The effect of free quenching on the mechanical, thermal, and thermophysical properties of polystyrene has been investigated. Three different thermal treatments were investigated: a first quenching from the melt state to different temperatures, a second quenching from T g + 7 • C, and finally an annealing. The results have shown that a slight improvement of the impact strength can be obtained after a second quenching at 40 • C, and a correlation between the mechanical and thermal properties is observed. The improvement of this property was obtained at the expense of other properties such as the elastic modulus, density, hardness, and the heat distortion temperature (HDT). The little improvement of the impact strength after the second quenching is probably linked to the existence of a relaxation mode located around 40 • C. However, no effects have been shown on the thermophysical properties.

ABSTRACT:The effects of quenching temperature including different thermal histories on mechanical, physical, and thermal properties of pigmented polycarbonate (PC/ TiO 2 ) were investigated. Tensile test, Izod impact strength and heat distortion temperature (HDT) were performed on specimens of 3 mm thickness. Pigment content and quenching temperature are two key factors that affect the properties of the materials. A higher content of pigments results in an increase of modulus of elasticity and a decrease of unotched and notched Izod impact strength, as well as elongation at break. A maximum of yield stress and HDT is obtained at 3% of TiO 2 , which was considered as the optimum level of pigment. An additional second quenching at 408C has allowed to improve Izod impact strength and elongation at break of specimens with 3% of TiO 2 ; whereas modulus of elasticity, density, yield stress, and HDT were minimum at this quenching temperature.

ABSTRACT:The effect of different thermal treatments on the mechanical and thermal properties of polycarbonate was investigated. The first quenching procedure which involves the quench of the samples from the melt state to different temperatures allowed improving impact strength and elongation at break for a quenching temperature of 08C. A second quenching procedure, corresponding to specimens heated again at 1608C (T g 1 158C) and quenched a second time, showed a better enhancement of the impact strength and elongation at break to the detriment of other properties such as elastic modulus, density, yield stress, and heat distortion temperature, for a quenching temperature of 408C. This effect was associated to the existence of a relaxation mode around 358C.