PVC heat stabilizer mechanism

Where to improve the thermal stability of the polymer added for the purpose of heat stabilizer additives are known. In addition to a small amount of heat stabilizers used in rubber and other resin processing, mainly used for thermal stability problem is very prominent PVC processing. Thus, said heat stabilizer is usually refers to a copolymer of PVC and 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 complicated, the same, the mechanism of thermal stabilizer is also very complicated. Comprehensive results of the current study, thermal stabilizer preventive action can be summarized as (and in HCl, Cl atoms instead of unstable and preventing auto-oxidation) and remedies type (with PVC, the unsaturated site reactions, damage  circuit breakers ) two kind. As follows: 1. Absorption and HCl, inhibit its catalytic automatically. Such stabilizers include lead salts, organic acids, metal soaps, organic tin compounds, epoxy compounds, amines, metal alkoxide and a phenolic salts and metal thiolate salt. They are available with HCl to de-HCl reaction inhibition PVC. (2) replacement of PVC unstable allylic chlorine molecule or a tertiary carbon atom chlorine atom, inhibit de PVC. Such as organic tin stabilizer of PVC unstable molecule of chlorine  Circuit breaker  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. A salt of an unsaturated acid or ester containing double bonds, and the PVC molecules conjugated diene double bond addition reaction, thereby destroying the conjugated structure, and color. 4 capture free radicals and prevent the oxidation reaction. Such as adding phenolic heat stabilizer can block off HCl, is due to give phenol H 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 can achieve the following functions: 1. Replacement lively, unstable substituent, such as the connection on the tertiary Cl Cl atom or allyl chloride, to form a stable structure; 2 absorbed and the PVC during processing and release of HCl, HCl elimination autocatalytic degradation; 3 and in catalytic degradation or passivating the metal ions and other harmful impurities; 4 by chemical reaction forms an unsaturated bond can block the continued growth of the degradation suppressing coloration; 5. preferably a protective shielding to ultraviolet light.