Polyimide Matrix Composites Research Articles

Thermal-Fatigue Oxidation of Carbon-Fiber Reinforced Polyimide Composite

Extensive studies of thermal oxidation have mostly focused on the isothermal oxidation of high-temperature polyimide-matrix composites; very few have addresses thermal fatigue or nonisothermal oxidation and the associated weight loss kinetics in the literature. According to thermal activation theory and experimental results concerning isothermal oxidation, a method for predicting anisotropic thermal-fatigue oxidation is developed for the composites.

Processing and properties of carbon fiber reinforced triple-A polyimide (Tri-A PI) matrix composites

This paper presents experimental results for the processing and mechanical properties of carbon fiber reinforced composites of a newly developed amorphous, asymmetric, and addition type polyimide (Triple-A PI). The imide oligomers were synthesized from the reaction of 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA), 4,4′-oxydiaminine (ODA), and phenylethynyl phthalic anhydride (PEPA). Because of amorphous structure, the melting point and melt viscosities of the polymer are relatively lower as compared with similar polyimides such as LaRC™ PETI-5. In spite of the lower molecular weight of the imide oligomer (<2500 g/mol), the cured polymer exhibits excellent mechanical properties because of the irregular and asymmetric structure as well as flexible end-capper. Carbon fiber reinforced composites were fabricated by routing prepreg consolidation. The composites exhibit excellent mechanical properties with high glass transition temperature (>320°C).

Increased fracture toughness in nanoporous silica–polyimide matrix composites

Silica–polyimide nanocomposites were prepared by hot-pressing mixtures of polyimide and highly porous silica powder. The silica powder was produced using a sol-gel process that generates pores as small as 15 Å. The effects of loading, cure, and post-cure temperature on fracture toughness were investigated. The addition of silica particles improved the fracture toughness from 0.5 to a maximum of 1.9 MPa m0.5. However, fracture toughness dropped at silica weight percentages ≥30%. The cure and post-curing temperatures have a strong influence on toughness; post-curing exposure ≥400 °C reduced toughness. Transmission electron microscopy examination of the fracture surfaces indicated that the toughness improvements may occur at the nanometer scale due to crack pinning and branching induced by the nanoporous silica particles.

Carbon fibre composites based on polyimide/silica ceramers: aspects of structure-properties relationship

Polyimide/silica ceramers, based on the products of the hydrolysis of tetraethoxysilane (TEOS) and a commercial poly(amic acid) solution, were used to fabricate unidirectional carbon fibre composites, which were subsequently evaluated with respect to thermal and mechanical properties. There is evidence to suggest that the silica component of these ceramers is present as dispersed discrete particles at low silica concentration (i.e. ∼7 wt%) and as fine interconnected domains trapped within the polyimide matrix at higher silica content (i.e. ∼14 wt%). The dimensions of the silica domains were in the region of 7–20 nm. Carbon fibre composites produced from ceramer solutions (CF/ceramers) were found to exhibit lower thermal expansion and a greater retention of flexural and interlaminar shear properties at elevated temperature than the corresponding polyimide-matrix composites (CF/polyimide). The properties of CF/ceramers were generally better for systems containing the higher amount of silica and were improved further by lowering the pH value of the precursor ceramer solution. This is believed to have resulted from the enhanced fluidity of the ceramer gel within the pre-impregnated fibres, giving rise to a higher packing density of the fibres and a more homogeneous distribution of fibres. CF/ceramers were also found to exhibit a better thermal oxidative stability at 350°C than the corresponding CF/polyimide, although a substantial amount of porosity developed in the case of ceramers with the higher silica content.

Recent advances in polyimide composites

Polyimide matrix composites possess an excellent balance of physical and thermal properties. However, currently available systems suffer from a number of drawbacks. Much of R &amp; D is aimed at overcoming these drawbacks and developing new and novel polyimide materials. This review paper will examine recent developments in polyimide composites in the areas of thermo-oxidative stability, resistance to microcracking, toughness, toxicity and processability.

Thermal ageing of PMR15 polyimide matrix

This study deals with the determination of the role of carbon fibre in the thermal ageing of PMR 15 polyimide matrix composite. The gravimetric behaviour of a neat resin is compared with that of a composite based on the same resin, both polymerized with a very similar cure schedule. Rates of degradation in the stationary stage of gravimetric curves are analysed with an Arrhenius model.

Heated Stage IR Microscopy for Cure Studies of Polyimide Matrix Composites

Heated Stage IR Microscopy for Cure Studies of Polyimide Matrix Composites

Characterization of surface pretreatments of carbon fiber–polyimide matrix composites

AbstractVarious surface pretreatments of carbon fiber–polyimide matrix composites have been studied by XPS, ISS, PASFTIR (photoacoustic Fourier transform infrared spectroscopy) and high‐resolution SEM. Reduction of fluorocarbons from release cloth contamination and increase in carbon–oxygen‐containing functional groups was observed on the surface of composite samples treated in an oxygen plasma. These plasma‐treated samples also showed differences in surface topography, but no change in the photoacoustic infrared spectra when compared to a methanol‐washed sample.