Modelling and optimization of epoxy-PMMA microcapsule synthesis parameter: A response surface methodology approach

The efficiency of self-healing microcapsule in restoring damages incurred by polymeric or composite materials is heavily dependent on modelling of encapsulation conditions to achieve optimized microcapsule with desired characteristics. This study modelled the effects of encapsulation conditions (core–shell ratio, agitation rate, and temperature) on the morphological, chemical, and thermal characteristics of epoxy-polymethylmethacrylate (epoxy-PMMA) microcapsules using response surface methodology (RSM). Epoxy-PMMA microcapsules were synthesized by encapsulating epoxy resin in polymethylmethacrylate (PMMA) at varied encapsulation conditions using solvent evaporation method. The morphology of the synthesized microcapsule using optical microscope (OP) revealed that the microcapsules are either mononuclear or irregular capsule types. The modelled effect showed that microcapsule percentage yield varied between 74.96 to 96.56%, was highly influenced by core–shell ratio and the effect of studied encapsulation conditions on percentage yield was best described by quadratic model. The core content of the microcapsules varied between 54.8 to 67.2%, observed to be highly influenced by both core–shell ratio and agitation rate which fit into linear model. The microcapsule average diameter was between 26 to 74 μm, highly influenced by agitation rate and fit linear model. Fourier transform infrared (FTIR) spectra of synthesized microcapsules revealed epoxy characteristic peak of C–O–C at 913 cm−1 and C–O-ph stretching at 1032 cm−1. C–O doublet of PMMA was observed at 1386 cm−1 and 1189 cm−1. Thermogravimetric analysis (TGA) of epoxy-PMMA microcapsule showed three stages of decomposition attributed to water evaporation, epoxy degradation, and PMMA shell degradation. Lastly, optimization process to achieve maximum yield, maximum core content and minimum capsule diameter was obtained with core–shell ratio of 1.5:3 and agitation rate of 1000 rpm at 40 °C. The synthesized epoxy-PMMA microcapsules exhibited chemical, thermal, morphological stability and the models can be optimized to achieve microcapsule with desired characteristics.