Hemp From Disordered Lines for New Staple Fibre Yarns and High-Performance Composite Applications

Abstract

The use of natural fibre-reinforced plastics for higher-stressed applications is currently often limited by the high price of high-quality semi-finished products. Therefore, the present study deals with developing yarns from cost-effective hemp from a disordered separation process (total fibre line) for composite reinforcements. Composites were fabricated using a miniature pultrusion process with thermosetting matrices from the yarns. The results show that around 90% of the flexural strength and flexural modulus of identically produced flax composites could be achieved with maximum values of 282 MPa for the flexural strength and 23.4 GPa for the flexural modulus. The yarns were additionally used to manufacture quasi-unidirectional fabrics to produce composite laminates using different manufacturing processes. The highest values were obtained for a laminate with 39 vol% fibre content, produced with a resin injection process in an autoclave, achieving a tensile strength of 155 MPa, Young’s modulus of 19.4 GPa, a flexural strength of 174 MPa and bending modulus of 12.4 GPa. The characteristic values are sufficient to use the materials in applications with higher mechanical requirements.

A Bio-Inspired Approach to Improve the Toughness of Brittle Bast Fibre-Reinforced Composites Using Cellulose Acetate Foils

“…For example, bast and glass fibres or bast and carbon fibres are used to combine the positive properties of both fibre types. For example, the combination of bast and glass fibres significantly improves toughness compared to pure bast fibre-reinforced composites [ 11 , 12 , 13 , 14 ]. A combination of bast and carbon fibres can lead to an increase in the stiffness and toughness of pure bast fibre-reinforced composites and, at the same time, significantly improve the damping properties of pure carbon fibre-reinforced composites [ 63 , 64 , 65 , 66 ].…”

“…A bio-based epoxy resin was used as the matrix (type SR GreenPoxy 56 resin with hardener SD 7561, mixing ratio 100:36 by mass; Sicomin, Châteauneuf Les Martigues, France). The test specimens were manufactured as described in [ 13 ].…”

“…Various approaches exist in the literature; for example, bast and glass fibres or bast and carbon fibres are combined to bring together the favourable properties of both fibre types. The combination of bast and glass fibres, for example, significantly improves toughness and strength compared to pure bast fibre-reinforced composites and leads to better damping characteristics than pure glass fibre-reinforced composites [ 11 , 12 , 13 , 14 ]. An overview of the hybridisation of kenaf with different kinds of fibres for composite applications can be found in [ 15 , 16 ].…”

An Overview of Natural Fiber Composites for Marine Applications

“…Another study by the same authors developed hemp yarns from the total fiber line with no preferred fiber orientation, processing more fibers from the plant's stem, which reduced the cost of raw natural reinforcement to less than 1 EUR/kg, even cheaper than using flax tow at 1-1.5 EUR/kg, as disordered hemp processing is the most common processing method in Europe with various production lines [125]. The downside of using this recently developed cost-effective hemp manufacturing process was a 40-50% reduction in impact properties compared to flax, while in terms of planar properties (tensile and flexural), the new material was able to retain around 80% [126]. For hemp, the cost could be significantly decreased by multiple factors, such as relaxed regulations on the plants driving the seed cost down and field retting decreasing the cost of fertilization [55].…”

“…Hybridizing hemp with glass fibers was found to significantly improve the mechanical properties of the composite laminates, especially in terms of impact strength, showing the potential of this process [126]. The combination of two types of natural fibers has also been researched to maximize the advantages of the two types of natural fibers, although this can lead to further deterioration of mechanical properties due to water absorption in some cases.…”