ABSTRACT
Phenyl polyhedral oligomeric silsesquioxane (POSS) is modified onto the GO surface by using the strong π-π coupling between a large number of benzene rings at the end of the phenyl POSS structure and the graphite structure in the GO sheet, realizing the non-covalent functionalization of GO (POSS-GO). The POSS-GO-reinforced EP (POSS-GO/EP) composite material is prepared using the casting molding process. The surface morphology of GO before and after modification and its peel dispersion in EP are examined. Furthermore, the mechanical properties, cross-sectional morphology, and reinforcement mechanism of POSS-GO/EP are thoroughly examined. The results show that the cage-like skeleton structure of POSS is embedded between the GO layers, increasing the spacing between the GO layers and leading to a steric hindrance effect, which effectively prevents their stacking and aggregation and improves the dispersion performance of GO. In particular, the 0.4 phr POSS-GO/EP sample shows the best mechanical properties. This is because, on the one hand, POSS-GO is uniformly dispersed in the EP matrix, which can more efficiently induce crack deflection and bifurcation and can also cause certain plastic deformations in the EP matrix. On the other hand, the POSS-GO/EP fracture cross-section with a stepped morphology of interlaced "canine teeth" shape is rougher and more uneven, leading to more complex crack propagation paths and greater energy consumption. Moreover, the mechanical meshing effect between the rough POSS-GO surface and the EP matrix is stronger, which is conducive to the transfer of interfacial stress and the strengthening and toughening effects of POSS-GO.
ABSTRACT
In order to improve the interface and mechanical properties of aramid fiber (AF)-reinforced epoxy resin (EP) composites (AF/EPs), the surface modification of AF was carried out with atmospheric pressure air plasma, and the effects of plasma treatment time and discharge power on the AF surface and the interface and mechanical properties of AF/EPs were investigated. The results show that, when plasma treatment time was 10 min and discharge power was 400 W, AF showed the best modification effect. Compared to the unmodified material, the total content of active groups on the surface of AF increased by 82.4%; the contact angle between AF and EP decreased by 20%; the interfacial energy and work of adhesion increased by 77.1% and 19.1%, respectively; the loss of AF monofilament tensile strength was controlled at only 8.6%; and the interlaminar shear strength and tensile strength of AF/EPs increased by 45.5% and 10.4%, respectively. The improvement in AF/EP interfacial and mechanical properties is due to the introduction of more active groups on the AF surface with suitable plasma processing parameters, which strengthens the chemical bonding between the AF and EP matrix. At the same time, plasma treatment effectively increases the surface roughness of AF, and the mechanical meshing effect between the AF and EP matrix is improved. The synergistic effect of chemical bonding and mechanical meshing improves the wettability and interfacial bonding strength between the AF and EP matrix, which enables the load to be transferred from the resin to the fiber more efficiently, thereby improving the mechanical properties of the AF/EP.
ABSTRACT
To improve the mechanical properties of aramid fiber (AF) reinforced epoxy resin (EP) composites without damaging the strength of the AF body, in this paper, poly(ethyleneimine) (PEI) and aminoated carbon nanotubes (NH2-CNTs) were successfully deposited on the AF surface layer by layer using poly(dopamine) (PDA) as the initial layer. The modified aramid fibers PDA-AF, PEI-PDA-AF, and NH2-CNTs-PEI-PDA-AF were prepared. The microstructure and chemical composition of the AF surface at different modification stages were systematically characterized. The interfacial properties, mechanical properties, and strengthening mechanism of AF surface-modified composites were studied. The results showed that with the successful deposition of PDA, PEI, and NH2-CNTs layer by layer, the interfacial properties and mechanical properties of the composites gradually improved. Among them, NH2-CNTs-PEI-PDA-AF showed the best strengthening effect. Compared with the unmodified aramid fiber (R-AF), the monofilament tensile strength of NH2-CNTs-PEI-PDA-AF increased by 8.1%, the contact angle with EP decreased by 21.9%, and the interface energy and adhesion energy increased by 115 and 21.4%, respectively. Compared with R-AF/EP, the interlaminar shear strength (ILSS), bending strength, and tensile strength of NH2-CNTs-PEI-PDA-AF/EP were increased by 75, 44.5, and 14.9%, respectively. The significant improvement of the interface properties and mechanical properties between NH2-CNTs-PEI-PDA-AF and EP can be attributed to the introduction of a large number of amino active groups in the NH2-CNTs-PEI-PDA coating layer on the AF surface, which strengthens the chemical-bond cooperation between the AF and EP matrix. At the same time, a large number of NH2-CNTs deposited on the surface effectively increased the surface roughness of AF, improved the mechanical meshing between the AF and EP matrix, and then improved the contact angle, surface energy, and interface bonding strength between the AF and EP matrix. Moreover, a large number of NH2-CNTs on the surface of AF also modified and enhanced the EP in the interface region, which could make the load more effectively transfer from the resin to the fiber, so that AF could carry the load more uniformly, significantly improving the mechanical properties of NH2-CNTs-PEI-PDA-AF/EP.
ABSTRACT
In order to improve the interfacial properties of graphene oxide (GO) and epoxy resin (EP), hyperbranched polyesters with terminal carboxyl (HBP) non-covalently functionalized graphene oxide (HBP-GO) was achieved by strong π-π coupling between hyperbranched polyesters and GO nanosheets. The effects of non-covalent functionalization of GO on the dispersibility, wettability and interfacial properties were analyzed. The mechanical properties and enhancement mechanism of HBP-GO/EP composites were investigated. The results show that the hyperbranched polyesters is embedded in the GO layer due to its highly branched structure, which forms the steric hindrance effect between the GO nanosheets, effectively prevents the agglomeration of GO nanosheets, and significantly improved the dispersibility of GO. Simultaneously, the contact angle of HBP-GO with EP is reduced, the surface energy, interfacial energy and adhesion work are increased, then the wetting property of HBP-GO is significantly improved. The main toughening mechanism of HBP-GO is microcrack deflection induced by HBP-GO and plastic deformation of the EP matrix. In the microcrack propagation zones, HBP-GO may produce the pinning effect near the microcrack tips and change their stress state, resulting in microcrack deflection and bifurcation. So, the microcrack propagation path is more tortuous, which will consume much more fracture energy. Therefore, the mechanical properties of the HBP-GO/EP composites are greatly improved.
ABSTRACT
Epoxy resin was grafted to graphene oxide (GO) via esterification reaction and 3D structure hybrids were prepared by combining 1D carbon nanotube (CNT) and 2D functionalized GO through π-stacking interaction. Epoxy composites filled with 3D structure hybrids were fabricated. The results show that functionalized GO effectively improves the dispersibility of CNTs in epoxy matrix due to good compatibility. Excellent mechanical properties were achieved by epoxy composites filled with 3D structure hybrids. The fracture surface analysis indicated improved interfacial interaction between 3D structure hybrids and epoxy matrix, which may due to the covalent bonding formed between the epoxy molecular chain grafted on EGO and the hardener agent during the curing process. In the 3D structure filler network, the mechanisms of crack deflection/bifurcation induced by functionalized GO make the crack path tortuous, which causes the cracks to encounter more CNTs and then promote the mechanisms of CNT fracture and crack bridging, resulting in more energy dissipation. This is the key mechanism for its excellent reinforcing and toughening effects.