Fiber orientation control of short‐fiber reinforced thermoplastics by ram extrusion

In this study we examine the fiber orientation distribution, fiber length and Young's modulus of extruded short‐fiber reinforced thermoplastics such as polypropylene. Axial orientation distributions are presented to illustrate the influence of extrusion ratio on the orientation state of the fibrous phase. Fibers are markedly aligned parallel to the extrusion direction with increasing extrusion ratio. The orientation state of extruded fiber‐reinforced thermoplastics (FRTP) is almost uniform throughout the section. The control of fiber orientation can be easily achieved by means of ram extrusion. Experimental results are also presented for Young's modulus of extruded FRTP in the extrusion direction. Young's modulus follows a linear trend with increasing extrusion ratio because the degree of the molecular orientation and the fiber orientation increases. The model proposed by Cox, and Fukuda and Kawada describes the effect of fiber length and orientation on Young's modulus. The value of the orientation coefficient is calculated by assuming a rectangular orientation distribution and calculating the fiber distribution limit angle given by orientation parameters. By comparing the predicted Young's modulus with experimental results, the validity of the model is elucidated. The mean fiber length linearly decreases with increasing extrusion ratio because of fiber breakage due to plastic deformation. There is a small effect on Young's modulus due to fiber breakage by ram extrusion.     

Toughness optimization of elastomer‐modified glass–fiber reinforced PA6 materials

To investigate the influence of moisture and EPR‐g‐MA content on the fracture behavior of glass–fiber reinforced PA6 materials, brittle‐to‐tough transition temperatures (T_btt) were determined. Water absorption was taken into account by conditioning the analyzed materials. Tensile tests could reveal the temperature range of the largest moisture dependence of mechanical properties between 10 and 50°C. J‐integral values were used to describe the fracture behavior under conditions of impact load as a function of temperature. The brittle‐to‐tough transition of reinforced polyamides was found to be less approximate than in unreinforced materials. Two different characteristic temperature points T_s and T_e were identified, which were the intercept between elastic and elastic–plastic deformation on the one hand and the starting point of dominating stable crack propagation with strong plastic deformation on the other hand. Characteristic brittle‐to‐tough transition temperatures T_btt could be calculated as the arithmetic average of these two points. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Swelling of glass‐fiber reinforced polyamide 66 during conditioning in water,ethylene glycol,and antifreeze mixture

The weight and dimensional changes of injection‐molded glass‐fiber reinforced polyamide 66 composites based on two glass fiber products with different sizing formulations and unreinforced polymer samples have been characterized during conditioning in water, ethylene glycol, and a water‐glycol mixture at 50°C and 70°C for a range of times up to 900 h. The results reveal that hydrothermal ageing in these fluids causes significant changes in the weight and dimensions of these materials. All conditioned materials showed a time dependent weight and dimension increase. The change observed in water could be well modeled by a simple Fickian diffusion process; however, the absorption process followed a more complex pattern in the other conditioning fluids. It was not apparent that changing the glass fiber sizing affected the dimensional stability of the composites under these relatively mild conditions. There was a strong correlation between the swelling of these samples and the level of fluid absorption. The composites exhibited highly aniosotropic levels of swelling. These effects were well in line with the influence of fibers on restriction of the matrix deformation in the fiber direction. The polymer and composite swelling coefficients correlated well with data previously obtained at higher conditioning temperatures. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Water absorption and hygrothermal ageing of ultraviolet cured glass‐fiber reinforced acrylate composites

In this article, an ultraviolet curable glass fiber reinforced polymer (UV‐GFRP) composite developed for fast repair or strengthening of concrete structures, was investigated on its water absorption and hygrothermal ageing behaviors. Cured UV‐GFRP coupons were subjected to immersion in distilled water or concrete pore solution (pH value around 13) for 4–8 months at room temperature and elevated temperatures (40 and 60°C), respectively. Water absorption and thermomechanical properties of the samples were tested as a function of immersion time. Water uptake curves of UV‐GFRP exposed to elevated temperatures and/or alkaline solutions show serious mass loss. Debonding of fibers from resin matrix brought in increased coefficient of diffusion along fiber directions, due to the capillary effect. After 4 months of immersion in both media, the tensile strength of UV‐GFRP was deteriorated remarkably, while the tensile modulus was less affected. According to Arrhenius equation, the tensile strength of UV‐GFRP is predicted to remain 77.6% of its original value after50 years when immersed in water at 20°C, but only 24.5% left in the case of alkaline solution. This suggests that the present UV‐GFRP system does not suit for the application in strong alkaline environments. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Investigation of fiber orientation states in injection‐compression molded short‐fiber‐reinforced thermoplastics

Injection‐compression molding (ICM) has received increased attention because of its advantages over conventional injection molding (CIM). This article aims to investigate the effects of five dominating ICM processing parameters on fiber orientation in short‐fiber‐reinforced polypropylene (SFR‐PP) parts. A five‐layer structure of fiber orientation is found across the thickness under most conditions in ICM parts. This is quite different from the fiber orientation patterns in CIM parts. The fibers orient orderly along the flow direction in the shell region, whereas most fibers arrange randomly in the skin and the core regions. Additionally, the fiber orientation changes in the width direction, with most fibers arranging orderly along the flow direction at positions near the mold cavity wall. The results also show that the compression force, compression distance, and compression speed play important roles in determining the fiber states. Thicker shell regions, in which most fibers orient remarkably along the flow direction, can be obtained under larger compression force or compression speed. Moreover, the delay time has an obvious effect on the fiber orientation at positions far from the gate. However, the effect of compression time is found to be negligible. POLYM. COMPOS., 31:1899–1908, 2010. © 2010 Society of Plastics Engineers.     

Injectin molding of short fiber reinforced thermoplastics in a center‐gated mold

We have studied injection molding of a rectangular box using short fiber reinforced polypropylene. The fiber orientation distribution and the local stiffness properties in radial and transverse directions have been measured in the bottom plane. The deduced orientation tensors are compared with predictions of a commercial computer code. Discrepancies are related to approximations made in the calculations and effects not accounted for by the present modeling approach. In the calculations the fiber interaction coefficient was varied seeking to fit experiments. We comment on the out‐of‐plane components of the orientation tensor, the relative thickness of skin and core layers, and the radial dependence of the fiber orientation in each layer. Values of the components of the 4^th‐order orientation tensor calculated from the measured orientation distribution are used to compare different closure approximations referred in the literature. Anisotropy in the stiffness properties, calculated form the measured fiber orientation, agree well with measurements.     

Heat distortion of phenolic fiber reinforced thermoplastics

Heat distortion temperature of phenolic short fiber-reinforced thermoplastics (FRTP) (polystyrene, polypropylene, nylon 66), which are molded by injection, have been estimated by an ASTM standard and the reinforced effect is examined from the standpoint of the dependence on the fiber content and maximum fiber stress (bending stress). For polystyrene (PS), the temperature dependence on the fiber content and the maximum fiber stress dependence on the gradient (increase in heat distortion temperature with an increase in 1% of fiber) of these lines show a fine relation, and in regard to the heat distortion temperature, also indicates a nearly linear relation on a log–log scale. However, for the other two polymers, a good relation cannot be recognized but shows a nonlinear one. For polypropylene (PP), a decrease in the phenomenon in the heat distortion temperature dependence on fiber content is found and an interpretative explanation of the results is given.     

国外纤维增强热塑性塑料发展概况

纤维增强热塑性塑料（FRTP）因其重量轻,抗冲击性和疲劳韧性好,成型周期短,可循环利用等诸多优点,近年在稳定发展。本文概述了国外纤维增强热塑性塑料的发展形势、材料种类、知名厂商及其产品和FRTP最终制品的成型工艺。     

A comparison between the static and fatigue properties of glass‐fiber and carbon‐fiber reinforced polyetherimide composites after prolonged aging

The static and fatigue behavior of two fiber‐reinforced composites was characterized after samples were subjected to both natural and accelerated aging. The composites consisted of a thermoplastic matrix (PEI: polyetherimide) reinforced with glass or carbon fabric. Natural aging involved exposing samples to the elements over a period of two years, while accelerated aging was conducted in a saline solution during 200 days. Subsequently, static (tensile and interlaminar shear) and fatigue tests were carried out with the aim of determining the mechanical properties of the materials after exposure. A negligible decrease in the value of these properties was observed, while different behavior was detected depending on the type of aging of the material.     

Effect of glass fiber length on the creep and impact resistance of reinforced thermoplastics

Impact and flexural creep testing were conducted at temperatures between −22°F (−30°C) and 250°F (121°C) to evaluate and compare the end-use performance of continuous long glass fiber-reinforced thermoplastic sheet composites to that of short glass fiber-reinforced thermoplastics. The matrices studied consisted of amorphous (polycarbonate and acrylonitrile-butadiene-styrene) and semicrystalline (polypropylene) polymers. Data were obtained from both injection-molded specimens (short fibers), and from specimens machine-cut from compression-molded test panels (continuous long fibers). The creep results of this study demonstrated that continuous long fibers are more efficient than short fibers in reinforcing the thermoplastic matrices, resulting in enhanced load-bearing ability at elevated temperatures. The addition of continuous long glass fibers to the thermoplastic matrices led to a significant increase in the notched Izod impact strengths between the temperatures of −22°F (−30°C) and 77°F (25°C), and only slight improvement in the drop-weight impact strengths. The lack of correlation between notched Izod impact and drop-weight strengths is largely due to the difference in crack propagation and fracture initiation energies. Results of the Rheometrics instrumented impact test indicated a higher total fracture energy for the long glass-reinforced thermoplastic sheet composites than for the short glass-reinforced injection-molded thermoplastics. The decreased ease of crack propagation in thermoplastic sheet composites is associated with the high energy-absorbing mechanisms of fiber debonding and interply delamination. The results of this study point to the significant property improvement of continuous long fibers vs. short fibers. The creep strength of short fiber-reinforced thermoplastics are greatly affected by the nature of the stress transfer which in turn is influenced by the critical fiber length and temperature, which is not the case for the long fiber-reinforced thermoplastic sheet composites. Long fibers dramatically increase the impact resistance of thermoplastics. The retention of toughness at low temperatures coupled with elevated temperature performance greater than similar short glass fiber-reinforced thermoplastics effectively extends the capabilities of thermoplastic sheet composites at both temperature extremes.     

Characterization of bulk agro‐green composites: Sisal fiber reinforced wheat flour thermoplastics

Starch based thermoplastic composites reinforced by short sisal fibers having length less than 1 mm were fabricated by extrusion followed by compression molding. The sisal fiber content varied from 0 to 10% w/w keeping the amount of glycerol (plasticizer) as constant (23% w/w). Investigation proved that an increase in the amount of sisal fibers will decrease the ductile nature of composites. The Young's modulus and hardness value increases as a function of fiber content. The impact strength varied as a function of fiber content. Contact angle analysis showed that incorporation of sisal fibers to the matrix increases its hydrophilic nature. The polar factor and total surface energy increases as a function of fiber content whereas dispersive factor decreases. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Weld-line characteristics in short fiber reinforced thermoplastics

Fibers can greatly improve the mechanical properties of polymers but may also severely weaken molded parts at their weld-line compared to their bulk strength. The tensile properties and fiber orientation of injection and compression molded fiber reinforced Noryl and polypropylene samples with and without a weld-zone were studied. Distinct differences in structure and mechanical properties of weld-containing and weld-free samples were identified. In unfilled Noryl and unfilled polypropylene, the presence of a weld-line was found to only have a small effect on the tensile strength and modulus, while in the corresponding fiber reinforced systems, orientation of the fibrous reinforcement parallel to the weld-line caused a significant reduction of the tensile strength compared to the weld-free products. The strength ratio of welded and unwelded specimens was found to decrease with increasing fiber concentration. Quantitative determination of the glass fiber orientation distribution within the weld-line region and in the bulk was carried out by analyzing photomicrographs of polished sections at desired locations.     

Fatigue characteristics of a glass‐fiber‐reinforced polyamide

This paper deals with prediction of the temperature rise in the stress‐controlled fatigue process of a glass‐fiber‐reinforced polyamide and the application of a temperature and frequency superposition procedure to the S‐N curve. An experimental equation was derived to predict the temperature rise from calculations based on the fatigue test conditions and viscoelastic properties of the material. The temperature rise (ΔT) can be expressed as a product of a coefficient term Φ(L, κ) concerning heat radiation and the test‐specimen shape and a function term P_fat concerning the viscoelastic properties and fatigue test conditions. Φ(L, κ) was found experimentally to derive the equation for predicting the temperature rise blow or above the glass transition temperature (T_g) of the material. The equation σ_R = −S_Tf A log N_fR + S_Tf B was obtained as a procedure for applying temperature and frequency superposition to S‐N curves in consideration of ΔT. This procedure was obtained by combining both temperature‐ and frequency‐superposition techniques. Here, σ_R and log N_fR represents the stress and the fatigue lifetime calculated at a given temperature and frequency, A and B denote the slope and intercept of any arbitrarily chosen S‐N curve, and S_Tf is a shift factor for temperature and frequency superposition. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1783–1793, 1999     

Fatigue of glass and carbon fiber reinforced engineering thermoplastics

Cyclic tension fatigue S-N curves are given for injection moleded Nylon 6/6, polycarbonate, polysulfone, polyphenylene sulfide, and poly(amide-imide) matrices with glass and carbon fibers as well as for unreinforced material. The S-N curves for most composites appear linear, with no evidence of a fatigue limit up to 10⁶ cycles. Some nonlinearity is evident with the Nylon 6/6 composities, and these appear to fail at a cumulative strain similar to the ultimate static strain. The remainder of the composites appear to fail by a crack propagation mechanism. The glass reinforced materials all degrade at a similar rate in fatigue, while the carbon reinforced materials with brittle matrices degrade more slowly than do those with ductile matrices. The latter effect may be due to greater integrity of the cracked regions for brittle matrix systems.     

Surface quality characterization of textile‐reinforced thermoplastics

To allow cost effective mass production of reinforced thermoplastics for visible parts, in‐situ a surface quality with “Class‐A” standard must be achieved. Furthermore, after the application of varnish, an appearance (gloss, waviness, color) similar to that of the traditional metal component is required. Porosity and fiber readout are the common surface defects. Fiber readout results from the significantly higher volume shrinkage of the thermoplastic resin (higher CLTE) in comparison to that of the reinforcement during the cooling process in production combined with the uneven distribution of resin and fibers. While glass mat reinforced thermoplastic (GMT) parts show a disorderly readout influenced (among other factors) by fiber length, processing and fiber content of the semi‐finished material, the fabric reinforced thermoplastics (organic sheets) suffer from a regular print‐through—a display of the textile reinforcement. Modern tools of measurement enable one to quantify gloss, roughness, and waviness of the surfaces. Thus parameters significantly influencing the surface characteristics can be identified. This leads to the development of procedures for improving the surface quality.     

Effect of packing pressure on fiber orientation in injection molding of fiber‐reinforced thermoplastics

Injection molding of fiber‐reinforced polymeric composites is increasing with demands of geometrically complex products possessing superior mechanical properties of high specific strength, high specific stiffness, and high impact resistance. Complex state of fiber orientation exists in injection molding of short fiber reinforced polymers. The orientation of fibers vary significantly across the thickness of injection‐molded part and can become a key feature of the finished product. Improving the mechanical properties of molded parts by managing the orientation of fibers during the process of injection molding is the basic motivation of this study. As a first step in this direction, the present results reveal the importance of packing pressure in orienting the fibers. In this study, the effects of pressure distribution and viscosity of a compressible polymeric composite melt on the state of fiber orientation after complete filling of a cavity is considered experimentally and compared with the simulation results of Moldflow analysis. POLYM. COMPOS. 28:214–223, 2007. © 2007 Society of Plastics Engineers     

Enhancing particle erosion resistance of glass‐reinforced polymeric composites using carbon nanofiber‐based nanopaper coatings

Sand erosion may cause severe damage of blades in wind turbine and helicopter blades as well as many surface components of airplanes. In this study, thin nanopapers made of carbon nanofibers (CNFs) are used to enhance the resistance of solid particle erosion of glass fiber (GF)/wind epoxy composites. Finite element computer simulations are used to elucidate the underlying mechanisms. The much higher particle erosion resistance of nanopapers compared to GF‐reinforced epoxy composites is attributed to the high strength of CNFs and their nanoscale structure. The excellent performance in particle erosion resistance makes the CNF‐based nanopaper a prospective protective coating material for the turbine blades in the wind energy industry. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Fire performance of brominated and halogen‐free flame retardants in glass‐fiber reinforced poly(butylene terephthalate)

This paper investigates the effects of brominated and halogen‐free fire retardants on the fire performance of glass‐fiber (GF) reinforced poly(butylene terephthalate) (PBT). Brominated polystyrene was used as the brominated fire retardant, whereas aluminum diethylphosphinate with/without nanoclay as halogen‐free fire retardants (HFFRs). Tests were conducted by using thermogravimetric analysis, limiting oxygen index (LOI), UL94, and the cone calorimeter. Thermogravimetric analysis results show that decomposition of GF plus PBT (PBT + GF) starts earlier in the presence of all fire retardants (FRs). In the cone calorimeter, all FRs reduce significantly the heat release rate (HRR) compared with PBT + GF, with brominated polystyrene achieving lowest HRR primarily because bromine released in the pyrolysis gases inhibits combustion. Brominate polystyrene does not, however, affect the mass loss rate. Aluminum diethylphosphinate alone has significant effects on reduction of both HRR and mass loss rate, which become considerably more when combined with nanoclay. It was also found that the combustion efficiency of the brominated polystyrene compound is much lower than that of HFFRs, indicating that brominated polystyrene has higher gas phase flame retardant efficiency compared with HFFRs because the bromine radicals released during degradation of brominated polystyrene effectively quench the chemical reactions of the pyrolysis gases due to degradation of PBT.     

Short fiber reinforced thermoplastics. I. Rheological properties of glass fiber reinforced Noryl

An experimental study on the flow behavior of glass fiber reinforced Noryl (a commercial poly(phenyleneoxide)/polystyrene blend) using a capillary rheometer is described. The effect of fiber concentration on shear viscosity and die swell was studied at various temperatures. Breakage of glass fibers during flow through the rheometer is discussed; it was found that the average fiber length (about 230 μm) was not significiantly altered, except at the highest shear rate (575 s⁻¹) studied. The incorporation of short fibers into thermoplastic polymer melts increases their viscosity without changing the basic rheological character-shear rate dependency. No discernible viscosity changes were measured by incorporating 10 weight percent fibers, and upon further increase of fiber concentration from 20 to 30 weight percent no appreciable increase in viscosity was noted. It is shown that short glass fibers cause a large reduction in extrudate swell. The presence of voids and fiber orientation contribute to the decrease of the die swell, an effect greater than expected from volumetric considerations alone.     

Creep behavior of glass‐fiber‐reinforced nylon 6 products

The creep properties, that is, the velocity constant, activation energy, stress index, and time index, of a test piece (TP) cut from a glass‐fiber‐reinforced nylon 6 product were successfully determined by a compression creep test. In the determination of the creep properties, the experimental creep curves for the TP were fitted by finite element analysis (FEA). Fiber‐reinforced nylon 6 beams with different fiber orientations were also prepared, and their creep properties were successfully determined by a combination of the bending creep test and the corresponding analysis. The creep behavior of the press‐fit component composed of a metal collar and a fiber‐reinforced nylon 6 product was predicted by FEA with the determined creep properties of the TP. The predicted retention forces were in good agreement with the experimental ones. The effects of the fiber orientation on the long‐term reliability of the press‐fit component are also discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012