A method for recycling skim latex based on artificial latex preparation process

Abstract

The present invention provides a method for recycling skim latex based on the artificial latex preparation process, belonging to the field of polymer material synthesis and preparation. The method includes the steps of skim latex treatment and skim latex recycling to prepare artificial latex. The skim latex treatment comprises mixing low-concentration skim latex produced during the artificial latex preparation process with insoluble cellulose, beating the mixture, and subjecting it to adsorption treatment. Centrifugation and filtration are then performed to collect the separated skim latex liquid to obtain a skim latex treated liquid. The present invention solves the current problem of handling low-concentration skim latex produced as a byproduct during the artificial latex preparation process, improves and optimizes the artificial latex preparation process, reduces and minimizes wastewater discharge, and realizes a green preparation process.

Description

Technical Field

[0001] The invention belongs to the field of polymer material synthesis and preparation, and particularly relates to a method for recycling low-concentration skim latex in the process of preparing artificial latex. Background Art

[0002] Medical latex products, due to their contact with the human body, have high performance requirements and numerous restrictions. They are strictly restricted latex products, requiring high rubber properties, including mechanical properties, breathability, and softness, and also placing strict restrictions on protein content. Currently, the latex raw materials widely used in latex products include PVC latex, natural latex, and synthetic latex. PVC latex products offer high strength and low price, but suffer from poor breathability and insufficient softness. Natural latex is flexible and strong, but the casein and other proteins in natural latex are prone to allergic reactions, making it difficult to remove proteins from natural latex. Synthetic latexes, such as chloroprene, nitrile, and styrene-butadiene latex, utilize free radical polymerization, resulting in poor stereoregularity of the polymer structure and high gel content, leading to significant differences in mechanical properties and flexibility of their products.

[0003] Polyisoprene rubber, similar in structure to natural rubber, can be obtained by polymerizing isoprene monomers with rare earth elements. This can be used to produce artificial polyisoprene rubber that mimics natural latex through post-emulsification. This artificial polyisoprene rubber, which is protein-free and possesses properties similar to natural latex, is protein-free. Chinese patent CN201210332915.3 discloses a method for directly preparing polyisoprene latex from polyisoprene glue. This method employs active anion solution polymerization to prepare polyisoprene glues of varying molecular weights and narrow molecular weight distributions. The artificial latex is then prepared through emulsification, desolventization of the crude polyisoprene latex, and centrifugal concentration. Chinese patent ZL116891543A discloses a method for preparing artificial latex using a parallel-series continuous kettle distillation process, significantly simplifying the process. The above inventions all adopt the four steps of emulsification, continuous distillation, reduced pressure distillation and centrifugal concentration of rubber liquid to obtain high-concentration artificial latex, but at the same time produce a large amount of low-concentration skim latex. If it is directly recycled instead of the emulsifier aqueous solution, the prepared latex particle size is too large, resulting in poor latex stability and unqualified products. How to deal with and recycle low-concentration skim latex is a thorny problem in the industry. Summary of the Invention

[0004] The object of the present invention is to provide a method for recycling skim latex based on the preparation process of artificial latex, so as to solve the problems existing in the prior art mentioned in the above background technology.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions.

[0006] The present invention provides a method for recycling skim latex based on a process for preparing artificial latex, comprising the following steps:

[0007] (1) Skim cleaning treatment

[0008] ① Cellulose beating treatment: The low-concentration skim latex produced during the preparation of artificial latex is mixed with insoluble cellulose and beaten for adsorption treatment;

[0009] ② Separation treatment: centrifuge and filter the skim latex after adsorption treatment, collect the separated skim latex liquid to obtain skim latex treatment liquid for standby use;

[0010] (2) Recycling of skim latex to prepare artificial latex

[0011] ① All or part of the skim latex solution obtained after the treatment in step (1) is mixed with fresh emulsifier, stirred at 50-60°C for 4-8h, and the pH is adjusted to 10-12 with KOH to prepare a composite skim latex solution;

[0012] ② Adding the compounded latex solution to the rubber latex, performing an emulsification operation, and then performing normal pressure distillation, reduced pressure distillation, and centrifugal concentration operations to prepare a high-concentration artificial latex; in the process of preparing the high-concentration artificial latex, the low-concentration latex produced is recycled using the above steps.

[0013] Furthermore, in step (1)-①, the insoluble cellulose and low-concentration skim latex are mixed in a mass ratio of 5-50:100, the rubber content in the low-concentration skim latex is 0.5-1wt%, and the emulsifier concentration is 2-4.5wt%; the beating is carried out by stirring and beating at room temperature for 4-6 hours.

[0014] Furthermore, in step (1)-①, in step (1)-①, the insoluble cellulose includes at least one of cellulose fibers, lignin, and cellulose particles.

[0015] Preferably, the cellulose fiber is selected from at least one of cotton, short fibers of linen, and pulp slurry.

[0016] Preferably, the lignin is natural unmodified lignin or modified lignin excluding sulfonated lignin.

[0017] Preferably, the cellulose particles are selected from at least one of cellulose microcrystals and nanocellulose.

[0018] Furthermore, in step (1)-②, the centrifugal speed is 5000-10000 rpm, and the filtration adopts a 200-400 mesh filter.

[0019] Furthermore, in step (2)-①, the skim latex treatment liquid is first mixed with deionized water in a mass ratio of 1:1 to form a skim latex treatment aqueous solution, and the skim latex treatment aqueous solution is then mixed with a fresh emulsifier to form a compounded skim latex aqueous solution. The compounded skim latex aqueous solution is used for rubber latex emulsification operation, and then subjected to normal pressure distillation, reduced pressure distillation, and centrifugal concentration operations to prepare a high-concentration artificial latex.

[0020] Furthermore, in step (2)-①, the mass ratio of the skim clear liquid used in the preparation process of the compounded skim clear liquid or the compounded skim clear aqueous solution to the skim clear liquid obtained after the treatment in step (1) is 10-100%; the fresh emulsifier includes a main emulsifier, an auxiliary emulsifier and a stabilizer in a mass ratio of 2:3:1; the main emulsifier accounts for 2-5% of the mass of the compounded skim clear liquid or the compounded skim clear aqueous solution.

[0021] Preferably, the main emulsifier is sodium dodecylbenzene sulfonate, the auxiliary emulsifier is potassium disproportionate rosin acid, and the stabilizer is Tween 80.

[0022] Furthermore, in step (2)-②, the step of preparing high-concentration artificial latex specifically includes:

[0023] S1. Emulsifying rubber glue: emulsifying the rubber glue and the compound glue serum or compound glue serum aqueous solution in a mass ratio of 1:1. The specific operation steps are as follows: at room temperature, first adding a portion of the compound glue serum or compound glue serum aqueous solution to the rubber glue, stirring at a speed of 400-500 r / min for 30-60 minutes to form an oil-in-water pre-emulsified glue; then adding the remaining compound glue serum or compound glue serum aqueous solution to the above-mentioned oil-in-water pre-emulsified liquid, using a shear emulsification method, and emulsifying at a shear speed of 3000-4000 rpm for 3-5 minutes; subsequently increasing the shear speed to within the range of 4000-5000 rpm, shearing and homogenizing for 5-10 minutes to form a stable oil-in-water coarse emulsion;

[0024] S2, continuous distillation: when hexane is used as the solvent, atmospheric distillation is first performed at a distillation temperature of 70-72°C and an average residence time of 6-8h to remove 80-90% of the total solvent amount, and then vacuum distillation is performed at 80°C and 60kPa for 1h to remove the residual solvent to obtain a dilute emulsion; when pentane is used as the solvent, the distillation temperature is 45-50°C and the average residence time is 7-9h to remove 80-90% of the total solvent amount, and then vacuum distillation is performed at 60°C and 60kPa for 1h to remove the residual solvent to obtain a dilute emulsion;

[0025] S3. Centrifugal concentration: Place the dilute emulsion in a high-speed centrifuge, set the speed to 6000-10000 rpm, centrifuge for 5-20 min, and centrifuge to obtain a high-concentration artificial latex with a solid content of 50-60%, and at the same time obtain a low-concentration skim latex.

[0026] Preferably, in step S1, the rubber types used in the rubber glue include but are not limited to polyisoprene rubber, polybutadiene rubber, and styrene-butadiene rubber, with a number average molecular weight of 50,000-800,000. The rubber glue is obtained by dissolving a rubber block in a solvent, or directly obtained by polymerizing a rubber monomer in a solvent. The solvent is selected from one or more of C5-C9 linear alkanes, C5-C9 cycloalkanes, and benzene. The mass concentration of rubber in the rubber glue is between 2% and 15%.

[0027] Compared with the prior art, the present invention has the following beneficial technical effects: the present invention uses skim latex generated in the process of preparing artificial latex, and mixes it with insoluble cellulose for pulping, adsorption and separation treatment, removes low-concentration rubber particles in the skim latex liquid, retains the emulsifier components in the skim latex liquid, and can recycle all or part of it to perform emulsification, atmospheric distillation, reduced-pressure distillation, and centrifugal concentration operations on the rubber latex, thereby completing the process of preparing artificial latex, solving the problem of treating the by-product low-concentration skim latex in the current process of preparing artificial latex, improving and optimizing the artificial latex preparation process, reducing and minimizing the discharge of wastewater, and realizing a green preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a graph showing the particle size change of the skim latex before it is treated with nanocellulose in Example 1;

[0029] Figure 2 This is a graph showing the particle size change of the skim latex after it is treated with nanocellulose in Example 1;

[0030] Figure 3 is the particle size distribution diagram of the artificial latex in Example 3;

[0031] Figure 4 is the particle size distribution diagram of the artificial latex in Example 5;

[0032] Figure 5 is a particle size distribution diagram of the artificial latex in Example 8;

[0033] Figure 6 This is a graph showing the particle size distribution of the artificial latex in Example 9. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0035] Comparative Example 1: Production process of low-concentration skim latex as a by-product of artificial latex

[0036] The method disclosed in Chinese patent ZL201210332915.3 is used to prepare artificial latex, which specifically includes:

[0037] Sol preparation: A certain amount of rare earth isoprene rubber was added to hexane, stirred and refluxed at 55°C for 14 hours to dissolve, to prepare a rubber solution with a rubber solid content of 8%. 1% sodium dodecylbenzene sulfonate, 1.5% potassium disproportionate rosin acid, 0.5% Tween 80, and the balance deionized water were added to the container in order by mass. The pH was adjusted to 12 with KOH to obtain an emulsifier aqueous solution.

[0038] Emulsification process: The rubber glue and the emulsifier aqueous solution are mixed and emulsified simultaneously in a mass ratio of 1:1. Specifically, at room temperature, 1 / 3 of the emulsifier aqueous solution is first added to the rubber glue for pre-emulsification, and stirred at a speed of 450r / min for 45 minutes to form an oil-in-water pre-emulsified glue; then the remaining emulsifier aqueous solution is slowly added, and shear emulsification is carried out at the same time, and the emulsification is carried out at a shear speed of 3500rpm for 4 minutes; the shear speed is further increased for shear homogenization, and the shear speed is homogenized at a shear speed of 4500rpm for 7 minutes to form a stable water-in-oil coarse emulsion;

[0039] Distillation to remove solvent: A two-stage process was used to remove solvent from the crude emulsion. First, atmospheric distillation was performed at 71°C and an average residence time of 7 hours to remove 85% of the total solvent. Then, vacuum distillation was performed at 80°C and 60 kPa for 1 hour to remove the residual solvent, obtaining a dilute emulsion that was almost solvent-free.

[0040] Centrifugal concentration: The dilute emulsion is subjected to high-speed centrifugation, with the centrifugal speed set at 6000 rpm and the centrifugal time set at 20 min, to prepare a high-concentration artificial latex with a solid content of 50%, and at the same time obtain a by-product of low-concentration skim latex.

[0041] Comparative Test Example 1 High Concentration Artificial Latex Particle Size Test

[0042] The particle size of the high-concentration artificial latex prepared in Comparative Example 1 was measured using a laser particle size analyzer.

[0043] After testing, the average particle size of the high-concentration artificial latex prepared in this comparative example is 800 nm.

[0044] Comparative Test Example 2 Analysis of skim latex characteristic parameters

[0045] (1) Skim latex content test: Weigh 10g of skim latex and place it in an oven at 105℃. Measure the weight every 10 minutes until the value remains unchanged after three consecutive measurements. After constant weight, record the weight of the evaporation residue and compare it with the weight of the skim latex before evaporation to obtain the skim latex solid content value. The skim latex solid content of many batches is between 3.1-3.5% (mass ratio), which includes rubber and emulsifier; then wash the evaporation residue with 50g of ethanol three times, and dry it at 105℃ to constant weight. Compared with the weight of the skim latex before evaporation, the rubber solid content value in the skim latex is obtained. The rubber content in many batches of skim latex is between 1.1-1.5% (mass ratio).

[0046] (2) Skim latex particle size analysis: A laser particle size analyzer was used to analyze the skim latex. The skim latex was diluted with 0.6% sodium dodecylbenzene sulfonate solution to a concentration gradient of 0.04-0.07% (mass ratio) for particle size analysis. The average particle size of the skim latex was 600 nm.

[0047] (3) Emulsification characteristics test of skim milk by-product of artificial latex: The low-concentration skim milk by-product of the preparation of high-concentration artificial latex in Example 1 was used instead of the emulsifier aqueous solution to prepare high-concentration artificial latex, and the particle size of the high-concentration artificial latex was measured using a laser particle size analyzer.

[0048] The specific method of adopting skim latex to replace emulsifier aqueous solution to carry out high concentration artificial latex preparation is as follows:

[0049] Sol emulsification: cis-1,4-polyisoprene rubber was added to hexane, stirred and refluxed at 50°C for 12 hours to dissolve, to prepare a rubber solution with a rubber solid content of 8%; the rubber solution and skim latex were mixed and emulsified in a mass ratio of 1:1. Specifically, at room temperature, 1 / 3 of the skim latex was first added to the rubber solution for pre-emulsification, and stirred at 400 rpm for 30 minutes to form an oil-in-water pre-emulsified solution; then the remaining skim latex was slowly added and sheared and emulsified at a shear speed of 3000 rpm for 3 minutes; the shear speed was further increased for shear homogenization, and the mixture was homogenized at a shear speed of 4000 rpm for 5 minutes to form a stable oil-in-water coarse emulsion;

[0050] Distillation to remove solvent: A two-stage process was used to remove solvent from the crude emulsion. First, atmospheric distillation was performed at 70°C with an average residence time of 6 hours to remove 80% of the total solvent. Then, vacuum distillation was performed at 80°C and 60 kPa for 1 hour to remove the residual solvent, obtaining a dilute emulsion that was almost solvent-free.

[0051] Centrifugal concentration: The dilute emulsion was subjected to high-speed centrifugation with a centrifugal speed of 6000 rpm and a centrifugal time of 20 min to prepare a high-concentration artificial latex with a solid content of 50%.

[0052] After testing, it was found that the average particle size of the high-concentration artificial latex prepared by using skim milk instead of the emulsifier aqueous solution based on the method of Comparative Example 1 was 1200 nm.

[0053] Example 1 Nanocellulose treatment of skim latex

[0054] Weigh nanocellulose and skim latex, mix them in a mass ratio of 5-50:100, stir and beat at room temperature for 4-6 hours, then slowly add them into a butterfly centrifuge for centrifugal separation, set the centrifugal speed to 10000rpm, shut down the centrifuge regularly, clean the nanocellulose rubber adsorbent attached to the butterfly, collect the separated treatment liquid, and then filter it with a 400 mesh net to obtain the treated skim latex, i.e., skim latex treatment liquid.

[0055] Please refer to the attached Figure 1-2 , tested by a laser particle size analyzer, the average particle size of the skim latex treated in this embodiment is 120nm.

[0056] Example 2 Lignin treatment of skim latex

[0057] Weigh unmodified lignin and skim latex, mix them in a mass ratio of 5-50:100, stir and beat at room temperature for 4-6 hours, then slowly add them into a butterfly centrifuge for centrifugal separation, set the centrifugal speed to 10000rpm, shut down the centrifuge regularly, clean the lignin rubber adsorbent attached to the butterfly, collect the separated treatment liquid, and then filter it with a 200 mesh screen to obtain the treated skim latex, i.e. skim latex treatment liquid.

[0058] The laser particle size analyzer test showed that the average particle size of the skim latex treated in this embodiment was 130 nm.

[0059] Example 3 Pulp Treatment Skim Latex

[0060] Weigh a pulp slurry with a concentration of 25wt%, mix it with skim latex in a mass ratio of 5-15:100, stir and beat at room temperature for 4-6h, then slowly add it to a butterfly centrifuge for centrifugal separation, set the centrifugal speed to 10000rpm, shut down the centrifuge regularly, clean the pulp fiber and rubber adsorbents attached to the butterfly, collect the separated treatment liquid at the same time, and then filter it with a 200 mesh net to obtain the treated skim latex, i.e. skim latex treatment liquid.

[0061] Please refer to the attached Figure 3 , tested by a laser particle size analyzer, the average particle size of the skim latex treated in this embodiment is 130nm.

[0062] Comparative Example 2: Direct recycling of latex to prepare artificial latex

[0063] Sol emulsification: A certain amount of rare earth polyisoprene rubber was added to a hexane solvent and stirred at 50°C for 10 hours to prepare a polyisoprene rubber solution with a mass ratio of 8%. To the low-concentration skim solution obtained in Comparative Example 1, 2% of the total amount of sodium dodecylbenzene sulfonate, 3% of potassium disproportionate rosin acid, and 1% of Tween 80 were added. The solution was stirred at 55°C for 4 hours and the pH was adjusted to 10 with KOH to obtain a skim solution.

[0064] Emulsification process: emulsify the rubber glue and the skim water solution in a mass ratio of 1:1. Specifically, at room temperature, first add 1 / 3 of the skim water solution to the rubber glue for pre-emulsification, and stir at a speed of 400r / min for 30 minutes to form an oil-in-water pre-emulsified glue; then slowly add the remaining skim solution while shearing and emulsifying, and emulsify at a shear speed of 3000rpm for 3 minutes; continue to increase the shear speed for shear homogenization, and homogenize at a shear speed of 4000rpm for 5 minutes to form a stable water-in-oil coarse emulsion;

[0065] Distillation to remove solvent: A two-stage method is used to remove solvent from the crude emulsion. First, atmospheric distillation is performed at a distillation temperature of 45°C and an average residence time of 7 hours to remove 80% of the total solvent. Then, vacuum distillation is performed at 80°C and 60 kPa for 1 hour to remove residual solvent and obtain a dilute emulsion that is almost solvent-free.

[0066] High-speed centrifugal concentration: The dilute emulsion was subjected to high-speed centrifugation with a centrifugal speed of 6000 rpm and a centrifugal time of 5 min to prepare a high-concentration artificial latex with a solid content of 55%.

[0067] The average particle size of the artificial latex in this comparative example was 1200 nm as measured by a laser particle size analyzer.

[0068] Example 4: Treatment of latex solution for recycling and preparation of artificial latex

[0069] Sol emulsification: A certain amount of rare earth polyisoprene rubber was added to a hexane solvent and stirred at 50°C for 10 hours to prepare a polyisoprene rubber solution with a mass ratio of 8%. To the treated latex solution obtained in Example 1, 2% of the total amount of sodium dodecylbenzene sulfonate, 3% of potassium disproportionate rosin acid, and 1% of Tween 80 were added. The mixture was stirred at 55°C for 4 hours, and the pH was adjusted to 10 with KOH to obtain a composite latex solution.

[0070] Emulsification process: emulsify the rubber glue and the compound glue clear liquid in a mass ratio of 1:1. Specifically, at room temperature, first add 1 / 3 of the compound glue clear liquid to the rubber glue for pre-emulsification, and stir at a speed of 400r / min for 30 minutes to form an oil-in-water pre-emulsified glue liquid; then slowly add the remaining compound glue clear liquid while shearing and emulsifying, and emulsify at a shear speed of 3000rpm for 3 minutes; continue to increase the shear speed for shear homogenization, and homogenize at a shear speed of 4000rpm for 5 minutes to form a stable water-in-oil coarse emulsion;

[0071] Distillation to remove solvent: A two-stage method is used to remove solvent from the crude emulsion. First, atmospheric distillation is performed at a distillation temperature of 45°C and an average residence time of 7 hours to remove 80% of the total solvent. Then, vacuum distillation is performed at 60°C and 60 kPa for 1 hour to remove residual solvent and obtain a dilute emulsion that is almost solvent-free.

[0072] High-speed centrifugal concentration: The dilute emulsion was subjected to high-speed centrifugation with a centrifugal speed of 6000 rpm and a centrifugal time of 5 min to prepare a high-concentration artificial latex with a solid content of 55%.

[0073] The average particle size of the artificial latex in this embodiment was 700 nm as measured by a laser particle size analyzer.

[0074] Example 5 Treatment of latex for recycling and preparation of artificial latex

[0075] Sol emulsification: A certain amount of rare earth polyisoprene rubber was added to a hexane solvent and stirred at 50°C for 10 hours to prepare a polyisoprene rubber solution with a mass ratio of 8%. To the treated latex solution obtained in Example 2, 2% of the total amount of sodium dodecylbenzene sulfonate, 3% of potassium disproportionate rosin acid, and 1% of Tween 80 were added. The mixture was stirred at 55°C for 4 hours, and the pH was adjusted to 10 with KOH to obtain a composite latex solution.

[0076] Emulsification process: emulsify the rubber glue and the compound glue clear liquid in a mass ratio of 1:1. Specifically, at room temperature, first add 1 / 3 of the compound glue clear liquid to the rubber glue for pre-emulsification, and stir at a speed of 400r / min for 30 minutes to form an oil-in-water pre-emulsified glue liquid; then slowly add the remaining compound glue clear liquid while shearing and emulsifying, and emulsify at a shear speed of 3000rpm for 3 minutes; continue to increase the shear speed for shear homogenization, and homogenize at a shear speed of 4000rpm for 5 minutes to form a stable water-in-oil coarse emulsion;

[0077] Distillation to remove solvent: A two-stage method is used to remove solvent from the crude emulsion. First, atmospheric distillation is performed at a distillation temperature of 45°C and an average residence time of 7 hours to remove 80% of the total solvent. Then, vacuum distillation is performed at 60°C and 60 kPa for 1 hour to remove residual solvent and obtain a dilute emulsion that is almost solvent-free.

[0078] High-speed centrifugal concentration: The dilute emulsion was subjected to high-speed centrifugation with a centrifugal speed of 6000 rpm and a centrifugal time of 5 min to prepare a high-concentration artificial latex with a solid content of 55%.

[0079] Please refer to the attached Figure 4 , tested by a laser particle size analyzer, the average particle size of the artificial latex in this embodiment is 670nm.

[0080] Example 6 Treatment of latex for recycling and preparation of artificial latex

[0081] Sol emulsification: A certain amount of rare earth polyisoprene rubber was added to a hexane solvent and stirred at 50°C for 10 hours to prepare a polyisoprene rubber solution with a mass ratio of 8%. To the treated latex solution obtained in Example 3, 2% of the total amount of sodium dodecylbenzene sulfonate, 3% of potassium disproportionate rosin acid, and 1% of Tween 80 were added. The mixture was stirred at 55°C for 4 hours, and the pH was adjusted to 10 with KOH to obtain a composite latex solution.

[0082] Emulsification process: emulsify the rubber glue and the compound glue clear liquid in a mass ratio of 1:1. Specifically, at room temperature, first add 1 / 3 of the compound glue clear liquid to the rubber glue for pre-emulsification, and stir at a speed of 400r / min for 30 minutes to form an oil-in-water pre-emulsified glue liquid; then slowly add the remaining compound glue clear liquid while shearing and emulsifying, and emulsify at a shear speed of 3000rpm for 3 minutes; continue to increase the shear speed for shear homogenization, and homogenize at a shear speed of 4000rpm for 5 minutes to form a stable water-in-oil coarse emulsion;

[0083] Distillation to remove solvent: A two-stage method is used to remove solvent from the crude emulsion. First, atmospheric distillation is performed at a distillation temperature of 45°C and an average residence time of 7 hours to remove 80% of the total solvent. Then, vacuum distillation is performed at 60°C and 60 kPa for 1 hour to remove residual solvent and obtain a dilute emulsion that is almost solvent-free.

[0084] High-speed centrifugal concentration: The dilute emulsion was subjected to high-speed centrifugation with a centrifugal speed of 6000 rpm and a centrifugal time of 5 min to prepare a high-concentration artificial latex with a solid content of 55%.

[0085] The average particle size of the artificial latex in this embodiment was 680 nm as measured by a laser particle size analyzer.

[0086] Example 7 Treatment of latex for recycling and preparation of artificial latex

[0087] Sol emulsification: a certain amount of rare earth polyisoprene rubber was added to a hexane solvent and stirred at 50°C for 10 hours to prepare a polyisoprene rubber glue solution with a mass ratio of 8%; the treated glue solution obtained in Example 1 was mixed with deionized water at a mass ratio of 1:1, and then 2% of the total amount of sodium dodecylbenzene sulfonate, 3% of potassium disproportionate rosin acid, and 1% of Tween 80 were added, and stirred at 55°C for 4 hours. The pH was adjusted to 10 with KOH to obtain a composite glue solution;

[0088] Emulsification process: emulsify the rubber glue and the compound glue clear water solution in a mass ratio of 1:1. Specifically, at room temperature, first add 1 / 3 of the compound glue clear water solution to the rubber glue for pre-emulsification, and stir at a speed of 400r / min for 30min to form an oil-in-water pre-emulsified glue solution; then slowly add the remaining compound glue clear water solution and shear emulsify at the same time, emulsifying at a shear speed of 3000rpm for 3min; continue to increase the shear speed for shear homogenization, and homogenize at a shear speed of 4000rpm for 5min to form a stable water-in-oil coarse emulsion;

[0089] Distillation to remove solvent: A two-stage method is used to remove solvent from the crude emulsion. First, atmospheric distillation is performed at a distillation temperature of 45°C and an average residence time of 7 hours to remove 80% of the total solvent. Then, vacuum distillation is performed at 60°C and 60 kPa for 1 hour to remove residual solvent and obtain a dilute emulsion that is almost solvent-free.

[0090] High-speed centrifugal concentration: The dilute emulsion was subjected to high-speed centrifugation with a centrifugal speed of 6000 rpm and a centrifugal time of 5 min to prepare a high-concentration artificial latex with a solid content of 55%.

[0091] The average particle size of the artificial latex in this embodiment was 500 nm as measured by a laser particle size analyzer.

[0092] Example 8 Treatment of latex for recycling to prepare artificial latex

[0093] Sol emulsification: a certain amount of rare earth polyisoprene rubber was added to a hexane solvent and stirred at 50°C for 10 hours to prepare a polyisoprene rubber glue solution with a mass ratio of 8%; the treated glue solution obtained in Example 2 was mixed with deionized water at a mass ratio of 1:1, and then 2% of the total amount of the system, 3% of potassium disproportionate rosin acid, and 1% of Tween 80 were added, and stirred at 55°C for 4 hours. The pH was adjusted to 10 with KOH to obtain a composite glue solution;

[0094] Emulsification process: emulsify the rubber glue and the compound glue clear solution in a mass ratio of 1:1. Specifically, at room temperature, first add 1 / 3 of the compound glue clear solution to the rubber glue for pre-emulsification, and stir at a speed of 400r / min for 30 minutes to form an oil-in-water pre-emulsified glue; then slowly add the remaining compound glue clear solution and shear emulsify at the same time, emulsifying at a shear speed of 3000rpm for 3 minutes; continue to increase the shear speed for shear homogenization, and homogenize at a shear speed of 4000rpm for 5 minutes to form a stable water-in-oil coarse emulsion;

[0095] Distillation to remove solvent: A two-stage method is used to remove solvent from the crude emulsion. First, atmospheric distillation is performed at a distillation temperature of 45°C and an average residence time of 7 hours to remove 80% of the total solvent. Then, vacuum distillation is performed at 60°C and 60 kPa for 1 hour to remove residual solvent and obtain a dilute emulsion that is almost solvent-free.

[0096] High-speed centrifugal concentration: The dilute emulsion was subjected to high-speed centrifugation with a centrifugal speed of 6000 rpm and a centrifugal time of 5 min to prepare a high-concentration artificial latex with a solid content of 55%.

[0097] Please refer to the attached Figure 5 , tested by a laser particle size analyzer, the average particle size of the artificial latex in this embodiment is 450nm.

[0098] Example 9 Treatment of latex for recycling to prepare artificial latex

[0099] Sol emulsification: a certain amount of rare earth polyisoprene rubber was added to a hexane solvent and stirred at 50°C for 10 hours to prepare a polyisoprene rubber glue solution with a mass ratio of 8%; the treated glue solution obtained in Example 3 was mixed with deionized water at a mass ratio of 1:1, and then 2% of the total amount of sodium dodecylbenzene sulfonate, 3% of potassium disproportionate rosin acid, and 1% of Tween 80 were added, and the solution was stirred at 55°C for 4 hours. The pH was adjusted to 10 with KOH to obtain a composite glue solution;

[0100] Emulsification process: emulsify the rubber glue and the compound glue clear water solution in a mass ratio of 1:1. Specifically, at room temperature, first add 1 / 3 of the compound glue clear water solution to the rubber glue for pre-emulsification, and stir at a speed of 400r / min for 30min to form an oil-in-water pre-emulsified glue solution; then slowly add the remaining compound glue clear water solution and shear emulsify at the same time, emulsifying at a shear speed of 3000rpm for 3min; continue to increase the shear speed for shear homogenization, and homogenize at a shear speed of 4000rpm for 5min to form a stable water-in-oil coarse emulsion;

[0101] Distillation to remove solvent: A two-stage method is used to remove solvent from the crude emulsion. First, atmospheric distillation is performed at a distillation temperature of 45°C and an average residence time of 7 hours to remove 80% of the total solvent. Then, vacuum distillation is performed at 60°C and 60 kPa for 1 hour to remove residual solvent and obtain a dilute emulsion that is almost solvent-free.

[0102] High-speed centrifugal concentration: The dilute emulsion was subjected to high-speed centrifugation with a centrifugal speed of 6000 rpm and a centrifugal time of 5 min to prepare a high-concentration artificial latex with a solid content of 55%.

[0103] Please refer to the attached Figure 6 , tested by a laser particle size analyzer, the average particle size of the artificial latex in this embodiment is 390nm.

Claims

1. A method for recycling skim latex based on a process for preparing artificial latex, characterized in that: The following steps are involved: (1) Skim cleaning treatment ① Cellulose beating treatment: low-concentration skim latex produced during the preparation of artificial latex is mixed with insoluble cellulose or lignin and beaten, and subjected to adsorption treatment; specifically, the insoluble cellulose or lignin and low-concentration skim latex are mixed in a mass ratio of 5-50:100, the rubber content in the low-concentration skim latex is 0.5-1wt%, and the emulsifier concentration is 2-4.5wt%. The beating is carried out by stirring and beating at room temperature for 4-6 hours; the insoluble cellulose is at least one of cellulose fibers and cellulose particles; ② Separation treatment: centrifuge and filter the skim latex after adsorption treatment, collect the separated skim latex liquid to obtain skim latex treatment liquid for standby use; (2) Recycling of skim latex to prepare artificial latex ① All or part of the skim latex solution obtained after the treatment in step (1) is mixed with a fresh emulsifier, stirred at 50-60° C. for 4-8 hours, and the pH is adjusted to 10-12 with KOH to prepare a composite skim latex solution; specifically, the skim latex solution used in the preparation of the composite skim latex solution accounts for 10-100% by mass of the skim latex solution obtained after the treatment in step (1); the fresh emulsifier includes a main emulsifier, an auxiliary emulsifier, and a stabilizer in a mass ratio of 2:3:1; the main emulsifier accounts for 2-5% of the mass of the composite skim latex solution; ② Adding the compounded latex solution to the rubber latex, performing an emulsification operation, and then performing normal pressure distillation, reduced pressure distillation, and centrifugal concentration operations to prepare a high-concentration artificial latex; in the process of preparing the high-concentration artificial latex, the low-concentration latex produced is recycled using the above steps.

2. A method for recycling skim latex based on an artificial latex preparation process according to claim 1, characterized in that: The cellulose fiber is selected from at least one of cotton, short fibers of hemp, and pulp slurry; the lignin is selected from natural unmodified lignin or modified lignin excluding sulfonated lignin; and the cellulose particles are selected from at least one of cellulose microcrystals and nanocellulose.

3. A method for recycling skim latex based on an artificial latex preparation process according to claim 2, characterized in that: In step (1)-②, the centrifugal speed is 5000-10000 rpm, and the filtration adopts 200-400 mesh filter.

4. The method for recycling skim latex based on the preparation process of artificial latex according to claim 3, wherein: In step (2), the skim latex treatment liquid is mixed with deionized water at a mass ratio of 1:1 before use to form a skim latex treatment aqueous solution, and the skim latex treatment aqueous solution is then mixed with a fresh emulsifier to form a compounded skim latex aqueous solution. The compounded skim latex aqueous solution is used for rubber latex emulsification operation, and then subjected to normal pressure distillation, reduced pressure distillation, and centrifugal concentration operations to prepare a high-concentration artificial latex.

5. A method for recycling skim latex based on an artificial latex preparation process according to claim 4, characterized in that: In step (2)-①, the main emulsifier accounts for 2-5% of the mass of the compound glue clear liquid or the compound glue clear aqueous solution; the main emulsifier is sodium dodecylbenzene sulfonate, the auxiliary emulsifier is potassium disproportionate rosin acid, and the stabilizer is Tween 80.

6. The method for recycling skim latex based on the preparation process of artificial latex according to claim 5, characterized in that: In step (2)-②, the steps of preparing high-concentration artificial latex specifically include: S1. Emulsifying rubber glue: emulsifying the rubber glue and the compound glue serum or compound glue serum aqueous solution in a mass ratio of 1:

1. The specific operation steps are as follows: at room temperature, first adding a portion of the compound glue serum or compound glue serum aqueous solution to the rubber glue, stirring at a speed of 400-500 r / min for 30-60 minutes to form an oil-in-water pre-emulsified glue; then adding the remaining compound glue serum or compound glue serum aqueous solution to the above-mentioned oil-in-water pre-emulsified liquid, using a shear emulsification method, and emulsifying at a shear speed of 3000-4000 rpm for 3-5 minutes; subsequently increasing the shear speed to within the range of 4000-5000 rpm, shearing and homogenizing for 5-10 minutes to form a stable oil-in-water coarse emulsion; S2, continuous distillation: when hexane is used as the solvent, atmospheric distillation is first performed at a distillation temperature of 70-72°C and an average residence time of 6-8h to remove 80-90% of the total solvent amount, and then vacuum distillation is performed at 80°C and 60kPa for 1h to remove the residual solvent to obtain a dilute emulsion; when pentane is used as the solvent, the distillation temperature is 45-50°C and the average residence time is 7-9h to remove 80-90% of the total solvent amount, and then vacuum distillation is performed at 60°C and 60kPa for 1h to remove the residual solvent to obtain a dilute emulsion; S3. Centrifugal concentration: Place the dilute emulsion in a high-speed centrifuge, set the speed to 6000-10000 rpm, centrifuge for 5-20 min, and centrifuge to obtain a high-concentration artificial latex with a solid content of 50-60%, and at the same time obtain a low-concentration skim latex.

7. The method for recycling skim latex based on the preparation process of artificial latex according to claim 6, characterized in that: In step S1, the rubber types used in the rubber glue include but are not limited to polyisoprene rubber, polybutadiene rubber, and styrene-butadiene rubber, with a number average molecular weight of 50,000-800,000. The rubber glue is obtained by dissolving a rubber block in a solvent, or directly obtained by polymerizing a rubber monomer in a solvent. The solvent is selected from one or more of C5-C9 linear alkanes, C5-C9 cycloalkanes, and benzene. The mass concentration of rubber in the rubber glue is between 2-15%.

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