1. A preparation method of a retanning agent based on chrome-free leather scraps comprises the following steps:

pretreating the chrome-free tanning scraps by adopting urea and hydrochloric acid to obtain pretreated chrome-free tanning scraps;

mixing the pretreated chrome-free tanning waste with sodium hydroxide and a substance containing calcium oxide, and carrying out basic hydrolysis reaction to obtain a hydrolysis product;

and mixing the hydrolysate with an emulsifier, the (methyl) acrylic acid and the methyl methacrylate, and carrying out polymerization reaction to obtain the retanning agent.

2. The method according to claim 1, wherein the temperature of the pretreatment is 70 to 80 ℃ and the time of the pretreatment is 60 to 90 min.

3. The preparation method according to claim 1, wherein the temperature of the basic hydrolysis reaction is 75-85 ℃, and the time of the basic hydrolysis reaction is 120-180 min.

4. The method according to claim 1 or 3, wherein the basic hydrolysis reaction further comprises: adjusting the pH value of the obtained hydrolysis reaction system to 6-7, and carrying out solid-liquid separation to obtain hydrolysis filtrate; and concentrating the hydrolysis filtrate to obtain a hydrolysate.

5. The method according to claim 4, wherein the hydrolysate has a solid content of 35 to 40 wt%.

6. The production method according to claim 1, wherein the (meth) acrylic acid is added in the form of a (meth) acrylic acid solution; the method for preparing the (meth) acrylic acid solution comprises: mixing (methyl) acrylic acid with water, and adjusting the pH value to 5.0-5.5 to obtain a (methyl) acrylic acid solution.

7. The production method according to claim 1, wherein the polymerization reaction is carried out in the presence of an initiator; the initiator is ammonium persulfate solution.

8. The method according to claim 1, wherein the polymerization temperature is 85 to 90 ℃ and the polymerization time is 90 to 120 min.

9. The method of claim 1, further comprising, after the polymerization: and adjusting the pH value of the obtained polymerization reaction system to 5.0-5.5, and mixing with a broad-spectrum bactericide to obtain the retanning agent.

10. The method of claim 1, wherein the chrome-free tanned leather chips comprise any of chrome-free tanned waste leather chips produced by a chrome-free tanning process.

Background

The leather industry is one of the traditional characteristic industries in China, and is used for processing raw hide, one of byproducts of animal husbandry, into leather fabric for people to use. In the leather production process, tanning is an important process for converting leather into leather, and directly determines the quality of finished leather. In the prior tanning agent and the corresponding tanning method, chrome tanned leather prepared by adopting the chrome tanning agent has excellent comprehensive performances of softness, fullness, high strength, storage resistance, washing resistance, difficult decoanning, good damp-heat resistance stability and the like, and is the first of all leather products. Therefore, more than 90% of leather enterprises in the world adopt chrome tanning to prepare leather products.

But the absorptivity of the bare skin to the chromium is 65-75%, and the unabsorbed chromium is discharged into the waste liquid, thereby causing the waste of chromium resources and the pollution to the environment. Meanwhile, a large amount of chromium-containing solid waste (including chromium-containing waste leather scraps, chromium-containing sludge and the like) which is difficult to effectively utilize is generated, and the pollution to the environment is caused. Therefore, the development of clean tanning (including clean less-chromium tanning and clean chromium-free tanning) is a necessary way for ensuring that the leather industry goes through a sustainable development way. In recent years, the tanning industry has gradually begun to produce low chrome or chrome-free tanned hide by making wet white hide. Thus, the environmental pollution caused by chromium is greatly reduced. But at the same time, part of the wet white leather scraps are generated, which causes waste of resources. The main component of the wet white leather scraps is collagen, which is a renewable precious resource, and how to utilize the precious resource is one of the problems to be solved by the industry.

In the research on the recycling of chrome leather scraps, a lot of reports are made in the literature on the methods for the deconning and the treatment, and the methods for the decolouring and the treatment are respectively adopted for the decolouring and the extraction of collagen, industrial gelatin and the like (wary, innocent, heavy, and the like, and the research on the hydrolysis of chrome leather scraps by neutral protease [ J ]. Chinese leather, 2011,30(21): 3-5). However, the methods of debanning and treating chrome-free tanned leather scraps have not been studied.

Disclosure of Invention

The invention aims to provide a preparation method of a retanning agent based on chrome-free tanned leather scraps.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a preparation method of a retanning agent based on chrome-free leather scraps, which comprises the following steps:

pretreating the chrome-free tanning scraps by adopting urea and hydrochloric acid to obtain pretreated chrome-free tanning scraps;

mixing the pretreated chrome-free tanning waste with sodium hydroxide and a substance containing calcium oxide, and carrying out basic hydrolysis reaction to obtain a hydrolysis product;

and mixing the hydrolysate with an emulsifier, the (methyl) acrylic acid and the methyl methacrylate, and carrying out polymerization reaction to obtain the retanning agent.

Preferably, the temperature of the pretreatment is 70-80 ℃, and the time of the pretreatment is 60-90 min.

Preferably, the temperature of the basic hydrolysis reaction is 75-85 ℃, and the time of the basic hydrolysis reaction is 120-180 min.

Preferably, the basic hydrolysis reaction further comprises: adjusting the pH value of the obtained hydrolysis reaction system to 6-7, and carrying out solid-liquid separation to obtain hydrolysis filtrate; and concentrating the hydrolysis filtrate to obtain a hydrolysate.

Preferably, the solid content of the hydrolysate is 35-40 wt%.

Preferably, the (meth) acrylic acid is added in the form of a (meth) acrylic acid solution; the method for preparing the (meth) acrylic acid solution comprises: mixing (methyl) acrylic acid with water, and adjusting the pH value to 5.0-5.5 to obtain a (methyl) acrylic acid solution.

Preferably, the polymerization reaction is carried out in the presence of an initiator; the initiator is ammonium persulfate solution.

Preferably, the temperature of the polymerization reaction is 85-90 ℃, and the time of the polymerization reaction is 90-120 min.

Preferably, the polymerization reaction further comprises: and adjusting the pH value of the obtained polymerization reaction system to 5.0-5.5, and mixing with a broad-spectrum bactericide to obtain the retanning agent.

Preferably, the chrome-free tanned leather chips comprise any of the chrome-free tanned waste leather chips produced by the chrome-free tanning process.

The invention provides a preparation method of a retanning agent based on chrome-free leather scraps, which comprises the following steps: pretreating the chrome-free tanning scraps by adopting urea and hydrochloric acid to obtain pretreated chrome-free tanning scraps; mixing the pretreated chrome-free leather scraps with sodium hydroxide and a substance containing calcium oxide, and carrying out basic hydrolysis reaction to obtain a hydrolysate; and mixing the hydrolysate with an emulsifier, (methyl) acrylic acid and methyl methacrylate, and carrying out polymerization reaction to obtain the retanning agent. In the invention, the chrome-free tanning scraps are pretreated by urea and hydrochloric acid, so that covalent bonds in the structure of the chrome-free tanning scraps can be broken or weakened, and the tanning removal is realized, thereby being beneficial to subsequent hydrolysis; according to the invention, sodium hydroxide and calcium oxide are adopted to carry out basic hydrolysis on the pretreated chrome-free tanning waste, so that the hydrolysis rate can be greatly improved and can reach 90-95%; under the condition of an emulsifier, the collagen-based polymer retanning agent can be obtained by adopting (methyl) acrylic acid, methyl methacrylate and hydrolysate to carry out polymerization reaction. The retanning agent prepared by the invention can endow leather with good retanning filling performance and natural hand feeling, and realizes resource high-value utilization of chrome-free tanning waste leather scraps. The invention treats and recycles the chrome-free tanning waste leather scraps produced by the chrome-free tanning method, which is one of the leather industrial clean production methods, and accords with the development concept of innovation, coordination, green, openness and sharing at present.

Detailed Description

The invention provides a preparation method of a retanning agent based on chrome-free leather scraps, which comprises the following steps:

pretreating the chrome-free tanning scraps by adopting urea and hydrochloric acid to obtain pretreated chrome-free tanning scraps;

mixing the pretreated chrome-free tanning waste with sodium hydroxide and a substance containing calcium oxide, and carrying out basic hydrolysis reaction to obtain a hydrolysis product;

and mixing the hydrolysate with an emulsifier, the (methyl) acrylic acid and the methyl methacrylate, and carrying out polymerization reaction to obtain the retanning agent.

In the present invention, all the raw material components are commercially available products well known to those skilled in the art unless otherwise specified.

According to the invention, the chrome-free tanning waste is pretreated by urea and hydrochloric acid to obtain the pretreated chrome-free tanning waste. In the present invention, the method of pretreatment preferably comprises: mixing the chrome-free leather scraps with water to obtain a mixed solution; and heating the mixed solution to a pretreatment temperature, and then adding urea and hydrochloric acid solution for pretreatment. In the present invention, the chrome-free tanning waste preferably comprises any one of chrome-free tanning waste produced by a chrome-free tanning process; the moisture content of the chrome-free tanned leather chips is preferably 20 wt%. In the invention, the mass ratio of the chrome-free leather scraps to the water is preferably 1: 5-6, and more preferably 1: 5.5. In the invention, the mass ratio of the chrome-free leather scraps to the urea is preferably 100: 5-6, and more preferably 100: 5.5; the mass ratio of the chrome-free tanned leather scraps to the hydrochloric acid solution is preferably 100: 2-3, and more preferably 100: 2.5; the mass concentration of the hydrochloric acid solution is preferably 37%.

In the invention, the temperature of the pretreatment is preferably 70-80 ℃, and more preferably 75 ℃; the pretreatment time is preferably 60-90 min, and more preferably 75-80 min.

According to the invention, the system obtained after pretreatment is preferably filtered to obtain the pretreated chrome-free tanning waste.

According to the invention, the chrome-free tanning scraps are pretreated by urea and hydrochloric acid, so that covalent bonds in the structure of the chrome-free tanning scraps can be broken or weakened, the tanning removal is realized, and the subsequent hydrolysis is facilitated.

After the pretreated chrome-free tanning bits are obtained, the pretreated chrome-free tanning bits, sodium hydroxide and a substance containing calcium oxide are mixed for basic hydrolysis reaction to obtain hydrolysis products. In the present invention, the method of mixing the pretreated chrome-free tanned leather scraps with sodium hydroxide and calcium oxide-containing substances preferably comprises: mixing the pretreated chrome-free tanning waste with water to obtain a mixed solution; and heating the mixed solution to the temperature of basic hydrolysis reaction, and then adding sodium hydroxide and a substance containing calcium oxide. In the invention, the mass ratio of the pretreated chrome-free tanning waste to water is preferably 100: 500-600, and more preferably 100: 550; the mass ratio of the pretreated chrome-free leather scraps to the sodium hydroxide is preferably 100: 3-4, and more preferably 100: 3.5; the mass ratio of the pretreated chrome-free leather scraps to the substances containing calcium oxide is preferably 100: 6-8, more preferably 100: 7. in the present invention, the calcium oxide-containing substance is preferably lime; the mass content of calcium oxide in the lime is preferably 80-90%, and more preferably 85%. The invention takes lime as a substance for providing calcium oxide, and has wide raw material source and lower cost.

In the invention, the temperature of the basic hydrolysis reaction is preferably 75-85 ℃, and more preferably 80 ℃; the time of the basic hydrolysis reaction is preferably 120-180 min, and more preferably 150-160 min.

According to the method, sodium hydroxide and a substance containing calcium oxide are adopted to carry out basic hydrolysis on the pretreated chrome-free tanning leather, so that the hydrolysis rate is greatly improved and can reach 90-95%.

The present invention preferably further comprises, after the basic hydrolysis reaction: adjusting the pH value of the obtained hydrolysis reaction system to 6-7, and carrying out solid-liquid separation to obtain hydrolysis filtrate; and concentrating the hydrolysis filtrate to obtain a hydrolysate. In the present invention, it is preferable to adjust the pH of the hydrolysis reaction system with acetic acid; the pH is more preferably 6.5. In a specific embodiment of the present invention, the mass ratio of the pretreated chrome-free leather shavings to the acetic acid is 100: 8-10, more preferably 100: 9. in the invention, the equipment adopted for concentration is preferably a three-effect energy-saving external circulation vacuum concentrator; the concentration method preferably adopts an external heating natural circulation method and a negative pressure evaporation method. The invention carries out concentration to remove the redundant water content, increases the content of effective substances and is convenient for later modification and application.

In the invention, the solid content of the hydrolysate is preferably 35-40%, and more preferably 37.5%. In the invention, the average molecular weight of the hydrolysate is preferably 3000-4000, and more preferably 3500.

After obtaining the hydrolysate, the invention mixes the hydrolysate with the emulsifier, (methyl) acrylic acid and methyl methacrylate for polymerization reaction to obtain the retanning agent. In the invention, when the solid content of the hydrolysate is 35-40%, the mass ratio of the hydrolysate to the emulsifier is preferably 100: 3-4, and more preferably 100: 3.5; the mass ratio of the hydrolysate to the (meth) acrylic acid is preferably 100:16 to 24, and more preferably 100: 20; the mass ratio of the hydrolysate to the methyl methacrylate is preferably 100: 5-8, and more preferably 100: 6.5.

In the present invention, the emulsifier preferably includes one or two of sulfated castor oil, sodium dodecylbenzenesulfonate and peregal O-25; the sulfation degree of the sulfated castor oil is preferably 25-30%. In the present invention, the (meth) acrylic acid is one or both of acrylic acid and methacrylic acid.

In the present invention, the (meth) acrylic acid is preferably added in the form of a (meth) acrylic acid solution; the method for preparing the (meth) acrylic acid solution preferably includes: mixing (methyl) acrylic acid with water, and adjusting the pH value to 5.0-5.5 to obtain a (methyl) acrylic acid solution. In the invention, the mass ratio of the (meth) acrylic acid to the water is preferably 16-24: 6-8, and more preferably 20: 7; the water is preferably distilled water. In the invention, the pH value of the system is preferably adjusted by using a sodium hydroxide solution; the mass fraction of the sodium hydroxide solution is preferably 30%; the mass ratio of the (methyl) acrylic acid to the sodium hydroxide solution is preferably 16-24: 10-16, and more preferably 20: 13; more preferably, the pH of the system is adjusted to 5.3. In the present invention, it is preferable that the system after the pH adjustment is filtered to obtain a (meth) acrylic acid solution.

In the present invention, the polymerization reaction is preferably carried out in the presence of an initiator. In the invention, when the solid content of the hydrolysate is 35-40%, the mass ratio of the hydrolysate to the initiator is preferably 100: 1-1.6, and more preferably 100: 1.3.

In the present invention, the initiator is preferably an ammonium persulfate solution; the preparation method of the ammonium persulfate solution preferably comprises the following steps: and dissolving ammonium persulfate in water to obtain an ammonium persulfate solution. In the invention, the mass ratio of the ammonium persulfate to the water is preferably 1-1.6: 4-5, and more preferably 1.3: 4.5. In the present invention, the water is preferably distilled water.

In the present invention, the method of mixing the hydrolysate, the emulsifier, the (meth) acrylic acid solution, the initiator and the methyl methacrylate preferably includes: mixing the hydrolysate with an emulsifier to obtain an emulsion; and heating the emulsion to 80-85 ℃, and simultaneously dropwise adding the (meth) acrylic acid solution, the initiator and methyl methacrylate. More preferably, the emulsion is heated to 82.5 ℃ in the present invention. In the invention, the dropping speed of the (methyl) acrylic acid solution is preferably 3.5-5 kg/min; the dropping speed of the initiator is preferably 0.4-0.45 kg/min; the preferable dropping speed of the methyl methacrylate is 0.55-0.65 kg/min. The invention adopts a dropping mode to replenish the active monomer and gradually react.

In the invention, the polymerization reaction temperature is preferably 85-90 ℃, and more preferably 87.5 ℃; the time of the polymerization reaction is preferably 90 to 120min, and more preferably 105 to 110 min. In the present invention, the polymerization reaction time is measured after the completion of the addition of methyl methacrylate. In the invention, the polymerization reaction is preferably carried out under a stirring condition, and the stirring speed is preferably 6-12 rpm.

The present invention preferably further comprises, after the polymerization reaction: and adjusting the pH value of the obtained polymerization reaction system to 5.0-5.5, and mixing with a broad-spectrum bactericide to obtain the retanning agent. According to the invention, the temperature of the obtained polymerization reaction system is preferably reduced to 50-56 ℃, and more preferably 53 ℃. The invention can reduce the reaction rate and is beneficial to the discharge and storage of the polymer by cooling.

In the present invention, it is preferable to adjust the pH of the resulting polymerization reaction system with a sodium hydroxide solution; the mass concentration of the sodium hydroxide solution is preferably 30%. In a specific embodiment of the present invention, the mass ratio of the polymerization reaction system to the sodium hydroxide solution is preferably 2000: 30-50, more preferably 2000: 40. more preferably, the pH of the polymerization system is adjusted to 5.3. In the invention, preferably, after the pH value of the polymerization reaction system is adjusted, stirring is carried out for 30-50 min, and more preferably for 40 min. The invention has the function of adjusting the pH value of the polymerization reaction system to improve the water solubility and reduce the viscosity.

In the invention, the broad-spectrum bactericide is preferably general-purpose cason, and is particularly preferably KF-88 cason bactericide. In the invention, the mass ratio of the polymerization reaction system to the broad-spectrum bactericide is preferably 2000: 1-3, and more preferably 2000: 2. According to the invention, after the broad-spectrum bactericide is preferably added, the mixture is stirred for 20-40 min, more preferably for 30min, so as to obtain the retanning agent.

The thickening rate of the leather retanned by the retanning agent prepared by the method is 15-30%, and the position difference of the leather is improved; the market price of the retanning agent prepared by the method is 12-16 yuan/kg, so that high-valued resource utilization of the chrome-free tanning waste leather scraps is realized, and the pollution of the chrome-free tanning waste leather scraps to the environment is reduced.

The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

(1) Pretreatment of

Placing 100kg of chrome-free tanning waste leather scraps with the water content of 20 wt% in a reaction kettle, adding 500kg of water, heating to 70 ℃, then adding 5kg of urea and 2kg of hydrochloric acid with the mass concentration of 37%, carrying out pretreatment for 60min, and filtering to obtain the pretreated chrome-free tanning waste leather scraps;

(2) hydrolysis

Adding 500kg of water into a reaction kettle filled with the pretreated chrome-free tanning waste leather scraps, heating to 75 ℃, then adding 3kg of sodium hydroxide and 6kg of lime, and carrying out basic hydrolysis reaction for 120min, wherein the molecular weight is 3000; adjusting pH to 6 with 8kg acetic acid, and filtering to obtain hydrolysis filtrate;

(3) concentrating

Taking 1000kg of hydrolysis filtrate, and concentrating the hydrolysis filtrate into 35% of mass concentration by using a triple-effect energy-saving external circulation vacuum concentrator by adopting an external heating natural circulation and negative pressure evaporation method to obtain a hydrolysate;

(4) polymerisation reaction

Placing 160kg of acrylic acid and 60kg of distilled water in a reaction kettle, stirring and mixing at room temperature, then adopting 100kg of 30 wt% sodium hydroxide solution to adjust the pH value to 5.0, and filtering to obtain acrylic acid monomer solution;

dissolving 10kg of ammonium persulfate in 40kg of distilled water to obtain an ammonium persulfate solution;

1000kg of the hydrolysate and 30kg of sulfated castor oil with 25-30% of sulfation degree) are placed in a reaction kettle, the mixture is heated to 80 ℃, the acrylic monomer solution, the ammonium persulfate solution and 50kg of methyl methacrylate are respectively dripped for 90min, and after the dripping is finished, the mixture is stirred at 85 ℃ to carry out polymerization reaction for 90 min;

cooling to 50 deg.C, adjusting pH to 5.0 with 30 wt% sodium hydroxide solution 30kg, stirring for 30min, adding Kathon bactericide 1kg, stirring for 20min, and filtering to obtain retanning agent.

In this example, the hydrolysis rate of the chrome-free tanned waste leather was 90%.

The retanning agent prepared by the embodiment is used for retanning leather, the thickening rate is 15%, the retanning filling performance is strong, and the position difference of the leather can be improved; the physical and mechanical properties of the finished leather after retanning meet the industrial standard.

Example 2

(1) Pretreatment of

Placing 100kg of chrome-free tanning waste leather scraps with the water content of 20 wt% in a reaction kettle, adding 600kg of water, heating to 80 ℃, then adding 6kg of urea and 3kg of hydrochloric acid with the mass concentration of 37%, carrying out pretreatment for 90min, and filtering to obtain the pretreated chrome-free tanning waste leather scraps;

(2) hydrolysis

Adding 600kg of water into a reaction kettle filled with the pretreated chrome-free tanning waste leather scraps, heating to 85 ℃, adding 4kg of sodium hydroxide and 8kg of lime, and performing basic hydrolysis reaction for 180min, wherein the molecular weight is 4000; then adjusting the pH value to 7 by using 10kg of acetic acid, and filtering to obtain hydrolysis filtrate;

(3) concentrating

Taking 1000kg of hydrolysis filtrate, and concentrating the hydrolysis filtrate into 40% of mass concentration by using a triple-effect energy-saving external circulation vacuum concentrator through an external heating natural circulation and negative pressure evaporation method to obtain a hydrolysate;

(4) polymerisation reaction

Placing 240kg of methacrylic acid and 80kg of distilled water in a reaction kettle, stirring and mixing at room temperature, adjusting the pH to 5.5 by adopting 160kg of 30 wt% sodium hydroxide solution, and filtering to obtain methacrylic acid monomer solution;

dissolving 16kg of ammonium persulfate in 50kg of distilled water to obtain an ammonium persulfate solution;

placing 1000kg of the hydrolysate and 40kg of emulsifier sodium dodecyl benzene sulfonate into a reaction kettle, heating to 85 ℃, respectively dropwise adding the methacrylic acid monomer solution, the ammonium persulfate solution and 80kg of methyl methacrylate for 120min, stirring at 90 ℃ after dropwise adding, and carrying out polymerization reaction for 120 min;

cooling to 56 deg.C, adjusting pH to 5.5 with 30 wt% sodium hydroxide solution 50kg, stirring for 50min, adding Kathon bactericide 3kg, stirring for 40min, and filtering to obtain retanning agent.

In this example, the hydrolysis rate of the chrome-free tanned waste leather was 95%.

The retanning agent prepared by the embodiment is used for retanning leather, the thickening rate is 25%, the retanning filling performance is strong, and the position difference of the leather can be improved; the physical and mechanical properties of the finished leather after retanning meet the industrial standard.

Example 3

(1) Pretreatment of

Placing 100kg of chrome-free tanning waste leather scraps with the water content of 20 wt% in a reaction kettle, adding 550kg of water, heating to 75 ℃, then adding 5.5kg of urea and 2.5kg of hydrochloric acid with the mass concentration of 37%, carrying out pretreatment for 75min, and filtering to obtain pretreated chrome-free tanning waste leather scraps;

(2) hydrolysis

Adding 550kg of water into a reaction kettle filled with the pretreated chrome-free tanning waste leather scraps, heating to 80 ℃, adding 3.5kg of sodium hydroxide and 7kg of lime, and performing basic hydrolysis reaction for 150min, wherein the molecular weight is 3500; then adjusting the pH value to 6.5 by using 9kg of acetic acid, and filtering to obtain hydrolysis filtrate;

(3) concentrating

Taking 1000kg of hydrolysis filtrate, and concentrating the hydrolysis filtrate into 37.5% of mass concentration by using a triple-effect energy-saving external circulation vacuum concentrator by adopting an external heating natural circulation and negative pressure evaporation method to obtain a hydrolysate;

(4) polymerisation reaction

Placing 200kg of methacrylic acid and 70kg of distilled water in a reaction kettle, stirring and mixing at room temperature, then adjusting the pH to 5.3 by adopting 130kg of 30 wt% sodium hydroxide solution, and filtering to obtain methacrylic acid monomer solution;

dissolving 13kg of ammonium persulfate in 45kg of distilled water to obtain an ammonium persulfate solution;

putting 1000kg of the hydrolysate and 35kg of emulsifier sodium dodecyl sulfate into a reaction kettle, heating to 82.5 ℃, respectively dropwise adding the methacrylic acid monomer solution, the ammonium persulfate solution and 65kg of methyl methacrylate for 105min, stirring at 87.5 ℃ after dropwise adding, and carrying out polymerization reaction for 105 min;

cooling to 53 ℃, adjusting the pH value to 5.3 by using 40kg of 30 wt% sodium hydroxide solution, stirring for 40min, adding 2kg of Kathon bactericide, stirring for 30min, and filtering to obtain the retanning agent.

In this example, the hydrolysis rate of the chrome-free tanned waste leather was 92.5%.

The retanning agent prepared by the embodiment is used for retanning leather, the thickening rate is 20%, the retanning filling performance is strong, and the position difference of the leather can be improved. The physical and mechanical properties of the finished leather after retanning meet the industrial standard.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.