Role of hardener, crosslinker, and pH in bare process of urea-formaldehyde polymerization and for in situ encapsulation of linseed oil

In this study, urea-formaldehyde polymerizations in bare process and for in situ encapsulation of linseed oil (LO) have been scrutinized either at pH 3.5 or in inherently developing acidic pH. The solid-state carbon nuclear magnetic resonance (C-13-NMR) revealed that the hardener and the crosslinker (NH4Cl and resorcinol) resulted in the formation of methylene linkage. The addition of NH4Cl and resorcinol slightly decreased the thermal stability of poly(urea formaldehyde) (PUF) resin. Optical microscopy (OM) images and scanning electron microscopy (SEM) micrographs show that most regular shapes of capsules were obtained when NH4Cl and resorcinol were used in the regular reaction medium. The increment of NH4Cl amount up to 0.124 mol resulted in a 41% decrement of capsule size, whereas increment resorcinol amount up to 0.062 mol increased the size by 14%. The capsule size range was found to be between 60 and 100 mu m. The capsules had a hardness of 22-74 MPa and an elasticity of 0.5-1.5 GPa. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46947.