Moisture Sorption Properties of Composite Boards from Esterified Aspen Fiber

One barrier to producing wood-plastic composites with wood fiber is the poor thermoplasticity of wood fiber. The objective of our study was to determine the plasticization of chemically modified wood fiber through tests on unmodified and esterified fiberboards. Attrition-milled aspen fiber was esterified with neat acetic, maleic, or succinic anhydride. Fourier transform infrared spectroscopy, gas liquid chromatography, and titrational methods were used to confirm derivatization and to characterize the end products of the esterification reaction. All anhydrides formed a simple monoester; succinic anhydride was found to be the most reactive anhydride with a molar gain of 6.0 mol anhydride per kilogram wood fiber. Gains of 4.5 and 2.0 mol anhydride per kilogram wood were found for fiber modified with acetic anhydride and maleic anhydride, respectively. Scanning electron micrographs of hot-pressed fiber mats indicated that esterification of the aspen fibers with maleic or succinic anhydride imparted thermoplasticity to the fibers, whereas acetylation did not affect thermal properties. Fiber modified with succinic anhydride appeared to exhibit the greatest thermoplasticity. Esterified fiber in fiberboards made with phenol-formaldehyde as an adhesive or combined with polypropylene to form polymer-wood fiber composites had reduced moisture sorption and reduced rate of swelling in liquid water. Polypropylene also imparted temporary water repellency to the fibers