凝固条件对PAN初生纤维微孔结构形态的影响

采用一维多取向小角X射线散射研究了聚丙烯腈细流在凝固过程中,凝固浴温度、浓度以及喷丝头拉伸比对初生纤维中微孔结构形态的影响。结果表明,凝固温度由30％提高到60℃时,微孔沿纤维轴取向增强,微孔尺寸减小,但微孔数量增加;凝固浴质量分数由67．5％升高到76．0％,微孔数量减少,但微孔尺寸变大,微孔沿纤维轴取向减弱;喷丝头拉伸比为-36．7％-10％时,微孔尺寸和取向角都增大。在凝固浴温度为52-55℃,凝固浴质量分数为70％,选择负拉伸能得到性能优异的初生纤维。     

利用小角度X射线散射法测定多孔硅胶粒子中微孔的平均尺寸

本文从园球形粒子的散射方程出发,讨论了利用小角X射线散射技术测量多孔硅胶粒子中微孔平均尺寸的基本原理和方法。文章对不同孔径的多孔硅胶粒子,给出利用逐级对数图解法,逐级切线图解法和相关函数法得到的具体结果,重点讨论了相关函数法。同时对小角X射线的具体实验技术也作了若干探讨。     

渗碳玻璃的X射线散射研究

以小角X射线散射(SAXS)、电子显微镜(EM)和大角X射线散射(LAXS)研究了在制造用作低温电阻温度计的渗碳玻璃过程中玻璃结构的变化。该玻璃是先由热处理后的硼硅酸盐玻璃经酸浸析成微孔玻璃,再在微孔中浸入有机溶液烧结制成的。实验结果表明,由熔体淬冷的原始玻璃中已潜伏着二相结构,热处理后发生液-液分相,分成富Na_2O-B_2O_3 相和富SiO_2 的连续玻璃相。估计了各相和微孔的平均尺寸(以个数为权)。X射线衍射鉴定出渗碳玻璃中除了存在非晶态C之外,尚有少量的Si微晶体。将渗碳玻璃分离后,用小角X射线散射测定了非晶态C的平均粒度约为100A(以重量为权)。     

氰乙基纤维素取向膜的形态结构[摘]

本文用热台偏光显微镜,小角光散射,X光衍射,DSC,电子显微镜等方法,研究了氰乙基纤维素取向膜的形态结构。发现氰乙基纤维素的各向异性溶液经剪切后凝固成     

激光小角散射测定PVDF的结晶形态和取向

利用激光小角散射(SALS)法测定PVDF的结晶形态和取向,并与X—射线衍射(WAXD)图谱相对照,确定了PVDF定向后获得β晶型取向结构的最佳工艺条件。     

X射线衍射在高聚物方面的应用(下)

<正> 五、小角X射线散射方法* (一) 大角与小角的比较 图47比较了大角与小角高聚物样品及底片实验装置的不同情况。 1.散射原理 X射线小角散射是在靠近原光束附近很小角度内,也就是在倒易点阵原点附近处电子对X射线相干散射现象。理论证明,小角散射花样、强度分布与散射体的原子组成以及是否结晶无关,仅与散射体的形状、大小     

小角X射线散射对不同碳纤维的比较和分析

应用X射线小角散射的方法研究了不同碳纤维试样的微孔特征.实验结果表明,通过散射强度与角度的曲线对比,说明了国产丝和日本丝在微观孔洞上的差异,日本丝从原丝到碳丝的散射强度都高于国产丝.通过两种碳纤维在生产过程中从原丝到碳丝的散射强度的变化对比,说明了原丝结构缺陷的遗传影响.     

SiC纤维中微孔含量的测定

SiC纤维中存在一定量的微孔,纤维中微孔含量的测定,对制备吸附纤维或高强度纤维都有重要的意义.然而纤维中的微孔有的处于开孔状态,有的处于封闭状态或开口较小,用N2吸附法难以完全测定,只采用小角X射线散射也只能得到微孔的比例.本文通过两种方法对照,确定了纤维中的微孔含量,900 ℃和1200 ℃裂解纤维的微孔孔容分别为0.00011 cm3/g和0.00062 cm3/g..     

小角X射线散射在高聚物中的应用

<正> X射线散射方法有大角散射和小角散射之分,有人把两者的界线定为2°,散射角(入射线与散射线夹角)小于2°属于小角散射。这个界线看来不甚妥当,其实“小角”之意并非指散射角2θ很小,而是指散射矢量h     

不同纺丝速度下聚醚酯纤维结构与性能的关系

为了说明聚醚酯纤维的性能和形态结构与纺丝速度之间的关系,对聚醚酯切片设计了不同纺丝速度的熔融纺丝试验。结果发现:当纺丝速度增加为750 m/min时,纤维的断裂强度和回弹性较好。进一步通过同步辐射广角X射线散射、小角X射线散射以及双折射、声速取向试验,分析了聚醚酯纤维不同尺度的形态结构变化,发现在高纺丝速度下,形成了纤维取向度高、结晶度高、长周期小的形态结构。     

Structure change of carbon fibers during axial compression

In situ wide-angle X-ray diffraction and small-angle X-ray scattering measurements have been performed during axial compression tests of composite strands of polyacrylonitrile-based carbon fibers with varying carbon layer stacking height and the changes in the crystallite and the microvoid structure have been analyzed. The longitudinal length of microvoids, the orientation parameter of the carbon layer stacks and the orientation parameter of the microvoids decreased almost linearly with increasing axial compression stress of the fiber. The decrease in the longitudinal length of microvoids up to the compression fracture of the fiber was in the range of about 4–10%, which was larger than the macroscopic compression fracture strain of the fiber. This indicated that a deformation larger than the macroscopic fiber strain arose in a local region of the fiber structure reflecting the deformability of the local microtexture. The axial compression strength of carbon fibers was calculated based on the equation proposed in a previous study using the measured values of the microvoid length. As compared with the strengths calculated using the initial longitudinal lengths of microvoids, the strengths calculated using the lengths at the compression fracture of the fibers showed better agreement with the measured strengths.     

Relationship between axial compression strength and longitudinal microvoid size for PAN-based carbon fibers

Single fiber axial compression strength has been determined on a series of polyacrylonitrile-based carbon fibers using micro compression test at a gage length of about 10 μm and a detailed analysis has been made on the distribution and the fiber diameter dependence of the axial compression strength. The length of the unsupported region of carbon layer stack calculated from the axial compression strength was well comparable with the longitudinal length of the microvoids determined with small-angle X-ray scattering. This indicated that the fracture of carbon fibers is initiated from the buckling of the unsupported region of carbon layer stack which is formed where the microvoid adjoins it. The tensile and the axial compression strengths of the carbon fibers showed different relationships between the coefficient of variation and the average. This indicated that the tensile and the axial compression strengths are governed by different factors although they showed a correlation. Comparison has also been made between the longitudinal length of the microvoid and the microvoid sizes perpendicular to the fiber axis.     

不同线密度粘胶原丝及其碳纤维的结构性能对比

用Weibull分析处理 10mm长的 4种不同线密度粘胶原丝和相应碳纤维的单丝断裂强度 ,得到原丝线密度、强度分布和碳纤维强度的对应关系。采用透射电镜 (TEM )和小角X散射 (SAXS)分析粗旦原丝 ,发现孔洞较多 ,并存在大于 70nm的大孔洞。截面和表面照片也揭示出细旦原丝截面相对规整 ,表面较光滑 ,粗旦原丝则反之。结果表明 ,原丝线密度小 ,截面形状圆整 ,缺陷少 ,所制得的碳纤维强度高。     

Extended-chain morphology in ultraoriented polyethylene

The morphology of ultraoriented polyethylene fibers was investigated by means of small-angle x-ray scattering and high-resolution line-broadening analysis of x-ray and electron-diffraction profiles. The comparative consideration of the experimentally-measured crystal thickness and long period along the c direction allowed the calculation of the fraction of extended-chain crystals for a simple three-phase model. The calculations were carried out with the unknown length of the extended-chain crystals as a variable parameter.     

Characterization of microvoids in mulberry and tussah silk fibers using stannic acid treatment

To investigate the volume, size, and number of microvoids in mulberry and tussah silk fibers, stannic acid gel was used as a contrasting medium to the small-angle X-ray scattering (SAXS). The influence of the stannic acid treatment on the structure of silk fibers was first investigated by using the wide-angle X-ray diffraction prior to characterization of the microvoids. The changes in crystallite size and degree of orientation with increasing stannic acid gel fraction in fibers are investigated, and it was found that the stannic acid treatment does not cause serious changes in crystallite size and degree of orientation. The changes in crystallinity indices were observed when the volume fractions of stannic acid gel in the fibers exceeded about 10%. Thus, it was confirmed that the structure of silk fibers was retained in the region of the stannic acid gel fraction less than 10%. SAXS measurements revealed that the number and the fraction of the microvoids are larger, while the sizes of the microvoids are smaller, for the mulberry silk fibers compared with the tussah silk fibers. The fraction macrovoids, however, is considered to be larger for the tussah silk fibers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 363–367, 1999     

The interfacial properties and porous structures of polymer blends characterized by synchrotron small-angle X-ray scattering

Microvoids are induced upon uniaxial drawing of films made from immiscible polypropylene (PP)/polystyrene (PS) binary blends and ternary blends of PP, PS, and a block copolymer SEEPS. The shape of the uniaxially oriented microvoids is rod- or slit-like with a high aspect ratio. Synchrotron small-angle X-ray scattering (SAXS) is used to characterize the dimensions of these microvoids. Their scattering image is an intense azimuthally narrow equatorial streak on a two-dimensional SAXS pattern. This streak is analyzed to obtain the diameter, length and misorientation of the microvoids. The microvoids length is identified as an effective measure of the interfacial adhesion and strength between phase domains. Drawn films of binary blends of PP/PS are found to have the longest microvoids. The initial addition of the block copolymer SEEPS as a compatibilizer enhances the interfacial adhesion and shortens the length of microvoids. Further addition of compatibilizer induces the formation of aggregates of a composite PS/SEEPS dispersed phase, and this leads to reduced interfacial adhesion and a longer microvoids. Interfacial properties are also dependent on the mixing protocol used to produce the blends.

The transport property of the films is determined by porosity and the degree of interconnectivity. A convenient measure of the degree of interconnectivity is proposed. The degrees of interconnectivity of these films are in accordance with the interfacial adhesion and strength. Non-equatorial streaks are observed and attributed to the microvoids with a complex orientation and geometry, which are responsible for the interconnectivity among microvoids.     

Positional small-angle X-ray scattering

Positional small-angle X-ray scattering has been implemented and developed as a new nondestructive technique to study the formation and growth of flaws in polymers. The technique consists of measuring the intensity of scattering at a constant scattering angle while the sample is moved through the incident x-ray beam. Examples of applications of the technique from several different materials are presented.     

Thermally-cured and e-beam-cured epoxy layered-Silicate nanocomposites

Summary Research on nanocomposites attracted a lot of attention because of their unique nanostructure and interesting properties. Layered-Silicate epoxy nanocomposites cured by traditional thermal cure processing were prepared, and the morphology was confirmed by the wide-angle x-ray diffraction, small-angle x-ray scattering and transmission electron microscopy. Layered-Silicate epoxy nanocomposites could also be cured through e-beam curing. The small-angle x-ray scattering and transmission electron microscopy indicated that the e-beam-cured nanocomposites showed intercalated nanostructure. Dynamic mechanical analysis showed some improvement of the Storage modulus for the nanocomposites with high T_g. Received 11 October 2002/Revised Version 22 January 2003/ Accepted 23 January 2003 Correspondence to Chenggang Chen     

On the origin of order-disorder in drawn polyacrylonitrile

Drawn polyacrylonitrile can be characterized only insufficiently with regard to its molecular and supermolecular structures which substantially determine the physical properties. This paper points out that the so-called “superstructure” of polyacrylonitrile fibers can be cleared up after suitable thermooxidative treatment using x-ray small-angle scattering technique. The chemical reactions during the thermo-oxidative treatment lead to a “self-contrasting” effect so that the fibers as such are severely damaged yet information about the supermolecular structure can be obtained. The investigations show that changes in the course of fiber production (spinning, drawing, and annealing processes) affect alterations of the superstructure. The described method of investigation represents a so far unknown possibility for the purpose of detecting the supermolecular structure of drawn polyacrylonitrile.     

The structural causes of the dyeing variations of nylon 66 yarn subjected to the false-twist texturing process

The structural variations in nylon 66 caused by heat and the mechanical action of the false-twist texturing process have been studied by measuring dyeing rates with Durazol Blue 2R, the determination of density, x-ray orientation, and lateral order, and also by consideration of x-ray small-angle scattering data. It is concluded that the morphologic units are probably shish-kebabs with straight-chain cores between which the dye penetrates.