YICHUN CITY KEYUAN CHEMICAL INDUSTRY CO,.LTD
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Polyvinyl chloride (PVC) has the advantages of low price, non-flammability and corrosion resistance, and is widely used in various fields of industrial and agricultural production. Defects exist in the structure of PVC, PVC is under the condition of high temperature and high shear processing, easy to take off on the molecular HCl and polymer degradation that cause, cause product color and the mechanical properties of the products to drop, affect its use and life.
Thermal stabilizer is the most effective method to ensure that PVC is not easily degraded in PVC processing. The commonly used thermal stabilizers are lead salt, metal soap, organic tin, rare earth and some auxiliary heat stabilizers. Various stabilizers have their own characteristics and are used in different fields. This article will introduce the thermal degradation and stabilization mechanism of PVC, market overview, type of stabilizer and its development trend.
Thermal stability mechanism of PVC.
Thermal stabilizers can inhibit the degradation of PVC by replacing unstable chlorine atoms, neutralizing hydrogen chloride and reacting with unsaturated parts. The thermal stabilizer can help reduce the reaction of the processing conditions. The HCl released during the early stage of degradation must be absorbed to prevent the occurrence of the internal autocatalytic reaction. The neutralization reaction of HCl is the general characteristic of most metal organic complexes. Chlorine atoms replace metal ligands and produce a substance that is not readily accessible.
The ideal PVC thermal stabilizer should be a multifunctional material, or a mixture of materials that can achieve the following functions:
(1) replace the active and unstable substituents, such as the chlorine atom or allyl chloride attached to the tertiary carbon atom, to produce a stable structure;
(2) to absorb and neutralize the HCl released in the process of PVC processing and eliminate the automatic catalytic degradation of HCl;
(3) neutralization or passivation of metal ions and other harmful impurities that catalyze the degradation;
(4) the continuous growth of unsaturated bonds can be blocked by various forms of chemical reactions, and the degradation of degradation is inhibited;
(5) it is better to have protective shielding effect on ultraviolet light.
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