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The development of multilayered polymeric/metallic materials by a PM route employing spark plasma sintering (SPS) has been explored. The aim is to produce composites that join a polymer with a metal for structural applications. In a first approach, the consolidation of polyimide-based composites by SPS was studied. For temperatures as low as 350°C, homogeneous mechanical properties were achieved in compression tests. In a second set of experiments, multilayered polyimide/aluminium composites were consolidated by SPS. These polymer-based composites could be used as an interlayer material to join effectively polyimide and aluminium.

Acrylate functionalities were grafted at the surface of carbon fibers in order to improve the adhesion strength with an acrylate matrix cured by electron beam. An isocyanate bearing aliphatic urethane acrylate was used as a coupling agent. As revealed by X-ray photoelectron spectroscopy, the isocyanate groups reacted with carboxylic acids and hydroxyl groups located at the surface of the fiber, leading to a covalent bonding of the acrylate groups. The adhesion strength was measured by a micromechanical test derived from the pull-out test. A significant improvement of the interfacial shear strength was obtained (+91%) with an electron beam curing. For comparison, an isothermal cure by UV was also investigated and led to the same level of adhesion strength. The improvement was also proved by an increase in the 90° flexural strength of unidirectional composites (+38%). Grafting functionalities that were compatible with the radical mechanism of the polymerization of the matrix appeared to be a promising strat...

Oxygen plasma was used to modify the surface properties of carbon fibers and their adhesion strength with an acrylate resin cured by electron beam. A characterization of the surface topography and the surface chemistry was carried out (topography at a micrometric and nanometric scale, specific surface area, temperature programmed desorption, and X-ray photoelectron spectroscopy). The topography remained unchanged. Regarding the surface chemistry, carboxylic acids, alcohols, lactones, and ethers were created and their location was at the outer surface of the fibers. A pull-out test was used to measure the adhesion strength with the acrylate resin cured by electron beam. For comparison, an isothermal UV curing was also investigated. The value of the interfacial shear strength was increased only in the case of UV curing. No improvement was observed with electron beam curing, which highlighted the generation of an interphase, the mechanical properties of which are dependent on the processing conditions.

The aim of this study was to analyze the effect of interfacial covalent bonds on the adhesive behavior of an elastomer, a crosslinked polydimethylsiloxane, and a glass substrate. These covalent bonds were created by applying to both materials an appropriate surface treatment by means of plasma polymerization. Adhesion measurements were carried out by analyzing the contact area between a rubber hemisphere and a flat rigid glass plate. The contact was forced under a given compressive loading for different times tc, then the load was removed and the fracture propagation at the interface was recorded as a function of relaxation time tr. Finally, adhesion energies were also determined by means of a probe test using a tensile testing machine.

The purpose of this study was to better understand the effect of non-rubber substances (mainly proteins and lipids) on adhesion (against glasses) and self-adhesion tack properties of uncrosslinked natural rubber (NR). Various types of NR, with or without non-rubber constituents, were prepared. Synthetic polyisoprene rubber was also used as a reference material. All the rubbers were first characterized by many techniques (FT-IR, DSC, GPC, etc.). Two experimental tests were specially utilized to measure the level of adhesion and self-adhesion: (i) at very short contact times (from a few milliseconds up to 0.1 s) the impact of a pendulum and (ii) for longer contact times (from 0.1 s to a few h) the contact of a probe using a tensile testing machine. The tack energy increased with contact time for all the rubbers studied. Natural rubber which did not contain proteins and lipids exhibited the highest adhesion and self-adhesion tack abilities. In contrast, whole natural rubber, containing both proteins and lipi...

This paper deals with the analysis of peel energy of assemblies measured in different environments, i.e. in air and in the presence of liquids, and constitutes a brief review of the work of Professor Schultz' team in this domain. It is shown how such measurements can lead to a better knowledge of the nature as well as of the magnitude of fundamental interactions established at the interface between two solids. Earlier experiments have shown that peel energy can be expressed as a product of three terms corresponding, respectively, to the reversible energy of interfacial adhesion, the hysteretic losses of the bulk materials and the molecular dissipation near the crack front during peeling. This approach is well-verified when only physical interactions (van der Waals) are involved at the interface. However, more complex cases correspond to systems where specific interactions are also established between both materials, in particular acid-base interactions and creation of chemical bonds. In both case...

This paper deals with the influence of interphase formation on the stress transfer capacity of the fibre-matrix interface in single fibre composites and constitutes a brief review of our recent work. This influence is studied through the deviation of the experimental results from a recent theoretical analysis relating the interfacial shear strength to the reversible work of adhesion established between the fibre and the matrix. Two examples of interphases are considered: a transcrystalline layer in carbon fibre-PEEK composites and a pseudo-glassy interphase in carbon fibre-elastomer systems. In the former case, the low transverse mechanical properties of the transcrystalline layer lead to a decrease of the interfacial shear strength, whereas, in the latter case, the glassy behaviour of the interphase explains the improved interfacial stress transfer capacity.

The effect on the peeling energy, G, of glass/styrene-butadiene rubber (SBR) assemblies of the length, N, of the alkyl chain, ranging from 4 to 30 carbon atoms, of silane coupling agents is determined. Experimentally, it is shown that G strongly increases with N. Therefore, considering that the rheological model of adhesion (or model of multiplying factors) is valid, G is assumed equal to the product of three terms: the reversible adhesion energy, W. at the interface, the viscoelastic dissipation factor, φ, of SBR and a “molecular factor” to be determined. Finally, it appears that this latter factor depends linearly on N. Such a result should be consistent with an extraction (“suction”) process of the silane alkyl links from bulk SBR during peeling experiments.

The stress transfer capacity of carbon fibre-SBR interfaces is analysed in terms of interfacial shear strength and measured by means of a fragmentation test on single fibre composites. For all the cases studied, the experimental values of the interfacial shear strength are largely higher than theoretically expected. Such a result is explained by the existence near the fibre surface of an interfacial layer in which the polymer chain mobility is greatly reduced. Such an interfacial region of low mobility is pointed out by mechanical spectrometry on unidirectional composites at different fibre contents. This interphase could exhibit a pseudo-glassy behaviour and, in particular, an elastic modulus close to that of the elastomer in its glassy state whatever the temperature.