Material Analysis
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Differences in calcium-zinc stabilizer adaptability in PVC resins with different K values
Problem Phenomenon
The same calcium-zinc stabilizer formulation has good thermal stability in K65 PVC resin, but when switched to K70 high polymerization degree resin, under the same processing conditions the product shows discoloration and degradation, and the stabilization effect is significantly reduced.
Cause Analysis
High K value PVC resin K70 has a polymerization degree of about 1300, higher melt viscosity, generates more shear heat during processing, and the actual material temperature is 10-15°C higher than the set value; high K value resin requires longer plasticization time, leading to extended residence; high polymerization degree resin has slightly higher proportions of unstable structures such as branched chlorine; the processing technology was not adjusted according to the resin type.
Solution
Adjust the calcium-zinc stabilizer dosage according to the resin K value; K70 needs 0.5-1 phr more than K65; reduce the screw speed by 10-15% to reduce shear heat; adjust the temperature setting so that the actual material temperature is controlled within the target range, using a melt temperature probe for real-time monitoring; select a calcium-zinc stabilizer grade with higher thermal stabilization efficiency (high-zinc type); appropriately reduce the feeding amount to extend the plasticization process.
Key Takeaway
The calcium-zinc stabilizer formulation needs to be specifically adjusted according to the polymerization degree and K value of the PVC resin used; high K value resins have higher requirements for the thermal protection capability of the stabilizer.
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