Poly alpha-hydroxy acrylic acid, process for its preparation and use thereof

Abstract

The application belongs to the technical field of papermaking, and discloses a poly-alpha-hydroxy acrylic acid, which comprises alpha-hydroxy acrylic acid units and anionic polymerizable surfactant units with sulfonic acid groups; the molar ratio of the alpha-hydroxy acrylic acid units and the polymerizable surfactant units is 1:0.05-0.15. The polymer has sulfonic acid groups in addition to the alpha-hydroxy acrylic acid units, the types of chelating groups are enriched by introducing the sulfonic acid groups, the sulfonic acid groups are copolymerized into the chain segments, the sulfonic acid groups have more obvious steric hindrance effects compared with the hydroxyl groups or carboxyl groups of the polymer itself, intramolecular esterification in the bleaching operation can be inhibited, the reduction of the polymer performance is effectively delayed, and the polymer can continuously maintain excellent hydrogen peroxide stability. Another purpose of the application is to provide a preparation method and application of the poly-alpha-hydroxy acrylic acid.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a poly(α-hydroxyacrylic acid) and its preparation method and uses. Background Technology

[0002] Pulp bleaching technology has undergone a transformation from traditional chlorine-containing bleaching (such as elemental chlorine and hypochlorite) to environmentally friendly chlorine-free bleaching (ECF, TCF). The core challenge lies in balancing bleaching efficiency, fiber damage, and environmental protection requirements: although early chlorine bleaching processes were highly efficient, they produced highly toxic dioxins, which have been gradually replaced by chlorine dioxide, ozone, and hydrogen peroxide.

[0003] Hydrogen peroxide, as a key oxidant in chlorine-free pulp bleaching, is widely used in multi-stage bleaching processes such as oxygen delignification and alkali extraction. Its core advantages lie in its outstanding environmental friendliness, minimal fiber damage, and stable bleaching effect, while also being compatible with various raw material systems such as wood pulp and bamboo pulp. However, it requires a high-temperature alkaline environment (pH 10-12, 80-95℃) and silicate stabilizers to control decomposition, resulting in high energy consumption and sensitivity to metal ions (Fe). 3+ / Mn 2+ (Concentration > 0.5 ppm accelerates decomposition) and addresses the challenge of neutralizing wastewater pH.

[0004] Prior Art 1: Japanese Patent Application JP2001289541 discloses a hydrogen peroxide stabilizer for bleaching, scouring, and soaping of fibers. It exhibits excellent alkali resistance and hydrogen peroxide stabilizing effect, maintaining the bleaching performance of hydrogen peroxide even in the presence of high concentrations of alkali. Furthermore, it is a hydrogen peroxide stabilizer that can improve the whiteness of fibers. The solution comprises: (a) obtained by free radical polymerization of at least one monomer selected from acrylic acid, methacrylic acid, maleic acid, and their salts with poly-α-hydroxyacrylic acid and / or its salts; (b) a water-soluble magnesium compound, wherein the weight ratio of the polymer to magnesium is 1:1 to 45:1, which is a hydrogen peroxide stabilizer.

[0005] Existing technology 1 uses free radical polymerization of poly-α-hydroxyacrylic acid and / or its salts to polymerize at least one monomer selected from acrylic acid, methacrylic acid, maleic acid and its salts to achieve the effect of stabilizing hydrogen peroxide.

[0006] Poly(α-hydroxyacrylic acid) exhibits significant advantages in paper bleaching, including stabilizing bleaching agent activity by chelating metal ions, improving decolorization efficiency by synergistically degrading chromophores, improving bleaching uniformity by adsorbing and dispersing impurities, and protecting fibers by reducing oxidative damage. It also has the advantages of biodegradability and synergistic effect with wastewater treatment, which meets the requirements of green papermaking. However, its application requires precise control of pH, temperature and molecular structure to adapt to different bleaching systems, and there are still optimization challenges in terms of stability under high concentration of metal ions. Summary of the Invention

[0007] One of the objectives of this invention is to provide a poly(α-hydroxyacrylic acid) polymer that, in addition to having α-hydroxyacrylic acid units, also has sulfonic acid groups. By introducing sulfonic acid groups, the types of chelating groups are enriched, and the sulfonic acid groups copolymerized into the chain segments have a more significant steric hindrance effect compared to the hydroxyl or carboxyl groups present in the polymer itself. This can inhibit intramolecular esterification during the bleaching process, effectively delay the degradation of polymer properties, and enable the polymer to maintain a relatively excellent hydrogen peroxide stability.

[0008] Another objective of this invention is to provide a method for preparing polyα-hydroxyacrylic acid and its uses.

[0009] To achieve the above objectives, the present invention provides a poly(α-hydroxyacrylic acid) comprising α-hydroxyacrylic acid units and anionic polymerizable surfactant units having sulfonic acid groups; the molar ratio of the α-hydroxyacrylic acid units to the polymerizable surfactant units is 1:0.05 to 0.15.

[0010] This invention introduces monomers with sulfonic acid groups into the poly(α-hydroxyacrylic acid) chain segments via copolymerization. The purpose of introducing the sulfonic acid groups is twofold:

[0011] I. Sulfonic acid groups have a significant chelating ability for metal ions; they exhibit strong chelating properties for divalent or higher valence metal ions, such as Ca. 2+ Mg 2+ Cu 2+ and Mn 2+ ;

[0012] Second, the steric hindrance effect of sulfonic acid groups is significantly stronger than that of carboxyl and hydroxyl groups in poly(α-hydroxyacrylic acid). They are interspersed in the chain segments and can inhibit intra- and inter-chain esterification, thus delaying the decrease in the polymer's stability against hydrogen peroxide during the papermaking process.

[0013] In the above-mentioned polyα-hydroxyacrylic acid, the polymerizable surfactant unit is sodium methyl allyl sulfonate and / or sodium allyl sulfonate.

[0014] In the above-mentioned polyα-hydroxyacrylic acid, the polyα-hydroxyacrylic acid is obtained by soap-free emulsion polymerization.

[0015] Meanwhile, this invention also discloses a method for preparing polyα-hydroxyacrylic acid as described in any of the above, comprising the following steps:

[0016] Step 1: Add water, polymerizable surfactant, and α-chloroacrylic acid to a reaction vessel under an inert atmosphere, stir until a uniform emulsion is formed, and heat the reaction system to and maintain the temperature at 70-85°C.

[0017] Step 2: Add the initiator solution to the reaction system of Step 1 to carry out the reaction, and the reaction time is 3 to 6 hours;

[0018] Step 3: After the reaction is complete, filter the mixture and collect the polymer solid.

[0019] Step 4: Add the polymer solid to an alkaline aqueous solution for hydrolysis to obtain poly-α-hydroxyacrylic acid.

[0020] In the above-described method for preparing poly(α-hydroxyacrylic acid), the initiator is a peroxide initiator; the amount of the initiator is 0.5 to 2 wt% of the total weight of the polymerizable surfactant and α-chloroacrylic acid.

[0021] In the above-described method for preparing polyα-hydroxyacrylic acid, the initiator is sodium persulfate, potassium persulfate, or ammonium persulfate.

[0022] In the above-described method for preparing polyα-hydroxyacrylic acid, the weight ratio of the polymerizable surfactant, the total weight of α-chloroacrylic acid, and water is 100:300-500.

[0023] In the above-mentioned preparation method of polyα-hydroxyacrylic acid, the hydrolysis temperature in step 4 is 75-85℃, and the hydrolysis time is not less than 2h.

[0024] Finally, the present invention also discloses the use of polyα-hydroxyacrylic acid as described above in the preparation of hydrogen peroxide stabilizers.

[0025] Beneficial effects

[0026] Compared with the prior art, the present invention has at least the following advantages:

[0027] This invention enriches the types of chelating groups by introducing sulfonic acid groups. Furthermore, the copolymerization of sulfonic acid groups into the chain segments has a more significant steric hindrance effect compared to the hydroxyl or carboxyl groups inherent in the polymer itself. This can inhibit intramolecular esterification during the bleaching process, effectively delay the degradation of polymer performance, and enable the polymer to maintain excellent hydrogen peroxide stability. Detailed Implementation

[0028] The present invention will be further described below with reference to embodiments, but this does not constitute any limitation on the present invention. Any limited modifications made within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0029] To illustrate the technical content of the present invention in detail, the following description is provided in conjunction with the embodiments.

[0030] Example 1

[0031] The preparation method of polyα-hydroxyacrylic acid includes the following steps:

[0032] Step 1: Add 341g of water, 7.2g of sodium allyl sulfonate (0.05mol), and 106.5g of α-chloroacrylic acid (1mol) to a reaction vessel under an inert atmosphere, stir until a uniform emulsion is formed, and heat the reaction system to and maintain the temperature at 80℃.

[0033] Step 2: Add 0.57g of sodium persulfate solution to the reaction system of Step 1 to carry out the reaction for 3 hours;

[0034] Step 3: After the reaction is complete, filter the mixture and collect the polymer solid.

[0035] Step 4: Add the polymer solid to a 1.5 mol / L sodium hydroxide aqueous solution for hydrolysis at a temperature of 80℃ for 3 hours to obtain poly-α-hydroxyacrylic acid.

[0036] Example 2

[0037] The preparation method of polyα-hydroxyacrylic acid includes the following steps:

[0038] Step 1: Add 483g of water, 14.4g of sodium allyl sulfonate (0.1mol), and 106.5g of α-chloroacrylic acid (1mol) to a reaction vessel under an inert atmosphere, stir until a uniform emulsion is formed, and heat the reaction system to and maintain the temperature at 80°C.

[0039] Step 2: Add 1.21g of sodium persulfate solution to the reaction system of Step 1 to carry out the reaction for 4 hours;

[0040] Step 3: After the reaction is complete, filter the mixture and collect the polymer solid.

[0041] Step 4: Add the polymer solid to a 1.5 mol / L sodium hydroxide aqueous solution for hydrolysis at a temperature of 85℃ for 4 hours to obtain poly-α-hydroxyacrylic acid.

[0042] Example 3

[0043] The preparation method of polyα-hydroxyacrylic acid includes the following steps:

[0044] Step 1: Add 640g of water, 21.6g of sodium allyl sulfonate (0.15mol), and 106.5g of α-chloroacrylic acid (1mol) to a reaction vessel under an inert atmosphere, stir until a uniform emulsion is formed, and heat the reaction system to and maintain the temperature at 80℃.

[0045] Step 2: Add 2.56g of sodium persulfate solution to the reaction system of Step 1 to carry out the reaction for 5 hours;

[0046] Step 3: After the reaction is complete, filter the mixture and collect the polymer solid.

[0047] Step 4: Add the polymer solid to a 1.5 mol / L sodium hydroxide aqueous solution for hydrolysis at a temperature of 75°C for 6 hours to obtain poly-α-hydroxyacrylic acid.

[0048] Example 4

[0049] The preparation method of polyα-hydroxyacrylic acid includes the following steps:

[0050] Step 1: Add 640g of water, 15.8g of sodium methacrylate sulfonate (0.1mol), and 106.5g of α-chloroacrylic acid (1mol) to a reaction vessel under an inert atmosphere, stir until a homogeneous emulsion is formed, and heat the reaction system to and maintain the temperature at 85℃.

[0051] Step 2: Add 1.21g of sodium persulfate solution to the reaction system of Step 1 to carry out the reaction for 4 hours;

[0052] Step 3: After the reaction is complete, filter the mixture and collect the polymer solid.

[0053] Step 4: Add the polymer solid to a 1 mol / L sodium hydroxide aqueous solution for hydrolysis at a temperature of 75℃ for 6 hours to obtain poly-α-hydroxyacrylic acid.

[0054] Example 5

[0055] The preparation method of polyα-hydroxyacrylic acid includes the following steps:

[0056] Step 1: Add 640g of water, 23.7g of sodium methacrylate sulfonate (0.15mol), and 106.5g of α-chloroacrylic acid (1mol) to a reaction vessel under an inert atmosphere, stir until a homogeneous emulsion is formed, and heat the reaction system to and maintain the temperature at 70℃.

[0057] Step 2: Add 1.95g of sodium persulfate solution to the reaction system of Step 1 to carry out the reaction for 5 hours;

[0058] Step 3: After the reaction is complete, filter the mixture and collect the polymer solid.

[0059] Step 4: Add the polymer solid to a 2 mol / L sodium hydroxide aqueous solution for hydrolysis at a temperature of 85℃ for 4 hours to obtain poly-α-hydroxyacrylic acid.

[0060] Comparative Example 1

[0061] The preparation method of polyα-hydroxyacrylic acid includes the following steps:

[0062] Step 1: Add 426g of water and 106.5g of α-chloroacrylic acid (1mol) to a reaction vessel under an inert atmosphere, stir until homogeneous, and heat the reaction system to and maintain a constant temperature of 80℃.

[0063] Step 2: Add 1.07g of sodium persulfate solution to the reaction system of Step 1 to carry out the reaction for 4 hours;

[0064] Step 3: After the reaction is complete, filter the mixture and collect the polymer solid.

[0065] Step 4: Add the polymer solid to a 1.5 mol / L sodium hydroxide aqueous solution for hydrolysis at a temperature of 85℃ for 4 hours to obtain poly-α-hydroxyacrylic acid.

[0066] Performance testing

[0067] 1. Pulp bleaching performance test

[0068] The pulp from a certain chemical pulping plant was concentrated and bleached. The pulp parameters under high-concentration bleaching operation conditions are shown in Table 1 below.

[0069] Table 1. Pulp parameters under high-consistency bleaching operation conditions at a certain chemical machinery pulp plant.

[0070]

[0071] The stabilizer's ability to stabilize hydrogen peroxide bleaching was tested according to the following experimental steps:

[0072] (1) Weigh a certain amount of slurry into a polyethylene self-sealing bag, add a certain amount of dilution water, add the required amount of bleaching reagent according to the amount of reagent required for bleaching, knead for 5 minutes and then put it into a water bath at 95°C for 90 minutes.

[0073] (2) After the bleaching time is up, weigh out 11g of slurry, take two bags, add 300g of purified water to each bag, and stir and disperse them with a mixer.

[0074] (3) Stir for 5 minutes and then filter.

[0075] (4) After filtration, the tablets are compressed for 3 minutes and then naturally dried under constant temperature and humidity conditions before testing the whiteness.

[0076] (5) After each bag of pulp is weighed, squeeze out the filtrate and measure the hydrogen peroxide residue.

[0077] The test results are shown in Table 2 below;

[0078] Table 2. Bleaching Performance Test of Hydrogen Peroxide Stabilizer

[0079]

[0080] The data above shows that, compared with Comparative Example 1, Examples 1-5 introduced sulfonic acid groups into the molecular chain of poly-α-hydroxyacrylic acid through copolymerization, which improved the bleaching performance of hydrogen peroxide under stable alkaline conditions. Comparative Examples 1-3 show that, within a certain range, the bleaching performance increases with the increase of sulfonic acid groups in the molecular chain. Further increasing the number of introduced sulfonic acid groups does not improve the bleaching performance but rather decreases it. Therefore, it can be concluded that the amount of sulfonic acid groups introduced should be within a certain range.

[0081] 2. Determination of metal ion chelation ability

[0082] The metal ion chelating agent performance of the products in Examples 1-5 and Comparative Example 1 was tested according to the method GB / T 21884-2008 for the determination of chelating ability of chelating agents in textile printing and dyeing auxiliaries. The test results are shown in Table 3 below.

[0083] Table 3 Metal ion chelation performance

[0084] Calcium chelation value (mg / L) Iron chelation value (mg / L) Example 1 72 56 Example 2 78 63 Example 3 73 59 Example 4 76 62 Example 5 70 58 Comparative Example 1 65 44

[0085] The data above show that the metal ion chelating performance of Examples 1-5 is significantly improved compared with that of Comparative Example 1, and the trend of metal ion chelating performance is the same as that of stable alkaline hydrogen peroxide bleaching performance, indicating that the solution provided by the present invention can effectively improve the practical application effect of poly-α-hydroxyacrylic acid.

[0086] The embodiments presented herein are merely selected implementations based on combinations of all possible embodiments. The appended claims should not be limited to the embodiments described herein. Some numerical ranges used in the claims include sub-ranges within them, and variations within these ranges should also be covered by the appended claims.

Claims

1. A poly(α-hydroxyacrylic acid), characterized in that, It is composed of structural units obtained from α-hydroxyacrylic acid structural units and anionic polymerizable surfactants with sulfonic acid groups; the molar ratio of the α-hydroxyacrylic acid structural units to the structural units obtained from the polymerizable surfactants is 1:0.05~0.1; The structural unit obtained by the polymerizable surfactant is a structural unit obtained by sodium methyl allyl sulfonate and / or sodium allyl sulfonate.

2. The polyα-hydroxyacrylic acid according to claim 1, characterized in that, The poly-α-hydroxyacrylic acid is obtained by soap-free emulsion polymerization.

3. A method for preparing polyα-hydroxyacrylic acid as described in any one of claims 1 to 2, characterized in that, Includes the following steps: Step 1: Add water, polymerizable surfactant, and α-chloroacrylic acid to a reaction vessel under an inert atmosphere, stir until a uniform emulsion is formed, and heat the reaction system to and maintain the temperature at 70~85℃. Step 2: Add the initiator solution to the reaction system of Step 1 to carry out the reaction, and the reaction time is 3~6 hours; Step 3: After the reaction is complete, filter the mixture and collect the polymer solid. Step 4: Add the polymer solid to an alkaline aqueous solution for hydrolysis to obtain poly-α-hydroxyacrylic acid; The polymerizable surfactant is sodium methyl allyl sulfonate and / or sodium allyl sulfonate.

4. The method for preparing polyα-hydroxyacrylic acid according to claim 3, characterized in that, The initiator is a peroxide initiator; the amount of the initiator is 0.5 to 2 wt% of the total weight of the polymerizable surfactant and α-chloroacrylic acid.

5. The method for preparing polyα-hydroxyacrylic acid according to claim 4, characterized in that, The initiator is sodium persulfate, potassium persulfate, or ammonium persulfate.

6. The method for preparing polyα-hydroxyacrylic acid according to claim 5, characterized in that, The total weight ratio of the polymerizable surfactant, α-chloroacrylic acid, and water is 100:300~500.

7. The method for preparing polyα-hydroxyacrylic acid according to claim 3, characterized in that, The hydrolysis temperature in step 4 is 75~85℃, and the hydrolysis time is not less than 2 hours.

8. Use of the polyα-hydroxyacrylic acid as described in any one of claims 1 to 2 to prepare a hydrogen peroxide stabilizer.

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