An Innovative Treatment Based on Sodium Citrate for Improving the Mechanical Performances of Flax Fiber Reinforced Composites

Abstract

The goal of this paper is to evaluate the effectiveness of a cost-effective and eco-friendly treatment based on the use of sodium citrate (Na3C6H5O7) on the mechanical properties of flax fiber reinforced composites. To this scope, flax fibers were soaked in mildly alkaline solutions of the sodium salt at different weight concentration (i.e., 5%, 10% and 20%) for 120 h at 25 °C. The modifications on fibers surface induced by the proposed treatment were evaluated through Fourier transform infrared analysis (FTIR), whereas scanning electron microscope (SEM) and helium pycnometer were used to obtain useful information about composites morphology. The effect of the concentration of the treating solution on the mechanical response of composites was determined through quasi-static tensile and flexural tests, Charpy impact tests and dynamical mechanical thermal (DMTA) tests. The results revealed that composites reinforced with flax fibers treated in 10% solution exhibit the best mechanical performances as well as the lowest void contents. SEM analysis supported these findings showing that, by treating fibers in solutions with concentration up to 10%, composites having better morphology can be manufactured, in comparison to untreated ones. Conversely, higher Na3C6H5O7 concentrations negatively affect both the morphology and the mechanical properties of composites.

Effectiveness of Sodium Acetate Treatment on the Mechanical Properties and Morphology of Natural Fiber-Reinforced Composites

“…Moreover, the fiber surface roughness could increase, along with the number of cellulose chains exposed on the fiber surface. In such a way, a positive influence on the number of bonds between the polymeric matrix and the fiber surface is obtained [27,46].…”

“…In more detail, a scarce fiber-matrix interface results in higher values of the damping factor. Stronger adhesion, limiting the mobility of the polymer chain, reduces the in addition to increase the glass transition temperature [27,52,53].…”

“…Furthermore, the highly alkaline treatment can significantly affect the mechanical properties of the fibers, hence dramatically limiting their suitability as reinforcement of composite materials [18][19][20]. In such a context, new eco-friendly and inexpensive treatments based on sodium bicarbonate and sodium carbonate salts have been considered recently [21][22][23][24][25][26][27]. Through these approaches, natural fibers are soaked in a mildly alkaline solution that has sodium cations, thus leading to a reaction analogous to the one described by Equation (1).…”

Lemongrass Plant as Potential Sources of Reinforcement for Biocomposites: A Preliminary Experimental Comparison Between Leaf and Culm Fibers

“…It is worth noting that before using lemongrass fibers as reinforcement of polymeric matrices, an opportune treatment must be carried out [33][34][35][36][37]. This approach is often required because, as widely known, the main drawback of natural fibers is their low compatibility with several hydrophobic polymeric matrices, due to the hydrophilic nature of lignocellulosic materials [38,39].…”

New Synthesis Routes toward Improvement of Natural Filler/Synthetic Polymer Interfacial Crosslinking

“…In general, a lignocellulosic biomass is a form of fiber or flour that is utilized as a reinforcing element in a polymer [ 6 , 7 ]. Natural fibers such as kenaf, flax sisal, and bamboo offer major advantages over their synthetic counterparts, such as carbon fillers and glass fillers, due to their low density, low cost, and ability to reduce mechanical wear during processing [ 8 ]. However, the degradation of natural fillers poses serious drawbacks, such as the decline of the mechanical properties over time.…”