| Polyvinyl chloride(PVC)is one of the important common plastics.It has many advantages such as high strength,corrosion resistant,antiflaming,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℃.Generally,the processing temperature of PVC is about 180℃,which results in severe discoloration and loss of mechanical properties.Therefore,thermal stabilizer is a necessary additive in PVC processing and application.Generally,heat stabilizer includes lead salts,organic tin,rare earth and Ca/Zn stabilizer.In recent years,becuse the requirements of environmental protection become increasingly strict,non-toxic calcium zinc series thermal stabilizer gets more and more attention.The traditional Ca/Zn stabilizer has the advantages of inexpensiveness and good lubrication.But it also has some disadvantages such as poor thermal stability and zinc buring phenomenon.Therefore,it is important to develop the novel,efficient and environmentally friendly heat stabilizers.In this paper,zinc cyanurate,calcium cyanurate,zinc barbiturate,calcium barbiturate as four heat stabilizer were prepared.By optimizing the synthesis conditions,the optimum synthesis conditions ultimately determined for the synthesis of calcium cyanurate and zinc cyanurate is the reaction temperature 100℃,molar ratio of reactants(oxide)and cyanuric acid 1.4:1,and the reaction time 2h.The optimal synthesis conditions of calcium barbiturate and zinc barbiturate is that the reaction temperature 105℃,molar ratio of reactants(oxide)and barbituric acid 1:1.2,and the reaction time 2h.The product was characterized and analyzed by infrared spectrum(IR),X-ray diffractometer(XRD),scanning electron microscope(SEM)and so on.The thermal stability of stabilizers for poly vinyl chloride(PVC)were investigated by thermogravimetric analyzer(TGA),Congo red test,Oven aging test and Torque rheological experiment.The results showed that the two stages’ thermal weightlessness rate of PVC which the four heat stabilizers were respectively added in were decreased compared with the pure PVC.The decrease of thermal weightlessness rate for zinc cyanurate was the most obvious,followed by calcium barbiturate.Thermal stabilization time by Congo red test was 28.01 min for zinc cyanurate,23.47 min for calcium cyanurate,38.48 min for zinc barbiturate,and 36.23 min for calcium barbiturate.The time for the samples blackening in Oven heat aging test was 65 min for zinc cyanurate,70 min for calcium cyanurate,70 min for zinc barbiturate,and 75 min for calcium barbiturate.The results of Torque Rheological tests show that the minimum torque(18N·m)and maximum torque(36.5 N·m)of zinc cyanurate,is less than the calcium cyanurate.The minimum torque(19.5N·m)and maximum torque(36.5N·m)of zinc barbiturate were less than the calcium barbiturate.But the plasticizing time of the zinc barbiturate was longer than the calcium barbiturate.The thermal stabilization effects of the pairwise composite heat stabilizers with zinc cyanurate,calcium cyanurate,zinc barbiturate and calcium barbiturate were investigated by Oven heat aging test and measuring conductivity of solution.The results showed that both calcium cyanurate / zinc barbiturate and calcium barbiturate / zinc cyanurate had a good synergy and excellent thermal stability,and when the mass ratio of calcium/zinc was 1.8: 1.2,the thermal stability the composite heat stabilizers was the best.Two kinds of homemade Ca/Zn composite heat stabilizers were compared with now recognized domestic and overseas Ca/Zn composite heat stabilizer on the market,the results showed that the order of thermal stability for the four kinds of Ca/Zn composite heat stabilizer from high to low was: calcium cyanurate/zinc barbiturate,overseas Ca/Zn,calcium barbiturate/zinc cyanurate,domestic Ca/Zn.And the related thermal stabilizing mechanisms were also discusseded and analyzed. |
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