THE EFFECT OF FUSION LEVEL ON THE DEMATTIA FLEX CRACK RESISTANCE OF CALCIUM-CARBONATE FILLED PLASTICIZED POLY(VINYL CHLORIDE)

PVC compounds of a vinyl leather formulation containing various amount s of calcium carbonate filler were prepared. The influences of mouldin g time and temperature on PVC fusion level were determined. The correl ation of fusion level to the behaviour during Demattia flex cracking a nd crack growth testing was investigated. Optimum flex cracking resist ance occurred at fusion levels of 53% and 63.5% for unfilled and fille d compounds, respectively, for the same PVC formulation. The slowest c rack growth rate occurred at the fusion level of 53% for both compound s. The flex cracking behaviour was characteristic of the thermal softe ning of PVC during fatigue. On flexing, the polymer temperature rose r apidly from 27-degrees-C to 50-degrees-C and then levelled off. The pr esence of filler led to accelerated failure due to voiding at the poly mer-filler interface and stress concentration effects. The heat build- up during flexing was not significantly different between the unfilled and filled polymer because of the lack of interfacial interaction bet ween the filler particles and the polymer matrix.