Release time:

2021-11-09

Industrial production of PVC heating to about 100 degrees Celsius will occur when the HCL reaction, of course, in the usual thermoplastic processing temperature, PVC in addition to HCL, but also the material color will continue to deepen until the blackening phenomenon, the physical and mechanical properties of the product will continue to decline until the loss of use value. Therefore, it is necessary to add a heat stabilizer for thermal degradation during thermoplastic processing. The thermal degradation of PVC has the following important kinetic characteristics: 1: the degradation rate is related to the actual structure of PVC polymer chain, the type and amount of plasticizer; 2: The degradation rate accelerates rapidly with the increase of temperature; 3: The degradation product HCL has a promoting effect on the degradation itself and is an autocatalytic reaction process; 4: Oxygen or air will accelerate the degradation; 5: metal ions, especially Fe3 ,Zn2 ,Cd2 and other metal ions with Lewis acid properties have a strong role in promoting the degradation of PVC. At present, a large number of PVC stabilizers are used in soft or semi-rigid formulations containing light calcium carbonate, but in less than a month, different degrees of reddening will occur. This is a common problem of most PVC stabilizers at home and abroad. Therefore, when choosing PVC stabilizers, you must be cautious and pay attention to observation. PVC products commonly used in the production of heat stabilizers mainly have several categories, generally non-transparent products to lead salt, supplemented by calcium soap, cheap is the main reason for the use. However, lead is toxic, harmful to the human body, will accumulate in the human body, is not easy to discharge, and will affect future generations; lead can damage the human nervous system, its harm is irreversible, any treatment can not make the dead nerve resurrection, children's sensitivity to damage. Therefore, considering the long-term interests of mankind, it should be gradually reduced to no longer use lead PVC stabilizers, and relevant regulations have been made abroad. Transparent PVC products generally use calcium zinc stabilizer, barium zinc stabilizer, the price is higher than the lead salt, and CaSt2 is still a toxic substance. Transparent and harmless PVC products, such as rigid PVC transparent sheets for food packaging, use organotin as the main PVC stabilizer, its price is high, and organotin itself will bring greater pollution in the production process.