Nanocellulose production from walnut pruning wastes using hydrated deep eutectic solvent as paper strength additives

The valorization potential of industrial walnut pruning wastes was investigated as a value-added product. Nanofibrillated cellulose (NFC) was prepared from walnut pruning wastes via hydrated choline chloride-lactic acid deep eutectic solvent (ChCl-LA DES) pretreatment followed by grinding, and these were used as paper strength additives. The effect of reaction time on NFC properties were investigated and compared. The structure of nanocellulose was determined by Fourier transform infrared, scanning electron microscopy (SEM), and rheological analysis. The results show that carboxylated NFC having high aspect ratio could be successfully isolated after DES-pretreatment with the average diameter of 39 to 77 nm. Prepared NFC was added to the bulk suspensions of papermaking slurries at various percentages (up to 8%) together with poly(diallyldimethylammonium chloride). The drainage and electrokinetic properties of the pulp and mechanical properties of fabricated handsheets were analyzed and compared. The addition of 1% NFC to the bulk suspensions increased tensile index by 14.2% and burst index by 6.3%. There were further increases observed up to 71.8% in tensile index and up to 72.3% in burst index at 8% NFC addition. Results indicate that DES pretreated cellulose nanofibrils have great potential as reinforcing agent in papermaking.