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.     

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     

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.     

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.     

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。     

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 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.     

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 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.     

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.     

Aging of modified glass‐reinforced polypropylene in air and in antifreeze

The thermal stability and the mechanical properties of modified and unmodified glass‐reinforced polypropylene during aging in air (135°C) and antifreeze (115°C) with exposure up to 80 days was investigated in this study. Aging leads to progressive phase separation. On the contrary, the original modified composite is characterized by a dense structure; aging leads to the structure compacting and pore size decreases. Unmodified composite displays a drastic failure of the mechanical properties after 10 days of heating. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 807–813, 2000     

New developments in flame retardancy of glass‐reinforced epoxy composites

This work involves the development of novel glass fiber–reinforced composite materials containing a commercially available epoxy resin, a phosphate‐based intumescent, and inherently flame‐retardant cellulosic (Visil, Sateri) and phenol–formaldehyde (Kynol) fibers. The intumescent and flame‐retardant fiber components were added both as additives in pulverized form and fiber interdispersed with the intumescent as a fabric scrim for partial replacement of glass fiber. Thermal stability, char formation, and flammability properties of these novel structures were studied by thermal analysis, limiting oxygen index, and cone calorimetry. The results are discussed in terms of effect of individual additive component on thermal degradation/burning behavior of neat resin. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2511–2521, 2003     

Rheological behavior and fiber orientation in slit flow of fiber reinforced thermoplastics

The flow behavior and fiber orientation in slit flow of a short fiber reinforced thermoplastic composite melt are investigated. A slit die with adjustable gap and interchangeable entrance geometries was designed and built. The slit die is fed by a single screw extruder. The bulk viscosity is calculated from the axial pressure profiles measured using three flush mounted pressure transducers. The effect of entrance geometry and gap dimensions on the fiber orientation and bulk flow behavior is specifically considered. A skin-core composite fiber orientation is observed in the thickness direction. Fibers are oriented in the flow direction and parallel to the walls in the skin region irrespective of the entrance geometry. Different fiber orientation distributions in the core region can be realized by using different entrance geometries. However, the changes in the core fiber orientation are not fully reflected by the measured viscosities, due to highly oriented skin layer. Exit pressures obtained by extrapolation of linear pressure profiles are found to be all positive, but dependent on the die geometry and entrance conditions, even for the unfilled melts.     

加快发展玻璃纤维增强热塑性塑料

1、关于玻纤增强热塑性塑料 塑料作为现代四大工业基础材料之一,越来越广泛地在各行各业应用.2002年全世界的塑料总产量已达1.65亿吨.塑料按受热后形态性能表现,可分为热固性塑料和热塑性塑料.后者是指能够多次受热软化的聚合物--聚合物的分子链间不发生交联,而且每次加工后分子链几乎没有变化.     

Description and modeling of fiber orientation in injection molding of fiber reinforced thermoplastics

As mechanical properties of short fiber reinforced thermoplastic injected components depend on flow induced fiber orientation, there is considerable interest in validating and improving models which link the flow field and fiber orientations to mechanical properties. The present paper concerns firstly the observation and quantification of fiber orientation in a rectangular plaque with adjustable thickness and molded with 30 and 50 wt% short fiber reinforced polyarylamide. An automated 2D optical technique has been used to determine fiber orientations. A classical skin (with orientation parallel to the flow)-core (with orientation perpendicular) structure is observed for thick plaques (thickness greater than 3 mm) but the core region is fragmentary for thickness less than 1.7 mm. It is shown that the gate design and different levels of fiber interactions, due to different fiber concentrations, are responsible for these observations. Secondly, computer simulations of flow and fiber orientation are shown. The agreement with the actual data is good, except in the case of the core for thin plaques. The limitations that have to be resolved come not only from the standard fiber orientation equations, but also from the flow kinematics computation.     

世界热塑性玻璃钢发展概况

3玻璃/热塑性塑料复合纤维 3.1 Twintex(R)复合纤维 Twintex(R)是法国圣戈班Vetrotex公司于1988年开发的玻璃/热塑性塑料复合纤维的商品名.在拉制玻璃纤维时即用热塑性塑料与其共挤相间复合而成紧密结合的复合纤维.可用塑料种类有聚丙烯、聚乙烯、聚酰胺、PET、PBT等.     

世界热塑性玻璃钢发展概况

玻璃纤维增强热塑性塑料(简称热塑性玻璃钢,英文缩写GRTP)最早出现于20世纪50年代,比热固性玻璃钢问世更晚.经过多年的发展,现今国际上热塑性玻璃钢已占玻璃钢总产量的四分之一以上,而且增长速度很快.据资料报道,在过去几年中,热塑性玻璃钢市场增长稳定,平均年增率为5%～6%.从现在到2007年,美国等国家对热塑性玻璃钢需求量的增长率将超过热固性玻璃钢.     

Mechanical properties of discontinuous fiber reinforced thermoplastics. II. Random-in-plane fiber orientation

The mechanical properties are presented for a series of discontinuous fiber-reinforced thermoplastic composites made with random-in-plane fiber orientation. The matrix and fiber materials were chosen to provide a wide range of strength, modulus, ductility and adhesive properties. In many cases strong, rigid, yet tough composites were fabricated. Strength levels of over 20,000 psi and modulus values over 1,000,000 psi were reached in several systems reinforced with short Kevlar-49 and graphite fibers. A strong dependence of composite strength and modulus on fiber strength and modulus was noted indicating good transfer of load from matrix to reinforcement. Fiber efficiency factors for modulus and strength were calculated for the experimental composite systems and averaged 0.19 and 0.11 respectively. Data were analyzed using basic composite theory. Properties of the experimental composites could not be predicted from constituent properties.