Influence of the carboxylic groups and degree of polymerization of cellulosic pulps on lignocellulosic nanofibers (LCNF) properties

EHMAN, N.V.; RAMIREZ, A.I.; CHINGA-CARRASCO, G.; VALLEJOS M.E; FELISSIA, F.E.; AREA, M.C.

Córdoba

Workshop; 2nd International Workshop on Biorefinery of Lignocellulosic Materials (IWBLCM2019); 2019

Pulp characteristics depend on the raw material and the pulping process. Knowledge of the influence of the kind of initial pulps on LCNF properties is necessary to prepare the adequate LCNF depending on its final use. The aim of this work was to evaluate the influence of initial characteristics of cellulosic pulps on the final properties of lignocellulosic nanofibers (LCNF). Six pulps based on pine sawdust, eucalyptus sawdust and sugarcane bagasse with different pulping process and bleaching were evaluated. Carboxylic groups and degree of polymerization of initial pulps were measured. The pulps were subjected to TEMPO mediated oxidation and then were passed through a colloidal grinder to completely break the fibril bundles. The fibrillation degree, morphology, surface chemical charge, and rheology of LCNF were characterized and analyzed using several complementary techniques. The rheology properties of LCNF were variable; eucalyptus sawdust LCNF (12.2 Pa.s messured at 0.6 rpm) showed lower viscosity than that of pine and sugarcane bagasse nanofibers, the bleached kraft pulp of pine showed the highest value (792.7 Pa.s). The carboxylic groups of LCNF varied between 638 µmol/g of over dry pulp (odp) for pine unbleached soda/oxygen LCNF and 1005 µmol/g of odp for pine bleached kraft LCNF. Carboxylic groups content is directly related to viscosity (r = +0.94), thus the increase in the oxidation degree caused an increase in viscosity. The morphological analysis showed differences between the different LCNF, i.e. low levels of roughness in the eucalyptus LCNF film (0.38 µm) compared to pine LCNF (1.39 µm for pine bleached kraft LCNF).