- Collection:
- Atlanta University and Clark Atlanta University Theses and Dissertations
- Title:
- Processing and Characterization of Poly(lactic) Acid Nanocomposites Prepared by High Torque Melt Mixing and Extrusion, 2019
- Creator:
- Simmons, William
- Date of Original:
- 2019-12
- Subject:
- Degrees, Academic
Dissertations, Academic - Location:
- United States, Georgia, Fulton County, Atlanta, 33.749, -84.38798
- Medium:
- theses
dissertations - Type:
- Text
- Format:
- application/pdf
- Description:
- Improving the processability and physical properties of sustainable bio-based polymers using bio-based fillers is essential to preserve biodegradability and make them suitable for end-user applications. Herein, we report the use of spray-dried lignin-coated cellulose nanocrystals (L-CNCs), a bio-based filler, to modify the crystallinity, rheological, and mechanical properties of two grades of poly(lactic acid) (PLA); NatureWorks 2500HP (injection molding grade) and NatureWorks 4043D (general-purpose grade), by preparing nanocomposites. The lignin coating on CNCs not only enabled the dispersion of CNCs but also enhanced the interfacial interaction between CNCs and the PLA matrix, resulting in a significant improvement in crystallinity, rheological, and mechanical properties. The crystallinity for both grades of PLA was significantly improved with the addition of L-CNCs. The rheological percolation threshold concentration obtained by power-law analysis for /L-CNC composites was found to be 0.66 wt. %, which is significantly lower than the reported values for other PLA/CNC composites. Such a low rheological percolation concentration of L-CNCs can be attributed to the excellent dispersion of L-CNCs in the PLA matrix. Addition of only 0.5 wt% of L-CNCs to the PLA matrix resulted in a significant improvement in storage and Young’s moduli relative to neat PLA, as measured by dynamic mechanical analysis and tensile testing, respectively. This improvement in mechanical properties can be attributed to a significant increase in the degree of crystallinity of the PLA in the nanocomposites. Excellent dispersion and compatibility of L-CNCs with PLA allowed the generation of a high density of nucleating sites increasing the degree of crystallinity of the PLA matrix. Improvement in the mechanical properties at higher loading of L-CNCs can be attributed to both high crystallinity and reinforcement by L-CNCs. Incorporation of only 0.3 wt% L-CNCs to the PLA matrix led to a significant increase in melt strength allowing the ready fabrication of a fully bio-based transparent and potentially biodegradable PLA film by film blowing. This present study demonstrates that L-CNCs can serve as excellent fillers for PLA for the development of fully bio-based nanocomposites composites which exhibit materials properties that allow them to compete with petroleum-based composite materials.
Date of award: 2019-12
Degree type: dissertation
Degree name: Doctor of Philosophy (PhD)
Granting institution: Clark Atlanta University
Department: Department of Biological Sciences
Advisor: Mintz, Eric - Metadata URL:
- http://hdl.handle.net/20.500.12322/cau.td:2019_simmons_william_l
- Holding Institution:
- Atlanta University Center Robert W. Woodruff Library
- Rights:
-
