Biodegradable polycarboxylic acid retanning agent and preparation method thereof

Abstract

The invention provides a biodegradable polycarboxylic acid retanning agent and a preparation method thereof, and belongs to the field of leather auxiliaries. The preparation method of the biodegradable polycarboxylic acid retanning agent comprises the following steps: taking itaconic acid, a nonionic monomer and a carboxyl monomer as raw materials, carrying out free radical copolymerization in a solvent environment in the presence of an initiator, and then adjusting the pH value to prepare the biodegradable polycarboxylic acid retanning agent. According to the biodegradable polycarboxylic acid retanning agent and the preparation method thereof, the defects of an existing chromium salt retanning agent and an existing acrylic acid resin tanning agent can be effectively overcome, the raw materials are renewable resources and easy to obtain, and the retanning agent is easy to biodegrade, high in environment friendliness and good in leather tanning effect.

Description

Technical Field

[0001] The invention relates to the field of leather auxiliaries, in particular to a biodegradable polycarboxylic acid retanning agent and a preparation method thereof. Background Art

[0002] There are many processes in the leather production process, among which retanning is an extremely important process in the leather production process. Retanning can not only enhance the tanning effect, but also improve the properties of leather in many aspects, greatly increasing the value of leather. Therefore, retanning is called the "alchemy" in leather production [Lv Bin, Jia Lu, Ma Jianzhong, et al., Research Progress of Retanning Agents with Darkening Effect, China Leather, 2014, 43 (21): 45-47; Chao W, Zeng Y, Liao X, et al; Effect of retanning agent on dry heat resistance of leathers. The Journal of the American Leather Chemists Association, 2013, 108 (8): 294-299]. The effect of retanning mainly depends on the retanning agent.

[0003] Retanning agents are materials that can react with collagen or leather to produce a tanning effect. Currently used retanning agents can be divided into two categories: inorganic metal salt retanning agents, mainly chromium salts, followed by aluminum salts, zirconium salts, etc.; organic retanning agents, mainly vegetable tanning agents, aldehyde tanning agents and polymer tanning agents. Chromium salts are the main tanning agents commonly used in the prior art. Although they have good tanning effects, they have a series of environmental and health risk issues. Specifically, after the chromium-containing waste produced by chromium salt tanning is landfilled, chromium will be deposited in the soil, polluting the soil and water sources; at the same time, Cr (Ш) is easily oxidized to Cr (VI), which can induce mutations in organisms, directly damage human skin, and accumulate in internal organs, inducing various diseases and cancers [Qiang TT, Chen L, Zhang Q, et al. A sustainable and cleaner speedy tanning system based on condensed tannins catalyzed by laccase, Journal of Cleaner Production, 2018, 197 (1): 1117-1123]. Therefore, the policies and regulations of developed countries and regions in the world strictly limit the amount of Cr (VI) in leather products [Gu Cuiping, Polymer metal chromium complex leather tanning agent and its preparation method, Anhui University thesis, 2005]. In addition, chromium resources are very limited and unevenly distributed around the world. my country's chromium resources are relatively scarce, and chromium reserves account for only 0.3% of the world's total. Therefore, how to avoid or reduce the use of chromium salt retanning agents, reduce the pollution caused by chromium emissions, and achieve clean tanning is an important direction for the sustainable development of the leather industry. Finding clean and green chrome-free retanning agents to replace chrome retanning agents has become a research hotspot in the leather industry [Yuan Xuzheng, Li Yan, Lu Vina, Comparative study on the retanning properties of common aldehyde and derivative tanning agents, Leather and Chemical Industry, 2015, 32 (5): 19-22; Sundar VJ, Rao JR, Muralidharan C, Cleaner chrome tanning-emerging options, Journal of Cleaner Production, 2002, 10 (1): 69-74].

[0004] Organic retanning agents have fewer environmental and safety issues, meet the requirements of sustainable development, and are the main development direction of chrome-free tanning agents. Existing acrylic polymer retanning agents are the most important organic retanning agents, which have good selective filling and thickening properties, can improve the flexibility and fullness of finished leather, and improve the physical properties of leather. The retanned leather has the advantages of light resistance, aging resistance, and good napping properties. Moreover, there are many types of copolymerizable monomers, and different copolymerizable monomers can be used to produce retanning agents with various properties, thereby meeting the needs of leathers of different styles. In addition. Acrylic polymer tanning agents can also effectively promote the fixation and absorption of chromium ions, and the waste liquid after tanning is less toxic and easy to handle. Therefore, acrylic polymer tanning agents are currently one of the most popular organic retanning agent varieties. Since its introduction, it has not only been one of the research hotspots of leather chemists, but also one of the "magic weapons" of leather engineers. Leather expert PS Venkatachulan called it a "miracle retanning agent". It is a type of retanning agent widely used in leather processing [Zhang Biao, Jin Yong, Cao Zhifeng, Research progress on the retanning mechanism and modification of acrylic resin retanning agents, Western Leather, 2010, 32 (11): 32-37; Bao Yan, Ma Jianzhong, Application and research progress of acrylic polymer tanning agents, China Leather, 2011, 40 (15): 51-55].

[0005] Despite this, acrylic resin tanning agents also have the following problems: acrylic resin tanning agents are high molecular polymer tanning agents made by free radical copolymerization of (meth) acrylic acid as the main component and other vinyl monomers. (Meth) acrylic acid and other monomers are deep-processed products of non-renewable petroleum resources. During the processing and post-processing process, more carbon dioxide emissions will occur, which is not in line with the current "double carbon" emission reduction trend; and when petroleum resources are exhausted, acrylic resin retanning agents will face the problem of raw material shortage. Furthermore, existing acrylic resin retanning agents are difficult to biodegrade, and will continue to accumulate when discharged into the environment, causing persistent pollution to the ecological environment; and acrylic resin retanning agents also have certain toxicity, especially irritation, and also pose certain hazards to human health. Summary of the invention

[0006] In order to solve the technical problems existing in the prior art, the present invention provides a biodegradable polycarboxylic acid retanning agent and a preparation method thereof, which can effectively avoid the defects of existing chromium salt retanning agents and acrylic resin tanning agents, the raw materials are renewable resources that are easy to obtain, the retanning agent is easily biodegradable, has high environmental friendliness, and has a good tanning effect on leather.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a biodegradable polycarboxylic acid retanning agent comprises the following steps: adding a first portion of deionized water into a reaction kettle, stirring and heating to 30-90°C, and keeping the temperature; then adding itaconic acid, a nonionic monomer, a carboxyl monomer and an initiator aqueous solution at the same time; controlling the itaconic acid, the nonionic monomer, the carboxyl monomer and the initiator aqueous solution to be added simultaneously within 1.5-3.5 hours; after the addition is completed, continuing the heat preservation reaction for 3-5 hours, and adjusting the pH value to 4.5-8.0 with a sodium hydroxide solution to prepare a biodegradable polycarboxylic acid retanning agent; The initiator aqueous solution is prepared by dissolving the initiator in the second portion of deionized water.

[0008] Further, the nonionic monomer is one of the following: acrylonitrile, acrylamide, N-hydroxymethyl acrylamide; The carboxyl monomer is one of the following: acrylic acid, methacrylic acid, and maleic anhydride.

[0009] Preferably, the weight of the first portion of deionized water is 50-80% of the total weight of all deionized water; the second portion of deionized water is the remaining weight of deionized water.

[0010] Preferably, the weight ratio of itaconic acid, nonionic monomer, carboxyl monomer and all deionized water is 1:0.2-0.8:0.1-0.6:2-7.

[0011] Preferably, the initiator is a persulfate or a redox initiation system.

[0012] Preferably, the persulfate is one of the following: ammonium persulfate, sodium persulfate, potassium persulfate; The redox initiation system is one of the following: a persulfate-sodium bisulfite initiation system and a persulfate-sodium pyrosulfite initiation system.

[0013] Preferably, the added weight of the initiator is 0.5-10% of the total weight of itaconic acid, nonionic monomer and carboxyl monomer.

[0014] Preferably, the mass concentration of the sodium hydroxide solution is 10-50wt%.

[0015] A biodegradable polycarboxylic acid retanning agent is prepared by the above-mentioned preparation method.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The preparation method of the biodegradable polycarboxylic acid retanning agent of the present invention uses itaconic acid monomer as raw material. It is prepared by chemical method, microbial fermentation method or whole cell catalysis method with biomass raw material as substrate, and is a renewable chemical raw material that is easy to obtain. In addition, the carbon dioxide emission in the preparation process using itaconic acid monomer is extremely low, which is in line with the "double carbon" emission reduction trend. At the same time, it is combined with non-ionic monomers and carboxylic acid monomers to obtain a biodegradable polycarboxylic acid retanning agent through free radical copolymerization. The biodegradable polycarboxylic acid retanning agent can effectively avoid the defects of existing chromium salt retanning agents and acrylic resin tanning agents, is easy to biodegrade, and will not accumulate when discharged into the environment after use, and will not cause persistent pollution to the environment. In addition, the raw material monomers selected by the present invention have high activity, the polymerization process is easy to control, and the preparation process is simple, safe and efficient. At the same time, the polycarboxylic acid retanning agent of the present invention has low toxicity, low irritation, and little harm to human health.

[0017] (2) The biodegradable polycarboxylic acid retanning agent of the present invention has a good retanning effect, good permeability to leather and is easily absorbed, and the leather obtained by the treatment has good softness, fullness and astringency. DETAILED DESCRIPTION

[0018] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific embodiments of the present invention are now described. It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those of ordinary skill in the art to which the present invention belongs.

[0019] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, "first", "second", etc. are used to distinguish similar objects, and are not used to describe a specific order or sequence. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0020] The embodiment of the present invention provides a method for preparing a biodegradable polycarboxylic acid retanning agent, which uses itaconic acid, a nonionic monomer, and a carboxyl monomer as raw materials, undergoes free radical copolymerization in a solvent environment in the presence of an initiator, and then undergoes pH adjustment to obtain a biodegradable polycarboxylic acid retanning agent. The nonionic monomer is one of the following: acrylonitrile, acrylamide, N-hydroxymethyl acrylamide; preferably acrylonitrile; The carboxyl monomer is one of the following: acrylic acid, methacrylic acid, maleic anhydride; preferably acrylic acid.

[0021] Specifically, the preparation method of the biodegradable polycarboxylic acid retanning agent comprises the following steps: using itaconic acid, nonionic monomers, and carboxyl monomers as raw materials, using water as solvent, and using persulfate or a redox initiation system as an initiator, and carrying out a free radical copolymerization reaction, and then adjusting the pH with a sodium hydroxide solution to obtain the biodegradable polycarboxylic acid retanning agent.

[0022] The preparation method of the biodegradable polycarboxylic acid retanning agent, when the nonionic monomer is acrylonitrile and the carboxyl monomer is acrylic acid, the synthesis route is:

[0023] .

[0024] The preparation method of the biodegradable polycarboxylic acid retanning agent comprises the following steps: (1) Raw material preparation: Weigh itaconic acid, nonionic monomer, carboxyl monomer, initiator and deionized water respectively; divide the deionized water into two parts to obtain the first part of deionized water and the second part of deionized water. The weight of the first part of deionized water is 50-80% of the total weight of the deionized water; the second part of deionized water is the remaining weight of deionized water.

[0025] (2) Synthesis of retanning agent: Add the first portion of deionized water to the reactor, stir and heat to 30-90°C and keep warm; add itaconic acid, nonionic monomer, carboxyl monomer and initiator aqueous solution (the initiator is dissolved in the second portion of deionized water) at the same time, and control the itaconic acid, nonionic monomer, carboxyl monomer and initiator aqueous solution to be added simultaneously within 1.5-3.5 hours (the addition time deviation of each material is ±3 minutes); after the addition of each material is completed, continue to react at 30-90°C for 3-5 hours; then adjust the pH to 4.5-8.0 with sodium hydroxide solution to obtain a biodegradable polycarboxylic acid retanning agent.

[0026] In the step (1), the mass ratio of itaconic acid, nonionic monomer, carboxyl monomer and deionized water is 1:0.2-0.8:0.1-0.6:2.0-7.0; preferably 1:0.3-0.6:0.2-0.4:2.5-6.5.

[0027] In step (2), the initiator is a persulfate or a redox initiation system. Persulfates include ammonium persulfate, sodium persulfate and potassium persulfate; preferably ammonium persulfate. The redox initiation system includes a persulfate-sodium bisulfite initiation system and a persulfate-sodium pyrosulfite initiation system; preferably an ammonium persulfate-sodium bisulfite initiation system.

[0028] In the step (2), the added weight of the initiator is 0.5-10% of the total weight of itaconic acid, nonionic monomer and carboxyl monomer; preferably 1-3%.

[0029] In the step (2), the temperature when the monomer and the initiator aqueous solution are added and the subsequent reaction temperature is 30-90° C. When the initiator is a persulfate, the reaction temperature is preferably 75-90° C. When the initiator is a redox initiation system, the reaction temperature is preferably 30-75° C.

[0030] In the step (2), the mass concentration of the sodium hydroxide solution is 10-50wt%, preferably 25-35wt%.

[0031] In the step (2), preferably, sodium hydroxide solution is used to adjust the pH to 7-8.

[0032] The embodiment of the present invention also provides a biodegradable polycarboxylic acid retanning agent prepared by the above method.

[0033] The present invention is further described below in conjunction with some specific embodiments.

[0034] In each embodiment and related determination, itaconic acid used is an industrial product, a product of Qingdao Kehai Biological Group Co., Ltd. of Qingdao Langyatai Group; acrylic acid is an industrial product, a product of Shandong Kaitai Group Co., Ltd.; acrylonitrile is an industrial product, a product of Tianjin Shengtongtai Chemical Co., Ltd.; ammonium persulfate, sodium persulfate and sodium bisulfite are all analytically pure reagents, a product of Sinopharm Chemical Reagent Co., Ltd.; the original cowhide and comparative retanning agent used are provided by Shandong Lining Science and Technology New Materials Co., Ltd.; R8008 is an acrylic resin retanning agent with excellent comprehensive performance used by Shandong Lining Technology Co., Ltd., as a comparative sample for the performance evaluation of the products of each embodiment of the present invention; DK is a multifunctional auxiliary agent of organic acid condensates, YS is a synthetic fatliquor of sulfonate derivatives and high molecular weight aliphatic hydrocarbons, and KC is a neutralizing retanning agent of a configuration of organic acid salts, inorganic salts, polyethylene glycol and polyols; among them, DK, YS and KC are all self-owned products of Shandong Lining Science and Technology New Materials Co., Ltd.; AB chromium powder is a chromium powder product of Guangzhou Deli Chemical Co., Ltd.

[0035] In each example, the monomer conversion rate was determined by double bond bromine addition method, referring to [Zhang Zhixian, Zhang Ruihao, Quantitative Analysis of Organic Functional Groups, Chemical Industry Press, 1990].

[0036] The viscosity of the polymer aqueous solution was measured using a NDJ-1 rotary viscometer produced by Shanghai Yueping Scientific Instrument Co., Ltd. The test temperature was 25 °C.

[0037] Molecular weight determination of polymer: water-soluble acrylic resin was used as standard sample and determined by gel permeation chromatography (GPC). The instrument used was American Waters 1515 gel chromatograph.

[0038] Determination of solid content of sample: Accurately weigh 10g of sample into a beaker, put it into an oven, and dry it at 110°C to constant weight. The percentage of dry weight to wet weight of the sample is the solid content of the sample.

[0039] Biodegradability evaluation: Evaluated according to the evaluation criteria in the literature [Han Minghan, Jin Yong, Principles and Applications of Green Engineering [M], Beijing: Tsinghua University Press, 2005.11].

[0040] Example 1 This embodiment provides a method for preparing a biodegradable polycarboxylic acid retanning agent, comprising the following steps: Itaconic acid, nonionic monomer (acrylonitrile), carboxyl monomer (acrylic acid), initiator and deionized water were weighed respectively; the deionized water was divided into two parts to obtain the first deionized water and the second deionized water for standby use; 100 mL of deionized water (i.e., the first deionized water) was added to a 500 mL four-necked flask equipped with a stirrer, a condenser, a thermometer and a feeding device, and heated to 80°C under stirring; then 50.0 g of itaconic acid, 12.5 g of acrylic acid, 20.0 g of acrylonitrile and an aqueous solution of ammonium persulfate (i.e., the initiator) were added at a uniform rate at the same temperature. The invention discloses a biodegradable polycarboxylic acid retanning agent (aqueous solution) and a polycarboxylic acid retanning agent (aqueous solution). The itaconic acid, nonionic monomer, carboxyl monomer and ammonium persulfate aqueous solution are added simultaneously within 3 hours. After the addition is completed, the reaction is continued at the above temperature for 4 hours. Then, 96.8 g of 30 wt % sodium hydroxide solution is used to adjust the pH to 7.5 to obtain 319.8 g of a biodegradable polycarboxylic acid retanning agent with a solid content of 30.9 wt %, a monomer conversion rate of 99.3%, a weight average molecular weight of 25631, a molecular weight distribution of Mw / Mn=2.46, and a viscosity of a 10 wt % aqueous solution of the product of 35.2 mPa·s.

[0041] The ammonium persulfate aqueous solution is prepared by dissolving 1.0 g of ammonium persulfate in 40 mL of deionized water (i.e., the second portion of deionized water).

[0042] The test showed that the biodegradable polycarboxylic acid retanning agent of the present embodiment had good biodegradability, and the biodegradation rates after 7 days and 28 days were 20.3 wt % and 45.3 wt %, respectively.

[0043] This embodiment also provides a biodegradable polycarboxylic acid retanning agent prepared by the aforementioned method.

[0044] Example 2 This embodiment provides a method for preparing a biodegradable polycarboxylic acid retanning agent, comprising the following steps: Itaconic acid, nonionic monomer (acrylonitrile), carboxyl monomer (acrylic acid), initiator and deionized water were weighed respectively; the deionized water was divided into two parts to obtain the first deionized water and the second deionized water for standby use; 100 mL of deionized water (i.e., the first deionized water) was added to a 500 mL four-necked flask equipped with a stirrer, a condenser, a thermometer and a feeding device, and heated to 82°C under stirring; then, 50.0 g of itaconic acid, 20.0 g of acrylic acid, 12.5 g of acrylonitrile and an aqueous solution of ammonium persulfate (i.e., an aqueous solution of the initiator) were added at a uniform rate at the same temperature, and itaconic acid, nonionic monomer, carboxyl monomer and aqueous solution of ammonium persulfate were added simultaneously within 3 hours; after the addition was completed, the reaction was continued at the above temperature for 4 hours; then 104.4 g of The pH value was adjusted to 7.5 with 30 wt % sodium hydroxide solution to obtain 327.4 g of biodegradable polycarboxylic acid retanning agent with a solid content of 30.5 wt %, a monomer conversion rate of 99.1%, a weight average molecular weight Mw of 26523, a molecular weight distribution Mw / Mn=2.49, and a viscosity of 10% product aqueous solution of 49.5 mPa·s.

[0045] The ammonium persulfate aqueous solution is prepared by dissolving 1.0 g of ammonium persulfate in 40 mL of deionized water (i.e., the second portion of deionized water).

[0046] The test showed that the biodegradable polycarboxylic acid retanning agent of the present embodiment had good biodegradability, and the biodegradation rates after 7 days and 28 days were 20.1 wt % and 48.7 wt %, respectively.

[0047] This embodiment also provides a biodegradable polycarboxylic acid retanning agent prepared by the aforementioned method.

[0048] Example 3 This embodiment provides a method for preparing a biodegradable polycarboxylic acid retanning agent, comprising the following steps: Itaconic acid, nonionic monomer (acrylonitrile), carboxyl monomer (acrylic acid), initiator and deionized water were weighed respectively; the deionized water was divided into two parts to obtain the first deionized water and the second deionized water for standby use; 100 mL of deionized water (i.e., the first deionized water) was added to a 500 mL four-necked flask equipped with a stirrer, a condenser, a thermometer and a feeding device, and heated to 85°C under stirring; then, 50.0 g of itaconic acid, 5.0 g of acrylic acid, 27.5 g of acrylonitrile and an aqueous solution of ammonium persulfate (i.e., an aqueous solution of the initiator) were added at a uniform rate at the same temperature, and itaconic acid, nonionic monomer, carboxyl monomer and aqueous solution of ammonium persulfate were added simultaneously within 3 hours; after the addition was completed, the reaction was continued at the above temperature for 4 hours; then 92.7 g of The pH value was adjusted to 7.5 with 30wt% sodium hydroxide solution to obtain 308.7g of biodegradable polycarboxylic acid retanning agent with a solid content of 29.9wt%, a monomer conversion rate of 99.1%, a weight average molecular weight Mw of 24365, a molecular weight distribution Mw / Mn=2.41, and a viscosity of 10wt% product aqueous solution of 27.1mPa·s.

[0049] The ammonium persulfate aqueous solution is prepared by dissolving 1.0 g of ammonium persulfate in 40 mL of deionized water (i.e., the second portion of deionized water).

[0050] The test showed that the biodegradable polycarboxylic acid retanning agent of the present embodiment had good biodegradability, and the biodegradation rates after 7 days and 28 days were 20.3 wt % and 40.6 wt %, respectively.

[0051] This embodiment also provides a biodegradable polycarboxylic acid retanning agent prepared by the aforementioned method.

[0052] Example 4 This embodiment provides a method for preparing a biodegradable polycarboxylic acid retanning agent, comprising the following steps: Itaconic acid, nonionic monomer (acrylonitrile), carboxyl monomer (acrylic acid), initiator and deionized water were weighed respectively; the deionized water was divided into two parts to obtain the first deionized water and the second deionized water for standby use; 100 mL of deionized water (i.e., the first deionized water) was added to a 500 mL four-necked flask equipped with a stirrer, a condenser, a thermometer and a feeding device, and heated to 82°C under stirring; then, 50.0 g of itaconic acid, 12.5 g of acrylic acid, 20.0 g of acrylonitrile and an aqueous solution of ammonium persulfate (i.e., an aqueous solution of the initiator) were added at a uniform rate at the same temperature, and itaconic acid, nonionic monomer, carboxyl monomer and aqueous solution of ammonium persulfate were added simultaneously within 3 hours; after the addition was completed, the reaction was continued at the above temperature for 4 hours; then 96.8 g of The pH value of the 30wt% sodium hydroxide solution was adjusted to 7.5 to obtain 30.8g of a biodegradable polycarboxylic acid retanning agent with a solid content of 30.8wt%, a monomer conversion rate of 98.7%, a weight average molecular weight Mw of 31235, a molecular weight distribution Mw / Mn=2.62, and a viscosity of a 10wt% aqueous solution of the product of 62.7mPa·s.

[0053] The ammonium persulfate aqueous solution is prepared by dissolving 0.5 g of ammonium persulfate in 40 mL of deionized water (i.e., the second portion of deionized water).

[0054] The test showed that the biodegradable polycarboxylic acid retanning agent of the present embodiment had good biodegradability, and the biodegradation rates after 7 days and 28 days were 20.1 wt % and 41.2 wt %, respectively.

[0055] This embodiment also provides a biodegradable polycarboxylic acid retanning agent prepared by the aforementioned method.

[0056] Example 5 This embodiment provides a method for preparing a biodegradable polycarboxylic acid retanning agent, comprising the following steps: Itaconic acid, nonionic monomer (acrylonitrile), carboxyl monomer (acrylic acid), initiator and deionized water were weighed respectively; the deionized water was divided into two parts to obtain the first deionized water and the second deionized water for standby use; 100 mL of deionized water (i.e., the first deionized water) was added to a 500 mL four-necked flask equipped with a stirrer, a condenser, a thermometer and a feeding device, and heated to 80°C under stirring, and then 50.0 g of itaconic acid, 12.5 g of acrylic acid, 20.0 g of acrylonitrile and an aqueous solution of ammonium persulfate (i.e., an aqueous solution of initiator) were added at a uniform rate at the same temperature, and itaconic acid, nonionic monomer, carboxyl monomer and aqueous solution of ammonium persulfate were added simultaneously within 3 hours; after the addition was completed, the reaction was continued at the above temperature for 4 hours; then 96.8 g of The pH value was adjusted to 7.5 with 30 wt % sodium hydroxide solution to obtain 319.6 g of biodegradable polycarboxylic acid retanning agent with a solid content of 30.9 wt %, a monomer conversion rate of 99.6%, a weight average molecular weight Mw of 21365, a molecular weight distribution Mw / Mn=2.10, and a viscosity of a 10 wt % aqueous solution of the product of 16.3 mPa·s.

[0057] The ammonium persulfate aqueous solution is prepared by dissolving 5.0 g of ammonium persulfate in 40 mL of deionized water (i.e., the second portion of deionized water).

[0058] The test showed that the biodegradable polycarboxylic acid retanning agent of the present embodiment had good biodegradability, and the biodegradation rates after 7 days and 28 days were 22.3 wt % and 43.4 wt %, respectively.

[0059] This embodiment also provides a biodegradable polycarboxylic acid retanning agent prepared by the aforementioned method.

[0060] Example 6 This embodiment provides a method for preparing a biodegradable polycarboxylic acid retanning agent, comprising the following steps: Itaconic acid, nonionic monomer (acrylonitrile), carboxyl monomer (acrylic acid), initiator and deionized water were weighed respectively; the deionized water was divided into two parts to obtain the first part of deionized water and the second part of deionized water for standby use; 100 mL of deionized water (i.e., the first part of deionized water) was added to a 500 mL four-necked flask equipped with a stirrer, a condenser, a thermometer and a feeding device, and heated to 80-85° C. under stirring; then 50.0 g of itaconic acid, 12.5 g of acrylic acid, 20.0 g of acrylonitrile and an aqueous solution of sodium persulfate (i.e., The initiator aqueous solution was added simultaneously with itaconic acid, nonionic monomer, carboxyl monomer and sodium persulfate aqueous solution within 3 hours; after the addition was completed, the reaction was continued at the above temperature for 4 hours; then, the pH was adjusted to 7.5 with 96.8g 30wt% sodium hydroxide solution to obtain 319.7g of biodegradable polycarboxylic acid retanning agent with a solid content of 30.8wt%, a monomer conversion rate of 97.1%, a weight average molecular weight Mw of 26123, a molecular weight distribution Mw / Mn=2.48, and a viscosity of a 10wt% product aqueous solution of 37.8mPa·s.

[0061] The sodium persulfate aqueous solution is prepared by dissolving 1.0 g of sodium persulfate in 40 mL of deionized water (i.e., the second portion of deionized water).

[0062] The test showed that the biodegradable polycarboxylic acid retanning agent of the present embodiment had good biodegradability, and the biodegradation rates after 7 days and 28 days were 20.2 wt % and 40.3 wt %, respectively.

[0063] This embodiment also provides a biodegradable polycarboxylic acid retanning agent prepared by the aforementioned method.

[0064] Example 7 This embodiment provides a method for preparing a biodegradable polycarboxylic acid retanning agent, comprising the following steps: Itaconic acid, nonionic monomer (acrylonitrile), carboxyl monomer (acrylic acid), initiator and deionized water were weighed respectively; the deionized water was divided into two parts to obtain the first deionized water and the second deionized water for standby use; 100 mL of deionized water (i.e., the first deionized water) was added to a 500 mL four-necked flask equipped with a stirrer, a condenser, a thermometer and a feeding device, and heated to 42°C under stirring; then, 50.0 g of itaconic acid, 12.5 g of acrylic acid, 20.0 g of acrylonitrile and an aqueous solution of a redox initiating system were added at a uniform rate at the same temperature, and itaconic acid, nonionic monomer, carboxyl monomer and ammonium persulfate aqueous solution were added simultaneously within 3 hours; after the addition was completed, the reaction was continued at the above temperature for 4 hours; then 96.8 g of The pH value was adjusted to 7.5 with 30 wt % sodium hydroxide solution to obtain 321.9 g of biodegradable polycarboxylic acid retanning agent with a solid content of 30.9 wt %, a monomer conversion rate of 98.6%, a weight average molecular weight Mw of 26531, a molecular weight distribution Mw / Mn=2.50, and a viscosity of a 10 wt % aqueous solution of the product of 39.7 mPa·s.

[0065] The redox initiation system aqueous solution is prepared by dissolving 3.0 g of ammonium persulfate and 1.0 g of sodium bisulfite in 40 mL of deionized water (i.e., the second portion of deionized water).

[0066] The test showed that the biodegradable polycarboxylic acid retanning agent of the present embodiment had good biodegradability, and the biodegradation rates after 7 days and 28 days were 20.5wt% and 40.9wt%, respectively.

[0067] This embodiment also provides a biodegradable polycarboxylic acid retanning agent prepared by the aforementioned method.

[0068] The polycarboxylic acid retanning agent and acrylic resin retanning agent R8008 (comparative sample) of Examples 1-7 were used to conduct leather retanning tests. The specific retanning process was as follows: using American cowhide, the leather embryo was first acid-washed and rewetted, and the pH value of the leather embryo was adjusted to 3.2±0.2; then the acid-washed and rewetted leather embryo was chrome-retanned, and the pH value of the leather embryo was 4.0; then the leather embryo was neutralized to pH 5 to facilitate material combination; finally, the polycarboxylic acid retanning agent or acrylic resin retanning agent R8008 of each embodiment was used to fill the leather embryo; the tanned leather was preliminarily evaluated when it was out of the drum, and the final evaluation was performed after drying. Among them, the dosage basis is the weight of cowhide.

[0069] During the retanning process, the operating conditions of each process are shown in the following table:

[0070] The evaluation method of retanning agent on leather tanning performance is shown in the following table:

[0071] After the leather retanning test, the performance indicators of the retanning agent on the leather tanning are as follows:

[0072] It can be seen that the biodegradable polycarboxylic acid retanning agents of Examples 1-7 of the present invention have the same tanning properties for leather as the acrylic resin retanning agent R8008, with good softness, fullness, astringency, clear pores and natural surface feel; the rest of the properties are similar to those of the acrylic resin retanning agent R8008.

[0073] Unless otherwise specified, all percentages used in the present invention are by mass.

[0074] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a biodegradable polycarboxylic acid retanning agent, characterized in that: Add the first portion of deionized water into the reactor, stir and heat to 30-90°C, and keep warm; then add itaconic acid, nonionic monomer, carboxyl monomer and initiator aqueous solution at the same time; control the itaconic acid, nonionic monomer, carboxyl monomer and initiator aqueous solution to be added simultaneously within 1.5-3.5 hours; after the addition is completed, continue to keep warm and react for 3-5 hours, and use sodium hydroxide solution to adjust the pH value to 4.5-8.0 to prepare a biodegradable polycarboxylic acid retanning agent; The initiator aqueous solution is prepared by dissolving the initiator in the second portion of deionized water.

2. The method for preparing the biodegradable polycarboxylic acid retanning agent according to claim 1, characterized in that: The nonionic monomer is one of the following: acrylonitrile, acrylamide, N-hydroxymethyl acrylamide; The carboxyl monomer is one of the following: acrylic acid, methacrylic acid, and maleic anhydride.

3. The method for preparing the biodegradable polycarboxylic acid retanning agent according to claim 1, characterized in that: The weight of the first portion of deionized water is 50-80% of the total weight of all deionized water; the second portion of deionized water is the remaining weight of deionized water.

4. The method for preparing the biodegradable polycarboxylic acid retanning agent according to claim 3, characterized in that: The weight ratio of the itaconic acid, the nonionic monomer, the carboxyl monomer and all the deionized water is 1:0.2-0.8:0.1-0.6:2-7.

5. The method for preparing the biodegradable polycarboxylic acid retanning agent according to claim 1, characterized in that: The initiator is a persulfate or a redox initiation system.

6. The method for preparing the biodegradable polycarboxylic acid retanning agent according to claim 5, characterized in that: The persulfate is one of the following: ammonium persulfate, sodium persulfate, potassium persulfate; The redox initiation system is one of the following: a persulfate-sodium bisulfite initiation system and a persulfate-sodium pyrosulfite initiation system.

7. The method for preparing the biodegradable polycarboxylic acid retanning agent according to claim 1, characterized in that: The added weight of the initiator is 0.5-10% of the total weight of itaconic acid, nonionic monomer and carboxyl monomer.

8. The method for preparing the biodegradable polycarboxylic acid retanning agent according to claim 1, characterized in that: The mass concentration of the sodium hydroxide solution is 10-50wt%.

9. A biodegradable polycarboxylic acid retanning agent, characterized in that: The method is prepared by the method according to any one of claims 1 to 8.

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