This article presents a study on the use of natural fibers and kaolin waste as sustainable alternatives in the manufacture of polymer matrix composites. In the present research, isophthalic unsaturated polyester matrix composites were manufactured in association with bamboo fibers (Bambusa vulgaris) and kaolin waste. The kaolin waste was used with a particle size of 50–100 MESH and the fibers in lengths of 15 mm and 30 mm, randomly arranged within the matrix. Bamboo fibers were used fresh and treated with NaOH (5%/2 h). The chemical characterization of the fibers was obtained followed by the morphological characterization using Scanning Electron Microscopy (SEM). The composites were mechanically evaluated through flexural and tensile tests. The mechanical properties obtained were treated by analysis of variance (ANOVA) and Tukey test. The fracture surfaces of the composites were verified by SEM. Bamboo fibers had a chemical composition similar to other natural fibers already studied, with 7.55% extractives, 17.95% total lignin and 74.5% holocellulose. Composites with 30 mm long treated fibers and 30% kaolin showed better flexural strength (137.0 MPa), with deformation of (1.59 mm) and flexural modulus of (19.27 GPa). Through tensile tests, it was possible to identify that the addition of kaolin waste provided a significant improvement in tensile strength of 66% (15BTKW20) and 54% (30BTKW20) compared to neat polyester. SEM micrographs of bamboo fibers, surface roughness, starch granules, micropores and parenchyma cells were identified. ANOVA reinforced the reliability of the results, highlighting the feasibility of manufacturing kaolin waste/bamboo fiber hybrid composites.
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