A study of the yearly reproducibility of flax fiber tensile properties

The substitution of glass by flax fiber as reinforcement in composites is a widespread research topic. In this paper, eight flax samples (Marylin variety) have been studied. They were cultivated in the same geographic area over three successive years 2009-2011, two of which were characterized by a rain deficit. The mean values of Young's modulus and the strength at rupture mean values of their elementary fibers ranged from 47 GPa to 64.4 GPa and from 853 MPa to 1109 MPa, respectively. The dispersion of the tensile parameters values was reduced compared to the values previously reported in the literature. However, the main experimental uncertainty, originating from the fiber-section measurement, still accounted for 32% and 23% of the standard deviation of the Young's modulus and the strength at rupture, respectively. The other major part of standard deviation originated from the plant-fiber history (growth, retting and scutching). Anova statistical analysis showed that the average tensile properties of Marylin fibers were relatively constant despite the year of cultivation. Considering flax fiber as a composite per se, biochemical data highlighted a constancy of the cellulosic residue percentage (around 84%) and the preponderance of alkali (representing the coating interphase) over the acid (considered as the composite matrix) extracted-matters (ratio range 1-1.7). This ratio was in favor of the establishment of bridges between microfibrils, by neutral hemicelluloses. Some variability was observed in the content and composition of the alkali extract of the 2011 samples which underwent to the most drastic drought stress but within a tendency which would reinforce the tensile properties of the elementary fibers. (C) 2013 Elsevier B.V. All rights reserved.