ULTRA-HIGH MODULUS ISOTACTIC POLYPROPYLENE .1. THE INFLUENCE OF ORIENTATION DRAWING AND INITIAL MORPHOLOGY ON THE STRUCTURE AND PROPERTIES OF ORIENTED SAMPLES

The influence of a number of factors (temperature-speed regime and the quantity of draw stages, molecular weight of a polymer, etc.) on the deformability of initial isotropic IPP and on mechanical characteristics of highly-oriented samples, obtained in the process of a two-stage isothermal orientation drawing, was studied. It was shown that the maximum achievable values of elastic modulus and draw ratio depended not only on the molecular weight of a polymer and the sizes of spherulites, constituting initial IPP, but on the structural organization of inner- and interspherulite regions. Upon physical aging of initial isotropic films, irreversible structural changes take place, which result in the formation of microvoids while being drawn and in the reduction of mechanical properties of obtained material. An extremal dependence of elastic modulus and draw ratio of maximum drawn IPP samples on draw speed was discovered. A structural model, which is supposed to possess tie molecules with various degrees of tautness in amorphous layers, was proposed. Higher effectiveness of two-stage drawing in comparison with one-stage drawing was established. The optimum temperature-speed regime of orientation drawing, which permits the reception of highly oriented, ultra-high modulus IPP with maximum high mechanical characteristics (elastic modulus approximately 30-35 GPa and tensile strength approximately 1,1 GPa), was determined.