heat stabilizer mechanism

Broadly speaking, all to improve the thermal stability of the polymer for the purpose of adding additives can be  plastic additive called heat stabilizers. In addition to heat stabilizer
Apply a small amount of rubber and other resin processing, mainly used for thermal stability problem is very prominent PVC processing. Thus, in general
Said heat stabilizers of PVC and specifically refers to a copolymer of PVC heat stabilizer.
 In the process of thermal degradation of PVC, almost no monomer, but generate a lot of HCl. PVC thermal degradation mechanism is very
Complex, the same, the mechanism of thermal stabilizer is also very complicated. Comprehensive results of the  PVC shoes stabilizer current study, the role of heat stabilizers can be summarized
For the prevention of type (neutralizing HCl, replace unstable Cl atoms and prevent auto-oxidation) and remedial-type (with PVC anti-unsaturated sites
Should undermine carbocation) two kinds.
As follows:
1 absorption and HCl, inhibit its catalytic automatically. Such stabilizers include lead salts, organic acids, metal soaps with
Organotin compounds, epoxy compounds, amines, metal alkoxide and a phenolic salts and metal thiolate salt. They are available with HCl to inhibit
PVC de-HCl reaction system.
 (2) replacement of PVC unstable allylic chlorine molecule or a tertiary carbon atom chlorine atom, inhibit de PVC. Such as organic tin stabilizer
Instability of PVC molecules of chlorine ligand binding occurs, the ligand, organic tin substitution with an unstable chlorine atoms.
3 with the addition reaction of a polyene structure, damage the formation of a large conjugated system and reduce coloration. Unsaturated acid salts or esters containing
There is a double bond, with PVC molecules conjugated diene double bond addition reaction, thereby undermining its conjugate structure, inhibit discoloration.
4 capture free radicals and prevent the oxidation reaction. Such as adding phenolic stabilizers can block off heat HCl, H is given as phenol
Atom radical degradation of PVC macromolecules with radical coupling reaction with O2 to form a substance can not be, and has a thermal stability. Such thermal stabilizers may have one or several functions of both.
 Ideal PVC heat stabilizer should be a multi-functional substance, or a mixture of some materials, they are able whitening agent  to achieve a
The following functions:
1 replacement lively, unstable substituent such as attached to the tertiary Cl Cl atom or allyl chloride, to form a stable structure
(2) to absorb and process the PVC processing and release of HCl, HCl elimination autocatalytic degradation;
 3 and in the degradation or passivating the catalytic metal ions and other harmful impurities; 4 by chemical reaction forms an unsaturated bond can block the continued growth inhibiting degradation coloring;
 5 The best protection against ultraviolet radiation shielding effect.