Flexural Properties Research Articles

Wood Plastic Composite Based on Recycled High-Density Polyethylene and Wood Waste (Sawdust)

The current work presents the reformulation of a composite based on high-density polyethylene obtained through the recycling of blow-molded containers (rHDPE) with natural fiber residues (wood sawdust). This material is technically and industrially known as WPC (wood plastic composite). The original formulation of this material contains 34% high-density polyethylene and 60% sawdust by weight fraction, while the remaining components include additives and coupling agents such as wax (Coupling Agent TPW 813 for plastic woods), stearic acid, and color pigment. The composite material was processed using the profile extrusion method, from which samples were obtained to conduct various experimental tests. The mechanical analysis revealed that both the strength and Young’s modulus of the tensile and flexural properties slightly increased with the addition of sawdust to the composite. Additionally, the stiffness was higher compared to high-density polyethylene, indicating a direct relationship between these properties and the amount of sawdust incorporated. Besides this, other characterization methods were performed on the material, including density, hardness, and compression tests, as well as differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), natural and accelerated aging tests, Vicat softening temperature, and heat deflection temperature analysis (HDT). The initial evaluation provides a guide to enhance the most important properties with the aim of using the extruded profiles as pergolas in the real estate sector. Therefore, new formulations are developed with the assistance of Minitab 21 software, maintaining a constant proportion of materials that do not affect the mechanical properties, such as wax, stearic acid, and color pigment. Once the formulations are made, each one is characterized through tensile tests to determine which has the best performance. The formulation with the highest strength is re-characterized using the techniques mentioned in the starting material to obtain a material with the most optimal characteristics.

Fully aminated p‐polyaramid effectively strengthen and toughen Bisphenol A epoxy resin and its warp‐knitted carbon fiber composites

AbstractStemming from the cost‐effectiveness and broad applicability, many modification researches on Bisphenol A epoxy resin (DGEBA) and its carbon fiber composites have been done extensively. Here, following the concept of molecular composite, we prepared fully aminated p‐polyaramid with reactive amino side groups by polycondensation and reduction reaction, aiming to construct a molecular distribution of the reinforcement within the resin matrix and achieve a satisfactory enhancement effect. Among them, after adding 1 wt% fully aminated p‐polyaramid, Young's modulus and tensile toughness of the DGEBA epoxy resin (EP) increased significantly to 2.34 ± 0.03 GPa (+68.3%) and 4402 ± 213 kJ/m3 (+30.5%), the flexural modulus and toughness reached 4.14 ± 0.04 GPa (+42.8%) and 0.44 ± 0.01 J (+83.3%). Moreover, the Tg of EP was only decreased by 2.7°C. In addition, their warp‐knitted bidirectional carbon fiber composites also have enhancements in both flexural properties and interlaminar shear strength (all improved by more than 20%). What is noticeable is that the preparation and blending of fully aminated p‐polyaramid are simpler and more effective than most other micro‐ or nanofillers, and the dispersion is more uniform. Thus, it can act as a highly effective reinforcement and strengthen the properties of DGEBA and its carbon fiber composite materials significantly.Highlights Fully aminated p‐polyaramid is uniformly dispersed in EP by chemical bonds. DGEBA is strengthened and toughened without a significant decrease in Tg. The tensile and flexural modulus of EP is increased by 68.3% and 42.8%. Fully aminated p‐polyaramid can reinforce warp‐knitted carbon fiber composite.

Flexural behaviours and heterogeneous interface fracture in overmoulded multi-material thermoplastic composites

The development of lightweight multi-material composites is imperative to meet the demands of the aerospace and automotive industries. Thermoplastic-based multi-material composites represent a novel approach, wherein two or more distinct composite materials are combined to create a hybrid material with enhanced performance characteristics. However, varying failure modes across multi-scale interfaces in the composites affect their mechanical performance in a complex manner. In this study, multi-material composites were manufactured through overmoulding of virgin polycarbonate (VP) and short-fibre reinforced polycarbonate (SFP) on continuous fibre-reinforced thermoplastic polycarbonate (CFRTP) laminate to assess behaviours of heterogeneous interfaces and structural performance under flexural loading. In the compression overmoulding process, the consolidation of thermoplastics creates interdiffusion of polymer chains across the multi-material interfaces. The multi-material composites successfully demonstrated enhanced flexural properties compared to single material constituent such as VP, SFP, and CFRTP. Benchmarking with CFRTP composite laminates, results revealed that overmoulding SFP on CFRTP results in 319 % higher flexural strength and 36 % higher of flexural modulus. VP/CFRTP composite offered 103 % more flexural strain and 175 % more specific energy absorption during fracture. Strategic optimization of the neutral axis (NA) and integration of high modulus materials in multi-material systems contributed to such performance enhancements. Failure analysis conducted using optical microscope and scanning electron microscopy (SEM) revealed progressive heterogeneous interface fracture and crack propagation in the CFRTP laminate layer. Results indicated that control of interface failure modes need to be considered in multi-material structure design to achieve desired flexural strength.

Effect of multi‐angle lamination on mechanical properties and damages behavior of carbon fiber reinforced resin matrix composites

AbstractCarbon fiber reinforced resin matrix composites, when subjected to multi‐angle delamination during vacuum hot pressing, suffered from defects such as uneven fiber distribution, resin‐rich zones, and voids. These defects caused varied damage and failure behaviors in the composites, seriously affecting their mechanical properties. In this paper, the defect distribution, tensile and flexural properties, and damage behaviors of multi‐angle lay‐up specimens prepared in an autoclave were studied. The results indicated that irregularly shaped voids in laminates with a 0° angle difference primarily led to local stress concentration. Elliptical and elongated voids in laminates with a 90° angle difference were mainly susceptible to delamination. The [0/90]8 layer exhibited the best overall mechanical properties. The proportion of 0° laminates had a direct impact on the mechanical properties, with 0° contact laminates on the bending‐compression side capable of withstanding higher bending loads. The [+45/−45]8 plyer demonstrated pseudo‐delayed behavior, enabling the laminate to show better toughness under load. Variations in damage due to the proportions and positions of the laminates influenced the mechanical properties and damages behavior of multi‐angle laminates.Highlights Angular differences were observed to affect void and resin distribution. The best overall mechanical properties were attributed to [0/90]8 laminates. Pseudo‐delay behavior was exhibited by [+45/−45]8 laminates. Proportion of 0° layers impacted mechanical properties. Greater bending loads were withstood by the 0° contact layer.

Mechanical assessment for enhancing hybrid composite performance through silane treatment using RSM and ANN

The study utilized Response Surface Methodology (RSM) and Artificial Neural Networks (ANN) to identify the optimal combination of three key factors for producing polymer composites: nanoparticle percentage, silane concentration, and silane dipping duration. RSM and Analysis of Variance (ANOVA) were applied to explore the relationships between these variables and their effects on composite properties. Additionally, the ANN was used to analyze multiple factors, revealing a strong correlation between predicted and observed results. The findings highlighted that silane treatment was the most influential factor in enhancing the composite's flexural strength. Fiber-related properties, particularly the duration of silane dipping, significantly impacted both flexural strength and hardness. Nanoparticles further strengthened the fiber matrix by encouraging effective agglomeration. The ANN demonstrated 95% accuracy in predicting flexural strength and hardness, and its predictions were validated by comparing them with experimental data and the regression model's outcomes. Silane concentration also notably influenced flexural properties. The RSM analysis identified the optimal combination for maximizing flexural strength and hardness: 5% nanoparticles, 10% silane concentration, and a 20-minute silane dipping time.

Mechanical, Thermal, and Morphological Analysis of Himalayan Agave Fiber /GO Coated Fly Ash Hybrid Polypropylene Composites.

Composites containing two different types of reinforcements offer a wide range of possibilities and synergistic properties. This study investigates the hybridization effect of chemically active fly ash (FA) (5 wt.%) on the composites made from alkali (1 wt.%) - APTES silane (2 wt.%) treated Himalayan agave fibers (HAF) (25 wt.%) and polypropylene (PP). Prior to FA activation, the planetary ball mill was used to suitably reduce the particle size of the FA with was confirmed by the dynamic light scattering approach. Secondary reinforcement FA was modified with APTES silane (1 wt.%), followed by treatment with graphene oxide (GO) (0.5, 0.75, and 1 wt.%). The highest tensile strength of 40.47 MPa and modulus of 1.49 GPa were observed for the hybrid composites fabricated from 0.75 and 1.0 wt.% GO treated fly ash. Interestingly, this trend differed for flexural properties, and the highest flexural strength of 53.52 MPa was demonstrated by 0.5 wt.% GO treated FA hybrid composite. Thermal characterization revealed that addition of fiber increased crystallinity but decreased thermal stability, whereas a good wettability of the fiber and FA in matrix was demonstrated through morphological characterization.

Enhanced Thermal and Flexural Properties of Alkalized Date Palm/Kenaf Fiber-Reinforced Epoxy Hybrid Composites: A Comparative Study of Untreated and Treated Fibers

ABSTRACT This study evaluates the thermal and mechanical behavior of hybrid composites made from date palm (DP) and kenaf fibers (KF) in an epoxy thermoset matrix. Both DP and KF fibers are abundant and renewable, reducing environmental impact. KF offers high tensile strength and stiffness, improving composite strength and rigidity, while DP fibers offer toughness and impact resistance, enhancing durability. The composites were developed in 30%, 50%, and 70% DP-KF compositions using layup and hot-pressing methods. Fiber treatment through alkalization was analyzed for its impact on mechanical and thermal properties to find the optimal fiber ratio. The hybrid composites were subjected to DMA, TGA, and flexural tests. The treated composites exhibited fewer impurities and increased cellulose content, resulting in enhanced flexural performance. This improvement was evident through higher storage modulus, lower loss modulus, and reduced tan δ when exposed to thermal stress. The 30% DP and 70% KF composites exhibited best performance. The treated 30DP-70KF exhibited improvement in the flexural strength and modulus by 13.8% and 2.7%, respectively. TGA demonstrated that treated 30DP-70KF composites had a higher glass transition temperature (Tg) and better thermal degradation resistance. These findings highlight the potential of natural fiber hybrids in creating sustainable, high-performance composite materials for construction and industrial applications.

Experimental research on the flexural properties and pore structure characteristics of engineered geopolymer composites prepared by calcined natural clay

The synthesis of high ductility geopolymer composites using excavated natural clay is an economical and environmentally friendly method to realize the utilization of excavated natural clay. This paper presents an experimental research on the flexural properties and pore structure characteristics of engineered geopolymer composites (EGC) prepared by calcined natural clay. The EGC with different slag and fiber contents were prepared and the four-point bending tests were conducted on the EGC. The effect of slag and fiber content on the flexural strength, flexural deflection and flexural toughness were discussed. The microscopic pore structure characteristics of EGC were further analyzed. The optimal mixture ratio of calcined clay-based EGC with the highest flexural toughness was proposed. The results show that fiber can significantly enhance the flexural properties and cracking control ability of EGC. The ultimate flexural strength, flexural deflection, flexural strengthening index and flexural toughness of EGC all increase with increasing fiber content. The results also show the addition of 10.0% slag can increase the flexural strength and flexural toughness, while excessive slag content reduces the flexural properties. The EGC with 10.0% slag content and 2.5% fiber content exhibits excellent flexural properties and cracking control ability. The ultimate flexural strength and flexural toughness index reach 9.75 MPa and 486.11, showing the highest flexural toughness.

Mitigating aging infrastructure risks: An optimized epoxy resin system for water supply pipeline rehabilitation

Urban water supply networks are crucial for ensuring the delivery of safe drinking water to urban populations; however, the aging infrastructure in these systems has led to a rising incidence of leaks and frequent pipeline failures, posing serious risks. Traditional repair approaches encounter limitations in terms of efficiency, durability, and environmental safety, particularly when employed in potable water pipelines. To address these challenges, we developed a novel multi-component amine-cured epoxy resin system specifically optimized for in-situ curing under ambient conditions. This study comprehensively examines the mechanical properties, water absorption behavior, and curing kinetics of this resin system, formulated to reduce volatile organic compound emissions while enhancing durability under prolonged water exposure. Experimental findings demonstrate that the E2 formulation exhibited superior tensile strength, flexural properties, and fracture toughness relative to other formulations, with a two-stage water absorption model accurately predicting resin behavior in moisture-laden environments. Moreover, finite element modeling and laboratory testing confirmed the influence of bubble defects on mechanical performance, and a negative pressure defoaming technique effectively reduced defect volume, resulting in a 17.6% improvement in tensile strength. Collectively, this research advances the practical application of rapid-curing resins, offering a resilient, safe, and sustainable solution for the rehabilitation of aging water pipeline networks.

Experimental Investigation The Effect of Bamboo Micro Filler on Performance of Bamboo-Sisal-E-Glass Fiber-Reinforced Epoxy Matrix Hybrid Composites

The numerous advantages of natural fiber reinforced hybrid composites, such as their light weight, biodegradability, recyclability, availability, and low cost, have brought them to the forefront for various structural applications in the automotive and aerospace industries. Aim of this study was to evaluate the impact of varying the weight fractions of bamboo micro filler on the tensile, flexural, impact, and water absorption properties of the Sisal-Bamboo-E-glass fiber reinforced epoxy matrix hybrid composite prepared by manual hand layup method. To enhance the bond between natural and synthetic fibers and reduce the hydrophilic nature of natural fibers, bamboo and sisal fibers were treated with 5% NaOH for 6 and 8 hours, respectively. The E-glass fiber content was kept constant at 10%, while the weight fractions of sisal, bamboo fiber, epoxy matrix, and bamboo micro filler were varied. The bamboo micro filler size ranged from 75 to 100 μm. Tensile and flexural tests were conducted using a computer-controlled universal electromechanical testing machine, while impact testing was performed with a Charpy impact test machine. The results showed that the hybrid composite containing 15% sisal, 10% glass, 15% bamboo fiber, 57% epoxy, and 3% bamboo micro filler exhibited the highest tensile strength (87 MPa),flexural strength (77 MPa), high impact energy (8.9 J) and high toughness (24.64 J/cm2). Conversely, the highest water absorption capacity was observed in composites with 6% bamboo micro filler. Overall, the tensile, flexural, impact, and water absorption properties of the hybrid composites were significantly influenced by the weight fractions of the fibers and bamboo micro filler.

Effect of Films on In‐Mold Decoration and Microcellular Foaming Injection Molding Parts: Cell Structure, Surface, Warpage, and Mechanical Properties

ABSTRACTThe in‐mold decoration and microcellular foaming injection molding (IMD‐MIM) process was proposed to solve the apparent quality problem of polypropylene in microcellular foaming injection molding. Based on physical experiments and finite element simulation, stainless steel (ST) and polyethylene glycol terephthalate (PET) decorative films were selected for analysis, and the influence of the type and thickness of the decorative films on the cell structure, surface morphology, warpage deformation, and mechanical properties was revealed. The results show that the surface quality of the samples coated is significantly improved, and the asymmetric temperature field caused by the films changes the structure and distribution of the cells. The cell density on the coated side is higher than that on the non‐coated side, and the average cell diameter is smaller, and the foam core layer is shifted to the coated side. The warpage caused by ST film is larger, up to 2.836 mm. With the intervention of ST film and PET film, the impact properties of the samples have little change, but the tensile and flexural properties of the foamed samples have been effectively improved. The tensile strength increased by 28.6% and 25.9%, while the flexural strength increased by 28.6% and 28.1%, respectively. This study provides new insights into the comprehensive optimization of the structure and performance of polypropylene microcellular foaming materials and provides support for the development and application of lightweight materials in the future.

Effect of thermocycling on flexural strength of dental CAD/CAM ceramics of variable thicknesses and structures: an in vitro study

Background This study examined the effect of thermocycling on the flexural strength properties of four CAD/CAM ceramic materials at different thicknesses. Methods Four CAD/CAM ceramics of different types: advanced lithium disilicate (ALD), zirconia-reinforced lithium silicate (ZLS) lithium disilicate (LD), and leucite reinforced (LE), and at three varying thicknesses 0.5, 1.0 and 1.5 mm were examined. After subjecting all specimens to 5000 thermomechanical cycles, flexural strength was determined using a universal testing apparatus. Scanning electron microscopy (SEM) was employed for analysis. Two factorial ANOVA models assessed the association of different factors (ceramic type and thickness) with flexural strength and elastic modulus. The 95% confidence intervals (CIs) and adjusted means were computed. A p-value < 0.05 was designated significant. Results ZLS exhibited the highest flexural strength at 1.5 mm thickness, while LD showed the highest Young’s modulus of elasticity. The lowest flexural strength was observed in the 0.5 mm thickness group. There were notable variations in flexural strength across all ceramic materials, with the highest adjusted mean strength in the ZLS group, ALD, LD, and LE, respectively. Additionally, significant differences were noted in ceramic thickness, with 1.5 mm thickness showing the highest strength and 0.5 mm thickness the lowest. Conclusions Ceramic material thickness significantly impacts flexural strength, with 1.5 mm thickness deemed suitable for posterior restorations. Ceramic materials with zirconia fillers or matrix demonstrated higher flexural strength than other ceramics.

Extrusion‐Based Additive Manufacturing of Cranial Implants Using High‐Performance Polymers: A Comparative Study on Mechanical Performance and Dimensional Accuracy

Fused filament fabrication (FFF) offers great potential to fabricate patient‐specific implants to treat large size defects resulting from craniectomy. Such cranial implants impose critical requirements on material and design. So far, the field has focused on printing cranial implants from polyetheretherketone (PEEK), which is semicrystalline in nature and, therefore, not ideal for FFF because of warping and nonhomogeneous crystallization. Consequently, this work aims at exploring alternative amorphous high‐performance polymers. The tensile and flexural mechanical properties of printed samples from PEEK, polyetherketoneketone (PEKK), and polyphenylsulfone (PPSU) according to ISO standards are compared. Testing of specimens obtained from three orthogonal build directions reveals nearly isotropic mechanical behavior (e.g. ultimate tensile strength differed no more than 8% between print orientations). This enables printing of patient‐specific cranial implants in vertical orientation with minimal support structures, which result in dimensional accuracies in the clinically acceptable range for craniofacial reconstructions. Mechanical assessment via an in‐house designed indentation set‐up shows that both PEKK and PPSU should be considered valid alternatives to PEEK for cranial implants. This work showcases the maturity of FFF for high‐performance polymers and leverages it for complex patient‐specific geometries such as a cranial implant.

Performance of Hybrid Fiber Reinforced Geopolymer Composites: Scientometric and Conventional Review

Hybrid fibers are an interesting addition to reinforce geopolymer-based composites due to their advantages over single-fiber reinforcement. The performance of hybrid fibers is dependent on the fibers' composition, type, properties, length, and volume fraction. Therefore, this review discusses the state-of-the-art hybrid fiber-reinforced geopolymer composites (HFRGC) through two approaches: scientometric analysis and conventional review of HFRGC based on data extracted from Scopus from 2013 until 2023. The scientometric analysis was carried out by adopting VOS Viewer software and focuses on the annual publication of documents, top publication sources, co-occurrence keywords, researchers, top-cited papers, and countries. In contrast, the desk study refers to experimental data on the fresh properties and compressive, tensile, and flexural properties of HFRGC. This review output aids researchers in networking, promoting cooperative research, exchanging ideas, and creating joint ventures among researchers of HFRGC worldwide. The performance of HFRGC obtained from the desk study showed the potential of HFRGC as an option for a greener composite that will benefit the construction industry.

Time-varying deterioration of bamboo mechanical properties

Bamboo is a type of fast-growing and renewable natural resource that is an ideal building material. In this study, the longitudinal tensile, longitudinal compressive, flexural, longitudinal shear, transverse tensile, and transverse compressive stress-strain and strength properties of bamboo with a period of 240 days were conducted to study the time-varying deterioration performance of bamboo. The results showed that the mechanical properties of bamboo decreased gradually with the passage of time. The transverse compressive strength deteriorated the most, and the longitudinal tensile strength deteriorated the least. After 240 days of tests, bamboo CCS decreased by 52.5% and UTS decreased by 25.4%. Formulas to predict deterioration of mechanical properties were put forward and validated. It was found that the nodes of bamboo influenced its mechanical properties. The deterioration degree of the test specimens with nodes was slightly higher than that of the test specimens without nodes. These findings provide evidence about the deterioration mechanism of bamboo and are significant for promoting the development of bamboo architecture.

Study on the polymerization shrinkage and mechanical-physical properties of dental resin composite modified by polyurethane dimechacrylate and glass flake fillers

ObjectivesWe intend to explore the polymerization shrinkage and mechanical-physical properties of the dental resin composite modified by polyurethane oligomer PU-MA and glass flakes fillers, and provide some experimental information for developing new dental materials. MethodsBased on Bis-GMA/TEGDMA, the new dental resin composite was hand fabricated by combining PU-MA with different content (65 wt% ∼ 75 wt%) of glass flakes/Si-Al-borosilicate glass mixed fillers. The kinetics of polymerization shrinkage was investigated by using an experimental set-up based on laser triangulation. The mechanical-physical properties of specimens after 60 days water immersion and 5000 times thermo-cycles were measured by three-point bending test and micro vickers hardness tester. Data were submitted to one-way ANOVA/LSD-test (α = 0.05). Independent sample T test was used to analyze the data before and after aging. Two-way ANOVA was adopted to analyze the effect of composition and aging condition on the mechanical-physical properties (α = 0.05). ResultsPU-PG-75 % performs lower volume shrinkage (1.35%). As the increase of filler content, the water sorption and solubility increased and the depth of cure decreased significantly (P < 0.05). After aging, the flexural strength, elasticity modulus and vickers hardness of commercial products dropped obviously and PU-PG-75wt% was relatively stable. Conclusions20 wt% PU-MA could decrease the volume shrinkage of dental resin composite effectively. 60 days water immersion and 5000 times thermal cycles simultaneously resulted in a significant reduction in the flexural properties for experimental materials. PU-PG-75 % may have the potential to be taken as a low shrinkage dental resin composite with good mechanical properties. Clinical SignificanceThis new synthesized composite could perform low polymerization shrinkage and better mechanical resistance, which may provide a new idea for improving the lifespan of direct restoration.

Development of Kagome-based functionally graded beams optimized for flexural loadings

This study is concerned with the development of an innovative beam geometry based on a tessellation of Kagome unit cells and the improvement of its geometry with the aim of increasing its flexural properties. This aspect was achieved by generating a functionally graded metamaterial structure based on a novel approach that considers the well-established analytical beam theory models as the basis of for the optimization of the structural parameters of the unit cells at an individual level. The starting premise is that the optimal strut thickness variation with the height of the beam will cause the material to yield uniformly in the critical cross-section. Preliminary studies were conducted in order to numerically determine the variation of the stiffness and the strength of the Kagome structure with the thickness of its struts. Considering the equivalent stress distribution during bending in the critical cross-section, an optimal variation of the stiffness with the height of the beam was evaluated. Based on these results, different values for the strut diameter were imposed at corresponding coordinates relative to the neutral axis, assuring a continuous transition across the height of the beam. The flexural properties of the developed functionally graded structure were evaluated using finite element analyses and determined superior characteristics when compared with the data obtained from simulations performed on an uniform Kagome beam with of the same mass. The investigated structures were manufactured through stereolithography and subjected to three-point bending tests, the results being in agreement with the numerical data, thus validating the design.

Effect of Dispersing Agents on the Electrical and Mechanical Performance of GNPs Filled Epoxy Nanocomposite

In this work, graphene nanoplatelets (GNPs) filled epoxy nanocomposites with the addition of different dispersing agents were fabricated using a method combines mechanical mixing and tip sonication. The loading of GNPs used is 0.8 vol% determined previously as the amount required to achieve the percolation threshold to conduct electricity. Three dispersing agents were used in this work: Sodium dodecyl sulphate (SDS), ethanol and Phenyl glycidyl ether (PGE), with loadings varying from 2 vol% to 10 vol%. The incorporation of dispersing agent enhanced the electrical bulk conductivity of GNPs filled nanocomposites. The mechanical performance (flexural properties and fracture toughness) of the nanocomposite were evaluated and compared. The optimum loading of SDS to obtain the highest flexural strength and fracture toughness is 2 vol%, where further increases will deteriorate the performance of nanocomposites. On the other hand, the optimum loading of ethanol and PGE are 4 vol%. The fracture toughness of GNPs filled nanocomposites improved with the addition of 2 vol% SDS and deteriorated with increasing loadings of SDS up to 10 vol%. By incorporating 4 vol% of ethanol, the optimum fracture toughness of the nanocomposite is achieved. Fracture toughness is then dropped with further increases in ethanol. The addition of PGE caused deterioration in fracture toughness of GNPs filled epoxy nanocomposite.

Semi-Alicyclic Thermoplastic Polyimide Matrixes Based on Hydrogenated Pyromellitic Dianhydride and Asymmetrical 3,4′-Oxydianiline with Good Thermal Stability and Improved Optical Transparency

Thermoplastic polyimide (PI) matrixes, including PI-a (cc-34ODA) and PI-b (ct-34ODA) were prepared via the hot-pressing procedures of the resins derived from the 3,4′-oxydianiline (34ODA) and two alicyclic dianhydrides of 1S,2R,4S,5R-hydrogenated pyromellitic dianhydride (ccHPMDA) and 1R,2S,4S,5R-hydrogenated pyromellitic dianhydride (ctHPMDA), respectively. The resins exhibited thermoplastic features with good formability at higher temperatures. The afforded semi-alicyclic PI sheets exhibited enhanced properties in comparison to commercially available, wholly aromatic thermoplastic PIs, such as PI-ref1, which are derived from 3,3′,4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-oxydianiline (44ODA), as well as PI-ref2, which is based on pyromellitic dianhydride (PMDA) and 4,4′-bis(3-aminophenoxy)biphenyl (mBAPB). In addition, the developed PI sheets exhibited high heat deflection temperatures (HDT) of 267.4 °C for PI-a and 268.6 °C for PI-b. There values were significantly higher when compared with those of PI-ref1 (Ratem® YS20, HDT: 239.0 °C), PI-ref2 (Aurum® PL450C, HDT: 238.0 °C), PI-ref3 (Ultem® 1000, HDT: 206.0 °C), PI-ref4 (Therplim® TO65, HDT: 180.0 °C), and PI-ref5 based on phthalic anhydride-terminated fluorinated PIs (HDT: 215.0 °C). In terms of mechanical properties, the current PI sheets showed superior flexural properties among the polymers with the flexural strength of 189.0 ± 11.7 MPa (PI-a) and 200.5 ± 4.2 MPa (PI-b), respectively. In addition, the PI sheets exhibited comparable compression properties, inferior impact strength, and tensile properties compared with the referenced PI counterparts. Basically, the PI-b sheet showed better comprehensive properties than those of the stereoisomeric PI-a analog.

Characterization of the thermomechanical and aging behaviour of PAEK and CF/PAEK composites under long-term high-temperatures

The growing use of poly(aryl ether ketone) (PAEK) polymers reinforced with carbon fiber (CF) aims to meet the increasing demand for thermoplastic composites in applications that require excellent mechanical properties and thermal stability at higher temperatures. This study investigated the physicochemical properties of PAEK and CF/PAEK composites under long-term high-temperature exposure (150 °C, 200 °C and 250 °C) for durations of 15, 30, and 45 days, aiming to elucidate the durability mechanisms and enhance understanding of their performance. Specifically, the changes in the flexural properties and dynamic thermo-mechanical properties of the materials were evaluated after long-term high-temperature treatment. The results indicated that both PAEK and CF/PAEK composites possess substantial potential for long-term high-temperature applications, with CF not significantly altering the fundamental high-temperature response of the PAEK matrix. Regarding durability mechanisms, at 150 °C, PAEK's amorphous region undergoes chain reorientation, while temperatures of 200 °C and 250 °C induce significant secondary crystallization, which significantly improved the high-temperature mechanical properties of these materials. Additionally, at temperatures up to 250 °C, shorter linear chain fragments form through oxidative scission in PAEK's amorphous molecular chains. This work not only enriches the existing data on the properties of PAEK and CF/PAEK composites after long-term high-temperature treatment, but also provides further insights into their durability mechanisms.