SK500532021U1 - Method for deacidification and increasing stability of lignocellulosic materials - Google Patents

Abstract

The invention provides a method of deacidifying and enhancing the stability of lignocellulosic materials by treating the lignocellulosic material with a magnesium diamide of the general formula (I) wherein R1 and R2 are independently selected from the group consisting of C1 to C6 alkyl, branched C3 to C6 alkyl or cyclohexyl, in a solvent selected from the group consisting of C5 to C7 alkane, C4 to C6 cycloalkane, C2 to C6 chlorofluorocarbon, C1 to C4 chlorinated hydrocarbon, C2 to C6 fluorocarbon, toluene, xylene, chlorobenzene, C4 to C8 dialkyl ethers, tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, acetonitrile, hexamethyldisiloxane or mixtures thereof. The deacidified lignocellulosic material can be further treated with an amino alcohol of the general formula (II) and/or magnesium oxide, basic magnesium oxide or magnesium carbonate. The treated lignocellulosic material is then conditioned and further compressed or dried.

Description

Field of technology

The technical solution relates to a method of deacidification and increasing the stability of lignocellulosic materials by the application of organomagnesium reagents.

Prior art

The term paper aging refers to the deterioration of the mechanical (brittleness), chemical (increase in acidity) and optical (yellowing) properties of the paper, which is caused by the use of unstable wood, high-ligated pulp and acid sizing. Alumina-potassium alum or aluminum sulfate were an essential component of the components used in papermaking. However, the by-product of decomposition was sulfuric acid, which causes the acidity of the paper. Atmospheric pollutants such as sulfur dioxide or nitrogen oxides, also increase the acidity of the paper. Most books published in the 19th - 20th centuries have a pH value in the acidic range; 80-90% of books in the Slovak National Library had a pH below 5 (Hanus et al. 2006 Conference Paper (Oniine); similarly, most books in the Swiss National Library in Bern had a pH below 6; 93% of books in the Royal Library in Denmark had In addition to atmospheric pollutants or components from papermaking, organic acids can also be formed by the degradation of cellulose itself.Acid papers cause the hydrolysis of the glycosidic bond of the cellulose chain and the formation of other hydroxyl groups due to acid hydrolysis due to the action of light and oxygen oxidative and photochemical degradation and formation of carbonyl and carboxyl groups can occur.

These processes are associated with a decrease in the strength of the fibers and paper, the formation of colored lesions or darkening of the paper. Mechanisms of reactions in the presence of atmospheric oxygen and other factors are discussed in Baty et al. Bioresources. 2010, 1955-2023.

The concept of deacidification of paper was developed by Schierholtz (1936) and Barrow in the 1930s. The application of bicarbonates or alkaline earth metal hydroxides in an aqueous medium or the simple washing of paper with water has been described in many publications, (e.g. Amey et al. J. Amer. Inst. Concer. 1979, 34-41). Deacidification technologies have evolved towards non-aqueous deacidification systems when Baynes-Cope (1969) and Smith (1970) introduced the application of bamate oxide in methanol and the carbon dioxide / magnesium methoxide system in methanol. The advantage of applying a non-aqueous environment is the minimization of paper swelling and gentleness to printing. An overview of the deacidification processes used in Germany and an evaluation of their quality is given in Restaurátor, 2005, 63-75. An overview of patents, applied technologies and their evaluation for deacidification of lignocellulosic materials was compiled by Cedzová et al. Restorator, 2006, 35-45, Baty et al. Bioresources. 2010, 1955-2023, Zervos et al. Cellulose, 2015, and Hubbe et al., Bioresources, 2017, 4410-4477. The use of nanoparticles of hydroxides, oxides, alkaline earth carbonates for deacidification aqueous and non-aqueous processes is summarized in Bagliony et. al. Soft Matter, 2006, 2, 293-303.

The "Wei Tó" process described in Smith, RD Restorer, 1987, 69-93 uses a solution of methoxymagnesium methyl 1 carbonate CH ₃ OMgOCOOCH ₃ in methanol or isopropanol and chlorofluorocarbons and / or perfluorocarbons, which reacts with water in the paper in the following reactions: CH ₃ OMgOCOOCH ₃ + H ₂ O 2 MgCO ₃ + 2CH ₃ OH CH ₃ OMgOCOOCH ₃ + 2H ₂ O 2 Mg (OH) ₂ + 2CH ₃ OH + CO ₂ 4MgCO ₃ + Mg (OH) ₂ + 4H ₂ O 2 4MgCO ₃ . Mg (OH) ₂ .4H ₂ O

The reagent acts on the paper material after drying for 36 hours at a temperature of about 60 ° C to 0.5% water. The drying, working and conditioning cycle lasts about 80 hours. 0.7% of the magnesium carbonate formed acts as an alkaline reserve.

The following documents describe the use of various agents to deacidify cellulosic materials: US 2003/0150571 protects the use of C2-C5 fluorocarbons and micronized alkaline earth metal oxides, hydroxides, carbonates, or a combination thereof in the presence of surfactants.

WO 2013090684 protects the use of C2-C6 fluorinated olefins and micronized alkaline earth metal oxides, hydroxides, carbonates or a combination thereof in the presence of surfactants. U.S. Pat. No. 6,774,336 protects the use of n-propanol and magnesium carbonate di-n-propylate and C2-C5 fluorocarbons.

The "Bookkeeper" technology has been used in the United States since 1994. A suspension of magnesium oxide in a fluorocarbon is applied, with the advantage of omitting pre-drying and vacuum drying (Hon NS (1989) In: Zeronian H, Needles HL (eds)) History Textile and Paper Materials II, vol 410. ACS Publications, pp 13-33).

Papersave Technology, Andres H, et. Al. (2008) Restorer 29: 3-28 doi: 10.1515 / rest.2008.002, uses magnesium titanium alkoxide, which impregnates paper material dried in a vacuum to 1% water, and

SK 50053-2021 U1 subsequent evaporation of the hexamethyl-disiloxane solvent. The technological process lasts about 3 days, while magnesium carbonate formed by reaction with residual water acts as a 2% alkaline reserve.

The "FMC" process generates as an alkaline reserve magnesium carbonate formed by the decomposition of magnesium butyl glycolate. Heptane or fluorocarbons are used as solvents and the process involves dielectric predrying to 2% water. Maclnnes et al. J. Mat. Chem. 1992, 1049-156.

Reducing agents used for light bleaching of paper are also used in deacidification, as they stabilize oxidized cellulose by reducing the carbonyl groups formed by cellulose autooxidation. Borane-tert complex, butylamine Bicchieri et. al Restorer, 1999, 22-29, sodium borohydride, tetramethylammonium borohydride Block et al. (1986) In: Needles HL, Zeronian SH (eds). Advances in Chemistry Šerieš, vol 212. American Chemical Society, Washington, DC, pp 411-425. A combination of individual treatments is described: first deacidification with magnesium bicarbonate, then a reduction step with sodium borohydride and finally a bath in dilute calcium hydroxide solution. Tang (1986) In: Needles HL, Zeronian SH (eds) Advances in Chemistry Šerieš, vol 212. American Chemical Society, Washington, DC, pp 427-441. In addition to the multi-stage, the application of the aquatic environment is also a disadvantage.

EP 3072933 protects the use of a composition comprising alkaline earth oxides, hydroxides, carbonates, bis (hexamethyldisilazides) or mixtures thereof and hydrophilic cellulose derivatives, such as e.g. carboxymethylcellulose and stabilizers selected from polysaccharides and silanized polysaccharides, for paper stabilization.

The Slovak utility model UV 5527 protects the preparation for deacidification and subsequent increase of strength and stability of paper carriers and the method of its use, while using an aqueous solution of potassium zirconate and subsequent application of polysaccharide.

Slovak patent specification 286525 protects a method of surface treatment of paper with chitosan or its derivatives, activated by atmospheric plasma, where solutions of chitosan or its derivatives are applied to the surface of the paper before or after activation by atmospheric plasma. This allows the protective layers to be covalently or ionically bonded to the surface of the paper.

Slovak patent specification 286410 describes a multicomponent mixture for stabilizing and strengthening paper sheets consisting of chitosan and methyl-hydroxyethyl cellulose and starch dissolved in magnesium bicarbonate.

Slovak patent specification 286412 protects a process for the treatment of paper carriers after removal of acidic soluble products by pre-washing with deionized water and subsequent deacidification, in which the carriers are immersed in a solution of reagents such as magnesium bicarbonate or calcium bicarbonate. After deacidification or each step, the paper carrier is dried for at least 24 hours. Subsequently, the neutralized paper carriers are subjected to stabilization with an antioxidant solution.

Slovak patent specification 287799 describes a composition for extending the life of waste paper consisting of poly (2- (C1-C4) alkyl-2-oxazoline) or poly (2-phenyl-2-oxazoline) and an organic or inorganic base.

Slovak patent specification 287856 describes a method of modifying documents in a closed chamber, where they are subjected to repeated cyclic treatment with a true or supersaturated solution of the modifying substance. The leaves are then pressed and dried. This cycle is repeated until a pH in the range of 7 to 8.5 or an alkaline reserve in the range of 0.5 to 2.5% CaCO ₃ equivalent is reached.

Slovak patent application 5068-2009 describes a mixture and its use for one-step modification of acid papers. The mixture is a deacidification solution consisting of magnesium bicarbonate and calcium bicarbonate solutions, potato starch and potassium iodide.

In Isca et. al. Cellulose 2016, DOI 10.1007 / sl0570-016-0880-7 describes the use of soluble polyamidoamines in water or alcohol for deacidification and biostatic protection of cellulosic material. The IR method was used to characterize the material and the efficiency of the deacidification.

The use of ammonia and morpholine to deacidify the cellulosic material is also described, but the disadvantage is the zero alkaline reserve of the treated material, as the reagent rapidly evaporates from the treated material. (Cheradame et al. Restorer. 2003, 227-239.)

Sancches et al. Tet. Lett., 1988, 138-142 described the use of magnesium diisopropylamide for the reduction of aldehydes and ketones to alcohols.

The processes used so far are demanding for technological operations, especially long drying to a residual water content of about 1 - 0.5%, long-term secondary drying from solvent residues and conditioning. The insoluble inorganic reagents used in organic solvents do not allow uniform distribution on the surface and in the microstructure of the paper or cause deposits on the surface. In some processes it is necessary to book resp. paper material to "untie", which is unsuitable for old prints. Another disadvantage is damage to the print or the appearance of significant ghost differences after adjustment. The above overview shows that our proposed use of a solution of an organomagnesium compound simultaneously combining the reduction of oxidized cellulose, deacidification with a higher amine and magnesium hydroxide and the formation of an alkaline reserve, which eliminates the shortcomings of hitherto known solutions, is not described anywhere.

SK 50053-2021 U1

The essence of the technical solution

The present technical solution relates to a method for deacidifying and increasing the stability of lignocellulosic materials, the essence of which consists in the fact that the lignocellulosic material is treated with a magnesium diamide of general formula (I).

[(R ₁ R 2 CH) ₂ N] ₂ Mg I, wherein R 1 and R ₂ are independently selected from the group consisting of C 1 to C 6 alkyl, branched C 3 to C 6 alkyl or cyclohexyl, in a solvent selected from the group consisting of C 5 to C 7 alkane, cycloalkane C4 to C6, chlorofluorocarbons C2 to C6, chlorinated hydrocarbons C1 to C4, fluorocarbons C2 to C6, toluene, xylene, chlorobenzene, C4 to C8 dialkyl ethers, tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, acetonitrile, hexamethyldisiloxane or diamide mixtures thereof, of formula (I) in said solvent is at least 0.05 M, preferably 0.05 to 2 M, most preferably 0.05 M to 1 M, to form a deacidified lignocellulosic material. The treated material is then dried or pressed and meets the requirements and parameters of DIN 6738. In newly produced papers in the highest service life class, DIN 6738 recommends a minimum content of 2% CaCO ₃ (equivalent to other deacidifying agents) and this concentration should be target value also during deacidification. (Chemistry 55 (2001) 981-989). Magnesium diamides of formula (I) are commercially available or can be easily prepared from commercial materials. (US532774, KR20130136445, WO2008087057, J. Am. Chem. Soc. 1989, 8016, Organometallics 2005, 836, Nutzel K. in: Organo-magnesium compounds, Houben-Weyl, Vol. 13, 2a, p. 154).

In the reaction cascade, the primary magnesium diamide solution of formula (I) reacts with the acidic impurities generated in the paper and also those which enter the paper from the environment to form magnesium compounds, at the same time reducing the carbonyl groups of the pulp fibers and acidic groups of the adjuvants used. . The resulting magnesium hydroxide is coordinated to the hydroxyl groups of the fibers and auxiliaries in the paper, which ultimately neutralizes their acidity while increasing their strength, stability and durability, and adjusts the paper to the desired pH. The use of a solution of the magnesium reagent of formula (I) is particularly advantageous due to the easy penetration of the reagent solution into the paper microstructure, and after a cascade of reactions leads to deacidification and the formation of an alkaline reserve in the whole material profile. Another effect over the organomagnesium reagents used is the ongoing reduction of carbonyl groups, carboxyl precursors, to the corresponding alcohols. The reduction suppresses the formation of carboxyl groups and thus affects the long-term stability of the paper. The residual magnesium diamide of formula (I) is hydrolysed with residual water in the paper and during the conditioning cycle to form magnesium hydroxide contributes to the alkaline reserve of the treated material, e.g. paper, archival documents and books. The conditioning aims to create an equilibrium state of the lignocellulosic material at ambient temperature and humidity. Under normal conditions, the material is conditioned as standard at a temperature of 21 to 25 ° C and an ambient relative humidity of 45 to 65% for several hours, or an air conditioning chamber can be used. The conditioning process is well known to the person skilled in the art. The advantage of the magnesium diamides of general formula (I) used for technological processes is their non-pyrophoric behavior. This is particularly advantageous since it is not necessary to dry the paper material to the low values required so far, the magnesium diamides themselves react with the residual water in the desired direction of the reaction to form a neutralizing agent. The commercial availability of said magnesium diamides is also an advantage. The use of the magnesium diamides of the general formula (I) thus suitably utilizes their properties.

Preferably, they are added to the lignocellulosic material deoxygenated by the process of the present invention described above

a) amino alcohols of general formula (II),

CH3- (HO) CH- (CH2) n-NH- (CH2) n-CH (HO) -CH3 II, where n is 0 to 3, and / or

(b) magnesium oxide, basic magnesium oxide or magnesium carbonate.

The amino alcohols of formula (II) may be added to the reaction mixture directly per se or in a solvent selected from the group consisting of C1 to C5 alcohols, C2 to C4 ethers, C2 to C4 cycloethers, toluene, dimethylacetamide, dimethylformamide or mixtures thereof, wherein the amino alcohol concentration in said solvent is 0.05 to 5% by weight.

Magnesium oxide, basic magnesium oxide or magnesium carbonate may also be added to the reaction mixture directly per se or in a solvent selected from the group consisting of C1 to C5 alcohols, C2 to C4 ethers, C2 to C4 cycloethers, toluene, dimethylacetamide, dimethylformamide or mixtures thereof. wherein the concentration of magnesium oxide, basic magnesium oxide or magnesium carbonate in said solvent is 0.05 to 5% by weight.

The addition of amino alcohols of the general formula (II) leads, in addition to the primary treatment of acidity, also to the improvement or maintenance of the desired mechanical properties, especially in the case of natural aging. The biocidal effect of amino alcohols in the preservation of museum materials is particularly important. The addition of magnesium oxide, basic magnesium oxide or magnesium carbonate contributes to the further formation of the alkaline reserve.

SK 50053-2021 U1

Preferably, the whole process of treating the lignocellulosic material according to the present technical solution takes place at a temperature of 15 to 45 ° C.

In addition, by the method according to the present technical solution, it is possible to obtain reinforced lignocellulosic materials at the same time in the process of treating the lignocellulosic material. It is known to the person skilled in the art that after deacidification it is possible to apply solutions of hydrophilic cellulose derivatives selected e.g. from carboxymethyl cellulose, methyl or hydroxyethyl cellulose, starch, which makes it possible to repair eroded areas and increase its mechanical strength and stability.

Determination of deacidified paper properties:

The input material for determining the properties of deacidified paper is NOVO paper (basis weight 90 g / m ² , composition> 55% mechanical wood pulp (CTPM), lignin (17%) + bleached paper pulp, pH 4.5 (alum treatment), filler 12 - 15% kaolin). The alkaline reserve was determined by titration according to ISO 10716. The color difference was determined according to Zmeškal O. et. al. Color spaces and color management. [Online] Brno University of Technology, 2002.

After the treatment process, values with a color difference ΔΕ of 0.2-1.5 were measured. The oxidation index was determined as the ratio of the height of the absorption bands of the IR spectra at 1730 cm and 1650 cm -1. I _{ox of the} starting material was 0.685, I _{ox of the} treated material was 0.564 to 0.630. The surface pH of the paper was determined as the average of 5 measurements. The surface pH of the test sheets increased after deacidification from an initial pH of 3.45 - 4.51 to a good pH of 6.30 - 9.84.

The following examples describe a method of deacidifying paper according to the present invention. The examples serve to further illustrate the present technical solution without limiting it to the given examples.

Examples of embodiments

Example 1

400 ml of terahydrofuran and 30 ml of a 0.7 M solution of magnesium diisopropylamide in tetrahydrofuran are fed to 25 sheets of NOVO paper in a model reactor at 25 ° C. The mixture was stirred gently for 1.5 hours. The paper is removed, dried from the solvent in a stream of air for 1 hour and allowed to freely condition at 65% RH for 5 hours. A deacidified paper with a pH of 9.84 is obtained, an alkaline reserve of 4.0% (expressed as% CaCO ₃ ). Tetrahydrofuran from the process is recovered by distillation.

Example 2

To sheets of NOVO paper (as defined in Example 1) with a total weight of 6.0 g are added 100 ml of toluene and 100 ml of cyclohexane followed by 7.5 ml of a 0.4 M solution of Ν, Ν-dicyclohexylmethylamide magnesium in tetrahydrofuran under a nitrogen atmosphere. The mixture was stirred gently at 35 ° C for 3 hours. The reaction medium is decanted, 200 ml of toluene are added and the mixture is stirred for 30 minutes. 0.2 g of diisopropanol amine is added to the reaction mixture and stirring is continued for another hour. The paper is removed and dried in a stream of air for 1 hour and then dried under a water pump vacuum at 35 ° C. A deacidified paper with a pH of 9.8 is obtained, an alkaline reserve of 4.1% (expressed as% CaCO ₃ ).

Example 3

To sheets of NOVO paper (as defined in Example 1) with a total weight of 6.1 g was added 200 ml of hexamethyldisiloxane followed by 15 ml of a 0.8 M solution of magnesium diisopropylamide in tetrahydrofuran. The mixture was stirred gently at 25 ° C for 3 hours. The paper is removed and stirred in 150 ml of 96% ethanol for another hour with the addition of 0.5 g of basic magnesium oxide. The paper is then dried in a stream of air for 4 hours. A deacidified paper with a pH of 8.5 is obtained, an alkaline reserve of 4.1% (expressed as% CaCO ₃ ).

Example 4

In analogy to Example 1, except that NOVO paper (as defined in Example 1) is dried to 0.4% water according to Karl Fischer and 1.7 g of magnesium oxide in 100 ml of methanol are added. Subsequently, the paper is dried at 40 ° C under vacuum for 4 hours. A deacidified paper with a pH of 8.5 is obtained, an alkaline reserve of 4.1% (expressed as% CaCO ₃ ).

Example 5

In analogy to Example 1, except that NOVO paper (as defined in Example 1) was dried to 0.4% water according to Karl Fischer, magnesium diisobutylamide in hexamethyldisiloxane and ethylene glycol dimethyl ether were used instead of tetrahydrofuran and magnesium diisopropylamide in tetrahydrofuran and the reaction product in

SK 50053-2021 U1 is then washed with a 5% solution of diisobutanolamine in methanol. The alkaline reserve is 4.1% (expressed as% CaCO ₃ ).

Example 6

In analogy to Example 1, except that NOVO paper (as defined in Example 1) is dried to 0.4% water according to Karl Fischer. 2.5 g of magnesium carbonate and 250 ml of a 5% solution of diisobutanolamine in propan-2-ol are then added to the reaction product and stirred for 3 hours. The paper is removed, dried in a stream of air for 3 hours and allowed to freely condition at room temperature and humidity 45% RH for 5 hours, alkaline reserve 4.15% (expressed as% CaCO ₃ ).

Example 7

In analogy to Example 1, except that NOVO paper (as defined in Example 1) was dried to 0.4% water according to Karl Fischer, 2.1 M magnesium di-sec-butylamide was used instead of tetrahydrofuran and magnesium diisopropylamide in tetrahydrofuran. in tetrahydrofuran. The paper is removed, dried from the solvent in a stream of air for 1 hour and allowed to freely condition at 65% RH for 12 hours.

Industrial applicability

The presented technical solution is used in the deacidification of lignocellulosic materials in a non-aqueous environment of organic solvents by solutions of magnesium diamides. The advantage is a homogeneous reaction environment and direct use of the reducing properties of magnesium compounds for paper stabilization and deacidification and at the same time the formation of magnesium hydroxide to create the required alkaline reserve. The benefits are deacidification in the entire volume of material, simple implementation of the process and application of available, non-pyrophoric and stable organomagnesium reagents.

Claims (7)

PROTECTION REQUIREMENTS A process for deacidifying and increasing the stability of lignocellulosic materials, characterized in that the lignocellulosic material is treated with a magnesium diamide of general formula (I), [(R ₁ R 2 CH) ₂ N] 2Mg (I), wherein R 1 and R ₂ are independently selected from the group consisting of C 1 to C 6 alkyl, branched C 3 to C 6 alkyl or cyclohexyl, in a solvent selected from the group consisting of C 5 to C 7 alkane, C4 to C6 cycloalkane, C2 to C6 chlorofluorocarbon, C1 to C4 chlorinated hydrocarbon, C2 to C6 fluorocarbon, toluene, xylene, chlorobenzene, C4 to C8 dialkyl ethers, tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, acetonitrile, hexamethyldisiloxane, mixtures thereof of magnesium of general formula (I) in said solvent is at least 0.05 M, to form a deacidified lignocellulosic material. Process according to claim 1, characterized in that the concentration of the magnesium diamide of general formula (I) in said solvent is 0.05 M to 2 M. Process according to Claim 1 or 2, characterized in that a) amino alcohols of the general formula (II), CH 3 - (HO) CH- (CH 2) n -NH- (CH 2) n -CH are further added to the deacidified lignocellulosic material. (HO) -CH 3 (II), where n is 0 to 3 and / or b) magnesium oxide, basic magnesium oxide or magnesium carbonate. Process according to claim 3, characterized in that the amino alcohols of general formula (II) are added directly to the reaction mixture per se or in a solvent selected from the group consisting of C1 to C5 alcohols, C2 to C4 ethers, C2 to C4 cycloethers, toluene, dimethylacetamide, dimethylformamide or mixtures thereof, wherein the concentration of amino alcohol in said solvent is 0.05 to 5% by weight. Process according to Claim 3, characterized in that magnesium oxide, basic magnesium oxide or magnesium carbonate are added to the reaction mixture directly per se or in a solvent selected from the group consisting of C1 to C5 alcohols, C2 to C4 ethers, C2 to C4 cycloethers. C4, toluene, dimethylacetamide, dimethylformamide or mixtures thereof, wherein the concentration of magnesium oxide, basic magnesium oxide or magnesium carbonate in said solvent is 0.05 to 5% by weight. Process according to any one of Claims 1 to 5, characterized in that it is carried out at a temperature of 15 to 45 ° C. Process according to any one of claims 1 to 6, characterized in that the deacidified lignocellulosic material is conditioned and further dried or pressed.