Flax fibers were modified by argon and air atmospheric pressure plasma treatments to improve the mechanical properties of flax fiber-reinforced unsaturated polyester composites. Plasma treatments were carried out at plasma powers of 100, 200, and 300 W. Both plasma surface treatments were conducted to improve the tensile strength, tensile modulus, flexural strength, flexural modulus, interlaminar shear strength (ILSS), Mode I interlaminar fracture toughness (G_IC), and Mode II interlaminar fracture toughness (G_IIC). Moreover, the maximum improvement in the mechanical properties was obtained after air plasma treatment of flax fiber at a plasma power of 300 W. Tensile strength, flexural strength, ILSS, G_IC, and G_IIC values of flax fiber-reinforced polyester composites increased by nearly 34%, 31%, 39%, 35%, and 42%, respectively. However, for argon plasma-treated flax fiber-reinforced polyester composites, the mechanical properties of composite increased up to argon plasma power of 200 W.

The purpose of this study was to investigate the extract of Catalpa bignonioides plants and characterize novel natural cellulosic fibers from the fruits as an alternative material for sustainable products. The Catalpa bignonioides tree contains pharmacologically active compounds and is found all over the world. The sustainable natural fibers were easily extracted in an environmentally friendly manner from the fruits of the plant and characterized in terms of their chemical, thermal, and physical properties. The Catalpa bignonioides fibers (CBF) were composed of cellulose (58.3%), hemicellulose (3.1%), and lignin (38.6%) and had a low density (0.713 g/cm³). Fourier transform (FT-IR) analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses were used to search for the chemical groups, crystalline structures, and surface morphology of the CBF fibers. The results suggest that CBF fibers are a suitable alternative for composite and textile applications.