Can thermally degraded glass fibre be regenerated for closed-loop recycling of thermosetting composites?

Abstract

Commercially manufactured E-glass fibres were heat-conditioned to mimic the effects of thermal recycling of glass fibre thermosetting composites. Degradation in the strength and surface functionality of heat-treated fibres was identified as a key barrier to reusing the fibres as valuable reinforcement in composite applications. A chemical approach has been developed to address these issues and this included two individual chemical treatments, namely chemical etching and post-silanisation. The effectiveness of the treatments was evaluated for both thermal degraded fibres and corresponding composites. Drastic reduction was observed in the properties of the composites with the heat-conditioned preforms indicating thermally degraded glass fibres have no value for second-life reinforcement without further fibre regeneration. However, significant regeneration to the above properties was successfully obtained through the approach developed in this work and the results strongly demonstrated the feasibility of regeneration of thermally degraded glass fibres for potential closed-loop recycling of thermosetting composites

Glass Fibre Strength—A Review with Relation to Composite Recycling

“…Consequently, the loss in reinforcement performance of the RGF compared to pristine GF is actually proportionally much greater than the measured loss in composite performance. This has been confirmed in recent work by Thomason et al [17,119] and Yang et al [120], where heat-conditioned fibres were used to produce RGF-PP composites and RGF-epoxy composites. In both cases, reference values for the polymer matrix were produced, and in both cases, the tensile strength of the RGF composites was a little better than the unreinforced polymer matrix.…”

“…A very recent paper by Yang et al further explored the potential of HF treatment in glass fibre recovery [120]. They reported on a systematic study of the effects of heat treatment, HF treatment and silane treatment on the strength of boron-free E-glass fibres and RGF-epoxy composites produced by vacuum infusion moulding.…”

“…Following a similar protocol to that of the HF work by Yang et al [120], the authors presented the use of a combination of thermal conditioning, hot NaOH treatment and silanisation on the average strength of single fibres, the interfacial shear strength between the fibres and PP and the performance of random in-plane GMT laminates. Results indicated that the GF lose 80% or more of their strength when exposed to temperatures typically found in GRP thermal recycling processes, which makes them unsuitable for reuse as a composite reinforcement.…”

Kinetics of dissolution of glass fibre in hot alkaline solution

“…We have recently developed a simple chemical approach to address this key issue and have successfully proved that these damaged filaments can be reused as reinforcements again if their strength is restored [11]. It was found that the strength of glass fibres heat-conditioned at 450-600°C can almost triple after a few minutes of immersion in dilute hydrofluoric acid (HF) [12]. HF is proven to be an effective chemical etchant and is thought to strengthen glass by removing surface flaws [13].…”

Glass Fibers: Quo Vadis?

“…As a preliminary conclusion, they summarize that heat-treated fibers with HF treatment followed by silanisation resulted in composites with high levels of composite performance recovery. The authors also review their own work [6,7] on 'non-HF based (e.g., short treatment in hot NaOH solution and further application of a silane sizing) glass fiber strength regeneration treatment towards a cost-effective closed-loop glass fiber recycling technology'. It should be mentioned that this review highlights the available knowledge on the thermally induced strength loss in recycling of glass fibers, discusses some of the related phenomena, and presents the status of research, besides many open questions connected with surface flaws, glass fiber durability, repair of fiber surfaces and interphase built-up in composites.…”