Meaning
Chemical breakdown of a common trisarylphosphite antioxidant occurs when it is exposed to heat and moisture during resin processing. Monitoring irgafos 168 degradation is vital for moulders because the loss of this stabilizer leaves the polymer vulnerable to thermal oxidation. As the phosphite is consumed, it converts into a phosphate, which does not provide the same level of protection to the polymer melt.
Processing Impact
High melt temperatures and long residence times in the barrel accelerate the consumption of the antioxidant. During irgafos 168 degradation, the material can lose its molecular weight, leading to a higher melt flow index and reduced mechanical properties in the final part. This is a significant concern when using regrind, as the stabilizer may have already been partially depleted during the first heat cycle.
Moisture Sensitivity
Hydrolysis is another pathway for the loss of this stabilizer, especially if the resin is not dried properly before moulding. When irgafos 168 degradation occurs via hydrolysis, it can form acidic by-products that might corrode the tool steel or cause yellowing of the plastic. Maintaining a low moisture level in the hopper is the most effective way to preserve the stabilizer package.
Additive Tracking
Laboratory analysis can measure the ratio of active phosphite to inactive phosphate to determine the remaining shelf life of the resin.
