Toughening Epoxy Thermosets with Block Ionomers: The Role of Phase Domain Size

Abstract

Herein we report a novel approach to toughen epoxy thermosets using a block ionomer, i.e., sulfonated polystyrene-block-poly­(ethylene-co-butylene)-block-polystyrene (SSEBS). SSEBS was synthesized by sulfonation of SEBS with 67 wt % polystyrene (PS). Phase morphology of the epoxy/SSEBS blends can be controlled at either nanometer or micrometer scale by simply adjusting the sulfonation degree of SSEBS. It has been found that there exists a critical degree of sulfonation (10.8 mol %) forming nanostructures in these epoxy/SSEBS blends. Above this critical value, macrophase separation can be avoided and only microphase separation occurs, yielding transparent nanostructured blends. All epoxy/SSEBS blends display increased fracture toughness compared to neat epoxy. But the toughening efficiency varies with the phase domain size, and their correlation has been established over a broad range of length scales from nanometers to a few micrometers. In the nanostructured blends with SSEBS of high sulfonation degrees, the fracture toughness decreases with decreasing size of the phase domains. In the macrophase-separated blends, only a slight improvement in toughness can be obtained with SSEBS of low sulfonation degrees. The epoxy blend with submicrometer phase domains in the range 0.05–1.0 μm containing SSEBS of a moderate degree of sulfonation (5.8 mol %) displays the maximum toughness. This study has clearly clarified the role of phase domain size on toughening efficiency in epoxy thermosets.

Effect of Na-ionomer on dynamic rheological, dynamic mechanical and creep properties of acrylonitrile styrene acrylate (ASA)/Na+1poly (ethylene-co-methacrylic acid) ionomer blend

“…The research activities on ionomer are gaining interests day by day. Ionomer is used for toughening of epoxy thermosets using block ionomers, as shape memory material and self‐healing material under high‐energy impact conditions . The antibacterial activity sulfonated polystyrene (SPS) and silver nanocomposites (SPS/Ag) was also explored.…”

Strategies for Designing Stretchable Strain Sensors and Conductors

“…It should be noted that high loadings of conductive fillers are usually required to achieve high electrical conductivity which can degrade the stretchability of the composites and leads to lower processability. Moreover, it was demonstrated that the strain sensitivity of the composites increases upon decreasing the conductive filler content and the highest sensitivity was found to occur at a filler concentration near the percolation threshold . Therefore, the conductivity/sensitivity, stretchability/processability dilemma should be taken into account in the design of conductive polymer composites.…”

Toward simultaneous toughening and reinforcing of trifunctional epoxies by low loading flexible reactive triblock copolymers

“…hydrogen bonding), which have been reported by others. 12,20 For BCP/TDE-85/DDS blends, oxygen atoms of epoxy-philic blocks (e.g., PEG) can form hydrogen bonding with the amino groups of DDS (or with hydroxyl groups inevitably formed from TDE-85 via ring-opening reaction during melt blending), which can result in miscibility. Aer curing, the nonreactive EPE80-modied thermoset becomes obscure (Fig.…”

“…The most common toughening way is incorporating a second phase, such as elastomers, 1-3 thermoplastic polymers, 4-6 nanoparticles 7-9 and block copolymers (BCPs). [10][11][12][13][14][15][16] For elastomers or thermoplastic polymers, it usually requires an optimizing loading of ca. 10-20 wt% to obtain a desirable toughening effect.…”