The limiting irregularity of single wool fibers

Fiber irregularity affects fiber mechanical properties. This study has, for the first time, introduced the concept of limiting irregularity to single wool fibers. The limiting irregularity is the minimum variation in fiber cross sectional area that can be expected of a single wool fiber, assuming a random length-wise distribution of its constituent cortical cells. Cortical cells were extracted from merino wool fibers and their dimensions were measured from SEM images to calculate their cross sectional area variations both between cortical cells and within cortical cells, and to work out the average number of cortical cells in the cross section of wool fibers of a given diameter. Single wool fibers were also measured at 5 μm interval along length for fiber diameter variations. These variations were found to be larger than that based on fiber limiting irregularity.     

The combined tensile and torsional behavior of irregular fibers

Most fibers are irregular, and they are often subjected to combined loading conditions during processing and end-use. In this paper, polyester and wool fibers under the combined tensile and torsional loads have been studied for the first time, using the finite element method (FEM). The dimensional irregularities of these fibers are simulated with sine waves of different magnitude and frequency. The breaking load and breaking extension of the fibers at different twist or torsion levels are then calculated from the finite element model. The results indicate that twist and level of fiber irregularity have a major impact on the mechanical properties of the fiber and the effect of the frequency of irregularity is relatively small.     

Mechanical properties of wool fiber in the stretch breaking process

Short wool fibers obtained by the stretch breaking process can be blended with cotton fibers and processed in a cotton spinning system, which has a high production rate. For the structural property of the wool fiber after stretch breaking, the diameter and length of the wool fiber were measured as a function of time. The diameter of the broken fibers was finer than the diameter of untreated fibers. The fiber diameter at the break point was the finest and was more irregular than the original fiber. The broken fiber showed mechanical properties of increased modulus, decreased breaking strain, and increased breaking strength.     

Modeling the tensile strains of non-uniform fibers

The maximum strain experienced by the thinnest segment of a non-uniform fiber governs fiber breakage, yet this maximum strain can not be obtained from a normal single fiber test. Only the average strain of the whole fiber specimen can be obtained from a normal single fiber tensile test. This study has examined the relationship between the average strain, the maximum strain and the degree of fiber non-uniformity, expressed in coefficient of variation (CV) of fiber diameters along fiber length. The tensile strain of irregular fibers has been simulated using the finite element method (FEM). Using this method, average and maximum tensile strains of non-uniform fibers were calculated. The results indicate that for irregular fibers such as wool, there is an exponential relationship (i.e.ɛ _ave ɛ _max=ae ^{−b CV} ) between the ratio of average breaking strain and maximum breaking strain (ɛ _ave ɛ _max) and the along-fiber diameter variation (CV). The strain ratio decreases with the increase of the along-fiber diameter variation.     

Experimental and numerical analysis of fiber characteristics effects on fiber dispersion for wet-laid nonwoven

Dispersion and separation of fiber bundles into individual fibers, requires exposing them to a shear stress field to overcome inter-fiber frictional forces. To this end, fiber-mixing tanks are usually used to enhance shear and agitation in water and help the dispersion process. The required time and necessary agitation to separate and disperse fibers depend on fibers’ characteristics. It is well known that excessive agitation will give rise to the formation of rope defects in the output because of the high-energy vortices and optimizing the break up time is important in wet-lay process. In this work, experimental and numerical studies were done to investigate the effects of fiber characteristics on their dispersion in water for wet-laid nonwoven. The effective forces were analyzed using a one-way modeling of fiber behaviors in a stirred mixing tank. Results show that when the fiber diameter is increased, the required time for breaking up of fiber bundles and clumps is increased. The effects of fiber types on fibers break up and dispersing time, were also investigated. In the experimental work, an on-line vision system was designed to observe the dispersion behavior of polyester fibers. The effects of fiber length and fineness on the created defects (i.e. logs and ropes) in dispersion process, as well as on the dispersion speed, were studied. The results confirm that defects are increased by rising fiber length and fineness. It is also shown that increasing fiber length and fineness, decreases the required time for fiber clumps to be opened and reach a maximum number of individual fibers. On the other hand, when fiber length and fineness is increased, the dispersion speed increases.     

Relations between the characteristics of Angora rabbit fibre

Angora rabbit fibre is one of the finest specialty animal fibres with its well-known reputation for fineness, lightness and softness. This study evaluated the Angora fibre shape and morphology in comparison with Cashmere fibre and wool as well as the relation between characteristics of Angora fibre. Unlike other keratinous textile fibres, single Angora fibre composes of two sections named as body and head, each of which has individual surface characteristics. Differences between the scale shapes, scale length and scale frequency of Angora hair types were explained in details. Medullation in Angora fibre was explained for different types of Angora hairs defined as down, awn and bristle. This classification was done according to the fibre fineness starting from the finer one. Relation between fibre shape and comfort factor was also analyzed. The relation between mean fibre diameter (MFD), fibre curvature (FC) and percentage of medullation by volume (MEDV) for Angora rabbit fibre was not as strong as wool and Cashmere fibre. Accordingly, when Angora hair types were analyzed individually, it was observed that relation between FC and MEDV for Angora fibre was stronger than wool and Cashmere fibre. Multiple regression analysis was also performed. Diameter distribution along the snippet length (about 200μm) of Angora fibre is uneven compared to Cashmere fibre and wool.     

Water and dye-free coloration of wool

A water and dye-free heat treatment method was used to color wool fibers. The heat effect changed wool fibers to different colors from white in a nitrogen atmosphere. The influences of heating temperature and time on the colors of wool were investigated and the mechanical property of colored wool fibers was evaluated. The color strength of wool fibers increased as heat treatment temperature and time increased. The tensile strength retention rate of wool fiber was relatively high (≥90 %) when the heat temperature was below 200 °C. The surface morphologies of wool fibers scarcely changed during the heat treatment. The carbon content of fibers was found to reduce by heat treatment, indicating oxidization of components in the wool fibers in the process of coloration. Heat treatment may provide a water and dye-free approach to color wool and other textile fibers, albeit within a limited color range.     

Identification of wool, cashmere, yak, and angora rabbit fibers and quantitative determination of wool and cashmere in blend: a near infrared spectroscopy study

Near infrared spectroscopy coupled with chemiometric analysis was investigated as a fast and non destructive method for the identification of wool, cashmere, yak, and angora rabbit fibers in the raw and combed sliver state and for the quantitative determination of cashmere in cashmere/wool blends. The main differences among spectra of different animal hair arise from physical charateristics rather than chemical characteristics (mainly pigmentation and mean diameter) of animal fibers. The Soft Independent Modelling by Class Analogy method allows the classification of distinct fibers into separate groups with interclass distances ranging from 12.64 for the nearest classes (white cashmere and wool) to above 1000 for the most distant classes of white and pigmented fibers. Percentages of recognition and rejection of 100 % were found with the exception of a yak sample that was not rejected from the pigmented cashmere class (98 % of rejection). The prediction capacity of the model was also evaluated. Quantitative analysis was carried out using samples obtained by carefully mixing known amounts of wool and white cashmere. A standard error of the estimate of 8.5, a standard error of prediction of 13.10 and a coefficient of determination of 0.95 were calculated. From the results obtained, it can be concluded that near infrared spectroscopy can be used as a tool for an initial and rapid screening of unknown animal fiber samples in the raw and combed sliver states and for a fast and coarse estimate of the amount of cashmere in wool/cashmere blends.     

Frictional and tensile properties of conducting polymer coated wool and alpaca fibers

Wool and alpaca fibers were coated with polypyrrole by vapor-phase polymerisation method. The changes in frictional and tensile properties of the single fibers upon coating with the conductive polymer are presented. Coating a thin layer of polypyrrole on the alpaca and wool fibers results in a significant reduction in the fiber coefficient of friction, as the conducting polymer layer smooths the protruding edges of the fiber scales. It also reduces the directional friction effect of the fibers. Depending on the type of fiber, the coating may slightly enhance the tensile properties of the coated fibers.     

Modification of polyacrylonitrile precursor fiber with hydrogen peroxide

Polyacrylonitrile (PAN) precursor fibers were modified for different periods of time using hydrogen peroxide aqueous solution. A variety of tests were employed to characterize the fibers. The modification could induce cyclization and oxidation in the precursor fibers, as reflected by the changes in length and diameter of the fibers, and the results of Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Compared with the unmodified fiber, the modified fibers released less heat during a heating process similar to stabilization of PAN precursor fiber. Also, the modified fibers showed lower characteristic temperatures on differential scanning calorimetry (DSC) thermograms, and lower onset temperature of weight loss on thermal gravimetry (TG) curves. The modified fibers had more surface defects and hence exhibited lower tenacity and tensile modulus. Compared with the unmodified fibers, however, the modified fibers had smoother surface and fewer defects after stabilization. The strain decreased with increasing temperature under a constant tension for all the fibers. At the temperatures above 200 °C, the shrinkage of the fibers decreased with the increase of modification time, because a certain degree of cyclization and oxidation occurred in modified fibers, making them shrink less in the temperature range equivalent to stabilization.     

The effect of irrigation rates and nitrogen and phosphorus fertilizers on fiber characteristics of Gossypium hirsutum L. cotton

This article reports the estimated relationships between fiber properties of the Acala 4–42 cultivar and N- and P-fertilizers and irrigation. Increasing water rates in the range of 4200–7200 m³/ha weakened the tensile strength of the fibers and increased their fineness; the regression of maturity, length and uniformity ratio was curvilinear: positive on initial rates and negative on those exceeding 5800 m³/ha. N-fertilizer favorably affected all fiber properties determined: fineness and upper quartile length throughout the rate range tested but strength, mean length and uniformity ratio only up to 250–500 kg ammonium sulfate per ha. The most favorable effect of P-fertilizer was in considerably increasing the length uniformity ratio; it also increased length and fineness but suppressed the maturity index.     

A joint influence of the distributions of fiber length and fineness on the strength efficiency of the fibers in yarn

The length and fineness of fibers are critical to the strength of yarns. Much research has been conducted on the issue in the past decades. Zeidman and Sawhney introduced a new parameter called strength efficiency (SE) of fibers in a yarn using an elaborate probabilistic method. Their final formula, a non-dimensional measure, describes the influence of the fiber length distribution on the strength of yarn. The result, however, is based on the assumption that the fibers are identical in all respects including their cross-sectional area. The influence of fiber fineness can not be seen in their formula. In fact the joint influence of fiber length and fineness is rarely studied. We derive a new strength efficiency of the joint influence of fiber length and fineness on the basis of Zeidman’s result. The conclusion is helpful to the understanding of the comprehensive influence of fiber length and fineness on the strength of yarn. Furthermore, we give a plausible method to estimate the critical length defined by Zeidman. The result can be applied to the research of the properties between fibers and yarns.     

Evaluation of the fineness of degummed bast fibers

Fiber fineness characteristics are important for yarn production and quality. In this paper, degummed bast fibers such as hemp, flax and ramie have been examined with the Optical Fiber Diameter Analyzer (OFDA100 and OFDA2000) systems for fiber fineness, in comparison with the conventional image analysis and the Wira airflow tester. The correlation between the results from these measurements was analysed. The results indicate that there is a significant linear co-relation between the fiber fineness measurement results obtained from those different systems. In addition, the mean fiber width and its coefficient of variation obtained from the OFDA100 system are smaller than those obtained from the OFDA2000 system, due to the difference in sample preparation methods. The OFDA2000 system can also measure the fiber fineness profile along the bast fiber plants, which can be useful for plant breeding.     

Weibull distribution analysis of the tensile strength of the kenaf bast fiber

This paper presents the influence of the gage length on the kenaf fiber Young’s modulus and the tensile strength characterization. Four different gage lengths of 10 mm, 15 mm, 20 mm and 25.4 mm are selected in this study and the tensile testing is performed at a quasi-static loading rate of 1 mm/min. The cross-sectional area of the fiber after failure is considered for the stress calculations. Weibull probability distribution is used to characterize the tensile strength of the kenaf fiber. The Weibull parameters are obtained for the two parameter, three parameter and Weibull of Weibull models and the average tensile strength of the fibers are evaluated. The predicted average tensile strength from all the three approaches are in good agreement with the experimental results for the obtained parameters.     

Surface characterization of low temperature plasma treated wool fiber

Previous investigation results revealed that after the Low Temperature Plasma (LTP) treatment, the hydrophilicity of wool fiber was improved significantly. Such improvement enhances the wool dyeing and finishing processes which might be due to the changes of the wool surface to a more reactive one. In this paper, wool fibers were treated with LTP with different gases, namely, oxygen, nitrogen and gas mixture (25 % hydrogen/75 % nitrogen). Investigations showed that chemical composition of wool fiber surface varied differently with the different plasma gas used. The surface chemical composition of the different LTP-treated wool fibers was evaluated with different characterization methods, namely FTIR-ATR, XPS and saturated adsorption value. The experimental results were thoroughly discussed.     

Fiber dispersion and breakage in deep screw channel during processing of long fiber-reinforced polypropylene

Long glass fiber-reinforced thermoplastics are usually processed by pultruded granules, but glass fiber rovings were used to process long glass fiber-reinforced thermoplastics in this study. This article investigated the dispersion and breakage of fibers during extrusion processing of long glass fiber-reinforced polypropylene containing 30 wt% glass fibers at a certain processing conditions. For this study, the morphology of the surface and polished cross-section of helices was observed by digital photography, as was the morphology of the remaining fiber after burning. On this basis, the fiber/polymer system behavior in the screw channel and the dispersion mechanism of the fiber bundles were analyzed. Moreover, scanning electron microscopy (SEM) was used to observe individual fiber cross-sections to analyze the mechanism of fiber breakage. Finally, the effect of processing conditions such as temperature, screw speed and fiber content on fiber length and dispersion was studied. The results show that the fiber agglomerates composed of fiber bundles form near the barrel surface at the fiber feed point and then undergo three main stages: compression, impregnation, and dispersion. The fiber bundles separate into daughter bundles and individual fibers in different parts of the screw channel. In addition, the results indicate that the fibers can suffer tensile fracture and bending fracture during the extrusion processing. Finally, this paper includes suggestions for improving fiber bundle dispersion and reducing fiber breakage.     

Effect of strand spacing and twist multiplier on structural and mechanical properties of Siro-spun yarns

The effect of strand spacing and twist multiplier on strength of Siro-spun yarns with reference to the yarn structural parameters was investigated. Of the various structural parameters for staple yarns, fiber migration has a crucial influence on the yarn strength, which in turn to a considerable extent is influenced by the strand spacing and twist multiplier. Achieving the objectives of this research, the yarns were produced from lyocell fibers at five strand spacings and four different twist multipliers. Tracer fiber technique combined with image analysis were utilized to study the yarn migration parameters. Afterwards, the yarns were subjected to uniaxial loading by a CRE tensile tester. The measured results are presented in forms of diagrams and tables. The findings reveal that, as strand spacing is increased, yarn tenacity increases up to strand spacing of 8 mm beyond which it reduces. Analysis of the results indicates that the higher tenacity values at the strand spacing of 8 mm can be attributed to the higher mean fiber position, higher migration factor, higher proportion of broken fibers and lower hairiness.     

麻类纤维细度数据分析测试软件的开发

本文根据优化出的麻类纤维细度与直径的相关回归模型，设计制作了通用型麻类纤维细度及细度分布的数据分析测试软件(Uitra—0FDA)，将该软件装入0FDAl00纤维直径分析仪，使0FDAl00纤维直径分析仪用于麻类纤维细度及细度分布的自动测定。U1tra—0FDA通用软件亦可应用于其它类似纤维直径分析仪。     

Improved compressive strength of poly(p-phenylene benzobisoxazole) copolymer fiber containing multi-functional comonomer

Multi-functional comonomer from pentaerythritol (PE) and terephthaloyl chloride (TPC) was synthesized and used for polymerization of poly(p-phenylene benzobisoxazole) (PBO) copolymer. PBO copolymer fibers were prepared from PBO copolymers using a dry-jet wet spinning. The tensile strength of PBO copolymer fibers was higher than that of PBO, and showed 42 % increase at 0.5 mol% loading of comonomer. The tensile modulus of PBO copolymer fiber at 0.5 mol% loading showed 192 % increase compared to PBO fiber. The compressive strength of PBO copolymer fiber had values between 0.46 GPa and 0.6 GPa with the comonomer content. 64-114 % increase in compressive strength of PBO copolymer fibers was observed compared to PBO fiber.     

Relationship between chemical composition,crystallinity, orientation and tensile strength of kenaf fiber

The physical properties of natural growth fibers such as chemical composition content and fiber diameter are highly affected by environmental issues such as environmental changes and fiber extraction methods. These irregularities of the natural fibers seriously affect its utilization in composite as reinforcements. In this study, taking into account the importance of the fiber tensile strength, the correlation degrees between the kenaf fiber tensile strength and the fiber chemical composition, crystallinity, orientation degree were analyzed by the grey relational analysis method. Both the kenaf single fiber and fiber bundle were used as XRD and tensile strength test sample. The chemical composition content and the FTIR were carried out to obtain a correct result of the chemical composition content. It found that for the different XRD and tensile strength test samples, the single fiber showed lower crystallinity, higher orientation degree and tensile strength compared with the fiber bundle. The cellulose content and the orientation degree got the higher correlation degree with single fiber tensile strength, which was 0.674 and 0.640. The highest factor associated with the fiber bundle tensile strength was the orientation degree, the correlation degree was 0.747. The hemicellulose content and the crystallinity also got high correlation degree with the fiber bundle strength, which was 0.687 and 0.640.