The Effects of Initial Crystalline Morphology on the Properties of Drawn Polypropylene

Abstract

Proton spin-spin relaxation times, linear thermal expansivity and tensile modulus have been measured for drawn polypropylene prepared from both bulk-crystallized spherulitic materials (MGC) and solution grown crystals (SGC). Effects of initial morphology are found for chain mobility in the noncrystalline regions and for crystalline orientation function, which produced the difference in the efficiency of draw between MGC and SGC. The mass fraction of the highly strained noncrystalline component (Fi) changed with draw ratio. At higher draw ratio, the stepwise decreases of the MGC were accompanied by corresponding increases in the crystalline mass fraction (Fc). However, the Fc of the SGC remained almost constant for the draw ratio investigated. A large rubber-elastic contraction observed for highly drawn samples suggests that the axial length of the crystalline bridges is not enough and/or the bridge content is not sufficiently large to resist the contraction. At any draw ratio, the tensile modulus was higher for MGC than for SGC, which indicates the higher efficiency of draw for MGC than for SGC.