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Title: Effects of chemical versus enzymatic processing of kenaf fibers on poly(hydroxybutyrate-co-valerate)/poly(butylene adipate-co-terephthalate) composite properties

Author
item YANG, BING - University Of North Texas
item NAR, MANGESH - University Of North Texas
item VISI, DAVID - University Of North Texas
item ALLEN, MICHAEL - University Of North Texas
item AYRE, BRIAN - University Of North Texas
item Webber Iii, Charles
item LU, HONGBING - University Of North Texas
item D'SOUZA, NANDIKA - University Of North Texas

Submitted to: Composites Part B Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/2013
Publication Date: 1/1/2014
Publication URL: http://handle.nal.usda.gov/10113/59431
Citation: Yang, B., Nar, M., Visi, D.K., Allen, M., Ayre, B., Webber III, C.L., Lu, H., D'Souza, N.A. 2014. Effects of chemical versus enzymatic processing of kenaf fibers on poly(hydroxybutyrate-co-valerate)/poly(butylene adipate-co-terephthalate) composite properties. Composites Part B Engineering. 56:926-933.

Interpretive Summary: The use of natural fibers for composites is an attractive alternative from an environmental and sustainable perspective. Natural fibers are used to reinforce polymers to improve mechanical properties of composites. Kenaf (Hibiscus cannabinus L.), an annual plant species, is planted largely because of its ease of growth and higher fiber yields than flax and ramie. Plant fibers are separated from the extraneous plant material by a process called retting. Research was conducted to determine the impact of the two retting methods (NaOH and Pectinase) and fiber lengths (5 and 10 mm) on fiber quality for polymer blend composites. The NaOH retted fibers produced a synergistic benefit when the two fiber lengths were combined into a single composite blend. The pectinase retted fibers did not show a similar benefit when combining the two fiber lengths, but when comparing the use of single length composites the pectinase retted fibers outperformed NaOH retted composites using the same fiber lengths. The retting methods also impacted the recrystallization temperature and surface smoothness of the polymer blend composites. Pectinase retting produced a higher recrystallization temperature than NaOH retting. This increase in the onset of recrystallization is an indication that the pectinase provided additional locations for the polymers to crystallize. Also, the pectinase retted fibers produced smoother surfaces than the NaOH retted fibers. This research provides new and foundational information and parameters for the use of retting methods and fiber lengths to specifically design natural polymer composite blends with a range of polymer characteristics for multiple industrial applications. Depending of the technical requirements for the natural polymer composites, specific retting and fiber lengths can be utilized to fulfill those needs.

Technical Abstract: The effect of fiber retting on crystallization and mechanical performance was investigated. A poly(hydroxybutyrate-co-valerate) (PHBV) and poly(butylene adipate-co-terephthalate) (PBAT) blend in a 80/20 ratio was modified using 5% by weight kenaf (Hibiscus cannabinus L.) fiber. Fibers were retted using two methods: NaOH alkaline soak and enzymatic retting using pectinase. Two fiber lengths, 5 and 10 mm and a hybrid 1:1 fiber mixture were utilized. From dynamic mechanical analysis (DMA) results, the NaOH retted fibers showed synergistic benefits of using hybrid fiber lengths on modulus. The pectinase retted samples did not show synergistic benefits of fiber lengths, but composites of the same fiber length retted by pectinase outperformed the corresponding composites with NaOH retted fibers. The fiber retting method also affected recrystallization of the biopolymer. Pectinase retting showed a higher recrystallization temperature than NaOH retting. Transcrystallization resulting from fiber presence was analyzed using polarized optical microscopy. Environmental scanning electron microscope (ESEM) revealed smoother surfaces on the pectinase retted fibers compared to NaOH.