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Strengthening Epoxy/High Impact Polystyrene Interfaces Using End Grafting Polymer Chains

The fracture toughness G c of epoxy/high impact polystyrene (HIPS) interfaces was measured as a function of grafting chain density Σ of dPS-COOH chains of various degrees of polymerization N. For short chains, no effective entanglements can be formed between the dPS chains and the PS matrix of the HIPS, thus no enhancement in G c over that of a bare interface. For very long chains, even though each chain is well entangled with the HIPS, the maximum grafting density achievable is very low and such an interface fails by scission of the grafting chains so that the interface fracture toughness is also low. Large values of G c are observed at intermediate chain lengths where both effective entanglements can be formed and a large Σ can be achieved. Under these conditions the interface fails initially due to the formation of crazes and the subsequent break down of one of these crazes at the interface. The transition areal chain density from chain scission to crazing, Σ c ,is independent of N.