| Polyvinyl chloride(PVC)is one of the important common plastics.It has many advantages such as high strength,corrosion resistant,flame retardant,insulation,transparency and so on.Its products are widely used in construction,chemical industry,electrical appliances,packaging,etc.However,it has poor thermal stability and will degrade by dehydrochlorination when heated to 130 ?,which results in severe discoloration and loss of mechanical properties,while the processing temperature of PVC is generally about 180 ?.Therefore,thermal stabilizer is a necessary additional agent in PVC processing and application.Generally,heat stabilizer includes lead salts,Organic tin,Rare earth and Ca/Zn stabilizer.In recent years,with the strengthening of environmental protection requirements,non-toxic calcium zinc series thermal stabilizer gets more and more attention.The current Ca/Zn stabilizer has the advantages of non-toxic,inexpensive and good lubrication.But it also has some disadvantages such as poor thermal stability and zinc buring phenomenon often happen.Therefore it is important to develop a kind of heat stabilizer which is novel,efficient and environmentally friendly.In this paper,calcium glycerolate,zinc glycerolate as primary stabilizer and mixed polyol ester as auxiliary stabilizer were prepared.Polyols were also screeninged.The process conditions were optimized,the product was characterized by thermogravimetric analyzer(TGA),scanning electron microscope(SEM),X-ray diffractometer(XRD),infrared spectrum(IR),inductively compiled plasm(ICP)and liquid chromatograph mass spectrometer(LC-MS).The thermal stability of stabilizers for poly vinyl chloride(PVC)were investigated by Congo red test,Oven aging test and Torque rheological experiment.Comparing with calcium/zinc stearare system,the result showed that zinc glycerolate and calcium/zinc glycerolate obviously enhance the heat stability of PVC.In the presence of calcium/zinc stearate,polyols and mixed polyol ester as auxiliary heat stabilizers could obviously enhance the heat stability of PVC and no zinc burning phenomenon is found.In this paper,the influence of the process conditions on calcium/zinc glycerolate was studied,such as the ratio of raw materials,reaction temperature and reaction time.The thermal stability time of PVC containing zinc glycerolate instead of zine stearare could reach 44 min.The thermal stability time of PVC containing calcium/zinc glycerolate was 29 min,nearly 5 times that of conventional calcium/zine stearare system.The complex of calcium glycerolate and zinc glycerolate broke the model in which the zinc content should not be set too high.The zinc glycerolate and calcium/zinc glycerolate obviously enhanced the heat stability of PVC and no zinc burning phenomenon was found,which was superior to conventional calcium/zinc stearate system.The synergistic effect of pentaerythritol,dipentaerythritol,mannitol,sorbitol with calcium/zinc thermal stabilizer in PVC was respectively investigated,which is compared with the heat stability of those above directly as the stabilizer of PVC.The mixed polyol ester was synthesized by adipic acid and polyol which was screened.The esterification technology conditions were optimized,such as the ratio of raw materials,reaction temperature,type of the catalyst,dosage of the catalyst and reaction time.The optimum process conditions of esterification reaction are as follows: the best ratio of pentaerythritol,dipentaerythrito and adipic acid was 2.5/2.1/2.0 for mole,the reaction temperature was 190 ?,paratoluenesulfonic acid as catalyst and dosage 2.2 % of adipic acid,xylene as dehydrant,dosage 22 % of the total amount of raw materials,reaction time was 2 h.In these conditions,the mixed polyol ester as auxiliary heat stabilizer had better synergistic effect with Ca/Zn system and presents good thermal stability. |
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