Enhanced flame retardancy and thermal stability of zinc borate and magnesium carbonate as a promising alternative for Sb2O3 toward polyvinyl chloride

Inorganic zinc compounds such as zinc carbonate (ZC) and zinc borate (ZB) are considered as promising alternatives for harmful antimony trioxide in the future, but may result in poor thermal stability for flexible polyvinyl chloride (PVC). To enhance the flame retardancy and static thermal stability of flexible PVC, zinc compounds with environmentally friendly magnesium carbonate (MC) were introduced into PVC matrix. Findings reveal that the simultaneous use of 5 phr ZB and 5 phr MC for flexible PVC exhibits satisfactory properties containing pronounced flame retardancy with a limiting oxygen index of 30.2% and a UL-94 V-0 rating without dripping, enhanced static thermal stability with high color stability by discoloration tests, reduced smoke emission, and decent mechanical properties, which are advantageous over the standalone use of ZC, ZB, and MC. The enhancement mainly due to that the incorporation of ZB can accelerate the dehydrochlorination and promote the charring of flexible PVC in the early stage of flame burning, and MC can perform the long-term static thermal stability due to the HCl absorption capacity.