Role of PVC Heat Stabilizers
2021-11-04
Poly(vinyl chloride (PVC) is one of the most important commercial plastic and its compounds have a great diversity of applications and methods of processing. But, PVC is thermally unstable at processing temperatures.
The amount and type of energy input varies considerably among the many different production methods and end-use applications of PVC. In fact, resin degradation starts in the polymerization reactor. It can continue under storage conditions through oxidation, carbonyl formation, etc. even before use.
Once PVC gets heated up to 170°, hydrogen and chlorine are eliminated. Decomposition starts and leads to the release of HCl (autocatalytic dehydrochlorination). Unstable molecules (allylic chlorine structure) appear, which in turn, stimulate the next HCl loss. And so on, this is a chain reaction.
Thermal Degradation of PVC
The factors which promote PVC degradation include:
-Mixing cycles (dry blend, banbury, high speed plastisol dispersators)
-Processing (calender, extruder, molder)
-Fabricating (embossing, thermoforming, laminating)
-Scrap re-work
-Heat and light energy of outdoor exposure
-Heat of a product`s use environment (auto interior, hot air duct)
-Gamma ray sterilization
Thus, heat stabilizers play a crucial role to improve the resistance of PVC compounds to heat or high temperatures. The goal of heat stabilizers is to safeguard the vinyl product at all stages. To prevent degradation of PVC compounds, heat stabilizers work by:
-Neutralizing hydrogen chloride
-Replacing weakened carbon-chlorine bonds
-Preventing oxidation
Nowadays, compounding industry also expects PVC heat stabilizers to fill many specific requirements on top of heat stabilization.
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