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I. Sasimowska


Brittle cracking of polypropylene injection mouldings


Polimery 1988, No 7-8, 260


DOI: dx.doi.org/10.14314/polimery.1988.260

Summary

The Polish-made commercial isotactic polypropylene (PP-i, Malen-P J-400) has been modified by the addition of 10% by weight of high-molecular-weight and low-molecular-weight fractions of atactic polypropylene. It has been found that only the addition of high-molecuiar-weight fraction of PP-a in an amount of 4% resulted in a statistically essential increase in the stress corrosion resistance in the direction perpendicular to the material flow in the mould with a simultaneous improvement of the processing properties (an increase in the melt flow index) and impact resistance at temperature of +20°C and — 10°C. The static tensile strain properties of the mouldings deteriorated negligibly. The results of the corrosion; resistance studies have been compared with the observations of supermolecular structure (polarization microscope method) as well as with the obserwations of cracked surfaces (scanning electron microscope method). It has been demonstrated that the increase in stress corrosion resistance in a direction perpendicular to the direction of flow of PP- i samples' modified with high-molecular-weight PP-a fraction can be attributed to a decrease of the thickness of the external layer oriented in the direction of material flow.



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