Direct solvent nanowelding of cellulose fibers to make all-cellulose nanocomposite

Abstract

Highly purified cellulose fibers were directly welded at nanoscale using dimethyl acetamide containing lithium chloride (DMAc/LiCl) solvent. For welding fibers directly at nanoscale, lignin and hemicelluloses were first removed from the nano-disconnection between laterally adjacent nanofibrils through proper bleaching; hence, nano-scale pores were created between lateral nanofibrils. The solvent penetrated deeply into these pores, making disordered chains to freely move onto the outer part of nanofibrils leaving the nanofibril core undissolved. During solvent rinsing and drying, the disordered chains entangled and re-solidified, acting as a weld layer joining undissolved nanofibril cores (averagely 38 nm in diameter): through which a nano-welded sheet (NWS-1) was prepared directly from the microscale cellulose fibers. The physical and mechanical properties of NWS-1 had dramatically improved compared to those of fiber sheets. For comparison, cellulose fibers were also indirectly welded at nanoscale; the highly purified cellulose fibers were first ground to nanofibers (averagely 32 nm in diameter), which were afterwards partially dissolved in DMAc/LiCl to indirectly prepare nano-welded sheet (NWS-2). The undissolved nanofiber cores of NWS-2 had a diameter of 26 nm on average. The NWS-1 and NWS-2, so-called all-cellulose nanocomposites, showed the same structures at macro-, micro- and nanoscales with the same functional properties.