Improvement of delamination resistance of glass-phenolic composites through matrix toughening mechanism using poly (vinyl butyral)

There are various types of composites among which these with layered structure are susceptible to delamination under the applied loads. Phenolic resin/glass fiber composites, one of the most commonly used composites, are prone to delamination. In this research, the improvement of the delamination resistance of phenolic composites via the addition of polyvinyl butyral (PVB), a thermoplastic additive at various contents (i.e. 1, 3, 5, 10 and 20 phr) has been studied. For this purpose a phenolic/glass fiber prepreg modified with thermoplastic additive was prepared and brought to a partially cured (B-stage) by using a specified temperature-time condition. The flow ability of the prepared prepregs was measured. Samples for the flexural test were then prepared by compression molding of the prepregs having the flow abilities of 10%. Three-point bending test results showed that the addition of PVB relatively improves the strength and delamination resistance of the composites, the extent of which depends on the additive content. The addition of PVB at 3 phr increased the fracture toughness up to 58.2%, however beyond which it was reduced; hence 3phr was regarded as the optimum value. Inspection of the fracture surface morphology by SEM revealed the inhibition of crack propagation even at 1 phr of PVB.