1. Because PVC resin is a kind of heat-sensitive plastic, its light stability is poor. Under the action of heat and light, the branched chain undergoes de-HCI reaction and polyene structure molecules. When the number of conjugated double bonds in the main chain is not too much, trace Color difference, hydrogen chloride will first react with the potential acid-reactive substances around it, and the conjugated double bond becomes a new active site in the PVC molecular chain. After being triggered by light into a large molecular free radical, PVC is susceptible to oxidation and produces color change.
2. There is a certain amount of low molecular weight components in PVC resin, which reduces the thermal stability of the polymer. The mechanism of PVC decomposition includes free radical mechanism, ionic mechanism, single molecule mechanism and so on. In addition to the PVC destabilizing agent, the quality of the PVC resin itself may be affected, such as whether there is too much residual initiator in the PVC resin.
3. If there are certain impurities in the polymer, such as the incomplete removal of initiators, catalysts, acids, alkalis, etc. added during the polymerization process, or the absorption of moisture during storage and transportation, the stability of the polymer will be reduced. Because these substances can cause molecular-ion degradation reactions, CPE contains more low molecular substances such as Cl2 and HCl, which is easy to accelerate the thermal decomposition of the resin. Therefore, for the poorly stabilized PVC + CPE system, some pipe yellowing problems can also be eliminated by increasing the amount of stabilizer.
4. PVC pipe is a mixed system consisting of a multi-phase polymer with PVC as a continuous phase kneaded with a heat stabilizer, a light stabilizer lubricant, a filler and a pigment. When the PVC pipe is exposed to the natural environment, once the PVC component After dehydrochlorination, the original component of calcium carbonate will be converted into a new component of calcium chloride, which is dispersed in the layer of oxidative degradation products and forms a potential water absorption site, which is one of the reasons for the yellowing of the pipe.
5. In addition to temperature, there are stresses. Before molding, plastics are subjected to shear stress and tensile stress in the process of high agitation, cold agitation, and extrusion to cause thermal degradation.
When solving chromatic aberrations, a single method can not deal with the problem better. For example, considering the following four aspects, the solution is faster:
1. Lower the processing temperature than whitening without lowering the processing temperature;
2. The effect of adding a single lead salt in the composite stabilizer is not better than that of adding the composite stabilizer;
3. It is better to use some stabilizers than white stabilizers or high-whiteness fillers to increase the titanium dioxide powder.
4. It is better to simply add titanium dioxide and add some internal lubricants.
HENGSHUI HOMART TECHNOLOGY CO.,LTD （JIUZ GROUP）founded in 1999 which is a professional factory of PVC Additives, we pay all our attentions to PVC Chemicals. We would like to offer the best economic solution to our clients to be the front of their competitors.