Hydrothermal Effect on Ramie-Fiber-Reinforced Polymer Composite Plates: Water Uptake and Mechanical Properties

Abstract

Ramie-fiber-reinforced polymer composites (RFRP) have the advantages of low price and low energy consumption, but they have high hydrophilicity due to their special chemical composition. In order to study the effect of water absorption on the performance degradation of RFRP in a hydrothermal environment, the authors prepared RFRP sheets by compression molding. Manufactured composites were exposed to a hydrothermal environment with a temperature of 40 °C and a humidity of 50% RH, 85% RH and 98% RH to study the water absorption and diffusion, mechanical properties (tensile properties, flexural properties and shear properties) of the RFRP, and their mechanical properties after drying. The research shows that the equilibrium moisture absorption rate of RFRP is mainly affected by the ambient humidity. The moisture absorption and diffusion of ramie-fiber-reinforced polymer composites (RFRP) in a hydrothermal environment conform to Fick’s law. Before reaching the moisture absorption equilibrium (1~2 weeks), the mechanical properties decline rapidly, and then tend to be flat, and the mechanical properties of the RFRP decrease significantly with the increase in humidity; the water molecules reduce the interfacial bonding performance and the modulus degradation degree of RFRP in the hydrothermal environment is greater than that of strength. After the samples were completely dried, the mechanical properties of the RFRP rebounded greatly, but less than the initial value, and the hydrothermal environment produced irreversible changes to the substrates.

Effect of Various Concentrations of Sodium Hydroxide/Hot Alkali Treatment on the Physical Properties of Ramie Fibres

“…The alkali process that was introduced caused the hydrogen bonds to break and the amorphous area to terminate [17]. The treatment may result in a decrease in non-cellulosic materials and an increase in the fibres surface area, which may raise the quantity of hydrophilic groups on the fibres surface [18]. The outcome showed that the alkali process's elimination of contaminants like lignin and hemicellulose considerably lowers the ramie fibres diameter and prevents defibrillation [19].…”

“…It is well known that ramie fibres have potent hydrophilic qualities [20]. The hydrophilic group on the surface of ramie fibres ameliorates when they were treated with increasing concentrations of alkali, which enhanced the fibre's ability to absorb water [18]. However, the performance of sodium hydroxide's dispersion stability was diminished when the concentration raised to 15%.…”