SeitenanfangMarianne Leupin, Swiss Federal Research Station for Agroecology and Agriculture, Reckenholzstrasse 191, CH-8046 Zurich, Switzerland, e-mail: marianne.leupin@fal.admin.ch
Quelle: Hemp, Flax and other Bast Fibrous Plant – Production, Technology and Ecology Symposium, 24 and 25 September 1998, Poznan, Poland: 119-120
Abstract
Conventional water retting of bast fibre is expensive and pollutes the environment. Therefore we are developing a new process less polluting and more economical than the water retting. Based on preliminary data it is most promising to extract fresh fibre directly on the field from the green stands (mechanical decortication) and to process this fibre enzymatically through alkalophilic microorganisms occuring naturally on the fibre (biological degumming).
Green Mechanical Decortication
The principle of the mechanical decorticator is to subject the stem to a succession of blows to break up the woody core. The stems are held against a rotating drum fitted with blunt blades which pass over a fixed plate leaving only a restricted clearance. The stems are fed into the drum where the high velocity blades disintegrate them, causing the fibre to separate, fan out and bend down into the restricted space between the blades and the fixed plate. The blades then scrape away the epidermal, parenchymatous and woody tissues from the fibre (Jarman et al. 1978). Mechanical decortication may be carried out on either fresh green stems or dry stems. Dry decortication is said to be quicker and not to be confined to the harvesting season. However, decortication of fresh stems produces a fibre of better quality (Luniak, 1954; Morweiser, 1962).
Our experiments were done with fresh green hemp stems with a so-called raspador, which consists of a covered drum on a stand (Kirby, 1963). Holding the stems on one end, the operator feeds the other ends to the drum. This decorticates the stem half-way along its length. Then he draws back the stems, reverses them and decorticates the other ends.
Quality tests
Before starting the biological degumming experiments, reliable tests for the determination of the quality of the bast fibre needed to be established. Because the fibres will be used in different ways, different quality characteristics are demanded. Our aim was, therefore, to separate the fibre bundles as far as possible without damaging the single fibre. The fibre quality was assessed by means of molecular weight of cellulose, fibre content and remaining gum-content (uronic acid, pentose and lignin).
In order to assess the quality of the biologically degummed fibre it was compared to primary material (fresh decorticated fibre / BaFa / ATB) and to chemically treated fibre (chemical / ultrasonic / steam explosion) (Tab. 1).
Biological degumming
Preliminary results for biological degumming of decorticated hemp fibre show that bacteria occuring naturally on the fibre have the ability to degum fresh decorticated fibre under alkaline, unsterile conditions (Tab. 1). Treatment lasting 4 days showed no damage of the fibre. Based on the molecular weight of cellulose, the quality of biologically degummed fibres seems to be better than the quality of chemically treated hemp.
The uronic acid content could be reduced to 18.57 % and the pentose content to 44.14 % compared to fresh decorticated hemp. Thus the uronic acid and the pentose content of the biologically degummed fibre is around 10 % lower than in ultrasonic treated fibre.
Tab 1: Uronic acid, pentose, lignin, fibre content and molecular weight of cellulose of fresh decorticated fibre and other primary fibre (BaFa / ATB), chemically (chemical / ultrasonic / steam explosion) treated fibre and biologically degummed fibre (*-preliminary results)
|
uronic acid content |
pentose content |
lignin index * |
fibre content |
molecular weight of cellulose |
||
|
% |
% |
% |
||||
| fresh decorticated hemp |
4.34 |
5.54 |
0.05 |
67.60 |
1'597'110 |
|
| BaFa |
2.86 |
4.1 |
0.03 |
74.91 |
1'595'432 |
|
| ATB |
3.24 |
3.23 |
0.06 |
76.66 |
1'592'015 |
|
| chemical |
1.33* |
2.02* |
0.03 |
90.75* |
1'379'126 |
|
| ultrasonic |
1.24 |
3.02 |
0.05 |
80.63 |
1'419'487 |
|
| steam explosion |
1.52* |
84.15* |
1'404'261 |
|||
| biologically degummed |
0.81 |
2.45 |
0.03 |
82.15 |
1'580'685 |
|
Lignin index: the higher the number, the higher the lignin content
Further Prospect
Green mechanical decortication: Working with the raspador is dangerous and time-consuming. Therefore it would be very interesting to build a machine which combines the harvesting with the mechanical decortication.
Biological degumming: The next steps will be the scale-up from Erlenmeyer trials (50 g) to a laboratory pilot plant (1 - 6 kg) and to optimise the biological degumming process.
Literatur
Jarman C.G., Canning A.J., Mykoluk S. (1978): Cultivation, extraction and processing of ramie fibre: a review. Trop. Sci., 20(1): 91 - 116
Luniak B. (1954): Ramie - decortication. Text. Q., 4 (January): 57 - 64
Morweiser K.F. (1962): Problems in the extraction and processing of ramie fibre. Melliand Textilber., 43 (11): 1137 - 1141
Kirby, R.H. (1963): Vegetable fibres, pp. 148 - 180. London: Leonard Hill, 464 pp.
suppliers of fibre
ATB (1998): Institut für Agrartechnik, Bornim e.V.
BaFa (1997): Badische Naturfaser Aufbereitung GmBH, Malsch
Steam explosion (1997): Institut für angewandte Forschung (IAF), Reutlingen
Ultrasonic (1997). Ecco Gleittechnik GmbH, Seeshaupt
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