Fig. 6

Self-healing tests for PI–xNA at room temperature. a Optical microscopic images of a razor scratch on a PI–55Na film surface healed at 28 °C for various periods. The scale bar is 200 μm. b. Photographs of the healed PI–90Na films before and after stretching. The PI–90Na film was cut into completely separate pieces using a razor blade, and one cut film was painted black. c and d Stress–strain curves of PI–55Na (c) and PI–90Na (d) films healed at 28 °C for the indicated periods. The stretching speeds were 200 mm min⁻¹ and 50 mm min⁻¹ for PI–55Na (c) and PI–90Na (d), respectively