The effect of ammonium polyphosphate on the Crescentia cujete fruit shell polymer composites for automotive heat shield

This research work aims to investigate new polymer composites using Crescentia cujete fruit shell fiber (CF)-loaded epoxy composites prepared in an open mould with varying wt.% of ammonium polyphosphate (APP) in the ranges of 0, 10, 15, and 20 wt.%. The composite specimens were fabricated by ASTM standards and tested for tensile strength, thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical flammability (UL-94 V), field-emission scanning electron microscopy (FE-SEM), and water absorption. The 20 wt.% APP-loaded CF composites had the highest tensile strength of 36.83 MPa, a LOI value of 28, and a flammability ignition time of 21 s, achieving a V-2 rating and dripping. According to UL-94 and LOI measurements, the APP in CF composites improves flame retardancy. Fourier-transform infrared spectroscopy was used on the APP-loaded epoxy composite specimen to identify the presence of various functional groups. Loading APP disrupts epoxy-fiber compatibility, as evidenced by FE-SEM. TGA indicates that higher temperatures result in more char residue, leading to enhanced flame retardancy. The water absorption results indicate that the addition of APP in CF composites absorbs less water compared with the pure composite due to increased resistance and limited flow directions. The TGA result shows, the sample containing 15% APP had an initial weight loss of 5% at 276.48°C and a residue weight of 28.16% at 500°C, indicating that this sample has a higher temperature despite its nature and superior thermal stability when compared to the other samples of this work making it suitable for automotive heat shield applications.