FR2958946A1 - Modifying surface of vegetable fibers comprises contacting the fibers by immersing/spraying a solution of alkaline silicate having a miscible surfactant and compatible with the alkaline silicate and triglyceride and heat treatment - Google Patents

Abstract

Process for modifying the surface of vegetable fibers comprises: (a) contacting the plant fibers by immersing or by spraying a solution of alkaline silicate containing a miscible surfactant and compatible with the alkaline silicate and triglyceride, preferably a liquid triglyceride of plant original, which is in the form of an emulsion in the alkaline silicate solution; and (b) heat treatment, at a temperature of ambient to 110[deg] C, then drying of fibers thus treated and adding silicate on the surface of the fibers. An independent claim is included for plant fibers modified by the process.

Description

PRODUCT AND PROCESS FOR THE MODIFICATION OF THE SURFACE OF PLANT FIBERS, TO IMPROVE THEIR USE PROPERTIES

The subject of the present invention is a process for modifying lignocellulosic surfaces, especially the surface of plant fibers, in order to provide them with new functionalities and to improve their properties of use, in particular in building materials, and in particular to make them compatible both with hydraulic binders and with organic and polymeric matrices, to flame retard them, to protect them from the attack of microorganisms. lignocellulosic origin, whatever the macroscopic nature of the lignocellulosic surface considered. The invention also relates to the use of modified plant fibers in composite materials based on mineral matrices as based on organic matrices, for industries and industrial activities using composite materials, in particular the building and construction sectors. public. The surface modification according to the invention provides, among other properties, flame retardancy, that is to say the resistance to ignition, as well as the improvement of the compatibility and adhesion between the plant fibers. and hydraulic binders such as Portland cement, aluminous cements, plaster, gypsum, hydraulic or aerated lime, as well as various forms of clays for the preparation of bricks. Also, the surface modification according to the invention, by modulating the components of the binder and gelling system, can provide compatibilization of the plant fibers with polymeric surfaces or matrices, such as polyethylenes, polystyrenes, polyesters, and the like. kind of plastic, this list is neither complete nor limiting. Finally, the modification of the surface according to the invention may make it possible to reduce the hygroscopicity, that is to say the moisture recovery capacities of the treated vegetable materials.

The modification of the lignocellulosic surfaces is obtained by contacting said surfaces and in particular the plant fibers in the dry state with an alkali silicate, preferably a sodium silicate, in aqueous solution, in which a triglyceride has been emulsified, preferably a triglyceride of vegetable origin in liquid form, this using a surfactant in aqueous solution miscible and compatible with the silicate solution. The emulsion is made by vigorously stirring the mixture of the three components defined above, namely the aqueous alkali silicate solution, the aqueous solution of compatible surfactant and the triglyceride. Optionally, the emulsion may also contain additional products such as insoluble calcium salts in suspension, alkali carbonates or bicarbonates, mixed organo-mineral silicates such as siliconates, which contain Si-OMe bonds, and bonds Si-CH3, Me being an alkali metal, but these additives do not constitute the core of the invention. These optional additives, especially those which are in solid form, can also be added directly to the plant product object of the treatment.

Alkali silicate in aqueous solution is understood to mean a product corresponding to the general formula nSiO 2, Me 2 O, in which n can take a value of between 0.5 and 4, Me is an alkali metal, preferably sodium, its concentration in the water being between 1 and 55%. The preferred value of the ratio n is between 2 and 3.5

By the term miscible surfactant compatible with the alkali silicate solution is meant any surfactant, i.e. any amphiphilic compound, which can be mixed without difficulty with the silicate solution and give a monophasic mixture, homogeneous, stable over time and retaining the intrinsic properties of said surfactant. This surfactant is itself in aqueous solution. The surfactant will therefore be chosen from products capable of mixing with concentrated solutions of alkaline silicates, and the list is rather limited because the water / alkali silicate system is a particular medium where the availability of water is low.

An amphoteric surfactant in aqueous solution of alkyl-imidodicarboxylate type, preferably sodium, is preferably used, in particular Mirataine H2CHA® (registered trademark of Rhodia) or a product chosen from alkylpolyglucosides, in particular Glucopon CS 600® or Plantaren ® (registered trademarks of Henkel) or among fatty acid sucroesters, without this list being limiting, the selection criterion being the miscibility with concentrated solutions of alkali silicates and the physical and chemical stability in said medium .

The term triglyceride of natural origin means fatty substances of animal origin, but preferably those of vegetable origin, and preferably those which are liquid at ambient temperature. Soybean, rapeseed, sunflower, walnut, grapeseed, peanut, palm, coconut, and more generally all vegetable oils may be used in the context of the invention. Also, any plant product, especially residual, still containing triglycerides and / or free acids associated with these triglycerides may be used in the context of the invention.

By the term contact between the ligno-cellulosic surface products and the alkali silicate solution supplemented with triglyceride, it is meant either a total immersion of the cellulosic surface in the aqueous solutions, or an impregnation or coating of the surface. by any means known to those skilled in the art, such as in particular the spraying of the solution or the deposition by a brush, or by a paint roller, or any other means of impregnation known to those skilled in the art. 'art.

In the case of immersion contacting, which will be preferred for the treatment of divided cellulosic forms having large exchange surfaces, especially vegetable fibers, but also chips, fibrils, pulps, time contact between the cellulosic surface and the triglyceride emulsion in the silicate solution is at least 1 minute, but preferably between 10 and 20 minutes. The suspension is then filtered or sieved, for example on a grid

metallic, so as to separate the plant fibers from the excess aqueous solution. The final treatment consists of drying the plant fibers, either at room temperature or in a specific drying apparatus, in particular a ventilated oven, or preferably, a fluidized-bed dynamic dryer, at an air temperature of between 10 ° C. ambient and 110 ° C. Drying is continued until the treated cellulosic fibers have a water content close to or less than their initial water content, that is to say only differing by more or less 5% by weight, and preferably less than plus or minus 3% by weight. This means that if the initial moisture content of the plant fibers is 15%, the final moisture content of the treated fibers will be between 10 and 20% and preferably between 12 and 18%. The above-mentioned water content is measured by subjecting exactly 10g of fibers (weighed to the milligram accuracy balance) to a temperature of 110 ° C for 1 hour, and then weighing again the obtained fiber mass. after cooling in desiccator. A simple calculation makes it possible to know the mass lost by the sample and thus its water content, which will be expressed in grams lost per hundred grams weighed. In the case of an impregnation treatment, which may be preferable if it is desired to modify the surface of large cellulosic articles, the contacting will be by means of spraying or coating by the aqueous solution of alkali silicate supplemented with triglyceride, and by means similar to those already mentioned and known to those skilled in the art. After a rest period identical to that of the previous phase, the final drying of the objects treated under conditions similar to the case by immersion. This drying is intended to promote the fixing of the treatment system 30 by accelerating the gelation and therefore the adherent deposition on the lignocellulosic surfaces.

The vegetable fibers thus treated are therefore in fact covered by a layer of silicate gelled or crosslinked by the hydrolysis in situ of the emulsified triglyceride in the solution of said silicate, the crosslinked silicate itself being a refractory and therefore insensitive mineral product fire. The crosslinked silicate adheres strongly to the surface of the plant fibers, in particular cellulose fiber, but also in the case where the fiber contains silica, thanks to the in situ crosslinking of the alkaline silicate, which causes a very intimate coating of the vegetal surface of nature. cellulosic whatever its state of division

If these treated plant fibers and the untreated vegetable fibers are compared at a temperature of 500 ° C or with the flame of a butane gas lamp, the untreated fibers are ignited and produce flames. even in the absence of external flame, while the fibers treated according to the invention blacken without inflammation, and do not produce flight of fine incandescent particle, nor flaming.

By the general term "plant fibers" according to the invention, it is necessary to understand all the natural cellulosic fibers, such as wood fibers, cotton, but also hemp, flax, and tropical fibers such as banana, without this list being exhaustive or exhaustive. These plant fibers can be in all kinds of physical forms readily accessible by existing mechanical, hydromechanical or other processes, and their size or degree of aggregation is not critical to the invention. Macroscopic objects, such as planks, boards, bars, rods or wood chips, are considered as well as smaller objects such as fibers, fiber bundles or elementary fibrils of wood, linen, hemp, cotton , alpha, shives, straws, coconut, sisal, banana, rice balls, without this list being complete or limiting.

Recycled products based on plant fibers are also included within the scope of the invention. In the past, many processes have been claimed to modify or render flame retardant vegetable fibers or cellulosic fibers, but none employs a gelled sodium silicate mineral system crosslinked in situ during fiber processing. There are also prior patents which describe the addition of alkali silicates to cellulosic systems, but none of them makes it possible to obtain modification and / or fireproofing of the cellulose, since these systems do not comprise a phase intended to adhere long-lasting and intimate way the alkaline silicate on the surface of the fiber.

In particular, European patent EP1280960 describes a process for preparing a cellulosic product with the addition of an aluminum compound, and not an alkaline earth compound, and an alkali silicate, but the product obtained is intended for use in making a paper and is not dried so as to obtain a surface modification or fireproofing.

Also, PCT / US2000 / 034221 patent claims the addition of a complex soluble metal silicate to a cellulose slurry, which does not disadvantage the process according to the invention, which is based on insolubilization, crosslinking or gelling an alkali silicate on cellulose or plant surface in general, all these terms being considered synonymous here. In addition, said US patent does not include drying phase of the cellulose and silicate system, unlike the method according to the invention.

The method according to the invention in its detail is therefore characterized by the following chronological operations: a) contacting the plant fibers, in the broad sense, by immersion in, or by spraying with a silicate solution alkali silicate-containing alkali-containing surfactant and a triglyceride, preferably a liquid triglyceride of vegetable origin, which is in the form of an emulsion in the alkali silicate solution. b) a heat treatment, at a temperature between ambient and 110 ° C., leading to the evaporation of the aqueous part of the system and to the crosslinking of the alkali silicate by the fatty acids originating from the hydrolysis of the triglyceride, drying the fibers thus treated and the adhesion of the silicate system to the surface of these fibers.

The immersion contacting technique can make it possible to use a continuous treatment process, with recycling and reuse of alkali silicate solutions supplemented with the compatible surfactant and triglyceride. The technique of contacting the treatment solution on the plant surfaces with spray can be carried out in a powder / liquid mixer, batchwise, in the case where the plant cellulose product has a divided form. fibrous or granular. The plant fibers according to the invention may be of any physical form and any level of aggregation and consist of any fibrous products of plant origin that can be used in the industrial applications of the composite materials. The plant fibers are brought into contact by immersion in the alkali silicate solution in the proportion of 1 g to 500 g of dry vegetable fibers per liter of aqueous silicate solution, and preferably between 10 and 300 g of vegetable fibers per liter. of aqueous silicate solution. The proportions of liquid mixture with respect to the amount of vegetable fibers are chosen so as not to cause agglomeration of the fibers.

The contact time between the plant fibers and the silicate solution is greater than 1 minute and preferably between 10 and 15 minutes. The vegetable fibers thus impregnated are filtered on a metal grid and then treated at a temperature of between 20 ° and 110 ° C., the duration of this treatment being such that the water content of the treated vegetable fibers is substantially equal to the initial water of said fibers, that is to say only differing by plus or minus 5% by weight, and preferably less than plus or minus 3% by weight. The invention also relates to plant fibers superficially modified by the method described above, as well as the use of said modified vegetable fibers in composite materials for the building and public works industries, in particular for sound insulation functions. and / or thermal.

EXAMPLE 1 The process according to the invention will be more easily understood by the description of the following example, which describes a treatment carried out by immersion in an aqueous suspension in a container with a useful volume of two liters and equipped with a stirrer. In the case of a paint stirrer driven by an electric motor, 1 kg of 35% solution is introduced into the sodium silicate water of formula 3.3 SiO 2, also called trisilicate Na 2 O. This product corresponds to many commercial products sold in this state of concentration. 25 g of Mirataine H2CHA (registered trademark Rhodia), which is a 30% aqueous solution of sodium laurylimidodipropionate, and thus an amphoteric surfactant which is miscible and compatible with the concentrated silicate solution, are added to this alkaline silicate solution. After stirring until a homogeneous liquid is obtained, 75 g of a liquid, food grade rapeseed oil are added to the above mixture. Stirring is continued until an oil emulsion is obtained in the silicate. The best indicator to determine the acquisition of this emulsion is the visual appearance of the mixture which becomes more and more opaque and white, until the appearance of the milk is then introduced 200 g of dry wood chips (content in water measured at 15.5% by weight by the method described above) in this emulsion, and is left in contact for 10 minutes, still stirring. At the end of this time, the wood chips are separated from the sodium silicate solution by means of a 0.25 mm mesh metal grid and allowed to drain. The wet chips are finally transferred to a crystallizer and the mixture is treated for 2 hours at 100 ° C. in a ventilated oven, stirring every half hour, so as to avoid the aggregation of the chips between them. The water content measured on the chips treated after this drying is 18.3%.

The wood chips thus obtained are subjected to the flame of a lamp at 8

gas soldering and not ignited despite several minutes of exposure. The shavings charcoal, blacken without igniting durably, while the untreated chips catch fire without difficulty.

EXAMPLE 2 Starting from a second sample of chips treated in the same manner as in the previous example, the chips are deposited on the surface of a freshly prepared portland cement slurry and the cement is allowed to set in bulk. same experiment, for comparison, from untreated wood chips. After a setting time of 24 hours, it is found that the treated chips strongly adhere to the cement caked, while the untreated chips do not adhere to the cement. The flameproofing and cement adhesion properties thus evidenced are due to the fact that the treated chips are covered with a cross-linked alkali silicate sheath in the form of silica gel and residual film-forming silicate fixed by intimate coating on the cellulosic surface of the wood.

EXAMPLE 3 In a second embodiment, outside the scope of the invention, the same operation as above is carried out, but the amphoteric surfactant is not introduced into the silicate solution. It is found that the emulsification of the triglyceride in the silicate solution is not obtained. On wood chips treated in this manner, all other things being equal to the previous example, it is found that the wood chips after treatment have an oily feel. The triglyceride did not react with the silicate. The crosslinking did not take place and the treatment of the plant surface was not properly carried out. Properties, including flame retardancy, are not improved with respect to untreated wood chips.

Example 4 The process according to the invention will also be more easily understood by the example

next, which describes another form of process according to the invention, namely a treatment carried out by spraying the silicate solution added according to the invention on flax shives, in a small powder / liquid laboratory mixer, Lodige M5G ( registered trademark Lodige).

By anas, we mean the woody parts of textile plants, mainly flax, located behind the fiber and reduced during the grinding operation scutching small particles. These shives are a by-product generally used for the manufacture of chipboard, feed for farm animals, litter for pets and fuel.

In a Lodige laboratory mixer with a working volume of 5 liters, 2 liters of flax shives are introduced, which represents a mass of about 200 g of this by-product of the flax culture. In addition, a silicate solution added according to the invention is prepared as follows:

In a liquid / liquid mixer with mechanical stirring, sodium silicate 3.5 SiO 2, Na 2 O, 35% solution 200g Mirataine H2CHA ® (registered trademark Rhodia) 5g Isio4® (food grade) is added in the order indicated. This mixture is agitated until a milky appearance of the mixture is obtained, which is significant for obtaining an emulsion of the oil in the silicate solution.

In the rotating Lodige apparatus, containing 200 g of flax shives, 80 g of this liquid mixture according to the invention are immediately sprayed. The flax shives absorb this quantity of liquid without difficulty, keeping their free flow characteristics. The proportion of the liquid mixture with respect to the quantity of flax shives is chosen so as not to cause agglomeration of the shives.

The mixture obtained is treated for 2 hours at 70 ° C. It can be seen by a very visible change in appearance and coloration that the coating with the gelled form of the inorganic silicate is effective. However, it is also noted that the apparent density of the sample of treated shives has not been modified, and that its thermal insulation properties have thus been preserved.

Then, as in Example 1, an ignition test is carried out using a butane-fed welding lamp. Again, the untreated shives catch fire under the open flame, while the treated shives blacken, char, but without a tendency to inflammation. It is also noted during the flammability test, that there is no flight of glowing particles with the anas treated, unlike the untreated control.

The surface properties obtained by the process according to the invention will allow advantageous and improved uses of the treated plant fibers in many applications such as composite materials, fibrociments, ready-mixed additive mortars, agglomerated panels, products aggregated or powdered insulators, and any prefabricated materials for the building and public works industry. The plant products treated by the method according to the invention can also acquire a lipophilic or hydrophobic behavior, by varying the proportions of the constituents of the binder system, in particular by increasing the rate of use of the triglyceride. They can thus also be made compatible for incorporation into organic matrices, in particular to obtain reinforced plastics materials by virtue of better adhesion between the fibers and the matrix. 30

Claims (10)

CLAIMS 1) A process for modifying the surface of plant fibers characterized by the following chronological operations: a) contacting the plant fibers, in the broad sense, by immersion in or by spraying an alkali silicate solution containing a miscible surfactant compatible with the alkali silicate and a triglyceride, preferably a liquid triglyceride of plant origin, which is in the form of an emulsion in the alkali silicate solution. b) A heat treatment, at a temperature between ambient and 110 ° C, leading to the drying of the fibers thus treated and the adhesion of the silicate system to the surface of the fibers. 2) Process according to claim 1, characterized in that the alkali silicate solution contains between 1 and 55% of a silicate whose chemical formula is n SiO2, Me2O, in which n is between 0.5 and 4, and Me is an alkali metal. 3) Method according to claim 1, characterized in that the surfactant miscible and compatible with the alkali silicate solution is selected from amphoteric surfactants, such as alkyl imidodicarboxylates, especially sodium salts, or alkyl poly glucosides, or sucroesters. 4) Process according to claim 1, characterized in that the triglyceride is a product of natural origin, animal or vegetable, but preferably plant, and is in liquid form at room temperature. 5) Process according to claim 1) characterized in that the plant fibers can be of any physical form and any level of aggregation and consist of any fibrous products of plant originusable in industrial applications of composite materials. 6) Process according to claim 1) characterized in that the placing in contact by immersion of the plant fibers to be treated with the aqueous solution of silicate containing additives is in the proportion of 1g to 500 g of dry vegetable fibers per liter of solution aqueous, and preferably between 10 and 300g of plant fibers per liter of aqueous solution, the proportions of the liquid mixture with respect to the amount of plant fibers being chosen not to cause agglomeration of the fibers. 7) Process according to claim 1), characterized in that the contact time between the plant fibers and the silicate solution containing the additives is greater than 1 minute and preferably between 10 and 15 minutes. 8) Process according to claim 1) characterized in that the impregnated plant fibers are filtered on a metal grid, and then dried at a temperature between 20 and 110 ° C, the duration of this drying being such that the water content of the fibers treated vegetable is substantially equal to the initial water content of said fibers, that is to say, differing by more or less than 5% by weight, and preferably less than plus or minus 3% by weight. 9) Plant fibers superficially modified by the process described in claims 1) to 9). 10) Use of modified plant fibers according to claims 1) to 9) in the composite materials based on mineral matrices as based on organic matrices, for industries and industrial activities using composite materials, including the building and construction sectors. public works.