Fracture resistance of polyblends and polyblend matrix composites - Part III - Role of rubber type and location in nylon 6,6/SAN composites

The role of rubber particle type, location and morphology on toughening in blends of nylon 6,6 with styrene acrylonitrile (SAN), with and without fibr e reinforcements was examined in this study. The rubber used was ethylene p ropylene diene monomer (EPDM) rubber and the results were compared to a pre vious study that used butadiene rubber. The compositions of the blends rang ed from pure nylon 6,6 to pure SAN. EPDM rubber was chemically compatibiliz ed with one of them atrixphases rather than grafted, as in the ABS. In orde r to study the effect of rubber location on fracture behaviour, the approac h was to compatibilize EPDM with either the mi nor phase or the major phase component of the blend. Attention was focused on fracture initiation tough ness and fracture propagation toughness, measured through the parameters J( IC) and J(SS), respectively. J(SS) refers to the steady-state, or plateau v alue of the material R-cu rye and was therefore a measure of total toughnes s which included the additional component derived from crack extension. The results indicated that EPDM rubber was not as effective a toughening agent as was butadiene in the Acrylonitrile Butadiene Styrene (ABS) system, prim arily due to the morphology of EPDM and its interface character with the ny lon 6,6 or SAN matrix. It was demonstrated that the embrittlement effects o f a second rigid polymer phase can be mitigated by selectively adding rubbe r to that phase in the alloy or blend. With regard to the role of fibre rei nforcement, a strong fibre matrix interface was found to be essential for t oughening. Further, the extent of rubber toughening was larger when fibres were present than when fibres were absent, provided the fibre matrix interf ace was strong. Fibres also, like rubber, enhanced local matrix plasticity as well as reduced the embrittlement effects associated with a second polym er phase. (C) 1998 Kluwer Academic Publishers.