Simultaneously stiffening and toughening epoxy by urea treated hydroxylated halloysite nanotubes

Epoxy and its composites have been extensively applied in widespread applications, such as encapsulation of electronics, automobile parts, aircraft components, and so on. The stiffening and toughening of epoxy via the incorporation of nanofillers, such as halloysite nanotubes (HNTs), a naturally occurring and low-cost alumino-silicate, have attracted increasing research attention. Herein, we introduce an effective and facile method that substantially enhances the interface of hydroxylated HNTs (h-HNTs) and epoxy matrix by the introduction of urea molecules. As confirmed by the characterization results, urea formed hydrogen bonds with the external surface of the h-HNTs and covalent bonds with the epoxy matrix. The resultant epoxy/h-HNT-urea nano -composites exhibited significant enhancements simultaneously in tensile strength, Young's modulus, and fracture toughness by 23.4%, 31.4%, and 61.4%, respectively, as compared with the neat epoxy. Through systematic investigation, it was determined that micro-cracking, nanotube bridging, and crack pinning were responsible for the toughening of the epoxy/h-HNT-urea nanocomposites.

Automated summary

Epoxy and its composites have been widely used in various applications, and the incorporation of nanofillers, such as halloysite nanotubes, has been shown to strengthen and toughen the epoxy. In this study, a method using urea molecules to enhance the interface between hydroxylated halloysite nanotubes (h-HNTs) and the epoxy matrix was introduced. The resulting epoxy/h-HNT-urea nanocomposites exhibited significant improvements in tensile strength, Young's modulus, and fracture toughness due to micro-cracking, nanotube bridging, and crack pinning.