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The deterioration of cellulose nitrate artefacts in museum and art collections is a complex problem facing conservators and conservation scientists. This study has looked at several aspects of the degradation by analysing artefacts and model samples. Initial work concentrated on a survey of a collection of artefacts, many of which showed active degradation, by visual inspection and FTTR spectroscopy. A more thorough analysis of the artefacts was carried out, using ion chromatography, xray fluorescence spectroscopy and atomic absorption spectroscopy, to identify compositional differences between samples, which may relate to degradation. The results of these studies suggested that residual sulphate in the plastics is a cause of increased degradation. The presence of oxalate in degraded artefacts also indicated that chain scission is occurring during deterioration. Later work using gel permeation chromatography confirmed this. Work has also involved the use of accelerated ageing tests to study the effect of sulphate in the degradation and also the influence of inorganic fillers, iron and humidity. It has been concluded that the degradation of cellulose nitrate artefacts is dependent on the presence of sulphate and humidity. The process is diffusion controlled which indicates that loss of plasticiser is a vital factor. This work also suggests simple procedures that can be used to assess an artefact's stability.

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Melt blending of polyethylene, in particularly HDPE and LLDPE, have been shown to be a major success, especially in the film markets. In this thesis studies are reported on the stress rupture performance of pipes produced from selected polyethylene materials blended to a chosen MDPE pipe grade. The pipes were tested, notched or unnotched, at a single temperature of 80oC and at internal pressures designed to induce slit-mode failure. Results showed the simple concept of increasing the stress rupture performance of a pipe material by the addition of a higher molecular weight polymer was invalidated when applied to the blends system used in these studies. However molecular weight does have an influence to some degree as was illustrated by the addition of a very low molecular weight material, which produced the poorest stress rupture properties of the additives used. Charaterization techniques, including Differential Scanning Calorimetry and Dynamic Mechanical Thermal Analysis, showed good compatibility of the blends at all addition levels studied, illustrating that there was no seperation of the polyethylene phases. Fracture analysis of pipe failures showed variations between the blends, except for a MDPE additive which had similar molecular characteristics to the base resin. Some of the blends fracture surfaces were found to vary in fibre height and distribution from the bore region to the outside of the pipe. On the morphological front spherulites from pipe samples were found to be a poor indication of stress rupture behaviour. Pipe blends were produced which had fine/featureless morphologies but whose 80oC stress rupture behaviour was found to be good and poor in comparison to the control MDPE pipe resin which had a spherulitic structure much larger than all the blends studied. Models presented here infer that a number of mechanisms may be operating in producing these changes in stress rupture properties. One may be due to a dilution of a polyethylene system by materials of varying molecular weight and molecular weight distributions. This was evident in MDPE-AlMDPE-P blends (MDPE-P being a high molecular weight, low branch length additive), where the stress rupture performance initially decreased and then increased after addition levels of 10wt%. The main mechanisms for this system was postulated to be the initial dilution of octene branching levels within the MDPE-A blend causing a reduction in the ability of the branches to sterically hinder crack propagation under stress, to one of chain entanglement after sufficient levels of the additive was present in the blend to contribute to increasing the stress rupture behaviour. It was found that good blending can be produced using materials with similar branching types and distributions (especially in the high molecular weight tail), similar molecular weights and distributions and comparable crystallization temperatures.

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No description available.