High-performance Thermoplastic Composites Research Articles

Preparation and application of continuous fiber reinforced high-performance thermoplastic composites

Preparation and application of continuous fiber reinforced high-performance thermoplastic composites

Adhesion of high performance thermoplastic composites: Development of a bench and procedure for kinetics identification

Thermoplastic welding, tape placement, 3D printing, overmoulding or even thermostamping involve adhesion of thermoplastic polymer at high temperature. Build-up of the mechanical resistance between two substrates is usually assumed to be driven by the diffusion of macromolecules at the interface, called healing phenomenon. Moreover, in continuous processes, such as some used in manufacturing of composites for aerospace structures, cycles are very short. Thus, there is a need for quantifying the adhesion of such materials especially when processed for short durations. With this aim, a temperature and pressure controlled welding bench was designed to enable the welding of double cantilever beam samples for short time (down to 1 s). Adhesion of a carbon-PEKK composite was characterized over a wide range of residence times ranging from 1 s to 1 h. Three bonding regimes were observed, corresponding to different stages of the adhesion build-up at the interface. Finally, the healing kinetics was identified.

Post-process annealing of large-scale 3D printed polyphenylene sulfide composites

Large-scale extrusion-based additive manufacturing of high-performance thermoplastic composites like fiber reinforced polyphenylene sulfide (PPS) is well-suited for tooling applications to lower manufacturing costs and lead times. Autoclave tooling requires good mechanical performance at temperatures even above the glass transition temperature (Tg). In this work, the authors have investigated a post-process isothermal annealing technique to improve the mechanical properties of various grades of carbon fiber reinforced PPS components printed on the Big Area Additive Manufacturing (BAAM) system. Since PPS is a semi-crystalline polymer, crystallinity can change during annealing and affect the mechanical properties of the part. In addition, isothermal annealing can also lead to solid-state structural changes in the form of thermal and oxidative branching and/or crosslinking reactions in some grades of PPS which can alter the crystallization process. This work reports the effect of annealing on dynamic mechanical properties of BAAM printed components, along with studies to determine the effect of annealing on crystallinity and the occurrence of oxidative reactions. Results showed that isothermal annealing at 250 °C for 18 h improved the storage modulus of all selected grades (neat and reinforced) of PPS at temperatures above Tg. Annealing led to an overall increase in the degree of crystallinity, with secondary crystallization taking place. Although oxidative structural changes were observed to occur more on the surface of the PPS parts, they primarily influenced the size of crystals formed and did not significantly alter the degree of crystallinity at various regions within the sample.

Preparation of short CF/GF reinforced PEEK composite filaments and their comprehensive properties evaluation for FDM-3D printing

Fused deposition modeling (FDM) has been successfully applied to fabricating short fiber reinforced polymer composites parts. However, due to the intrinsically limited mechanical properties of matrix polymers, there is critical need to develop fiber reinforced high-performance thermoplastic composites for FDM-3D printing to expand engineering applications. In this work, the potential of FDM-3D printing short carbon fiber (CF) and glass fiber (GF) reinforced high-performance PEEK composites has been investigated. Composite filaments with fiber contents of 5 wt%, 10 wt% and 15 wt% were prepared using extrusion process and characterized by micromorphology observation; and thermal properties testing demonstrated its better thermal stability than pure PEEK. The performance evaluation of printed CF/GF-PEEK parts was focused, including mechanical properties, microstructure, surface quality and porosity. The results indicate that the addition of CF/GF to PEEK can significantly enhance the tensile and flexural strength at the cost of ductility. Lower fiber content of 5 wt% is conducive to increasing mechanical properties, improving surface quality and reducing porosity of printed CF/GF-PEEK. GF/PEEK has better interfacial bonding than CF/PEEK due to the different surface treatments on fibers. Furthermore, microstructure observation suggests that fibers aligned along the printing orientation can strengthen the properties, while pores lead to performance degradation of 3D printed CF/GF-PEEK.

Effects of strain rate and high temperature environment on the mechanical performance of carbon fiber reinforced thermoplastic composites fabricated by hot press molding

The mechanical performance of continuous large tow carbon fiber reinforced polyamide 6 laminates fabricated by hot press molding was studied using quasi-static and dynamic tests. The effects of layup, strain rate and high temperature were discussed. The results show that the thermoplastic composites possess strain rate strengthening effects and high temperature weakening dependence. Different layup laminates exhibit different sensitivities. The elastic modulus difference of unidirection/cross-ply laminates decreases but that of unidirection/quasi-isotropic or unidirection/angle-ply laminates increases with the increasing strain rate. However, the failure strength difference changes insignificantly as the strain rate increases. The modulus or strength difference between unidirectional laminate and the other laminates decreases with the increasing temperature. The weakening effect of high temperature is stronger than the strengthening effect of strain rate for tensile mechanical properties. Furthermore, the failure behavior and mechanism were analyzed. These experimental data and research results could provide some insight for high-performance thermoplastic composites.

Processing of waste carbon and polyamide fibers for high-performance thermoplastic composites: Modifications to the auto-leveling system to enhance the quality of hybrid drawn sliver

The auto-leveling system of a modern draw frame is widely used for conventional fibers to develop homogeneous, uniform, and defect free drawn slivers. This auto-leveling system also improves the quality of tapes and hybrid yarn structures by eliminating mass irregularities in hybrid sliver. However, the existing auto-leveling system exerts very high loads on feedstock, thus diminishing the quality of waste carbon in the delivered sliver. The aim of the present study was to process hybrid sliver based on waste carbon and polyamide fibers on a modern draw frame and modify the auto-leveling system to enable the damage-free processing of carbon fiber. For this purpose, hybrid card slivers were processed on an industrial draw frame with auto-leveling system. The different auto-leveling parameters, e.g., scan roller width and scan roller load, were modified and optimized for the uniform and damage-free processing of hybrid sliver. Results revealed that the scan roller load has a significant influence on the quality of waste carbon fiber in hybrid sliver. A uniform hybrid sliver ensures the reproducibility of unidirectional tapes and hybrid yarn at industrial scale, while simultaneously maintaining the quality of recycled carbon fiber-reinforced thermoplastics.

Thermal treatment as an effective method of carbon/glass fibers surface modification for high-performance thermoplastic polymer matrix composites

Fiber reinforced high-performance thermoplastic polymer composites are one of the most promising materials in modern materials science. At the same time the challenges with high processing temperatures and melt viscosity, poor interfacial adhesion has slowed adoption of this materials. Most commonly used as reinforcements carbon and glass fibers are usually has an inert surface that prevent good wettability and formation of strong fiber–matrix interface. In this work, thermal treatment of carbon and glass fibers was used as a method of the fibers’ surface modification. A polyethersulfone (PES) based composites reinforced with initial and modified carbon and glass fibers were developed using solution impregnation method followed by compression molding technique. Mechanical and thermal behavior of the composites before and after the modification was studied. It was shown that thermal treatment of the fibers results in improved interfacial interaction as well as higher strength-elastic properties of the PES based composites.

Processing of waste carbon and polyamide fibres for high-performance thermoplastic composites: influence of carding parameters on fibre orientation, fibre length and sliver cohesion force

The processing of waste carbon fibre on carding machine for the developments of nonwovens, tapes and hybrid yarn structures is an emerging trend. These structures are widely used to enhance the performance efficiency of recycled carbon fibre reinforced thermoplastic composites. The aim of the research presented in this study is to process waste carbon fibre on a carding machine and to investigate the influence of different carding parameters on waste carbon fibre. For this purpose, card slivers composed of waste carbon and polyamide fibres were developed on a double cylinder card machine by varying technical parameters. Then, effect of these parameters on card sliver quality was assessed in terms of fibre orientation, fibre length and sliver cohesion force. Results revealed that fibre orientation and fibre length is significantly affected by technological parameters carding zones, whereas the sliver cohesion force is significantly affected by the speed of feed roller and doffer.

Synergistic effect of hydrogen bonding and π-π stacking in interface of CF/PEEK composites

Due to the extraordinary thermal stability, chemical resistance and processability, carbon fiber (CF) reinforced polyetheretherketone (PEEK) composites are widely applied in aviation, aerospace, medical fields, etc. However, the non-polar nature and low wettability of CFs limited the interfacial bonding between CFs and PEEK and results in unsatisfied mechanical properties for CF/PEEK composites. In order to enhance interactions between fibers and matrix, the interface in CF/PEEK composites was built through coating a mixture of polyetherimide (PEI) and functionalized multi-walled carbon nanotubes (COOH-MWCNTs) on CFs. The combination of hydrogen bonding between COOH-MWCNT and PEI as well as the π-π interaction between PEI and PEEK significantly improved the miscibility and interfacial interlocking. As a result, the flexural strength, modulus and interlaminar shear strength (ILSS) of modified CF/PEEK were remarkably improved by 76% (667.8 MPa), 119% (40.0 GPa), and 85% (90.7 MPa) respectively. The failure mechanism changed from smooth cracking in interface destruction to zigzag cracking and resin breakage, suggesting that the resultant interface became strong enough to ensure efficient stress transfer from PEEK to CF. The synergistic interfacial interactions via hydrogen bonding and pi-pi stacking are believed to supply an effective strategy for building high-performance thermoplastic composites.

Microstructures and mechanical properties of thermoplastic composites based on polyarylate/nylon6 islands‐in‐sea fibers

Polyarylate (PAR) fiber‐reinforced nylon6 composites are manufactured by molding uniaxially‐aligned islands‐in‐sea fibers at different temperature (190–210°C), pressure (0.69–6.89 MPa), and time (1–10 min). For the purpose, the islands‐in‐sea fibers, in which 74 PAR islands act as reinforcing microfibers and nylon6 sea part serves as a semicrystalline matrix in the thermoplastic composites, are prepared by a conjugate melt‐spinning. The tensile and dynamic mechanical properties of the thermoplastic composites are investigated by taking into account their microstructural and morphological features, which are influenced by the molding conditions, as examined by differential scanning calorimetry, 2D‐X‐ray diffraction, scanning electron microscopy, micro‐CT, and polarized optical microscopy (POM) analyses. The thermoplastic composite manufactured at 200°C and 2.07 MPa for 3 min is found to have maximum tensile strength of ∼630 MPa and initial modulus of ∼70 GPa owing to multiple synergistic effects such as high crystallinity of nylon6 matrix, good alignment of PAR microfibers, interfacial crystallization of nylon6 on the reinforcing PAR microfibers, and low porosity. The findings of this study indicate that PAR/nylon6 inland‐in‐sea fibers can be utilized effectively for manufacturing high performance thermoplastic composites for sports, automotive, and protective applications. POLYM. COMPOS., 40:E484–E492, 2019. © 2018 Society of Plastics Engineers

Effect of Poly(phthalazinone ether ketone) with amino groups on the interfacial performance of carbon fibers reinforced PPBES resin

In this study, novel aminated poly(phthalazinone ether ketone) (PPEK-NH2) with amino groups on main chains was synthesized by typical condensation polymerization of 4-(4-Hydroxylphenyl)(2H)-phthalazin-1-one (DHPZ), 4,4’-difluoro benzophenone (DFK), and the third active monomer, 1,5-diamino-4,8-dihydroxyanthraquinon (DDT). As a type of compatibilizer, PPEK-NH2 was utilized to modify the interface properties of carbon fibers (CF) reinforced copoly(phthalazinone ether sulfone)s (PPBES) composites. The composites were prepared by solution impregnation and compression molding, where PPEK-NH2 was distinguished by different mole ratios of DHPZ/DFK/DDT. And the effects of amino structural unit quantity in PPEK-NH2 chains on compatibility was investigated. Of all the compatibilizers, PPEK-NH2 (4) exhibits the best compatible effect. The interlaminar shear strength and flexural strength of CF/PPBES increased significantly by 15.8% and 26.2%, respectively. According to DMA test, the storage modulus and service temperature increase by 12 GPa and 7 °C, respectively. Beside, CF/PPBES/PPEK-NH2 (4) exhibits excellent mechanical behaviours with at 240 °C and 250 °C. Moreover, this composite also demonstrates excellence in hydrothermal aging tests. This method contains simple process, large-scale application potential, which offers new insights for fabricating high-performance advanced thermoplastic composites.

Void reduction of high-performance thermoplastic composites via oven vacuum bag processing

In this study, void reduction mechanisms during oven vacuum bag processing of high-performance carbon fiber thermoplastic composites are investigated. Entrapped air exists within the prepreg tape and between layers during lay-up and must be removed during processing to achieve aerospace quality (<1% void content) Key void reduction mechanisms during oven vacuum bag processing include through-thickness air diffusion and in-plane flow to the laminate edges through the permeable interlayer regions created by the prepreg surface roughness. Interlayer permeability between unidirectional and cross-ply laminates is measured experimentally and is sufficiently high for effective air removal during oven vacuum bag processing. Thick 72-layer carbon fiber/PEEK (poly (ether ether ketone)) laminates were fabricated with oven vacuum bag process under different edge sealing conditions. Void reduction in the laminate with sealed perimeter is dominated by air diffusion through the entire laminate thickness, and the laminate exhibits very high void content levels after oven vacuum bag processing. In the laminates with edges open to vacuum, air diffusion through a single layer and flow through the permeable interlayer lead to essentially void-free laminates. The findings show the importance of the interlayer permeability and edge conditions on the void reduction, and demonstrate that low void content can be achieved in thick section thermoplastic composite laminates via cost effective oven vacuum bag processing.

Preparation of carbon fiber-reinforced polyimide composites via in situ induction heating

Induction heating, a direct and contactless heating method, is generally more rapid and energetically more efficient than other heating methods used. In this work, we report the high-temperature imidization of carbon fiber/polyimide (PI) composites using an in situ induction heating method. Furthermore, we compare the advantages of the method to a conventional thermal procedure. The formed composites feature almost identical imidization rates, glass transition temperatures, and thermal oxidative stabilities cured at the same heating temperatures using a different heating process. Upon doping with ferriferous oxide, the ability of the magnetic nanoparticles in an alternating current field was studied to further drive the heating process and increase the rising and cooling time. The in situ induction heating process proves to be a powerful method for the high-temperature polymerization of high-performance thermoplastic composites, particularly for a PI matrix.

A novel surface modification of carbon fiber for high-performance thermoplastic polyurethane composites

Properties of carbon fiber (CF) reinforced composites depend largely on the interfacial bonding strength between fiber and the matrix. In the present work, CF was grafted by 4,4′-diphenylmethane diisocyanate (MDI) molecules after electrochemical oxidation treatment. The existence of functional groups introduced to the fiber surface and the changes of surface roughness were confirmed by FTIR, AFM, XPS, SEM and Raman spectroscopy. To evaluate the possible applications of this surface modification of carbon fiber, we examined the mechanical properties as well as the friction and wear performance of pristine CF and MDI-CF reinforced thermoplastic polyurethane (TPU) composites with 5–30 wt.% fiber contents, and found that the mechanical properties of TPU composites were all significantly improved. It is remarkable that when fiber content was 30wt.%, the tensile strength of TPU/MDI-CF was increased by 99.3%, which was greater than TPU/CF (53.2%), and the friction loss of TPU/MDI-CF was decreased by 49.09%. The results of DMA and SEM analysis indicated the positive effects of MDI modification on the interfacial bonding between fibers and matrix. We believed that this simple and effective method could be used to the development of surface modified carbon fiber for high-performance TPU.

Effect of fabric orientation and impact angle on the erosion behavior of high-performance thermoplastic composites reinforced with ductile fabric

How composites reinforced with plain-weave polybenzoxazole (PBO) fibers were eroded by solid particles was investigated. By evaluating the erosion rates of plain polymers and these composites at various impact angles (α=15–90°), we confirmed that the polymers and their composites were ductile. The relationship between erosion behavior and fabric orientation from an energy perspective was studied, and our experimental results agreed well with our analytical results showing that the erosion behavior did not depend on fabric orientation. Using these results and scanning electron micrographs, a mathematical model was produced and it was used to predict the erosion rates of ductile materials. To verify this model, the theoretical and measured erosion rates of three high-performance ductile-fabric-reinforced thermoplastic composites were compared, showing that our mathematical model can accurately characterize their erosion behaviors.

Determination of void statistics and statistical representative volume elements in carbon fiber-reinforced thermoplastic prepregs

Void consolidation of high-performance thermoplastic composites strongly depends not only on average void content but also on the distributions of void size, shape, and location within the prepreg materials. High-resolution 3-D X-ray microcomputed tomography shows that voids in carbon/poly(ether ether ketone) (AS4/APC2) prepreg are rodlike with major axis along the fiber axial direction. In order to accurately characterize the void microstructure, a detailed study was conducted to quantify the statistical distribution of void content, void length, equivalent void diameter, and void aspect ratio. Resolution of 1.48 μm/pixel provided a balance of measurement accuracy and inspection time. Suitable statistical distribution functions were found to describe the void length, diameter, and aspect ratio. For each void property, a sub-statistical representative volume element (SRVE) was determined. The SRVE of the overall void microstructure is defined as the maximum dimensions of the sub-SRVEs. In case of AS4/APC2 tape, the SRVE was found to be 6.1 mm in length (fiber direction), 27 mm in width (transverse to fiber direction), and 0.18 mm of full prepreg thickness.

On avoiding thermal degradation during welding of high-performance thermoplastic composites to thermoset composites

One of the major constraints in welding thermoplastic and thermoset composites is thermal degradation of the thermoset resin under the high temperatures required to achieve fusion bonding of the thermoplastic resin. This paper presents a procedure to successfully prevent thermal degradation of the thermoset resin during high-temperature welding of thermoplastic to thermoset composites. The procedure is based on reducing the heating time to fractions of a second during the welding process. In order to achieve such short heating times, which are much too short for commercial welding techniques such as resistance or induction welding, ultrasonic welding is used in this work. A particularly challenging scenario is analysed by considering welding of carbon-fibre reinforced poly-ether-ether-ketone, with a melting temperature of 340°C, to carbon-fibre reinforced epoxy with a glass transition temperature of 157°C.

Advanced laser welding of high-performance thermoplastic composites

Thermoplastic composite structures based on continuous carbon fiber reinforcements are gaining importance in many industrial applications. These comprise basic technical functions as well as high-performance applications in the aerospace sector. Welding techniques are applicable for composites based on thermoplastic matrix materials in contrast to thermoset systems. In this context, welding steps are not limited to the joining of carbon fiber reinforced plastic (CFRP) parts among themselves, but extend to the connection of various components, consisting of unreinforced and glass fiber reinforced thermoplastics to CFRP components. In this work, a laser transmission welding process is evaluated with respect to the influence of the carbon fiber reinforcement within the laser absorbing part as well as the glass fiber reinforcement within the laser transparent part on the weld seam formation. Thermoplastic base material nylon (PA 6.6) and polyphenylene sulfide are used. By applying two different strategies, contour and quasisimultaneous welding, the influence of continuous fiber reinforced composites on the welding process is studied. Significant differences to the process characteristics known from the joining of unreinforced thermoplastics emerge from the fiber reinforcement inducing high thermal conductivity and fluctuating absorption properties for the laser wavelength, resulting in an essentially altered plastification performance which is directly mirrored in the inhomogeneous formation of the weld seam structure.

Process–structure relationship of carbon/ polyphenylene sulfide commingled hybrid yarns used for thermoplastic composites

Commingling is a prospective manufacturing process for the production of hybrid yarn in which a reinforcement material and a thermoplastic matrix in the form of filaments are mixed to form continuous filament yarn. In this work, hybrid two-component carbon/ polyphenylene sulfide (PPS) yarns designed for high-performance thermoplastic composites were developed. Experiments were carried out to investigate the manufacturing process of commingled yarn and quantify the homogeneity of distribution of carbon and PPS fibers in cross section of commingled hybrid yarns. The effect of process parameters in commingling including degree of overfeeding, production speed, and air pressure on the filament distribution in the cross section of commingled hybrid yarns was investigated. The results show that process parameters play a large part in improving blend uniformity and filament distribution in hybrid commingled yarns. A correlation between the observed homogeneity and the process parameters was established.

High-performance thermoplastic composites poly(ether ketone ketone)/silver nanowires: Morphological, mechanical and electrical properties

High-performance conductive thermoplastic composites poly(ether ketone ketone) (PEKK)/silver nanowires were elaborated by melt blending. Silver nanowires (AgNWs) with high aspect ratio (ξ~220) were elaborated through the polyol process in presence of poly(vinyl pyrrolidone) (PVP) and ethylene glycol. Scanning electron microscopy observations of nanowires were performed after an adapted cleaning process. The dispersion of NWs in the polymeric matrix was evaluated. A very low percolation threshold of 0.6vol% was obtained. Electrical conductivity values obtained above the percolation threshold were among the highest measured for low-filled conductive polymer composites. The influence of AgNWs on the PEKK matrix has been investigated by differential scanning calorimetry and dynamic mechanical analyses. It is important to note that thermal and dynamic mechanical performances of the polymeric matrix were preserved in composites.