Investigation of the strength loss of glass fibre after thermal conditioning

Abstract

Single fibre tensile testing of thermally conditioned water sized and γ – aminopropyltriethoxysilane (APS) sized boron-free E-glass has been carried out. The fibres were produced from identical melts following which bare fibre had only water applied to it before winding whereas the sized fibre had a solution containing only APS applied to its surface. Both fibre types experience a loss of room temperature tensile strength after exposure to elevated temperature. By application of a novel method of single fibre thermal conditioning it was demonstrated that the tensile strength of heat treated glass fibre can be significantly underestimated. Strength loss was found, in most cases, to be caused by a combination of thermal effect and mechanical handling damage. The latter is found to be influenced by thermal loading of the fibre. The onset of mechanical handling damage in APS sized fibre was found to be controlled by the thermal degradation of the silane sizing. This suggests that silane-based coatings, even when they are present as only a relatively thin surface layer, can protect fibres from the development or growth of critical surface flaws. The relative contribution to overall fibre strength loss from mechanical handling damage highlights the need to minimise processes which may cause fibre mechanical damage during glass fibre recycling procedures

The influence of removing sizing on strength and stiffness of conventional and high modulus E-glass fibres

“…The fibres after soxhlet extraction exhibit strengths close to the one obtained for the pristine fibres with no significant difference. They are however close to strengths measured on bare E-glass fibres [11]. It should be noted that a compliance correction have not been executed since only one gauge length was used.…”

“…The strength of the pristine fibres are much lower than values given in literature [2,3,19] from which a strength of around 3 GPa was expected. The burned fibres do however still follow the decreasing tendency and have similar values as found in literature [11][12][13]20]. The low strength is related to enlargement of existing surface flaws that become vulnable to attack from water [20].…”

“…Furthermore the sizing is suggested to heal flaws in the glass fibre surface and also reduce the risk of new flaws to arise [9,10]. Sized glass fibres exhibited higher strength compared to unsized fibres [11]. It has previously been shown that removing the sizing by heating increases the stiffness but at the cost of a decrease in the fibre strength [3,12,13].…”

Kinetics of dissolution of glass fibre in hot alkaline solution

“…Due to the harsh conditions employed in this procedure, the glass fibres suffer from a severe loss in their ultimate strength and therefore cannot be reused in many forms of composite applications [7][8][9][10]. 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].…”

Glass Fibre Strength—A Review with Relation to Composite Recycling

“…Jenkins et al [41] also confirmed the effect of thermal conditioning on the single fibre strength of these same APS sized and bare GF. They observed that many researchers studying this strength loss phenomenon carried out the heat conditioning process on the "as-received" fibre roving or mats.…”