Influence of swelling of noncrystalline regions in silk fibers on modification with methacrylamide

The degrees of swelling of noncrystalline regions of domestic and tussah silk fibers were investigated by measuring the small-angle X-ray scattering intensity of the fibers in wet conditions and analyzing the scattering intensity based on a two-phase model, i.e., crystalline regions and water-swollen noncrystalline regions. The influence of the degree of swelling of noncrystalline regions on the graft treatment of these fibers with methacrylamide was investigated. The changes in the structure caused by the graft treatment were also analyzed using the wide-angle X-ray diffraction measurements. As compared with the tussah silk fibers, the domestic silk fibers showed a larger degree of swelling of the noncrystalline regions, and gained a larger amount of resin by the graft treatment. The crystallites with smaller sizes in the tussah silk fibers were destroyed preferentially by the graft treatment. For the domestic silk fibers, the crystallites were destroyed more seriously and rather homogeneously independent of the crystallite sizes. © 1996 John Wiley & Sons, Inc.     

Mechanical properties of tussah silk fibers treated with methacrylamide

Tussah silk fibers were treated with methacrylamide (MAA). The polymerization of MAA onto tussah silk fibers and the mechanical properties of the MAA-treated tussah silk fibers were investigated. The tanning agent contained in tussah silk fibers acted as an inhibitor to the radical polymerization of MAA. The alkali treatment enhanced the swelling of noncrystalline regions of the tussah silk fibers and promoted the polymerization of MAA onto the tussah silk fibers. The cross-sectional area of the MAA-treated tussah silk fiber was given by the sum of the cross-sectional area of the original silk fiber and that of the MAA polymer. Breaking load of the fibers was almost unchanged by the MAA treatment, while rigidity was markedly increased. Young's modulus of the MAA-treated tussah silk fibers decreased with decreasing volume fractions of the fiber in the MAA-treated tussah silk fibers. Young's modulus of the MAA polymer in the MAA-treated tussah silk fibers was estimated by extrapolating the relation between Young's moduli and the volume fractions of the fiber to zero volume fraction. Young's modulus of the MAA polymer in the MAA-treated tussah silk fibers was significantly larger than the modulus of a MAA polymer plate. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2051–2057, 1997     

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.     

Physical properties and dyeability of NaOH-treated silk fibers

Domestic (Bombyx mori) and wild (tussah, Antheraea pernyi) silk fabrics were treated with diluted NaOH solutions by the pad/batch method. The equillbrium moisture regain of tussah silk fibers increased steadily with alkaline treatment, while that of B. mori did not change. B. mori tensile strenght and elongation at break were slightly impaired. The average molecular orientation and crystallinity of both kinds of silk remained unchanged. Differential scanning calorimetry (DSC) and thermomechanical analysis(TMA) showed that the thermal behavior of B. mori silk was almost unaffected, while that of tussah exhibited slight changes in the temperature range 250–300°C. By dynamic mechanical measurements (DMA) it was elucidated that both storage and loss moduli of B. mori silk fibers decreased following NaOH treatment. On the other hand, tussah silk exhibited a noticeable upward shift of the major loss peak. Alkali-treated tussah silk fibers, dyed with an acid dyestuff, attained a lower degree of dye-bath exhaustion. © 1995 John Wiley & Sons, Inc.     

Structure and physical properties of epoxide-treated tussah silk fibers

The structural characteristics and physical properties of epoxide-treated tussah silk fibers from Antheraea pernyi silkworm are discussed in relation to the increasing weight gain values. Ethyleneglycol diglycidylether (E) and glycerin diglycidylether (G) were used as modifying agents. The noticeably high weight gain values (about 140%) obtained were attributed to the catalytic effect of SCN^? anion absorbed by the fibers during the pretreatment under reduced pressure conditions. The amino acid analysis showed that epoxide G exhibited a slightly higher reactivity toward tyrosine, while arginine preferably reacted with epoxide E. The peak of loss modulus (E″) determined by dynamic viscoelastic measurements became broader and its position linearly shifted to lower temperature when the weight gain increased, and a minor peak appeared in the low-temperature region below 50°C. Differential scanning calorimetry (DSC) thermograms showed that the position of the decomposition peak of modified silk fibers shifted to lower temperature with increasing weight gain values. The minor and broad endothermic peaks, appearing in the reference sample at about 234 and 290°C, disappeared by epoxide treatment. X-ray diffraction patterns of tussah silk fibers suggested that the epoxide treatment does not affect directly the crystalline regions but causes a decrease of molecular orientation in the amorphous regions. Both briefringence (Δn) and isotropic refractive index (n_iso) of tussah silk fibers decreased by the reaction with epoxides, although with different rate and extent, confirming the decrease of average molecular orientation. The extent of decrease of strength and elongation depends on the kind of epoxide and on the weight gain value. Epoxide-treated tussah silk fibers did not show significant changes of surface characteristics as the weight gain values attained up to 60%.     

桑丝与龙胆酸交联反应电子光谱研究

本文采用白色桑蚕丝素与龙胆酸进行交联反应,得到黄褐色桑蚕丝素,其电子光谱与黄褐色的柞蚕茧丝谱图相同。进一步证实了柞蚕丝黄色生色物质为龙胆酸与丝蛋白的交联物这个结论是正确的。     

Structural changes of polyacrylonitrile fibers in the process of wet spinning

In this article, the structural changes of polyacrylonitrile (PAN) fibers at the key stages of wet spinning are systemically studied. According to the X-ray diffraction and scanning electron microscopy analysis, the as-spun fibers show a homogeneous three-dimensional fibrillar network structure with random crystallite orientation, low crystallinity, and abundant pores. As the draw ratio increases, the crystallite orientation and crystallinity increase firstly in the skin and then in the core. The uneven force distribution in fiber is responsible for the inhomogeneous change of fibrillar network. According to the X-ray scattering and scanning electron microscopy analysis, the size, shape, and volume fraction of pores are strongly dependent on the compactness degree of fibrillar network. As the fibrillar network inhomogeneously shrinks, the total pore volume decreases, and the volume fraction of small-sized pores increased considerably from 25 to 96%, leaving a handful of large-sized pores in the core. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48905.     

Effect of plasma treatment on the structure and allied textile properties of mulberry silk

Studies on the effect of nitrogen plasma on morphology and textile properties of mulberry silk fibers and fabrics have been conducted. The changes in the morphological structure have been monitored by transmission electron microscopy, X-ray diffraction, and internal reflection infrared spectroscopy. The changes in some of textile properties such as wettability, drying rate, and crease recovery owing to plasma treatment have also been investigated. It has been found that the surface of mulberry silk gets etched away, even affecting the crystalline region. This behavior is opposite to our findings on tassar silk. Therefore, an explanation of this differential behavior of mulberry with tasar on the basis of amino acid linkages vis-à-vis bonding, wettability, drying rate, and water retention capacity has been attempted. These results have been used to arrive at an understanding of internal structure of mulberry.     

Effect of physical and chemical modifications on microcrystalline parameters of silk fibers

Wide-angle X-ray diffraction studies of physically and chemically treated silk fibers like bivoltine mulberry silk and tassar silk were carried out to evaluate their crystal size, lattice distortion, and minimum enthalpy, as these determine the properties of silk fibers. The results are also compared with tenacity measurement. © 1996 John Wiley & Sons, Inc.     

碳纤维中微孔缺陷的小角X射线散射研究方法

碳纤维的小角X射线散射表明存在沿纤维轴方向取向的针形微孔。应用小角X散射可以得到微孔的尺寸和分布等的信息。文章主要阐述了微孔长度L、取向角Beq,孔隙率P,回转半径Rt,横截面积S等参数的计算方法。     

Mechanical properties of silk fibers treated with methacrylamide

Silk fibers were treated with methacrylamide (MAA), and changes in the mechanical properties of the silk fibers were investigated. The breaking load of the silk fibers was almost unchanged, whereas rigidity was markedly increased by the methylmethacrylate (MAA) treatment. Elongation at break of the silk fibers decreased significantly when the fibers were treated with MAA up to polymer add-on (ca. 300%). The cross-sectional area of the MAA-treated silk fiber was given by the addition of the cross-sectional area of the original silk fiber and that of the MAA polymer. The Young's modulus of MAA-treated silk fibers increased linearly with increasing volume fractions of fiber in MAA-grafted silk fibers. The Young's modulus of the MAA polymer in the MAA-treated silk fibers was estimated by extrapolating the relation between Young's moduli and volume fractions of fiber to the zero volume fraction of fiber. The Young's modulus of the MAA polymer in the MAA-treated silk fibers was larger than the sonic modulus measured for an MAA polymer plate. © 1996 John Wiley & Sons, Inc.     

Tensile stress–strain and recovery behavior of Indian silk fibers and their structural dependence

The tensile stress–strain and recovery behavior of all the four commercial varieties of Indian silk fibers, namely Mulberry, Tasar, Eri, and Muga, have been studied along with their structures. Compared to the non‐Mulberry silk fibers, Mulberry silk fiber is much finer and has crystallites of smaller size, higher molecular orientation, and a more compact overall packing of molecules. These structural differences have been shown to result in (1) the presence of a distinct yield and a yield plateau in non‐Mulberry silk and their absence in Mulberry silk, and (2) relatively higher initial modulus and tenacity along with lower elongation‐to‐break and toughness and superior elstic recovery behavior of mulberry silk compared to non‐Mulberry silk. It is also observed that fine silk fibers have a relatively more ordered and compact structure with higher orientation compared to their coarse counterparts, and this gives rise to higher initial modulus and higher strength in the finer fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2418–2429, 2000     

X-ray studies of regenerated cellulose fibers wet spun from cotton linter pulp in NaOH/thiourea aqueous solutions

Regenerated cellulose fibers were fabricated by dissolution of cotton linter pulp in NaOH (9.5 wt%) and thiourea (4.5 wt%) aqueous solution followed by wet-spinning and multi-roller drawing. The multi-roller drawing process involved three stages: coagulation (I), coagulation (II) and post-treatment (III). The crystalline structure and morphology of regenerated cellulose fiber was investigated by synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. Results indicated that only the cellulose II crystal structure was found in regenerated cellulose fibers, proving that the cellulose crystals were completely transformed from cellulose I to II structure during spinning from NaOH/thiourea aqueous solution. The crystallinity, orientation and crystal size at each stage were determined from the WAXD analysis. Drawing of cellulose fibers in the coagulation (II) bath (H₂SO₄/H₂O) was found to generate higher orientation and crystallinity than drawing in the post-treatment (III). Although the post-treatment process also increased crystal orientation, it led to a decrease in crystallinity with notable reduction in the anisotropic fraction. Compared with commercial rayon fibers fabricated by the viscose process, the regenerated cellulose fibers exhibited higher crystallinity but lower crystal orientation. SAXS results revealed a clear scattering maximum along the meridian direction in all regenerated cellulose fibers, indicating the formation of lamellar structure during spinning.     

正交试验在腐植酸作柞蚕丝漂白稳定剂工艺参数筛选中的应用

用正交试验法，对腐植酸作柞蚕丝漂白稳定剂进行了研究，找出了漂白柞蚕丝的最佳反应条件．确定了腐植酸作柞蚕丝漂白稳定剂的最佳使用量。     

The structure of never-dried cotton fibers

The X-ray photographs of fresh never-dried cotton fibers are compared with those of dried fibers. The crystallite size of never-dried cotton fibers shows no significant correlation with maturity and orientation and is about the same as those of dried cotton fibers.     

Structural analysis of methacrylamide-grafted silk fibers

The structural changes and the thermal behavior of silk fibers grafted with methacrylamide (MAA) were investigated as a function of the weight gain. The refractive index parallel to the fiber axis decreased with increasing weight gain, whereas that perpendicular remained almost unchanged. Accordingly, birefringence decreased with a steeper slope in the weight gain range 0–80%, suggesting a lower degree of average molecular orientation. Only small changes in the isotropic refractive index were detected, suggesting that the crystallinity of the fibers remained essentially unaffected by MAA grafting, as confirmed by the X-ray diffraction data. The molecular orientation in the crystalline regions remained unchanged in the weight gain range 0–60%, then sharply decreased. The strength and the initial tensile resistance of grafted silk fibers decreased both in the dry and wet states, while elongation at break increased in the dry state and remained almost constant in the wet state. The results of the thermal behavior, investigated by differential scanning calorimetry, thermomechanical and thermogravimetric analysis, and dynamic mechanical measurements, were consistent with an increased thermal stability conferred on silk fibers by MAA grafting. The cross-sectional area of MAA-grafted silk fibers increased. Moreover, ion-etched cross sections of the grafted silk fiber showed the presence of fibrils with a diameter larger than that of the untreated control. © 1993 John Wiley & Sons, Inc.     

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。     

Elastic response of copolyether-ester fiber on its phase morphology under different heat-treatment condition

In order to verify the elastic response of copolyether-ester (PEE) fibers on their phase morphology and structure, the PEE fibers based on poly(butylene terephthalate) (PBT) as hard segments and poly(terramethylene glycol) (PTMG) as soft segments were prepared by melt spinning, the as-spun fibers were then heat-drawn and heat-set at different conditions. From the analysis of the mechanical properties, it is shown that the tenacity as well as elastic recovery of the fibers increased with the increasing heat-draw ratios, the elongation at break decreased. The morphological and structural were evaluated by small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS) and birefringence. When the melt-spun PEE fibers were heat-drawn, higher crystallinity and orientation, larger size of lamellae structure was formed within the fibers, it is also much easier to form higher phase separation. This structure will contribute to better elastic performances of PEE fibers.     

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.