Abstract：During the past decade, plant fibers have been thrust into the global spotlight as environment-friendly materials with attractive advantages of low cost, renewability and biodegradability, and have become promising alternatives to traditional synthetic fibers in making fiber-reinforced composites owing to their interesting mechanical and physical properties. However, the limited benefits of the mechanical properties of plant-fiber-reinforced composites (PFRCs) become the bottleneck for their large-scale industrial applications. As we all know, the mechanical performances of composite materials are largely dependent on their interfacial properties owing to the decisive role of the interface in composite structure design. The poor interfacial bonding between hydrophilic plant fibers and hydrophobic polymer matrices is one of the main reasons for the unsatisfactory mechanical properties of PFRCs. In this paper, the unique microstructure, chemical composition and mechanical properties of plant fibers were introduced, together with a review of the latest research progress in improving the interfacial mechanical properties of PFRCs by fiber surface modifications. The limitative effects of the reported improvements by ignoring the hierarchical structure of plant fibers were then analyzed and discussed. Furthermore, the distinct multi-layer and multi-scale microstructure characteristics of plant fibers were considered from the point of views of structural design and manufacturing of the composites. Hybrid technology and nano-modification techniques were employed to design and optimize the interfacial properties of PFRCs. The improved interfacial properties and high mechanical performances of PFRCs were achieved by fully taking advantages of their multi-layer and multi-scale interfacial failure behaviors and damage mechanisms. Based on this, the structural design principles focusing on the mechanical properties, flame-retardant properties and acoustic properties of PFRCs were proposed. In addition, the demonstration applications of the above fundamental research findings on the high mechanical performances and multi-functionality of PFRCs in aviation, railway transportation and automotive industries were introduced. Finally, some suggestions on future research were put forward for achieving the structural and functional integrated green eco-composite materials, so that the large-scale real applications of PFRCs in the fields of aerospace, railway transportation, automotive engineering, civil infrastructures, and so on could be fulfilled. At the same time, expansions of the theories on multi-scale mechanics of composite materials could be expected.
2017, Vol. 38 
