Effect of graphite morphology on water absorption and fatigue properties of biopolyamide matrix composites

This study examines graphite morphology's impact on water absorption and fatigue properties of biopolyamide-based composites.Graphite is incorporated in flake and expanded forms.Flake graphite consists of thin, flat flakes with layered crystalline structure, high purity, and thermal/electrical conductivity.Expanded graphite, produced by intercalating flake graphite with acid and heating, has a worm-like, porous structure with low density and high surface area.The methodology includes density measurement, water absorption testing, and mechanical assessments.Fatigue behavior is assessed using the Lehr method, with mechanical hysteresis loops analyzed.Graphite enhances mechanical performance of biopolyamides.The modulus of elasticity increases by 40% for material modified with flake graphite, while expanded graphite presents a 10% increase.However, tensile strength decreases by a few percent with flake graphite and 30% with expanded graphite.Water absorption is reduced by up to 20% due to graphite's lamellar structure.Graphite composites show increased fatigue and dynamic creep resistance, with fatigue strength increasing 30% relative to matrix material.Expanded graphite influences friction behavior under low-load conditions.Graphite-filled composites maintain mechanical properties upon thermal aging, while neat BioPA degrades significantly.After accelerated thermal aging, unmodified material presents a 30% and 70% decrease in elastic modulus and tensile strength, while flake graphite composites shows a 20% and 15% decrease, respectively.The findings demonstrate graphite morphology's role in improving tribological properties, moisture uptake and fatigue resistance.