Usually, the processing aids used for PVC are acrylic polymers; alpha-methyl styrenes are also used for this purpose. Processing aids can either decrease or increase the melt viscosity.

They increase the frictional heat generated and reduce the non-uniform flow from the die. In the compounds, they enhance flow and act like internal lubricants. Increasing the amount of processing aids allows for lowering the cylinder temperature.

Their dosage ranges between 0 and 5 PHR depending on the process. High-shear twin-screw or single-screw extruders require less processing aid.

For products with more complex molds, it is recommended to definitely use processing aids — such as in PVC fittings, door and window profiles, etc.

Processing aids are substances that, when added in small amounts to the formulation, improve the quality of the final product. Increasing their amount in the formulation enhances fusion and melt strength. Other advantages of using acrylic processing aids include:

• Increased fusion rate along with improved uniformity and melt strength.
• Higher output speed without reducing the final product quality.
• Better wall thickness control and dimensional tolerance.
• Reduction of sagging, flow marks, and surface defects.
• Complete elimination of melt fracture.