Effect of Stacking Sequence and Sodium Bicarbonate Treatment on Quasi-Static and Dynamic Mechanical Properties of Flax/Jute Epoxy-Based Composites

Abstract

The present paper deals with the investigation of quasi-static and dynamic mechanical response of epoxy-based composites reinforced with flax and/or jute plain weave fabrics. In order to evaluate the influence of the stacking sequence, two monolithic laminates reinforced with flax or jute fibers and two hybrid flax/jute laminates were manufactured through the vacuum infusion technique. Furthermore, an eco-friendly and cost-effective surface treatment based on fiber soaking in a sodium bicarbonate solution was employed to improve the fiber-matrix adhesion. The mechanical characterization (by means of quasi-static flexural, dynamic mechanical thermal analysis and Charpy impact tests) allowed to evidence that the sodium bicarbonate treatment leads to noticeable improvement of the mechanical performances of flax reinforced composites, whereas jute composites experience a slight decrease of their mechanical properties. Overall, the hybridization allows to achieve intermediate mechanical properties among those of monolithic composites. Furthermore, the coupled action of hybridization and surface treatment does not lead to a beneficial and reliable effect on the mechanical response of the resulting composites.

Dynamic Mechanical Behavior Analysis of Flax/Jute Fiber-Reinforced Composites under Salt-Fog Spray Environment

“…In particular, the storage modulus E' at 25 • C of Flax-T laminates (i.e., 5.0 ± 0.1 GPa) was about 47% higher than that of Flax-AR laminates (i.e., 3.4 ± 0.2 GPa). This result confirms that the adhesion between flax fibers and epoxy matrix becomes strongest due to the fiber treatment, as already stated in our previous papers [46,48].…”

“…In particular, epoxy laminates reinforced with untreated or raw jute fabrics (i.e., Jute-AR) showed E' at room temperature (i.e., 4.3 ± 0.1 GPa) about 47% higher than Jute-T laminates (i.e., 2.9 ± 0.3 GPa). This experimental result confirms that the adverse effect of the sodium bicarbonate treatment on the adhesion between jute fibers and epoxy resin leads to decreasing the dynamic modulus of the resulting composites [48].…”

“…To pre-treat the natural reinforcement, flax and jute fabrics were soaked in a 10 wt.% distilled water sodium bicarbonate (i.e., NaHCO 3 ) solution at 25 • C for 5 days, washed with distilled water and dried at 40 • C for 24 h and at 103 • C for further 24 h. All the compared laminates (see Table 1) showed fiber volume fraction equal to about 30%, while the voids content was lower than 5%, as reported in our previous paper [48]. In particular, the voids volume content (v V ) of each composite was evaluated by comparing its experimental and theoretical densities:…”

“…In the present paper the evolution of the dynamic mechanical properties of flax, jute and hybrid flax/jute fiber-reinforced epoxy laminates [48] was analyzed by increasing their exposition time in a salt-fog environment. In particular, two kinds of balanced 2 × 2 twill weave woven fabrics were used as reinforcement, i.e., flax (areal weight 320 g/m 2 ) and jute fabrics (400 g/m 2 ), supplied by Lineo (Valliquerville, France) and Composites Evolution (Chesterfield, UK), respectively.…”

“…To overcome this problem, an eco-friendly and cost-effective treatment consisting of the immersion of natural fibers in sodium bicarbonate solution was investigated in the last years by several researchers [32,[43][44][45][46][47][48][49]. In particular, they showed that the interaction between the mildly alkaline solution and the fiber surface is considered similar to that of traditional alkalization treatment [43].…”