The industrial purity of calcium stearate is 40-97%, and it is white or yellowish or lumpy. It is a mixture of stearic acid and palmitic acid (hexadecanoic acid) with a small amount of oleic acid and a slightly fatty taste. There are many kinds of stearic acid in the commodity, and it is better to use iodine value and ester value as lubricant, which will not affect the heat resistance and weather resistance of the product.
In polyethylene PE, the more widely used stearate metal salts are calcium stearate and zinc stearate, and in polypropylene PP, calcium stearate is used more widely. Formulations containing calcium stearate showed better stability against "radical recombination" than formulations containing zinc stearate. Calcium stearate used as PVC lubricant, generally judged to be an internal lubricant. Calcium stearate is a medium alkaline calcium stearate with strong electrical polarity. The chemical active point of PVC resin particles used in production can form a stable combination system with calcium stearate.
However, the two long-chain alkyl groups of calcium stearate are less compatible with the polar resin of PVC, and further constitute a small local two-phase interface inside the PVC resin, that is, the lubrication film formed. The microscopic nature of calcium stearate lubrication is that the local lubricating interface formed by the non-polar long-chain alkyl group and the interaction force between the polar resin chain segments is smaller than that between the resin chain segments. Another reason is that there are many small pores between the resin chain segments, so when the position of the resin chain segment is moved, it can be squeezed into other pores adjacent to it from any deformed alkyl group, so as to reduce the resistance when the resin chain segment is displaced, and play the role of internal lubrication.
However, the use of calcium stearate alone in the formulation of PVC production can accelerate the plasticization of resin, improve the melt viscosity, increase the torque, and has a certain release effect. If only paraffin wax is used, it shows delayed plasticization, reduced torque, and no demoulding effect. When the calcium stearate and polyethylene wax are mixed in a certain proportion, it shows good effect, and the torque value of the material can be reduced a lot. This is because the paraffin infiltrates the calcium stearate between molecules, which strengthens the lubrication effect, shows a strong synergistic effect, and changes the dispersion of lubricant.
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