Fine structural characteristics and physical properties of raw silk

Summary The theories of KRATKY, DEBYE and BUESCHE and POROD have been applied to evaluate macromolecular parameters which speak of the fine structural characteristics of raw silk — a natural polymer in the solid state. The small-angle KRATKY camera has been utilised for the measurements of the scattering intensities. The macromolecular parameters evaluated are the percentage of void (w₁), the specific inner surface (O/V), length of coherence (1_c), range of inhomogeneity (1_r), transversal length –s – and which were found to be equal to 0.13%, 25.15 × 10^–4 Å^–1, 21.84 Å, 2.11 Å, 1.59 × 10³ Å and 2.11 Å respectively The physical properties as evaluated by Scott's IP2 Tester have been reported.     

Effect of Functionalization of Lignocellulosic Fibers on Their Physico-Chemical and Thermal Properties

In this paper Agave fiber has been functionalized through graft copolymerization and physico-chemical and thermal properties have been investigated. The graft copolymerization of methyl methacrylate and acrylonitrile onto Agave americana fibers was carried out under pressure using ceric ammonium nitrate as redox initiator. The chemical resistance studies were carried out in hydrochloric acid and sodium hydroxide. Water absorption studies were also carried out by exposing grafted fibers to accelerated weathering under different humidity levels ranging from 40 to 95%. Characterization of functionalized fibers was done through Fourier Transform Infra Red spectroscopy, scanning electron microscopy, and X-ray diffraction techniques.     

Coalescence of an emulsion in a fibrous bed: Part II. Experimental

A model of a fibrous bed relating the ratio of the outlet and inlet particle number densities to the various system parameters is tested experimentally. The degree of bed saturation is also determined from single phase and two phase flow data. The inlet and outlet particle number densities are determined by light scattering. It was found that the model does predict the effect of particle size, fiber size, bed length, and degree of saturation consistent with experimental observations. However, the coalescence efficiency based upon aerosol filtration theory is not amenable to the fibrous bed over the widest range of flow velocities.     

Physical and mechanical properties of henequen fibers

A study of morphology, physical, and mechanical properties of henequen (Agave fourcroydes) fibers have been performed in this article. It has been concluded that properties of the fibers are more uniform in their middle section. As other natural hard fibers, henequen has a relative high tenacity, low elongation at break and a low modulus. These properties suggest that the fiber could be used as reinforcing agent in composite materials.     

碳纤维中微孔缺陷的小角X射线散射研究方法

碳纤维的小角X射线散射表明存在沿纤维轴方向取向的针形微孔。应用小角X散射可以得到微孔的尺寸和分布等的信息。文章主要阐述了微孔长度L、取向角Beq,孔隙率P,回转半径Rt,横截面积S等参数的计算方法。     

Structure change of carbon fibers during axial compression

In situ wide-angle X-ray diffraction and small-angle X-ray scattering measurements have been performed during axial compression tests of composite strands of polyacrylonitrile-based carbon fibers with varying carbon layer stacking height and the changes in the crystallite and the microvoid structure have been analyzed. The longitudinal length of microvoids, the orientation parameter of the carbon layer stacks and the orientation parameter of the microvoids decreased almost linearly with increasing axial compression stress of the fiber. The decrease in the longitudinal length of microvoids up to the compression fracture of the fiber was in the range of about 4–10%, which was larger than the macroscopic compression fracture strain of the fiber. This indicated that a deformation larger than the macroscopic fiber strain arose in a local region of the fiber structure reflecting the deformability of the local microtexture. The axial compression strength of carbon fibers was calculated based on the equation proposed in a previous study using the measured values of the microvoid length. As compared with the strengths calculated using the initial longitudinal lengths of microvoids, the strengths calculated using the lengths at the compression fracture of the fibers showed better agreement with the measured strengths.     

Relationship between axial compression strength and longitudinal microvoid size for PAN-based carbon fibers

Single fiber axial compression strength has been determined on a series of polyacrylonitrile-based carbon fibers using micro compression test at a gage length of about 10 μm and a detailed analysis has been made on the distribution and the fiber diameter dependence of the axial compression strength. The length of the unsupported region of carbon layer stack calculated from the axial compression strength was well comparable with the longitudinal length of the microvoids determined with small-angle X-ray scattering. This indicated that the fracture of carbon fibers is initiated from the buckling of the unsupported region of carbon layer stack which is formed where the microvoid adjoins it. The tensile and the axial compression strengths of the carbon fibers showed different relationships between the coefficient of variation and the average. This indicated that the tensile and the axial compression strengths are governed by different factors although they showed a correlation. Comparison has also been made between the longitudinal length of the microvoid and the microvoid sizes perpendicular to the fiber axis.     

Experimental characterization of the alignment of short fibers during flow

An experimental approach has been made to investigate and characterize the alignment of short fibers contained in a suspension, during flow of the suspension through a convergent channel. Flow patterns have been obtained and analyzed for suspensions of various fiber concentrations. The influence of parameters such as fiber length, volume fraction and viscosity of the carrier medium on the degree of fiber alignment, has been examined. In order to minimize jamming, the viscosity of the carrier medium must be larger than a certain critical viscosity that is dependent on fiber length and volume fraction.     

Dynamic mechanical analysis and image analysis characterization of crimped yarns

The Quantimet image analysis system and dynamic mechanical analysis have been applied to characterization of crimped yarns. The image analysis system is useful for obtaining accurate measurements of crimps per inch, uncrimped versus crimped length, crimp wavelength, and crimp amplitude. In addition, the dynamic tensile mechanical properties of fibers and the dynamic compression mechanical properties of the fiber masses were examined. These analyses identify the relationships between crimp parameters and loss tangents for the first time. The loss tangents of fiber masses increase with increasing crimp frequency. The higher loss tangents of crimped yarns in the glassy region quantify both the internal friction of constituent fibers and the external fiber to fiber friction separately.     

Kinetic Modeling Study on Methylene Blue Sorption onto Agave americana fibers: Fractal Kinetics and Regeneration Studies

Kinetics sorption study was carried out with varying pH, concentration, and temperature to determine the potential of Agave americana fiber for the removal of methylene blue. The thermodynamic properties (ΔG°, ΔH° and ΔS°) were determined. In order to investigate the sorption mechanisms, kinetic parameters were determined using the Lagergren, the pseudo-second order and the recently established fractal kinetic equations. The experimental kinetics data have been fitted with the non linear form of the new Brouers sotolongo kinetic model. Fractal kinetic equation gives higher correlation coefficients, indicating that this model can be considered accurate for describing the sorption methylene blue kinetics.     

Absorption of steam and water at ambient temperature in wood polymer composites prepared from agro-waste and Novolac

Banana (Musa paradisica), Hemp (Hibiscus cannabinus), and Agave (Agave jourcroydes) fibers were treated with Novolac resin for the formation of their composites in the ratio of 50 : 50 (wt/wt). These fibers were also treated with maleic anhydride, and it was found that composites based on treated fibers showed higher absorption of steam (at 100°C) up to 12 h; and beyond 18 h, it is less than the untreated fiber composites. However, at ambient temperature, the absorption of water is lesser for composites based on maleic anhydride-treated fiber than for composites based on untreated fibers. The SHORE-D hardness was commonly higher for composites based on maleic-anhydride-treated fibers. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1417–1421, 1998     

Characterization and modeling of direct-write fabrication of microscale polymer fibers

A new direct-write system for fabricating suspended microscale and sub-microscale polymer fibers has been developed and characterized. This system is capable of generating arrays of precisely-positioned fibers with controllable diameters in three-dimensional space. The driving mechanism behind this process harnesses the surface tension of liquid bridges to promote the controlled thinning of a macroscale polymer solution filament into the desired micro- or sub-microscale fiber. The correlation between fiber diameter and several experimental parameters including solution concentration, drawing rate, and fiber length was characterized using a series of viscous poly(methyl methacrylate) (PMMA) solutions. A dimensional analysis of the physics of the fiber drawing process was used to adapt this data into an empirical relationship describing fiber formation from a generalized polymer solution. This information was subsequently utilized to predict fiber diameter from several other non-PMMA-based polymer solutions with accuracy comparable to the intrinsic variation of the process itself, thereby eliminating the need to perform lengthy characterizations on new polymer solutions.     

Agave lechuguilla Torrey fiber as reinforcement of polyester resin

This study was aimed to evaluate the application of lechuguilla fiber (Agave lechuguilla Torrey), with no treatment, as reinforcement of polyester resin. Mechanical assays and pull‐out tests were performed on specimens of one fiber and strands of 10 fibers and on lechuguilla fiber/polyester composites and polyester matrix alone. The results indicated that there was no important improvement in composite rigidity, as the Young's modulus in both the fiber and the polyester resin were similar; however, an important improvement in composite resistance, in respect to the matrix alone, attributed to a good interfacial adherence fiber‐matrix, was observed. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Simulating fiber distribution in thin sheets

A model is presented that simulates on a microcomputer the fiber distribution in a planar arrangement applicable to thin sheets of composites. Although it does not take into account spatial fiber interference, the software allows one to investigate a number of important design parameters. The inputs used in the simulation are: thickness of the composite sheet, diameter and volume fraction of fibers along with fiber length, and angular position which can be specified in a number of ways. The program utilizes the internal random function to depict each fiber, as it is generated, in a “simulation window” of the monitor while the mathematics of the system are being done simultaneously within the smaller “valid window”. The procedure prescribes that the center of gravity of all fibers be uniformly distributed over the simulation window area. For that reason and because the 2D model is extended to simulate a three-dimensional sheet, results will represent the ideal configuration or upper bonds of a corresponding practical case. Graphical representations and statistics are thus produced to quantify the geometric pattern of the system. One use of the model is, for instance, to see how the geometric patterns and their associated statistical parameters compare at a given volume fraction when the fiber length is fixed or when fiber length can be modeled as a normal, a uniform, or another specific distribution.     

Theoretical Analysis of the Fiber Pullout and Pushout Tests

The fiber pullout and pushout tests have been analyzed to predict the load-displacement behavior in terms of fiber/matrix interface parameters. The effects of residual axial strain in the fiber and fiber surface topography were included. The residual axial strain was found to be a significant parameter. It is shown that the interface failure can be progressive or catastrophic. In the case of a progressive failure of the interface, the load-displacement curve is nonlinear. The portion of the curve from above the first nonlinearity to near the peak load can be predicted in terms of parameters of the interface, viz., the friction coefficient, the radial stress at the interface, the fracture toughness of the interface, and the residual axial strain in the fiber. Values for these parameters can be obtained from a single loaddeflection curve. The peak load and load drop, which are usually reported, are found not to be directly relatable to any interface property, since the length of the last portion of the fiber to debond is influenced by end effects and hence not easily predicted. However, for data which describe the peak load as a function of initial embedded length, that factor can be eliminated and the data reduced to yield the relevant interface parameters. In pullout, the peak and friction loads saturate with large specimen thickness. Catastrophic failure is favored when the debond initiation load is high or when residual stress is low. Finally, a methodology to extract interface parameters from experimental data is suggested.     

Mullite—Alumina Composites by Extrusion

The rheological properties of a paste containing chopped alumina fiber and particulate silica suspended in a gelled boehmite liquid phase have been evaluated using a physically based extrusion model. When sintered, the paste formed a mullite-alumina fiber composite. Extrudates with fiber volumes up to 30% in the sintered product were prepared. During extrusion, the pressure drop was largely independent of extrudate velocity, fiber length, and the fiber concentration. All pastes showed significant yield behavior leading to good postextrusion shape retention. For any given fiber length, it was shown that there exists a critical volume fraction above which fiber-fiber interactions are so great that both yield and wall shear stresses increase. At these high concentrations of fiber, inhomogeneities also increase. Up to the critical volume fraction, dispersed wet fibers produced lower extrusion parameters than when dry fibers were used as the starting material. The observed behavior is explained in terms of low viscosity liquid formation above the yield point of the boehmite gel.     

Mechanical degradation of glass fibers during compounding with polypropylene

The objective was to study the fiber length degradation during compounding of glass fiber with polypropylene. The effect of parameters such as viscosity, total work, concentration on fiber length and dispersion was studied using an automatic particle size analyzer. The length degradation is most severe during the very first stage of the process, i.e., when fiber bundles are being filamentized. The mode of glass fiber incorporation into the melt (fiber addition to the molten resin versus to polypropylene powder prior to compounding) was found to have no effect on the final fiber length. Matrix resin viscosity affects the fiber length significantly. Concentration dependencies of fiber length for different times of compounding suggest that the degradation results from both fiber-fiber and fiber-melt interactions.     

Spinning of hydroalcoholic chitosan solutions: Mechanical behavior and multiscale microstructure of resulting fibers

The morphology and mechanical properties of chitosan fibers obtained by spinning of hydroalcoholic (1,2propanediol/water) chitosan solutions of low DA and high molecular mass are reported. The impact of processing parameters on final fiber properties, such as fiber stretching at different steps of the spinning process, is investigated. A stretching ratio applied during the fiber coagulation appeared to have no significant effect on mechanical properties, whereas fiber drawing after the coagulation step, that is, during the washing step was a key parameter for the control of macromolecular orientation, fiber tenacity, and Young's modulus. The microstructure and morphology of the various as-spun chitosan fibers were studied by means of wide-angle and small-angle X-ray scattering and scanning electron microscopy. Microstructure impacts mechanical properties from the interplay of different deformation mechanisms acting at different length scales of the microstructure, namely the macromolecular orientation, the semicrystalline morphology, and the core–shell structure. The obtained monofilament fibers (45–70D) can be knitted. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47130.     

Effect of initial fiber length on the rheological properties of sisal fiber/polylactic acid composites

The rheological properties of sisal fiber (SF)/polylactic acid (PLA) composites of different SF content and initial fiber length were evaluated using a torque rheometer. Since the SF configuration directly affected the rheological properties of the composites, the length and width of SFs in the final composites were measured. The effect of fiber content, angular velocity, and initial fiber length on the fiber aspect ratio (length to width ratio) and composite rheological properties were analyzed. Initial fiber length significantly affects the rheological properties of SF/PLA composites at low SF content, while fiber content predominantly affects rheological properties at high SF content, and rheological parameters are similar for the composites of different initial fiber length. The average shear stress and mixing temperature are affected by feeding speed for composites of very high SF content. POLYM. COMPOS., © 2011 Society of Plastics Engineers.