Influence of the emulsifying system to obtain linseed oil-filled microcapsules with a robust poly (melamine-formaldehyde)-based shell

In the present study, PMF-based microcapsules (MCs) containing linseed oil were synthesized via a two-stage in-situ polymerization method. As shell material was synthesized, micrometric spherical PMF particles, which could be mistaken for microcapsules, were isolated at the bottom of the vessel. This event drew our attention to the relevance of using characterization techniques to verify the effective encapsulation of core material. The physical properties of microcapsules obtained by four synthesis methods were examined and compared through optical microscopy and scanning electronic microscopy (SEM). Different combinations of dodecylbencensulfonate (SDBS) solution and polyvinyl alcohol (PVA) solution were chosen for the two first syntheses. A third synthesis was conducted with the couple of emulsifiers formed by purified gum arabic (GA) and sodium dodecylsulfate (SDS). The fourth batch, with the emulsifying system based on solutions of both commercial GA in grain and SDS, was the only one that allowed to obtain robust MCs. Fortunately, these MCs could undergo the conditioning operations leading to a powder of linseed oil-filled MCs with an estimated average diameter of 30.5 μm. Further characterization was carried out on synthesis products of the successful batch. Confocal Raman Microscopy was used for chemical characterization of synthesis products. Thermo Gravimetric Analysis (TGA) and Scanning Differential Calorimetry (DSC) studies were performed to evaluate thermal behavior. In addition, the use of characterization techniques helped to prove the effective encapsulation of linseed oil and the existence of a small fraction of MCs at the bottom layer obtained by the centrifugation of the reaction medium.