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.

Perlite is a glassy amorphous volcanic rock and generally used in construction industries. Possible uses of perlite powder in polymeric composites allow producing value-added products. In this study, expanded Turkish perlite (TP) powder was characterized by particle size distribution and Brunauer–Emmett–Teller analysis. TP-filled high-density polyethylene (HDPE) composites were manufactured via thermokinetic mixer by adding various weight fractions of TP powder (5, 10, 20, and 30 wt%) into HDPE matrix. Produced composites were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, dynamic mechanic analysis, X-ray diffraction, and mechanical and thermal conductivity tests. From mechanical tests, it was observed that HDPE + 5% TP exhibited the greatest tensile strength. Flexural strength of the TP-filled HDPE composite was increased with the increasing TP content. Morphological properties of TP-filled HFPE composites were examined by scanning electron microscopy. As the weight fraction of TP was increased, storage modulus and loss modulus of the composites were increased. Moreover, the relaxation peak of HDPE was increased by the incorporation of TP into HDPE.