CN108948236B

CN108948236B - Polystyrene macroscopic molding block and preparation method thereof

Info

Publication number: CN108948236B
Application number: CN201810681528.8A
Authority: CN
Inventors: 陶莹; 李德望; 杨全红; 张辰
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2018-06-27
Filing date: 2018-06-27
Publication date: 2020-02-14
Anticipated expiration: 2038-06-27
Also published as: CN108948236A

Abstract

The invention discloses a polystyrene macroscopic molding block and a preparation method thereof, belonging to the field of polymer material preparation. The preparation method comprises the following steps: firstly, taking persulfate as an initiator, deionized water as a medium, an anionic surfactant as an emulsifier and styrene as a monomer, carrying out emulsion polymerization to obtain a polystyrene microsphere emulsion, then adding a water-soluble organic solvent into the obtained polystyrene microsphere emulsion to demulsify and aggregate the polystyrene microsphere emulsion, and drying to obtain a polystyrene macroscopic forming block; compared with the prior art, the preparation method has simple process and is easy to realize large-scale production, and the polystyrene macroscopic molding block obtained by the invention has a compact three-dimensional network structure and excellent thermal stability.

Description

Polystyrene macroscopic molding block and preparation method thereof

Technical Field

The invention relates to the field of polymer material preparation, in particular to a polystyrene macroscopic molding block and a preparation method thereof.

Background

Polystyrene (PS) is a common plastic in industry and life, and is characterized in that the polystyrene is generally hard in texture, rigid in electrical insulation, heat insulation and small in hygroscopicity, chemical properties are stable below 300 ℃, but the polystyrene can be gradually softened and melted at the temperature higher than 100 ℃ so as to have processability, a common polystyrene type in industrial mass production is ① general polystyrene (GPPS), which has physical properties of the conventional PS and good light transmittance, and a molecular weight of 10-20 ten thousand, ② High Impact Polystyrene (HIPS), which is a copolymer (such as ABS, SAN and the like) formed by grafting a small amount of polybutadiene or other common rubber onto a polystyrene matrix, because PS is a brittle material and is poor in environmental stress resistance and easy to crack or deform, a common rubber solution is copolymerized during polymerization so as to toughen polystyrene, ③ Expanded Polystyrene (EPS), a light porous high polymer material, a conventional polystyrene resin synthesis process is characterized in that a dispersing agent and a foaming agent are added during the synthesis process of polystyrene resin, gas generated at a certain temperature and pressure is mixed into HIPS beads, the HIPS is toughened by a low-temperature foaming agent, and the polystyrene resin is subjected to a low-temperature polymerization process, and a low-temperature polymerization process is not uniform, and a low-temperature polymerization process is required for the polystyrene resin, and the polystyrene resin is obtained by a low-temperature polymerization process, and the conventional melt polymerization process is not uniform polymerization process, and the conventional processes are adopted.

Therefore, there is an increasing interest in developing a chemical synthesis process that allows styrene to be directly polymerized and crosslinked in situ into a macroscopically shaped block. The chemical synthesis method disclosed in the prior art is a high internal phase emulsion method (HIPE), which is to add water dropwise into a continuous phase composed of a surfactant with a low HLB (lipophilic property) value and a styrene/copolymerization crosslinking agent precursor monomer Divinylbenzene (DVB) to form an emulsion with a W/O structure until the volume of the aqueous phase is more than 74%, to form a high internal phase emulsion, and then to copolymerize and crosslink the styrene and the DVB in the continuous phase under the action of an initiator, so as to directly form a three-dimensional macroscopic block in one step. After polymerization, the dispersed phase is dried or extracted to remove the polymer, and the formed body rich in macropores can be obtained. The structure such as pore diameter, pore volume and the like can be regulated and controlled by adjusting the concentration of the surfactant, the proportion of the water phase and the oil phase, adding the pore-foaming agent and the like, but a compact structure is difficult to form finally, so that the mechanical property is lost.

Disclosure of Invention

Based on the technical defects in the background art, one of the purposes of the invention is to provide a preparation method of a polystyrene macroscopic molding block, which has the advantages of simple process, low cost and easy realization of large-scale production.

In order to achieve the purpose, the invention adopts the technical scheme that:

a method for preparing a polystyrene macroscopic shaping block comprises the following steps:

step one, taking deionized water as a medium, styrene as a monomer, an anionic surfactant as an emulsifier and persulfate as an initiator, and polymerizing for 5-8 hours at 70-80 ℃ to obtain a polystyrene microsphere emulsion;

step two, adding a water-soluble organic solvent into the polystyrene microsphere emulsion obtained in the step one, and demulsifying and coagulating the polystyrene microsphere emulsion to obtain a suspension containing precipitates; wherein the surface tension of the water-soluble organic solvent is less than 45.0 mN/m;

and step three, drying the suspension containing the precipitate obtained in the step two, and obtaining the polystyrene macroscopic molding block along with the volume shrinkage process.

Preferably, the preparation of the polystyrene microsphere emulsion in the first step comprises the following steps: sequentially adding styrene, anionic surfactant and persulfate into deionized water in Ar or N₂And (3) under the protection of atmosphere, carrying out heat preservation reaction at 70-80 ℃ for 6-8h, and cooling to room temperature to obtain the polystyrene microsphere emulsion.

Preferably, the anionic surfactant in the first step is at least one of sodium dodecyl sulfate, sodium dodecyl sulfate and sodium dodecyl benzene sulfonate; further preferably at least one of sodium lauryl sulfate and sodium lauryl sulfate.

Preferably, the weight of the anionic surfactant is 1.8 to 25 wt%, more preferably 2.3 to 20 wt%, and particularly preferably 9.8 to 20 wt% of styrene.

Preferably, the persulfate is at least one of potassium persulfate, ammonium persulfate and sodium persulfate;

preferably, the weight of the persulfate is 0.52 to 3.0 wt%, more preferably 0.85 to 1.7 wt%, and particularly preferably 1.2 to 1.5 wt% of that of styrene.

Preferably, the particle size of the polystyrene microsphere emulsion is 20-100nm, more preferably 20-85nm, and particularly preferably 25-40 nm.

Preferably, the water-soluble organic solvent in the second step is an organic solvent that is miscible with water, more preferably at least one of acetone, methanol, ethanol, tetrahydrofuran, acrylic acid, 1, 4-dioxane, and N-methylpyrrolidone, and particularly preferably ethanol.

Preferably, the volume ratio of the polystyrene microsphere emulsion to the water-soluble organic solvent in the second step is (1-6): (6-1), more preferably (1-5): (4-1), particularly preferably (2-5): (3-1).

Preferably, the drying temperature in the third step is 70-95 ℃, and the drying time is 10-50 h;

the second purpose of the present invention is to provide a polystyrene macroscopic formed block obtained by the above preparation method, wherein the polystyrene macroscopic formed block is a macroscopic formed block with a dense three-dimensional network structure.

In the preparation method of the polystyrene macroscopic forming block, the polystyrene microsphere emulsion with small grain diameter is put into a water-soluble organic solvent, so that the polystyrene microsphere emulsion is demulsified and coagulated, and the principle is as follows: since the larger the concentration of the surfactant in the system, the more micelles are generated, the less the styrene monomer content is coated in the micelles, the smaller the particle size of the polystyrene microspheres obtained after polymerization, and the larger the specific surface energy of the particles with smaller particle size is, it is also necessary to adsorb a high concentration of surfactant to lower the interfacial tension between itself and the aqueous phase to maintain stability. Due to the large surface tension of water (72.3N/m), once a sufficient amount of water-soluble organic solvent with small surface tension, such as ethanol (22.3N/m), is introduced, the interfacial tension between the continuous phase and the latex particles in the system is remarkably reduced, the adsorption binding energy of the particles to the surfactant in the emulsion is reduced from the thermodynamic perspective, and the original adsorption-desorption balance of the surfactant between the particle surface and the continuous phase is broken and tends to be more dissolved in the continuous phase; the polystyrene microsphere emulsion with small particle size and high specific surface energy, the surface of which is lack of sufficient surfactant protection, is continuously polymerized to reduce the specific surface area until emulsion breaking and coagulation, and polymer chains are gradually extended from the coiled conformation in the microsphere and are mutually crosslinked into a three-dimensional network; because the water-soluble organic solvent such as ethanol and the like and the organic high polymer such as polystyrene microsphere emulsion have a more obvious affinity effect than water, the subsequent drying process is a capillary evaporation process, and the continuous phase film layer pulls the high polymer interface to continuously shrink in the continuously thinning process by virtue of the surface tension effect until the continuous phase film layer is completely dried to form a macroscopically-formed block with a compact three-dimensional network structure.

Advantageous effects

Compared with the prior art:

(1) the preparation method has simple process, the polystyrene microsphere emulsion obtained by the emulsion polymerization method is demulsified, coagulated and dried at normal temperature and pressure to obtain the polystyrene macroscopic formed block with compact and solid structure, a high-temperature and high-pressure device is not needed, the condition is mild, and the energy consumption and the safety risk are greatly reduced;

(2) the polystyrene macroscopic molding block obtained by the preparation method has a compact three-dimensional network structure and excellent thermal stability.

Drawings

FIG. 1 is an SEM topography of a polystyrene macroscopic shaped block prepared in example 1;

FIG. 2 shows that the volume ratio of the polystyrene microsphere emulsion obtained in example 1 to the water-soluble organic solvent is 1: 2 diagram of coagulation effect after mixing.

Detailed Description

The technical solution of the present invention will be described in detail below with reference to specific examples.

Example 1

Step one, weighing 100mL of deionized water, 5.5mL of styrene and 1.3g of sodium dodecyl sulfate in sequence, adding the deionized water, the 5.5mL of styrene and the 1.3g of sodium dodecyl sulfate into a 250mL four-neck flask, fixing the four-neck flask in a water bath kettle with an iron stand, and respectively connecting the four-neck flask with N₂An air inlet, a thermometer, a condenser tube and a rubber plug, wherein the stirring speed is set to be 400r/min, and N is introduced₂The flow rate was controlled to 40mL/min by a flow meter, and 6.8mL of a potassium persulfate aqueous solution was injected into the flask by a syringeHeating in water bath at 70 deg.C for 6h, cooling to room temperature to obtain polystyrene microsphere emulsion, and observing with Transmission Electron Microscope (TEM) to obtain polystyrene microsphere emulsion with uniform particle size distribution (25 nm);

step two, weighing 5mL of the polystyrene microsphere emulsion obtained in the step one into a reagent bottle, then adding 10mL of ethanol into the reagent bottle to demulsify, aggregate and precipitate the polystyrene microsphere emulsion, and standing the reagent bottle to obtain a suspension containing precipitate;

and step three, placing the suspension containing the precipitate obtained in the step two into a forced air dryer, setting the temperature to be 80 ℃, and drying for 24 hours to obtain the polystyrene macroscopic molding block.

Example 2

The difference from the embodiment 1 is that: and replacing the ethanol in the second step with acetone, adding 5mL of the ethanol, and drying the ethanol in the third step at 70 ℃ for 10 hours, wherein the parameters of other steps are the same as those in the example 1.

Example 3

The difference from the embodiment 1 is that: the organic solvent in the second step is methanol, the drying temperature in the third step is 75 ℃, the drying time is 15h, and other parameters are the same as those in the example 1.

Example 4

The difference from the embodiment 1 is that: and replacing the ethanol in the second step with tetrahydrofuran, wherein the drying temperature in the third step is 75 ℃, the drying time is 15 hours, and other parameters are the same as those in the example 1.

Example 5

The difference from the embodiment 1 is that: and replacing the ethanol in the second step with acrylic acid, wherein the drying temperature in the third step is 90 ℃, the drying time is 48 hours, and other parameters are the same as those in the example 1.

Example 6

The difference from the embodiment 1 is that: replacing ethanol in the second step with 1, 4-dioxane, wherein the addition amount is 20mL, the drying temperature in the third step is 85 ℃, the drying time is 48h, and other parameters are the same as those in the first step

Example 1.

Example 7

The difference from the embodiment 1 is that: the addition amount of the ethanol in the second step is 20mL, the drying temperature in the third step is 80 ℃, the drying time is 36h, and other parameters are the same as those in the example 1.

Example 8

The difference from the embodiment 1 is that: in the first step, the mass of the sodium dodecyl sulfate is 0.56g, the temperature of the polymerization reaction is 75 ℃, the heat preservation time is 7h, and other parameters are the same as those of the example 1; wherein the particle size of the polystyrene microsphere emulsion obtained in the step one is 40 nm;

example 9

The difference from the embodiment 1 is that: in the first step, the mass of the sodium dodecyl sulfate is 0.25g, the initiator is sodium persulfate, the temperature of the polymerization reaction is 75 ℃, the heat preservation time is 8 hours, and other parameters of the steps are the same as those of the example 1; wherein the particle size of the polystyrene microsphere emulsion obtained in the step one is 60 nm;

example 10

The difference from the embodiment 1 is that: in the first step, the mass of the sodium dodecyl sulfate is 0.13g, the initiator is sodium persulfate, the temperature of the polymerization reaction is 75 ℃, the heat preservation time is 8h, and other parameters of the steps are the same as those of the example 1; wherein the particle size of the polystyrene microsphere emulsion obtained in the step one is 85 nm;

firstly, topography determination: the polystyrene molded block obtained in example 1 is observed in a scanning electron microscope, the observation result is shown in fig. 1, and as can be seen from fig. 1, the polystyrene macroscopic molded block prepared by the invention has a compact three-dimensional network structure.

Secondly, performance test:

1) coagulation phenomenon: weighing 8 parts of 5mL of the polystyrene microsphere emulsion prepared in example 1, adding ethanol (EtOH), Acetone (Acetone), methanol (MeOH), Tetrahydrofuran (THF), Acrylic Acid (AA), 1, 4-dioxane (1, 4-dioxane), N-methyl pyrrolidone (NMP), ethylene glycol, glycerol and deionized water with the same volume respectively, standing, and observing the coagulation condition of the polystyrene microsphere emulsion, wherein the precipitation molding in the description of the phenomenon refers to that the emulsion becomes turbid after an organic solvent is added, and flocculent blocks are rapidly formed and suspended on the liquid surface without heating and drying, but in addition, a large amount of precipitation particles free from the flocculent blocks exist, and the precipitation particles cannot be crosslinked with the blocks to form a unified whole after drying, so the uncontrollable molding phenomenon is not researched as a preferred scheme; light precipitation means that the emulsion became cloudy after addition of the organic solvent, but the color was not as dark as the other samples that precipitated, and the transmittance was between that of the precipitated and non-precipitated samples, as shown in FIG. 2 and Table 1:

TABLE 1

As can be seen from the results in Table 1, the coagulation of the polystyrene microsphere emulsion is caused by the change of the surface tension of the system after the addition of the water-soluble organic solvent, wherein the water-soluble organic solvent which is more different from the surface tension of water is more likely to cause the polystyrene microsphere emulsion to coagulate until the emulsion breaking coagulation (see FIG. 2), such as acetone, which can directly precipitate and form the polystyrene microsphere emulsion; the water-soluble organic solvent with smaller surface tension difference with water, such as N-methyl pyrrolidone, is not enough to obviously reduce the surface tension of the continuous phase, so that the adsorption-desorption balance of the surfactant between the surface of the emulsion particles and the continuous phase cannot be greatly changed, and the coalescence and demulsification degree among the particles are not sufficient; when an organic solvent having a higher surface tension than that of N-methylpyrrolidone, such as ethylene glycol (46.5mN/m), glycerin (63.3mN/m), or deionized water was directly added for dilution, no coagulation phenomenon was observed.

To illustrate the above condition ①, namely the relationship between the polystyrene microsphere emulsion coagulation and the amount of water-soluble organic solvent, the present invention provides reference examples 1-5, wherein ethanol (EtOH) is taken as an example, 5mL of the polystyrene microsphere emulsion with a particle size of 25nm prepared in example 1 is measured and mixed with ethanol in different volume ratios, and then the mixture is placed into an oven to be dried at 80 ℃ until being completely dried, and the coagulation phenomenon and the molding after drying are observed, and the results are shown in table 2:

TABLE 2

From the results in table 2, it can be seen that when the volume ratio of the polystyrene microsphere emulsion to ethanol is 1:1, coagulation phenomenon can be observed, and a light-weight formed product can be obtained, which indicates that the tendency of mutual bonding between the primary particles is not strong enough, and in order to reduce the surface tension of the system to be small enough, the polystyrene microsphere emulsion (25nm) with small particle size is coagulated and finally cross-linked and formed after drying, sufficient ethanol solvent needs to be added, i.e. the volume ratio of the polystyrene microsphere emulsion to the volume ratio of the ethanol solvent is more than 1: 1.

In order to investigate the ② condition, that is, the relationship between the coagulation and the particle size of the polystyrene microsphere emulsion, reference examples 6-10 were designed, wherein 5mL of the polystyrene microsphere emulsions with particle sizes of 25nm, 40nm, 60nm and 85nm obtained in the first step of example 1, example 8, example 9 and example 10 and the polystyrene microsphere emulsion with particle size of 400nm obtained when the mass of the surfactant Sodium Dodecyl Sulfate (SDS) is 0g were measured in sequence, 10mL of ethanol was added to the above samples, and then the samples were put into an oven to be dried at 80 ℃ until being completely dried, and the coagulation phenomenon and the molding condition after drying were observed, and the results are shown in table 3:

TABLE 3

As can be seen from table 3, by adding a surfactant with a higher concentration to a dispersion of water and styrene monomer, a greater number of solubilizing micelles with smaller particle size can be formed, so that a polystyrene microsphere emulsion with smaller particle size can be obtained after polymerization, and a sample of the emulsion with smaller particle size is more unstable in an environment where the interface balance is destroyed, and the particles aggregate and break emulsion, aggregate and finally crosslink more strongly than a sample with larger particle size; the emulsion samples with small particle size in reference examples 6 and 7 are finally formed into a unified whole after being added with ethanol and dried, while the emulsion samples with larger particle size in reference examples 8 and 9 are added with ethanol to be observed with precipitates, and a light-degree formed product is obtained after drying, which indicates that the tendency of mutual combination and crosslinking among original particles is not strong enough; in reference example 10, in which a stable submicron particle is maintained by copolymerizing a small amount of charges carried at the terminal of the initiator on the particle surface without adding a surfactant, there is no change in the adsorption balance of the surfactant between the two phases due to a change in interfacial tension between the two phases, and thus the addition of a water-soluble organic solvent that changes the surface tension of the system has no effect on the stability of the polystyrene microsphere emulsion in a short period of time.

2) Thermal stability performance:

thermogravimetric analysis of the polystyrene macroshaped blocks obtained in example 1 (labelled PS-EtOH) with the currently commercially available polystyrene particles (labelled PS-C) was carried out. The test conditions were: in N₂Raising the temperature from normal temperature to 700 ℃ under the protection of atmosphere, obtaining TG and DTA curve graphs at the temperature raising rate of 10 ℃/min, and obtaining dTG/dT curves corresponding to the two samples by deriving the obtained TG curves from the temperature, wherein the meaning is the weight loss rate at the temperature raising unit and represents the thermal decomposition rate, and the results are shown in Table 4:

TABLE 4

Sample name	Initial decomposition temperature (. degree. C.)	Fastest decomposition temperature (. degree. C.)
			PS-C	357.4℃	410℃
PS-EtOH	398.4℃	423.2℃

Compared with a commercial PS-C sample, PS-EtOH firstly degrades surfactant sodium dodecyl sulfate within the range of 200-300 ℃, but the initial and end temperatures of PS degradation are obviously improved compared with the commercial sample; in the dTG/dT curve, the initial decomposition temperature of the PS-EtOH sample is 398.4 ℃ (determined by the intersection point of two tangent lines respectively made by the curve of the section where decomposition does not occur and the curve of the section where decomposition is accelerated) and the fastest decomposition temperature is 423.2 ℃ (the minimum value of the curve), therefore, compared with the commercial PS-C sample, the polystyrene macroscopic formed block obtained by the invention has excellent thermal stability.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims

1. The preparation method of the polystyrene macroscopic molding block is characterized by comprising the following steps:

step two, adding a water-soluble organic solvent into the polystyrene microsphere emulsion obtained in the step one, and demulsifying and coagulating the polystyrene microsphere emulsion to obtain a suspension containing precipitates;

step three, drying the suspension containing the precipitate obtained in the step two, and obtaining a polystyrene macroscopic molding block along with a volume shrinkage process;

wherein the surface tension of the water-soluble organic solvent is less than 41.0mN/m, the particle size of the polystyrene microsphere emulsion is less than 25nm, and the volume ratio of the polystyrene microsphere emulsion to the water-soluble organic solvent in the second step is 1:1 or less;

or

The surface tension of the water-soluble organic solvent is less than 22.3mN/m, the particle size of the polystyrene microsphere emulsion is less than 85nm, and the volume ratio of the polystyrene microsphere emulsion to the water-soluble organic solvent in the second step is 1: 2 or less;

in the first step, the anionic surfactant is sodium dodecyl sulfate.

2. The method for preparing a polystyrene macroscopic molding block according to claim 1, wherein the step one for preparing the polystyrene microsphere emulsion comprises the steps of: sequentially adding styrene, anionic surfactant and persulfate into deionized water in Ar or N₂And (3) under the protection of atmosphere, carrying out heat preservation reaction at 70-80 ℃ for 6-8h, and cooling to room temperature to obtain the polystyrene microsphere emulsion.

3. The method of claim 1, wherein in step one, the persulfate is at least one of potassium persulfate, ammonium persulfate, and sodium persulfate.

4. The method of claim 1, wherein the persulfate is present in an amount of 0.52 to 3.0 wt.% based on the weight of styrene.

5. The method of claim 4, wherein the persulfate is present in an amount of 0.85 to 1.7 wt.% based on the weight of styrene.

6. The method of claim 5, wherein the persulfate is present in an amount of 1.2 to 1.5 wt.% based on the weight of styrene.

7. The method for preparing the polystyrene macroscopic shaped block according to claim 1, wherein the drying temperature in the third step is 70-95 ℃ and the drying time is 10-50 h.

8. The method of claim 1, wherein the water-soluble organic solvent is at least one of acetone, ethanol, methanol, tetrahydrofuran, acrylic acid, 1, 4-dioxane, and N-methyl pyrrolidone.

9. A polystyrene macroscopic shaped block obtained by the preparation method according to any one of claims 1 to 8, characterized in that the polystyrene macroscopic shaped block is a macroscopic shaped block with a compact three-dimensional network structure.