A process for continuous degumming of fibres of bast plants and a device for continuous degumming of fibres of bast plants

The subject matter of the invention includes a process for continuous degumming of fibres of bast plants and a device for continuous degumming of fibres of bast plants, in particular flax fibre.

Apart from cotton fibre, several other types of fibre have been known for a long time, such as flax, hemp, jute, sisal, ramie and kenaf; however, it is flax fibre which is one of the types most widely known and utilised by humans; it is used to manufacture many varieties of fabrics from which garments and underwear are produced and bed linen and table linen as well; as for other types of plant fibres, they are used mainly in the manufacture of industrial products, such as a wide variety of belts, mats and strings, ropes and bags.

The oldest known methods used to obtain plant fibres, and especially flax fibre, include the dew retting process and the water process, hi the dew-retting process, dew or atmospheric precipitation moistens the surface of stems and water diffuses inside the phloem which becomes wet and swells while organic compounds present in the phloem are consumed by fungi which decompose the substances causing the fibres to stick together. Alternating atmospheric precipitation rinses out the adhesive substances and other substances, being products of chemical reactions which occur. The dew-retting process is totally dependent on accidental weather changes; therefore, its duration and the quality of the resulting product remain unpredictable and virtually uncontrollable.

As for the water process, also called water-retting process, the straw of fibrous plants is soaked in retting vats or natural water reservoirs in which reactions similar to those in the dew- retting process occur; however, they are controllable to some extent. The process is, though, fairly expensive due to a significant water consumption at the level of 30 to 35 m ³ per one tonne of straw and a considerable consumption of energy needed to heat water to the temperature of 30 to 34 ⁰ C.

Biochemical phenomena are used in the water-retting process, which occur under the influence of bacteria responsible for anaerobic fermentation of pectin substances and separation of ligneous parts of stalks from fibres, a source of unpleasant smell produced.

Due to the increasing importance of flax fibre used in the manufacture of clothing healthy and friendly for the human body, efforts started to develop industrial methods and devices for the degumming of plant fibres.

Known in the art is the process and device for flax processing disclosed in Canadian patent no. 1 449 652. The process includes washing of flax in cold water, washing in acidified water, washing in hot water and washing again in cold water; subsequently, fibres are treated with enzymes which make them desize; the fibres are washed with cold water, treated with a mixture of peregal and machine oil, opened and finally carded.

A process for the degumming of plant fibres is known, described in patent PCTVPL 2005/000064; it involves placing stalks of fibrous plants in a retting vat or tank which is filled with water, characterised in that the stalks of fibrous plants laid in the vat or tank are treated with water in the proportion of 10: 1 - 70 : 1 with respect to the weight of stalks; subsequently, extraction is carried out using water diffusion and/or osmosis, and the process is divided into three stages; in the first stage stalks immersed in water soften and swell, and soluble substances which contain mineral salts, pectins, retting bacteria and dyes are leached from the stalks; in the second stage osmotic pressure is generated inside the stalks in such a way that the osmotic pressure of water molecules inside the stalks is higher than the pressure outside; in the third stage the pressure which has built up inside the stalks causes them to burst. The water in a pool or tank is periodically changed; alternatively, constant flow is maintained, and water temperature is kept between 7 and 60°C. The leaching process is carried out over time which depends on the drop of pH values to the limit value of pH 5; the degumming process occurs in aqueous solution with a pH of 8 to 5.

A device for the degumming of raw materials obtained from fibrous plants is known, described in patent PCT/PL2006/000085. A distinguishing feature of the device is that it consists of two tanks: the process water tank and the apparatus which constitutes the working tank, equipped with one opened main drain and one fixed main drain with the following equipment in the main drains: flow guides and ultrasonic generators; the process liquid is fed to the apparatus which constitutes the working tank using a chemical pump and it is directed from the control valve to the opened main drain and/or to the fixed main train of the apparatus which constitutes the working tank, while the excess of liquid fed through the chemical plant is directed through a two-way control valve to the process water tank and the range of adjustment

of the two-way valve is set by a manual control valve. Furthermore, in the process water tank the following equipment is fitted: heaters, temperature sensor, pH sensor, liquid level sensor, feeding valve which feeds fresh water from a pipeline, overflow and drain valve. The process for the processing of raw materials obtained from fibrous plants consists in that the raw material to be processed is fed to the apparatus which constitutes the working tank and water and/or other liquid is passed through the tank with a uniform flow rate of the liquid throughout the volume of the apparatus ensured, and the process liquid is fed into the apparatus in a controlled fashion. Preferably, the processing is carried out using liquid aqueous solutions of chemical substances and/or enzymatic and/or biological treatment and/or physical treatment or by ultrasonic methods.

The subject of invention is a process for the continuous degumming of plant fibres of the invention which consists in the soaking of stalks of fibrous plants in water with chemical agents added or without chemical agents added for a specified time and subjecting the stalks to ultrasounds, and the straw which consists of stalks of fibrous plants is shaped in a form of band and it is fed to the technological process area by means of a continuous stream and moves through the area with a specified linear velocity, and the area is divided into sections with each section having a separate water supply. The water flows through individual sections in a counter-current fashion with respect to the direction of band movement, and the water circulates in a closed circuit. The band is subjected to ultrasonic treatment within each section. The temperature of water fed to individual sections should be between 15 and 40°C, and the water flow rate in individual sections should be between 5 to 30 running metres per minute with pH values between 5.5 and 7 and the frequency of ultrasonic waves generated in each section should be between 15 and 30 kHz at the band movement speed uniform for all sections which should preferably be between 0.1 and 0.3 m/hour. Furthermore, the number of sections is preferably not less than five.

The next subject of invention is a device for the continuous degumming of plant fibres having at least five vats which form five sections; one above the other, drawing and pressing rollers are positioned between the vats; at the inlet to the first vat crushing rollers are fitted and at the outlet from the last vat collecting rollers are mounted. Every vat which constitutes one section is equipped with a conveyor, acidity meter and ultrasonic converter. The device has a process liquid tank which is additionally filled with municipal water and connected in parallel with supply pumps, each of which is in turn connected with one vat; furthermore, the vats are connected through the collecting pump and the filter with the process liquid tank. Flow- through heaters for the process liquid and dispensers are fitted between the process liquid feed

pumps and vats. The vats which constitute individual sections can be positioned in one plane parallel to the ground plane or in a plane which descends stepwise at the angle of 3 to 5° with respect to the ground plane or in a plane which rises stepwise at the angle of 3 to 5° with respect to the ground plane.

At the inlet to device a mechanism known in the art is fitted which feeds the band of arranged stalks of fibrous plants coiled into a bale; at the outlet from the device a collecting mechanism and dryer, both known in the art, are fitted.

The device for the constant degumming of plant fibres of the invention is visualised as one exemplary embodiment in the figure, in which the layout of the device is shown (side view), with five vats positioned in the plane parallel to the ground, the process liquid circulation system and the band of stalks of fibrous plants (marked).

The device is shown in the figure, whereby in Fig. 1 respective numbers denote the following:

1 - vat, 2 - pressing rollers, 3 - crushing rollers, 4 - collecting rollers, 5 - feeding hoist, 6 - collecting conveyor, 7 — conveyor, 8 - dryer, 9 — meter, 10 — net conveyor, 11 — ultrasonic converter, 12 - process liquid tank, 13 - connector pipe, 14 - pipe conduit, 15 - feed pump, 16 - pipe conduit, 17 - filter assembly, 18 - collecting pump, 19 - drain valves, 20 - pipe conduit, 21 - flow-through heater, 22 - check valves, 23 - dispenser, 24 - overflow conduit.

The device shown in the exemplary embodiment consists of five vats 1 which constitute sections; one above the other, pressing rollers 2 are positioned between vats 1; at the inlet to the first vat 1 crushing rollers 3 are fitted one above the other and at the outlet from the last vat 1 collecting rollers 4 are mounted one above the other. Feeding conveyor 5 is located immediately before crushing rollers 3_ and collecting conveyor 6 is located immediately after collecting rollers 4 which operates together with conveyor 7 whose major part is located in dryer 8. Inside vats i the probes of acidity meters 9 are fitted and net conveyors H) are located; below their bottoms, ultrasonic converters j_l are fitted. Furthermore, the device contains process liquid tank JL2, for example for hard or soft water, connected through connector pipe 13_ with fresh water supply; moreover, the tank is connected on one side through pipe conduit 14 with five feed pumps 1_5 which feed process liquid to respective vats I; on the other side, the tank is connected via pipe conduit 16 through filter assembly 17 and collecting pump 18 and drain valves 19 with respective vats 1. At pipe conduits 20 which connect feed pumps 15 with vats 1 flow-through heaters 21 for process liquid are fitted with check valves 22 and connected

dispensers 23 which contain washing detergents. Li addition, vats 1 are fitted with overflow pipe conduits 24 connected with pipe conduit 16.

Band 25_, preferably coiled into a bale, is formed from stalks of fibrous plants, such as flax stalks, and the band is fed into feeding conveyor £ and from the conveyor between crushing rollers 3 and net conveyor JlO of the first vat 1, from which the band is fed to the first pair of pressing rollers 2 and so on until the last vat I. From the last vat 1 band 25 is fed between collecting rollers 4 and it is moved to collecting conveyor 6 from which in turn it is fed to cooperating conveyor 7 whose major part is located in dryer 8. Vats 1 are filled with process liquid in a form of soft water at the temperature of 20°C heated in flow-through heaters 21, and the water flows through each vat 1 in the direction opposite with respect to the movement of band 25 at a speed of JLO running metres per minute; the band movement speed is 0.2 m/hour and the pH of the soft water in each vat I is 6. Furthermore, ultrasonic converters H are switched on, located on the bottoms of vats 1; the frequency of ultrasonic waves is maintained at 20 kHz. Water is fed to vats I through respective pumps 15 _. in the amount which ensures that the defined flow rate is maintained in vat 1; the resulting excess water contains products leached from softened stalks of fibrous plants which are removed through overflow pipe conduits 24 via collecting pump JjS and are directed through filter assembly 17 to process liquid tank 12. After the end of the process, the process liquid is removed from vats 1 through drain valves 19.

The process of the invention utilises the ability of water to interact with various components present in the stalks of fibrous plants; the components need to be removed from the stalks to enable separation of fibres from stalks and ensure that the resulting fibres have the best quality possible. The process of the invention makes it possible to obtain premium quality fibres at a short time and it completely eliminates the necessity to use processes which occur in traditional retting; the process is highly efficient both in terms of technology and economy, contrary to the processes known in the art.