Technical Manual on Utilization of Sympodial Bamboos - ITTO

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Chapter 1 The Fundamental Properties of Bamboo Timber 5 1 . 3 Chemical Composition of Bamboo Timber The organic composition of bamboo timber is quite similar to that of wood. It consists of cellulose (about 55 % ) , lignin (about 25 %) and hemicellulose (pentosan, about 20% ) . 1.3.1 Hemicellulose It is mostly composed of peritosan, with little hexoan. 90% of hemicellulose in bamboo timber is made up of xylan. Experiments have shown that bamboo xylan is D-glucuranate arabinoxylan, which comprises 4-oxygen-methyl D-glucuranate, L-arabinose and D-xylose. Their molecule ratio is 1.0: 1.0 -1.3: 24 - 25, as follows: Figure 1. 2 Macrostructure of Cross Section of Stem Wall 1. Bamboo skin 2. Fundamental tissue 3. Vascular bundle 4. Pitch I-j3-D-xylose -(1-4) -j3-D-xylose-(1-4 ) -j3-D-xylose -(1-4) -j3-D -xylose-l 2 3 r 4-oxyten-methy-D-glucuranate r a-L-arabinose The composition of arabinoxylan of bamboo is different from that of conifers and broad-leaved trees. The polymerized molecules of bamboo xylan are more than that of tree. The content of pentose in bamboo timber is between 19% and 23% , which is close to that of broadleaves and much higher than that of conifers (10 % - 15% ). This indicates that bamboo timber can not only be used to make pulp or hydrolyze, but also be synthetically used as uronic acid. 1.3.2 Lignin bamboo timber lignin is a typical herbaceous lignin, which is composed of three phenyl propane units, i. e. paradinum, guaiacyl and mauve in the ratio of 10:68:22. This means the bamboo lignin is similar to broad-leaved lignin qualitatively, not quantitatively. The specific features of bamboo lignin lie in the existence of dehydrogenated polymerides and 5% - 10% of acrylic ester. The lignin content of one-year old bamboo is in the range of20% -25% , approaching to broad-leaved wood and some grass (such as straw of wheat 22 % ) and is a little lower than that of conifers. Less lignin content means less consumption of chemicals in pulping process and easier
6 Part I Processing and Utilization of Sympodial Bamboos pulping process. 1 . 4 Physical Properties of Bamboo Timber 1.4.1 Moisture Content As the rule, the moisture content of growing bamboo is rather high, but it varies as seasons change. It also varies among different bamboo species and different bamboo culms. The moisture content of moso bamboos at cutting age is approximately 80%. The equilibrium moisture content after air-drying varies as air temperatures and humidity change. According to the statistics, the equilibrium moisture content of moso bamboo in Beijing area is 15.7%. 1.4.2 Density The basic density of bamboo timber (the mass of the whole culml the volume of the raw bamboo timber) is between O. 40 and O. 8 (0. 9) g/ cm 3 • This is mainly depends on the density and the composition of vascular bundles. As a rule, the density of a culm grows gradually from inner to outer part, and from lower to upper part. The thickness of the culm reduces as it grows taller and the density of the culm's inner part increases while its exterior part has little change. The density of bamboo timber node is a little bigger than that of the internode. 1.4.3 Dry Shrinkage After it is cut, during the process of its drying, the bamboo timber is shrunk because of water evaporation. The shrinkage of the bamboo timber has obvious differences in different directions. From its air-drying to full drying, when its moisture content is reduced by 1 % , the average shrinkage of moso bamboo is measured and the results are: longitudinal direction O. 024 % , tangential direction O. 1822 % , radial direction O. 1890% (on node parts 0.2726% , on inter node parts O. 1521 % ) . Obviously, the shrinkage in longitudinal direction is much less than that in radial direction, while there is not much difference between the shrinkage in tangential direction and that in radial direction. The shrinkages of the inner part and the exterior part are also different even at the same horizontal height of a bamboo culm. The shrinkage of "bamboo green" part in longitudinal direction is so small that it can be purely ignored while its shrinkage in radial direction is the biggest; the absolute value of the shrinkage of "bamboo yellow" part in longitudinal direction is still small even though it is bigger than that of "bamboo green" while its shrinkage in radial direction is much smaller 11 ·1
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CHAPTER 4 Bamboo-based Panel Accord
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CHAPTER 5 Production Technologies,
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CHAPTER 6 Utilization of Bamboo Sho
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CHAPTER 8 Preserving Techniques Bes
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Riferences 187 Wang Hongfeng, Chen
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Technical Manual on Utilization of Sympodial Bamboos - ITTO

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