Effect of Hydrothermal Cycling on CNT-Embedded Glass Fiber-Reinforced Polymer Composites: An Emphasis on the Role of Carboxyl Functionalization

In this article, the effect of pristine and carboxyl functionalized carbon nanotube (CNT and FCNT) reinforcement on the durability of glass fiber-reinforced epoxy (GE) composite has been assessed under repeated hydrothermal cycling (HC) and compared with that of control GE composites. Each HC constitutes of 24 h conditioning in a water bath maintained at 15 °C followed by further 24 h water aging at 50 °C. Control GE, 0.1 wt % pristine CNT-embedded GE (CNT-GE) and 0.1 wt % FCNT-embedded GE (FCNT-GE) were exposed to 20, 40, and 60 number of HC in order to assess their durability. Initially, for a lower number of HC, FCNT-GE composite was found to have the best water resistance followed by CNT-GE and GE composites, whereas after 40 and 60 number of HC, the trend got modified. Flexural testing was conducted to evaluate the durability of these composites upon 20, 40, and 60 number of HC. Also, the degree of recovery in the flexural properties of the composites after 60 number of HC was evaluated by conducting desorption process. The cyclic changes in water bath temperature caused interfacial debonding at the CNT/matrix interface resulting in accelerated water absorption and reduced flexural performance. The water absorption by the composites had deleterious effect on their glass transition temperature (T g ) and matrices chemical bonding. The variation in the failure modes in these composites, before cycling and after 60 number of HC, was compared using SEM analysis. Graphical Abstract