Processing and Characterization of Nanocellulose Composites: the Leap from Poly(Lactic Acid) to Polyamide 6
Abstract
Cellulose nanomaterials (CNMs) are abundant, renewable nanomaterials with unique properties leading to the exploration of these materials in industries such as the textile, electronics, automotive and packaging industries. In polymer-composites, they have been heavily investigated as mechanical reinforcements since CNMs have densities comparable to polymers, but high axial strength and stiffness. One of the key challenges in nanocellulose composites is processing. Early studies focused on solution processes that would be challenging to make industrially viable or they focused on water-soluble polymers with limited application space, while more recent research has emphasized melt-processing. Some of the key challenges to creating CNM/polymer composites are overcoming temperature stability differences and chemical compatibility. This thesis concentrates primarily on poly(lactic acid) (PLA). PLA is a biopolymer derived from corn known for its use as 3D printer filament, biomedical applications, and packaging. The focus for PLA was two-fold: 1) to improve mechanical properties like stiffness and strength, and 2) to drive the crystallization rate, in turn leading to improvements in properties. Two projects for creating PLA nanocomposite fibers were explored, with the second leading to the development of a generalizable process for the solvent-less dispersion and distribution of CNMs into polymers. In the first project, a dry-spinning process for creating nanocomposite fibers was developed. In the second project, a melt-spinning process was developed in which CNMs were exchanged from their native solvent (water) into a known plasticizer which acted as a compatibilizer and processing aid as well. By exchanging the CNMs, no solvents were spent in the melt-processing step and the plasticizer served multiple functions during processing, but also served a final purpose in the composite as well. The fiber spinning projects fell under the first direction for PLA. The process developed became the basis for a preliminary investigation into the bulk properties of plasticized PLA. Since the process produced very small concentrations of CNMs in PLA, concentrations typical of commercial heterogeneous nucleation agents, the crystallization kinetics were investigated for very small concentrations in plasticized PLA; this fell under the second direction for PLA. Both the first and second set of projects under the two directions suggest that small concentrations of PLA can be effective in modifying composite properties. Lastly, the plasticizer method was investigated in a preliminary study on nylon 6 where the primary goal is to create dispersed nanocomposites.
Degree
Ph.D.
Advisors
Youngblood, Purdue University.
Subject Area
Environmental management|Plastics|Polymer chemistry
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