Date of Award

Spring 5-6-2022

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

Mehdi Tajvidi

Third Committee Member

William Gramlich

Additional Committee Members

Yousoo Han

Todd Rushing

Abstract

The work within this dissertation involved the production and utilization of cellulose nanomaterials within the context of electrospraying and electrospinning. The production of nano-dimension cellulose nanocrystal (CNC) powders was a novel contribution to the multi-decade efforts surrounding the drying of CNC suspensions, and the powders were produced by electrospraying reduced surface tension suspensions at room temperature. The CNC powders were used as a control for comparison with electrospun fibers in thermoplastic composites. Nano-diameter (submicron) fibers generated most of the work outlined in this dissertation and were produced using a water-soluble, sustainably derived, poly (vinyl alcohol) (PVA). The CNC suspension was added to the PVA and water as the polymer dissolved to create a composite electrospinning solution. The addition of 50 wt.% CNC suspension to the PVA solution increased the viscosity and ultimately decreased the fiber production capacity. However, by slightly reducing the CNC content to 40 wt.%, electrospun fibers could be consistently produced. The fiber diameters were measured and analyzed by a 3x3 factorial experimental iii design involving the addition of 0, 20 and 40 wt.% CNC in PVA solutions and altering the machine settings to produce varied samples. The measurement sampling methodology created the most variation in fiber diameter, rather than the machine settings. While obtaining information about the fiber production characteristics, spun mats were collected and post processed for application as a fiber reinforcement in a thermoplastic poly (lactic acid) (PLA) matrix. The PLA polymer was chosen because it has chemical compatibility with both PVA and CNC as well as sustainable attributes. By reinforcing PLA with 15% composite nanofiber (cNF) composed of 20 wt.% CNC loaded PVA fibers via melt compounding, improvements in the mechanical and thermal properties were observed. The neat PLA tensile modulus increased 30% from 3.64 ± 0.76 to 4.74 ± 0.34 GPa and the tensile strength increased 21% from 56.4 ± 13.6 to 68.3 ± 1.2 MPa. Impact strength showed significant improvement, increasing 54% from 3.15 ± 0.26 to 4.85 ± 0.86 MJ/cm3. The flexural modulus showed a 6% improvement from 3.68 ± 0.09 to 3.91 ± 0.21 GPa and the flexural strength increased 1% from 99.65 ± 6.4 to 100.4 ± 0.6 GPa. The fiber reinforcement contributed to improvements in tensile properties without sacrificing flexural properties or impact strength as normally observed in composites containing microscale CNC powders. This improvement can contribute to additional applications for thermoplastic PLA and the electrospun fiber reinforcement methodology shows applicability to other polymer systems.

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