Multiaxial impact measurements of polypropylenes

A new puncture tester of the falling weight type for conducting impact tests has been developed. With this tester, impact energy can be measured by means of an accelerometer fixed in the falling weight, and strength by a compression type load cell placed under a pot clamping a sample. Puncture behaviors are traced on an oscilloscope. Results of puncture measurements of isotactic propylene homopolymers and copolymers with ethylene showd that impact behaviour depended noticeably upon temperature. Ethylene concentration, isotacticity and molecular weight of polypropylene resins were not more effective in sustaining impact resistance in the range of temperatures below the brittle point than in bringing down the brittle point itself. It was confirmed by means of tensile impact tests that energy to failure depended not upon yield strength but upon deformation in ductile rupture, whereas in the brittle rupture case energy to failure depended primarily on the strength of the material. Dynamic mechanical measurement was also carried out to secure the relationship between crystallinity and impact resistance.