High-performance Thermoplastic Composites Research Articles

Preparation of continuous carbon fiber reinforced PA6 prepreg filaments with high fiber volume fraction

High-performance continuous carbon fiber prepreg filaments have been a research hotspot in the field of additive manufacturing in recent years, and are considered to be an effective option for improving the mechanical strength of thermoplastic composite parts. However, the effect of fiber volume fraction on the microstructure and tensile properties of 3D printed prepreg filaments remains miss. Therefore, this study selected suitable impregnation processes and materials to prepare prepreg filaments with different fiber volume fraction and investigated their mechanical properties and microscopic morphologies. The results show that the increase of fiber volume fraction effectively promoted the interface bonding between fiber and resin, and increased capacity for load transfer. When the fiber volume fraction was 54.0 %, the tensile strength of the prepreg filaments and specimens reached 1977 MPa and 334 MPa, respectively. This study can provide a process optimization strategy for the preparation of more types of continuous fiber prepreg filaments with high fiber volume fraction, as well as a data reference for the preparation of high-performance 3D-printed thermoplastic composites.

The Effects of Laser-Assisted Winding Process Parameters on the Tensile Properties of Carbon Fiber/Polyphenylene Sulfide Composites.

Currently, there is limited research on the in situ forming process of thermoplastic prepreg tape winding, and the unclear impact of process parameters on mechanical properties during manufacturing is becoming increasingly prominent. The study aimed to investigate the influence of process parameters on the mechanical properties of thermoplastic composite materials (CFRP) using laser-assisted CF/PPS winding forming technology. The melting point and decomposition temperature of CF/PPS materials were determined using DSC and TGA instruments, and based on the operating parameters of the laser-assisted winding equipment, the process parameter range for this fabrication technology was designed. A numerical model for the temperature of laser-heated CF/PPS prepreg was established, and based on the filament winding process setup, the heating temperature and tensile strength were simulated and tested. The effects of process parameters on the heating temperature of the prepreg and the tensile strength of NOL rings were then analyzed. The non-dominated sorting genetic algorithm (NSGA-II) was employed to globally optimize the process parameters, aiming to maximize winding rate and tensile strength. The results indicated that core mold temperature, winding rate, laser power, and their interactions significantly affected mechanical properties. The optimal settings were 90 °C, 418.6 mm/s, and 525 W, achieving a maximum tensile strength of 2571.51 MPa. This study provides valuable insights into enhancing the forming efficiency of CF/PPS-reinforced high-performance engineering thermoplastic composites.

Comprehensive evaluation of interfacial interactions optimization for CF reinforced high-performance thermoplastic composites by electrochemical deposition of conjugated polymers

The mechanical properties of carbon fiber (CF) reinforced high-performance thermoplastic composites are significantly compromised due to inadequate interface bonding between CF and matrix. In this study, electrochemical polymerization techniques were employed to modify CFs with polypyrrole (PPy), poly-aniline (PANI), and poly-o-phenylenediamine (PoPd), to systematically investigate the impact of conjugated polymers on the interfacial properties of CF/copoly (phthalazinone ether sulfone ketone)s (PPESK) composites through a combination of experimental and molecular dynamics (MD) approaches. The findings revealed distinct differences among these conjugated polymers in terms of their effects on both IFSS and ILSS for CF/PPESK composites. Among all tested laminates, PoPd@CF-60s/PPESK exhibited the highest IFSS, ILSS and flexural strength values of 39.8 MPa, 75.6 MPa, and 1494 MPa, respectively, 94.1 %, 20.6 %, and 47.6 % higher than those of CF-desized/PPESK, without compromising CFs strength and thermal resistance of CF/PPESK composites. MD simulations combined with fracture morphology analysis confirmed that compatibility between conjugated polymers and matrix played a pivotal role in enhancing interface properties for CF/PPESK composites. Furthermore, the AFM outcomes demonstrated that the PoPd layer could serve as the modulus transition layer between the CF phase and the PPESK phase, which effectively enhancing the load transfer efficiency between the two phases under external forces. To summarize, this work presents a straightforward yet non-destructive approach that effectively enhances the interface strength within advanced CF reinforced high performance thermoplastic polymer composites (CFRHPTPs).

An anchor-inspired interface for improving interfacial properties of carbon fiber-reinforced high-performance thermoplastic composites

Carbon fiber-reinforced thermoplastic composites are promising materials with many application prospects. However, surface inertness of CFs weakens the interfacial properties of these composites. Therefore, in this study, an anchor-inspired structure was designed and grafted onto CFs by using an anchor-inspired segmented copolymer, comprising of polyimide as the “chain” and polyhedral oligomeric silsesquioxane (POSS) as the “anchor”. In combination with atom transfer radical polymerization with the advantage of controllable molecular weight, degree of polymerization of the anchor-shaped structure with the best compatibility with poly (phthalazinone ether nitrile ketone) (PPENK) resin was pre-determined through molecular dynamics simulations, which reduced the experimental costs. The results of X-ray photoelectron spectroscopy indicated the successful connection of the numerous anchor-shaped structures to the CFs. Compared to composite made of origin fibers and PPENK, the interfacial shear strength at the microscopic level and interlaminar shear strength at the macroscopic level of grafted CF and PPENK composite increased by 184.9 % and 44.2 %, respectively. This is mainly attributed to the synergistic effect of mechanical interlocking and interfacial interaction between the anchor-shaped structure and the PPENK resin. This study serves as a feasible path to enhance the interfacial adhesion of composites by designing an anchor-shaped structure of organic macromolecules and inorganic nanoparticles on CFs.

Effect of Electrochemical Aryl Diazonium Salt Modification on Interfacial Properties of CF/PEEK Composites.

The interfacial properties between carbon fiber (CF) and thermoplastic resin are relatively weak, which can be problematic for composites in structural applications. Improving the surface roughness of CF is regarded as an effective way to enhance the interface of composites. However, most CF modifying methods are complex and time-consuming, which cannot meet the demand for industrial production. Therefore, it is of great significance to research a fast technique of CF surface modification to strengthen the interface of composites. Herein, a one-pot reaction based on the aryl diazonium salt modification was applied to enhance the interface between CF and poly ether ether ketone (PEEK) resin. Carbon nanotubes (CNTs) were linked to CF by p-phenylenediamine (PPD) via cyclic voltammetry (CV). The surface morphology, chemical characteristics and surface energy of modified CF illustrated the effectiveness of this method, and the interfacial properties of as-prepared modified CF/PEEK demonstrated the increased tendency. All the CF was treated within 5 min and the interfacial shear strength (IFSS) of CF/PEEK was increased to the maximum of 99.62 MPa by aryl diazonium salt modification. This work may shed some light on the industrialized application of CF reinforced high-performance engineering thermoplastic composites.

Enhanced mechanical performance of bamboo fiber/polypropylene composites via micro-nano reinforcing strategy

Developing high-performance plant fiber-reinforced thermoplastic polymer composites using environmentally friendly and cost-effective methods remains a significant challenge. In this study, we present a novel micro-nano strategy for producing robust short bamboo fibers (BFs) reinforced polypropylene (PP) composites (SBFPCs) without the need for chemical modification. Our approach involves the utilization of purified short micron BFs, which is surface-coated with holocellulose nanofibers (HNFs) extracted from bamboo parenchyma cells (BP). Through conventional injection processing, the resulting SBFPCs demonstrate remarkable mechanical enhancements with just a 0.2 wt% addition of HNFs compared to control samples. Notably, the mechanical properties of our SBFPCs surpass those of most reported short plant fiber-reinforced thermoplastic composites. The superior mechanical performance of our SBFPCs can be attributed to several factors, including the use of purified micron BFs with optimal aspect ratios as the primary reinforcement phase, enhanced interfacial mechanical interlocking between BFs and the PP matrix facilitated by the addition of HNFs, and the potential dispersion of HNFs within the PP matrix at submicron or nanoscale as a secondary reinforcement phase. This study highlights the promising application of SBFPCs in engineering areas with stringent mechanical requirements.

Morphology-controlled ZnO nanoarrays in situ grown on the basalt fiber surface for improving the interfacial properties of the high-performance thermoplastic composites

In this work, a biomimetic root-soil-like interfacial phase structure was constructed to improve the weak interfacial bonding of the fibers and resin based on the mechanical interlocking theory. Unidirectional basalt fiber (BF) reinforced high-temperature resistant thermoplastic poly (phthalazinone ether nitrile ketone) (PPENK, Tg = 278 °C) composites with multiscale structures were prepared. By utilizing a whiskerization technique, the zinc oxide nanoarrays (ZnO-NAs) with controllable morphologies grown on the BF surface through a pyrolysis-hydrothermal method. The remarkable field emission properties of the ZnO-NAs allow for visually characterizing the interfacial phase structures. The flexural, interlaminar shear, and interfacial shear strengths of BF-ZnO-PEI-2/PPENK composite were increased by 43 %, 65 %, and 177 %, respectively. Further investigations revealed that the flexural strength retention was 61 % at 250 °C, respectively. This study introduces a novel and viable approach to enhance the interfacial properties of BF-reinforced high-performance thermoplastic composites and expands their applications within high-temperature environments.

Interfacial Enhancement and Composite Manufacturing of Continuous Carbon-Fiber-Reinforced PA6T Composites via PrePA6T Ultrafine Powder.

Semi-aromatic poly (hexamethylene terephthalamide) (PA6T) oligomer (prePA6T) ultrafine powder, with a diameter of <5 μm, was prepared as an emulsion sizing agent to improve the impregnation performance of CF/PA6T composites. The prePA6T hyperfine powder was acquired via the dissolution and precipitation "phase conversion" method, and the prePA6T emulsion sizing agent was acquired to continuously coat the CF bundle. The sized CF unidirectional tape was knitted into a fabric using the plain weave method, while the CF/PA6T laminated composites were obtained by laminating the plain weave fabrics with PA6T films. The interfacial shear strength (IFSS), tensile strength (TS), and interlaminar shear strength (ILSS) of prePA6T-modified CF/PA6T composites improved by 54.9%, 125.3%, and 120.9%, respectively. Compared with the commercial polyamide sizing agent product PA845H, the prePA6T sizing agent showed better interfacial properties at elevated temperatures, especially no TS loss at 75 °C. The SEM observations also indicated that the prePA6T emulsion has an excellent impregnation effect on CF, and the fracture mechanism shifted from adhesive failure mode to cohesive failure mode. In summary, a facile, heat-resistant, undamaged-to-fiber environmental coating process is proposed to continuously manufacture high-performance thermoplastic composites, which is quite promising in mass production.

Synergistic enhancement in mechanical properties of graphene/MWCNT reinforced Polyaryletherketone – carbon fiber multi-scale composites: Experimental studies and finite element analysis

This investigation focuses on the synergistic performance improvement in graphene/MWCNT reinforced Polyaryletherketone (PAEK) - carbon fiber (CF) multi-scale composites. FTIR revealed the chemical interactions while HRTEM, XRD and 3D X-ray microscopy gave insight into nanofiller dispersion and microstructural features. The functional groups on nanofillers along with structural features integrated various components of the multi-scale composites by formation of graphene/MWCNT/CF complex network that provided larger interfacial area, bridging effect and physico-chemical interaction with PAEK while restricting its segmental mobility. Multi-scale composites displayed significantly improved strength, fracture toughness, interlaminar shear strength, glass transition temperature and tribological performance. Under dynamic load, graphene/MWCNT reinforcement of matrix and CF synergistically increases the storage modulus and energy absorption characteristics. Wear and fracture surface morphology of nano and multi-scale composites showed ductile failure confirming interfacial adhesion. The failure behavior in experimental studies was supported by Abaqus/Explicit-based FEM models of fracture toughness response. This work provides a promising avenue to develop next generation high performance thermoplastic composites for structural applications.

Experimental characterisation and statistical modelling of woven carbon fibre weld conductors for electrical resistance welding of thermoplastic composites

Resistance welding of high-performance thermoplastic composites is a promising joining technique for the structural assembly of aerospace components. Knowledge of the weld conductor resistance as a function of its dimensions, as well as external boundary conditions such as contact preparation and pressure, can be used to scale welding parameters. This paper presents a comprehensive review on the weld conductor contact preparation, length, width and contact pressure dependent resistance with respect to the Toray 5HS T300JB carbon woven prepreg 281 gsm fibre architecture. The study is based on a 4-wire resistance measurement of the carbon fibre fabric weld conductors and was conducted to provide a solid basis for defining the weld conductor’s resistance, considering the dependence on length, width and contact pressure. The experimentally determined resistance values were approximated using linear and non-linear regression functions and combined into a general formulation with respect to the investigated carbon fibre fabric architecture. The least squares fit of experimental versus model data confirmed a very high model confidence. Thus, the model allows a simplified transfer of electrical properties for process pre-design and scaling considering weld conductors with the same fibre architecture.

Characterization of Interlaminar Friction during the Forming Processes of High-Performance Thermoplastic Composites

Friction is a pivotal factor influencing wrinkle formation in composite material shaping processes, particularly in novel thermoplastic composites like polyetheretherketone (PEEK) and low-melting polyaryletherketone (LM-PAEK) matrices reinforced with unidirectional carbon fibers. The aerospace sector lacks comprehensive data on the behavior of these materials under forming conditions, motivating this study’s objective to characterize the interlaminar friction of such high-performance thermoplastic composites across diverse temperatures and forming parameters. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were employed to analyze the thermomechanical behaviors of PEEK and LM-PAEK. These data guided friction tests covering room-to-forming temperatures. Horizontal pull-out fixed-plies tests were conducted to determine the friction coefficient and shear stress dependency concerning temperature, pressure, and pulling rate. Below the melting point, both materials adhered to Coulomb’s law for friction behavior. However, above the melting temperature, PEEK’s friction decreased while LM-PAEK’s friction increased with rising temperatures. These findings highlight the distinct responses of these materials to temperature variations, pulling rates, and pressures, emphasizing the need for further research on friction characterization around glass transition and melting temperatures to enhance our understanding of this phenomenon.

Processing and characterization of high-performance thermoplastic composites manufactured by laser-assisted automated fiber placement in-situ consolidation and hot-press

Due to the short dwell time of processing temperature and pressure, the quality of the composite manufactured by AFP was not equal to the traditional processing method like autoclave or hot-press. Deeply understanding the mechanism of differences was conducive to improving the performance of the composite manufactured by AFP. In this study, the properties of high-performance carbon fiber reinforced polyphenylene sulfide (CF/PPS) thermoplastic composites manufactured by laser-assisted automated fiber placement (LAFP) in-situ consolidation and hot-press was characterized and compared. The temperature history of LAFP in situ consolidation indicated that the heating and cooling process occurred during a few seconds. And the crystallinity was only 21.6% for the laminate from LATP, while the void content was 2.75%. Due to the low crystallinity, high void content and low interlaminar bonding, the ILSS of the laminate from LAFP in situ consolidation was 34.9% lower than that of hot-press. However, the mode Ⅰ fracture toughness was 103.7% higher than hot-press.

Resistance-welded thermoset composites: A Bayesian approach to process optimisation for improved fracture toughness

Joining thermoset composites via resistance welding offers a novel highly efficient assembly method for next-generation aerospace structures. Resistance-welded joints combine the benefits of bonding with the capacity for high-volume manufacturing rates and eliminate the need for complex surface preparation. The influence of key welding parameters on the joint performance is investigated by assessing the Mode I fracture toughness. Double Cantilever Beam specimens with different welding parameter combinations are manufactured, tested and compared with each other. Thermoset laminates are made weldable by co-curing a chemically compatible thermoplastic film with an uncured thermoset laminate. A Bayesian approach is used to study the correlation between processing parameters and to select parameters yielding high performance by training a Gaussian process emulator. Observed Mode I fracture toughness values are comparable to high-performance thermoplastic composites. This is equivalent to an improvement of approximately 290% in Mode I fracture toughness when compared to a co-cured thermoset joint.

Polyphenylene sulfide for high-rate composite manufacturing: Impacts of processing parameters on chain architecture, rheology, and crystallinity

High performance semi-crystalline thermoplastics necessitate high temperature processing to form useful structures, but the effects of repeated exposure to these extreme environments on key polymer properties are not well understood. This work investigates the influence of degradation-driven structural changes resulting from exposure to standard melt processing conditions in oxygen rich environments on the rheological properties, crystallization behavior, and crystal structure of polyphenylene sulfide (PPS). Melt processing temperatures (300°C, 320°C, and 340°C) and hold times (up to 60 min) are varied to probe the effects of thermal exposure on polymer properties. Extended melt-state exposure causes an increase in PPS melt viscosity due to the formation of complex branched/crosslinked structures where increasing temperature causes this process to occur more rapidly. Dynamic isothermal rheology of PPS displays a 70x increase in the complex viscosity at 10 rad/s after 60 minutes at 340°C. Frequency sweep rheological experiments reveal a notable deviation from linearity (terminal slope = 2) with slopes as low as 0.14 after thermal exposure. Stress recovery experiments indicate thermally processed PPS requires more time to relax stress under an applied strain. Imperfections along the polymer backbone in the form of branches/crosslinks decrease overall crystallinity and reduce lamellar thickness, with no changes to the unit cell structure. For semi-crystalline high performance thermoplastic matrix composites relying on high degrees of crystallinity to provide solvent resistance and strength, these results have serious implications for the need to tightly control melt processing steps and understand the final material state. Furthermore, viscoelastic properties of post-processed PPS polymers should be considered for recycling and reuse strategies.

Improving mechanical performances at room and elevated temperatures of 3D printed polyether-ether-ketone composites by combining optimal short carbon fiber content and annealing treatment

Development of high performance polyether-ether-ketone (PEEK)) composites is of great significance for aerospace engineering application. The fused filament fabrication (FFF)-based 3D printing process is promising for manufacturing high performance short carbon fiber (SCF) reinforced PEEK composites. However, a comprehensive investigation of the combined effects of SCF content and annealing condition has not been conducted on the mechanical performances of SCF/PEEK composites; also, elevated temperature mechanical properties that are required for aerospace engineering have not been reported for 3D printed SCF/PEEK composites. This work develops a creative strategy that combines the optimal short carbon fiber (SCF) content with annealing treatment to achieve significant improvements in the mechanical properties both at room and elevated temperatures of FFF-3D printed SCF/PEEK composites. First, the influences of SCF content on the mechanical performances of 3D printed SCF/PEEK composites are studied to determine the optimal fiber content (5 wt%) for the best mechanical performances of non-annealed PEEK composites. Then, the effects of SCF content and annealing on room temperature and elevated temperature mechanical performances are examined for both PEEK and the 5 wt% SCF/PEEK composite. It is elucidated that the increase of interface strength and crystalline region as well as the reduction of residual stress by annealing are all responsible for the observed improvements in mechanical performances. This work presents a comprehensive study of 3D printed short fiber reinforced thermoplastics and serves as a valuable reference for the 3D printing of high-performance thermoplastic composites.

High mechanical performance short carbon fiber reinforced polyetherimide composites via solution mixing process

Proper preparation processes of short fiber reinforced thermoplastics are critical to achieving high residual fiber lengths in final composites, which in turn greatly influences the mechanical properties of short fiber reinforced polymers. In this work, the injection molding process was respectively combined with conventional extrusion compounding and a newly developed solution mixing process to fabricate short carbon fiber (SCF) reinforced polyetherimide (PEI) composites. Carbon fiber-filled PEI master batches were prepared for injection molding respectively by conventional extrusion compounding (denoted by CE-MB) and solution mixing process (denoted by SM-MB) diluted with PEI powders. Afterwards, the corresponding two types of composites (SCF/PEIE and SCF/PEIS + D) were prepared by injection molding. Compared with the SCF/PEIE composites, the SCF/PEIS + D composites exhibit significantly enhanced mechanical performances due to greatly higher residual fiber lengths in final composites. As a result, the 20 vol fraction (vol%) SCF/PEIS + D composite obtained shows a record high tensile strength of 239.6 MPa for injection molded PEI composites. Moreover, it is worth mentioning that the tensile strength of the SCF/PEIS + D composite with only 5 vol% SCFs is even higher than that of the SCF/PEIE composite with 25 vol% SCFs. Consequently, the injection molding process combined with the newly proposed solution mixing process is promising to replace the conventional extrusion process for developing high mechanical performance short fiber reinforced high-performance thermoplastic composites, particularly for the cases with low to medium fiber contents (≤25 vol%).

A chemically modified MWCNT/PEEK multiscale thermoplastic composites: Forming, mechanical performance, and application

AbstractCarbon nanotubes can be used to enhance interlaminar mechanical performance of polymer composites due to its physicochemical properties. In this article, a novel method for preparing multi‐walled carbon nanotubes/polyether ether ketone (MWCNT/PEEK) thermoplastic composite film is proposed. The microstructure and interfacial bonding performance of chemically modified and unmodified composites films are analyzed by molecular dynamics simulation and experiment. The composite films are used in CF/PEEK laminates. The results show that MWCNT significantly improve the crystallinity of PEEK resin. Compared with the MWCNT/PEEK composites without chemical modification, the MWCNT‐COOH/PEEK‐OH composite film has a denser structure, and the tensile strength and elastic modulus are increased by 94.5% and 15%, respectively. Furthermore, the interlaminar shear strength of the CF/PEEK laminates doped with MWCNT/PEEK and MWCNT‐COOH/PEEK‐OH composite films increased by 8.3% and 12.7%, respectively.Highlights The interfacial bonding performance between MWCNT and PEEK is obtained by molecular dynamics simulation. A novel method for preparing BP/PEEK composite film is proposed. MWCNT/PEEK composite films can effectively enhance the interlaminar performance of CF/PEEK high performance thermoplastic composites.

Repair of Impacted Thermoplastic Composite Laminates Using Induction Welding.

The lack of well-developed repair techniques limits the use of thermoplastic composites in commercial aircraft, although trends show increased adoption of composite materials. In this study, high-performance thermoplastic composites, viz., carbon fibre (CF) reinforced Polyetherketoneketone (PEKK) and Polyether ether ketone (PEEK), were subjected to low-velocity impact tests at 20 J. Post-impact, the damaged panels were repaired using an induction welder by applying two different methods: induction welding of a circular patch to the impacted area of the laminate (RT-1); and induction welding of the impacted laminates under the application of heat and pressure (RT-2). The panels were subjected to compression-after-impact and repair (CAI-R), and the results are compared with those from the compression-after-impact (CAI) tests. For CF/PEKK, the RT-1 and RT-2 resulted in a 13% and 7% higher strength, respectively, than the value for CAI. For CF/PEEK, the corresponding values for RT-1 and RT-2 were higher by 13% and 17%, respectively. Further analysis of the damage and repair techniques using ultrasonic C-scans and CAI-R tests indicated that induction welding can be used as a repair technique for industrial applications. The findings of this study are promising for use in aerospace and automotive applications.

Excellent and effective interfacial transition layer with an organic/inorganic hybrid carbon nanotube network structure for basalt fiber reinforced high-performance thermoplastic composites

Basalt fiber reinforced high-performance thermoplastic (BFRHTP) composites are promising materials for application in military, aerospace, chemical, automobile, and other high-tech industries. However, their mechanical properties are still largely limited by poor interfacial properties because of the smooth, inert, and low-energy surface of BF. In this study, an organic/inorganic hybrid sizing agent was used for BF surface modification to construct an appropriate modulus transition layer for the interface with a combination of soft and rigid phases. Organic poly(ether nitrile) (PEN) and inorganic carboxylic multi-walled carbon nanotubes (MWCNT-COOH) in hybrid sizing agents (PEN/CNT) were respectively used as soft and rigid phases to design the interfacial structure. The tensile strength, flexural strength, interlaminar and interfacial shear strength of the basalt fiber reinforced poly(phthalazinone ether nitrile ketone) composites were increased by 60, 33, 62, and 144%, respectively. This approach provides a simple, green, and promising strategy for enhancing the interfacial properties of BFRHTP composites.

Application of Box Behnken experimental design to analyze the influence mechanism of process parameters on mechanical properties of high-performance thermoplastic composites

Composite processing relies heavily on process parameters, which are the key factors that determine the quality of the finished product. In this investigation, carbon fiber (CF)-reinforced polyetherketone (PEK) thermoplastic composites are fabricated through film-fiber stacking and consolidation process. In this method, carbon fabric and polymer film are alternately stacked, and the stacks are then consolidated via compression molding to create a laminate. The mechanical properties of CF/PEK composites are studied in relation to crucial process parameters such as molding temperature, molding pressure, and holding time. To identify the optimal process parameters for CF/PEK fabrication, the tensile and interlaminar shear strengths of these composites were evaluated. Non-linear quadratic equations employing Box-Behnken Design in Response Surface Methodology and validation trials were used to model these features. To obtain the optimal mechanical properties of fabricated composites, the combination of factor ranges was discovered by overlaying contour plots within the practical constraints. The ideal process parameters for achieving maximum mechanical qualities were determined to be around molding temperature of 400°C, a holding period of 60 min, and a molding pressure of 10 bar.