Fabrication of torsion-resistant alumina fibers via coating polyurethane adhesives

Abstract

Alumina fibers are high-performance ceramic fibers renowned for their mechanical strength, high elastic modulus, thermal stability, and superior creep resistance. Their applications are in aerospace thermal protection systems, thermal insulation for nuclear reactors, and structural reinforcement for high-temperature industrial equipments. However, the complex multiaxial loading conditions prevalent in the automotive and construction sectors, fibers are susceptible to intricate failure mechanisms including transverse stress concentration and torsional buckling. Consequently, their intrinsic brittleness limits their broader applicability. To overcome this limitation, a flexible composite coating was formulated using polyurethane (PU) adhesive as the matrix, 3-glycidoxypropyltrimethoxysilane (KH560) as the compatibilizer, and tetrahydrofuran (THF) as the solvent. The primary objective of this study is to enhance the mechanical performance of alumina fibers, by ameliorating their inadequate torsional resistance. The effects of this coating on fiber microstructure and mechanical behavior were evaluated using scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, INSTRON universal testing machine, and a dedicated torsion tester. The results demonstrated that the PU–THF coating increased the static torsional twist angle of alumina fibers from 20–40 wt%. Mechanistic analysis reveals that the coating enhanced fiber performance through two key mechanisms: Filling inherent surface defects and forming robust chemical bonds at fiber-coating interface. These results indicated that the PU–THF coating effectively improved the mechanical integrity of the alumina fibers. This work presents a viable strategy for surface modification and toughening of ceramic fibers, providing novel insights into the design of multifunctional coatings for high-performance inorganic fiber reinforcements.