Tying together the ultrastructural modifications of wood fibre induced by pulping processes with the mechanical properties of paper

The composition and ultrastructural arrangement of cell wall polymers in wood fibres have determining influence on the properties of wood derived materials. It is therefore important to improve our understanding of the relationship between fibres organisation, the modifications induced by pulping treatments, and the resulting paper sheet mechanical properties. The different treatments to which fibres are subjected during the manufacturing of pulps and papers induce morphological and micro-structural alterations due to the removal of wall constituents and of microfibrillar elements. The impact of pulping processes on fibres was investigated at the ultrastructural scale of transmission electron microscopy. Particular attention was given to the effects of beating in refiners at various intensities on the ultrastructure of fibres. The most characteristic effects consisted of delaminations, microfibril disorganisation, and even fractures, of varying importance depending on the intensity of the mechanical refining. The consequences of internal alterations and surface modifications of the fibres were examined in relation to the paper sheet mechanical properties. Correlations between the type of alteration observed in the fibres and its possible impact on a given paper mechanical property are suggested. With similar approaches, the effects of drying and recycling were studied.     

Cytoskeletal involvement in cotton fiber growth and development

The organization of cellulose microfibrils in plant cell walls influences physical properties of the wall and thus cell expansion characteristics. Developing cotton fiber represents an excellent model system for the analysis of the biological regulation of cell wall patterns. Current research indicates that the cytoskeleton has a major role in directing the deposition and organization of cellulose microfibrils in the cell walls of many plant systems, including developing cotton fibers. Both microtubules and microfilaments appear to be involved in regulating changes observed in microfibril patterns during fiber development. The polylamellate architecture of the fiber wall can be attributed to changes in the orientation of cytoplasmic microtubules which appear to direct the orientation of microfibril deposition in each successive layer of the fiber wall. In the drug-induced absence of microtubules, cellulose is deposited in the fiber wall in a swirled pattern of bundled microfibrils. Interaction between adjacent microfibrils may influence cell wall organization on a localized level. In contrast to the direct involvement of microtubules on wall organization, microfilaments appear to be indirectly involved in the deposition of cellulose microfibrils. Current evidence indicates that microfilaments influence wall organization by controlling changes in microtubules patterns. Although a greater understanding of the relationship between the cytoskeleton and the fiber wall is needed, there is sufficient evidence to indicate that genetic manipulation of cytoskeletal components is one path toward future direct manipulation of cell expansion characteristic in many plant systems and may lead to improvements in the textile qualities of cotton fibers.     

Atomic force microscopy and transmission electron microscopy of cellulose from Micrasterias denticulata; evidence for a chiral helical microfibril twist

Atomic force microscopy (AFM), tapping mode atomic force microscopy (TM-AFM) and transmission electron microscopy (TEM) have been used to image the cell wall, ultrathin sections of whole cells and cellulose microfibrils prepared from the green alga Micrasterias denticulata. Measurements of the microfibril dimensions are in agreement with earlier observations carried out by electron microscopy. Images at the molecular level of the surface of the microfibrils were obtained with AFM and show regular periodicities along the microfibril axis that correspond to the fibre and glucose repeat distances of cellulose. Twisted regions visible at intervals along the microfibrils dried down onto substrates were noted to be right-handed in over 100 observations by TEM, AFM and TM-AFM. This revised version was published online in August 2006 with corrections to the Cover Date.     

原位复合材料研究进展

本文综述了近年来原位成纤复合材料的研究状况，介绍了得到广泛应用的两大类原位成纤复合体系，分别讨论了它们的成纤机理、影响成纤的条件及组分间的相互影响，并介绍了此类复合体系的流变性能及物理、机械性能以及它们随组分含量和加工条件变化的规律。     

Accessibility and size of <Emphasis Type="Italic">Valonia</Emphasis> cellulose microfibril studied by combined deuteration/rehydrogenation and FTIR technique

We report an FTIR method to measure the accessibility and the size of cellulose microfibrils from the cell wall of Valonia ventricosa. This method is similar to the conventional deuteration technique for measuring the accessibility of cellulosic materials; however, the difference in our method is that the hydroxyl groups O2H, O3H, and O6H in the crystalline region were initially completely deuterated. The sample was then rehydrogenated by soaking in water at 25 °C, so that the OD groups on the surface were rehydrogenated. The ratio of OH to OD absorbance was used to calculate the number of surface vs. core cellulose chains in a microfibril. The obtained experimental ratio of 0.934 was consistent with the value calculated for a previously published 33 × 38 chain Valonia model (Sugiyama et al. 1984). The rehydrogenation process was further investigated by immersing the sample in water at elevated temperatures. At temperatures above 120 °C, rehydrogenation was more efficient, and the efficiency plots vs. rehydrogenation temperature showed two inflection. These points may correspond to the temperature where the cleavage of inter-chain hydrogen bonds and/or crystalline-phase transition would have been occurred.     

毛细管流变仪中尼龙6在聚丙烯中的原位成纤

将聚丙烯与尼龙6的共混物在毛细管流变仪中挤出，通过显微形态观察发现，在研究的共沸比范围和较宽的剪切速度和温度范围内尼龙6均能在聚丙烯基体中成纤，表明这种热塑性树脂的成纤性比热致液晶聚合物的更好。     

木材微纤丝角四种测试方法对比研究

分别采用X射线衍射法、偏振光显微镜法、纹孔观察法和近红外光谱预测法对杉木木材的微纤丝角进行了测定,结果表明：对于同一株杉木,纹孔观察法测得的微纤丝角平均值最大,X射线衍射法次之,偏振光显微镜法最小,三种方法得到的微纤丝角差异不显著;对于不同年轮的微纤丝角,X射线衍射法测定值于第20年轮以后变得最大,纹孔观察法测定值上下浮动最大,偏振光显微镜法测定值相对最为集中,越远离髓心三种方法的测定值曲线吻合得越好,同一年轮微纤丝角采用不同方法测定时差异不显著;对于同一年轮的微纤丝角,偏振光显微镜法得到的最大值与最小值相差不大于4°,而纹孔观察法相差达到21.53°,其标准偏差也达到4.75。近红外光谱预测法和X射线衍射法均属于无损检测法,它们两个联立建立的模型精度高,预测性和重现性好、便于实现在线分析,其校正模型和验证模型的相关系数R2分别达到了0.81和0.75,校正标准误差和预测标准误差分别为1.79和2.02。另外,其他三种方法均可以与近红外光谱技术联用来预测该木材的微纤丝角,显示了近红外光谱技术无与伦比的优越性。同时,文章分析了这四种方法的优缺点,探讨了产生这种结果的原因,以便为广大研究者提供参考。     

Spin-lattice relaxation behaviour of water in cellulose materials in relation to the tablet forming ability of microcrystalline cellulose particles

Medical tablet forming ability of microcrystalline cellulose (MCC) was investigated in relation to the mobility of water molecules in MCC particles. For this purpose, the spin-lattice relaxation time T1 of water in the system was measured by 1H-NMR. Over a wide range of water contents (0.02 H2O/cellulose (g/g) 1.79), two different T1 (T1,l and T1,s) values were observed for water in each MCC sample. Below the equilibrium water content, water having these two different T1 values exchange with each other in an MCC particle reaching an equilibrium state within a given time scale (equilibrium constant K). The T1,l, T1,s and K values for water in MCC, estimated at the equilibrium water content, showed fairly good correlations with the hardness of the tablets made by the MCC samples. Sample with a shorter T1, or larger K tended to have a stronger tablet forming ability. In the spin-spin relaxation time T2 measurements for protons in an MCC/D2O system, two T2 components originating from the glassy cellulose solid (T2,G) and the swelling region (T2,l) were observed. It was found that the mole fraction xL of protons with T2,L in the system exhibits a clear linear correlation with K. From these results, a structural model for the distribution of water in MCC particles was propoed by taking the surface of each microfibril and the disordered region within the microfibril into consideration     

Nonisothermal Crystallization Nucleation of In‐Situ Fibrillar and Spherical Inclusions in Poly (Phenylene Sulfide)/Isotactic Polypropylene Blends

Nonisothermal crystallization nucleation and its kinetics of in‐situ fibrillar and spherical dispersed phases in poly (phenylene sulfide) (PPS)/isotactic polypropylene (iPP) blends are discussed. The PPS/iPP in‐situ microfibrillar reinforced blend (MRB) was obtained via a slit‐die extrusion, hot stretching, and quenching process, while PPS/iPP common blend with spherical PPS particles was prepared by extrusion without hot stretching. Morphological observation indicated that the well‐defined PPS microfibrils were in situ generated. The diameter of most microfibrils was surprisingly larger than or equal to the spherical particles in the common blend (15/85 PPS/iPP by weight). The nonisothermal crystallization kinetics of three samples (microfibrillar, common blends, and neat iPP) were investigated with differential scanning calorimetry (DSC). The PPS microfibrils and spherical particles could both act as heterogeneous nucleating agents during the nonisothermal crystallization, thus increasing the onset and maximum crystallization temperature of iPP, but the effect of PPS spherical particles was more evident. For the same material, crystallization peaks became wider and shifted to lower temperature when the cooling rate increased. Applying the theories proposed by Ozawa and Jeziorny to analyze the crystallization kinetics of neat iPP, and microfibrillar and common PPS/iPP blends, both of them could agree with the experimental results.     

Varietal difference in cellulose microfibril dimensions observed by infrared spectroscopy

We have previously reported a novel Fourier transform infrared (FTIR) method for evaluating both the accessibility and lateral dimensions of cellulose microfibrils. This method differs from conventional deuteration in that the OH groups in the crystalline region were initially completely deuterated. The samples were then rehydrogenated by immersing them in water at 25 °C, during which only the OD groups on the surface were rehydrogenated. The ratio of OD to OH groups measured for cellulose from various origins was used to estimate microfibril dimensions, which were compared with the data from X-ray diffractometry. The rehydrogenation process was further investigated by immersing the deuterated samples in water at elevated temperatures. The behavior of rehydrogenation under heat treatment was converted to observe the microfibril shape, which was in good agreement with the cross-sectional images obtained by diffraction contrast transmission electron microscopy techniques.