阅读说明：本技术 一种发泡聚苯乙烯的制备方法 (Preparation method of expanded polystyrene ) 是由 李书召 陈志强 于 2021-09-28 设计创作，主要内容包括：本申请公开了一种发泡聚苯乙烯的制备方法,属于反应挤出聚合发泡的领域,该制备方法包括如下步骤：将苯乙烯单体、低温引发剂、中高温引发剂进行混合,在惰性气体保护下,进行反应挤出聚合,得苯乙烯的预聚体；将苯乙烯的预聚体注入挤出机中,进行反应挤出,在挤出机的前段加入发泡剂,苯乙烯单体与发泡剂均匀混合,进行反应挤出聚合；再通过发泡模具,在口模外释放压力,制得发泡聚苯乙烯；本申请的发泡剂在高压环境下,有助于均匀分散在液态的预聚体中,有助于制得泡孔均匀、独立、尺寸一致性佳的聚苯乙烯发泡产品。(The application discloses a preparation method of expanded polystyrene, belonging to the field of reactive extrusion polymerization foaming, and the preparation method comprises the following steps: mixing a styrene monomer, a low-temperature initiator and a medium-high temperature initiator, and carrying out reactive extrusion polymerization under the protection of inert gas to obtain a prepolymer of styrene; injecting a prepolymer of styrene into an extruder, carrying out reactive extrusion, adding a foaming agent into the front section of the extruder, uniformly mixing a styrene monomer and the foaming agent, and carrying out reactive extrusion polymerization; then, releasing pressure outside the neck mold through a foaming mold to prepare foamed polystyrene; the foaming agent disclosed by the application is beneficial to being uniformly dispersed in a liquid prepolymer in a high-pressure environment, and is beneficial to preparing a polystyrene foaming product with uniform and independent foam pores and good size consistency.)

1. A preparation method of expanded polystyrene is characterized by comprising the following steps:

mixing a styrene monomer and an initiator, and carrying out prepolymerization reaction at 50-180 ℃ under the protection of inert gas to obtain a styrene prepolymer; wherein, the initiator is a composition of a low-temperature initiator and a medium-high temperature initiator;

injecting a prepolymer of styrene into an extruder, carrying out reactive extrusion polymerization, adding a foaming agent into the front section of the extruder, uniformly mixing a styrene monomer and the foaming agent, and continuing the polymerization reaction;

and then releasing pressure outside the neck mold through a foaming mold to obtain the foamed polystyrene.

2. The method for preparing expanded polystyrene according to claim 1, wherein: the weight percentage of the styrene monomer in the reaction system is 60-99.9%; the weight percentage of the initiator in the reaction system is 0.1-20%.

3. The method for preparing expanded polystyrene according to claim 1, wherein: the low-temperature initiator is azo initiator, and the medium-high temperature initiator is peroxide initiator.

4. The method for preparing expanded polystyrene according to claim 1, wherein: in the step, besides styrene monomer and initiator, auxiliary agent and comonomer are added and mixed together; wherein the weight percentage of the auxiliary agent in the reaction system is 0-50%; the weight percentage of the comonomer in the reaction system is 0-50%.

5. The method for preparing expanded polystyrene according to claim 4, wherein: the auxiliary agent comprises one or more of flame retardant, nucleating agent, filler, antibacterial agent, mildew preventive and toughening agent; the comonomer includes various types of monomers capable of undergoing radical copolymerization with styrene.

6. The method for preparing expanded polystyrene according to claim 4, wherein: in the prepolymerization reaction in the step, a styrene monomer, an initiator, an auxiliary agent and a comonomer are added into a prepolymerization device with an online viscometer according to a certain proportion, the components are uniformly mixed by a stirring or shearing method under the protection of inert gas, then the temperature is gradually increased to 90-160 ℃, and when the viscosity of a system reaches 20-800 centipoises, the heating is stopped, so that the styrene prepolymer is obtained.

7. The process for producing expanded polystyrene according to claim 1The preparation method is characterized by comprising the following steps: the foaming agent is selected from aliphatic hydrocarbon foaming agent or supercritical CO₂A blowing agent.

8. The method for preparing expanded polystyrene according to claim 1, wherein: the type of the extruder used in the polymerization reaction is any one of a double-screw extruder, a single-screw extruder, a double-stage extruder with a single screw and a single screw connected in series, a double-stage extruder with a double screw and a double screw connected in series, a double-stage extruder with a single screw and a double screw connected in series, and a double-stage extruder with a double screw and a single screw connected in series.

9. The method for preparing expanded polystyrene according to claim 1, wherein: the retention time of the prepolymer in the extruder is 30-60 minutes.

10. The expanded polystyrene product obtained by the method for preparing expanded polystyrene according to any one of claims 1 to 9, wherein: comprises any one of expanded polystyrene plates, expanded polystyrene sheets, expanded polystyrene particles, expanded polystyrene rattans, expanded polystyrene flat belts and pre-expanded polystyrene beads.

Technical Field

The invention relates to the field of polystyrene foaming, in particular to a preparation method of expanded polystyrene.

Background

Polystyrene (GPPS), one of five general-purpose plastics, is widely used for producing electronic and electric appliances, optical instruments and transparent models, such as lamp shades, instrument covers, packaging containers and the like, and daily necessities, such as combs, boxes, toothbrush handles, ball-point pen holders, school supplies, children toys and the like.

In recent years, one of the other uses of GPPS is to produce polystyrene foamed products, including polystyrene foamed sheets (XPS) and polystyrene foamed beads (EPS), which are widely used. The polystyrene extrusion foaming process is characterized in that GPPS is used as a raw material and is mixed with a flame retardant, a nucleating agent, an antioxidant and other functional auxiliaries, the mixture is added into an extruder to be heated, melted and blended, meanwhile, the mixture is fully and uniformly mixed with a gas foaming agent injected into the front section of the extruder under the shearing and mixing action of the extruder, and finally, pressure release is carried out at a neck mold, so that a polystyrene foaming product is obtained.

However, the above method has obvious disadvantages that the injected foaming agent is difficult to enter into the viscous polystyrene melt, and even if part of the foaming agent enters into the polystyrene melt under higher pressure, the dispersibility of the foaming agent in the melt is poor, so that the cells of the polystyrene foamed product are different in size and uneven in dispersion, and the foamed product with a microcellular structure is difficult to make.

Disclosure of Invention

In order to develop a polystyrene foamed product with uniform and independent foam holes and good size consistency, the application provides a preparation method of foamed polystyrene and the foamed polystyrene product.

In a first aspect, the present application provides a method for preparing expanded polystyrene, the method comprising the steps of:

mixing a styrene monomer and an initiator, and carrying out prepolymerization reaction at 50-180 ℃ under the protection of inert gas to obtain a styrene prepolymer; wherein, the initiator is a composition of a low-temperature initiator and a medium-high temperature initiator;

injecting a prepolymer of styrene into an extruder, carrying out reactive extrusion polymerization, adding a foaming agent into the front section of the extruder, uniformly mixing a styrene monomer and the foaming agent, and continuing the polymerization reaction;

and then releasing pressure outside the neck mold through a foaming mold to obtain the foamed polystyrene.

The existing preparation method of expanded polystyrene usually takes expandable polystyrene (GPPS) as raw material, functional auxiliary agent is added for blending, and the gas foaming agent is difficult to be uniformly dispersed in polystyrene melt.

The application improves the existing preparation method of expanded polystyrene, styrene monomer, low-temperature initiator and medium-high temperature initiator are used for preparing prepolymer at 50-180 ℃, and then the prepolymer is injected into an extruder for continuous reaction; because the foaming agent is added at the front section of the extruder, the foaming agent is beneficial to being uniformly dispersed in the liquid prepolymer under the high-pressure environment; after the foaming agent and the prepolymer are fully mixed, the prepolymer enables polymerization reaction to continue under the shearing and heating actions of the extruder, which is beneficial to improving the full reaction of styrene monomers, so that a polystyrene foaming product with uniform and independent foam holes and good foam hole size consistency is prepared. In addition, the method directly takes styrene monomer as raw material, adopts one-step method to directly generate the expanded polystyrene, saves the price difference of GPPS intermediate products, and the technical scheme is initiated in the world.

Preferably, the weight percentage of the styrene monomer in the reaction system is 60-99.9%; the weight percentage of the initiator in the reaction system is 0.1-20%.

Preferably, the low-temperature initiator is an azo initiator, and the medium-high temperature initiator is a peroxide initiator.

According to the method, the composition of the peroxide initiator and the azo initiator is adopted, in the prepolymerization process, when the temperature is below 130 ℃, the azo initiator can initiate the polymerization of the styrene monomer, and when the temperature is raised to above 130 ℃, the high-temperature initiator continues to initiate the polymerization of the monomer, so that the improvement of the conversion rate of the styrene monomer is facilitated.

Preferably, in the step, an auxiliary agent and a comonomer are added and mixed together besides the styrene monomer and the initiator; wherein the weight percentage of the auxiliary agent in the reaction system is 0-50%; the weight percentage of the comonomer in the reaction system is 0-50%.

Preferably, the auxiliary agent comprises one or more of flame retardant, nucleating agent, filler, antibacterial agent, mildew preventive and toughening agent; the comonomer includes various types of monomers capable of undergoing radical copolymerization with styrene.

Preferably, in the prepolymerization reaction in the step, the styrene monomer, the initiator, the auxiliary agent and the comonomer are added into a prepolymerization device with an online viscometer according to a certain proportion, the components are uniformly mixed by a stirring or shearing method under the protection of inert gas, then the temperature is gradually increased to 90-160 ℃, and when the viscosity of the system reaches 20-800 centipoises, the heating is stopped, so that the styrene prepolymer is obtained.

Preferably, the prepolymerization device comprises an internal mixer, various reaction kettles and other equipment. The selection is to achieve uniform mixing of the reaction system and to perform prepolymerization, so that the prepolymerization device needs to have good stirring and dispersing effects and good heat exchange effects, and the type of the prepolymerization device is not particularly limited.

Preferably, the foaming agent is selected from aliphatic hydrocarbon foaming agent or supercritical CO₂A blowing agent.

Supercritical CO of the present application₂The foaming agent has the characteristics of gas diffusivity and liquid solubility, low viscosity and low surface tension, and can play a role similar to a solvent after being dissolved in a styrene monomer reaction system, so that the mass and heat transfer are accelerated. In addition, supercritical CO₂The high pressure environment created by the blowing agent accelerates the styrene chain extension reaction, thereby further reducing the polymerization time.

Preferably, the type of the extruder used in the polymerization reaction is any one of a twin-screw extruder, a single-screw and single-screw tandem twin-stage extruder, a twin-screw and twin-screw tandem twin-stage extruder, a single-screw and twin-screw tandem twin-stage extruder, and a twin-screw and single-screw tandem twin-stage extruder.

Preferably, the retention time of the prepolymer in the extruder is 30-60 minutes.

By adopting the technical scheme, when the retention time of the materials in the extruder is too short, the conversion rate of the styrene monomer is reduced; when the residence time of the materials in the extruder is too long, the equipment investment is overlarge, the yield is reduced, and therefore, the residence time of the materials in the extruder is preferably 30-60 minutes in the application.

In a second aspect, the present application provides an expanded polystyrene product prepared by the above method for preparing expanded polystyrene, which comprises any one of expanded polystyrene boards, expanded polystyrene sheets, expanded polystyrene particles, expanded polystyrene rattans, expanded polystyrene ribbons, and pre-expanded polystyrene beads.

By adopting the technical scheme, the foamed polystyrene product prepared by the preparation method has no limitation on product style, can be any one of plates, sheets, particles, rattans, flat belts or beads, and has uniform and independent foam pores and good consistency of foam pore sizes.

In summary, the present application has the following beneficial effects:

1. the method comprises the following steps of taking a styrene monomer as a raw material, adding a low-temperature initiator and a medium-high temperature initiator for compounding, preferably selecting a prepolymerization reaction temperature of 90-160 ℃, so that the styrene monomer is prepolymerized to a certain extent, then injecting the prepolymer into an extruder, wherein a foaming agent can be uniformly dispersed in the liquid prepolymer, and continuously carrying out polymerization reaction, so that the conversion rate of the styrene monomer is remarkably improved and can reach 97.8% to the maximum;

2. the method directly takes styrene monomer as raw material, adopts one-step method to directly generate the expanded polystyrene, and saves the difference of GPPS intermediate products;

3. after nano calcium carbonate or nano silicon dioxide auxiliary agent is added into a prepolymer system, the nano calcium carbonate or nano silicon dioxide is uniformly dispersed in the prepolymer system in an in-situ polymerization mode, and the heterogeneous nucleating agent is played, so that foamed polystyrene cells are finer and denser, have uniform, independent and micron-sized cell structures, and have the diameter of about 98 mu m;

4. after the comonomer is added into a reaction system, the conversion rate of the styrene monomer is promoted, and the prepared expanded polystyrene has no taste of the styrene monomer;

5. the viscosity of the prepolymer is 200-500 centipoises, the prepolymer with the viscosity range is injected into an extruder, and after extrusion polymerization foaming reaction, the conversion rate of a styrene monomer is maintained to be more than 98.2%;

6. according to the reaction system, the length-diameter ratio of the screw of the extruder is preferably 65, the rotating speed of the screw is 30rpm, and under the condition, the polymerization time in the extruder is 30-60 min, so that the higher conversion rate of the styrene monomer can be realized, and the preparation of the foamed polystyrene with uniform and independent foam pores and good foam pore size consistency is facilitated.

Drawings

FIG. 1 is a cell topography for example 4.

FIG. 2 is a cell topography for example 8.

FIG. 3 is a cell morphology map of comparative example 1.

FIG. 4 is a cell morphology map of comparative example 2.

Detailed Description

The embodiment provides a preparation method of expanded polystyrene, which comprises the following steps:

mixing a styrene monomer, an initiator, an auxiliary agent and a comonomer, and carrying out prepolymerization reaction under the protection of inert gas to obtain a prepolymer of styrene;

injecting the prepolymer of the styrene into an extruder, carrying out reactive extrusion polymerization, adding a foaming agent into the front section of the extruder, uniformly mixing the foaming agent and the prepolymer of the styrene, and continuing the polymerization reaction;

and then releasing pressure outside the neck mold through a foaming mold to obtain the foamed polystyrene.

The styrene monomer mentioned in the method for producing expanded polystyrene of the present embodiment is not particularly limited, and may be obtained by a commercially available or synthetic method.

The initiator mentioned in the method for producing expanded polystyrene of the present embodiment is not particularly limited, and a combination of a peroxide-based initiator and an azo-based initiator is preferably used; peroxide initiators such as hydrogen peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide-t-butyl peroxide, methyl ethyl ketone peroxide, dicumyl peroxide, lauroyl peroxide, di-t-butyl peroxide, t-butyl hydroperoxide, t-butyl peroxybenzoate, 1, 4-bis (t-butylperoxyisopropyl) benzene, and the like; azo initiators, for example, azobisisobutyronitrile, dimethyl azobisisobutyrate, azobisisoheptonitrile, and the like. These initiators may be used alone or in combination of two or more. The above-mentioned initiators are only illustrative examples and are not intended to limit the scope of the use of the initiators used, and other initiators capable of initiating a free radical polymerization are included.

The auxiliary agent mentioned in the method for preparing expanded polystyrene of the present embodiment is an auxiliary agent capable of imparting certain properties to the expanded polystyrene product, and includes, but is not limited to, flame retardants, nucleating agents, fillers, antibacterial agents, mildewcides, toughening agents, and the like. More specific examples include various types of wood flour, wood fiber, various types of starch, various types of shell powder, glass fiber, calcium carbonate, talc, silica, montmorillonite, molecular sieve, titanium dioxide, kaolin, various types of brominated flame retardants, various types of phosphorus flame retardants, various types of intumescent flame retardants, glass microspheres, carbon black, various types of graphite, zinc oxide, magnesium oxide, antibacterial anion, antibacterial copper ion, zinc hydroxide and the like; also included are rubbers which may be used as toughening agents, such as natural rubber, butyl rubber, and various copolymer rubbers of styrene with isoprene and butadiene, and the like. The size of these auxiliaries is not particularly limited as long as the addition thereof has no significant influence on the reaction and the properties of the final polystyrene foamed product, and these auxiliaries may be added singly or in combination of two or more kinds according to the product requirements.

The comonomers mentioned in the process for preparing expanded polystyrene of the present embodiment include various monomers capable of undergoing radical copolymerization with styrene, including monomers currently commercially available on the market and various monomers prepared by synthesis, including, by way of example and not limitation, ethylene, propylene, vinyl chloride, vinyl fluoride, butadiene, isoprene, divinylbenzene, α -methylstyrene, vinyl acetate, acrylamide, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, maleic anhydride, ethyl methacrylate, butyl methacrylate, polycyclic norbornene methacrylate, pentyl methacrylate, hydroxyethyl methacrylate, N-o-chlorobenzmaleimide, N-methylmaleimide, N-tolylmaleimide, N-vinyltoluene, vinyl acetate, vinyl chloride, butadiene, isoprene, divinylbenzene, vinyl acetate, alpha-methylstyrene, vinyl acetate, acrylamide, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, maleic anhydride, ethyl methacrylate, butyl methacrylate, polycyclic norbornene methacrylate, pentyl methacrylate, hydroxyethyl methacrylate, N-o-chlorobenzmaleimide, N-methylmaleimide, N-tolylmaleimide, and the like, Acrylonitrile, N-cyclohexylmaleimide, N-phenylmaleimide, fumaric acid monoesters, fumaric acid diesters, itaconic acid esters, sorbic acid esters, undecylenic acid, glycidyl methacrylate, N-methylolacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, glycidyl acrylate, dicyclopentenyl methacrylate, phenyl methacrylate, various types of fluorine-containing ethylene, various types of chlorine-containing ethylene, various types of unsaturated fatty acids, and the like. Among them, one or a combination of methyl methacrylate, maleic anhydride and glycidyl methacrylate is preferably used.

The prepolymerization device mentioned in the preparation method of expanded polystyrene in this embodiment includes an internal mixer and various reactors, and is intended to achieve uniform mixing of the reaction system and perform prepolymerization, so that the prepolymerization device needs to have good stirring and dispersing effects and good heat exchange effects, and the type of the prepolymerization device is not particularly limited.

The temperature of the prepolymerization reaction is set to be between 50 ℃ and 180 ℃, preferably between 70 ℃ and 170 ℃, more preferably between 90 ℃ and 160 ℃, and if the temperature is too low, the prepolymerization speed is slow and the time is long; too high a temperature tends to cause runaway of the prepolymerization reaction, resulting in depolymerization.

For the conversion rate of the prepolymerization reaction, the viscosity of the reaction system is controlled to be between 20 and 800 centipoise, preferably between 200 and 500 centipoise, and too high conversion rate is easy to cause the reaction to be out of control to cause the polymerization.

In the extrusion foaming process mentioned in the preparation method of expanded polystyrene according to the present embodiment, the reaction system subjected to prepolymerization is injected into an extruder, and the reaction is continued in the extruder by using the shearing and heating actions of the extruder; after the materials react in the extruder for a period of time, a foaming agent is added into the front section of the extruder, and under the high-pressure environment and the synergistic action formed by the foaming agent, the styrene monomer is fully mixed with the foaming agent in the extruder and is further reacted and polymerized. At the later stage of the reaction, after the polystyrene which is fully and uniformly mixed with the foaming agent and has been polymerized passes through the static mixer and the foaming mould, the pressure is released outside the mouth mould, so that the foamed polystyrene material with high performance or other customized special properties can be prepared.

The type of extruder mentioned in the production method of expanded polystyrene of the present embodiment may be a general twin-screw extruder, a single-screw and single-screw tandem twin-stage extruder, a twin-screw and twin-screw tandem twin-stage extruder, a single-screw and twin-screw tandem twin-stage extruder, or a twin-screw and single-screw tandem twin-stage extruder. The diameter (Φ D) of the extruder screw is not particularly limited and may be determined according to the amount of the throughput and the amount of the torque.

For the polymerization reaction mentioned in the method for producing expanded polystyrene of the present embodiment, the residence time of the materials in the entire production line is preferably 20 to 90 minutes, preferably 30 to 60 minutes. Too short a residence time of the material in the extruder reduces the conversion of the monomers; theoretically, the longer the residence time, the higher the conversion of the polymerization reaction, but too long a residence time leads to an excessive investment in equipment and a decrease in productivity.

As mentioned in the process for the preparation of expanded polystyrene of the present embodiment, the blowing agent is injected in the front stage of the extruder, preferably in the third or fourth heating stage of the extruder, at a temperature of 70 ℃ in order to keep the reaction system in a liquid state at this point in order to facilitate sufficient dissolution of the blowing agent in the reaction system.

For the reaction temperature in the extruder mentioned in the present embodiment, a range of 20 ℃ to 250 ℃ is set, wherein 30 ℃ to 200 ℃ is preferable, and 70 ℃ to 180 ℃ is further preferable. The rotating speed of the extruder is set to be 1rpm-1000rpm, preferably 10rpm-500rpm, and more preferably 20rpm-300rpm, and the yield is reduced by excessively low rotating speed; too high a rotational speed would result in too short a residence time of the material in the extruder to complete the reaction.

The blowing agent mentioned in the production method of expanded polystyrene of the present embodiment is not particularly limited, and completely non-halogenated aliphatic hydrocarbon gases such as propane, n-butane, isobutane, n-pentane, isopentane, cyclopentane, hexane, etc.; halogenated hydrocarbon compounds mainly composed of chlorinated hydrocarbon gases such as 1, 2-dichlorotetrafluoroethane, 1, 1-difluoroethane, 1-chlorotetrafluoroethane and 1,1,1, 2-tetrafluoroethane and freon substitutes such as HFC134a, HFC152a and HCFC142 b; azodicarbonamide (AC foaming agent), hydrazine derivatives (such as p-toluenesulfonyl hydrazide), semicarbazides, tetrazoles, nitroso compounds, carbonates and other chemical foaming agents; and supercritical CO₂And nitrogen, and the like. Among them, pentane is preferably used as a blowing agent, and supercritical CO is more preferably used₂As a blowing agent.

The amount of the blowing agent added is preferably 1% to 30%, more preferably 2% to 20%, most preferably 4% to 15% based on the total weight of the monomers. If the amount of the blowing agent is less than 1%, the expansion ratio of the expanded polystyrene is lowered or the cell diameter is enlarged, while if the amount of the blowing agent exceeds 30%, the pressure in the extruder is excessively increased, which may cause a risk.

The foaming die of the extruder mentioned in the method for preparing expanded polystyrene of the present embodiment includes, but is not limited to, an annular die, a T-die, a flat die, a circular die, or an underwater pelletizing die.

The expanded polystyrene product prepared by the method for preparing expanded polystyrene of the present embodiment includes, but is not limited to, expanded polystyrene sheets, expanded polystyrene particles, expanded polystyrene rattans, expanded polystyrene ribbons, and pre-expanded polystyrene beads.

Next, the present embodiment will be described with reference to examples and drawings.

Examples 1 to 7:

as shown in Table 1, examples 1 to 7 are different in the composition and the compounding ratio of the raw materials.

The following description will be given by taking example 1 as an example.

The preparation of expanded polystyrene provided in example 1 is as follows:

pre-polymerization: simultaneously adding a styrene monomer and an initiator into a reaction kettle with an online viscometer, wherein the volume of the reaction kettle is 20L, screwing down a kettle cover of the reaction kettle, and stirring at room temperature at the stirring speed of 150rpm for 30 min; and then heating to 90 ℃, continuously stirring for reaction for 1 hour after the temperature is stable, then continuously heating to 130 ℃, continuously stirring for reaction for 1 hour, heating to 160 ℃ again, stopping heating when the viscosity of the on-line viscometer reaches 200 centipoises, cooling to 60 ℃ to slow down the prepolymerization reaction, and still keeping the stirring state to obtain the styrene prepolymer.

Polymerization: starting a diaphragm metering pump to inject the prepolymer into a CO-rotating tightly-meshed double-screw extruder with a screw diameter phi 48 and a length-diameter ratio L/D of 65 at a metering rate of 5kg/h, wherein the rotating speed of the screw is 30rpm, the injection position of the prepolymer is positioned in a second heating section of the extruder, and after 10min of injection, starting supercritical CO₂The foaming agent begins to be injected into the metering pump, and the metering pumpThe injection speed of the foaming agent is 1000mL/h, the injection port of the foaming agent is positioned in the 4 th heating section of the extruder, the temperature of the screw cylinder of the extruder is set to be 70-180 ℃, and the reaction time is about 30 min; and (3) after the polystyrene subjected to the reaction passes through a static mixer, releasing the pressure outside a flat die, and cooling by a shaping roller to obtain the foamed polystyrene board.

TABLE 1 compositions and proportions of the raw materials in examples 1-7

Examples 8 to 10:

as shown in Table 2, examples 8 to 10 are different from example 4 in that an auxiliary agent is added to the prepolymerization system, and the prepolymerization process is as follows: styrene monomer, initiator and assistant are added into a prepolymerization device with an online viscometer according to a certain proportion, all components are uniformly mixed by a stirring and shearing method under the protection of inert gas, and the rest steps are kept consistent with those in example 4.

Table 2 Components and proportions of the raw materials of examples 8 to 10

Examples 11 to 13:

as shown in Table 3, examples 11 to 13 are different from example 8 in that a comonomer was added to the prepolymerization system in the following manner: styrene monomer, initiator, auxiliary agent and comonomer are added into a prepolymerization device with an online viscometer according to a certain proportion, all components are uniformly mixed by a stirring and shearing method under the protection of inert gas, and the rest steps are kept consistent with those in the embodiment 8.

TABLE 3 Components and ratios of the raw materials of examples 11 to 13

Example 14:

a method for preparing expanded polystyrene, which is different from example 8 in that: observing that the viscosity of the on-line viscometer reaches 20 centipoises, and stopping heating; the remaining steps were as in example 8.

Example 15:

a method for preparing expanded polystyrene, which is different from example 8 in that: observing that the viscosity of the on-line viscometer reaches 500 centipoises, and stopping heating; the remaining steps were as in example 8.

Example 16:

a method for preparing expanded polystyrene, which is different from example 8 in that: observing that the viscosity of the on-line viscometer reaches 800 centipoises, and stopping heating; the remaining steps were as in example 8.

Example 17:

a preparation method of expanded polystyrene is different from the embodiment 8 in the used extruder in the polymerization process, the extruder adopted in the embodiment adopts a co-rotating tightly meshed twin-screw extruder with the screw diameter phi of 48 and the length-diameter ratio L/D of 48, the screw rotating speed is 30rpm, and the reaction time is about 18 min; the remaining steps were as in example 8.

Example 18:

a preparation method of expanded polystyrene is different from the embodiment 8 in the used extruder in the polymerization process, the extruder adopted in the embodiment adopts a co-rotating tightly meshed twin-screw extruder with screw diameter phi 48 and length-diameter ratio L/D of 75, the screw rotating speed is 30rpm, and the reaction time is about 60 min; the remaining steps were as in example 8.

Comparative example 1:

a method for preparing expanded polystyrene, which is different from example 8 in that a prepolymerization process is different from that of the comparative example: simultaneously adding the materials into a reaction kettle with the volume of 20L, screwing down a kettle cover of the reaction kettle, starting stirring at room temperature, setting the stirring speed at 150rpm, and stirring for 3 hours, wherein all the initiators are completely dissolved in styrene monomers; the remaining steps were as in example 8.

Comparative example 2:

a preparation method of expanded polystyrene is different from that of example 8 in that only 1, 4-bis (tert-butylperoxyisopropyl) benzene single initiator is adopted as the initiator, the addition amount is 0.1kg, and the other method steps are consistent with that of example 8.

And (3) performance detection:

(1) conversion rate: the nuclear magnetic resonance hydrogen spectrum of the prepared polystyrene foaming material is tested. In a hydrogen spectrum of a nuclear magnetic resonance image, a methylene hydrogen peak of a double bond of a styrene monomer is positioned at delta of 5.2-5.8, a methylene hydrogen peak on a polystyrene main chain is positioned near delta of 2.76, the ratio of the two peak areas can be calculated according to the ratio of the two peak areas, and the conversion rate of the styrene monomer can be obtained through further calculation.

(2) Cell structure: the sample was cut open and photographed by SEM scanning electron microscopy.

TABLE 4 tables of Performance test data for examples 1-18 and comparative examples 1-2

Sample (I)	Conversion (%)
		Example 1	96.5
Example 2	96.7
		Example 3	96.5
Example 4	97.4
		Example 5	97.3
Example 6	97.6
		Example 7	97.8
Example 8	98.7
		Example 9	98.3
Example 10	98.5
		Example 11	98.7
Example 12	99.3
		Example 13	99
Example 14	83.3
		Example 15	98.5
Example 16	98.2
		Example 17	81.6
Example 18	98.8
		Comparative example 1	65.9
Comparative example 2	80.2

According to table 4 and the detection results of examples 1 to 7 and comparative example 1, it can be seen that in the preparation method of the present application, a styrene monomer is used as a raw material, a low temperature initiator and a medium temperature initiator are added for compound use, preferably, the prepolymerization reaction temperature is 90 to 160 ℃, so that the styrene monomer is prepolymerized to a certain extent, and then, the prepolymer is injected into an extruder, and a foaming agent can be uniformly dispersed in the liquid prepolymer to continue a polymerization reaction, which is beneficial to significantly improving the conversion rate of the styrene monomer, and can reach 97.8% at most, thereby improving the foaming effect of the extruded and foamed product. The sample prepared in example 4 is used, the appearance of the cells is observed by using an SEM scanning electron microscope, and referring to FIG. 1, the foaming structure is uniform and independent, the size of the cells is slightly larger, and the diameter can reach 200 μm.

The expanded polystyrene of comparative example 1 has a strong taste of styrene monomer, the conversion rate of styrene monomer obtained by nuclear magnetic resonance hydrogen spectroscopy is only 65.9%, referring to fig. 3, the cell structure of comparative example 1 is observed, most of the cells are open or collapsed, which indicates that comparative example 1 lacks prepolymerization reaction, and the retention time of the material in the extruder is too short and the polymerization reaction is insufficient under the premise of the same extrusion polymerization time, so that a large amount of styrene monomer is remained in the expanded product, which is not favorable for the expansion performance of the expanded product.

The expanded polystyrene of comparative example 2 also had a strong taste of styrene monomer, and the conversion rate reached 80.2%; the obvious collapse state of the product surface can be obviously observed by naked eyes; referring to fig. 4, observing the cell structure of comparative example 2, the cells are mostly in a through-hole or broken-hole structure, and the cell distribution is very uneven, which is difficult to support the integrity of the product surface; this is because the comparative example lacks low temperature initiator such as azo initiator, it is difficult to generate free radical in 1, 4-bis (t-butylperoxyisopropyl) benzene in the same time when the temperature is below 130 ℃ in the prepolymerization process, and 1, 4-bis (t-butylperoxyisopropyl) benzene can initiate the polymerization of styrene monomer only when the temperature is raised to high temperature, so that under the same prepolymerization time condition, the use of a single initiator can lead to insufficient effective prepolymerization time and reduce the conversion rate of styrene monomer.

The detection results of table 4 and examples 8 to 10 show that the conversion rate of examples 8 to 10 can reach more than 98.3%, which indicates that after the nano calcium carbonate or nano silica and other additives are added, the nano calcium carbonate or nano silica is uniformly dispersed in a prepolymerization system in an in-situ polymerization manner to play a role of a heterogeneous nucleating agent, so that the foamed polystyrene cells are finer and denser; by using the sample prepared in example 8 and observing the cell structure by SEM scanning electron microscope, referring to FIG. 2, example 8 has a uniform, independent, micron-sized cell structure, and the diameter of the cells is about 98 μm. Aiming at the example 10, the flame retardant grade reaches B1 grade, while the sheet material obtained by commercial GPPS through the extrusion foaming method needs to be added with 3.5% of hexabromine flame retardant to reach the requirement of B1 grade, which also indicates that the hexabromine flame retardant is well dispersed in the reaction system, thereby greatly enhancing the flame retardant property of the foaming product, and simultaneously remarkably reducing the addition amount of raw materials and the production cost.

The results of the tests in Table 4 and examples 11 to 13 show that the conversion rate of examples 11 to 13 can reach as high as 99.3%, which indicates that the addition of the comonomer in the reaction system can help to promote the conversion rate of the styrene monomer, and the polystyrene foam produced has no taste of the styrene monomer.

The detection results of table 4 and examples 14 to 16 show that the prepolymer in example 14 stops prepolymerization when the viscosity of the prepolymer is 20 cps, and the prepolymer has a low viscosity, so that the conversion rate of styrene monomer is slightly low under the same polymerization reaction time condition; the conversion rates of examples 15 to 16 were close, that is, when the viscosity of the prepolymer reached 500 cps or 800 cps, the conversion rates of the styrene monomers were close after polymerization for the same period of time, and the prepolymerization reaction was stopped when the viscosity of the prepolymer was 500 cps.

As can be seen from table 4 and the detection results of examples 17 to 18, in example 17, in the polymerization stage, when the length-diameter ratio of the screw of the extruder is 48, the reaction time is about 18min, and the conversion rate of the styrene monomer is about 80%, it can be seen that the reaction time is not enough in the polymerization stage, and a part of the styrene monomer is not converted, so that a strong smell of the styrene monomer can be smelled; example 18 was conducted using an extruder screw having a length to diameter ratio of 75, and a polymerization time of about 60min at a constant rotation speed, and the conversion rate of example 18 was close to that of example 17, and thus it was confirmed that the reaction time of example 17 was sufficient to convert styrene monomer.