Flammability and thermal degradation behavior of flame retardant treated wood flour containing intumescent LDPE composites

In the current study, the flame retardant wood-plastic composites (WPC) were produced by reducing the flammability of both the wood flour (WF) and the matrix material. Accordingly, WF was treated either with bis[tetrakis (hydroxymethyl) phosphonium] sulfate (THPS) or with dicyandiamide-formaldehyde-phosphoric acid flame retardants (DFP). The synergistic mixture of ammonium polyphosphate (m-APP) was used to improve the flame retardancy of matrix material based on low density polyethylene (LDPE). The flame retardant properties of LDPE based composites were investigated using limiting oxygen index (LOI), UL-94 standard, thermogravimetric analysis (TGA), and cone calorimeter. The addition of 30 wt% m-APP increased the LOI value from 17.5 to 24.2 and still burned to a clamp (BC) in UL-94 test. The THPS and DFP treatments of WF did not have any remarkable effects on the flammability properties (LOI and UL-94 ratings) with respect to LDPE/WF/APP composite. According to cone calorimeter test results, the treatments of WF with THPS and DFP improved the fire performance with approximately 25 % reduction in total heat evolved (THE) with respect to LDPE/WF/APP. The high reduction in THE value demonstrated that there was an increase in the fire performance of the LDPE based composites when THPS or DFP treated WF was used with m-APP due to the increase in the amount of foamed char providing barrier effect.