Improving the flame retardancy, smoke suppression and mechanical properties of polyurethane using novel organic–inorganic hybrid composite microspheres of zirconium modified phenolic resin and montmorillonite

In this work, novel organic–inorganic hybrid microspheres (MZr-PF) of the zirconium modified phenolic resin with montmorillonite (MMT) were synthesized and used to prepare polyurethane (PU) composites. The hybrid microspheres could significantly improve the flame retardancy and thermal insulation of PU composites, with a 62.1 % reduction in the release of toxic gases CO. Compared with pure PU, the LOI, PHRR, THR and TSP of the flame retarded PU containing 25 wt% MZr-PF (PU/25MZr-PF) were decreased by 34 %, 61.8 %, 49 % and 34.4 %, respectively. When PU/25MZr-PF was coated on steel sheet, the backside temperature of PU/25MZr-PF/steel was reduced by 36.5 % during combustion. The combined action of catalytic carbonation by Zr 4+ or MMT and enhancement by MMT promoted the formation of highly graphitized char layer with C-O-Si, C-O-Zr and Si-O-Zr crosslinking structure. Furthermore, Zr 4+ or –OH on MZr-PF could form coordination or hydrogen bonds with N–H in PU structure, which facilitated the interfacial interaction between MZr-PF and PU. The tensile strength and elongation at break of PU/ 25MZr-PF were increased by 225 % and 94.1 %.