Solvent-induced crack growth in poly(methyl methacrylate)/multiwalled carbon nanotube composites

Understanding the structural integrity of polymer composites in service conditions is of practical importance for the applications of polymer composites. In this work, we investigate the solvent-induced crack growth in poly (methyl methacrylate)/multiwalled carbon nanotube (PMMA/MWCNT) composites in respective organic solvents of 2-ethylhexyl alcohol (2 EA), cyclohexanol, and 1-butanol at different temperatures after being immersed in methanol at 50 degrees C for 25 min. The areal density of crack lengths and growth rate of a single crack in the PMMA/MWCNT composites increase with the immersion time and temperature for the solvents of 2 EA and cyclohexanol. The areal density of crack lengths in the PMMA/MWCNT composites immersed in 1-butanol is largest at 30 and 40 degrees C and smallest at 50 degrees C. The 1-butanol solvent causes the fastest, steady-state crack growth at 30 and 40 degrees C and the slowest crack growth at 50 degrees C. Increasing the fraction of MWCNTs reduces the areal density of crack lengths and the growth rate of a single crack in the healed and non-cracked areas. The crack growth is controlled by a thermally activated process. The crack growth rate is faster in the healed area than in the non-cracked area for the same composite and solvent. The activation energy for the motion of polymer chains associated with the single-crack growth in the non-cracked area is smaller than that for solvent-induced cracking because the interaction between cracks hinders crack growth.