Thermal release of vegetable oils loaded in hydrophobic polymer nanoparticles

Abstract

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.

Bio-Based Coatings for Paper Applications

“…A new way to make hydrophobic paper has been discussed by combining the layer-by-layer (LbL) technique with the adsorption of a colloidal paraffin wax onto the multilayer structure [167]: thermal curing for 30 min at 160 °C can initiate the cross-linking between the adsorbed layers and cellulose fibers, which further increases the surface roughness followed by an increase in contact angle up to 150°, probably because of intensification of wax hydrophobic properties. Especially, the functionality of the SMI/oil nanoparticle coatings with encapsulated oils as presented in the previous paragraph has been enhanced by studying the controlled thermal release of oil during heating up to 250 °C [168], affecting the surface hydrophobicity of coated papers by exposure of oil.…”

Exploiting thermally-reversible covalent bonds for the controlled release of microencapsulated isocyanate crosslinkers

“…change in pH or solvent), [10,11] light, [12,13] ultrasound [14,15] and exposure to elevated temperature. [16][17][18][19][20][21][22][23][24] Release of the core contents from microcapsules using heat can be achieved by heating above the boiling point or degradation temperature of the encapsulated core to increase the internal pressure sufficient to cause rupture of the microcapsule shell. [17,18,22] This approach has been further developed by adhering microcapsules containing blowing agents to magnetic particles -upon application of a magnetic field the particles oscillate creating localised hotspots sufficient to induce degradation of the encapsulated blowing agent, raising the internal pressure and bursting the microcapsules.…”

“…A similar strategy has incorporated polymers with low glass transition temperatures (Tg) within the microcapsule shell -upon reaching the Tg, the microcapsule shell collapses and the core is released. [24] More recently, the thermal release of the core from microcapsules has been achieved by incorporating thermallyreversible Diels-Alder adducts within the shell wall of polyelectrolyte microcapsules synthesised using a complex coacervation technique. [ Certain covalent bonds are known to undergo a reverse reaction when exposed to heat.…”