These FTIR results confirm that MDFP is successfully coated onto the surface of ZHS nanocore to yield ZHS@MDFP composite flame retardant with core-shell structure.
Figure 3 shows the TG curves of as-synthesized ZHS, MDFP, and ZHS@MDFP.
At the third step, positively charged M-F and D-F prepolymers are attracted by nano-ZHS; and M-F and DF prepolymers containing hydroxyl group form hydrogen bonds with polyvinylpyrrolidone while MDFP shell is anchored on the surface of ZHS core through in situ polymerization of M-F and D-F prepolymers under acidic condition.
In the meantime, the SDR of flexible PVC filled with 15% ZHS@MDFP is much lower than that of blank PVC and PVC filled with 6.7% ZHS, which indicates that both the inorganic ZHS core and organic MDFP shell of ZHS@MDFP possess smoke suppression capability.
When ZHS@MDFP is added, resultant ZHS@MDFPPVC composite sample has similar TG curve and thermal decomposition data as ZHS-PVC sample, which well conforms to the coexistence of both ZHS core and MDFP shell in ZHS@MDFP composite flame retardant.