Investigation of Melting Behaviors and Crystallinity of Linear Polyamide with High-Aliphatic Content

The melting behaviors and crystal structures of a long alkyl chain polyamide and nylon 18 18, were investigated under annealing and isothermal crystallization conditions. Nylon 18 18 showed multiple melting peaks in differential scanning calorimetry (DSC) thermograms depending on thermal history of the samples. The origin of the multiple melting peaks may be a result of a melting and recrystallization mechanism during DSC scans. Wide-angle X-ray diffraction patterns showed two new diffraction peaks, which appeared at 0.44 and 0.37 nm, and are characteristic peaks of alpha-form (triclinic structure) of even-even nylons with increasing annealing temperature. The intensities of these peaks increased, and they split further apart, with elevated annealing temperatures. The solid-state (15)N CP/MAS NMR spectra of the nylon 18 18 samples that had been quenched and annealed also confirmed the alpha-crystalline form. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 92-98, 2012