DE10308949B4 - Process for the preparation of inorganic modified cellulosic materials and inorganic modified material - Google Patents

Abstract

A process for the preparation of inorganic modified cellulose-containing materials such as wood, by treating the raw or untreated material with a precursor in the form of a sol prepared via the alkoxide sol-gel pathway or its precursor and subsequent fixation, characterized in that a precursor used obtained by catalyzed two- or multi-stage hydrolysis of alkoxides in alcoholic solution or solutions of alcohol derivatives at a temperature between 20 ° C and the boiling temperature of the solvent, wherein in the first stage a substoichiometric water content and the second hydrolysis step, a molar ratio from water to alkoxide (r _W ) in the range between 0.5: 1 and 1.5: 1 is maintained.

Description

The The invention relates to a method for producing an inorganic modified cellulosic material by treating a corresponding cellulose-containing raw or material with a via the alkoxide sol-gel process prepared special sol or its precursors. The invention further relates to such an inorganic modified material.

cellulosic Materials, in particular wood and derived wood materials represent the widest as renewable raw materials in natural diversity Material pallet for the production of building materials. Low resistance of wood against biological attack usually make a number of preserving treatment steps such. B. with biocides, the often have to be repeated periodically to have a long-term effect to achieve required. However, these treatments often lead to polluting Side effects due to re-release of the active components (Emissions) and their absorption in soil, air and water (contamination). The loss of mechanical strength of wood structural elements due to moisture, rot and attack by wood pests is about it also problematic and leads to a restriction the application possibilities.

in the State of the art are therefore also numerous wood preservatives and tempering agents known. These wood preservatives and tempering agents are based on this on different substance groups. So are wood preservatives and tempering agents based on natural high molecular weight compounds such as bone or skin glue, gelatin, Casein and oils, Waxing and Cellulosderivaten known. The protective effect caused by such Is achieved, but is generally low and the Water and swelling of said natural polymers of disadvantage. Improved protection is achieved by synthetic polymers, z. B. based on formaldehyde, epoxy and polyester resins, polyacrylic or polymethacrylic compounds and polyurethanes. The application of this wood preservative and remedy but has a number of disadvantages, especially the beginning mentioned Problem of contamination and environmental impact.

In the prior art, it is also already known, einzu polysiloxanes or silicone resins for dimensional stabilization and solidification of wood set ( DE-OS 322 2963 ). From the EP 0 747 184 A2 Furthermore, a protective and consolidating agent for renewable raw materials based on starch, cellulose and / or their degradation products is known, which consists of a modified metal oxide organosol. The protective and consolidating agent according to the above mentioned European patent application is an organosol obtained by acid or base catalyzed hydrolysis of metal oxides. This organosol is then infiltrated into the lignocellulosic material.

Furthermore, from the following documents still further composite materials and wood preservatives are known. In detail, these are the DE-OS 196 47 368 A1 , which relates to a composite, the DE 198 33 479 A1 that describes a wood preservative as well as the DE 198 40 009 A1 which relates to a process for producing thermally-deformed solgug-coated substrates. Further moldings and manufacturing processes are known from DE 198 16 136 A1 , as well as from the article of Prof. Dr. med. Horst Böttcher, both gel coatings Innovation for the protection of materials from Coating 11/99, p. 431 ff. As well as the WO 80/02249 A1 nd the EP 1 027 355 B1 known.

It However, it has been shown that with the Organosol, as in the mentioned above European Patent application is described, produced wood materials only have unsatisfactory properties. This applies in particular on the moisture absorption, the biological resistance and the mechanical Properties of these wood-based materials.

Starting from the EP 0 747 184 A2 It is therefore an object of the invention to provide an improved method by which wood-based materials can be obtained which have improved properties, in particular with regard to their moisture absorption, dimensional stability, biological resistance, their fire behavior and their mechanical properties. It is a further object of the present invention to propose corresponding wood-based materials.

The The object of the present invention is related to the method by the features of claim 1, with respect to the inorganic modified material by the features of claim 18 solved. The dependent claims show advantageous developments.

The invention thus provides a process for the preparation of inorganic-modified cellulose containing materials, in which the cellulosic raw material or material is subjected to a treatment with a special liquid precursor. According to claim 1, the precursor of the invention is characterized in that it is a sol prepared by the alkoxide sol-gel method or one of the low molecular weight precursors obtained by catalyzed hydrolysis of alkoxides in a generally alcoholic solution, which is essential for the invention, in the preparation of the precursor this is obtained at elevated temperature, preferably a temperature between 20 ° C and the boiling temperature of the solvent. By means of this measure according to the invention, it is obviously achieved that ultrafine particles and chemical species are obtained which are particularly suitable for the process according to the invention. They are characterized in that they are very small and relatively compact and / or have a reactive surface. The precursor used in the process according to the invention is prepared by a two- and multi-stage hydrolysis. The introduction of the precursor takes place in the entire volume of the cellulose-containing raw material or material and can be carried out with all methods known to those skilled in the impregnation of cellulose-containing raw materials and materials, in particular by impregnation under vacuum and / or pressure.

In the case, that a one-step hydrolysis is carried out, it follows that very small and apparently compact particles are formed smaller than the particles of uncooked samples, d. H. of samples of the same composition under process conditions, as they usually do for the Production of this brine can be used (temperatures around 20 ° C, atmospheric pressure).

The mean particle size, the is in the range of 1 to 15 nm, but especially preferably in the range of 1 to 6 nm. The particles can be in every stage between production and gelation, d. H. spatial Crosslinking, good detection of photon correlation spectroscopy. In contrast, the particles of equivalent approaches that under usual Ambient conditions (about 20 ° C, Normal pressure) can be obtained at all not or poorly detectable, indicating a delayed particle formation and loosely packed particles which differ greatly from the spherical shape shut down leaves.

It It has been shown that when using a sol, as above described, a treatment of a cellulosic material carried out is, by the obtained particle size, a filling of the open supply channels in the cellulose-containing materials is achieved. The result is a composite material, in its supply channels the colloidal particles of the sol become columnar stable gel monoliths crosslink in the longitudinal direction of growth of the wood. This leads to significant Improvements in the properties of the materials treated thereby in terms of dimensional stability, biological resistance, the fire behavior and partly the mechanical properties.

In this method, as described above, it is particularly preferred if the molar ratio of water to alkoxide (r _W ) in the range of 0.5: 1 to 15: 1, but preferably from 2: 1 to 5: 1. The molar ratio of solvent to alkoxide (r _L ) should be chosen to be between 0.5: 1 and 20: 1, more preferably between 1.5: 1 and 7: 1. Another characteristic is that an acidic catalysis is carried out in the first reaction phases, wherein the catalyst is used in very low concentrations (molar ratio of catalyst to alkoxide 0.1: 1 to 0.00001: 1), preferably 0.001: 1 to 0.0001: 1st

From a material point of view it is preferred if precursors are used for the process according to the invention, which are selected from the systems SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , P ₂ O ₅ or B ₂ O ₃ or mixtures thereof. The precursor used in the process according to the invention is further distinguished by the fact that the solvent used is a polar organic solvent, preferably alcohol or its derivatives. The solvent is in the special case of alcohol use at the same time solvent and reactant. In this case, the solvent is preferably the mother alcohol of the alkoxide used, ie the alcohol corresponding to the OR groups of the alkoxide [M (OR) _x ], in the preferred case ethanol (R = C ₂ H ₅ ). As catalysts for the acidic catalysis in particular mineral acids such as hydrochloric acid and nitric acid can be used, but also organic acids such. As acetic acid and citric acid are in principle suitable.

As mentioned in the introduction, the process with a one-stage hydrolysis leads to such sols being incorporated in the open supply channels (and cross-connections thereof) of the cellulose-containing material and forming columns of alco- or xerogels there, so that markedly improved properties result. Alko- or xerogels are gels that have lost their fluid, which also changes the spatial arrangement of the network. The gel, which itself can bind considerable amounts of water (up to 25% by mass), acts as a mechanical barrier and buffer with respect to the water absorption of the cellulose-containing material when.

In contrast, the process now uses a precursor for the process which is obtained from an alkoxide in a two-stage or multistage hydrolysis. In the hydrolysis in two or more steps, in particular substoichiometric water content and elevated temperature in the first step, the ratio between the different possible species changes significantly compared to the one-stage hydrolysis of the same total composition with further addition of water. By such multi-stage hydrolyses, in particular by a two-stage synthesis, z. B. increase in the system SiO _2, the proportion of cyclic oligomers ren. Such cyclic oligomers obviously lead to more compact polymer units. Compared to chainlike species, these apparently have a more favorable spatial constellation for attachment to the reactive OH groups of the wood constituents. The method procedure described above also makes it possible for the catalyst concentration to be chosen to be very low. The molar ratio of catalyst to alkoxide (r _S ) can be in the range of 0.01: 1 to 0.00001: 1. Obviously, the process described above also leads to an increase in the number of species carrying OH groups, and in particular those carrying two or three OH groups. As a result, a very reactive precursor is obtained. It has been found that it is favorable in the two-stage synthesis, when the molar ratio of water to alkoxide (r _S ) in the first hydrolysis step in the range of 1: 1 and the subsequent second hydrolysis step in the range of 0.5: 1 to 1.5: 1. The molar ratio of solvent to alkoxide is in the same range as already described above in the one-stage hydrolysis.

Precursors prepared according to the invention as described above contain, depending on the composition and process control, in some cases condensed units which, as the inventors have been able to show, are at the limit of detectability. That is, the solutions are not real sols at the time of treatment, but rather precursors. The total water content is calculated so low (for the system SiO _2, for example, water to tetraethoxysilane about 2: 1 [molar]), that for a rapid further reaction, the OH groups of the cellulose - and lignocel lulosehaltigen materials additionally the of lignin - needed locally on the cell walls. Condensation of Precursorspecies with each other is thus apparently largely prevented. If such a precursor, which has been prepared as described above, is used for the treatment as proposed in the method according to the invention, it causes the cell walls to be occupied, ie a reaction takes place with the OH groups of the cell walls. The composite-forming inorganic material penetrates virtually directly into the cell walls and can significantly contribute to the improvement of the properties. Due to the blocking of the OH groups of the wood components z. Example, by the inorganic modification not only, as shown in the modification with precursors based on the one-step process, dimensional stability, biological resistance and fire behavior improved, but also significantly reduces the moisture absorption. The mechanical properties (flexural strength, Young's modulus, hardness) remain unchanged or are slightly improved.

As described above, opened thus the inventive method the possibility to use a sol or an oligomeric precursor as a precursor to the sol, the above a two- or multi-step hydrolysis have been prepared, wherein such a sol or such Precursor causes that the composite-forming inorganic material penetrates into the cell walls and make a cast there.

As Of course, known from the prior art, too in multi-stage syntheses drying control additives, so-called DCCA's (Drying Controlling Chemical Additives), such. B. glycerol and organic acids, be added, which the hydrolysis and condensation process in With regard to the pore size distribution Cheap influence.

At the inventive method it is furthermore, as already known in principle from the prior art, does not require the gelation of the inorganic composite component at higher Temperatures occur (fixation). Consequently, the cellulose-containing Material after treatment z. B. by impregnation not a targeted heat treatment get abandoned. Tempering, d. H. Heat treatment at higher temperatures accelerates the gel drying. Preferably is at Temperatures below the temperature at which the damage to the cellulosic material begins (eg T ≤ 103 ° C for wood), and low Heating rates (1-10 K / h) annealed.

It is also known from the prior art that sol-gel processes are equilibrium reactions and consequently unreacted alkoxy groups can still be present in the gel. This circumstance is in previously known solutions of the impregnation of cellulosic raw materials and materials for property improvement ( EP 0 747 184 A2 ) not considered at all. To these alkoxy groups, in particular at remain stoichiometric water content, remove, the impregnated cellulosic material is subjected to a moisture treatment, preferably following the impregnation. The moisture treatment can be coupled with the heat treatment. Duration and intensity depend on the precursor used. Guide times are treatment times of 1 to 100 hours, preferably 10-30 hours, and relative humidities of 10 to 100%.

The invention further relates to (claim 18) an inorganic modified cellulosic material, in particular based on wood. The material according to the invention is a composite material, the material being characterized in that it contains alco- or xerogels in the cell walls, which are connected via a covalent bond to the cell walls. The cellulosic material is preferably wood and the alco- or xerogel is preferably selected from SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , P ₂ O ₅ and / or B ₂ O ₃ . It is preferred in this case if the cellulose-containing material as described above is produced by a process as described above. Reference is made to the relevant disclosure.

Of the inorganic according to the invention modified cellulose-containing material is characterized for. In case Wood in particular by superior Properties off. The material as described above shows a Reduced moisture absorption (with moisture storage, 100% relative humidity, 23 ° C), the less than 10 mass% based on the dry mass of the composite. The composite further provides reduced swelling Moisture storage of at least 60% based on the swelling analog tested untreated comparative samples, wherein the swelling of untreated wood is set equal to 100%. It has too have shown that the inventive inorganic modified composite improved biological resistance has. The mass reduction in the DIN test (DIN EN 113) by various test fungi is improved by at least 60%. Injury caused by larvae of the domestic beetle in Insect tests according to DIN EN 46 and DIN EN 47 are completely prevented. Furthermore, it should be noted that the inventive inorganic modified composite also a conservation or slight improvement mechanical properties (flexural strength, modulus of elasticity, Hardness, Abrasion resistance). The density of the material is at least 10%, preferably 10-50%, particularly preferred 20-25% elevated.

Of the material according to the invention shows surprisingly even more positive effects. So the inventors could show that the fire behavior or burn-off loss or flame resistance a material according to the invention across from untreated control samples is significantly improved. Furthermore could be found that in the material according to the invention the time to to self-ignition at 600 ° C extended by about 50% and the rel. Mass loss during burning is reduced by about 50% compared to an untreated reference sample.

The The invention is described below with reference to tables / figures and exemplary embodiments explained in more detail.

Tab. Figure 1 shows the densities of various methods of the invention treated woods (pine, Beech) in comparison to the density of these woods.

1 shows an electron micrograph of a saturated with silica sol pine wood and a corresponding electron beam microanalytical representation, in which the element distribution of the silicon and thus the silica gel is illustrated.

2 shows measurement results illustrating the moisture uptake of treated pine wood and untreated control samples.

3 shows an electron micrograph of a treated pine wood (not according to the invention), in which case the column structure is recognizable.

4 shows measurement results of fungus tests according to DIN EN 113 of treated pine wood and untreated control samples.

5 shows the condition of a pine wood sample and an untreated comparative sample after performing a fire test.

Example 1 (not according to the invention)

Preparation of an alkoxide-based sol with a one-stage hydrolysis system SiO ₂

For this purpose, a tetraalkoxysilane in alcohol, preferably in the respective mother alcohol, is converted by acid-catalyzed hydrolysis in a silica sol. In the example, commercial tetraethoxysilane, ethanol and hydrochloric acid were used. In Example 1, an r _W value of 4, an r _L value of 2 and an r _S value of 0.01 are used. All components were mixed and held at 78 ° C for about 3 hours. After cooling the resulting silica sol, this can be used for the treatment.

Example 2

Preparation of an alkoxide-based sol with a two-stage hydrolysis system SiO ₂

Starting components are used as in Example 1, but in the first step r _W = 1, r _L = 2 and r _S = 0.001. All components are mixed again and kept at 78 ° C for 3 hours. In the second step, additional water is added at room temperature (r _W = 1). Subsequently, this sol prepared in this way is suitable for the process according to the invention.

Example 3 (not according to the invention)

Preparation of an alkoxide-based sol with a one-stage synthesis system Al ₂ O ₃

For this purpose, an Al alkoxide, preferably Al-sec-butylate (ASB), in alcohol, preferably in 2-butanol, after complexing with organic chelating ligands (CL) such as β-diketones or organic acids by acid-catalyzed hydrolysis in an alumosol. In the example, ASB, 2-butanol, ethyl acetoacetate and nitric acid were used. In Example 3, an r _W value of 2.5, an r _L value of 1.1, an r _CL value of 1 and an r _S value of 0.005 are used. All components are mixed and held at 60 ° C for about 1 hour. After cooling this alumosol it can be used for treatment.

Example 4

Preparation of an alkoxide-based sol with a two-stage hydrolysis with the addition of a drying-controlling auxiliary system SiO ₂

It are starting components and compositions as in Example 2 used, but will be additional Glycerol (glycerol: alkoxide = 0.15 [molar]) added in the second step. The following is the sol thus prepared for the process of the invention suitable.

1 shows in the upper left part of an electron micrograph of a pine wood sample, which had been treated according to the invention with a precursor of Example 2. In the upper right part, the distribution of the silicon and thus also of the silica gel (SiO ₂ ) is documented in the sample excerpt by means of electron beam microanalysis (bright spots). This shows that the silicon and thus the gel is bound in the cell walls. In the lower part is shown schematically using the example of wood with silica sol as the connection to the OH groups of cellulosic raw material or material takes place.

In 2 is now exemplified a graph reproduced from the shows that the absorption of moisture in the composite compared to the untreated materials is significantly reduced. 2 shows the time-dependent moisture uptake of pine wood samples that have been inorganically modified with different sols. The storage was at a rel. Humidity of about 100 at about 20 ° C performed. At regular intervals, the moisture content was determined by the increase in mass. In the best case, the inorganic modified wood reaches a moisture content of only about 5% after 12 weeks. The untreated wood strives for the fiber saturation moisture for pine wood after just a few days. The increase in volume due to swelling was reduced by up to 60% compared to untreated pinewood, which suggests a massive blockage of the cell walls through the reaction with the impregnation medium. The assumption of a homogeneous dense inner coating of the wood sample and thus a chemical attachment of the mineral phase to the wooden surfaces could, as in 1 represented by the microprobe recordings confirmed.

3 finally shows an inorganic modified wood material, this with a silica sol was treated as prepared in Example 1. From the figure it can be clearly seen that columnar gel monoliths are arranged in the supply channels.

4 shows by way of example the significant improvement in the biological resistance of pine wood after treatment with various silica sols. The mass loss of the specimens is shown after a fungus test according to DIN EN 113 in comparison to untreated pine wood. It can be clearly seen that the loss of mass could be reduced by at least 60% compared to untreated wood.

5 shows the state of a treated pine wood sample (right, precursor see example 1) compared to an untreated pine wood sample (left) after performing a firing test (dimensions 50 × 25 × 15 mm ³⁾ The samples were individually exposed to a temperature of 600 ° C and the time to self-ignition was measured After ignition, the samples were taken out of the oven and the time taken to extinguish the flames was recorded.

The Sample ignited only twice as long as the reference sample and also went out much earlier. The inorganic modified sample essentially has its shape maintained while the untreated sample was partially ashed.

Table 1:

Density and density increase in percent of different treated according to the process variants of the invention woods (pine, beech) compared to the bulk density of the two untreated species. Species Untreated bulk density Two-stage hydrolysis Two-step hydrolysis with DCCA g / cm ³ g / cm ³ % g / cm ³ % jaw 0.51 0.73 43.1 0.66 29.4 beech 0.68 - - 0.84 23.5

Claims (21)

A process for the preparation of inorganic modified cellulose-containing materials such as wood, by treating the raw or untreated material with a precursor in the form of a sol prepared via the alkoxide sol-gel pathway or its precursor and subsequent fixation, characterized in that a precursor used obtained by catalyzed two- or multi-stage hydrolysis of alkoxides in alcoholic solution or solutions of alcohol derivatives at a temperature between 20 ° C and the boiling temperature of the solvent, wherein in the first stage a substoichiometric water content and the second hydrolysis step, a molar ratio from water to alkoxide (r _W ) in the range between 0.5: 1 and 1.5: 1 is maintained. Method according to claim 1, characterized in that that the alkoxide is completely or partially complexed. Method according to claim 2, characterized in that that complex formation with chelating ligands such as organic acids or β-diketones he follows. Method according to one of the preceding claims, characterized in that the sol prepared by the alkoxide sol-gel method or its precursors is selected from the systems SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , P ₂ O _{5 ,} B ₂ O ₃ or mixtures thereof. Method according to Claims 1 to 4, characterized that the alkoxide as starting material is partially soluble in salts, acids, oxides, Hydroxides or the like Replaces connections of the corresponding network-building component becomes. Method according to Claims 1 to 5, characterized that in two- or multi-component systems, the second and each further network forming component completely as salt, acid, oxide, Hydroxide or the like is used. Method according to one of claims 1 to 6, characterized in that a two-stage hydrolysis is carried out and the molar ratio of water to alkoxide (r _W ) in the first hydrolysis step is about 1: 1. Method according to one of the preceding claims, characterized in that the molar ratio of solvent to alkoxide (r _L ) is 0.5: 1 to 20: 1. A method according to claim 8, characterized in that the molar ratio r _{L is} 1.5: 1 to 7: 1. Method according to one of the preceding claims, characterized in that the molar ratio of catalyst to alkoxide (r _S ) is 0.1: 1 to 0.00001: 1. Method according to one of the preceding claims, characterized characterized in that drying-controlling additives are added. Method according to claim 11, characterized in that the dryness control additive is glycerol. Method according to one of the preceding claims, characterized characterized in that the solvent selected is from lower alcohols having 2-4 carbon atoms or their Derivatives. Method according to at least one of the preceding Claims, characterized in that the catalyst is a mineral acid. Method according to one of the preceding claims, characterized characterized in that the cellulose-containing material by impregnation with the precursor prepared by the alkoxide sol method is treated. Method according to one of the preceding claims, characterized characterized in that the fixation of the treated cellulosic Material by tempering at temperatures below 100 ° C over a period of time from 1 to 100 hours. Method according to claim 16, characterized in that that the fixation with a moisture treatment at 10-100% rel. Moist is coupled. Inorganically modified cellulosic material, in particular wood, producible according to one of claims 1 to 17th Inorganically modified material according to claim 18, characterized in that the wood material under preservation its mechanical properties a reduced moisture absorption in moisture storage (100% RH 23 ° C), which is smaller as 10% by mass based on the dry mass of the composite and that under these conditions a reduced swelling of at least 60% based on the swelling analogously tested untreated control samples is present. Inorganically modified material according to claim 19, characterized in that the density of the material by at least 10% based on the untreated condition is increased. Inorganically modified material according to claim 20, characterized in that the density by 10 to 50%, preferably 20 to 25% increased is.