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A novel B-stage resin system is developed for the „Resin Transfer Pressing“ (RTP) process. This composite manufacturing technique makes use of nonwoven and recycled carbon fibres (rCF) that are oversaturated with a thermosetting resin. The new resin system is based on two different hardeners, allowing to easily impregnate the rCF, storing the semi-finished parts at room temperature and finally curing them via compression molding. It is shown that a commercially available resin system can be tailored to the required needs by the smart combination of state-of-the art, latent hardener systems.The present study focusses on the route for B-staging of the resin system. The viscosity for impregnation and oversaturation was adjusted to be in the range of 5 to 40 Pa·s at 60°C. The viscosity increases to above 50 Pa·s at room temperature, allowing storage and handling of the semi-finished parts and processing them whenever it is required. Choosing a proper processing temperature is important during the B-staging process to avoid any unintended activation of the second hardener, which is responsible for the final curing stage of the system.

The toughening performance of hybridized core-shell rubber particles and block copolymers on bulk epoxy and epoxy based carbon fibre reinforced composites was investigated. The results reveal that the interlaminar fracture toughness of the fibre reinforced laminates increased by more than 300% due to an enhanced fibre-matrix adhesion because of a combination of BCP and CSR particles. However, no synergistic improvement of the fracture mechanics properties of the bulk materials was found. Thereby, the critical energy release rate of the bulk and fibre reinforced materials is related to the interparticle distance to particle size ratio of the modifiers in the bulk/matrix systems and the plastic zone size. Furthermore, the fibre volume content of the CFRP influences the final BCP phase morphology, and thus the fracture toughness.

This study systematically investigates the influence of a Polymethylmethacrylate-block-Polybutylacrylate-block-Polymethylmethacrylate (PMMA-b-PBuA-b-PMMA) triblock copolymer (BCP) on the flexural properties, the static fracture toughness and especially the resistance to fatigue crack propagation (FCP) of a cycloaliphatic amine cured bisphenol A based epoxy resin (EP). The results show that already small concentrations of BCP can significantly improve fracture toughness and the resistance to fatigue crack propagation. Crack growth rate as well as the Paris' law exponent m were considerably reduced from m = 15.5 of the neat epoxy to m = 8.1 for the BCP toughened materials. Simultaneously, the resistance to fatigue crack propagation was found to increase drastically from a critical stress intensity factor range ΔKIc of 0.39 MPam to 0.81 MPam. Fractography and structural analysis reveal that the improved resistance to fatigue crack propagation correlates to crack shielding and zone shielding mechanisms caused by the synergistic interaction of BCP-rich domains and dispersed nanometer sized, presumably BCP-rich particles in epoxy-rich regions. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

The effect of the hybridization of a triblock copolymer and a rigid TiO2 nanofiller on the tensile, fracture mechanics and thermo-mechanical properties of bisphenol F based epoxy resin were studied. The self-assembling block copolymer, constituted of a center block of poly (butyl acrylate) and two side blocks of poly (methyl) methacrylate-co-polar co-monomer was used as a soft filler, and TiO2 nanoparticles were employed as rigid modifiers. Toughening solely by block copolymers (BCP&rsquo, s) led to the highest fracture toughness and fracture energy in the study, KIc = 2.18 MPa&middot, m1/2 and GIc = 1.58 kJ/m2. This corresponds to a 4- and 16-fold improvement, respectively, over the neat reference epoxy system. However, a reduction of 15% of the tensile strength was observed. The hybrid nanocomposites, containing the same absolute amounts of modifiers, showed a maximum value of KIc = 1.72 MPa&middot, m1/2 and GIc = 0.90 kJ/m2. Yet, only a minor reduction of 4% of the tensile strength was observed. The fracture toughness and fracture energy were co-related to the plastic zone size for all the modified systems. Finally, the analysis of the fracture surfaces revealed the toughening mechanisms of the nanocomposites.

Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite.To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance a...