Vol.2 No.4 2010

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Research paper : Bioethanol production from woods with the aid of nanotechnology (T. Endo)−275−Synthesiology - English edition Vol.2 No.4 (2010) 4.2 Application of macromolecular chemistry techniquesSince the aforementioned experiment results indicated that the fine breakdown of wood, amorphization of cellulose, and separation of lignin, which were the empirical rules of conventional technology, were not important in increasing the enzymatic saccharification of wood, analysis from a new viewpoint became necessary.NMR is used frequently as an analysis tool of molecular structure in the fields of organic chemistry, and in the macromolecular field, the evaluations of mixture of molecules in complexes and molecular aggregation size (domain size) are conducted by relaxation time measurement using solid-state NMR. Relaxation time measurement is a method in which pulse signals are irradiated to a substance using the NMR device, and how fast the signal decays is measured. If the aggregation (domain) of the substance is large, the pulse signal takes more time to travel far. If the domain size is small, the pulse signal decays fast. In a case where different substances are mixed at the molecular level and placed in the same environment, the different substances will have the same relaxation time. The result of using this method to evaluate the mechanochemically treated product is as follows.Solid-state NMR measurement was conducted at a similar moisture condition as the enzymatic saccharification reaction, and the relaxation time (T1H) of hydrogen atoms of the cellulose molecules was measured. As a result, the relaxation time decreased (the molecular motion increased in the macromolecular substance such as cellulose) with more mechanochemical treatment, and it was 0.05 sec. after 4-hour milling when saccharification reached maximum (Fig. 6). When the domain size was calculated from this value, it was 5.5 nm[11]. The wood became wood powder of about 20 m in appearance by the mechanochemical treatment, but this wood powder is actually composed of domains of about 5 nm, which is much finer. Since this 5 nm size approached the width of the cellulose microfibril, it was hypothesized that the major factor for the promotion of enzymatic saccharification was that the microfibrils separated from each other through the mechanochemical treatment, thereby increasing the surface area where the enzymes can adsorb. The studies hereafter were based on this working hypothesis to clarify the effective mechanochemical treatment for enzymatic saccharification, and we developed a new pretreatment methodology. While the cellulose became amorphous by the mechanochemical treatment, it is thought that the orientation of cellulose molecules such as microfibril remained[12]. Looking at the size level of the fibril separation, the cellulose crystallization occurs at a lower level, and whether it is high crystallinity or amorphous is not particularly important.5 Microfibril treatmentThe enzymatic saccharification reaction of cellulose is a solid-liquid reaction of solid cellulose and enzyme dissolved in water. In general, to promote the solid-liquid reaction efficiently, the solid can be broken down finely to increase the contact surface with the liquid. The microfibril in the wood is the minimum unit of solid cellulose. Saccharification is expected to progress smoothly if the cellulose can be dissolved and separated into one unit of molecule, but the enzyme will easily become deactivated in a solvent that can dissolve cellulose.Therefore, to confirm the working hypothesis based on the results obtained from the aforementioned solid-state NMR measurement, we investigated the method for actually unraveling the microfibril, which is a microscopic wood fiber. In the papermaking technology, the process called “beating” is done to increase the strength of the paper. In this process the fibers are fluffed by mechanically applying Fig. 6 Change in relaxation time T1H by milling time (figures in parenthesis are assignments of wood components in NMR).Fig. 7 Scanning Electron microscope photograph of wet mechanochemically-treated product.Milling time (h)Relaxation time T1H of hydrogen atom (sec)0012340.020.040.060.080.10.12Hemicellulose derived (21 ppm)Lignin derived (56 ppm)Cellulose (C6)Cellulose (C235)Cellulose (C1)Lignin derived (154 ppm)5 µm

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