Improving the mechanical performance of phase change microcapsule/epoxy composites via alternately enhancing interface bonding and strength of microcapsules

Microcapsules containing phase change materials (MPCMs) can be integrated with polymeric matrices to develop intelligent thermoregulating composites for applications in temperature management and thermal energy storage. However, the mechanical properties of such composites can be severely compromised due to the weak interfacial adhesion and the poor microcapsule rupture strength. This paper aims to investigate the failure mode of microcapsule/epoxy composites and present corresponding implementable methods to improve their strength. The MPCMs/epoxy composite primarily fails due to poor microcapsule-matrix interface debonding resulting from the poor compatibility between MPCMs and epoxy resin. A silane coupling agent (EPTMS) was employed to modify the surface of MPCMs, forming E-MPCMs, and created a crosslinked interface network during the epoxy curing process. The tensile strength of composite containing 20 wt% E-MPCMs has been improved by 23.55 % while the failure mode switching to microcapsule rupture. Furthermore, the microcapsule shell enhanced by TiO2 nano-reinforcements achieves a 105.20 % improvement in microcapsule rupture strength. The incorporation of EPTMS modified TiO2-MF hybrid microcapsules (ET-MPCMs) resulted in a significant increase of 33.79 % in the tensile strength of ET-MPCMs/epoxy composite with the failure mode changing to microcapsule-matrix interface debonding again. The strategy of alternately enhancing subset properties derived from the competition failure mode of the composite opens new perspectives for the preparation of high-performance multifunctional composites.