PVC thermal stability issues
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PVC resin can be characterized by aging whiteness, thermal stabilization temperature, and thermal stabilization time. Are there any differences between these three indicators? Because for a long time there was a problem of aging whiteness of 85 and thermal stability temperature of 130 degrees (or even lower). Note: Normally, the aging whiteness is about 84, and the thermal stable temperature is about 150. Many processing users now use thermal stabilization time to judge the thermal stability of resin. What is the difference between it and the other two indicators?
We usually test the heat aging whiteness of PVC during production. It is 10 minutes at 165 degrees, usually between 81 and 85. We basically no longer do heat stabilization time. I wonder if this is scientific or not?
Thermal stabilization time and thermal stabilization temperature are usually tested with Congo red, which feels inaccurate. Sometimes the PVC is discolored very seriously, but the Congo red test paper does not discolor.
I also encountered this problem, the thermal aging whiteness and thermal decomposition temperature do not correspond. I think this way, the thermal aging whiteness reflects the total amount of easily decomposable substances (unsaturated bonds) contained in the sample, and the thermal decomposition temperature reflects the unsaturated bonds with the lowest decomposition temperature. However, we are still investigating how to specifically increase the thermal decomposition temperature (without adding additives such as heat stabilizers). Welcome to communicate.
As mentioned before, the heat aging whiteness is the artificially specified measurement condition, that is, the whiteness value measured after stabilization for 10 minutes at 160°C. Thermal decomposition temperature is the temperature at which hydrogen chloride starts to decompose and release hydrogen chloride according to a certain heating rate using the Congo red test. There is no unified standard for this. The time when it begins to decompose and release hydrogen chloride at a certain temperature (artificially set, usually 160°C) is the thermal stability time.