Date of Award
Fall 12-15-2023
Level of Access Assigned by Author
Open-Access Thesis
Degree Name
Master of Science (MS)
Department
Chemical Engineering
Advisor
David J. Neivandt
Second Committee Member
Douglas J. Gardner
Third Committee Member
Mehdi Tajvidi
Abstract
Cellulose nanofibrils (CNF) are one form of cellulose nanomaterial and are produced via mechanical refining of lignocellulosic materials. CNF has a hierarchical structure ranging from the micron scale down to nanometer dimensions with desirable characteristics including biodegradability, low density, high surface area, high aspect ratio and superior mechanical properties. Potential fields of application of CNF include biomedical and health care, electronics and sensors, construction, food and packaging, consumer products, and as a reinforcing agent in thermoplastic feedstocks for large scale additive manufacturing. One of the challenges in employing CNF is the ability to dry it without it undergoing hydrogen bond-driven aggregation and concomitant loss of its nanoscale structure. Conventional methods of drying such as oven drying and spray drying result in micron size and larger monoliths, while freeze drying and supercritical CO2 drying have been shown to preserve the nanostructures but are expensive, slow, and difficult to scale up. Therefore, a need exists to thermally dry CNF without it undergoing significant aggregation, nor degradation. Consequently, a new method of drying CNF; High Shear High Residence Time Drying (HSHRD) was developed in the present work which employs high shear coupled with modest heating. CNF of 90 % to 100 % fines in a 3 wt. % suspension was dried to a powdered form while largely maintaining the nanofibrillar structure. Nanofibrous CNF yields of 30 - 50 % were consistently obtained. Preliminary Brunauer-Emmett-Teller specific surface area (BET-SSA) analysis revealed an 89 % increase in the surface area of HSRHD dried CNF in comparison to spray dried CNF. The impact of HSHRD dried CNF on the mechanical properties of CNF/polylactic acid (PLA) composites were determined; it was found that the tensile strength showed an increasing trend with CNF content (although the trend was not statistically significant), and that the tensile modulus of elasticity increased with CNF content. An analysis of the projected energy consumption of the HSHRD process at the pilot scale was performed; it was determined that the HSHRD process would consume just 23 % of the energy of a pilot scale spray drier on a dry mass of CNF basis, making the newly developed process highly attractive from not just the perspective of maintenance of the CNF nanostructure, but also the energy required for drying.
Recommended Citation
Eme, Charles, "High Shear-High Residence Time Drying of Cellulose Nanofibrils" (2023). Electronic Theses and Dissertations. 3896.
https://digitalcommons.library.umaine.edu/etd/3896