PC/ABS accounts for a large proportion of automotive interior plastics. Especially for luxury cars, PC/ABS materials can reach 5-10KG/car. The volatile small molecule (VOC) in PC/ABS should not be underestimated. Let's learn about the source of VOC in PC/ABS.
First, residual monomers and emulsifiers in raw materials; No matter phosgene method or transesterification method, there are few residual monomers in PC. PC is generally of high purity, which is inseparable from advanced production technology and its own polymerization mode. However, phenol will be produced in the process of transesterification PC production, and phenol will inevitably remain. Styrene and acrylonitrile monomers will remain during ABS production. In addition, in the production of ABS by the lotion method, 80% of the emulsifier - dodecyl benzene sulfonic acid will remain in the rubber powder, which is difficult to remove. There are also some AS molecular weight regulators, such as dodecyl mercaptan or Diao *******, which will remain, but they are easily soluble in water, so they are easier to remove.
Secondly, the solvent in the raw material production process; The solvent often used in PC is CH2Cl2, and the solvent in bulk ABS is toluene or ethylbenzene. Because of the high toxicity of toluene, ethylbenzene solvent is the majority. Finally, the deashing device is not perfect, and the solvent will remain in the product and become VOC substance. It is worth mentioning that benzene is the key control object of VOC.
Third, additives, such as compatibilizers, lubricants and release agents; PC is partially compatible with SAN in ABS, but incompatible with PB, so compatibilizers will be added to improve their compatibility. Some low molecular compatibilizers may affect VOC emission levels. In addition, in order to increase the internal lubrication between substances, lubricants will be introduced into the formula. These small molecules are also VOC substances. Finally, in order to improve the demoulding property during processing, some release agents sprayed out are benzene containing substances, all of which are VOC substances.
Finally, the by-products are degraded. PC is easier to decompose than ABS. In PC/ABS system, acid-base degradation or affinity reagent degradation generally does not occur. Without additives, PC/ABS will mainly undergo hydrolysis and alcoholysis. The water absorption rate of PC is generally about 0.2%, and the ester group on the PC molecular chain is very sensitive to water. Especially, it is easy to hydrolyze to form small molecules at high temperature, so the water content of PC is generally required not to exceed 0.02% during processing.
At high temperature, hydroxyl group will attack ester group to react, and PC molecular chain will break to form small molecules. The hydroxy end content of phosgene PC is about 5%, and that of ester exchange PC is about 20%. Therefore, ester exchange PC is more prone to alcoholysis than phosgene PC, and more small molecules are generated.
