Abstract
The outstanding diffusivity and permeability of supercritical carbon dioxide (scCO2) are extremely beneficial for grafting reaction. In this work, aramid fibers (AF) are modified in scCO2 by glycidyl-polyhedral oliomeric silsesquioxane (POSS) with 2-ethyl-4-methylimidazole (2E4MZ) on the basis of cleaning with acetone. The surface morphology and chemical structure of the modified AF were measured and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM), Thermogravimetric (TG), and Atomic force microscope (AFM). The interfacial shear strength (IFSS) was measured by a micro-bond pull-out test, then the modified AF/EP composites were prepared and the interlaminar shear strength (ILSS) was characterized. Research has shown that some of the glycidyl-POSS molecular chains permeated into the surface of the fiber and grafted onto the surface of the AF after modification, and the other glycidyl-POSS self-assembled on the surface of the fiber. XPS indicated the introduction of C–O and –COO–, which confirmed the existence of chemical reactions between AF and glycidyl-POSS. AFM and SEM images revealed that 2E4MZ, not only promoted the grafting reaction of glycidyl-POSS, but also intensified the self-assembly of glycidyl-POSS, both of which increased the roughness of the fiber. A monofilament tensile test and micro-bond pull-out test showed that there was a negative effect on the tensile strength after scCO2 processing. The tensile strength of modified AF, with glycidyl-POSS, increased the highest strength of 25.7 cN dtex−1, which was 8% higher than that of pristine AF. The improvement of ILS roughness and the polar chemical groups produced in grafting reaction. These results indicated that AF, treated in scCO2, with glycidyl-POSS, which is a suitable way of fiber modification, can significantly improve the surface adhesion of AF reinforced composites.
Highlights
Aramid fiber (AF), called aromatic polyamide fiber, is a new type of high performance industrial fiber with high modulus, high strength, low density, high temperature resistance, low elongation at a break and low lag loss
It was found that two distinct characteristic diffraction peaks appeared nearby 2θ = 20.0◦, 23.8◦, which correspond to [110] and [200], indicating that the crystal type of AF does not change after surface cleaning and surface grafting treatment with glycidyl-polyhedral oliomeric silsesquioxane (POSS) solution [9,12]
It was found that two distinct characteristic diffraction peaks appeared nearby 2θ = 20.0°, 23.8°, which correspond to [110] and [200], indicating that the crystal type of AF does not change after surface cleaning and surface grafting treatment with glycidyl-POSS solution [9,12]
Summary
Aramid fiber (AF), called aromatic polyamide fiber, is a new type of high performance industrial fiber with high modulus, high strength, low density, high temperature resistance, low elongation at a break and low lag loss. AF has disadvantages, such as surface smoothness, high crystallinity, and low chemical activity, which result in weak interfacial adhesion between the fiber and matrix materials [1,2,3]. The development of novel and effective modification technology, to improve interfacial adhesion, is an issue. In order to improve the surface adhesion between fibers and matrix materials, two ways were used for AF modification. One was a physical method [4,5], and the Polymers 2019, 11, 700; doi:10.3390/polym11040700 www.mdpi.com/journal/polymers. The commonly used chemical modification methods include surface grafting [6,7], surface modification by plasma [8,9], and ultrasonic infiltration [10]. The surface coating as a physical method has been widely used because of simple equipment and convenient operation
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