Abstract
Two halogen-free inorganic flame retardants, ammonium polyphosphate (APP) and aluminum hydroxide (ATH) were added to wood-flour/polypropylene composites (WPCs) at different APP to ATH mass ratios (APP/ATH ratios), with a constant total loading of 30 wt % (30% by mass). Water soaking tests indicated a low hygroscopicity and/or solubility of ATH as compared to APP. Mechanical property tests showed that the flexural properties were not significantly affected by the APP/ATH ratio, while the impact strength appeared to increase with the increasing ATH/APP ratio. Cone calorimetry indicated that APP appeared to be more effective than ATH in reducing the peak of heat release rate (PHRR). However, when compared to the neat WPCs, total smoke release decreased with the addition of ATH but increased with the addition of APP. Noticeably, WPCs containing the combination of 20 wt % APP and 10 wt % ATH (WPC/APP-20/ATH-10) showed the lowest PHRR and total heat release in all of the formulations. WPCs combustion residues were analyzed by scanning electron microscopy, laser Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). Thermogravimetric analysis coupled with FTIR spectroscopy was used to identify the organic volatiles that were produced during the thermal decomposition of WPCs. WPC/APP-20/ATH-10 showed the most compact carbonaceous residue with the highest degree of graphitization.
Highlights
Wood-plastic composites (WPCs), consisting of wood processing residue and thermoplastic polymer, have been showing a rapid growing usage in the last decades due to their significant advantages, such as high durability, low maintenance and cost, relatively high strength and stiffness, sustainability, and wood-like material appearance and properties [1,2,3,4].wood-flour/polypropylene composites (WPCs) have been widely used in both exterior and interior applications, including decking, fencing, cladding, window and door frames, landscaping timbers, and automotive components, etc. [5,6,7,8].the high flammability of WPCs may limit their application
Several researchers have focused on the method to improve the flame retardancy of WPCs [9,10,11,12,13,14,15]
This was attributed to the slow diffusion of water molecules into the WF/polymer interface, likely promoting by hydrogen bonding between the water molecules and the free –OH groups in the WF [48]
Summary
WPCs have been widely used in both exterior and interior applications, including decking, fencing, cladding, window and door frames, landscaping timbers, and automotive components, etc. The high flammability of WPCs may limit their application. Several researchers have focused on the method to improve the flame retardancy of WPCs [9,10,11,12,13,14,15]. The most widely used method is to incorporate flame retardants (FRs) directly into WPCs during the melt processing [16,17,18,19,20]. Halogenated compounds based on chlorine or bromine are effective FRs
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