Meaning
Thermal degradation process in chlorinated polymers where hydrogen chloride gas is released from the molecular chain. Occurrence of dehydrochlorination usually happens when polyvinyl chloride is processed above its stable temperature window. This reaction leaves behind double bonds in the polymer backbone, causing extensive discoloration and structural weakening.
Process Damage
Corrosive gases generated during the breakdown of the resin attack the polished surfaces of the mould. Because dehydrochlorination releases hydrochloric acid, it can cause pitting in steel tooling that is not properly coated. Proper ventilation and stainless steel components are required to manage these corrosive byproducts.
Additive Function
Stabilization of the melt relies on heat stabilizers that scavenge the acid before it can catalyze further breakdown. Effective dehydrochlorination control involves the use of calcium zinc stabilizers that extend the processing window of the resin. These additives are consumed during the run, meaning the stability of the material decreases every time it is reheated.
Quality Indicator
Yellowing of the finished part acts as the primary visual sign that the material has begun to break down. While minor degradation might only affect the aesthetics of an industrial pipe, severe dehydrochlorination renders the plastic brittle and prone to catastrophic failure under load. Monitoring the melt temperature is the most effective way to prevent this chemical shift.
