Thermal properties of tropical wood–polymer composites

Wood–polymer composites (WPC) of Geronggang (GE; Cratoxylon arborescens), a light tropical hardwood, impregnated with methyl methacrylate (MMA), styrene-co-acrylonitrile (3: 2; STAN), methyl methacrylate-co-bis (2-chloroethyl) vinyl phosphonate (3 : 1; MVP) and methyl methacrylate-co-bis (chloropropyl)-2-propene phosphonate (3:1;MPP), were prepared by in situ polymerization using γ-radiation or catalyst-heat treatment. Thermal characterization of these WPC by limiting oxygen index measurements (LOI), thermogravimetry (TG), and differential scanning calorimetry (DSC) showed that the impregnants greatly modified the wood properties. The LOI values of the GE–MVP and GE–MPP composites were much higher than that for GE and the other composites, indicating the effectiveness of the phosphonates as flame retardants. Concomitantly, the flaming characteristics also compared favorably against that for GE and the other composites. The decomposition temperature and maximum rate of weight loss determined by TG for GE–MVP and GE–MPP were substantially reduced, whereas the char yields were greatly higher. These observations again indicate that phosphonates imparted flame-retarding properties to their composites. The thermal properties of GE–MMA and GE–STAN composites were not vastly different from that of untreated GE. Flame retardancy in the phosphonate-containing composites was effected through both the condensed- and gaseous-phase mechanisms due to the presence of phosphorus and chlorine, respectively. Indication of grafting of polymer to wood was found for GE–STAN, GE–MVP, and GE–MPP composites, but not for GE–MMA. Composites prepared by γ-radiation or by the catalyst-heat treatment had similar thermal characteristics.