Use of sugar beet cellulose nanofibers for paper coating

Sugar beet pulp (SBP) is a widely available byproduct from sugar industry in several countries. In the current work, cellulose nanofibers (CNFs) were isolated from SBP depectinated using two different methods, namely sulfuric acid hydrolysis and hydrothermal extraction, to obtain nanofibers with different residual pectic substance. The isolated CNFs had width of ~ 5 nm and several microns in length using both methods of pectin extraction. Chemical composition was studied regarding α-cellulose, pentosans, residual pectic substance, and degree of polymerization (DP). Films cast from CNFs were characterized regarding their crystallinity, mechanical properties (tensile strength, Young's modulus, and strain), water contact angle measurement, as well as by Fourier transform infrared (FTIR). The results showed higher tensile strength properties and higher hydrophilicity for films made from CNFs isolated from the hydrothermal-depectinated SBP (HDCNF) than those from the acid-depectinated SBP (ADCNF). Both of HDCNF and ADCNF were used as coating for bagasse paper sheets; the coated paper sheets were characterized regarding their tensile strength, burst strength, water vapor permeability, air porosity, and grease-proof properties. Coating of paper sheets with CNFs resulted in remarkable increase in their mechanical properties and decrease in air porosity; higher effect was recorded in case of using the HDCNF coating. Paper sheets coated with HDCNF or ADCNF showed good grease-proof property. Finally, measuring the overall migration of the CNFs-coated paper sheets showed safety of the applied coatings for food packaging applications.