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Published studies of silks focus on processed fibres or the optimum conditions for their production. Consequently, the effects of the environment on the physical properties of the cocoon are either poorly understood or kept as closely guarded industrial secrets. In this study, we test the hypothesis that silkworms as ectothermic animals respond to environmental conditions by modifying their spinning behaviour in a predictable manner, which affects the material properties of the cocoons in predictable ways. Our experiments subjected spinning Bombyx mori silkworms to a range of temperatures and relative humidities that, as we show, affect the morphology and mechanical properties of the cocoon. Specifically, temperature affects cocoon morphology as well as its stiffness and strength, which we attribute to altered spinning behaviour and sericin curing time. Relative humidity affects cocoon colouration, perhaps due to tanning agents. Finally, the water content of a cocoon modifies sericin distribution and stiffness without changing toughness. Our results demonstrate environmentally induced quality parameters that must not be ignored when analysing and deploying silk cocoons, silk filaments or silk-derived bio-polymers. [ABSTRACT FROM AUTHOR]

Two drawbacks of the traditional electrospinning process when used for producing nanofibers for drug release are that clogging of the spinneret is often experienced, and the fibers produced often exhibit a tailing-off of drug release over sustained periods. The present study investigates the preparation of ferulic acid (FA) sustained-release cellulose acetate (CA) nanofibers, in which a third component, polyvinylpyrrolidone (PVP), was included into the nanocomposites for an improved sustained drug release profile. A modified coaxial electrospinning process, in which only organic solvent N, N-dimethylacetamide was used as a sheath fluid, was exploited for a smooth and continuous fabrication of multiple-component nanofibers. Under an applied voltage of 16 kV and an optimized sheath-to-core flow rate ratio of 0.11, three types of FA/PVP/CA composite nanofibers (with varied of PVP content) were generated. These nanofibers had higher quality in terms of size and distribution of nanofiber diameter, as indicated by FESEM images. Analysis of double- and triple-component nanofibers by XRD, DSC, and ATR-FTIR confirmed the compatibility of components producing homogenous fibers in both cases, but the triple-component nanofibers exhibited better release profiles over sustained periods than the double-component nanofibers in terms of release completeness, reduced tailing-off, and adjustable release rates. The modified coaxial process and the resulting multiple-component nanocomposites should provide a new way for developing novel drug sustained materials and drug delivery systems. [ABSTRACT FROM AUTHOR]

A series of organ-soluble copolyimides (co-PIs) were synthesized from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 2,2′-bis(trifluoromethyl)-4, 4′-diaminobiphenyl (TFMB), and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) via a one-step polymerization in N-methyl-2-pyrrolidone (NMP). The polyimide solutions were used to fabricate as-spun polyimide fiber by a wet-spinning process. SEM images of the round cross-section of the fibers indicated that a homogeneous and dense fibrous structure was produced in the coagulation bath of HO /NMP = 90/10 (v/v) and many microfibrils appeared on the surface. The drawn fibers exhibit excellent mechanical properties, and the strength and modulus of BTDA/TFMB/BIA co-PI fibers (TFMB/BIA = 50/50) reached 2.25 and 102 GPa with a draw ratio of 3.0. The 5 % weight loss temperature of the co-PI fibers in thermogravimetric analysis spectra achieved 548-563 °C in an air atmosphere. The glass transition temperatures were found to be between 340 and 366 °C according to the DMA results. Annealed BTDA/TFMB/BIA co-PI fibers displayed distinct wide-angle X-ray patterns, and crystallinity and crystal orientation with various draw ratios were observed. [ABSTRACT FROM AUTHOR]

The reason for the upper limit on the height of spinnable carbon nanotube (CNT) forests was studied. To analyze the differences between CNT forests with different heights, we synthesized CNT forests using different growth times (3, 6, 9, 12, 15, and 60 min). The height of the CNT forests increased from 260 μm at 3 min to 1.7 mm at 60 min, and the spinnability decreased sharply after 9 min of growth, where a wavy morphology first appeared. Raman analysis of the CNT forest grown for 9 min showed that the intensity ratio of G-band to D-band at the upper region was 1.50 and that near the bottom was 1.14. We also found that the reaction termination process affected the spinnability of the CNT forests. Depending on the termination process, both spinnable and non-spinnable CNT forests could be selectively synthesized, because of the different morphologies in their lower regions. The results suggested that any wavy morphology produced due to a disturbance in growth conditions causes a loss of spinnability. [ABSTRACT FROM AUTHOR]

Yarn made from natural fibers, synthetic fibers, or other types of fibrous materials is all formed by twisting an assembly of short or long fibers and its performance is significantly influenced by the physical behavior of these fibers in the yarn forming region-a small triangle area called spinning triangle. In spinning process, the fibers in spinning triangle where they are finally twisted into a yarn are subject to dynamic loads. However, earlier theoretical models are all based on the static assumptions and it cannot reflect the real status of the spinning process. Therefore, in this study, a new dynamic model of spinning triangle was developed by using finite-element method with consideration of the dynamic effects such as the inertia and damping forces of constituent fibers for a more complete and accurate description. With consideration of dynamic characteristics of fiber, earlier static model of spinning triangle can be considered as a special case of the proposed dynamic model. In order to verify the developed theoretical model, comparisons of the proposed model with earlier model and experimental measurements were carried out and good agreements were achieved. Furthermore, the dynamic behavior of fibers in spinning triangle, such as the natural frequency, mode shape, resonant response, harmonic analysis, and response under a time-varying tension, has been numerically studied. The results show that dynamic parameters have a great influence on the amplitude and attenuation of the response of constituent fibers in spinning triangle. [ABSTRACT FROM AUTHOR]

The use of low-cost renewable natural fibres as reinforcements for structural composites is attractive but requires specific considerations over that of textile industry requirements. Textile yarns are twisted for processability and increased tensile strength. However, reinforcements employing twisted yarns produce poorer composites due to hindered yarn impregnation, inadequate wettability and compromised orientation efficiency. Whilst assessing the physical properties of select plant fibre yarns that determine reinforcement/composite properties, a strong correlation between yarn twist and compaction is observed. This manuscript also examines a novel plant fibre treatment method using hydroxyethylcellulose (HEC). HEC treatment not only enables intra- and inter-yarn binding thus allowing easy preparation of aligned fabrics, but also improves yarn mechanical properties whilst maintaining physical properties such as low twist. It is noticed that low twist yarns are more responsive to HEC treatment; the tenacity and stiffness of low twist flax is observed to increase by 230 and 75%, respectively. [ABSTRACT FROM AUTHOR]

A series of PpPTA aramid fibres with various degree of lateral orientation ranging from their usual radial-oriented lateral texture to a full random lateral texture were prepared by employing a series of different coagulating media in the fibre spinning process. The resulting variation in lateral texture did not lead to differences in linear tensile properties or crystallite dimensions. Raman spectroscopy measurements on embedded axially compressed filaments showed that the stresses for kink band initiation and propagation were independent of the degree of lateral texture. The kink band morphology and the final kink band density upon further straining were found to correlate with the shear modulus derived from combined mechanical and XRD data. [ABSTRACT FROM AUTHOR]

Composite materials based on poly(ε-caprolactone) (PCL) and carbon nanofibres (CNFs) were processed by solvent casting and electrospinning. The main objective was to investigate the effects of the CNFs on the microstructural, thermal and mechanical properties of the PCL matrix composites processed by two different routes. The hybrid materials obtained with different CNF content (1, 3 and 7 wt%) were analysed by electron microscopy (FESEM), differential scanning calorimeter (DSC), thermogravimetry (TGA) and mechanical testing. The composite films showed a good dispersion in the PCL matrix while electrospun samples were consisted of homogeneous and uniform fibres up to 3 wt% CNFs with average fibre diameter ranged between 0.5 and 1 μm. Composite films and mats revealed an increased crystallization temperature with respect to the neat PCL matrix. Mechanical properties of solvent cast films and electrospun mats were assessed by uniaxial tensile tests. A stiffness increase was achieved in PCL films depending on the CNF content, while mechanical properties of mats were only slightly affected by CNF introduction. [ABSTRACT FROM AUTHOR]

In this paper a range of acid aqueous solutions are studied towards their suitability for developing chitosan nanofibres by electrospinning. It was found that parameters such as type of solvent, pH, concentration of chitosan, viscosity, charge density, applied voltage, solution flow rate, distance from nozzle tip to collector surface and time play a role in the characteristics of the obtained nanofibrous structures. After a preliminary study to select the most suitable composition of the chitosan containing solution (90% acetic acid), a detailed study was done to find the optimal conditions for chitosan nanofibrous structure development. Finally long-term experiments were performed, which showed that the formation of the nanofibrous structure distorts the electrical field. [ABSTRACT FROM AUTHOR]

Nano-sized beads and non-woven porous fiber constructs of poly(ε-caprolactone) were produced by electrospinning. Nearly spherical beads with diameters between 900 nm and 5 ,am were produced with dilute solutions with less than 3 wt% PCL. In this case, the initial jet of solution may split into many mini jets almost at the end of the needle and each minijet gradually disintegrates into small droplets. Beyond a critical solution concentration of about 4 wt% PCL, the jet may undergo extensional flow, splitting and splaying to produce a web of interconnected fibers with mean diameters on the order of 300 to 900 nm. Intermolecular entanglements play a dominant role in stabilizing the fibrous structure. A uniform fibrous structure was obtained at 40 kV while at 20 kV a large fraction of beads were present in the electrospun polymer. The fiber diameter in the PCL deposited on the collector typically exhibits a bimodal distribution. Electrospinning lowers the degree of crystallinity in the polymer. [ABSTRACT FROM AUTHOR]

A test procedure for evaluating the cut resistance of yarns under tension-shear loading conditions is described and demonstrated. A knife blade is pressed transversely at a constant rate against a yarn gripped at its ends, the load-deflection relation is measured, and the energy required to cut through the yarn is computed. Results for Zylon (polybenzobisoxazole or PBO) are presented. The cut energy and strain to initiate cutting depend on the sharpness of the blade, the slicing angle, and the pre-tension in the yarn. The dependencies are explained by changes in failure mode of the fibers within the yarn. The test provides information needed to extend a computational model of ballistic response of fabrics to sharp fragments and to design a cutting tool. [ABSTRACT FROM AUTHOR]