Degree

Doctor of Philosophy (PhD)

Department

Renewable Natural Resources

Document Type

Dissertation

Abstract

Comparative flame retardancy of micro wood fiber plastic composites (WPCs) with fire retardants (1,2-bis(pentabromophenyl) ethane, metal hydroxides and nanoclay) was studied. The fire additives (1,2-bis(pentabromophenyl) ethane as well as magnesium hydroxide) obviously enhanced the fire retarding properties of WPCs. Especially, 1,2-bis(pentabromophenyl) ethane significantly reduced the total heat release as well as heat release rate. In addition, a synergistic effect of 1,2-bis(pentabromophenyl) and nanoclay was achieved for the enhanced fire retarding performance of WPCs.

A copolymer of cellulose nanocrystals (CNCs) and poly(N-vinylcaprolactam) (PVCL) (PVCL-g-CNCs) for use as thermally-responsive polymers with low critical solution temperatures (LCSTs) was synthesized via atom transfer radical polymerization (ATRP). The rod like morphology of CNCs was well preserved after the grafting modification. The dynamic rheology measurement confirmed the thermally induced phase transition behavior of PVCL-g-CNCs aqueous suspensions (1.0 wt%) with the LCST value at 36 oC.

The surface of CNCs was modified with poly(butyl acrylate) (PBA) and poly(methyl methacrylate) (PMMA) through ATRP technique. The successful grafting modification led to the increased thermal stability of modified CNCs (MCNCs). The increase in Young’s modulus of more than 25-fold and in tensile strength of about 3 times for 7 wt% MCNCs/PBA-co-PMMA nanocomposites was achieved compared to those of neat PBA-co-PMMA. A micro-phase separated morphology (PBA- soft domains, and PMMA- as well as CNCs- hard domains) of MCNCs/PBA-co-PMMA nanocomposites was also observed. In addition, the interfacial miscibility and phase separated morphology of PMMA-g-CNCs (PMCNCs)/PBA-co-PMMA nanocomposites were further studied. The 10 wt% PMCNCs/PBA-co-PMMA nanocomposites showed increases in Young’s modulus of more than 20-fold and in tensile strength of about 3-fold when compared to those of neat PBA-co-PMMA. Morphological analysis indicated the presence of microphase separation in PMCNCs/PBA-co-PMMA nanocomposites. Therefore, the surface modification of CNCs played a crucial role in reinforcing mechanical performance, controlling interfacial miscibility and tuning phase morphology of the nanocomposites.

Date

9-26-2018

Committee Chair

Wu, Qinglin

Available for download on Thursday, September 26, 2019

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