ORIENTED PP PS COMPOSITES OBTAINED BY POLYMERIZATION OF STYRENE INSIDE ORIENTED PP MATRICES .2. SHRINKAGE BEHAVIOR AND MECHANICAL-PROPERTIES

Thermal shrinkage and the mechanical properties of oriented polypropyl ene-polystyrene (PP-PS) composites obtained by in situ polymerization of styrene in the oriented PP matrices were examined by the analysis o f shrinkage stress curves and dynamic mechanical data. It has been sho wn that by changing the structure of the oriented matrices it is possi ble to control the properties of the obtained oriented composites. Som e composites reveal an increased stability of the molecular network at higher temperatures and the modulus of the material obtained from the matrix drawn at 90-degrees-C to the natural draw ratio is significant ly increased. It is also shown that the differences between the untrea ted matrices and the PP component of the respective composites observe d in the relaxation of the shrinkage stresses correspond very well wit h the differences seen in the mechanical loss in the frequency range o f about 0.02 Hz. Such behavior suggests that similar molecular motions are involved both in the relaxation of shrinkage stresses and in this part of the mechanical loss. (C) 1993 John Wiley & Sons, Inc.