MICROHARDNESS-STRUCTURE CORRELATION OF IPP EPR BLENDS - INFLUENCE OF MOLECULAR-WEIGHT AND EPR PARTICLE CONTENT/

The influence of molecular weight on the mechanical properties of isot actic poly(propylene) (iPP) and iPP blended with ethylene-propylene co polymers has been investigated by means of the microhardness technique . The hardness (H) of iPP is shown to slightly decrease with increasin g molecular mass, within the range of molecular weights investigated. The H-decrease is correlated to a loss of crystallinity as the average molecular weight increases. On annealing, the mechanical properties a re enhanced as a consequence of an increase in both, the degree of cry stallinity and the crystalline lamellar thickness. A value of H-c(infi nity) for iPP crystals of infinite thickness in the alpha-form is prop osed for the first time. The inclusion of EPR particles in the iPP mat rix softens the material. This result could be explained in terms of a n increase in the basal surface free energy of the iPP crystals with i ncreasing amount of rubber content.