RU2674208C1 - Antipyrene, a method for its obtaining and a method for fire-protective treatment of wood - Google Patents

Abstract

FIELD: woodworking industry.

SUBSTANCE: invention relates to means and methods for improving the fire resistance of wood and can be used for fire-retardant treatment of building materials from wood, wooden structures and other wood products. Fire retardant is described, which is an aqueous composition containing a mixture of products of liquid-phase oxidation of a substrate of plant origin by air in an aqueous medium in the presence of alkali and a salt of a divalent metal, characterized in that said substrate is a mixture of wood flour of coniferous species and crushed rice grains, taken in quantitative ratios, % by weight: wood flour of coniferous species – 60–40, crushed rice grain – 40–60, and their joint oxidation is carried out under a pressure of 3–5 atm. Method for producing a flame retardant and a method for flame retardant treatment of wood are described.

EFFECT: proposed product with good flame retardant properties.

10 cl, 3 tbl, 11 ex

Description

The invention relates to means and methods for increasing fire resistance of wood and can be used for flame retardant treatment of building materials from wood, wooden structures and other wood products.

Wood is widely used as a building material for structural purposes. Wooden structures have a high fire hazard, therefore, to prevent fires and reduce the severity of the consequences of fires, the supporting and enclosing wooden structures, finishing and facing materials from wood must be treated with flame retardants (fire retardants).

A large number of flame retardants are known for wood, which differ from each other in a combination of low molecular weight inorganic substances, mainly mono-, di- and polyphosphates, and derivatives of organic compounds containing halogens and phosphorus. Phosphates are environmentally harmful products, since during the operation of the wooden structures they have treated in the open air, pollution of natural water bodies and soil occurs, causing a violation of the natural natural bio-balance. Nevertheless, the development and patenting of ways to reduce the fire hazard of wood, based on the use of flame retardants of this type, continues. An example is a wood processing method that uses an aqueous fire retardant composition containing phosphoric acid, diammonium phosphate, ammonium sulfate, urea, a complexing agent, as well as an intumescent agent selected from guanidine, guanidine hydrochloride, glycine and other amino acids and their derivatives . [US 9132569, publ. 15.09.2015].

Halogen and phosphorus-containing organic compounds are the most effective flame retardants, however, today their use is also undesirable due to the growing environmental safety requirements. Bromine and chlorine-containing dioxins and dibenzofurans, global ecotoxicants with mutagenic, immunosuppressive, carcinogenic, teratogenic and embryotoxic effects, were found in the products of combustion and pyrolysis of halogen-containing flame retardants [Lomakin S.M., Zaikov G. Int. Polymer. Sci. Publ. Utrecht, Boston, pp. 274, (2003)].

In this regard, fire-retardant agents based on the use of environmentally friendly natural materials or products of their processing or processing are of interest. For example, according to [RU 2469843 C2, publ. 12.20.2012], the composition of the fire retardant as the main components includes bischofite salt and water, as well as additives - magnesium acetate, oxalic acid and ferrous hydroxide. According to the authors, the product is characterized by high flame retardant and bioprotective properties and low toxicity. The main disadvantage of using bischofite as a flame retardant is that its effect is limited only by the physical insulation of the wood surface. At the same time, to achieve satisfactory fire retardant properties, it is required to apply a significant amount of bischofite, which affects the operational and physico-mechanical characteristics of wood materials.

In the document [RU 2204547 C2, publ. 05/20/2003] a flame retardant is described, including salts of polyoxycarboxylic acids obtained by oxidizing disaccharides or polysaccharides, including plant materials containing starch, and replacing the hydrogen ion of the carboxyl group with a metal or ammonium cation. Products obtained by this method are effective flame retardants, are characterized by low smoke formation and do not emit during the decomposition of toxic substances. They relate to flame retardants of the intumescent coke-forming type. In the process of combustion, foaming and carbonization of the coating occur simultaneously on the surface of the material treated with intumescent flame retardant, which creates an insulating barrier between the flame and the surface of the material subjected to high temperature exposure. The disadvantages of this invention include the low moisture resistance of salts of polyoxycarboxylic acids, as a result of which the fire-retardant characteristics of wooden structures are worsened when they are used outdoors. It should also be noted that our studies showed that the treatment of wood with flame retardants based on oxidized starch-containing products, in particular rice grain, significantly reduces its strength characteristics.

As a prototype of the present invention, the invention is taken [RU 2425069 C2, publ. 07/27/2011], which relates to flame retardants, as well as to methods for their preparation and use. The described flame retardants are a mixture of products of liquid-phase oxidation of a lignin-containing substrate in an alkaline medium without a catalyst or in the presence of a catalyst, mainly a copper (II) salt or cobalt (II). The oxidation is carried out at atmospheric pressure at temperatures up to 90 ° C under the action of an oxidizing agent selected from the group: air, oxygen, ozone, hydrogen peroxide. Fire retardant is designed to reduce the combustibility of various materials, including wood by means of surface fire retardant treatment of products. The disadvantages of this invention include the impossibility of obtaining a group of flame retardant efficacy above the second, because the flame retardant effect of the flame retardant is based solely on the surface coke formation and is not accompanied by the intumescent effect.

It should be noted that in the development of flame retardants, the main attention is paid to their influence on thermal stability and the main fire hazard indicators of modified wood. At the same time, as a rule, issues related to the mechanical strength of wood treated with flame retardants are left without due attention. However, it is known that impregnation with flame retardants largely affects the mechanical properties of wood, and in most cases the effect is negative [http://www.drevesinas.ru/protection/rotting/9.html]. It is also known that wooden structures during operation in the air partially lose strength over time, and there is very little information about the impact of climatic influences on the physicomechanical characteristics of fireproof wood.

The present invention extends the arsenal of technical means that increase the fire resistance of wood by creating a fire retardant, a method for its production and a fire retardant treatment of wood based on the use of this flame retardant, providing I or II groups of fire retardant efficiency and, at the same time, obtaining materials that are close or exceed the strength characteristics of wood not subjected to flame retardant treatment.

The proposed flame retardant is an aqueous composition containing a mixture of products of liquid-phase oxidation of a substrate of plant origin with air in an aqueous medium in the presence of alkali and a divalent metal salt, characterized in that the substrate is a mixture of coniferous wood flour and crushed rice grain taken in quantitative proportions ( % mass):

coniferous wood flour - 60-40, crushed rice grain - 40-60,

and their joint oxidation is carried out under a pressure of 3-5 atm.

The method of obtaining the proposed flame retardant includes liquid-phase oxidation of a substrate of plant origin with air in an aqueous medium in the presence of alkali and a divalent metal salt, and characterized in that the substrate is a mixture of coniferous wood flour and crushed rice grain taken in quantitative proportions (% mass):

coniferous wood flour - 60-40, crushed rice grain - 40-60,

and their joint oxidation is carried out under a pressure of 3-5 atm.

The proposed method of fire retardant treatment of wood involves impregnating wood with a flame retardant, characterized in that an aqueous composition containing a mixture of liquid-phase oxidation products of a combined substrate, including softwood flour and crushed rice grain, taken in quantitative proportions (% of mass) is used as a flame retardant:

coniferous wood flour - 60-40, crushed rice grain - 40-60,

and their joint oxidation is carried out with air under a pressure of 3-5 atm. in the presence of alkali and divalent metal salt.

In contrast to the known technical solutions, in which to obtain flame retardants, a one-component substrate of plant origin, for example, of carbohydrate nature, in particular rice [RU 2204547], or a lignocellulosic substrate, in particular wood sawdust [RU 2425069], is subjected to oxidation to obtain a flame retardant oxidation of the combined substrate, which is a mixture of crushed rice grains and coniferous wood flour, taken in the indicated quantitative ratios. It is this unique composition of the initial oxidized combined substrate that allows one to obtain a flame retardant that provides a level of fire-retardant efficiency of wood corresponding to groups I and II according to GOST 53292-2009, and not only does not adversely affect its strength, but even increases its strength . It will be shown below that wood treated with the proposed flame retardant is characterized by higher strength indicators according to GOST 16483.4-73 and GOST 16483.3-84. In addition, wood treated in accordance with the invention, during climatic tests simulating the natural conditions of use of the products, shows strength according to GOST 16483.10-73, close to the strength of the raw material.

Thus, the joint oxidation of these products, taken in the indicated quantitative ratios, leads to a non-obvious non-additive effect due to the fact that during the joint oxidation of starch-containing and lignocellulosic substrates, a complex mixture is formed, including salts of polyoxycarboxylic acids and polyoxyphenol compounds, low molecular weight and hydroxyphenol compounds. , as well as products of their interaction with each other. Compared to protective coatings containing monosubstrate oxidation products, as in the analogue or prototype, the coating formed by processing wood in accordance with the present invention not only has intumescent fire retardant properties, but is also more stable against external climatic factors due to the formation of additional chemical crosslinking on the surface of the material. An additional factor contributing to the preservation or enhancement of the strength characteristics of the fire-retardant material is the good penetration of the flame retardant deep into the wood, especially under conditions of vacuum impregnation. Moreover, in addition to the formation of a surface coating, products formed during the joint liquid-phase catalytic oxidation of a mixture of starch-containing and lignocellulosic products diffuse into the wood and form additional hydrogen bonds in the microfibrillar structure of cellulose fibers, as well as with the participation of methoxy, hydroxyl and carbonyl groups contained in the wood lignin. The result of the formation of a combination of such additional weak bonds is the physical hardening of the wood structure.

Significant differences between the method of producing flame retardant from the known methods of liquid-phase oxidation of starch-containing and lignin-containing products [RU 2204547 and RU 2425069, respectively] are that the process is carried out in the mode of co-oxidation of a combined substrate, comprising a mixture of coniferous wood flour and crushed (crushed) rice grain, taken in ratios (% mass):

coniferous wood flour - 40-60, crushed rice grain - 60-40,

and their joint oxidation is carried out under a pressure of 3-5 atm.

To obtain a technical result, both the qualitative and quantitative composition of the initial combined substrate are essential. Of the possible starchy components, the use of crushed rice grain is optimal, because allows you to get the final product with the best consumer properties. From the point of view of economic feasibility, it is preferable to use products that are not suitable for food - substandard rice grain with expired shelf life or other waste containing food production containing rice. The experiments showed that the best result is achieved by using coniferous wood flour as a lignocellulosic component of the combined substrate, rather than sawdust, as in the prototype, since it allows to reduce the process temperature to 60-65 ° C. The use of wood flour or hardwood sawdust as an alternative does not allow to obtain a product with the required properties. Outside of the indicated quantitative ranges of the ratios of the components, a product is obtained that has good flame retardant properties, however, as will be shown below, treated wood samples show worse strength indicators than untreated samples.

Carrying out the process at atmospheric pressure does not allow complete oxidation of the components of the mixture in an acceptable time. Increasing the pressure to 5 atm, permissible for safe operation of the reactor, and the use of crushed components allows to achieve complete oxidation of the substrate with air in an acceptable time of 10-14 hours while reducing energy consumption by reducing the process temperature. At a pressure below 3 atm. oxidation slows down significantly and the efficiency of the process decreases.

As a catalyst, various salts of divalent metals can be used, for example, sulfates, chlorides, acetates of copper, cobalt, etc. In the examples below, one of the possible catalysts is aqueous copper sulfate.

The inventive flame retardant is obtained using standard processing equipment, including a heated steel sealed reactor, a mixing device, an air supply line. The oxidation reaction in a sealed reactor at elevated pressure using a substrate of a high degree of grinding allows to reduce the energy consumption for production by reducing the temperature and reaction time.

The viscosity of the final product and the technological conditions of oxidation depend on the total amount of substrate introduced into the reaction, which is selected empirically depending on the specific characteristics of the feedstock. Experiments on the selection of oxidation conditions showed that the use of initial mixtures containing 20-22% of the mass. oxidizable substrate, allows the reaction to be carried out under optimal conditions, and the final product obtained after filtration is an aqueous composition containing a mixture of products of co-oxidation of the combined substrate, suitable for use as a flame retardant without further concentration and purification. During bulk processing of samples, it easily penetrates into the pores of the material, and during surface treatment it exhibits good adhesion to the surface and, after drying in air, forms a durable, almost transparent coating that preserves the natural appearance of the treated wooden surface.

The inventive flame retardant is environmentally friendly, since the products of its combustion are not more toxic than the products of combustion of wood and cereals.

The flame retardant according to the following examples 1-7, obtained as follows. 19-20 g of CuSO ₄ × 5H ₂ O and 3.0-3.3 kg of a combined substrate, including crushed (crushed) rice grain and coniferous wood flour, taken in a 40-liter steel reactor containing 15 liters of water, are added ratios determined by the experimental conditions (see Table 1). The mixture is stirred with a mechanical overhead stirrer for 2 minutes with a stirring speed of about 50 rpm./min, then 1.3-1.4 kg of NaOH is added and the stirring speed is increased to 140-150 rpm, the reactor is sealed and fed from above air at a rate of 0.2-0.3 l / min. Throughout the process, the pressure in the reactor is maintained at a level of 3-5 atm., A temperature of 60-65 ° C. The end of the reaction is determined by reducing the concentration of free alkali in the mixture to 0.5-0.8 M (titration of 0.1 N Hcl). Depending on the composition of the starting substrate, the reaction time is 10-14 hours. The reaction mixture is filtered on a nylon filter to separate from solid impurities and used as a flame retardant.

Some examples of the implementation of the method of producing flame retardant, not exhaustive of all the possible variants of the quantitative composition of the initial combined substrate covered by the claims, are given in Table. 1. Examples 1 and 7, in which coniferous wood flour or crushed rice is separately subjected to oxidation, are given as comparative examples. The composition of the components of the plant substrate in examples 2-6 smoothly varies in the intervals: wood flour - 80-20% of the mass., Crushed rice -20-80% of the mass.

For tests on fire-retardant efficiency according to GOST R 53292-2009, wood samples were used in the form of rectangular bars of pine with a cross section of 30 × 60 mm and a length along the fibers of 150 mm, treated with flame retardant variants obtained according to examples 1-7. Methods of flame retardant treatment of wood are modeled by laboratory processes described in examples 8-11 below, including four sample processing options: example 8 - volumetric vacuum treatment (vacuum impregnation), example 9 - impregnation under atmospheric pressure, example 10 - vacuum impregnation in combination with surface treatment, example 11 - surface treatment.

Example 8. Vacuum impregnation.

Vacuum impregnation is carried out in the alternating operation of evacuating a sample immersed in a flame retardant under oppression for 120 minutes at room temperature and a residual pressure of about 0.1 atm, followed by impregnation of wood in the same composition at atmospheric pressure at room temperature for 120 minutes . Then the sample is dried in air at room temperature for 24 hours.

Vacuum impregnation can be carried out in the form of a sequence of cycles, including the operations described above, with the final drying of the sample in air at room temperature.

Example 9. Impregnation under atmospheric pressure.

The sample is impregnated by immersion in a flame retardant composition under oppression at atmospheric pressure at room temperature for 24 hours. Then the sample is dried in air at room temperature for 24 hours.

Example 10. Vacuum impregnation in combination with surface treatment.

Vacuum impregnation is carried out in the alternating operation of evacuating a sample immersed in flame retardant under oppression for 40 minutes at a residual pressure of 30-40 Torr. and subsequent impregnation of wood by immersion in a flame retardant composition at atmospheric pressure at room temperature for 40 minutes. Then the sample is dried in air at room temperature for 24 hours, after which a double surface treatment is carried out with a brush with intermediate drying in air for 2 hours and final drying for 18 hours.

Example 11. Surface treatment.

A three-time surface flame retardant treatment of the sample with a brush is carried out with intermediate drying in air for 2 hours and final drying for 18 hours.

The specific conditions given in examples 8-11 relate to laboratory samples whose characteristics correspond to the requirements of GOSTs, according to which they were further tested. In the case of the practical implementation of the flame retardant treatment of wood products according to the invention, the number of treatment cycles, the duration of impregnation and drying, the degree of vacuum, the multiplicity of operations and other specific conditions are determined empirically taking into account the geometric shape, weight, humidity of the processed product, type of wood and other specific conditions. In practice, flame retardant treatment of wood can be carried out in the form of alternation or other empirically selected combination of operations described in examples 8-11, or other operations used by industrial wood processing technologies. The proposed flame retardant is suitable for use in any of the known technological schemes.

Tests to determine the fire-retardant effectiveness of the wood compounds were carried out in accordance with GOST R 53292-2009 at the Federal State Budgetary Institution VNIIPO EMERCOM of Russia. Table 2 shows the results of determining the fire-retardant effectiveness of the tested flame retardant samples prepared according to examples 1-7, on wood samples processed according to examples 8-11.

* In accordance with GOST 53292-2009 “Fire retardant compounds and substances for wood and materials based on it. General requirements, Test methods ”, group I includes the means ensuring the production of fire-resistant wood, for which the weight loss during testing does not exceed 9%. Group II includes the means that ensure the production of hardly flammable samples, for which the weight loss of wood during testing is from 9 to 25%.

As can be seen from Table. 2, the use of the proposed compositions provides I or II group of flame retardant efficiency with any version of the method of processing wood with a fire retardant obtained according to any one of examples 1-7. The best results are shown by flame retardants obtained by oxidizing combined substrates containing starch-containing and lignocellulosic components in close weight ratios (examples 3-5). High fire-retardant efficiency is ensured due to the intumescent behavior of the flame retardant under combustion conditions, as a result of which penocox is formed on the surface of the burning wood, which drastically slows down heat and mass transfer between the surface and the combustion zone. The formation of chemical crosslinks between the products of co-oxidation in the composition of the flame retardant increases the strength and moisture resistance of the surface coating in comparison with the analogue and prototype.

The study of the physical and mechanical properties of wood treated with the inventive flame retardant was carried out at the National Research Moscow State University of Civil Engineering (NRU MGSU) in accordance with GOST 16483.4-73 and GOST 16483.3-84. For research, we took wood samples 20 × 20 × 30 mm, processed by the vacuum impregnation method of Example 8 with a flame retardant, obtained according to Examples 1-7. The test results are shown in Table. 3.

The results show that the samples treated with flame retardants obtained in examples 3-5, show strength indicators that exceed the indicators for control: bending strength for samples treated with flame retardants obtained by oxidation of the initial mixtures containing 60-40% of the mass. coniferous wood flour and, accordingly, 40-60% of the mass. crushed rice grain, about 20% higher than the corresponding indicator for control. For the same samples, the excess of the indicator of strength under static bending relative to the control is 5-7%. The processing of wood under similar conditions with a flame retardant obtained in comparative example 1, which is close to the prototype RU 2425069 (oxidation of wood flour only), is accompanied by an increase in strength under static bending, however, the impact strength during bending of a fireproof sample is reduced. The treatment of wood with a flame retardant based on the oxidation products according to comparative example 7, corresponding to the analogue of RU 2204547 (oxidation of rice grains only) noticeably reduces both the impact strength during bending and the strength under static bending of wood.

Similar results can be obtained by impregnating the samples under atmospheric pressure, however, under these conditions, for the effective impregnation and the formation of a network of internal crosslinks necessary to increase the strength of the material, it takes significantly more time, which reduces the efficiency of the process. Additional surface treatment with a flame retardant mainly affects the strength of the surface coating and the improvement of fire protection.

A comparative assessment of the strength of fire-retardant and untreated flame retardant wood during climatic tests was carried out at NRU MGSU in accordance with GOST 16483.10-73 to change the compressive strength along wood fibers. Climatic tests simulating the natural operating conditions of wood in the open air in the middle band are carried out in a climatic chamber WK3-180 / 70 (Germany). One cycle of freezing and thawing involves reducing the temperature in the climatic chamber of natural humidity for 30 minutes. from + 23 ° С to -30 ° С followed by exposure of the studied samples for 2 hours at a temperature of minus 30 ° С. After that, for 30 minutes. the temperature is raised to + 23 ° C and the samples are kept at this temperature for 2 hours. Before conducting tests for compressive strength along the fibers, the samples are incubated for a day at a temperature of + 23 ° C.

Tests were made on wood samples treated with vacuum impregnation (according to Example 8) with a flame retardant obtained by co-oxidizing a mixture of 60% by weight, softwood flour and 40% by weight, crushed rice grain (according to Example 3). The strength of both treated and non-flame retardant wood decreases as the number of climatic test cycles increases. The decrease in the strength of the source wood after 10 cycles of freezing and thawing is about 12%, for fire-resistant wood this figure is 14.4%. According to the conclusion of the NRU MGSU, the results indicate that the use of the inventive flame retardant practically does not affect the durability of fire-resistant wood under conditions of multiple temperature fluctuations, simulating operation in natural climatic conditions.

Thus, the inventive flame retardant not only ensures the achievement of fire-retardant efficiency, corresponding to groups I and II in the conditions of wood processing, including flame retardant impregnation, but also provides materials that exceed the strength characteristics of wood not subjected to flame retardant treatment, and resistant to external climatic conditions.

Claims (16)

1. Fire retardant, which is an aqueous composition containing a mixture of products of liquid-phase oxidation of a substrate of plant origin with air in an aqueous medium in the presence of alkali and a divalent metal salt, characterized in that the substrate is a mixture of coniferous wood flour and crushed rice grains taken in quantitative ratios (% wt.): coniferous wood flour 60-40 crushed rice grain 40-60 and their joint oxidation is carried out under a pressure of 3-5 atm. 2. Fire retardant according to claim 1, characterized in that the content of the combined substrate in the initial mixture taken for oxidation is 20-22% by weight. 3. The method of producing a flame retardant according to claim 1, including liquid-phase oxidation of a plant-based substrate by air in an aqueous medium in the presence of alkali and a divalent metal salt, characterized in that said plant-based substrate is a mixture of coniferous wood flour and crushed rice grains taken in quantitative ratios (% wt.): coniferous wood flour 60-40 crushed rice grain 40-60 and their joint oxidation is carried out under a pressure of 3-5 atm. 4. The method according to p. 3, characterized in that as the salt of the divalent metal using CuSO ₄ × 5H ₂ O. 5. The method according to p. 3, characterized in that the oxidation is carried out within 10-14 hours. 6. The method of fire-retardant treatment of wood involves impregnating wood with a flame retardant, characterized in that an aqueous composition containing a mixture of liquid-phase oxidation products of a combined substrate, including softwood flour and crushed rice grain, taken in quantitative proportions (% wt.) Is used as a flame retardant: coniferous wood flour 60-40 crushed rice grain 40-60 and their joint oxidation is carried out with air under a pressure of 3-5 atm in the presence of alkali and a divalent metal salt. 7. The method according to p. 6, characterized in that the wood impregnation is a vacuum impregnation. 8. The method according to p. 7, characterized in that the vacuum impregnation is carried out in the form of alternating operations, including evacuation at room temperature of wood immersed in a flame retardant according to claim 1, and subsequent impregnation of wood in the same flame retardant at atmospheric pressure at room temperature, after which the wood is dried in air at room temperature. 9. The method according to p. 6, characterized in that the wood is impregnated at atmospheric pressure. 10. The method according to any one of paragraphs. 7-9, characterized in that it further includes surface treatment of wood with a flame retardant according to claim 1.