FIBERS AND POLYMERS, vol.23, no.7, pp.2017-2029, 2022 (SCI-Expanded)
This study aims to examine the physical and mechanical properties of novolac matrix glass fibers (GFs) and graphite particles (GPs) reinforced hybrid composites as the function of the GFs and GPs content. In accordance with this purpose, the GFs content was kept constant at 20 %wt., while the GPs ratio was changed at 20 %wt., 30 %wt., and 40 %wt. On the other hand, the GPs ratio remained constant at 40 %wt., and the GFs ratio was changed between 20 %wt., 30 %wt., and 40 %wt. To obtain homogeneous hybrid composite powders, the GFs/GPs/Novolac resin powders was blended by a mechanical mixer. Then, the hybrid composite powders were placed in a steel mold and kept in the oven followed by the pressing at 20 MPa. The morphology of the matrix and additive particles used in the production of hybrid composites, the microstructures and fracture surfaces of hybrid composites were examined by scanning electron microscopy (SEM) while the crystalline phases of the materials were investigated by X-ray difftaction (XRD). The density measurements were made by the Archimed's method. The mechanical properties of hybrid composites (hardness and tensile strength) were investigated. Thermal and flammability analyses were performed using thermogravimetric analysis (TGA) and by limited oxygen index (LOI) tests. According to the results, an increase in hardness, maximum tensile strength was determined with the increase in GFs and GPs content in hybrid composites. The hardness and maximum tensile strength obtained in pure novolac were determined as 32 HRM and 12 MPa, respectively, while those determined in hybrid composites were 98 HRM and 33.8 MPa (30 %wt. GFs and 40 %wt. GPs). When the limited oxygen index (LOI) test results were examined, 40 %wt. GPs and 40 %wt. GFs-added composites were determined to be the material with the highest non-flammability. This value shows that the flammability was improved when the required amount of oxygen increased from 37 % to >50 % compared to that of pure novolac.