PVC resin belongs to a class of strong polar polymer,the intermolecular force is large,resulting in PVC softening temperature and melting temperature is high,pure PVC resin generally needs to be plasticized in 160~2100C.In addition,the substituted chlorine group contained in PVC molecules is easy to lead to HCl removal reaction of PVC,which leads to the degradation of PVC.Therefore,PVC is extremely unstable to heat,and the rise of temperature will greatly promote the HCl removal reaction of PVC.When the temperature of pure PVC reaches 1200C,the HCl removal reaction starts,which leads to the thermal degradation of PVC.In view of the above two characteristics of PVC,pure PVC in the softening temperature has begun to occur thermal degradation,resulting in pure PVC can not be processed by plasticizing melting method,therefore,it is necessary to modify pure PVC,add various additives to change the performance of PVC,so that it can be processed by plasticizing method.When selecting the variety and dosage of additives,it is necessary to consider various factors,such as physico-chemical properties,flow properties,molding properties,and finally establish the ideal formula.
　　The design and determination of a PVC formula generally goes through the following steps
　　1,according to the performance of the product,determine the brand of PVC resin;
　　2,according to the hardness of the product,determine the amount of plasticizer added;
　　3,according to the performance(such as transparency,toxicity,etc.)and economy,determine the type and amount of stabilizer;
　　4,according to the product performance,equipment and stability of the category and the amount of plasticizer addition,determine the composition of the lubrication system and the amount of addition;
　　5,according to the main composition of PVC formula and equipment,determine the amount of processing additives;
　　6,according to the cost and performance,determine the amount of filler(and adjust the proportion of lubricant);
　　7,according to the product performance,determine whether to add other additives.
　　Formula design is good,after material mixing,processing molding test,according to the processing and product situation,adjust the formula proportion,finally determine the formula.