Abstract
We report on a versatile method for chemically grafting multiwalled carbon nanotubes (MWCNTs) onto the surface of conventional glass fibers (GFs), as well as depositing further silica (SiO2) or superparamagnetic (SPM) magnetite (Fe3O4) nanoparticles (NPs) creating novel hierarchical reinforcements. The CNT-grafted GFs (GF-CNT) were utilized further as the support to decorate nano-sized SiO2 or Fe3O4 via electrostatic interactions, resulting finally into double hierarchy reinforcements. SiO2 NPs were first used as model nano-particulate objects to investigate the interfacial adhesion properties of binary coated GFs (denoted as GF-CNT/SiO2) in epoxy matrix via single fiber pull-out (SFPO) tests. The results indicated that the apparent interfacial shear strength (IFSS or τapp) was significantly increased compared to the GF-CNT. Fe3O4 NPs were assembled also onto CNT-grafted GFs resulting into GF-CNT/Fe3O4. The fibers exhibited a magnetic response upon being exposed to an external magnet. Scanning electron microscopy (SEM) revealed the surface morphologies of the different hierarchical fibers fabricated in this work. The interphase microstructure of GF-CNT and GF-CNT/SiO2 embedded in epoxy was investigated by transmission electron microscopy (TEM). The hybrid and hierarchical GFs are promising multifunctional reinforcements with appr. 85% increase of the IFSS as compared to typical amino-silane modified GFs. It could be envisaged that, among other purposes, GF-CNT/Fe3O4 could be potentially recyclable reinforcements, especially when embedded in thermoplastic polymer matrices.
Highlights
Fiber reinforced polymer (FRP) composites represent a unique family of structural materials combining extraordinary specific strength and stiffness, both of which can be exploited in various high performance applications i.e., aerospace, aeronautics, automotive, energy, etc. [1]
The successful functionalization of multiwalled carbon nanotubes (MWCNTs) by oxidation and further SOCl2 treatment could be proven by the obtained transmission electron microscopy (TEM) microstructures, since a great number of defects could be observed in Figure 2b (MWCNT-COCl)
The size of SiO2 and Fe3O4 NPs was determined from the corresponding TEM images, while the mean diameter and standard deviation were derived from the measurement of around 100 NPs
Summary
Fiber reinforced polymer (FRP) composites represent a unique family of structural materials combining extraordinary specific strength and stiffness, both of which can be exploited in various high performance applications i.e., aerospace, aeronautics, automotive, energy, etc. [1]. There are many different methods to increase the interfacial interaction and interfacial bond strength between the polymer matrix with the reinforcing fibers, employing fiber surface modification protocols [6] Such methods endow end terminal surface functional groups that could increase the wettability, as well as the chemical interaction via covalent or non-covalent bonds with the polymeric resin [7]. It can be realised that upon aiming to achieve a high mechanical performance composite material, it is a prerequisite that optimal interphases with high interfacial adhesion strength, otherwise defined as interfacial shear strength (IFSS), should be developed This will further facilitate the efficient stress transfer from the continuous polymer matrix phase to the reinforcing fibers [10]
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