Degradation of a plastic material can occur as a result of reduction in molecular weight, separation of the polymer and its additives, damage to the additives, or a chemical reaction. Conditions leading to material degradation during injection molding can include: too high of a melt temperature, long residence times, excessive shear rates and frictional heating in a runner, poor venting, and dead or low flow areas in the injection barrel or hot runner system. Additionally, some materials can degrade as a result of improper drying. For example, drying a material at too high of a temperature for too long can create oxidation. Additionally, injection molding certain materials with too much moisture, such as Nylon, PC and polyurethanes can cause the material to undergo hydrolysis.
