The Degree of Disorder in Hardwood Kraft Pulps Studied by Means of LODP

The amount of disordered material in two types of hardwood kraft pulps was estimated by determining the weight loss at the point where the levelling-off degree of polymerisation (LODP) was reached. The pulps used were commercial pulps viz (1)one conventional birch kraft and (2)one mixed hardwood (MHW) kraft pulp that had been prehydrolysed prior to cooking. The results indicated that the hemicellulose xylan is closely associated with the cellulose in commercial birch pulps. It is therefore only possible to use LODP as a measure of the crystallite length of hardwood cellulose in highly purified pulps, such as prehydrolysed kraft pulp. A model explaining the LODP-results is proposed.     

Sorption of spruce O-acetylated galactoglucomannans onto different pulp fibres

Sorption of spruce acetylated galactoglucomannans (GGM) onto different pulps, among which unbleached and peroxide-bleached mechanical pulps, and unbleached and bleached kraft (BK) pulps, was studied as a means of understanding the retention of acetylated GGMs in mechanical pulping and papermaking. The fibre surface coverage of lignin and carbohydrates was estimated by X-ray photoelectron spectroscopy (XPS) or electron spectroscopy for chemical analysis (ESCA). GGM sorption was clearly favoured on kraft pulps. Hardly any differences in sorption were, however, observed between unbleached and BK pulps, even if the surface coverage of lignin was lower on the bleached pulp. Neither thermomechanical pulp (TMP) nor chemithermomechanical pulp (CTMP) manufactured from spruce sorbed any acetylated GGMs. Peroxide bleaching of the pulp did not increase sorption. Only CTMP produced from aspen sorbed some GGMs. The anionic charge of neither chemical nor mechanical pulps influenced GGM sorption.     

Utilization of thermodesorption coupled to GC-MS to study stability of different wood species to thermodegradation

Thermodesorption coupled to gas chromatography coupled to mass spectroscopy (TD-GC-MS) has been investigated to identify volatile degradation products generated during wood heat treatment by mild pyrolysis. For this purpose, wood samples of different softwood and hardwood species have been heat treated under nitrogen for different temperatures comprised between 180 and 230 °C during 15 min in the glass thermal desorption tube of the thermodesorber and the volatile wood degradation products trapped. The trapped products were then thermodesorbed and analysed by GC-MS. Chromatograms of the different samples indicated the formation of different products resulting from degradation of lignin and hemicelluloses. Hardwoods were shown to be more sensitive to thermodegradation than softwoods, for which degradation products appear at slightly higher temperature. The important formation of acetic acid is concomitant with the formation of most of degradation products and at the origin of the difference of reactivity observed between softwoods and hardwoods.     

Gas- and solid/liquid-phase reactions during pyrolysis of softwood and hardwood lignins

Pyrolytic reactions of Japanese cedar (Cryptomeria japonica, a softwood) and Japanese beech (Fagus crenata, a hardwood) milled wood lignins (MWLs) were studied with thermogravimetry (TG) and by pyrolysis in a closed ampoule reactor (N₂/600 °C). The data were compared with those of guaiacol/syringol as simple lignin model aromatic nuclei. Several DTG peaks were observed around 300-350, 450, 590 and 650 °C. The first DTG peak temperature (326 °C) of beech was lower than that (353 °C) of cedar. This indicates that the volatile formation from cedar MWL is slightly delayed in heating at 600 °C. The gas-phase reactions via GC/MS-detectable low MW products were explainable with the temperature-dependent reactions observed for guaiacol/syringol in our previous paper. The methoxyl groups became reactive at ∼450 °C, giving O-CH₃ homolysis products (catechols/pyrogallols) and OCH₃ rearrangement products (cresols/xylenols). The former homolysis products were effectively converted into gaseous products (mainly CO) at >550-600 °C. However, the GC/MS-detectable tar yields, especially syringyl unit-characteristic products, were much lower than those from guaiacol/syringol. Thus, contributions of higher MW intermediates and solid/liquid-phase reactions are more important in lignin pyrolysis. From the results of stepwise pyrolysis of char + coke fractions at 450 and 600 °C, the methoxyl group-related reactions (450 °C) and intermediates gasification (600 °C) were suggested to occur also in the solid/liquid phase. This was consistent with the DTG peaks observed around these temperatures. These solid/liquid-phase reactions reduced the tar formation, especially catechols/pyrogallols and PAHs. Different features observed between these two MWLs are also focused.     

Catalytic pyrolysis of oak via pyroprobe and bench scale, packed bed pyrolysis reactors

The pyrolytic conversion of oak sawdust at 500 °C in flowing He over eight proprietary catalysts is described and compared to the control bed material, quartz sand. The reactions were conducted and compared in two reactors, an analytical, μg-scale pyroprobe reactor and a bench, g-scale packed bed reactor. The catalysts examined were modified acid catalysts, dealuminated-zeolite Y, β-zeolite, a naturally occurring metal hydroxide containing mineral, mordenite, and a mesoporous aluminosilicate molecular sieve. The packed bed reactor allowed the collection of three bulk product fractions, char, liquid, and gas, all of which could not be obtained from the μg-scale pyroprobe reactions. The catalysts effect on the mass balance of the bulk fractions tended toward more chars and less liquid compared to the sand control. The catalysts’ effects on the liquid products obtained in both reactors shifted away from acetic acid, furfural and higher molecular weight phenolics obtained with sand to lower molecular weight aromatics. This halved the total acid number of the liquid fraction and raised the pH by up to 1.4 units. The modified catalysts’ effects on the gas products from both reactors did not follow a specific trend. Instead, specific catalysts were able to enrich specific gas species up to a factor of 15 while suppressing the formation of others compared to the sand control. Two catalysts, β-zeolite and a naturally occurring metal hydroxide containing mineral, were regenerated and recycled up to five times with no loss of activity.     

利用傅里叶变换研究阔叶材纤维细胞尺寸

利用傅里叶变换图像处理技术测量阔叶材纤维细胞尺寸。把每一个纤维细胞都用其中心的一个长九个像素点,宽两个像素点的线段点图(LCDM)来表示,进行傅里叶变换(FFT),其能量光谱图(PSP)在水平和垂直方向上的频率分布,除零值以外的最大值,即为细胞径向、弦向直径。实验结果表明,该方法与光学显微镜、图像处理软件的结果基本相同,说明该方法也适用于阔叶材纤维细胞尺寸的测定,扩大了其应用领域,为木材的微观分析提供新方法和新的研究方向。     

Acid hydrolysis of some industrial pulps: effect of hydrolysis conditions and raw material

Dilute acid hydrolysis of pulps was studied by following the decrease in intrinsic viscosity of preparations of microcrystalline cellulose. The decrease in intrinsic viscosity and the loss of weight during hydrolysis at reaction temperatures of 60 and 80 °C was investigated, using acid concentrations from 0.5 to 4 M and two different acids (HCl and H₂SO₄). The same levelling-off degree of polymerisation (LODP) was reached under all hydrolysis conditions, but a longer time was needed under milder conditions. An appropriate method of determining the intrinsic viscosity at LODP was established and used in this investigation. The greatest difference in LODP was found between a birch prehydrolysed kraft pulp and a mixed hardwood prehydrolysed kraft pulp; the intrinsic viscosities at LODP being 178 and 72 dm³/kg, respectively. The effect of the intrinsic viscosity of a given starting material was also investigated, but only a small difference (10%) in the LODP was found for pulp samples with very different initial intrinsic viscosities.     

近红外光谱技术快速识别针叶材和阔叶材的研究

对一种针叶材和一种阔叶材的横切面采集波长范围为780～2 500 nm的近红外漫反射光谱,结合偏最小二乘判别分析法(PLS-DA)对针叶材杉木和阔叶材桉树快速识别的可行性进行了研究,结果表明：(1)利用近红外光谱结合PLS-DA法建立的识别模型对建模样品的识别正确率达到100%,识别模型预测的分类变量值与实际值之间相关系数r达到0.99,SEC为0.07;(2)即使采用短波区域780～1 100 nm的近红外光谱也可以获得理想的识别结果(识别正确率为100%),识别模型的r也达到0.99,SEC为0.07;(3)利用近红外光谱建立的识别模型对未知样本的识别正确率都为100%,说明近红外光谱技术可以快速、准确识别针叶材和阔叶材,这为木材识别提供了一种新方法和技术,也为开发低成本的近红外光谱识别仪器提供了科学依据。     

Extraction and characterization of native heteroxylans from delignified corn stover and aspen

Dimethylsulfoxide-solubilized polysaccharides from delignified corn stover and aspen were characterized. The biomass was delignified by two different techniques; a standard acid chlorite and a pulp and paper QPD technique comprising chelation (Q), peroxide (P), and acid-chlorite (D). Major polysaccharides in all fractions were diversely substituted xylan. Xylan acetylation was intact after chlorite delignification and, as expected, xylan from QPD-delignified fraction was de-acetylated by the alkaline peroxide step. The study of DMSO-extractable xylans from chlorite-delignified biomass revealed major differences in native acetylation patterns between corn stover and aspen xylan. Xylan from cell walls of corn stover contains 2-O- and 3-O-mono-acetylated xylan and [MeGlcA-α-(1 → 2)][3-OAc]-xylp units. In addition, aspen xylan also contains 2,3-di-O-acetylated xylose. 1,4-β-d-xylp residues substituted with MeGlcA at O-2 position are absent in chlorite-delignified aspen xylan. Sugar composition in accord with NMR-spectroscopic data indicated that corn stover xylan is arabinosylated while aspen xylan is not. We have shown that corn stover xylan has similar structure with xylans from other plants of Poales order. No evidence was found to indicate the presence of 1,4-β-d-[MeGlcA-α-(1 → 2)][Ara-α-(1 → 3)]-xylp in corn stover xylan fractions.     

Cryo-scanning electron microscopic study on freezing behavior of xylem ray parenchyma cells in hardwood species

Differential thermal analysis (DTA) has indicated that xylem ray parenchyma cells (XRPCs) of hardwood species adapt to freezing of apoplastic water either by deep supercooling or by extracellular freezing, depending upon the species. DTA studies indicated that moderately cold hardy hardwood species exhibiting deep supercooling in the XRPCs were limited in latitudinal distribution within the −40°C isotherm, while very hardy hardwood species exhibiting extracellular freezing could distribute in colder areas beyond the −40°C isotherm. Predictions based on the results of DTA, however, indicate that XRPCs exhibiting extracellular freezing may appear not only in very hardy woody species native to cold areas beyond the −40°C isotherm but also in less hardy hardwood species native to tropical and subtropical zones as well as in a small number of moderately hardy hardwood species native to warm temperate zones. Cryo-scanning electron microscopic (cryo-SEM) studies on the freezing behavior of XRPCs have revealed some errors in DTA. These errors are originated mainly due to the overlap between exotherms produced by freezing of water in apoplastic spaces (high temperature exotherms, HTEs) and exotherms produced by freezing of intracellular water of XRPCs by breakdown of deep supercooling (low temperature exotherms, LTEs), as well as to the shortage of LTEs produced by intracellular freezing of XRPCs. In addition, DTA results are significantly affected by cooling rates employed. Further, cryo-SEM observations, which revealed the true freezing behavior of XRPCs, changed the previous knowledge of freezing behavior of XRPCs that had been obtained by freeze-substitution and transmission electron microscopic studies. Cryo-SEM results, in association with results obtained from DTA that were reconfirmed or changed by observation using a cryo-SEM, revealed a clear tendency of the freezing behavior of XRPCs in hardwood species to change with changes in the temperature in the growing conditions, including both latitudinal and seasonal temperature changes. In latitudinal temperature changes, XRPCs in less hardy hardwood species native to tropical and subtropical zones exhibited deep supercooling to −10°C, XRPCs in moderately hardy hardwood species native to temperate zones exhibited a gradual increase in the supercooling ability to −40°C from warm toward cool temperate zones, and XRPCs in very hardy hardwood species native to boreal forests exhibited extracellular freezing via an intermediate form of freezing behavior between deep supercooling and extracellular freezing. In seasonal temperature changes, XRPCs in hardwood species native to temperate zones changed their supercooling ability from a relatively low degree in summer to a high degree in winter. XRPCs in hardwood species native to boreal forests changed their freezing behavior from deep supercooling to −10°C in summer to extracellular freezing in winter. These results indicate that the freezing behavior of XRPCs in hardwood species tends to shift gradually from supercooling of −10°C, to a gradual increase in the deep supercooling ability to −40°C or less, and finally to extracellular freezing as a result of cold acclimation in response to both latitudinal and seasonal temperature changes. It is thought that these temperature-dependent changes in the freezing behavior of XRPCs in hardwood species are mainly controlled by changes in cell wall properties, although no distinct changes were detected by electron microscopic observations in cell wall organization between hardwood species or between seasons. Evidence of temperature-dependent changes in the freezing behavior of XRPCs in hardwood species provided by the results of studies using a cryo-SEM has indicated the need for further investigation to clarify cold acclimation-induced cell wall changes at the sub-electron microscopic level in order to understand the mechanisms of freezing adaptation.