Date of Award

8-2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Chemical Engineering

Advisor

Ogale, Amod A

Committee Member

Dawson , Paul

Committee Member

Kitchens , Christopher

Abstract

Bio-composite fibers have attracted increasing attention from environmentally-conscious consumers because of their low cost and biodegradability. Soy protein isolates and other purified forms have been proposed as bio-based substitutes for pure synthetic polymers for use in textiles. However, fibers from pure soy proteins do not possess adequate properties for use as textile fibers. Therefore, this research aimed to investigate composite fibers consisting of soy and polyethylene for their microstructure and mechanical properties. Changes in properties with increasing filler content and long-term properties of fibers were systematically examined.
First, the microstructure of the fibers was investigated by optical analysis. Six different compositions of soy, compatibilizer, and polyethylene were examined: 0-0-100, 0-10-90, 20-0-80, 23-7-70, 20-20-60, and 30-20-50. The pure PE and C-PE fibers had very smooth surfaces, which became rough after soy particles were added. Without a compatibilizer, soy-PE fibers had the lumpiest surface with large soy agglomerates. The soy particles on fibers made from 23-7-70 composition had a more homogenous distribution, and better dispersion (less agglomerates) than that on other fibers. Overall, the soy agglomerates oriented along the fiber direction due to shear and extensional stresses induced during flow and draw-down.
Second, the mechanical properties of fibers were analyzed. For fibers produced from 23-7-70 composition, tensile modulus reduced from 921 ±85 MPa to 570±94 MPa, and ultimate strength reduced from 500±90% to 67±63 % with the addition of soy to PE. Adding soy flour to polyethylene resulted in a decrease in tensile modulus and ultimate strain. Yield stress and tensile strength did not differ significantly between the fibers having 100% PE and 50% PE. However, tensile strength of 23-7-70 fibers increased to 84.2±10.6 MPa compared with that of pure PE measured at 42±6 MPa. Moreover, tensile strength of 23-7-70 fibers decreased after two month of aging. However, at ambient conditions, another four months of aging had no further effect. Overall, it changed from 84.2±10.6 MPa (non-aged) to 24.2 ±1.1 MPa after six months of aging at ambient conditions, whereas other mechanical and physical properties were not affected significantly. Exposure to boiling 0.1 M NaOH aqueous solution for 10 min (to simulate accelerated washing) caused a decrease in tensile strength, but additional exposure of 90 min did not cause any further reduction in tensile strength (25±4 MPa). The fiber surface became smoother due to the removal of soy particles from the surface after boiling. Thus, over-washed fibers had a lower strength at break, but the fibers retained a moderate strength. These results indicate that soy-PE fibers possess moderate mechanical, physical and long-term properties for likely use in textile applications. The primary advantage of such fiber is their lower cost relative to that of pure PE fibers.

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