Date of Award

Summer 8-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

Committee Chair

Joshua U Otaigbe

Committee Chair Department

Polymers and High Performance Materials

Committee Member 2

Robson F. Storey

Committee Member 2 Department

Polymers and High Performance Materials

Committee Member 3

Sarah E. Morgan

Committee Member 3 Department

Polymers and High Performance Materials

Committee Member 4

Jeffrey S. Wiggins

Committee Member 4 Department

Polymers and High Performance Materials

Committee Member 5

Sergei I. Nazarenko

Committee Member 5 Department

Polymers and High Performance Materials

Abstract

Over the past two decades, the increasing concern about the negative environmental impacts of synthetic materials has led to rising interests in utilizing renewable natural resources to develop polymer materials with comparable properties and performance to their synthetic counterparts. One of the major fields of interest is polymer composites where the replacement of synthetic fibers with bio renewable natural fibers is of great potential. However, the processing difficulties, in terms of fiber dispersion and thermal stability have limited the application of cellulosic fibers to polymers with low processing temperatures which are mostly hydrophobic polymers. As a result, the true reinforcing ability of the fiber could not be fully exploited due to polymer-fiber incompatibility.

This dissertation discusses a novel approach to develop nanocomposite and composite materials based on high melting point polyamide 6 engineering thermoplastic matrix utilizing the in-situ ring-opening polymerization Both nanoscale cellulose nanocrystals as well as macroscale natural fibers were used as reinforcement. The initial study consisted of a detailed analysis of physical, viscoelastic and rheological properties polyamide 6 nanocomposites reinforced with cellulose nanocrystals in correlation with the morphology and microstructure of the nanocomposites. These nanocomposites were then used a masterbatch for further processing via melt extrusion technique. The effect of surface modification of cellulose nanocrystals with silane coupling agents on isothermal and non-isothermal crystallization of the obtained nanocomposites were fully investigated using a number of different theoretical models to gain a better understanding of the interrelation of surface functionality, microstructure and crystallization behavior. In addition, the effect of polymer-particle interfacial modification on shear and extensional rheological behavior as well as the mechanical properties of the nanocomposites were investigated. The results were correlated with the development of “interphase” in modified systems as confirmed by quantitative nanomechanical analysis.

In addition, a series of polyamide 6 composites reinforced with flax fabric and kraft pulp cellulose fibers were successfully developed using vacuum assisted resin infusion process and a through processing-structure-property relationship study was conducted. The findings of this research effort provide a better understanding of the complex processing-structure-property relations of engineering thermoplastics reinforced with cellulosic fibers.

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