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A remarkable synergistic increase in fracture toughness by 130% is demonstrated for a CFRP high performance epoxy composite when adding an equal weight combination of phenoxy thermoplastic and core-shell rubber (CSR) toughening agents, as compared to a single toughener at a comparable total concentration of around 10 wt%. The dual-toughened matrix exhibits an unusual morphological arrangement of the two toughener agents. The interlaminar shear strength of the composites is also synergistically improved by about 75% as compared to the reference while the compression modulus reduction and viscosity increase are significantly smaller than for the single phenoxy toughened system. A partial filtering of the CSR particles by the dense CF fabric during pre-pregging leads to a less than optimum CSR dispersion in the composites, showing that the synergy can be further optimized, possibly to the same level as the unreinforced systems.

The hybrid assembling of thermoplastics with thermosets through controlled interdiffusion is an attractive approach towards integrated structural composite bonding. The fracture toughness of the interphase between the high Tg thermoplastic polyetherimide and the RTM6 epoxy is found to be four times higher than the corresponding RTM6 value under specific curing cycle. The origin of this remarkable cracking resistance is elucidated by analyzing the crack path in relationship with the morphology and local elastoplastic and fracture properties of the interphase. The crack is trapped inside a morphological gradient involving a relatively low PEI concentration. Uniaxial compression and nanoindentation tests on homogenous blends exhibit an unexpected softening in this PEI content window. This efficient crack trapping mechanism originates thus from a synergistic coupling between a lower local strength and higher local fracture toughness. This finding opens to many new options for interface toughening beyond the system addressed in this research.

A new block copolymer-thermoplastic dual toughening concept for high performance RTM6 epoxy matrix composites is elaborated through a comprehensive microstructural study of well-defined model systems. A blend of phenoxy and MAM (copolymer of poly(methyl methacrylate) and poly(butyl acrylate)) increases the toughness of the corresponding carbon fiber reinforced composite by 125%, a five-fold synergistic improvement over the situation where the tougheners are used alone at the same total concentration. Selective intercalation of blended toughener thin films in the preform gives rise to a diffusion-induced composition gradient during the RTM process, which generates a morphology gradient upon curing. The observed microstructures results from MAM self-assembly in the miscible mixture of phenoxy and the epoxy resin precursor, followed by reaction induced phase separation, forming wormlike micelles, interconnected micelles and co-continuous morphologies. The resulting microstructures activate different toughening mechanisms responsible for the observed synergy.

The mechanical properties of an unmodified reference composite panel based on a highly crosslinked epoxy resin are compared with several corresponding toughened versions, all containing the same amount of representative hard or soft tougheners. The panels are prepared and tested under identical conditions. In terms of tougheners, soft MAM block copolymers and CTBN rubber are compared with two high glass transition temperature (Tg) amorphous thermoplastics, PES and phenoxy. The high Tg thermoplastic tougheners yield considerable improvements of the composites mechanical properties, especially the interlaminar fracture toughness, as compared to the reference panel. On the contrary, MAM and CTBN modification are much less effective. The analysis of the morphology strongly suggests that effective toughening of composite panels based on densely crosslinked epoxy resins requires the combination of at least two key factors: (i) a fine dispersion of the toughener and (ii) strong matrix-toughener and matrix-carbon fibers interfaces. The study provides valuable insights for the choice of suitable tougheners for high performance epoxy systems, based on the link with the physical toughening mechanisms.

The aim of this work is to encapsulate a self-healing photo-polymerisable material for aerospace applications. To meet the technical requirements of space applications - low and high temperatures: -120 °C (dark side) to +250 °C (solar side); UV radiations: 200-400 nm; low pressure: 10(-4 )Pa - we chose trimethylolpropane triacrylate as healing agent. This monomer polymerises at 190 °C. To avoid its earlier thermal polymerisation, an inhibitor was added to the monomer/photo-initiator formulation. Moreover, among several microencapsulation techniques tested, we chose the sol-gel process to form silica microcapsules containing the self-healing formulation. These microcapsules were characterised by different analysis (scanning electron microscopy (SEM), thermo gravimetric analysis (TGA), Fourier transform infra-red spectroscopy (FTIR), etc.) and satisfied our requirements (size 1-30 μm, thermal stability >250 °C). After the microcapsules breakage, the generation of poly(TMPTA) film by radical photopolymerisation of the released TMPTA monomer was proved by disappearance of the IR peak at 1635 cm(-1) (assigned to TMPTA). The obtained film has a thermal stability above 300 °C.

International audience; The present study is devoted to the validation of a new method for in line electrokinetic characterisation of deposits on membrane surfaces. This method is based upon simultaneous measurements of transversal streaming potential and permeates flux at constant pressure before and during the deposit formation. Dead-end filtration experiments were conducted with negative flat membranes forming a narrow slit channel, negative hollow fiber membranes and mono-dispersed suspensions of (negatively charged) polystyrene latex and (positively charged) melamine particles at various concentrations. It was observed that the overall streaming potential coefficient increased in absolute value with the deposited latex quantity, whereas it decreased and changed of sign during the filtration of melamine suspensions. By considering a resistance-in-series model, the streaming potential coefficient of the single deposit (SPd) was deduced from the electrokinetic and hydraulic measurements. The independence of SPd with respect to growth kinetics validates the measurement method and the reliability of the proposed procedure for calculating SPd. It was found that SPd levelled off much more quickly when filtration was performed through the slit channel. This different behaviour could result from a non-uniform distribution of the deposit thickness along the membrane given that the position of measuring electrodes is different between the two cells.

The interdiffusion between a low and a high viscosity epoxy resin was studied on model systems representing the novel composite manufacturing process called “Same Qualified-Resin Transfer Molding” (SQ-RTM). Neat resin model systems were first characterized after curing by Raman spectroscopy, energy dispersive X-ray microscopy, and nano-indentation, all methods reveal an interdiffusion distance of about 700–900 µm. Transmission electron microscopy further revealed a complex morphological gradient structure in the interdiffusion zone. The interdiffusion distance was about 800 µm in the absence of carbon fibers, reducing down to 500 µm when the viscous resin was replaced by the corresponding prepreg, due to the geometrical constraints imposed by the fibers. Moreover, some asymmetry was observed in the interdiffusion profile because of the viscosity difference between the resins. The results obtained on the model systems were found to match very well the interdiffusion profiles generated in real SQ-RTM composites processed with the same combination of resins. POLYM. ENG. SCI. 56:1061–1069, 2016. © 2016 Society of Plastics Engineers

The electrokinetic properties of hollow fiber polymer membranes were investigated from tangential streaming current/streaming potential and electric conductance measurements. The experiments were conducted with a number of fibers n between 1 and 10 and for three fiber lengths l . The quite good linearity of (i) streaming current/potential data versus pressure difference and (ii) streaming current coefficient and “ SP × G ” ( SP : streaming potential coefficient; G : cell electric conductance) data versus n / l shows that expressions of the streaming current and streaming potential derived in laminar flow are also valid for turbulent flux conditions (provided the electrical double layer lies within the laminar sublayer near the surface). The high experimental conductance, the nonlinear dependence of electric conductance on the number of fibers and the variation of streaming potential coefficient with n and l suggest that the solution in which fibers are immersed makes contribution to the cell electric conductance. A non negligible part of the total streaming current is likely to flow through the macroporous body of fibers. Unlike flat membranes, the contributions of the skin surface and the porous body of the fibers to the streaming current cannot be separated for this type of material due to the impossibility of varying channel cross section. The conversion of tangential electrokinetic measurements into zeta-potential of lumen surface is then no more possible. In such cases, it is advisable to carry out streaming current measurements (or to combine streaming potential measurements with electric conductance measurements) because the streaming current (or the product SP × G ) is not affected by the cell electric conductance and can then be considered a property of membrane surface.