Changes In Fiber Structure Research Articles

Follicle characteristics, seasonal changes in fibre cross-sectional area and ellipticity in Australasian specialty carpet wool sheep, Romneys and Merinos

Data was collected on secondary:primary follicle ratio, relative follicle density, and seasonal changes in fibre cross-sectional area and fibre ellipticity (ratio of major-to-minor fibre cross-sectional axis) in the Australasian specialty carpet wool breeds (Carpetmaster, Drysdale, Elliottdale, Tukidale), Romneys and Merinos. Merinos had a higher secondary:primary follicle ratio ( p<0.001), relative primary follicle density ( p<0.05), relative secondary and relative total follicle density ( p<0.01) than the other breeds. Both breed and follicle type (primary or secondary) had a significant effect on fibre cross-sectional area ( p<0.05). While both fibre types (primary and secondary) showed changes in cross-sectional area during the experiment, a more distinct seasonal pattern was seen in the secondary fibres with summer maxima and winter minima in all breeds. Relative change in fibre diameter was higher in secondary fibres than in primary fibres. Changes in fibre ellipticity were also noted throughout the duration of the experiment. It is apparent that there are differences between primary and secondary follicle populations in the way the fibres produced contribute to seasonal changes in average fibre diameter of fleeces. The changes suggest there are separate control mechanisms for each follicle type and that the number, size and arrangement of the cells in each type of fibre vary independently of one another throughout the year, bringing about dynamic changes in fibre growth and form. Further work is required to examine the influence of feed quality on these factors and to determine the mechanisms through which these changes in fibre structure are brought about.

Mechanical and Impact Properties of Needle Punched Nonwoven Composites

The effect of changes in fiber structure on the mechanical properties of nonwoven composite with different punching densities was studied through the testing of tensile, bending, impact, compression after impact, fatigue, friction/wear and mode-I interlaminar fracture properties. The tensile strength and mode-I interlaminar fracture toughness of nonwoven composite was increased with increasing punching densities due to the increased fiber entanglement. The flexural, impact, fatigue and wear properties were decreased with punching densities due to the damage to fibers during the punching process which resulted in the reduction of fiber length. The impact resistant properties showed its maximum at the punching density of 30 penetrations/cm2. The tensile modulus and the compression strength were determined from the orientation of the reinforcing fibers which was affected with the punching densities. The mechanical properties of nonwoven composite showed rather isotropic properties with increased random distribution of the fibers at high punching densities. In the range of adequate punching densities, the nonwoven composite showed substantially improved mechanical and impact properties compared to the woven laminate composite. The nonwoven composite showed improved properties of flexural and compression strengths as well as mode-I interlaminar fracture toughness.

Fine structure and physical properties of polyethylene/poly(ethylene terephthalate) bicomponent fibers in high-speed spinning. I. Polyethylene sheath/poly(ethylene terephthalate) core fibers

The high-speed melt spinning of sheath/core type bicomponent fibers was performed and the change of fiber structure with increasing take-up velocity was investigated. Two kinds of polyethylene, high density and linear low density (HDPE, LLDPE) with melt flow rates (MFR) of 11 and 50, [HDPE(11), LLDPE(50)], and poly(ethylene terephthalate) (PET) were selected and two sets of sheath/core combinations [HDPE(11)/PET and LLDPE(50)/PET bicomponent fibers] were studied. The fiber structure formation and physical property effects on the take-up velocities were investigated with birefringence, wide-angle X-ray diffraction, thermal analysis, tensile tests, and so forth. In the fiber structure formation of PE/PET, the PET component was developed but the PE components were suppressed in high-speed spinning. The different kinds of PE had little affect on the fine structure formation of bicomponent fibers. The difference in the mechanical properties of the bicomponent fiber with the MFR was very small. The instability of the interface was shown above a take-up velocity of 4 km/min, where the orientation-induced crystallization of PET started. LLDPE(50)/PET has a larger difference in intrinsic viscosity and a higher stability of the interface compared to the HDPE(11)/PET bicomponent fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2254–2266, 2000

Fine-structure and physical properties of polyethylene fibers in high-speed spinning. I. Effect of melt-flow rate in the high-density polyethylene

High-density polyethylene (HDPE) fibers, obtained from a melt-flow rate (g/10 min) of 11 and 28, was produced by a high-speed melt-spinning method in the range of take-up velocity from 1 to 8 km/min and from 1 to 6 km/min, respectively. The change of fiber structure and physical properties with increasing take-up velocity was investigated through birefringence, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), a Rheovibron, and a Fafegraph-M. With an increase in take-up velocity, the birefringence showed a sigmoidal increase, which has distinct changes in the range of 1–5 km/min. Throughout the whole take-up velocities, the birefringence of HDPE(11) was higher than that of HDPE(28). With increasing take-up velocity, the crystalline orientation was transformed from a-axis orientation to c-axis orientation. These crystalline relaxations are confirmed by the tan δ peak of high-speed spun HDPE fibers. The intensity of the crystalline relaxation peak decreases with increasing take-up velocity in both HDPE(11) and HDPE(28). As above, the crystalline relaxation peaks shift to lower temperature with increasing take-up velocity. With increasing take-up velocity, the ultimate strain decreases while both specific stress and the initial modulus increase. The mechanical behavior may be closely related to, as investigated by birefringence, orientation of the amorphous region, etc., the take-up velocity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1182–1195, 2000

Fine structure and physical properties of poly(ethylene terephthalate)/polyethylene bicomponent fibers in high-speed spinning. II. Poly(ethylene terephthalate) sheath/polyethylene core fibers

The high-speed melt spinning of sheath/core type bicomponent fibers was performed and the change of fiber structure with increasing take-up velocity was investigated in comparison with the results of our previous study. Two kinds of polyethylene, high density and linear low density (HDPE, LLDPE) with melt flow rates (MFR) of 11 and 50 [HDPE(11), LLDPE(50)], and poly(ethylene terephthalate) (PET) were selected and two sets of sheath/core combinations [PET/HDPE(11) and PET/LLDPE(50) bicomponent fibers] were studied. The structure of each component in high-speed spun bicomponent fibers was analyzed through the birefringence, wide-angle X-ray scattering pattern, differential scanning calorimetry thermogram measurements, tensile tests, and so forth. In the PET/PE bicomponent fiber the structural formation of the PET component was promoted but that of the PE component was suppressed as compared to those of single-component fibers. Neither HDPE nor LLDPE affected the fine structure formation of the bicomponent fiber. Because the thermal properties of PE and PET are quite different from each other, the interfacial instability of the PET/PE bicomponent fiber was found to be serious compared to that of the PE/PET bicomponent fiber. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2267–2277, 2000

Mechanical and Impact Properties of Needle Punched Nonwoven Composites

The effect of changes in fiber structure on the mechanical properties of nonwoven composite with different punching densities was studied through the testing of tensile, bending, impact, compression after impact, fatigue, friction/wear and mode-I interlaminar fracture properties. The tensile strength and mode-I interlaminar fracture toughness of nonwoven composite was increased with increasing punching densities due to the increased fiber entanglement. The flexural, impact, fatigue and wear properties were decreased with punching densities due to the damage to fibers during the punching process which resulted in the reduction of fiber length. The impact resistant properties showed its maximum at the punching density of 30 penetrations/cm2. The tensile modulus and the compression strength were determined from the orientation of the reinforcing fibers which was affected with the punching densities. The mechanical properties of nonwoven composite showed rather isotropic properties with increased random distribution of the fibers at high punching densities. In the range of adequate punching densities, the nonwoven composite showed substantially improved mechanical and impact properties compared to the woven laminate composite. The nonwoven composite showed improved properties of flexural and compression strengths as well as mode-I interlaminar fracture toughness.

Biobleaching effect of xylanase preparation from an alkalophilic Bacillus sp. on ramie fibers

Cellulase-free xylanase from an alkalophilic Bacillussp. was maximally active at pH 10 and 60 °C. Enzyme treatment of ramie fibers removed 40% of its hemicellulose and some chromophoric material which resulted in a brightness increment of 5.2% and boosted the effect of H2O2bleaching. Enzyme-treated ramie fibers were increased by 3.9% in elongation and retained appropriate tenacity. X-ray and scanning electron micrograph studies revealed some changes in fiber structure.

Effect of Stretch-ratio and Heat-treatment at Spinning on Thermo-elastic Properties of Acrylic Fiber in Water.

Relations between quasi-equilibrium stress and temperature under constant length in water have been determined in the range of strain up to 60% for wet-spun acrylic fibers prepared under different spinning condition, and in the range of strain up to 140% for cross-linked acrylic fiber. From analysis of these data, the changes of the entropy component and internal energy component of the fibers with strain were calculated.Quasi-equilibrium stress-strain curves are separated into 2 parts, in which the first elastic region has modulus of 10MPa order, and the second elastic region has modulus of 1MPa order, close to that of natural rubber. In the first region, relatively small stress relaxation and large elastic recovery after stress relaxation are observed.Relaxation of acrylic fibers in steam after stretch in process lowers contribution of energy component and raises glass transition temperature of the fiber. These changes of fiber structure reflect to the lower stress relaxation and the higher elastic recovery.

Changes in fiber structure of Japanese oak silk fibers by the treatment with methacrylamide

Changes in the fiber structure and properties of Japanese oak silk fibers treated with methacrylamide (MAA) were investigated. The cross-sectional area of the Japanese oak silk fiber impregnated with the MAA polymer was given by the sum of the cross-sectional area of the original silk fiber and that of the MAA polymer. Tensile strength and Young's modulus of the Japanese oak silk fibers impregnated with the MAA polymer decreased with increasing polymer add-on. Scanning electron microscopic observations of fracture surfaces of Japanese oak silk fibers impregnated with the MAA polymer revealed that the silk fibers were split into fibrils by the polymerization of MAA infused in the fibers. Wide-angle x-ray diffraction measurements suggested that the destruction of crystallites in the fibers occurred homogeneously, independent of the sizes of the crystallites, by the MAA treatment.

Ultrasound Reversibly Disaggregates Fibrin Fibers

Ultrasound accelerates fibrinolysis in vitro and in vivo, primarily through non-thermal mechanisms including cavitation. We have previously observed that ultrasound reversibly increases flow through fibrin gels, a property primarily determined by the structure of the fibrin matrix. Therefore, the effect of ultrasound on the ultrastructure of fibrin gels was examined using scanning electron microscopy. Non-crosslinked fibrin gels were fixed and prepared for microscopy before, during and after exposure to 1 MHz ultrasound, and quantitative analysis of fiber population density and diameter was performed. Gels exposed and fixed in the presence of ultrasound exhibited an increase in density of 65 +/- 26% (mean +/- SD) at 4 W/cm2 (p <0.000001) accompanied by a decrease in fiber diameter of 27 +/- 9% (p <0.000001). Gels fixed 15 min following ultrasound exposure showed no significant change in either density or diameter compared to unexposed gels, indicating that the ultrasound-induced change in fiber structure was reversible. Factor XIII-crosslinked fibrin gels exhibited no change in population density or diameter when exposed to ultrasound. These results indicate that ultrasound exposure causes reversible disaggregation of uncrosslinked fibrin fibers into smaller fibers, an effect that may alter flow resistance and create additional binding sites for fibrinolytic components, improving fibrinolytic efficacy.

Fine Structure of Chemically Modified Flax Fibre

The changes in fibre structure caused by the realignment of the microfibrils of fibre and yarn samples treated with swelling agents, such as NaOH, LiOH, ZnCl2, and butyltrimethyl ammonium hydroxide (BTMAH), both under tension and slack, were studied by light and electron microscopy. The structural effects of treatment of the microfibrils and the ultimate fibres correlated with the measured variations in fibre tenacity and moisture regain. The results of differential thermogravimetric analysis suggested that structural realignment of the cellulosic crystals had taken place during the treatments.

Fiber Structure Formation in High-speed Melt Spinning of Sheath-Core Type Bicomponent Fibers.

High-speed melt spinning of sheath-core type bicomponent fibers was performed and the change of fiber structure with increasing take-up velocity was investigated. Four kinds of polymers, poly (ethylene terephthalate) (PET), polypropylene (PP), high-density polyethylene (PE) and polystyrene (PS), were selected and three sets of core/sheath combinations, PET/PP, PET/PE and PET/PS, were studied. The structure of each component in high-speed spun bicomponent fibers was analyzed through the birefringence, wide-angle X-ray scattering pattern and DSC thermogram measurements. The development of the molecular orientation and the starting of the orientationinduced crystallization of PET in PET/PP and PET/PE bicomponent fibers occurred at lower take-up velocities as compared to those in the single component spinning. On the other hand, PP in PET/PP fiber showed low orientation pseudo-hexagonal structure at all the take-up velocities investigated and the birefringence of PE in PET/PE fibers obtained at 6km/min was almost negligible, meaning fiber structure formation of PP and PE components was suppressed. On the contrary, in the PET/PS combination, structure formation of PET was suppressed and there was no indication of orientation-induced crystallization even at 7km/min. Oppositely, the molecular orientation of PS component was enhanced. The mechanism of the mutual interaction of two components on structure formation in the high-speed spinning of bicomponent fibers was speculated based on the characteristics of the constituent polymers, and it was concluded that the structure formation of a component having higher temperature-dependent elongational viscosity and higher solidification temperature is expected to be enhanced.

Regional 31P magnetic resonance spectroscopy of exercising human masseter muscle

Changes in fibre structure and function associated with exercise have been quantified ultrastructurally and biochemically in selected limb muscles, but the biochemical events associated with contraction are rarely studied in the human jaw muscles. Here, 31P NMR spectroscopy, or MRS, was used to examine the multipennate masseter in six adult men at rest and while performing isometric clenching exercises. NMR spectra were acquired from three locations within the muscle with a 2 × 3cm, single-turn, copper receiver coil. The spectra, corrected for partial saturation effects, were quantified on the basis of relative peak area and position. The inorganic phosphate (P i) to creatine phosphate (PCr) ratio ( P i PCr ), which has been shown to be indirectly related to the phosphate potential and hence the metabolic activity, as well as pH, were calculated for each site and exercise. The mean resting P i PCr ratio was greater for the deep part of the muscle than for the superficial and intermediate parts; these differences were significant to p < 0.01. The mean pH was similar in all parts of the muscle at rest. During exercise, a significant increase in mean P i/PCr was found in the superficial and intermediate parts of the muscle; both these differences were significant to p < 0.05. An accompanying decrease in mean pH was observed in all parts of the muscle during exercise. In the superficial part, this decrease was significant to the p < 0.05 level, and in the deep part, to the p < 0.001 level. No significant differences were found for these measures between left and right molar clenching. These findings show that metabolic activity may be monitored in the masseter by 31P NMR spectroscopy, and that task-dependent and regional variations may be demonstrated both at rest and during exercise. They are promising enough to encourage future studies of metabolism in subjects with jaw muscle disorders.

Thermomechanical Analysis of the Stress History in Heat Set Nylon 6 Carpet Yarns

Tension effects during a commercial heat setting process were investigated through the analysis of the thermomechanical behavior of heat set nylon 6 carpet yarns. The stress history of these yarns was modified by altering the yarn tension level at various positions along the Superba continuous heat setting process. Changes in fiber structure and morphology were characterized by mechanical testing, shrinkage measurements, differential scanning calorimetry, and thermal stress analysis. A model based on the hypothesis that there are two domains of molecular order that respond differently to the effects of stress, such that structural and morphological changes proceed via two distinct mechanisms, was fit to the experimental shrinkage force-temperature curves and described the experimental curves very well. Changes in the calculated curve parameters were highly correlated with the observed changes in shrinkage and initial moduli. Each of these changes was a function of the tension state of the nylon 6 yarns during the heat setting process. Analysis of the shrinkage force curves and their characteristic parameters showed that this technique is capable of identifying subtle variations in fiber microstructure and therefore has significant applications to the identification of stress history differences in heat set fibers and yams.

Qualitative and quantitative evaluation of chrysotile and crocidolite fibers with IR-spectroscopy: application to asbestos-cement products.

Infrared (IR) spectrophotometry allows simple and quick qualitative and quantitative evaluations of different kinds of asbestos, as well as of other inorganic particles. In particular, chrysotile and crocidolite have characteristic IR spectra and optical density measures of 2,710 nm band for chrysotile, of 12,820 nm band for crocidolite permit quantitative evaluation of each fiber alone or in mixture. IR spectra also give informations about changes of fiber structure and of chemical composition due, for example, to thermal treatment or acid leaching. The analytical method we developed can detect levels as low as 0.1 mg of fiber in a 300 mg disk of KBr using a low cost IR spectrophotometer. The use of a Fourier Transform IR spectrophotometer (FTIR) improves dramatically the sensitivity and selectivity. Computer assisted analysis of spectra offers the possibility to reduce matrix interferences and to compare different spectra. Examples of IR technique applied to asbestos-cement products and insulating materials are presented.

Analysis of the process of sheath expansion in swollen nerve fibers

1. Reactive axon swellings in the proximal stumps of rat sciatic nerves were studied at 1–8 days after transection of the nerves. Sheath thickness and axon circumference were measured in plastic-embedded 1 μm sections; the axon circumference, the number of turns of myelin lamellae in the sheath and the interperiod width were determined in electron micrographs. Measurements in 1 μm sections were a reliable implement for the analysis of pathological fiber population. All data were subjected to statisticak regression analysis by computer. 2. Reconstruction of fibers from serial 1 μm sections showed that reactive axon swellings did not develop in the terminal stump of the fiber, but, rather, at some distance from the stump; the portion distal to the zone of swelling was continuous with the rest of the fiber, and the sheaths were collapsed. 3. Swelling of the axon was accompanied by an increase in axon circumference, a reduction in the number of turns of myelin lamellae, and by an unaltered interperiod width. These data constitute proof of slippage of myelin lamellae. Excessive slippage resulted in denudation of the axon. 4. The changes in fiber structure resulting from different degrees of axonal swelling were calculated; these calculated changes agreed with actual measurements in swollen fibers. Accordingly, the number of turns of myelin lamellae and the axon circumference of a swollen fiber permit determination of the degree of axonal swelling. An estimate of the dimension of the fiber before the onset of swelling is also possible. 5. Fibers with marked slippage of the sheath showed islands of cytoplasm underneath an intact basement membrane. These were interpreted as resulting from sequestration by tearing of the outer mesaxon, which presumably cannot be displaced with the same speed as the myelin leaflets in the sheath can slip. 6. The expansion of the sheath and the denudation of excessively swollen fibers was an acute process, occurring mostly during the first 4 days after cutting; thereafter, the majority of fibers showed normal proportions between axon and sheath, or they were denuded because of excessive swelling. 7. A new technique, using plastic-embedded 1 μm sections, was developed for the demonstration of oxidative enzyme activity in mitochondria. This technique showed swelling of the fiber to correspond to a progressive increase in mitochondrial density in the axoplasm. Maximum mitochondrial density was found in excessively expanded or denuded fibers.

Changes in the T-system of muscle fibres under the influence of influx and efflux of glycerol.

A STUDY of the permeability of isolated frog muscle fibres to glycerol, urea and its derivatives, amides and glycols led to the observation that fibres become filled with vacuoles, clearly visible under the light microscope, when they are returned to Ringer solution after being kept for 30–300 min in Ringer to which 220 mM of one of these non-electrolytes has been added1,2. The changes in fibre structure begin 1–2 min after the fibre has been returned to normal Ringer solution and attain their maximum in 15–20 min. If the fibre is left in Ringer solution, these alterations either persist for many hours or disappear gradually so that 2–4 h later the fibre structure is completely or partially restored to normal. As a rule, however, the vacuolation disappears within 3–10 min if the fibre is returned to the same non-electrolyte solution the washing out of which led to vacuolation in the first place, or if it is transferred to Ringer solution with an equal concentration of another, more slowly penetrating, non-electrolyte.

The effect of oil and air annealing on the structure of drawn poly(ethylene terephthalate)

Oil annealing produces changes in fibre structure of drawn PET not found in air annealing. The results are similar to those found in drawn nylon 66 but there are some differences especially in the effect of annealing on the small-angle intensity. It is suggested that the shrinkage of drawn PET in oil is due to chain folding, or fold regularization of crystals, and to relaxation in the non-crystalline regions.

SOME RESULTS OF HEAT-TREATMENT OF POLYPROPYLENE FIBERS

Polypropylene filaments drawn at 98°C were subjected, under tension or tensionless state, to dry heat-treatment or to wet heat-treatment in polyethyleneglycohol of lower molecular weight, at 100_??_140°C. Shrinking behaviour in heat-treatment and properties of heat-treated filaments, such as density, birefringence, Young's modulus, disperse-dye absorption and shrinkage in boiling water, were observed. The results obtained were as follows.i) Heat-treatment under tensionless state: Filaments shrink more in wet heat-treatment than in dry heat-treatment, and thus birefringence decreases more by the former treatment than by the latter. Density increases by heat-treatment, especially greatly by wet heat-treatment; this is supposed to be caused by the increase of the degree of crystallinity. By wet heat-treatment, however, Young's modulus seems to rather decrease and dye absorption increases remarkably. Dimensional stability to boiling water is better for filaments wet-heat-treated than for those dry-heat-treated.ii) Heat-treatment under tension: The effect of heat-setting is more remarkable in wet heattreatment than in dry heat-treatment. The increase of the tension in the treatment increases the density and Young's modulus.iii) The above tendencies are increased with rising temperature of treatment, especially greatly above 120°C. We may conclude, therefore, that the optimum temperature of heat-treatment for polypropylene fibers is 120_??_130°C. Furthermore changes in fiber structure by heat-treatment were discussed, in connection with the role of heating medium for loosing the packing of intermolecular structure in the amorphous regions.

CHANGE IN FIBRE STRUCTURE OF VISCOSE FIBRES BY TREATMENT WITH CAUSTIC SODA SOLUTIONS

Changes in fibre structure of viscose fibres during treatment with caustic soda solutions of various concentrations and during subsequent drying have been investigated experimentally.Degrees of crystallinity of fibres after swelling and deswelling were determined with iodine absorption method and relative sizes of void betwden crystalline areas were estimated by measuring equilibrium dye absorption, and following facts were observed:(1) After swelling treatment fibres show maximum incvease in crystallinity at NaOH concentration 4_??_6%; below concentration 4_??_6% they crystalize, in the range of above 4_??_6% they decrystalize, and this decvystallizing effect becomes constant approaching 12%.(2) After deswelling fibres show gradual increase in crystallinity in proportion to NaOH concentration due to the recrystallization of cellulose during dehydration, in consistence with previous works. This recrystallizing effect is much greater in fibres more decrystallized by swelling.(3) Increase in dye absorption is observed after both in swelling and deswelling. Dye absorption decrease by deswelling treatment, but the increased absorption by swelling treatment is irreversible.