Effects of flow induced orientation of ferromagnetic particles on relative magnetic permeability of injection molded composites

Composite samples consisting of ferromagnetic asymmetric particles incorporated into a polyolefin binder were injection molded using custom designed molds which produced preferential fiber orientations. The relative magnetic permeability values of the composites were measured as a function of the filler volume fraction, injection rate, gate diameter, temperature, aspect ratio of the fibers, and fiber orientation. Fiber orientation was affected by the molding conditions and controlled the relative magnetic permeability of the composites. The degree of fiber orientation was significantly affected by the size of the opening (gate) to the mold, or by the mold geometry going from an edge-gated cylindrical to a center-gated disk cavity. Relative permeability values of the composites were observed to increase when the fiber orientation and the applied field were parallel to one another. For instance, highly aligned composite samples exhibited up to 30% greater relative permeability values compared to those samples which exhibit fiber orientation distributions approaching a random distribution. To our knowledge this is the first study that provides data linking the fiber orientation distribution functions of ferromagnetic asymmetric particles to the relative magnetic permeability values of injection molded composites.     

Prediction of mechanical properties of short kevlar fiber-nylon-6,6 composites

Injection molded short Kevlar (DuPont) fiber/nylon-6,6 composites have been studied. Fiber length and length distribution were measured as a function of processing variables. Critical fiber length was measured by an embedded single-fiber method. Tensile modulus of the molded composites was predicted by an adapted classical lamination analogy. Fiber and matrix orientation factors, derived from X-ray diffraction, were introduced to modify Kelly Tyson equation to estimate the composite tensile strength. It has been found that fiber length is dramatically shortened by the injection molding process, and is affected by processing conditions. Predictions gave reasonable agreement with data for tensile modulus and strength.     

注塑模具设计过程中浇口尺寸对塑料制品力学性能的影响

以高密度聚乙烯（PE-HD）为原料,采用自行设计加工的一套1模4腔注射标准试样模具进行注塑,通过调整熔体温度、模具温度和注射压力等工艺参数,考察了不同浇口截面尺寸的模具对注塑样品拉伸、冲击和弯曲性能的影响。结果表明,模具浇口截面尺寸修改后,注射试样的力学性能明显提升,其中,拉伸强度、冲击强度、弯曲强度和弯曲模量最高分别提升了3.40 %、79.86 %、18.11 %和113.36 %;模具浇口修改后注塑所的样品充填饱满,无塌陷等缺陷;修改浇口后的模具设计整体结构布局合理,可为同类标准测试样的成型模具设计提供有益借鉴。     

A model for determining fiber reinforcement efficiencies and fiber orientation in polymer composites

Fiber length contributions to the reinforcement potential in composites have been decoupled from fiber orientation effects with the use of a fiber orientation model. Fiber length efficiency factors and fiber orientation factors are calculated based upon a procedure that requires measuring the composite properties in specified directions relative to a reference direction. The procedure is straightforward and relatively quick compared to the tedious task of actually measuring the fiber length distribution. An example illustrating the utility of the procedure is given and then followed by a discussion qualifying the significance of the factors and the results.     

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.     

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.     

Thermo‐physical,thermal degradation,and flexural properties of betel nut husk fiber reinforced vinyl ester composites

This study aims to investigate the thermo‐physical, mechanical, and thermal degradation properties of betel nut husk (BNH) fiber reinforced vinyl ester (VE) composites. These properties were evaluated as a function of fiber maturity, fiber content, and fiber orientation. Thermo‐physical properties were analyzed experimentally using a hot disk TPS method. The introduction of BNH was found to reduce the thermal conductivity of neat VE. The thermal conductivity and thermal diffusivity of BNH reinforced VE composites decreased with the increase in fiber content. Short fiber BNH reinforced VE composites showed the lowest thermal conductivity as compared to the unidirectional and random nonwoven composites. The TGA analysis shows lower resin transition peak for the BNH reinforced VE composites than the peak of neat VE. Fiber maturity had a notable effect on the flexural modulus of the BNH fiber reinforced VE composites. Incorporation of 10 wt% BNH fibers into the composite has increased the composites' flexural modulus by 46.37%. However, further increases in the fiber content reduced both flexural strength and modulus of the composites. POLYM. COMPOS., 37:2008–2017, 2016. © 2015 Society of Plastics Engineers     

Numerical simulation of three‐dimensional fiber orientation in injection molding including fountain flow effect

It is essential to predict the nature of flow field inside mold and flow‐induced variation of fiber orientation for effective design of short fiber reinforced plastic parts. In this investigation, numerical simulations of flow field and three‐dimensional fiber orientation were carried out in special consideration of fountain flow effect. Fiber orientation distribution was described using the second‐order orientation tensor. Fiber interaction was modeled using the interaction coefficient C_I. Three closure approximations, hybrid, modified hybrid, and closure equation for C_I=0, were selected for determination of the fiber orientation. The fiber orientation routine was incorporated into a previously developed program of injection mold filling (CAMPmold), which was based on the fixed‐grid finite element/finite difference method assuming the Hele‐Shaw flow. For consideration of the fountain flow effect, simplified deformation behavior of fountain flow was employed to obtain the initial condition for fiber orientation in the flow front region. Comparisons with experimental results available in the literature were made for film‐gated strip and centergated disk cavities. It was found that the orientation components near the wall were were accurately predicted by considering the fountain flow effect. Test simulations were also carried out for the filling analysis of a practical part, and it was shown that the currently developed numerical algorithm can be effectively used for the prediction of fiber orientation distribution in complex parts.     

PEN短纤维增强PET复合材料的结构与性能研究

通过在PET树脂中混入聚对苯二甲酸乙二脂（PEN）短纤维，制备了聚萘二甲酸乙二酯（PEN）增强PET复合材料，并以X射线衍射，DSC，扫描电镜，力学测试等手段分析了样品的结构，热学及力学性能，结果表明：复合材料中的PET树脂呈无定型状态，PEN纤维的加入使PET的冷结晶温度移向高温；此方法能够在一定程度上提高复合材料的断裂强度与初始模量，但可能由于复合材料中纤维含量较低。且与基体的粘结性能尚不理想，造成样品的力学性能随纤维含量和长度的变化规律并不明显。     

Injection molding of unsaturated polyester compounds

A bulk-molding compound made of unsaturated polyester resin, glass fiber, calcium carbonate fillers, and low profile additives is studied. The viscosity of the compound in the absence of cure reaction is measured by capillary rheometry. The compound exhibits a shear-thinning behavior. Injection molding in a rectangular plaque equipped with pressure transducers shows that the crosslinking reaction can begin during mold filling for low flow rate or high mold temperature. Fiber orientation in the plaque is complex as the reinforcement appears under two aspects, bundles or filaments. Their lengths and orientations are different. A layered structure throughout the thickness is observed at the mold entrance, whereas the orientation becomes progressively unidirectional in the plaque. Two fiber-free layers near the the mold walls are observed. A numerical simulation of mold filling assuming inelastic non-Newtonian kinetic dependent behavior is presented. The results agree well with pressure measurements. A simplified decoupled fiber motion calculation is finally proposed. A qualitative explanation of the basic phenomena which induce fiber orientation is presented.     

汽车内饰用酚醛树脂/黄麻纤维复合材料的拉伸性能

采用正交试验方法,用5%Na OH溶液对黄麻毡进行预处理,利用模压成型工艺制备酚醛树脂/黄麻纤维复合材料,通过对正交试验结果进行极差分析和方差分析,研究树脂含量、模具温度、模具压力和保压时间4个工艺参数对复合材料拉伸性能的影响程度和显著性水平,并通过多指标综合评分法对材料的拉伸性能综合评价,分析各个工艺参数对材料拉伸性能的影响规律。结果显示,树脂含量和模具压力对复合材料的拉伸性能影响非常显著,当树脂含量为20%、模具温度为180℃、模具压力为10 MPa、模压时间为6 min时,复合材料的拉伸性能最好,此时拉伸强度为24.06 MPa,拉伸弹性模量为113.17 MPa。     

New composites based on short melamine fiber reinforced epdm rubber

Melamine fibre is a new category of advanced synthetic fiber having superior heat and flame resistance with decomposition temperature above 350°C. It suitability as a reinforcing fiber for ethylene propylene diene terpolymer, abbreviated as EPDM rubber, where ‘M’ stands for polymethylene chain, was investigated. It has been observed that tensile strength and stress at 100% strain of EPDM‐melamine fiber composites increase with the addition of a three‐component dry bonding system, comprising hexamethylene tetramine (hexa), resorcinol, and hydrate silica, abbreviated HRH system. Moreover, the fiber‐filled composites anisotropy in stress‐strain properties due to preferential of the short fibers along the milling direction (longitudinal), which is substantiated by the results of swelling and fractography studies. Aging causes an increase in the modulus, tensile strength and hardness of the composites. The fractographs show an increase in interfacial adhesion between the fibers and the matrix during aging, which is further confirmed by the reduction in tan δ peak height of the aged composites during dynamic mechanical studies. Atomic Force Microscopy (AFM) studies reveal the formation of an interphase with the addition of bonding agents and a better fiber‐matrix adhesion due to aging. AFM images also confirm the role of dry bonding systems in improving the fiber‐matrix adhesion of the aged vulcanizates. The composite modulus has been theoretically calculated using the well‐known Halpin‐Tsai equation. It is found that in the transverse direction, observed modulus values are greater than the calculated values, while in the longitudinal direction, the experimental modulus values are found to be lower than the calculated values for both unaged and aged composites owing to some degree of anisotropy in fiber orientation.     

玻璃纤维毡增强聚丙烯在压缩模塑流动过程中的纤维分布

通过测定玻璃纤维毡增强聚丙烯经挤压流动后不同区域的纤维含量,研究了基体树脂,增强材料的结构与性质,坯料设计,模具温度及坯料的预热温度等对玻璃纤维毡增强聚丙烯在压缩模塑流动过程中纤维发布的影响。结果表明,适当提高基体的粘度及采用多层坯料叠层的坯料设计方法,有利于制品内纤维的均匀分布;针刺密度适当的连续针刺毡及由短切纤维组成的复合针刺毡与聚丙烯形成的复合材料（GMT0,在压缩模塑的流动过程中纤维分布的均匀性较好,随着针刺密度的增加,纤维分布的均匀性下降;用粘结剂粘结而成的连续原丝毡与聚丙烯复合得到的GMT材料,纤维分布的均匀性较差,经适当针刺以后,纤维分布的均匀性得到一定程度的改善,过低的模具温度及坯料预热温度,会引起材料充模流动能力下降,但模具温度及坯料预热温度过高时,流动前沿区域的树脂富集现象将加剧。     

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     

Kinetics of strain-induced crystallization during injection molding of short fiber composites of poly(ether ether ketone)

Crystallization kinetics of short glass and carbon fiber composites of poly(ether ether ketone) (PEEK) under melt-strain conditions have been obtained for the first time, using in-situ wide angle X-ray scattering, and have been correlated to a model based on the Avrami equation in order to enable minimization of the processing time for injection molding of these materials. It has been demonstrated that increased flow rate of the melt in the mold and, consequently, increased shear rate accelerates the crystallization process of PEEK composites, analogous to similar trends observed previously in PEEK resin. Short glass fiber composites of PEEK crystallize slower than the resin under identical processing conditions, while short carbon fiber composites crystallize faster than the resin, except at the highest mold temperatures and the lowest flow rates. A model based on the Avrami equation has been proposed to fit the kinetics data obtained experimentally. The Avrami coefficient has been calculated and Arrhenius plots have been used to predict the crystallization kinetics at temperatures lower than those at which experimental data have been obtained here. Fiber orientation, flexural elastic modulus, and flexural fracture toughness of the composites have also been evaluated.     

Processing,microstructure, and failure behavior in short-fiber-reinforced poly(ether ether ketone) composites

Short-fiber-reinforced poly(ether ether ketone) (PEEK) composites were prepared by a specially designed mold. Both compression- and extrusion-molded plaques were obtained under the same thermal history. The fiber length distribution, fiber volume fraction, and fiber orientation are characterized. The fibers show an in-plane random orientation in compression-molded plaques, but they exhibit a 3-layer fiber orientation well-known for injection moldings in extrusion-molded composites. It is the final aim to simulate the rheological and morphologic behavior in injection moldings by using the laboratory designed extrusion/compression mold. Static compact tension (CT) specimens and electron microscopy (EM) were used to investigate the failure behavior. Results showed that crack initiation is the dominant failure energy absorption process in a brittle fracture, whereas crack propagation is dominant in a ductile failure. The extruded composites were mechanically characterized in two orthogonal directions (T- and L-type). The anisotropy factor is reported as 1.2.     

Dynamic mechanical analysis of fiber reinforced composites

Dynamic mechanical and thermal properties were determined for unidirectional epoxy/glass composites at various fiber orientation angles. Resonant frequency and relative logarithmic decrement were measured as functions of temperature. In low angle and longitudinal specimens, a transition was observed above the resin glass transition temperature which was manifested mechanically as anadditional damping peak and thermally as a change in the coefficient of thermal expansion. The new transition was attributed to a heterogeneous resin matrix induced by the fiber. The temperature span of the glass-rubber relaxation was found to broaden with decreasing orientation angle, reflecting the growth of fiber contribution and exhibiting behavior similar to that of Young's modulus. The change in resonant frequency through the glass transition was greatest for samples of intermediate fiber angle, demonstrating behavior similar to that of the longitudinal shear modulus.     

Some features of the injection molding of short fiber reinforced thermoplastics in center sprue-gated cavities

This paper describes an investigation into the fiber orientation in a number of center sprue fed cavities in short glass fiber filled polypropylene and nylon. The data have been interpreted in terms of a generalized five-layer structure resulting from the frozen skin formation and the high and low shear levels in the flowing melt. The implications for scaling up the mold size are discussed from the results obtained with different shot volumes. The fiber structure was observed to depend on location in the molding, local injection time, and injection rate. In addition the occurrence of fiber-free layers within the moldings using the filled polypropylene increases with an increase in shot volume, which produces an inherent ‘scale-up’ problem. Notwithstanding the mold geometry subtleties, the fiber orientation in all the moldings follows similar patterns and trends.     

短纤维复合材料注射成型纤维取向数值模拟研究进展

综述了国内外短纤维复合材料注射成型过程中纤维取向数值模拟的研究成果,包括纤维取向的描述、复合体系流变模型、工艺参数对纤维取向的影响和纤维取向数值模拟状况.展望了该领域的发展趋势.     

Preparation of rubber composites from ground tire rubber reinforced with waste‐tire fiber through mechanical milling

Composites made from ground tire rubber (GTR) and waste fiber produced in tire reclamation were prepared by mechanical milling. The effects of the fiber content, pan milling, and fiber orientation on the mechanical properties of the composites were investigated. The results showed that the stress‐induced mechanochemical devulcanization of waste rubber and the reinforcement of devulcanized waste rubber with waste‐tire fibers could be achieved through comilling. For a comilled system, the tensile strength and elongation at break of revulcanized GTR/fiber composites reached maximum values of 9.6 MPa and 215.9%, respectively, with 5 wt % fiber. Compared with those of a composite prepared in a conventional mixing manner, the mechanical properties were greatly improved by comilling. Oxygen‐containing groups on the surface of GTR particles, which were produced during pan milling, increased interfacial interactions between GTR and waste fibers. The fiber‐filled composites showed anisotropy in the stress–strain properties because of preferential orientation of the short fibers along the roll‐milling direction (longitudinal), and the adhesion between the fiber and rubber matrix was improved by the comilling of the fiber with waste rubber. The proposed process provides an economical and ecologically sound method for tire‐rubber recycling. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 4087–4094, 2007