Reinforced Polyimide Composites Research Articles

Effect of electrochemical anodic oxidation modification on the interfacial properties of carbon fiber reinforced polyimide composites

Effect of electrochemical anodic oxidation modification on the interfacial properties of carbon fiber reinforced polyimide composites

Thermal protective and hydrophobic coating on polyimide resin matrix composites surface for improved aging resistance

AbstractPolyimide composites are easily degraded in high temperature and high humidity environments for long service, which reduces their reliability and stability in aerospace, electronic components, weapons, and other fields. In this paper, the inorganic and organic multiphase double‐layer coating was prepared. The insulating layer was made of vinyl polysilazane resin as the base material and hollow glass microspheres as the filler. The hydrophobic layer consisted of polydimethylsiloxane as the base material, hollow phenolic microspheres, and nano‐TiO2 as the filler. The heat resistance, hydrophobic properties, and aging resistance of the coated polyimide resin matrix composites were studied. The results showed that the thickness of the double‐layer coating was about 200 μm. Under the 200°C thermal insulation test, the maximum temperature drop can be achieved at 59.7°C. After adding 5 wt% TiO2, the static contact angle of composites was increased from 86.2° to 127.7°. Significantly, the hydrophobic performance was improved by 48.1%, which was due to the construction of micro‐nano structures in the surface layer coating. In the accelerated hydrothermal aging tests, the bending properties of coated composite materials can be improved by 8.5%, 3.2%, and 8.7% in water, alkali, and acid environments, respectively. The moisture absorption of glass fiber and the pyrolysis of polyimide led to the degradation of the mechanical properties. The existence of heat‐resistant and hydrophobic coating could effectively eliminate this adverse effect, which was of great significance for polyimide composites to cope with various service environments.Highlights A novel coating consisting of thermal insulating and hydrophobic layers was developed on glass fiber reinforced polyimide composites (G/PI) composites. The maximum temperature drop of coating can be achieved at 59.7°C. The static contact angle of coated G/PI composites was increased from 86.2° to 127.7°. In the aging tests, the protective effect of the coating resulted in improved mechanical strengths of G/PI composites. The microscopic damage morphology was performed to analyze the anti‐aging properties of the coating.

Investigation on flame‐retardant, thermal and mechanical properties of glass fiber reinforced polyimide composites

AbstractComposites with excellent flame retardant and mechanical properties are in high demand in the aerospace and various industrial fields. Glass fiber (GF) reinforced polyimide (PI) composites (GFRPCs) were fabricated using a simple ball milling and hot pressing technique. The effect of GF content on the thermal stability, mechanical and flame retardant properties of composites has been systematically studied. The Rockwell hardness of GFRPCs increase with increasing GF content, while the compressive strength, impact strength and flexural strength initially show an increase followed by a decrease due to the excellent dispersibility of the fillers and the strong interfacial interaction between the one‐dimensional GF and PI matrix. Thermogravimetric analysis results show that the addition of GF with very low thermal conductivity and excellent temperature resistance can effectively improve the thermal stability of PI. Adding GF into PI can obviously improve the limiting oxygen index value. Moreover, as the GF content increased, the time to ignition of the composites prolonged while total heat release decreased. These findings suggest a viable solution for enhancing both the flame retardance and mechanical properties of PI‐based composites.Highlights GFRPCs with high GF content fabricated via ball milling‐hot pressing method. Silane modified GF obviously improves the thermal stability of PI matrix. GFRPCs‐28 exhibits superior mechanical properties. An increases in time to ignition (TTI) and mass residual rate (MRR) of the GFRPCs was observed on adding GF.

Effect of carbon nanotubes modification on bending fatigue properties of carbon fiber reinforced polyimide composites

Polyimide-based composites have been widely used as structural materials in aerospace and automotive industries. In the present work, carbon fiber fabric reinforced polyimide composites (CF/PI) were modified by carbon nanotubes (CNTs). The monotonic bending properties and bending fatigue performance of CNTs modified CF/PI were investigated at room temperature. Both bending strength and bending modulus of CF/PI can be increased by CNTs. The CNTs filler could inhibit crack initiation and retard crack propagation. The fatigue resistance is significantly enhanced in CNTs modified CF/PI, which is related to the CNTs enhanced matrix crack resistance and fiber/matrix debonding.

Inhibition behavior of milling hole outlet defects inhibition on quartz fiber polyimide composite through LN2 inner cooling

The helical milling hole process of quartz fiber reinforced polyimide composites (QFRP) aimed to remove high-strength fiber and low-strength resin through thermodynamic interaction. But the defects, especially delamination at hole outlet, were difficult inhabited because of heterogeneous and anisotropic of composite. A mechanics model of milling hole force of QFRP was established by considering the shearing force of single fiber and temperature. A liquid nitrogen (LN2) inner-cooling machining equipment was employed for cryogenic milling hole testes. Compared with the conventional dry milling hole, the processed composite surface morphologies, cutting temperature, and milling force were investigated at hole outlet in detail. The study results show the predict values of the established model are compared and verified through the experimental measurement. And the cryogenic coolant processes can improve the composite mechanics properties, milling forces, and cutting heat. The composite can be completely chip breaking in cryogenic cooling, and the burr and delamination are effectively inhabited at hole outlet. Meanwhile, the rapid decline of cutting force and lower interlamination bonding force problems can be solved by the cryogenic cooling cutting. And the fiber avoidance can be improved through the increased tangential force, and the fiber can be efficiency chip breaking under the bigger tangential force. In addition, LN2 cooling can inhabit the cutting high temperature and increase the bonding force, the delamination defect of composite can be adequately improved in cryogenic.

High temperature phenylethynyl-terminated imide oligomers derived from asymmetric diphenyl ether diamines for resin transfer molding

Resin transfer molding (RTM) require phenylethynyl-terminated imide oligomers (PETIs) to exhibit low melt temperatures and better melt stability. To decrease the melt temperatures of PETIs and improve their resin transfer moldable processability, asymmetric 4,4′-diaminodiphenyl ether substituted by fluorine (F-ODA), trifluoromethyl group (3F-ODA) or phenyl group (p-ODA) were introduced. Asymmetric molecular structure and substituent groups decrease the melt temperatures of PETIs, endowing PETIs with the wider processing temperature windows and low minimum melt viscosity (<1 Pa s). These polyimides show pot lives of 30–60 min at 260–280 °C. Furthermore, the effects of backbone structure on melt fluidity of imide oligomers were discussed by the calculation of viscous activation energy (Ea,η) and analysis of Molecular Dynamics. PETI-3F and PETI-P based on 3F-ODA and p-ODA exhibit low and stable melt viscosities (<1 Pa s) at 250–270 °C and 260–270 °C for 4 h respectively, enabling the successful fabrication of carbon fiber reinforced polyimide composites via RTM process. After cured at 380 °C, the thermosets of PETI-3 and PETI-4 show high Tg of 412 °C and 402 °C and good thermal stability (Td5>550 °C). Cured PETI-3 and PETI-4 also show good mechanical properties (tensile strength >50 MPa). In comparison with p-ODA, 3F-ODA could provide PETIs with superior resin transfer moldable processability and higher heat-resistance and is more suitable to synthesize PETIs for RTM application, because of better balance between polymer segmental mobility and polymer chain packing.

Enhanced mechanical and electrical properties of ECR-glass reinforced polyimide composites with incorporation of TiO2 for insulation applications

This paper presents the mechanical behaviour of novel class composites consisting of ECR-glass type reinforced polyimide (PI) composite loaded with TiO2 nanoparticles. ECR glass reinforced PI composites were fabricated by adding TiO2 particles at three different concentrations namely; 2, 4, and 6 wt% using 3D-Turbula dispersion and Spark Plasma Sintering (SPS) method. The morphologies, crystallinity, mechanical, and electrical properties of the produced composites were evaluated using scanning electron microscope (SEM), X-ray diffractometer, nanoindentation test, and LCR meter device. The SEM results revealed that the TiO2 nanoparticles were homogenously dispersed into the PI composites. The mechanical properties, such as hardness, stiffness, and elastic modulus of the pure PI and ECR glass reinforced PI composite was improved by the incorporation of TiO2 nanoparticles. Maximum hardness and elastic modulus values of 2.19 GPa and 13.99 GP, respectively, was observed in ECR reinforced PI composited loaded with 6 wt% TiO2 nanoparticles. In addition, ECR glass reinforced PI composites with 6 wt% TiO2 nanoparticles depicted the lowest dielectric constant (1.18), dielectric loss (1.14) and electrical conductivity (3.16 × 10−6 S/cm). Finally, the findings suggest the easy processability of PI nanocomposites and their potential for mechanical and electrical insulation applications.

Mechanical and tribological properties of electrical corrosion resistance-glass reinforced polyimide composites for high voltage applications

In recent times, glass fiber reinforcements are extensively used in the development of polymer matrix composites to improve their performance especially when used for engineering applications. As such, the focus of the present study remains on the effects of electrical corrosion resistance (ECR) glass particles on the mechanical and tribological properties of polyimide (PI) composites fabricated by the spark plasma sintering (SPS) process. SPS is a novel powder metallurgy method in producing homogeneous composite materials in short sintering time with finer microstructure. However, the PI composites were produced at different contents of ECR-glass reinforcement particles (5, 10, 15, and 20 wt %). The microstructural characterization of the samples was conducted using scanning electron microscope (SEM). Nanoindentation tests and pin-on-disc wear tests (under dry condition) were conducted to evaluate the mechanical and tribological properties of the composites. The SEM results revealed that the reinforcement’s particles were well distributed in the PI matrix phase. Incorporation of ECR-glass particles into the PI composites improved its hardness and elastic modulus. The ECR-glass/PI matrix composite loaded with 15 wt% ECR displayed a significant reduction in coefficient of friction from 0.091 to 0.015 and wear rate from 0.81 × 10−4 to 0.14 × 10−4 mm3/Nm. In addition, the ECR/PI composites exhibited improved dielectric properties over the pure PI. Hence, corroborating the potential of this ECR-glass reinforced PI for industrial (automobile and power) applications requiring high hardness, elastic modulus, good wear resistance, and low dielectric constant.

Effect of ECR-glass additions in the mechanical and tribological properties of TiO2 reinforced polyimide composites

ABSTRACT The use of polyimide-reinforced composite materials in the design and fabrication of components for mechanical and tribological operation systems remains a research focus. As such, the present study investigated the effect of electrical corrosion resistance (ECR) glass on the mechanical and tribological properties of hybrid-polyimide composites using spark plasma sintering (SPS) method. The hardness and elastic modulus of the thermoplastic polyimide reinforced with TiO2 and ECR particles was investigated in this study with a nanoindentation tester under applied load of 200 mN. While the friction and wear behavior of the composites was ascertained with pin-on-disc tester under 10 N at 150 rpm with a stainless steel counterpart at room temperature. The results showed that the ECR glass addition remarkably improved the hardness and elastic modulus of the hybrid composites. Incorporation of the 10 wt% ECR glass effectively reduced the friction coefficient and wear rate by 55.5% and 92.2%, respectively, corroborating the potential of these ECR-TiO2-PI composites for applications requiring a low friction coefficient and wear rate with high mechanical properties.

Elastic modulus and Poisson’s ratio of graphene nanoplatelet/glass fiber-reinforced polymer hybrid composites subjected to off-axis loading

Effective elastic properties of the graphene nanoplatelet (GNP)/unidirectional glass fiber (GF)-reinforced polyimide composites subjected to off-axis loading are predicted using a closed-form hierarchical micromechanical approach. The effects of volume fraction, agglomeration and non-flat structure of GNPs, graphene/polymer interfacial region, and fiber volume fraction on the off-axis elastic modulus and off-axis Poisson’s ratio are investigated. In order to verify the accuracy of the present micromechanical method, predictions are compared with the experimental data. Adding GNPs into the polymeric resin increases the elastic modulus of all off-axis coupons. When flat GNPs are uniformly dispersed in the polyimide resin, much more improvement in the off-axis elastic properties is achieved. The results indicate that agglomeration and non-flat structure of the GNP can drastically decrease the off-axis elastic modulus. It is observed that the off-axis elastic response of hybrid composites may be sensitive to the material property and thickness of the interfacial region.

Synthesis and characterization of fluorine functionalized graphene oxide dispersed quinoline‐based polyimide composites having low‐k and UV shielding properties

AbstractPolyimide nanocomposites having low‐k and UV shielding properties have been developed using fluorine functionalized graphene oxide and bis(quinoline amine) based polyimide. The polyimide was synthesized using bis(quinoline amine) and pyromellitic dianhydride at appropriate experimental conditions, and its molecular structure was confirmed through various spectral analysis such as FTIR and NMR. The polyimide (PI) composites were prepared using bis(quinoline amine), pyromellitic dianhydride, and separately filled with 1, 5, 10 wt% of fluorinated graphene oxide (FGO) through in situ polymerization. The polymer composites were characterized using thermo gravimetric analysis (TGA), X‐ray powder diffraction (XRD), and scanning electron microscopy (SEM). In addition, the water contact angle, dielectric behavior, and UV–Vis shielding behavior of FGO/PI composites were evaluated. The value of the water contact angle of the polyimide was increased with increment of FGO in the polyimide matrix. The highest water contact angle of polyimide composites observed 108° was obtained for 15 wt% FGO reinforced polyimide composite. The value of the dielectric constant for neat, 1, 5, and 15 wt% FGO reinforced polyimide composites was obtained as 4.5, 3.7, 2.6, and 2.0, respectively. It is also observed from by UV–Vis spectroscopy analysis that the FGO reinforced polyimide composites have good UV shielding behavior.

Synthesis and characterization of graphene oxide reinforced triphenyl pyridine-based polyimide composites having UV shielding and low k properties

ABSTRACT Graphene oxide (GO) reinforced polyimide composites with low-k, improved thermal stability, surface behavior and UV shielding properties have been developed. A new 2,6-bis(4-aminophenyl)-4-(4-(octyloxy)phenyl)pyridine (PyDA) was synthesized and its molecular structure has been confirmed by FT-IR and 1H-NMR spectroscopy. Polyimide (PI) was prepared using pyridine-based amine and pyromellitic dianhydride and characterized. The varying weight percentages of (5, 10, 15 wt%) of GO have been reinforced into polyimide matrix to obtain nanocomposites and were characterized using TGA, XRD, SEM and TEM analysis. The thermal studies infer that the value of decomposition temperature (Td) obtained for neat PI matrix and GO-PI composites are 453°C and 520°C respectively and the percentage char yield are 38.9% and 40.5% respectively. The value of water contact angle of PI matrix has been steadily raised with the increasing incorporation of GO in the PI matrix. The values of contact angle observed for neat PI matrix and 15 wt% of GO reinforced PI nanocomposites are 87° and 98° respectively. Similarly, the values of dielectric constant obtained for neat polymer matrix and 15 wt% GO reinforced polyimide nanocomposites are 3.9 and 2.1 respectively. Results obtained from the UV studies indicated that the GO reinforced PI possesses better UV shielding behavior.

Effects of TiO2 decorated reduced graphene oxide on mechanical and tribological properties of thermosetting polyimide

ABSTRACT In this paper, TiO2 decorated reduced graphene oxide nanocomposite (TiO2@RGO), synthesized with the help of 3-Triethoxysilylpropylamine (APTES), was utilized to reinforce polyimide (PI), and the mechanical and tribological properties of this hybrid reinforced nanocomposite were investigated. Compared with RGO, TiO2, and TiO2/RGO mixture added to PI, TiO2@RGO showed synergistic effect and significant enhancement of the compress performance and wear resistance of PI composites. The compressive strength and modulus are increased by about 31% and 43%, respectively, compared to pure PI. Under high-load 300 N, the wear rate of TiO2@RGO reinforced PI composite decreased to one-tenth of that of pure PI, and was also much lower than other comparatively studied filler reinforced PI composites. In the analysis of the mechanical and friction mechanism, the excellent mechanical and tribological properties of TiO2@RGO/PI composite are attributed to the ‘ball-on-plane’ structure of TiO2@RGO composite and the chemical bonds between RGO and TiO2, which are assumed to stop crack propagation in the friction and lead to the wear reduction of PI composite. The outstanding mechanical and tribological properties of TiO2@RGO/PI composite show its promising potential of application as the tribological film that high wear resistance is required under heavy load.

Influence of cryogenic cooling on milling hole exit of QFRP based on thermal–mechanical coupling

Quartz fiber–reinforced polyimide composites (QFRP) had heterogeneous and anisotropic properties. Because of the gradient change of cutting force at hole exit, some fibers could not be effectively chipping breaking and the defect of delamination burr was often inevitable. In this paper, a cutting force model of fiber fracture stripping considering thermal–mechanical coupling was constructed based on the mechanism of cutting force and thermal action. A series of milling hole tests at different temperatures (from 290 to 80 K) was carried out using liquid nitrogen inner-cooling equipment. Similarly, the hole exit morphology, milling force, and cutting temperature were investigated and the delamination factors were calculated in detail. The results show that the model can explain the reason of hole exit defect, which is attributed to the lack of tangential cutting force and the large gradient change of axial force considering the high cutting temperature. Meanwhile, cryogenic cooling can reduce the effect of cutting temperature for hole exit defect. Although the cutting force is increased, the gradient degree of axial force can be reduced, and the delamination factor can be decreased from 1.08 at low-speed dry cutting to 1.01 of high-speed cryogenic one. At the same time, the increase of tangential force and the decrease of fiber ductility improve the chip breaking ability and the processing efficiency. Conclusion: the spiral hole milling process with cryogenic medium intervention can inhibit the milling hole delamination defects.

Comparative study of tribological properties of carbon fibers and aramid particles reinforced polyimide composites under dry and sea water lubricated conditions

Moving components used under air and lubricated conditions are constantly subjected to friction and wear, which poses a challenge to their reliability and service life. This work addressed the influence of short carbon fibers (SCF) and aramid particles (AP) on tribological performance of polyimide (PI) composites adding with polytetrafluoroethylene under dry and sea water lubrication conditions. A systematic study on the tribological mechanisms of SCF- and AP-reinforced PI composites was carried out. Under the controlled sliding conditions (i.e., velocity, pressure, and working conditions), the AP was more effective than SCF for enhancing the tribological performance under dry condition, but reversed under lubrication. Hard SCF exposed to the sliding interface could cause removal of the wear debris, thereby the tribofilm was patchy to lose excellent lubricated property. When sliding occurred under sea water lubrication, the weak interfacial interaction was beneficial to the formation of a robust boundary film for SCF-reinforced PI composite rather than AP-reinforced PI composite. Moreover, tribo-chemical reactions occurring between polytetrafluoroethylene and copper sustained the lubrication property of tribofilm and prevented tribo-corrosion when subjected to lubricated condition.

The effect of coupling agents on the interfacial properties of wood‐fiber–reinforced polyimide composites

Wood‐fiber–reinforced polyimide (PI) has been widely used in many engineering fields because of its high specific strength and stiffness. However, PI does not adhere well with wood fibers because it has a low free surface energy. In addition, high viscosity in the melted phase causes poor impregnation. In this study, surface treatment methods, ie, coupling agents with plasma treatment on wood fibers, were applied to increase the interfacial strength between the wood fibers and the PI matrix. The modified wood fiber surfaces were analyzed by X‐ray photoelectron spectroscopy and scanning electron microscopy. To analyze the effectiveness of the surface treatment method, the interlaminar shear strength (ILSS) was measured using the 3‐point bending test. From the test results, the ILSS of the specimens treated with the silane coupling agent after the plasma treatment increased by 48.7% compared with those of the untreated specimens.

Electrical properties of flexible graphene reinforced polyimide composites

ABSTRACTThe electrical properties of polyimide and the composite at different volumes fractions were studied in the frequency range 200–20 kHz and in the temperature range 30–200 °C. Increasing the volume fraction of graphene up to 10%, resulted in an extremely large increase in the dielectric constant, which indicates the composites remarkable ability to store electric potential energy under the effect of alternating electric field. An increase in dielectric constant was also observed with increasing temperature and decreasing frequency. The outstanding dielectric properties of polyimide graphene nanocomposites are attributed to the large volume fraction of interfaces in the bulk of the material. The measured increase in dielectric constant with increasing temperature was attributed to the segmental mobility of the polymer chains. The AC conductivity for polyimide and the composites was calculated from the loss factor and a remarkably high conductivity was obtained for the composites due to the formation of conducting paths in the matrix by the graphene sheets. Also this study showed that the thermal conductivity of the composites increased sharply with increasing graphene concentration. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45372.

Mechanical performance of nanosilica filled quartz fiber/polyimide composites at room and elevated temperatures

The polyimide (PI) composites reinforced with silanized nanosilica (SNS) and/or quartz fabrics had been fabricated. Influences of the SNS dispersion on morphology, Vickers hardness, thermal stability and mechanical properties of these composites were studied. The uniform dispersion of SNS in PI resulted from the crosslink of silane pretreated on the surface of nanosilica and PI chains. The measurement results indicated that density, Vickers hardness and flexural strength were enhanced due to the addition of SNS into the PI matrix and the optimum content of SNS was 2 wt%. The thermal stability of the SNS reinforced PI composites increased with an increase in weight fraction of SNS, compared with the neat PI resin. The effects of quartz fabric on the mechanical properties of quartz fabric-reinforced PI composites with different volume fractions and effects of post-curing on the flexural strength were also investigated. Results also showed that better mechanical properties of quartz fabric-reinforced PI composites were obtained when the volume fraction of quartz fabric was 50%. The quartz fabric-reinforced PI composites containing 2 wt% SNS after post-curing exhibited the highest flexural strength and elasticity modulus by virtue of good fiber-matrix interface, and flexural strength was almost 500 MPa at 300 °C. It is pointed that the composites have a great application prospect as one of engineering materials with high strength and high temperature resistance.

Flexible hdC-G reinforced polyimide composites with high dielectric permittivity

Carbon nanotubes (CNTs) reinforced composites with high dielectric permittivity empower miscellaneous applications in flexible electronics but are hindered by the large addition and agglomeration of fillers and weak mechanical performance. Here, we prepare homogeneous dispersion of CNTs and graphene oxide (hdC-G) via solvent-exchange, and fabricate hdC-G/polyimide (PI) composite films by in situ polymerization and thermal imidization. The achieved hdC-G can construct a 3D network and keep a long term stability. The hdC-G/PI composites show high dielectric permittivity of 124.9 at 100Hz, 4000% higher than that of pure PI. The hdC-G/PI composites also exhibit enhanced thermal stability and improved tensile strength without sacrificing the flexibility. This solvent-exchange approach can greatly enrich the applications of synergistic uses of CNTs and GO in composites and the hdC-G/PI composites with simultaneously high dielectric permittivity, low content of fillers, good mechanical and thermal performances can be good candidates for flexible electronics.

Nano-boria reinforced polyimide composites with greatly enhanced thermal and mechanical properties via in-situ thermal conversion of boric acid

High performance materials with excellent thermal stability and mechanical properties are highly required in high temperature area. The addition of inorganic particles is effective to improve the thermal and mechanical properties of polymers. In this work, B2O3 nanoparticles and their polymeric composites, B2O3/PI composite films, were formed by an in-situ thermal conversion. The morphology of B2O3/PI composite films were investigated by SEM, EDS and TEM. TGA and DMA were used to monitor the thermal properties of B2O3/PI composite films. The mechanical properties of the B2O3/PI composite films were characterized by tensile testing. The results indicated that the addition of B2O3 nanoparticles could significantly improve the thermal and mechanical properties of B2O3/PI composite films.