Thermal release of vegetable oils loaded in hydrophobic polymer nanoparticles
The encapsulation of vegetable oils during imidization of poly(styrene-co-maleic anhydride) provides stable aqueous dispersions of oil-filled nanoparticles with 50 wt% oil. The functionality of nanoparticles with soy-, corn-, rapeseed-, sunflower-, castor-, and hydrogenated castor-oil, can be controlled by thermal release upon heating at 120–250°C for 2 min to 6 h. In a first part, the intrinsic thermal properties of the nanoparticles have been determined by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The differences in calculated imide content illustrate that the transition phenomena depend on complex interactions between the oil and imide phase. The TGA results show that bursting of the particles is not a main release mechanism while the oil is either progressively released below or above the glass transition temperature, which is best monitored by DMA. In a second part, the release profiles are determined from FTIR and Raman spectra following different trends according to the type of encapsulated oil and nanoparticle morphology, i.e., solid, nanoporous, cauliflower-like, or true core-shell. Also the interference with imidization during heating influences the oil release. The kinetics and mechanism of oil release can be systematically described after fitting with mathematical models.



Practical applications: The nanoparticles can be incorporated as coating pigments for packaging paper or used for surface functionalization of natural fibers, where controlled release of the oil provides a required degree of hydrophobicity.







Different types of vegetable oil were incorporated in imidized nanoparticles, resulting in various particle morphologies (e.g., solid, nanoporous, cauliflower-like, or true core-shell) with characteristic release profiles of the oil as a function of temperature and time.