Compounding thermally sensitive fillers

Compounds containing fillers are usually more sensitive to thermal decomposition due to the acceleration of thermo-oxidative reactions by a number of additives at elevated temperatures. Fillers could allow sintering compounds at lower temperatures due to an increase in the conductivity of the part. For example, a metal-filled PTFE compound (steel, lead, or bronze) has a significantly higher thermal conductivity than PTFE, which leads to rapid heating of the part. 

PVC is very sensitive to thermal degradation compared to other thermoplastics. Thermal stabilizers are used about 0.3 to 3.0 phr, depending on heat history of the compoimd. Calcium carbonate is the most widely used filler used in rigid PVC. The usual dosage levels of calcium carbonate ranges from about 3 to 10 phr however, in sewer pipe and conduit application, 40 phr are used. Calcium stearate is the most common lubricant for PVC compound. It has both internal and external lubrication characteristics, and it provides improved fusion time, better metal release, and reduced melt viscosity. 

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