Overview
The aim of this proposal was to develop hybrid epoxy resin composites, where both the matrix and the carbon fibre reinforcement contains nanoparticles, in order to improve the mechanical, electrical and thermal properties of the carbon fibre reinforced aeronautical structures.
The dispersion of the selected nanoparticles in epoxy resin matrix was carried out by a three step masterbatch technique, resulting in low viscosity, evenly dispersed CNT filled epoxy resin systems ready for industrial size use. Rheological, morphological and spectroscopic (Raman, FTIR) characterization of the loaded materials was carried out.
Polymer nano/microfibers loaded with CNT and other nanoparticles, which serve as precursors for carbon fibres, were produced by electrospinning method from PAN/DMF solution of CNTs. Optimal parameters for the graphitization of these yarns were determined.
Parallelly arranged CNT reinforced nanofibrous yarns were carbonized and consequently infiltrated by the CNT filled matrix mixed with the curing agent. The final outcome was a tape consisting of an epoxy/CNT hybrid matrix and quasi-unidirectional carbon nanofibre/CNT yarn hybrid reinforcement.
Thermal and electrical conductivity of the prepared laminate samples were determined according to standard methods in the function of dispersion method and nanoparticles loading. Laminate samples were evaluated against conducted lightning current pulses.
Static (tensile, bending, interlaminar shear strength properties), dynamic (instrumented Charpy impact, instrumented falling weight impact, dynamic interlaminar properties) and fatigue testing of the composites was carried out.
After testing the mechanical, electrical and thermal properties of composites, the industrial applicability of the developed electrospinning and graphitization methods and prepreg tape product were studied.
Funding
Results
This project aimed at the development of hybrid epoxy resin composites, where both the matrix and the carbon fibre reinforcement contain nanoparticles, in order to improve the mechanical, electrical and thermal properties of the carbon fibre reinforced aeronautical structures. In WP1, two kinds of untreated multiwall carbon nanotubes (MWCNTs) have been characterised by scanning electron microscopy (SEM) and atomic force microscopy (AFM) tests in terms of aggregate structure. Composites with two MWCNT types have been compared through mechanical tests. Based on mechanical test results Bayer BT C150 HP MWCNTs have been selected for further use. Rheological and mechanical characterization of four epoxy resins combined with six curing agents has been performed with multiple amounts of MWCNTs. For further use the low viscosity AH-12 epoxy resin with T-111 curing agent has been chosen. According to the results of the mechanical and electric conductivity tests performed on MWCNT/ carbon fibre (CF) reinforced hybrid composites prepared by vacuumbag technology 0.3 wt% MWCNT filling has been selected. The masterbatch dispersion method has been characterized and compared to a competitor direct mixing technology. WP2 aimed at developing processes to produce polymer nanofibres loaded with carbon nanotubes (CNTs), for CF production.
The concentration and viscosity of polyacrilonitrile (PAN) solutions were optimised for electrospinning. A novel technique involving both mechanical and ultrasonic mixing was developed for dispersion of CNTs and the efficiency was evaluated. Nanofibre samples were produced with NanoSpiderTM method. The nanofibrous mats were examined by SEM and AFM. The average fiber diameters were found to be approximately 200 nm. The stabilization and carbonization processes were optimized using differential scanning calorimetry (DSC), thermogravimetry (TG), Fourier transform infrared spectrometry (FTIR) and wide angle X-ray spectroscopy (WAXS). The suggested heat treatment program consists of a hot-stretching, a multistep stabilization taking 10 minutes, respectively, and a two step carbonization at higher temperatures. Carbon nanofibers with a diameter of approximately 100 nm were successfully produced.
In WP3 four samples (unwoven carbon nanofabric reinforced MWCNT filled epoxy, unwoven carbon nanofabric reinforced epoxy, CF reinforced MWCNT filled epoxy and CF reinforced epoxy) have been prepared to characterize the effect of CNT filling and to be able to compare the developed nanofiber reinforced composites to the conventional microsized CF reinforced ones in guarded hot plate thermal conductivity and four-pin surface resistivity measurements. The thermal conductivity of the samples has increased by approximately 3 times with the inclusion of MWCNTs in the carbonized nanofibers. The electrical conductivity is significantly higher in case of MWCNT containing carbonized nanofiber reinforced composites compared to the CF reinforced composites. The inclusion of MWCNTs in the PAN precursor fibers is essential for the formation of conductive carbonized nanofibers by the mediation of the formation of a more perfect and aligned graphite structure.