Vol.2 No.4 2010

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Research paper : Bioethanol production from woods with the aid of nanotechnology (T. Endo)−274−Synthesiology - English edition Vol.2 No.4 (2010) the average particle diameter of the product ceased to change from about 20 m even after milling for 1 hour or more. This indicated that the equilibrium value for the particulation and aggregation of the particles was about 20 m. Looking at the enzymatic saccharification of the product, the saccharification degree was extremely low even though the untreated raw material was of fine powder of 0.2 mm or less. However, saccharification increased as the time of mechanochemical treatment increased. After four hours, the saccharification was 20 times or more compared to the raw material. Similar trend was seen for Douglas fir, a softwood. However, major difference in results was observed when the mechanochemical treatment was conducted using refined wood pulp (fibrous, width about 20 m, length about 200 m) in a comparative experiment. In pulp, saccharification was high even in the untreated material, and the effect of mechanochemical treatment was small (Fig. 4). From these results, it was found that enzymatic saccharification property could not be estimated from the size of the material alone.Next, the relationship between the crystallinity of cellulose and saccharification was investigated by x-ray diffraction. As a result, in case of wood, crystallinity decreased rapidly with mechanochemical treatment whereas saccharification increased gradually. On the other hand, in the case of pulp, saccharification was high even though the raw material had high crystallinity, and crystallinity decreased rapidly by mechanochemical treatment just as in wood, but the relationship between crystallinity and saccharification was low (Fig. 5). The results of the mechanochemical treatment experiment conducted using woods such as Eucalyptus as raw materials did not greatly contradict the previous understanding that amorphization of cellulose was important for enzymatic saccharification. However, when pulp was used as the raw material, high saccharification was obtained with highly crystallized material, and there was a contradiction. The phenomenon where the enzymatic saccharification gradually decreased despite being amorphous when amorphized cellulose was processed for a long time by mechanochemical process had been known for some time.From the above, it was shown that the enzymatic saccharification could not be sufficiently explained by the particle size of the mechanochemically treated product or the crystallinity of cellulose. In the above experiments, enzymatic saccharification was conducted without purification of the mechanochemically treated products, but the enzymatic saccharification degree was high. This means the enzymatic saccharification progressed even when the wood components such as lignin that supposedly inhibit enzymatic reaction remained. Moreover, from other experiments, the lignin component had high molecular weight as in an untreated wood structure even after undergoing mechanochemical treatment. Also, solid-state nuclear magnetic resonance (NMR) measurement and infrared spectrometry showed that there was hardly any transformation of wood components such as oxidization by the mechanochemical treatment.Fig. 4 Change in degree of enzymatic saccharification by milling time.Enzymatic saccharification time (h)Degree of cellulose saccharification (%)Refined wood pulp0204002040010100304050607080902001030405060708020Milling time: raw material, 15 min, 30 min,1 h, 2 h, 3 h, 4 hEucalyptusMilling time (h)Cellulose saccharification (%)Cellulose crystallinity (%)Refined wood pulpEucalyptus0123401030405060702001030405060702001234010100304050607080902001030405060708020Fig. 5 Relationship between degrees of crystallinity and enzymatic saccharization.

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