Alkali treatment of jute fibers: Relationship between structure and mechanical properties

The mechanical properties of tossa jute fibers were improved by using NaOH treatment process to improve the mechanical properties of composites materials. Shrinkage of fibers during this process has significant effects to the fiber structure, as well as to the mechanical fiber properties, such as tensile strength and modulus. Isometric NaOH‐treated jute yarns (20 min at 20°C in 25% NaOH solution) lead to an increase in yarn tensile strength and modulus of ∼ 120% and 150%, respectively. These changes in mechanical properties are affected by modifying the fiber structure, basically via the crystallinity ratio, degree of polymerization, and orientation (Hermans factor). Structure–property relationships, developed for cellulosic man‐made fibers, were used with a high correlation factor to describe the behavior of the jute fiber yarns. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 623–629, 1999     

Structure changes during tensile deformation and mechanical properties of a twisted carbon nanotube yarn

The small-angle X-ray scattering measurements during tensile deformation have been performed for studying the structure and mechanical property relationships of twisted carbon nanotube (CNT) yarns. The tensile strength distribution and the diameter changes during tensile deformation have also been measured. The orientation distribution of the CNTs in the yarn has been determined and its changes during tensile deformation have been related to the variation of the tensile modulus with the twist angle. The tensile modulus and Poisson’s ratio of the yarns decreased with increasing twist angle, whereas the tensile strength of the yarn showed a maximum at the twist angle of 25°. At this twist angle, the distribution width of the tensile strength was minimum indicating the higher uniformity of the yarn structure.     

Tension–tension fatigue behavior of carbon nanotube wires

The tension–tension fatigue behavior of three types of as-received carbon nanotube (CNT) wires, comprising of 30-, 60-, and 100-yarn, was investigated. Fatigue tests were conducted at 35%, 50%, 60%, 75% and 80% of their ultimate tensile strengths which provided the fatigue life data (S–N curves). Their electrical conductivities were measured as a function of the number of cycles. Fatigue strength of the CNT wires at a given number of cycles decreased with an increase in the number of yarns. Their electrical conductivity increased with increase of applied fatigue load and number of fatigue cycles. Damage and failure mechanisms involved relative sliding of yarns in CNT wires leading to the formation of kink bands, followed by plastic deformation and then breakage of yarns. Microtomography density measurements provided the evidence that the increase in conductivity was due to the reduction of micro/nano voids between and inside the yarns, which decreased with increasing fatigue load and number of fatigue cycles.     

Strengthening and stiffening of ramie yarns by applying cyclic load treatment

A cyclic load treatment was developed by applying a load on ramie yarns up to a proper value and then unloading for different number of cycles under high temperature or wet state. The results of tensile tests revealed that compared to the untreated yarns, a significant increase of around 20–50% in tensile strength was obtained for the cyclic load-treated yarns. Young's modulus of cyclic load-treated yarns was increased drastically, one to two times higher than the initial value. The number of cycles had an influence on improving the tensile properties of ramie yarns. After the individual heat or wet treatment without cyclic load, it was found that tensile strength of treated yarns remained unchanged as the original value while Young's modulus was decreased remarkably, which implies that the introduction of cyclic load to individual heat or wet treatment plays a crucial role in strengthening and stiffening of ramie yarns. It was considered that the improved effect was correlated with the decreased microfibrillar angle and the increased orientation of amorphous region in fiber microstructure because the crystallinity and crystalline orientation of ramie yarns calculated from X-ray diffraction diagrams showed little change after cyclic load treatment. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hydrolysis of resin-coated poly(ethylene terephthalate) yarns

A comparison of the resistance of resin coated and uncoated poly(ethylene terephthalate) (PET) yarns to steam exposure at 160°C shows that the coated yarn degrades more rapidly. The decrease in tensile strength upon steam exposure results from hydrolytic scission which is accelerated by acidic hydrolysis products. The resin coating on the yarn acts as a skin around the filaments, a skin which apparently does not retard steam penetration, but does trap hydrolysis products in the yarn structure. A comparison study of PET films substantiated these conclusions. Hydrolysis products in films and small bundles of monofilaments taken from yarns were measured by infrared spectroscopy.     

Solvent‐induced modifications in polyester yarns. I. Mechanical properties

The mechanical properties of polyester (PET) yarns, fine filament, and microdenier (original and heat‐set), treated with a trichloroacetic acid–chloroform (TCAC) mixture were investigated. The treatments were carried out in an unstrained state with various concentrations of the TCAC reagent at room temperature. The TCAC treatment on PET yarns resulted in notable changes in the tensile behavior. The TCAC‐treated yarns exhibited higher extensibility and work of rupture without much loss in strength. The improvement in elongation was less in the case of heat‐set polyester yarns due to solvent treatment. The depression of the glass transition temperature (T_g) of TCAC‐treated PET yarns, even at the minimum concentration, showed its effectiveness to plasticize the fibers and the closeness of the solubility parameter of TCAC and PET. The T_g depression favors molecular relaxation, which has resulted in a higher shrinkage percentage of TCAC‐treated PET yarns and the effective shrinkage was reached more easily for the original fine‐filament polyester (FFP) and microdenier polyester (MDP) yarns at the lowest concentration. The effects of the concentration of TCAC on the strength, elongation, yield behavior, and work of rupture on PET were also investigated. A significant plastic flow was observed in the TCAC‐treated yarns. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1500–1510, 2003     

Tensile fatigue behavior of polyamide 66 nanofiber yarns

Nanofiber yarns with twisted and continuous structures have potential applications in fabrication of complicated structures such as surgical suture yarns, artificial blood vessels, and tissue scaffolds. The objective of this article is to characterize the tensile fatigue behavior of continuous Polyamide 66 (PA66) nanofiber yarns produced by electrospinning with three different twist levels. Morphology and tensile properties of yarns were obtained under static tensile loading and after fatigue loading. Results showed that tensile properties and yarn diameter were dependent on the twist level. Yarns had nonlinear time‐independent stress–strain behavior under the monotonic loading rates between 10 and 50 mm/min. Applying cyclic loading also positively affected the tensile properties of nanofiber yarns and changed their stress–strain behavior. Fatigue loading increased the crystallinity and alignment of nanofibers within the yarn structure, which could be interpreted as improved tensile strength and elastic modulus. POLYM. ENG. SCI., 55:1805–1811, 2015. © 2014 Society of Plastics Engineers     

Effects of alkali and ultraviolet treatment on colour strength and mechanical properties of jute yarn

In this study, jute yarns were treated with an aqueous alkali solution and ultraviolet light to improve dyeability. Ultraviolet light treatments were carried out at an air pressure of 1 atm, under water and vacuum, and all the samples were dyed with reactive dyes. Virgin samples and treated jute yarns were analysed by Fourier Transform–infrared spectroscopy. K/S values were determined by a reflective spectrophotometer and used to establish the fixation values and colour strength of the dyed samples. The tensile mechanical properties of the samples were also measured by a tensile testing apparatus and were compared with the virgin samples. Alkali treatment resulted in a reduction in carbonyl group concentration. However, atmospheric ultraviolet light treatment increased carbonyl group concentration. Dyeability and dye fixation values for atmospheric and underwater ultraviolet light‐treated samples increased. Furthermore, the loss of tensile strength for alkali‐treated samples was much greater than others (up to 50%) in comparison with ultraviolet light‐treated samples.     

Certain fine structure and thermal properties of benzhydrylated cotton cellulose

The present paper describes the results of a preliminary study of certain physical and thermal properties of benzhydrylated cotton yarns. The 200-yd. lengths of 7/2 yarn consisting of purified mercerized cellulose were reacted in a special reactor to various degrees of substitution from DS 0.31 to DS 1.22 with benzhydryl bromide in a mixture of equal volumes of 2,6-lutidine and dimethylformamide. The products were examined for tensile strength at break, which decreased only slightly with substitution; ultimate elongation, which was relatively uniform at 60–70% of the control yarn; and tenacity, which decreased with substitution largely due to added weight. The energy of rupture remained relatively constant at about 50% above the control. Tensile stiffness decreased progressively with substitution to about 25% of the control. Density decreased 10–11% with substitution. Crystallinity of the cellulose largely disappeared with substitutions above DS 1, and the lattice of benzhydryl cellulose began to appear. Stiffness, elastic recovery and work recovery were measured on 5-in. specimens of the yarn in an oven while they were subjected to repeated extension to about 1–2% and relaxed as the temperature was raised twice to 200°C. and lowered. During the heating phase of the first cycle the yarn underwent considerable heat adaptation. However, during the cooling phase and during both heating and cooling phases of the second cycle, the yarns showed generally favorable behavior. Attempts are made to interpret the results in terms of molecular modifications.     

Effect of alkali and ultraviolet (UV) radiation pretreatment on physical and mechanical properties of 1,6‐hexanediol diacrylate–grafted jute yarn by UV radiation

To improve the physicomechanical properties of jute yarn, grafting with 1,6‐hexanediol diacrylate (HDDA) monomer was performed by a UV radiation technique. A series of HDDA solutions of various concentrations in methanol were prepared. A small quantity of photoinitiator (Darocur‐1664) was also added to HDDA solutions. To optimize the conditions for grafting, the effects of monomer concentration, soaking time, and radiation doses were studied by varying the number of soaking times along with variation of monomer concentrations and UV radiation intensities. The extent of polymer loading and the mechanical properties like tensile strength (TS), elongation at break (Eb), and tensile modulus of both treated and untreated jute were investigated. The highest tensile strength, polymer loading, and modulus were achieved with 5% HDDA concentration, 5 min soaking time, and the 4th pass of UV radiation. This set of conditions was selected as optimum and produced enhanced tensile strength (67%), modulus (108%), and polymer loading (11%) over those of virgin fiber. To further improve the mechanical properties the jute yarns were pretreated with alkali (5% NaOH) solution and after that the alkali‐treated yarn were treated under UV radiation of various intensities. The pretreated samples were grafted with optimized monomer concentration (5% HDDA). Increased properties of alkali + UV‐pretreated and grafted samples such as polymer loading (12%), tensile strength (103%), elongation at break (46%), and modulus (114%) were achieved over those of virgin jute yarn. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 18–24, 2004     

Mechanical and electrical properties of the PA6/SWNTs nanofiber yarn by electrospinning

In this article, continuous PA6/single‐wall nanotubes (SWNTs) nanofiber yarns were obtained by a special electrospinning method; the mechanical and electrical properties and the electric resistance‐tensile strain sensitivity of the as‐spun yarns were specially studied. The main parameters in the spinning process were systematically studied. Scanning electron microscope images and mechanical tests indicated that the optimum parameters for the electrospinning process were operation voltage = 20 kV, spinning flow rate = 0.09 ml/h, and winding speed = 150 rpm. Transmission electron microscopy images showed that the SWNTs have aligned along the axis of the nanofibers and thus formed a continuous conductive network which greatly improved the electrical conductivity of the PA6 nanofiber yarn and the percolation threshold was about 0.8 wt%. The electric conductivities of the yarns at different stretching ratios were also measured with a custom‐made fixture attached to the high‐resistance meter, and for a given carbon nanotube concentration, the conductivity changes almost linearly with the tensile strain applied on the yarns. POLYM. ENG. SCI., 54:1618–1624, 2014. © 2013 Society of Plastics Engineers     

In situ jute yarn composite with HEMA via UV radiation

Jute yarns soaked for 30 min in 2‐hydroxyethylmethacrylate (HEMA) + MeOH solutions at different proportions [1–20% HEMA in MeOH (v/v)] were irradiated in situ with a UV lamp for different periods. The treated jute yarns that were washed in acetone after the irradiation to remove the unused excess monomer HEMA gained about 10% polymer loading with enhanced tensile strength (80%) and elongation (95%). The tenacity was not further increased by incorporation of a minute amount (1%) of novel additives into the HEMA + MeOH solutions, but elongation was enhanced up to 140% when the additive urethane acrylate (1%) was mixed with the solution. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 841–846, 1999     

A modeling and experimental study of the influence of twist on the mechanical properties of high‐performance fiber yarns

Little data exist on how twist changes the properties of high‐performance continuous fiber yarns. For this reason, a study was conducted to determine the influence of twist on the strength and stiffness of a variety of high‐performance continuous polymeric fiber yarns. The materials investigated include Kevlar 29®, Kevlar 49®, Kevlar 149®, Vectran HS®, Spectra 900®, and Technora®. Mechanical property tests demonstrated that the initial modulus of a yarn monotonically decreases with increasing twist. A model based on composite theory was developed to elucidate the decrease in the modulus as a function of both the degree of twist and the elastic constants of the fibers. The modulus values predicted by the model have good agreement with those measured by experiment. The radial shear modulus of the fiber, which is difficult to measure, can be derived from the regression parameter of experimental data by the use of the model. Such information should be useful for some specialized applications of fibers, for example, fiber‐reinforced composites. The experimental results show that the strength of these yarns can be improved by a slight twist. A high degree of twist damages the fibers and reduces the tensile strength of the yarn. The elongation to break of the yarns monotonically increases with the degree of twist. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1938–1949, 2000     

捆绑纱对预定向经编织物性能的影响

通过用玻璃纤维／涤纶捆绑纱及不同经编组织结构,研究捆绑纱对预定向经编织物性能的影响。结果表明,玻纤可用于捆绑纱组织中,其编织后强度比涤纶纱高33．3％。玻纤捆绑纱可改善树脂对织物的浸渍性,降低最终复合材料的孔隙率,提高复合材料的拉伸和剪切等力学性能。不同的捆绑纱组织结构对复合材料的力学性能影响显著,玻纤做捆绑纱时,经平组织比编链组织复合材料的经向拉伸强度高7．97％,弯曲强度高约5％。     

Mechanisms of degradation of cotton and effects of mercerization-stretching upon the course of these mechanisms. V. Weathering

Scoured ply cotton yarn was slack mercerized followed by restretching the cotton yarn to 90–103% of the original length in the mercerizing solution. The scoured and the mercerized cotton yarns were subjected to weathering for up to 14 months. Regardless of the cotton substrates, exposure to weathering was accompanied by an increase in copper number, decrease in both degree of polymerization (DP) and iodine sorption, and a loss in strength properties. No significant change in the carboxyl content of scoured and mercerized cottons could be observed after weathering. However, mercerized cottons retained higher strength in spite of higher degradation as compared to scoured cotton. This was interpreted in terms of removal of structural imperfections or weak links in cotton during the combined as swelling and stretching process evidenced by interrelationships between tenacity and percentage of bonds broken, as well as tensile strength and DP together with measurement of the average distances between crystallite centers in scoured and mercerized degraded cotton.     

Effect of single yarn twist and ply to single yarn twist ratio on strength and elongation of ply yarns

The amount of ply twist required to bring the surface fibers of the strand parallel to ply yarn axis is half the single yarn twist and, is experimentally verified by viewing the multifilament yarns longitudinally under Scanning Electron Microscope. The effect of single yarn twist and ply to single yarn twist ratio on strength and elongation of two‐ply cotton yarn have been studied. As the single yarn twist increases the tensile strength of the ply yarns with different levels of ply to single yarn twist ratio increases and at 130–140% of normal single yarn twist level, the ply yarns attain almost the same strength. Rate of improvement in tensile strength of cotton two‐ply yarn with respect to single yarn twist is more than that with respect to ply twist. The effect of ply to single yarn and cable to ply yarn twist ratio on strength and elongation of ply and cable multifilament yarns have been studied. Tensile strength of ply and cable multifilament yarns do not vary with the change in ratio of ply to single yarn twist and cable to ply twist respectively, particularly when the resultant yarn is finer. The cosine of average filament inclination to the ply yarn axis and that to the cable yarn axis do not vary much with different levels of ply to single yarn twist ratio and cable to ply yarn twist ratio respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2245–2252, 2005     

Modification Jute Yarn with HEMA by Thermal Curing Method

Jute, an important lignocellulosic fiber, can be incorporated in monomer like HEMA in different ways for achieving desired properties and texture. But its high level of moisture absorption, poor wettability and insufficient adhesion between untreated fiber and the polymer matrix lead to debonding with age. In order to improve the above qualities, adequate surface modification is required. In our present work, jute yarn surface modification was done by graft copolymerization of 2-hydroxyethylmethacrylate (HEMA). Jute yarns soaked into HEMA (5–30%) + MeOH and benzoyl peroxide (2%) solution and were cured in an oven at different temperature (30–70°C) for different curing time (15–60 min). Concentration of monomer, soaking time, curing temperature and curing time were optimized with the extent of tensile properties and polymer loading (%PL). Enhanced tensile strength (137%) and polymer loading (36%) were achieved by 20% HEMA solution with 15 min soaking time, 30 min curing temperature at 50°C. The fiber surface was pretreated with 0.05–0.5% KMnO₄ solution and grafted with the optimized conditions. It was observed that KMnO₄ treatment only increases the PL while it decreases the tensile properties a lot, which is even lower than the raw fiber. An experiment involving water absorption capacity shows that water uptake by treated sample is much lower than that of the untreated samples. During weathering in accelerated weathering tester, the treated samples exhibited less loss of the physico-mechanical properties than untreated yarns.     

n-C7H16/CCl4热解处理对粘胶基碳纤维性能的影响

采用浸渍热解法,以n-C_7H_(16)/CCl_4为热解质,讨论浸渍液体积比、热解温度等对粘胶基碳纤维(RCF)拉伸性能的影响。结果表明,经热处理后纤维线密度降低,表面缺陷减少,当n-C_7H_(16)/CCl_4为2:3(体积比),热解温度900～1100℃时,碳纤维拉伸强度可提高17％。用韦氏统计理论对强度分布进行分析.证实经热解处理后,RCF强度分布更集中,均匀性更好。     

Morphological and mechanical properties of drawn poly(l‐lactide) electrospun twisted yarns

In this study, the continuous twisted PLLA yarns were produced using an electrospinning device consists of two oppositely charged nozzles. The electrospinning process was performed at different twist rates. The electrospun twisted yarns were drawn at different extension ratios of 50% and 100% and their morphological and mechanical properties of post‐drawn yarns were investigated. The morphological studies at all twist rates shown that uniform and smooth fibers without any bead were formed. Increasing the twist rate up to 240 rpm resulted to a decrease in the average diameter of the fibers in the yarn structure. After uniaxially drawing of the yarns, the average diameter of fibers and thus the yarn diameter decreased. The post‐drawing process enhanced the crystallinity of the fibers in the yarn structure. Furthermore, by increasing the extension ratio, the tensile strength and modulus of yarns increased, while the elongation at break (%) decreased. POLYM. ENG. SCI., 58:1091–1096, 2018. © 2017 Society of Plastics Engineers     

Mechanical properties of Bombyx mori silk yarns studied with tensile testing method

The mechanical properties of Bombyx mori silk yarns and baves were investigated with tensile testing method. After silk yarns were pre‐extended at different strain levels and fixed for a while followed by recovery process, the tensile characteristics were examined in detail. It was commonly observed that low preliminary extensions up to 2–3% do not cause the changes of the mechanical properties and stress‐strain curves because they result in small structural changes and distortions, which were recovered within relatively short time (～ 1 min) in recovery process. However, pre‐extension values >3% strain lead to great changes of the mechanical properties and fibre structure, i.e., the changes of the shape of stress‐strain curve where additional transition point was observed, increase in the rigidity and stress at rupture, but decrease in extensibility as a result of orientation and destruction of the fibre structure especially in the amorphous region. It was stated that silk fibre consists of two distinct deformation regions, namely first linear region extending up to 2–3% strain and the second region beyond 2–3% strain where the main reorganization processes of the fibre structure, that is, the straining of macromolecular chains especially in the amorphous regions, the orientation of structural units such as β‐sheet microcrystals in stretching direction, and the destruction of macromolecules take place. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009