Preparation Of Thermally Reversible Crosslinking Zinc Salt And Its Cross-linking And Stabilizing Performance For PVC

Polyvinyl chloride(PVC)is one of the most important polymer materials.It occupies an important position in the industry.PVC products are widely used in various fields because of their good mechanical and chemical properties.However,due to its structure characteristic,PVC has poor thermal stability.Therefore,stabilizers are usually added into PVC to improve its stability during processing.Cross-linking agents are sometime added to improve its mechanical performance.Commonly used stabilizers are lead-salt stabilizers and calcium-zinc stabilizers,while lead-salt stabilizers are gradually eliminated by the market due to their toxicity.Thermo-reversible cross-linking of PVC has been studied for a long time in our research laboratory.It was found that the degree of cross-linking was low due to the competition between the esterification crosslinking reaction of sodium dicyclopentadienate with the active chlorine moieties and the stabilizating reaction calcium-zinc stabilizer with PVC polymer chains.Thus,in the present work zinc dicyclopentadiene dicarboxylate is used to displace sodium dicyclopentadiene dicarboxylate to achieve both thermal stability and reversible cross-linking of PVC.The main research work includes:1.Zinc dicyclopentadiene dicarboxylate(DZn)was prepared by neutralization method and metathesis method respectively.The preparation conditions of the salt were investigated.The structure,the de-dimerization temperature and the decomposition temperature of the salt were characterized by FTIR,DSC and TG measurements.2.The salt(DZn)and sodium dicyclopentadiene dicarboxylate(DNa)were used,respectively,as cross-linking agent for poly(chloromethyl styrene)(PCMS).The results obtained indicate that the zinc salt is more effective in crosslinking of PCMS than the sodium salt due to better dispersibility of the zinc salt in PVC.3.The zinc salt(DZn)and calcium stearate were added to PVC as stabilizer.The color change of the PVC samples was observed by heating the sample at 180? in order to compare the stability.The results obtained demonstrate that the PVC sample added with zinc dicyclopentadiene dicarboxylate exhibits better thermal stability than that of the PVC sample added with zinc stearate.Meanwhile,zinc dicyclopentadiene dicarboxylate provides further improved thermal stability to PVC when it is combined with calcium stearate and polyalcohols.4.The degree of cross-linking and the tensile strength of PVC samples containing DZn/CaSt2 and containing Ca-Zn stabilizer were investigated.The results showed that when the dosage of plasticizer DOP was lOphr in PVC,the gel content(51.1%)of the sample suing DZn/CaSt2 was much higher than that of the sample using Ca-Zn(21.2%)and the tensile strength of the former(54.4 MPa)was 10%higher than the letter one(49.2 MPa).5.The effect of DZn loading amount on the tensile strength of the PVC sample was also investigated.It was found that both of the thermal reversible crosslinking performance and the tensile strength of PVC sample are satisfied when 2phr of DZn is added to the PVC.This finding would be helpful in the thermoreversibly cross-linking modification of PVC and the application of such material.