Thermoplastic Research Articles

A review of helicoidal composites: From natural to bio-inspired damage tolerant materials

Helicoidal composites have been found in shrimp club, lobster claw, beetle cuticle, crab shell, scorpion pincer, and fish scale as a natural material. The helicoidal composite possesses excellent impact resistance and extraordinary damage tolerance due to its hierarchical structure and the unique helicoidal arrangement of its reinforcement fibres. Its structure and performance have been studied through various characterisation and mechanical testing methods. Based on the structure-property relationship of the natural helicoidal composite, researchers have been able to mimic the unique fibre arrangement and develop bio-inspired helicoidal composites with enhanced impact performance. Various helicoidal composites comprising of synthetic fibrous materials such as carbon fibre (CF), glass fibre (GF), and aramid fibre, and matrix materials such as thermoset and thermoplastic polymers have been developed through biomimicry. The failure mechanisms of the bio-inspired helicoidal composites have been studied and the advantages of arranging the fibre reinforcement into helicoidal architectures have been elucidated over conventional composite constructions such as quasi-isotropic (QI) and cross-ply layups. This review systematically elaborates the recent progress of the research work on both natural and bio-inspired helicoidal composites. It sheds light on the distinctive construction of the natural helicoidal composites found in different animals such as shrimps, lobsters, crabs, beetles, scorpions, and fish, and their energy absorption mechanisms. Different manufacturing methods for developing bio-inspired helicoidal composites are discussed and various reinforcements and matrix materials used in the composites are described. The processing-structure-property interrelationship of the bio-inspired helicoidal composites is summarised. This review will contribute to the advancement of the knowledge of the natural helicoidal composite and potentially help researchers to develop highly efficient bio-inspired damage tolerant helicoidal composites.

Synthesis and Characterization of Graft Copolymers with Poly(ε-caprolactone) Side Chain Using Hydroxylated Poly(β-myrcene-co-α-methyl styrene)

Graft copolymers have unique application scenarios in the field of high-performance thermoplastic elastomers, resins and rubbers. β-myrcene (My) is a biomass monomer derived from renewable plant resources, and its homopolymer has a low glass transition temperature and high elasticity. In this work, a series of tapered copolymers P(My-co-AMS)k (k = 1, 2, 3) were first synthesized in cyclohexane by one-pot anionic polymerization of My and α-methyl styrene (AMS) using sec-BuLi as the initiator. PAMS chain would fracture when heated at high temperature and could endow the copolymer with thermal degradation property. The effect of the incorporation of AMS unit on the thermal stability and glass transition temperature of polymyrcene main chain was studied. Subsequently, the double bonds in the linear copolymers were partially epoxidized and hydroxylated into hydroxyl groups to obtain hydroxylated copolymer, which was finally used to initiate the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) to synthesize the graft copolymer with PCL as the side chain. All these copolymers before and after modifications were characterized by proton nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC), thermogravimetry analysis (TGA), and differential scanning calorimeter (DSC).

Carbon fiber‐reinforced thermoplastic synthesized by the hypercrosslinking reaction of polyether ether ketone

AbstractRecently, thermoplastic resins were used as matrix to synthesize carbon fiber‐reinforced thermoplastic (CFRTP) for recycling it easily. In this study, a CFRTP with excellent mechanical properties and heat resistance was synthesized using a polyether ether ketone (PEEK) as a matrix resin. The PEEK resin was modified to form cross‐linked structures through Friedel–Crafts reaction alkylation. The synthesis temperature of CFRTP was optimized considering the mechanical properties of PEEK, and its heat resistance was enhanced because of the cross‐linked structures. Further, the cross‐linked PEEK resin was partially used as a matrix resin, and the mechanical properties of the CFRTP were enhanced. We plan to develop a method for recycling CFRTP using PEEK and crosslinked PEEK for synthesizing C/C composites by focusing on the high heat resistance of the crosslinked PEEK containing a large amount of carbon and reducing mass loss after heat treatment.Highlights CC bonds were introduced into the polyether ether ketone (PEEK) resin by Friedel–Crafts reaction alkylation. Thermal properties of PEEK were enhanced by hypercrosslinking reaction. Optimization of synthesized temperature was investigated to fabricate carbon fiber‐reinforced thermoplastic (CFRTP). Mechanical properties were enhanced CFRTP modified with hypercrosslinking reaction.

Thermoplastic composites reinforced chemically modified kenaf fibre: current progress on mechanical and dynamic mechanical properties

Thermoplastic composites reinforced chemically modified kenaf fibre: current progress on mechanical and dynamic mechanical properties

Characterization of fly ash reinforced wood polypropylene composites

In this study, fly ash, which is released as waste from thermal power plants and has negative effects on the environment, was evaluated as a filler in wood-plastic composite materials (WPC). For this purpose, inorganic fly ash from thermal power plants was mixed with polypropylene (PP) thermoplastic polymer at 10%, 20%, 30%, 40%, and 50% by extrusion method instead of wood flour used in wood plastic composite materials. Maleic anhydride-treated polypropylene (MAPP) was used to strengthen the bonding during WPC production. The material mixed in extrusion was passed through a crusher and turned into pellets. Test samples were prepared using injection molding of pelletized WPC material. Density, thickness swelling, water absorption, modulus of rupture, impact strength, modulus of elasticity in bending, tensile strength, janka hardness, differential scanning calorimetry (DSC), and thermogravimetric analyses (TGA) were performed on the prepared test samples. The results indicated that as the amount of fly ash used in the wood-plastic composite material increases, the density increases but the thermal degradation temperature of the material, water uptake, the swelling ratio to its thickness, tensile strength, impact strength, janka hardness, modulus of rupture, and modulus of elasticity decrease.

Tensile behavior of polycarbonate: Key aspects for accurate constitutive modelling and simulation

Polycarbonate (PC) is a thermoplastic polymer used in many engineering applications such as safety devices and aerospace components. However, the unique behavior of PC under tensile load and its effects on the estimation of its constitutive curve are often overlooked in the literature, neglecting to consider crucial aspects of the characterization process. This work carries out a comprehensive analysis of the mechanical behavior of PC to understand the key points for accurate constitutive modeling and simulation of its static tensile performance, including its unconventional deformation mechanisms. The work starts from the accurate analysis of a representative experimental static tensile test on a rectangular section PC specimen and the evaluation of its true stress-strain curve. This analysis, carried out considering the classic length-based approach and the more accurate area-based approach, makes it possible to evaluate in detail the peculiar tensile behavior of this material. The mathematical form of the PC true stress-strain curve is then justified and the coincidence of the obtained length-based and area-based estimates of the same is demonstrated. Then, based on the in-depth understanding of the dynamics underlying the mechanical behavior of PC and making use of FEM simulations, the key points for obtaining its constitutive curve are defined. It is demonstrated that the constitutive curve is able to completely determine the behavior of PC, including its peculiar deformation mechanism. It is also highlighted which specific characteristics of the constitutive curve are critical in affecting various aspects of the material's behavior. The final constitutive curve of PC at hand is then obtained with an inverse approach, capable of accurately simulating all aspects of its tensile behavior. The validity of the proposed modelling key points is then confirmed, effectively explaining the underlying phenomena controlling the tensile behavior of PC and massively reducing uncertainty in the estimation of its constitutive curve starting from its area-based true curve.

Development of a heavy vehicle torque rod applying continuous fiber reinforced thermoplastic composite materials instead of forged steel material: Design, analysis and optimization

The torque rod is an important component of the suspension system that connects the axle to the chassis in heavy commercial vehicles. The main motivation of this study is the development of a torque rod made of (1) plus cross-section, (2) continuous carbon and glass fiber reinforced hybrid thermoplastic composites, which can replace a forged steel torque rod used in heavy vehicles, has superior mechanical properties, provides minimum cost and weight. This study aims to develop a torque rod before its production within the framework of integration with Computer Aided Design (CAD), Finite Element Analysis (FEA), and Multi-Criteria Decision Making (MCDM). In this study, the design data and the properties of the composite materials were chosen as control factors. The minimum displacement, the best mechanical properties such as tensile stress, compressive stress, torsional shear stress, maximum critical buckling load, and the minimum part weight minimum production cost per piece were selected as quality characteristics. As a result of the FEA study, considering the experimental set of the Taguchi Method L25 orthogonal array, the data on mechanical properties, weight, and production cost per piece were subjected to the MCDM process using the Entropy Weighted TOPSIS method. As a result of the MCDM study, a torque rod made of continuous fiber-reinforced thermoplastic composite material, instead of a torque rod produced by forged steel, had the highest mechanical properties produced, the weight of the torque rod can be reduced by 64.76%, and the production costs per piece can be reduced by 37.5%. This study’s findings have shown that the torque rod produced from continuous fiber-reinforced thermoplastic composite materials in a new geometry with a plus cross-section can be substituted for the torque rod produced by steel forging. Thus, it will contribute to reducing the fixed vehicle weight, especially in heavy commercial vehicles, reducing CO2 emissions, and increasing the range of the vehicles.

High-speed spinning of collagen microfibers comprising aligned fibrils for creating artificial tendons.

Bundles of engineered collagen microfibers are promising synthetic tendons as substitutes for autogenous grafts. The purpose of this study was to develop high-speed and continuous spinning of collagen microfibers that involves stretching of collagen stream. Our study revealed the "critical fibrillogenesis concentration (CFC)" of neutralized collagen solutions, which is defined as the upper limit of the collagen concentration at which neutralized collagen molecules remain stable as long as they are cooled (≤10°C). Neutralized collagen solutions at collagen concentrations slightly below the CFC formed cord-like collagen gels comprising longitudinally aligned fibrils when extruded from nozzles into an ethanol bath. Dry collagen microfibers with a controlled diameter ranging from 122 ± 2 to 31.2 ± 1.7 μm can be spun from the cord-like gels using nozzles of various sizes. The spinning process was improved by including stretching of collagen stream to further reduce diameter and increase linear velocity. We extruded a collagen solution through a 182-μm-diameter nozzle while simultaneously stretching it in an ethanol bath during gelation and fiber formation. This process resembles the stretching of a melted thermoplastic resin because it solidifies during melt spinning. The mechanical properties of the stretched collagen microfibers were comparable to the highest literature values obtained using microfluidic wet spinning, as they exhibited longitudinally aligned fibrils both on their surface and in their core. Previous wet spinning methods were unable to generate collagen microfibers with a consistent tendon-like fibrillar arrangement throughout the samples. Although the tangent modulus (101 ± 16 MPa) and stress at break of the swollen bundles of stretched microfibers (10.5 ± 0.5 MPa) were lower than those of ACL, they were within the same order of magnitude. We developed a spinning technique that produces narrow collagen microfibers with a tendon-like arrangement that can serve as artificial fiber units for collagen-based synthetic tendons.

Lignocellulosic abaca fibre-reinforced thermoplastic composites as future sustainable structural materials: a bibliometric analysis and literature review

Lignocellulosic abaca fibre-reinforced thermoplastic composites as future sustainable structural materials: a bibliometric analysis and literature review

Thermal-force coupling simulation of carbon fibre-reinforced poly-ether-ether-ketone thermoplastic composites during the laser-assisted automated tape placement process

To reveal the thermal-force coupling characteristics of the laser in-situ consolidation (ISC) of carbon fibre-reinforced poly-ether-ether-ketone (CF/PEEK) composites, a two-dimensional transient thermal-force model of CF/PEEK composites was constructed using COMSOL Multiphysics finite element simulation software to calculate the temperature history and the thermal stress variation of CF/PEEK composites during the laser-assisted automated tape placement (LATP) process. The results show that the temperature field formed on the surface of each layer by the laser spot during LATP is stable, and the temperature gradient at the front of the spot movement direction is higher than that at the back edge. The maximum stresses in the laminate occur on both sides of the first CF/PEEK layer and the stresses are unevenly distributed along the length and thickness directions of the lay-up. The composite material on both sides of the laminate tends to ‘shrink’ compared to its original position.

Mechanical, Flame-Retardant and Dielectric Properties of Intumescent Flame Retardant/Glass Fiber-Reinforced Polypropylene through a Novel Dispersed Distribution Mode

The application of continuous glass fiber-reinforced polypropylene thermoplastic composites (GF/PP) is limited due to the inadequate flame retardancy of the polypropylene (PP) matrix. Apart from altering the composition of the flame retardants, the distribution modes of flame retardants also impact material performance. In this study, an alternative approach involving non-uniform distribution is proposed, namely, dispersed distribution, in which non-flame-retardant-content layers (NFRLs) and/or low-flame-retardant-content layers (LFRLs) are dispersed among high-flame-retardant-content layers (HFRLs). The mechanical, flame retardant and dielectric properties of GF/PP with intumescent flame retardant (IFR/GF/PP) are investigated comparatively under uniform, gradient, and dispersed distributions of the flame retardants. The results demonstrate that non-uniform distribution exhibits superior flame retardant performance compared to uniform distribution. Dispersed distribution enables IFR/GF/PP to attain enhanced mechanical properties and reduced dielectric constants while maintaining excellent flame-retardant properties.

Thermoplastic polymers as water substitutes

Background. New applications of 3D printing have recently appeared in the fields of radiotherapy and radiology, but the knowledge of many radiological characteristics of the compounds involved is still limited. Therefore, studies are needed to improve our understanding about the transport and interaction of ionizing radiation in these materials. Purpose. The purpose of this study is to perform an analysis of the most important radiation interaction parameters in thermoplastic materials used in Fused Deposition Modeling 3D printing. Additionally, we propose improvements to bring their characteristics closer to those of water and use them as water substitutes in applications such as radiodiagnosis, external radiotherapy, and brachytherapy. Methods. We have calculated different magnitudes as mass linear attenuation, mass energy absorption coefficients, as well as stopping power and electronic density of several thermoplastic materials along with various compounds that have been used as water substitutes and in a new proposed blend. To perform these computations, we have used the XCOM and ESTAR databases from NIST and the EGSnrc code for Montecarlo simulations. Results. From the representation of the calculated interaction parameters, we have been able to establish relationships between their properties and the proportion of certain chemical elements. In addition, studying these same characteristics in different commercial solutions used as substitutes for water phantoms allows us to extrapolate improvements for these polymers. Conclusion. The radiological characteristics of the analyzed thermoplastic materials can be improved by adding some chemical elements with atomic numbers higher than oxygen and by using polyethylene in new blends.

In-situ consolidation of thermoplastic composites by automated fiber placement: Characterization of defects

The emergence of automated manufacturing of composites has not only transformed the manufacturing of optimized and geometrically complex structures but has also expanded the promising prospect of in-situ manufacturing of thermoplastic composites (TPC), where both material placement and consolidation are carried out by automated fiber placement (AFP) equipment, streamlining the process into single step manufacturing. However, the inherent complexities in different aspects of robotic automation, imperfections in the supplied material, and the occurrence of multi-physical phenomena during in-situ consolidation introduce various manufacturing-induced defects. While the defects in thermoset composites (TSC) made by AFP have been widely studied in the past, this study explores the diverse defects at micro and macro scales for TPCs made by AFP, with a focus on carbon-fiber/poly-ether-ether-ketone (CF/PEEK) tapes consolidated using hot gas torch (HGT) heating system. An overview of defects and associated characteristics is presented across three phases: defects in supplied impregnated tapes, defects and limitations in performance of AFP system, and defects in the final in-situ consolidated composite. For the defects subject to studies in the past, the description is limited to a concise review, while those with limited understanding are supported by new empirical observations in this work.

Flexible, High Thermal Conductivity, and EMI Shielding Performance Thermoplastic Polyurethane Composites through Reinforced-Orientation Carbon Fiber

Flexible, High Thermal Conductivity, and EMI Shielding Performance Thermoplastic Polyurethane Composites through Reinforced-Orientation Carbon Fiber

Sulfonation Treatment of Polyether-Ether-Ketone for Dental Implant Uses

There has been a recent uptake in the use of polyether-ether-ketone (PEEK), which is an organic thermoplastic polymer, in the manufacturing of various medical devices, implants, and equipment. Finding the best time and procedure for PEEK after sulfonation is the goal of this research. A total of 30 PEEK discs were sulfonated in this study by immersing them in concentrated (H2SO4) sulfuric acid for various durations and subsequently treated using various post-treatment techniques. Five experiments were carried out, aimed studying the effect of immersion time (5 s–2 min). The methods used as post-treatment were hydrothermal treatment, immersion in NaOH, and washing with acetone. The sulfonation time was measured, and the post-treatment techniques, surface characterizations, were conducted using scanning electron microscopy (SEM) (Electron Optics Instruments, LLC., West Orange, NJ, USA), atomic force microscopy (AFM) (AFM, Vía Burton, CA, USA), and hydrophilic properties. The results were confirmed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The findings of this study demonstrate that sulfonating PEEK caused a structure with a porous network to form in every sample. As the sulfonation time increased, the porous structure became more noticeable and the concentration increased. As a consequence, the roughness of the surface increased notably, and the modified PEEK surface’s wettability improved noticeably. Hydrothermal treatment was determined to be the most successful way for eliminating the leftover sulfuric acid, and sulfonation for 2 min was determined to be ideal. By understanding the best post-treatment procedures and ideal sulfonation duration, a theoretical foundation for the production of sulfonated PEEK for orthopedic uses may be laid.

Effect of in-situ activated core-shell particles on fatigue behavior of carbon fiber reinforced thermoplastic composites

In this unique study, the effect of adding core-shell particles (CSPs) on fatigue performance of carbon-fiber reinforced PA6 (CF-PA6) laminates is investigated. The thermoplastic laminates were prepared using compression molding and were reinforced at ply interfaces with 2 wt% and 4 wt% CSPs of the polymer mass. A manual method was used to disperse CSPs using a sieve and carefully selected process parameters. The cyclic tests were conducted and assessed, considering S–N curve, stiffness degradation, and energy dissipation. Consequently, the fatigue life of modified composites improved respectively by eight and four times when 2 wt% and 4 wt% CSPs were used. The results showed that an optimal improvement was achieved with a 2 wt% CSPs. The fatigue strength coefficient and fatigue strength exponent of CF-PA6 composites improved by 22.13 % and 9.85 %, respectively. The findings have the potential to establish a new frontier in thermoplastic research and would help designers to enhance the fatigue properties of thermoplastic laminates in specific elastic tailoring structures.

Response Surface Methodology Optimization of Resistance Welding Process for Unidirectional Carbon Fiber/PPS Composites

The use of thermoplastic composites (TPCs) as one of the lightweight solutions will inevitably encounter problems in connection. Resistance welding has the characteristics of high strength, simplicity, and high reliability, and is considered a very potential hot-melt connection technology. The resistance welding technology of unidirectional carbon fiber-reinforced polyphenylene sulfide composites (UCF/PPS) was systematically studied. The experimental results show that the 100-mesh brass mesh has the best resin wetting effect and heating efficiency, and the PPS/oxidized 100-mesh brass mesh composite resistance element (Ox-RE/PPS) has the highest welding strength. The welding failure mode changes from interface failure and RE failure to interlayer structure damage and fiber fracture. The single-factor experimental results show that the maximum welding strength is reached at 310 °C, 1.15 MPa, and 120 kW/m2. According to the conclusion of the single-factor experiment, the Box–Behnken method was further used to design a three-factor, three-level experiment, and a quadratic regression model was established according to the test results. The results of variance analysis, fitting curve analysis, and perturbation plot analysis proved that the model had high fitting and prediction abilities. From the 3D surface diagram analysis, the influence of power density is the largest, and the interaction between welding temperature and power density is the most significant. Combined with the analysis of Design Expert 13 software, the optimal range of process parameters was obtained as follows: welding temperature 313–314 °C, welding pressure 1.04–1.2 MPa, and power density 124–128 kW/m2. The average strength of resistance welding joints prepared in the optimal range of process parameters was 13.58 MPa.

Recent Trends of Recycling and Upcycling of Polymers and Composites: A Comprehensive Review

This review article gathers the most recent recycling technologies for thermoset and thermoplastic polymers. Results about existing experimental procedures and their effectiveness are presented. For thermoset polymers, the review focuses mainly on fibre-reinforced polymer composites, with an emphasis on epoxy-based systems and carbon/glass fibres as reinforcement, due to the environmental concerns of their end-of-life management. Thermal processes (fluidised bed, pyrolysis) and chemical processes (different types of solvolysis) are discussed. The most recent combined processes (microwave, steam, and ultrasonic assisted techniques) and extraordinary recycling attempts (electrochemical, biological, and with ionic liquids) are analysed. Mechanical recycling that leads to the downgrading of materials is excluded. Insights are also given for the upcycling methodologies that have been implemented until now for the reuse of fibres. As for thermoplastic polymers, the most state-of-the-art recycling approach for the most common polymer matrices is presented, together with the appropriate additivation for matrix upcycling. Mechanical, chemical, and enzymatic recycling processes are described, among others. The use of fibre-reinforced thermoplastic composites is quite new, and thus, the most recent achievements are presented. With all of the above information, this extensive review can serve as a guide for educational purposes, targeting students and technicians in polymers recycling.

Mechanical property characterizations of woven natural fiber-reinforced polymers 3D printed through a laminated object manufacturing process

ABSTRACT The mechanical properties of woven natural fiber reinforced polymers additively manufactured through Laminated Object Manufacturing (LOM) technology are investigated in this paper. The benefits of both the material and manufacturing process were combined into a sustainable practice, as a potential alternative to traditional synthetic composite materials made from nonrenewable crude oil with limited end-of-life alternatives. Woven jute fiber reinforcements are used to strengthen both synthetic and bio- thermoplastic polymers in creating highly biodegradable composite structures. Such materials, as one of the prospective alternatives for synthetic composites, can be used in many engineering fields such as automobile panels, construction materials, and commodity and recreational products including sports and musical instruments. A LOM 3D printer prototype was designed and built by the authors. All woven jute/polymer biocomposite test specimens made using the built prototype in this study had their mechanical (both tensile and flexural) properties assessed using ASTM test standards and then compared to similar values measured from pure polymer specimens. Improved mechanical characteristics were identified and analyzed. Finally, SEM imaging was performed to identify the polymer infusion and fiber-matrix bonding conditions.

Carbon nanotube-induced localized laser heating toward simultaneously enhanced laydown efficiency and fracture toughness of in-situ consolidated glass fiber thermoplastic composites

Thermoplastic composites suffer from weak inter-tape bonding during high-rate laser-assisted automated fiber placement (L-AFP). Here, we propose a strategy to simultaneously enhance the laser heating efficiency and fracture toughness of glass fiber-reinforced polypropylene prepreg tape for L-AFP process by depositing carbon nanotubes (CNTs) on the tape surface by a low-cost bath coating process. CNTs function as efficient light absorbing and photothermal coating to promote molecular inter-diffusion and interfacial healing between successive tapes, as well as toughen the weak interface by CNT pull-out and rupture. A 56 % increase in the near-infrared laser absorption of tapes results in a 946 % improvement in the laydown rate. CNTs also remarkably improve transverse temperature uniformity. Furthermore, double cantilever beam and pants tearing tests show that 0.5 wt% CNTs improve the mode I interlaminar fracture toughness and mode III fracture strength by 17 % and 52 %, respectively, attributed to the enhanced molecular inter-diffusion and CNT bridging effect.