Stearate Coatings on Particulate Fillers - the Effects on Resulting Compound Properties *

Conditions have been established for coating particulate fillers (magnesium hydroxide and calcium carbonate) with metal stearates. The coating process was followed using a quantitative DRIFT (Diffuse Reflectance Fourier Transform Infra Red Spectroscopy) technique. Polyethylene compounds containing 40 weight % filler were produced. Compounds containing stearate coated fillers were found to possess better impact properties than those containing uncoated fillers, or fillers coated with an equivalent level of stearic acid. For the magnesium hydroxide filler, optimum impact properties were obtained with a monolayer stearate coating. When stearate type was varied, property changes in calcium carbonate filled samples were small, but optimum performance was obtained with calcium stearate for magnesium hydroxide-containing compounds. Of the three stearates studied, this was the only one which did not react with the filler to produce stearic acid. Polyethylene crystallinity was increased by stearate coatings, but did not appear to be a major factor controlling properties.