Environment-friendly low-chlorine wet strength agent as well as preparation method and application thereof

Abstract

The invention provides an environment-friendly low-chlorine wet strength agent and a preparation method and application thereof.The preparation method comprises the steps that adipic acid and tetraethylenepentamine are mixed and react for 2-6 h at the temperature of 170-190 DEG C, and a prepolymer is obtained; cooling the prepolymer to 120-140 DEG C, adding a modifier, carrying out a heat preservation reaction for 2-3 h, and adding deionized water to adjust the solid content to 55-65% so as to obtain a modified polyamide solution; adding a cationizing agent and epoxy chloropropane into the modified polyamide solution, heating to 65-75 DEG C, reacting, and adding acid to adjust the pH value to 2.5-4.5 when the viscosity of the system reaches 50-80 mPa.s; adding sodium hydrogen sulfite, and carrying out heat preservation reaction for 1-2 hours; and adding deionized water to adjust the solid content to 12-13%, thereby obtaining the environment-friendly low-chlorine wet strength agent. The specific modifier is adopted to modify a polyamide main chain, and the cationizing agent is introduced, so that the prepared wet strength agent not only can remarkably reduce the content of organic chlorine in a product, but also can improve the dry and wet strength, water resistance and folding resistance of paper. In addition, the product can also shorten the curing time of the paper.

Description

Technical Field

[0001] This invention relates to the field of papermaking chemicals, and in particular to an environmentally friendly low-chlorine wet strength agent, its preparation method, and its application. Background Technology

[0002] In the field of papermaking chemicals, wet strength agents are key additives used to significantly improve the mechanical strength of paper in a wet state. The wet strength of paper depends not only on the properties of the fibers themselves but also on the number and bonding strength of the inter-fiber bonding points. As a raw material for papermaking, cellulose is hydrophilic; when it comes into contact with water, the intermolecular forces weaken significantly, leading to a sharp decline in the mechanical strength of the paper. By adding wet strength agents during the papermaking process, the bonding network between fibers can be effectively strengthened, significantly improving the wet tensile strength of the paper. Even with small amounts, the wet strength of the paper can be increased by several orders of magnitude.

[0003] Currently, polyamide epichlorohydrin (PAE) resin is a widely used type of wet-strength agent. It is typically prepared by grafting and crosslinking other polymeric monomers and functional monomers onto the main chain of polyamines and diacids, and by adjusting the initiator. During the preparation process, residual organochlorine is removed in the later stages, resulting in a new generation of wet-strength agents with good wet and dry strength and low organochlorine content. This type of wet-strength agent is suitable for neutral and alkaline environments and is a water-soluble cationic polymer resin. However, this type of resin has a significant drawback in its production: epichlorohydrin is prone to hydrolysis, generating organochlorine byproducts including 1,3-dichloro-2-propanol (DCP) and 3-chloro-1,2-propanediol (MCPD). These chloropropanols have been proven to pose potential health hazards, resulting in a high residual organochlorine content in the final wet-strength agent product. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing an environmentally friendly low-chlorine wet strength agent, its preparation method, and its applications. The wet strength agent prepared using the method described in this application not only significantly reduces the organic chlorine content in the product but also improves the dry and wet strength, water resistance, and folding endurance of paper. Furthermore, this product can shorten the paper curing time.

[0005] This invention is achieved using the following technical solution:

[0006] A method for preparing an environmentally friendly low-chlorine wet strength agent includes the following steps:

[0007] (1) Mix adipic acid with tetraethylenepentamine and react at 170℃~190℃ for 2~6h to obtain a prepolymer;

[0008] (2) Cool the prepolymer to 120-140°C, add a modifier, keep it at the temperature for 2-3 hours, add deionized water to adjust the solid content to 55%-65%, and obtain a modified polyamide solution.

[0009] (3) Add a cationic agent and epichlorohydrin to the modified polyamide solution, heat to 65-75°C to react, and when the viscosity of the system reaches 50-80 mPa·s, add acid to adjust the pH to 2.5-4.5;

[0010] (4) Add sodium bisulfite and keep the reaction at a warm temperature for 1-2 hours;

[0011] (5) Add deionized water to adjust the solid content to 12-13% to obtain the environmentally friendly low-chlorine wet strength agent.

[0012] As a further embodiment of the present invention: in step (1), the amount of adipic acid used is 20-30 parts by weight, and the amount of tetraethylenepentamine used is 25-40 parts by weight.

[0013] As a further aspect of the present invention: the modifier in step (2) is selected from at least one of acrylamide, N-methylacrylamide, and N,N-dimethylacrylamide.

[0014] As a further aspect of the present invention: in step (2), the amount of modifier used is 1 to 10 parts by weight.

[0015] As a further embodiment of the present invention: the cationizing agent in step (3) is selected from at least one of tetramethylammonium chloride, tetraethylammonium bromide, benzyltrimethylammonium chloride, and hexadecyltrimethylammonium bromide.

[0016] As a further aspect of the present invention: the acid used in step (3) is sulfuric acid.

[0017] As a further embodiment of the present invention: in step (3), the amount of cationic agent used is 2 to 5 parts by weight, and the amount of epichlorohydrin used is 10 to 20 parts by weight.

[0018] As a further embodiment of the present invention: in step (4), the amount of sodium bisulfite used is 1 to 5 parts by weight.

[0019] In a second aspect, the present invention provides an environmentally friendly low-chlorine wet strength agent, which is prepared by the above-described method for preparing an environmentally friendly low-chlorine wet strength agent.

[0020] In a third aspect, the present invention provides the application of the above-mentioned environmentally friendly low-chlorine wet strength agent as a wet strength agent in papermaking.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) This invention significantly improves the grafting efficiency of polyamide and epichlorohydrin by modifying the polyamide backbone with a specific modifier and introducing a cationic agent, thereby fundamentally reducing the hydrolysis side reaction of epichlorohydrin and effectively inhibiting the generation of organochlorine byproducts such as 1,3-dichloro-2-propanol and 3-chloro-1,2-propanediol, thus significantly reducing the organochlorine content of the obtained wet strength agent.

[0023] (2) The wet strength agent prepared by this invention not only exhibits excellent wet and dry strength enhancement effects, but also significantly shortens the curing time required for paper. This product is environmentally friendly, with extremely low organic chlorine content, meeting higher safety standards, and is particularly suitable for the production of household paper, possessing significant market application value. Furthermore, the method and process of this invention are mature and have low cost. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solutions of the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples, but these should not be construed as limiting the present patent. Unless otherwise specified, the experimental methods or testing methods described in the following embodiments are conventional methods; the reagents and materials, unless otherwise specified, are obtained from conventional commercial sources or prepared using conventional methods.

[0025] Example 1

[0026] A method for preparing an environmentally friendly low-chlorine wet strength agent, the specific steps of which are as follows:

[0027] (1) Mix 20 parts by weight of adipic acid and 25 parts by weight of tetraethylenepentamine and react at 180°C for 4 hours;

[0028] (2) Cool down to 120℃, add 4 parts by weight of acrylamide, keep warm for 2 hours, add deionized water to adjust the solid content to 55%, and obtain a modified polyamide solution.

[0029] (3) Add 2 parts by weight of tetramethylammonium chloride and 10 parts by weight of epichlorohydrin, heat to 65°C to start the reaction, and when the viscosity of the system rises to 50 mPa·s, add sulfuric acid to adjust the pH of the system to 4.0.

[0030] (4) Add 1 part by weight of sodium bisulfite and keep warm for 1 hour;

[0031] (5) Add deionized water to adjust the solid content to 12.5% ​​to obtain a low-chlorine wet strength agent.

[0032] Example 2

[0033] A method for preparing an environmentally friendly low-chlorine wet strength agent, the specific steps of which are as follows:

[0034] (1) Mix 23 parts by weight of adipic acid and 29 parts by weight of tetraethylenepentamine and react at 180°C for 4.5 h;

[0035] (2) Cool down to 125℃, add 5 parts by weight of acrylamide, keep warm for 2 hours, add deionized water to adjust the solid content to 55%, and obtain a modified polyamide solution.

[0036] (3) Add 3 parts by weight of tetramethylammonium chloride and 12 parts by weight of epichlorohydrin, heat to 68°C to start the reaction, and when the viscosity of the system rises to 52 mPa·s, add sulfuric acid to adjust the pH of the system to 3.5.

[0037] (4) Add 1.5 parts by weight of sodium bisulfite and keep warm for 1 hour;

[0038] (5) Add deionized water to adjust the solid content to 12.5% ​​to obtain a low-chlorine wet strength agent.

[0039] Example 3

[0040] A method for preparing an environmentally friendly low-chlorine wet strength agent, the specific steps of which are as follows:

[0041] (1) Mix 26 parts by weight of adipic acid and 33 parts by weight of tetraethylenepentamine and react at 185°C for 4.5 h;

[0042] (2) Cool down to 130℃, add 6 parts by weight of N-methylacrylamide, keep warm for 3h, add deionized water to adjust the solid content to 58%, and obtain a modified polyamide solution.

[0043] (3) Add 4 parts by weight of benzyltrimethylammonium chloride and 14 parts by weight of epichlorohydrin, heat to 68°C to start the reaction, and when the viscosity of the system rises to 55 mPa·s, add sulfuric acid to adjust the pH of the system to 3.5.

[0044] (4) Add 2 parts by weight of sodium bisulfite and keep warm for 2 hours;

[0045] (5) Add deionized water to adjust the solid content to 12.5% ​​to obtain a low-chlorine wet strength agent.

[0046] Example 4

[0047] A method for preparing an environmentally friendly low-chlorine wet strength agent, the specific steps of which are as follows:

[0048] (1) Mix 30 parts by weight of adipic acid and 38 parts by weight of tetraethylenepentamine and react at 190°C for 5 hours.

[0049] (2) Cool down to 130℃, add 7 parts by weight of N,N-dimethylacrylamide, keep warm for 3h, add deionized water to adjust the solid content to 60%, and obtain a modified polyamide solution.

[0050] (3) Add 5 parts by weight of hexadecyltrimethylammonium bromide and 15 parts by weight of epichlorohydrin, heat to 70°C to start the reaction, and when the viscosity of the system rises to 60 mPa·s, add sulfuric acid to adjust the pH of the system to 3.0.

[0051] (4) Add 2.5 parts by weight of sodium bisulfite and keep warm for 2 hours;

[0052] (5) Add deionized water to adjust the solid content to 12.5% ​​to obtain a low-chlorine wet strength agent.

[0053] Comparative Example 1

[0054] The wet strength agent was synthesized according to the comparative method in Chinese patent CN 116856199 A.

[0055] Comparative Example 2

[0056] The only difference from Example 3 is that in step (2), the addition of 6 parts by weight of N-methylacrylamide and the incubation for 3 hours are not performed. In addition, in step (3), 4 parts by weight of benzyltrimethylammonium chloride are not added.

[0057] Comparative Example 3

[0058] The only difference from Example 3 is that step (4) is omitted.

[0059] Comparative Example 4

[0060] The only difference from Example 3 is that the tetraethylenepentamine in step (1) is replaced with diethylenetriamine in equimolar amounts.

[0061] Comparative Example 5

[0062] The difference from Example 3 is only that in step (3), the temperature is raised to 68°C and the reaction is carried out for 1.5 hours, and sulfuric acid is added to adjust the pH of the system to 3.5.

[0063] Comparative Example 6

[0064] The only difference from Example 3 is that in step (2), N-methylacrylamide is replaced with caprolactam.

[0065] Comparative Example 7

[0066] The only difference from Example 3 is that in step (3), benzyltrimethylammonium chloride is replaced with triethylamine hydrochloride.

[0067] Example 1

[0068] The wet strength agents prepared in Examples 1-4 and Comparative Examples 1-7 were subjected to the following tests, and the test standards or methods are as follows:

[0069] I. Determination of Organochlorine Content: An Agilent gas chromatography-mass spectrometry (GC-MS) system was used, instrument model: Agilent 8860-5977B. Column model: HP-5ms ultra-high inert column, 30m, 0.32mm, 0.25μm, 7-inch column holder. Gas chromatography conditions: Injector temperature: 260℃, flow rate: 2ml / min, splitless. Column oven temperature: Initially 60℃, stabilized for 3 minutes, then increased to 200℃ at 15℃ / min, held for 5 minutes. Mass spectrometry conditions: Quadrupole: 150℃; Ion source: 230℃.

[0070] Detection method: 1. Chloropropanol mixed standard stock solution (1000mg / L): Prepare one bottle each of 1,3-dichloro-2-propanol and 3-chloro-1,2-propanediol standard samples (100mg each). Transfer the two chloropropanol standards into a 100ml brown volumetric flask, dilute to the mark with ethyl acetate, and store in a sealed container at 0℃-4℃ for 6 months.

[0071] 2. Chloropropanol mixed standard intermediate solution: Transfer 0.25 ml, 0.5 ml, 0.75 ml, 1 ml, and 1.5 ml of chloropropanol mixed standard stock solution (1000 mg / L) to 10 ml brown volumetric flasks, respectively, and dilute to the mark with ethyl acetate to prepare standard solutions of 25 ppm, 50 ppm, 75 ppm, 100 ppm, and 150 ppm.

[0072] 3. Sample pretreatment: Use a pipette to transfer 2 ml of the test solution and 6 ml of ethyl acetate (chromatographic grade) into a 10 ml centrifuge tube, shake on a shaker for 5 minutes, let stand for half an hour, and then take the supernatant as the injection sample. The chromatographic injection volume is 1 μl.

[0073] 4. Detection Process: Load the prepared sample into the chromatographic vial, place it in the corresponding position on the automated sampler, click batch processing, input the sample injection data, select the analytical method, data file name, etc., save the information, and start the run. After the run is complete, find the corresponding peak and substitute the data into the standard curve to obtain the corresponding content.

[0074] II. Determination of solid content: Weigh the sample using aluminum foil, weigh the tare weight P, weigh 1.5-2.0g of sample M after removing the tare, dry it in an oven at 150℃ for 30 minutes, cool it to room temperature in a desiccator, and weigh the actual weight m.

[0075] Solid content % = [(mP) / M] x 100%.

[0076] III. pH value determination: Adjust the sample temperature to 25℃ and measure it with a pH meter.

[0077] The wet strength agents prepared in Examples 1-4 and Comparative Examples 1-7 were tested, and the test results are shown in Table 1.

[0078] Table 1

[0079]

[0080]

[0081] As shown in Table 1, the low-chlorine wet-strength agents prepared using Examples 1-4 of this invention have organic chlorine content between 114 and 218 ppm, which is lower than that of Comparative Examples 1-6. Comparative Example 3, which did not include sodium bisulfite for dechlorination, showed a sharp increase in organic chlorine content. Comparative Example 4, using diethylenetriamine, had a significantly higher organic chlorine content than the examples. Comparative Example 5, reacting for 1.5 hours, had an excessively long reaction time, resulting in high system viscosity and increased organic chlorine content from side reactions. Comparative Example 6, using caprolactam as a modifier, did not show a significant dechlorination effect. Comparative Example 7, using triethylamine hydrochloride as a cationizing agent, had a higher organic chlorine content than Example 3.

[0082] Example 2

[0083] The wet strength agents prepared in Examples 1-4 and Comparative Examples 1-7 were tested using the following methods:

[0084] Unbleached sulfate pulp was used, with a softwood pulp:hardwood pulp ratio of 2:8 and a freeness of 38. 0 SR. The filler dosage is 15%, the retention aid dosage is 400 ppm, the pulp concentration is diluted to 1.0% (mass percentage) with tap water, the wet strength agent dosage is 1% (wet strength agent oven-dry weight / pulp oven-dry weight percentage), after adding the wet strength agent of each of the above examples and comparative examples, stir for 1 min, and the paper basis weight is 120 g / m². 2 Retention rate was compared based on the quantitative analysis of hand-made sheets, and filtration performance was compared based on the beating degree of various slurries. Dry tensile strength and wet tensile strength were then tested according to GB / T2914-2008 and GB / T465.2-2008, respectively, and the wet / dry tensile index ratio was calculated. The test results are shown in Table 2. The blank sample is the sample without added wet strength agent.

[0085] Table 2 Results of wet strength paper performance tests

[0086]

[0087] As can be seen from the results in Table 2, the wet and dry tensile coefficients and wet / dry ratios of the paper in Examples 1 to 4 are significantly higher than those in Comparative Examples 1, 2, 4, 5, 6, and 7. Among them, the wet and dry tensile coefficients and wet / dry ratios of the paper in Comparative Example 3 are relatively high, but the chlorine content is much higher, indicating that the wet strength agent of the present invention has a low chlorine content and better wet and dry strength performance.

[0088] Table 3. Changes in wet tensile index over time

[0089]

[0090]

[0091] As shown in Table 3, the wet tensile index of Examples 1 and 2 reached the value after curing at 40 days, indicating that the curing time was about 40 days. The curing time of Examples 3 and 4 was about 30 days. Compared with the curing time of Comparative Examples 1 to 7, which was about 60 days, this shows that the wet strength agent of the present invention can significantly shorten the curing period.

[0092] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an environmentally friendly low-chlorine wet strength agent, characterized in that, The method comprises the following steps: (1) mixing adipic acid with tetraethylenepentamine, and reacting at 170-190 DEG C for 2-6 hours to obtain a prepolymer; (2) cooling the prepolymer to 120-140 DEG C, adding a modifier, and reacting for 2-3 hours, then adding deionized water to adjust the solid content to 55-65%, to obtain a modified polyamide solution; (3) adding a cationizing agent and epichlorohydrin to the modified polyamide solution, and reacting at 65-75 DEG C until the viscosity reaches 50-80 mPa s, then adding acid to adjust the pH to 2.5-4.5; (4) adding sodium bisulfite, and reacting for 1-2 hours; (5) adding deionized water to adjust the solid content to 12-13%, to obtain the environment-friendly low-chlorine wet strength agent.

2. The method for preparing the environment-friendly low-chlorine wet strength agent according to claim 1, characterized in that, In the step (1), the amount of adipic acid is 20-30 parts by weight, and the amount of tetraethylenepentamine is 25-40 parts by weight.

3. The preparation method of the environmentally friendly low-chlorine wet strength agent according to claim 1, characterized in that, The modifier in the step (2) is at least one selected from the group consisting of acrylamide, N-methyl acrylamide and N,N-dimethyl acrylamide.

4. The method for preparing the environment-friendly low-chlorine wet strength agent according to claim 1, characterized in that, In the step (2), the amount of the modifier is 1-10 parts by weight.

5. The method for preparing the environment-friendly low-chlorine wet strength agent according to claim 1, characterized in that, The cationizing agent in the step (3) is at least one selected from the group consisting of tetramethylammonium chloride, tetraethylammonium bromide, benzyltrimethylammonium chloride and cetyltrimethylammonium bromide.

6. The method for preparing the environment-friendly low-chlorine wet strength agent according to claim 1, characterized in that, The acid used in the step (3) is sulfuric acid.

7. The preparation method of the environmentally friendly low-chlorine wet strength agent according to claim 1, characterized in that, In the step (3), the amount of the cationizing agent is 2-5 parts by weight, and the amount of epichlorohydrin is 10-20 parts by weight.

8. The method for preparing the environment-friendly low-chlorine wet strength agent according to claim 1, characterized in that, In the step (4), the amount of sodium bisulfite is 1-5 parts by weight.

9. An environmentally friendly low-chlorine wet strength agent, characterized by, The environment-friendly low-chlorine wet strength agent is prepared by the method of any one of claims 1-8.

10. Use of the environment-friendly low-chlorine wet strength agent of claim 9 as a wet strength agent in papermaking.

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