EFFECT OF LENGTH ON THE ALIGNMENT OF CELLULOSE MICROFIBRILS: A SMALL ANGLE NEUTRON SCATTERING STUDY

摘要

Cellulose microfibrils obtained by the acid hydrolysis of cellulose fibers were aligned in magnetic and shear fields. Small angle neutron scattering, SANS, was used to describe the effect of particle size on alignment. In a 2 Telsa magnetic field, aqueous suspensions of microfibrils exhibit enhanced cholesteric ordering; i.e. the entire sample becomes aligned in a helicoidal, chiral nematic arrangement with the chiral nematic axis aligned in the field direction. In a shear field, cellulose microfibrils align in a simple nematic arrangement, with no evidence of the chiral nematic (cholesteric) packing. The SANS interference peaks indicative of microfibril alignment sharpen with increasing shear rate regardless of the size of microfibrils. Length has a significant effect on the relaxation of enhanced ordering, with longer particles (280 nm in length) remaining remarkably ordered for many hours after cessation of shear, while shorter particles (<180 nm) lose their order within minutes.