Polyimide Matrix Composites Research Articles

5‐aminobenzimidazole@graphene oxide nanosheets doped polyimide nanocomposites: Low‐temperature curing and improved mechanical properties

AbstractThe preparation of polyimide matrix composites with low curing temperature and high mechanical properties is of great importance. In this study, a low‐cost and multi‐functional nanofiller, 5‐aminobenzimidazole grafted graphene oxide (5‐ABZ@GO) has been designed. By nucleophilic attack on 5‐aminobenzimidazole basic groups and doping of GO, the above requirements of polyimide composites were skillfully realized. The results show that when the addition of 5‐ABZ@GO is 1%, the 5‐ABZ@GO/PI nanocomposites can achieve complete imidized at 200°C. Moreover, the nanocomposite prepared by imidization at 200°C has good mechanical and thermal properties (tensile strength is 141.64 MPa, modulus is 6.05 GPa, T5% is as high as 543.5°C), which is better than the PI composites prepared at 320°C. This study provides an innovative approach to preparing polyimide composites that meet mechanical performance requirements while utilizing comparatively lower curing temperatures, low curing temperature polyimide resins provide a new path for integrated composites with structure–function integration.

Investigation on corrosion and mechanical behavior of sintered electrical corrosion resistance glass-reinforced polyimide composites under acidic environment

ABSTRACT In this study, the effects of electrical corrosion resistance (ECR) glass fiber on corrosion and mechanical behavior of polyimide (PI) matrix composites prepared using spark plasma sintering (SPS) process were investigated. The morphologies, corrosion properties, and mechanical properties were characterized using scanning electron microscope (SEM), immersion and polarization tests, and nanoindentation tests, respectively. The SEM results revealed that the ECR glass particles were evenly distributed in the PI matrix. The resulting analysis depicts that the introduction of ECR particles contents (5, 10, and 15 wt%) in the PI matrix improved its hardness and elastic modulus both before and after corrosion. The corrosion rate of the pure PI was recorded to be reduced by 61.8%, 50.4%, and 38.9%, respectively, at 5, 10, and 15 wt% loading of ECR particles. This depicts that the ECR glass particles lead to anti-corrosion performance improvement of the pure PI. Finally, the findings suggest the potential of ECR filler materials in the development of novel PI composites for anti-corrosion and mechanical load-bearing applications.

Silica nanofillers-reinforced polyimide composites for mechanical, thermal, and electrical insulation applications and recommendations: a review

Owing to the specific properties of polyimide, its nanocomposites have in recent years shown to be a promising polymer composite for mechanical, thermal, and electrical insulation applications. Studies have in many ways revealed the utilization of the polyimide reinforced nanofillers in the area of insulation practice be it thermal or electrical insulation. However, reinforced polyimide nanocomposites were observed to undergo interfacial bonding issues that have badly influenced their insulation behaviour during service. Dielectric properties and electrical discharge (corona discharge) resistance lifespan of polyimide composites are found degrading during long periods of exposure to elevated temperature conditions. Notwithstanding, efforts have been made on improving the electrical and thermal insulation behaviour of polyimide nanocomposites. As such, the current review study focused on the influence of silica nanoparticles on the thermal, electrical, and mechanical characteristics of polyimide matrix composites for insulation practice and applications. Thus, the vision of the authors is to contribute to the future trend of designing and processing polyimide nanocomposites for insulation applications. Thus, the authors ended the article with furtherance, challenges, and recommendations of further enhancement of polyimide nanocomposites as a candidate material for insulation (electrical and thermal). Hence, the study will pave the way for future studies.

Effect of thermal aging on the mechanical and dielectric properties of quartz fiber reinforced polyimide matrix composite

Effect of thermal aging on the mechanical and dielectric properties of quartz fiber reinforced polyimide matrix composite

Study on the Preparation and Properties of Several Dielectric Composites Applied to Capacitors

Polyaniline, polyvinylidene fluoride or liquid acrylonitrile-butadiene rubber as high-dielectric organic fillers were added to the polyimide matrix to synthesize several all-organic polyimide-based dielectric composite materials, and then dielectric properties and energy storage density of these composites were investigated. Experimental results indicated that the dielectric properties of the three polyimide matrix composites were enhanced through the introduction of fillers. In addition, compared with Polyaniline or polyvinylidene fluoride as fillers, the composites prepared by liquid acrylonitrile-butadiene rubber as fillers exhibited superior dielectric properties and energy storage density.

Characterization of carbon fiber-reinforced thermoplastic and thermosetting polyimide matrix composites manufactured by using various synthesized PI precursor resins

Currently, it is important to manufacture thermoplastic advanced composites with high mechanical and thermal properties because of their higher impact resistance than thermoset composites. In this study, carbon fiber (CF)-reinforced thermoplastic and thermosetting polyimide (PI) matrix composites were manufactured by vacuum bagging followed by compression molding . Before the manufacturing process, prepregs were also prepared with various PI precursor resins by using two-step impregnation. These precursors were synthesized as poly (amic acid) (PAA), polyester amine salts (PEAS) and poly (amic acid) ammonium salts (PAAS). The PAAS precursor resin was applied as a novel method for manufacturing CF-reinforced PI matrix advanced composites. The advanced thermoplastic composite obtained from the PAAS precursor (PAAS-T) exhibited superior mechanical properties and enhanced thermal properties (near the thermal properties of thermoset advanced composites) in comparison to the other advanced composites in this study and those in the literature. However, the NA-terminated PAAS precursor (thermosetting PI precursor) did not exhibit a similar effect in terms of mechanical properties. On the other hand, the thermosetting composites exhibited highly enhanced storage modulus values up to 400 °C and outstanding thermal stability at TGA . The thermosetting composite that was obtained from the NA-terminated PAA precursor resin exhibited high mechanical properties besides its thermal properties.

High-throughput screening the micro-mechanical properties of polyimide matrix composites at elevated temperatures

In this work, a novel high-throughput methodology based on combinations of nanoindentation, indentation creep and push-in methods, is proposed to measure in-situ the micro-mechanical properties of typical polymer matrix composites at a wide temperature range. The Young's modulus and strain rate sensitivity of a polyimide matrix and the interfacial shear strength in a quartz fiber reinforced polyimide matrix composite are measured at 25–350 °C for the first time. The results highlight a linear softening of the polyimide matrix at high temperatures, which is evidenced by the approximate linear decrease of Young's modulus from ≈5.0 GPa at 25 °C to ≈1.1 GPa at 350 °C. In comparison, the strain rate sensitivity of the polyimide matrix is increased, from ≈0.032 at 25 °C to ≈0.062 at 350 °C. This evidences a stronger visco-plasticity of polyimide at higher temperatures. The shear strength of the fiber/matrix interface is also temperature dependent. As the testing temperature increases from 25 to 300 °C, the shear strength is decreased from ≈147 MPa to ≈40 MPa. Specially, the interfacial strength is extremely low at 350 °C (≈4 MPa), evidencing a failure of the composite at this temperature.

Friction and wear behavior of polyimide matrix composites filled with nanographite

AbstractIn this study, nanographite (NG), as a lubricant additive, and polyimide (PI) were used to fabricate NG/PI composites via a hot compression molding process. The tribological properties of the NG/PI composites with different NG mass contents (0–10 wt%) were tested using a reciprocating ball‐on‐disc contact tribometer matched with a GCr15 rubbing pair. The thermal stability, surface hardness, and compression strength of the composites were discussed. The results revealed that a small quantity of nanofillers greatly reduced the friction coefficient and increased the wear resistance of the NG/PI composites. Despite a minor decrease in mechanical performance, the composite with 5 wt% of NG filler exhibited improved tribological properties; it showed a 55.63% reduction in the friction coefficient and a reduction of 97.39% in the wear rate compared with neat PI. Moreover, an increase in the glass transition temperature (Tg) of the NG/PI composites indicated the enhancement of their thermal stability and wear resistance. Scanning electron microscopy (SEM) analyses showed that the main wear mechanism of the composites was fatigue wear. These findings suggest that the 5 wt% NG/PI composite could be a significant contribution to the field of tribological engineering plastics.

Recent progress on improving the mechanical, thermal and electrical conductivity properties of polyimide matrix composites from nanofillers perspective for technological applications

Abstract The adoption of polymer nanocomposites in the design/manufacturing of parts for engineering and technological applications showcases their outstanding properties. Among the polymer nanocomposites, polyimide (PI) nanocomposites have attracted much attention as a composite material capable of withstanding mechanical, thermal and electrical stresses, hence engineered for use in harsh environments. However, the nanocomposites are limited to the application area that demands conduction polymer and polymer composites due to the low electrical conductivity of PI. Although, there has been advancement in improving the mechanical, thermal and electrical properties of PI nanocomposites. Thus, the review focuses on recent progress on improving the mechanical, thermal and electrical conductivity properties of PI nanocomposites via the incorporation of carbon nanotubes (CNTs), graphene and graphene oxide (GO) fillers into the PI matrix. The review summarises the influence of CNTs, graphene and GO on the mechanical and conductivity properties of PI nanocomposites. The authors ended the review with advancement, challenges and recommendations for future improvement of PI reinforced conductive nanofillers composites. Therefore, the review study proffers an understanding of the improvement and selection of PI nanocomposites material for mechanical, thermal and electrical conductivity applications. Additionally, in the area of conductive polymer nanocomposites, this review will also pave way for future study.

Influence of Bond Coat on Thermal Shock Resistance and Thermal Ablation Resistance for Polymer Matrix Composites

Polymer matrix composites (PMCs) have been widely used in aero industry because of its low density and high strength-to-weight ratio. However, the application of PMCs is still limited by poor abrasion resistance, weak oxidation resistance and low operation temperature. In this study, Cu (Al)/NiCrAlY/YSZ triple layer coating system was deposited on glass fiber reinforced polyimide matrix composites (FPM) by means of High Velocity Oxygen Fuel (HVOF) for metallic coatings and Atmospheric Plasma Spraying (APS) for YSZ coating. The influences of different bond coats and different thickness of the top coat on the thermal shock resistance and thermal ablation resistance of the coating system was investigated. Compared with Al particle, Cu particle has a high density and correspondingly a high kinetic energy during spraying by HVOF, resulting in a high bonding strength between the Cu coating and FPM substrate. In the thermal shock test, the coating Cu/NiCrAlY/YSZ has a much longer lifetime than the coating Al/NiCrAlY/YSZ. After high-speed impact on the substrate, there is a great compressive stress at the interface, which makes a plastic deformation to the substrate, and the particles are closely embedded into the substrate to form a strong mechanical interlock. The coating system consisting of 50 μm Cu, 50 μm NiCrAlY, and 200 μm 8YSZ exhibited the best thermal shock resistance, thermal ablation resistance and bonding strength. The increase of the top coat thickness will lead to the increase of residual stress and the decrease of bonding strength. The failure mechanism of the coating is mainly attributed to the residual stress in the deposition process and the thermal stress caused by thermal expansion mismatch.

Multiscale modeling to evaluate combined effect of covalent grafting and clustering of silica nanoparticles on mechanical behaviors of polyimide matrix composites

A multiscale model was developed to simultaneously investigate the effect of covalent grafting and clustering of silica nanoparticles on the mechanical behaviors of polyimide nanocomposites. The interphase percolation model was utilized to account for the enhanced interfacial load transfer efficiency by covalent grafting and weaken formation of the interphase zone by agglomeration. Through homogenization analysis of the degree of agglomeration for each grafting ratio, we concluded that the highly grafted interface offsets the negative effects of nanoparticle clustering. The proposed multiscale framework was validated against existing experimental data, which implies that this approach can be used effectively for the design of grafted nanoparticle-reinforced polymer matrix composites.

Polyimide fabric-reinforced polyimide matrix composites with excellent thermal, mechanical, and dielectric properties

Two types of thermosetting polyimide (PI) resin were prepared using a polymerization monomeric reactant method, and high performance PI fabric/PI resin composites were fabricated through a wet infiltration and thermoforming process. The properties of a PI fabric, PI resin, and PI/PI composites were comprehensively analyzed. The experimental results indicate that a resin end-capped with phenylacetylene achieves a better processability and heat resistance. The two composites exhibit excellent thermal, mechanical, and dielectric properties. They achieve a glass transition temperature of higher than 320°C and a 5% weight loss temperature of over 600°C under an air atmosphere. During mechanical testing, an interlaminar shear strength exceeding 35 MPa was achieved, whereas the maximum flexural strength was found to be greater than 400 MPa. Moreover, their dielectric constant at 1 MHz was below 3.4, with a dielectric loss of no more than 0.01.

Milling force of quartz fiber–reinforced polyimide composite based on cryogenic cooling

The structure and physical properties of polyimide matrix composites lead to serious tool wear. And the cutting force is the obvious effect on machining efficiency in dry and cryogenic milling process. A predicted model was fabricated considering cutting temperature. The cryogenic cooling milling method was executed for a series of processing experiments. At the same time, the machining surface morphology, roughness, and cutting force were measured and analyzed compared with dry cutting. Meanwhile, the tool wear regular and mechanism were discussed. The result shows that the cutting force model of composite materials is improved based on cryogenic cutting performance. The friction coefficient of tool/workpiece on contact surface is greatly affected by the cutting heat, and the friction coefficient is reduced in the cutting force model. At the same time, the mechanical properties such as modulus in the model are increased with the decrease of temperature, and it leads to the increase cryogenic milling force. In the milling test, the increase of tensile and compressive strength of composite material is caused by cryogenic cooling. The change leads to the increase of material brittleness with bigger cutting force. Meanwhile, the breaking chip is changed with the improvement of processing quality. Similarly, the better cutting parameter is vc = 100/min, ap = 1.5 mm, and = 40°. In cryogenics, because of the poor thermal conductivity of composite material, part of the fiber material is still not effectively cryogenic treated with the increase in cutting depth; it cannot be brittle cutting for bigger cutting depth material.

A novel quartz fibre reinforced dense polyimide matrix composite: effect of preform stitching

ABSTRACTA dense polyimide (PI) composite reinforced by quartz fibres (QFs), was prepared by vacuum assisted polymer infiltration and hot-pressing in this work. The microstructures and the mechanical properties of the as-fabricated composites were investigated. The results show a high flexural strength (≈686 MPa) of the composite, due to its dense nature. Moreover, there was no significant change in the bending strength of the stitched composites. The laminates mainly suffered delaminations and fracture of the QFs. The intralaminar bonding of the composite was enhanced by a novel stitching technique (all 28 layers stitched together by untwisted quartz filament tows in the plain stitch). As a result, the interlaminar fracture energy with 1 stitches cm−2 stitch density was increased by 87.1%, compared to that of the unstitched composite. In the case of stitched specimens, stitching plays an important role in improving the Gc and suppresses the influence of in-plane fibre orientation.

Mechanical, dielectric and microwave absorption properties of SiO2f/SiCf/PI composites

Structural radar absorbing material attracts increasing attention as an important part of microwave absorbing material. In this study, fiber cloths reinforced polyimide (PI) matrix composites consisting of different proportion of quartz glass fiber (SiO2f) and silicon carbide fiber (SiCf) cloth were designed and prepared by adjusting the proportion. The morphology, mechanical, dielectric properties and electrical conductivity of the composites were thoroughly studied in X band (8.2–12.4 GHz). The results showed that the position of SiCf cloth in the composite had little effect on the dielectric properties of the composite. Under the action of load, the fracture of composites containing different contents of SiCf cloth showed different fracture modes. As the content of SiCf cloth increased in the composite material, both the real and imaginary parts of complex permittivity showed an increasing trend. The electrical conductivity of the composites also increased gradually with content of SiCf cloth rise. The reflectivity of the composites was calculated according to transmission line theory. Variation of fiber cloth composition in this study offered a new strategy to simultaneously improve the mechanical and microwave absorbing properties of PI-based structural absorbing materials.

Fabrication and enhanced dielectric properties of polyimide matrix composites with core–shell structured CaCu3Ti4O12@TiO2 nanofibers

Core–shell structured CaCu3Ti4O12@TiO2 (CCTO@TiO2) nanofibers were prepared via a normal coaxial electrospinning technique with sol precursors. Polyimide (PI) nanocomposite films containing the core–shell structured CCTO@TiO2 nanofibers were fabricated by the solution casting method. The core–shell structure of the CCTO@TiO2 nanofibers was confirmed through transmission electron microscope. The percolation of the CCTO/TiO2 interfaces leads to much enhanced interfacial polarization of the CCTO@TiO2 nanofibers, which gives rise to substantially increased dielectric constant of the nanocomposites. Compared to the nanocomposites with CCTO nanofibers, the breakdown strength of the nanocomposites with CCTO@TiO2 nanofibers is also increased due to the charge shifting is limited to the interfacial zone of CCTO/TiO2 interfaces, instead of in the PI matrix to form a percolation path. For the nanocomposites with 5 vol% nanofibers, the dielectric constant of 5.55 was enhanced to 5.85 and the breakdown strength of 201 kV/mm was increased to 236 kV/mm by utilizing the TiO2 coated CCTO nanofibers, while the dielectric loss shows no obvious change. Meanwhile, the PI nanocomposite film filled with 1 vol% CCTO@TiO2 nanofibers exhibits a maximal energy density of 1.6 J/cm3. The core–shell structured nanofibers open up an effective way to optimize the dielectric properties of polymer nanocomposites with high energy density.

Microstructural, mechanical and thermal shock properties of triple-layer TBCs with different thicknesses of bond coat and ceramic top coat deposited onto polyimide matrix composite

In this study, a triple-layer thermal barrier coating (TBC) of Cu-6Sn/NiCrAlY/YSZ was deposited onto a carbon-fiber reinforced polyimide matrix composite. Effects of different thicknesses of YSZ ceramic top coat and NiCrAlY intermediate layer on microstructural, mechanical and thermal shock properties of the coated samples were examined. The results revealed that the TBC systems with up to 300µm top coat thicknesses have clean and adhesive coating/substrate interfaces whereas cracks exist along coating/substrate interface of the TBC system with 400µm thick YSZ. Tensile adhesion test (TAT) indicated that adhesion strength values of the coated samples are inversely proportional to the ceramic top coat thickness. Contrarily, thermal shock resistance of the coated samples enhanced with increase in thickness of the ceramic coating. Investigation of the TBCs with different thicknesses of NiCrAlY and 300µm thick YSZ layers revealed that the TBC system with 100µm thick NiCrAlY layer exhibited the best adhesion strength and thermal shock resistance. It was inferred that thermal mismatch stresses and oxidation of the bond coats were the main factors causing failure in the thermal shock test.

Fabrication and property of novel double-layer coating deposited on polyimide matrix composites by atmospheric plasma spraying

Thermal shock resistance of double-layer Al/Nd2Zr2O7 coating plasma-sprayed on the polymer substrate was optimized and its oxidation resistant property was evaluated. During thermal shock test at 723K, thermal cycling lifetime of coating was prolonged by decreasing Al layer thickness or increasing Nd2Zr2O7 layer thickness. Relatively, the A45N225 coating with 45µm Al layer and 225µm Nd2Zr2O7 layer exhibited the best thermal shock resistance. Based on the microstructure evolution, coating failure was mainly attributed to the appearance of delamination at the substrate/Al interface or the formation of microcracks in the coating, resulted from stress accumulation and substrate oxidation during thermal cycling. After oxidation at 723K for 22h, with the protection of A45N225 double-layer coating, the weight loss of specimen reduced from 33.96wt% to 5.31wt%, and the corresponding weight loss per unit decreased from 90.58mgcm−2 to 15.47mgcm−2. However, at the later stage of oxidation, heat transfer and oxygen diffusion through the micro-defects of coating might lead to the oxidation of part resins.

Pressure, hydrolytic degradation and plasticization drive high temperature blistering failure in moisture saturated polyimides

Polyimides and polyimide matrix composites are used in electronics, automotive, aerospace and other applications, particularly in situations where high temperature resistance and low weight are required. Under conditions in which polyimides have absorbed water, either by exposure to high humidity or by direct immersion, if the material is rapidly heated it may fail by high pressure water vapor induced blistering and/or delamination. Such hygrothermal failures can be a limiting factor to the use of polyimides and their composites in extreme environments. Despite prior experimental studies, the mechanisms of such failures remain a question due to the lack of complete material model for polyimide. In this work, a novel time, temperature and moisture dependent constitutive model is developed and presented for the first time. This model is built on previous experimental and modeling studies of high temperature viscoelastic and viscoplastic deformation in the polyimide HFPE-II-52 and on studies of the effects of moisture degradation on the mechanical properties. The model is implemented in a finite element simulation providing a means for the study of blistering under different heating rates and moisture levels. The results show for the first time that high temperature blistering failures are driven not only by steam pressure and thermal softening but by the synergy of pressure loading and material softening due to hydrolytic degradation and plasticization.

Microstructure, Tensile Adhesion Strength and Thermal Shock Resistance of TBCs with Different Flame-Sprayed Bond Coat Materials Onto BMI Polyimide Matrix Composite

In this study, thermal barrier coatings (TBCs) composed of different bond coats (Zn, Al, Cu-8Al and Cu-6Sn) with mullite top coats were flame-sprayed and air-plasma-sprayed, respectively, onto bismaleimide matrix composites. These polyimide matrix composites are of interest to replace PMR-15, due to concerns about the toxicity of the MDA monomer from which PMR-15 is made. The results showed that pores and cracks appeared at the bond coat/substrate interface for the Al-bonded TBC because of its high thermal conductivity and diffusivity resulting in transferring of high heat flux and temperature to the polymeric substrate during top coat deposition. The other TBC systems due to the lower conductivity and diffusivity of bonding layers could decrease the adverse thermal effect on the polymer substrate during top coat deposition and exhibited adhesive bond coat/substrate interfaces. The tensile adhesion test showed that the adhesion strength of the coatings to the substrate is inversely proportional to the level of residual stress in the coatings. However, the adhesion strength of Al bond-coated sample decreased strongly after mullite top coat deposition due to thermal damage at the bond coat/substrate interface. TBC system with the Cu-6Sn bond coat exhibited the best thermal shock resistance, while Al-bonded TBC showed the lowest. It was inferred that thermal mismatch stresses and oxidation of the bond coats were the main factors causing failure in the thermal shock test.