Material Analysis
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Decline in thermal stability efficiency of calcium-zinc stabilizers in DOP plasticized systems
Problem Phenomenon
In PVC soft product formulations using large amounts of DOP 50-60 phr, the thermal stabilization effect of calcium-zinc stabilizers is significantly lower than in rigid product formulations, with the dynamic thermal stability time (Congo red method) shortened by more than 30%.
Cause Analysis
DOP plasticizer has a dissolving and diluting effect on calcium-zinc metal soaps, reducing the effective stabilizer concentration; the plasticizer itself generates trace peroxides at high temperatures that accelerate PVC degradation; although the processing temperature of soft products is lower at 140-160°C, the residence time is long; plasticizer molecules interpose between PVC chains, hindering contact between metal soaps and unstable chlorine atoms.
Solution
Linearly increase the calcium-zinc stabilizer addition amount according to the plasticizer dosage (for every 10 phr increase in plasticizer, increase the stabilizer by 0.3-0.5 phr); select stabilizer varieties with low solubility in the plasticizer; incorporate 2-3 phr epoxidized soybean oil into the formulation, which has both plasticizing and auxiliary stabilizing effects; add 0.3-0.5 phr phosphite-type chelating agent; optimize the processing temperature not to exceed 165°C.
Key Takeaway
The diluting effect of plasticizers on calcium-zinc stabilizers needs to be compensated by sufficient addition and formulation synergy; the dual function of epoxidized soybean oil is particularly important in this scenario.
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