A chlorine-free wet strength agent and its preparation method and application

Abstract

The present invention discloses a chlorine-free wet strength agent and a preparation method and application thereof. The preparation method of the chlorine-free wet strength agent of the present invention comprises the following steps: 1) adding biomass branched polysaccharide to periodic acid / periodate solution, heating in the dark for reaction, and obtaining biomass-based branched polyaldehyde; 2) adding biomass-based branched polyaldehyde to polyamine solution, heating for reaction, and obtaining chlorine-free wet strength agent. The chlorine-free wet strength agent of the present invention is a hyperbranched polymer with abundant hydroxyl groups, aldehyde groups and amino groups, and has the characteristics of being chlorine-free, soluble in water, environmentally friendly, low cost, and having a wide source of raw materials. It can improve the dry strength and wet strength of paper through multiple interactions, and can be used to prepare chlorine-free high wet strength paper that is easy to degrade and has easy to recycle damaged paper.

Description

Technical Field

[0001] The invention relates to the technical field of pulping and papermaking, and in particular to a chlorine-free wet strength agent and a preparation method and application thereof. Background Art

[0002] Paper is a thin sheet made of plant fibers, and its importance in people's daily lives is increasing day by day. When paper is wet, the interactions between the cellulose fibers inside it (i.e., hydrogen bonds and van der Waals forces) will be severely weakened by water molecules, and the mechanical strength will drop sharply. In addition, the fiber swelling and softening caused by water absorption will also affect the transmission of local mechanical stress in the paper, which may eventually cause the paper to disintegrate. The mechanical properties of paper in a wet state will directly affect its application in certain aspects (for example: packaging board, label paper, map paper, toilet paper, etc.), so the wet strength of paper is crucial.

[0003] At present, the main method for preparing high wet-strength paper with stable mechanical properties is to strengthen the cellulose fiber network by adding wet-strength agents. Traditional wet-strength agents such as urea-formaldehyde resin and phenol-formaldehyde resin prevent the intrusion of water molecules by self-crosslinking to form a network (which will not react with cellulose fibers), thereby improving the wet-strength performance of paper. However, such wet-strength agents will corrode and damage mechanical equipment under acidic processing conditions, and the use of such wet-strength agents will also leave a large amount of free formaldehyde in the paper, posing potential health and safety risks. Polyamide epichlorohydrin resin (PAE) is a common commercial wet-strength agent on the market. It uses the reaction of epichlorohydrin with the secondary amine of the amide main chain to first generate a 3-hydroxyazetidine ring, and then react with another secondary amine of the main chain to make the polymer self-crosslinked and react with the carboxyl group in the pulp fiber to make the resin crosslink with the fiber, thereby improving the wet-strength performance of paper. However, PAE usually contains toxic and mutagenic byproducts such as 1,3-dichloro-2-propanol (DCP) and 3-chloro-1,2-propanediol (MCPD), which are often referred to as absorbable organic halides, abbreviated as AOX, which are harmful to human health and the ecological environment. In addition, paper made with PAE is not easy to degrade after being matured and cured, making it difficult to recycle broken paper.

[0004] Therefore, it is of great significance to develop a chlorine-free wet strength agent and prepare an easily recyclable chlorine-free high wet strength paper. Summary of the invention

[0005] The object of the present invention is to provide a chlorine-free wet strength agent and a preparation method and application thereof.

[0006] The technical solution adopted by the present invention is:

[0007] A method for preparing a chlorine-free wet strength agent comprises the following steps:

[0008] 1) adding biomass-based branched polysaccharide to a periodic acid / periodate solution, and then heating in the dark to react, thereby obtaining a biomass-based branched polyaldehyde;

[0009] 2) Adding the biomass-based branched polyaldehyde into the polyamine solution and heating the solution for reaction, a chlorine-free wet strength agent is obtained.

[0010] Preferably, a method for preparing a chlorine-free wet strength agent comprises the following steps:

[0011] 1) adding biomass branched polysaccharide to periodic acid / periodate solution, heating to react in the dark, filtering, washing the filtered solid with water and alcohol, and drying to obtain biomass-based branched polyaldehyde;

[0012] 2) adding the biomass-based branched polyaldehyde into the polyamine solution, heating for reaction, and filtering to remove impurities to obtain a chlorine-free wet strength agent.

[0013] Preferably, the biomass branched polysaccharide in step 1) is at least one of konjac glucomannan, pullulan, xanthan gum, guar gum, locust bean gum and konjac gum.

[0014] Preferably, the concentration of the periodic acid / periodate solution in step 1) is 0.5 mol / L to 0.9 mol / L.

[0015] Preferably, in step 1), the molar ratio of monosaccharide units to periodic acid / periodate in the biomass branched polysaccharide is 1:0.5-1.3.

[0016] Preferably, the heating and light-shielding reaction in step 1) is carried out at a temperature of 25° C. to 55° C., and the reaction time is 1 h to 72 h.

[0017] Preferably, the heating and light-shielding reaction in step 1) is carried out under mechanical stirring at a stirring rate of 1000 rpm to 2000 rpm.

[0018] Preferably, the drying in step 1) is carried out at a temperature of 35° C. to 65° C., and the drying time is 4 h to 24 h.

[0019] Preferably, the polyamine in step 2) is at least one of ethylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, 1,5-pentanediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and tris(2-aminoethyl)amine.

[0020] Preferably, the mass fraction of the polyamine solution in step 2) is 10% to 50%.

[0021] Preferably, in step 2), the mass ratio of the biomass-based branched polyaldehyde to the polyamine is 1:0.1-0.4.

[0022] Preferably, the heating reaction in step 2) is divided into two stages. The first stage is to react at a temperature of 75°C to 95°C for 0.1h to 1h. The second stage is to dilute with water and then react at a temperature of 50°C to 80°C for 2h to 24h.

[0023] Preferably, the heating reaction in step 2) is carried out under the condition that the pH value of the reaction solution is 4-9.

[0024] Preferably, the heating reaction in step 2) is carried out under mechanical stirring at a stirring rate of 1000 rpm to 2000 rpm.

[0025] Preferably, the mass fraction of the solute in the chlorine-free wet strength agent in step 2) is 1% to 30%.

[0026] A chlorine-free wet strength agent is prepared by the above preparation method.

[0027] A chlorine-free high wet-strength paper, the wet-strength agent used in its preparation is the above-mentioned chlorine-free wet-strength agent.

[0028] A method for preparing the chlorine-free high wet-strength paper as described above comprises the following steps: beating the cellulose fiber pulp board, adding a chlorine-free wet-strength agent to decompress it, and then papermaking, pulping, vacuum dehydration, drying and aging to obtain the chlorine-free high wet-strength paper.

[0029] Preferably, the addition amount of the chlorine-free wet strength agent is 0.5% to 10% of the mass of the cellulose fiber pulp board.

[0030] Preferably, the drying is carried out at a temperature of 25° C. to 55° C., and the drying time is 1 h to 6 h.

[0031] Preferably, the aging is carried out at a temperature of 100° C. to 140° C., and the aging time is 5 min to 30 min.

[0032] The beneficial effects of the present invention are as follows: the chlorine-free wet strength agent of the present invention is a hyperbranched polymer with abundant hydroxyl groups, aldehyde groups and amino groups, and has the characteristics of being chlorine-free, soluble in water, environmentally friendly, low cost, and having a wide source of raw materials. The chlorine-free wet strength agent can improve the dry strength and wet strength of paper through multiple interactions, and can be used to prepare chlorine-free high wet strength paper that is easily degradable and whose damaged paper is easily recyclable.

[0033] Specifically:

[0034] 1) The chlorine-free wet strength agent of the present invention is a hyperbranched polymer with abundant hydroxyl groups, aldehyde groups and amino groups, and has a positive charge. On the one hand, it can be adsorbed on the fiber surface (the pulp fiber has abundant hydroxyl groups, carboxyl groups and aldehydes and ketones) through charge interaction, and form hydrogen bonds with the fiber through the hydroxyl groups and amino groups. On the other hand, the branched structure makes it easy for itself to undergo acetal reaction, aldol reaction and Schiff base reaction to produce self-crosslinking. At the same time, it can also undergo esterification reaction, acetal reaction, aldol reaction and Schiff base reaction with the fiber to crosslink the fiber. The multiple interactions improve the dry strength and wet strength of the paper. The effect of increasing the wet strength is equivalent to that of PAE, and the effect of increasing the dry strength is better than that of PAE. At the same time, the harm of chlorinated organic matter is avoided.

[0035] 2) The chlorine-free wet strength agent of the present invention uses biomass-based materials as raw materials, which have a wide range of sources, low cost, and natural properties such as non-toxicity and biodegradability;

[0036] 3) The preparation system of the chlorine-free wet strength agent of the present invention is a water system, which is environmentally friendly and does not require modification of the original production line of the papermaking enterprise, and does not affect the production efficiency;

[0037] 4) The chlorine-free high wet-strength paper of the present invention is easy to recycle. During the recycling process, reverse reactions of acetal reaction, hydroxyaldehyde reaction and Schiff base reaction will occur between polymers and polymers, polymers and fibers, and fibers and fibers. At the same time, some hydrogen bonds are opened, so that the environmentally friendly chlorine-free high wet-strength paper has a higher re-slurry rate than PAE paper, which solves the problem that traditional wet-strength agent paper is not easy to degrade after mature curing and the damaged paper is difficult to recycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The Fourier transform infrared spectra of the amylopectin, biomass-based branched polyaldehyde and chlorine-free wet strength agent in Example 4 are shown.

[0039] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of the biomass-based branched polyaldehyde, tris(2-aminoethyl)amine and chlorine-free wet strength agent in Example 4.

[0040] Figure 3 The figures are the test results of dry tensile strength and wet tensile strength of paper prepared with different wet strength agent addition amounts according to Example 4 and Comparative Example 3.

[0041] Figure 4 This is a graph showing the test results of the anti-disintegration performance of the chlorine-free high wet-strength paper of Example 4 and the papers of Comparative Examples 1 to 3.

[0042] Figure 5 The water contact angle test results of the chlorine-free high wet strength paper of Example 4 and the papers of Comparative Examples 1 to 3 are shown.

[0043] Figure 6 This is a graph showing the resizing performance test results of paper prepared with different wet strength agent addition amounts according to Example 4 and Comparative Example 3. DETAILED DESCRIPTION

[0044] The present invention will be further explained and illustrated below in conjunction with specific embodiments.

[0045] Embodiment 1:

[0046] A chlorine-free wet strength agent, the preparation method of which comprises the following steps:

[0047] 1) adding amylopectin to a sodium periodate solution with a concentration of 0.7 mol / L in a mechanically stirred state, wherein the molar ratio of the monosaccharide unit in the amylopectin to the sodium periodate is 1:1.1, the stirring rate is 1000 rpm, and then heating to 40° C. to react for 4 hours in the dark, filtering, washing the filtered solid with distilled water and anhydrous ethanol in turn, and then drying at a temperature of 50° C. for 8 hours to obtain a biomass-based branched polyaldehyde;

[0048] 2) adding the biomass-based branched polyaldehyde to a 35% 1,5-pentanediamine solution in a mechanically stirred state, the mass ratio of the biomass-based branched polyaldehyde to 1,5-pentanediamine is 1:0.2, the stirring rate is 1000 rpm, and then adjusting the pH value of the reaction solution to 8, heating to 90° C. for reaction for 30 minutes, and then adding distilled water to dilute the mass fraction of the solute in the reaction solution to 20%, and then cooling to 70° C. for reaction for 6 hours, and then adding distilled water to dilute the mass fraction of the solute in the reaction solution to 10%, and then filtering to remove impurities to obtain a chlorine-free wet strength agent.

[0049] A chlorine-free high wet-strength paper, the preparation method of which comprises the following steps:

[0050] Hardwood pulp fiber (Shandong Huatai Paper Co., Ltd.) was beaten to a beating degree of 30°SR, and then the chlorine-free wet strength agent of the present embodiment was added to be debonded, and the amount of the chlorine-free wet strength agent added was 5% of the absolute dry weight of the hardwood pulp fiber, and then papermaking was performed, and then the pulp was hung on a forming net, and then vacuum dehydration was performed, and then dried at 50°C for 1 hour, and then aged at a temperature of 130°C for 5 minutes, so as to obtain chlorine-free high wet strength paper (base weight of 80g / m 2 , without any other additives).

[0051] After testing, the chlorine-free high wet-strength paper in this embodiment has a dry tensile strength of 2515 N / m±105 N / m, a wet tensile strength of 544.67 N / m±6.67 N / m, and a relative wet strength of 21.66%.

[0052] Note:

[0053] Dry tensile strength: Tested in accordance with "GB / T22898-2008 Paper and paperboard - Determination of tensile strength - Constant rate tensile method (100 mm / min)";

[0054] Wet tensile strength: Tested in accordance with "GB / T465.2-2008 Determination of tensile strength of paper and paperboard after immersion in water";

[0055] Relative wet strength: Tested in accordance with "GB / T465.2-2008 Determination of tensile strength of paper and paperboard after immersion in water".

[0056] Embodiment 2:

[0057] A chlorine-free wet strength agent, the preparation method of which comprises the following steps:

[0058] 1) adding amylopectin to a sodium periodate solution with a concentration of 0.7 mol / L in a mechanically stirred state, wherein the molar ratio of the monosaccharide unit in the amylopectin to the sodium periodate is 1:1.1, the stirring rate is 1000 rpm, and then heating to 40° C. to react for 4 hours in the dark, filtering, washing the filtered solid with distilled water and anhydrous ethanol in turn, and then drying at a temperature of 50° C. for 8 hours to obtain a biomass-based branched polyaldehyde;

[0059] 2) Add the biomass-based branched polyaldehyde to a 35% diethylenetriamine solution in a mechanically stirred state, the mass ratio of the biomass-based branched polyaldehyde to the diethylenetriamine is 1:0.1, the stirring rate is 1000 rpm, and then adjust the pH value of the reaction solution to 8, heat it to 90°C for reaction for 30 minutes, add distilled water to dilute the mass fraction of the solute in the reaction solution to 20%, cool it to 70°C for reaction for 6 hours, add distilled water to dilute the mass fraction of the solute in the reaction solution to 10%, and then filter to remove impurities to obtain a chlorine-free wet strength agent.

[0060] A chlorine-free high wet-strength paper, the preparation method of which comprises the following steps:

[0061] Hardwood pulp fiber (Shandong Huatai Paper Co., Ltd.) was beaten to a beating degree of 30°SR, and then the chlorine-free wet strength agent of the present embodiment was added to be debonded, and the amount of the chlorine-free wet strength agent added was 5% of the absolute dry weight of the hardwood pulp fiber, and then papermaking was performed, and then the pulp was hung on a forming net, and then vacuum dehydration was performed, and then dried at 50°C for 1 hour, and then aged at a temperature of 130°C for 5 minutes, so as to obtain chlorine-free high wet strength paper (base weight of 80g / m 2 , without any other additives).

[0062] After testing, the chlorine-free high wet-strength paper in this embodiment has a dry tensile strength of 2550 N / m±20 N / m, a wet tensile strength of 507.33 N / m±15.33 N / m, and a relative wet strength of 19.90%.

[0063] Embodiment 3:

[0064] A chlorine-free wet strength agent, the preparation method of which comprises the following steps:

[0065] 1) adding amylopectin to a sodium periodate solution with a concentration of 0.7 mol / L in a mechanically stirred state, wherein the molar ratio of the monosaccharide unit in the amylopectin to the sodium periodate is 1:1.1, the stirring rate is 1000 rpm, and then heating to 40° C. to react for 4 hours in the dark, filtering, washing the filtered solid with distilled water and anhydrous ethanol in turn, and then drying at a temperature of 50° C. for 8 hours to obtain a biomass-based branched polyaldehyde;

[0066] 2) adding the biomass-based branched polyaldehyde to a 35% tetraethylene pentamine solution in a mechanically stirred state, the mass ratio of the biomass-based branched polyaldehyde to the tetraethylene pentamine being 1:0.2, the stirring rate being 1000 rpm, adjusting the pH value of the reaction solution to 8, heating to 90° C. for reaction for 30 min, adding distilled water to dilute the reaction solution to 20% of the mass fraction of the solute, cooling to 70° C. for reaction for 6 h, adding distilled water to dilute the reaction solution to 10% of the mass fraction of the solute, filtering to remove impurities, and obtaining a chlorine-free wet strength agent.

[0067] A chlorine-free high wet-strength paper, the preparation method of which comprises the following steps:

[0068] Hardwood pulp fiber (Shandong Huatai Paper Co., Ltd.) was beaten to a beating degree of 30°SR, and then the chlorine-free wet strength agent of the present embodiment was added to be debonded, and the amount of the chlorine-free wet strength agent added was 5% of the absolute dry weight of the hardwood pulp fiber, and then papermaking was performed, and then the pulp was hung on a forming net, and then vacuum dehydration was performed, and then dried at 50°C for 1 hour, and then aged at a temperature of 130°C for 5 minutes, so as to obtain chlorine-free high wet strength paper (base weight of 80g / m 2 , without any other additives).

[0069] After testing, the chlorine-free high wet-strength paper in this embodiment has a dry tensile strength of 3065 N / m±35 N / m, a wet tensile strength of 642 N / m±0.67 N / m, and a relative wet strength of 20.95%.

[0070] Embodiment 4:

[0071] A chlorine-free wet strength agent, the preparation method of which comprises the following steps:

[0072] 1) adding amylopectin to a sodium periodate solution with a concentration of 0.7 mol / L in a mechanically stirred state, wherein the molar ratio of the monosaccharide unit in the amylopectin to the sodium periodate is 1:1.1, the stirring rate is 1000 rpm, and then heating to 40° C. to react for 4 hours in the dark, filtering, washing the filtered solid with distilled water and anhydrous ethanol in turn, and then drying at a temperature of 50° C. for 8 hours to obtain a biomass-based branched polyaldehyde;

[0073] 2) adding the biomass-based branched polyaldehyde to a 35% tris(2-aminoethyl)amine solution in a mechanically stirred state, the mass ratio of the biomass-based branched polyaldehyde to the tris(2-aminoethyl)amine being 1:0.2, the stirring rate being 1000 rpm, adjusting the pH value of the reaction solution to 8, heating to 90° C. for reaction for 30 min, adding distilled water to dilute the reaction solution to 20% of the mass fraction of the solute, cooling to 70° C. for reaction for 6 h, adding distilled water to dilute the reaction solution to 10% of the mass fraction of the solute, filtering to remove impurities, and obtaining a chlorine-free wet strength agent.

[0074] A chlorine-free high wet-strength paper, the preparation method of which comprises the following steps:

[0075] Hardwood pulp fiber (Shandong Huatai Paper Co., Ltd.) was beaten to a beating degree of 30°SR, and then the chlorine-free wet strength agent of the present embodiment was added to be debonded, and the amount of the chlorine-free wet strength agent added was 5% of the absolute dry weight of the hardwood pulp fiber, and then papermaking was performed, and then the pulp was hung on a forming net, and then vacuum dehydration was performed, and then dried at 50°C for 1 hour, and then aged at a temperature of 130°C for 5 minutes, so as to obtain chlorine-free high wet strength paper (base weight of 80g / m 2 , without any other additives).

[0076] After testing, the chlorine-free high wet-strength paper in this embodiment has a dry tensile strength of 3580 N / m±110 N / m, a wet tensile strength of 933.67 N / m±17 N / m, and a relative wet strength of 26.08%.

[0077] Comparative Example 1:

[0078] A paper, the preparation method of which comprises the following steps:

[0079] Hardwood pulp fiber (Shandong Huatai Paper Co., Ltd.) was beaten to a beating degree of 30°SR, then papered, and then pulped on a forming net, and then vacuum dehydrated, and then dried at 50°C for 1h, and then aged at 130°C for 5min to obtain paper (base weight 80g / m 2 , without any other additives).

[0080] After testing, the dry tensile strength of the paper in this comparative example is 2635 N / m±85 N / m, the wet tensile strength is 123 N / m±0.33 N / m, and the relative wet strength is 4.67%.

[0081] Comparative Example 2:

[0082] A paper, the preparation method of which comprises the following steps:

[0083] 1) adding amylopectin to a sodium periodate solution with a concentration of 0.7 mol / L in a mechanically stirred state, wherein the molar ratio of the monosaccharide unit in the amylopectin to the sodium periodate is 1:1.1, the stirring rate is 1000 rpm, and then heating to 40° C. to react for 4 hours in the dark, filtering, washing the filtered solid with distilled water and anhydrous ethanol in turn, and then drying at a temperature of 50° C. for 8 hours to obtain a biomass-based branched polyaldehyde;

[0084] 2) Hardwood pulp fiber (Shandong Huatai Paper Co., Ltd.) was beaten to a beating degree of 30°SR, and then biomass-based branched polyaldehyde was added for decomposition, the addition amount of biomass-based branched polyaldehyde was 5% of the absolute dry mass of hardwood pulp fiber, and then papermaking was performed, and then pulp was hung on a forming net, and then vacuum dehydration was performed, and then dried at 50°C for 1h, and then aged at a temperature of 130°C for 5min to obtain paper (base weight of 80g / m 2 , without any other additives).

[0085] After testing, the dry tensile strength of the paper in this comparative example is 2670 N / m±30 N / m, the wet tensile strength is 224.33 N / m±1.67 N / m, and the relative wet strength is 8.40%.

[0086] Comparative Example 3:

[0087] A paper, the preparation method of which comprises the following steps:

[0088] Hardwood pulp fiber (Shandong Huatai Paper Co., Ltd.) was beaten to a beating degree of 30°SR, and then a polyamide epichlorohydrin resin wet strength agent (Shandong Huatai Paper Co., Ltd.) was added to disperse the hardwood pulp fiber. The amount of the polyamide epichlorohydrin resin wet strength agent added was 5% of the absolute dry weight of the hardwood pulp fiber. Then, papermaking was performed, and then the pulp was hung on a forming net, and then vacuum dehydration was performed, and then dried at 50°C for 1h, and then aged at a temperature of 130°C for 5min to obtain paper (base weight of 80g / m 2 , without any other additives).

[0089] After testing, the dry tensile strength of the paper in this comparative example is 3310 N / m±10 N / m, the wet tensile strength is 874 N / m±10.67 N / m, and the relative wet strength is 26.40%.

[0090] Performance Testing:

[0091] 1) The Fourier transform infrared spectra of the amylopectin, biomass-based branched polyaldehyde and chlorine-free wet strength agent in Example 4 are as follows: Figure 1 shown.

[0092] Depend on Figure 1 It can be seen that the biomass-based branched polyaldehyde is at 1730 cm -1 The characteristic vibration peak of aldehyde C=O appeared at 1570cm, indicating that the amylopectin was oxidized and converted into biomass-based branched polyaldehydes; the characteristic peak of aldehyde C=O of the chlorine-free wet strength agent was weakened, and the peak at 1570cm -1 The imine C=N characteristic peak appears at , indicating that the biomass-based branched polyaldehyde has been further branched and modified to become a chlorine-free wet strength agent.

[0093] 2) The H NMR spectra of the biomass-based branched polyaldehyde, tris(2-aminoethyl)amine and chlorine-free wet strength agent in Example 4 are as follows: Figure 2 shown.

[0094] Depend on Figure 2 It can be seen that the absorption peaks of the hydrogen of the amine unit in the chlorine-free wet strength agent are 3.16ppm and 2.90ppm. Due to the electron-withdrawing ability of C=N imine, the specific displacement values ​​of the chlorine-free wet strength agent compared with the amine monomer are 2.67ppm and 2.51ppm. The hydrogen absorption peak shift is obviously shifted to the low field, indicating that the biomass-based branched polyaldehyde is further branched and modified to become a chlorine-free wet strength agent.

[0095] 3) Referring to Example 4 and Comparative Example 3, the amount of wet strength agent added was adjusted, and the dry tensile strength and wet tensile strength test results of the prepared papers with different amounts of wet strength agent added were as follows: Figure 3 shown.

[0096] Depend on Figure 3 It can be seen that compared with the polyamide epichlorohydrin resin wet strength agent of Comparative Example 3, the chlorine-free wet strength agent of Example 4 has higher dry tensile strength and wet tensile strength of the prepared paper at the same addition amount, indicating that the chlorine-free wet strength agent of Example 4 has a better effect.

[0097] 4) The chlorine-free high wet strength paper of Example 4 and the papers of Comparative Examples 1 to 3 were immersed in water and stirred at room temperature. The anti-disintegration performance test results were as follows: Figure 4 shown.

[0098] Depend on Figure 4It can be seen that the chlorine-free high wet-strength paper of Example 4 is not damaged after being stirred in a water bath at room temperature for 24 hours, and has a certain high wet strength. The performance is close to that of the paper of Comparative Example 3 (adding a polyamide epichlorohydrin resin wet strength agent), while the paper of Comparative Example 1 (without adding a wet strength agent) and the paper of Comparative Example 2 (adding a biomass-based branched polyaldehyde) are obviously damaged after stirring.

[0099] 5) The water contact angle test results of the chlorine-free high wet strength paper of Example 4 and the papers of Comparative Examples 1 to 3 are as follows: Figure 5 shown.

[0100] Depend on Figure 5 It can be seen that the chlorine-free high wet-strength paper of Example 4 can show near-hydrophobicity (large contact angle) at the moment when water contacts the paper, indicating that the imine C=N group in the chlorine-free wet strength agent helps to improve the water resistance of the paper; the water contact angle of the chlorine-free high wet-strength paper of Example 4 is significantly higher than that of the papers of Comparative Examples 1 to 3, indicating that the water resistance effect of the chlorine-free high wet-strength paper of Example 4 is more excellent.

[0101] 6) Referring to Example 4 and Comparative Example 3, the amount of wet strength agent added was adjusted, and the test results of dry reslurry performance of paper with different amounts of wet strength agent added (measured with reference to "PTS method PTS-RH:021 / 97" for the proportion of recycled fiber) were as follows: Figure 6 shown.

[0102] Depend on Figure 6 It can be seen that: compared with the polyamide epichlorohydrin resin wet strength agent of Example 3, the chlorine-free wet strength agent of Example 4 has a higher repulping rate of the prepared paper at the same addition amount, which shows that the chlorine-free wet strength agent of Example 4 not only has an excellent effect of increasing the wet strength performance, but also the dynamic chemical bonds in the chlorine-free wet strength agent are helpful for paper repulping and recycling, which solves the problem that the traditional wet strength agent paper is not easy to degrade after mature curing and the damaged paper is difficult to recycle.

[0103] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a chlorine-free wet strength agent, characterized in that: The following steps are involved: 1) adding biomass-based branched polysaccharide to a periodic acid / periodate solution, and then heating in the dark to react, thereby obtaining a biomass-based branched polyaldehyde; 2) adding the biomass-based branched polyaldehyde into the polyamine solution and heating the solution for reaction to obtain a chlorine-free wet strength agent; Step 1) the biomass branched polysaccharide is at least one of konjac glucomannan, pullulan, xanthan gum, guar gum, locust bean gum and cyperus gum; Step 1) The molar ratio of monosaccharide units in the biomass branched polysaccharide to periodic acid / periodate is 1:0.5-1.3; Step 2) the polyamine is at least one of tetraethylenepentamine and tris(2-aminoethyl)amine; Step 2) The mass ratio of the biomass-based branched polyaldehyde to the polyamine is 1:0.1-0.

4.

2. The preparation method according to claim 1, characterized in that: Step 1) The heating and light-shielding reaction is carried out at a temperature of 25° C. to 55° C., and the reaction time is 1 h to 72 h.

3. The preparation method according to claim 1, characterized in that: Step 2) The heating reaction is divided into two stages. The first stage is to react at a temperature of 75°C to 95°C for 0.1h to 1h. The second stage is to dilute with water and then react at a temperature of 50°C to 80°C for 2h to 24h.

4. A chlorine-free wet strength agent, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 3.

5. A chlorine-free high wet-strength paper, characterized in that: The wet strength agent used in the preparation is the chlorine-free wet strength agent described in claim 4.

6. A method for preparing chlorine-free high wet-strength paper as claimed in claim 5, characterized in that: The following steps are involved: The cellulose fiber pulp board is pulped, and then a chlorine-free wet strength agent is added to loosen it, and then papermaking, pulping, vacuum dehydration, drying and aging are carried out to obtain chlorine-free high wet strength paper.

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