Abstract
AbstractThe mechanical behavior of poly(di‐methyl siloxane) (PDMS) composites containing high volume fractions of natural CaCO3 particles of various particle size distributions was studied under tensile and oscillatory bending stresses, emphasizing the unique behavior of high filler loaded compositions. Composites containing the maximal possible solid loading of raw CaCO3 were investigated for the effect of fatty acids surface treatment. The elastic modulus increased with increasing filler loading, following Chantler's model for dental composites when correlated with the absolute filler volume fraction. Good fit to “traditional” models, e.g., Frankle‐Acrivos and Halpin‐Tsai, was obtained by correlating the modulus values with the volume fraction relative to the maximal possible filler loading. A master curve of different particle size distributions and filler levels composites was obtained by using the relative volume fraction values, illustrating the effect of particle packing characteristics on small deformation mechanical behavior. A minor increase in Tg was found in parallel to the appearance of a Tm relaxation peak at approximately −40°C. A peak temperature shift at Tm and a pronounced increase in this peak with increasing filler fraction was found as well. The changes in the melting transition are attributed to the constraints of the filler particles acting on the crosslinked melting polymer. Surface treatment with fatty acids significantly degraded the tensile properties. Interestingly, an increase of 4 vol% filler was enabled owing to the surface treatment, while restoring reasonable tensile properties. No significant effect was observed for excess of fatty acids resulting from physically adsorbed acids. Tan δ curves reveal low PDMS‐CaCO3 particles interactions, and mobility of the PDMS chains in the increased filler fraction as in the treated 64 vol% composite, both higher than those in the raw composite. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
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