Effects of rubber content and matrix structure on static and fatigue fracture in ABS copoymers

Rubber toughening mechanisms in acrylonitrile-butadiene-styrene (ABS) may be affected by the dispersed phase size, structure and content and by the characteristics of the styrene-acrylonotrile copolymer (SAN) matrix, namely by its molecular weight distribution and acrylonitrile (AN) content. In this work a series of ABS samples having different matrix average molecular weights and AN contents, and different disperse rubber-phas content were prepared. For all materials time to fracture initiation and crack speed as a function of the stress intensity factor were determined under cyclic loading, while J-resistance curves were determined under static loading. Directly compared, the results obtained indicate that fatigue frecture is positively affected by the molecular weight, but scarcely or, sometimes, negatively by the rubber content; on the contrary, stati J-resistance is higher for higher contents, but not significantly affected by matrix molecular weight. Howevere, a proper consideration of the time scale in which fracture occurs in the two loading modes, and of the strain energy release rates involved in fatigue testing, shows that these results are only apparently contrasting.