Mechanical Properties of the Epoxy Resin Composites Modified by Nanofiller under Different Aging Conditions

The materials used were commercially available bisphenol-A EP (Yehao Co., Ltd. Wuxi, China), JD-230 curing agent (Qiwei Chemical Co., Ltd. China), and halloysite nanotubes (HNTs, Mingchuag Technology Co., Ltd. China).For the preparation of neat EP and its composites, mix EP and curing agent and stir for about 30 minutes. Then, the mixture was made available for a vacuum drying oven to remove bubbles, and then, the resin composites were poured into the mold. Afterward, in the curing process, a two-step curing process was used for a total of 5 hours, and then, the composites were cooled to room temperature.For the preparation of HNT/EP nanocomposites, HNTs were ultrasonically dispersed in 50 ml acetone, and the HNT acetone dispersion was added to that appropriate amount of EP to obtain 2 wt.% content in a beaker under stirred effect for 3 h. And then, the mixture was put into a vacuum drying oven to remove bubbles. Afterward, in the curing process, a two-step curing process was used for a total of 5 hours, and then, the nanocomposites were cooled to room temperature.Neat EP and HNT/EP nanocomposites were soaked in deionized water at different temperatures (20°C, 40°C, and 60°C), HCl solution (5 wt.%) at 20°C, and NaOH solution (10 wt.%) at 20°C for 720 h. These conditions are generally applied in some aging tests reported in previous studies .Sudden temperature changes of neat EP and HNT/EP nanocomposites from the hot chamber (100°C) for about 7 min to the cold chamber (0°C) for about 3 min were applied, and the thermal shock cycling (TSC) was repeated 100 cycles, which is similar to TSC test reported in previous studies .Composite aging conditions were combined soaking condition with TSC condition. The samples are firstly soaked in deionized water, HCl solution, and NaOH solution at 20°C, and then, they are dried and employed in TSC for 100 repeated times.The tensile test is carried out by the universal material testing machine (MTS810, USA), and the test rate is 2 mm/min. Referring to GB/T2567-2008, the resin casting was machined in the appropriate size. To ensure the accuracy of the data, the experiment was repeated five times, and the calculated average value was used in this study.