Self-Healing Mechanisms in Cellulosic Natural Fiber Polymer Composites: A Comprehensive Review of Recent Advances

Natural fiber composites (NFCs) have been regarded as sustainable materials, offering an alternative to synthetic fiber – reinforced polymers due to their biodegradability, low density, cost-effectiveness, and acceptable mechanical performance. Nevertheless, their durability is a critical concern, mainly due to moisture absorption, fiber swelling, micro-crack development, interfacial debonding, and material degradation under normal environmental conditions. All these factors are detrimental to structural reliability, particularly during mechanical loading and outdoor conditions. To overcome these shortcomings, self-healing technologies have been put forward as an effective way to increase damage tolerance and service life. This research critically reviews several self-healing strategies, such as microcapsule-based systems, vascular networks, reversible chemistries (e.g. Diels-Alder, DA), supramolecular and thermoplastic systems, shape memory-based healing, and carbon nanotube-based electrically activated strategies. These methods are comparatively analyzed in terms of healing efficacy, activation stimuli, and compatibility as well as structural performance. Lastly, the main challenges and future research directions are presented to further advance the design of robust self-healing NFC systems for specific applications.