Insight into the Effects of Solvent Treatment of Natural Fibers Prior to Structural Composite Casting: Chemical, Physical and Mechanical Evaluation

Abstract

This paper presents an optimized washing protocol for as-received natural fibers, prior to large-scale composite manufacturing, for the structural strengthening of historic masonry. The aim was to achieve a simple protocol for standard cleaning of fiber surfaces from low molecular weight constituents that may be detrimental towards interfacial strength without damaging the fibers. The proposed procedure employs the application of the solvent sequence: ethanol, acetone, hexane, with optimized incubation times and stirring conditions. Additionally, this procedure may change the surface of the fiber, thereby enhancing the durability of the fiber-matrix interface. The washing protocol resulted in an increase of tensile strength by 56%, 52% and 22% for flax, hemp and sisal fibers, respectively, as compared to the corresponding non-washed fibers, without loss of elongation. The static contact angle measurements confirmed exposure of a higher fraction of the hydrophilic crystalline cellulose, with a higher wettability observed after washing protocols.

Reducing Water Absorption and Increasing the Density of Kapok (Ceiba pentandra, L.) Fibers from Kapok Production Center in Indonesia

“…The presence of wax makes the fiber hydrophobic, which can be removed by dissolving the wax with a hexane solvent. Hexane lowers the hydrophobic properties of the fiber by extracting the wax [21].…”

“…The high oil absorption of kapok fiber is due to the waxy nature of the fiber surface [17], while its absorption of water is due to its thin cell wall, wide lumen, and porosity of more than 80% [18,19]. The oil absorption ability of the fiber can be removed by changing the surface characteristics through chemical treatment with acid or alkaline [14,[20][21][22]. Alkali treatment is mostly expected to decompose lignin and damage cell structure, which can further reduce fiber porosity and water absorption.…”

Evaluation of Novel Compatibility Strategies for Improving the Performance of Recycled Low-Density Polyethylene Based Biocomposites

“…The absorption bands of the filler in all the forms are almost the same in any of the FTIR observations. According to FTIR, carboxyl/aldehyde groups in acids found in hemicellulose, carbonyl/carboxyl groups in pectin, lignin segments, and aliphatic fatty acids found in fibre wax are all represented by a 1746 cm −1 band [42]. After treatment with NaOH, the primary changes are identified by the removal of the peak at approximately 1746 cm −1 indicating that the surface impurities of the filler were eliminated.…”

“…Thus, the topography and functionality of the surface are enhanced [16,43] as indicated by the increased intensity of the OH peak at 3300 cm −1 , which promote access to the OH groups [44]. Furthermore, OP-UT shows a series of bands in the 2950-2800 cm −1 range attributed to C-H asymmetric and symmetric stretching vibrations in the cellulose and hemicellulose groups [42]. The peak at 2861 cm −1 decreased substantially, suggesting that the residual OP-T composition was largely made up of cellulose [45,46].…”

“…When a load is applied, crystallinity also indicates how well molecular chains are structured and slide over one another. As a result of the increased crystallinity, the load transfer capacity among composite ingredients improved, indicating better filler/polymer compatibility [42]. However, for treated filler, there is a slight increase in the degree of crystallinity, which indicates improved interfacial bonding of the filler-polymer surfaces.…”