Optimization of Porosity and Water Absorption Behaviour of Coconut Fiber-Calabash Ash Hybrid Epoxy Composites for Automotive Dashboard Application

Abstract

This study investigates the porosity and water absorption behaviour of coconut fiber–calabash ash reinforced polymer composites developed as potential materials for automotive dashboard applications. The research addresses the challenge of minimizing internal void formation and moisture susceptibility commonly associated with natural fiber reinforced composites. The objective of the study was to evaluate the influence of epoxy–hardener ratio, coconut fiber content, and calabash ash particulate loading on porosity formation and water absorption characteristics.A Box–Behnken experimental design was employed to systematically analyze the effects of these processing parameters. Treated coconut fibers and finely sieved calabash ash were incorporated into an epoxy matrix through a dispersion technique, after which composite specimens were fabricated and cured under controlled conditions. Porosity was determined using theoretical and experimental density relationships, while water absorption behaviour was evaluated following ASTM D570 procedures. Statistical analysis using ANOVA revealed that the epoxy–hardener ratio exerted the most significant influence on porosity, followed by calabash ash and coconut fiber content. The optimized composite formulation consisting of a 9.5:1.5 epoxy–hardener ratio, 7 wt.% calabash ash, and 4 wt.% coconut fiber produced low average porosity (1.467%) and moderate water absorption (1.313%).The findings demonstrate that controlled hybrid reinforcement of coconut fiber and calabash ash significantly enhances structural compactness while limiting moisture uptake.

Introduction

The study focuses on developing a sustainable automotive dashboard composite using coconut fiber and calabash ash reinforced in an epoxy matrix as an eco-friendly alternative to petroleum-based polymers. Traditional materials like ABS and polypropylene, though strong, raise environmental concerns, motivating the use of natural fiber and waste-derived composites.

Coconut fiber is used for reinforcement due to its strength and availability, while calabash ash acts as a filler to improve stiffness, thermal stability, and durability. However, challenges such as porosity and water absorption affect performance, making optimization essential.

A Box–Behnken experimental design is used to study the effects of epoxy–hardener ratio, coconut fiber content, and calabash ash content on porosity and moisture absorption. Testing follows ASTM D570 standards for water absorption and density-based methods for porosity estimation.

Statistical analysis (ANOVA) shows that all factors significantly influence both porosity and water absorption, with the epoxy–hardener ratio having the strongest effect. Interaction and quadratic effects also play a role in material behavior. The developed regression models are statistically significant and reliable.

Results indicate that increasing fiber and filler content generally increases porosity and water absorption, while the epoxy–hardener ratio strongly controls microstructure quality. Optimization identifies a formulation that minimizes both properties, and validation confirms good consistency, low porosity, and improved moisture resistance.

Conclusion

Overall, the research demonstrates that coconut fiber–calabash ash epoxy composites can provide a lightweight, sustainable, and mechanically viable material for automotive dashboard applications when properly optimized.

References

[1] M. Ali, A. Liu, H. Sou, and N. Chouw, “Mechanical and dynamic properties of coconut fibre reinforced concrete,” Constr. Build. Mater., vol. 30, no. 1, pp. 814–825, 2018. [2] A. K. Bledzki, S. Reihmane, and J. Gassan, “Properties and modification methods for vegetable fibres for natural fibre composites,” J. Appl. Polym. Sci., vol. 59, no. 8, pp. 1329–1336, 2007. [3] A. K. Bledzki and J. Gassan, “Composites reinforced with cellulose-based fibres,” Prog. Polym. Sci., vol. 24, no. 2, pp. 221–274, 1999. [4] O. Faruk, A. K. Bledzki, H. P. Fink, and M. Sain, “Biocomposites reinforced with natural fibers: 2000–2010,” Prog. Polym. Sci., vol. 37, no. 11, pp. 1552–1596, 2012. [5] S. V. Joshi, L. T. Drzal, A. K. Mohanty, and S. Arora, “Are natural fiber composites environmentally superior to glass fiber reinforced composites?,” Compos. Part A Appl. Sci. Manuf., vol. 35, no. 3, pp. 371–376, 2004. [6] S. Kalia, B. S. Kaith, and I. Kaur, “Pretreatments of natural fibers and their application as reinforcing material in polymer composites,” Polym. Eng. Sci., vol. 51, no. 2, pp. 274–285, 2011. [7] N. Saba, M. Jawaid, and O. Y. Alothman, “A review on natural fiber reinforced polymer composites,” J. Mater. Res. Technol., vol. 5, no. 3, pp. 201–211, 2016. [8] K. L. Pickering, M. G. A. Efendy, and T. M. Le, “A review of recent developments in natural fibre composites and their mechanical performance,” Compos. Part A Appl. Sci. Manuf., vol. 83, pp. 98–112, 2016. [9] M. J. John and S. Thomas, “Biofibres and biocomposites,” Carbohydr. Polym., vol. 71, no. 3, pp. 343–364, 2016. [10] E. Muzenda et al., “Properties of coconut fiber reinforced composites,” Procedia Manuf., vol. 7, pp. 171–178, 2016. [11] N. Chikhi et al., “Fire retardant properties of agricultural ash reinforced polymer composites,” J. Compos. Mater., vol. 47, no. 12, pp. 1451–1462, 2013. [12] A. Nourbakhsh and A. Ashori, “Effects of nanoclay and agricultural ash on polymer composites,” Polym. Compos., vol. 31, no. 10, pp. 1685–1692, 2010. [13] R. Kumar et al., “Agricultural waste ashes as sustainable fillers in polymer composites,” Mater. Today Sustain., vol. 7, p. 100032, 2020. [14] E. I. Nwankwo, S. N. K. Onyegirim, K. C. Owuama, and C. A. Ubani, “Engineering Crucible Pots: A Review of Kaolin-Based Composites with Functional Additives”, IJANS, vol. 3, no. 2, pp. 50–62, Jun. 2025. [15] V. Raja, “Polymer materials in automotive interior applications,” Mater. Sci. Forum, vol. 1123, pp. 45–58, 2025. [16] Z. Liqin and L. Hongtong, “Sustainable materials development in automotive engineering,” J. Clean. Prod., vol. 410, p. 137298, 2025. [17] D. C. Montgomery, Design and Analysis of Experiments, 9th ed. New York, NY, USA: John Wiley & Sons, 2017. [18] K. C. Owuama, S. N. K. Onyegirim, E. I. Nwankwo, and I. U. Onyenanu, “Advancements in coconut dehusking technologies: A comprehensive review of mechanization trends, performance metrics, and sustainability,” IPS Journal of Engineering Technology, vol. 1, no. 2, pp. 101–110, May 2025, doi: 10.54117/ijet.v1i2.17.

Copyright

Copyright © 2026 Kennedy Chinedu Owuama, Obong Mbuotidem Alexander Emifoniye Elvis. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.