Date of Award

12-2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Fiber and Polymer Science

Advisor

Brown, Philip

Committee Member

Lickfield , Gary

Committee Member

Kennedy , Marian

Committee Member

Sharp , Julia

Abstract

High-performance fibers such as para-aramids are used extensively in gloves for cut protection. However, the inherent cut resistance of these fibers and the relationship between cut resistance and other material properties is not known. To better understand cut resistance at the material level, an experiment was conducted using a lab-scale wet spinning system to produce and characterize aramid copolymer fibers.
To facilitate the use of lab-scale equipment, the experiment was conducted as a four-factor split-plot response surface design. The four treatment factors studied were solvent concentration in the coagulation bath, the amount of salt in the coagulation bath, the degree of stretching during coagulation, and the degree of stretching after coagulation. The cut resistance of the fibers was measured using a new cut testing device developed specifically for testing single-end yarns. Other physical properties as well as the morphology of the fibers were also investigated.
The cut strength of the fibers was improved by stretching after coagulation but was influenced more by the conditions of coagulation. In this experiment the optimum conditions for maximizing cut resistance occurred at slow rates of coagulation with high concentrations of solvent and salt in the bath. The resulting fibers were nearly isotropic in mechanical performance and had a coarse granular morphology that transitioned into domains of macrofibrils inside the fibers after stretching. As the coagulation rate slowed, the cross-section of the fibers became increasingly round, which also improved the cut resistance of the fibers. The tensile properties of the fibers were not significantly affected by the coagulation conditions but were improved by increasing molecular orientation as a result of stretching after coagulation. The degree of molecular orientation in the experimental fibers was relatively low, which resulted in lower tensile strength but improved transverse properties over commercial aramid fibers. Despite having low tensile strength, the cut strength of the experimental aramid copolymer fibers is predicted to exceed that of commercial aramid fibers under optimized processing conditions.

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