Showing papers in "Polymer Composites in 2004"

Big returns from small fibers: A review of polymer/carbon nanotube composites

Abstract: This paper reviews recent studies conducted on carbon nanotube/polymer composites. Carbon nanotubes are promising new materials for blending with polymers with potential to obtain low-weight nanocomposites of extraordinary mechanical, electrical, thermal and multifunctional properties. The size scale, aspect ratio and properties of nanotubes provide advantages in a variety of applications, including electrostatically dissipative materials; advanced materials with combined stiffness, strength and impact for aerospace or sporting goods; composite mirrors; automotive parts that require electrostatic painting and automotive components with enhanced mechanical properties. The various processing methods for producing these nanocomposites are discussed, in particular melt mixing, solution processing and in-situ polymerization. Some key results are summarized, relating to the mechanical, electrical, thermal, optical and surface properties. Finally, the challenges for the future are discussed in terms of processing, characterization, nanotube availability, nanotube tailoring, and the mechanisms governing the behavior of these remarkable nanoscale composites. Polym. Compos. 25:630–645, 2004. © 2004 Society of Plastics Engineers.

Desirable features in mold filling simulations for Liquid Composite Molding processes

Abstract: Numerical simulations of the mold filling process in various Liquid Composite Molding (LCM) techniques, in which the fiber reinforcements represent the porous media and the polymeric resin is the impregnating fluid, have been successfully utilized for over a decade now, but they continue to be under dynamic development. Some of the recent applications are the increased emphasis on design optimization, control of the impregnation process and the rapid introduction of new LCM techniques such as the Vacuum Assisted Resin Transfer Molding (VARTM). This paper describes the requirements that these new applications demand on the implementation of such numerical simulation for modeling mold filling in LCM processes, namely Resin Transfer molding (RTM) and VARTM. Liquid Injection Molding Simulation (LIMS) developed at the University of Delaware, which can simulate the flow in such processes, has been modified to encompass these features. It addresses practical issues concerning modeling the part geometry, such as the proper choice of one-, two- and three-dimensional elements and their effective combinations. It also describes the simulation of non-trivial boundary conditions, placement of sensors and allowing for resin injection control using the functions built into the simulation program and the embedded scripting language. Several examples are presented to highlight the importance of its flexibility. The paper also addresses some VARTM specific issues, such as the modeling of distribution media, dimensional change during filling and fiber tow saturation. Polym. Compos. 25:355–367, 2004. © 2004 Society of Plastics Engineers.

A systematic investigation on the influence of the chemical treatment of natural fibers on the properties of their polymer matrix composites

Abstract: This paper reports a systematic study of the effects on composite properties of different chemical treatments on natural fibers. Both short flax fibers and flax cellulose pulp in a polypropylene matrix have been investigated. The influence of treatments on fiber properties was investigated by means of spectroscopic, thermal and mechanical tests. Moreover, the effects of fiber treatment on the crystallinity of the matrix were analyzed using differential scanning calorimetry and optical microscopy. The mechanical properties of the composites obtained were studied using tensile and bending tests. It is shown that most of the main properties of the composites can be improved by adequately treating the fibers. The results of this study provide a database mainly devoted to material selection for the automotive industry. This research has been performed as a part of the ECOFINA project in the framework of the 5th European Research Program of the European Community. Polym. Compos. 25:470–479, 2004. © 2004 Society of Plastics Engineers.

The effect of curing additive on the mechanical properties of phthalonitrile-carbon fiber composites

Abstract: Unidirectional carbon fiber-reinforced phthalonitrile composite panels were fabricated by prepreg consolidation with bis[4-(4-aminophenoxy)phenyl]sulfone (p-BAPS) as the phthalonitrile curing additive. Rheometric measurements and elevated-temperature, short beam shear tests were used to evaluate the cure of the composite as a function of the cure and postcure conditions. These techniques revealed that a fully cured phthalonitrile composite was obtained when the composite was heated at 375°C for 8 hours. Room-temperature mechanical properties of the cured composite were then evaluated using short beam shear, tension, and flexural tests. The results are compared with those obtained by curing the phthalonitrile with 1,3-bis(3-aminophenoxy)benzene (m-APB). The data indicate that substitution of p-BAPS for m-APB has little effect on the mechanical properties of the cured composite. Elevated-temperature, short beam shear studies up to 371°C show that the cured phthalonitrile composite retains approximately 70% of its room-temperature apparent interlaminar shear strength. The composite also retains 70% of its room-temperature storage modulus up to 450°C. Polym. Compos. 25:554–561, 2004. © 2004 Society of Plastics Engineers.

UV aging of poly(propylene)/wood‐fiber composites

Abstract: The effect of accelerated UV-aging on properties of PP/wood-fiber composites has been studied. Plates containing 0, 25 and 50 wt% wood-fibers were subjected to accelerated UV-aging in a QUV weatherometer for up to 8 weeks. Stabilization against UV-degradation was made by adding 3% of a UV stabilizer. The results showed that both the unfilled PP and the PP/wood-fiber composites displayed good UV resistance with regard to mechanical properties. The color of the PP/wood-fiber composite plates changed from brown to chalky white at the exposed area because of the formation of a thin, strongly degraded surface layer. Physical and chemical analysis of these surface layers using differential scanning calorimetry, Fourier transform infrared spectroscopy, and scanning electron microscopy showed that degradation of the PP matrix had occurred, leading to chemicrystallization and extensive surface cracking. A decrease in PP melting temperature was also noted, due to molecular chain scission and the formation of extraneous groups, such as carbonyls and hydroperoxides. These results indicate that the wood-fibers act as chromophores when incorporated in the PP matrix. Increasing the fiber content from 25 to 50 wt% increases the rate of degradation of the PP matrix by approximately a factor of two. Polym. Compos. 25:543–553, 2004. © 2004 Society of Plastics Engineers.

Deformation mechanisms and mechanical properties of modified polypropylene/wood fiber composites

Abstract: Mechanical properties and deformation mechanisms of polypropylene (PP)/wood fiber (WFb) composites modified with maleated polypropylene as compatibilizer and styrene-butadiene rubber (SBR) as impact modifier have been studied. The addition of maleated polypropylene to the unmodified polypropylene/wood fiber composite enhances the tensile modulus and yield stress as well as the Charpy impact strength. SBR does not cause a drop in the tensile modulus and yield strength because of the interplay between decreasing stiffness and strength by rubber modification and increasing stiffness and strength by good interfacial adhesion between the matrix and fibers. The addition of both maleated polypropylene and rubber to the polypropylene/wood fiber composite does not result in an improvement of effects based on maleated polypropylene and rubber, which includes possible synergism. The deformation mechanisms in unmodified polypropylene/wood fiber composite are matrix brittle fracture, fiber debonding and pullout. A polymeric layer around the fibers created from maleated polypropylene may undergo debonding, initiating local plasticity. Rubber particle cavitation, fiber pullout and debonding were the basic failure mechanisms of rubber-toughened polypropylene/wood fiber composite. When maleated polypropylene was added to this composite, fiber breakage and matrix plastic deformation took place. Polym. Compos. 25:521–526, 2004. © 2004 Society of Plastics Engineers.

Durability and environmental degradation of glass‐vinylester composites

Abstract: FRP materials are emerging as cost-effective and high-performing materials in various structural applications ranging from aerospace and defense to automotive, sporting goods, construction and transportation. These breakthroughs were achieved through better design practice and innovative manufacturing processes in addition to an understanding of the mechanisms governing the performance of these materials. Much of the developed expertise was confined to one composite material system, i.e., epoxy-based composite materials. For emerging applications such as the rehabilitation of civil engineering structures and the oil industry, this material system is not cost-effective when compared to conventional materials. Glass-vinylester composites are considered a potential material system offering enhanced mechanical properties at a competitive cost. However, there is very little long-term durability data related to their environmental performance and their resistance to corrosive fluids. In this paper, durability and environmental degradation of glass-vinylester composites are evaluated when exposed to high temperature, moisture, seawater, and corrosive fluid. Polym. Compos. 25:609–616, 2004. © 2004 Society of Plastics Engineers.

Mechanical properties of polypropylene matrix composites reinforced with natural fibers: A statistical approach

Abstract: This work presents a systematic and statistical approach to evaluate and predict the properties of random discontinuous natural fiber reinforced composites. Different composites based on polypropylene and reinforced with natural fibers were produced and their mechanical properties are measured together with the distribution of the fiber size and the fiber diameter. The values obtained were related to the theoretical predictions, using a combination of the Griffith theory for the effective properties of the natural fibers and the Halpin-Tsai equation for the elastic modulus of the composites. The relationships between experimental results and theoretical predictions were statistically analyzed using a probability density function estimation approach based on neural networks. The results show a more accurate expected value with respect to the traditional statistical function estimation approach. In order to point out the particular features of natural fibers, the same proposed method is also applied to PP-glass fiber composites.

Creep behavior of biocomposites based on sisal fiber reinforced cellulose derivatives/starch blends

Abstract: Biodegradable composites based on cellulose derivatives/starch blends reinforced with sisal short fibers were fabricated by injection molding. Results of short-term flexural creep tests are reported to investigate the time-dependence behavior of the composites. Fiber content and temperature effects are also considered, taking into account various methods and equations. At short times, a creep power law is employed. A master curve with the Arrhenius model is used to determine the creep resistance at longer times and different temperatures. Good fitting of the experimental results with the four-parameter model is reported, leading to a relationship between the observed creep behavior and the composite morphology. The addition of sisal fibers to the polymeric matrix promotes a significant improvement of the composite creep resistance. Polym. Compos. 25:280–288, 2004. © 2004 Society of Plastics Engineers.

Thermally conductive carbon filled nylon 6,6

Abstract: Increasing the thermal conductivity of typically insulating polymers, such as nylon 6,6, opens new markets. A thermally conductive resin can be used for heat sink applications. This research focused on performing compounding runs followed by injection molding and through-plane thermal conductivity testing of carbon filled nylon 6,6 based resins. The three carbon fillers investigated included an electrically conductive carbon black, synthetic graphite particles, and a surface treated polyacrylonitrile (PAN) based carbon fiber. Conductive resins were produced and tested that contained varying amounts of these single carbon fillers. In addition, combinations of fillers were investigated by conducting a full 23 factorial design and a complete replicate. The objective of this paper was to determine the effects and interactions of each filler on the thermal conductivity of the resins. Synthetic graphite particles caused the largest increase in composite thermal conductivity. In addition, all the single fillers and combinations of fillers caused a statistically significant (at the 95% confidence level) increase in composite thermal conductivity. Polym. Compos. 25:186–193, 2004. © 2004 Society of Plastics Engineers.

Flow modeling and simulation for vacuum assisted resin transfer molding process with the equivalent permeability method

Abstract: Vacuum assisted resin transfer molding (VARTM) offers numerous advantages over traditional resin transfer molding, such as lower tooling costs, shorter mold filling time and better scalability for large structures. In the VARTM process, complete filling of the mold with adequate wet-out of the fibrous preform has a critical impact on the process efficiency and product quality. Simulation is a powerful tool for understanding the resin flow in the VARTM process. However, conventional three-dimensional Control Volume/Finite Element Method (CV/FEM) based simulation models often require extensive computations, and their application to process modeling of large part fabrication is limited. This paper introduces a new approach to model the flow in the VARTM process based on the concept of equivalent permeability to significantly reduce computation time for VARTM flow simulation of large parts. The equivalent permeability model of high permeable medium (HPM) proposed in the study can significantly increase convergence efficiency of simulation by properly adjusting the aspect ratio of HPM elements. The equivalent permeability model of flow channel can simplify the computational model of the CV/FEM simulation for VARTM processes. This new modeling technique was validated by the results from conventional 3D computational methods and experiments. The model was further validated with a case study of an automobile hood component fabrication. The flow simulation results of the equivalent permeability models were in agreement with those from experiments. The results indicate that the computational time required by this new approach was greatly reduced compared to that by the conventional 3D CV/FEM simulation model, while maintaining the accuracy, of filling time and flow pattern. This approach makes the flow simulation of large VARTM parts with 3D CV/FEM method computationally feasible and may help broaden the application base of the process simulation. Polym. Compos. 25:146–164, 2004. © 2004 Society of Plastics Engineers.

Studies on physico‐mechanical properties and thermal characteristics of polypropylene/layered silicate nanocomposites

Abstract: Polypropylene/layered silicate nanocomposites were prepared from base polymer (10 MFI) and octadecylamine modified montmorillonite (1.30P nanomer), melt compounded with and without compatibilizer, i.e., maleic anhydride grafted polypropylene (Epolene-G3015). Physico-mechanical properties of the virgin PP and nanocomposites with different nanomer percentages and compatibilizer loadings were studied and compared. Thermal characteristics of nanocomposites were also compared with those of the virgin polymer. TEM analysis of the nanocomposites was carried out to study the dispersion of nanomer in the resulting hybrids. The nanocomposites showed improved mechanical properties over those of the virgin polymer with a marginal increase in specific gravity. Addition of compatibilizer further enhanced the mechanical properties of nanocomposites because of the compatibilization of the clay and host polymer interface. The uncompatibilized nanocomposites showed an increase in thermal stability and a higher melting point. However, the compatibilized nanocomposites showed delayed crystallization due to the presence of an oligomeric fraction of the added Epolene. Polym. Compos. 25:646–652, 2004. © 2004 Society of Plastics Engineers.

Compaction of thick composites: Simulation and experiment

Abstract: A realistic process simulation model for heat transfer and compaction along the bleeder-composite assembly was developed. Two case studies were presented with this model in which one took advantage of variable resin properties while the other used constant values. The predicted results were then experimentally validated with 228-ply and 380-ply AS4/3501-6 graphite/epoxy laminates cured under one-dimensional resin flow condition. The model-experiment correlation was quite good for the 228-ply laminate although results with variable resin properties predicted better through-the-thickness temperature distribution than with constant resin properties. The model also predicted faster compaction rate because the compressibility model appeared to predict higher fiber volume fraction for given effective stress. As for the 380-ply laminate, notable deviations were observed for both the temperature and compaction predictions. The discrepancies appeared to have manifested from inaccurate resin property and compressibility models.

Structure characterization and conductive performance of polypyrrol‐molybdenum disulfide intercalation materials

Abstract: Two types of polypyrrol/molybdenum disulfide nanocomposite were prepared by means of in situ polymerization of the intercalated monomers. The nanocomposites were characterized by means of powder X-ray diffraction, Fourier transformation infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The charge transport properties of the nanocomposites were determined by four-probe electrical conductivity measurement of pressed pellet samples. The relationship between the electrical conductivity at various temperatures and conformation of the polypyrrol/molybdenum disulfide nanocomposites were investigated. Results indicated that polypyrrol took two kinds of conformation in the interlayer of MoS 2 . The electrical conductivity of the intercalation nanocomposites at room temperature was dependent on the conformation and stereo-regular characteristics of the polypyrrol molecules in the MoS 2 layers; it was mainly determined by the number of the active charge carriers in polypyrrol at -60°C. The intercalation of polypyrrol into MoS 2 led to an increase in the electrical conductivity by six orders of magnitude.

A comparative study on the influence of epoxy sizings on the mechanical performance of woven carbon fiber-epoxy composites

Abstract: In the present work the effect of epoxy sizings on the fracture behavior of woven carbon fiber tetrafunctional epoxy composites has been investigated. Three-point flexural, short beam shear (SBS) and Mode-II interlaminar fracture toughness (ENF) tests have been carried out. Wettability and Atomic Force Microscopy (AFM) studies have been performed on commercial sized, desized and 0.7 wt% TGDDM and 0.7 wt% DGEBA sized carbon fibers. Dynamic mechanical thermal analysis and Scanning Electron Microscopy (SEM) studies were also carried out on the different carbon fiber/epoxy composites. The used sizing treatments provided composites with improved mechanical properties due to the enhancement achieved in the fiber-matrix adhesion. Polym. Compos. 25:319–330, 2004. © 2004 Society of Plastics Engineers.

Fatigue crack initiation and propagation in polyamide-6 and in polyamide-6 nanocomposites

Abstract: Recent developments in polymer nanocomposites have led to improvements in conventional short-term, but the long-term mechanical properties have received little attention. The objective of the present study was to characterize the effect of nanoparticles on the fatigue crack initiation and propagation mechanisms and on the fatigue properties of polyamide-6 (PA6) nanocomposite (PA6NC) prepared by in situ polymerization with montmorillonite clay. Two approaches were employed: fatigue life measurements and crack growth monitoring. Compared with non-filled PA6 at the same stress amplitude, the number of cycles to fracture was higher for the nanocomposite, which suggests an increase in the intrinsic resistance of the material to crack initiation. However, the crack growth rate results indicated that nanoparticles decreased the resistance to crack propagation. Post-fatigue fractographic observations indicated a change in the fatigue crack propagation mechanism resulting from the addition of nanoparticles, primarily attributed to the increase in yield stress, which favors the development of a fibrillated deformation zone. The fibrillation process in the relatively high crack propagation rate regime appeared to be preceded by plastic deformation at approximately constant volume. Most of the effect of nanoparticles on the fatigue behavior and properties results probably from the mechanical reinforcement on the microstructure and its effect on the yield stress and Young's modulus rather than from the effect of the inorganic filler to act as a stress concentrator. Polym. Compos. 25:433–441, 2004. © 2004 Society of Plastics Engineers.

Improvement of the interfacial compatibility between sugar cane bagasse fibers and polystyrene for composites

Abstract: Sugar cane bagasse fibers were modified by surface treatments using either physical or chemical methods in order to improve their adhesion to polystyrene matrices. The surface treatment methods used were alkaline treatment, treatment with silane coupling agents, physical coating with polystyrene and grafting of polystyrene with and without crosslinker. Fiber modifications were monitored by Fourier Transform Infrared Spectroscopy (FTIR), Differential Thermal Analysis coupled with Thermogravimetric Analysis (DTA-TGA) and Scanning Electron Microscopy (SEM). On the other hand, the improvement of the adhesion between sugar cane modified fibers and polystyrene was assessed by micromechanical pull-out and by macromechanical Iosipescu tests. It was found, from Interfacial Shear Strength values (IFSS), that substantial improvements in fiber-matrix compatibility were achieved. According to micro- and macromechanical test results, the IFSS increased for all treated fibers as compared to non-treated fibers. Particularly, both the coating the fibers or grafting with polystyrene using crosslinker resulted in substantial adhesion improvement to the polystyrene matrix in comparison with the non-treated fibers and fibers treated by alkaline and silane methods only. Polym. Compos. 25:134–145, 2004. © 2004 Society of Plastics Engineers.

Void transport in resin transfer molding

Abstract: The transport of single drops through a hexagonal cylinder array is used to study the void movement and deformation in a resin transfer molding process A transparent flow cell is used to visualize the transport of voids through a porous media model Experiments are conducted with nearly inviscid water drops and viscous glycerol drops with drop sizes ranging from 04 to 80 μl, and with both a Newtonian fluid and Boger fluid with average resin velocities ranging from 0011 to 0140 cm/s Two critical capillary numbers, which determine the breakup (Cab) and mobilization (Ca*) of drops, are measured to better understand the flow dynamics of voids As demonstrated by the experiments, there is a critical drop size, below or above which a quite different flow behavior is observed Such a transition is analyzed with consideration of the geometry characters in the flow field Results expand the former studies in this area to a significantly larger range of drop sizes and capillary numbers Particle Tracking Velocimetry is also used to quantify the local velocity, shear stress, extensional stress and energy dissipation in the flow field Polym Compos 25:417–432, 2004 © 2004 Society of Plastics Engineers

The impact response of aluminum foam sandwich structures based on a glass fiber-reinforced polypropylene fiber-metal laminate

Abstract: The fracture properties and impact response of a series of aluminum foam sandwich structures with the glass fiber–reinforced polypropylene-based fiber-metal laminate (FML) skins have been studied. Initially, the manufacturing process for producing the FML skins was optimized to obtain a strong bond between the composite plies and the aluminum layers. The degree of adhesion between the composite plies and the aluminum was characterized by conducting single cantilever beam tests. Here, it was found that the composites could be successfully bonded to the aluminum using a simple short stamping procedure. A detailed examination of the fracture surfaces indicated that crack propagation occurred within the composite ply in the fiber-metal laminates and along the composite-aluminum foam interface in the sandwich structures. The low velocity impact response of the FMLs and the sandwich structures was investigated using an instrumented drop-weight impact tower and a laser-Doppler velocimeter. The energy absorption characteristics of the sandwich structures were investigated along with the failure processes. Finally, a series of tensile tests on the damaged FMLs and thermoplastic sandwich structures showed that both systems offer promising residual load-bearing properties. Here, shear failure in the aluminum foam was observed in the sandwich structures, indicative of a strong bond between the FML skins and the aluminum core. Polym. Compos. 25:499–509, 2004. © 2004 Society of Plastics Engineers.

A new kinetic and viscosity model for liquid composite molding simulations in an industrial environment

Abstract: Liquid composite molding is broadly used for manufacturing composite parts. Apart from the preforming of the dry fibrous material, mold filling and curing of the resin are the main steps in the manufacturing process. For process simulation numerical methods, like finite element methods are applied. Flow models describing the flow behavior through a porous medium are well established. The ability to predict and monitor the curing process in liquid composite molding is crucial for manufacturing process optimization in case of application of rapid curing resin systems. Based on differential scanning calorimetry and rheological experiments, cure kinetics and viscosity of a resin system were characterized. A new kinetic and complex viscosity model is proposed to predict epoxy resin properties in numerical modeling of liquid composite molding. The semi-empirical models are simple to use and therefore suitable for process optimization in an industrial environment. Both models were validated by a fitting to the experimental data by the Levenberg-Marquardt method. A process to determine the initial values for the fitting procedure is also proposed. The predictions of the validated models were in good agreement with the measured data, and are therefore applicable for numerical process optimization.

Fiber orientation structures and mechanical properties of injection molded short glass fiber reinforced ribbed plates

Abstract: In this paper we describe a study of the fiber orientation structures present within a model ribbed injection molded plate. The details of the fiber orientation at each chosen location on the injection molded parts were measured using an in-house developed image analysis system, which enabled large areas to be scanned (up to 200 mm2) up to a limit of 1 million fiber images. Two materials were used for these experiments, short glass fiber filled PBT and short glass fiber filled nylon 66. First, a comparison was made between the fiber orientation at an identical position, 28 mm from the injection gate on a transverse rib, on two plates made from glass fiber filled PBT. It was found that the fiber orientation in these two separately manufactured components was virtually identical when comparing the whole scanned area, but the differences became more significant when comparing areas on the length scale of an individual fiber (∼ 200 μm). Second, the fiber orientation at the same position was compared for two plates made using the glass/PBT and glass/nylon 66 materials. The differences for the complete scanned areas were small, confirming that mold geometry plays a crucial role in determining fiber orientation structures, and that matrix properties are secondary. Third, the fiber orientation structures at various positions across one of the glass/PBT plates were examined in greater detail, in particular across a number of the transverse ribs: the chosen ribs were of various widths and heights. Differences in structure were found depending on the local rib geometry. Finally, the effect of the measured fiber orientation structures in determining the mechanical properties of the ribbed plate was investigated using simple modeling schemes. While the stiffness of the rib/web assembly was found to depend on the average fiber orientation of the two parts, the different thermal expansions of the web and the rib, caused by the different fiber orientation in the two regions, led to significant warpage of the rib/web assembly. Polym. Compos. 25:237–254, 2004. © 2004 Society of Plastics Engineers.

Processing-properties relationship of sandwich panels with polypropylene-core and polypropylene-matrix composite skins

Abstract: This paper reports on the development and the optimization of a thermoforming process (compression molding) for thermoplastic sandwich panels. The skins of the panels are fabricated from polypropylene (PP)/continuous glass fibers dry prepregs in the form of a commingled fabric. The use of two different types of core material has been used, a PP foam and a PP honeycomb. Additionally, two alternative methods for the thermoforming process have been analyzed, using either a one-stage or a two-stage process. In the one-step process, skin molding and skin-core bonding are carried out simultaneously. In the two-stage process, the skins are first thermoformed and then bonded to the core as the second stage. The influence of the selected process parameters on the mechanical properties of the panels has been experimentally investigated, leading to the identification of the preferred processing conditions. Polym. Compos. 25:307–318, 2004. © 2004 Society of Plastics Engineers.

Influence of polyethersulfone modification of a tetrafunctional epoxy matrix on the fracture behavior of composite laminates based on woven carbon fibers

Abstract: In this study, the influence of poly(ethersulfone) (PES) as a modifying agent of a tetrafunctional epoxy matrix (TGDDM) on the mechanical behavior of composite laminates based on woven carbon fibers has been investigated. Dynamic mechanical experiments were performed on neat matrix resins and on their corresponding laminate composites. Mode-I and Mode-II fracture toughness tests for the bulk matrices and their composites, respectively, and also flexural and short beam shear tests (SBS) were carried out. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to investigate the morphologies obtained. A nanoscopic phase separation was obtained after PES addition, which was not able to stabilize the fracture process, leading, as a consequence, to a poor extent of improvement on fracture toughness properties. Polym. Compos. 25:480–488, 2004. © 2004 Society of Plastics Engineers.

Elastomeric conductive composites based on conducting polymer–modified carbon black

Abstract: Thermally stable elastomeric composites were prepared via melt processing from poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) and conducting polymer-modified carbon black (CPMCB) additives. CPMCB additives represent a novel thermally stable conductive compound made via “in-situ” deposition of polyaniline or polypyrrole on carbon black particles. Incorporating CPMCB is advantageous to the melt processing of composites, as it reduces the melt viscosity in comparison to the use of pure carbon black. Thermogravimetric analyses (TGA) showed that the composites are thermally stable with no appreciable degradation at temperatures as high as 300°C. In addition, the electrical conductivity of the composites was found to be very stable at high temperatures. Polym. Compos. 25:617–621, 2004. © 2004 Society of Plastics Engineers.

The effect of steel fiber orientation on frictional properties of asbestos-free friction materials

Abstract: The frictional properties of the composites reinforced with continuous steel fibers have been evaluated in LNBR modified phenolic resin based friction materials. The fiber orientations are introduced regarding the sliding direction, i.e. parallel (P) along the fiber direction, normal (N) and antiparallel (AP). The specific wear rates are increased if the sliding path is shifted from the P to the AP and N direction. The coefficient of friction is also dependent on the fiber alignment directions. The coefficients of these materials fall in the range of 0.49 to 0.54. The initial sliding interaction is plowing action if the turnplate temperature is below 250°C. Meanwhile, with the increase of the temperature, as ironed transfer film developed on the specimen, the interaction became adhesive and steady-state friction is established. The wear resistance of the composite is found to relate to the stability of the film.

Study of interphase in glass fiber–reinforced poly(butylene terephthalate) composites

Abstract: It is well known that application of a coupling agent to a glass fiber surface will improve fiber/matrix adhesion in composites. However, on commercial glass fibers, the coupling agent forms only a small fraction of the coating, the larger part being a mixture of processing aids whose contribution to composite properties is not well defined. The interfacial region of the composite will therefore be affected by the coating composition and also by the chemical reactions involved in the vicinity of the fiber and inside the surrounding matrix. The main feature of this study consists in dividing the interface region into two separate regions: the fiber/sizing interphase and the sizing/matrix interphase. A wide range of techniques was used, including mechanical and thermomechanical tests, infrared spectroscopy, gel permeation chromatography, carboxyl end group titrations, extraction rate measurements, and viscosity analysis. Experiments were performed on poly(butylene terephthalate) composites and results indicate that the adhesion improvement is due to the presence of a short chain coupling agent and of a polyfunctional additive, which may react both with the coupling agent and the matrix. According to the nature of this additive, it may be possible to soften the interphase and then to increase the composite impact strength.

Shielding effectiveness of carbon-filled nylon 6,6

Abstract: Electrically conductive resins can be made by adding electrically conductive fillers to typically insulating polymers. Resins with an electrical resistivity of approximately 100 ohm-cm or less can be used for electromagnetic and radio frequency interference shielding applications. This research focused on performing compounding runs followed by injection molding and shielding effectiveness testing of carbon filled nylon 6,6 based resins. The three carbon fillers investigated included an electrically conductive carbon black, synthetic graphite particles, and a surface-treated polyacrylonitrile (PAN)-based carbon fiber. Conductive resins were produced and tested that contained varying amounts of these single carbon fillers. In addition, combinations of fillers were investigated by conducting a full 23 factorial design and a complete replicate. The objective of this paper was to determine the effects and interactions of each filler on the shielding effectiveness properties of the conductive resins. Carbon fiber caused the largest increase in shielding effectiveness. Also, all the single fillers and combinations of fillers were statistically significant at the 95% confidence level, except the composite containing carbon black and synthetic graphite particles tested at 800 MHz. Polym. Compos. 25:407–416, 2004. © 2004 Society of Plastics Engineers.

Synergistic effects of carbon fillers on tensile and impact properties in nylon 6,6 and polycarbonate based resins

Abstract: Electrically and thermally conductive resins can be produced by adding conductive fillers to insulating polymers. Mechanical properties such as tensile modulus, ultimate tensile strength, strain at ultimate tensile strength, and notched Izod impact strength are also important and cannot be ignored. This research focused on performing compounding runs followed by injection molding and tensile and impact property testing of carbon filled nylon 6,6 and polycarbonate based resins. The three carbon fillers investigated included an electrically conductive carbon black, synthetic graphite particles, and a milled pitch based carbon fiber. For each polymer, resins were produced and tested that contained varying amounts of these single carbon fillers. In addition, combinations of fillers were investigated by conducting a full 23 factorial design and a complete replicate in each polymer. The objective of this paper was to determine the effects and interactions of each filler on the tensile and impact properties. The results showed that, in many cases, combining two and three different fillers caused a statistically significant effect at the 95% confidence level. Polym. Compos. 25:172–185, 2004. © 2004 Society of Plastics Engineers.

Effect of Reinforcing Glass Fibers on Morphology and Properties of Thermoplastic Modified Epoxy-Aromatic Diamine Matrix

Abstract: A usual way to improve the fracture toughness of thermosetting polymers consists of using an initially miscible thermoplastic that phase separates at a particular conversion, depending on composition and reaction temperature. This work deals with the effect of glass reinforcing fibers on the morphologies of polyetherimide and aminografted polyetherimide toughened epoxy-diamine systems. The presence of fibers in these systems does not affect the phase separation process, but the final morphology changes in the case where polyetherimide (PEI) is used as an additive. Furthermore, the use of aminografted PEI does not change the previously observed morphology. In terms of mechanical properties, the use of fibers leads to a great improvement in the fracture energy, indicating that good adhesion between fiber and matrix is also achieved. Polym. Compos. 25:368–374, 2004. © 2004 Society of Plastics Engineers.

Tensile properties of cellulose fiber reinforced hydroxypropylcellulose films

Abstract: The tensile properties of cross-linked and uncross-linked composite films (thickness 20-35 m) prepared from Hydroxypropylcellulose (HPC) with incorporation of microcrystalline cellulose fibers (Avicel) were studied The concentration of fibers in the composites ranged from 0 to 30 w/w% and cross-linked composites were obtained by the reaction of HPC-Avicel mixtures with 1,4-butyldiisocyanate It was demonstrated that the inclusion of fibers in a HPC matrix produces composites with enhanced mechanical properties that are improved by cross-linking Mechanical results seem to indicate that the elastic deformation of the cross-linked composites is predominantly dominated by the fiber content while the cross-linking affects mainly the plastic deformation Maximum values of the Young's Modulus, yield stress and tensile stress were observed at 10 w/w% for the cross-linked and 20 w/w% for the uncross-linked composites Furthermore cross-linked films with 10 w/w% of fibers present values of yield stress and tensile stress that are in average 15 to 20% higher than those obtained for uncross-linked composites with 20 w/w% of fibers Studies in Polarizing Optical Microscopy and Atomic Force Microscopy (AFM) seem to indicate that tensile properties of these composites are correlated to the packing of fibers For the concentration of the utilized cross-linking agent, and for a fiber content of 10 w/w%, an optimal packing of fibers throughout the matrix has been correlated to the minimal difference between the roughness parameters obtained by AFM analysis of the top and bottom surfaces of the films