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Carbon fibre reinforced polymers (CFRPs) have high strength and stiffness, low density, long fatigue life in the fibre direction and good corrosion resistance. Nowadays, CFRPs are been used in aeronautics, wind turbine blades, sports goods and civil industry. However, one fundamental limitation of CFRPs is their brittleness (low ductility): CFRPs fail catastrophically at a relatively low strain (1.5% to 1.8%) under the tension with little warning or residual load-carrying capacity. To overcome this weakness, there is considerable interest to enhance the ductility of CFRPs exhibiting increased failure strains under tension and more progressive, graceful failure modes. In this work, three different methods were developed to improve the ductility of unidirectional (UD) CFRPs. The first method was to introduce fibre waviness into UD composites. The fibre alignment angles of the resulting composites and control composites were assessed and it was found that fibre waviness in UD composite did result in a stepwise tensile failure mode and an enhanced strain to failure. The second method was using an air-assisted fibre tow spreading and commingling technology to manufacture continuous intermingled carbon fibre/glass fibre hybrid tows. After defining and quantifying the degree of hybridisation (at the filament level) of two carbon fibre/glass fibre hybrid tows, the one with the higher degree of hybridisation was selected to manufacture intermingled UD hybrid composites. It was found that hybridising of continuous glass and carbon fibres resulted in the composites with an increased failure strain. Moreover, these hybrid composites failed more gradually. The final method investigated for introducing ductility was the introduction of ply cuts into PEEK interleaved UD carbon fibre/PEEK composites, which were manufactured by compression moulding. The resulting cut-ply interleaved carbon fibre/PEEK composite possessed a non-linear tensile stress-strain curve and ductility strain of 0.4%, which is due to shearing of the PEEK interleaves in the overlap regions between the cut carbon fibre plies.

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This study explores how bioplastics come into being and are changing by focusing on the relationship between bioplastic materials and the products into which they are made. Bioplastics, which are types of plastics that are made from plant sources and/or can be decomposed by microbial activity, are a challenging set of materials not only because of their variety, but also because of the multitude of industries, actors and socio-technical arrangements involved in their making. I explore the different places in which bioplastics are made; in practices of categorising and standardising and so defining bioplastics, in production and the realisation of bioplastics in everyday life through their substitution for other materials, and in branding where bioplastics are made variously visible, as well invisible, as their particular qualities are enacted in specific material-product relationships. I draw conclusions about the nature of the relationship between materials and products, how they are separate but also intricately interconnected, at the same time acknowledging that what is named as a material and as a product is contingent upon the stakeholder in the production chain of materials and products. I detail the ways in which materials get shaped by and also shape the standardization and production infrastructures, interests of different actors, competitor materials, and values at stake within their interaction to specific products. The aim of my study is to open up new connections and pathways for the study of materials, as well as objects, within the social sciences.

Polyethylene terephthalate (PET) is used to make textile fibres, bottles and packaging films. The global production in 2013 was 65 Mt, growing at 5-7% per year over the last decade. PET is manufactured by the continuous polymerisation of ethylene glycol and terephthalic acid, both of which are produced from fossil fuels. This Dissertation examines the environmental impact of manufacturing PET using process modelling and life cycle assessment. The work focused on ways of reducing the environmental impact of the polymer manufacture by using biomass instead of conventional fossil fuels, either as a raw material for producing ethylene glycol or terephthalic acid, or as a fuel to supply process heating or electricity. The environmental impacts of producing a PET bottle using ethylene glycol derived from two types of biomass, sugarcane and willow, were investigated and compared with conventional production. For sugarcane, the sugars were fermented to bioethanol, then dehydrated to ethylene. By using sugarcane, it was found that the global warming potential (GWP) and non-renewable resource use could be reduced by 28% and 16% respectively. Ethanol, and hence ethylene, can also be produced from willow, a lignocellulosic biomass, which could also potentially reduce nonrenewable resource use by 16%. However, for sugarcane there was a significant increase in other environmental impacts, e.g. acidification and eutrophication potential; these increases were smaller when using willow. From supply chain analysis, the transport of finished and intermediate products only made a minor contribution to the environmental impacts. The principal raw material for terephthalic acid is p-xylene, conventionally made from naphtha. It is feasible, however, to manufacture p-xylene by the catalytic conversion of sugars extracted from biomass sources. A PET bottle made using p-xylene derived from willow could reduce the GWP and non-renewable energy use by 32% and 2%, respectively, or 87% and 26% using sugarcane. Again, the disadvantage of using biomass was that all other environmental impact categories were increased over materials derived from petrochemicals. Biomass can also be used for generating process heat or electricity. It was found that the best possible use of biomass within the PET value chain would be combustion to supply process heat, followed closely by burning to generate electricity. In fact, only where ethylene is produced via the fermentation of sugars from hydrolysed willow, and for one measure, GWP, was producing a chemical from biomass more sustainable than combustion for process heating. This conclusion is sensitive to the energy sources from which heat and grid electricity are otherwise produced and might therefore alter as future conventional energy sources change. Finally, the possible savings in GWP and energy use by recycling PET bottles were evaluated for both closed-loop and open-loop systems. Open-loop recycling gave better savings for GWP and energy use when compared with closed-loop recycling. The transport associated with the international trade of baled bottles, largely imported by China, has a minimal effect on the possible savings by recycling. This work has established that there is scope for improving the sustainability of the polyester industry; however trade-offs need to be carefully considered on a case by case basis.

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The work aims to understand bulk transport mechanisms in epoxy resins and their influence on partial discharge and electrical treeing phenomena. The charge transport processes in two bisphenol-A epoxy resin systems were studied using dielectric spectroscopy and related to moisture uptake. In both resins, absorbed moisture was implicated in the formation of a bulk quasi-dc (QDC) charge transport mechanism above the glass transition temperature. Complementary investigations of the electrical degradation process in epoxy resins, principally electrical treeing, were also found to be dependent on temperature and moisture absorbed by the samples. A model for electrical tree growth in flexible epoxy resins has been proposed. The novelty of the model is that it considers a QDC charge transport through the bulk polymer, where proton hopping is suggested as a long range transport mechanism. The time needed for the neutralisation of the space charge accumulated ahead of a growing tree structure by charges involved in the QDC process is suggested as a governing parameter of the tree growth rate. Electrical tree growth is related to changes in the time constant of the QDC process and hence the percolation distance that the protons can travel. At high levels of moisture and/or temperature, multiple percolation paths can be established thus increasing the effective ionic conductivity of the material leading to thermal breakdown when tanδ is greater than 1.

Phenol-formaldehyde resins (P/F ratio 1/1.75) were synthesized using paraform and 97% phenol as reactants under the influence of a basic catalyst (0.5 mole catalyst/mole phenol). Three catalysts (i) sodium hydroxide, (ii) barium hydroxide, (iii) triethylamine were used to monitor the effect that the chemical nature of the catalyst had on the course of the reaction.