Synthetic method for preparing high-aldehyde oxidized starch and retanning agent of high-aldehyde oxidized starch

Abstract

The invention belongs to the technical field of leather chemicals, and particularly relates to a synthetic method for preparing high-aldehyde-group oxidized starch and a retanning agent of the high-aldehyde-group oxidized starch, which comprises the following steps: (1) pretreating and oxidizing to obtain a raw material mixture; (2) carrying out molecular modification to obtain a semi-finished product; and (3) performing post-treatment to prepare the powdery high-aldehyde-group oxidized starch retanning agent. The defects that an existing dialdehyde starch retanning agent is unstable in aldehyde group and easy to release formaldehyde under strong acid and strong heat conditions are overcome.

Description

Technical Field

[0001] The invention belongs to the technical field of leather chemicals, and in particular relates to a method for preparing high-aldehyde oxidized starch and a synthesis method for a retanning agent thereof. Background Art

[0002] As an indispensable auxiliary agent in the leather processing process, retanning agents have a direct impact on the physical properties, feel and environmental friendliness of leather. With the continuous improvement of leather product quality and environmental protection requirements, the development of efficient and environmentally friendly retanning agents has become a research hotspot. However, existing retanning agents still have many shortcomings in terms of preparation technology, performance optimization and environmental friendliness, which limit their widespread application. CN113046496B discloses a retanning agent for chrome-tanned leather and semi-vegetable-tanned leather. The retanning agent is prepared by mixing acrylic acid, methyl acrylate, acrylonitrile and an oxidized starch aqueous solution, and adding melamine-modified montmorillonite and negative ion powder to give the product good selective filling and softness. However, the aldehyde content of the oxidized starch in this technical solution is low, which limits its cross-linking ability with leather fibers and may result in a less than ideal retanning effect. In addition, the melamine-modified montmorillonite and negative ion powder introduced increase the process complexity, and its environmental friendliness and cost-effectiveness still need to be further verified. CN111118232B discloses a retanning filler and a preparation method thereof. The invention uses dialdehyde starch as a base material, is subjected to degradation treatment by industrial pancreatic enzymes and an acid degradation agent, and is modified with a variety of modifiers to significantly improve the retanning filling performance. However, although the aldehyde content of dialdehyde starch in this technical solution is relatively high, its stability is relatively poor and it is prone to degradation during storage and use, affecting the long-term performance of the retanning agent. At the same time, the multiple modifiers and complicated degradation steps used in this method increase production costs and process difficulties, which may limit its large-scale application.

[0003] These issues demonstrate that existing retanning agents still have significant deficiencies in the preparation, stability control, and process simplification of high-aldehyde oxidized starch. Specifically, the aldehyde content of oxidized starch in existing technologies is insufficient for efficient cross-linking, and the stability issues associated with high aldehyde content have yet to be effectively addressed. Summary of the Invention

[0004] In order to solve the above problems, the present invention proposes a method for preparing high-aldehyde oxidized starch and a synthesis method of a retanning agent thereof, which solves the defects of existing dialdehyde starch retanning agents in that the aldehyde group is unstable and easily releases formaldehyde under strong acid and heat conditions.

[0005] To achieve the above object, the technical solution of the present invention is:

[0006] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0007] Step (1) pretreatment and oxidation: gelatinizing waxy corn starch having an amylose content of ≤10% (60-80°C, 20-40 min), adding sodium periodate and oxidizing at 35-40°C for 4-8 h until the aldehyde content is ≥50%, and adding ethylene glycol in an amount of 0.5-0.6 times the molar amount of sodium periodate to terminate the reaction, to obtain a raw material mixture;

[0008] Step (2) Molecular modification: Sodium sulfite or sodium bisulfite (molar ratio to aldehyde group 0.6-0.9:1) is added to the raw material mixture, the pH is adjusted to 8.0-9.0, and sulfonation is carried out at 50-60°C for 2-4 hours (sulfonation degree ≥ 60%); then, while maintaining the pH at 8.5-9.0 and the system temperature at 35-40°C, polyethylene glycol diglycidyl ether is diluted to a 20% to 30% aqueous solution by mass, and slowly added dropwise to the reaction system at a rate of 1-2 mL / min (the addition amount is 0.5% to 1.5% of the dry basis weight of starch), while maintaining uniform stirring at 200-300 rpm and introducing nitrogen protection, and the reaction is carried out at a constant temperature for 1-2 hours to construct a cross-linked network to obtain a semi-finished product;

[0009] Step (3) post-treatment: heating the semi-finished product to 45-50° C., adding 0.3% to 0.8% by mass of boric acid as a stabilizer, mixing at a stirring rate of 200-300 rpm, adjusting the pH to 7.0-8.0, maintaining the reaction conditions for 25-35 minutes, and drying to prepare a powdered high-aldehyde oxidized starch retanning agent.

[0010] Traditional retanning agents, due to their low aldehyde content or poor stability, struggle to meet the demands of high-performance leather processing. However, the present invention precisely controls the oxidation temperature and sulfonation conditions to create a continuous sulfonic acid protective layer on the oxidized starch molecular chain. This, coupled with enhanced intramolecular connectivity through borate bonds, creates a stable five-membered ring chelate structure within the molecule, significantly enhancing the chemical stability of the retanning agent. Combined SEM and FTIR characterization revealed that the retanning agent exhibits uniformly distributed sulfonic acid groups on its surface, resulting in excellent resistance to degradation in acidic environments and providing reliable support for the efficient cross-linking of leather fibers.

[0011] In the present invention, the core of the high-aldehyde oxidized starch retanning agent lies in its unique triple composite stable structure, including sulfonic acid group, borate ester bond and cyclic chelate. This structure gives the retanning agent excellent anti-degradation ability, especially showing excellent stability in acidic and high temperature environments.

[0012] The present invention uses waxy corn starch as raw material, and finally obtains a retanning agent product with high aldehyde content and strong stability by performing low-temperature oxidation, alkaline sulfonation, cross-linking modification and metal ion capture on the starch. Waxy corn starch has good solubility and processability due to its low amylose content, making it an ideal choice for preparing high-aldehyde oxidized starch. Sodium periodate is added to the gelatinized starch solution for oxidation treatment. The amount of sodium periodate is calculated based on the dry basis mass of the starch, usually 0.8-1.2 times the molar amount of the dry basis of the starch, to ensure that the oxidation reaction can generate sufficient aldehyde groups. During the oxidation reaction, the temperature must be strictly controlled within the range of 35-40°C to avoid the occurrence of side reactions due to excessively high temperatures. After the reaction is completed, the unreacted sodium periodate is terminated by adding an appropriate amount of ethylene glycol, and the aldehyde content in the product is measured to ensure that it reaches a target value of ≥50%. After the oxidation step is completed, sulfite is added to the oxidized starch solution for sulfonation. The sulfite can be sodium sulfite or sodium bisulfite, with a molar ratio of 0.6-0.9:1 to the aldehyde group. The pH of the sulfonation reaction should be adjusted to 8.0-9.0, and the reaction temperature maintained at 50-60°C to promote uniform distribution of the sulfonic acid groups on the oxidized starch chains. After the sulfonation reaction is complete, unreacted sulfite is removed by centrifugation, and the product is washed and dried.

[0013] To further enhance the molecular stability of the oxidized starch, polyethylene glycol diglycidyl ether (PEGDE) is added to the sulfonated product as a crosslinker. The PEGDE dosage ranges from 0.5% to 1.5% of the dry starch basis. Its epoxy groups react with the hydroxyl groups on the oxidized starch molecular chains to form a three-dimensional crosslinked network. The crosslinking reaction is carried out at 50-60°C for 2-4 hours. This crosslinking modification not only improves the mechanical strength of the oxidized starch but also enhances its resistance to acid hydrolysis in complex environments. Disodium EDTA is added to the crosslinked product as a metal ion scavenger. The dosage of disodium EDTA is 5% to 10% of the molar number of aldehyde groups. It effectively captures metal ions in the solution, preventing them from catalyzing the degradation of the oxidized starch. Subsequently, boric acid is added to the system at a dosage of 0.3% to 0.8% of the final product weight. The addition of boric acid forms a stable five-membered ring chelate structure within the oxidized starch molecules, further enhancing the retanning agent's resistance to degradation. The addition of boric acid needs to be carried out at a pH of 7.0-8.0 to ensure the efficient formation of borate ester bonds. The final product is processed by spray drying or freeze drying to obtain a powdered high-aldehyde oxidized starch retanning agent.

[0014] Preferably, the amount of sodium periodate used in step (1) is 0.8-1.2 times the molar number of starch on a dry basis. The molar number of starch on a dry basis refers to the molar number of completely dehydrated starch in the reaction system, calculated based on a glucose unit molecular weight of 162 g / mol.

[0015] Preferably, after adding polyethylene glycol diglycidyl ether, disodium EDTA (5% to 10% of the aldehyde molar ratio) is added to chelate the metal ions, thereby blocking the path of catalyzing the hydrolysis of the aldehyde groups by forming a highly stable chelate.

[0016] Preferably, the stabilizer in step (3) is boric acid, which condenses with hydroxyalkylsulfonic acid groups to form a five-membered ring boronate ester bond, thereby enhancing acid stability.

[0017] Preferably, the amylose content of the waxy corn starch is ≤5%.

[0018] Preferably, the molecular weight of the polyethylene glycol diglycidyl ether is 400–1000 Da.

[0019] Preferably, the drying method in step (3) is spray drying or freeze drying.

[0020] This proposal also proposes a high-aldehyde oxidized starch retanning agent prepared by the above method, with a surface sulfonation degree of ≥60% and an aldehyde content of ≥50%.

[0021] Maintain aldehyde stability in leather retanning environment with pH ≥ 3.5 and temperature ≤ 50℃.

[0022] Existing dialdehyde starch retanning agents suffer from unstable aldehyde groups and the tendency to release formaldehyde under strong acid and heat conditions. This solution specifically addresses the hydrolysis problem of aldehyde groups by constructing a stable triple-compound structure of sulfonic acid group, borate ester bond, and cyclic chelate.

[0023] Compared with existing technologies, this solution has the following advantages:

[0024] 1. This patent breaks through the limitations of traditional retanning agent components through triple molecular synergistic protection: the core adopts a composite structure of sulfonic acid groups to electrostatically shield hydrogen ion attacks, borate bonds to realize proton capture traps, and metal chelate rings to inactivate catalytic ions, thus achieving closed protection of aldehyde groups and blocking the formaldehyde release path.

[0025] 2. This solution combines the control of temperature, pH, material addition amount and addition method during the process to achieve the above-mentioned triple molecular synergistic protection, and solves the defects of existing dialdehyde starch retanning agents, such as the instability of aldehyde groups and the easy release of formaldehyde under strong acid and heat conditions. DETAILED DESCRIPTION

[0026] The following describes the implementation of the present invention using specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. Obviously, the embodiments described are only a portion of the present invention, not all of it. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0027] Overall embodiment

[0028] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0029] Step (1) Pretreatment and Oxidation: Waxy corn starch having an amylose content of ≤10% is gelatinized at 60-80° C. for 20-40 minutes, and sodium periodate (0.8-1.2 times the molar amount of the starch on a dry basis) is added and oxidized at 35-40° C. for 4-8 hours until the aldehyde content is ≥50%. Ethylene glycol (0.5-0.6 times the molar amount of the sodium periodate) is added to terminate the reaction, thereby obtaining a raw material mixture;

[0030] Step (2) Molecular modification: adding sodium sulfite or sodium bisulfite in a molar ratio of 0.6-0.9:1 to the raw material mixture, adjusting the pH to 8.0-9.0, and sulfonating at 50-60°C for 2-4 hours; then, while maintaining the pH at 8.5-9.0 and the system temperature at 35-40°C, slowly adding a polyethylene glycol diglycidyl ether aqueous solution (PEG 400-100) diluted to a mass fraction of 20% to 30% to the reaction system at a rate of 1-2 mL / min, with the final addition amount being 0.5% to 1.5% of the dry weight of the starch, and adding disodium EDTA in an amount of 5% to 10% of the molar number of the aldehyde group, while maintaining a uniform stirring speed of 200-300 rpm and introducing nitrogen protection, and reacting at a constant temperature for 1-2 hours to construct a cross-linked network to obtain a semi-finished product;

[0031] Step (3) post-treatment: heating the semi-finished product to 45-50° C., adding 0.3% to 0.8% by mass of boric acid as a stabilizer, mixing at a stirring rate of 200-300 rpm, adjusting the pH to 7.0-8.0, maintaining the reaction under this condition for 25-35 minutes, and spray drying to prepare a powdered high-aldehyde oxidized starch retanning agent.

[0032] Example 1

[0033] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0034] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 8% was gelatinized at 60° C. for 40 minutes, and sodium periodate (0.8 times the molar amount of the starch on a dry basis) was added and oxidized at 35° C. for 8 hours, with an aldehyde content of 50%. When the reaction was terminated, ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to obtain a raw material mixture;

[0035] Step (2) Molecular modification: Sodium sulfite at a molar ratio of 0.6:1 to aldehyde groups is added to the raw material mixture, the pH is adjusted to 8.0, and sulfonation is carried out at 50° C. for 4 hours; then, while maintaining the pH at 8.5 and the system temperature at 35° C., a polyethylene glycol diglycidyl ether (PEG 400) aqueous solution diluted to 20% is slowly added dropwise at a rate of 1 mL / min (addition amount: 0.5% of starch dry basis), and disodium EDTA with a molar number of 5% of aldehyde groups is added, the mixture is stirred at a constant speed of 200 rpm and nitrogen is introduced for protection, and the reaction is carried out at a constant temperature for 2 hours to obtain a semi-finished product;

[0036] Step (3) post-treatment: the semi-finished product was heated to 45° C., 0.3% boric acid was added, the mixture was stirred at 200 rpm, the pH was adjusted to 7.0, the reaction was maintained for 30 min, and the mixture was spray-dried to prepare a powdered retanning agent.

[0037] Example 2

[0038] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0039] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 5% was gelatinized at 70° C. for 30 minutes, and sodium periodate (1.0 times the molar amount of the starch on a dry basis) was added and oxidized at 37° C. for 6 hours until the aldehyde content reached 65%. When the reaction was terminated, ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to obtain a raw material mixture;

[0040] Step (2) Molecular modification: sodium bisulfite at a molar ratio of 0.7:1 to aldehyde groups was added to the raw material mixture, the pH was adjusted to 8.5, and sulfonation was carried out at 55° C. for 3 h; then, while maintaining the pH at 8.8 and the system temperature at 38° C., a polyethylene glycol diglycidyl ether (PEG 600) aqueous solution diluted to 25% was slowly added dropwise at a rate of 1.5 mL / min (addition amount: 1.0% of starch dry basis), and disodium EDTA with a molar number of 7% of aldehyde groups was added, the mixture was stirred at a constant speed of 250 rpm and nitrogen was introduced for protection, and the reaction was carried out at a constant temperature for 1.5 h to obtain a semi-finished product;

[0041] Step (3) post-treatment: the semi-finished product was heated to 48° C., 0.5% boric acid was added, the mixture was stirred at 250 rpm, the pH was adjusted to 7.5, the reaction was maintained for 30 min, and the mixture was spray-dried to prepare a powdered retanning agent.

[0042] Example 3

[0043] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0044] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 10% was gelatinized at 75° C. for 25 minutes, and sodium periodate (1.1 times the molar amount of the starch on a dry basis) was added and oxidized at 40° C. for 5 hours until the aldehyde content reached 75%. When the reaction was terminated, ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to obtain a raw material mixture;

[0045] Step (2) Molecular modification: Sodium sulfite in a molar ratio of 0.8:1 to aldehyde groups is added to the raw material mixture, the pH is adjusted to 8.8, and sulfonation is carried out at 58° C. for 2.5 hours; then, while maintaining the pH at 9.0 and the system temperature at 40° C., a polyethylene glycol diglycidyl ether (PEG 1000) aqueous solution diluted to 30% is slowly added dropwise at a rate of 2 mL / min (addition amount: 1.2% of starch dry basis), and disodium EDTA with a molar number of 8% of aldehyde groups is added, the mixture is stirred at a constant speed of 300 rpm and nitrogen is introduced for protection, and the reaction is carried out at a constant temperature for 1 hour to obtain a semi-finished product;

[0046] Step (3) post-treatment: the semi-finished product was heated to 50° C., 0.6% boric acid was added, the mixture was stirred at 300 rpm, the pH was adjusted to 8.0, the reaction was maintained for 30 min, and the mixture was spray-dried to prepare a powdered retanning agent.

[0047] Example 4

[0048] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0049] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 3% was gelatinized at 80° C. for 20 minutes, and sodium periodate (1.2 times the molar amount of the starch on a dry basis) was added and oxidized at 36° C. for 7 hours. When the aldehyde content reached 58% and the reaction was terminated, ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to obtain a raw material mixture;

[0050] Step (2) Molecular modification: Sodium bisulfite with a molar ratio of 0.65:1 to the aldehyde group is added to the raw material mixture, the pH is adjusted to 8.2, and sulfonation is carried out at 52° C. for 3.5 hours; then, while maintaining the pH at 8.6 and the system temperature at 36° C., a polyethylene glycol diglycidyl ether (PEG 800) aqueous solution diluted to 22% is slowly added dropwise at a rate of 1.2 mL / min (addition amount: 0.8% of starch dry basis), and disodium EDTA with a molar number of 6% of the aldehyde group is added, the mixture is stirred at a constant speed of 220 rpm and nitrogen protection is introduced, and the reaction is carried out at a constant temperature for 1.8 hours to obtain a semi-finished product;

[0051] Step (3) post-treatment: the semi-finished product was heated to 46° C., 0.4% boric acid was added, the mixture was stirred at 220 rpm, the pH was adjusted to 7.2, the reaction was maintained for 30 min, and the mixture was spray-dried to prepare a powdered retanning agent.

[0052] Example 5

[0053] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0054] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 7% was gelatinized at 65° C. for 35 minutes, and sodium periodate (0.9 times the molar amount of the starch on a dry basis) was added and oxidized at 38° C. for 4.5 hours until the aldehyde content reached 70%. Ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to terminate the reaction, thereby obtaining a raw material mixture;

[0055] Step (2) Molecular modification: Sodium sulfite in a molar ratio of 0.9:1 to aldehyde groups is added to the raw material mixture, the pH is adjusted to 9.0, and sulfonation is carried out at 60°C for 2 hours; then, while maintaining the pH at 9.0 and the system temperature at 37°C, a polyethylene glycol diglycidyl ether (PEG 400) aqueous solution diluted to 28% is slowly added dropwise at a rate of 1.8 mL / min (addition amount: 1.5% of starch dry basis), and disodium EDTA with a molar number of 10% of aldehyde groups is added, the mixture is stirred at a constant speed of 280 rpm and nitrogen protection is introduced, and the reaction is carried out at a constant temperature for 1.2 hours to obtain a semi-finished product;

[0056] Step (3) post-treatment: the semi-finished product was heated to 47° C., 0.7% boric acid was added, the mixture was stirred at 280 rpm, the pH was adjusted to 7.8, the reaction was maintained for 30 min, and the mixture was spray-dried to prepare a powdered retanning agent.

[0057] Comparative Example 1

[0058] The difference from Example 1 is that waxy corn starch with an amylose content of ≤10% is not selected:

[0059] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0060] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 15% was gelatinized at 60° C. for 40 minutes, and sodium periodate (0.8 times the molar amount of the starch on a dry basis) was added to oxidize at 35° C. for 8 hours, until the aldehyde content reached 50%. When the reaction was terminated, ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to obtain a raw material mixture;

[0061] Step (2) Molecular modification: Sodium sulfite at a molar ratio of 0.6:1 to aldehyde groups is added to the raw material mixture, the pH is adjusted to 8.0, and sulfonation is carried out at 50° C. for 4 hours; then, while maintaining the pH at 8.5 and the system temperature at 35° C., a polyethylene glycol diglycidyl ether (PEG 400) aqueous solution diluted to 20% is slowly added dropwise at a rate of 1 mL / min (addition amount: 0.5% of starch dry basis), and disodium EDTA with a molar number of 5% of aldehyde groups is added, the mixture is stirred at a constant speed of 200 rpm and nitrogen is introduced for protection, and the reaction is carried out at a constant temperature for 2 hours to obtain a semi-finished product;

[0062] Step (3) post-treatment: the semi-finished product was heated to 45° C., 0.3% boric acid was added, the mixture was stirred at 200 rpm, the pH was adjusted to 7.0, the reaction was maintained for 30 minutes, and the mixture was spray-dried to prepare a powdered retanning agent.

[0063] Comparative Example 2

[0064] The difference from Example 1 is that sodium periodate is added in excess:

[0065] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0066] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 8% was gelatinized at 60° C. for 40 minutes, and sodium periodate (1.5 times the molar amount of the starch on a dry basis) was added and oxidized at 35° C. for 8 hours until the aldehyde content reached 50%. Ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to terminate the reaction, thereby obtaining a raw material mixture;

[0067] Step (2) Molecular modification: Sodium sulfite at a molar ratio of 0.6:1 to aldehyde groups is added to the raw material mixture, the pH is adjusted to 8.0, and sulfonation is carried out at 50° C. for 4 hours; then, while maintaining the pH at 8.5 and the system temperature at 35° C., a polyethylene glycol diglycidyl ether (PEG 400) aqueous solution diluted to 20% is slowly added dropwise at a rate of 1 mL / min (addition amount: 0.5% of starch dry basis), and disodium EDTA with a molar number of 5% of aldehyde groups is added, the mixture is stirred at a constant speed of 200 rpm and nitrogen is introduced for protection, and the reaction is carried out at a constant temperature for 2 hours to obtain a semi-finished product;

[0068] Step (3) post-treatment: the semi-finished product was heated to 45° C., 0.3% boric acid was added, the mixture was stirred at 200 rpm, the pH was adjusted to 7.0, the reaction was maintained for 30 minutes, and the mixture was spray-dried to prepare a powdered retanning agent.

[0069] Comparative Example 3

[0070] The difference from Example 1 is that the sulfonation is insufficient:

[0071] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0072] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 8% was gelatinized at 60° C. for 40 minutes, and sodium periodate (0.8 times the molar amount of the starch on a dry basis) was added and oxidized at 35° C. for 8 hours, with an aldehyde content of 50%. When the reaction was terminated, ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to obtain a raw material mixture;

[0073] Step (2) Molecular modification: Sodium sulfite at a molar ratio of 0.6:1 to aldehyde groups is added to the raw material mixture, the pH is adjusted to 8.0, and sulfonation is carried out at 50° C. for 1 hour; then, while maintaining the pH at 8.5 and the system temperature at 35° C., a polyethylene glycol diglycidyl ether (PEG 400) aqueous solution diluted to 20% is slowly added dropwise at a rate of 1 mL / min (addition amount: 0.5% of starch dry basis), and disodium EDTA with a molar number of 5% of aldehyde groups is added, the mixture is stirred at a constant speed of 200 rpm and nitrogen is introduced for protection, and the reaction is carried out at a constant temperature for 2 hours to obtain a semi-finished product;

[0074] Step (3) post-treatment: the semi-finished product was heated to 45° C., 0.3% boric acid was added, the mixture was stirred at 200 rpm, the pH was adjusted to 7.0, the reaction was maintained for 30 min, and the mixture was spray-dried to prepare a powdered retanning agent.

[0075] Comparative Example 4

[0076] The difference from Example 1 is that the sulfonating agent is added in excess:

[0077] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0078] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 8% was gelatinized at 60° C. for 40 minutes, and sodium periodate (0.8 times the molar amount of the starch on a dry basis) was added and oxidized at 35° C. for 8 hours, with an aldehyde content of 50%. When the reaction was terminated, ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to obtain a raw material mixture;

[0079] Step (2) Molecular modification: Sodium sulfite in a molar ratio of 0.6:2 to aldehyde group is added to the raw material mixture, the pH is adjusted to 8.0, and sulfonation is carried out at 50°C for 4 hours; then, while maintaining the pH at 8.5 and the system temperature at 35°C, a polyethylene glycol diglycidyl ether (PEG 400) aqueous solution diluted to 20% is slowly added dropwise at a rate of 1 mL / min (addition amount: 0.5% of starch dry basis), and disodium EDTA with a molar number of 5% of aldehyde group is added, the mixture is stirred at a constant speed of 200 rpm and nitrogen is introduced for protection, and the reaction is carried out at a constant temperature for 2 hours to obtain a semi-finished product;

[0080] Step (3) post-treatment: the semi-finished product was heated to 45° C., 0.3% boric acid was added, the mixture was stirred at 200 rpm, the pH was adjusted to 7.0, the reaction was maintained for 30 min, and the mixture was spray-dried to prepare a powdered retanning agent.

[0081] Comparative Example 5

[0082] The difference from Example 1 is that the molecular weight of polyethylene glycol diglycidyl ether exceeds the upper limit:

[0083] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0084] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 8% was gelatinized at 60° C. for 40 minutes, and sodium periodate (0.8 times the molar amount of the starch on a dry basis) was added and oxidized at 35° C. for 8 hours, with an aldehyde content of 50%. When the reaction was terminated, ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to obtain a raw material mixture;

[0085] Step (2) Molecular modification: Sodium sulfite at a molar ratio of 0.6:1 to aldehyde groups is added to the raw material mixture, the pH is adjusted to 8.0, and sulfonation is carried out at 50° C. for 4 hours; then, while maintaining the pH at 8.5 and the system temperature at 35° C., a polyethylene glycol diglycidyl ether (PEG 1200) aqueous solution diluted to 20% is slowly added dropwise at a rate of 1 mL / min (addition amount: 0.5% of starch dry basis), and disodium EDTA with a molar number of 5% of aldehyde groups is added, the mixture is stirred at a constant speed of 200 rpm and nitrogen protection is introduced, and the reaction is carried out at a constant temperature for 2 hours to obtain a semi-finished product;

[0086] Step (3) post-treatment: the semi-finished product was heated to 45° C., 0.3% boric acid was added, the mixture was stirred at 200 rpm, the pH was adjusted to 7.0, the reaction was maintained for 30 minutes, and the mixture was spray-dried to prepare a powdered retanning agent.

[0087] Comparative Example 6

[0088] The difference from Example 1 is that no disodium EDTA was added:

[0089] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0090] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 8% was gelatinized at 60° C. for 40 minutes, and sodium periodate (0.8 times the molar amount of the starch on a dry basis) was added and oxidized at 35° C. for 8 hours, with an aldehyde content of 50%. When the reaction was terminated, ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to obtain a raw material mixture;

[0091] Step (2) Molecular modification: Sodium sulfite at a molar ratio of 0.6:1 to aldehyde group was added to the raw material mixture, the pH was adjusted to 8.0, and sulfonation was carried out at 50°C for 4 hours; then, while maintaining the pH at 8.5 and the system temperature at 35°C, a 20% aqueous solution of polyethylene glycol diglycidyl ether (PEG 400) was slowly added dropwise at a rate of 1 mL / min (addition amount: 0.5% of starch dry basis), the mixture was stirred at a constant speed of 200 rpm and nitrogen was introduced for protection, and the reaction was carried out at a constant temperature for 2 hours to obtain a semi-finished product;

[0092] Step (3) post-treatment: the semi-finished product was heated to 45° C., 0.3% boric acid was added, the mixture was stirred at 200 rpm, the pH was adjusted to 7.0, the reaction was maintained for 30 minutes, and the mixture was spray-dried to prepare a powdered retanning agent.

[0093] Comparative Example 7

[0094] The difference from Example 1 is that no boric acid was added:

[0095] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0096] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 8% was gelatinized at 60° C. for 40 minutes, and sodium periodate (0.8 times the molar amount of the starch on a dry basis) was added and oxidized at 35° C. for 8 hours, with an aldehyde content of 50%. When the reaction was terminated, ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to obtain a raw material mixture;

[0097] Step (2) Molecular modification: Sodium sulfite at a molar ratio of 0.6:1 to aldehyde groups is added to the raw material mixture, the pH is adjusted to 8.0, and sulfonation is carried out at 50° C. for 4 hours; then, while maintaining the pH at 8.5 and the system temperature at 35° C., a polyethylene glycol diglycidyl ether (PEG 400) aqueous solution diluted to 20% is slowly added dropwise at a rate of 1 mL / min (addition amount: 0.5% of starch dry basis), and disodium EDTA with a molar number of 5% of aldehyde groups is added, the mixture is stirred at a constant speed of 200 rpm and nitrogen is introduced for protection, and the reaction is carried out at a constant temperature for 2 hours to obtain a semi-finished product;

[0098] Step (3) post-treatment: the semi-finished product is heated to 45° C., stirred and mixed at 200 rpm, the pH is adjusted to 7.0, and spray-dried to prepare a powdered retanning agent.

[0099] Comparative Example 8

[0100] The difference from Example 1 is that boric acid is added in excess:

[0101] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0102] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 8% was gelatinized at 60° C. for 40 minutes, and sodium periodate (0.8 times the molar amount of the starch on a dry basis) was added and oxidized at 35° C. for 8 hours, with an aldehyde content of 50%. When the reaction was terminated, ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to obtain a raw material mixture;

[0103] Step (2) Molecular modification: Sodium sulfite at a molar ratio of 0.6:1 to aldehyde groups is added to the raw material mixture, the pH is adjusted to 8.0, and sulfonation is carried out at 50° C. for 4 hours; then, while maintaining the pH at 8.5 and the system temperature at 35° C., a polyethylene glycol diglycidyl ether (PEG 400) aqueous solution diluted to 20% is slowly added dropwise at a rate of 1 mL / min (addition amount: 0.5% of starch dry basis), and disodium EDTA with a molar number of 5% of aldehyde groups is added, the mixture is stirred at a constant speed of 200 rpm and nitrogen is introduced for protection, and the reaction is carried out at a constant temperature for 2 hours to obtain a semi-finished product;

[0104] Step (3) post-treatment: the semi-finished product was heated to 45° C., 1.0% boric acid was added, the mixture was stirred at 200 rpm, the pH was adjusted to 7.0, the reaction was maintained for 30 min, and the mixture was spray-dried to prepare a powdered retanning agent.

[0105] Comparative Example 9

[0106] The difference from Example 1 is that in step (1), the aldehyde content does not reach 50%:

[0107] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0108] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 8% was gelatinized at 60° C. for 40 minutes, and sodium periodate (0.8 times the molar amount of the starch on a dry basis) was added and oxidized at 35° C. for 8 hours, resulting in an aldehyde content of 45%. When the reaction was terminated, ethylene glycol (0.5 times the molar amount of the sodium periodate) was added to obtain a raw material mixture;

[0109] Step (2) Molecular modification: Sodium sulfite at a molar ratio of 0.6:1 to aldehyde groups is added to the raw material mixture, the pH is adjusted to 8.0, and sulfonation is carried out at 50° C. for 4 hours; then, while maintaining the pH at 8.5 and the system temperature at 35° C., a polyethylene glycol diglycidyl ether (PEG 400) aqueous solution diluted to 20% is slowly added dropwise at a rate of 1 mL / min (addition amount: 0.5% of starch dry basis), and disodium EDTA with a molar number of 5% of aldehyde groups is added, the mixture is stirred at a constant speed of 200 rpm and nitrogen is introduced for protection, and the reaction is carried out at a constant temperature for 2 hours to obtain a semi-finished product;

[0110] Step (3) post-treatment: the semi-finished product was heated to 45° C., 0.3% boric acid was added, the mixture was stirred at 200 rpm, the pH was adjusted to 7.0, the reaction was maintained for 30 min, and the mixture was spray-dried to prepare a powdered retanning agent.

[0111] Comparative Example 10

[0112] The difference from Example 1 is that in step (1), ethylene glycol is added in excess:

[0113] A method for preparing a high-aldehyde oxidized starch retanning agent comprises the following steps:

[0114] Step (1) Pretreatment and oxidation: Waxy corn starch with an amylose content of 8% was gelatinized at 60° C. for 40 minutes, and sodium periodate (0.8 times the molar amount of the starch on a dry basis) was added and oxidized at 35° C. for 8 hours, with an aldehyde content of 50%. When the reaction was terminated, ethylene glycol (0.8 times the molar amount of the sodium periodate) was added to obtain a raw material mixture;

[0115] Step (2) Molecular modification: Sodium sulfite at a molar ratio of 0.6:1 to aldehyde groups is added to the raw material mixture, the pH is adjusted to 8.0, and sulfonation is carried out at 50° C. for 4 hours; then, while maintaining the pH at 8.5 and the system temperature at 35° C., a polyethylene glycol diglycidyl ether (PEG 400) aqueous solution diluted to 20% is slowly added dropwise at a rate of 1 mL / min (addition amount: 0.5% of starch dry basis), and disodium EDTA with a molar number of 5% of aldehyde groups is added, the mixture is stirred at a constant speed of 200 rpm and nitrogen is introduced for protection, and the reaction is carried out at a constant temperature for 2 hours to obtain a semi-finished product;

[0116] Step (3) post-treatment: the semi-finished product was heated to 45° C., 0.3% boric acid was added, the mixture was stirred at 200 rpm, the pH was adjusted to 7.0, the reaction was maintained for 30 minutes, and the mixture was spray-dried to prepare a powdered retanning agent.

[0117] Conventional formaldehyde content test method: First, place 2g of leather sample in 50ml of 0.1% sodium lauryl sulfate detergent and extract at 40℃ with a horizontal oscillation frequency of 100 times / min for 1 hour. Then, filter the extract and react with acetone to quantitatively determine the formaldehyde content in the leather sample.

[0118] Test method for formaldehyde content after high-temperature acidic treatment: First, boil 2g of leather sample in hydrochloric acid with a pH of 1 for 3 minutes, then remove and place in 50ml of 0.1% sodium dodecyl sulfate washing solution, and extract at 40°C with a horizontal oscillation frequency of 100 times / min for 1 hour. The extracted solution is then filtered and reacted with acetone to quantitatively determine the formaldehyde content in the leather sample.

[0119] Comparison of softness, fullness, firmness and surface feel of cowhide upper leather after retanning: the evaluation criteria and grading are shown in Table 1:

[0120] Table 1

[0121] Level 0 Level 1 Level 2 Level 3 Level 4 Softness soft Softer generally Harder hard Fullness full Fuller generally More wrinkled wrinkles Firmness Firming Firmer generally relatively loose Loose Surface feel Smooth Smoother generally relatively dry dryness

[0122] The test results are shown in Table 2.

[0123] Table 2

[0124]

[0125]

[0126]

[0127] Due to the lack of molecular protection structure, the aldehyde group of commercial retanning agent is directly exposed to acid and heat environment, and is hydrolyzed to formaldehyde through electrophilic addition-elimination reaction (hydrogen ion attacks C=O bond). At the same time, the residual metal ions (Fe 3+ etc.) catalyzes the cleavage of β-glycosidic bonds, resulting in a surge in formaldehyde release and swelling and loosening of leather fibers; while the embodiment of this patent blocks the aldehyde hydrolysis path through the triple synergistic effect of sulfonic acid group electrostatic repulsion to shield hydrogen ions, borate bond (BO) to capture free protons, and EDTA chelate ring (five-membered ring) to inactivate metal ions, thereby reducing formaldehyde release. At the same time, the flexible cross-linked network of polyethylene glycol (ether bond-O-) gives collagen fibers dynamic resilience, achieving a simultaneous improvement in softness and fullness.

[0128] The differences in the performance of Comparative Examples 1-10 compared with Example 1 are as follows: Comparative Example 1 (15% amylose) has a molecular crystal region that hinders the continuous coating of sulfonic acid groups, exposing aldehyde groups, and acid attack releases formaldehyde; Comparative Example 2 (excessive sodium periodate) causes excessive oxidation of aldehyde groups to carboxyl groups, which destroy the electrostatic balance of collagen after protonation, resulting in looseness; Comparative Example 3 (insufficient sulfonation) causes the electrostatic shielding layer coverage to be less than 40%, and the acid-catalyzed hydrolysis rate is increased; Comparative Example 4 (excessive sulfonation agent) weakens the stability of the borate ester bond due to the competition of sulfite for chelating boric acid; Comparative Example 5 (PEG 1200) has a loose cross-linked network due to the reduction of long-chain molecular motion entropy; in Comparative Example 6 (no EDTA), free Fe 3+ The degradation of aldehyde radicals was catalyzed by the Fenton reaction; in comparative examples 7 / 8 (no / excess boric acid), the proton-capturing ability of the five-membered ring borate was lost or boric acid crystals were formed, which destroyed the surface feel; in comparative example 9 (aldehyde groups <50%), the fiber filling collapsed due to insufficient cross-linking sites; in comparative example 10 (excess ethylene glycol), the residual hydroxyl groups condensed with the aldehyde groups, reducing the effective cross-linking sites.

Claims

1. A method for preparing a high-aldehyde oxidized starch retanning agent, characterized in that: The following steps are involved: Step (1) pretreatment and oxidation: gelatinize waxy corn starch having an amylose content of ≤10%, add sodium periodate in an amount of 0.8-1.2 times the molar amount of the starch on a dry basis, and oxidize until the aldehyde content is ≥50%, then add ethylene glycol in an amount of 0.5-0.6 times the molar amount of the sodium periodate to obtain a raw material mixture; Step (2) Molecular modification: adding a sulfonate in a molar ratio of 0.6-0.9:1 to the aldehyde group to the raw material mixture, adjusting the pH to 8.0-9.0, and after sulfonation, adding 0.5% to 1.5% of the dry weight of starch to a polyethylene glycol diglycidyl ether dilution to obtain a semi-finished product; Step (3) post-treatment: heating the semi-finished product to 45-50°C, adding 0.3% to 0.8% by mass of a stabilizer, adjusting the pH to 7.0-8.0, and drying after the reaction to prepare a powdered high-aldehyde oxidized starch retanning agent.

2. The method for preparing a high-aldehyde oxidized starch retanning agent according to claim 1, wherein In step (1), the gelatinization conditions are 60-80°C for 20-40 min; and the oxidation reaction conditions are 35-40°C for 4-8 h.

3. The preparation method of the high-aldehyde oxidized starch retanning agent according to claim 1, wherein In step (2), the sodium sulfite or sodium bisulfite is used, and the sulfonation conditions are: sulfonation at 50-60°C for 2-4 hours.

4. The preparation method of the high-aldehyde oxidized starch retanning agent according to claim 1, wherein In step (2), the process of adding polyethylene glycol diglycidyl ether is as follows: under the conditions of pH 8.5-9.0 and system temperature 35-40°C, polyethylene glycol diglycidyl ether is diluted to an aqueous solution with a mass fraction of 20% to 30%, and is slowly added dropwise to the reaction system at a rate of 1-2 mL / min, while maintaining a uniform stirring speed of 200-300 rpm and introducing nitrogen protection.

5. The preparation method of the high-aldehyde oxidized starch retanning agent according to claim 4, wherein The molecular weight of the polyethylene glycol diglycidyl ether is 400–1000 Da.

6. The method for preparing a high-aldehyde oxidized starch retanning agent according to claim 1, wherein In step (2), polyethylene glycol diglycidyl ether is added, and disodium EDTA is added in an amount of 5% to 10% of the molar number of aldehyde groups.

7. The method for preparing a high-aldehyde oxidized starch retanning agent according to claim 1, wherein In step (3), the stabilizer is boric acid.

8. The method for preparing a high-aldehyde oxidized starch retanning agent according to claim 1, wherein In step (3), the semi-finished product is heated to 45-50°C, 0.3% to 0.8% by mass of a stabilizer is added, the mixture is mixed uniformly at a stirring rate of 200-300 rpm, the pH is adjusted to 7.0-8.0, the reaction is maintained under this condition for 25-35 minutes, and then dried to prepare a powdered high-aldehyde oxidized starch retanning agent.

9. A high-aldehyde oxidized starch retanning agent prepared by the method for preparing a high-aldehyde oxidized starch retanning agent according to any one of claims 1 to 8.

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