Lattice Conversion of Cellulose in Wood

When peracetylated wood, prepared in an acetic anhydride-pyridine medium, was saponified and recrystallized, almost no conversion of cellulose I to cellulose II took place. Neither was conversion detected, when thirteen species of wood, differing in density from 0.17 to 0.71, as well as in lignin content from 18.1 to 38.8 %, were treated with 17.5 % aqueous NaOH, followed by recrystallization. The corresponding treatments for cellulose triacetate or cellulose resulted in complete conversion to cellulose II. Partial delignification of wood preceding the alkali-induced mercerization was found to cause partial lattice conversion to cellulose II, and the ratio of lattice conversion (L.C.R.) increased with the degree of delignification. The L.C.R. value reaches slightly more than 50 %, when one third of the lignin is removed, and the removal of about two third of the lignin from wood results in an almost complete conversion. The effect of lignin removal on lattice conversion was similar among the wood species, irrespective of their density and lignin content, Introduction of acyl groups larger than caproyl into wood, followed by saponification and mercerization resulted in a high conversion of cellulose in wood from cellulose I to cellulose II.     

Characterisation of cellulose treated by the steam explosion method. Part 3: Effect of crystal forms (cellulose I,II and III) of original cellulose on changes in morphology,degree of polymerisaion,solubility and supermolecular structure by steam explosion

An attempt was made to clarify the effect of the crystal form of untreated cellulose on the morphological and structural changes of cellulose during steam explosion treatment (steam pressure P = 2.9MPa (T = 508K), treatment time t = 15-300 s). For this purpose, the crystal form of soft wood pulp (cellulose I) was converted by solid-to-solid transition, with minimal unavoidable change in other structural characteristics including morphology and average degree of polymerisation, into cellulose II or cellulose III. It was proved by both X-ray and solid-state cross-polarisation/magic-angle sample-spinning (CP/MAS) ¹³C NMR analyses that even a simple addition of water at room temperature brought about a significant structural change in the steam-untreated cellulose samples. The solubility towards 9.1 wt% aqueous sodium hydroxide, S_a, of the cellulose samples of crystal forms I and III could be improved from 31-33% up to almost 100% by selecting appropriate steam explosion conditions (for example, P = 2.9MPa, t = 30 s). Such a magnificent increase in S_a by the steam explosion treatment was not observed for the cellulose II sample, even under the rather severe conditions of the steam explosion treatment at which the cellulose III crystal was converted to a large extent to cellulose I, as confirmed by X-ray diffraction. X-ray diffraction analysis showed that crystallisation of samples with cellulose I or II crystal occurred to some extent during the steam explosion treatment. Contrary to this, the degree of breakdown of the intramolecular hydrogen bond O₃…O'₅, as estimated by CP/MAS ¹³C NMR analysis, significantly increased for cellulose I and I11 during the treatment. The decrease in the viscosity-average degree of polymerisation, P, observed for all treated samples can be roughly categorised into two or three steps of the first-order decomposition reaction with different reaction rates.     

Change of pyrolysis characteristics and structure of woody biomass due to steam explosion pretreatment

Steam explosion (SE) pretreatment has been implemented for the production of wood pellet. This paper investigated changes in biomass structure due to implication of steam explosion process by its pyrolysis behavior/characteristics. Salix wood chip was treated by SE at different pretreatment conditions, and then pyrolysis characteristic was examined by thermogravimetric analyzer (TGA) at heating rate of 10 K/min. Both pyrolysis characteristics and structure of biomass were altered due to SE pretreatment. Hemicellulose decomposition region shifted to low temperature range due to the depolymerization caused by SE pretreatment. The peak intensities of cellulose decreased at mild pretreatment condition while they increased at severe conditions. Lignin reactivity also increased due to SE pretreatment. However, severe pretreatment condition resulted in reduction of lignin reactivity due to condensation and re-polymerization reaction. In summary, higher pretreatment temperature provided more active biomass compared with milder pretreatment conditions.     

爆炸波膨化法对木质纤维材料形态结构的影响

采用爆炸波膨化法对速生杨木片进行处理,用扫描电镜观测分析爆炸波膨化处理前后杨木片的组织形态变化。实验结果表明:未经爆炸波处理的原始状态的杨木(片)材料,其纤维组织的扫描显微图像呈致密的导管状分布,而且导管间纵向平行排列;经爆炸波处理后,杨木材料的扫描显微图像呈现无序排列的纤维形态,纤维组织的致密度大大降低,这将有利于增强液体对木质纤维组织的浸渍、润胀等作用。     

硬木纤维素蒸汽闪爆处理机理的研究

研究了硬木纤维素在蒸汽闪爆改性过程中的各种状态及蒸汽闪爆对硬木纤维素超分子结构的影响。用SEM、X-射线衍射、FT-IR分析及对聚合度Pv、溶解度Sa的研究结果表明,蒸汽闪爆改性后硬木纤维素的结晶度Xc(X)和微晶尺寸L002有所增加,但其超分子结构遭到破坏,游离羟基和可及度有所增加,尤其是纤维素内部氢键的断裂与纤维素的Sa有十分密切的关系。     

Wood particle/high‐density polyethylene composites: Thermal sensitivity and nucleating ability of wood particles

The thermal sensitivity, nucleating ability, and nonisothermal crystallization of high‐density polyethylene (HDPE) with different wood fillers during wood/HDPE melt processing were investigated with thermogravimetric analysis and differential scanning calorimetry. The results showed that the wood degraded at a lower temperature than HDPE. The thermal decomposition behavior was similar across wood species. The most remarkable dissimilarities were observed between wood and bark in the decomposition rate around a processing temperature of 300°C and in the peak temperature location for cellulose degradation. The higher degradation rate for bark was explained by the devolatilization of extractives and the degradation of lignin, which were present in higher amounts in pine bark. The nucleating ability for various wood fillers was evaluated with the crystalline weight fraction, crystal conversion, crystallization half‐time, and crystallization temperature of the HDPE matrix. The nucleation activity improved with the addition of wood particles to the HDPE matrix. However, no effect of wood species on the crystal conversion was found. For composites based on semicrystalline matrix polymers, the crystal conversion may be an important factor in determining the stiffness and fracture behavior. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

改性软木纤维素的NaOH水溶液体系成膜性研究

对天然软木纤维素进行了闪爆改性,同时以一定浓度的NaOH溶液为溶剂,采用H2SO4水溶液为凝固剂,制备出再生纤维素膜。分析了NaOH溶液浓度、H2SO4浓度、纤维素—NaOH溶液浓度及温度、时间等条件对成膜的影响,确定最佳软木纤维素闪爆条件。     

NaOH/尿素冷冻活化木材纤维的工艺研究

利用NaOH/尿素混合水溶液在冷冻条件下对木材纤维进行活化处理,通过无胶胶合压制纤维板的力学性能测试、傅里叶变换红外光谱以及X射线衍射分析表征了木材纤维的冷冻活化效果。结果表明：冷冻条件下NaOH/尿素的混合水溶液对木材纤维具有一定的活化效果,优选的活化工艺为NaOH和尿素的总质量（NaOH与尿素质量比为7：12）与木材纤维质量比为1：12,冷冻温度-15℃,冷冻时间1.0 h,木材纤维含水率20%。木材纤维经NaOH/尿素混合水溶液冷冻活化后,所得无胶胶合板材的静曲强度和内结合强度分别由未处理的32.16和0.29 MPa提高至45.53和1.21 MPa,吸水率和厚度膨胀率由未处理的53.95%和22.57%降低至43.62%和10.34%。傅里叶变换红外光谱和X射线衍射表征发现,NaOH/尿素混合水溶液的冷冻活化破坏了木材纤维中纤维素的氢键结构,促使了纤维素I型晶格扩张,产生了新的结晶变体,使分子缔合程度变小,木材纤维表面的羟基活性增强。     

木质纤维的冷冻活化及其制备无胶板材

利用氢氧化钠-聚乙二醇-尿素混合溶液对木质纤维进行冷冻活化处理,然后制备无胶纤维板,通过对比无胶胶合纤维板力学性能,确定木质纤维较佳冷冻活化工艺,并利用傅里叶变换红外光谱、X射线衍射分析、差式扫描量热分析、热重分析、X射线光电子能谱分析对木质纤维的冷冻活化效果进行表征。研究结果表明:木质纤维较佳冷冻活化工艺为氢氧化钠、聚乙二醇、尿素的质量比7∶4.2∶12,活化剂质量(以氢氧化钠与尿素的总质量计)与木质纤维的质量比1∶12,冷冻温度-15℃,冷冻时间45 min;以此工艺活化处理的木质纤维为原料,所制备纤维板的吸水厚度膨胀率、内结合强度、静曲强度、弹性模量分别优于GB/T 11718—2009《中密度纤维板》性能要求(各指标数值分别提升了45%、238%、177%和129%);冷冻活化处理会破坏木质纤维中纤维素间的氢键,提高羟基的反应活性并增加活性羟基的数量,在扩张纤维素晶格的同时产生新的结晶并且降低木质纤维的热稳定性。     

Characterisation of Oligosaccharides Released by Steam Explosion of Sulphur Dioxide ImpregnatedPinus Radiata

The nature of the solubilized oligosaccharides released from the softwood Plnus radiata by the steam explosion process in the presence or absence of sulphur dioxide are described in this paper. Steam explosion in the absence of sulphur dioxide (215δ, 3 min) resulted in partial solubilization of only the hemicelluloses (14.5 g of neutral sugars/100 g o.d. wood) to their respective oligomers, which ranged in degree of polymerization from 1 to at least 12. The effect of adding 2.5% sulphur dioxide to the substrate was to facilitate the removal and hydrolysis of both hemicellulose and cellulose components (29.5 g of neutral sugars/100 g o.d. wood) by acid catalysis. Steam explosion of the substrate at an elevated temperature of 248° in the presence of 2.5% sulphur dioxide, caused almost complete cellulose and hemicellulose solubilization, and subsequent degradation reflected in poor carbohydrate survival (24.7 g of neutral sugars/100 g o.d. wood). The addition of sulphur dioxide to the process results in enhanced hydrolysis of the solubilized material to mainly mono- and disaccharides. However, the acid reversion products such as isomaltose and gentiobiose are formed, although their effect on total fermentable sugar yield is very small. Under normal steam explosion conditions the acidic aldooligouronic acid hydrolysis products represent only about 6% of total soluble carbohydrate. Interestingly, some demethylation of 4–0-methyl-D-glucuronic acid residues were observed as a consequence of sulphur dioxide catalysis.     

Aqueous Thermomechanical Pretreatment of Aspen in a Batch Reactor System

The fractionation of wood consists of the separation of the fibrous material into its constitutive polymers (i.e. extractives, hemicellulose, cellulose and lignin) in a sequential and selective way. The thermochemical or biochemical upgrading of each fraction leads to the production of common and fine chemicals. The first step of the fractionation process is the pretreatment which permits the solubilization of extractives and hemicellulose. The residue thus obtained is more accessible to chemicals and enzymes. The goal of this paper is to prove that a thermomechanical pretreatment in aqueous phase (without adding any chemical) may solubilize, in a relatively selective way, the hemicellulose. This process consists of the following steps: 1) Steeping of aspen sawdust (0·25–0.·50 mm) in water at 7% consistency for 16 h; 2) Cooking at 165–235°C; 3) Rapid discharge (i.e explosion) at δp=6·9 MPa; 4) Quenching. The extent (i.e conversion) and selectivity (i.e. hemicellulose removal vs delignification) of wood solubilization have been studied as a function of cooking temperature in a batch reactor system.     

NaOH处理对杨树木质特性的影响

用不同浓度NaOH对杨树进行预处理,分析经过处理后不同品种杨树的纤维素、半纤维素、木质素含量的变化。结果表明,经NaOH处理后杨树中的纤维素含量明显增加,半纤维素和木质素含量明显减少。2%的NaOH溶液处理效果最好。NaOH溶液处理可以显著促进杨树木质素和半纤维素向纤维素的转化,是一种较为有效的以杨树为原料制取燃料乙醇的预处理方法。     

Processing Pine Wood into Vanillin and Glucose by Sequential Catalytic Oxidation and Enzymatic Hydrolysis

Extractive-free pine wood was processed into vanillin (up to 18 wt.% of the initial lignin) and cellulose (typically 84–93% of the initial amount in the wood) by one-step catalytic oxidation followed by enzymatic hydrolysis of the resulting cellulose into glucose (reducing sugar yield up to 70% based on the post-oxidation cellulose). Correlation between the cellulose conversion in hydrolysis and the lignin content in the post-oxidation lignocellulosic material was established, which follows the general trend for the products of various delignification methods. The obtained results demonstrate the practical possibility of efficient two-step processing of wood into vanillin and glucose.     

Steam pretreatment of Salix to upgrade biomass fuel for wood pellet production

Steam explosion (SE) pretreatment is served to separate the main components of woody biomass. In general there is a noticeable gap in literature in terms of application of steam explosion process to upgrade biomass fuel for wood pellet production. In order to study the influence of steam explosion pretreatment on biomass fuel, Salix wood chips was used as raw material. Four different SE experiments were performed by varying two key process factors; time and temperature. Elementary quality and ash properties of the pretreated residue were investigated. Moreover, physical and thermochemical properties of the pellet, produced from the residue, were also investigated. Reduction in ash content especially in alkali metals was observed in steam treated residue. Pretreatment of biomass also enhanced carbon content and reduced oxygen amount in the fuel which enhanced the heating value of the fuel. Moreover, pretreatment enhanced pellet density, impact resistance, and abrasive resistance of pellet. However, small degradation in ash fusion characteristics and char reactivity was also observed as the severity of the process increased.     

汽爆预处理技术在纤维素乙醇工业化中的应用及实践

纤维素乙醇技术是推动秸秆高值化利用、缓解环境压力的重要途径之一。在整个工艺过程中,原料预处理对于纤维素乙醇技术的发展起着至关重要的作用。其中,蒸汽爆破是目前应用最广、工业化水平最高的预处理技术之一。综述了汽爆技术在纤维素乙醇工业化装置中的应用,按照汽爆方式、汽爆设备类型、工艺流程和添加的化学试剂的不同,对汽爆工艺和设备分别进行了介绍。综合而言,两段式连续汽爆预处理能够有效的降低半纤维素降解产生的抑制物,提高木糖回收率,降低原料成本,是比较有应用前途的技术之一,对设备的耐压能力和稳定性以及系统控制水平要求较高。从化学试剂的使用来看,中性或低酸汽爆是未来工业发展的方向。     

慈竹机械浆（RMP）氨法预处理工艺研究

研究了在氨水中添加少量KOH或K3PO4预处理慈竹机械浆(RMP)的工艺。考察了预处理条件对酶解还原糖产率的影响。单因素实验得到氨水加KOH最佳预处理条件为:预处理温度120℃、固液比〔即1 g绝干浆加入液体的体积(mL),下同〕1∶6、时间3.5 h、氨水用量70%(即氨水质量占绝干浆质量的百分数,下同)、KOH用量5%(即KOH质量占绝干浆质量的百分数,下同)。在此最佳条件下,慈竹RMP的纤维素保留率为90.66%,半纤维素保留率为92.90%,木质素脱除率为41.05%;在pH=4.8、加酶量20 FPU/g预处理后底物、反应温度50℃的条件下酶解24 h,还原糖产率为23.95%,纤维素转化率为44.61%。虽然氨水加K3 PO4预处理酶解纤维素转化率可达56.95%,但是纤维素保留率仅为74.59%,与氨水加KOH相比,纤维素损失较大。     

Selecting the Pre-Hydrolysis Conditions for Eucalyptus Wood in A Fractional Exploitation Biorefining Scheme

The operating conditions for the autohydrolysis of eucalyptus wood were optimized with a view to maximizing hemicellulose extraction while preserving the integrity of glucan. The influence of the operating conditions used in the soda–anthraquinone pulping of the solid phase resulting from the autohydrolysis process was examined. Autohydrolysis of the raw material at a liquid/solid ratio of 8 kg water/kg material at 180°C for 30 min was found to provide a commercially useful liquid phase containing most of the starting hemicellulose. The autohydrolysis treatment allowed the subsequent production of soda–anthraquinone cellulose pulp and paper with properties as good as or even better than those obtained without the pretreatment.     

The Effect of Wood Drying on Crystallinity and Microfibril Angle in Black Spruce (Picea mariana)

Abstract

The effect of drying on wood cellulose crystallinity, crystallite size, and microfibril angle was investigated using wide angle X-ray diffraction. Forty replicated specimens of black spruce (Picea mariana) wood were dried at constant temperatures of 40°C and 80°C and relative humidities of 34% and 47% in attempts to attain samples possessing final moisture content of 15% and 8% at each temperature. X-ray evaluation of wood specimens, comparing individual samples pre- and post-drying, revealed that both the mass fraction of crystalline cellulose and crystallite width increased with drying. In contrast, mean microfibril angle of the wood was not significantly affected by drying. It was also apparent that the changes in wood ultrastructure resulting from drying were not influenced by the drying conditions, including temperature, relative humidity, and final moisture contents.     

Thermoplastics Reinforced with Wood Fillers: A Literature Review

Problems concerning the processing of thermoplastics reinforced with wood fillers are discussed. The high level of moisture absorption by the filler, its poor wettability, as well as the insufficient adhesion between untreated filler and the polymer matrix are reasons for the low tensile strength and high moisture sorption of composites. These shortcomings of composites can be prevented by the modification of the interface. The fiber-matrix compatibility and the composites properties can be improved by using some physical (e.g., steam explosion, corona, cold plasma) and chemical (cross-linking and acetylation of cellulose, grafting, use of coupling agents) methods. Modified wood-polymer interaction mechanisms are complex and specific for each definite system and processing conditions. Cellulose cross-linking and acetylation reduce hygroscopicity and swelling of wood and wood composites. Grafting of styrene to wood is effective for wood-polystyrene systems. The best coupling agent for wood-thermoplastics is polymethylenepolyphenyl isocyanate. Silanes coupling effect can be increased with additives to the polymer matrix. Optimizing of technological parameters of wood-thermoplastics processing is necessary.     

木质纤维原料蒸汽爆破-生物联合预处理及其生物脱毒研究进展

在木质纤维素类生物质结构中,木质素是生物质中纤维素与半纤维素进行生物降解的天然抗性屏障,预处理是打破木质纤维素抗性结构这一阻碍生物转化与利用瓶颈的最主要途径。本文分别概述了木质纤维素蒸汽爆破预处理技术与生物预处理技术的研究现状,介绍了蒸汽爆破-生物联合预处理的研究进展,分析了蒸汽爆破预处理过程中抑制物产生的机理和主要抑制物的种类,并提出了具有脱毒效果的蒸汽爆破-生物联合预处理技术,以及木质纤维素高效预处理技术研究发展方向。