Pure PVC resin is extremely sensitive to heat. When the […]
Pure PVC resin is extremely sensitive to heat. When the heating temperature reaches above 90 °C, a slight thermal decomposition reaction occurs. When the temperature rises to 120 °C, the decomposition reaction is intensified. At 150 ° C for 10 minutes, the PVC resin is from the original. The white color gradually turns yellow-red-brown-black. The decomposition process of PVC resin is a series of chain reactions caused by the de-HCL reaction, which eventually leads to the breakage of macromolecular chains. Although the thermal decomposition mechanism of PVC is not very mature, the thermal stabilization mechanism for preventing thermal decomposition of PVC is relatively mature. It achieves the purpose of thermal stabilization by the following aspects.
(1) Capturing HCl generated by thermal decomposition of PVC to prevent catalytic degradation of HCl. Lead stabilizers mainly function according to this mechanism, in addition to metal soaps, organotins, phosphites and epoxys.
(2) Replacing the active allyl chloride atom. Metal soaps, phosphites and organotins can act according to this mechanism.
(3) reacting with a radical to terminate the reaction of a radical. Organotin and phosphite act according to this mechanism.
(4) inhibiting the growth of the conjugate chain by co-twisting double bond addition. Organotin and epoxy act according to this mechanism.
(5) Decompose peroxides and reduce the number of free radicals. Organotin and phosphite play a role in this mechanism.
(6) Passivating metal ions having catalytic de-HCl action.