Date of Award
1-1-2025
Document Type
Thesis
Degree Name
M.S. in Engineering Science
First Advisor
Byron S. Villacorta
Second Advisor
Sasan Nouranian
Third Advisor
Songtao Xie
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
Optimized extrusion melt-blending of polylactic acid (PLA) polymer with a minor biopolymeric phase, polybutylene adipate terephthalate (PBAT), and compatibilized with random ethylene-methyl acrylate-glycidyl methacrylate terpolymer (EMA-GMA, Trademark: Lotader® AX-8900) led to an outstanding improvement in mechanical properties. At the non-compatibilized PLA/PBAT (80/20) blend point, significant enhancement (~4500%) in toughness and elongation-at-break was already obtained without compromising any elastic properties. Lotader content at 2 wt.% was determined to be optimal by numerical optimization methodology to maximize toughness and elongation-at-break. Upon adding the compatibilizer, the original phase-separated morphology of the blends changed from PBAT quasi-spherical domains to nearly elongated elliptical ones. The thermostability of the blends remained largely unaltered following the incorporation of PBAT and Lotader. The compatibilizer at the optimal point in the optimized blend ratio led to the formation of a phase-separated morphology that combined internal cavitation, interfacial cavitation, and strong adhesion features at the right proportions in the microstructure which underlies the micro-mechanisms driving the remarkable enhancement of as much as 7100% in toughness and ductility.
In the next stage of the investigation, multiwalled carbon nanotubes (MWCNT) were systematically added to the PLA/PBAT blend system. A selective deposition and encapsulation of nano-dispersed MWCNT exclusively within the PBAT microdomains in the phase-separated microstructure of 80/20 PLA/PBAT polymer nanobiocomposites (PNCs) were achieved by means of a three-step processing strategy. The resulting PNC morphology displayed prickly-chayote-squash-like domains embedded and distributed within the PLA matrix, which led to an ultra-toughening effect in the PNCs at 1 wt% MWCNT, yielding ductility values of 6500% and 50% higher than the virgin PLA and the pristine 80/20 PLA/PBAT blend, respectively. Moreover, a toughening nano-mechanism by MWCNT was proposed to account for the tougher behavior. The validity of this mechanism was corroborated by the observation of closed-ended and parallel nano-cracks in the fractured PNCs’ cross-sections. Furthermore, the preferential localization of MWCNTs exclusively within the PBAT domains constrained the transfer of MWCNT into the brittle PLA matrix during melt-mixing, while the presence of interfacial cavitations eliminated the likelihood of interfacial bridging by MWCNT. The PLA-based hybrid PNCs developed in this study remained electrically insulative and displayed an ultra-tough, ultra-ductile, and cytocompatible behavior, which makes them potential candidates for biomedical and bioelectronic applications.
Recommended Citation
Ayan, Utsab Roy, "Polylactic Acid-based Sustainable Hybrid Nanobiocomposites" (2025). Electronic Theses and Dissertations. 3238.
https://egrove.olemiss.edu/etd/3238