The value of recycled glass fibres is reduced significantly due to loss in strength and surface functionality during recycling. This work investigates the potential of a variety of treatments to regenerate the strength and surface functionality of glass fibres recycled from retired wind turbine blades using an in-house developed fluidised bed process. It was found that soaking in hot NaOH solution could provide approximately a 130% increase in the tensile strength of recycled glass fibre; concluding that changes to surface morphology due to etching was the restrengthening mechanism. The interfacial adhesion between recycled glass fibre and polypropylene was also examined. A significant reduction in interfacial shear strength was observed after recycling which is attributed to the loss of original sizing after recycling. Regenerating the interfacial shear strength between recycled glass fibre and polypropylene proved challenging with the use of aminopropyltriethoxysilane coupling agent alone, however, a twofold increase in the interfacial shear strength was attained by modifying the polypropylene matrix with maleic anhydride. It was found that NaOH and silane treatments restored the interfacial shear strength between interfacial shear strength and epoxy to that obtained with as received glass fibres. This work shows that substantial improvements in recycled glass fibre strength and fibre-polymer adhesion can be achieved after utilising various regeneration treatments, in turn producing recycled glass fibres with significantly enhanced reinforcement potential.
An investigation into catalysed thermal recycling of glass fibre (GF) reinforced epoxy was carried out to improve its commercial viability. Strength degradation was established as a key barrier in retaining the value of fibres after recycling. Several metal oxides were examined to assess their ability at reducing the high operating temperatures currently limiting the reusability of recovered fibres. It is proposed that such a material could be integrated within a thermal recycling system facilitating an increase in fibre residual strength while reducing energy consumption of the process. It was found that CuO, CeO2 and Co3O4 were able to significantly accelerate the thermal degradation of epoxy. When applied to GF-epoxy, both the temperature and time required for fibre liberation were significantly lowered, reducing energy consumption by approximately 40%. The strength of fibres recovered with the aid of the metal oxides was increased, with the full potential for the strength retention yet to be achieved
An investigation of the effect of metal catalysts on thermal recycling of glass fiber-reinforced epoxy was carried out within a fluidized bed system. CuO nanopowder was integrated with epoxy to assess its ability in reducing the epoxy thermal stability and in turn reducing the typical temperatures required thermal recycling for epoxy composites. It was found that the CuO was able to significantly accelerate the thermal degradation of the selected epoxy. The CuO loading of 5 wt% of epoxy provided the largest reduction in thermal stability and activation energy of the second stage of decomposition. It was also demonstrated that the addition of CuO did not negatively affect epoxy mechanical properties or curing and in fact increased the epoxy glass transition temperature. When applied to glass fiber-epoxy (GF-epoxy) recycling within the fluidized bed process, glass fibers were recycled at just 400 C with a yield of up to 59%. POLYM. COMPOS., 40:3510-3519, 2019.
The value of recycled glass fibres is significantly reduced due to the loss of fibre strength and surface functionality that occurs during recycling. Results are presented from the ReCoVeR project on the regeneration of the strength of thermally conditioned glass fibres. Thermal recycling of end-of-life glass fibre reinforced composites or composite manufacturing waste delivers fibres with virtually no residual strength or value. Composites produced from such fibres also have extremely poor mechanical performance. Data is presented showing that a short hot alkali treatment of glass fibres which have been heat treated at typical composite recycling temperatures can more than triple their strength and restore their ability to act as an effective reinforcement in second life composite materials. Glass fibre recovered from fluidised bed recycling of composite materials exhibited much greater levels of mechanical abrasion damage. However, the strength of these fibres could also be increased to levels required in composite reinforcement by longer or more aggressive alkali treatment. The implications of these results for real materials reuse of recycled glass fibres as replacement for pristine reinforcement fibres are discussed.
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