Hemp fibres

For many thousand years cannabis sativa has been a valuable source of hemp fibre. The (ab)use of its psychoactive constituents has also been know in many cultures for a very long time. With the advent of superior alternative medications the medical use of cannabis extracts faded in the last century. Cannabis was removed from the US Pharmacopoeia in 1942 and from the British Pharmacopoeia in 1976 when it was classified as a drug with no therapeutic benefit. 

Hemp, fibre principally from annual herbaceous Cannalissativa but also from many other plants. 

Placet, V., Characterization of the thermo-mechanical behaviour of hemp fibres intended for the manufacturing of high performance... 

Sawpan, M.A., Pickering, K.L., Femyhough, A. Improvement of mechanical performance of industrial hemp fibre reinforced polylactide biocomposites. Compos. A 42, 310-319 (2011)... 

A. Bourmaud, A. Le Duigou, C. Baley, What is the technieal and environmental interest in reusing a recyeled polypropylene-hemp fibre eomposite Polym. Degrad. Stab. 96(10), 1732-1739 (2011)... 

M. Pracella, D. Chionna, 1. Anguillesi, Z. Kulinski, E. Piorkowska, Functionalization, compatibihzation and properties of polypropylene composites with hemp fibres. Compos. Sei. Technol. 66(13), 2218-2230 (2006)... 

Y. Li, K.L. Pickering, R.L. Farrell, Analysis of green hemp fibre reinfraced composites using bag retting and white rot fungal treatments. Ind. Crops Prod. 29(2), 420-426 (2009)... 

A. Keller, Compounding and mechanieal properties of biodegradable hemp fibre eomposites. Compos. Sci. Technol. 63(9), 1307-1316 (2003)... 

Fig. 1. Frequency dependences of sound absorption coefficient a for the samples No. 1 - PP, No. 2 - PP + 40 wt. % of crumble hemp plant. No. 3 - PP + 40 wt. % of long hemp fibres...

Natural fibres are harvested or produced more or less directly from natural bio-products. Flax, coconut and hemp fibres are the most widely used fibres. As these materials have limited strength and other weaknesses (e.g. a tendency to decay organically), they are not widely used in the building sector. A famous example of their use in the car industry was the Trabant car manufactured in the former German Democratic Republic which used cotton-reinforced fibres for the exterior skin. 

Figure 5.17 Deposition of Pt on natural fibres left picture (a) with suspension 1 (150 mg Pt/l) on soft wood fibres right picture (b) suspension 2 (1500 mg Pt/L) on hemp fibres. ( Fraunhofer ICT, 2013.)...

The combination with fibres has proved difficult however. Often there are issues with compatibility between bio-resins and fibres (both natural and synthetic), which cause defects in the composite structure and ultimately poorer physical properties. Castor-oil polyurethane was compared with phenolic resins when infused over sisal fibres however, the phenolic resins showed better structural performance when compared with the castor oil-based material [52]. This is not always the case, as some improvements have been made. Soybean oil thermoset polymers were used in a glass/flax hybrid composite resulting in improved mechanical performance [73], Thermoset resins were produced from triglyceride oils with a wide range of properties (tensile modulus 1-2 GPa, glass transition temperature Tg 70-120 °C) and glass- and hemp- fibre composites were manufactured [74,75]. 

Since the early 2000s, plant-derived biobased fibrous fillers have been frequently used for the reinforcement of PLA-based materials. A well known and frequently used plant-derived fibrous filler is kenaf. Like the case of pollen as an additive, the wettability between PLLA and kenaf should be improved by the addition of a compatibilizer. Other fibrous materials are cellulose fibrous materials or fibres [383,384], cellulose whiskers [385], recycled cellulose fibre [386], cotton fibre [387], sugar beet pulp [388], flax [389], bamboo fibre [390], kenaf [391-393], papyrus [394], hemp fibre [395], cuphea and lesquerella [396], ramie [397], rice straw fibre [398], red algae fibre [399], miscanthus fibre [400], abaca fibre [401], milkweed [402], wood fibre [403] and recycled newspaper fibre [404], Poly(L-lactic acid) fibre can also be used to reinforce soft plastics such as PCL [405],... 

The utilisation of hemp as a source of fibres was known in China for at least 4,800 years. Also the Egyptians had used it, as documented by texts dating back to the end of the Fifth Dynasty (ca. 2350 BC), carved in pyramid stones, and hemp fibres were found in the tomb of Amenhotep IV (alias Akhenaten or Echnaton, ca.1334 BC). [119] The Greeks encountered hemp only in the 5th century BC... 

From the bark of the hemp stems, bast is obtained. The bast fibres are separated mechanically from the woody parts modern separation methods employ enzymes or steam pressure, surfactant or ultrasound processes. The best hemp fibres are obtained from the male plants being very durable. They are used for the manufacture of ropes, cords, nets, strings, yarn, carpets, textiles and sailcloth. The wood is used for the manufacture of insulating material, but it is also well suited for the production of paper, cardboard and cartons, since its lignin content amounts to only 10% (compared to 20-25% from trees). 

Wotzel K, Wirth R, Flake R. Life cycle studies on hemp fibre reinforced components and ABS for automotive parts. Angew Makromol Chem 1999 272 121-127. 

The Institute of Natural Fibres in Poznan, Poland has developed new barrier fabrics, both woven and non-woven. The first was a cotton weave containing a small addition of polyester. The latter was made of flame retardant flax and hemp fibres. The flame retardant and its application method were developed by the institute. The flame retardant, called FOBOS M2T, was based on urea polyborates and the sodium salt of alkyl-aryl sulfonic acid. The method of impregnation is cheap and simple. It can be carried out on typical finishing equipment and increase manufacturing costs by only 10-15%. 

AFM characterization of the surface wettability of hemp fibre was reported by [41]. These images detailed the rough primary cell wall, which is characteristic of the hemp fibre. The fibres showed lower adhesion force and were presumably hydrophobic. Surface roughness averages of the fibre samples were measured to be between 10 and 20 nm on 1 mm areas, which were significantly rougher than the... 

Fig. 1.8 Morphology of hemp fibre surface detailing the rough primary cell wall [41]...

Fig. 1.9 Interaction of water with hemp fibre demonstrating the hydrophobic nature of hemp fibre [42]...

---