Luffa fibers as promising reinforcement for polymer composites: Mechanical characterization of NaOH treated and untreated dumbbell test-pieces with Weibull statistics

Different materials require specific test-piece dimensions and designations for their mechanical characterization, present either in ASTM, ISO, or DIN norms. Natural polymers or bio-fibers are materials that have lignocellulosic fibrils that can be mechanically characterized as single fibers, which tend to be bundles of thinner hollow fibrils. In this work, a new approach has been applied to the unique natural fiber Luffa cylindrica, also called loofah or scourer, as loofah dumbbell test-pieces (LDTs) similar in length to the Type IV ASTM D-638 samples for unreinforced or reinforced plastics. 60 LDTs of 120 mm and 40 mm in length and width respectively were cut by hand, with and without alkali treatment (aqueous 2%NaOH), in transversal and longitudinal directions, to be characterized using testing speeds of 1 mm/min and 50 mm/min, SEM, XRD, statistics, and Weibull analysis. The resultant force vs. elongation/stress vs. strain graphs revealed a high variability of LDTs, and mercerization was found to increase their mechanical resistance. SEM images confirmed a microtubular cellular structure, XRD exposed an increment in crystallinity after alkali treatment, and Weibull indicated the probability of failure in 10 samples per configuration.