Temperature-controlled slow-release solid expanding agent, preparation method and application thereof

Abstract

According to the temperature-control slow-release type solid expanding agent, the preparation method and the application thereof, a proper amount of alkali and sodium polyacrylate are dispersed in water, and a first mixed system is formed; acrylic acid and a cross-linking agent are continuously added into the first mixed system, and a second mixed system is formed; adding a proper amount of initiator into the second mixed system to enable the second mixed system to be subjected to cross-linking reaction, and drying to obtain the solid expanding agent formed by coating alkali with sodium polyacrylate copolymer gel. When the gel absorbs water and expands, the purpose of slowly and uniformly dissolving alkali in the depilating-liming liquid is achieved, the temperature stability of the depilating-liming liquid is effectively improved, and skin protein damage caused by alkali heat release is avoided. Besides, the solid expanding agent has wide applicability, is suitable for a depilation-alkali expansion process taking various animal skins as raw materials, can improve the product quality and the processing efficiency, can completely replace lime, can reduce environmental pollution, and has remarkable economic and environmental benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of animal skin processing, and particularly relates to a temperature-controlled slow-release solid swelling agent, a preparation method and application thereof. BACKGROUND

[0002] The main component of animal skin is collagen fiber, which can be used to produce products such as leather, gelatin, food and biomedical materials. Among them, the unhairing process as the core link of animal skin collagen utilization is directly related to the quality, production efficiency and environmental benefits of the product.

[0003] In recent years, sulfur-free and ash-free cleaning technologies represented by enzyme unhairing and oxidation-reduction unhairing have become an important innovation direction due to their environmental friendliness, representing the technical progress and future development trend in this field. These technologies aim to eliminate or significantly reduce the use of harmful substances to meet increasingly stringent environmental regulations. In the practical application of sulfur-free and ash-free unhairing processes (such as enzyme unhairing and oxidation-reduction unhairing), controlling the state of the hide, especially the swelling degree of the skin surface, is crucial for unhairing efficiency. Currently, sodium hydroxide (NaOH) and potassium hydroxide (KOH) are still the most commonly used ash-free chemical swelling agents in this field due to their strong alkalinity and ability to effectively promote hide swelling.

[0004] However, using sodium hydroxide / potassium hydroxide solution as a swelling agent has significant defects and limitations: such as heat damage to the skin caused by the alkaline solution, difficulty in controlling the solution concentration, strong corrosiveness, high transportation and storage costs, and other problems. SUMMARY

[0005] In view of the problems in the background art, the present application provides a temperature-controlled slow-release solid swelling agent, a preparation method and application thereof. By dispersing an appropriate amount of alkali and sodium polyacrylate in water to form a first mixed system, adding acrylic acid and a crosslinking agent to the first mixed system to form a second mixed system, and adding an appropriate amount of initiator to the second mixed system to cause crosslinking reaction of the second mixed system, a solid swelling agent formed by sodium polyacrylate copolymer gel coating alkali is obtained after drying. The alkali is selected from sodium hydroxide and / or potassium hydroxide. By absorbing water with the solid swelling agent, the purpose of slow and uniform dissolution of sodium hydroxide / potassium hydroxide in the unhairing- liming solution is achieved. The specific content is as follows:

[0006] According to a first aspect of the present application, a preparation method of a temperature-controlled slow-release solid swelling agent is provided, which specifically comprises the following steps:

[0007] S1, dispersing an appropriate amount of alkali and sodium polyacrylate in water to form a first mixed system;

[0008] S2, continuing to add acrylic acid and a crosslinking agent to the first mixed system to form a second mixed system;

[0009] S3, adding an appropriate amount of initiator to the second mixed system to make the second mixed system undergo cross-linking reaction, and drying to obtain a solid swelling agent formed by sodium polyacrylate copolymer gel coating alkali;

[0010] The alkali is selected from sodium hydroxide and / or potassium hydroxide.

[0011] The mass ratio of the alkali, sodium polyacrylate, acrylic acid and cross-linking agent is (10-50):(4-20):(0-10):(0.01-0.5).

[0012] Optionally, in step S3, the temperature of the cross-linking reaction is 40-60°C.

[0013] Optionally, in step S3, the time of the cross-linking reaction is 2-10h.

[0014] Optionally, the mass ratio of the alkali, sodium polyacrylate, acrylic acid and cross-linking agent is (15-30):(5-10):(2-8):(0.1-0.4).

[0015] Optionally, the cross-linking agent is selected from N,N-methylene bisacrylamide, divinylbenzene, ethylene glycol dimethyl acrylate or epichlorohydrin.

[0016] Optionally, the initiator is selected from persulfate, azo compound, potassium persulfate-sodium bisulfite or ammonium persulfate-sodium bisulfite.

[0017] Optionally, steps S1-S3 are all carried out under stirring, wherein the stirring rate is 60-150r / min.

[0018] According to a second aspect of the present application, a temperature-controlled slow-release solid swelling agent is provided, which is obtained according to the preparation method described above.

[0019] According to a third aspect of the present application, an application of a temperature-controlled slow-release solid swelling agent is provided, which is used for the unhairing-alkali swelling treatment of animal hides.

[0020] Optionally, the unhairing-alkali swelling treatment comprises:

[0021] The animal hides, water and unhairing enzyme preparation are added to the unhairing drum for the first rotation treatment to loosen the roots of the hairs on the surface of the animal hides.

[0022] The solid swelling agent is continuously added to the unhairing drum for the second rotation treatment to make the hairs on the surface of the animal hides fall off, and the raw hides are obtained.

[0023] adding the bare skin and the solid swelling agent into a dehairing drum and performing a third rotation process, so that the bare skin swells under the action of the alkali released by the solid swelling agent;

[0024] Wherein, in the first rotation treatment and the second rotation treatment, the mass ratio of the animal skin, water, dehairing enzyme preparation and solid expander is 100: (50-300): (0.1-3.0): (0.5-10.0);

[0025] In the third rotation treatment, the mass ratio of the naked animal skin to the solid expander is 100:(1-15).

[0026] Compared with the existing technology, this application has the following advantages:

[0027] The present application provides a temperature-controlled sustained-release solid expansion agent, a preparation method, and its application. The preparation method comprises the following steps: dispersing an appropriate amount of alkali and sodium polyacrylate in water to form a first mixed system; continuously adding acrylic acid and a cross-linking agent to the first mixed system to form a second mixed system; adding an appropriate amount of initiator to the second mixed system to cause a cross-linking reaction in the second mixed system, and after drying, obtaining a solid expansion agent formed by a sodium polyacrylate copolymer gel coated with alkali; the alkali is selected from sodium hydroxide and / or potassium hydroxide; the mass ratio of the alkali, sodium polyacrylate, acrylic acid, and cross-linking agent is (10-50):(4-20):(0-10):(0.01-0.5). The temperature-controlled sustained-release solid expansion agent obtained by the above preparation method can be used for dehairing-alkali expansion treatment of animal skins.

[0028] The preparation method of the temperature-controlled slow-release solid expansion agent provided in the present application is as follows: a first mixed system is formed by dispersing an appropriate amount of alkali and sodium polyacrylate in water; acrylic acid and a cross-linking agent are continuously added to the first mixed system to form a second mixed system; an appropriate amount of initiator is added to the second mixed system to cause a cross-linking reaction in the second mixed system, and after drying, a solid expansion agent formed by a sodium polyacrylate copolymer gel-coated alkali is obtained; wherein the alkali is selected from sodium hydroxide and / or potassium hydroxide. The solid expansion agent formed by the sodium polyacrylate copolymer gel-coated alkali absorbs water and expands. On the one hand, the purpose of slowly and evenly dissolving sodium hydroxide and / or potassium hydroxide in the dehairing-liming liquid is achieved, overcoming the problem of excessive dissolution speed of traditional expansion agents; the release rate of the alkali can also be accurately controlled, so that the solid expansion agent continues to play a role in the animal skin processing process, ensuring that the skin fibers are fully and evenly expanded, effectively improving the temperature stability of the dehairing-liming liquid, avoiding leather damage and collagen loss, and providing an efficient and safe expansion effect for the dehairing-liming treatment of animal skins.

[0029] On the other hand, the pH value and the degree of skin surface expansion caused by the slow dissolution of the solid expanding agent are coordinated with the penetration of the enzyme and other depilatory materials, which can achieve the rapid penetration of the enzyme to the bottom of the hair follicle and the loosening of the hair root, and at the same time, the loosened hair is removed from the skin by mechanical friction, thereby achieving the purpose of efficient and safe depilation. The above-mentioned solid expanding agent is especially suitable for the depilation-alkali expansion link of the sulfur-free and ash-free depilation process, which can effectively improve the product quality and processing efficiency, reduce the pollution to the environment, and has significant economic and environmental benefits.

[0030] In addition, the expanding agent of the present application is in a solid form, which is convenient for transportation, storage and use. Compared with traditional alkali expanding agent, it does not need complex concentration adjustment and transportation equipment, which reduces the operation difficulty and cost. At the same time, its use process is simple, which can improve the process efficiency and reduce manual intervention. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0032] Figure 1 The preparation method flow chart of the temperature-controlled slow-release solid expanding agent provided by the embodiments of the present application is shown. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely in the embodiments of the present application combined with the drawings. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. The following description of at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, anyone can obtain any product same or similar to the present application under the inspiration of the present application or by combining the present application with other prior art features, which falls within the protection scope of the present application. In addition, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0034] Unless otherwise indicated, conventional methods of chemistry, biochemistry, molecular biology, recombinant DNA techniques and pharmacology, including the generation of transgenic animals, are described in detail in the literature of which the disclosure is aware, and to which the skilled person will be familiar. The experimental procedures and conditions described in the examples below are not intended to be limiting, and modifications can be made within the scope of the present application. Reagents and other materials used are conventional reagents available commercially unless otherwise indicated. In addition, the drawings accompanying the present application are schematic illustrations of embodiments of the present application and are not necessarily drawn to scale. Like reference numerals in the various drawings indicate like or similar elements, so that repeated description is omitted for clarity. Some of the block diagrams shown in the drawings are functional entities that do not necessarily correspond to physically or logically independent entities.

[0035] Techniques, methods, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail herein. However, where appropriate, such techniques, methods, and apparatus can be regarded as part of the present disclosure.

[0036] Furthermore, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict between them.

[0037] Traditional unhairing processes rely on sodium sulfide and lime (lime-alkali method), which are effective but generate a large amount of pollution waste containing sulfur and lime, severely restricting the green and sustainable development of the industry. In recent years, sulfur-free and lime-free cleaning technologies represented by enzymatic unhairing and oxidation-reduction unhairing have become an important innovation direction due to their environmental friendliness, representing the technical progress and future development trend in this field. These technologies aim to eliminate or significantly reduce the use of harmful substances to meet increasingly stringent environmental regulations.

[0038] In the practical application of sulfur-free and lime-free unhairing processes (such as enzymatic unhairing and oxidation-reduction unhairing), the regulation of the state of the hide, especially the degree of swelling of the skin surface, is crucial to the efficiency of unhairing. Moderate swelling can increase the mechanical friction of the skin surface, facilitating the loosening of the hair roots and the removal of the hair; and a soft skin grain structure is conducive to the penetration of the unhairing agent (enzyme or oxidation-reduction material) into the skin to act on the hair roots. The degree of swelling of the hide is closely related to the pH value of the unhairing bath, while the pH value significantly affects the activity and stability of the enzyme or oxidation-reduction material. Therefore, precise regulation of the pH value of the bath and the resulting degree of skin swelling is a key link to achieve efficient and safe clean unhairing. Currently, sodium hydroxide (NaOH) and potassium hydroxide (KOH) are still the most commonly used lime-free chemical swelling agents in this field due to their strong alkalinity and the ability to effectively promote the swelling of the hide.

[0039] However, using sodium hydroxide / potassium hydroxide solution as a swelling agent has significant defects and limitations:

[0040] Dissolution heat and skin damage: the dissolution process of sodium hydroxide / potassium hydroxide is exothermic, which can easily cause the local or overall temperature of the depilatory bath to rise sharply. High temperature can promote the hydrolysis of skin collagen fibers, destroy their natural structure, cause significant decline in the physical and mechanical properties of leather strength and toughness, and lead to collagen loss, which seriously damages product quality.

[0041] Concentration control difficulty and uneven effect: the dissolution rate of alkali is too fast, and it is difficult to accurately control the dissolution rate and final concentration. High concentration of alkali itself is also accompanied by exothermic effect. This leads to uneven distribution of alkali concentration in the bath, making it difficult to achieve slow, uniform and controllable swelling of the hide. Concentration fluctuations directly affect the stability of pH value and the uniformity of hide swelling, thereby affecting the synergy of depilatory agent penetration and depilation effect, often requiring repeated adjustment of process parameters, reducing process efficiency and stability.

[0042] Operation safety and cost: strong alkaline sodium hydroxide / potassium hydroxide solution has strong corrosive properties, posing a corrosion threat to production equipment, storage and transportation containers, and posing a greater risk to the safety of operators. Its transportation and storage also require special conditions, which is relatively high in cost.

[0043] Poor process adaptability: the existing alkali agent has the characteristics of fast dissolution, which is fundamentally contradictory to the process requirement of slow and uniform swelling, and cannot meet the requirement of fine and gradual pH value control for modern clean depilation technology, especially enzyme method and oxidation-reduction method.

[0044] In order to overcome the inherent defects of existing alkali agent application and solve the problems of skin damage caused by dissolution heat, concentration control difficulty, uneven swelling, operation risk, etc., the first aspect of the present application provides a preparation method of a temperature-controlled slow-release solid swelling agent. Figure 1 The preparation method of the temperature-controlled slow-release solid swelling agent provided by the embodiments of the present application is shown in the flow chart of the preparation method; as shown in Figure 1 The preparation method specifically includes the following steps:

[0045] S1, dispersing an appropriate amount of alkali and sodium polyacrylate in water to form a first mixed system;

[0046] S2, continue to add acrylic acid and a crosslinking agent to the first mixed system to form a second mixed system;

[0047] S3, adding an appropriate amount of initiator to the second mixed system to make the second mixed system undergo crosslinking reaction, and obtaining a solid swelling agent formed by sodium polyacrylate copolymer gel coating alkali after drying;

[0048] Among them, the alkali is selected from sodium hydroxide and / or potassium hydroxide;

[0049] The mass ratio of the base, sodium polyacrylate, acrylic acid, and crosslinking agent is (10-50):(4-20):(0-10):(0.01-0.5).

[0050] It should be noted that the appropriate amount of base and sodium polyacrylate are dispersed in water to form a first mixed system, which includes dissolving sodium hydroxide and / or potassium hydroxide solids in water, at which time the solution releases a large amount of heat, and after the temperature of the base solution cools to 20-40℃, the sodium polyacrylate solution is slowly added to the base solution, and the slow addition rate is 0.5-2.0 mL / min·L.

[0051] It should be noted that, for example, the temperature of the base solution can be one of 20℃, 25℃, 30℃, 35℃, 40℃, or a range value of any two thereof. When the temperature of the base solution is controlled at 20-40℃, it is beneficial to maintain the physicochemical properties of the sodium polyacrylate solution stable, avoid "local overheating", and make the sodium polyacrylate solution uniformly dispersed, so as to ensure the stability of the subsequent reaction.

[0052] It should be noted that, for example, the slow addition rate can be 0.5 mL / min·L, 0.8 mL / min·L, 1.0 mL / min·L, 1.2 mL / min·L, 1.5 mL / min·L, 1.8 mL / min·L, 2.0 mL / min·L, and the slow addition can control the pH value fluctuation of the solution within ±0.3, the mixing heat of the base solution and the sodium polyacrylate is uniformly released, and the local temperature is prevented from exceeding 40℃, and at the same time, the carboxylate (-COO - ) of the sodium polyacrylate can be fully chelated with Na + , K + of the sodium hydroxide and / or potassium hydroxide to form a stable water-soluble complex. For the slow addition rate, this application is only as an enumeration, not as a limitation to the reaction system.

[0053] It should also be noted that when the content of acrylic acid is 0, the sodium polyacrylate and the crosslinking agent in the second mixed system are crosslinked in the presence of the initiator, the sodium hydroxide and / or potassium hydroxide is dispersed in the form of an aqueous solution in the pores of the sodium polyacrylate crosslinked network, and its migration is limited by the three-dimensional structure of the gel. The carboxyl group (-COO - ) of the sodium polyacrylate exchanges ions with Na + , K + of the sodium hydroxide and / or potassium hydroxide, and OH - may form hydrogen bonds with the crosslinking agent or the sodium polyacrylate segment, enhancing the coating stability, and obtaining a solid expanding agent formed by the sodium polyacrylate copolymer gel coated with the base.

[0054] When the content of acrylic acid is greater than 0, the second mixed system is poly sodium acrylate, acrylic acid and crosslinking agent, which are crosslinked in the presence of initiator. The acrylic acid is free radical polymerized under the action of initiator to generate poly acrylic acid segment, and at the same time, the carboxylate ion (-COO - ) of poly sodium acrylate forms an ion-covalent mixed network. Further, the crosslinking agent reacts with the acrylic acid / poly sodium acrylate segment through double bond to form a three-dimensional network structure. The carboxyl group in the interpenetrating network poly sodium acrylate copolymer ion-exchange reacts with sodium / potassium ions in the alkali solution to form a crosslinked structure. The molecular chains of the copolymer interact with each other through hydrogen bonds and van der Waals forces to further enhance the stability of the gel.

[0055] It should be further noted that the mass ratio of the alkali, poly sodium acrylate, acrylic acid and crosslinking agent is (10-50):(4-20):(0-10):(0.01-0.5). For example, the mass ratio of the alkali, poly sodium acrylate, acrylic acid and crosslinking agent can be one of 10:4:0:0.01, 10:4:1:0.01, 15:5:2:0.2, 20:5:2:0.2, 25:5:2:0.2, 30:8:5:0.3, 40:10:6:0.4, 50:15:8:0.5, 50:20:10:0.5 or a range value of any two thereof. When the mass ratio of the alkali, poly sodium acrylate, acrylic acid and crosslinking agent is controlled to be (10-50):(4-20):(0-10):(0.01-0.5), the poly sodium acrylate copolymer gel network structure is stable, the crosslinking density is high, the efficiency of alkali coating is good, and the diffusion path of the alkali in the network is long. When the gel solid absorbs water and swells, the release rate of the alkali is slowed down.

[0056] Table 1 is a comparison table of traditional sodium hydroxide / potassium hydroxide solution swelling and the temperature-controlled slow-release solid swelling agent of the present application. As shown in Table 1, the traditional sodium hydroxide / potassium hydroxide solution swelling has fast heat release and is not easy to control, and the transportation is complex. When the solid swelling agent of the present application is subjected to depilation-alkali treatment, the alkali is coated in the poly sodium acrylate copolymer gel network. When the gel absorbs water and swells, the alkali dissolves relatively slowly and uniformly, which can maintain the temperature stability of the bath. At the same time, the solid form is convenient to operate, and the swelling effect is uniform, which can further improve the product quality.

[0057] Table 1

[0058] Comparison item Traditional sodium hydroxide / potassium hydroxide solution expander Temperature-controlling slow-release solid expander of the present application Dissolution speed Fast, difficult to control Relatively slow, uniform Temperature stability Poor, dissolution heat release easily damages egg white Good, can maintain bath temperature stable Operation convenience Liquid alkali transportation, storage and preparation are complex Solid form, simple operation Expanding effect Uneven, affecting product quality Uniform, improving product quality

[0059] The preparation method of the temperature-controlled slow-release solid expansion agent provided in the present application can adjust the slow-release performance, strength and stability of the alkali in the sodium polyacrylate copolymer gel-coated alkali by controlling parameters such as the concentration of the alkaline solution, the addition amount of sodium polyacrylate, acrylic acid and cross-linking agent, thereby achieving precise control of the dissolution rate and heat release rate of the solid expansion agent. The above-mentioned solid expansion agent is suitable for the dehairing-alkali expansion process using various animal skins as raw materials, and is particularly suitable for the dehairing-alkali expansion link of the sulfur-free and ash-free dehairing process. It has a slow and uniform dissolution effect, can overcome the problem of the excessively fast dissolution rate of traditional expansion agents, and ensure that the leather fibers are fully and evenly expanded; at the same time, it ensures that the temperature is effectively controlled during the animal skin processing process to avoid damage to the skin protein, and can achieve a uniform alkali expansion effect on the skin fibers.

[0060] In some embodiments, in step S3, the temperature of the cross-linking reaction is 40-60°C.

[0061] It should be noted that the temperature of the cross-linking reaction is 40-60°C. For example, the temperature of the cross-linking reaction can be in the range of one or any two of 40°C, 45°C, 50°C, 55°C, and 60°C.

[0062] In this embodiment, when the cross-linking reaction temperature is controlled between 40°C and 60°C, the cross-linking agent uniformly releases active sites, and the cross-linking reaction between the acrylic acid monomer and the sodium polyacrylate chain segments proceeds simultaneously, forming a uniform three-dimensional network with moderate gel porosity, which facilitates uniform alkali coating. Temperatures above 60°C may result in concentrated reaction heat release, leading to localized overheating and implosion.

[0063] In some embodiments, in step S3, the cross-linking reaction time is 2 to 10 hours.

[0064] It should be noted that the cross-linking reaction time is 2 to 10 hours. For example, the cross-linking reaction time can be in the range of one or any two of 2 hours, 3 hours, 4 hours, 5 hours, 8 hours, and 10 hours. The preferred cross-linking reaction time is 2 to 4 hours.

[0065] In this embodiment, the cross-linking reaction time is controlled within 2 to 10 hours, the cross-linking point density is moderate, and a uniform cross-linking network is formed. The cross-linking degree of the polyacrylic acid can be controlled, and the stability of the gel can be improved. At this time, the alkali coating efficiency is optimal, thereby achieving the purpose of uniform and slow release of the alkali.

[0066] In some embodiments, the preferred mass ratio of the base, sodium polyacrylate, acrylic acid, and cross-linking agent is (15-30): (5-10): (2-8): (0.1-0.4).

[0067] It should be noted that the mass ratio of the base, sodium polyacrylate, acrylic acid and crosslinking agent is preferably (15-30):(5-10):(2-8):(0.1-0.4), for example, the mass of the base, sodium polyacrylate, acrylic acid and crosslinking agent can be one of 15:5:2:0.2, 20:5:3:0.3, 25:5:5:0.3, 30:10:8:0.4 or a range value of any two.

[0068] In this embodiment, by controlling the mass ratio of the base, sodium polyacrylate, acrylic acid and crosslinking agent to be (15-30):(5-10):(2-8):(0.1-0.4), the precise design of the gel network can be realized, the ideal three-dimensional network structure is balanced, and the efficiency of base coating and the controllability of slow release are considered.

[0069] In some embodiments, the crosslinking agent is selected from N,N-methylenebisacrylamide, divinylbenzene, ethylene glycol dimethacrylate or epichlorohydrin.

[0070] It should be noted that the crosslinking agent in this application is preferably N,N-methylenebisacrylamide.

[0071] In this embodiment, the crosslinking agent is selected from N,N-methylenebisacrylamide, divinylbenzene, ethylene glycol dimethacrylate or epichlorohydrin, which is beneficial to uniform distribution of crosslinking points, good stability of sodium polyacrylate copolymer gel, high base coating rate, and unobstructed release channel, realizing the swelling-coating balance of the gel network.

[0072] In some embodiments, the initiator is selected from persulfate, azo compound, potassium persulfate-sodium bisulfite or ammonium persulfate-sodium bisulfite.

[0073] It should be noted that the persulfate includes potassium persulfate, sodium persulfate, ammonium persulfate, and the persulfate initiator is preferably potassium persulfate, sodium persulfate. The azo compound includes azobisisobutyronitrile, azobisisoheptyl nitrile, dimethyl azobis isobutyrate, and the azo compound initiator is preferably azobisisobutyronitrile, dimethyl azobis isobutyrate. In this embodiment, the initiator is selected from persulfate, azo compound, potassium persulfate-sodium bisulfite or ammonium persulfate-sodium bisulfite, the free radical generation rate is stable during initiation, the sodium polyacrylate copolymer chain growth has high synchronicity, the crosslinking points are uniformly distributed, the base is efficiently coated, and the subsequent slow release of the base is facilitated.

[0074] In some embodiments, steps S1-S3 are all carried out under stirring, wherein the stirring rate is 60-150 r / min.

[0075] It should be noted that the stirring rate is 60-150 r / min, and for example, the stirring rate can be one of 60 r / min, 70 r / min, 80 r / min, 90 r / min, 100 r / min, 120 r / min, 150 r / min or a range value of any two thereof.

[0076] In this embodiment, the physical properties (such as solubility, viscosity) of the alkali, sodium polyacrylate, acrylic acid and crosslinking agent are quite different. When the stirring rate is controlled at 60-150 r / min, it is beneficial to uniformly disperse the sodium polyacrylate and the acrylic acid monomer, and at the same time, it allows the crosslinking agent (such as N,N-methylenebisacrylamide) to be fully dissolved, avoiding uneven reaction caused by too high local concentration. In addition, the stirring rate of 60-150 r / min is beneficial to the more orderly reaction of sodium polyacrylate and acrylic acid with the crosslinking agent during polymerization, forming a dense and uniform network structure, ensuring that the alkali is uniformly coated in the sodium polyacrylate copolymer gel network with a dense structure and stable mechanical properties, and avoiding reaction out of control or structural defects caused by improper stirring.

[0077] In a second aspect, the present application provides a temperature-controlled slow-release solid swelling agent, which is obtained according to the above preparation method.

[0078] In a third aspect, the present application provides an application of a solid swelling agent, and the above-mentioned solid swelling agent is used for the unhairing-alkali swelling treatment of animal hides.

[0079] In this embodiment, by using the solid swelling agent for the unhairing-alkali swelling treatment of animal hides, the purpose of slow and uniform dissolution of sodium hydroxide / potassium hydroxide in the unhairing- liming liquid is achieved, which can effectively improve the temperature stability of the unhairing- liming liquid and avoid damage to the skin protein caused by the heat release of sodium hydroxide / potassium hydroxide.

[0080] In some embodiments, the above unhairing-alkali swelling treatment comprises: adding animal hides, water and unhairing enzyme preparation into an unhairing drum, and performing a first rotation treatment to loosen the hair roots on the surface of the animal hides; continuing to add the solid swelling agent into the unhairing drum to perform a second rotation treatment, so that the hairs on the surface of the animal hides fall off to obtain bare hides; adding the bare hides and the solid swelling agent into the unhairing drum to perform a third rotation treatment, so that the bare hides swell under the action of the alkali released by the solid swelling agent; wherein in the first rotation treatment and the second rotation treatment, the mass ratio of the animal hides, water, unhairing enzyme preparation and solid swelling agent is 100:(50-300):(0.1-3.0):(0.5-10.0); and in the third rotation treatment, the mass ratio of the bare animal hides and the solid swelling agent is 100:(1-15).

[0081] It should be noted that the depilation enzyme preparation is selected from one or more of alkaline protease, neutral protease, keratinase, collagenase, elastase, trypsin, glycosidase, cutinase, lipase, cellulase.

[0082] It should be noted that the mass ratio of the animal skin, water, depilation enzyme preparation and solid expanding agent is 100:(50-300):(0.1-3.0):(0.5-10.0), for example, the mass ratio of the animal skin, water, depilation enzyme preparation and solid expanding agent can be one of 100:50:0.5:0.5, 100:100:0.5:4.0, 100:200:2.0:7.0, 100:300:3.0:10.0 or a range value of any two.

[0083] It should be noted that the mass ratio of the bare animal skin and the solid expanding agent is 100:(1-15), for example, the mass ratio of the bare animal skin and the solid expanding agent can be one of 100:1, 100:5, 100:10, 100:15 or a range value of any two.

[0084] In specific implementation, the animal skin treated by sufficient water soaking is put into a depilation drum, the solid-liquid ratio of the animal skin and water is controlled to be 20wt%-30wt%, the temperature is controlled to be 25-30°C, the drum is started, the rotating speed is set to be 2-4r / min, the depilation enzyme preparation is added, the first rotation treatment is performed, and the animal skin surface is loosened for 4 hours. The above-mentioned solid expanding agent is put into the drum according to 0.1-1.5% of the weight of the animal skin, and the second rotation treatment is performed. Within the first 2 hours after the addition of the material, the temperature in the drum is controlled to be 25-30°C, the pH value is monitored every 30 minutes, and it is ensured that the pH value is maintained between 10-12. After 2 hours, the temperature is increased to 30°C, and the rotation is continued for 3 hours. During this period, the pH value is monitored every hour, and the addition amount of the above-mentioned solid expanding agent is adjusted in time according to the monitoring result, so that the pH value is stabilized at about 10.5. After the hair is checked to have been sufficiently removed, clean water is added to enlarge the liquid ratio to 200-300%, the hair is filtered, the hair on the animal skin surface is removed, and the bare skin is obtained. The above-mentioned solid expanding agent is put into the drum according to 2-4% of the weight of the bare skin, the third rotation treatment is performed, the expanding liquid temperature is maintained to be not higher than 20-25°C, the rotation is performed for 30 minutes and the standing is performed for 30 minutes, which is repeated twice, the rotation is performed for 5 minutes every hour, and the total rotation is 18 times, so that the bare skin is subjected to alkali expansion under the action of the alkali released by the solid expanding agent.

[0085] It should be further explained that when the animal skin is yak skin, the yak skin in the alpine region is affected by the low temperature environment during growth, and the fibers are more tough, so more solid expanding agent is needed to achieve the ideal expansion effect. Therefore, in actual application, the amount of expanding agent needs to be adjusted according to the specific characteristics of yak skin, generally increasing by 1% to 2% compared with the amount of cattle skin. During the feeding process of the solid expanding agent, due to the characteristics of yak skin, higher temperature and longer reaction time are required. The initial temperature in the drum is set to 30°C, and the total reaction time is extended to 6 hours. At the same time, due to the low water content of yak skin, the water amount needs to be appropriately increased during the unhairing process to ensure the full dissolution and action of the expanding agent.

[0086] In this embodiment, the solid expanding agent, animal skin and water are mixed, at this time, the solid expanding agent absorbs water and expands, and the sodium polyacrylate copolymer gel coated alkali begins to slowly and uniformly dissolve, overcoming the problem of too fast dissolution speed of traditional expanding agents; the release speed of alkali can also be precisely controlled, so that the solid expanding agent can continuously play a role during the animal skin treatment process, ensuring that the skin fibers are fully and uniformly expanded, effectively improving the temperature stability of the unhairing- liming liquid (the temperature can be maintained at not higher than 30°C), avoiding damage to the skin and loss of collagen, and providing efficient and safe expansion effect for the unhairing- liming treatment of animal skin.

[0087] The change of pH value (i.e. the pH value can be maintained at 10-12) and the expansion degree of the skin surface caused by the slow dissolution of the solid expanding agent is coordinated with the penetration of enzymes and other unhairing materials, which can realize the rapid penetration of enzymes to the bottom of the hair follicle and loosen the hair root, and at the same time, the loosened hair is removed from the skin by mechanical friction, thereby achieving the purpose of efficient and safe unhairing. The above-mentioned solid expanding agent is especially suitable for the unhairing-alkali expansion link of sulfur-free and ash-free unhairing process, which can effectively improve the product quality and processing efficiency, reduce the pollution to the environment, and has significant economic and environmental benefits.

[0088] In order to enable those skilled in the art to more clearly understand the present application, the following examples are used to describe the preparation method and application of the temperature-controlled slow-release solid expanding agent in detail.

[0089] Example 1

[0090] (1) Preparation of solid expanding agent

[0091] 100 kg of sodium hydroxide was placed in a reaction kettle and dissolved in water to form a sodium hydroxide solution. The stirring device was turned on and the stirring speed was maintained at 120 r / min to mix the solution uniformly.

[0092] Sodium polyacrylate solution was prepared by dissolving 30 kg of sodium polyacrylate in water. When the temperature of the sodium hydroxide solution in the reactor was reduced to 25°C, the sodium polyacrylate solution was slowly added to the sodium hydroxide solution. The addition process lasted for 30 min, and stirring was maintained to ensure that the sodium polyacrylate solution was fully dispersed in the sodium hydroxide solution. At this time, a first mixed system was formed.

[0093] N,N-methylenebisacrylamide crosslinking agent solution containing acrylic acid was prepared by dissolving 0.8 kg of N,N-methylenebisacrylamide as a crosslinking agent and 20 kg of acrylic acid in deionized water. The crosslinking agent solution was added to the first mixed system to form a second mixed system.

[0094] The second mixed system was initiated by dropwise addition of 0.1 kg of sodium persulfate initiator. The temperature of the reactor was raised to 50°C to allow the second mixed system to undergo crosslinking reaction. The reaction temperature was maintained at 50°C for 2.5 h. The state of the solution was closely observed during the reaction. As the reaction proceeded, the solution gradually formed a gel solid. After the reaction was completed, the gel solid was allowed to cool naturally to room temperature in the reactor. At this time, the performance of the gel solid was optimal. The gel solid was dried at 80°C under ventilation to obtain a solid swelling agent formed by sodium polyacrylate copolymer gel coating alkali.

[0095] (2) Hair removal of animal skin - alkali swelling treatment

[0096] Yellow cowhide was used as the animal skin. 100 kg of yellow cowhide treated by sufficient water soaking was put into a hair removal drum, and 50 kg of water was added. The temperature was controlled at 28°C. The drum was started, and the rotation speed was set to 2-4 r / min. 0.5 kg of hair removal enzyme preparation was added for the first rotation treatment, and the drum was rotated for 4 hours.

[0097] 1.0 kg of the temperature-controlled slow-release solid swelling agent prepared in step (1) was put into the drum for the second rotation treatment. During the first 2 hours after the addition of the solid swelling agent, the temperature in the drum was controlled at 28°C, and the pH value was monitored every 30 minutes to ensure that the pH value was maintained at 10-12. After 2 hours, the temperature was increased to 30°C, and the drum was rotated for another 3 hours. During this period, the pH value was monitored every hour, and the amount of the solid swelling agent was adjusted in a timely manner based on the monitoring results to stabilize the pH value at about 10.5. After checking that the hair had been fully removed, the liquid ratio was increased to 200% by adding clean water, and the hair was filtered to complete the hair removal process of the yellow cowhide and obtain yellow cowhide crust.

[0098] 5 kg of the solid swelling agent prepared in step (1), 100 kg of yellow cowhide crust, and 100 kg of water were put into the drum for the third rotation treatment. The temperature of the swelling liquid was not higher than 24°C. The drum was rotated for 30 minutes and then rested for 30 minutes. After repeating this process twice, the drum was rotated for 5 minutes every hour for a total of 18 times to complete the alkali swelling of the yellow cowhide crust.

[0099] The dehairing rate of the yellow cowhide was 100%, the swelling rate was 143%, and the collagen loss rate was 1%.

[0100] Example 2

[0101] Compared with Example 1, the difference lies in that:

[0102] In the preparation of the solid swelling agent in step (1), the mass of sodium hydroxide, sodium polyacrylate, N,N-methylene bisacrylamide, and acrylic acid was adjusted to 150 kg, 40 kg, 1.0 kg, and 25 kg, respectively; the stirring rate was adjusted to 100 r / min; and the crosslinking reaction temperature and reaction time were adjusted to 60°C and 4 h, respectively.

[0103] In the dehairing-alkali swelling treatment of the animal hide in step (2), the animal hide was adjusted to yak hide. In the first and second rotation treatments in the dehairing-alkali swelling treatment of the animal hide in step (2), the mass of the yak hide, water, dehairing enzyme preparation, and solid swelling agent was adjusted to 100 kg, 100 kg, 1.0 kg, and 2.0 kg, respectively; the temperature of the second rotation treatment was increased from 30°C to 32°C; the ratio of the added water to the expansion liquid was 300%; and the mass of the solid swelling agent and the yak raw hide in the third rotation treatment was adjusted to 7 kg and 100 kg, respectively.

[0104] The remaining implementation steps and amounts were the same as in Example 1, and the alkali swelling of the yak raw hide was completed.

[0105] The dehairing rate of the yak hide was 100%, the swelling rate was 145%, and the collagen loss rate was 1%.

[0106] Example 3

[0107] Compared with Example 1, the difference lies in that:

[0108] In the preparation of the solid swelling agent in step (1), the base and the initiator were adjusted to potassium hydroxide and potassium persulfate, respectively.

[0109] The remaining implementation steps and amounts were the same as in Example 1, and the alkali swelling of the yellow cowhide was completed.

[0110] The dehairing rate of the yellow cowhide was 100%, the swelling rate was 148%, and the collagen loss rate was 2%.

[0111] Example 4

[0112] Compared with Example 1, the difference lies in that:

[0113] In the preparation of the solid swelling agent in step (1), the base was adjusted to potassium hydroxide and sodium hydroxide.

[0114] The remaining implementation steps and amounts were the same as in Example 1, and the alkali swelling of the yellow cowhide was completed.

[0115] The hair removal rate of the yellow cowhide was 100%, the swelling rate was 146%, and the collagen loss rate was 2%.

[0116] Example 5

[0117] Compared with Example 1, the difference is that:

[0118] The mass of acrylic acid in the preparation of the solid swelling agent in step (1) is adjusted to 0.

[0119] The remaining implementation steps and amounts are the same as in Example 1, and the alkaline swelling of the yellow cowhide is completed.

[0120] The hair removal rate of the yellow cowhide was 100%, the swelling rate was 153%, and the collagen loss rate was 3%.

[0121] Example 6

[0122] Compared with Example 1, the difference is that:

[0123] The masses of sodium hydroxide, sodium polyacrylate, N,N-methylenebisacrylamide, and acrylic acid in the preparation of the solid swelling agent in step (1) are adjusted to 500 kg, 200 kg, 5 kg, and 100 kg, respectively. The remaining implementation steps and amounts are the same as in Example 1, and the alkaline swelling of the yellow cowhide is completed.

[0124] The hair removal rate of the yellow cowhide was 100%, the swelling rate was 162%, and the collagen loss rate was 5%.

[0125] Example 7

[0126] Compared with Example 1, the difference is that:

[0127] The masses of sodium hydroxide, sodium polyacrylate, N,N-methylenebisacrylamide, and acrylic acid in the preparation of the solid swelling agent in step (1) are adjusted to 100 kg, 40 kg, 0.1 kg, and 0 kg, respectively.

[0128] The remaining implementation steps and amounts are the same as in Example 1, and the alkaline swelling of the yellow cowhide is completed.

[0129] The hair removal rate of the yellow cowhide was 95%, the swelling rate was 132%, and the collagen loss rate was 1.0%.

[0130] Comparative Example 1

[0131] Compared with Example 1, the difference is that:

[0132] The preparation of the solid swelling agent in step (1) is not needed.

[0133] The solid swelling agent in the unhairing-alkali swelling treatment of animal hides in step (2) was adjusted to be sodium hydroxide solution. Temperature 28°C, pH 11.0.

[0134] The remaining implementation steps and amounts were the same as in Example 1, and the alkali swelling of the rawhide of the cowhide was completed.

[0135] The unhairing rate of the cowhide was 100%, the swelling rate was 122%, and the collagen loss rate was 10%.

[0136] Comparative Example 2

[0137] Compared with Example 1, the difference is that:

[0138] The preparation of the solid swelling agent in step (1) is not needed.

[0139] The solid swelling agent in the unhairing-alkali swelling treatment of animal hides in step (2) was adjusted to be potassium hydroxide solution. Temperature 28°C, pH 11.0.

[0140] The remaining implementation steps and amounts were the same as in Example 1, and the alkali swelling of the rawhide of the cowhide was completed.

[0141] The unhairing rate of the cowhide was 100%, the swelling rate was 125%, and the collagen loss rate was 15%.

[0142] The unhairing rate, swelling rate, and collagen loss rate of each example were compared with the comparative examples. The alkali swelling of the skin surface increases the mechanical friction of the skin surface, which is beneficial for the hair to fall off from the skin. After the addition of the solid swelling agent in Examples 1-7, the temperature change in the drum was within the range of 0.5°C, the skin was uniformly swollen, and the degree of hydrolysis of collagen was low. After the addition of the alkali swelling solution in Comparative Examples 1-2, the temperature in the drum increased by 5-10°C, the skin surface was excessively swollen, the skin core was insufficiently swollen, and the collagen was severely hydrolyzed.

[0143] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in the present specification.

[0144] For the method embodiments, the acts performed as part of the method embodiments are illustrated in a manner generally most helpful in understanding the pertinent process. The subsequent recitation of acts should not be construed as a limitation on the order in which the acts are performed. Subsequently, the embodiments described in the specification are preferred embodiments, and the acts and components involved are not necessarily essential to the application.

[0145] The temperature-controlling slow-release solid expanding agent, the preparation method and the application thereof are described in detail above. The principles and implementation manners of the application are described by using specific examples. The above description of the embodiments is only used to help understand the method and the core idea of the application. Meanwhile, for those skilled in the art, the specific implementation manners and the application range can be changed according to the idea of the application. In conclusion, the content of the specification should not be understood as a limitation on the application.

Claims

1. A method for preparing a temperature-controlled sustained-release solid expansion agent, characterized in that: The preparation method specifically comprises the following steps: S1. Dispersing an appropriate amount of alkali and sodium polyacrylate in water to form a first mixed system; S2, continuing to add acrylic acid and a cross-linking agent to the first mixed system to form a second mixed system; S3, adding an appropriate amount of initiator to the second mixed system to cause a cross-linking reaction in the second mixed system, and obtaining a solid expansion agent formed by a sodium polyacrylate copolymer gel coated with an alkali after drying; Wherein, the base is selected from sodium hydroxide and / or potassium hydroxide; The mass ratio of the alkali, sodium polyacrylate, acrylic acid and cross-linking agent is (10-50): (4-20): (0-10): (0.01-0.5).

2. The preparation method according to claim 1, characterized in that In step S3, the temperature of the cross-linking reaction is 40-60°C.

3. The preparation method according to claim 1, characterized in that In step S3, the cross-linking reaction time is 2 to 10 hours.

4. The preparation method according to claim 1, characterized in that The mass ratio of the alkali, sodium polyacrylate, acrylic acid and cross-linking agent is (15-30): (5-10): (2-8): (0.1-0.4).

5. The preparation method according to claim 1, characterized in that The crosslinking agent is selected from N,N-methylenebisacrylamide, divinylbenzene, ethylene glycol dimethacrylate or epichlorohydrin.

6. The preparation method according to claim 1, characterized in that The initiator is selected from persulfate, azo compound, potassium persulfate-sodium bisulfite or ammonium persulfate-sodium bisulfite.

7. The preparation method according to claim 1, characterized in that Steps S1 to S3 are all carried out under stirring conditions. Wherein, the stirring rate is 60-150 r / min.

8. A temperature-controlled slow-release solid expansion agent, characterized in that: The solid expansion agent is obtained according to the preparation method according to any one of claims 1 to 7.

9. Use of the solid expansion agent according to claim 8, characterized in that: The solid expander is used for dehairing-alkali expansion treatment of animal skins.

10. The use according to claim 9, characterized in that The depilation-alkali swelling treatment comprises: Adding animal skin, water and dehairing enzyme preparation into a dehairing drum and performing a first rotation treatment to loosen the hair roots on the surface of the animal skin; Continuing to add the solid expander to the dehairing drum for a second rotation process, so that the hair on the surface of the animal skin falls off to obtain bare skin; adding the bare skin and the solid swelling agent into a dehairing drum and performing a third rotation process, so that the bare skin swells under the action of the alkali released by the solid swelling agent; Wherein, in the first rotation treatment and the second rotation treatment, the mass ratio of the animal skin, water, dehairing enzyme preparation and solid expander is 100: (50-300): (0.2-3.0): (0.5-10.0); In the third rotation treatment, the mass ratio of the naked animal skin to the solid expander is 100:(1-15).

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