Biocomposite of wood flour (WF)/polypropylene
(PP) composite (WPC)
is not easily flame-retarded because of the different flame retardant
mechanisms of PP and WF. In order to improve the flame retardancy
of WPC, a single flame retardant of ammonium polyphosphate (APP) modified
via ion exchange reaction with ethanolamine, which is named as ETA-APP,
was used to prepare flame-retardant WPC. The flammability was investigated
by limiting oxygen index (LOI), UL-94 vertical burning test, and cone
calorimeter. The results show the flame retardant properties of the
flame-retardant WPC are improved greatly. The limiting oxygen index
is 43.0%, which is increased by 71.6% compared with that of WPC with
the same content of APP. And the vertical burning test can pass UL-94
V-0 rating. The results of cone calorimeter test show that the heat
release rate (HRR) and total heat release (THR) of the WPC with ETA-APP
are decreased in comparison with WPC/APP. The flame-retardant mechanism
of WPC/ETA-APP system was investigated by thermogravimetric analysis
(TGA), Fourier transform infrared (FTIR), and X-ray photoelectron
spectroscopy (XPS). It is found that the hydroamine groups and phosphate
acid in ETA-APP might promote the etherification and dehydration reactions
in WPC/ETA-APP, which facilitated the formation of stabile char residue
of WPC. Consequently, the flame-retardant efficiency is improved greatly.
The flexural properties of WPC/30 wt % ETA-APP increase a lot in comparison
with WPC/30 wt % APP, which is because of the better compatibility
of ETA-APP with WF.
To improve the flame retardancy and maintain the ideal mechanical properties of the widely used wood fibre (WF) reinforced polypropylene (PP) composite (WPC), a novel intumescent flame retardant (IFR) system consisting of poly[N 4 -bis(ethylenediamino)-phenyl phosphonic-N 2 ,N 6 -bis(ethylenediamino)-1,3,5-triazine-N-phenyl phosphonate] (PTPA) and ammonium polyphosphate (APP) was developed. Addition of APP, a high performance flame retardant, improves flame retardancy but has a negative effect on flexural properties and the Notched Izod impact strength. Combining self-designed PTPA with WPC has a positive effect on the mechanical properties whereas it just slightly increases the flame retardancy. The flame retarded WPC system with both PTPA and APP, i.e. WPC/PTPA/APP, combines bilateral advantages. The selected formula has a flexural modulus of 4.4 GPa, flexural strength of 37.2 MPa and impact strength of 1.8 kJ m À2 , only the flexural strength is slightly lower than that of neat WPC.And the formula has a high limiting oxygen index (LOI) of 31.5%, which passes the UL-94 V-0 rating for a vertical burning test. The results of cone calorimetry show that the heat release rate (HRR) of the WPC/ PTPA/APP system is significantly reduced compared to the neat WPC. The pyrolysis and char residue of the WPC/PTPA/APP system were investigated by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). These results reveal the flame-retardant mechanism that PTPA/APP can synergistically catalyze the etherification, dehydration and char formation of WPC.
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