Influences of processing methods and chemical treatments on fracture toughness of halloysite–epoxy composites

This study presented experimental reports on effects of processing methods (mechanical mixing and ball milling homogenization) on the fracture toughness of as-received and phenylphosphonic acid (PPA) treated halloysite–epoxy composites. It was demonstrated that with halloysite added, the composites held higher fracture toughness value than that of neat epoxy. Large-sized particle clusters occurred during mechanical mixing process can significantly decrease by ball milling homogenization and much more uniform dispersion was obtained in the cured composites. With PPA treatment, the morphology of halloysite changed from nanotubes to nanoplatelets with a substantial increase in the total contact area between halloysite and epoxy, it further enhanced fracture toughness in PPA-treated composites. The fracture toughness mechanisms of each nanocomposite with different processing methods and chemical treatments have been illustrated.

► Fracture toughness values and mechanisms change with processing and treatment varies. ► Ball milling homogenization causes more uniform dispersion of smaller HNT in EP. ► PPA treatment causes the change of HNT morphology from nanotubes to nanoplatelets. ► Ball milling and PPA treatment cause HNT/EP have higher values of toughness.