Thermomechanical history effects on rigid PVC microstructure and impact properties

Rigid PVC microstructure strongly depends on processing conditions: under both shear and heat influence, gelation process occurs, and the resulting morphology can be characterized by the so-called gelation level parameter. But thermomechanical history also affects several other features of the microstructure. In this work, two different aspects mainly related to (i) orientation and (ii) molecular mobility are pointed out, and their respective effects on poly(vinyl chloride) (PVC) impact properties are described. Charpy impact tests have been carried out on a typical extruded window profile formulation, evidencing a strong anisotropy effect in those extrudates. It turned out that modulated differential scanning calorimetry was able to evidence macromolecular orientation. Then, the effects of heat treatments on impact properties were investigated. Below the glassy transition temperature (Tg) of PVC, physical ageing results in a decrease of the impact performance, without affecting PVC anisotropy. The reason of this performance loss is the reduction of the molecular mobility, as evidenced by dynamical mechanical analysis experiments. After performing a heat treatment above Tg, another important decrease of the impact performance was observed. This decrease was attributed to (i) partial disorientation of the PVC macromolecular chains and (ii) reduction of the molecular mobility. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2009–2017, 2007