writer：Zhang Y, Li XN, Fang ZP, Hull TR, Kelarakis A, Stec AA
keywords：Fire; Intumescent flame retardant; Polypropylene; Metal acetate; Rheology; Mechanism
source：期刊
specific source：Polymer Degradation and Stability, 2017, 136: 139-145
Issue time：2017年

The effects of cobalt acetate (CoAc), manganese acetate (MnAc), nickel

acetate (NiAc) and zinc acetate (ZnAc) as fire retardant additive in

intumescent polypropylene (PP) formulations containing PP/ammonium

polyphosphate (APP)/pentaerythritol (PER) are reported. The limiting

oxygen index (LOI) and vertical burning (UL94) tests and cone

calorimetry were used to quantify the enhancement. Environmental chamber

rheometry, thermal gravimetric analysis and the morphology of the

residual char were used to investigate the mechanism of enhancement. The

incorporation of small quantities of metal acetates had a significant

influence on the fire behaviour. As an example, 0.7 wt% MnAc improved

the UL 94 rating of PP/APP + PER (mass ratio 100/25, with APP/PER = 3/1)

sample from V-2 to V-0, while 1 wt% MnAc reduced the peak heat release

rate and the total heat release by 18% and 12% in the cone calorimeter.

Rheological data, cone calorimetry, and photographs of the residual char

showed how the fire retardancy of the systems were affected by the melt

viscosity, which depended on the loading of metal acetate. During

thermal decomposition, the metal acetates promote the crosslinking of

the polymer and the fire retardant, reinforcing the protective

intumescent layer. While, the effect is most potent at the optimal metal

loadings. At higher MnAc loadings, the benefit of a stronger char is

overwhelmed by the adverse effect of crosslinking on the transition char

layer. Thus, this paper offers a new insight into the mechanism of the

intumescent fire retarded PP system.