Meaning
Ability of a polymer to maintain its molecular structure during the high-heat and high-shear conditions of moulding defines its thermal endurance. Processing stability is maintained through the use of antioxidant packages that prevent chain scission or cross-linking when the resin is molten. This property determines how many times a material can be reprocessed as regrind without losing its original mechanical properties.
Thermal Protection
Primary and secondary antioxidants work together to scavenge free radicals and decompose hydroperoxides before they can attack the polymer backbone. Without adequate processing stability, the melt will change in viscosity during the run, leading to inconsistent part weights and dimensions.
Recycled Content
Incorporating regrind into production increases the stress on the stabilization system of the resin. Every time the material passes through the extruder, the additives are consumed as they protect the polymer. Moulders often add stabilizer concentrates to the mix to ensure that the processing stability remains high enough to prevent discoloration and embrittlement.
Run Consistency
Maintaining a stable melt flow index over several days of production requires a resin with high resistance to thermal degradation. If the processing stability is poor, the material may build up on the die lips or form gels that cause holes in thin films. Consistent monitoring of the melt temperature and residence time helps prevent these issues.
