Polystyrene foam material with high cell size and preparation method thereof

Abstract

The invention relates to a polystyrene foam material with a high cell size. The polystyrene foam material comprises 80-95 wt% of a polymer base material, 0.5-3 wt% of a nucleating agent, 1-5 wt% of a flame retardant, 2.5-10 wt% of a physical foaming agent and 1-10 wt% of a cell stabilizer. The invention has the following beneficial effects: the cell stabilizer is introduced to enhance cell wall strength, promote gas directional aggregation, reduce heat convection and heat conductivity coefficient, maintain compression strength at 180 kPa or more, and significantly improve foaming ratio in a cell growth stage; the high-foam-size polystyrene foam can improve the firmness degree of the foam wall in the foam growth process, further improves the stability of the foam structure, also can ensure that the foam is not broken in the growth process, ensures the overall performance and the percentage of close area of the foam, further ensures the stability of the performance of the high-foam-size polystyrene foam for a long time, and saves the cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of energy-saving insulation for buildings, and particularly relates to a polystyrene foam material with large cell size and a preparation method thereof. BACKGROUND

[0002] Extruded polystyrene foam (XPS) is a common building insulation material. In the preparation of XPS by using a continuous extrusion foaming method, first, raw materials and additives are melted to obtain a homogeneous melt, then a physical foaming agent is injected into the homogeneous melt through a metering pump, then the homogeneous melt into which the physical foaming agent is injected is cooled to a temperature range suitable for foaming and molding through a second-stage single-screw extruder, and then the homogeneous melt is rapidly depressurized through a slit die, so that the homogeneous melt contacts the external environment through the slit die, the steady state between the homogeneous melt and the foaming agent is broken, the gaseous foaming agent escapes from the homogeneous melt through the slit die, and a porous structure is formed inside the homogeneous melt.

[0003] Further, as shown in Figure 1 , the foaming process of the physical foaming agent in the homogeneous melt can be divided into four stages:

[0004] 1) gas dissolution stage; gas dissolution refers to dissolving the foaming agent in the homogeneous melt under a specific pressure and temperature, and as the amount of the foaming agent dissolved increases, the power for the next two stages (bubble nucleation and cell growth) also increases, and the foaming ratio also increases;

[0005] 2) bubble nucleation stage; bubble nucleation refers to the process of converting gas from a bulk phase to a new phase (such as converting gas from a metastable phase to another stable phase with multiple phases, which is a first-order phase transition) under the introduction of a third phase (such as a nucleating agent); bubble nucleation is related to the critical radius of the bubble and the energy barrier required for the gas to break the critical radius; when the external environment changes (such as sudden heating or depressurization), the steady state of the system is broken, the gas begins to escape, and the bubble nucleus is formed; when the diameter of the bubble nucleus is greater than the critical radius, the bubble will gradually grow to form a stable bubble structure; when the diameter of the bubble nucleus is less than the critical radius, the bubble will gradually explore, and the gas will be re-dissolved in the polymer; as shown in Figure 2 , the introduction of the third phase (such as the nucleating agent) will form a site with lower interfacial energy between the gas and the polymer melt, and bubble nucleation is more likely to occur at the site, and the energy barrier and the critical bubble size are also smaller;

[0006] 3) bubble growth stage; as shown in Figure 3As shown, when the cell nucleus is greater than the diameter of the critical cell, the cell gradually grows to form a stable cell structure; at this time, the growth process of the cell can be divided into: delay stage, initial growth stage and diffusion growth stage; in the delay stage, the viscoelasticity of the polymer will hinder the sudden drop of pressure, and the cell cannot grow immediately; then enter the initial growth stage, the viscosity of the polymer is controlled, high temperature and high blowing agent concentration can reduce the strength of the melt and accelerate the bubble growth rate, low temperature and low blowing agent concentration can increase the melt strength and weaken the growth rate; finally into the diffusion growth stage, the diffusion growth stage is the most important stage to control the cell diameter and even the foaming ratio, in this stage, the gas near the cell is depleted, and the gas molecules far away from the cell diffuse into the cell, the main influencing factor of the long-distance gas molecule diffusion is the gas diffusion path, the strength of the melt is controlled by the blowing agent concentration and the mold temperature, and the strength of the melt finally affects the final form of the cell;

[0007] 4) Bubble shaping and solidification stage.

[0008] In the conventional technology, the strength of the melt is generally controlled by adjusting the temperature, thereby controlling the size of the cell: for example, increasing the temperature can appropriately reduce the strength of the melt, the reduction of the strength of the melt reduces the restriction on the growth of the cell, thereby gradually increasing the size of the cell and the foaming ratio, reducing the apparent density and material cost; however, when the temperature is too high, the cell wall cannot limit the escape of the blowing agent due to the too low strength, causing the cell wall to break and affecting the overall performance of the foam; although appropriately reducing the temperature can increase the strength of the melt, limit the growth of the cell, and thereby obtain a foam product with small cell size, the reduction of the foaming ratio is not conducive to cost optimization, and in severe cases, it can also cause large-area non-foaming, the microcellular structure can affect the macro performance, and the thermal insulation performance of the foam product is reduced. SUMMARY

[0009] The purpose of the present application is to overcome the shortcomings in the prior art, and to provide a high-cell-size polystyrene foam material and a preparation method, which solves the difficulties encountered in the cell growth process.

[0010] The high-cell-size polystyrene foam material comprises, by mass fraction: 80-95 wt% of a polymer base material, 0.5-3 wt% of a nucleating agent, 1-5 wt% of a flame retardant, 2.5-10 wt% of a physical blowing agent, and 1-10 wt% of a cell stabilizer; the polymer base material is polystyrene (general-purpose polystyrene, GPPS), the nucleating agent is talc, the flame retardant is methyl octabromoether or brominated SBS, the physical blowing agent includes at least one of alcohol, carbon dioxide, dimethyl ether, dichloromonofluoromethane (R22) and 1,1-difluoroethane (R142b), and the cell stabilizer includes at least one of sodium dodecyl sulfate, polyethylene glycol and glycerol monostearate.

[0011] As preferred: the flame retardant is methyl octabromo ether.

[0012] As preferred: the cell stabilizer is polyethylene glycol.

[0013] The preparation method of the polystyrene foam material with high cell size comprises the following steps:

[0014] Step 1, the polymer base material, nucleating agent, flame retardant and cell stabilizer are metered by a metering device according to the set mass fraction, and then continuously and stably conveyed from the feeding port to the twin-screw extruder, the temperature of each region of the twin-screw extruder is controlled within 200-230℃, so that the polymer base material is fully melt-blended with the nucleating agent, the flame retardant and the cell stabilizer, and a melt-blended body is obtained;

[0015] Step 2, the physical foaming agent in the foaming agent storage tank is stably injected into the twin-screw extruder, the physical foaming agent is quickly dissolved in the melt-blended body by high-speed rotation and shearing of the shearing block in the twin-screw extruder, and a homogeneous mixture system is obtained;

[0016] Step 3, after the homogeneous mixture is filtered by the screen changer in the twin-screw extruder to remove impurities, it is conveyed to the single-screw extruder through the conveying pipeline, the single-screw extruder adopts a zoned step-down temperature mode, the temperature of each region of the single-screw extruder is set within 90-170℃ according to a certain temperature difference decreasing mode, the homogeneous mixture after impurity removal is fully cooled to reach the foaming temperature interval in the single-screw extruder to improve the strength of the melt; the rotation speed of the single screw in the single-screw extruder should not be too fast, so as to avoid the heat generated by screw shearing from heating the homogeneous mixture, and the cooling rate of the homogeneous mixture should be efficient and rapid;

[0017] Step 4, the homogeneous mixture after reaching the foaming temperature interval and filtering out impurities is rapidly discharged through the die opening of the single screw extruder to form polystyrene foam (in the process of foaming after the homogeneous mixture reaches the foaming temperature interval and filters out impurities from the die opening, the bubble nucleation and bubble growth are in a competitive relationship, and when the gas is used for bubble growth, the driving force of bubble nucleation will gradually disappear, the introduced bubble stabilizer can stabilize the bubble structure in the initial growth stage of the bubble, so that the gas can quickly gather in the formed bubble structure, promote bubble growth, and further inhibit bubble nucleation, effectively increase the average bubble diameter and improve the foaming ratio; during the bubble growth process, the bubble stabilizer can prevent bubble wall rupture, reduce foam opening phenomenon, and improve foam closed cell rate, which is more conducive to improving the comprehensive performance of the foam), the polystyrene foam is shaped through a shaping module (in the bubble forming process, the bubble stabilizer is compounded on the inner surface of the bubble to form a film, which can effectively slow down the escape of the foaming agent and slow down the gas exchange inside and outside the bubble, which is beneficial to long-term maintenance of the thermal conductivity and other properties of the foam), and after cooling through a cooling rack, a high-bubble-size polystyrene foam is formed.

[0018] As preferred, in step 3: the screen changer is a replaceable device, and the screen changer should be replaced and cleaned of large impurities on the wire mesh after a period of operation to avoid affecting the production efficiency; the conveying pipeline does not contain a screw, and the barrel temperature of the conveying pipeline should not be too low to avoid material blockage.

[0019] As preferred, in step 3: the front part of the single screw extruder is also provided with a static mixer or a melt pump for controlling and maintaining the pressure of the homogeneous mixture to prevent premature pressure relief of the homogeneous mixture and pre-foaming; the static mixing temperature of the static mixer is higher than the temperature in the twin screw extruder to prevent flow stagnation dead zones in the melt at this point.

[0020] The beneficial effects of the present application are:

[0021] The present application introduces a bubble stabilizer (sodium dodecyl sulfate, polyethylene glycol, glycerol monostearate) to achieve the following effects during the bubble growth stage: 1) strengthen the bubble wall strength: the stabilizer forms a protective film on the inner wall of the bubble, which significantly reduces the risk of bubble rupture; 2) promote directional gas aggregation: it can inhibit disordered nucleation, guide the gas to concentrate on the formed bubble, increase the average bubble diameter, and the increase of the bubble size can reduce the heat convection and thermal conductivity, keep the compressive strength above 180 kPa, and significantly improve the foaming ratio.

[0022] The preparation method of the application: by setting a static mixer / melt pump to accurately control the melt pressure, avoid early pressure relief in the single screw conveying stage, and inhibit pre-foaming; the single screw extruder adopts a zoned stepwise cooling mode, combined with a screwless conveying pipeline, which can eliminate material blockage and improve the cooling rate; the synergistic use of flame retardants (methyl octabromide / brominated SBS) and cell stabilizers improves the flame retardant grade of polystyrene foam material;

[0023] The preparation method of the high-cell-size polystyrene foam material of the application can improve the strength of the cell wall during cell growth under the premise of ensuring high foaming ratio, thereby improving the stability of the cell structure, and can also ensure that the cells will not be broken during growth, ensure the overall performance and closed cell rate of the foam, and thus long-term guarantee the stability of the performance of the high-cell-size polystyrene foam, saving costs. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a schematic diagram of the foaming process of the physical foaming agent in the homogeneous melt in the prior art;

[0025] Figure 2 It is a comparison diagram of heterogeneous nucleation and homogeneous nucleation in the prior art;

[0026] Figure 3 It is a schematic diagram of the growth process of the cell in the bubble growth stage in the prior art;

[0027] Figure 4 It is a preparation flow chart of the high-cell-size polystyrene foam material.

[0028] Explanation of reference signs: foaming agent storage tank 1, metering feeding device 2, double screw extruder 3, single screw extruder 4, head 5. DETAILED DESCRIPTION

[0029] The application will be further described below in conjunction with examples. The following examples are only used to help understand the application. It should be noted that for ordinary people in the technical field, several modifications can be made to the application without departing from the principles of the application, and these improvements and modifications also fall within the protection scope of the claims of the application.

[0030] Example 1

[0031] As Figure 4As shown, the first method for preparing a high-cell-size polystyrene foam material, polystyrene virgin material: 100 parts, talcum powder: 1 part, methyl octabromo ether: 3 parts, polyethylene glycol: 1 part, accurately proportioned by the loss-on-ignition balance and fed into the twin-screw extruder, the temperature of each zone of the twin-screw extruder: Zone 1 200°C, Zone 2 210°C, Zone 3 230°C, Zone 4 200°C, Zone 5 200°C, Zone 6 200°C, so that the polymer matrix is fully melt-blended with the nucleating agent, the flame retardant, and the cell stabilizer to obtain a melt-blended body. The physical foaming agent is injected into the twin-screw extruder 3 in the following proportions: alcohol: 1 part, carbon dioxide: 3.5 parts, 1,1-difluoroethane (R142b): 3 parts; the physical foaming agent is quickly dissolved in the melt-blended body by high-speed rotary shearing of the shearing block in the twin-screw extruder 3 to obtain a homogeneous mixture system. After the homogeneous mixture is filtered to remove impurities by the screen changer in the twin-screw extruder 3, it is conveyed to the single-screw extruder 4 through the conveying pipeline, and the single-screw extruder 4 adopts a zoned stepwise temperature reduction mode, and the temperature of each zone of the single-screw extruder 4 is set according to a certain temperature difference decreasing formula: core 150°C, Zone 2 100°C, Zone 3 170°C, Zone 4 150°C, Zone 5 150°C, Zone 6 150°C, Zone 7 150°C, Zone 8 150°C; the homogeneous mixture after impurity removal is fully cooled to reach the foaming temperature range in the single-screw extruder 4 to improve the strength of the melt; the rotation speed of the single screw in the single-screw extruder should not be too fast, so as not to heat the homogeneous mixture due to the heat generated by screw shearing, and the cooling rate of the homogeneous mixture should be efficient and rapid. The homogeneous mixture after impurity removal and after reaching the foaming temperature range is quickly pressure-released and foamed into a polystyrene foam material through the die opening on the single-screw extruder 4, and after the polystyrene foam material is shaped by the shaping module and cooled by the cooling rack, a high-cell-size polystyrene foam material is formed.

[0032] The performance of the product is tested by using a universal testing machine, a thermal conductivity tester, a water density tester, and other equipment.

[0033] Example 2

[0034] The second method for preparing a polystyrene foam material with a large cell size comprises: 100 parts of polystyrene virgin material, 1 part of talcum powder, 3 parts of methyl octabromo ether, and 5 parts of polyethylene glycol are accurately weighed by a loss-on-ignition balance and then fed into a twin-screw extruder, and the temperature of each zone of the twin-screw extruder is set as follows: 200°C for zone 1, 210°C for zone 2, 230°C for zone 3, 210°C for zone 4, 210°C for zone 5, 210°C for zone 6, so that the polymer base material is fully melt-blended with the nucleating agent, the flame retardant, and the cell stabilizer to obtain a melt-blended body. The physical foaming agent is injected into the twin-screw extruder 3 in the following proportions: 1 part of alcohol, 3.5 parts of carbon dioxide, and 3 parts of 1,1-difluoroethane (R142b); the physical foaming agent is quickly dissolved in the melt-blended body by high-speed rotation and shearing of the shearing block in the twin-screw extruder 3 to obtain a homogeneous mixture system. After the homogeneous mixture is filtered to remove impurities by a screen changer in the twin-screw extruder 3, it is conveyed to a single-screw extruder 4 through a conveying pipeline, and the temperature of each zone of the single-screw extruder 4 is set in a stepwise decreasing temperature mode with a certain temperature difference: 160°C for the core, 100°C for zone 2, 170°C for zone 3, 160°C for zone 4, 160°C for zone 5, 160°C for zone 6, 160°C for zone 7, and 150°C for zone 8, so that the homogeneous mixture after impurity removal is fully cooled to reach the foaming temperature range in the single-screw extruder 4 to improve the strength of the melt; the rotation speed of the single screw in the single-screw extruder should not be too fast, so as to prevent the heat generated by the screw shearing from heating the homogeneous mixture, and the cooling rate of the homogeneous mixture should be high and efficient. After reaching the foaming temperature range, the homogeneous mixture after impurity removal is quickly depressurized and foamed into a polystyrene foam material through the die opening of the single-screw extruder 4, and the polystyrene foam material is shaped by a shaping module and cooled by a cooling rack to form a polystyrene foam material with a large cell size.

[0035] The performance of the product is tested by using a universal testing machine, a thermal conductivity tester, a water density tester, and other equipment.

[0036] Example 3

[0037] The third method for preparing polystyrene foam with large cell size comprises: 100 parts of polystyrene virgin material, 1 part of talcum powder, 3 parts of methyl octabromo ether, and 10 parts of polyethylene glycol are accurately weighed by a loss-on-ignition balance and then fed into a twin-screw extruder, and the temperature of each zone of the twin-screw extruder is set as follows: 200°C for zone 1, 210°C for zone 2, 230°C for zone 3, 220°C for zone 4, 220°C for zone 5, 220°C for zone 6, so that the polymer base material is fully melt-blended with the nucleating agent, the flame retardant, and the cell stabilizer to obtain a melt-blended body. The physical foaming agent is injected into the third twin-screw extruder according to the following proportion: 1 part of alcohol, 3.5 parts of carbon dioxide, and 3 parts of 1,1-difluoroethane (R142b); the physical foaming agent is quickly dissolved in the melt-blended body by high-speed rotation and shearing of the shearing block in the third twin-screw extruder to obtain a homogeneous mixture system. After the homogeneous mixture is filtered to remove impurities by a screen changer in the third twin-screw extruder, the homogeneous mixture is conveyed to a single-screw extruder 4 through a conveying pipeline, and the temperature of each zone of the single-screw extruder 4 is set according to a certain temperature difference decreasing mode: 150°C for the core, 100°C for zone 2, 170°C for zone 3, 150°C for zone 4, 150°C for zone 5, 150°C for zone 6, 150°C for zone 7, and 160°C for zone 8, so that the homogeneous mixture after impurity removal is fully cooled to reach the foaming temperature range to improve the strength of the melt; the rotation speed of the single screw in the single-screw extruder should not be too fast, so as to prevent the heat generated by the screw shearing from heating the homogeneous mixture, and the cooling rate of the homogeneous mixture should be high and efficient. After reaching the foaming temperature range, the homogeneous mixture after impurity removal is quickly depressurized and foamed into polystyrene foam through the die opening of the single-screw extruder 4, and the polystyrene foam is shaped by a shaping module and cooled by a cooling rack to form polystyrene foam with large cell size.

[0038] The performance of the product is tested by using a universal testing machine, a thermal conductivity tester, a water density tester, and other equipment.

[0039] Comparative Example 1

[0040] The polystyrene virgin material: 100 parts, talcum powder: 1 part, methyl octabromo ether: 3 parts, polyethylene glycol: 0 parts, are accurately put into the double screw extruder by the loss on drying scale in proportion, the temperature of each zone of the double screw is 200-230℃, the foaming agent is injected in the following proportion: alcohol: 1 part, carbon dioxide: 3.5 parts, R142b: 3 parts. The uniformly mixed melt is transported to the single screw extruder through the transition section, the temperature of each zone of the single screw is set: core 150℃, second zone 100℃, third zone 170℃, fourth zone 150℃, fifth zone 150℃, sixth zone 150℃, seventh zone 150℃, eighth zone 150℃, a step-down cooling mode is adopted, and then the product is formed by foaming through the mold.

[0041] The performance of the product is tested by using a universal testing machine, a thermal conductivity tester, a water density tester and other equipment.

[0042] The test results of Examples 1 to 3 and Comparative Example 1 are shown in Table 1 below. It is undoubtedly known that the introduction of the cell stabilizer (polyethylene glycol) can stabilize the cell structure in the initial growth stage of the cell, enable the gas to quickly gather into the formed cell structure, promote cell growth, and further inhibit cell nucleation, effectively increase the average cell diameter and improve the foaming ratio; during the cell growth process, the cell stabilizer can prevent cell wall rupture, reduce foam opening phenomenon, and improve foam closed cell rate, which is more conducive to improving the comprehensive performance of the foam; during the cell forming process, the cell stabilizer is compounded on the inner surface of the cell to form a film, which can effectively slow down the escape of the foaming agent and slow down the gas exchange inside and outside the cell. The three examples all use polyethylene glycol as a cell stabilizer, and the test data shows that as the amount of polyethylene glycol increases, the cell size increases and the thermal conductivity decreases, while maintaining sufficient mechanical strength. Although the compressive strength of Comparative Example 1 (without adding a cell stabilizer) is slightly higher, the thermal conductivity is significantly inferior to Examples 1 to 3, which proves the key role of the cell stabilizer.

[0043] Table 1: Parameter performance table of extruded polystyrene foam materials in examples and comparative examples

[0044] Test item Unit Example 1 Example 2 Example 3 Comparative Example 1 Apparent density kg / m 3 ]] 31.6 30.7 30 32 Thickness mm 20.0 20.2 20.5 19.9 Compressive strength kPa 203 198 180 211 Thermal conductivity, 25°C W / (m·K) 0.023743 0.023032 0.02271 0.02486 Combustion performance % B2 B2 B2 B2

Claims

1. A polystyrene foam material with high cell size, characterized in that, The product comprises, by mass fraction: 80–95 wt% polymer substrate, 0.5–3 wt% nucleating agent, 1–5 wt% flame retardant, 2.5–10 wt% physical foaming agent, and 1–10 wt% cell stabilizer; wherein the polymer substrate is polystyrene, the nucleating agent is talc, the flame retardant is methyl octabromoether or brominated SBS, the physical foaming agent comprises at least one of the following: alcohol, carbon dioxide, dimethyl ether, dichlorofluoromethane, and 1,1-difluoroethane, and the cell stabilizer comprises at least one of the following: sodium dodecyl sulfate, polyethylene glycol, and glyceryl monostearate.

2. The polystyrene foam material with high cell size according to claim 1, characterized in that: The flame retardant is methyl octabromoether.

3. The polystyrene foam material with high cell size according to claim 2, characterized in that: The cell stabilizer is polyethylene glycol.

4. The polystyrene foam material with high cell size according to claim 3, characterized in that: The physical foaming agents are alcohol and carbon dioxide.

5. A method for preparing a polystyrene foam material with high pore size as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: The polymer substrate, the nucleating agent, the flame retardant and the cell stabilizer are metered according to the set mass fraction by the metering feeding device (2) and then conveyed from the feed port to the twin-screw extruder (3). The temperature of each area of ​​the twin-screw extruder (3) is controlled within 200-230°C, and the polymer substrate is melt-blended with the nucleating agent, the flame retardant and the cell stabilizer to obtain a melt blend. Step 2: Inject the physical foaming agent from the foaming agent storage tank (1) into the twin-screw extruder (3). The physical foaming agent is rapidly dissolved in the melt blend by the rotating shear block in the twin-screw extruder (3) to obtain a homogeneous mixture. Step 3: After the homogeneous mixture is filtered to remove impurities by the screen changer in the twin-screw extruder (3), it is transported to the single-screw extruder (4) through the conveying pipeline. The single-screw extruder (4) adopts a zoned stepped cooling mode, and the temperature of each zone of the single-screw extruder (4) is set within 90 to 170°C according to a certain temperature difference. The homogeneous mixture after removing impurities is cooled in the single-screw extruder (4) to reach the foaming temperature range. Step 4: The homogeneous mixture after reaching the foaming temperature range and filtering out impurities is rapidly depressurized and foamed into polystyrene foam material through the die orifice on the single screw extruder (4). The polystyrene foam material is shaped by the shaping module and cooled by the cooling rack to form a polystyrene foam material with high cell size.

6. The method for preparing polystyrene foam material with high cell size according to claim 5, characterized in that, In step 3: the screen changer is a replaceable device; the conveying pipeline does not contain a screw.

7. The method for preparing polystyrene foam material with high cell size according to claim 6, characterized in that, In step 3: the front part of the die head (5) of the single screw extruder (4) is also equipped with a static mixer or melt pump; the static mixing temperature of the static mixer is higher than the temperature in the twin screw extruder (3).

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