bluuebunny/crossref_metadata_2025 huggingface dataset:
Crosslinking characterization of a polyimide: AFR700B
Authors: Russell John D. , Kardos John L.
Published: April 2004

Crosslinking in AFR700B polyimide was studied using several techniques. Crosslinking could not be detected using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Swelling in n‐methyl pyrrolidone (NMP) showed network formation occurs at cure temperatures ≥325°C (617°F), but the reaction kinetics could not be determined from the data. Dynamic mechanical analysis (DMA) studies have shown that the storage modulus (G′) increased with increasing cure temperature up to 350°C (662°F), and was constant above 350°C (662°F), indicating that crosslinking via the reverse Diels‐Alder reaction was occurring. A broad secondary transition was seen in the loss modulus (G″) curves, centered between 150 and 180°C (302 and 356°F). This secondary transition appeared at a cure temperature of 300°C (572°F) and became more dominant with increasing temperature and time. This secondary transition was not seen for cures <300°C (572°F) when the chains have not crosslinked. Therefore, this is likely due to a crosslink bond rather than one in the backbone. At 1 atm, crosslinking followed second‐order kinetics based on the increase in glass transition temperature (Tg). The Arrhenius plot of the rate constant showed a break in the slope, possibly indicating a change in reaction mechanism. At 1.38 MPa (200 psi), the Tg data was too scattered to determine the kinetics.
Experimental investigation of flow through multi‐layered preforms
Authors: Mogavero Jeffrey , Advani Suresh G.
Published: April 2004

This research investigates resin flow phenomena through preforms composed of multiple layers of reinforcement material. Two complete studies were performed: the first investigates the effect of varying the order of lay‐up of a fixed number of plies, and the second studies the impact of varying the thickness of the individual layers of a thick preform. In each case, a set of compression experiments were first performed to characterize the preforms so that in‐situ layer thicknesses can be calculated. Next, flow experiments were performed upon the preforms to determine the permeability and flow front behavior. In the first study, it was found that the weighted average scheme provides a reasonable estimate for the effective permeabilities of the preforms, with errors ranging from 14.2% to 23.8%. In the second study, however, the weighted average scheme was found to provide only a rudimentary estimate of the permeability, with an error that was seen to increase in magnitude during the course of each experiment. In addition, computer simulations were performed for the second study, which show the possibility of deriving transverse permeability values without direct measurement, although significant errors in inlet pressures were once again evident.
Forced in‐plane flow through complex deformable structures: Influence of an imposed curve
Authors: Friedman Henry L. , Johnson Robert A. , Miller Bernard , Salem David R. , Parnas Richard S.
Published: April 2004

Forced in‐plane flow of liquids through contiguous flat and curved regions of confined fabrics has been studied both as a general phenomenon and for predicting the flow of polymers during injection molding of monolithic composite structures with complex configurations. A controlled pressure difference is applied to drive the flow, while the mass flow rate is measured gravimetrically by Liquid/Air Displacement Analysis (LADA). Measurements have been carried out along fabric paths that are first vertical, then curved, and finally horizontal. Fluid flow equations have been adapted for analyzing flow in the flat sections, leading to the evaluation of permeability constants and capillary pressures. A saturated flow rate measured at constant hydrodynamic pressure is used to evaluate the overall permeability coefficient of the encapsulated fabric. Data are presented showing that permeability can be reduced as a consequence of flow through the curved region.
Resin flow in a pultrusion process
Authors: Giordano M. , Nicolais L.
Published: April 2004

A simple model for the resin flow in a pultrusion die based on the theory of lubrication has been developed. The velocity field in the pultrusion die has been calculated together with the pressure drop. A useful tool to evaluate the energy loss due to the viscosity dissipation along the die has been developed. Model results have been evaluated, by using chemorheological submodels, in terms of the contribution to the pulling force due to the viscous drag.
Injection molding of poly(ethylene terephthalate) reinforced with pregenerated thermotropic liquid crystalline polymer microfibrils
Authors: McLeod M. A. , Baird D. G.
Published: April 2004

This work was concerned with the injection molding of poly(ethylene terephthalate) (PET) reinforced with pregenerated thermotropic liquid crystalline polymer (TLCP) fibrils, where the TLCP had a higher melt processing temperature than PET. These composites, referred to as pregenerated microcomposites, were produced using a two step processing scheme. First, a novel dual extrusion process was used to spin strands of PET reinforced with nearly continuous TLCP fibrils. Second, these strands were subsequently chopped into pellets and injection molded below the melt processing temperature of the TLCP but above that of PET. This allowed the high modulus TLCP fibrils generated in the spinning step to be retained in the injection molded samples. TLCP concentration and strand draw ratio were varied in the composite strands to determine how they affected mechanical properties. It was shown that the best properties were obtained using strands containing 50 weight percent TLCP with draw ratios greater than 50, which were diluted to the desired loading level with a low viscosity injection molding grade of PET. Specifically, these composites had tensile moduli as high as 5.7 GPa when reinforced with 30 weight percent HX1000. Also, it was determined that pregenerated microcomposites had smoother surfaces than glass‐filled PET.
Interfacial properties and initial step of the water sorption in unidirectional unsaturated polyester/vegetable fiber composites
Authors: Riccieri J. E. , Vázquez A. , De Carvalho L. Hecker
Published: April 2004

In this work the interfacial properties of polyester/vegetable fiber composites were analyzed by flexural testing. The compressive/tensile (σ) and shear (τ) stresses were determined for each composite in function of the span‐to‐depth ratio (λ). The general behavior of the composites was similar to that of composites reinforced with DuPont Kevlar fiber, i.e., a maximum σ stress value is obtained. Flexural test validity for determining the Young's and shear moduli, E11 and G12, was ascertained. The Young's modulus agreed with that expected from the rule of mixtures for the composites with lowest fiber content. Short beam tests were performed on the composites. The shear stress value was improved by means of the matrix modification. Moisture sorption experiments and dynamic mechanical analysis were also performed on the natural fiber composites in the first Fickian step. Water sorption at 50% RH and 90% RH can be satisfactorily described by using a diffusional model. Water diffusion on parallelepiped samples shows a positive deviation from the Fickian behavior. Fiber capillary flow occurs through the fiber and the debonded matrix/fiber interphase during the initial Fickian step.
Processing of highly elastomeric toughened cyanate esters through a modified resin transfer molding technique
Authors: Hillermeier Roman W. , Hayes Brian S. , Seferis James C.
Published: April 2004

Model cyanate ester resins containing different quantities of epoxy functional butadiene‐acrylonitrile rubber (ETBN) to improve the fracture performance were developed as matrices for composites. With the elastomeric modification, the resin systems exhibited rheological characteristics inappropriate for laminate fabrication by conventional resin transfer molding (RTM). To fabricate the carbon fiber based laminates in one liquid molding operation successfully, a process named bleed resin transfer molding (BRTM) was established. The BRTM process combines features of RTM and resin film infusion processes (RFI) and was therefore appropriate for processing high viscosity matrix resins. A novel catalyst was selected for the cyanate ester resin that provided enough latency for the impregnation steps in the BRTM process. Through the use of thermal analytical tools, a high degree of phase separation and conversion was obtained. The conversion and the glass transition temperature were found not to decrease with increasing elastomer content, which is in contradiction to most toughening modifications. Mode I and Mode II interlaminar fracture toughness were found to increase significantly with increasing elastomer content. In Mode I, an increase of up to 140% was observed. Collectively, this work showed that through the use of the BRTM technique, matrices with toughness improvements usually only achieved by prepreg systems can be processed in an RTM‐like manner.
Compressibility and relaxation of a new sandwich textile preform for liquid composite molding
Authors: Luo Yiwen , Verpoest Ignaas
Published: April 2004

In liquid composite molding, such as RTM or SRIM, the dry reinforcement is first compressed in the mold, and then the resin is injected into the mold cavity and cured. Knowledge of the compressibility of the reinforcement is important in order to estimate the mold closing force and the attainable range of fiber volume fraction. Moreover, in a lay‐up composed of several types of fabrics, the compressibility of each fabric should be known to predict the thickness of each fabric layer, which is a prerequisite for the mold filling simulation. In this work, the relaxation and compressibility of a new sandwich fabric, Multimat®, and its components (a weft knit and a random mat) were studied and compared with a woven fabric. The different fabric relaxation behavior is explained in terms of fabric stiffness and volumetric dissipation energy. Fabric compression tests were performed by taking the fabric relaxation behavior into account. Fabric compression curves are fitted with the power law equation and agree well with the clamping pressure experimentally measured with a pressure transducer in an RTM mold. The influence of the number of layers was also investigated. Finally the compressibility of the Multimat is correlated to its components with a simple model.
An analytical method for prediction of the damping in symmetric balanced laminated composites
Authors: Yim Jong Hee , Jang Bor Z.
Published: April 2004

To obtain the effective damping of a laminated composite beam, two different analytical methods were compared. Also, we modified the basic loss factors on the basis of experimental data. In the first method, Ni and Adams's theory was used. In the second method, new energy approach was developed to determine the damping of laminated composite beams. Five typical laminated composites with [±Θ]s, [0/±Θ]s, [0/Θ]s, [0/±Θ/90]s and [90/±Θ/0]s stacking sequences were employed for this study. The present method was favorably compared with Ni and Adams's method. In this study, we found that damping was highly influenced by fiber volume fraction, fiber orientation and stacking sequence.
Mechanical properties of aligned long glass fiber reinforced polypropylene. I: Tensile strength
Authors: Yang Shean‐Wei , Chin Wei‐kuo
Published: April 2004

Long‐fiber reinforced thermoplastic composites were made from 9 mm long glass fiber reinforced PP pellets by alternative procedures of roll‐mill and hot‐press molding. The severe problem of fiber breaking during the process could be avoided by this method. The average fiber length of this composite was ∼7 mm long. More than 80% of fibers in the composite were aligned within the 20° range. In the major fiber‐oriented direction, at 25°C, the tensile strength of this composite was 205 MPa. At elevated temperatures in the range of 25°C to 125°C, the tensile strength was inversely proportional to the temperature. The two‐parameter Weibull distribution function was used to simulate the strength distribution of the composite. Results showed that the strength distribution curve shifted from high to low as the temperature increased.
Mechanical properties of aligned long glass fiber reinforced polypropylene. II: Tensile creep behavior
Authors: Yang Shean‐wei , Chin Wei‐kuo
Published: April 2004

The creep behavior of long glass fiber reinforced thermoplastic composite was investigated under different constant tensile stress and temperature. From the time‐dependent strain curve, the critical creeping time was defined as the transition point from steady to unsteady deformation and measured correspondingly. A statistical Weibull distribution function was adopted to describe the critical creeping time distribution at each stress level. A power law was employed to analyze the behavior of steady deformation stage of strain during loading. The relation between the critical creeping time and the parameter (m) of the power law is analyzed and discussed.
Yield behavior and energy absorbing characteristics of rubber‐modified epoxies subjected to biaxial stress states
Authors: Kody Robert S. , Lesser Alan J.
Published: April 2004

Hollow cylinders of aromatic‐amine cured epoxies, modified with 0%, 10%, and 20% CTBN rubber by weight were tested in stress states ranging from uniaxial compression to biaxial tension. Our results showed that rubber particles decrease the yield strength uniformly over all stress states and suppress brittle fracture in the more demanding stress states. Particle size has no effect on yield strength. Samples were also biaxially loaded and unloaded to varying stress levels to monitor and study their dissipative characteristics. From these tests, a threshold stress was observed where the stiffness of the rubber‐modified resin decreases and the deformation becomes increasingly irreversible. By comparing the changes in damage morphology with the change in loading path, we determined that a significant amount of energy is absorbed in the rubber‐modified samples prior to macroscopic yield. Additionally, this irreversibility does not appear to be associated with rubber particle cavitation or inelastic void growth.
Modeling of the consolidation of polycarbonate/carbon fiber towpregs
Authors: Nunes J. P. , Bernardo C. A. , Pouzada A. S. , Edie D. D.
Published: April 2004

Towpregs are a new class of pre‐impregnated materials that can be used to obtain structural composites by compression molding. Consolidation is an important part of this process. In this work, a mathematical model was developed to predict the evolution of the compression pressure during the isothermal consolidation of thermoplastic matrix towpregs. The model relates the applied pressure to operational variables (speed and temperature) and material variables (viscosity, particle size, and polymer volume fraction). Tests were carried out at different temperatures and platen closing speeds, using carbon fiber‐reinforced polycarbonate towpregs. The data obtained was compared with theoretical calculations, demonstrating the applicability of the model.
Study of the flow behavior of polymer‐natural fiber suspensions in the power law validity range
Authors: Márquez Alfredo , Quijano Jafet , Ríos Rolando , Ayora‐cámara Martha Helena
Published: April 2004

The melt flow properties of PVC suspensions with henequen, coconut and bovine leather, in their raw condition, and after extraction of all their low molecular weight substances were studied. The experimental results show that, at the strain rates employed, the behavior of the suspensions is described by a power law (η = mγn–1). It is important to mention that in the present work we do not restrict our analysis to the evolution of the suspension Newtonian viscosity with the fiber concentration (as commonly is reported in the literature), but a more complete analysis is performed by describing the evolution of the consistency (m) and the power law (n) indices with the fiber concentration. Both indices were evaluated using a technique previously developed. The flow index (n) presents an anomalous behavior, it increases when the fibers are incorporated into the melted matrix at low fiber concentrations. This unexpected behavior is very different from that commonly reported in the literature and is apparently due to the flexibility of fibers. Moreover, the influence of the fiber extractable materials on the behavior of these suspensions was also evaluated. It was found that these latter materials apparently influence the value of the consistency index (m) of suspensions, at fiber concentrations above the critical pigment volume fraction; however, they do not have a significant effect on the power law index (n). Concerning the mechanical behavior of composites molded from the previous suspensions, it was found that when the fiber content augments, their elastic modulus increases, but their tensile strength falls. This behavior, however, could be improved by increasing the adhesion between the fibers and matrix.
Analysis of resin transfer/compression molding process
Authors: Kang Moon Koo , Il Lee Woo
Published: April 2004

Resin transfer/compression molding (RT/CM) is a two‐step process in which resin injection is followed by mold closing. This process can enhance the resin flow speed and the fiber volume fraction, as well as reducing the mold filling time. In this study, a simulation program for the mold filling process during RT/CM was developed using the modified control volume finite element method (CVFEM) along with the fixed grid method. The developed numerical code can predict the resin flow, temperature, pressure, and degree of cure distribution during RT/CM. The compression force required for squeezing the impregnated preform can also be calculated. Experiments were performed for a complicated three‐dimensional shell to verify the feasibility of the RT/CM process and the numerical scheme. The compression force and the compression speed were measured. A close agreement was found between the experimental data and the numerical results. The resin front location obtained from a short shot experiment was compared with the numerical prediction. Again, a close agreement was observed. In order to demonstrate the effectiveness of the numerical code, simulations were performed for more complicated process conditions with anisotropic permeability of the preform at higher fiber volume fractions.
Effect of interfacial modification on metal fiber filled polypropylene composites and property balance
Authors: Tan Song‐ting , Zhang Ming‐qiu , Rong Min‐zhi , Zeng Han‐min
Published: April 2004

Mechanical properties and electrical conductivity of discontinuous stainless steel fiber (SSF) filled polypropylene (PP) composites were considered as candidates for shielding electromagnetic interference (EMI) applications. In order to improve the unsatisfied impact resistance, surface treatments of SSF and modified PP were introduced. By means of a microdroplet pull‐out test, polypropylene grafted maleic anhydride copolymer (PP‐g‐MAH) was found to be able to enhance the poor interfacial adhesion between fiber and matrix. On this basis, PP‐g‐MAH was used to prepare conventional composites, and the macromechanical measurements showed evidence that PP‐g‐MAH helped increase both flexural and impact strength of the composites. However, the good affinity of PP‐g‐MAH for SSF reduced composite conductivity accordingly. Finally, blends of PP and PP‐g‐MAH proved to be a solution for the problem, i.e., the impact strength was increased significantly while acceptable electrical resistivity was maintained.
Simulation of compression resin transfer molding to manufacture thin composite shells
Authors: Pham Xuan‐tan , Trochu François
Published: April 2004

The resin flow through fiber reinforcements in Compression Resin Transfer Molding (CRTM) has been modeled by Pham et al. (1). First the preform is partially filled by resin during the injection phase. Then it is compressed by the mobile part of the mold. The resin flow in the fiber bed is governed by Darcy's law. The consolidation of the saturated preform is described by the total mass conservation. A mathematical model is developed for thin curved composite parts. A filling algorithm based on resin conservation on a deformable grid is used to advance the flow front at each time step. Resin pressure and velocity are calculated by the finite element method. Several control parameters of the CRTM process are investigated in this study, such as the compaction speed of the mold upper wall, the injection pressure and the closing/opening of the injection gate. The numerical model allows the calculation of pressure distribution in the mold, which is compared with analytical solutions and experimental results.
Microstructures of 3‐D carbon/carbon composites using solid rods as reinforcements
Authors: Kuo Wen‐shyong , Ko Tse‐hao , Chi Yuan‐chen
Published: April 2004

This paper examines microstructures of 3‐D woven carbon/carbon composites. Unidirectional carbon/phenolic rods, with 1 mm in diameter, were made by the pultrusion technique and then combined into 3‐D preforms in the axial direction. The preforms were of three‐axis orthogonal structures based on 3‐D weaving. A special weaving setup to incorporate the rods has been developed, and three types of preforms with varying the weaving yarn sizes have been made. Another conventional type composed of carbon yarns in all axes was also made for purpose of comparison. The geometrical aspects of both types of preforms have been studied. Using the rods was found to effectively eliminate fiber crimp in the axial direction. The fabrication of the carbon/carbon composites has been carried out based on multiple impregnation and carbonization of the phenolic resin. Open and close pores of the materials have been measured after each densification process. The variations in open and close pores differ greatly in response to the densification process. The induced matrix cracks due to pyrolysis shrinkage have been examined based on microscopic observations. Dictated by the preform types, matrix cracks were regularly developed in the weaving yarns. While a dominant transverse crack was formed in each of the yarns, small pores were extensively created in the rods. Separation of bundle interfaces was also observed. Formation of these cracks in relation to processing and microstructures is discussed in detail.
Low moisture absorptive epoxy formulations for Gr/Ep laminates
Authors: Lin King‐fu , Yeh Ren‐jie
Published: April 2004

The incorporation of 2‐undecyl‐imidazole (C11Z) and chromium acetylacetonate (Cr(acac)3) additives into N, N, N′, N′‐tetraglycidyl diaminodiphenylmethane (TGDDM)/diaminodiphenylsulfone (DDS) epoxy formulations was found to significantly decrease the moisture absorption of their prepared graphite/epoxy laminates. However, the same additions did not much affect the moisture absorption of the cured TGDDM/DDS neat resins. Thus, the former case was attributed to the processing effects in view of the fact that C11Z pre‐reacting with TGDDM during lay‐up process produced the ether‐linkage polymer chains in the epoxy networks and raised the viscosity. The following compacting stage of laminates was believed to squeeze the small molecules such as unreacted TGDDM, DDS and Cr(acac)3, toward the surface of carbon fibers and increase the chance of Cr(acac)3 to block the hydroxyl groups in the epoxy networks produced by the reactions between TGDDM and DDS. Some evidence was provided to support the above hypothesis in this study.
Three‐dimensional simulations of the curing step in the resin transfer molding process
Authors: Choi Mi Ae , Lee Mi Hye , Chang Jaeeon , Lee Seung Jong
Published: April 2004

The curing step in resin transfer molding process involves heat transfer coupled with the curing reaction of thermoset resin. In order to examine the curing behavior under a specified cure cycle in the resin transfer molding process, numerical simulations are carried out by three‐dimensional finite elements method. An experimental study for isothermal cure kinetics of epoxy resin is conducted by using differential scanning calorimetry. Kinetic parameters based on the modified Kamal model are determined from the calorimetric data for the epoxy system, and by using these parameters, numerical simulations are performed for a hat‐shaped mold. It is found from the simulation results that the temperature profile and the degree of cure are well predicted for the region inside the mold. This numerical study can provide a systematic tool in the curing process to find an optimum cure cycle and a uniform distribution of the degree of cure.
A numerical model of the viscosity of an epoxy prepreg resin system
Authors: Theriault R. P. , Osswald T. A. , Castro J. M.
Published: April 2004

The development of the viscosity of a thermoset material during processing is complicated because of the dependence of the initial material state and the kinetic rate of conversion from a liquid to a solid material. Uncured thermoset materials typically have a low enough viscosity such that the consumption of energy to generate flow is relatively low. However, as the curing process advances, the flow mechanisms become hindered by the development of a network gel during crosslinking. Once the resin has reached the appropriate degree of cure for gelation, the resin system is incapable of large fluid‐like deformations. In this research, the rheological properties of an epoxy resin system used in laminate processing were measured and numerically fit with a modification to the dual Arrhenius model to predict the progression of the viscosity during cure. The numerical results were compared with the experimental measurements, and it was found that the model predicts the experimental observations quite well. It was found that the initial degree of cure of the prepreg is not as significant a factor as the temperature rate dependence on the processing time between the point of flow onset and gelation. However, the minimum viscosity during processing is strongly influenced by the initial degree of cure of the prepreg system.
A study of the thermomechanical properties of carbon fiber‐polypropylene composites
Authors: Van Hattum F. W. J. , Bernardo C. A. , Finegan J. C. , Tibbetts G. G. , Alig R. L. , Lake M. L.
Published: April 2004

Short fiber composites were produced using polypropylene as matrix and polyacrylonitrile (PAN)‐based fibers or vapor grown carbon fibers (VGCF) as reinforcement. The strength, stiffness, and coefficient of thermal expansion (CTE) of the composites were measured. The VGCF‐composites showed strength and CTE that are competitive with those of “conventional” PAN‐fiber composites, but the stiffness was marginally lower. Micromechanical modeling of the PAN composite properties gives results consistent with the measurements. The models can be used to infer the apparent VGCF‐properties from their composites.
A study on the determination of in‐plane permeability of fiber preforms
Authors: Um Moon‐kwang , Lee Sang‐kwan
Published: April 2004

One of the parameters most frequently used in modeling and designing the mold filling process is the permeability of fibrous preforms. To obtain radial propagation of a viscous polymer into a homogeneous orthotropic porous medium, an approximate solution is derived and its results are compared with numerical ones obtained from boundary element method (BEM). A simple and direct procedure incorporating approximate solution with experimental data has been proposed to determine the principal in‐plane permeabilities of the reinforcements. A scheme is also suggested in order to increase the accuracy in the determination of degree of anisotropy. The effect of resin injection type on permeability is investigated through the experiments.
The effect of interface characteristics on the morphology, rheology and thermal behavior of three‐component polymer alloys
Authors: Fisher I. , Siegmann A. , Narkis M.
Published: April 2004

Immiscible polymer blends are interesting multiphase host systems for fillers. Such systems exhibit, within a certain composition limits, either a separate dispersion of the two minor phases or a dispersion of encapsulated filler particles within the minor polymer phase. Both thermodynamic (e.g. interfacial tension) and kinetic (e.g. relative viscosity) considerations determine the morphology developed during the blending process.

The effect of interfacial characteristics on the structure‐property relationships of ternary polymer alloys and blends comprising polypropylene (PP), ethylene‐vinyl alcohol copolymer (EVOH) and glass beads (GB), or fibers (GF), was investigated. The system studied was based on a binary PP/EVOH immiscible blend, representing a blend of a semi‐crystalline apolar polymer with a semicrystalline highly polar copolymer. Modification of the interfacial properties was obtained through using silane coupling agents for the EVOH/glass interface and compatibilization using a maleic anhydride grafted PP (MA‐g‐PP) for the PP/EVOH interface. The compatibilizer was added in a procedure aimed to preserves the encapsulated EVOH/glass structure. Blends were prepared by melt extrusion compounding and specimens by injection molding. The morphology was characterized using scanning electron microscopy (SEM) and high resolution SEM (HRSEM), the shear viscosity by capillary rheometry and the thermal behavior using differential scanning calorimetry (DSC).

The system studied consisted of filler particles encapsulated by EVOH, with some of the minor EVOH component separately dispersed within the PP matrix. Modification of the interfaces resulted in unique morphologies. The aminosilane glass surface treatment enhanced the encapsulation in the ternary [PP/EVOH]GB blends, resulting in an encapsulated morphology with no separtely dispersed EVOH particles. The addition of a MA‐g‐PP compatibilizer preserves the encapsulated morphology in the ternary blends with some finely dispersed EVOH particles and enhanced PP/EVOH interphase interactions.

The viscosity of the binary and ternary blends was closely related to the blend's morphology and the level of shear rate. The treated glass surfaces showed increased viscosity compared to the cleaned glass surfaces in both GB and GF containing ternary blends.

Both EVOH and glass serve as nucleating agents for the PP matrix, affecting its crystallization process but not its crystalline structure. The aminosilane glass surface treatment completely inhibited the EVOH crystallization process in the ternary blend.

In summary, the structure of the multicomponent blends studied has a significant effect on their behavior as depicted by the rheological and thermal behavior. The structure‐performance relationships in the three‐component blends can be controlled and varied.
Production of leather‐like composites using chemically modified short leather fibers. I: Chemical modification by emulsion polymerization
Authors: Madera‐Santana T. J. , Aguilar‐Vega M. J. , Márquez‐Lucero Alfredo , Vázquez‐Moreno F.
Published: April 2004

In order to evaluate the possible use of short leather fibers to produce leather‐like composites, five kilograms of fibers (extracted from leather wastes) were modified by in situ emulsion polymerization of methyl methacrylate (MMA). This treatment was performed in order to increase the compatibility of leather fibers with several commodity polymers used in the shoe and furrier industries. The chemical modification was carried out by aqueous emulsion polymerization initiated by a redox system (potassium persulfate and sodium metabisulfite). The effects of the monomer and redox initiator content as well as the reaction temperature were evaluated. The modified short leather fibers were characterized by instrumental techniques such as Infrared Spectroscopy (IR), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), X‐ray Diffraction and Scanning Electronic Microscopy (SEM). The results show that the polymer is formed on the exterior of fibers (deposited fraction) as well as in the interior (by grafting or forming interpenetrated networks). The treatment significantly improves the thermal stability of fibers. It also reduces their water adsorption capacity, as a coating of PMMA is produced over the leather surface, as microscopic analysis has revealed. The last characteristic could be an advantage in certain applications.
Factors influencing viscoelastic properties of a poly (butylene terephthalate) reinforced with short glass fibers
Authors: Beaudoin O. , Bergeret A. , Quantin J. C. , Crespy A.
Published: April 2004

Short glass fiber/poly(butylene terephthalate) composites with different glass fiber treatments were characterized within a temperature range from −150°C to + 150°C by dynamic tests in torsion and tensile modes. Untreated fibers or fibers coated by silane coupling agents associated or not with sticking agents were used. It was observed that the magnitude of β and α relaxations depends strongly on the microstructural parameters of such composites: fiber content, degree of crystallinity of the matrix, fiber length distribution, level of adhesion.
Interfacial strength of PTFE fiber/i‐PP composites with transcrystalline layers of different thickness
Authors: Wang Chi , Chen C.‐C.
Published: April 2004

Transcrystallization of isotactic polypropylene (i‐PP) on the surface of polyte‐trafluroethylene (PTFE) fibers was investigated. Using the single‐fiber pull‐out test, the effect of the transcrystalline layers (TCLs) on the adhesive fracture energy was studied as well. To induce TCL with different thickness, two‐step crystallization of i‐PP was carried out; the PTFE/i‐PP composites were first crystallized at 140°C for a specified time and were subsequently quenched in 25°C water to conclude the crystallization. Specimens with TCL thickness of 45 ± 6 and 126 ± 15 μm were thus prepared for crystallization time of 1 and 3 hrs, respectively. In addition, the bulk portion surrounding the TCL showed a transparent appearance that indicated crystallization of i‐PP spherulites was much limited. In spite of the difference in the crystallization time, it is suggested that the mechanical properties of the individual constituents in the matrix (TCL and spherulites) prepared in this way remain unchanged, leaving the TCL thickness alone as the major controlling factor. Pull‐out results show that adhesive fracture energy is independent of the TCL thickness and the measured value is 3.0 ± 1.5 J/m2 in spite of the large variation in the TCL thickness. Compared to specimens without TCL whose adhesive fracture energy is 2.1 ± 1.1 J/m2, promotion of the adhesion level seems much limited, if any, through the presence of TCL and its thickness. However, the friction stress at the debonded PTFE fiber/i‐PP TCL is increased when TCL are produced at high crystallization temperatures. Toughness of composites with TCL can be enhanced in this manner although the neat adhesive fracture energy remains intact.
Analysis of void removal in liquid composite molding using microflow models
Authors: Shih Chih‐Hsin , Lee L. James
Published: April 2004

Void removal in liquid composite molding was studied. Two void removal mechanisms were observed during flow visualization. Owing to the complicated geometry in the fiber reinforcement, micron‐sized flow channels were fabricated in order to carry out quantitative analysis. The mobility of voids in both straight and constricted channels was investigated. It was found that the mobility of the bubble is related to both the bubble size and the wetting between the fluid and the solid surface (i.e. contact angle). A snap‐off effect of the gas bubble was observed when the bubble passed through the constricted channel. The snap‐off time was found to be a function of constriction geometry and the capillary number.
Metal particle modification of composite matrices for customized density applications
Authors: Gilbert Eric N. , Hayes Brian S. , Seferis James C.
Published: April 2004

A key aspect of composite technology lies in the ability to design a part to a specific strength and thickness. Recently, new applications were identified where it was desirable to vary the density in specific areas of a part. In this work, a model prepreg system was modified with fine metal and thermoplastic particles for specific weight tailoring. These particles were placed on the prepreg surface, forming a partially interlayer modified composite when laid up and cured. Experiments were performed on the specific gravity and fracture toughness of laminates made from the prepregs. The results showed that it is possible to tailor the density of a composite system without changing the manufacturing process or fracture toughness requirements.
Hygrothermal cycling effects on the durability of phenolic based composites
Authors: Chung Kimo , Yoshioka Kenichi , Seferis James C.
Published: April 2004

Work has been performed to investigate the thermal and mechanical properties of carbon fiber/phenolic resin composites as engineering materials for the aerospace industry. These materials are cost effective while displaying excellent temperature and fire resistance as well as good mechanical properties. All phenolic and epoxy composite specimens used here were prepared by resin transfer molding (RTM) to model a cost‐effective process. Hygrothermal cycling effects on the property changes of phenolic composites were evaluated through thermal, mechanical, and morphological tests. The fracture performance of a phenolic composite modified with a silicone‐based additive decreased after fewer hygrothermal cycles than unmodified phenolic and epoxy composites. Results from dynamic mechanical analysis (DMA) experiments showed that the modified phenolic composite was more significantly affected by the hygrothermal cycling than the unmodified phenolic composites. Fatigue tests showed that the phenolic composites that were not exposed to hygrothermal cycling had more resistance to fatigue cycles than the epoxy composites.
Prototypes for building applications based on thermoplastic composites containing mixed waste plastics
Authors: Xanthos M. , Dey S. K. , Mitra S. , Yilmazer U. , Feng C.
Published: April 2004

Automotive shredder residue (ASR) and a complex residue obtained as a by‐product in the tertiary recycling of nylon‐6 fibers from used carpets were evaluated as potential additives in thermoplastic composites to be used for building applications. Prototype blocks were prepared by the “intrusion” process using various ratios of the waste streams and low‐density polyethylene (LDPE) in the absence of compatibilizers. Hence, product morphologies and corresponding properties were largely controlled through processing. They were evaluated for their short‐term and longterm mechanical properties, flammability, thermal conductivity, and heavy‐metal and total organic carbon leaching characteristics. Encapsulation of the waste feedstock by LDPE during molding in a single‐screw extruder significantly reduced the leachable content. In an effort to further reduce the leachable content, the mixtures were processed in two stages by precompounding in adevolatilizing twin‐screw extruder prior to molding. In comparison to the as‐received wastes, improved homogenization decreased the leachable heavy‐metal content by at least 98%. The carpet residue feedstock consisting of polypropylene, styrene‐butadiene rubber and calcium carbonate appears to be an attractive low‐cost, high‐volume material with consistent properties and could be used as filler in thermoplastic composites. Comparison of their performance characteristics suggested that the carpet residue composites would be favored versus ASR composites as replacement of the wood thermal barrier components in a novel steel‐based stud assembly.
The influence of chemical surface modification on the performance of sisal‐polyester biocomposites
Authors: Misra S. , Misra M. , Tripathy S. S. , Nayak S. K. , Mohanty A. K.
Published: April 2004

This article concerns the effectiveness of various types and degrees of surface modification of sisal fibers involving dewaxing, alkali treatment, bleaching cyanoethylation and viny1 grafting in enhancing the mechanical properties, such as tensile, flexural and impact strength, of sisal‐polyester biocomposites. The mechanical properties are optimum at a fiber loading of 30 wt%. Among all modifications, cyanoethylation and alkali treatment result in improved properties of the biocomposites. Cyanoethylated sisal‐polyester composite exhibited maximum tensile strength (84.29 MPa). The alkali treated sisal‐polyester composite exhibited best flexural (153.94 MPa) and impac strength (197.88 J/m), which are, respectively, 21.8% and 20.9% higher than the corresponding mechanical properties of the untreated sisal‐polyester composites. In the case of vinyl grafting, acrylonitrile (AN)‐grafted sisal‐polyester composites show better mechanical properties than methyl‐methacrylate (MMA)‐grafted sisal composites. Scanning electron microscopic studies were carried out to analyze the fiber‐matrix interaction in various surface‐modified sisal‐polyester composites.
Creep and recovery behavior of novel organic‐inorganic polymer hybrids
Authors: Adalja Sunil B. , Otaigbe Joshua U.
Published: April 2004

A novel class of organic‐inorganic polymer hybrids were developed by meltblending up to 50 (v/v) % [about 83 (w/w) %] tin‐based polyphosphate glass (Pglass) and low‐density polyethylene (LDPE) in conventional plastics processing equipment. The creep and recovery behavior of these polymer hybrids at 30°C were studied to understand the effect of the Pglass on the creep resistance of the LDPE. The results suggest that the Pglass acts as a reinforcement and an increase in the Pglass loading leads to significantly lower creep strains. This creep resistance is further enhanced by pretreating the Pglass with coupling agents prior to incorporating them into the Pglass‐LDPE hybrids. The experimental creep compliance of these materials conformed excellently with empirical power‐law equation and a modified Burger's model, suggesting that the materials are linearly viscoelastic under the test conditions.
Interfacial interaction in sisal/epoxy composites and its influence on impact performance
Authors: Rong Min Zhi , Zhang Ming Qiu , Liu Yuan , Yan Hui Ming , Yang Gui Cheng , Zeng Han Min
Published: April 2004

To obtain comprehensive knowledge of the interfacial effect on the impact performance of sisal fiber reinforced epoxy composites, the fiber surface was modified in different ways prior to compounding. By using a surface tensiometer and dynamic mechanical analyzer, interfacial interactions in the composites were characterized. The results indicated that the chemical treatments brought about strong bonding between sisal bundles and the epoxy matrix. The subsequent impact tests revealed that the microfailure mechanism involved is a function of interfacial adhesion and fiber length continuity (i.e., continuous or discontinuous fiber). In the case of unidirectional laminates, an optimum fiber treatment should be able to result in an increased affinity between fiber bundles and matrix and a decreased intercellular adhesion. In this way, extension and uncoiling of the spirally arranged microfibrils, a main energy consumption process of plant fibers, can impart significant toughness to the composites. For short fiber composites, the interfacial strength should be properly tailored so as to increase energy dissipation through debonding and pullout of fiber bundles.
A fractal in‐plane permeability model for fabrics
Authors: Yu Boming , Lee L. James , Cao Hanqiang
Published: April 2004

In this paper, a fractal in‐plane permeability model for various fabrics is developed. The model is based on the fractal characteristics of pores in fiber preforms. Four different glass fabrics are considered in the modeling: plain woven, 4‐harness, bidirectional stitched, and continuous strand random mats. The fractal in‐plane permeability model can be expressed as a function of the pore area fractal dimension and architectural parameters of the fiber preform. This model also relates the permeability to porosity changes of fiber preforms under compression, which usually occurs in the molding processes. To verify the applicability of the model, the results from the present fractal model are compared with those from the one‐dimensional analysis model and with a set of permeability measurements. Good agreement is found between the two models and the permeability measurements in the general porosity ranges of interest.
Influence of processing rate and formulation on the interface strength of vinyl ester/E‐glass composites
Authors: McDonough W. G. , Dunkers J. P. , Holmes G. A. , Feresenbet E. , Kim Y. H. , Parnas R. S.
Published: April 2004

The single fiber fragmentation test was used to investigate the effect of gelation time on interfacial shear properties of fast reacting resin systems. We developed a processing system capable of producing single fiber fragmentation samples with gelation times that ranged from 2 min to 45 min. The interfacial properties of E‐glass fibers in vinyl ester resin were measured with single fiber fragmentation tests using a manual and an automated testing machine. We found that vinyl ester resins catalyzed with methyl ethyl ketone peroxide and promoted with cobalt naphthenate and dimethylaniline gelled in less than two minutes and had an estimated interfacial shear strength of 105 MPa. Specimens cured without the promoter gelled in 45 min and had an interfacial shear strength of 72 MPa. Further curing of the unpromoted specimens resulted in an increase in shear strength to 96 MPa. We have demonstrated the ability to make and test rapidly cured specimens, thus expanding the range of materials that can be tested using the single fiber fragmentation testing technique.
Effects on the melt rheology of systems of Nd‐Fe‐B particles suspended in a poly(phenylene sulfide) and liquid crystalline polymer blend
Authors: Guschl Peter C. , Otaigbe Joshua U.
Published: April 2004

The melt rheology of blends of a liquid crystalline polymer (LCP) and poly(phenylene sulfide) (PPS) and their composites with ferromagnetic Nd‐Fe‐B particles (MQP) was studied. We investigated the effects of LCP concentration, Nd‐Fe‐B particle volume fraction and size, distribution, and shear rate on the rheological properties of these composites. Enthalpy of fusion changes that were observed resulted from the addition of the LCP and Nd‐Fe‐B particles to the polymer blends/composites. The shear rate and frequency dependencies of the materials revealed a viscosity reduction at low (1–3 wt%) and moderate (10–15 wt%) LCP concentrations, and strong effects on the shear‐thinning characteristics of the melt. The suspensions of polydispersed Nd‐Fe‐B particle configurations in PPS that were of lower size ratios gave better processability, which is contradictory to previously reported behavior of suspensions containing spherical particles. Specifically, the compositions with unimodal and a bimodal distribution of Nd‐Fe‐B particles gave the lowest viscosities. The experimental data were correlated with semi‐empirical viscosity model equations of Maron‐Pierce, Krieger‐Dougherty, Eilers, and Thomas and were found to be consistent with the data. The maximum packing fraction, ϕm, of the MQP particles was estimated to be within the range of 0.78 ϕ ≤m ≤ 1.0 through graphical and parametric evaluation methods.