Bast fibres: structure, processing, properties, and applications

There is an increasing demand for natural fibres worldwide due to their renewable and biodegradable nature. This paper reviews many aspects of natural fibres, focusing on the bast fibres of plants including hemp, flax, kenaf, jute, and ramie. Important characteristics of these plant fibres include physical, mechanical, dielectric, degradation, hygroscopic, and surface properties. These properties are highly variable, depending on both the chemical composition of the fibre and the environmental conditions. Retting and mechanical are the two main fibre extraction methods. When executed properly, retting produces the highest purity fibre; however, it is time-consuming and generates large amounts of wastewater. In contrast, mechanical extraction is faster and more environmentally friendly but results in low-purity fibre. Despite the drawbacks of bast fibres (e.g. low thermal stability, low hygroscopicity, low surface energy), they have been successfully used in insulation, composite, and geotextiles and many further applications are currently being explored.Abbreviations: AFM: Atomic force microscopy; CSA: Cross-section area; ρ: Density; DTG: Derivative thermogravimetric; γsd: Dispersive (d) component of surface free energy; γsp: Polar (p) component of surface free energy ; EMC: Equilibrium moisture content ; FACF: Fibre area correction factor; f: Fibre fineness; IGC: Inverse gas chromatography; LCA: Life cycling assessment; LLG: Limited life geotextile; LDPE: Low-density polyethylene ; MFA: Microfibril angle; RTM: Resin transfer moulding; γs: Surface free energy; WA: Thermodynamic work of adhesion; TGA: Thermogravimetric