Materials Science

Naturally Sticky

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Science  01 Aug 2008:
Vol. 321, Issue 5889, pp. 612-613
DOI: 10.1126/science.321.5889.612c

A key property of good composites is a strong adhesion of the reinforcing material to the matrix. Pommet et al. sought to optimize this feature while advancing the environmentally friendly goal of deriving plastics from renewable sources. They took beds of sisal or hemp fibers and used them as substrates for the bacterium Acetobacter xylinum. During fermentation, a thin film of bacterial cellulose was deposited onto the fibers; to improve coverage, fibers were treated with acetone to remove any waxy coatings. Pullout tests showed greater interfacial shear strength, a measure of adhesion, for both fiber types when they were embedded in a matrix of polymeric cellulose acetate butyrate. For a composite of sisal fibers and poly(lactic acid), Juntaro et al. showed that the tensile strength and Young's modulus improved by about 50% in the direction of the fiber orientation. In the transverse direction, the Young's modulus was greater than that of the pure matrix polymer, but the strength decreased significantly, possibly because of adhesive failure or internal failure of the fibers themselves. Because the cellulose coating technique should work with any natural fiber that has a sufficiently hydrophobic surface, it may be possible to improve further the properties of a biologically sourced and potentially biodegradable polymer composite. — MSL

Biomacromolecules 9, 1643 (2008); Adv. Mater. 20, 10.1002/adma.200703176 (2008).

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