Chemical modification of sugarcane bagasse and sisal fibers using hydroxymethylated lignin: Influence on impact strength and water absorption of phenolic composites

Abstract

Chemical modification of fiber surfaces can increase wettability of composites reinforced by vegetal fibers and, consequently, the dispersion of the fiber in the matrix and mechanical properties can be improved. Although there are some studies about agents for chemical modifications of vegetal fiber surfaces, there are few data and discussion about the usage of lignin. In the present work, chemical modifications of sugarcane bagasse and sisal fibers using lignin (previously hydroxymethylated) were carried out under different reaction times (15, 30, and 60 min). The composition (holocellulose, hemicelluloses, cellulose, and lignin contents) of the treated and untreated fibers was evaluated. Phenolic composites were prepared using unmodified and modified fibers via compression molding process under temperature. Izod impact, water absorption tests, and scanning electron microscopy were performed to evaluate composite properties. The resin and lignin were characterized by size exclusion chromatography. Results showed that there was a tendency of reducing water absorption for composites prepared from modified fibers. Impact strengths of composites reinforced with sugarcane bagasse with modified fibers were similar to the ones with unmodified fibers (around 20 J/m). However, impact strengths for composites reinforced with modified sisal fibers (around 104 J/m for 15 min of reaction time) were higher than the ones with unmodified fibers (around 95 J/m). Therefore, the usage of lignin as a modifier agent of vegetal fiber surfaces to increase fiber–matrix adhesion for phenolic composites is a strategic alternative for improving products through simple, eco-friendly, and low-cost procedures.

Hybrid composites with glass fiber and natural fibers of sisal, coir, and luffa sponge

“…The following density values were adopted in the calculation: glass fiber (2500 kg/m 3 ), sisal fiber (1500 kg/m 3 ), coconut fiber (1200 kg/m 3 ), luffa fiber (920 kg/m 3 ). 4,11,13–15,21–23 The mass fraction of the constituents, also shown in Table 2, was determined by weighing the materials before and after the composites manufacture.…”

“…All fibers have similar structure, i.e., small fibrils distributed around the hollow center called lumen (see Figure 6(b) and (c)). 4,23,29 Interfacial debonding was observed in some natural fibers (see Figure 6(a) and (c)), as a result of the weak fiber/matrix adhesion. It is noteworthy that these fibers were used without any special treatment to improve interfacial adhesion.…”

“…1–3 Chemical modification of the fiber surfaces can reduce the water absorption and improve the mechanical properties. 4 Another option to improve the mechanical properties is to make hybrid composites by adding small amounts of synthetic fiber, such as glass fiber. Besides improving the mechanical properties, the glass fiber can act as a chemical barrier reducing the water absorption of the composite.…”

“…20 The difference in properties between the sisal fibers, coir fibers, and luffa sponge is remarkable. 4,11,13–15,21–23 The sisal fiber presents higher properties than the coir and the luffa sponge fibers.…”

Mechanical, water uptake properties, and biodegradability of polystyrene‐coated sisal fiber‐reinforced high‐density polyethylene

“…[1,2] There are many natural fibers produced from plants and used as reinforcing materials to enhance the biodegradability of polymeric materials. Many researchers have investigated the use of natural fibers such as sugarcane, [3] sisal, [4] banana, [5] jute, [6] and bamboo [7] for these purposes. Among the available plant fibers, sisal is a hard fiber produced from the Agave sisalana plant.…”