The reaction of boric acid with wood in a polystyrene matrix

The reaction of boric acid with wood fibers in a polymer melt was examined using ¹³C-nuclear magnetic resonance (NMR), ¹¹B-NMR, differential scanning calorimetry, dynamic mechanical analysis, and component extraction and by the determination of material properties. Samples were blended at 350and 380°F in a roll mill. The use of a plasticizer in the melt to facilitate the reaction of the acid with the wood fiber was studied. NMR data showed that no significant reaction occurred between the boric acid and the polystyrene. Experimental evidence supports the reaction of boric acid with wood components. The ultimate strength of the composites was either reduced or not significantly altered by the reaction, depending upon conditions. However, the stiffness increased significantly with boric acid additions for the 350°F reactions, but behaved differently for the same additions at 380°F. The glass transition temperature of the polystyrene was lowered by the addition of plasticizer, as expected, while boric acid addition had little effect. Extracted samples showed that some boric acid remained with the wood fraction. These preliminary data suggest that boric acid does react with wood fiber under the conditions of this study. These investigations illustrate the feasibility of performing chemical reactions on the wood phase of wood/polymer composites during the extrusion process. Further research is recommended. © 1996 John Wiley & Sons, Inc.