Simultaneous Preparation and Dispersion of Regenerated Cellulose Nanoparticles Using a Facile Protocol of Dissolution-Gelation-Isolation-Melt Extrusion

摘要

As a consequence of an inter- (or intra-) molecular hydrogen bond, cellulose molecular chains or cellulose nanoparticles have a strong force for aggregation. Therefore, on one hand the broad use of cellulose nanoparticles is stifled by the lack of effective methods for the preparation of them. On the other hand, researchers have been struggling to directly disperse nanocellulose in a polymeric matrix. Here a facile method of "dissolution-gelation-isolation-melt extrusion" is proposed to achieve regenerated cellulose (RC) nanoparticles from cellulose hydrogel and disperse them into a polymeric matrix simultaneously. A water-soluble poly(ethylene oxide) (PEO) molecular chain is used to isolate the cellulose nanoparticle precursors in the hydrogel. The following melt extrusion process provides a shear force to break up cellulose nanoparticles into smaller ones. By means of scanning electron microscopy and transmission electron microscopy, a hierarchical structure of cellulose aggregations with size in the range 50-100 nm composed of cellulose quasi-nanospheres at the nanoscale (10-30 nm) can be clearly observed. The tensile strength and Young's modulus of the PEO/RC composite films are enhanced by about 146% and 276%, respectively, compared with those of the pure PEO film. X-ray diffraction data show that the crystal structure of RC is cellulose II. The dynamic rheology results reveal that the PEO/RC systems show much more liquid-like behavior with higher gel point frequency and lower viscosity than the contrast samples; thus, a melt compounding process could be accessible for redispersion of the RC nanoparticles into thermoplastic polymers.