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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.

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 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.

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.

The chemical and physical property changes produced in polypropylene samples by γ-irradiation in air have been measured for a range of potential stabilizers. Impact properties of post-irradiation aged samples were compared with the yields of tertiary and secondary hydroperoxides, peroxyl radicals and ketones. Some additives markedly increased the initial rate of peroxyl radical decay, but this effect did not correlate with subsequent stability. Retention of impact strength was found for additives which minimized the initial formation of hydroperoxides and ketonic, backbone scission products. A piperidyl additive gave good protection but was especially effective when used in combination with some benzophenone derivatives. The latter were largely ineffective radiation stabilizers when used alone. None of the stabilizers appeared to reduce the initial yield of peroxyl radicals produced in the γ-irradiated polymer and the piperidyl compound was only converted to its nitroxide during the post-irradiation period.

The effects of exposure to processing conditions and strongly acidic gases on the photo-stability of polypropylene films stabilized with hindered amine light stabilizers (HALS) have been studied. A series of monofunctional hindered amines based on tetramethylpiperidine containing 〉NH〉NO〉NCOCH₃ and 〉N--OC(==O0CH₃ substituents in the piperidyl ring was compared with a bifunctional secondary amine. Exposure to heat and shear in a Brabender Plastograph caused loss by volatilization and decomposition of the 〉N O C(==O)CH₃ additive. All of the HALS derivatives formed salts upon exposure to gaseous HCl and their photo-stabilizing ability was greatly impaired although the monofunctional secondary amine was superior to the bifunctional amine under these conditions. The 〉N-COCH₃ additive was extensively decomposed by the HCl exposure.

The conversion products from a commercially important photo-stabilizer based on 2,2,6,6-tetramethylpiperidine have been identified and quantified during the photo-oxidation of polypropylene. From a comparison with model compounds and model systems, direct evidence for the dominant involvement of grafted substituted hydroxylamine species was obtained by infra-red spectroscopy. Non-stabilizing conversion products, including N -acyloxy compounds, were also identified and the overall mechanism of photo-protection by hindered amine stabilizers is discussed.

A new procedure has been developed for the identification and quantification of key products from the oxidation of solid polyolefins, based on reactions with gaseous nitric oxide. Alcohol and hydroperoxide groups are converted to nitrites and nitrates, respectively, and can be detected with high sensitivity by infrared spectroscopy. Furthermore, the nitrate and nitrite absorptions are influenced by the primary, secondary or tertiary nature of the alkyl substituents so that it is possible to identify differing sites of attack in branched polyolefins. Preliminary results from the application of nitric oxide reactions to the analysis of polyethylene and polypropylene oxidized by γ-irradiation are used to illustrate the potential of the technique and a comparison made with other current methods.

Chromic acid solutions were used to oxidatively etch linear (high density) and branched (low density) polyethylene and isotactic polypropylene. Etched surfaces were characterized by surface IR spectroscopy, wettability, electron microscopy and aqueous adhesive bonding (peel test). Polypropylene was found to etch rapidly, but showed little residual chemical or topographical change. The polyethylenes etched more slowly, especially in the case of the linear polymer, but showed large changes in surface chemistry as a result of oxidative attack. Adhesion onto polyolefin films and fabric increased very rapidly during the first few seconds of attack. This increase is interpreted in terms of wettability, topography and cohesive strength of the surface layer. The differences in etch behavior between the polyolefins is interpreted in terms of ease of oxidative attack at branch points, and surface accessibility to the acid.