High-performance Thermoplastic Composites Research Articles

Kraft Lignin/Tannin as a Potential Accelerator of Antioxidant and Antibacterial Properties in an Active Thermoplastic Polyester-Based Multifunctional Material.

This research focuses on key priorities in the field of sustainable plastic composites that will lead to a reduction in CO2 pollution and support the EU’s goal of becoming carbon neutral by 2050. The main challenge is to develop high-performance polyphenol-reinforced thermoplastic composites, where the use of natural fillers replaces the usual chemical additives with non-toxic ones, not only to improve the final performance but also to increase the desired multifunctionalities (structural, antioxidant, and antibacterial). Therefore, poly (lactic acid) (PLA) composites based on Kraft lignin (KL) and tannin (TANN) were investigated. Two series of PLA composites, PLA-KL and PLA-TANN, which contained natural fillers (0.5%, 1.0%, and 2.5% (w/w)) were prepared by hot melt extrusion. The effects of KL and TANN on the PLA matrices were investigated, especially the surface physicochemical properties, mechanical properties, and antioxidant/antimicrobial activity. The surface physicochemical properties were evaluated by measuring the contact angle (CA), roughness, zeta potential, and nanoindentation. The results of the water contact angle showed that neither KL nor TANN caused a significant change in the wettability, but only a slight increase in the hydrophilicity of the PLA composites. The filler loading, the size of the particles with their available functional groups on the surfaces of the PLA composites, and the interaction between the filler and the PLA polymer depend on the roughness and zeta potential behavior of the PLA-KL and PLA-TANN composites and ultimately improve the surface mechanical properties. The antioxidant properties of the PLA-KL and PLA-TANN composites were determined using the DPPH (2,2′-diphenyl-1-picrylhydrazyl) test. The results show an efficient antioxidant behavior of all PLA-KL and PLA-TANN composites, which increases with the filler content. Finally, the KL- and PLA-based TANN have shown resistance to the Gram-negative bacteria, E. coli, but without a correlation trend between polyphenol filler content and structure.

Processing of waste carbon and polyamide fibers for high performance thermoplastic composites: A novel manufacturing technology for unidirectional tapes structure

This paper presents an innovative, eco-friendly and sustainable tape manufacturing technology that transforms waste carbon and polyamide fibers into a new class of fibrous structure with unidirectional fiber orientation, termed “unidirectional tapes structure” for the fabrication of high performance composites. This novel technology imparts homogeneity, uniformity, orientation and thermal stability in unidirectional tapes structure that resemble conventional prepreg material. Unidirectional configuration of the tapes structure brings a revolution towards development of cost efficient carbon fiber composites for load bearing structural applications. This paper introduces the concept of tape manufacturing technology and highlights the modifications, optimization, and technological developments carried out to develop unidirectional tapes. The structural parameters that play a significant role in the properties of the high performance composite, such as fiber length, fiber orientation, fiber damage, and uniformity, were assessed during tape manufacturing. The results reveal composites fabricated from unidirectional tape structures with optimum parameters deliver tensile strength and modulus of 1370 ± 22 MPa and 85 ± 4 GPa, respectively.

Numerical Simulation of Impregnation Process of Reactive Injection Pultrusion for Glass Fiber/PA6 Composites.

Pultrusion of thermoplastic composites has been the hotspot of manufacturing high-performance thermoplastic composites in recent years. The optimization of process parameters in the pultrusion usually needed repeated attempts, which wasted lots of manpower and material resources. A numerical simulation method can accelerate the optimization of process parameters. In this work, the impregnation process of reactive injection pultrusion for glass fiber reinforced nylon 6 (GF/PA6) composites was modeled and numerically simulated by a finite element/controlled volume (Fe/CV) method. Based on Darcy’s law, the impregnation process can be regarded as the two-phase flow (liquid resin and air) in porous media (undirectional glass fibers). The distribution of resin flow during the impregnation was explored. The effects of pulling rate and injection pressure on the impregnation time and resin reflux distance were analyzed, and the appropriate range of relevant process parameters was determined. The results showed that increasing the pulling rate can significantly control the reflux distance of resin in the impregnation mold and shorten the impregnation time, but too high a pulling rate would increase the impregnation time. Increasing the injection pressure can greatly shorten the resin impregnation time, but it would significantly increase the resin reflux distance. This work can effectively guide the subsequent optimization of process parameters of reactive injection pultrusion for GF/PA6 composites.

Inverse heat transfer optimization of stamping with over-molding process involving high performance thermoplastic composites: experimental validation

Inverse heat transfer optimization of stamping with over-molding process involving high performance thermoplastic composites: experimental validation

Determination of thermal degradation for high-performance thermoplastic composites manufactured by laser-assisted automated fibre placement

In in situ consolidation of thermoplastic composites by laser-assisted automated fibre placement (AFP), high laser irradiation temperature can improve the fluidity of the resin matrix, which usually enhances the performances of composites. However, it leads to a tendency for thermal degradation as the resin matrix of the composites is exposed to high temperatures for a long time. The thermal degradation behaviours of continuous carbon fibre (CF)-reinforced polyphenylene sulfide (PPS) composites during in situ consolidation by laser-assisted AFP were studied. A thermogravimetric analysis shows that the thermal degradation of CF/PPS composites is quite complex, with multi-step reactions. The thermal degradation of the composites was further analysed via kinetic methods. A thermal degradation kinetic model of the resin matrix was obtained and verified. According to the kinetic model, the thermal degradation of the composites under different placement conditions was predicted. The results were confirmed by Fourier-transform infrared spectroscopy and scanning electron microscopy. With the combination of the kinetic model, AFP in situ consolidation, and characterisation techniques, processing parameters such as laser irradiation temperature and placement speed can be adjusted and optimised.

Effect of melt spinning on the integrity of poly(ether ether ketone) for commingled yarn based composite preforms

PEEK yarns are used for commingled yarn based preforms in order to manufacture high performance thermoplastic composites. In a previous work, characterizations of PEEK commingled yarns revealed degradation, causing poor consolidation of final composites. The sizing applied onto the yarn surface in the melt spinning was identified as a degradation factor. Thus, the aim of this work is to assess the effect of different melt spinning parameters: extrusion, sizing and draw ratio, on PEEK integrity and its degradation process. Yarns at different stages of melt spinning were characterized through various techniques. For all yarns, degradation was identified during further transformation, in the molten state, inducing a decrease of the crystallization temperature and an increase of viscosity due to crosslinking. Extrusion initiates degradation earlier without changing the PEEK decomposition process. Sizing is responsible for an acceleration and modifications of degradation steps.

Development of high-performance thermoplastic composites based on polyurethane and ground tire rubber by in-situ synthesis

The aim of this paper is to make full use of the hydroxyl groups on the ground tire rubber (GTR) surface to realize the high valuable utilization of waste tires in the field of high-performance polyurethane elastomers. In this work, the Polyurethane/Ground tier rubber (PU/GTR) thermoplastic composite with excellent performance was in-situ synthesized by adding untreated GTR to polyurethane. With incorporating 3.44 wt% GTR to polyurethane, the tensile strength of the PU/GTR thermoplastic composites was improved by approximately 166.7 % compared with pure PU. And the dynamic heat generation index (ratio of the tan δ at 90 °C and 30 °C) of the thermoplastic composites was reduced to 0.97, being far lower than that of pure PU (1.62), which exhibits this material has low dynamic heat generation when subjected to alternating stress. As expected, X-ray photoelectron spectra (XPS) results showed that the GTR indeed participated in the in-situ synthesis of polyurethane, thus, resulting in the GTR particles with micro size being evenly distributed in the polyurethane matrix via a network structure, which was proved by the morphology analysis and rheological measurement part. Additionally, the microphase separation of the PU matrix of the composites was greatly weakened according to Cole-Cole plots and the small angle X-ray scattering (SAXS) analysis. And the outcome of the study provided a low-cost and rational approach for recycling of waste tires while avoiding resource waste.

Thermal design methodology to hybrid manufacturing process of high performance thermoplastics composites

Thermal analysis plays a key role in the design of hybrid manufacturing processes of High-Performance Thermoplastic Composites (HP-TPC) parts. Indeed, an inadequate temperature distribution, during the transformation of these materials, could not only lead to mechanical and surface defects but also to inefficient energy consumption. These problems become difficult to avoid with the interaction of different materials within the part, and also with the influence of subsequent stages on the process. To overcome this challenge, the methodology proposed in this work aims to determine the spatial and temporal distribution of the heat sources that must be applied at each sequential stage of a process to reach a thermal objective within the part. The methodology is based on the concept of conformal cooling [1]. A surface enveloping the part is created [2]. Once a computational model is set up, the optimization problem is treated as an inverse problem subjected to constraints that depend on the process response in terms of temperature cycles. Thus, it requires the calculation of the direct problem, the adjoint-state solution, and the development of the sensitivity equations to implement a first-order gradient-based algorithm. As an application example, a thermo-stamping of HP-TPC with a metal insert followed by an over-molding process has been chosen because of the different stages and materials involved. The first results show a reduction of temperature gradients on the part surface at each stage while arriving at the established temperature level. Further analysis will include a constraint problem taking into account adhesion and/or energy criteria.

Temperature and contact pressure effects on the adhesion development of high performance thermoplastic composites

Thermoplastic composites offer new manufacturing prospects, thanks to the ability to melt the matrix. Welding, tape placement, 3D printing, overmoulding, or even stamping involve adhesion of the thermoplastic polymer at high temperature. First, under heat and pressure, contact at the microscopic scale is ensured by the deformation of surface roughness, this is the intimate contact step. Then, the development of the mechanical strength of the assembly is controlled by the diffusion of macromolecules at the interface which is defined as the healing step. Nowadays, continuous manufacturing processes tend to be faster and present very short residence time which could limit the adhesion development. A good understanding of these mechanisms is therefore very important to control and predict such industrial processes. Welding tests at different temperatures and contact pressures were carried out over a large range of residence times using a controlled welding bench enabling very short welding times (down to 1 second). The mechanical adhesion between PEKK-carbon composite samples was characterized using double cantilever beam fracture tests. Adhesion was found to develop in two steps which could be described as an intimate contact-healing coupled step and a pure healing step. From this, the healing kinetics was identified and an empirical model was developed to account for the effect of pressure on adhesion build-up. This model could then be compared with existing models to describe the establishment of intimate contact between the coupons.

The Out-of-Plane Compression Response of Woven Thermoplastic Composites: Effects of Strain Rates and Temperature.

The dynamic mechanical response of high-performance thermoplastic composites over a wide range of strain rates is a challenging research topic for extreme environmental survivability in the field of aerospace engineering. This paper investigates the evolution of the dynamic properties of woven thermoplastic composites with strain rate and damage process at elevated temperatures. Out-of-plane dynamic-compression tests of glass-fiber (GF)- and carbon-fiber (CF)-reinforced polyphenylene sulfide (PPS) composites were performed using a split Hopkinson pressure bar (SHPB). Results showed that thermoplastic composites possess strain-rate strengthening effects and high-temperature weakening dependence. GF/PPS and CF/PPS composites had the same strain-rate sensitivity (SRS) below the threshold strain rate. The softening of the matrix at elevated temperatures decreased the modulus but had little effect on strength. Some empirical formulations, including strain-rate and temperature effects, are proposed for more accurately predicting the out-of-plane dynamic-compression behavior of thermoplastic composites. Lastly, the final failure of the specimens was examined by scanning electron microscopy (SEM) to explore potential failure mechanisms, such as fiber-bundle shear fracture at high strain rates and stretch break at elevated temperatures.

Quality Prediction of Continuous Ultrasonic Welded Seams of High-Performance Thermoplastic Composites by means of Artificial Intelligence

Thermoplastic composites (TCs) are a famous choice when it comes to high performance designs for industrial applications. Since the growing demand on the use of this material, it is important to be able to evaluate suitable processing technologies. One of those technologies is continuous ultrasonic welding (CUSW) which creates continuous joints, also called seams, between two or more TCs parts. In CUSW mechanical oscillations are applied to the material and result in melting and connecting of the welding parts.The approach to predict joint strength (qualities) of continuous ultrasonic welded TCs by training different neural networks is investigated in this study. Quality class prediction around 72 % accuracy is achieved with a fully connected neural network. Concluding, quality prediction of welded TCs with the help of artificial intelligence seems to be a suitable approach for quality observation but more research could lead to more reliable neural networks for industrial applications.

Design and optimization of oven vacuum bag (OVB) processing for void air removal in high-performance thermoplastic composites

Oven vacuum bag processing is an emerging process to manufacture high quality thermoplastic parts with void reduction using vacuum consolidation only. This paper models void air removal as a combination of through-the-thickness gas diffusion and in-plane airflow through the interlayer region for a flat plate of finite in-plane dimensions consisting of an arbitrary number of layers. A finite difference model assumes Fickian diffusion, simplifies the microstructure of the multi-layer prepreg stack and allows evaluation of various material and process conditions (inter- and intra-layer void content, temperature and pressure cycle, etc.) on the through-thickness diffusion behavior of the volatiles. In-plane airflow in the intra-layer is modeled using Darcy’s flow and requires high permeability of the interface created by the porous volume in between adjacent layers and the ability to vent the gas at the part edge. The dual mechanism model evaluates part geometries and processing cycles to reduce void content equivalent to autoclave parts with previously generated material properties of AS4/APC2 carbon PEEK prepreg. The modeling results based on the proposed mechanism shows that processing with through-the-thickness diffusion and standard processing cycles limits part thickness to five layers or less for APC2 while in-plane gas reduction can be used to make large parts of up to 10 m in the in-plane direction independent of part thickness. Very large parts require the addition of an intermediate lower temperature dwell cycle where diffusivity is high but interlayer permeability is unaffected allowing gas flow to the part edges for an extended period of time. The edge vent approach ensures a robust process even for as received materials with significant void variability often seen in thermoplastic prepreg tapes.

High-performance molded composites using additively manufactured preforms with controlled fiber and pore morphology

In this work, large-scale multimaterial preforms produced by additive manufacturing (AM) underwent compression molding (CM) to produce high-performance thermoplastic composites reinforced with short carbon fibers. AM and CM techniques were integrated to control the fiber orientation (microstructure) and to reduce void content for the improved mechanical performance of the composite. The new integrated manufacturing technique is termed “additive manufacturing-compression molding” (AM-CM). For the present study, the most common materials were used for large-scale printing, i.e., acrylonitrile butadiene styrene (ABS), carbon fiber (CF)–filled ABS (CF/ABS) and glass fiber (GF)–filled ABS (GF/ABS). Three different manufacturing processes; (a) AM (b) extrusion compression molding (ECM), and (c) AM-CM were used to prepare four different panel configurations: (1) neat ABS, (2) CF/ABS, (3) overmold (CF/ABS over neat ABS), and (4) sandwich (neat ABS between two CF/ABS layers). The mechanical properties (tensile and flexural strength and modulus, and Izod impact energy) of samples prepared via all three manufacturing processes were compared. X-ray microcomputer tomography was employed to evaluate the fiber orientation distribution and the volumetric porosity content. The preform maintained high fiber alignment (≈ 82% of fibers within the range of 0–20° in the deposition direction), and the volumetric porosity was reduced by 50% from 3.79% to 1.91% after compression. The alignment of long pores along the deposition direction was also observed. The mechanical properties are discussed with correlation to the fiber alignment and void content in the samples. CF/ABS samples prepared by AM-CM showed significant improvement of 11.15%, 35.27%, 28.6%, and 74.3% in the tensile strength, tensile modulus, flexural strength, and flexural modulus, respectively, when compared with samples prepared by ECM. Unique aspects of this study are the demonstration of large-scale multimaterial AM and the use of multimaterials as preforms to make high-performance composites.

Polyaryletherketone (PAEK) thermoplastic composites via in-situ ring opening polymerisation

This work investigates the synthesis and characterisation of macrocyclic oligomers (MCO) from 4, 4′-difluoro benzophenone and catechol, their ring opening polymerisation, fabrication into carbon fibre reinforced composite materials and depolymerisation. The MCOs are polymerized using Caesium fluoride at a variety of temperatures, times, and catalyst concentrations to produce ortho polyaryletherketone polymers (oPAEK) of varying glass transition temperature (Tg) and molecular weight. A dimer formed during synthesis which does not polymerise is removed enabling a more convenient synthesis using lower temperature and catalyst concentration. The first carbon fibre composite of oPAEK fabricated using in-situ ring opening polymerisation methods is therefore presented with and without MCO dimer. Composites made without dimer formed are able fabricated at 10 °C lower temperature than the corresponding MCO containing dimer and have improved thermal and mechanical properties. Depolymerisation of the MCO and the re-emergence of cyclic structures is reported, highlighting the reversible nature of the chemistry. The results presented here provide important guidance on the future development of in-situ polymerisation of high performance thermoplastic composites.

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.