Self‐healing efficiency of cinnamaldehyde‐crosslinked soy protein resins with elongated soy protein microcapsules

Abstract Self‐healing green thermoset soy protein isolate (SPI) based resins, crosslinked with cinnamaldehyde (CA), were developed. Self‐healing was achieved using elongated microcapsules (MCs) as against spherical MCs that have been used in most earlier studies. MCs containing SPI solution as healant within poly(d,l‐lactide‐co‐glycolide) shells were prepared using Water‐in‐oil‐in‐water (w/o/w) emulsion solvent evaporation (ESE) technique. Process parameters such as sodium tripolyphosphate (STP) and poly(vinyl alcohol) (PVA) concentrations and stirring speed were optimized to obtain elongated MCs. The average aspect ratio of MCs was over four. SPI resins crosslinked with 10% CA (10%CA‐SPI) increased Young's modulus and fracture stress by 54% and 87%, respectively, compared with their noncrosslinked counterpart. The resins containing 15% elongated MCs (15%MC‐10%CA‐SPI) showed self‐healing efficiencies of over 42% in fracture stress and about 35% in toughness recovery, after 24 h of healing. Improvement in self‐healing can be attributed to the high aspect ratio of the MCs that increases the probability of MCs being in the path of the microcracks and releasing the healant. Elongated MCs also contain higher amount of healant than spherical ones of same diameter. Self‐healing resins and composites can not only help prevent their premature failure but also improve their performance as well as service life and safety.