Lignin/ammonium polyphosphate-modified wood flour/high-density polyethylene composites

Abstract

Wood plastic composite (WPC) is a kind of green composite materia due to utilizing recycled wood flour and thermoplatics. It has been widely used in decking and furniture application. However, both plant fibers and plastics are flammable, severely limiting their application. In the present study, combinning with ammonium polyphosphate (APP), lignin (L) was developed to function in flame retardant as a char former agent to prevent the combustion of wood flour/high density polyethylene (WF/HDPE) composites. The optimum proportion of L/APP ratio was determined by cone calorimeter and TG tests, and the combustion process was analyzed. The L/APP/WF/HDPE composite could reach V-0 level at the total amount of L/APP (1:1) of 50% when L/APP was distributed throughout the whole composite. In order to provide the protection at a lower usage and cost, the L/APP mixture of 20% amount was concentrately ditributed in the surface layer of the WF/HDPE composite. When the surface layer was 0.5 and 1 mm in thicknesses, the sandwiched WF/HDPE board of 4 mm thickness could meet the requirement of V-0 level, too. Compared with the throughout distribution of L/APP in the composite, the concentrated distribution of L/APP in surface layer of the composite provided prolonged ignition time, reduced smoke release, and other improved flame retardant performance for WF/HDPE composite at the same L/APP usage; meanwhile, the sandwiched WF/HDPE composite remained better mechanical properties.