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The effect of intermittent heat treatment on cellulose crystallites in wood was studied to evaluate quantitatively the changes of crystallinity induced by intermittent and continuous heating. The changes in crystallinity were found to be strongly affected by the intermittent heat treatment. The increased crystallinity, the width of the crystals, and the piezoelectric properties were the same for the first intermittent heating as for continuous heating. Further intermittent heating for the same time duration and temperature had no effect on the above properties, probably due to the stopping of the thermal reaction during the interval. Our results suggested that intermittent heat treatment has certain critical cooling temperatures that stop the thermal reaction and are closely related to the duration of the interval. Samples once exposed to a certain duration of heat treatment and then cooled need more time, about twice that of the first duration of intermittent heating compared with continuous heating, to reach maximum crystallinity in wood cellulose. 相似文献
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A new approach is proposed for the evaluation of the brittleness of heat-treated Styrax tonkinensis wood. Heat treatment made wood more brittle when wood was heated at a higher temperature or for a longer time. The brittleness
increased to four times that of the control when wood was heated at 200°C for 12 h. For treatment at 160°C, the increase in
brittleness without any change in weight is thought to be possibly caused by the relocation of lignin molecules. At higher
temperatures, loss of amorphous polysaccharides due to degradation is thought to become the main factor affecting brittleness.
The crystallites that were newly formed after 2 h of treatment showed brittleness that was different from that of the inherent
crystallites remaining after 12 h of heat treatment. This inherent crystalline cellulose possibly plays a role in brittleness.
There is also the possibility of using color to predict the brittleness of heat-treated wood. 相似文献
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Crystallinity of wood and the size of cellulose crystallites in Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis>) 总被引:5,自引:0,他引:5
Seppo?Andersson Ritva?SerimaaEmail author Timo?Paakkari Pekka?Saranp?? Erkki?Pesonen 《Journal of Wood Science》2003,49(6):531-537
X-ray diffraction was used to study variations in the crystallinity of wood and the average thickness and length of the crystallites of cellulose as a function of the number of the year ring in Norway spruce [Picea abies (L.) Karst.]. The crystallinity increased from ring 4 to ring 10 from the pith and was constant after ring 10. The crystallinity of mature wood was about 30% ± 5%. The average thickness and average length of the crystallites were 3.2 ± 0.1nm and 28 ± 2nm, respectively; and no systematic variation of these values with the number of the year ring was observed. The mean microfibril angle decreased near the pith but was constant in the mature wood. 相似文献
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The structural feature of macromolecular component of dhaincha, cotton stalks, jute fiber, rice straw and wheat straw, which are commonly used in paper pulp production in forest deficient countries, was thoroughly studied. Lignin was isolated by classical Bjorkman method and characterized by elemental and methoxyl analysis, alkaline nitrobenzene oxidation, FTIR and 1H NMR spectroscopy. The C9 formulas for cotton stalks, jute fiber, dhaincha, rice straw and wheat straw were C9H8.95O3.53(OCH3)1.00, C9H8.12O4.03(OCH3)1.65, C9H8.10O4.65(OCH3)1.32, C9H8.58O3.74(OCH3)1.23 and C9H8.31O3.54(OCH3)1.23, respectively. The alkaline nitrobenzene oxidation products showed that syringyl to vanilin ratio of these nonwood varied from 1.1 to 2.9. Jute fiber showed the highest syringyl to vanilin ratio that are consistent with C9 formula. The β-O-4 units in these nonwood lignins had predominately erythro stereochemistry type. The crystalline structure of these nonwood cellulose was also studied using X-ray diffraction and FTIR spectroscopy. The proportions of crystallinity, crystal size were varied from plant to plant. Jute fiber showed the highest proportion of crystallinity (73.4%) and crystal size (4.2 nm). The degree of polymerization of these nonwoods cellulose has also been studied. Degree of polymerization of jute cellulose was also the highest (3875). FTIR spectroscopy showed that these nonwoods cellulose was monoclinic unit cell structure (Iβ). Carbohydrate analysis showed that the main sugar component in the hydrolyzates of these nonwoods were xylose apart from glucose. 相似文献
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Carmen M.O. Müller João Borges LaurindoFabio Yamashita 《Industrial Crops and Products》2011,33(3):605-610
The objective of this study was to investigate the influence of nanoclay incorporation procedure on the mechanical and water vapor barrier properties of starch/nanoclay composite films. Cassava starch films were prepared with (nanocomposite) and without nanoclay (control) in two steps: firstly the production of extruded pellets and secondly thermo-pressing. The nanocomposite films were prepared via two different methods: in D samples the nanoclay was dispersed in glycerol and subsequently incorporated into the starch; and in ND samples all ingredients were added in a single step before the extrusion. All the composite-films were prepared with cassava starch using 0.25 g of glycerol/g of starch and 0.03 g of nanoclay/g of starch. Control samples showed VA-type crystallinity induced by the manufacturing process and the nanocomposites presented a semicrystalline and intercalated structure. The nanoclay improved the water vapor barrier properties of the starch film and this effect was more pronounced in D samples, where the water vapor permeability (Kw) was 60% lower than that of the control samples. The Kw reduction was associated with decreases in the effective diffusion coefficient (approximately 61%) and in the coefficient of solubility (approximately 22-32%). On the other hand, the incorporation of nanoclay increased the tensile strength and the rigidity of the films and this effect was more significant when the nanoclay was dispersed in glycerol. Thus, the incorporation of nanoclay into starch-based films is a promising way to manufacture films with better mechanical and water vapor barrier properties. 相似文献
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结晶度对云杉属木材声振动特性参数的影响 总被引:5,自引:2,他引:5
选择7种我国具有代表性的云杉属木材及1种做对比用的美国产西加云杉试材,分析了纤维素结晶度对木材声振动特性参数的影响。根据纤维素结晶度与木材声振动特性参数之间存在的关系,总结出一些基本规律,云杉属木材纤维素结晶度达到59%后,木材声振动特性可达最佳。 相似文献
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为了研究催化剂(硫酸铜、硫酸亚铁)对氧化淀粉羧基质量分数及结构方面的影响,采用淀粉糊滴定法测定了两种氧化淀粉的羧基质量分数,并比较了其X射线衍射图谱和傅里叶红外光谱。试验结果为:硫酸铜氧化淀粉的羧基质量分数为0.048%,结晶度为33.76%;硫酸亚铁氧化淀粉的羧基质量分数为0.001 7%,结晶度为34.12%。试验表明:硫酸铜对双氧水的催化效果缘于硫酸亚铁;双氧水不能打破淀粉结晶结构,氧化反应主要是在非结晶区进行。 相似文献
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Study of crystalline behavior of heat-treated wood cellulose during treatments in water 总被引:1,自引:0,他引:1
The crystalline behavior of heat-treated wood cellulose treated at 85% relative humidity (RH), in water, or boiled in water after heat treatment was investigated. The normal increased crystallinity was significantly depressed for samples that were oven-dried and then treated in 85% RH or in water. In the case of boiling-water treatment, a more pronounced increased in crystallinity was initially observed, which then decreased gradually. The crystallinity decreased more than untreated wood for samples that were heat treated for long periods and was slightly higher than the decreased crystallinity from the beginning of the above two treatments. On the other hand, no significant change in crystallinity was observed for samples of increased crystallinity or decreased crystallinity that were treated under high-moisture conditions, for all three treatments. The results show that the crystalline state of wood cellulose heat treated under oven dry or high-moisture conditions behave differently if treated in water after heat treatment. Results suggested that the mechanism of crystallization might be different for samples that are subjected to heat treatment under oven-dry and high-moisture conditions. 相似文献