the fibrillar zones are more resistant to photo-oxidative scission than the surrounding nonfibrillar matrix. The formation of cracks in the outer sheath of the fiber and through the nonfibrillar regions correlates with the drop in elongation-to-break. Fibrils are not severed until after long uv exposure times, corresponding to the observed drop in tensile strength. Fiber melting temperatures estimated from DSC endotherms drop steadily during photo-oxidation. This drop and the observed decrease in x-ray crystallinity may be associated with the photo-oxidative cleavage of tie molecules and chain-extended crystalline zones.