Towards the design of high-performance plant fibre composites

Abstract

For the past 15 years, there has been tremendous and ever-increasing industrial and academic interest and technological material development concerning plant fibre reinforced composites.Plant fibres can be sourced from a multitude of natural agro-sources, with the preferred choice as a composite reinforcement material often being driven by abundance, geographical location, and historical use. While from a product designer's or engineer's point of view, all plant cell walls are 'similar', there is indeed substantial diversity in plant fibre cell walls. Indeed, a growing body of research demonstrates how cell wall mechanical behaviour is strongly linked to its *Manuscript structure, biochemical composition and the plant growing conditions. At the same time, significant progress has been realised on the knowledge of plant fibre cell wall reinforcement mechanisms in biocomposites. Here, we provide a holistic overview of the main types of plant cell walls used as reinforcements for polymer composites. By synthesising a large body of bibliographic data, we present and discuss the useful diversity in cell walls, illustrated by original schematics for clear comparison. The link between their structures and main properties, in constant link with potential associated composite, is specifically discussed. Then, the different fibre extraction and cultivation modes are discussed and compared, especially through an environmental assessment. We also show how a scientist's point of view on cell wall structure and associated experimental approach and use of characterisation techniques lead to distinct results; following a critical review, we make recommendations on appropriate characterisation techniques for a specific fibre. A final discussion concludes this work by highlighting the pertinent parameters that accurately define a composite reinforcement cell wall. The review will serve as a useful handbook reference for researchers in the field of bio-based materials, and will provide important insights to designers and engineers for appropriate selection of plant fibre cell walls for specific composite applications.

Low‐temperature compounding of flax fibers with polyamide 6 via solid‐state shear pulverization: Towards viable natural fiber composites with engineering thermoplastics

“…In terms of stiffness, the addition of scutched flax enhanced both tensile and flexural moduli of PA6 significantly. The modulus increase is expected because the reported elastic modulus of flax is 45–60 GPa . However, the extent of stiffness enhancement is dictated by the processing methodology.…”

“…revealed that the lack of compounding kept the flax fibers in MIXsc mostly in their original, bundled technical fibers state. Based on previous studies that have reported slightly lower tensile modulus for technical fibers (~45 GPa) in reference to elementary fibers (60 GPa) , the E f quantity in Eq . is then an averaged technical/elementary fiber stiffness, which would be lower for MIXsc than SSSPsc.…”

“…As a comparison to the highest tensile modulus reported in this study, 5.5 GPa for SSSPsc, the maximum attainable modulus for a theoretical PA6/flax composite is calculated to be 10.6 GPa via Eqs . – , using orientation factor η O,E = 1; E f = 60 GPa ; E m = 1.68 GPa (measured, Fig. a); L = 2 mm (nominal fiber length); ν f = 0.16 (measured in SSSPsc, Table ); d = 15 μm ; υ = 0.4 (reported by the manufacturer).…”

“…One technical fiber is made up of 10–40 individual fiber entities called elementary fibers, which are 2–5 cm in length and 10–20 μm in diameter. Considering the tensile strength of elementary fibers of ~1,300 MPa compared with that of technical fibers at ~600 MPa , a desired state of flax reinforcement is one where individual elementary fibers are well‐dispersed (i.e., separated) and distributed (spread) within the polymer matrix.…”

“…A highly viable option are fibers derived from natural plant components (natural fibers), which have environmental benefits such as sustainable production, CO 2 neutrality, and minimal energy embodiment [3][4][5][6]. Natural fibers can contribute additional, often unique, combinations of optical, haptic, and acoustic/vibrational damping properties, as well as practical advantages like low density, low cost, and low wear to processing equipment and tooling [4,[7][8][9][10].…”