Selective fractionation and in situ synthesis of cellulose/calcium oxalate biocomposites from sugarcane bagasse using asymmetric Type 3 deep eutectic solvents

This study provides a sustainable biorefinery paradigm by combining high-performance biomass fractionation with a low impact effluent stream using a tunable ChCl:OA asymmetric pseudo-DES platform. The technique exploits extreme proton density for selective cell wall delignification while simultaneously driving a one pot in situ synthesis of a functional cellulose/calcium oxalate inorganic-organic biocomposite matrix at highly asymmetric molar ratios (1:5-1:15). The 1:15 arrangement provides an optimal processing window by preserving the native Cellulose I polymorph and generating a 45% solid pulp recovery with a 98% alkali insoluble structural fraction. A dual phase crystallization process, in which hydronium ions methodically remove the amorphous coatings while directly reacting with native calcium rich bagasse ash to bind crystalline whewellite domains onto the porous fibrillar skeleton, is confirmed by advanced characterisation (XRD, FTIR, and SEM). Due to solid phase acid migration, this targeted breakdown changes the downstream effluent chemistry, increasing the baseline BOD₅/COD biodegradability ratio to 0.135 while lowering the COD from 2600 to 1400 mg L^-1. This self-regulating architecture eliminates harmful AOX formation, prevents industrial sodium salt shocks, and maintains a low TDS footprint while operating entirely without chlorine.