Mechanical properties of the glass fibre-polyester interphase

Abstract

Single-fibre pull-out experiments have been carried out with glass fibres with and without silane coupling agents. Debonding was easiest when the fibre had a commercial coating on it which contained a silane and processing aids, and was relatively thick. Solvent extraction of the coating increased the bond strength, and total removal of it increased it still further. The strongest bonds were stronger than the polymer and probably failed by brittle fracture with a work of about 0.25 kJ m⁻², much less than the estimated work of fracture of the polymer. After debonding, frictional sliding took place, with an interfacial pressure of 17 M Pa, and with a coefficient of friction that was influenced by the interface in the same way as was the bond strength, i.e. greatest for the bare fibre, and least for the coated fibre. The silane coupling agent plasticized the polyester, and it seems highly probable that debonding took place in the interphase, when the fibre was coated, so that frictional sliding during post-debond pull-out was between the chemisorbed layer of silane and the polymer. The physisorbed layer of silane probably dissolved in the polymer, because the friction was not affected by solvent extraction.