Influence of Alkali Treatment on the Microstructure and Mechanical Properties of Coir and Abaca Fibers

Abstract

Composite materials with natural fillers have been increasingly used as an alternative to synthetically produced materials. This trend is visible from a representation of polymeric composites with natural cellulose fibers in the automotive industry of the European Union. This trend is entirely logical, owing to a preference for renewable resources. The experimental program itself follows pronounced hypotheses and focuses on a description of the mechanical properties of untreated and alkali-treated natural vegetable fibers, coconut and abaca fibers. These fibers have great potential for use in composite materials. The results and discussion sections contribute to an introduction of an individual methodology for mechanical property assessment of cellulose fibers, and allows for a clear definition of an optimal process of alkalization dependent on the content of hemicellulose and lignin in vegetable fibers. The aim of this research was to investigate the influence of alkali treatment on the surface microstructure and tensile properties of coir and abaca fibers. These fibers were immersed into a 5% solution of NaOH at laboratory temperature for a time interval of 30 min, 1 h, 2 h, 3 h, 6 h, 12 h, 24 h, and 48 h, rinsed and dried. The fiber surface microstructures before and after the alkali treatment were evaluated by SEM (scanning electron microscopy). SEM analysis showed that the alkali treatment in the NaOH solution led to a gradual connective material removal from the fiber surface. The effect of the alkali is evident from the visible changes on the surface of the fibers.

Experimental Investigation of Wavy-Lap Bonds with Natural Cotton Fabric Reinforcement under Cyclic Loading

“…Polymers 2021, 13,2872 12 of 17 due to alkali treatment is negative [36,61] and may have a significant negative impact on the mechanical properties of the fibers in the fabric [62][63][64][65]. The cross-section of adhesive bonds presented in Figure 11 clearly shows the difference between each tested variant of adhesive bonds.…”

“…The Figure 10C also shows no disintegration of the fiber bundles caused by the NaOH solution treatment. Disintegration of the fibers due to alkali treatment is negative [36,61] and may have a significant negative impact on the mechanical properties of the fibers in the fabric [62][63][64][65].…”

“…Alkali treatment with NaOH solution improves the surface structure of the reinforcement. The improvement is caused by removal of unwanted layers, e.g., lignin, oils, and fats, from the reinforcement fiber surface [34][35][36]. The surface treatment leads to improvement of interaction at the interphase boundary, i.e., on the interface of the natural reinforcement and matrix [37].…”

Service Life of Adhesive Bonds under Cyclic Loading with a Filler Based on Natural Waste from Coconut Oil Production

“…The low adhesion of the composite adhesive layer could be caused by insufficient preparation of the bonded material, an undesirable layer on the surface of the filler, e.g., grease, which affects the whole structure of the composite layer and, thus, the adhesion to the bonded material. This problem can be solved by a suitable surface treatment of the natural filler [40][41][42]. Another reason for the occurrence of adhesive failure in bonds with a composite adhesive layer, such as AB10, AB20, and AB30, could be the increased thickness of the adhesive layer compared to adhesive bonds AB0, as shown in Table 2, which showed an adhesion-cohesion type of failure.…”

Geopolymers Reinforced with Natural Fibers: A Comparison among Different Sources

“…The use of natural fibers may cause some problems related to their hydrophobicity, porosity and the presence of incoherent material on their surfaces. In some cases, pretreatments have been made in order to overcome these problems, although this increases the overall economic and environmental impact of the process [24][25][26][27][28]. Another problem related to the use of natural fibers as substitutes for synthetic fibers is the variability of the chemical composition, which affects the final mechanical properties.…”