Synthesis And Application Study Of Non-toxic Solid Thermal Stabilizer Of Polyvinyl Chloride

Polyvinyl chloride(PVC)is one of the five most popular plastics and is one of the most important functional polymer materials.its output is only second to that of polyethylene.But when it is heated,its defect structure can easily initiate PVC's degradation,so we must add thermal stabilizer in PVC when it is used.Traditional heavy metal stabilizer such as lead salt stabilizer does not meet the concept of'environmental protection'and'green chemistry',although it has excellent effect.While, some of organotin stabilizers are not only toxic,but their cost is relatively high.Therefore Ca/Zn stabilizer has become hot research.In my research,calcium stearate was synthesized by direct method and other fatty acid salts such as zinc stearate by double decomposition.Furthermore,these fatty acid salts act as intermediates for thermal stabilizer.I studied the mechanism of thermal stability and optimum ratio of calcium and zinc stearates,and improvement of plasticizing properties of PVC which is caused by lanthanum stearate.The results show that:calcium stearate can absorb hydrogen chloride which comes from degradated PVC,therefore inhibit PVC from automatic degradation;zinc stearate can substitute for the unstable chlorine atoms in PVC chain;there is good synergy between calcium and zinc stearates,and the optimum ratio of calcium stearate to zinc stearate is 2% to 1%;lanthanum stearate does not inhibit zinc burning as good as calcium srearate,but when we substituted lanthanum stearate for calcium stearate with a little amount,we found that heat stability did not change but plasticizing properties of PVC was improved.The effect of several kinds of auxiliary stabilizers on thermal stability was studied by means of heat aging test,conductivity test and TGA.The results indicate that there is almost no heat stability with only pentaerythritol(PER);PER can chelate zinc chloride so PER can delay zinc burning;PER can absorb hydrogen chloride,which is catalysed by zinc chloride;diisooctyl phenyl phosphate(PDOP) alone can exhibit a little thermal stability;the optimum ratio of PDOP to zinc stearate is 4% to 2%;ternary stabilizer including PDOP is obviously better than binary stabilizer;β-double ketone can not chelate zinc chloride,so it is always applied in low zinc formula;β-double ketone alone can exhibit a little thermal stability as well;epoxy soybean oil(ESO) can absorb hydrogen chloride,so it can exhibit a little thermal stability when it is used alone;antioxidants can prevent PVC from being oxidated by air,delaying degradation of PVC.In my research the thermal stability of several kinds of fatty acid salts was contrasted.The results show that calcium stearate exhibit best heat stability;Ca/Zn stearate has best synergy;Ca/Zn lauric and PDOP exhibit best synergy;Ca/Zn lauric and PER can inhibit PVC from forming conjugated long-chain alkene,while,Ca/Zn stearate and PER can inhibit PVC from forming conjugated short-chain alkene.