Epoxy, a thermoset resin with myriad applications, suffers from drawbacks such as brittleness and lack of fracture toughness. A breakthrough in reinforcing epoxy-based composites can be achieved by developing cost-effective and environment-friendly nanoparticles with high elastic modulus and low density such as cellulose nanocrystals (CNCs). In this research work, CNCs were used to reinforce biaxial E-glass fabric/epoxy composite. The impact of CNCs mixing medium, i.e. hardener or a mixture of epoxy and hardener, was highlighted, as also illustrated in the graphical abstract. Biaxial E-glass fabric/CNCs/epoxy (BE2CE) nanocomposite containing optimum content of CNCs exhibited significantly enhanced mechanical properties, i.e. tensile strength and modulus, fracture toughness and Charpy impact strength. This was discussed considering synergistic contribution of CNCs and E-glass fibers to reinforce epoxy-based composite, which was manifested by increased E-glass fiber-epoxy interfacial shear strength (IFSS) at the presence of CNCs. The IFSS was measured using single fiber micro-droplet pull-out test. Additionally, regardless of CNC content, considering hardener as the mixing medium yielded superior results in manufacturing BE2CE nanocomposite.

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Incorporation of hollow fibers in polymer base composites has gained great interest due to their flexibility and lightweight structure. Among many research studies on this subject, the mechanical performance of polyester hollow fiber/E-glass reinforced polymer composites has not been investigated. The main objective of the present work was to investigate the fracture toughness and impact resistance of E-glass/epoxy composites hybridized by a separate layer of polyethylene terephthalate hollow fibers (PETHFs). The samples were prepared by placing a layer of PETHFs in different contents (0, 0.23, 1.18, or 2 wt.%) and in two different forms of filaments (PETHF-FIs) or staple fibers (PETHF-STs) between two layers of biaxial or triaxial E-glass fabrics. The mechanical behaviors of the samples were investigated by performing a set of tensile and impact tests. Scanning Electron Microscopy (SEM) and Field Emission Scanning Microscopy (FESEM) were also used to evaluate the surface morphologies of the hollow fibers and the fractured samples. The results revealed that, unlike PETHF-FIs, PETHF-STs could weaken the mechanical performance of the pristine E-glass/epoxy composites. The internal channel blockage of PETHF-STs was observed in the FESEM images of the fractured PETHF-STs hybrid samples. The highest toughening effects were observed with incorporation of 1.18 wt.% PETHF-FIs in biaxial E-glass/Epoxy composites and 2 wt.% PETHF-FIs in triaxial E-glass/Epoxy composites. The highest value of impact resistance belonged to the samples hybridized with 2 wt.% of PETHF-FIs. Crack deflection, fiber pull out, and fiber stretching were the predominant fracture mechanisms observed in the PETHF-FIs hybrid composites.