With the aim of developing a deeper understanding of particle behaviour within nano-hybrid materials, this thesis investigates the particle-particle and particle-polymer interactions that influence and control cellulose nanocrystal dispersion in aqueous and non-aqueous environments. / Cellulose nanocrystals (CNCs) are rigid rod-shaped nanoparticles derived from bio-based resources and are considered an emerging nanomaterial based on their commercial availability and favourable properties. CNCs have great potential as reinforcing agents in hybrid materials and composite applications if they are well-dispersed. Whereas colloidal stability is effectively described by established theories, dispersing nanoparticles from an aggregated state, and their interaction with polymers can be difficult to predict and control. Herein, the particle-particle and particle-polymer interactions that govern CNC dispersibility in aqueous and non-aqueous environments are examined. The surface chemistry, morphology and colloidal/thermal stability of CNCs from North American industrial producers were extensively characterized such that particle interactions could be reproducibly measured from a known starting material. Industrially produced CNCs compared well to those produced at the bench-scale, implying that laboratory results should be translatable to the development of new CNC-based products. To examine particle-particle interactions within dry CNC aggregates, a surface plasmon resonance-based platform was developed to monitor CNC film swelling in a range of solvents and salt solutions. Water was observed to interrupt particle-particle hydrogen bonding most effectively, however film stability, and ultimately particle aggregation, was maintained by strong van der Waals interactions. Moreover, particle spacing and overall film thickness was found to be independent of the CNC surface chemistries and surface charge densities examined, yet the rate of film swelling scaled with the ionic strength of the surrounding media. Polyethylene glycol (PEG) was used as a model, non-ionic, water-soluble polymer to investigate polymer adsorption to CNC surfaces in water. PEG did not adsorb to CNCs despite the abundance of hydroxyl groups, which is in direct contrast to silica particles that are well known to hydrogen bond with PEG. Combining the knowledge of both particle-particle and particle-polymer interactions, PEG nanocomposites reinforced with CNCs and silica were compared and particle dispersibility was related to composite performance. Although PEG does not adsorb to CNCs in aqueous environments, polymer adsorption does occur in dry polymer nanocomposites leading to good dispersibility and improved mechanical properties. Overall, the work presented here yields new insight into the forces that govern CNC dispersion and provides a foundation from which a variety of new CNC-based products can be developed. / Thesis / Doctor of Philosophy (PhD) / Using particles derived from renewable resources to reinforce plastics and other materials has the potential to make products lighter, stronger and more environmentally friendly. However, to make these products we need to understand how to control and distribute particles uniformly throughout hybrid/composite materials. This work uses particles extracted from trees and cotton, known as cellulose nanocrystals, to reveal which factors govern particle dispersion in reinforced composite materials. To do so, first the properties and performance of commercially available cellulose nanocrystals were extensively analyzed and compared to form the basis from which interactions can be understood. Next, particle films were measured in water, organic solvents and salt solutions to better understand how aggregated cellulose nanocrystals can be separated within composite materials. The interactions between water-soluble polymers and cellulose nanocrystals were then investigated to reveal how polymer adsorption impacts particle dispersibility. Finally reinforced polymer composites were prepared with uniformly distributed cellulose nanocrystals and the crystallization and mechanical properties were investigated. By developing a deeper understanding of the factors that control cellulose nanocrystal dispersion we can learn how to make a variety of new and improved environmentally conscious products.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22096 |
| Date | January 2017 |
| Creators | Reid, Michael |
| Contributors | Cranston, Emily, Chemical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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