Effects of Zinc Borate, Aluminum Hydroxide, and Magnesium Hydroxide on the Flame‐Retardant Performance and Mechanical Properties of Glass Fiber‐Reinforced Epoxy Composites

ABSTRACT Fiber‐reinforced polymer composites are widely used in industries such as automotive, aerospace, and defense due to their exceptional properties. In the automotive sector, these composites are particularly required to exhibit high flame‐retardant characteristics. However, the flame‐retardant capabilities of conventional fiber‐reinforced polymer composites are often insufficient for applications demanding enhanced fire safety. This study systematically investigates the individual and combined effects of zinc borate (Z), aluminum hydroxide (A), and magnesium hydroxide (M) microparticles on the flame‐retardant and mechanical properties of glass fiber‐reinforced epoxy composites. In addition to single‐additive systems, multi‐component hybrid formulations incorporating Z, A, and M particles were developed to evaluate the efficacy of single versus multi‐component systems. During composite fabrication, flame‐retardant additives were incorporated into the epoxy matrix at various weight percentages and combinations, followed by lamination using the hand lay‐up method. Subsequently, horizontal burning and mechanical tests (flexural and impact) were conducted on composite specimens according to international standards. The unfilled (neat) composite exhibited the highest flexural and impact strength. As the additive content increased, particle agglomeration due to high surface energy promoted stress concentration sites, leading to a slight reduction in mechanical properties. Conversely, flammability tests revealed that microparticle reinforcement significantly reduced the horizontal burning rate. Specifically, specimens containing 20 wt.% flame‐retardant additives (20A, 20Z, 20M, 10A10Z, and Hybrid2) achieved burning rate reductions of 41.97%, 47.68%, 12.95%, 35.02%, and 23.20%, respectively, compared to the neat composite. Overall, single zinc borate formulations (20Z) demonstrated superior fire suppression efficiency compared to hybrid combinations, offering a practical optimization pathway for fire‐safe automotive composite structures.