Date of Award

Spring 5-3-2024

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Forest Resources

Advisor

Douglas J. Gardner

Second Committee Member

Yousoo Han

Third Committee Member

Ling Li

Additional Committee Members

Soydan Ozcan

Colleen Walker

Abstract

Cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) are promising alternatives to inorganic fillers in polymer matrix composites (PMCs) attributable to their biodegradability and nanometer-sized fibrils. The drying process is crucial for their incorporation into PMCs, which affects final production cost and performance. The University of Maine has researched spray drying (SD) for CNCs and CNFs, finding that SD is a cost-effective method and enhances the mechanical properties of the thermoplastic matrix attributable to the excellent distribution and dispersion of small particles into plastic matrices. The primary objective of this dissertation is to enhance the viability of spray-dried CNC/CNF powders. Three SD technologies were utilized in this dissertation: a lab-scale ultrasonic-assisted spray dryer, two-fluid nozzle (TFN), and a pilot-scale rotary disk atomizer. The morphological properties of spray-dried CNCs (SDCNCs) and CNFs (SDCNFs) were examined to determine their impact on the optical, physical, and mechanical properties of polyvinyl alcohol (PVA) and polypropylene (PP). Furthermore, the feasibility of utilizing SDCNCs- and SDCNFs in nanocomposites for film production and additive manufacturing (AM) was assessed. In addition, it is believed that SD becomes more viable by lowering the manufacturing cost of CNFs and the subsequent production cost of SDCNFs through enzyme treatment. After incorporating 20 wt.% CNC nanoparticles dried via an ultrasonic-assisted spray dryer into the PVA matrix, the tensile properties of the filled PVA nanocomposite films increased while maintaining their transparency. In contrast, the tensile properties of PVA nanocomposite films decreased after adding micrometer CNC particles dried by a TFN spray dryer. Using a pilot-scale disk atomizer for spray drying, the type of feedstock, fibrillation levels, and solids contents of CNF suspensions influenced the size and morphological properties of the SDCNFs. After adding 5 wt.% and 10 wt.% SDCNFs into the PP matrix with maleic anhydride polypropylene (MAPP), the mechanical properties increased with higher filler content and less fibrillation degree of CNF suspensions, while impact strength showed the opposite trend. SDCNFs-reinforced PP composites were applied in AM, demonstrating that SDCNFs enhanced the printability of PP. The enzyme treatment reduced energy consumption by up to 61% during CNFs refining. The mechanical properties of PP filled with enzyme-treated SDCNFs showed no significant difference compared to untreated SDCNFs reinforced PP composites.

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