Fig. 4.

Mechanical and fire-retardant properties of various materials. a Stress–strain curves of the core–sheath PCCs with different BNNS loading. b Optical photographs of the PEG@TPU/BNNS-es film under curling, folding and knotting conditions (top), and before and after shape recovery (bottom). c Thermal conductivity versus elongation at break of PEG@TPU/BNNS-es films and previously reported flexible PCNs [31, 33, 41, 47, 49, 50]. d Optical photographs showing the burning of various material by an alcohol lamp. e Ignition delay time of TPU and different PCNs