Submitted to: Journal of Applied Polymer Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2008
Publication Date: 1/15/2009
Citation: Rosa, M.F., Chiou, B., Medeiros, E.S., Wood, D.F., Mattoso, L.H., Orts, W.J., Imam, S.H. 2009. Biodegradable Composites Based on Starch/EVOH/Glycerol Blends and Coconut Fibers. Journal of Applied Polymer Science. 111(2):612-618. Interpretive Summary: Starch is one of the most abundant natural polymers and is relatively inexpensive; however, the use of pure starch in composites results in brittle materials. To overcome this drawback, starch was blended with biodegradable polymer and agriculturally derived fibers. Such blends provided interesting polymer systems with a wide range of useful mechanical and thermal properties. New uses of starch in non-food applications would help American farmers and starch based agro-industry in the U.S.
Technical Abstract: Unripe coconut fibers were used as fillers in a biodegradable polymer matrix of starch/Ethylene vinyl alcohol (EVOH)/glycerol. The effects of fiber content on the mechanical, thermal and structural properties were evaluated. The addition of coconut fiber into starch/EVOH/glycerol blends reduced the ductile behavior of the matrix by making the composites more brittle. At low fiber content, blends were more flexible, with higher tensile strength than at higher fiber levels. The temperature at the maximum degradation rate slightly shifted to lower values as fiber content increased. Comparing blends with and without fibers, there was no drastic change in melt temperature of the matrix with increase of fiber content, indicating that fibers did not lead to significant changes in crystalline structure. The micrographs of the tensile fractured specimens showed a large number of holes resulting from fiber pull-out from the matrix. There was no evidence of matrix resin adhering to the fiber, indicating a poor adhesion between fiber and matrix. While starch alone degraded readily, starch/EVOH/glycerol blends exhibited much slower degradation in compost. Composites produced 10.3 to 12.6% less CO2 compared to starch in a closed circuit respirometer. Addition of increasing amount of fiber in starch/EVOH/glycerol composite had no impact on its biodegradation.