Calcium Stearate

Calcium stearate is the most widely used organometallic compound in rigid PVC. It is the reacted product of an organic acid derived from tallow or palm oil and calcium. The basic molecular structure of calcium stearate is as follows:

Precipitated calcium stearate has a very fine particle size, low-bulk density and is extremely dusty. The very fine particles precipitated calcium stearate disperse easily in PVC compounding. The fusion method yields a higher density, coarser particle size, but still very dusty calcium stearate. Fusion process calcium stearate does not disperse as quickly as precipitated calcium stearate during compounding. The resulting harder, larger particles may delay fusion of rigid PVC during the early stages of processing. Calcium stearate prepared by either method does not melt, but rather forms a thick taffy-like gel. Tin stabilizer contributes to breaking up or melting this gel.

The solution process—used to prepare our standard calcium stearate product, RX-5050—yields a very different product. Calcium stearate prepared by this method is fully melting and disperses easily during rigid PVC compounding. The product form is a non-dusting, free-flowing, easy-to-handle prill ideal for automated blending systems. As opposed to the other methods, solution process calcium stearate has reliable and reproducible melting characteristics and easily combines, reproducibly, with the other ingredients typically present in rigid PVC formulations.

Solution process calcium stearate has less of a tendency for rigid PVC impact failures due to over-processing.  When over-processed, precipitation or fusion process calcium stearate have a tendency to “invert” out of solution, creating sites where cracks can initiate.