A Comprehensive Review of Adhesive, Mechanical, and Thermal Joining Methods for Natural Fiber Composites (NFCs)

Abstract

 Driven by growing environmental and economic concerns, natural fiber composites (NFCs) have gained recognition as eco‑friendly substitutes for traditional synthetic composites. However, their use in structural applications depends on effective joining techniques. This review systematically examines three main joining methods for NFCs: mechanical fastening, adhesive bonding, and microwave‑based welding by analyzing their working principles, reported mechanical performance, and current limitations. The main findings show that adhesive bonding provides the most uniform stress distribution (average shear strengths up to 9.75 MPa in sisal/epoxy joints after alkali treatment), while mechanical fastening suffers from drill‑induced delamination (thrust force strongly dependent on feed rate and drill geometry). Microwave welding offers rapid volumetric heating but lacks sufficient data for NFCs. Key research gaps are identified: (i) scarce fatigue data for NFC joints, (ii) lack of validated finite element models accounting for fiber loading effects on microwave heating, and (iii) underexplored hybrid (bonded‑bolted) configurations. This review consolidates current knowledge and provides a roadmap for developing reliable joining strategies to facilitate the broader industrial adoption of NFCs.