阅读说明：本技术 一种低温吸附制备浓缩聚异戊二烯胶乳的方法 (Method for preparing concentrated polyisoprene latex through low-temperature adsorption ) 是由 崔广军 王锦昌 李辉阳 张文文 陈雷 于 2021-11-15 设计创作，主要内容包括：一种低温吸附制备浓缩聚异戊二烯胶乳的方法,依次包括如下步骤：(1)向稀聚异戊二烯胶乳中加入吸附剂,搅拌浓缩；(2)浓缩后分离吸附剂得到浓缩胶乳。所述吸附剂的制备方法依次包括如下步骤：(a)取小麦淀粉加入到10-15倍重量的水中,然后在80-95℃下糊化0.5-1h,得糊化小麦淀粉；(b)称取环己烷、丙烯酰胺、丙烯酸盐、羟丙基甲基纤维素、聚乙烯醇、海藻酸钠和交联剂加入到所述糊化小麦淀粉中,得混合溶液；(c)将所述混合溶液在50-60℃条件下加入引发剂搅拌1-2h,产物经离心分离,干燥,得到球状吸附剂。该方法采用的吸附剂为规则、光洁的球状,表面不易附着胶粒；且吸附剂经热干燥可循环再生,降低成本。(A method for preparing concentrated polyisoprene latex by low-temperature adsorption sequentially comprises the following steps: (1) adding an adsorbent into the dilute polyisoprene latex, and stirring and concentrating; (2) and separating the adsorbent after concentration to obtain concentrated latex. The preparation method of the adsorbent sequentially comprises the following steps: (a) adding wheat starch into 10-15 times of water, and gelatinizing at 80-95 deg.C for 0.5-1 hr to obtain gelatinized wheat starch; (b) weighing cyclohexane, acrylamide, acrylate, hydroxypropyl methylcellulose, polyvinyl alcohol, sodium alginate and a cross-linking agent, and adding the weighed materials into the gelatinized wheat starch to obtain a mixed solution; (c) adding an initiator into the mixed solution at 50-60 ℃, stirring for 1-2h, and performing centrifugal separation and drying on a product to obtain the spherical adsorbent. The adsorbent adopted by the method is regular, smooth and spherical, and colloidal particles are not easy to attach to the surface of the adsorbent; and the adsorbent can be regenerated circularly by thermal drying, so that the cost is reduced.)

1. A method for preparing concentrated polyisoprene latex by low-temperature adsorption is characterized by sequentially comprising the following steps:

(1) adding an adsorbent into the dilute polyisoprene latex, and stirring and concentrating;

(2) and separating the adsorbent after concentration to obtain concentrated latex.

2. The method for preparing the concentrated polyisoprene latex through low-temperature adsorption according to claim 1, wherein the raw materials of the adsorbent comprise starch, acrylamide, acrylate, hydroxypropyl methylcellulose, polyvinyl alcohol, sodium alginate and an initiator, wherein the weight ratio of the starch, the acrylamide, the acrylate, the hydroxypropyl methylcellulose, the polyvinyl alcohol and the sodium alginate is 10: 0.5-1: 0.2-1:0.2-0.5:0.3-0.5: 0.1-0.2;

the preparation method of the adsorbent sequentially comprises the following steps:

(a) adding wheat starch into 10-15 times of water, and gelatinizing at 80-95 deg.C for 0.5-1 hr to obtain gelatinized wheat starch;

(b) weighing cyclohexane, acrylamide, acrylate, hydroxypropyl methylcellulose, polyvinyl alcohol, sodium alginate and a cross-linking agent, and adding the weighed materials into the gelatinized wheat starch to obtain a mixed solution;

(c) adding an initiator into the mixed solution at 50-60 ℃, stirring for 1-2h, and performing centrifugal separation and drying on a product to obtain the spherical adsorbent.

3. The method for preparing a concentrated polyisoprene latex by cryogenic adsorption as claimed in claim 2, wherein the amount of cyclohexane used in step (b) is 3-5 times the amount of water used in step (a).

4. The method for preparing a concentrated polyisoprene latex by low temperature adsorption according to claim 2, wherein the initiator is ammonium persulfate-sodium bisulfite composite initiator, and the weight ratio of the two initiators is 1: 1-2, wherein the addition amount of the composite initiator accounts for 0.1-0.5% of the total mass of the monomers; the cross-linking agent is N, N-methylene bisacrylamide, and the addition amount accounts for 0.01-0.1% of the total mass of the monomers.

5. The method for preparing a concentrated polyisoprene latex by low temperature adsorption as claimed in claim 2, wherein the monomer methyl methacrylate and acrylamide are added in a weight ratio of 20: 1-2.

6. The method for preparing concentrated polyisoprene latex by low temperature adsorption as claimed in claim 2, wherein the concentration is carried out in three stages, that is, the adsorbent is separated after the adsorbent is added into the container, then the diluted polyisoprene latex is added into the container to the original volume, 1/2 of the amount of the primary adsorbent is added for adsorption, and 1/3 of the amount of the primary adsorbent is added for the third time.

7. The method for preparing the concentrated polyisoprene latex by the low-temperature adsorption method according to claim 1, wherein the index of the dilute polyisoprene latex in the step (1) is as follows: solid content is 5-10%, and particle size is 1-2 μm; wherein the mass fraction of the adsorbent in the dilute polyisoprene latex in the step (1) is 1-3%.

8. The method for preparing a concentrated polyisoprene latex by low temperature adsorption as claimed in claim 1, wherein the stirring speed in step (1) is as follows: 100-.

9. The method for preparing a concentrated polyisoprene latex by low temperature adsorption according to claim 1, wherein the separation method in step (2) is: after the adsorbent adsorbs water, its diameter is expanded to 0.5-15mm, and the adsorbent is filtered and drained.

10. The method for preparing the concentrated polyisoprene latex by low-temperature adsorption according to claim 1, further comprising the step of regenerating the adsorbent, wherein the method comprises the following steps:

spreading the drained adsorbent on a screen with a thickness of about 2-3 layers, introducing hot air with a temperature of 30-80 ℃ from bottom to top, penetrating through the screen and the adsorbent layer, taking out the adsorbent after 0.5-12h, and putting the adsorbent in the dilute polyisoprene latex again for recycling.

Technical Field

The invention belongs to the technical field of rubber emulsion concentration, and particularly relates to a method for preparing concentrated polyisoprene latex through low-temperature adsorption.

Background

The latex product is widely used in production and life, the natural latex product has good adhesiveness and excellent mechanical property, but the oil resistance and the aging resistance are poor, and the problem of contact allergy of a solvent occurs; although synthetic latex such as butylbenzene, butyronitrile and the like has excellent oil resistance and aging resistance, the synthetic latex has the problems of poor comfort, poor tearing resistance and poor elongation at break and the like when a film product is prepared. The molecular structure of the polyisoprene rubber is close to that of natural rubber in height, the polyisoprene rubber has a high cis-structure, few branched chains and similar molecular weight, the molecular weight is narrower, and the rubber films of the polyisoprene rubber and the natural rubber have similar characteristics, so that the polyisoprene rubber can be used as the best substitute of natural rubber latex. Unlike natural latex, isoprene latex uses industrial emulsifiers, is completely protein-free, and does not have the contact allergy of latex products.

The preparation method of the polyisoprene latex mainly comprises 2 methods of emulsion polymerization and solution emulsification. The emulsion polymerization method for producing the polyisoprene latex takes isoprene as a monomer, and an initiator and an emulsifier are used for emulsion polymerization in a water phase to obtain the polyisoprene emulsion. Latex prepared by an emulsion polymerization method has small particle size, narrow distribution and good stability, but the isoprene emulsion has long polymerization reaction time, low monomer conversion rate, poor product structure regularity, belongs to a random polymer, has high content of impurities and gel in rubber, has undesirable mechanical properties, various used auxiliaries and generates industrial wastewater which has great harm to the environment, so the emulsion polymerization is not a preferred method for preparing polyisoprene latex.

The solution emulsification method is a kind of latex prepared by forming solid rubber into a milky aqueous dispersion by means of a physical process. The current industrial polyisoprene latex product is an artificial latex prepared by a solution emulsification method, namely, polyisoprene rubber is taken as a basic raw material, and emulsion is prepared through 4 processes of dissolution, emulsification, solvent removal and concentration.

Wherein the thin latex after desolventization contains a large amount of water and needs to be concentrated, otherwise the thin latex cannot be stored and transported. The preparation of the high solid content polyisoprene latex has difficulties, and the factors such as small particle size, large viscosity, poor stability and the like bring challenges to the concentration technology. The commonly used concentration method mainly comprises 3 methods of centrifugation, creaming and evaporation. Centrifugation refers to the process of adding dilute latex to a high-speed centrifuge and separating most latex particles from whey by the action of centrifugal force to obtain concentrated latex. Because the whey after centrifugation contains a small amount of tiny latex particles, repeated centrifugation not only consumes a large amount of energy, but also causes a certain loss of the latex particles. The creaming method is characterized in that creaming agents such as alginates, casein, gelatin and the like are added into dilute latex, the addition of the creaming method reduces Brownian motion of latex ions, the latex ions float upwards spontaneously to concentrate the latex, latex with solid content of 40-50% is usually prepared, but the creaming agents flocculate and easily cause emulsion breaking and creaming of the latex, and the evaporation method easily causes latex caking and deterioration.

In order to solve the above problems, chinese patent CN202110577238.0 discloses a method for concentrating rubber emulsion and a product thereof, wherein a highly water-absorbent resin is added into a rubber emulsion with a solid content of 0.01-70%, and the highly water-absorbent resin is separated after stirring and concentration to obtain a concentrated latex. The method for concentrating the rubber has simple production equipment and low power consumption, and can obtain polymer emulsion with high solid content (up to 76 percent); the adopted adsorption resin can be recycled after being dried, so that the production cost is effectively reduced; the method for concentrating the natural latex has the advantages of high dry rubber preparation rate, less waste water generation and excellent mechanical property, aging resistance and adhesive property of a product prepared from the concentrated natural latex; the method of the invention is adopted to concentrate the synthetic latex, and agglomeration in advance is not needed, thus reducing the production steps and effectively improving the production efficiency.

However, the super absorbent resin used in this patent is not suitable for the polyisoprene latex system for the following reasons:

after the super absorbent resin absorbs water, the mechanical property of the super absorbent resin is reduced, the resin becomes soft, when the water absorption time is longer, the resin is subjected to swelling deformation, and in the subsequent cycle use, the resin is easy to break into fine particles and can enter the rubber emulsion; the water-absorbent resins of the polyacrylate type are generally irregular particles, and during the water absorption process, latex enters irregular cracks and gaps, resulting in the loss of latex and lowering the actual content of the emulsion.

Thus, there is a need to develop a low temperature adsorption concentration process suitable for polyisoprene latex systems.

Disclosure of Invention

The invention aims to overcome the problems in the prior art and provides a method for preparing condensed isoprene latex by low-temperature adsorption, which adopts physical low-temperature adsorption and can reduce the energy consumption generated in the concentration process; the skinning phenomenon can not occur; the prepared adsorbent is regular, smooth and spherical, and colloidal particles are not easy to attach to the surface of the adsorbent; and the adsorbent can be regenerated circularly by thermal drying, so that the cost is reduced.

The technical scheme of the invention is as follows:

a method for preparing concentrated polyisoprene latex by low-temperature adsorption sequentially comprises the following steps:

(1) adding an adsorbent into the dilute polyisoprene latex, and stirring and concentrating;

(2) and separating the adsorbent after concentration to obtain concentrated latex.

Further, the concentration is multi-time gradual concentration or one-time concentration, and the single concentration time is 4-8 h.

The multiple step-by-step concentration refers to adding the adsorbent into a container, then separating the adsorbent, then supplementing the diluted polyisoprene latex into the container to the original volume, then adding 1/2 of the dosage of the primary adsorbent for adsorption, adding 1/3 of the dosage of the primary adsorbent for the third time, and repeating for multiple times, preferably for three times.

The adsorbent in the step (1) comprises raw material components of starch, acrylamide, acrylate, hydroxypropyl methyl cellulose, polyvinyl alcohol, sodium alginate, an initiator and the like, wherein the weight ratio of the starch, the acrylamide, the acrylate, the hydroxypropyl methyl cellulose, the polyvinyl alcohol and the sodium alginate is (10: 0.5-1): 0.2-1:0.2-0.5:0.3-0.5: 0.1-0.2.

The preparation method of the adsorbent sequentially comprises the following steps:

(a) adding wheat starch into 10-15 times of water, and gelatinizing at 80-95 deg.C for 0.5-1 hr to obtain gelatinized wheat starch;

(b) weighing cyclohexane, acrylamide, acrylate, hydroxypropyl methylcellulose, polyvinyl alcohol, sodium alginate and a cross-linking agent, and adding the weighed materials into the gelatinized wheat starch to obtain a mixed solution;

(c) adding an initiator into the mixed solution at 50-60 ℃, stirring for 1-2h, and performing centrifugal separation and drying on a product to obtain the spherical adsorbent.

The amount of cyclohexane used in step (b) is 3-5 times the amount of water used in step (a).

Wherein the initiator is an ammonium persulfate-sodium bisulfite composite initiator, and the weight ratio of the two initiators is 1: 1-2, the reaction is more stable when the ammonium persulfate-sodium bisulfite composite initiator is adopted, and the obtained super absorbent resin has good water absorption, high strength and more times of recycling.

Wherein the addition amount of the composite initiator accounts for 0.1-0.5% of the total mass of the monomers.

Wherein the crosslinking agent is N, N-Methylene Bisacrylamide (MBA), and the addition amount accounts for 0.01-0.1% of the total mass of the monomers.

Preferably, the monomer methyl methacrylate can be added in the step (a), the weight ratio of the monomer methyl methacrylate to the acrylamide is 20:1-2, and the hydrophobic monomer methyl methacrylate is added to be matched with a low-temperature composite initiator to initiate copolymerization, so that the water absorption rate and the gel strength of the resin are improved; when the amount of the added methyl methacrylate is too large, the obtained resin is too dense, the water absorption capacity is rather poor, and when the amount of the added methyl methacrylate is too small, the corresponding effect cannot be achieved.

Wherein the indexes of the polyisoprene latex in the step (1) are as follows: solid content is 5-10%, and particle diameter is 1-2 μm.

Wherein the mass fraction of the adsorbent in the dilute polyisoprene latex in the step (1) is 1-3%.

The stirring speed in the step (1) is as follows: at the speed of 100-400r/min and low rotation speed, the concentration of the solution is uneven, the concentration of the solution close to the surface of the adsorbent is high, colloidal particles in the emulsion are easy to agglomerate, the concentration of the solution far away from the surface of the adsorbent is low, and the efficiency of adsorbing water is reduced; under the condition of higher rotating speed, emulsion breaking phenomenon occurs to the emulsion due to the electrostatic adsorption effect of the stirring paddle or the rotor, so that colloidal particles are agglomerated.

The separation method in the step (2) comprises the following steps: after adsorbing water, the adsorbent expands to 0.5-15mm in diameter, and the simplest separation method is to filter and drain the adsorbent by using a screen.

The method for preparing the concentrated polyisoprene latex by low-temperature adsorption also comprises the step of regenerating the adsorbent, and the specific method comprises the following steps:

spreading the drained adsorbent on a screen with a thickness of about 2-3 layers, introducing hot air with a temperature of 30-80 ℃ from bottom to top, penetrating through the screen and the adsorbent layer, taking out the adsorbent after about 0.5-12 hours, and putting the adsorbent in latex emulsion again for recycling. The method is energy-saving and green, and meanwhile, the adsorbent cannot be damaged.

The action principle of the adsorbent is as follows:

the adsorbent in the invention is a polyelectrolyte containing hydrophilic groups and a cross-linked structure. Before water absorption, the polymer chains are mutually close and wound together and are mutually crosslinked, so that the integral fastening is realized. When the resin is contacted with water, because the water-absorbing resin contains a plurality of hydrophilic groups, after the surface of the resin is wetted, water molecules permeate into the resin through the capillary action and the diffusion action, and the ionized groups on the chains are ionized in the water. The polymer chains are stretched and swollen due to electrostatic repulsion between the same ions on the chains. Due to the requirement of electric neutrality, counter ions cannot migrate to the outside of the resin, and the ion concentration difference between the solution inside and outside the resin forms reverse osmosis pressure. The water further enters the resin under the action of reverse osmosis pressure to form hydrogel, so that the effect of water adsorption is achieved. The process is a physical process, and therefore the process is reversible and does not consume any energy.

The invention has the following beneficial effects:

the physical low-temperature adsorption is adopted, so that the energy consumption generated in the concentration process can be reduced, the temperature in the dehydration process is normal temperature, and compared with the processes such as evaporation and the like which need heating, the skinning can not occur; the spherical adsorbent is easy to clean, is not easy to adsorb colloidal particles and is coated by the colloidal particles, and the loss of latex is small; the adsorbent can be regenerated circularly by thermal drying, and the cost is reduced.

Detailed Description

The present invention is further illustrated by the following examples, which are intended to be illustrative of the present invention and are not intended to limit the scope of the present invention.

Example 1

The preparation method of the adsorbent A comprises the following steps:

(a) adding wheat starch into 10 times of water, and gelatinizing at 85 deg.C for 0.5h to obtain gelatinized wheat starch;

(b) weighing cyclohexane, acrylamide, acrylate, hydroxypropyl methylcellulose, polyvinyl alcohol, sodium alginate and a cross-linking agent, and adding the weighed materials into the gelatinized wheat starch to obtain a mixed solution;

(c) adding an initiator into the mixed solution at the temperature of 55 ℃, stirring for 1h, and performing centrifugal separation and drying on a product to obtain a spherical adsorbent;

wherein the weight ratio of starch, acrylamide, acrylate, hydroxypropyl methylcellulose, polyvinyl alcohol and sodium alginate is 10: 1: 1:0.5:0.5: 0.2;

the amount of cyclohexane used in step (b) is 3 times the amount of water used in step (a);

wherein the initiator is an ammonium persulfate-sodium bisulfite composite initiator, and the weight ratio of the two initiators is 1: 1.5, wherein the adding amount of the composite initiator accounts for 0.2 percent of the total mass of the monomers (the monomers refer to starch, acrylamide and acrylate);

wherein the cross-linking agent is N, N-Methylene Bisacrylamide (MBA), and the addition amount accounts for 0.05 percent of the total mass of the monomers;

the test shows that the tap water absorption capacity (tap water g/g resin) of the adsorbent A is 151.

Example 2

The preparation method of the adsorbent B comprises the following steps:

(a) adding wheat starch into 10 times of water, and gelatinizing at 85 deg.C for 0.5h to obtain gelatinized wheat starch;

(b) weighing cyclohexane, acrylamide, acrylate, hydroxypropyl methylcellulose, polyvinyl alcohol, sodium alginate and a cross-linking agent, and adding the weighed materials into the gelatinized wheat starch to obtain a mixed solution;

(c) adding an initiator into the mixed solution at the temperature of 55 ℃, stirring for 1h, and performing centrifugal separation and drying on a product to obtain a spherical adsorbent;

wherein the weight ratio of starch, acrylamide, methyl methacrylate, acrylate, methyl methacrylate, hydroxypropyl methyl cellulose, polyvinyl alcohol and sodium alginate is 10: 1: 0.05: 1:0.5:0.5: 0.2;

the amount of cyclohexane used in step (b) is 3 times the amount of water used in step (a);

wherein the initiator is an ammonium persulfate-sodium bisulfite composite initiator, and the weight ratio of the two initiators is 1: 1.5, wherein the adding amount of the composite initiator accounts for 0.2 percent of the total mass of the monomers (the monomers refer to starch, acrylamide and acrylate);

wherein the crosslinking agent is N, N-Methylene Bisacrylamide (MBA), and the addition amount of the crosslinking agent accounts for 0.05 percent of the total mass of the monomers.

The test showed that the adsorbent B had a tap water absorption capacity (tap water g/g resin) of 173.

Example 3

A method for preparing concentrated polyisoprene latex by low-temperature adsorption sequentially comprises the following steps:

(1) adding an adsorbent A into dilute polyisoprene latex with the solid content of 10%, wherein the mass fraction of the adsorbent in the dilute polyisoprene latex is 2%, stirring and concentrating for 5h, and the stirring speed is as follows: 300 r/min;

(2) and separating the adsorbent after concentration to obtain concentrated latex with the solid content of 55%, wherein the concentrated latex does not have skinning and has the mechanical stability of 1500 s.

If the adsorbent A is added to obtain latex with the solid content of 60%, a demulsification phenomenon can occur, so that the latex precipitates and deteriorates.

Example 4

A method for preparing concentrated polyisoprene latex by low-temperature adsorption sequentially comprises the following steps:

(1) adding an adsorbent B into dilute polyisoprene latex with the solid content of 10%, wherein the mass fraction of the adsorbent in the dilute polyisoprene latex is 2%, stirring and concentrating for 5h, and the stirring speed is as follows: 300 r/min;

(2) and separating the adsorbent after concentration to obtain concentrated latex with the solid content of 61%, wherein the concentrated latex has no demulsification phenomenon, no skin formation and the mechanical stability of 1523 s.

If the adsorbent A is added to obtain latex with the solid content of more than 65%, a demulsification phenomenon can occur, so that the latex is precipitated and deteriorated.

Example 5

(1) Adding an adsorbent B into a container of dilute polyisoprene latex with the solid content of 10%, wherein the mass fraction of the adsorbent in the dilute polyisoprene latex is 2%, stirring and concentrating for 4h, and the stirring speed is as follows: 300 r/min;

(2) separating the adsorbent B after concentration, transferring the primarily concentrated polyisoprene latex after the adsorbent is separated to the original container, then supplementing the dilute polyisoprene latex in the container until the volume of the dilute polyisoprene latex before the adsorbent B is added for the first time, then adding 1/2 of the dosage of the primary adsorbent for adsorption, stirring and concentrating for 1h, wherein the stirring speed is as follows: 300 r/min; adding 1/3 of the amount of the primary adsorbent for adsorption for the third time, and stirring and concentrating for 1h at the stirring speed: 300 r/min;

(3) separating the adsorbent after concentration to obtain concentrated latex with solid content of 71%, without demulsification and skinning, and with mechanical stability of 1532 s.

As can be seen from examples 3 to 5, when the water-absorbent resin having a comonomer comprising methyl methacrylate was used to gradually concentrate the dilute polyisoprene latex several times, it was easier to obtain highly concentrated polyisoprene latex, and the emulsion breaking and skin formation did not occur during the concentration, and the obtained latex was more stable mechanically.

The water-absorbent resin prepared in examples 1-2 of the present invention can be recycled for 20 times after regeneration.

Comparative example 1

A method for preparing concentrated condensed isoprene latex by an adsorption method sequentially comprises the following steps:

(1) adding sodium polyacrylate water-absorbent resin into dilute polyisoprene latex with the solid content of 10%, wherein the mass fraction of the adsorbent in the rubber latex is 2%, stirring and concentrating for 3h, and the stirring speed is as follows: 300 r/min;

(2) after concentration, the water-absorbent resin is separated to obtain concentrated latex with the solid content of 53 percent, the phenomenon of skinning and demulsification occurs, so that the latex is precipitated and deteriorated, and the sodium polyacrylate super-absorbent resin is easy to break during recycling and cannot be recycled.

In the test process, when the sodium polyacrylate water-absorbent resin and the adsorbent A with the same amount are used for preparing the condensed isoprene latex, the concentrated latex with the same solid content is obtained, the time required by the sodium polyacrylate super-absorbent resin is two thirds of that of the adsorbent A, and the surface tension of the latex is influenced because the absorption rate of the sodium polyacrylate super-absorbent resin is too high, so that the latex is easy to demulsify and unstable; if the amount of the sodium polyacrylate water-absorbent resin is reduced, the contact surface of the sodium polyacrylate water-absorbent resin and latex is too small, local demulsification can be caused, the production efficiency is reduced, and the particle size of the obtained concentrated latex is non-uniform, so that the subsequent use effect is influenced, and therefore, the sodium polyacrylate water-absorbent resin is not suitable for preparing the concentrated polyisoprene latex.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the principle of the invention after the examination are included in the protection scope of the invention.