To investigate the interfacial effect on properties of epoxyacrylate-silica composites, sub-micron silica particles were synthesized by sol-gel reaction in an ammonia/ethanol solution and their surfaces were endowed with different functional groups by reaction with several silanes including 3-methacryloxypropyl trimethoxysilane (MPTMS), vinyl trimethoxysilane (VTMS), 3-glycidoxypropyl trimethoxysilane (GPTMS) and 3-aminopropyl trimethoxysilane (APTMS). Except the APTMS-modified silica particles due to its severe aggregation, the modified silica particles with size ranging from 150∼250 nm were then added to the pre-synthesized difunctional epoxyacrylate resin at a concentration of 15 phr, in addition to the photo- and thermo-curing agents. Tensile mechanical properties and the fracture toughness were all increased by adding the silica particles into the epoxyacrylate. Particularly, the composite filled with the MPTMS-modified silica particles (EA-MPS15) had the best performance. The reason is that the vinyl double bond of the MPTMS on the surface of the silica particles could took part in the curing reaction of the epoxyacrylate, thus providing strong interfacial chemical bonding between the silica particles and the polymer matrix and also improving the dispersion of the silica particles. The increase of fracture toughness was due to the crack deflection and particle-matrix debonding as evidenced by SEM pictures on the fracture surface.
A dual-curable epoxyacrylate (EA) oligomer with one epoxide group and one vinyl group at each end was synthesized for the application as adhesive sealant in the liquid crystal display panels. However, after UV and thermal cure, the EA resin was brittle with a poor resistance to crack initiation and propagation. Liquid rubbers with different functional end groups were thus tried as toughening agents for the EA resin. Among all the rubber-toughened EAs, the EA-V5A5 added with vinyl-terminated and aminoterminated butadiene-acrylonitrile copolymers (VTBN and ATBN) each at 5 phr had the highest fracture toughness, tensile strength, and elongation at break but a lower initial modulus. To raise the modulus, submicron-sized silica particles (170 nm) with surface vinyl functional groups were further added to the EA-V5A5 to prepare the hybrid composites. Because of interfacial chemical bonding provided by the surface vinyl functional groups, both modulus and fracture toughness were increased by adding silica particles, without any appreciable decrease in extensibility. For the hybrid composite at 20 phr silica particles, the initial modulus, fracture toughness, and fracture energy were raised by 10.3, 100, and 267%, respectively, when compared to the neat epoxyacrylate. Owing to their strong interfacial bonding, the increase of fracture toughness was mainly due to the crack deflection and bifurcation on silica particles, in addition to the rubber particle bridging and tearing as evidenced by SEM pictures on the fracture surface. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41820.
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