Effect of Matrix Type and NaOH Treatment on the Mechanical Behavior of Glass–Flax Fiber Hybrid Laminates

Natural fiber–reinforced composites have attracted increasing attention, particularly in the automotive industry, due to their lightweight structure and environmental sustainability advantages. This study aims to evaluate the effects of different matrix systems and alkali surface treatments on the mechanical performance of hybrid composites reinforced with glass fiber and flax fabric. Hybrid laminates were produced using glass fiber and flax fabric as reinforcement materials. Epoxy, vinyl ester, and polyester resins were selected as matrix materials. Sodium hydroxide (NaOH) was applied to the fibers as an alkali surface treatment, and magnesium hydroxide (Mg(OH)₂) was incorporated into the matrix as an additive. To determine the mechanical properties of the produced composite specimens, density, tensile, flexural, and impact tests were performed. The results showed that epoxy-based composites provided the lowest density values and exhibited the highest tensile strength and impact resistance among the investigated matrix systems. The flexural test results indicated that the average values of different matrix systems were close to each other, although the highest flexural strength values were obtained in epoxy-based samples. In addition, the NaOH alkali treatment level and the amount of Mg(OH)₂ additive incorporated into the matrix were found to significantly influence the mechanical performance of the composites. Overall, the results indicate that epoxy-based hybrid glass–flax composites provide the most balanced mechanical performance among the investigated systems and may represent a promising lightweight material alternative for transportation structures requiring improved sustainability and structural efficiency. • Epoxy laminates exhibited highest tensile strength among tested systems. • Polyester composites improved with higher NaOH fiber surface treatment. • NaOH enhanced fiber–matrix adhesion, boosting hybrid laminate performance. • Hybrid laminates achieved lightweight and cost-effective mechanical balance. • Results support sustainable composites for transport and structural uses.