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<p>Natural fiber-reinforced polymer composites exhibit significant vulnerability to prolonged moisture absorption, resulting in the deterioration of mechanical integrity and constraining their use in humid and outdoor settings. This work created epoxy composites reinforced with okra fiber (OF) and modified with nano-alumina (Al₂O₃) to improve moisture resistance and strength retention. The composites were produced with 35 wt% alkali-treated OF and Al₂O₃ nanoparticles at 0, 2, 4, and 6 wt% using the hand lay-up and vacuum bagging methods followed by post-curing. Hygrothermal aging was performed through water immersion for durations of 550, 1050, and 2050&#xa0;h, and the flexural, interlaminar shear (ILSS), dynamic mechanical, and moisture absorption properties were assessed. Alkali treatment enhanced fiber density from 451 to 472&#xa0;kg m⁻³ and elevated the crystallinity index from approximately 37.3% to approximately 41.0%, hence enhancing fiber–matrix compatibility. In arid conditions, the peak flexural strength of around 53&#xa0;MPa was attained at 2 wt% Al₂O₃, indicating an enhancement of about 18% compared to the unfilled composite, which measured around 45&#xa0;MPa. After 2050&#xa0;h of moisture exposure, composites containing 6 wt% Al₂O₃ maintained approximately 76% of their flexural strength and almost 75% of their interlaminar shear strength, demonstrating exceptional hygrothermal durability. The maximum dry ILSS of approximately 15.8&#xa0;MPa was recorded for the 6 wt% Al₂O₃ composite. Dynamic mechanical analysis indicated a rise in flexural modulus from approximately 6.0 GPa (neat composite) to around 8.2 GPa (6 wt% Al₂O₃), with approximately 76% modulus retention during extended immersion. Moisture absorption adhered to Fickian diffusion, exhibiting diminished diffusion coefficients at elevated Al₂O₃ loadings as a result of barrier effects generated by nanoparticles. The findings indicate that nano-Al₂O₃ successfully mitigates moisture-induced deterioration while improving mechanical properties, rendering OF/epoxy hybrid composites appropriate for automotive, agricultural, construction, and outdoor structural applications.</p>

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Performance evaluation of nano-Al₂O₃ modified okra fiber epoxy composites under hygrothermal aging

  • 期刊论文

  • 发表日期：

    2026年4月24日

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  • Jyotsna Kalpana V,
  • Karthi C.,
  • Mohanapriya D.,
  • Vasanthakumar R.,
  • Sathyapriya A.,
  • Velmurugan S.,
  • Vijayasekaran G.

摘要

Natural fiber-reinforced polymer composites exhibit significant vulnerability to prolonged moisture absorption, resulting in the deterioration of mechanical integrity and constraining their use in humid and outdoor settings. This work created epoxy composites reinforced with okra fiber (OF) and modified with nano-alumina (Al₂O₃) to improve moisture resistance and strength retention. The composites were produced with 35 wt% alkali-treated OF and Al₂O₃ nanoparticles at 0, 2, 4, and 6 wt% using the hand lay-up and vacuum bagging methods followed by post-curing. Hygrothermal aging was performed through water immersion for durations of 550, 1050, and 2050 h, and the flexural, interlaminar shear (ILSS), dynamic mechanical, and moisture absorption properties were assessed. Alkali treatment enhanced fiber density from 451 to 472 kg m⁻³ and elevated the crystallinity index from approximately 37.3% to approximately 41.0%, hence enhancing fiber–matrix compatibility. In arid conditions, the peak flexural strength of around 53 MPa was attained at 2 wt% Al₂O₃, indicating an enhancement of about 18% compared to the unfilled composite, which measured around 45 MPa. After 2050 h of moisture exposure, composites containing 6 wt% Al₂O₃ maintained approximately 76% of their flexural strength and almost 75% of their interlaminar shear strength, demonstrating exceptional hygrothermal durability. The maximum dry ILSS of approximately 15.8 MPa was recorded for the 6 wt% Al₂O₃ composite. Dynamic mechanical analysis indicated a rise in flexural modulus from approximately 6.0 GPa (neat composite) to around 8.2 GPa (6 wt% Al₂O₃), with approximately 76% modulus retention during extended immersion. Moisture absorption adhered to Fickian diffusion, exhibiting diminished diffusion coefficients at elevated Al₂O₃ loadings as a result of barrier effects generated by nanoparticles. The findings indicate that nano-Al₂O₃ successfully mitigates moisture-induced deterioration while improving mechanical properties, rendering OF/epoxy hybrid composites appropriate for automotive, agricultural, construction, and outdoor structural applications.