Isothermal and nonisothermal crystallization of polymers : analysis with a shear differential thermal analyzer

The working principle of an instrument developed for studying the effects of controlled shear pulses on the isothermal and nonisothermal solidification of polymers is presented. The device combines a capillary rheometer and a differential thermal analyzer DTA . The capillary rheometer part of the system allows the production of shear pulses with controlled duration and intensity at any prescribed temperature up to 300 °C, and the DTA records the thermal effects resulting from the solidification. Results obtained for quiescent isothermal and nonisothermal crystallizations compare well with those obtained from power compensation differential scanning calorimetry. The effect of controlled shear pulses on the overall isothermal crystallization kinetics enables the evaluation of a critical strain responsible for the saturation of crystallization in sheared polymer melts. Additional shear increase of the shear rate or of the shearing time does not accelerate the crystallization kinetics. The shear-induced nonisothermal crystallization of polyethylene filled with talc shows the acceleration of the crystallization kinetics with the shear rate increase, thus confirming this device as a valuable experimental tool for studying the effect of shear on the solidification of fast crystallizing materials.Fundação para a Ciência e a Tecnologia (FCT) - CTM/33061/200