Effect of the Explosion Pretreatment on the Thermal Softening and Melting of Esterified Wood

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Abstract
The explosion treatment has been used with the objective of increasing the accessibility of wood. After the explosion treatment wood meal was esterified. Acyl groups introduced were acetyl, caproyl and lauroyl. Caproylation was carried out by three different methods - PCA catalyst method, TFAA catalyst method and DMF/PY/acid chloride method. The PCA catalyst method was not used for lauroylation since it is not an effective procedure for introducing higher acyl groups. The DMF/PY/acid chloride method could not be used successfully for acetylation. Thermal softening and apparent melting behaviour of the exploded-esterified wood meal was studied by following the collapse of a column of powder under a constant load in a glass capillary tube 3 mm in diameter at a programmed rate of heating. Samples exploded at various conditions and esterified by the DMF/PY/acid chloride method showed thermal flow in nearly the same temperature range. The thermal flow was observed at considerably lower temperature for the corresponding samples acylated by TFAA catalyst method. Also, the thermal softening or apparent melting temperature (flow temperature) of the samples acylated by TFAA method was found to be dependent on the condition of explosion. The more severe the explosion treatment, the lower was the flow temperature. In other words, an increase in the explosion temperature or duration at a particular temperature resulted in a decrease in the thermal softening or melting temperature. This fact has been attributed to the loosening of wood texture in combination with the action of trifluoroacetic acid (TFA) formed during the acylation by the TFAA method. The larger the size of the acyl group introduced the lower the flow temperature became.