Tokuo Yokota

Lattice Conversion of Cellulose in Wood

Abstract When peracetylated wood, prepared in an acetic anhydride-pyridine medium, was saponified and recrystallized, almost no conversion of cellulose I to cellulose II took place. Neither was conversion detected, when thirteen species of wood, differing in density from 0.17 to 0.71, as well as in lignin content from 18.1 to 38.8 %, were treated with 17.5 % aqueous NaOH, followed by recrystallization. The corresponding treatments for cellulose triacetate or cellulose resulted in complete conversion to cellulose II. Partial delignification of wood preceding the alkali-induced mercerization was found to cause partial lattice conversion to cellulose II, and the ratio of lattice conversion (L.C.R.) increased with the degree of delignification. The L.C.R. value reaches slightly more than 50 %, when one third of the lignin is removed, and the removal of about two third of the lignin from wood results in an almost complete conversion. The effect of lignin removal on lattice conversion was similar among the wood...

Homogeneous Tritylation of Cellulose in A Sulfur Dioxide – Diethylamine – Dimethyl Sulfoxide Medium

Abstract The present investigation was undertaken to see if a practical method could be developed for homogeneous tritylation of cellulose in a non-aqueous solvent of cellulose. Our new procedure of tritylation of cellulose can easily be carried out under homogeneous conditions by dissolving cellulose in a sulfur dioxide(SO2)-diethylamine (DEA)-dimethyl sulfoxide(DMSO) solvent system, one or the non-aqueous cellulose solvents, followed by addition of trityl chloride and pyridine. This new method can avoid the time consuming pretreatment for the decrystallization of cellulose which has been necessary in the traditional procedure and can lower the reaction temperature. IR spectra of the products indicated the formation of trityl cellulose. Measurements of dielectric properties of the products confirmed that trityl groups were selectively introduced at the primary hydroxyl groups in cellulose. This conclusion was also confirmed by a H-NMR study in which the tritylated products was first acetylated, detrityla...

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

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...

Effect of the Loosening of Wood Texture on the Mercerization of Cellulose in Wood

Abstract When wood was treated with 23% aqueous sodium hydroxide followed by washing with water and drying, no lattice conversion of cellulose was observed under the experimental conditions employed. On the other hand, wood subjected to a pretreatment that results in the loosening of its morphological texture, upon mercerization, showed a varying degree of lattice conversion. The explosion process and the TFA (trifluoroacetic acid) treatment were used to achieve the loosening of wood texture. The lattice conversion of cellulose was studied by X-ray diffractograms. The extent of lattice conversion was found to depend on the conditions of the pretreatment used to achieve the loosening of wood texture. The extent of lattice conversion increased with an increase in the explosion temperature and the time at temperature, within the range of these experiments. Increased duration of TFA pretreatment, at a particular temperature, resulted in a higher degree of lattice conversion. These observed facts have been asc...

Preparation and Thermal Properties of Acetates Derived From Cellulose Dissolved in Dmso-Pf

Abstract Homogeneous acetylation of cellulose dissolved in the dimethyl sulfoxide(DMSO)/paraformaldehyde(PF) system was investigated. Characterization of the acetylated products was performed to evaluate the dissolution mechanism. The dissolution reactions are reasonably divided into three steps: (1)immediately after the dissolution, initial methylolation of cellulose; (2)further methylolation to form oligo-oxymethylene side chains on the cellulose backbone; (3)de-methylolation, that is, the break down of the side chain by prolonged heating. The possible methylolation reaction sites are all hydroxyls of the anhydrous glucose unit while the C-6 position is most reactive. Manipulation of the side chain lengths by control of the dissolution conditions makes it possible to prepare acetates with different thermal properties: Tg varied 35°-102.5°C and Tm 65° -122.5°C, depending upon the side chain length. Triethylamine(TEA) was prefered to pyridine, as a promotor of acetylation, in order to understand the disso...