High-temperature Thermoplastics Research Articles

High-performance Thermoplastic-based Magnetic Composites

Magnetic polymer-based composites combine the cost-effectiveness, low density, and manufacturing flexibility of conventional polymers with the unique characteristics of magnetic powders/fillers to form multi-functional magneto polymeric composites that offer superior properties to conventional materials. At higher temperatures, magnetic properties change significantly and the particles within the magnetic powders experience sporadic motion due to the heat which causes misalignment of the magnetic domains, leading to a decrease in magnetism. Due to these adverse temperature effects, high-performance polymers such as polyetheretherketone (PEEK), polyetherimide (PEI), high-performance polyamides (HPPA), or other high-temperature thermoplastics have been considered suitable matrix for the magnetic fillers, thereby creating a much wider usage for magneto polymeric composite in applications that requires higher temperature (typically above 175°C). Thus, this review discusses the fabrication processes-injection molding, fused filament fabrication; magnetic performance, and applications of high-performance thermoplastic-based magnetic composites that can be viable for stringent engineering devices such as sensors, actuators, motors, and generators.

Synthesis of Biobased Poly(butylene Furandicarboxylate) Containing Polysulfone with Excellent Thermal Resistance Properties.

A synthetic biopolymer derived from furandicarboxylic acid monomer and hydroxyethyl-terminated poly(ether sulfone) is presented. The synthesis involves 4,4'-dichlorodiphenyl sulfone and 4,4-dihydroxydiphenyl sulfone, resulting in poly(butylene furandicarboxylate)-poly(ether sulfone) copolyesters (PBFES) through melt polycondensation with titanium-catalyzed polymerization. This facile method yields segmented polyesters incorporating polysulfone, creating a versatile group of high-temperature thermoplastics with adjustable thermomechanical properties. The PBFES copolyesters demonstrate an impressive tensile modulus of 2830 MPa and a tensile strength of 84 MPa for PBFES55. Additionally, the poly(ether sulfone) unit imparts a relatively high glass transition temperature (Tg), ranging from 36.6 °C for poly(butylene 2,5-furandicarboxylate) to 112.3 °C for PBFES62. Moreover, the complete amorphous film of PBFES exhibits excellent transparency and solvent resistance, making it suitable for applications, such as food packaging materials.

Additive Manufacturing of High-Temperature Thermoplastic Polysulfone with Tailored Microstructure via Precipitation Printing.

Current additive manufacturing processes for polymers, including material extrusion, vat photopolymerization, material jetting, and powder bed fusion, have limitations in manufacturing high-temperature thermoplastics including narrow material selection, compromised mechanical properties, and potential degradation of materials during processing. Polysulfone (PSU) is a high-temperature thermoplastic with outstanding chemical resistance, flame retardancy, and toughness. However, besides injection molding, additive manufacturing of PSU has only been achieved through extrusion or solvent-cast three-dimensional (3D) printing without obtaining high mechanical properties. In this work, precipitation printing is applied to fabricate high-temperature thermoplastics such as PSU for the first time, where tailoring of the microstructure and mechanical properties is enabled through control of solvents and printing parameters. The printed PSU can either be dense and strong with 2.47 GPa Young's modulus and 70.6 MPa tensile strength or porous and highly anisotropic. After drying at a maximum temperature of 190 °C, both the printed dense and porous PSU samples have a glass-transition temperature of about 200 °C, which allows them to be used in high-temperature environments. Thus, precipitation printing provides an alternative approach to manufacture high-temperature thermoplastics like PSU with scalability and tailorable properties.

Analysis for understanding and standardization of additive manufacturing processes

The market segment of additive manufacturing is showing an annual growth of more than ten percent, with extrusion-based processes being the larger segment of the market. The scope of use is limited to secondary structures. Equipment manufacturers try to guarantee constant material characteristics by closed systems. The characteristic values are up to 50% below the ones from injection molding. The processing of high-performance polymers with reinforcing fibers is an additional challenge. Further development requires an opening of the material and manufacturing systems. The guidelines and standardization for this are still missing. For this reason, a functional analysis (FA) according to TRIZ ("theory of the resolution of invention-related tasks") is performed within this study. This identifies the undesired functions and quantifies their coupling with process components and parameters. In the FA, the manufactured part is the target component in order to address its quality. This way the FA identifies five undesirable functions in the process. These are: deform, cool, weaken, swell and shape. For hightemperature thermoplastics, thermal shrinkage is the primary cause of geometric tolerance. Therefore, the deformation is largely dependent on the cooling mechanism. For a detailed analysis, the polymer melt is further disassembled. The results are six sub-components. The weakening is mainly due to the physical phase of the voids, which exists during the entire processing. The breakdown comprises physical fields such as stress, temperature and flow. These determine the output properties as well as the bonding between the layers. The associated functions are the swelling and shaping. In order to generate broadly applicable standardizations, research questions for further investigation are derived from this study.

Interfacial adhesion of carbon fiber to special engineering plastics: Effect of the functional groups in the matrix

We studied the interfacial shear strength (IFSS) in carbon fiber (CF) and special engineering plastics matrix, with an emphasis on the effect of the functional group in the matrix. The IFSS was analyzed to quantify the interfacial adhesion between the fiber and the matrix. To obtain the apparent IFSS of the composites, microdroplet test was measured at single-fiber composites. Results of the microdroplet test displayed that the apparent IFSS in the composites was directly determined by their inherent surface properties and the functional groups in the matrix. Compared with other matrices, polyetherimide (PEI) exhibited relatively strong mechanical bonding and interfacial adhesion, showing that the imide groups had good interfacial compatibility with the pristine CF surface. Based on the results of this study, polymers containing imide groups were one of the best candidates for sizing agent of CF used as reinforcement of high-temperature thermoplastics.

Adhesion of High Temperature 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. One of the leading mechanism that enable to build up strength of adherent over the substrate is called healing. It is classically described as the diffusion of the macromolecular chains across the interface that enable bridging. In continuous processes, such as some which are used in advanced manufacturing of aerospace structures, cycle times are very short. Thus, it is unclear how suitable these materials are for fast continuous processes – the limiting factor being the time required to gain adhesion. To model and predict such processes, a controlled welding bench was designed enabling very short welding times (~5s). The mechanical adhesion between coupons was assessed by fracture of the welded interface via double cantilever beam fracture test. The welding kinetics were observed for the initial stages of healing with a behavior that should fit the t1/2trend. From this, it was possible to compare the accuracy and repeatability of interface healing at short time scales to that of samples which were closer to fully welded. Concurrently, the reptation of the polymer melt was assessed on a commercial rheometer, by computing relaxation time from the viscoelastic response. The correlation confirms that the mechanical quality is associated with the macromolecule diffusion. It was also observed that for high temperature thermoplastics, reticulation occurs, which inhibits molecular diffusion and increases the relaxation time. The major implication is that the preprocessing of the polymer will impact the subsequent adhesion step. For example, plates processed with an autoclave for a couple of hours would require a welding time an order of magnitude longer than the adhesion of a virgin prepreg in the tape placement process.

Rheological survey of carbon fiber-reinforced high-temperature thermoplastics for big area additive manufacturing tooling applications

Carbon fiber (CF)-reinforced thermoplastic composites have been widely used in different structural applications due to their superior thermal and mechanical properties. The big area additive manufacturing (BAAM) system, developed at Oak Ridge National Laboratory’s Manufacturing Demonstration Facility, has been used to manufacture several composite components, demonstration vehicles, molds, and dies. These components have been designed and fabricated using various CF-reinforced thermoplastics. In this study, the dynamic rheological and mechanical properties of a material commonly used in additive manufacturing, 20 wt% CF-acrylonitrile butadiene styrene (ABS), as well as three CF-reinforced high-temperature polymers, 25 wt% CF-polyphenylsulfone (PPSU), 35 wt% CF-polyethersulfone (PES), and 40 wt% CF-polyphenylene sulfide (PPS), used to print molds were investigated. The viscoelastic properties, namely storage modulus, loss modulus, tan delta, and complex viscosity, of these composites were studied, and the rheological behavior was related to the BAAM extrusion and bead formation process. The results showed 20 wt% CF-ABS and 40 wt% CF-PPS to display a more dominant elastic component at all frequencies tested while 25 wt% CF-PPSU and 35 wt% CF-PES have a more dominant viscous component. This viscoelastic behavior is then used to inform the deposition and bead formation process during extrusion on the BAAM system.

Making a strong adhesion between polyetherketoneketone and carbon nanotube fiber through an electro strategy

High temperature thermoplastics are gaining popularity due to their superior toughness and durability. For a new member in the polyaryletherketone (PAEK) family, polyetherketoneketone (PEKK) has shown the highest melting temperature, up to 380 °C. Meanwhile, it requires a high temperature to improve the interfacial shear strength (IFSS) between PEKK and a fiber, toward advanced thermoplastic composites. Owing to the strong Joule heating in carbon nanotube (CNT) fibers, a more efficient strategy is designed to enhance the IFSS. Under the electro treatment, the surrounding PEKK starts the melting at the fiber surface, and even impregnates into the CNT assemblies. As a result, the interfacial interaction can be remarkably enhanced. The highest IFSS is up to 80.4 MPa for the electro-treated interface between a CNT fiber and PEKK, higher than the thermal-treated IFSS (52.5 MPa) and that between an aramid fiber and PEKK (59.8 MPa).

Study of the Geometric Characteristics of Carbon Fiber Fillers on the Properties of Polyphenylene Sulfone

The effect of the length and concentration of carbon fibers on the rheological, mechanical and thermal properties of high-temperature thermoplastics – polyphenylene sulfone was investigated. As fillers fibers with a length of 0.2 and 3 mm are used.

What makes a material printable? A viscoelastic model for extrusion-based 3D printing of polymers

This article presents a practical model for evaluating polymer feedstock materials as candidates for 3D printing across a variety of extrusion-based platforms. In order for a material to be successfully utilized for 3D printing operations, a series of fundamental conditions must be met. First, pressure-driven extrusion must occur through a given diameter nozzle at a specified flow rate. Second, the extruded material must form and sustain the desired shape. Third, the extruded structure must be able to bridge a specified gap and serve as a mechanically sound foundation for successive deposits. Finally, the deposited structure must be dimensionally stable during the transition to the final state (i.e. fully cured at room temperature). This article presents a framework for extrusion-based printing and a simple viscoelastic model for each of these conditions based on the rheological and thermo-physical properties of the candidate material and the processing parameters of the extrusion-based deposition platform. The model is demonstrated to be a useful tool for the evaluation of example test cases including: high temperature thermoplastics (polyphenylsulfone), fiber reinforced thermoplastics (acrylonitrile butadiene styrene), low-viscosity thermosets (epoxy resins), and thermoplastics with a high coefficient of thermal expansion (polypropylene).

Fast Desktop-Scale Extrusion Additive Manufacturing

Significant improvements to the throughput of additive manufacturing (AM) processes are essential to their cost-effectiveness and competitiveness with traditional processing routes. Moreover, high-throughput AM processes, in combination with the geometric versatility of AM, will enable entirely new workflows for product design and customization. We present the design and validation of a desktop-scale extrusion AM system that achieves a much greater build rate than benchmarked commercial systems. This system, which we call ‘FastFFF’, is motivated by our recent analysis of the rate-limiting mechanisms to conventional fused filament fabrication (FFF) technology. The FastFFF system mutually overcomes these limits, using a nut-feed extruder, laser-heated polymer liquefier, and servo-driven parallel gantry system to achieve high extrusion force, rapid filament heating, and fast gantry motion, respectively. The extrusion and heating mechanisms are contained in a compact printhead that receives a threaded filament and augments conduction heat transfer with a fiber-coupled diode laser. The prototype system achieves a volumetric build rate of 127cm3/hr, which is approximately 7-fold greater than commercial desktop FFF systems, at comparable resolution; the maximum extrusion rate of the printhead is ∼14-fold greater (282cm3/hr) than our benchmarks. The performance limits of the printhead and motion systems are characterized, and the tradeoffs between build rate and resolution are assessed and discussed. High-speed desktop AM raises the possibility of new use cases and business models for AM, where handheld parts are built in minutes rather than hours. Adaptation of this technology to print high-temperature thermoplastics and composite materials, which require high extrusion forces, is also of interest.

Rheological and crystallization enhancement in polyphenylenesulfide and polyetheretherketone POSS nanocomposites

ABSTRACTPolyhedral oligomeric silsesquioxane (POSS) additives have been shown to increase melt‐flow and crystallization in thermoplastics. In this study, the effect of incorporation of trisilanolphenyl‐POSS molecules in polyphenylenesulfide (PPS) and polyetheretherketone (PEEK) on rheology, crystallization kinetics, and thermal and mechanical properties was evaluated. Parallel plate rheometry revealed a reduction in the viscosity of PPS and PEEK with the addition of POSS. The magnitude and concentration dependence of rheological modification were shown to depend on the polymer structure and POSS solubility. Isothermal crystallization kinetics were analyzed using the Avrami model and it was found that the addition of POSS accelerated the crystallization rate of PPS blends with no significant effect on PEEK blends. Interestingly, no statistical difference in degradation temperature, tensile modulus, or tensile strength of PPS or PEEK blends was observed. The findings indicate the potential for improvements in melt viscosity and crystallization of high temperature thermoplastics with tailored POSS/polymer interactions. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44462.

Synthesis and Characterization of Polysulfone-Containing Poly(butylene terephthalate) Segmented Block Copolymers

A facile synthetic approach to segmented polysulfone-containing polyesters affords a versatile family of high-temperature thermoplastics with tunable thermomechanical properties. End-capping of phenol-terminated polysulfone (PSU) using ethylene carbonate generated telechelic oligomers with primary alcoholic functionality. Melt transesterification of dimethyl terephthalate and 1,4-butanediol in the presence of PSU oligomers yielded high molecular weight segmented block copolymers with alternating PSU and poly(butylene terephthalate) (PBT) sequences. Systematic variation in PSU incorporation resulted in tunable PBT segment length and accompanying thermal properties. DSC and SAXS elucidated a miscible, amorphous PSU and PBT phase, and PBT crystallinity remained below an 80 wt % incorporation of PSU. Dynamic mechanical analysis (DMA) revealed a crystallinity-dependent plateau regime above the copolymers glass transition temperature (Tg), while SAXS and WAXD confirmed a semicrystalline morphology below 80 wt %...

Inorganic Nanoparticle-Modified Poly(Phenylene Sulphide)/ Carbon Fiber Laminates: Thermomechanical Behaviour.

Carbon fiber (CF)-reinforced high-temperature thermoplastics such as poly(phenylene sulphide) (PPS) are widely used in structural composites for aerospace and automotive applications. The porosity of CF-reinforced polymers is a very important topic for practical applications since there is a direct correlation between void content and mechanical properties. In this study, inorganic fullerene-like tungsten disulphide (IF-WS2) lubricant nanoparticles were used to manufacture PPS/IF-WS2/CF laminates via melt-blending and hot-press processing, and the effect of IF-WS2 loading on the quality, thermal and mechanical behaviour of the hybrid composites was investigated. The addition of IF-WS2 improved fiber impregnation, resulting in lower degree of porosity and increased delamination resistance, compression and flexural properties; their reinforcement effect was greater at temperatures above the glass transition (Tg). IF-WS2 contents higher than 0.5 wt % increased Tg and the heat deflection temperature while reduced the coefficient of thermal expansion. The multiscale laminates exhibited higher ignition point and notably reduced peak heat release rate compared to PPS/CF. The coexistence of micro- and nano-scale fillers resulted in synergistic effects that enhanced the stiffness, strength, thermal conductivity and flame retardancy of the matrix. The results presented herein demonstrate that the IF-WS2 are very promising nanofillers to improve the thermomechanical properties of conventional thermoplastic/CF composites.

Temperature-Dependent Lap Shear Strength of Adhesively Bonded High-Temperature Resistant Thermoplastics

Due to the development of high-temperature resistant thermoplastics, e. g. polyetheretherketone, these plastics have become more attractive for several applications which require good mechanical properties at high service temperatures. In addition to conventional production processes, adhesive bonding is more and more used to build assemblies with a mix of materials to achieve certain product properties. These products are exposed to high temperatures during their product life, driving the need for a thorough understanding of the substrates, adhesives and their bonds. In order to investigate the temperature-dependent behaviour of the mechanical properties of high-temperature resistant joints, different thermoplastics were analysed in shear tension tests. In these tests three substrates (polyetheretherketone, polyetherimide, and polyamide) and two adhesives (one- and two-component epoxy resin) were tested. The tests were performed at four testing temperatures equally spaced between 20 °C and 200 °C to analyse the temperature-dependent material properties. The specimens were built up as a single-lap joint with a constant adhesive thickness. After curing at definite conditions the adhesively bonded joints were tested in a shear tension test. The results of this test are the lap shear strength and failure patterns. The results were correlated with thermal and mechanical properties of substrates and adhesives, e. g. glass transition temperature and Young’s modulus. The experimental analysis reveals a distinct temperature-dependent behaviour of the lap shear strength and failure patterns within the temperature range examined. In general, the lap shear strength decreases with rising testing temperature. Moreover, the failure patterns change from substrate failure to adhesive and cohesive failure of the examined adhesives with rising testing temperature. This implies a significant demand for high-temperature resistant adhesives in the future which can exhibit improved mechanical properties at high temperatures to guarantee an excellent joint between the substrate materials.

New hybrid nanocomposites containing carbon nanotubes, inorganic fullerene-like WS2 nanoparticles and poly(ether ether ketone) (PEEK)

Single-walled carbon nanotubes (SWCNTs) and inorganic fullerene-like WS2 nanoparticles were successfully dispersed in poly(ether ether ketone) (PEEK) by advantageously traditional melt processing techniques. This strategy offers an attractive way to combine the merits of organic and inorganic materials into novel hybrid systems that challenge emerging polymer/CNT nanocomposites in terms of performance, cost and processability. In particular, the incorporation of IF-WS2 has shown to be efficient to produce well-dispersed PEEK/SWCNT composites influenced in turn by the processing method. The morphology, thermal stability, crystallization behaviour, thermal conductivity as well as mechanical and electrical properties of PEEK/SWCNT composites were tuneable by the introduction of small amounts of IF-WS2. The overall structural, thermal, mechanical and electrical performances confirm the potential use of SWCNTs and IF-WS2 for the preparation of advanced hybrid nanocomposites as lightweight alternatives for use in critical industrial applications of high-performance and high-temperature thermoplastics like PEEK.

Synthesis of polyphosphate glasses

Multicomponent spatially cross-linked polymers based on ultraphosphates with vitrification temperature 123 – 302°C have been synthesized. Their hydraulic stability (rate of mass loss when boiled in water) was measured and equals 0.0075 – 0.123 g/min. It is shown that there is a correlation between the vitrification temperature of polymers and their water resistance. Aquantitative relation was obtained for the flow temperature and the vitrification temperature of the polymers: t f = t v + (25 – 35)°C. It is shown that in principle it is possible to obtain on the basis of ultraphosphates high-temperature inorganic thermoplastics with flow temperature varying over wide limits.

Dithioacetalisation of PEEK: a general technique for the solubilisation and characterisation of semi-crystalline aromatic polyketones

The family of semi-crystalline, aromatic, high-temperature thermoplastics known as poly(ether-ketone)s are insoluble in conventional organic solvents, but undergo completely general and quantitatively reversible reactions with alkanedithiols in strong acid media, to give soluble poly(dithioacetal)s, which are readily characterisable by GPC and light scattering techniques.

Processing technologies for continuous fibre reinforced thermoplastics with novel polymer blends

Continuous fibre reinforced thermoplastics (CFRT) for high performance applications are often based on the high-priced PEEK matrix combined with a carbon fibre reinforcement. The potential of blending PEEK with less expensive high temperature thermoplastics like PEI, PES and PSU will help to reduce costs. The research work mainly focuses on the production of semi-finished sheets consisting of such polymer blends and carbon fibre reinforcements. In this context a continuous prepregging method has been realised which combines the matrix (powder) with the textile to a manageable material with a defined weight composition. A subsequent static pressing process leads to fully impregnated and consolidated CFRT sheets. The laminates are then characterised regarding thickness, bending stiffness and quality of impregnation. So far a strong influence of the pressing dwell time on impregnation could be proved. Thereby a generally good correlation between the microscopic views and the mechanical data of neat PEEK and the blend systems occurred. Some blends were identified to enable mechanical properties and permit processing methods that are comparable to neat PEEK. Thus the blend technology can be considered as an alternative to provide more cost-effective CFRT sheets for high performance demands.

Effects of chemical composition and thermal stability of finishes on the compatibility between glass fiber and high melting temperature thermoplastics

AbstractExperimental studies were made on the surface characteristics of glass fibers with two different finishes. The effects of the chemical composition and thermal stability of the finishes on the compatibility between glass fibers and high melting temperature thermoplastics were investigated. Thermogravimetric Analysis (TGA) was used to characterize the composition of surface finishes and their thermal stability. The chemical composition of surface finishes was investigated using a combination of X‐ray photoelectron spectroscopy (XPS) and Time‐of‐Flight secondary ion mass spectrometry (ToF SIMS). Static contact angle measurements were performed at room temperature to characterize the interfacial tension between the glass fibers and thermoplastics. The study provides a fundamental understanding on some important compatibility issues between thermoplastic resins and glass fiber related to composite fabrication and application.