Molds & Tooling
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Dispersion problem of hydrotalcite-modified calcium-zinc stabilizers
Problem Phenomenon
After introducing hydrotalcite LDH as an auxiliary stabilizing component into the calcium-zinc stabilizer, white particles or plaques appear in PVC products, the product surface roughness increases, and mechanical properties, especially impact strength, decrease by more than 15%.
Cause Analysis
Hydrotalcite is an inorganic nano-layered material with poor compatibility with PVC resin and easily agglomerates to form micron-scale aggregates; conventional high-speed mixing processes can hardly achieve nano-level dispersion; the hydrotalcite surface has not been organically treated, resulting in weak interfacial bonding; excessive hydrotalcite particle size >5 μm leads to stress concentration effects.
Solution
Select hydrotalcite that has undergone surface organic treatment (stearic acid modification, silane coupling agent treatment); adopt a pre-dispersion process to first prepare a high-concentration masterbatch and then dilute it; use a three-roll mill or ball mill for mechanochemical dispersion; control the hydrotalcite addition amount to no more than 1 phr; raise the material temperature to 120-130°C in the high-speed mixing stage to enhance the coupling agent reaction activity.
Key Takeaway
The key to the effective utilization of hydrotalcite in calcium-zinc systems lies in nano dispersion and surface modification; pre-dispersed masterbatching is a practical way to solve the dispersion problem.
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