Toughening multiple shear deformation

Toughened Polymers with Semicrystalline Matrix. It is well known that toughness of semicrystalline polymers such as PA (polyamide) and PP can be increased similar to the amorphous poljuners by the addition of relatively small amounts of rubber particles such as EPR or EPDM. As in HIPS and ABS, the modifier particles act as stress concentrators, initiating a plastic deformation of matrix strands between the particles as the main energy absorption step. In impact-modified PA and PP at room temperature, plastic deformation takes place through shear deformation (mechanism of multiple shear deformation). 

Next we looked at the microvoid situation in a bisphenol A modified CTBN-epoxy system. This sample had the highest toughening properties that we developed in the epoxy system because of a two-particle size rubber population that uniquely gives a combination of shear deformation and tensile crazing. Only some of the large particles had microvoid development. Consequently the whitening was much less than when only crazing occurs. The multiple failure sites were still evident. 

It is well known that the main mechanisms of inelastic deformation are shear yielding and multiple crazing in the rigid matrix phase, as well as cavitation in the soft dispersed phase in rubber-toughened plastics and multiphase polymers [42]. Eor many years, these mechanisms have been studied using microscopy techniques. 

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