Analysis of an image processing method for fiber orientation in polymer composites

The errors in fiber orientation distribution measurements of compression molding materials have been investigated, for generated as well as for real distributions. Because of the size of the sample, only a finite number of fibers are visible in a picture leading to a statistical error in the measurement. A method is proposed to express this error as function of the number of visible fibers and the number of subintervals the distribution is divided into. Studies of the error In a Fraunhofer/FT based fiber orientation distribution analysis have been performed, including effects of increasing number of fibers (fiber‐fiber intersections) in generated pictures and investigation of the errors in real fiber images. All steps in a fiber orientation distribution analysis of SMC/GMT kind of material are described, including suitable equipment, image enhancement methods and investigation of the errors present in analysis of a real image as well as comparisons to hand–measured data.     

Nylon fiber reinforcement for polyurethane composites

The potential of a nylon 6 fiber was evaluated for composite applications involving rigid polyurethane systems. A study showed that the use of COMPET N, a nylon 6 based fiber surface treated to enhance wetout and adhesion, in an ISP polyurethane system results in composites with higher impact values and lower weight than those reinforced with glass fiber. A 2 percent loading of COMPET N matt increased impact values by more than 300 percent over an unreinforced control while a 3 percent loading of glass matt resulted in increases of less than 100 percent. A drop impact test showed COMPET N fabric reinforced composites to absorb twice as much energy as an unreinforced and glass reinforced composite without major damage. These advantages have also been observed in COMPET N/Glass hybrids, in which layer orientation can be used to produce composites with specific properties. Cut fiber reinforced composites were found to exhibit similar properties as fabric reinforced ones resulting in the commercialization of a canoe end cap containing cut nylon fiber. Additional property benefits such as improved impact fatigue and decreased stress cracking have also been observed in nylon 6 reinforced composites resulting in the consideration of these materials for a wide range of applications.     

A Wide-angle X-ray diffraction method of determining chopped fiber orientation in composites with application to extrusion through dies

A method of determining fiber orientation in composites using wide-angle X-ray diffraction (WAXS) is described. Oriented crystalline fibers are suspended in an amorphous polymer matrix. The WAXS reflects characteristics of the fiber are used to determine the mean orientation and orientation distribution of the crystallographic axes representing the polymer chain relative to preferred axes located in the test specimen. The chain direction crystallographic axis is taken as representing the fiber axis, and the orientation of this axis to represent the orientation of the fibers. Experimental studies were carried out using Kevlar (poly(p-phenylene terephthalamide)) fibers suspended at a 20 volume percent loading in a polymethyl methacrylate matrix. The Kevlar fibers had Hermans orientation factors of 0.92. Specific attention is given to how through circular dies. We have examined both extrudates and the material frozen-in when the composite in the reservoir and die is cooled to room temperature. Fiber orientation factors, corresponding to Hermans orientation factors, 0.3 to 0.38 were obtained for the extrudates. Orientation factors for fibers within the die is about 0.45. Specially prepared completely oriented samples had orientation factors of 0.93, which closely corresponds to the orientation of the fiber.     

Future prospects for wood cellulose as reinforcement in organic polymer composites

Wood cellulose, a versatile and renewable natural resource, has potential for use as a reinforcement for synthetic organic polymers. During the past 80 years a number of materials using the reinforcing properties of wood cellulose have found major markets. Forms of wood cellulose proposed as reinforcements include: wood fibers, cellulose fibers, microfibillar, and microcrystalline cellulose. Recent attention has been given to them as fillers/reinforcements in thermoplastics and elastomers. Most cellulosic composites derive their existence from their comparatively low materials cost and the filling rather than reinforcing properties of cellulose. However, cellulose chains have a potential stiffness much higher than glass and in the same range as superstiff aramid fibers. This paper examines the state of the art of combining wood cellulose with synthetic organic polymers to from composites and considers new ways for better using cellulose's reinforcing potential.     

Effect of fiber orientation on viscoelastic properties of polymer matrix composites subjected to thermal cycles

Fibers in polymer composites can be designed in various orientations for their usage in service life. Various fiber orientated polymer composites, which are used in aeroplane and aerospace applications, are frequently subjected to thermal cycles because of the changes in body temperatures at a range of −60 to 150°C during flights. It is an important subject to investigate the visco‐elastic properties of the thermal cycled polymer composite materials which have various fiber orientations during service life. Continuous fiber reinforced composites with a various fiber orientations are subjected to 1,000 thermal cycles between the temperatures of 0 and 100°C. Dynamic mechanic thermal analysis (DMTA) experiments are carried out by TA Q800 type equipment. The changes in glass transition temperature (T_g), storage modulus (E′), loss modulus (E′′) and loss factor (tan δ) are inspected as a function of thermal cycles for different fiber orientations. It was observed that thermal and dynamic mechanical properties of the polymer composites were remarkably changed by thermal cycles. It was also determined that the composites with [45°/−45°]_s fiber orientation presented the lowest dynamic mechanical properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Electrical conductivity model evaluation of carbon fiber filled liquid crystal polymer composites

Electrically conductive resins may have applications as fuel cell bipolar plates. The current trend in this technology is a thermosetting polymer as the matrix containing high concentrations of various types of fillers. These fillers are carbon based and electrically conductive powders, particles, or fibers. In this study, we utilized two composite formulations of polyacrylonitrile fibers (Fortafil 243 and Panex 30) in a liquid crystal polymer (Vectra A950RX) with increasing concentrations. Electrical conductivity tests were performed and modified Mamunya and additive models were applied to the experimental data. These models fit the entire range of data for each composite tested. Four alternate models were also produced: linear, quadratic, exponential, and geometric, with a restricted range of electrical conductivity data greater than 10^?2 S/cm. The exponential and the geometric resulted in the best fits over this restricted data range. These particular models may allow researchers to extrapolate beyond the maximum filler concentrations studied here. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Prediction of elastic properties for curved fiber polymer composites

The objective of this article is to study the effect of fiber curvature on the elastic properties of a long‐fiber composite. The study was carried out using a unit cell homogenization approach and micromechanical modeling. In the first approach, a unit cell with a fiber bundle was defined and used in the analysis. Appropriate boundary conditions were prescribed to extract the elastic stiffness components. The second approach made use of the Eshelby‐Mori‐Tanaka model to compute the stiffness of the aligned fiber composite. Fiber curvature was then accounted for through the variation of fiber orientation within a prescribed range that corresponds to a given degree of fiber curvature. It was found that curved fibers significantly affect the composite properties since they lead to a significant stiffness reduction in the longitudinal direction while relatively small increase in stiffness is achieved in the transverse direction in the plane containing the fiber tow. POLYM. COMPOS., 2008. Published 2008 Society of Plastics Engineers     

Moisture absorption phenomenon in permeable fiber polymer composites

Studies were conducted on the moisture absorption characteristics of jute fiber composites based on polyester and epoxy resin systems, under constant humidity (ø) and ambient temperature (T) conditions. The initial slope of the moisture absorption curve (a direct measure of the composite diffusivity) increased with increased superficial fiber volume fraction (V_f), where as the time (t_m'), needed to reach the equilibrium moisture absorption value showed a reversed trend. This behavior is just a reverse to that observed¹ in case of composites with practically impermeable fibers (e.g., glass and graphite) in the same resin matrices. The theoretical expressions governing moisture diffusion phenomenon in impermeable fiber composites were modified and analyzed for the case of composites containing a permeable fiber. The experimental data obtained on the latter were then discussed in relation to the modified theory. The meaning of a correct fiber volume fraction (V_f,) as applicable to permeable fiber composites was defined.     

Liquid crystal polymer-carbon fiber composites. Molecular orientation

The objective of this work has been to study composite systems in which carbon fibers are dispersed in a liquid crystal polymer matrix. The fundamental point of interest here has been the interfacial response that fiber surfaces can potentially induce in self-ordering polymers. The matrix material used was a thermotropic liquid crystal polyester synthesized in our laboratory from the monomers p-acetoxybenzoic acid, diacetoxyhydroquinone, and pimelic acid. The aromatic-aliphatic polymer was characterized by NMR as a chemically disordered polymer of the three structural units which exhibits a nematic phase at temperatures above 150°C. Breadline proton NMR above the solid to liquid crystal transition was used to measure the rate of magnetic alignment of molecules in the matrix and polarized optical microscopy was used to analyze interfacial zones in composite samples. Fiber surfaces were found to influence the orientation and orientational dynamics of a liquid crystal polymer matrix. This was revealed by enhanced rates of magnetic orientation in the polymer melt when carbon fibers are dispersed in the medium. Fiber surfaces were also found to stabilize nematic ordering of the polymer as the melt was heated towards complete isotropization. The phenomena discovered here may originate in the development of zones around fibers with a common molecular orientation anchored by the carbon surface.     

Novel ceramic matrix composites with tungsten and molybdenum fiber reinforcement

Ceramic matrix composites usually utilize carbon or ceramic fibers as reinforcements. However, such fibers often expose a low ductility during failure. In this work, we follow the idea of a reinforcement concept of a ceramic matrix reinforced by refractory metal fibers to reach pseudo ductile behavior during failure. Tungsten and molybdenum fibers were chosen as reinforcement in SiCN ceramic matrix composites manufactured by polymer infiltration and pyrolysis process. The composites were investigated with respect to microstructure, flexural- and tensile strength. The single fiber strengths for both tungsten and molybdenum were investigated and compared to the strength of the composites. Tensile strengths of 206 and 156 MPa as well as bending strengths of 427 and 312 MPa were achieved for W/SiCN and Mo/SiCN composites, respectively. The W fiber became brittle across the entire cross section, while the Mo fiber showed a superficial, brittle reaction zone but kept ductile on the inside.     

Newsprint paper waste as a fiber reinforcement in rubber composites

The investigation of the economical use of lignocellulose waste, which is one of the environmental problems facing third‐world nations, is ongoing. In this study, we intended to increase the use of newsprint fibers in the rubber industry. For this reason, we treated newsprint fibers with sodium silicate and magnesium chloride, and we examined the water retention values and thermal degradation analyses of the treated fiber waste. The activation energy of degradation was evaluated with the Coats–Redfern method of analysis. The effects of the addition of different amounts [0–60 parts per hundred parts of rubber by weight (phr)] of untreated and treated newsprint fibers on both the electrical and mechanical properties of two different types of rubber (natural rubber and acrylonitrile rubber) were studied. This study led us to the conclusion that the addition of treated newsprint fiber waste at a concentration of 40 phr could lead to an end product characterized by good electrical and mechanical properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 469–478, 2004     

Newsprint paper waste as a fiber reinforcement in rubber composites

The investigation of the economical use of lignocellulose waste, which is one of the environmental problems facing third‐world nations, is ongoing. In this study, we intended to increase the use of newsprint fibers in the rubber industry. For this reason, we treated newsprint fibers with sodium silicate and magnesium chloride, and we examined the water retention values and thermal degradation analyses of the treated fiber waste. The activation energy of degradation was evaluated with the Coats–Redfern method of analysis. The effects of the addition of different amounts [0–60 parts per hundred parts of rubber by weight (phr)] of untreated and treated newsprint fibers on both the electrical and mechanical properties of two different types of rubber (natural rubber and acrylonitrile rubber) were studied. This study led us to the conclusion that the addition of treated newsprint fiber waste at a concentration of 40 phr could lead to an end product characterized by good electrical and mechanical properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3410–3420, 2004     

A model for estimation of electromechanical characteristics of piezoelectric polymer composites

The constitutive equations, of piezoelectric polymer composite materials used for their electromechanical characterisation are complicated and their analytical solution is difficult. Earlier models assumed either stress or strain components to be constant. In this paper we present a model for electromechanical characterisation of piezoceramic polymer composites. The assumptions are (i) the samples have complete stress free boundary conditions at the polymer piezoelectric interfaces, (ii) the materials are lossless, (iii) the co-ordinate axes are pure mode propagation directions and (iv) the electric potential and the displacements are assumed to be independent degrees of freedom. Based on these assumptions, expressions for impedance, phase velocities and electromechanical coupling constant are developed for piezoelectric polymer composites.     

A radial infusion model for transverse permeability measurements of fiber reinforcement in composite materials

The goal of this article was to develop a method for simultaneously determining the principal values of an unsaturated permeability tensor for fibrous reinforcements which accounts for finite dimension of the inlet gate, when its diameter is comparable or larger than thickness of a fabric preform. An analytic solution for the direct problem of liquid spreading in a transversely orthotropic fabric preform is derived and analyzed. This solution is compared with a point source approximate solution used by other authors. Algorithms for evaluating the principal components of transverse and equivalent in-plane permeability are proposed. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Effect of additives on reinforcement of radiation-induced jute-urethane polymer composites

Thick polymer film was prepared under gamma irradiation using urethane acrylate in the presence of N-vinylpyrrolidone, ethyl hexyl acrylate, and trimethylol propane triacrylate. Both jute dust and hessian cloth (jute fabric) were used to constitute composites based on the prepared resin matrix. Some of their physical and mechanical properties were studied. Some additives such as acetic acid, acrylamide, urea, talc, and titanium oxide were incorporated into the formulation to investigate their effect on the physical and mechanical properties. Water absorption and weathering resistance of the resin and composites were also investigated. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 79–85, 1998     

Research progress of basalt fiber reinforced polymer composites

玄武岩纤维的综合性能优异,是聚合物复合材料的理想增强体,在高强度、耐高温、耐酸碱腐蚀、耐烧蚀和耐摩擦等特殊领域展示了良好的应用前景。本文对玄武岩纤维聚合物基复合材料研究中的纤维与基体的界面改性、不同聚合物基体的复合材料以及玄武岩纤维与其它纤维的混杂三个方面进行了综述。目前对于玄武岩纤维界面性质的基础研究深度不足,有些复合材料的研究和制备方法还没有应用于玄武岩纤维上,使得玄武岩纤维复合材料的优势还没有得到充分的发挥。因此,应结合玄武岩纤维及其复合材料的特性,开发适用性强的和性价比好的产品,扩大应用范围。     

Wide-angle X-ray scattering study of crystalline orientation in reticulate-doped polymer composites

Reticulate doping consists of casting a composite film from a solution containing both a polymer and a charge-transfer complex (CTC) and allowing the conductive free radical salt to recrystallize as the solvent is removed from the polymer. In this study, a highly branched, low molecular weight polyethylene (PE) was doped with the CTC tetrathiafulvalene–tetracyanoquinodimethane (TTF–TCNQ). Wide-angle X-ray scattering (WAXS), conductivity, optical microscopy, stress relaxation, and differential scanning calorimetry (DSC) measurements were used to show the effect of the addition of filler and uniaxial orientation on the mechanical and electrical properties of the composites. It has been shown that increasing TTF–TCNQ concentration shifts the preferential orientation of the crystalline phase of the PE from slightly perpendicular to slightly parallel to the casting surface. WAXS measurements were made on samples that were uniaxially stretched at 80°C and cooled to room temperature. These experiments showed a smaller incremental increase in crystalline orientation with increasing TTF–TCNQ. This observation was consistent with a drop in initial relaxation times calculated from room temperature stress relaxation experiments. In the unoriented composites, increasing TTF–TCNQ loading had no effect on PE crystallinity; however, the increase in crystallinity caused by uniaxial stretching was decreased by the presence of TTF–TCNQ. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1785–1794, 1998