Crystalline Character of Agave americana L. Fibers

Abstract

The crystalline character of Agave americana L. fibers and its relationship with mechanical properties were studied. Comparative investigations between three different types of fiber extraction were made: raw fibers, distilled water extracted fibers and seawater extracted fibers. A wide angle X-ray diffraction technique was used and cellulosic phases in the three samples were identified. A diffractometric analysis was applied to determine percent crystalline component, microcrystallite sizes, unit cell dimensions and monoclinic angle. The crystallinity of raw fibers was 51.2 % and dropped with extraction in water. The unit cell dimensions a, b and c for raw fibers were 8.9 Å, 10.3 Å and 7.9 Å, respectively, and the monoclinic angle was 83.6°. When extracted in distilled water, the values of a and c slightly increased, whereas that of the monoclinic angle decreased. These variations were more pronounced for seawater extracted fibers. Our results demonstrated that differences in the molecular and fine structure caused different mechanical properties. High tenacity and initial modulus values were observed for raw fibers which presented the highest crystallinity. On the other hand, the low tenacity and great extensibility of seawater extracted fibers were attributable to their amorphous character and to the increased unit cell dimensions.