Noncovalently Functionalized Halloysite Nanotubes\nfor Use in Reinforced Polymer Composites

Abstract

The inorganic halloysite nanotube\n(HNT) is a promising type of\nnaturally occurring fillers with many important uses in different\nfields. An HNT has a relatively low content of hydroxyl groups on\nits surface, which makes it relatively hydrophobic, although this\nis not always sufficient to guarantee good interfacial adhesion in\ncomposite systems. Further surface treatment is required to improve\nthe compatibility of HNTs with polymer matrixes, maximizing interfacial\ninteractions. The aim of the present work was to study a noncovalent\nfunctionalization of halloysite with 2,2′-(1,2-ethenediyldi-4,1-phenylene)\nbisbenzoxazole (EPB), based on electron transfer, for further use\nof EPB as a coupling agent in polymer/HNT compatibility. A set of\ncharacterization techniques were performed to evaluate the chemical\nand physical properties and evidence the functionalization. The results\nrevealed the surface modification of halloysite upon functionalization.\nEmphasis was for powder wettability by tensiometry based on Washburn\nbecause no studies about halloysite powders using this technique could\nbe found in the literature. The results demonstrate a reduction in\nthe total surface energy of the system, usually accompanied by a reduction\nin the polar component upon HNT modification.