Method for polymerizing expandable polystyrene particles with uniform particle size based on seed polymerization and venturi mixing

Abstract

The invention discloses a polymerization method of uniform-particle-size expandable polystyrene particles based on seed polymerization and venturi mixing. A Venturi mixer is adopted for material mixing in a breakthrough mode, gaseous styrene is crushed into micron-sized bubbles through high-speed turbulent mixed liquid, gas-liquid-solid three-phase instantaneous homogeneous dispersion is achieved, and added styrene monomers can be rapidly adsorbed by polystyrene seed particles and subjected to a polymerization reaction. The seed particles are screened as the unique growth starting point, the initial particle size difference is eliminated, the sub-CMC environment is combined to inhibit nucleation of new micelles, monomer styrene is forced to only diffuse to the surfaces of the seeds, secondary nucleation is completely eradicated, single-core oriented growth is achieved, and the uniformity of the particles is guaranteed. A nanoscale flaky hydroxyl calcium phosphate isolation system is created for the first time and cooperates with a subCMC emulsifier to enhance the surface double electric layer repulsive force, the nanoscale flaky hydroxyl calcium phosphate is directionally adsorbed on the surfaces of seed particles in a turbulent suspension to form a nanoscale isolation layer, the contact energy barrier between the particles is improved, and particle adhesion can be effectively prevented in the polymerization process.

Description

Technical Field

[0001] The invention relates to the field of expandable polystyrene polymerization, and in particular to a polymerization method for expandable polystyrene particles with uniform particle size based on seed polymerization and Venturi mixing. Background Art

[0002] Expandable polystyrene (EPS) is widely used in building insulation (exterior wall sandwich panels), precision instrument packaging (cushioning materials), food cold chain (insulated boxes) and artistic modeling (decorative lines) due to its light weight, heat insulation and impact resistance.

[0003] Traditional suspension polymerization methods suffer from numerous problems. Random nucleation during the initial polymerization phase results in a wide range of particle diameters, resulting in a low yield of target-sized particles. During the high-temperature polymerization phase, the particle surfaces melt, and mechanical agitation creates localized low-velocity zones that cause particle collisions and fusion. When styrene monomer is added to the reactor, mechanical agitation hinders homogeneous gas-liquid-solid three-phase mass transfer, leading to locally high monomer concentrations and the initiation of secondary nucleation.

[0004] Seed polymerization, through its "templated growth" strategy, has overcome many bottlenecks of traditional emulsion polymerization in terms of structural precision, high solid-state low viscosity, and functional customization, and has become a core technology for the synthesis of high-performance polymers. However, some technical challenges still exist in the industrial production of EPS. The EPS seed surface is highly hydrophobic and requires high-temperature softening to adsorb monomers, which exacerbates particle collision and adhesion. Traditional aqueous dispersants cover the seed surface unevenly, resulting in differences in monomer adsorption sites and dispersed particle size after growth. Continuous addition of monomers during the seed growth phase leads to uneven dispersion, resulting in excessively high local monomer concentrations and an explosion of new particles.

[0005] Based on the Bernoulli principle, the Venturi tube generates high-speed turbulence through a constricted throat, achieving instantaneous micron-level homogeneous dispersion with the low-pressure inhaled gas, thus overcoming the mass transfer limitations of traditional mixing. Its application in EPS polymerization offers unique advantages, allowing solid seed particles to undergo repeated acceleration and deceleration in the Venturi expansion section, maintaining continuous renewal of the particle surface and maximizing the probability of monomer adsorption.

[0006] Controlling the sub-CMC environment (emulsifier concentration 0.5-0.8×CMC) eliminates micelle "competitive adsorption." Combining seed polymerization with a Venturi device eliminates reaction dead zones, forces 100% directional diffusion of monomers to the seed surface, ensures uniform interparticle spacing, and reduces the coefficient of variation in particle size. Furthermore, nanoscale flake-like calcium hydroxyphosphate preferentially adsorbs on the seed surface in a sub-CMC environment, forming a nanoscale physical barrier, building a double-layer repulsion force, increasing the particle contact energy barrier, and reducing particle adhesion. Therefore, combining these advantages to develop a safe, efficient, and economical styrene polymerization method is of great practical significance. Summary of the Invention

[0007] The present invention improves upon the shortcomings of the prior art and provides a polymerization method for uniformly sized expandable polystyrene particles based on seed polymerization and Venturi mixing. The method comprises seed screening, Venturi gas-liquid-solid mixing, subcritical micelle concentration (CMC) control, and the synergistic action of a nano-isolator to prepare highly uniform expandable polystyrene particles.

[0008] The invention aims to provide a polymerization method for preparing highly uniform expandable polystyrene particles by seed screening, venturi gas-liquid-solid mixing, subcritical micelle concentration (CMC) control and synergistic action of nano-spacer.

[0009] To achieve the above-mentioned purpose, the present invention is implemented through the following technical solutions:

[0010] The present invention discloses a polymerization method for uniform-sized expandable polystyrene particles based on seed polymerization and Venturi mixing, comprising the following steps:

[0011] 1) Add deionized water, sodium dodecyl sulfate (SDS), sodium citrate, and dicumyl peroxide (DCP) to a reactor and stir to dissolve; then add nano-scale flaky calcium hydroxyphosphate, keep stirring, and heat up;

[0012] 2) adding polystyrene seed particles and stirring at high speed to form a suspended slurry;

[0013] 3) The suspended slurry is fed into the contraction section of the Venturi ejector for circulation at a flow rate of 15-20 m / s. Atomized styrene monomer is added to the throat of the Venturi ejector, mixed with the circulating liquid at high speed in the throat, and then sprayed into the reactor for reaction;

[0014] 4) Control the monomer addition rate. After adding half of the required monomers, raise the temperature to 105-115°C for polymerization reaction. After adding 3 / 4 of the required monomers, raise the temperature to 115-125°C for polymerization reaction. After adding all the monomers, keep warm and mature for 1 hour.

[0015] 5) After the polymerization reaction is completed, cool to 90-100°C, inject liquid foaming agent into the reactor, maintain the pressure at 1-1.5 MPa, and stir at low speed for 2 hours;

[0016] 6) After the reaction is completed, the mixture is cooled to room temperature, filtered, acid-washed, washed with water, and dried to obtain the product polystyrene particles.

[0017] As a further improvement, the amount of surfactant SDS used in step 1) of the present invention is 1.2-1.8 g / L.

[0018] As a further improvement, the amount of sodium citrate used in step 1) of the present invention is 1-3 g / L.

[0019] As a further improvement, the amount of the initiator DCP used in step 1) of the present invention is 0.3-0.7% of the mass of the styrene monomer.

[0020] As a further improvement, the amount of nano-scale flaky calcium hydroxyphosphate used in step 1) of the present invention is 5-15 g / L.

[0021] As a further improvement, the method for controlling the monomer addition rate in step 4) of the present invention is as follows: the single amount of monomer added per unit time is less than 60% of the total amount of polymerized styrene in the reactor.

[0022] As a further improvement, the pressure in the reactor in step 5) of the present invention is 1-1.5 MPa.

[0023] As a further improvement, the liquid blowing agent of the present invention is pentane.

[0024] As a further improvement, the polystyrene particles obtained by the present invention have a particle size variation coefficient CV <5%, a sticking rate <0.7%, and a target particle size yield >97.8%, which can reach 99.2%.

[0025] The beneficial effects of the present invention are as follows:

[0026] This invention utilizes a groundbreaking Venturi mixer for material mixing. Its high-speed turbulent mixed liquid (20 m / s) breaks gaseous styrene into micron-sized bubbles, achieving instantaneous homogeneous dispersion of the gas-liquid-solid three-phase system. This overcomes the mass transfer limitations of traditional mixing, allowing the added styrene monomer to be rapidly adsorbed by the polystyrene seed particles and undergo polymerization. By combining screened seed particles as the sole starting point for growth, eliminating initial particle size differences and combining a sub-CMC environment to inhibit the nucleation of new micelles, the styrene monomer is forced to diffuse only to the seed surface, eliminating secondary nucleation, achieving single-nuclear directional growth, and ensuring particle uniformity.

[0027] This invention pioneers a nanoscale, flake-like calcium hydroxyphosphate isolation system that synergistically enhances surface double-layer repulsion with a sub-CMC emulsifier. In turbulent suspensions, it adheres to the surface of seed particles, forming a nanoscale isolation layer. This increases the interparticle contact energy barrier and effectively prevents particle adhesion during polymerization. Sodium citrate ensures long-lasting dispersion of the nano-isolation agent through its integrated ion chelation, electrostatic stabilization, and buffering regulation.

[0028] The invention adopts a closed Venturi feeding system to prevent the escape of styrene gas phase, hydroxy calcium phosphate can be recovered by acid washing, and the sub-CMC environment reduces the amount of emulsifier used, thereby reducing the subsequent three waste treatment loads. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments, but the scope of the present invention is not limited to the embodiments.

[0030] Example 1 (seed particle size 3±0.1 mm)

[0031] 1) Add 1000 ml of deionized water to a reactor, add 1.2 g of SDS, 1 g of sodium citrate, and 0.3 g of DCP, and stir to dissolve; then add 5 g of nano-scale flake calcium hydroxyphosphate, and heat to 80°C while stirring at 500 rpm;

[0032] 2) Add 200 g of polystyrene seed particles and stir at 1000 rpm for 10 minutes to form a suspension slurry;

[0033] 3) The suspended slurry is fed into the contraction section of the Venturi mixer for circulation (flow rate 20 m / s), heated to 100°C, and 100 g of atomized styrene monomer is added in batches to the throat of the Venturi mixer. After high-speed mixing with the circulating liquid at the throat, the slurry is sprayed into the reactor for reaction;

[0034] 4) Control the monomer addition rate, add half of the required monomers, raise the temperature to 110°C for polymerization reaction, add 3 / 4 of the required monomers, raise the temperature to 120°C for polymerization reaction, and keep aging at 120°C for 1 hour after adding all the monomers.

[0035] 5) After the polymerization reaction, the mixture was cooled to 90° C., 80 g of pentane was injected into the reactor, the pressure was maintained at 1 MPa, and the mixture was stirred at a low speed of 300 rpm for 2 hours.

[0036] 6) After the gas filling is completed, the mixture is cooled to room temperature, filtered, acid-washed, washed with water, and dried to obtain the product polystyrene particles.

[0037] Result analysis: The average particle size of the product was 3.65 mm, the particle size distribution was 3.5–3.8 mm (particle size variation coefficient CV < 5%), the adhesion rate was less than 0.7%, the monomer conversion rate was greater than 99%, and the target particle size yield was 97.8%.

[0038] Example 2 (seed particle size 3±0.1 mm)

[0039] 1) Add 1000 ml of deionized water to a reactor, add 1.5 g of SDS, 2 g of sodium citrate, and 0.5 g of DCP, and stir to dissolve; then add 10 g of nano-scale flake calcium hydroxyphosphate, and heat to 80° C. while stirring at 500 rpm;

[0040] 2) Add 200 g of polystyrene seed particles and stir at 1000 rpm for 10 minutes to form a suspension slurry;

[0041] 3) The suspended slurry is fed into the contraction section of the Venturi mixer for circulation (flow rate 20 m / s), heated to 100°C, and 100 g of atomized styrene monomer is added in batches to the throat of the Venturi mixer. After high-speed mixing with the circulating liquid at the throat, the slurry is sprayed into the reactor for reaction;

[0042] 4) Control the monomer addition rate, add half of the required monomers, raise the temperature to 110°C for polymerization reaction, add 3 / 4 of the required monomers, raise the temperature to 120°C for polymerization reaction, and keep aging at 120°C for 1 hour after adding all the monomers.

[0043] 5) After the polymerization reaction, the mixture was cooled to 90° C., 80 g of pentane was injected into the reactor, the pressure was maintained at 1.2 MPa, and the mixture was stirred at a low speed of 300 rpm for 2 hours.

[0044] 6) After the gas filling is completed, the mixture is cooled to room temperature, filtered, acid-washed, washed with water, and dried to obtain the product polystyrene particles.

[0045] Result analysis: The average particle size of the product was 3.78 mm, the particle size distribution was 3.7–3.84 mm (particle size variation coefficient CV < 2%), the adhesion rate was less than 0.2%, the monomer conversion rate was greater than 99%, and the target particle size yield was 99.2%.

[0046] Example 3 (seed particle size 3±0.1 mm)

[0047] 1) Add 1000 ml of deionized water to a reactor, add 1.8 g of SDS, 3 g of sodium citrate, and 0.7 g of DCP, and stir to dissolve; then add 15 g of nano-scale flake calcium hydroxyphosphate, and heat to 80° C. while stirring at 500 rpm;

[0048] 2) Add 200 g of polystyrene seed particles and stir at 1000 rpm for 10 minutes to form a suspension slurry;

[0049] 3) The suspended slurry is fed into the contraction section of the Venturi mixer for circulation (flow rate 20 m / s), heated to 100°C, and 100 g of atomized styrene monomer is added in batches to the throat of the Venturi mixer. After high-speed mixing with the circulating liquid at the throat, the slurry is sprayed into the reactor for reaction;

[0050] 4) Control the monomer addition rate, add half of the required monomers, raise the temperature to 110°C for polymerization reaction, add 3 / 4 of the required monomers, raise the temperature to 120°C for polymerization reaction, and keep aging at 120°C for 1 hour after adding all the monomers.

[0051] 5) After the polymerization reaction, the mixture was cooled to 90° C., 80 g of pentane was injected into the reactor, the pressure was maintained at 1.5 MPa, and the mixture was stirred at a low speed of 300 rpm for 2 hours.

[0052] 6) After the gas filling is completed, the mixture is cooled to room temperature, filtered, acid-washed, washed with water, and dried to obtain the product polystyrene particles.

[0053] Result analysis: The average particle size of the product was 3.72 mm, the particle size distribution was 3.6–3.88 mm (particle size variation coefficient CV < 3%), the adhesion rate was less than 0.3%, the monomer conversion rate was greater than 99%, and the target particle size yield was 98.8%.

[0054] Comparative Example 1

[0055] Venturi mixing was eliminated and replaced with dropwise addition of styrene monomer and mechanical stirring, with other conditions being the same as in Example 2. The experimental results showed that the average particle size of the product was less than 3 mm, a large amount of fine particles were produced, and the yield of the target particle size was less than 5%.

[0056] It can be seen that, compared with Control Example 1, Example 2 only uses mechanical stirring for mixing, resulting in insufficient monomer dispersion and severe secondary nucleation.

[0057] Comparative Example 2

[0058] The sub-CMC environment was replaced with a super-CMC environment, the SDS dosage was 3.0 g / L, and other conditions were the same as in Example 2. The experimental results showed that the average particle size of the product was less than 3 mm, a large number of fine particles were produced, and the yield of the target particle size was less than 15%.

[0059] Comparative Example 3

[0060] No SDS was added, and other conditions were the same as in Example 2. The experimental results showed that the average particle size of the product was less than 3 mm, a large number of fine particles were produced, and the yield of the target particle size was less than 5%.

[0061] It can be seen that, compared with Control Examples 2 and 3, in Example 2, either the super-CMC environment or the non-CMC environment cannot inhibit the nucleation of new micelles, resulting in severe secondary nucleation and extremely low yield of the target product.

[0062] Comparative Example 3

[0063] Ordinary calcium phosphate was used instead of the nano-sized flaky calcium phosphate, and other conditions were the same as those in Example 2. The experimental results showed that the product particle size distribution was 3.1-3.8 mm (particle size variation coefficient CV>30%), the adhesion rate was>30%, and the target particle size yield was <50%.

[0064] Comparative Example 4

[0065] Without adding the nano-scale flaky calcium hydroxyphosphate, other conditions were the same as those in Example 2. The experimental results showed that all the particles were adhered into agglomerates.

[0066] It can be seen that, compared with Example 2 and Comparative Examples 3 and 4, the isolation effect of ordinary calcium phosphate is poor, the particle adhesion rate is significantly increased, and without adding an isolation agent, all the particles are adhered into agglomerates.

[0067] Comparative Example 5

[0068] No sodium citrate was added, and other conditions were the same as in Example 2. The experimental results showed that the product particle size distribution was 3.2-3.8 mm (particle size variation coefficient CV>30%), the adhesion rate was>30%, and the target particle size yield was<55%.

[0069] It can be seen that, compared with Example 5, without the addition of sodium citrate, the nano-isolating agent cannot be effectively dispersed for a long time in Example 2, the particle adhesion rate is significantly increased, and the target particle size yield is significantly reduced.

[0070] Example 6

[0071] The amount of initiator DCP used was less than 0.3% of the mass of the styrene monomer. Other conditions were the same as in Example 2. The experimental results showed that the average particle size was less than 3 mm, a large number of fine particles were produced, and the yield of the target particle size was less than 5%.

[0072] Example 7

[0073] The amount of initiator DCP used is greater than 0.7% of the mass of the styrene monomer. Other conditions are the same as those in Example 2. The experimental results show that the product particle size is uneven, the particle sphericity is extremely poor, and the yield of the target particle size is less than 5%.

[0074] As can be seen from the comparison between Examples 6 and 7, the initiator dosage in Examples is too low, resulting in slow monomer polymerization and monomer accumulation in the reactor. After exceeding the isolation capacity of the release agent, the monomers aggregate into small particles. Excessive initiator dosage leads to overly rapid polymerization, increased particle variation coefficient, and poor particle sphericity.

[0075] Finally, it should be noted that the above examples are merely specific implementation examples of the present invention. Obviously, the present invention is not limited to the above examples and is subject to numerous variations. All variations that can be directly derived or conceived by a person of ordinary skill in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for polymerizing expandable polystyrene particles of uniform particle size based on seed polymerization and Venturi mixing, characterized in that: The following steps are involved: 1) Add deionized water, sodium dodecyl sulfate (SDS), sodium citrate, and dicumyl peroxide (DCP) to a reactor and stir to dissolve; then add nano-scale flaky calcium hydroxyphosphate, keep stirring, and heat up; 2) adding polystyrene seed particles and stirring at high speed to form a suspended slurry; 3) The suspended slurry is fed into the contraction section of the Venturi ejector for circulation at a flow rate of 15-20 m / s. Atomized styrene monomer is added to the throat of the Venturi ejector, mixed with the circulating liquid at high speed in the throat, and then sprayed into the reactor for reaction; 4) Control the monomer addition rate. After adding half of the required monomers, raise the temperature to 105-115°C for polymerization reaction. After adding 3 / 4 of the required monomers, raise the temperature to 115-125°C for polymerization reaction. After adding all the monomers, keep warm and mature for 1 hour. 5) After the polymerization reaction is completed, cool to 90-100°C, inject liquid foaming agent into the reactor, maintain the pressure at 1-1.5 MPa, and stir at low speed for 2 hours; 6) After the reaction is completed, the mixture is cooled to room temperature, filtered, acid-washed, washed with water, and dried to obtain the product polystyrene particles.

2. The method for polymerizing expandable polystyrene particles of uniform particle size based on seed polymerization and Venturi mixing according to claim 1, characterized in that: The amount of surfactant SDS used in step 1) is 1.2-1.8 g / L.

3. The method for polymerizing expandable polystyrene particles of uniform particle size based on seed polymerization and Venturi mixing according to claim 1, characterized in that: The usage amount of sodium citrate in the step 1) is 1-3 g / L.

4. The method for polymerizing expandable polystyrene particles of uniform particle size based on seed polymerization and Venturi mixing according to claim 1, 2 or 3, characterized in that: In the step 1), the amount of the initiator DCP used is 0.3-0.7% of the mass of the styrene monomer.

5. The method for polymerizing expandable polystyrene particles of uniform particle size based on seed polymerization and Venturi mixing according to claim 4, characterized in that: The amount of the nano-scale flaky calcium hydroxyphosphate used in step 1) is 5-15 g / L.

6. The method for polymerizing expandable polystyrene particles of uniform particle size based on seed polymerization and Venturi mixing according to claim 5, characterized in that: The method for controlling the monomer addition rate in step 4) is as follows: the single amount of monomer added per unit time is less than 60% of the total amount of polymerized styrene in the reactor.

7. The method for polymerizing expandable polystyrene particles of uniform particle size based on seed polymerization and Venturi mixing according to claim 6, characterized in that: In the step 5), the pressure in the reactor is 1-1.5 MPa.

8. The method for polymerizing expandable polystyrene particles of uniform particle size based on seed polymerization and Venturi mixing according to claim 7, characterized in that: The liquid blowing agent is pentane.

9. The method for polymerizing expandable polystyrene particles of uniform particle size based on seed polymerization and Venturi mixing according to claim 1, 2, 3, 5, 6 or 7, characterized in that: The particle size variation coefficient CV of the obtained polystyrene particles is less than 5%, the adhesion rate is less than 0.7%, and the target particle size yield is greater than 97.8%, which can reach 99.2%.