CN115215961A - Water-absorbing foam based on double emulsifiers and preparation method thereof - Google Patents
Water-absorbing foam based on double emulsifiers and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a water-absorbing foam based on a double emulsifier and a preparation method thereof, wherein the water-absorbing foam is a mixture of a water phase system and an oil phase system and is obtained by emulsion polymerization under the action of an initiator solution; the water phase system is electrolyte aqueous solution with the mass fraction of 0.5-3%; the oil phase system is a mixture of 50-90% of acrylate monomers, 5-20% of vinyl monomers, 0.1-5% of cross-linking agents and 4-30% of double emulsifying agents by mass fraction, and the double emulsifying agents are a mixture of lipophilic surfactants and nano metal particles; the mass ratio of the water phase system to the oil phase system is (10-20): 1. The double emulsifiers are selected in the oil phase system, so that the stability of the emulsion and the strength of foam are effectively improved, the water-absorbing foam obtained after polymerization and drying has uniformly dispersed pores, and the average water-absorbing and water-retaining capacity of the water-absorbing foam is not lower than 20g/g.
Description
Technical Field
The invention belongs to the field of water-absorbing materials, and particularly relates to water-absorbing foam based on a double emulsifier and a preparation method thereof.
Background
Acrylic acid ester water-absorbing materials are widely used in the field of sanitary products due to their excellent water-absorbing and water-retaining properties, and nowadays, water-absorbing materials used in the fields of diapers, feminine sanitary products and the like are mainly composed of particulate acrylic acid esters. It has a "dough effect" after absorption of water, causing discomfort and leading to excessive central absorption without water absorption at the edges. Therefore, the development of the water-absorbing foam based on the acrylate is of great significance for improving the water absorbing and retaining capacity of the material and promoting commercial application.
Researches find that the high internal phase emulsion constructed by taking the existing emulsifier and acrylate materials as monomers has the problem of poor stability, and the stability of the emulsion can be damaged under the conditions of standing, reduction of stirring rotating speed, temperature rise or polymerization and the like, so that the oil-water separation condition of different degrees is caused, and the water absorption and water retention performance of the foam is further influenced. Particularly, when the initiator is added for emulsion polymerization, 10 to 40 weight percent of oil-water separation phenomenon can be caused, so that the water absorption and retention capacity of foam is greatly reduced, and the oil-water separation phenomenon of 30 to 80 weight percent can be caused after the foam modifier is added. The stability problem of the emulsion seriously influences the performance of the foam and the industrial production and modification research thereof.
Disclosure of Invention
The invention aims to overcome the technical defects, provides the water-absorbing foam based on the double emulsifier and the preparation method thereof, and solves the technical problem that the water-absorbing foam prepared in the prior art has poor water absorbing and water retaining capacities due to the instability of emulsion.
In order to achieve the technical purpose, the technical scheme of the water-absorbing foam based on the double emulsifier is as follows:
the water-absorbing foam is a mixture of a water phase system and an oil phase system and is obtained by emulsion polymerization under the action of an initiator solution; the water phase system is electrolyte aqueous solution with the mass fraction of 0.5-3%; the oil phase system is a mixture of 50-90% of acrylate monomers, 5-20% of vinyl monomers, 0.1-5% of cross-linking agents and 4-30% of double emulsifying agents by mass fraction, and the double emulsifying agents are a mixture of lipophilic surfactants and nano metal particles; the mass ratio of the water phase system to the oil phase system is (10-20): 1.
Further, the oil phase system comprises the following components: 60 to 70 weight percent of acrylic monomer, 7 to 15 weight percent of vinyl monomer, 0.1 to 2 weight percent of cross-linking agent and 10 to 15 weight percent of double emulsifier.
Furthermore, the acrylic monomer is isooctyl acrylate, propyl acrylate or butyl acrylate, the vinyl monomer is divinylbenzene, vinylphenol, vinylaniline or vinylbenzyl alcohol, and the crosslinking agent is ethylene glycol dimethacrylate.
Furthermore, the mass ratio of the lipophilic surfactant to the nano metal particles is (5-7): 1.
Further, the lipophilic surfactant is span-20, span-40, span-60, span-80 or span-85; the nano metal particles are nano titanium dioxide, nano silicon dioxide, nano zinc oxide, nano aluminum oxide or nano iron oxide.
Further, the electrolyte is anhydrous calcium chloride; the initiator solution is obtained by dissolving an initiator and calcium chloride in water, and the mass ratio of the initiator to the calcium chloride to the water is (0.6-1.2): (0.1-0.15) 10; the mass ratio of the initiator solution to the oil phase system is (0.7-0.9): 1.
Further, the initiator is dicumyl peroxide, di-tert-butyl cumene peroxide, di-tert-butyl peroxide or benzoyl peroxide.
The technical scheme of the preparation method of the water-absorbing foam based on the double emulsifier is as follows: the method comprises the following steps: adding the water phase system into the oil phase system, stirring until flocculent substances appear, dropwise adding an initiator solution, stirring uniformly after dropwise adding, carrying out emulsion polymerization, and drying the emulsion polymerization product to obtain the water-absorbing foam.
Further, the water phase system is added into the oil phase system at one time, and the stirring speed is 600-1000 RPM; and (4) dropwise adding an initiator solution, and regulating the rotating speed to be 1500-2500RPM.
Furthermore, the temperature of the emulsion polymerization is 70-90 ℃, and the time is 6-8 h.
Compared with the prior art, the invention has the beneficial effects that:
according to the invention, the double emulsifiers are selected in the oil phase system, wherein the surfactant has stronger emulsifying capacity on the water-in-oil emulsion, and the nano metal particles for promoting the dispersion of the emulsion are added, so that experiments show that the nano metal particles also have the effects of promoting the polymerization of the emulsion and enhancing the cross-linking of monomers, and the stability of the emulsion and the strength of foam are effectively improved. The emulsion prepared by the invention has excellent stability, and no obvious oil-water separation phenomenon occurs under the conditions of reduced stirring speed, heating or polymerization; the water-absorbing foam obtained after polymerization and drying has uniformly dispersed foam holes with the aperture of 5-10 mu m; the water-absorbing foam has good toughness and strength, and the average water absorption capacity and water retention capacity of the water-absorbing foam are not lower than 20g/g.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
The invention provides a high internal phase emulsion based on a double emulsifier with good stability, the stability of the emulsion is still good after a modifier is added, and the water-absorbing foam prepared by the emulsion has strong water absorbing and retaining capabilities.
The preparation method of the water-absorbing foam comprises the following steps:
s1, preparing an oil phase system: weighing 50-90 wt% of acrylate monomer, 5-20 wt% of ethylene monomer, 0.1-5 wt% of cross-linking agent and 4-30 wt% of double emulsifier, and uniformly stirring.
S2, preparing a water phase system: preparing electrolyte aqueous solution with the mass fraction of 0.5-3 wt%.
S3, preparing an initiator: preparing an initiator solution with the mass fraction of 5-15 wt%.
S4, adding the water phase system into the oil phase system at one time, stirring for 15-20 min at the stirring speed of 600-1000RPM, wherein the mass ratio of the water phase to the oil phase is 10-20: 1.
s5, after uniformly stirring, slowly dripping an initiator solution when flocculent substances appear (before emulsion is viscous), wherein the mass ratio of the initiator solution to an oil phase system is (0.7-0.9): 1; regulating the rotating speed to 1500-2500RPM. After the dripping is finished, stirring for 5-15 min. Regulating the temperature to 70-90 ℃, and carrying out emulsion polymerization for 6-8 h.
S6, drying the product at 50-70 ℃, washing and drying to obtain the water-absorbing foam product.
In step S1, the oil phase system preferably consists of: 60 to 70 weight percent of acrylic monomer, 7 to 15 weight percent of vinyl monomer, 0.1 to 2 weight percent of cross-linking agent and 10 to 15 weight percent of double emulsifier.
In step S1, the acrylic monomer is isooctyl acrylate, propyl acrylate, or butyl acrylate. The vinyl monomer is styrene monomer containing benzene, specifically divinylbenzene, vinylphenol, vinylaniline or vinylbenzyl alcohol. The cross-linking agent is ethylene glycol dimethacrylate. The acrylic monomer and the vinyl monomer are commonly used polymerization monomers in the field, and aim to form stable emulsion with water by utilizing the property of higher hydrophobicity.
In a most preferred embodiment, the acrylic monomer is isooctyl acrylate and the vinyl monomer is preferably divinylbenzene.
In step S1, the double emulsifier includes a lipophilic surfactant and nano metal particles.
The purpose of adding the double emulsifier in the invention is to reduce the interfacial tension of each component in a mixed system and form stable emulsion. The lipophilic surfactant used in the invention is more beneficial to emulsifying and dispersing monomers, and simultaneously, the nano metal particles with the function of reducing interfacial tension are added, thereby further enhancing the stability of the emulsion.
Preferably, the surfactant is span-20, span-40, span-60, span-80 or span-85. The nano metal particles are nano titanium dioxide, nano silicon dioxide, nano zinc oxide, nano aluminum oxide or nano iron oxide and the like.
As the optimal scheme, the surfactant is span-80, and the nano metal particles are nano zinc oxide.
In step S2, the electrolyte is anhydrous calcium chloride. The electrolyte adopted by the invention is a conventional raw material in the field, and has wide source and low cost; meanwhile, the addition of electrolyte can reduce the dissolving capacity of the continuous phase and inhibit the Oswald curing process, thereby improving the stability of the emulsion system.
In step S3, the initiator is an oil-soluble initiator, preferably a peroxide initiator, such as dicumyl peroxide, di-t-butylperoxide or benzoyl peroxide.
Most preferably, the peroxide initiator is benzoyl peroxide.
In the step S3, calcium chloride is contained in the initiator solution, and the mass ratio of the initiator, the calcium chloride and the water in the initiator solution is (0.6-1.2): (0.1-0.15): 10. The initiator is dissolved in water and added into the system, so that the stability of the emulsion is damaged, and particularly, the benzoyl peroxide is simply dissolved in the deionized water. Therefore, a small amount of calcium chloride is added to reduce the destabilizing effect on the emulsion.
And S4, adding the water phase into the oil phase at one time, adjusting the stirring rotation speed to 600-1000RPM after adding the water phase, and increasing the rotation speed to 1500-2500RPM when the initiator solution emulsion dropwise added in the S5 is thickened. The purpose of varying the rotation speed is to avoid that too high a rotation speed leads to sticking of the monomers to the container wall before the emulsion becomes viscous. The rotating speed is increased after the emulsion is viscous, so that the monomer is dispersed more uniformly, the emulsion stability is stronger, and the foam with uniform pore diameter can be easily prepared.
In the step S5, the polymerization temperature is preferably 70-90 ℃, and the polymerization rate can be increased and the polymerization time can be reduced by appropriately increasing the temperature, for example, at 70 ℃ for 8h, at 80 ℃ for 7.5h, at 90 ℃ for 6h, etc., but the polymerization temperature cannot be too high, so that the phenomena of implosion, too large and uneven product pore diameter, and the like are prevented, and the poor phenomena of too slow polymerization rate, even no polymerization, and the like are caused when the polymerization temperature is too low.
The invention mainly analyzes the mechanism:
(1) According to the invention, the surfactant with stronger emulsifying capacity to the water-in-oil emulsion is selected in the oil phase system, and the nano metal particles for promoting the dispersion of the emulsion are added, so that experiments show that the nano metal particles also have the effects of promoting the polymerization of the emulsion and enhancing the cross-linking of the monomers; it effectively improves the stability of the emulsion and the strength of the foam.
(2) The invention does not need to drip raw materials for a long time, and the reaction time is greatly reduced by directly mixing oil and water phases. The emulsion with good stability is synthesized by regulating and controlling the rotating speed, and the working procedures are saved. The stability is good, the phenomenon of oil-water separation is not easy to occur in the polymerization process of the emulsion, and only a small amount of oil-water separation occurs after the modified substance is added, so that the foam formed after drying has excellent water absorption and water retention properties.
(3) According to the invention, through a specific formula, the prepared emulsion has excellent stability, and no obvious oil-water separation phenomenon occurs under the conditions of long-time standing, reduced stirring rotating speed, heating or polymerization. The water-absorbing foam obtained after polymerization and drying has uniform dispersion of foam holes and good toughness and strength.
The emulsion prepared by the invention has excellent stability, and the water-absorbing foam obtained after polymerization and drying is suitable for the water-absorbing field of sanitary products and the like.
For avoiding redundancy, the main test items of the present invention are described herein:
1. internal phase volume fraction test
After the initiator is dripped in the step S5 and is stirred for 5-15 min, the water (V) on the surface of the emulsion sample is added 1 ) Sucking, putting into a centrifuge tube, and placing into a centrifuge for mild centrifugation at the rotation speed of 100-120 RPM for 3-5 min.
Then using a rubber head dropper to suck the surface water phase (V) after oil-water separation 2 ) The total volume of the oil phase and the water phase is V, and the volume fraction of the internal phase is (V-V) 1 -V 2 )/V×100％。
2. Cell size and diameter testing
Randomly selecting three samples on the dried water-absorbing foam, and observing the sizes of the cells and the diameters of the cells under a scanning electron microscope at 1000 times.
3. Tensile Strength test
The strength of the foam samples was tested using a foam tensile strength tester.
4. Water absorption and Water Retention test
0.5g of foam sample dried to constant weight is weighed three times at 25 ℃, placed in three 100ml beakers, 25ml of deionized water, physiological saline and artificial urine are respectively injected into the beakers, and the sample is placed in the beakers to be soaked for 10min. Subsequently, the foam is weighed, excess moisture on the surface of the foam is removed, and the weight M is recorded 1 、M 2 、M 3 . The average deionized water absorption rate of the sample is 2M within 10 minutes 1 g/g, average normal saline absorption rate of 2M 2 g/g, average absorption artificial urine rate of 2M 3 g/g。
In the water absorption test, the average water absorption of the foam within 10 minutes is experimentally measured, so that the index reflects both the water absorption performance and the water retention performance.
The inner phase is composed of water and forms a pore structure of foam after drying. Therefore, the larger the volume of the internal phase, the stronger the water-absorbing and water-retaining ability.
The mechanism of water absorption: first, due to the hydrophilic monomer on the foam surface; secondly, because the micro-cell structure absorbs and stores water, the smaller the cell size is, the stronger the water absorption and storage capacity is, for example, the diameter of the cell is 5-10 μm, and the water absorption and retention property is better than that of the cell with the diameter of 5-25 μm.
The present invention is further illustrated by the following specific examples.
Example 1
1. Preparation of water-absorbing foams based on dual emulsifiers
(1) Preparing an oil phase system, weighing 8.1g of isooctyl acrylate, 1.35g of divinylbenzene, 0.45g of ethylene glycol dimethacrylate, 3.0g of span-80 and 0.5g of nano zinc oxide, and uniformly stirring to obtain the oil phase system.
(2) Preparing a water phase system, weighing 1.5g of anhydrous calcium chloride and 120g of deionized water, and uniformly stirring to obtain the water phase system for later use.
(3) Preparing an initiator solution, weighing 0.9g of benzoyl peroxide, 0.125g of anhydrous calcium chloride and 10g of deionized water, and uniformly stirring to obtain the initiator solution for later use.
(4) Adding the prepared oil phase system into a 1000ml beaker, starting stirring, and adding the uniformly stirred water phase system into the beaker at one time, wherein the stirring speed is 800RPM. When the flocculent substance appears, slowly dripping an initiator, and adjusting the rotating speed to 2000RPM. After the dropwise addition, the mixture was stirred for another 5min.
(5) The stirred high internal phase emulsion was sealed and polymerized in a water bath at 70 ℃ for 8h.
(6) After the molding and curing, the mixture is put into a forced air drying oven to be dried for 12 hours at the temperature of 60 ℃. Taking out and repeatedly washing, and then putting into a forced air drying oven again to dry to constant weight.
2. Product testing
The high internal phase emulsion prepared in this example has good stability. After the initiator is dripped, the emulsion does not generate oil-water separation and is thick, and the volume fraction of the internal phase is 92.8 percent. No significant delamination occurred after polymerization. The tensile strength of the foam is 0.38MPa, the sizes of the foam holes are uniform, and the diameters of the foam holes are 5-10 mu m. Within 10 minutes, the average deionized water absorption rate is 25.77g/g (strong water absorption and retention capacity), the average physiological saline absorption rate is 23.41g/g, and the average artificial urine absorption rate is 21.37g/g.
Example 2
The difference from example 1 is that: replacing nano zinc oxide with nano silicon dioxide.
Namely, the oil phase system preparation of the step (1) comprises the following steps: 8.1g of isooctyl acrylate, 1.35g of divinylbenzene, 0.45g of ethylene glycol dimethacrylate-80.0 g of span and 0.5g of nano-silica are weighed. The other conditions were the same as in example 1.
The prepared emulsion has good stability. After the initiator is dripped, the emulsion is thick without oil-water separation; no significant delamination occurred after polymerization. The diameter of the cells of the resulting water-absorbing foam is 5 to 10 μm. The specific test results are detailed in table 1.
Example 3
The difference from example 1 is that: the nano zinc oxide is replaced by nano aluminum oxide.
The prepared emulsion has good stability. After the initiator is dripped, the emulsion is thick without oil-water separation; no significant delamination occurred after polymerization. The diameter of the cells of the resulting water-absorbing foam is 5 to 10 μm. The specific test results are detailed in table 1.
TABLE 1 test results for the products of examples 1-3
Because the main influence on the experiment is embodied in the diameter of the particles, the invention adopts the nano-scale metal particles, and the diameters of the obtained foam holes have small difference and are all 5-10 mu m; the invention is suitable for nano metal particle nano titanium dioxide, nano silicon dioxide, nano zinc oxide, nano aluminum oxide or nano iron oxide and the like.
As can be seen from Table 1, in examples 1 to 3, the types of the metal nanoparticles were changed, and the obtained water-absorbent foam had an internal phase volume fraction of 87.8 to 92.8%, a foam tensile strength of 0.34 to 0.38MPa, an average deionized water absorption rate of 22.48 to 25.77g/g, an average physiological saline absorption rate of 19.88 to 23.41g/g, and an average artificial urine absorption rate of 17.65 to 21.37g/g; the best effect is nano zinc oxide, so the nano metal particles are preferably nano zinc oxide.
Example 4
The difference from example 3 is that: polyvinyl alcohol (nano aluminum oxide + polyvinyl alcohol) is added in the oil phase system.
Namely, the step (1) of preparing the oil phase system comprises the following steps: 8.1g of isooctyl acrylate, 1.35g of divinylbenzene, 0.45g of ethylene glycol dimethacrylate, 3.0g of span, 0.5g of nano alumina and 0.2g of polyvinyl alcohol are weighed. The other conditions were the same as in example 3.
After polyvinyl alcohol is added as a strength modifier, the prepared emulsion is still thick, but a small amount of oil-water separation occurs, and the stability is good. The internal phase volume fraction after polymerization was 83.1%. The foam tensile strength is 0.41MPa, and the diameter of the foam hole is 5-10 mu m. The average deionized water absorption rate is 27.32g/g, the average physiological saline absorption rate is 26.44g/g and the average artificial urine absorption rate is 23.67g/g within 10 minutes. The specific test results are detailed in table 2.
Example 5
The difference from example 1 is that: 0.2g of polyvinyl alcohol (nano zinc oxide + polyvinyl alcohol) is added in the oil phase system.
Namely, the step (1) of preparing the oil phase system comprises the following steps: 8.1g of isooctyl acrylate, 1.35g of divinylbenzene, 0.45g of ethylene glycol dimethacrylate, 3.0g of span-80, 0.5g of nano zinc oxide and 0.2g of polyvinyl alcohol are weighed. The other conditions were the same as in example 3.
The specific test results are detailed in table 2.
Table 2 comparison of test results of example 1 and example 4
Example 4 is added with polyvinyl alcohol based on example 3, and span-80 and nano metal particles are used as a double emulsifier, so that the emulsion still maintains better stability after the polyvinyl alcohol is added as a modifier, and only a small amount of oil-water separation occurs, which shows that the volume fraction of the internal phase is slightly reduced; although the reduced volume of the internal phase reduces water absorption, the overall foam exhibits better water absorption and retention because the addition of polyvinyl alcohol increases the strength of the foam, effectively preventing the foam from collapsing during drying.
Comparing example 4 with example 5, compared with nano alumina + polyvinyl alcohol, the nano zinc oxide and polyvinyl alcohol adopted in example 5 are more beneficial to improving the overall performance, and especially the water-absorbing foam prepared in example 5 has high average water absorption rate and strong water-absorbing and water-retaining capacities.
Example 6
The obtained products were separately tested under the same conditions as in example 1 except that divinylbenzene was replaced with vinylphenol, vinylbenzyl alcohol and styrene, and the results are shown in Table 3 below.
TABLE 3 Water-absorbing foam Properties obtained with different vinylic monomers
As can be seen from Table 3, all the ethylene monomers adopted in the invention have good water absorption and retention capacities; since vinylphenol and vinylbenzyl alcohol contain hydrophilic groups, the stability of the emulsion is destroyed to a certain extent, so that oil-water separation is caused, the volume fraction of the internal phase is reduced, and the water absorption and retention capacity is reduced, which is also proved by the test results in table 3; therefore, in the reaction system of the invention, divinylbenzene, styrene and the like are adopted to have a synergistic effect with acrylic acid, and in consideration of comprehensive performance parameters, the vinyl monomer of the invention preferably adopts divinylbenzene and styrene, and the styrene has only one vinyl group, so that the crosslinking degree is inferior to that of divinylbenzene, the performance improving effect is slightly lower than that of divinylbenzene, and the divinylbenzene is most preferred.
Example 7 (preparation of Water-absorbing foams based on different initiators)
The difference from example 1 is that: the initiator was replaced with dicumyl peroxide and the other conditions were the same as in example 1.
Namely, the step (3) of configuring the initiator comprises the following steps: 0.9g of dicumyl peroxide, 0.125g of anhydrous calcium chloride and 10g of deionized water are weighed and stirred uniformly for later use.
Product testing was performed with different initiator species: after dicumyl peroxide is used, the oil-water separation phenomenon of the emulsion does not occur, and the volume fraction of an internal phase is 91.9%. No significant delamination occurred after polymerization. The tensile strength of the foam is 0.29MPa, the sizes of the foam holes are uniform, and the diameters of the foam holes are 5-10 mu m. Within 10 minutes, the average deionized water absorption rate is 20.87g/g, the average physiological saline absorption rate is 18.55g/g, and the average artificial urine absorption rate is 17.76g/g. Under the same conditions of temperature and time, experimental data show that compared with dicumyl peroxide, the initiation efficiency is lower than that of benzoyl peroxide, so that the initiator is preferably benzoyl peroxide in the invention.
Comparative example 1 preparation of Water-absorbing foam based on Single emulsifier
The difference from example 1 is that: the nano zinc oxide in the oil phase system is removed, and other conditions are the same as in example 1.
Namely, the step (1) of preparing the oil phase system comprises the following steps: 8.1g of isooctyl acrylate, 1.35g of divinylbenzene, 0.45g of ethylene glycol dimethacrylate and 3.0g of span-80 are weighed.
The prepared emulsion has good stability. After the initiator is dripped, the emulsion is thick due to a small amount of oil-water separation phenomenon; delamination occurred after polymerization and the specific test results are detailed in table 4.
Comparative example 2 preparation of Water-absorbing foam based on Single emulsifier
The difference from example 1 is that: span-80 in the oil phase system was removed and the other conditions were the same as in example 1.
Namely, the step (1) of preparing the oil phase system comprises the following steps: 8.1g of isooctyl acrylate, 1.35g of divinylbenzene, 0.45g of ethylene glycol dimethacrylate and 0.5g of nano zinc oxide are weighed.
The prepared emulsion has poor stability. After the initiator is added dropwise, the emulsion is obviously subjected to oil-water separation, and the layering phenomenon is generated after polymerization, and specific test results are detailed in table 4.
Comparative example 3 preparation of Water-absorbing foam based on Single emulsifier
The difference from example 1 is that: the dual emulsifier (span-80.0 g, nano zinc oxide 0.5 g) in the oil phase system was replaced with tween-80.0 g, and the other conditions were the same as in example 1.
Namely, the step (1) of preparing the oil phase system comprises the following steps: 8.1g of isooctyl acrylate, 1.35g of divinylbenzene, 0.45g of ethylene glycol dimethacrylate and 3.0g of tween-80 were weighed.
With the surfactant tween-80, which is commonly used in the art, as an emulsifier, severe phase separation occurred with a volume fraction of the internal phase of 12.0%, and no emulsion could be formed. The tensile strength of the foam is 0.1MPa, and the foam holes are different in size. Within 10 minutes, the average deionized water absorption rate is 4.12g/g, the average physiological saline absorption rate is 2.57g/g, and the average artificial urine absorption rate is 1.82g/g, and specific test results are detailed in Table 4.
Comparative example 4 (modified with a Mono-emulsifier + polyvinyl alcohol)
The difference from example 1 is that: the nano zinc oxide in the oil phase system was removed and 0.2g of polyvinyl alcohol was added, and the other conditions were the same as in example 1.
Namely, the step (1) of preparing the oil phase system comprises the following steps: the same procedures used in example 1 were repeated except that 8.1g of isooctyl acrylate, 1.35g of divinylbenzene, 0.45g of ethylene glycol dimethacrylate, 3.0g of span-80 and 0.2g of polyvinyl alcohol were weighed out.
The specific test results are detailed in table 4.
Table 4 test results of products of example 1 and comparative examples 1 to 2
As can be seen from the test results of example 1 and comparative examples 1-2 in Table 4, in the system of the present invention, the use of the double emulsifier can effectively improve the stability of the emulsion, the volume fraction of the internal phase of the emulsion is high, the pore size of the foam is small and uniform, and the strength, water absorption and water retention properties are excellent.
Comparative example 3 uses tween-80 commonly used in the field as a contrast, and because the hydrophilic-lipophilic balance value of the tween-80 is higher than that of span-80, the tween-80 cannot be well used as an emulsifier of the system, so that an obvious oil-water separation phenomenon is caused, and the performance is obviously reduced compared with that of comparative example 1.
Comparative example 4 is significantly reduced from comparative example 1, which shows that the stability of the emulsion is destroyed by adding a small amount of modifier polyvinyl alcohol in a single emulsifier system, thereby proving that the synergy is generated by adopting span-80, nano zinc oxide and polyvinyl alcohol in the invention example 5.
In conclusion, the emulsion with high dispersion phase coefficient and stability is prepared by using the double emulsifier and adopting an emulsion template method, and the water-absorbing foam with a space net-shaped structure is obtained after the emulsion is polymerized and dried, and has good strength and flexibility, uniform dispersion of foam holes and 5-10 mu m diameter of the foam holes; the internal phase volume fraction of the obtained water-absorbing foam is 85.7-92.8%, the foam tensile strength is 0.34-0.43 MPa, the average deionized water absorption rate is 20.87-28.07 g/g, the average physiological saline absorption rate is 18.55-27.44 g/g, and the average artificial urine absorption rate is 17.54-23.89 g/g, so that the water-absorbing foam can be applied to the water-absorbing field of sanitary products and the like. The double emulsifier and the preparation method thereof used by the invention effectively improve the stability of the emulsion, reduce the oil-water separation phenomenon of the emulsion in the polymerization process, and provide a feasible scheme for solving the stability of the emulsion and preparing the water-absorbing foam. The preparation process is simple and is favorable for industrial production.
The above-described embodiments of the present invention should not be construed as limiting the scope of the present invention. Any other corresponding changes and modifications made according to the technical idea of the present invention should be included in the protection scope of the claims of the present invention.
Claims (10)
1. A water-absorbing foam based on a double emulsifier is characterized in that the water-absorbing foam is a mixture of an aqueous phase system and an oil phase system and is obtained by emulsion polymerization under the action of an initiator solution;
the water phase system is an electrolyte aqueous solution with the mass fraction of 0.5-3%;
the oil phase system is a mixture of 50-90% of acrylate monomers, 5-20% of vinyl monomers, 0.1-5% of cross-linking agents and 4-30% of double emulsifying agents in percentage by mass, wherein the double emulsifying agents are a mixture of lipophilic surfactants and nano metal particles;
the mass ratio of the water phase system to the oil phase system is (10-20): 1.
2. The dual emulsifier based water absorbing foam of claim 1, wherein the oil phase system has a composition of: 60-70 wt% of acrylate monomer, 7-15 wt% of ethylene monomer, 0.1-2 wt% of cross-linking agent and 10-15 wt% of double emulsifier.
3. The double emulsifier-based water absorbent foam according to claim 1, wherein the acrylate monomer is isooctyl acrylate, propyl acrylate or butyl acrylate, the vinyl monomer is divinylbenzene, vinylphenol, vinylaniline or vinylbenzyl alcohol, and the crosslinking agent is ethylene glycol dimethacrylate.
4. The dual emulsifier based absorbent foam of claim 1, wherein the mass ratio of lipophilic surfactant to nano metal particles is (5-7): 1.
5. The dual emulsifier based water absorbing foam according to claim 1, wherein the lipophilic surfactant is span-20, span-40, span-60, span-80 or span-85; the nano metal particles are nano titanium dioxide, nano silicon dioxide, nano zinc oxide, nano aluminum oxide or nano iron oxide.
6. The dual emulsifier based water absorbing foam according to claim 1, wherein the electrolyte is anhydrous calcium chloride; the initiator solution is obtained by dissolving an initiator and calcium chloride in water, and the mass ratio of the initiator to the calcium chloride to the water is (0.6-1.2): (0.1-0.15) 10; the mass ratio of the initiator solution to the oil phase system is (0.7-0.9): 1.
7. The dual emulsifier based water absorbing foam of claim 6, wherein the initiator is dicumyl peroxide, di-t-butylperoxyisopropyl benzene, di-t-butyl peroxide or benzoyl peroxide.
8. Method for the preparation of a double emulsifier based absorbent foam according to any of the claims 1-7 comprising the steps of: adding the water phase system into the oil phase system, stirring until flocculent substances appear, dropwise adding an initiator solution, uniformly stirring after dropwise adding, carrying out emulsion polymerization, and drying the emulsion polymerization product to obtain the water-absorbing foam.
9. The method for preparing a double emulsifier-based water absorbent foam according to claim 8, wherein the aqueous phase system is added to the oil phase system at one time, and the stirring speed is 600-1000 RPM; and (4) dropwise adding an initiator solution, and adjusting the rotating speed to be 1500-2500RPM.
10. The method for preparing a dual emulsifier based water absorbent foam according to claim 8, wherein the emulsion polymerization temperature is 70-90 ℃ and the time is 6-8 hours.
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