Strawboard from vapor phase acetylation of wheat straw

Commercial ground wheat straw was used in a central composite response surf ace experimental design to examine four acetylating process variables: reac tion temperature, reaction time,initial moisture content of straw, and the vapor flow rate of chemical reagent. The response variable was acetyl conte nt determined as a function of straw weight gain. Diphenylmethyane diisocya nte was used as a binder to prepare board samples with a hot press. Equilib rium moisture content (EMC) was determined at 65 and 90% RH at 27 degrees C , and dimensional stability was determined using a humidity cycle of 30-90% RH at 27 degrees C, ASTM D1037-93 standard method for a 3-point flex test was used to measure mechanical properties. The microstructures of both trea ted and untreated wheat straw and boards were observed with a scanning elec tron microscope. The vapor phase acetylation system used acetylated ground wheat straw to a 24% weight gain (dry weight basis). A mathematical model ( R-2 = 0.97) was developed to predict the weight gain as a function of the f our acetylation processing variables. The maximum reduction in all strawboa rd properties occurred at the highest weight gain (24%). The strawboard EMC decreased (30% maximum reduction) as weight gain increased at both 65 and 90% RH. The strawboard dimensional stability increased as the weight gain i ncreased (maximum reductions of 80% in thickness swell and 50% in linear ex pansion). The initial mechanical properties of the strawboards decreased as the weight gain increased (maximum reductions of 64% in strength and 48% i n stiffness). The density of the strawboards decreased as the weight gain i ncreased (23% maximum reduction). SEM micrographs showed no physical eviden ce of structural damage to cell walls from the acetylation. (C) 2000 Elsevi er Science B.V. All rights reserved.