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Title: Recycling, regenerating and reusing reinforcement glass fibres
Author: Pender, Kyle Robert
ISNI:       0000 0004 7431 5013
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2018
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Over the last decades, the use of glass fibre reinforced thermosets (GRT) has become widespread and commonly used in many sectors. Currently no commercial recycling process exists for GRT and the amount of waste generated has reached an unsustainable level. The value of recycled glass fibres (RGF) is reduced significantly due to loss in strength and surface functionality during recycling. Thermal recycling processes involve decomposing the polymer matrix at elevated temperatures to recover the reinforcement fibres. Exposing to such high temperatures degrades the strength of the fibres as well as removes the sizing on the fibre surface. The focus of this thesis is to investigate the potential for retaining and regenerating the strength and interface properties of thermally recycled glass fibres; in order to produce composites reinforced with RGF that could complete with those using virgin/pristine glass fibres. In order to recycled GRT in-house, a lab scale thermal recycling system based on a fluidised bed reactor was initially designed and developed. To build on the already extensive research into this recycling process, this thesis aims to reduce the temperature required to recycle GRT within the fluidised bed by introducing a metal oxide catalyst to aid in the thermal decomposition of the thermosetting matrix. This novel line of research was selected due to the potential for reducing both the energy consumption of the recycling process and thermal damage sustained by the glass fibres during recycling. Using thermogravimetric analysis it was found that copper (II) oxide (CuO) was particularly active at catalysing the thermal decomposition of epoxy, reducing the decomposition temperature by up to 125 °C. When used within the fluidised bed recycling process, CuO facilitated recycling of glass fibre from glass fibre reinforced epoxy (GF-EP) at just 400 °C without compromising on fibre yield efficiency. Another avenue of research in this thesis was assessing the potential of a variety of chemical treatments to regenerate the strength and surface functionality of thermally recycled glass fibres. It was found that soaking in hot NaOH solution could provide approximately a 130% increase in the strength of RGF; concluding that changes to surface morphology due to etching was the re-strengthening mechanism. The interfacial adhesion between RGF and 1) polypropylene (PP) and 2) epoxy were examined. It was found that the interfacial shear strength (IFSS) between RGF and epoxy could be fully restored by first treating the RGF in NaOH solution. Regenerating the IFSS between RGF and PP proved more challenging despite the use of fibre sizing and PP matrix modification. GRP reinforced with RGF (with and without regeneration treatments) were prepare and mechanically characterised; however, the GRP exhibited significantly poorer mechanical properties than those prepared with virgin fibres. This drop in performance was typically attributed to a combination of 1) lower fibre strength, 2) poor fibre-polymer interfacial adhesion and 3) low fibre volume fraction within the GRP.
Supervisor: Thomason, James ; Yang, Liu Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral