Abstract
Polystyrene-b-polybutadiene-b-poly (methyl methacrylate) block copolymer (SBM) was incorporated into epoxy resin to access the nanostructures in epoxy thermosets, knowing the different miscibility of polymeric blocks on epoxy matrix during the curing treatment. The morphology of modified SBM/epoxy resins was examined by Transmission and Field Emission Gun Scanning Electron Microscopy (TEM and FEG-SEM), reveling a nanostructured epoxy matrix with a dispersed micro-scale phase. The modified resins presented enhanced flexural properties, which were dependent on the composition of blend. The resin reinforced with low SBM contents (2.5 and 5 wt%) presented high values of flexural modulus and strength, while the blend reinforced with higher SBM load (10 wt%) showed higher elongation ability. This different behavior was explained by SEM analysis of fracture surfaces, which showed different toughening mechanisms. The adhesive strength and toughness were determined using carbon fiber/epoxy laminates with peel ply surface treatment as adherends. The results showed a dramatic enhancement of both properties for modified SBM/epoxy adhesives. The highest increases measured were 50 and 70% for lap shear strength and mode-I adhesive fracture energy, respectively.
Highlights
Epoxy resins are one of the most important structural adhesives due to their good adhesive properties and high thermal and chemical strength
The study of phase structure of epoxy resins modified with different contents of SBM block copolymer confirmed the presence of two phases in different scale
Field Emission Gun Scanning Electron Microscopy (FEG-SEM) micrographs shows spherical micrometer-size particles with an average diameter which varies with the SBM load: 500 nm for 2.5 wt% and 1 μm for SBM contents of 5 and 10 wt%
Summary
Epoxy resins are one of the most important structural adhesives due to their good adhesive properties and high thermal and chemical strength. These adhesives show good wettability on carbon fibre/epoxy laminates due to the high compatibility with epoxy matrix. For this reason, they are being investigated in order to replace the mechanical joints. New engineering thermoplastic polymers and copolymers are being researched to achieve high toughness and thermal strength. Block copolymers have attracted attention as modifiers for toughening of epoxy resins [6,7] These tend to form nano-phase structures (1-100 nm). The efficiency of fillers is inversely proportional to size and directly proportional to the filler surface area and volume ratio [6]
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