Influence of solid particles on cavitation in poly(methylene oxide) during crystallization

Cavitation in pockets of melt occluded by impinging spherulites during isothermal crystallization of poly(methylene oxide) was explored. A reason for cavitation is a negative pressure buildup in pockets because of the change of density during crystallization. Compositions of poly(methylene oxide) with talc and chalks unmodified and modified with calcium stearate were studied to determine the influence of foreign solid particles on the cavitation. The crystallization and cavitation in polymer films were observed by a light microscopy; sample surfaces were examined also under SEM. The spherulite growth rate, decreasing under negative pressure, was measured and used to estimate the negative pressure level at the moment of cavitation that is the strength of the polymer melt. Chalk modified with calcium stearate drastically lowered the strength of poly(methylene oxide) melt, whereas unmodified chalk did not. The effect depended on the chalk content and on the particle size. The results demonstrate that the cavitation in a polymer melt under the negative pressure is nucleated by solid particles poorly adhering to a polymer. (c) 2007 Wiley Periodicals, Inc.