Comparison of methods for the measurement of fibre/matrix adhesion in composites

A new class of epoxy nanocomposites with completely defined organic/inorganic phases was prepared by reacting octakis(glycidyldimethylsiloxy)octasilsesquioxane [(glydicylMe2SiOSiO1.5)8] (OG) with diaminodiphenylmethane (DDM) at various compositional ratios. The effects of reaction curing conditions on nanostructural organization and mechanical properties were explored. A commercial epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) was used as a reference material throughout these studies. FTIR was used to follow the curing process and to demonstrate that the silsesquioxane structure is preserved during processing. OG/DDM composites possess comparable tensile moduli (E) and fracture toughness (KIC) to, and better thermal stabilities than, DGEBA/DDM cured under similar conditions. Dynamic mechanical analysis and model reaction studies suggest that the maximum cross-link density is obtained at N = 0.5 (NH2:epoxy groups = 0.5) whereas the mechanical properties are maximized at N = 1.0. Digestio...

Organic/Inorganic Hybrid Composites from Cubic Silsesquioxanes

Selected epoxy-functionalized cube nanocomposites were prepared from octa(aminophenyl)silsesquioxane (OAPS), poly(aminophenyl)silsesquioxane (PAPS), octa(dimethylsiloxypropylglycidyl ether) silsesquioxane (OG), diglycidyl ether of bisphenol A (DGEBA) and diaminodiphenylmethane (DDM). A systematic comparison of properties was conducted using GPC, FTIR, 29Si NMR, TGA, and DMA. In these studies, we find that (1) tethers with aromatic components increase char yields and decomposition temperatures, (2) cube loadings are important in thermal stabilities, (3) aromatic tether structure, short lengths and high cross-link densities reduce tether segmental relaxation motions which in turn stiffen the network and minimize macroscopic glass transitions. Finally, nanocomposites prepared from OAPS and PAPS exhibit nearly identical thermomechanical properties with PAPS offering a low cost alternative to OAPS.

Organic/Inorganic Hybrid Epoxy Nanocomposites from Aminophenylsilsesquioxanes

The effects of surface treatments, such as oxygen plasma and nitric acid treatment, on the mechanical properties of carbon fiber (CF)/polybenzoxazine composites were investigated. Interlaminar shear strength (ILSS) and flexural strength of CF/polybenzoxazine composites were measured and correlated with surface area and surface functionality. Both oxygen plasma treatment and nitric acid treatment were efficient in the enhancements of the ILSS and flexural strength of CF/polybenzoxazine composites. However, nitric acid treatment was more efficient than oxygen plasma treatment due to large increment of surface roughness. Cohesive failure was observed in surface treated composite due to adhesion improvement.

The effect of surface treatment on the performance improvement of carbon fiber/polybenzoxazine composites

The single fibre fragmentation test for measuring the properties of the fibre–matrix interface in fibre-reinforced composites is reviewed. Special emphasis has been paid to the recent stress transfer models in single fibre composites and its application to the development of a suitable data reduction technique for the fragmentation test. The complexities of the correlation of the micromechanical results to the properties of the macrocomposites have been highlighted.

Single fibre fragmentation test for assessing adhesion in fibre reinforced composites

Despite considerable attempts to increase aramid-epoxy adhesion, to date, the adhesion levels achieved between aramid fibres and epoxy matrices are less than optimum for some applications. A combination of the aramid fibres' morphology, physical and chemical properties, and the interfacial mechanical stresses is responsible for the lack of success in increasing aramid-epoxy adhesion level. A key to improving the aramid-epoxy adhesion is a basic understanding of the interfacial mechanisms by which fibre and matrix interact. There is a considerable number of publications on aramid fibres and their composites. This paper reviews some of the literature relevant to aramid-epoxy bonding mechanisms

The bonding mechanism of aramid fibres to epoxy matrices: Part 1 A review of the literature

In this study attempts are made to develop a basic understanding of the interfacial interactions resulting from the combination of aramid fibres with epoxy matrices in composite materials. The interfacial interactions examined are mechanical stresses due to fibre-matrix thermal strains and Poisson's ratio mismatch, covalent chemical bonding, fibre-matrix wetting, and effects of physicochemical weak boundary layers. Both aramid and carbon fibres have been examined to assess the interfacial interactions by comparing the behaviour of these two fibres in the same matrices. The results indicate that the adhesion of aramid fibres to epoxy matrices lack both the mechanical and the chemical interactions present at the carbon-epoxy interface. Aramid fibres exhibit an interfacial shear strength much lower than the expected theoretical value. Direct observation of the aramid-epoxy interface by transmission electron microscopy shows fibrillar separations within the fibre surface, which may be the limiting factor in achieving greater interfacial adhesion.

The bonding mechanism of aramid fibres to epoxy matrices

Quantitative analytical techniques were developed for the compositional characterization of the fiber-polymer interphase. Intermolecular diffusion at a DGEBA interphase was studied to simulate the cure in the interphase of a coated fiber-epoxy composite. In this study model interphases of halogenated DGEBA with standard DGEBA were created and spectroscopically probed for composition and spatial distribution of the halogen marker. Additionally, carbon fibers were coated with halogentated DGEBA and cured in a standard DGEBA-diamine resin. The effects of fiber coating on fibermatrix bond strength and failure mode will be presented.

Spectroscopic Characterization of Fiber-Polymer Interphases

Ultra-high molecular weight polyethylene fibers possess exceptional strength and stiffness combined with low density. Their use as reinforcements in polymer matrix composites has, however, been limited by poor fiber adhesion. In the present study, individual fibers of UHMW-PE (Allied-Signal SPECTRA-1000) were modified by direct implantation of N+, Ti+ and Ar+ ions, at energies between 30 and 100 KeV, to doses ranging between 1x1014 and lx1015 ions/cm2. Fiber tensile strength was generally unaffected by these irradiations. Single-fiber droplet pull-off tests using DGEBA Epoxy with m-PDA curing agent have shown that ion beam surface modification of the fibers can give an increase of over 300% in interfacial shear strength (ISS). The improvements were found to vary with dose but were relatively insensitive to implant species. TEM observation of transverse microtomed sections confirmed a substantial improvement in fiber-matrix adhesion for ion beam modified UHMW-PE composites.

J. Kalantar

Papers

The bonding mechanism of aramid fibres to epoxy matrices: Part 1 A review of the literature

The bonding mechanism of aramid fibres to epoxy matrices

Spectroscopic Characterization of Fiber-Polymer Interphases

Interfacial Shear Strength of Ion Beam Modified UHMW-PE Fibers in Epoxy Matrix Composites

Bonding mechanism of aramid fibers to epoxy matrices.