Characterization of Structure and Tensile Properties of Electrospun Web

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Title: Characterization of Structure and Tensile Properties of Electrospun Web
Author: Boppa, Venugopal
Advisors: Dr. Jeffrey Ray Thompson, Committee Member
Dr. Bhupender S Gupta, Committee Chair
Dr. Hechmi Hamouda, Committee Member
Abstract: Electrospinning has been considered a versatile method for producing nanofibers, which have generated great interest for use in many areas, including those of tissue engineering and filtration, due to their high surface area to volume ratio and high porosity. Mechanical properties of these materials are important for these and other applications. Although much work has been carried out in the area of electrospinning technology over the past decade, little has been focused on the structure of electrospun webs and their mechanical properties. This work was undertaken to close a part of this gap existing in the literature. Using PEO as the polymer and water as the solvent, a series of electrospun webs were produced. The primary variables used were polymer concentration and time of spinning and properties measured were peak stress-peak strain, initial modulus and yield point. It was found necessary to adjust voltage and the distance between the needle and collector plate to get a stable Taylor cone, which was essential for forming uniform fibers. Three levels of concentrations, 8, 10 and 12.5% PEO were used to produce electrospun webs and these led to nanofibers of diameter 210nm, 325nm and 550nm, respectively. Increase in concentration resulted in decrease in stress and modulus values, and increase in strain values. The time of spinning was varied to simply vary the areal density of the web that was expected to have an influence on peak force; areal density was particularly an important input parameter for the model used for predicting the tensile properties of a web. The model to predict the tensile properties of web required single fiber stress-strain properties. Difficulty of conducting tensile test on single fibers required the use of an alternative way, tensile testing of aligned fiber bundles. Aligned fiber bundles were produced using collector strips separated with gap. For these fibers, effect of concentration and spinning distance on fiber morphology and mechanical properties were investigated. Concentration showed similar effect as found in the case of unoriented webs, with increase in concentration fiber diameter increased, and stress and modulus values decreased. With increase in spinning distance, fiber diameter decreased, and stress and modulus values increased. A mathematical model is developed and proposed for predicting the stress-strain behavior of electrospun webs. The analysis method used was the “Force method†. Peak stress values were predicted using single fiber stress-strain properties in conjunction with the model. Predicted values of peak stress matched closely with the measured values within a correction factor of less than two. Reasons are given for the small differences noted between the measured and predicted values. The results noted in the measured values of peak stress and the difference found between the predicted and the measured values suggest that the fibers in the electrospun webs are bonded to some extent at the cross-over points. This leads to the suggestion that the structural model used for characterizing the tensile behavior should be modified by including bonding at the cross-over points.
Date: 2009-12-07
Degree: M
Discipline: Textile Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/1485


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