EP0253828B1 - Modified liber plant fibres and method for obtaining them - Google Patents

Abstract

Modified liber plant fibres, particularly flax, characterized by an enhanced fineness, a reduced quantity of non cellulosic materials, an at least as much ordered crystalline structure of the cellulose. They may be obtained by subjecting the fibres to a hydrolysis treatment in water vapor at high pressure during a limited period of time, followed by a sudden expansion to atmospheric pressure, and by a washing treatment. Application to textile linen fibres.

Description

The present invention relates to modified vegetable bast fibers, in particular flax, usable in particular in the textile industry; It also relates to a process for obtaining such fibers.

By "Liberian vegetable fibers" is meant fibers from the plant liber, such as those of flax, hemp, jute, kenaf, ramie ..., or families such as alfa, sisal, that is ie fibers having a similar structure in a bundle of fibers with cements.

In the following description and claims, reference will be made more particularly to in fibers, these being preferred, but not limiting.

In the technical rod of flax, the fibers are arranged in bundles of elementary fibers at the periphery of the rod between the bark and the wood. There are thirty to forty elementary fibers per bundle, associated with each other by organic cements (pectins, hemicellulose, lignin ...). In the various processes, mechanical or chemical, used to extract the fibers intended for example for the textile industry, one obtains what one commonly calls the technical fibers which are assemblies of elementary fibers, because cements do not have not been completely eliminated during the different transformation phases. These fibrous linens, by their own constitution, have a finesse which is dependent on the presence of the bundles of elementary fibers and also comprise a significant portion of non-cellulosic encrusting materials.

We have already tried to increase the fineness of this fibrous linen and to reduce its content of non-cellulosic materials, by chemical degumming and bleaching treatments.

Effectively compared to unbleached fibrous flax, degummed and bleached flax, hereinafter called bleached flax, has greater finesse, but still has a non-negligible number of bundles in the process of cleavage and sometimes intact; it also has less encrusting material, as can be seen from infrared spectroscopy and differential enthalpy analysis, but it still has a significant part. But in the opposite direction, it can be seen that bleaching degrades the crystalline structure of the cellulose.

Now we have found a modified Liberian vegetable fiber, in particular of flax, which, compared to the present unbleached or bleached fibers, has a greater fineness, a lower quantity of non-cellulosic materials and a crystal structure at least as ordered.

This modified fibrous linen, according to the invention, is, after carding and before spinning, essentially made up of elementary fibers, possibly with some remains of bundles but in negligible proportion compared to the constitution of bleached fibers and all the more unbleached. In addition, in transmission electron microscopy, it has almost no apparent annular structure, said annular structure being representative of the presence of encrusting materials. It is this preponderance of elementary fibers which gives it a standard fineness index significantly lower than that of other unmodified fibers: this index is less than 14.6, that is to say it is less than at least fifteen percent to the fineness index of bleached linen which is 17.2 in the example given later and at least thirty percent compared to unbleached linen.

The preferred modified fibrous linen, according to the invention, is characterized by a very high purity of the cellulose, marked both by a small residual amount of non-cel.lu- losiques encrusting materials and by an undegraded crystal structure, or even improved by the treatment she underwent. The residual quantity of non-cellulosic encrusting materials is determined by various analyzes, either direct, for example the measurement of the total mass of extractable sugars after gentle hydrolysis and assayable by ion exchange chromatography, or indirect, for example the measurement of the number of ketone groups, significant of encrusting materials such as lignin and pectins, by infrared spectroscopy, or comparative for example the examination of fine sections by transmission electron microscopy and the examination of the shape of so-called depolymerization peaks in analysis differential enthalpy. The non-cellulosic encrusting materials of flax include various compounds which, upon hydrolysis, generate sugars such as galactose, xylose, arabinose, rhamnose, mannose, glucose; pectins; lignin.

The preferred modified fibrous linen, according to the invention, has a significantly lower residual sugar content than that of unbleached and bleached linen; in fact, the assay of these sugars by the ion exchange chromatography technique after flax attack for four hours with molar sulfuric acid at 105 ° C. revealed that the total mass of sugars extracted from the flax modified according to the invention was less than 4.25%, that is to say at least two times less important than that extracted from unbleached flax, which is 8.5% in the example given later, or from bleached flax. It has also been noted that as regards the mass extracted from galactose it was less than 1%, that is to say at least three times less in the case of flax modified according to the invention than that extracted from flax ecru, which is 3% in the example given later.

The other analyzes, either indirect or comparative, all lead to the conclusion that the flax modified according to the invention overall contains a smaller amount of non-cellulosic encrusting materials. The value of the absorption support of the ketone group (C = 0) over that of the group (CH ₂ ), by infrared spectroscopy, is considerably less for that modified flax according to the invention than that obtained for unbleached flax and slightly lower than that obtained for the bleached linen. In transmission electron microscopy, the fine cuts of unbleached linen show a very apparent concentric ring structure; this structure is slightly weakened for bleached flax, on the other hand, for flax modified according to the invention, this annular structure has almost disappeared, only one or two rings closest to the lumen persist. In differential enthalpy analysis, the so-called depolymerization peak has a very great intensity in the case of linen modified according to the invention, an average intensity in the case of bleached linen, whereas it cannot be evaluated in the case of linen. ecru, this being no doubt due to the superposition of different peaks.

The modified fine fibrous material according to the invention has a crystalline structure which has not been altered by the treatment undergone, unlike bleached linen. Indeed, by X-ray diffractometry, it is observed on the one hand that the degree of crystallinity relative to a standard of amorphous cellulose is the same for the unbleached, bleached and modified linens according to the invention, but on the other hand that the size of the crystallites, measured in a direction perpendicular to the crystal plane 002, which decreases by more than ten percent during bleaching is equal to or greater than 5.14 nm, that is to say of the same order or even greater in the flax modified according to the invention compared to unbleached flax, according to the example given later.

Patents GB-A-388561, GB-A-476-569 and US-A-2633421 disclose treatments according to which a fiber plant is subjected to the action of steam under high pressure and then expanded to atmospheric pressure. and finally washed. These known treatments relate to the dehulling of fiber plants in the form of straw, leaves, grass, that is to say the separation of the bark or the woody part of the fibers themselves. To obtain such a result, the pressures used are between 38 and 62 bars in one step according to the patents GB-A-388561 and GB-A-476569 and in two steps according to the patent US-A-2633421.

The modified linen according to the invention can be obtained by a process of the aforementioned known type; typically the fiber plant is a previously stained linen under flax and the action of steam is carried out at a pressure of the order of thirty bars for a period of the order of ten seconds.

The modified flax according to the invention can also be obtained by subjecting a dyed, under-rye flax to a first treatment consisting of impregnation with a basic or acid solution, then to a hydrolysis treatment in water vapor at a lower pressure. high, for example of the order of fifteen bars, for a slightly longer time, for example of the order of ninety seconds, followed by a sudden expansion at atmospheric pressure, then a subsequent washing. According to a particularly advantageous mode, the impregnation solution of the first treatment is an alkaline solution containing from four to six percent by weight of soda.

• les figures 1 à 4 sont des photos en microscopie optique des quatre lins en question, respectivement: lin écru (figure 1), lin blanchi (figure 2), lin modifié A (figure 3), lin modifié B (figure 4).
• les figures 5 à 8 sont des photos en microscopic électronique en transmission des quatre lins, respectivement: lin écru (figure 5), lin blanchi (figure 6), lin modifié A (figure 7), lin modifié B (figure 8).
• Les figures 9 à 12 sont les courbes d'analyse enthalpique différentielle des quatre lins: lin écru (figur) 9), lin blanchi (figure 10), lin modifié A (figure 11), lin modifié B (figure 12).

The invention will be better understood thanks to the description which will be given of a comparative embodiment of four short fiber linens: an unbleached linen, a bleached linen and two modified linen according to the invention and attached photos and curves in which :

• Figures 1 to 4 are photos under light microscopy of the four linens in question, respectively: unbleached flax (Figure 1), bleached flax (Figure 2), modified flax A (Figure 3), modified flax B (Figure 4).
• Figures 5 to 8 are photos in electron microscopy in transmission of the four linens, respectively: unbleached flax (Figure 5), bleached flax (Figure 6), modified flax A (Figure 7), modified flax B (Figure 8).
• Figures 9 to 12 are the differential enthalpy analysis curves of the four linens: unbleached flax (figur) 9), bleached flax (figure 10), modified flax A (figure 11), modified flax B (figure 12).

Unbleached short fiber flax is a flax which, after scutching, has undergone a mechanical refining treatment, using different materials of the fine working type. This ecru short fiber linen is a linen produced industrially and marketed for several years. It is used by the textile industry for the production of threads containing flax mixed with synthetic fibers, these threads always being a minority in flax, with a proportion of flax which generally does not exceed twenty five percent.

The bleached flax used is a mechanically refined flax, as above, which has been subjected to a degumming and bleaching treatment known as four quarters, representative of the purest products existing on the market.

The first modified flax according to the invention, hereinafter called modified flax A, was obtained from an under-rye scorched flax, which was introduced into a reactor after having been cut into lengths of seventy millimeters, then subjected to a hydrolysis treatment in steam at 30 bar pressure for a period of ten seconds; at the expiration of this period, the opening of the discharge port of the reactor causes a sudden expansion on passage from high pressure to atmospheric pressure and therefore the ejection by said orifice of flax in a tank containing water slightly alkaline (0.4% soda) where it is washed and then rinsed.

The second modified flax according to the invention, hereinafter called modified B flax, was obtained from a dyed under rolled flax, which, cut into lengths of 70 millimeters, underwent a first treatment of impregnation by a alkaline solution containing 4% by weight of soda. The linen thus impregnated was introduced into the reactor as above and subjected to a hydrolysis treatment in steam, of water at 15 bars of pressure for ninety seconds. The subsequent operations are the same as for modified flax A.

All the comparative tests which will now be described were carried out using the materials (unbleached flax, bleached flax, modified linens A and B) after carding on a conventional card, and before the actual spinning.

Optical microscopy

The examination in light microscopy of the unbleached flax illustrated in Figure 1 (magnification 520) clearly shows the presence of a large number of fiber bundles either intact (1) or in the process of cleavage (2) the bleached flax (Figure 2 ) (magnification 325) still has beams in the process of cleavage (2) and sometimes intact (1) The modified lines A and B almost exclusively contain only elementary fibers (3) with perhaps some remains of bundles (4 ) in the case of modified flax A.

Standard fineness index

Les valeurs obtenues pour les quatre lins sont respectivement de 23,2 pour le lin écru, de 17,2 pour le lin blanchi, de 13,8 pour le lin modifié A, et de 11,3 pour le lin modifié B, avec, dans tous les essais, un coefficient de variation de 2 ou de 3%.The measurement of the standard fineness index (IFS) is carried out from a pad of material of constant mass, which is compressed in a mold under a predetermined pressure. We measure, in millimeters of propyl alcohol, the pressure drop AH undergone by a gas flow passing through a pad thus molded, and the IFS and obtained by the following equation:

The values obtained for the four flaxes are respectively 23.2 for unbleached flax, 17.2 for bleached flax, 13.8 for modified flax A, and 11.3 for modified flax B, with, in all tests, a coefficient of variation of 2 or 3%.

Ion exchange chromatography

The flax is first attacked for four hours with molar sulfuric acid at 105 °, then the extract obtained is analyzed according to the method of chromatographic analysis of sugars perfected by the Boulogne laboratory of the Textile Institute of France and described in the Scientific Bulletin of the Textile Institute of France volume 6, N ° 23, third quarter 1977. This method makes it possible to calculate in percentage the total mass of the extracted sugars, after the action of hydrolyzed managed carried out by l molar sulfuric acid. These sugars are representative of hemicelluloses and pentosans accessible in technical flax. These are in particular arabinose, xylose with the weakest glycosidic bonds, galactose, rhamnose, mannose and glucose. The values obtained, as to the total mass of sugars extracted as a percentage relative to the mass of flax analyzed, are respectively 8.5% for unbleached flax, 11% for bleached flax, 2.9% for modified flax A and 3% for modified flax B.

The values obtained, as regards the mass of galactose extracted as a percentage relative to the mass of flax analyzed, are respectively 3.0% for unbleached flax, 3.5% for bleached flax, 0.4% for modified flax A and 0.6% for modified flax B.

Infrared spectroscopy

The flax sample is powdered and then pelletized with anhydrous potassium bromide before recording its absorption spectrum. In the spectra obtained, the peak linked to the absorption of the ketone group (C = 0), at a wave number of 1730 cm ⁻¹ , shows variations according to the lines, which can be related to the presence in addition or less inlay material, including lignin and pectins. To further quantify these variations, an index defined as the ratio of absorption (C = 0) to absorption (CH ₂ ) was calculated.

The values of this index, obtained with the four linens, are respectively 0.635 for unbleached flax, 0.639 for bleached flax, 0.344 for modified flax A and 0.264 for modified flax B.

Transmission electron microscopy

The flax is successively treated with a 0.1 M solution of sodium periodate for one hour at 20 ° C, with a saturated thiocarbohydrate solution for one hour at 20 ° C and with a solution of osmium tetraoxide for 12 hours at 20 ° C. After rinsing with water and drying, the flax is included in an epoxy resin and cut into fine sections with an ultramicrotome before observation on an electron microscope.

The photos obtained for the four lines (Figures 5 to 8) allow the following observations. Unbleached linen (Figure 5) (magnification: 11,000) has a structure in concentric rings very characteristic of encrusting materials. In bleached flax (Figure 6) (magnification: 9000), there is a weakening of the annular structure, but which nevertheless remains very present. On the other hand, in the modified lines A and B (Figures 7 and 8) (11,000 magnification), the annular structure has almost disappeared; sometimes only one or two rings that are closest to the lumen, that is to say the core of the fiber, persist.

Differential enthalpy analysis

The measurement is made by increasing the linear temperature, at a rate of 20 ° C. per minute, from 1 to 5 milligrams of material under a flow of nitrogen and by recording the difference between the temperatures of the crucible containing the material and a witness crucible. The so-called depolymerization peak is significant both by the temperature at which it is located, and by its intensity.

The comparison of the curves corresponding to the four lines shows that the unbleached linen is clearly different from the others by the shape of its curve, which does not allow to correctly assess the intensity of the depolymerization peak, this being probably due to a superposition of peaks. The temperature of the depolymerization peak of unbleached flax is 375 ° C (Figure 9).

Bleached flax has a depolymerization peak of medium intensity, placed at a temperature of 369 ° C (fig. 10).

Modified flax has a high intensity peak, placed at 373.5 ° C (Figure 11), and the modified flax B has an even greater peak in intensity, placed at 378.5 ° C (Figure 12).

X-ray diffractometry

The flax is cut into 80 µm segments, disoriented and pelletized under a pressure of 350 kg / cm ² . The recording of the diffracted spectrum is done in an angular domain 20 from 10 to 40 °. Measuring the areas of the diffracted peaks makes it possible to assess the crystallinity of the sample compared to an amorphous cellulose standard.

The values obtained are substantially the same for the four flaxes, the crystallinity being 40% for unbleached flax and the modified flaxes A and B, and 39% for bleached flax.

To make the crystallite size measurements, a strand of fibers is diffracted and the thickness of the diffracted lines is measured. One can thus calculate one of the mean dimensions of the smallest crystalline entity of the material. The line chosen corresponds to an angle 20 of 22.5 ° and is related to the crystalline plane 002 of the cellulose.

The sizes of the crystallites measured in a direction perpendicular to the crystal plane 002 are respectively 5.14 nm for unbleached flax, 4.05 nm for bleached flax, 5.45 nm for modified flax A and 6 nm for modified flax B.

The bleaching treatment degraded the crystalline structure of the cellulose, while the flax according to the invention has a crystal structure as, or even more, ordered than unbleached flax.

Of course, given that the composition of a flax is a function of the climatic conditions which are allowed its growth then are retting and of its geographical origin, the quantified results given below are to be taken as orders of magnitude, because they could vary from year to year and from field to field. However, these figures clearly show the characteristics of the flax modified according to the invention compared to those of unbleached flax and of flax chemically treated according to traditional methods.

It should be emphasized that the material which served as a basis for the modified linen according to the invention is an under-rotted flax, for example a flax which has been prematurely gathered in the case of retting on the ground. Under-rotted flax, transformed in the classic processes, is always coarser than a normally rotted flax, insofar as the cements which bind the fibers between them and the bundles between them could not be sufficiently degraded by the agents bacteriological retting. This is how a rotted linen always contains more encrusting materials than a normally rotted flax. It is therefore remarkable that a linen modified according to the invention can have such good characteristics, starting from a linen having such mediocre characteristics.

Modified flax A was used in spinning to produce a flax yarn mixed with synthetic fibers, for example acrylic fibers. Comparatively son of the same type was produced with a mechanically refined linecru, as described in the embodiment example above. It is observed that, for a 75% acrylic / 25% linen mixed yarn, the yarn made from modified flax A is more regular than its counterpart made from unbleached flax. Furthermore, it has been possible to produce with modified flax A a majority thread of flax, which is not possible in industrial market with unbleached flax.

The fibers treated according to the invention, in particular linen, can be used in all conventional textile applications, in particular in admixture with other natural or chemical fibers in the most varied proportions, but also for other applications.

Claims (8)

1. Modified fibrous flax characterised in that it consists, after carding and before spinning, essentially of elementary fibres and in that, in electronic microscopy in transmission, it has practically no apparent annular structure, said annular structure being representative of the presence of encrusting substances.

2. Fibrous flax according to Claim 1, characterised in that the total relative mass of its extractable sugars after controlled hydrolysis and analysable by ion-exchange chromatography, said mass being representative of the quantity of non-cellulose encrusting substances, is less than 4.25%, i.e. at least half that extracted from the raw flax.

3. Fibrous flax according to Claim 2, characterised in that the total relative mass of galactose is less than 1%, i.e. at least one-third of that extracted from the raw flax.

4. Fibrous flax according to Claim 1, characterised in that its standard fineness index is less than 14.6, i.e. at least 15% less than the index of the bleached flax.

5. Fibrous flax according to Claim 1, characterised in that the size of the crystallites measured in a direction perpendicular to the crystalline plane 002 is equal to or greater than 5.14 nm, i.e. the size of the crystallitss of the raw flax.

6. A process for the production of a fibrous flax according to Claim 1 of the type comprising subjecting a fibrous plant to the action of highpressure steam, then expanding to atmospheric pressure and finally washing the same, characterised in that the fibrous plant is a previously scutched flax undergoing retting, and in that the action of the steam is carried out at a pressure of the order of 30 bars for a period of the order of ten seconds.

7. A process for the production of fibrous flax according to Claim 1, of the type comprising subjecting a fibrous plant to the action of highpressure steam, then expanding to atmospheric pressure and finally washing the same, characterised in that the fibrous plant is a previously scutched flax undergoing retting, in that the flax undergoes a first treatment by impregnation by a basic or acid solution, and in that the hydrolysis treatment is carried out at a pressure of the order of 15 bars for a period of the order of 90 seconds.

8. A process according to Claim 7, characterised in that the pretreatment solution is a solution containing from 4 to 6% by weight of soda.

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