Assessment of Mechanical Property Variation of As-Processed Bast Fibers

Abstract

Hemp, flax, and kenaf are bast fibers with promising material characteristics to sustainably displace synthetic fibers used in composites; however, their use in composite applications is hindered by high material property variability. More widespread adoption and application, as well as improved quality methods, of fibers is contingent on the reduction of this variability. Efforts made herein to assess variability in as-processed fibers and methods were found to identify key sources of variability by investigating four areas: cross-sectional area approximation, physical defects, color and stem diameter, and fiber composition. Using fiber gage lengths closer to those found in composites, different geometric approximations of cross-sectional areas resulted in mean elliptical approximation showing the lowest variability across all fiber types. Next, by removing fibers exhibiting physical defects, maximum variation in tested flax fibers was reduced from 66% to 49% for ultimate tensile strength and 74% to 36% for elastic modulus. Additionally, fibers of darker color were found to have lower mechanical property variation than lighter or spotted fibers, and those coming from smaller stem diameters were found to be stronger than fibers from large stem diameters. Finally, contrary to previous findings with other lignocellulosics, clear trends between the lignin content in a fiber and its mechanical properties were not readily evident. Overall, these factors combined to significantly reduce mechanical property variation, while identifying the underlying contributing parameters.

A critical review of the ultrastructure, mechanics and modelling of flax fibres and their defects

“…Moreover, major crop accidents (pronounced hydric stress or lodging phenomena, for instance) may have resulted in fibres with weak properties; these two extremes nevertheless remain rare. Beyond the agronomic conditions, the intrinsic structural parameters of the fibres, such as the MFA, fibre composition, diameter and presence of defects, have a substantial impact on the mechanical properties of plant fibres [161]. Aslan et al [38] referred to the distribution of defects along flax elementary fibres to explain the scattering of data and shape of the stress-strain curves.…”

Thermal and Mechanical Characterization of Banana Fiber Reinforced Composites for Its Application in Injection Molding

“…Several are the natural materials and vegetable waste that may have relevant mechanical properties, mainly in its fiber format, and which have been characterized by various authors in recent years. As observed in Table 1, showing a range of minimum and maximum values of mechanical data analyzed by different authors, the mechanical behavior of the different natural fibers is highly variable, significantly affecting the process of obtaining and pretreatment [2,3], in addition to the variability of the species itself, the specific conditions of the environment in which each plant develops, the moisture content or the uncertainty associated with the cross-section measurement process for calculating the stress-strain curve [4,5]. Classifying these fibers by their specific tensile strength, and except for the high performance of kenaf, the fibers obtained from the Canary banana are among the highest performance fibers, surpassing sisal, hemp or jute, and presenting a close behavior to the widely spread glass fibers, which places it in an advantageous position for use as a reinforcing material in plastic composites.…”

Fully bio‐based thermoset composites from UV curable prepregs: Vegetable oil acrylate impregnated hemp nanopaper

“…Various other authors have reported that using natural fibers leads to inconsistent composite properties. 19 Paper, fabrics, or mats can be prepared from natural fibers to reduce property variability. Paper preparation is especially beneficial in the case of various waste products that contain natural fibers.…”

“…The authors reported that viscosity was reduced by increasing the AESO temperature to 50°C, and composites with fiber loadings up to 70 wt% were produced. Various other authors have reported that using natural fibers leads to inconsistent composite properties 19 . Paper, fabrics, or mats can be prepared from natural fibers to reduce property variability.…”