(1) Calcium stearate:
This is a white powder with a melting point ranging from 148 to 155 degrees Celsius. It's non-toxic, offering excellent internal lubrication and processability. Moreover, it doesn't cause sulphide pollution. Typically, it's used at a dosage of 0.1 to 0.4 parts per hundred resin (PHR).
(2) Oxidized polyethylene wax:
Available in white or yellowish powder or particle form, this wax serves as both internal and external lubricants at high temperatures. Despite containing small amounts of polar groups, it remains incompatible with PVC. However, it boasts higher lubrication efficiency. It enhances the lubrication between polymer and metal, boosts extrusion efficiency, improves colorant dispersibility, and imparts good transparency and luster to products. The recommended dosage ranges from 0.1 to 0.5 PHR.
(3) Stearic acid:
Appearing as white particles with a melting point of 70-71 degrees Celsius, stearic acid acts as an external lubricant at high temperatures and an internal lubricant at low temperatures. The typical dosage is between 0.2 and 0.5 PHR. It also prevents chromatographic scaling, though excessive use may lead to frost spray.
(4) Glycerol stearate:
This lubricant comes in powder form with a melting point of 85-87 degrees Celsius. As an internal lubricant, it offers excellent heat resistance and fluidity, enabling increased filler content and promoting plasticization. Mixing with wax can enhance the thermal stability of PVC-U. Generally, it's used at 0.2-0.6 PHR.
(5) Paraffin wax:
With a melting point of 57-63 degrees Celsius and lacking polar groups, paraffin wax serves as a typical external lubricant. However, due to its low melting point, easy evaporation, and low melt viscosity, its lubrication range is limited. It's suitable for single-screw and twin-screw extruders, with a recommended dosage of 0.1-0.8 PHR. Note that this product may reduce transparency and increase whitening.
(6) Polyethylene wax:
This white powder has a softening point of approximately 100-117 degrees Celsius. Thanks to its relatively large molecular weight, high melting point, and low volatility, it exhibits significant external lubrication effects at higher temperatures and shear rates. It's ideal for hard PVC single-screw and twin-screw extrusion, typically used at 0.1-0.5 PHR.