The elaboration of an in-situ composite consisting of ethylene vinyl acetate copolymer (EVA) and polybutylenetherephtalate (PBT) was investigated. An interchain chemical reaction during processing operations was used to generate a grafted PBT-g-EVA copolymer at the interface of the two polymers. Composites with either nodular or fibrillar morphologies were obtained. Fibrillar morphology was achieved by stretching the extruded blend at the exit of the die. Elongational properties of such composites were investigated by using the fiber wind up technique. The influence of the aspect ratio of PET solid inclusions on the elongational viscosity was discussed for a series of EVA/PBT composites. Clearly, the strain hardening/ softening properties were found to be strongly affected by the aspect ratio. Increasing the aspect ratio of PBT solid particles made the strain hardening weaker and even gave strain-softening. This behavior is emphasized by the presence of the grafted PBT-g-EVA copolymer. The results suggest that strain-hardening or softening of such composites is correlated to the homogeneity of the flow at EVA-PBT interface: the elongational flow is disrupted in the interphase region so that the deformation around the particle is not homogeneous.

A study to evaluate the thermorheological properties of organic in situ composites with short polymer fibres dispersed in a thermoplastic matrix has been carried out. High-density polyethylene/Poly(butylene terephtalate) HDPE/PBT, HDPE/EVA-9/PBT and HDPE/(EVA-9-Bu2SnO)/PBT (in situ compatibilised blends) were melt blended in a twin-screw extruder, drawn at the die exit and cooled. Morphological results revealed that it is possible to generate fibrillar morphologies for high PBT concentration and draw ratios higher than 1. Compatibilisation with in situ generated PBT-g-EVA-9 compatibiliser was achieved. Rheological properties in the melt state and in the solid state were used to analyse the compatibilisation and the reinforcing effect of fibrils. Two phenomenological models, Takayanagi and Halpin-Tsaı̈, were used to describe the variations of E′ and tanδ as a function of temperature.

A study to evaluate the rheological properties of organic in situ short polymer fibres (poly(butylene terephtalate) (PBT))/high density polyethylene (HDPE) and high density polyethylene/poly(ethylene-co-vinyl acetate) (HDPE/EVA9) composites has been carried out. The in situ compatibilization of the HDPE/EVA9/PBT systems with the Bu2SnO catalyst was performed. The different systems were melt blended in a twin screw extruder, drawn at the die exit and cooled.The results indicate that it is possible to produce such composites using reactive extrusion for compatibilization and post extrusion drawing to control the aspect ratio of the PBT fibres. Morphological analysis allowed evaluation of parameters such as draw ratio, PBT concentration and compatibilization on the size and shape of the fibrils. Their influence on the solid rheological behaviour is discussed.

A study to evaluate the thermorheological properties of organic in situ composites with short polymer fibres dispersed in a thermoplastic matrix has been carried out. HDPE/PBT, HDPE/EVA9/PBT and HDPE/(EVA9-Bu2SnO)/PBT (in situ compatibilized blend) were melt blended in a twin screw extruder, drawn at the die exit and cooled. Morphological results indicate that it is possible to generate fibrillar morphologies for 20 and 30% PET blends. Increasing the draw ratio (from 2 to 3.5) results in a decrease of the aspect ratio of the fibrils for the non compatibilized blends. The presence of PBT-g-EVA9 copolymer improved dispersion and contributed to a decrease in the fibrils length and nodules diameter. The linear viscoelastic results showed an increase in the storage modulus G' as the PET concentration and/or the draw ratio increased. The presence of EVA9 in the matrix also resulted in an increase in G'. For 30% PET composites, a pseudo-equilibrium plateau was observed in the low frequency region and was attributed, as for the other multiphase systems, to interparticular interactions. The presence of EVA9 and/or PBT-g-EVA9 copolymer contributed to the increase of this plateau modulus. Injection moulding of such composites did not destroy the fibrillar morphology as far as the injection temperature was kept well below the melting temperature of the PET phase.