Then we have fillers. Calcium carbonate is often used as a filler in plastics. Depending on the amount used in a blend, calcium carbonate can increase the modulus, increase the hardness and at very high loadings decrease the cost of the formulation. It was found that at levels less than 7% by weight the physical properties were not significantly affected and that, at levels over 20%, the physical properties were compromised and the chemical resistance severely compromised.
Stanford et al. (1979) showed that high filler loadings resulted in excessive weight gain and, thus, poor chemical resistance. A PVC formulation incorporating high calcium carbonate amount is by far the most significant negative factor in acidic leachate environments. When exposed to acidic leachates, and with 37% HCl, formulations with less than 7% calcium carbonate, incorporating a branched or linear phthalate, had less than 5% weight change and – more importantly – were still very flexible.
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Calcium carbonate filler loadings of greater than 7% should be avoided in low pH (acidic) environments.