Thermostabilizers, PVC Stabilizers

Thio stabilizers are also used as peroxide decomposers, Fig. 3.5. The resulting numerous reaction possibilities go beyond the scope of this work. Thio stabilizers are generally used as costabilizers for sterically hindered phenols. Their reaction mechanisms depend on the chemical structure of the organo-sulfur compounds, the oxidizing substrate, and oxidation conditions. 

The substances typically used are sulfides, dialkyl dithiocarbonates or thiodipro-pionates, such as dilauryl thiodipropionate (DLTDP) and distearyl thiodipropionate (DSTDP) as well as disulfides. These products develop their effect mainly in the range of long-term service temperatures, i. e., at moderate temperatures, and they exhibit few process stabilizing effects (with the exception of disulfides). 

Bifunctional stabilizers exhibit various functions in the same molecule, such as sterically hindered phenols with sulfur substituents, which provide both an H-donor and a hydroperoxide decomposing effect. 

Under thermal load, PVC sustains damage caused by hydrogen chloride elimination (dehydrochlorination), autoxidation, and mechano-chemical fragmentation. Specifically effective stabilizers and costabilizers and/or mixtures of stabilizers delay dehydrochlorination and autoxidation. They neutralize the eliminated hydrogen chloride during thermoplastic processing and help maintain service properties [86]. The technically most important thermostabilizers and costabilizers are described in Section 3.7.5. 

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