A chemical approach to regenerating the performance of thermally damaged glass fibres

Student thesis: Doctoral Thesis

Abstract

Glass fibre reinforced thermosetting polymers (GRP) have been used in a wide range of applications over the past decades, such as in the production of wind turbine blades. Once these materials reach the end of their life cycle, they are often deposited in landfill sites, a disposal option that is becoming more expensive and environmentally unfriendly. The glass fibres can be recycled from the composite waste by degrading the polymer matrix at elevated temperatures, however this leads to fibres with drastically low mechanical strength. The main objective of this research project was to develop chemical treatments to regenerate the strength of such fibres, to allow their reuse in second life composite materials.In this work, glass fibres were heated in a furnace to mimic thermal recycling conditions, before chemical treatments were applied to regenerate their strength. It was discovered that a short treatment of fibres in hot and concentrated sodium hydroxide (NaOH) or potassium hydroxide (KOH) solution significantly increased their strength, likely due to etching of fibre surface flaws. Interestingly, these treatments had a detrimental effect on the strength of virgin fibres.A kinetic investigation was carried out to determine the etching rate of glass fibres in alkaline solutions. This was achieved by accurately measuring the diameter of individual glass fibres before and after alkaline treatment using a scanning electron microscope.It was found that NaOH solution was more corrosive towards the glass fibres than KOH solution, and that increasing the concentration and temperature of the alkaline solution led to an increase in etching rate.Later in the study, glass fibres were thermally recycled from an end of life wind turbine blade. The recycling procedure involved feeding the downsized blade section into an in house fluidised bed. Fluidised bed recycling is a common thermal recycling technique where elevated temperatures and oxygen lead to degradation of the composite matrix and recovery of the fibrous components. It was found that a short treatment of the recycled fibres in concentrated NaOH solution managed to considerably regenerate their strength. An effort was made in recovering the strength of the fibres under milder alkaline conditions, though the reported strength increase was not as significant. A case study was conducted to determine the industrial feasibility of treating recycled glass fibre in alkaline solution. It was discovered that the costs of solution preparation and processing conditions can be partially offset through charging businesses for collecting their composite waste, and selling the regenerated glass fibres as chopped fibre products.
Date of Award16 Aug 2019
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorLiu Yang (Supervisor) & John Liggat (Supervisor)

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