DISCRETE STRENGTH LEVELS IN MODIFIED POLYPROPYLENE TAPES

A statistical study of the strength of unmodified and modified uniaxia lly drawn polypropylene tapes was carried out. The results show that t he curve representing the distribution of strength for unmodified tape s reveals seven discrete levels corresponding to microdefects in the f orm of microcrazes and submicrocrazes. On introduction of modifying ad ditives, three discrete strength levels were observed, corresponding t o submicrocrazes. The strength of the modified polypropylene tape incr eases approximately twice compared to the strength of the initial mate rial. The polyfunctional effect of the additives as artificial nucleat ors and regulators of the structure leads to an increase of the degree of crystallinity which in turn restrains the submicrocrazes developme nt into microcrazes. The method used could be applied for objective an alysis of the tensile characteristics of polymeric materials.