Regulation of mechanical properties and self-healing performance of polyurethane nanocomposites by tuning the contents of free and associated hydrogen bonds

Abstract

Hydrogen bonds facilitate self-healing of polymers. However, free and associated hydrogen bonds have different effects on mechanical properties and self-healing performance. Here, both unmodified nano-silica (nano-SiO₂) and nano-SiO₂ modified by 2-ureido-4[1H]-pyrimidinone (UPy) and KH-550 (UK–SiO₂) were used to fill polyurethane (PU). The mechanical properties and self-healing properties of the PU nanocomposites can be regulated by changing the ratio of the two kinds of nano-SiO₂. In the PU containing 2 wt% unmodified nano-SiO₂ and 1 wt% UK–SiO₂, the UK–SiO₂ particles hinder the agglomeration of the unmodified nano-SiO₂ particles and facilitate the formation of hydrogen bonds between PU chains and the nanofillers. More associated hydrogen bonds exist, resulting in a higher mechanical strength but a weaker self-healing ability. In the PU containing more UK–SiO₂, the formation of hydrogen bonds between the unmodified nano-SiO₂ particles and between the unmodified nano-SiO₂ particles and PU chains is restricted by the UK–SiO₂ particles, leading to a lower mechanical strength but a stronger self-healing ability.