Effect of borosilicate residue as flame retardant and reinforcement filler in polypropylene/natural fiber composites

Abstract This study evaluated the influence of adding borosilicate residue (BS) as a flame retardant in polypropylene (PP) and natural fiber composites. The natural fibers used in this study come from the residue of the carpet industry, which is composed of PP and jute fibers (JT), while the PP used as the polymer matrix is postindustrial recycled material. The composites were produced by corotational twin‐screw extrusion and injection molding to obtain the test specimens. A coating process was carried out to add the water‐soluble fraction of BS to the surface of the compositions that did not receive it through incorporation during processing. To characterize the composites, flammability tests, thermogravimetric analysis (TGA), tensile strength test, and morphological analysis by scanning electron microscope (SEM) were performed. The addition of only 2 wt% BS content induces an increase in thermal stability of 32 and 109°C for composites with and without natural fibers, respectively. The addiction of 20 wt% BS elevates the elastic modulus up to 27% of the composites with and without natural fibers. The BS characterization indicates that it could be applied as a flame retardant when applied as coating methods using the water‐soluble fraction of BS, reducing the burning rate up to 92%. Flammability results are similar for formulations with and without natural fibers, indicating that the natural fibers did not influence the proposed flame retardant. The findings suggest that BS coating is a potential solution to improve the properties of natural fiber‐reinforced polymer composites while also promoting waste recycling. This approach produces composites with improved flammability, thermal stability, and mechanical properties, making them suitable for various end applications.