Evaluation of carbonized cotton stalk for development of novel form stable composite phase change materials for solar thermal energy storage

Abstract

Generating energy from the renewable sources is a pathway to attain sustainable energy systems. Utilizing bio-char produced from pyrolysis process as porous material would not only add great value to the waste discards, but also contributes towards enhancing the thermal properties. This work is focussed on the development of form stable phase change material (FSPCM) through a facile impregnation method by introducing cotton stalk biochar (CSB) as porous matrix along with polyethylene glycol having molar mass 10000 g/mol (PEG10000) as PCM. Cotton stalk is an agriculture waste material and biochar was produced by intermediate pyrolysis method at 550 °C. Thermal, chemical and surface characterization tests were executed on seepage free FSPCM (BCPCM4) as it showed no leakage at 60 °C. XRD, FTIR, FESEM, TGA, DSC, Raman spectroscopy and BET analysis were carried out to characterize thermal, chemical and surface properties of BCPCM4. The microporous structure of CSB was able to accommodate 80 wt% of PEG10000. Surface characterization tests demonstrated that adequate amount of PEG10000 was absorbed into the pores of CSB and the crystal structure of PEG10000 was not modified. The results of TGA illustrated that BCPCM4 was thermally stable. Additionally, cotton stalk derived FSPCM displayed high heat transfer rate which indicates an increase in thermal conductivity. To substantiate thermal reliability, 500 thermal cycles were run on BCPCM4 and about 1 % variation in latent heat has been noticed with meagre change in chemical properties. Therefore, biochar derived FSPCMs would serve as promising materials to accommodate solar thermal energy.