Advances in Carbon Fiber Reinforced Polyamide-Based Composite Materials

The chemical structure and the photo-resistance of some polyamides

Interfacial bonding property of SR/CF composites enhanced by secondary modification

<p>Geopolymers have been suggested in the literature as matrix materials for fibre reinforced composites due to a unique combination of low-temperature synthesis and high temperature stability. This study investigated several key aspects of fibre reinforced geopolymer matrix composites in order to improve the basic knowledge of these materials. It was demonstrated that geopolymer matrix composites show great potential as fire-resistant materials for near room temperature applications. In particular, basalt fibre composites were of great interest due to their comparatively low cost and good mechanical performance. Microstructural investigations indicated that basalt fibres can potentially be used in geopolymer matrices up to 600°C. However, the success of the application of geopolymer matrix composites at higher temperatures is seen as critical and depends on further development of suitable matrices. Several compositions within a sodium-metahalloysite model matrix system were evaluated in order to identify a suitable formulation for composite fabrication. An average compressive strength of ~ 79 MPa and flexural strength and modulus of ~ 10 MPa and 8.5 GPa, respectively, were achieved for the best batch of the main matrix composition. By optimising the matrix composition, the mechanical properties could be significantly improved, achieving an extremely high maximum compressive strength value of 145 MPa. Issues with reproducibility and the influence of various aspects of the fabrication process are discussed. The room temperature flexural properties of unidirectional fibre reinforced composite bars with basalt, carbon and alumina fibres were investigated. Besides the fibre type, the effects of several other parameters including fibre sizing, matrix strength, span-to-depth ratio and specimen dimensions on the flexural properties and the failure behaviour of the composites were studied. Significant improvements to the mechanical properties were achieved with all fibre types. However, the mechanical behaviour was highly influenced by the elastic modulus of the fibre. Furthermore, it was shown that the composite properties were affected by the overall sample dimensions, the testing span and the mixing time of the geopolymer binder. The alumina fibre composites achieved the highest flexural stress with a maximum value of 470 MPa and a fibre content of ~ 30 vol.-%. Basalt and carbon fibre composites showed maximum flexural strength values around 200 MPa. Although all composite types displayed considerable post-fracture strength, only the basalt composites failed in tensile mode. The applicability of the weak matrix composites (WMC) concept to describe the mechanical behaviour of geopolymer matrix composites was discussed. The fibre-matrix interactions were analysed between room temperature and 1000°C by means of electron microscopy, EDS and x-ray diffraction. All fibres were found to be chemically stable under the highly alkaline conditions of the geopolymer synthesis and showed no significant reaction with the geopolymer matrix at room temperature. The results indicate that basalt fibre composites may be used up to 600°C without significant degradation of the fibre. The heating of the carbon fibre composites to 600°C had drastic effect on the strength and integrity of the composite, in particular, when using sized carbon fibres. The alumina fibres showed good wetting and bonding behaviour but otherwise little reaction with the matrix even after heating to 1000°C.</p>

As an extension of reinforcing principles of composite materials in which macroscopic fibers are dispersed in a ductile matrix, rigid microfibrils of wholly aromatic polyamides such as poly(p-phenylene terephthalamide) (PPTA), poly-p-benzamide (PBA), and their block copolymers with blocks of nylon 6 or nylon 66 were dispersed in a matrix of nylon 6 or nylon 66. On blending polyaramides with aliphatic polyamides, the spherulitic texture disappeared and a locally birefringent homogeneous texture was obtained. Electron microscopy revelaed that microfibrils of PPTA with diameter of 15-30 nm were dispersed in a fractured surface of the polymer composite. Strong interaction between the fibril surface and the matrix was suggested by the fact that the crystallization of matrix polyamides was induced by the rigid polyaramides. Wide-angle x-ray diffraction intensity curves, DSC curves of cooling process from the melt, and isothermal crystallization curves indicated a marked tendency for induced crystallization with polyaramides. Viscoelastic relaxation curves indicated increased fraction of immobilized noncrystalline chains, increased modulus of the blend, and increased heat resistance of the blend as shown in retention of the blend modulus even at 200°C. By applying the modified Halpin-Tsai equation to the relationship between Young's modulus and the fraction of rigid molecules in the blend, the aspect ratio of microfibril was estimated at 15 to 25. Young's modulus and yield stress were remarkably improved by blending the polyaramides as low as 5%. With increasing molecular weight of PPTA, both modulus and yield strength systematically increased, while ultimate strength did not vary and ultimate elongation decreased. Blending the block copolymers of polyaramides and aliphatic nylon blocks with nylon matrix increased ultimate elongation compared with the physical blend of homopolyaramides and aliphatic polyamides. The orientation effect was very effective, as shown in the system of 3% PPTA and 97% nylon 6, in which the ultimate strength increased from 230 MPa of nylon 6 to 340 MPa of the blend. An ultimate strength of the PPTA microfibril of more than 4 GPa is realized in the blend, indicating full reinforcing effect of rigid fibrils at a supramolecular level.

Predicting the modulus of short fiber‐reinforced composites is complicated by simultaneous variations in fiber length, orientation, and volume fraction during processing. This work refines the classical modified rule of mixtures (MROM) by introducing two concentration‐dependent weighting functions, and , which capture the evolution of effective fiber length, fiber‐fiber interactions, fiber orientation, and loading‐angle effects. A microstructural efficiency coefficient is further incorporated to describe reinforcement degradation from dilute to crowded fiber conditions. The model was validated using ethylene‐vinyl acetate/short carbon fiber composites with fiber volume fractions of 1.37%–16.80%. Young's modulus measured at loading angles of 0°, 45°, and 90° showed excellent agreement with predictions, with the refined formulation outperforming the classical MROM, particularly at higher loading angles. Overall, the refined framework provides a compact and physically grounded framework for accurately predicting stiffness and supports the design and optimization of short fiber‐reinforced polymer systems.

This study concerns short-cut aramid fiber reinforcement of synthetic elastomer compounds and their influence on the processability and mechanical properties. Short-fiber reinforcement of elastomers is very complex, because it depends on many mutually interacting factors: fiber concentration, fiber orientation distribution, fiber length and distribution, fiber-matrix interfacial strength, and properties of the matrix. The relationship between these influencing factors is highlighted in an S-SBR compound by design of experiments. Two 3 mm long aramid fibers were used: an epoxy-amine–coated fiber and a virgin fiber without coating. To potentially achieve a fiber–matrix interaction, the following silane coupling agents were employed: bis-(triethoxysilylpropyl)-disulfane (TESPD), bis-(triethoxysilylpropyl)-tetrasulfane (TESPT), S-3-(triethoxysilylpropyl)-octanethioate (NXT), and an alkylpolyether-mercapto-silane (Si 363), all in combination with the adhesion-activated aramid fibers and in comparison with the virgin fibers. They are compared on equimolar basis with regard to the amount of reactive ethoxy groups versus TESPD, making use of a “design of experiments” approach of the experimental setup. The outcome shows that, contrary to common assumptions, the effect of the fiber–matrix interaction is grossly overshadowed by the effects of other factors (i.e., fiber concentration and orientation) on the vulcanization system. For each mechanical property response, an optimization prediction is calculated and confirmed with an experimental run, showing, for example, a 330% potential improvement in the Young's modulus.

Natural fiber composites' appealing properties have enabled their use in a wide range of engineering applications, including automotive and structural applications. Wear is a common issue in automotive and structural applications, increasing the likelihood of material failure. As a result, composites with increased wear resistance are required. Natural fiber composites have completely different wear properties than metals. Understanding the wear mechanism of natural fiber composites is critical for their potential use in a variety of applications. Wear is of different types, each with its own mechanism of material loss. Wear is determined by material properties, such as matrix and reinforcement properties. The critical factors influencing the wear performance of natural fiber composites are fiber loading, fiber orientation, fiber length, and fiber interface. This review attempted to investigate the different types of wear in fiber composites and their impact on natural fiber composites. This article could serve as a one‐stop shop for learning about the wear characteristics of natural fiber composites.

The application of basalt fibers are possible in many areas thanks to its multiple and good properties. It exhibits excellent resistance to alkalis, similar to glass fiber, at a much lower cost than carbon and aramid fibers. In the present paper, a comparative study on mechanical properties of basalt and E-glass fiber composites was performed. Results of apparent hoop tensile strength test of ring specimens cut from tubes and the interlaminar shear stress (ILSS) test are presented. Tensile tests using split disk method provide reasonably accurate properties with regard to the apparent hoop tensile strength of polymer reinforced composites. Comparison between the two tubes showed higher basalt fiber composite performance on apparent hoop tensile strength (45% higher) and on the interfacial property interlaminar shear stress (ILSS) (11% higher). New data obtained in this work on basalt fiber composite tubes confirm the literature for basalt fiber composite with other geometries, where it overcomes mechanical properties of the widely used glass fiber composites.

Electrodeposited carbon fiber and epoxy based sandwich architectures suppress electromagnetic radiation by absorption

Polyamides are one of the most widely used engineering plastics. Aliphatic polyamide represented by nylon has been previously synthesized by an interfacial polymerization reaction between an organic layer of diacyl chloride and a water layer of diamine. However, for more than 75 years, there has been no reported polymerization method that can enable the synthesis of both helical aliphatic polyamide (nylon) and aromatic polyamide (polyphthalamide) and can control their spiral morphologies. In this study, we developed a novel polymerization method based on chiral interfacial polycondensation using a chiral nematic liquid crystal (N*-LC) layer and a water layer and, for the first time, succeeded in synthesizing helical nylons and polyphthalamides with one-handed spiral morphologies. The swirling directions in the spiral morphology of the helical polyamides were controlled by selecting the chirality of the chiral dopant used for preparing the N*-LC. The present synthesis method should extend the applicability of asymmetric interfacial polymerizations using N*-LC to various types of polyamides.

Composites based on e.g. randomly oriented nonwovens and injection moulded structures from discontinuous carbon fibre (CF), which are processed industrially exhibit low tensile strengths of 200–300 MPa and 400 MPa, respectively. In contrast, composites based on twisted hybrid yarns from discontinuous CF and thermoplastic fibre show higher tensile strengths such as 1150 MPa. Reasons are improved fibre orientation and higher fibre volume content. However, tensile strength is still lower than that of uni-directional carbon fibre reinforced composites (CFRP) based on continuous filament yarn, which is around 1560 MPa. The reason is a low fibre orientation due to yarn twisting and high fibre shortening, which occurs throughout the yarn manufacturing process. As mechanical properties of composites largely depend on fibre orientation and length, there is a high potential to achieve higher mechanical properties in CFRP by ensuring gentle processing of CF and reducing yarn twist. However, due to brittleness and smooth surface of CF, spinning of yarns with low twist (<60 T/m (twist per meter)) is challenging. In order to exhaust the potential of hybrid yarns, a semi-industrial process chain to produce hybrid yarns while ensuring gentle processing of discontinuous CF (fibre length 100 mm) and polyamide 6 fibres (fibre length 80 mm) at significantly low level of twist 20 T/m is reported in this paper. Carbon fibre reinforced composite manufactured from these hybrid yarns show high tensile strength (1453 ± 27 MPa), Young’s modulus (94 ± 6 GPa), flexural strength (1090 ± 41 MPa) and flexural modulus (98 ± 5 GPa).

ABSTRACTMaterial extrusion (ME) enables additive manufacturing of continuous fiber‐polymer composites, with carbon, glass, and aramid fibers being the most widely used reinforcements. This study systematically investigates the fiber damage mechanisms in these three filament types during ME‐based 3D printing. Fiber damages initiate as the filaments feed through the 3D printer and intensify during deposition on the platform. The extent and modes of damage correlate strongly with inherent fiber properties. Carbon fibers, characterized by low toughness and failure strain, sustain the most severe damage and breakage, resulting in 21% and 42% reductions in filament stiffness and strength, respectively. Glass fibers also suffer breakage during fabrication, although the extent is less pronounced compared to carbon fibers, with the filament stiffness and strength reduced, respectively, by 15% and 32%. Aramid fibers, while resistant to breakage due to high toughness and ductility, undergo crimping and a 15% strength loss. Such damages induced by 3D printing significantly compromise the tensile properties of fabricated laminates. The study highlights the critical roles of fiber bending stiffness, fracture toughness, and failure strain in achieving minimal fiber damage and optimizing the mechanical performance of 3D printed continuous fiber composites.

Additive manufacturing is key in realizing highly complex and high-performance composite materials. Among all the various kinds of functionality that could be added to a composite component, continuous fiber-reinforced composites have been drawing much attention because of their attractive combination of properties. The comprehensive spectrum of knowledge that ranges from the basics concerned with structure, morphology, synthesis, physical, and chemical properties finally reaches to this analytical study of advanced composites. Most generally, such a composite is structured on a thermoplastic or thermoset polymer matrix that embeds the load-carrying reinforcing fibers; probably best known are carbon, glass, and aramid fibers. These composites, which involve fibers continuously reinforcing, have high strength relative to their weight. They are also anisotropic, meaning they have qualities that vary from one direction to another – something which might be customisable for specific load cases. They warp and shrink less during their life in an outside environment than conventionally made bioplastics due to a fact that short fibers can provide reinforcement to them. This 3-D printing object is manufactured by special additive manufacture technology during the manufacturing process after compounding and extruding the fiber-reinforced composite filament. The final properties of 3D printed parts could be tailorable through changing variables such a fiber type, fiber length, volume fraction, polymer matrix material, orientation of fibers, and printing process parameters. These continuous fiber-reinforced 3D printed composites could achieve tensile strengths up to one GPa, have stiffness values reaching even a rating of countless Gpa, and have ad thicknesses in the range from about 1.4–1.8 g/cm³. This finding could be applied in basically all major industries, from aerospace and the automotive industry to sports gear. Such conclusions from the analysis may be useful in the selection of appropriate materials and techniques while even guiding the development of new applications with respect to such advanced composite materials.

Carbon staple fiber composites are materials reinforced with discrete-length carbon fibers processed using traditional textile technologies, offering moderate mechanical properties and flexibility in manufacturing. These composites can be produced from recycled carbon staple fibers, aligned into yarn and tape-like structures, providing a more sustainable alternative while balancing performance, cost-effectiveness, and environmental impact. Aligning staple fibers into tape-like structures enables similar applications to those of continuous-fiber-based products, while allowing control over fiber orientation distribution, fiber volume fraction, and length distribution, which are all critical factors influencing both mechanical and thermo-mechanical properties. This study focuses on the experimental characterization and numerical investigation of Coefficients of Thermal Expansion (CTEs) in aligned carbon staple fiber composites. The effects of fiber orientation and volume fraction on coefficients of thermal expansion under different fiber alignment parameters are analyzed, revealing distinct thermal expansion behavior compared to typical aligned unidirectional continuous carbon fiber composite laminates. Unlike continuous unidirectional laminates, which typically exhibit transversely isotropic behavior without tensile-shear coupling, staple fiber composites demonstrate different in-plane axial, transverse, and out-of-plane CTE characteristics. To explain these deviations, a modeling approach is introduced, incorporating detailed experimental information on fiber distributions and microstructural features rather than averaged fiber orientation values. This involves a multi-scale analysis based on a laminate analogy through which all composite thermo-elastic properties can be predicted, accounting for variations in fiber orientations, volume fractions, and tape thicknesses. It is shown that while the local variation of fiber volume fraction has a small effect on the homogenized value of the coefficients of thermal expansion, fiber misalignment, tape thickness, and asymmetry in fiber orientation distribution will significantly affect the measurements of CTEs. For the case of carbon staple fiber composites, the asymmetry in fiber orientation distribution significantly influences the measurements of axial CTE. Fiber orientation asymmetry causes tensile-shear coupling under mechanical and thermal loading, leading to an unbalanced laminate with in-plane shear-tensile deformation. This coupling disrupts uniform displacement, complicating strain measurements and the determination of composite properties.

Fiber-reinforced composites were widely used in aerospace, automotive, and wind energy industries, due to their lightweight, high specific strength and stiffness, design flexibility, and durability. This study prepared hybrid fiber preforms using a three-dimensional braided technique. These preforms made of carbon fiber (CF) and aramid fiber (AF) were reinforced into resin-based (ER) composites by a vacuum infusion process (VIP). Our study focused on evaluating the mechanical properties of these composites under different blend arrangements and ratios, with four blend arrangements including layer-by-layer, half-by-half, bundle-by-bundle, and block-by-block. The results showed that the bending strain of the composites with a 3:1 aramid fiber/carbon fiber yarn ratio (3AF1CF) increased by 105.56% compared to that of CF/ER, and the addition of AF improved the toughness of the composite. The tensile strength and modulus of the composites with a 3:1 carbon fiber/aramid fiber yarn ratio (1AF3CF) were improved by 31.17% and 109.68%, respectively, compared to those of AF/ER, and the bending strength and modulus increased by 106.12% and 115.32%, respectively, and increasing the CF ratio thus significantly improved the mechanical properties of the composites. In addition, in four hybrid arrangements with the same AF/CF ratio, the aramid fiber/carbon fiber yarn ratio of 2:2 (2AF2CF-4) possessed the best mechanical properties, with tensile strength and of 608.36 MPa and 13.8 GPa, and bending strength and modulus of 417.203 MPa and 22.9 GPa, respectively.