从丝素水溶液中再生的丝纤维的结构与性能

通过使用表面皿直接拉伸、毛细管重力纺丝和人工拉伸3种不同的成丝方法,从高浓度再生丝素水溶液中制得了丝纤维。用偏光显微镜观察了丝纤维的取向,用拉曼光谱仪和Instron拉力仪表征了丝纤维的结构和力学性能。结果发现,经毛细管剪切流动后再拉伸有利于再生丝性能的提高,所得的丝有较好的取向和较多的β折叠结构,力学性能也相对较好。剪切在丝纤维的成形过程中起重要的作用。     

Effects of superfine silk protein powders on mechanical properties of wet‐spun polyurethane fibers

Mechanical measurements were employed to investigate the effects of three types of superfine silk protein powder on tensile strength, elongation, and elasticity of wet‐spun Pellethane^® 2363‐80AE polyurethane (PU) fiber. These superfine silk protein powders included undegummed silk (with both native silk fibroin and sericin, water insoluble), native silk fibroin (with native silk fibroin only, water insoluble), and regenerated silk fibroin (with regenerated silk fibroin only, water soluble) in powder form. Experimental data derived from the mechanical measurements illustrated that the miscibility between the PU and regenerated silk fibroin were superior to that between PU and the other two silk proteins. This may be attributed to the similar chemical structure and microphase separation of PU and regenerated silk fibroin with lower molecular weight than native silk fibroin. This preliminary work may provide some information for biomimetic processing of silk‐inspired PU biofibers, which combine elasticity of synthetic PU with biofunction of natural silk fibroin for special biomedical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The variability and interdependence of spider drag line tensile properties

There is considerable interest in producing fibres that mimic the impressive tensile properties of spider drag line silk. It must, however, be recognised that these properties have been assessed largely on the basis of their average values; there can be significant variability about these averages. The natural variability can also serve as a useful indicator of the range of values over which particular properties of biomimetic silk may be tailored. Here we quantify several tensile properties of drag line from Argiope trifasciata spiders. We distinguish between two groups of properties on the basis of their statistical coefficient of variation. There is significantly greater scope for tailoring the viscoplastic hardening aspects of drag line, compared to the variability of the initial elastic response or the yield strength. We also consider whether elastic modulus, yield strength and viscoplastic hardening can be controlled independently of one another.     

Tensile strength and its variation for PAN‐based carbon fibers. II. Calibration of the variation from testing

The tensile behavior of carbon fibers shows large scattering. This is due to the fiber itself and the testing operations. Because of the high tenacity and modulus, low strain, and easy breakability in bending, not only is the tensile test for single carbon fibers extremely difficult, but the measured results are also oppugned. To achieve a reliable and accurate characterization, several factors influencing the objective and exact testing of single carbon fibers have been measured and discussed, including the wrong pretension, nonaxial stretching, and adhesion effects. The experimental results indicate that the error of strain causing them ranges from 1.5 to 12.3%. Because of the typical linear stress–strain curves of carbon fibers, the ratio of the strain error to the modulus error is approximately equal to 1 : 1, so the calibration of the measured strain must be conducted for the accurate evaluation of the modulus and itself. The calibration is put forward. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2625–2632, 2007     

Active control of spider silk strength: comparison of drag line spun on vertical and horizontal surfaces

There is widespread interest in producing high-performance fibers that mimic the behavior of natural silks, especially spider drag line. Given the multiple roles of drag line in nature, it is pertinent to explore whether spiders can tailor the tensile properties of this material to match its intended use. Here we distinguish between the ability of spiders to control the quality (intrinsic stress-strain response) versus the amount (load-bearing cross-section) of drag line. The mechanical characteristics of drag line spun during a vertical climb differ from those of drag line spun when the spider crawls on a horizontal surface. Also, the intrinsic stress-strain response of drag line spun during a vertical climb is significantly more reproducible (i.e. dependable) than when this fiber is produced under other conditions. Implications for biomimetic polymer science are discussed.     

Mechanical and thermal degradation properties of silk from African wild silkmoths

Variations among silk of four African wild silkmoths, Argema mimosae, Anaphe panda, Gonometa postica, and Epiphora bauhiniae, was studied regarding their mechanical properties and thermal degradation behaviors. Cocoon shells and individual degummed fibers were examined using tensile testing, thermogravimetric analysis, and scanning electron microscope (SEM). A. mimosae and G. postica cocoon shells had marginally higher initial moduli and strains at maximum stress. The stress–strain curves of Bobmyx mori and A. panda degummed fibers lacked clear yielding points. G. postica fibers had the highest breaking energy (76.4 J/cm³) and breaking strain (41.3%). The ultimate tensile strength was the highest for B. mori (427 MPa). Fiber pull‐out and detachment was predominant in fracture surfaces of both the cocoon shells and the fibers. Wild cocoon shells and degummed fibers had higher temperature for dehydration loss than B. mori. A. mimosae fibers (11.9%) and G. postica cocoon shells (13.3 %) had the highest weight loss due to dehydration. E. bauhinae cocoon shells and B. mori fibers had the highest total weight losses of 97.2 and 93.4%, respectively. The African silks exhibited variations in their mechanical and thermal degradation properties related to their physical and chemical structure and composition. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical and thermal properties of waste silk fiber‐reinforced poly(butylene succinate) biocomposites

This article reports the mechanical and thermal properties of poly(butylene succinate) (PBS) biocomposites reinforced with industrially available waste silk fibers, fabricated with varying fiber contents and lengths. The result indicates that use of waste silk fibers may be a potential as reinforcement for effectively improving the static and dynamic mechanical properties of a biodegradable polymer matrix resin, depending on the waste silk fiber content and length in the present biocomposite system. The “as‐separated” waste silk/PBS biocomposites showed the maximum tensile and flexural properties at a fiber loading of 40 wt %, and the “chopped” waste silk/PBS biocomposites showed the optimal strength and modulus with waste silk fibers of 12.7 mm length. The chopped waste silk fibers play a more contributing role in improving the mechanical properties of waste silk/PBS biocomposites than the as‐separated waste silk fibers at a fixed fiber loading. Above the glass transition temperature, the storage modulus of waste silk/PBS biocomposites was significantly greater than that of PBS resin, especially in the higher temperature region. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4972–4980, 2006     

Tensile strength and its variation of PAN‐based carbon fibers. I. Statistical distribution and volume dependence

The effects of the diameter, gauge length, and volume of carbon fibers on the tensile properties and their variation are discussed on the basis of the weak‐link theory and Weibull distribution in a single‐filament test. As far as variation is concerned, the stress of carbon fibers should be obtained by the division of the force not by the mean cross section of all the fibers but by the cross section of individual fibers because of the diameter variation. The volume effect of carbon fibers influences not only the mean of the tensile properties but also their variation. The experimental results indicate that the volume dependence in the radial direction is much bigger than that in the axial direction. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3175–3182, 2006     

Mechanical properties of polypropylene fibers produced from the binary polymer blends of different molecular weights

The mechanical properties of multifilament yarns, spun from the blends of a plastic‐grade polymer with a fiber‐grade CR‐polymer in the composition range of 10–50 wt % added, were investigated. The predicted modulus of a two‐phase blend, calculated from several representative equations, was compared with the elastic modulus of drawn yarns, determined from the stress vs. strain curve and dynamic modulus obtained from the sound velocity measurements. The best fit was achived with the Kleiner's simplex equation. For both the static and dynamic elastic modulus, the largest negative deviation is seen at the 80/20 and 60/40 plastic/fiber‐grade polymer blend composition, while the largest positive deviation is seen at the 90/10 plastic/fiber‐grade polymer blend composition, suggesting good compatibility of both polymers, when only a small percent of the fiber‐grade CR‐polymer is added. Improved spinnability and drawability of blended samples led to the yarns with the tensile strength over 8 cN/dtex, elastic modulus over 11 GPa and dynamic modulus over 15.5 GPa. Structural investigations have shown that the improved mechanical behavior of blended samples, compared to the yarn spun from the pure plasic‐grade polymer, is the consequence of a higher degree of crystallinity, and above all, of a much higher orientation of macromolecules. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1211–1220, 2000     

High density polyethylene foams. III. Tensile properties

The room temperature tensile properties of closed‐cell polyethylene foams have been investigated. High density polyethylene (HDPE) foams of four different molecular weight were used to study the effect of molecular weight and foam density on mechanical properties during tension and at the break point. It was found that increasing the molecular weight changes the tensile behavior of polyethylene foams from brittle to ductile fractures. For brittle foams, the break strength follows a square power‐law model and the break strain is independent of the volume fraction of the voids. For ductile foams, the normalized yield strength also follows a square power‐law relation with normalized density, the yield strain is similar to the value of the solid polymer and remains constant for all void volume fractions, and the break strain increases with HDPE molecular weight. Finally, the toughness of the foams was found to increase with normalized density and HDPE molecular weight. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2130–2138, 2003     

Physical properties of silk fibroin/chitosan blend films

Silk fibroin/chitosan blend films were examined through IR spectroscopy to determine the conformational changes of silk fibroin. The effects of the fibroin/chitosan blend ratios (chitosan content) on the physical and mechanical properties were investigated to discover the feasibility of using these films as biomedical materials such as artificial skin and wound dressing. The mechanical properties of the blend films containing 10–40% chitosan were found to be excellent. The tensile strength, breaking elongation, and Young's modulus were affected by the chitosan contents of the blend films, which were also related to the density and degree of swelling. The coefficient of water vapor permeability of the blend films increased linearly with the chitosan content, and the values of 1000–2000 g m^?2 day^?1 were comparable to those of commercial wound dressings. Silk fibroin/chitosan blend films had good oxygen and water vapor permeabilities, making them useful as biomaterials. In particular, the blend film containing 40–50% chitosan showed very high oxygen permeability. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 928–934, 2001     

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     

Mechanical properties of single‐brin silkworm silk

Mechanical tests were performed on single brins of Bombyx mori silkworm silk, to obtain values of elastic modulus (E), yield strength, tensile breaking strength, and shear modulus (G). Specimen cross‐sectional areas, needed to convert tensile loads into stresses, were derived from diameter measurements performed by scanning electron microscopy. Results are compared with existing literature values for partially degummed silkworm baves. The tensile modulus (16 ± 1 GPa) and yield strength (230 ± 10 MPa) of B. mori brin are significantly higher than the literature values reported for bave. The difference is attributed principally to the presence of sericin in bave, contributing to sample cross‐section but adding little to the fiber's ability to resist tensile deformation. The two brins in bave are found to contribute equally and independently to the tensile load‐bearing ability of the material. Measurements performed with a torsional pendulum can be combined with tensile load‐extension data to obtain a value of E/ that is not sensitive to sample cross‐sectional dimensions or, therefore, to the presence of sericin. The value of E measured for brin can be used together with this result to obtain G = 3.0 ± 0.8 GPa and E/G = 5.3 ± 0.3 for brin. The latter value indicates a mechanical, and therefore microstructural, anisotropy comparable to that of nylon. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1270–1277, 2000     

Structural and physical properties of silk fibroin/alginate blend sponges

Silk fibroin/alginate blend sponges were examined through IR spectroscopy, X‐ray diffractometry, and differential scanning calorimetry to determine the structural changes of silk fibroin. The effects of fibroin/alginate blend ratios on the physical and mechanical properties were investigated to discover the feasibility of using these blend sponges as biomedical materials such as wound dressings. The compressive modulus of silk fibroin was increased up to 30 kPa, from 7.1 kPa, by blending with alginate. Thermal crystallization behavior of fibroin induced by heat treatment was restricted by blending with alginate. In spite of that, the structural characteristics of fibroin were not changed by incorporation with alginate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2174–2179, 2004     

Tensile properties of denture base resin reinforced with various esthetic fibers

This study was conducted to determine the reinforcement effect of five types of esthetic fibers on the tensile properties of a conventional denture base resin. E‐glass, polyester, rayon, nylon 6, and nylon 6/6 fibers were cut into 2, 4, and 6 mm lengths and added into resin randomly at a concentration of 3% by weight. For each formulation, five tensile specimens, as well as control specimens without fibers, were prepared in a dumbbell shape using a stainless steel mold, constructed according to ASTM Standard D638M‐91a. Tensile properties were evaluated by using a universal testing machine. Surfaces of the tensile sections were also observed under the scanning electron microscope (SEM). Tensile strength of the specimens reinforced with fibers in varying lengths was found to be lower than that of the unreinforced control group. Among the trial groups, the specimens reinforced with 6 mm long polyester fibers showed the highest tensile strength. All the SEM fractographs indicated both weak adhesion and pull out of fibers from the matrix. None of the incorporated esthetic fibers appeared to improve tensile strength of the resin. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Active control on molecular conformations and tensile properties of spider silk

The mechanical properties of spider dragline silk vary with the spinning conditions, and molecular conformation is one of the important factors for the strength and strain of materials. Four kinds of Araneus ventricosus spider dragline silk fibers, measured by Raman microscopic spectrometry, were produced under different conditions: (1) reeled at the rate of 2 cm/s; (2) secreted by a dropping spider from a 100‐cm‐high table; (3) spun by spiders raised in two different containers. The Raman spectra of these fibers showed that the spinning method and growing environment of spiders had evident influences on the molecular conformations and tensile properties of dragline silk, and the dragline silk obtained from a dropping spider contained the greatest number of molecules with highly oriented β‐sheet structures and gave higher stress/strain values. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 901–905, 2004     

Weibull parameters obtained from dependence of fiber strength on fiber length and area

Weibull strength parameters of ceramic fibers can be inferred from variations in strength with fiber diameter or gauge length. The goal of this article is to provide a critical assessment of the efficacy of these methods. The issues are addressed using theorems in regression analysis and uncertainty propagation as well as Monte Carlo simulations. The results show that, when Weibull moduli are obtained from strength variations with fiber area, inordinately large sample sizes (>1000) are required to achieve reliable results. In contrast, Weibull moduli can be accurately estimated from the dependence of average fiber strength on gauge length for a modest sample size at each of two gauge lengths, provided the gauge length range is sufficiently large. The dependence of strengths of bundles containing many (ca. 500) fibers on gauge length yields yet more reliable results. The results are used to assess the fidelity of Weibull moduli obtained from these methods and provide guidance for preferred test methods.     

Silk nanofibrils/chitosan composite fibers with enhanced mechanical properties

Chitosan (CS) fibers have been applied in various fields due to their biocompatibility, biodegradability, and antibacterial properties. However, weak mechanical properties remain as obstacles to further applications. Silk nanofibrils (SNFs) extracted from natural silk fibroin fibers preserve outstanding mechanical properties at the nanoscale, which are expected to impact structural programming and mechanical reinforcement for CS fibers. In this study, wet-spun CS/SNFs composite fibers were continuously collected from NaOH/ethanol coagulation. Scanning electron microscope (SEM) results showed that SNFs were uniformly distributed in the CS matrix, and obvious orientation was observed when the mass ratio of SNF/CS was 75/100. Tensile tests showed that the introduction of SNFs significantly enhanced the mechanical properties of CS fibers when the mass ratio of SNF/CS was more than 25/100. With the increasing of SNF content, the tensile strength gradually increased, and the tensile strength and modulus could be increased 2.9 times and 3.5 times, respectively, when 100% SNF was added. The improvement of mechanical properties was partially attributed to hydrogen bonding between SNF filaments and CS, which was confirmed by FTIR and XRD results. This study provides a facile and eco-friendly method to spin CS fibers with enhanced mechanical properties and a hierarchical structure.     

Structure and properties of cellulose fibers from ionic liquids

1‐Butyl‐3‐methylimidazolium chloride ([BMIM]Cl) was used as a solvent for cellulose, the rheological behavior of the cellulose/[BMIM]Cl solution was studied, and the fibers were spun with a dry‐jet–wet‐spinning process. In addition, the structure and properties of the prepared cellulose fibers were investigated and compared with those of lyocell fibers. The results showed that the cellulose/[BMIM]Cl solution was a typical shear‐thinning fluid, and the temperature had little influence on the apparent viscosity of the solution when the shear rate was higher than 100 s^?1. In addition, the prepared fibers had a cellulose II crystal structure just like that of lyocell fibers, and the orientation and crystallinity of the fibers increased with the draw ratio increasing, so the mechanical properties of the fibers improved. Fibers with a tenacity of 4.28cN/dtex and a modulus of 56.8 cN/dtex were prepared. Moreover, the fibers had a smooth surface as well as a round and compact structure, and the dyeing and antifibrillation properties of the fibers were similar to those of lyocell fibers; however, the color of these dyed fibers was brighter than that of lyocell fibers. Therefore, these fibers could be a new kind of environmentally friendly cellulose fiber following lyocell fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010