Nano-sized molybdenum trioxide doped magnesium hydroxide and its effect on flame retardancy and smoke suppression of flexible polyvinyl chloride

In order to solve the problem of low flame retarding efficiency and poor smoke suppression effect of magnesium hydroxide (MH), nano-sized molybdenum oxide doped magnesium hydroxide (MO@MH) was prepared by one-step hydrothermal method. The flame retarding and smoke suppression efficiency of MH was improved by the Lewis acid catalytic cross-linking effect of nano-sized molybdenum oxide. XRD, SEM, TEM and element distribution results showed that MoO₃ was deposited in magnesium hydroxide (MH) layers with thickness of 10~20 nm in the form of particles less than 10 nm. The MH layers were further stacked to form flower spheres with size of 20~30 μm. The results of flame-retardant tests showed that the flame retardant and smoke suppression efficiency of MO@MH fPVC was obviously better than that of MH. The peak heat release rate and peak smoke production rate of MO@MH-1/fPVC composite were 33.64% and 75.16% lower than those of MH/fPVC composite, respectively. MO@MH/fPVC composites also passed V0 rate in the vertical tests. The results of char residue analysis showed that the addition of MO@MH can produce the outer char residue mainly composed of MgO and MgMoO₄, and the inner char residue mainly composed of graphitized carbon, MgO and MgMo₂O₇. The quality, density and integrity of the char residue of MO@MH/fPVC composites were significantly improved compared with that of MH/fPVC composite. The + 6 Mo element participated in the charring process of fPVC matrix through oxidation-reduction reactions to form +4 Mo compounds. The mechanical properties test results showed that MO@MH had better toughening effect on fPVC matrix than MH, and the impact strength of MO@MH-1/fPVC composite was increased by 32.34% compared with the MH/fPVC composite. The main reason was the poor interface compatibility between MO@MH and fPVC matrix and the existence of interface defects caused by complex structure.