Development, processing, and characterization of cellulose nanocrystal neat films
Abstract
Methods for processing quality cellulose nanocrystal (CNC) suspensions using sulfuric acid hydrolysis of microcrystalline cellulose were developed and optimized. The resulting suspensions were used to develop shear-based methods for casting neat CNC films. These methods were used to produce oriented CNC films from the Purdue-made (long crystals, CNC-L) and FPL-made (short crystals, CNC-S) CNC suspensions. Increased casting shear rate increased the degree of CNC orientation as quantified by Hermans order parameter, S. The highest shear rate (100·s-1) produced maximum orientation, with resulting Hermans order parameter of S = 0.36 in the CNC-S film. Elastic modulus, ultimate tensile strength, and elongation at failure were measured with respect to film casting direction and CNC orientation. Elastic modulus in CNC films scaled directly with orientation and reached a maximum average of 23 GPa. Tensile strength did not scale with orientation, but was strongly linked to CNC length, where a maximum strength of 196 MPa was measured. In addition to CNC length and shear rate, suspension pH and heat treatment also affected film properties. As the pH of casting suspensions was increased from ∼3 to ∼7, orientation retention in films was increased, and a new maximum modulus of 30 GPa was observed at S = 0.53 for the CNC-S film. The mechanical properties of all neutral pH films were further enhanced through heat treatment, in which a 1-4 GPa increase in elastic modulus was observed, as well as a 40-80 MPa increase in tensile strength for all axially oriented films.
Degree
M.S.M.S.E.
Advisors
Moon, Purdue University.
Subject Area
Materials science
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