Form-stable phase change materials from mesoporous balsa after selective removal of lignin

Abstract

We produce balsa-based structures by selective removal of lignin. The changes that occur in the main components of balsa upon delignification, including tracheids, closed pits and tylosis vessels, allow the development of mesopores and a substantial increase in fluid permeability. Such system is ideally suited as a support of phase change materials, PCM. Vacuum-assisted impregnation with polyethylene glycol (PEG, a PCM), results in a form-stable PCM system (FPCM). The FPCM displays a high encapsulating capacity (83.5%) at temperatures above the melting PEG transition, with a latent heat of 134 J/g and low supercooling (12 °C). The results are rationalized by the affinity between the unidirectional mesoporous structure and the PCM polymer, involving capillary forces and hydrogen bonding. The leakage-proof FPCM outperforms available systems (based on PEG or other PCMs) supported on minerals or other wood species. Compared to the latter group, the results obtained with balsa relate to its morphology and the effect of residual hemicelluloses in hierarchically-aligned cellulose nano- and microfibrils. The FPCMs resist compressive loads and performs stably for at least 200 cycles of heating and cooling. An insignificant loss in latent heat is observed compared to that of pure PEG. The phase transition temperature fluctuation and non-leaking characteristics under load make the balsa-based FPCM a superior alternative for passive heating/cooling, especially for uses at high ambient temperatures. The reversible thermoregulatory capacity, low cost, high efficiency, renewability, and operability of the balsa-supported FPCM, indicate an excellent option for thermal energy storage and conversion devices.