Material Analysis
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Core layer scorching problem of PVC foamed products
Problem Phenomenon
The core layer of PVC foamed boards using calcium-zinc stabilizers shows scorched yellow or brown scorching areas, the cell structure collapses in the scorched areas, the board density is uneven with local density exceeding 1.2 g/cm³ (normal foaming density 0.5-0.7 g/cm³).
Cause Analysis
During the foaming process, the decomposition of AC foaming agent generates a large amount of heat; the exothermic reaction ΔH=-117 kJ/mol causes the local temperature to rise sharply above 220°C, exceeding the temperature protection range of calcium-zinc stabilizers; the foaming agent decomposition residue cyanuric acid has a catalytic degradation effect; the core layer of thick-walled foamed products has difficulty dissipating heat, forming heat accumulation.
Solution
Adopt a foaming agent + activator composite system AC+zinc oxide/ZnSt to lower the decomposition temperature; introduce organotin or rare earth stabilizers into the formulation to assist the calcium-zinc system at 0.5-1 phr to enhance stability in the high-temperature range; add endothermic foaming agent NaHCO₃ to balance heat release; optimize the foaming temperature curve to control the core layer temperature ≤195°C; increase the calcium-zinc stabilizer dosage to 4-5 phr.
Key Takeaway
The superposition of thermal effects in the foaming process poses severe challenges to calcium-zinc stabilizers; the scorching risk can be controlled by adjusting the foaming agent decomposition temperature and introducing auxiliary heat source management.
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