Production of thermoregulating slurries constituted by nanocapsules from melamine-formaldehyde containing n-octadecane

Abstract

The development of novel thermal fluids having large thermal energy storage (TES) capacity represents a research field of growing interest nowadays. One of the most explored alternatives is the employment of slurries containing encapsulated Phase Change Materials (PCM) at nano-scale range to avoid pumping problems. Slurries constituted by capsules from melamine-formaldehyde (MF) polymer containing n-octadecane (C18) have been synthesized by varying the paraffin/polymer (C18/MF) mass ratio within 1.50–4.00, in one single reaction step process, without waste generation and non-requiring additional purification treatments. All synthesized products presented high fluidity (viscosity around 4 mPa·s); Zeta-potential (ζ) values lower than −45 mV and pH values comprised between 5.5 and 6.0. Nevertheless, the thermal and physical properties of the slurries were function of the 18/MF mass ratio. While above a C18/MF mass ratio of 3.00 the slurry presented an undesirable large amount of non-encapsulated PCM, those ones produced with a C18/MF mass ratio bellow 3 exhibited high encapsulation yield and monodisperse particle size distribution (PSD). The slurries produced with C18/MF mass ratios larger than 2.33 satisfied the European Commission and ISO/TS 80004–1 classification as nanomaterials. Therefore, the highest encapsulation yield (98.7%), the dn0.5 of 63.7 ± 10.2 nm and the spherical shape and smooth morphology of nanocapsules allowed to select the slurry synthesized with C18/MF mass ratio of 2.33 as the optimal nano encapsulated PCM slurry (NPCS). This nanoslurry exhibited a latent heat of ~23 J/g, being constituted by 14.44 wt% of nanocapsules having a latent heat of 125.85 J/g. Finally, the properties of this NPCS are better than the reported in literature for this type of slurries, being suitable to be applied as thermal fluid in thermal energy storage active systems.