纤维素酶酶解苇浆纤维微观结构和结晶结构的变化

采用红外光谱(IR)、X射线衍射分析和扫描电镜对在纤维素酶解进程中苇浆纤维素大分子的结构及纤维形态的变化进行了研究.研究结果表明,纤维素酶酶解进程中,纤维素大分子的晶型没有改变,但结晶度呈现周期性变化,微晶尺寸略有降低.在酶解初期,纤维素酶不仅作用于纤维素无定形区,也开始作用在纤维素结晶区表面;在酶解中、后期,纤维素酶对纤维素结晶区和无定形区的作用呈现周期性变化.纤维素酶解过程中纤维表面呈现周期性"剥皮"现象,并且在纤维表面出现孔洞和沟槽,在孔洞处纤维易断裂,导致纤维长度和粗度的降低.     

XPS、AFM和ToF-SIMS的工作原理及在植物纤维表面分析中的应用

介绍了先进的表面分析仪器化学分析电子能谱(XPS)、原子力显微镜(AFM)、含飞行时间分析器的二次离子质谱仪(ToF-SIMS)的工作原理,回顾了近年来它们在植物纤维表面分析中的成功应用,综合利用XPS、AFM及ToF-SIMS方法,可分析和解决制浆造纸过程中的现象和问题。     

Promoted cell proliferation and mechanical relaxation of nanocomposite hydrogels prepared in cell culture medium

Nanocomposite hydrogels (NC gels) were synthesized through in situ polymerization of N-isopropylacrylamide (NIPAm) in the hectorite clay suspension made from cell culture medium Dulbecco’s modified Eagle medium (DMEM). Cell cultured on these NC gels (D-NC gels) surface proliferated faster compared with that on the NC gels synthesized in water due to the nutrients in the D-NC gels. Cells attached and proliferated faster on the D-NC gels with higher modulus. In addition, cell sheets with good viability spontaneously detached from the gel surface by lowering temperature. Their tensile elongation at break was higher than 7 and the true strength σ_true was up to 800 kPa. The stress–strain curves of the D-NC gels were described quantitatively with the Mooney–Rivlin equation. A stretched exponential stress equation was adopted to express the stress relaxation of the D-NC gels with an average relaxation time τ (～10² s) estimated from data fitting, showing a broad distribution (polydispersity k ～ 0.4). The τ value, which was used in simulation for the tensile creep compliance of the D-NC gels, became shorter with increasing clay concentration due to the decrease in the network chain length. The relaxation process was similar to the natural articular cartilage. This work provides a facile way to produce hydrogels with improved cell compatibility and satisfactory mechanical properties for biomedical applications.     

Compositional analysis and projected biofuel potentials from common West African agricultural residues

In recent years the focus on sustainable biofuel production from agricultural residues has increased considerably. However, the scientific work within this field has predominantly been concentrated upon bioresources from industrialised and newly industrialised countries, while analyses of the residues from most developing countries remain sparse. In this study the theoretical bioenergy potentials (bioethanol and biogas) of a spectrum of West African agricultural residues were estimated based on their compositions. We analysed 13 of the most common residues: yam peelings, cassava peelings, cassava stalks, plantain peelings, plantain trunks, plantain leaves, cocoa husks, cocoa pods, maize cobs, maize stalks, rice straw, groundnut straw and oil palm empty fruit bunches. The yam peelings showed the highest methane and bioethanol potentials, with 439 L methane (kg Total Solids)⁻¹ and 0.61 L bioethanol (kg TS)⁻¹ based on starch and cellulose alone due to their high starch content and low content of un-biodegradable lignin and ash. A complete biomass balance was done for each of the 13 residues, providing a basis for further research into the production of biofuels or biorefining from West African agricultural residues.     

Effects of periodically alternating temperatures on performance of single-chamber microbial fuel cells

Practical applications of microbial fuel cells (MFCs) for wastewater treatment are usually operated over a wide range of temperature, especially day–night temperature difference. Here, MFCs at alternating temperatures were compared with those at constant temperatures. MFCs at 6/18 °C reached a steady-state voltage of 0.41 ± 0.05 V at 6 °C and 0.36 ± 0.04 V at 18 °C, which were lower than that of MFCs at 18/30 °C (0.42 ± 0.01 V at 18 °C and 0.47 ± 0.02 V at 30 °C). MFCs at 18/30 °C produced the highest power density of 2169 ± 82 mW m⁻² at 30 °C, even higher than that of MFCs at constant temperature 30 °C. Moreover, MFCs at 6/18 °C and 18/30 °C obtained a comparable coulombic efficiencies (94.6 ± 5.2%, 83.2 ± 4.1%, respectively) compared with MFCs at constant temperatures (86.3 ± 7.3% at 18 °C and 84.1 ± 5.5% at 30 °C). These results demonstrate that MFCs could be successfully adapted for use under day–night temperature difference conditions.     

聚乙烯亚胺对白泥预处理及其加填对AKD施胶影响的研究

本文研究了聚乙烯亚胺(PEI)对白泥预处理后一些基本性能变化和用于加填时对施胶性能的影响。研究表明,通过不同pH值的PEI和机械处理白泥后,在粒径<10μm时,白泥的体积分数增大了9.37%-56.82%,而在10-30μm和>30μm的粒径范围内,白泥的体积分数都在减小。同时,预处理白泥加填后体系的Zeta电位值比未经处理白泥加填后体系的Zeta电位值小,体系变得不稳定。而预处理前后的白泥用于纸张加填时,经过预处理过程的白泥加填后施胶度比空白组PEI0的施胶度降低了56.60%-103.59%。     

乙醇浓度对桉木片醇水抽提预处理液成分的影响

采用回转式密封炉在醇水体系下对桉木片进行抽提预处理,分别采用3种不同浓度(醇/水比1/4、1/2、1/1)的混合液制备了不同的抽提物。对过滤后的抽提液首先进行糖分测定;其次将抽提液经冷冻干燥、苯/甲醇溶解、风干处理后,进行亲脂性化合物的测定;着重考察了乙醇/水体系中乙醇的浓度对预处理抽提液成分相对含量的影响。结果表明,抽提液中总含糖量分别为1.597mg/L、1.641mg/L、1.679mg/L,占物料总质量比例分别为5.39%、5.54%、5.66%,其中木糖的含量最高,三种样品均在78%以上;定性测得的预处理实验中抽提液亲脂性化合物为烷烃类、酯类和胶质类化合物,并且分子量大;主要的化合物为2,4’,5-三甲基二苯甲烷,2,6,11-三甲基-十五烷,十七烷,2,6,10,14-四甲基-十六烷,十九烷,槲皮素,二十六烷。     

化学机械浆过氧化氢漂白过程中草酸根产生的研究

本文以阔叶木CTMP为原料,对影响其过氧化氢漂白过程中草酸根产生的主要工艺条件(过氧化氢用量、温度、时间和氢氧化钠用量等)进行了研究。研究结果表明:在阔叶木CTMP过氧化氢漂白过程中,草酸根产生量是随着漂白过程的进行逐渐增加的,在漂白开始阶段增加较快;提高漂白温度,草酸根的产生量也会随之增加,且呈线性关系;过氧化氢和氢氧化钠用量的变化对草酸根的产生有显著的影响,增加过氧化氢和氢氧化钠的用量,草酸根的产生量也会随之增加。同时,根据Box-Benhnken的中心组合实验设计原理,在单因素实验的基础上,采用四因素三水平的响应面分析法,对草酸根产生量和漂后纸浆白度进行优化,从而达到控制草酸根产生的目的。实验结果表明,阔叶木CTMP过氧化氢漂白过程中控制草酸根产生的最优工艺条件为:H2O2用量6.51%,时间110.6min,温度90℃,NaOH用量1.47%。在此工艺条件下,草酸根产生量为0.90g/kg,纸浆白度为69.00%ISO。     

Effects of process and source on elastic modulus of single cellulose fibrils evaluated by atomic force microscopy

A test method to measure cellulose fibril elastic modulus using atomic force microscopy was used to investigate the effects of process and source on the moduli of single cellulose fibrils. The cellulose fibrils were generated from cellulose by mechanical treatments. Individual fibrils were suspended over a micro scale groove etched on a silicon wafer. A nano-scale three-point bending test was performed to obtain the elastic moduli. The results indicated that the elastic moduli of cellulose fibrils were not significantly different between 30 min and 60 min of high intensity ultrasonic treatment for Lyocell fiber, between isolation methods of ultrasonic and homogenizer treatment for pure cellulose fiber, and between different cellulose sources of pulp fibers treated by homogenizer regardless the effects of sample size coupled with inherent variation in the raw material. The elastic modulus of Lyocell fibrils with diameters from 150 to 180 nm was evaluated to be 98 ± 6 GPa. Modulus values decreased dramatically when the diameter was more than 180 nm.     

半纤维素及其衍生物作为造纸助剂的应用研究进展

随着全球化石资源的日益枯竭,对可再生性植物资源的利用越来越受到人们的重视。本文详细介绍了从植物中分离出的半纤维素及其衍生物作为造纸助剂的应用研究现状及其在造纸中的应用前景。