Active coating for packaging papers with controlled thermal release of encapsulated plant oils

Abstract

The surface properties and water repellence of paper substrates can be tuned by a waterborne nanoparticle coating containing hybrid organic nanoparticles with encapsulated vegetable oils. In particular, the release of oil from the deposited nanoparticle capsules can be activated upon thermal heating. The specific release tempera-ture allows to control the amount of free oil at the surface and consequent tuning of required hydrophobicity. This study particularly focusses on a detailed monitoring of variations in chemical surface composition upon controlled oil release by means of micro-Raman mapping. The coverage of surfaces with both free oil and imide moieties originating from the organic nanoparticles can be quantified after a calibration between Raman spectra and extraction studies of the nanoparticles. As such, different thermal release profiles were observed depending on the type of encapsulated oils, i.e. polyunsaturated oil (e.g., soy oil, corn oil), mono-unsaturated oil (e.g., rapeseed oil, castor oil), or saturated oil (e.g., hydrogenated castor oil). The oil release can interestingly be related to variations in surface chemistry and water contact angles, as it seems that the surface hydrophobicity increases with the chemical heterogeneity that is quantified by oil content, imide content and iodine value of the oil.