Transient elongational properties of an in situ generated polymer/polymer composite

The elaboration of an in-situ composite consisting of ethylene vinyl acetat e copolymer (EVA) and polybutylenetherephtalate (PBT) was investigated. An interchain chemical reaction during processing operations was used to gener ate a grafted PBT-g-EVA copolymer at the interface of the two polymers. Com posites with either nodular or fibrillar morphologies were obtained. Fibril lar morphology was achieved by stretching the extruded blend at the exit of the die. Elongational properties of such composites were investigated by u sing the fiber wind up technique. The influence of the aspect ratio of PET solid inclusions on the elongational viscosity was discussed for a series o f EVA/PBT composites. Clearly, the strain hardening/ softening properties w ere found to be strongly affected by the aspect ratio. Increasing the aspec t ratio of PBT solid particles made the strain hardening weaker and even ga ve strain-softening. This behavior is emphasized by the presence of the gra fted PBT-g-EVA copolymer. The results suggest that strain-hardening or soft ening of such composites is correlated to the homogeneity of the flow at EV A-PBT interface: the elongational flow is disrupted in the interphase regio n so that the deformation around the particle is not homogeneous.