Date of Award

8-2003

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forest Resources

Advisor

Douglas Gardner

Second Committee Member

Carl Tripp

Third Committee Member

Stephen Shaler

Abstract

The overall objective of this dissertation was to gain an understanding of the relationship between interfacial chemistry and the micromechanics of the cellulose-fiber/polymer composites. Regenerated cellulose (lyocell) fibers were treated with amine-, phenylamine-, phenyl-, and octadecyl-silanes, and also styrene-maleic anhydride copolymer. Inverse gas chromatography was conducted to evaluate the modified surfaces and to examine the adsorption behavior of ethylbenzene, a model compound for polystyrene, onto the fibers. Micro-composites were formed by depositing micro-droplets of polystyrene onto single fibers. The fiber was subjected to a tensile strain, and Raman spectroscopy was employed to determine the point-to-point variation of the strain- and stress-sensitive 895 cm-1 band of cellulose along the embedded region. Inverse gas chromatography studies reveal that the Ia-b values, calculated by matching the Lewis acid parameter (KA) and basic parameter (KB) between polystyrene and different fibers, were closely correlated to the acid-base adsorption enthalpies of ethylbenzene onto the corresponding fibers. Hence, Ia-b was subsequently used as a convenient indicator for fiberlmatrix acid-base interaction. The Raman micro-spectroscopic studies demonstrate that the interfacial tensile strain and stress are highest at the edge of the droplet, and these values decline from the edge region to the middle region of the embedment. The maximum of these local strains corresponds to a strain-control fracture of the matrix polymer. The minimum of the local tensile stress corresponds to the extent of fiber-to-matrix load transfer. The slope of the tensile stress profile allows for an estimation of the maximum interfacial shear stress, which is indicative of fiberlpolymer (practical) adhesion. As such, a novel micro-Raman tensile technique was established for evaluating the ductile-fiberlbrittlepolymer system in this study. The micro-Raman tensile technique provided maximum interfacial shear stress values of 8.0 to 13.8 MPa, ranking functional groups according to their practical adhesion to polystyrene: alkyl< untreated < phenyl = phenylamine = styrene copolymer < arnine. Overall, interfacial bonding can be increased by increasing the acid-base interactions (Ia-b) or reducing the chemical incompatibility (Δ δ) between the fibers and matrix. Therefore, interfacial chemistry can be employed to enhance and predict cellulose-fiberlpolymer adhesion to better engineer composite properties and ultimately better utilize bio-resources.

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