Green strategy guided by Raman spectroscopy for the synthesis of ammonium carboxylated nanocrystalline cellulose and the recovery of byproducts

A one-pot green procedure for the treatment of cellulosic biomass with ammonium persulfate (APS) was developed for the synthesis of highly crystalline carboxylated nanocrystalline cellulose (NCC-COOH), an emerging nanomaterial with a plethora of diversified applications. Raman spectroscopy proved applicable for monitoring the fate of APS and its two byproducts during the production of NCC-COOH from microcrystalline cellulose (MCC). The two main byproducts were then identified and quantified as ammonium sulfate (AS) and H₂SO ₄ with the latter accounted for 60% of the total sulfate ions in solution. On the basis of such findings, one-step neutralization of H ₂SO₄ and NCC with NH₄OH immediately after reaction was implemented for the formation of additional AS, followed by its quantitative recovery by precipitation. This was a very effective and critical step in waste stream management and cost reduction for the large scale production of NCC. In addition, the process resulted in highly crystalline NCC with COO^-NH₄⁺ groups, a nanomaterial with improved dispersion and thermal characteristics over NCC with COOH and COO ^-Na⁺ groups.