WO2006100560A1

WO2006100560A1 - Process and system for retting plant fibre for textile use

Info

Publication number: WO2006100560A1
Application number: PCT/IB2006/000614
Authority: WO
Inventors: Cesare Tofani; Marco Errani
Original assignee: GRUPPO FIBRANOVA Srl
Current assignee: GRUPPO FIBRANOVA Srl
Priority date: 2005-03-21
Filing date: 2006-03-17
Publication date: 2006-09-28
Anticipated expiration: 2007-09-21
Also published as: RU2007135121A; ITBO20050179A1; CN101142344A; EP1869231A1; KR20070113319A

Abstract

A process adn system for retting of plant fibres in a tank comprising the steps of placing crude fibre from scutched plants in a retting bath with a predetermined water / fibre proportion, or steeping ratio; inoculating the retting bath with strains of bacteria; recirculating the retting bath; controlling and keeping at predetermined values at least one of the following parameters: retting bath tempex-ature, pH value, redox value and oxygen content. In the system a tank is provided with means for supporting the immersed fibre; means for recirculating the liquid; means for reading and keeping at predetermined values at least one of the retting liquid parameters consisting of temperature, pH, redox index and oxygen content, and means for blowing air on command into the retting liquid.

Description

Process and system for retting plant fibre for textile use.

Technical Field

The present invention relates to the sector for processing fibrous plants for the production of plant fibre for textile use, (such as hemp, flax, ramie, kenaf, broom, jute, sisal, nettle) to obtain textile fibres.

It is known that the retting process is the operation used to degrade, break down into their component elements and remove the substances which hold the fibres together, mainly pectins, hemicelluloses and lignins, as a preliminary condition for obtaining fibres which can be used in the textile industry. Such substances may be dissolved mechanically, chemically, biochemically or microbiologically. Microbiological retting is generally based on the decomposition of pectins by micro-organisms present in the ground and on the plants .

Background Art

At present the stems of fibrous plants for textile use are retted with the following methods : a) chemical retting; using significant doses of chemical products (mainly NaOH, caustic soda) , with considerable disadvantages regarding the environment, operator safety and compliance with the regulations in force in many countries; b) retting on the ground; consists in leaving the cut plants lying on the ground, exposed to the weather and fungal microbial flora; c) retting in water; consists of immersing the plants in retting pits with still water, therefore in anaerobiosis conditions, sometimes in hot water to promote the development of bacteria, or in running water, such as that of a river or a stream; d) retting in the field; consists in leaving the plant standing for retting and, when retting is complete, cutting and harvesting the plant .

The fibres obtained from these known processes, in particular in cases b) and d) , may not be sufficiently separated from one another and/or may have characteristics which do not always allow suitable use in the textile industry.

Moreover, many processes which are alternatives to retting, also known as degumming, have been known and experimented with for decades. However, although they often gave good results in the laboratory, they too were disappointing when applied at industrial level .

Therefore, the need is very much felt for a controlled retting process for hemp and other plant fibres for textile use, such as flax and ramie, which is characterised by the high quality and textile workability of the fibre obtained, and by excellent environmental sustainability.

This result would hopefully be achieved both directly, therefore excluding the use of chemical products and processes, and also indirectly, with the construction of a specific system for the treatment of hemp, flax, ramie, etc. fibres, intended for textile production, which creates the conditions for starting a complete agricultural - industrial line and therefore crops on which pesticides are not used, with sustainable use of the raw materials deriving from agriculture.

The crude fibres treated in the invention are usually extracted from the stems with a mechanical action, called "scutching" .

In the conventional method for processing hemp and flax plants, the stems are retted before the scutching step. In accordance with the invention, the stems are scutched before being retted. During scutching the stems are placed parallel with one another and pass first through opposite grooved rollers (roller braking) then through turbines which rotate in the opposite direction (turbine braking) . At the turbine outfeed one or more operators collect the scutched fibre, called the "long fibre", in bundles and send them for spinning where they are first of all hackled.

The remaining fibre deriving from scutching, or from other stripping systems, may be available in the "short" form, called tow.

Accordingly the invention achieves the aims with a process and a system as described in the main claims herein.

Further advantages are obtained with a process and a system as described in the secondary claims.

Brief Description of the Drawings

The technical features of the invention, in accordance with the above-mentioned aims, are clearly indicated in the claims herein, and the advantages are more apparent in the detailed description which follows, with reference to the accompanying drawings, in which:

Figure Ia shows a first possible arrangement of fibres in a system in accordance with the present invention; Figure Ib shows a second arrangement of fibres in a system in accordance with the present invention;

Figure 2 shows a third arrangement of fibres in a system in accordance with the present invention;

Figure 3 shows an alternative to the arrangement of fibres illustrated in Figure 2;

Figure 4 shows a third arrangement of fibres in a system in accordance with the present invention;

Figure 5 is a diagram of a processing system in accordance with the invention; Figure 6 shows an alternative embodiment of the system illustrated in Figure 5 ;

Figure 7 shows a device for loading the fibre in a retting tank of a, system in accordance with the present invention.

Disclosure of the invention

In a preferred embodiment, the retting process involves placing the fibres, already scutched, in a retting bath. The crude, scutched long fibre 5 to be retted may have various shapes, depending on the type of system used for packing at the scutching line outfeed. In the process disclosed, retting takes place between the scutching step and the hackling step, therefore it is advantageous to keep the fibre in the same arrangement in which it was fed out of the scutching line and prepare it in the retting system in such a way that it can then be hackled without any further handling and waste of time and material . In Figure Ia the fibres 3 gathered in bales are placed in that form in a retting tank 1.

In Figure Ib the strips or bundles of long fibre 5 are picked up by an operator, who hangs them in a frame 4, which is then inserted in a retting tank 1. In another possible case (Figure 2), the long fibre 5 at the scutching line outfeed is placed on a conveyor web 6 in one or more fibre sheets 7 with predetermined thickness and width.

Advantageously, in this case the sheets 7 of the fibres 5 are placed on perforated supports (for example plastic meshes 8) or "sandwiched" between two perforated supports and placed on top of one another in a number of layers, which are then duly placed in the retting tank 1, with gaps between them if necessary.

Figure 3 illustrates the case in which the sheet 7 is continuous and can be rolled, so that each turn is separated from the previous and the next one (for example, using twines) . This allows the fibre sheet to be placed on a number of surfaces 9 to be immersed in layers in the retting bath.

The sheet 7 roll is preferably fed continuously to a retting tank so that the sheet is arranged in the tank concertina-style. Figure 7 shows a device for loading a continuous fibre sheet 7 in a retting tank 1.

In this embodiment, the continuous sheet 7 is conveyed by a belt 24 and its thickness is kept within the required limits by a roller 30 located a predetermined distance above the belt 24. At the belt 24 outfeed, the sheet 7 is joined " sandwich" - style to two meshes 8 unwound from reels 25 and picked up with it by a belt 26 which, has a succession of drive rollers which place the sheet 7 joined to the meshes 8 in the tank 1.

The sheet is preferably arranged in layers on top of one another concertina-style and as a result of a toing and froing movement between two opposite walls of the tank 1, with linear or curved trajectory, of the end 27 of the sheet 7 fed out from the belt 26.

In combination with the supply of the sheet 7 from the belt

26 and the toing and froing movement of the end 27 there is also a downward movement of the tank 1, which is mounted on a lift 28 for this purpose.

In this way, the sheet 7 with predetermined thickness is arranged in layers on top of one another until the tank 1 is filled with the required amount of fibres. Once the tank is full it can be moved on wheels 29 to the next treatment steps .

It shall be understood that filling with the fibres may be carried out both directly in the tank 1 and in a container or drum designed to then be immersed in the retting tank. In another case (Figure 4) , the fibre may be placed in perforated drums 11, suitably pressed into homogeneous shapes 13 by a pounder 12 , of the type widely used in staple fibre dyeing systems, or placed on layers of mesh on top of one another, after being fed out of a scribbler in the form of a continuous film. In all cases (long fibres arranged in bundles or sheets, or compacted short fibres) the fibres must be arranged in such a way as to achieve a predetermined density relative to the retting liquid in which they will be immersed.

This density, that is to say, the kilograms of fibre relative to the litres of retting liquid, called the "steeping ratio", using a technical term from textile dyeing processes, may be between 1:10 and 1:60.

For the retting bath a tank of the known type filled with water may be used. The water may be demineralised if necessary and/or the retting liquid already used in one or more previous cycles may be fully or partly reused. -S-

The tank may also be set up for recirculation and remixing of the liquid, preferably using pipes which draw the liquid from the upper part of the tank and return it to the lower part, with the aid of one or more circulating pumps . According to the invention, the retting process takes place using aerobic or anaerobic bacteria inoculation.

According to the invention, the inoculation may be of either type or mixed, provided that during the process one or more strains of bacteria are prevalent, on the basis of which the retting process control parameters are set, in order to maintain optimum process conditions .

By way of example, the following may be used: aerobic inoculation, for example Bacillus subtilis, anaerobic inoculation, for example Clostridium felsineum. Thanks to the invention, during the retting process, the activity of aerobic and anaerobic bacteria present may be stimulated and controlled by blowing in air, for example using perforated tubes 23 located under the layers of immersed fibre.

However, it must be emphasised that the activity of the bacteria may also be promoted by the creation of an anaerobic, stable or alternating environment, inhibiting the blowing in of air, or alternating the supply of air with periods of interruption of said supply.

In particular, retting bath recirculation makes the temperature of the retting liquid homogeneous and keeps it at a predetermined value, preferably within a range between 25° and

40⁰C, for example with the aid of a heat exchanger, located outside or in the lower part of the tank.

Moreover, by acting on the blowing in of air during retting and/or the recirculation of the retting liquid, it is also possible to control other critical parameters in the retting process, such as the pH value (which varies from 4 to 8), the redox index (which varies from -500 to +100) and the oxygen content in the retting bath. These values are preferably read by suitable sensors.

In a preferred embodiment of the process, the value of the parameters controlled (individual or in relation to one another) is continuously read (or is read at predetermined intervals) and constrained to follow a curve over time which describes an optimum trend for the retting process .

At the end of the retting process, which may, by way of example, last 3 - 4 days, the fibre is removed from the retting bath and spread out on a grille 14 for rinsing, preferably being held spread out on the grille by a counter-grille 15.

The fibre is rinsed with jets of water 16, 17 at a pressure which may vary from 20 to 250 bar, from above and from below, for several minutes.

During this step, the individual layers of fibres are arranged and transported on a mobile surface 18 and are subjected to the action of pressurised jets of water, which mechanically remove the substances which degraded during the retting process and the residues present.

Rinsing of the fibres is preferably performed using two opposite jets of water 16, 17 on both sides of the layer of fibres and slightly offset from one another, so that the second jet 17 effectively acts on the fibres just struck by the previous jet 16 without interfering with the latter.

Then the fibre, still spread out, is placed in a drying oven 19 and its humidity brought to a level useful for its preservation (roughly 10 - 15%) .

After the rinsing step treatments may be carried out to improve the intrinsic properties of the fibre before use in the hackling step which precedes the industrial spinning steps, for example using emulsifiable oil.

Finally, the dried fibre, either in bundles or in a carded layer, is sent to a softening apparatus 20, for example passed through a series of opposite pairs of grooved rollers 21 and a final rolling step, or (or in addition) is pressed with presses 22 of the known type (Figure 6) .

At the end of the process, the fibre has a high level of textile quality in terms of fineness ("count") and uniformity, and can therefore be spun, in particular in damp yarn systems, then used in textile machines, of the known type. From the above description it is evident that a first advantage of the retting process is the fact that the control of fibre retting guarantees a semi-finished product with a high level of textile quality, as required by the industry, on one hand, and on the other hand a valid market outlet for the agricultural production of hemp.

A second advantage is the fact that in the process for processing the hemp disclosed, the scutching and retting operations are inverted, the retting being performed on the stripped fibres rather than the stems, thus improving the efficiency of the retting step and bringing many advantages for the agricultural operators, mainly logistical, in the harvesting, storage and scutching step.

Moreover, inoculation of the retting liquid with strains of bacteria selected in a controlled way, in terms of quantity, type and conditions of operation, allows constant control over the process conditions.

Yet another advantage is the fact that the entire system is designed to be automated so that manual intervention is minimised. This drastically reduces the time needed for retting and treating fibres, and gives a more uniform product.

A further advantage is the fact that the system can use low- enthalpy renewable energies .

The invention described has evident industrial applications and can be modified and adapted without thereby departing from the scope of the inventive concept. Moreover, all details of the invention may be substituted by technically equivalent elements .

Claims

1. A process for retting plant fibres for textile use in a tank, characterised in that it comprises the following steps:

- placing a quantity of crude fibre from scutched plants in a retting bath with a predetermined water/fibre proportion, or steeping ratio;

- inoculating the retting bath with strains of bacteria;

- recirculating the retting bath;

- controlling and keeping at predetermined values at least one of the following parameters: retting bath temperature, pH value, redox value, oxygen content.

2. The process according to claim 1, wherein the steeping ratio may be from 1:10 to 1:60.

3. The process according to claim 1 or 2 , wherein the inoculation step involves aerobic and anaerobic inoculation.

4. The process according to any of the claims from 1 to 3 , wherein the retting liquid already used in one or more previous cycles is fully or partly reused.

5. The process according to any of the claims from 1 to 4, wherein air is blown in from an area under the layers of fibres.

6. The process according to one or more of the foregoing claims, wherein said retting bath recirculation occurs by drawing the liquid from the top and reintroducing it in the bath from the bottom.

7. The process according to one or more of the foregoing claims, comprising a step of controlling and keeping the retting bath temperature at a value between 25° and 40⁰C.

8. The process according to claim 6 or 7 , wherein the temperature is controlled by heating from the lower part of the retting bath.

9. The process according to one or more of the foregoing claims, wherein the step of placing the fibres in the retting bath takes place with the fibres in bundles placed on metal rods .

10. The process according to one or more of the claims from 1 to 8, wherein the retting bath is obtained starting with demineralised water.

11. The process according to one or more of the claims from 1 to 10, wherein the step of arranging the fibres involves arranging them in layers on top of one another.

12. The process according to claim 11, wherein the layers on top of one another are separated by meshes .

13. The process according to claim 11 or 12, wherein the layers on top of one another are obtained by folding a continuous layer vertically concertina-style.

14. The process according to any of the claims from 11 to 13, wherein the thickness of at least one of the layers on top of one another is controlled in order to keep it within predetermined values .

15. A process for processing crude fibres from plants for textile use, comprising a retting process according to one or more of the foregoing claims and a preliminary step of green scutching the plant stems .

16. The processing process according to claim 15, comprising a step of rinsing the retted fibre with pressurised jets of water on both sides of layers of spread out fibres, the two jets of water being offset from one another.

17. The processing process according to one or more of the claims from 11 to 16, comprising a step of drying the fibres.

18. The processing process according to claim 15 and/or claim 16, comprising a step of conditioning the rinsed fibres using suitable products, such as emulsifiable oil, anti-static products, colourings and other auxiliary textile products or additives.

19. The processing process according to one or more of the claims from 15 to 18, comprising a step of softening with mechanical apparatuses, by passing the dried fibres between one or more opposite pairs of grooved rollers.

20. A system for retting hemp fibres for textile use, comprising: a tank (1) for holding a retting liquid, having means (4, 8,

9, 11) for supporting the fibre immersed in the bath; retting liquid recirculating means; - means for reading and keeping at predetermined values at least one of the retting liquid parameters consisting of temperature, pH, redox index, oxygen content; and means (23) for blowing air, on command, into the retting liquid.

21. The system according to claim 20, comprising a station for rinsing the retted fibre, comprising a first grille (14) for supporting the fibre and a second grille (15) which can be placed on top of the first, and means for supplying, on both sides of the fibre arranged between the grilles, two pressurised jets (16, 17) of a rinsing liquid, opposite and offset from one another.

22. The system according to claim 20, comprising a fibre drying station.

23. The system according to any of the claims from 20 to 22, comprising a fibre softening station.

24. The system according to any of the claims from 20 to 23, comprising means (24, 25, 26, 27) for continuously feeding a sheet (7) of fibres and positioning it in a retting tank (1) in layers on top of one another concertina-style.

25. The system according to claim 24, wherein the means for feeding the sheet (7) and arranging it in the tank (1) concertina- style comprise a belt (24) at whose outfeed the sheet (7) is joined between two meshes (8) unwound from reels (25) and fed by a belt (26) with a succession of drive rollers (31) , the sheet (7) outfeed end (27) being able to perform a toing and froing movement between two opposite walls of the tank (1) , co-ordinated with a downward movement of a lift (28) supporting the tank (1) .