Graduate Thesis Or Dissertation

 

Photoinitiated Grafting of PMMA onto Cellulose Nanocrystals to Improve Nanocomposite Reinforcement-matrix Interface Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/sj139549f

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  • Cellulose nanocrystals (CNCs) are extremely abundant, biodegradable and light weight nanoparticles that have the potential to contribute in many fields including packaging, construction, solar cells and automotive. With the increasing interest in nanotechnology and nanocomposites, CNCs could provide a renewable, optically transparent and strong alternative to other nano-scale reinforcement phases. One challenge that limits the applications of CNCs in polymer composites is that the hydrophilic nanocrystals have poor dispersion and interfaces with hydrophobic polymer matrices. This project worked to improve the compatibility of CNCs with polymer matrices, specifically poly(methyl methacrylate) (PMMA). This was done by first immobilizing a UV-photoinitiator to the surface of the nanocrystals and then grafting PMMA from the CNCs surface using radical photopolymerization. It was found that the concentration of the immobilized initiator could be controlled using the length of the reaction. The photopolymerization with initiator modified CNCs successfully resulted in PMMA-grafted CNCs (CNC-g-PMMA), with up to 66% w/w PMMA covalently bonded to the cellulose surface. FTIR, DSC, TGA and elemental analysis all showed that CNC-g-PMMA had properties that were in between those of PMMA and ungrafted sulfonated CNCs (s.CNCs). When PMMA composites were made with ungrafted s.CNCs and CNC-g-PMMA, their properties were compared to each other and to those of neat PMMA. Optically, composites with both forms of CNCs were comparable to PMMA at around 1% w/w, however became cloudy at higher concentrations. The Young’s moduli of CNC-g-PMMA composites of 4% w/w CNCs or less were higher than those of s.CNC composites. These CNC-g-PMMA composites also had higher interface values when fit with the Shear-Lag Capped (SLC) model than the s.CNC composites. At higher concentrations of CNCs both types of composites showed reduced mechanical properties, most likely due to nanoparticle agglomeration and poor dispersion.
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  • 2017-08-22 to 2018-02-27

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