Effects of process conditions on Young's modulus and strength of extrudate in short‐fiber‐reinforced polypropylene

We examined the effects of process conditions on Young's modulus and tensile strength of extruded short‐fiber reinforced thermoplastics. With increasing extrusion ratio and decreasing extrusion temperature, the fiber alignment increases, the mean fiber length decreases, and the mechanical properties of the matrix are improved. The orientation parameter, mean fiber length, Young's modulus, and tensile strength of the matrix are described as a function of extrusion ratio and extrusion temperature. The models proposed by Fukuda and Kawata, and Fukuda and Chou are applied to predict Young's modulus and tensile strength of the composites using orientation parameter. By comparing the predicted Young's modulus and tensile strength with experimental results, the validity of the models is examined. The prediction of Young's modulus agreed quit with the experimental results. The tensile strength of composite extruded below the melting point nearly matched that of the neat matrix. There is no the strengthening effect of the fiber since the angle between fracture surface and fiber direction is very small. POLYM. COMPOS. 28:29–35, 2007. © 2007 Society of Plastics Engineers     

Mechanical properties of short fiber reinforced thermoplastic composites —I. Elastic properties and predictions

Twin roll-mill and compression molding machines were used to process the unidirectional ply of short fiber reinforced thermoplastics (FRTP). FRTP laminates were prepared by compression molding of angle plies with the desired stacking sequences.The fiber length and orientation distributions in FRTP took place after processing. Therefore, a statistical distribution function such as WeiBull distribution function was applied to represent the existing fiber length distribution. The orientation distribution in FRTP was characterized by a single parameter exponential function. Elastic moduli of the unidirectional ply were predicted by the Halpin-Tsai equation where the fiber length distribution was introduced to the estimation. The overall elastic moduli of laminates were estimated based on the simulated laminate-plate method. A comparison of measured elastic moduli with theoretical predicted results from unidirectional ply and laminate was discussed in this study.     

Uniaxial roll-drawing of isotactic polypropylene sheet

The process described as “roll-drawing” has been applied to commercial extruded sheets of isotactic polypropylene (M?_n = 70,900). Preheated billets were drawn into thin, clear, transparent sheets in a single pass, producing uniaxial orientation of the polymer molecules in the draw direction. At the maximum draw ratio of 20, the ultimate tensile strength and Young's modulus in the draw direction were 0.5 GPa and 20 GPa respectively. The mechanical properties transverse to the draw direction were virtually unchanged. The theory of fiber reinforcement for unidirectional anisotropic plates was applied to interpret the orientation dependence of the stress-strain behavior of the drawn sheets. From these results, it was estimated that the mechanical properties of biaxially laminated polypropylene sheets equaled the performance of aramid and carbon fiber composites, The roll-drawing process appears to be economically attractive for the production of ultra-high modulus crystalline thermoplastics in sheet form having excellent uniaxial or biaxial properties.     

Study of the flexural modulus of natural fiber/polypropylene composites by injection molding

Effect of fiber compression on flexural modulus of the natural fiber composites was examined. The kenaf, bagasse, and polypropylene were mixed into pellets, and composites were fabricated by injection molding. To predict flexural modulus of the composites, the Young's modulus of kenaf and bagasse fiber were measured. Using the obtained Young's modulus, the flexural modulus of the composites was predicted by Cox's model that incorporates the effect of fiber compression. It was found that those fibers with high Young's modulus were more compressed than that with low Young's modulus. Moreover, the distribution of fiber length and orientation in the composites were also investigated. To calculate the orientation factor for the prediction model, the distribution function of fiber orientation was determined to a triangular function. The flexural modulus of the composites increased with increase of volume fraction. The predicted values were in good agreement with the experimental values. Furthermore, it was revealed by SEM that the porous structure of the natural fibers was compressed. The fiber compression ratio (3.6) in bagasse was higher than that in kenaf (1.4) due to the difference in porous structure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 911–917, 2006     

连续纤维增强热塑性塑料开发动向分析

分析了国内外纤维增强热塑性塑料（ FRTP）的发展趋势，指出连续纤维增强热塑性塑料能最大限度发挥材料性能；对比了现行工艺技术的优劣、国内外发展现状，有助于对我国纤维增强热塑性塑料的发展有方向性的判断。     

Prediction of fiber orientation in injection molded parts of short-fiber-reinforced thermoplastics

Fiber orientation induced by injection mold filling of short-fiber-reinforced thermoplastics (FRTP) causes anisotropy in material properties and warps molded parts. Predicting fiber orientation is important for part and mold design to produce sound molded parts. A numerical scheme is presented to predict fiber orientation in three-dimensional thin-walled molded parts of FRTP. Folgar and Tucker's orientation equation is used to represent planar orientation behavior of rigid cylindrical fibers in concentrated suspensions. The equation is solved about a distribution function of fiber orientation by using a finite difference method with input of velocity data from a mold filling analysis. The mold filling is assumed to be nonisothermal Hele-Shaw flow of a non-Newtonian fluid and analyzed by using a finite element method. To define a degree of fiber orientation, an orientation parameter is calculated from the distribution function against a typical orientation angle. Computed orientation parameters were compared with measured thermal expansion coefficients for molded square plates of glass-fiber-reinforced polypropylene. A good correlation was found.     

Effects of fiber length and orientation distribution on the elastic modulus of short fiber reinforced thermoplastics

A method including the effects of fiber length and orientation distribution to predict elastic moduli of short fiber reinforced thermplastics (FRTP) is presented. The fiber length distribution in FRTP has an asymmetric character with a tail at the long fiber end. Statistical distribution functions such as Weibull or log-normal can be used to represent this kind of distribution. Orientation distribution of fibers in FRTP can be characterized by a single parameter exponential function, $F(\theta) = \frac{{1 - \lambda \theta }}{{1 - e^{ - \frac{\P}{2}\lambda } }}$. A large λ indicates a highly oriented material whereas small λ represents a quasi-isotropic material. As fiber length and orientation distribution functions have been characterized, the elastic moduli of FRTP can be predicted. First, the mean elastic moduli of unidirectional plies are predicted through the fiber length distribution. Then the stacking sequence of laminate is assumed to be as the fiber orientation distribution of FRTP, and the overall elastic moduli of FRTP are estimated based on the laminate-plate method.     

Auxetic polypropylene films

Auxetic materials are those exhibiting negative Poisson's ratio (ν) behavior. Polymeric auxetic extruded products in the form of cylinders and fibers have previously been reported. This article reports the successful production of auxetic polypropylene films (～0.15‐mm thick) using a melt extrusion process. Video extensometry and tensile testing techniques have been used to measure the in‐plane Poisson's ratios and Young's moduli of the auxetic film, both on an Instron tensile testing machine and a Deben microtensile testing machine. The film is elastically anisotropic with the Poisson's ratio and Young's modulus along the extrusion (x) direction being ν_xy = ?1.12 ± 0.06 and E_x = 0.34 ± 0.01GPa, respectively, while the Poisson's ratio and Young's modulus in the transverse (y) direction to the extrusion direction are ν_yx = ?0.77 ± 0.01 and E_y = 0.20 ± 0.01GPa, respectively. POLYM. ENG. SCI., 45:517–528, 2005. © 2005 Society of Plastics Engineers     

Morphological and mechanical property studies of polymer extrudates obtained by the rotational extrusion process

The orientation of the reinforcing fibers in glass fiber filled polypropylene tubular extrudates has been controlled effectively by the superposition of the linear flow in a melt extruder with torsional flow generated by rotating the capillary portion of the extrusion die of the extruder. The so produced extrudates have mechanical properties which can be balanced along the hoop and extrusion direction by adjusting the extrusion rate and the rotational speed of the die for example, the breaking load of 75N along the hoop direction increases by ～40% when the capillary of the die was rotated at 80 rpm. At the same time the Young's modulus in the extrusion direction decreased from 1100 MPa under conventional extrusion conditions to 800 MPa.     

High-strength polyethylene

Polyethylene (PE) continuous filaments having high tensile strength as well as high Young's modulus have been obtained from several linear polyethylene materials by stretching a partially oriented spun yarn to a draw ratio of ?30. The high draw ratio was readily attained for linear PE fiber extruded at a temperature of at least 250°C and quenched in air while under some intermediate tension. The number average molecular weight of the polymer was found to have the predominant effect on the ultimate tensile strength of the drawn fiber. Yarn with a tensile strength of 19 gpd (167 kg/mm²) and a Young's modulus of 854 gpd (7380 kg/mm²) was produced. Yarn with a Young's modulus of 1145 gpd (9890 kg/mm²) was made by sacrificing some tensile strength.     

热塑性复合材料制备工艺概述

本文介绍了热塑性复合材料的发展现状。综述了热塑性复合材料的主要制备技术和成型工艺方法。     

纤维增强热塑性复合材料的预浸渍技术发展概况

本文系统地介绍了纤维增强热塑性复合材料的预浸渍技术。     

Experimental investigation on the influence of the composition on the morphology and the mechanical properties of short glass fiber‐reinforced polypropylene nanocomposites

Polypropylene composites containing 0–5 wt% layered silicate and 0–30 wt% short glass fibers are prepared by melt compounding. To investigate the influence of different compositions on the mechanical properties of short glass fiber‐reinforced polypropylene nanocomposites, materials with various filler contents are prepared. At a glass fiber content of 10 wt% Young's modulus of the layered silicate‐containing composites decreases by around 30% compared to conventional glass fiber‐reinforced polypropylene. But at higher glass fiber loadings, an increasing modulus of up to 10% is observed. However, the addition of layered silicate results in large decreases of the tensile and the notched impact strength. A maleic anhydride‐grafted polypropylene enhances Young's modulus and the tensile strength. © 2012 Society of Plastics Engineers     

Effect of gamma radiation and annealing on ultra-oriented polyethylene

Filaments of ultra-oriented high density polyethylene were solid-state extruded at an extrusion (draw) ratio of 26 and subsequently irradiated under vacuum by a cobalt-60 source at doses of 10,15, 20, 40 and 60 megarads (MRad). Several identically prepared but unirradiated strands were also tested. One set of samples at each dose was immersed in a silicone oil bath for one half hour at 128°C and one set was given no post-irradiation thermal treatment. Characterization of the resultant morphologies included differential scanning calorimetry (DSC), birefringence, thermomechanical analysis (TMA), and tensile testing. Results from DSC measurements indicate that initial radiation crosslinking only slightly disrupts the crystal lattice, but on subsequent melting and re crystallization, the chains are unable to recrystallize effectively in their former habit. In all cases, melting point and crystallinity decrease with increasing radiation dose. Birefringence and TMA results indicate that orientation is not disrupted by irradiation. For unannealed samples, Young's modulus increases slightly then levels off while tensile strength and elongation at break increase initially, then drop, For annealed irradiated samples, Young's modulus rises at first, then levels off at higher doses. Tensile strength and elongation at break increase significantly with increasing radiation treatment, then essentially reach constant values at highest doses.     

Hydrostatically extruded glass fiber reinforced polyoxymethylene. II: Modeling the elastic properties

This paper describes an investigation into modeling the elastic properties of hydrostatically extruded short glass fiber reinforced polyoxymethylene (POM). The starting material for the extrusion was randomly arranged short glass fibers (25 wt%, average length 150 μm) in an isotropic POM matrix. Extrusion was carried out through a reducing conical die at 15°C below the melting point of the matrix phase (hence the composite was extruded in the solid state), such that after extrusion, preferential alignment along the extrusion direction was developed for both the fibers and for the crystalline fraction of the polymer matrix. The elastic properties of samples, made over a range of extrusion ratios, were measured using the ultrasonic immersion method, a technique that allows a complete set of elastic constants to be determined for a composite. Theoretical predictions for the elastic properties of the oriented extrudates were generated by combining a modification to the theory of Wilczynski to allow for the fibers' being surrounded by an oriented matrix phase, together with the aggregate model of Ward to model the effects of partial orientation of the fiber oriented matrix units.     

Processing of short‐fiber reinforced polypropylene. I. Influence of processing conditions on the morphology of extruded filaments

An experimental investigation of the processing of glass fiber reinforced polypropylene is presented. Final fiber orientation distribution, fiber distribution in filament sections, rheological properties, final fiber length distribution and surface morphology were analyzed. This analysis was done taking into account the quantity of fibers and their interactions and flow conditions. The final fiber orientation increased when shear rate increased and fiber concentration decreased. Moreover, inhomogeneities in fiber distribution increased as the concentration of fibers decreased. The density profile showed a significant variation with fiber concentration, but it was not dependent on the shear rate applied. The viscosity showed a linear dependence with shear rate. The average fiber length and the breadth of this distribution decreased with the increasing fiber concentration and extrusion rate. The extruded filament surface showed minor roughness when the shear rate increased or when the fiber concentration decreased. The results of this experimental characterization give useful information to determine the influence of the processing variables on the final properties of short‐fiber reinforced polypropylene and constitutes the first part of a more ambitious project that also includes the development of a modeling strategy of the processing behavior for short‐fiber composites.     

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     

Morphological studies of blends containing liquid crystalline polymers with poly(ethylene terephthalate)

The investigation involved the structure–property behavior of extruded cast films prepared from blends of thermotropic liquid crystalline copolyesters with poly(ethylene terephthalate) (PET). Data were obtained which showed not only the temperature dependence of the moduli and stress–strain behavior but also the orientation effects that must be prevalent in order to explain the differences between the moduli measured parallel and perpendicular to the extrusion direction. Only at high liquid crystal polymer (LCP) composition is the modulus particularly increased. The modulus enhancement with lower LCP content and utilization of process variables are discussed with respect to the induced morphological textures and nature of the process equipment. Specifically, the process variable extruder gear pump speed did not enhance Young's modulus at the same LCP content as extensively as did the process variable of extruder screw speed.     

Mechanical properties of injection molded long fiber polypropylene composites,Part 1: Tensile and flexural properties

Innovative polymers and composites are broadening the range of applications and commercial production of thermoplastics. Long fiber‐reinforced thermoplastics have received much attention due to their processability by conventional technologies. This study describes the development of long fiber reinforced polypropylene (LFPP) composites and the effect of fiber length and compatibilizer content on their mechanical properties. LFPP pellets of different sizes were prepared by extrusion process using a specially designed radial impregnation die and these pellets were injection molded to develop LFPP composites. Maleic‐anhydride grafted polypropylene (MA‐g‐PP) was chosen as a compatibilizer and its content was optimized by determining the interfacial properties through fiber pullout test. Critical fiber length was calculated using interfacial shear strength. Fiber length distributions were analyzed using profile projector and image analyzer software system. Fiber aspect ratio of more than 100 was achieved after injection molding. The results of the tensile and flexural properties of injection molded long glass fiber reinforced polypropylene with a glass fiber volume fraction of 0.18 are presented. It was found that the differences in pellet sizes improve the mechanical properties by 3–8%. Efforts are made to theoretically predict the tensile strength and modulus using the Kelly‐Tyson and Halpin‐Tsai model, respectively. POLYM. COMPOS., 28:259–266, 2007. © 2007 Society of Plastic Engineers     

Liquid crystalline copolyester/polyethylene in situ composite film: Rheology,morphology, molecular orientation,and tensile properties

A thermotropic liquid crystalline copolyester (TLCP) was blended with low density polyethylene using a corotating twin screw extruder and then fabricated by extrusion through a miniextruder as cast film. Rheological behavior, morphology, and tensile properties of the blends were investigated. Melt viscosities of neat components and blends measured by using plate‐and‐plate and capillary rheometers at 240°C, in the shear rate range 1–10⁴ s^?1, showed similar shear thinning effect. The viscosity values measured by the two techniques in the overlapping range of shear rate are found to be identical, which is in accord with the Cox–Merz rule. Addition of TLCP slightly reduces the matrix melt viscosity. TLCP dispersed phase in the extruded strand appeared in the form of spherical droplets. These droplets were elongated into fibrils with high aspect ratio (length to width) at the film extrusion step. As a result, the Young's modulus in machine direction (MD) of the composite film was greatly enhanced. At 20 wt % of TLCP, the MD Young's modulus was found to be about 16‐fold increase compared to that of the neat polyethylene film. However, the elongation at break sharply dropped with the increase of TLCP content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 561–567, 2002; DOI 10.1002/app.10307