Improving mechanical properties of novel flax/tannin composites through different chemical treatments

Abstract

Due to the inherent environmental benefits of using renewable materials, mimosa tannin resin (a natural phenolic resin) reinforced by flax fibres could offer desirable characteristics aiming at reducing carbon footprint of superlight electric vehicles. The non-woven flax mats were chemically treated (alkali, acetylation, silane and enzymatic treatment) to prepare tannin composites through compression moulding (130°C/35min/1.5MPa). The change in fibre morphology was seen in SEM (scanning electronic images). The treatments showed significant improvement in tensile properties, along with enhancement in flexural properties, but little effect on impact resistance. APS treated composites showed highest tensile strength of 60 MPa and modulus of 7.5 GPa. BTCA treatment led to the highest flexural strength of up to 70 MPa. NaOH treatment retained the impact failure force of about 0.5 KN and sustained the saturation energy (4.86 J) compared to untreated composites (4.80 J).

Grape stalk fibers as reinforcing filler for polymer composites with a polystyrene matrix

“…Thus, an increase of approximately 42% in the crystallinity index was observed after the alkaline treatment. Removal of the amorphous and low molecular weight regions with the alkaline treatment contributed to the increase in the crystalline regions of the samples, which could possibly provide better interaction of the fiber with the polymer matrix . According to the Lee et al .…”

“…In contrast, the alkali treatment of the fibers led to a cleaner, yet rougher surface as shown in Figure (b). This is due to the dissolution of lignin, hemicellulose, and waxy materials that increase the inter‐fibrillar region, and impart a rough texture to the surface . A decrease in diameter and more longitudinal grooves on the surfaces can be observed when compared to the FU.…”

“…According to literature, the improvement in the roughness of the fiber surface by the alkaline treatment is due to the better grape stalks/PS wettability, better interfacial adhesion, and, consequently, increased stress transfer at the interface . The mechanical properties of fiber reinforced composites are influenced by the interfacial adhesion between the polymer matrix and the fiber.…”

“…The fibers from the grape stalks were washed to remove dirt from their surface, and were then oven dried at 60 °C for 24 h, and ground in a knife mill. An alkali treatment of NaOH 5% solution (w/v) was used, according to adaptations from the literature . Fibers remained in the NaOH solution in the proportion of 10:1 (solution:fibers) for 2 h at 50 °C.…”

“…By depolymerizing the cellulose and exposing the crystalline cellulose to the interaction with the polymer matrix, the number of bonds between the cellulose and the polymer matrix increases. The alkaline treatment of natural fibers also increases the roughness of the surface, resulting in better interaction, and mechanical properties of the resulting polymer composites …”