Abstract
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’s) led to the highest fracture toughness and fracture energy in the study, KIc = 2.18 MPa·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·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.
Highlights
Epoxy resins are a class of highly cross-linked thermoset polymers used in a wide range of applications, e.g. automotive, aerospace, electronics, adhesives
The fracture energy can be increased by adding different modifiers to the epoxy resin, e.g. carboxyl-terminated butadiene acrylonitrile (CTBN), which can phase separate in micron-sized domains into the epoxy and increase its toughness, with a loss of strength and a deterioration of the thermal properties [1,2]
Various studies explained that the block copolymers (BCP) morphology, and the fracture mechanics properties of epoxy BCP systems depends on the BCP-block composition [18], the molecular weight of the immiscible block [9], the length of the BCP [10,19], the curing agent [20], and the curing process [21]
Summary
Epoxy resins are a class of highly cross-linked thermoset polymers used in a wide range of applications, e.g. automotive, aerospace, electronics, adhesives. The fracture energy can be increased by adding different modifiers to the epoxy resin, e.g. carboxyl-terminated butadiene acrylonitrile (CTBN), which can phase separate in micron-sized domains into the epoxy and increase its toughness, with a loss of strength and a deterioration of the thermal properties [1,2]. Dean et al [16] investigated the toughening effect of diblock copolymers in bisphenol A based epoxy resin cured by a tetrafunctional aromatic amine They reported nano-sized spherical BCP micelles and vesicles as dominating second phases. Totally different structures of triblock copolymer (ABA) toughened bisphenol A based epoxy in the nano-range were reported by Kishi et al [17], who quantified the morphology and respective fracture mechanics properties. EP EP_2 BCP EP_4 BCP EP_6 BCP EP_8 BCP EP_10 BCP EP_12 BCP EP_3 TiO2 EP_5 TiO2 EP_7 TiO2 EP_3 TiO2_4 BCP EP_3 TiO2_6 BCP EP_3 TiO2_8 BCP
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