Tin-containing layered double hydroxides: Synthesis and application in poly(vinyl chloride) cable formulations

摘要

Layered double hydroxides (LDHs) and Sn-containing LDHs have been synthesized using a co-precipitation method, and the resulting products have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET) surface area measurement, clearly showing that Sn-containing LDH hybrids have been successfully prepared. TEM shows the 'house-of-cards' structure of the Sn-LDHs produced, resulting from the edge-to-face interaction of the LDH layers. Higher tin levels lead to an additional magnesium hydroxystannate, MgSn(OH)_6, ('MHS') phase that is present in the form of approximately 40-nm cubic particles in an LDH/ MHS hybrid structure. FTIR and XRD suggest that, at low levels of Sn, the Sn~(4+) may exist in the form of amorphous hydrated tin(TV) oxide rather than being incorporated into the LDH lattice. These powders have been compounded into poly(vinyl chloride) (PVC), and their fire performance has been evaluated using limited oxygen index and cone calorimeter techniques. Peak rate of heat release and smoke parameter can be reduced by 64% and 81%, respectively, when replacing 10 wt% of the primary ATH fire-retardant filler by the synthesized Sn-LDHs, while keeping the total fire-retardant loading at 100 phr. Thermogravimetric analysis indicates that Sn-LDH is an effective char promoter for PVC.