Structure And Functionality Of Phosphoric Acid Regenerated Celluloses:Effects Of Preparation Methods And Underlying Mechanism

Natural cellulose is a highly crystalline biopolymer containing crystalline and amorphous regions.Nanostructured celluloses can be obtained by dissolving crystalline cellulose with a solvent,such as phosphoric acid and regenerating the cellulose in a non-solvent.Such a regenerated cellulose has good rheological and emulsion stabilization properties,which may find potential applications in the food industry.Herein the effects of preparation methods on the structure and functionality of phosphoric acid regenerated celluloses and the underlying mechanism were studied.Microcrystaline cellulose was submitted to a two-step preparation:dissolution with phosphoric acid at 5℃ for 24 h and treatments at 5℃ or 50℃ for certain duration.The yields of regenrated celluloses treated at 5℃ were constantly high,and the yields treated at 50℃ decreased with the increase of treatment time.The regenerated celluloses treated at 5℃ was fiber-like with diameter less than 50 nm and had low crystallinity.The latter was spherical with size from 500 nm to 2htm and had relative higher crystallinity.However,both crystallnities were lower than that of native cellulose.The degree of polymerization of regenerated celluloses decreased with the increase of treatment time,which was more evident at 50℃.The chemical structure of regenerated cellulose was not affected by both treatments significantly.Very little phosphoric acid group was introduced during treatment at 5℃,but more were introduced during treatment at 50 ℃,which were increased with the treatment time.The regenerated cellulose treated at 5℃ had greater dispersion stability,higher viscosity,better gel characteristic and emulsion stabilization ability than the one treated at 50℃.An addtional ultrasound treatment was empolyed between the dissolution and regeneration to reduce the molecular weight of cellulose.This process however led to aggregation of regenerated cellulose fibers and the decrease of dispersion stability,which showed that decrease of molecular weight of cellulose during treatments might be a key factor in controlling the morphological of regenerated cellulose.Our results show that regenerated cellulose prepared at low temperature has the morphology of nanofiber,better functionalities and greater potential for applications.Decrease of cellulose molecular weight during treatments may be a key factor to control the morphological of regenerated cellulose.