Molecular properties of hemicelluloses located in the surface and inner layers of hardwood and softwood pulps

The molecular properties of hemicelluloses located in the surface and inner layers of fibers present in hardwood and softwood pulps, together with the effects of different bleaching processes on these properties, have been investigated in this study. In order to separate the hemicelluloses located in these two layers, fibers were subjected to mechanical peeling and then separated by filtration into surface (filtrate) and inner layer materials. The materials thus obtained were characterized with respect to their polysaccharide compositions and uronic acid contents. The molar mass parameters of the hemicelluloses (extracted by alkali) were determined by employing size-exclusion chromatography in combination with off-line MALDI mass spectrometry. For all of the pulps examined, the relative content of xylan was found to be greater in the surface layer of the fiber than in the corresponding inner layer. The xylan polymers of the surface layer exhibited higher molar masses and lower frequencies of uronic acid side groups than did the xylans in the inner fiber layer. In connection with ozone treatment, hexenuronic acid residues in the surface layer xylan were removed to a greater extent than in the case of the inner layers, indicating a gradient for the reaction with ozone across the fiber wall. The xylan polymer remaining on the surface of the softwood pulps after completion of the chlorine dioxide bleaching process was predominantly uncharged.     

STRUCTURE EVOLUTION OF POLYMER CHAINS FOR NECKING FORMATION IN HIGH-SPEED FIBER SPINNING PROCESS

Finite element method is used to simulate the high-speed melt spinning process,based on the equation system proposed by Doufas et al.Calculation predicts a neck-like deformation,as well as the related profiles of velocity,diameter, temperature,chain orientation,and crystallinity in the fiber spinning process.Considering combined effects on the process such as flow-induced crystallization,viscoelasticity,filament cooling,air drag,inertia,surface tension and gravity,the simulated material flow behaviors are consistent with those observed for semi-crystalline polymers under various spinning conditions.The structure change of polymer coils in the necking region described by the evolution of conformation tensor is also investigated.Based on the relaxation mechanism of macromolecules in flow field different types of morphology change of polymer chains before and in the neck are proposed,giving a complete prospect of structure evolution and crystallization of semi-crystalline polymer in the high speed fiber spinning process.     

表面起伏光栅形成速率的影响规律 Ⅰ.偶氮生色团种类和官能度的影响

设计并合成了含有不同生色团以及不同官能度的环氧树脂基偶氮高分子 ,系统研究了偶氮生色团的种类和官能度对光栅形成速率的影响规律 .实验结果表明 ,偶氮苯对位是羧基的聚合物的光栅形成速率明显快于偶氮苯对位是硝基的聚合物 ,光栅形成速率随偶氮生色团官能度的增加而加快 .这两类聚合物都可以形成规整的可擦式表面起伏光栅     

可交联聚甲基丙烯酸甲酯的合成、表征及在阵列式波导光栅中的应用

合成了含环氧基团的可交联的甲基丙烯酸甲酯和甲基丙烯酸环氧丙酯的共聚物[Poly(MMA-co-GMA)],通过FTIR,NMR,GPC,DSC和AFM等技术对其进行了表征. 结果表明,所合成的聚合物材料具有较好的成膜性; 通过热固化使引入的环氧基团开环交联,该聚合物的玻璃化转变温度(Tg)比固化前提高了24 K,同时有效地降低了聚合物的双折射率. 用Poly(MMA-co-GMA)作为包层材料,双酚A型环氧化合物作为高折射率材料, 将其引入到包层材料中形成芯层材料的折射率在波长1.55 μm处可调,其范围是1.483~1.588. 采用旋涂、 铝掩膜和氧反应离子刻蚀的方法(RIE)制得了阵列式光波导. 测试结果表明,制作的波导在1.55 μm处实现了光的单模传输,光损小于3.0 dB/cm.      

晶须概念的泛化与学术影响

最初只称单晶短纤维为晶须,稍后结晶较好的多晶纤维也被称为"晶须",现在无定形纤维也归进了晶须专著,通过对晶须概念泛化过程的反思,希能澄清学术著作中10多年来相沿的一个模糊认知。     

光纤松耦合型传感器特性研究

本文介绍一种实用的光纤传感器,它由二根光纤或多根光纤紧靠一起,并在同一位置除去局部包层,成为松耦合状态,在这种状态下,研究了它的特性和应用。 当耦合间隙中充满某种液体介质时,耦合效率明显增大,因此可以方便地判别该介质是否存在。并且实验证明了一种光纤只能有一种相近于光纤芯子折射率的介质具有最大的灵敏度。当间隙内的介质不变时,耦合功率的大小决定于耦合距离d和耦合长度l,l一旦决定以后,d的调节精度为0.1mm量级,易于在机械结构上实现线性检测。     

Synchrotron X-ray structures of cellulose I<Subscript>β</Subscript> and regenerated cellulose II at ambient temperature and 100 K

Synchrotron X-ray data have been collected to 1.4 Å resolution at the NE-CAT beam-line at the Advanced Photon Source from fibers of cellulose I_β and regenerated cellulose II (Fortisan) at ambient temperature and at 100 K in order to understand the effects of low temperature on cellulose more thoroughly. Crystal structures have been determined at each temperature. The unit cell of regenerated cellulose II contracted, with decreasing temperature, by 0.25%, 0.22% and 0.1% along the a, b, and c axes, respectively, whereas that of cellulose I_β contracted only in the direction of the a axis, by 0.9%. The value of 4.6×10^?5 K^?1 for the thermal expansion coefficient of cellulose I_β in the a axis direction can be explained by simple harmonic molecular oscillations and the lack of hydrogen-bonding in this direction. The molecular conformations of each allomorph are essential unchanged by cooling to 100 K. The room temperature crystal structure of regenerated cellulose II is essentially identical to the crystal structure of mercerized cellulose II.     

光纤传感器低温啁啾现象的分析

介绍了光纤光栅传感原理,依据传感机理制作了两种结构材料的光纤光栅传感器,对它们进行了试验,将试验后的传感数据进行了拟合分析和比对,并对它们在低温环境下产生的啁啾现象进行了分析,验证了采用预拉工艺对解决啁啾现象的可行性。     

Designing a plano-convex aspheric lens for fiber optics collimator

A plano-convex aspheric lens is designed to collimate the emitted light of the fiber optics. In this paper even orders of general aspheres are used to describe the aspheric surfaces sag. To determine the aspheric coefficient, the even asphere polynomial are fitted on the computed sag data. The surface sag data is determined using genetic algorithm method. The surface sag was analyzed by the commercial optical software package ZEMAX. For typical fiber optics, the numerical aperture (NA) of 0.22 was assumed. With this specification, the expected output spot diagram of 20 mm and the maximum aperture of 25.4 mm have been obtained. A comparison between here presented lens and the similar type of conventional lens has been carried out; the proposed aspheric lens corrected the spherical aberration, which led to increase in the collimated distance.     

On the evaluation of bragg intensities in the low-temperature phase of C60

The temperature dependence of Bragg intensities in C₆₀ is discussed for the simple cubic Pa3 phase occurring below 260 K. It is shown that, generally, the intensities of Bragg reflections may be surprisingly strongly affected even by seemingly minor variations of certain parameters. Among these the most important are the respective molecular orientational angles of the so-called pentagon and hexagon orientations, the fractions of molecules adopting these orientations and the lattice parameter. Correct determination of the Debye-Waller factor is found to be unusually difficult because of this behaviour. Numerical calculations are used to provide explicit examples and lead to the conclusion that the evaluation of Bragg intensities in this system requires considerable care.