Graphite-grade expandable polystyrene bead and preparation process thereof

Abstract

The invention provides a graphite-grade expandable polystyrene bead body and a preparation process thereof, and belongs to the technical field of expandable polystyrene, the preparation process comprises the following steps: S1, injecting 150-230 parts by weight of deionized water into a reaction kettle, adding 0.5-1 part by weight of a dispersion stabilizer, stirring, and cooling to room temperature to obtain a graphite-grade expandable polystyrene bead body; adding 100 parts of styrene, 3.3-3.8 parts of intercalation-modified double-modified graphite, 0.3-0.35 part of an initiator and 0.9-1.1 parts of a phosphorus-nitrogen intumescent flame retardant, continuously stirring, heating to 86-90 DEG C, and keeping the temperature for 7-9 hours to obtain a particle dispersion phase; s2, adding 5.6-6.2 parts of a foaming agent into the particle dispersion phase, heating to 120 DEG C, continuously reacting for 4.5-5.5 hours, cooling, discharging, cleaning and filtering to obtain graphite-grade expandable polystyrene beads; the intercalation-modified double modified graphite is prepared by carrying out surface modification on oxidized intercalated graphite through poly (1, 3-propanediol succinate). According to the invention, excellent thermal stability of the prepared product is ensured, and the flame retardance of the product is improved.

Description

Technical Field

[0001] This invention belongs to the field of expandable polystyrene technology, specifically relating to a graphite-grade expandable polystyrene bead and its preparation process. Background Technology

[0002] Expandable polystyrene (EPS) possesses excellent thermal insulation properties, low water absorption, anti-aging properties, waterproof performance, and low cost, making it a widely used insulation material in energy-efficient buildings. Graphite is a black, carbon-based inorganic compound with good chemical stability, and can be used as a refractory material, conductive material, and wear-resistant lubricant. Natural graphite is mostly in a flake-like structure, which has excellent infrared reflective properties, thus improving the thermal conductivity of materials. To further reduce the thermal conductivity of EPS and improve its insulation performance, graphite-containing EPS can be prepared by adding graphite.

[0003] However, due to the presence of polymerization-inhibiting groups, such as quinone groups, on the surface of graphite, it has a strong inhibitory effect on the free radical polymerization of styrene. The higher the graphite content, the more obvious the inhibitory effect on the polymerization of styrene, the more obvious the inhibition of chain growth, and the lower the relative molecular mass of the product. With the increase of graphite addition, the initial decomposition temperature of the prepared graphite-containing expandable polystyrene shows a decreasing trend, and the thermal stability decreases. Summary of the Invention

[0004] To address the problems existing in the background art, the present invention provides a graphite-grade expandable polystyrene bead and its preparation process, which ensures that the product has excellent thermal stability while improving its flame retardancy.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a process for preparing graphite-grade expandable polystyrene beads, comprising the following steps: S1. By weight, inject 150-230 parts of deionized water into the reactor, add 0.5-1 parts of dispersant stabilizer, stir, then add 100 parts of styrene, 3.3-3.8 parts of intercalated-modified double-modified graphite, 0.3-0.35 parts of initiator and 0.9-1.1 parts of phosphorus-nitrogen intumescent flame retardant, continue stirring, heat to 86-90℃, maintain the temperature for 7-9 hours, polymerize to generate polymer particles, and obtain particulate dispersed phase; S2. Add 5.6-6.2 parts of foaming agent to the particulate dispersion obtained in S1, heat to 120℃, continue the reaction for 4.5-5.5h, cool, discharge, wash, and filter to obtain graphite-grade expandable polystyrene beads. The intercalated-modified graphite is prepared by surface modification of oxidized intercalated graphite with poly(1,3-propanediol succinate).

[0006] Furthermore, the preparation method of the intercalated-modified double-modified graphite is as follows: A1. Place the reactants 1,3-propanediol and succinic acid in a molar ratio of 1:(1.1-1.2) in a three-necked flask, add a polymerization inhibitor, and pre-polymerize at 180-190℃ for 1.5-1.8h under nitrogen protection. Add a catalyst, and continue the reaction at 220-225℃ under vacuum for 2-3h until the rod-climbing phenomenon occurs. Dissolve the product in chloroform, precipitate and purify with cold methanol, and then dry under vacuum at 45-50℃ to obtain poly(1,3-propanediol succinate). A2. Disperse oxidized intercalated graphite in water, sonicate for 1 hour, add N,N-dimethylformamide, remove water under reduced pressure to obtain graphite dispersion; A3. Dissolve the poly(1,3-propanediol) succinate obtained in A1 in the graphite dispersion obtained in A2. The mass ratio of poly(1,3-propanediol) succinate to oxidized intercalated graphite is (10-13):1. After stirring at room temperature for 24 hours, add 1-ethyl-3-3-dimethylaminopropylcarbodiimide and 4-dimethylaminopyridine as carboxyl activators to catalyze the esterification reaction. After stirring at room temperature for 72 hours, add a reducing agent and reduce at 75-80℃ for 22-24 hours. Then, pour in methanol to co-precipitate and dry to obtain intercalated-modified double-modified graphite.

[0007] Further, the preparation method of the oxide intercalated graphite is as follows: 1g of natural flake graphite is placed in a beaker, and 1.7-2.0g of concentrated nitric acid, 3.5-4.0g of perchloric acid and 0.18-0.22g of potassium permanganate are added to the beaker and then sealed. The beaker is placed in an ultrasonic environment at 25-30℃ and allowed to react for 50-65min. Then, 1.8-2.2g of glacial acetic acid is slowly added to the beaker at 30-35℃ and allowed to react for 25-35min. The resulting material is then filtered, washed with water until the pH reaches 7, and then dried in an oven at 55-60℃ for 24h to obtain oxide intercalated graphite.

[0008] Further, in A1, the mass of the polymerization inhibitor (p-hydroxyanisole) is 0.4-0.5% of the total mass of the reactants.

[0009] Furthermore, in A1, the mass of the catalyst (tetrabutyl titanate) is 0.4-0.5% of the total mass of the reactants.

[0010] Furthermore, in A2, the ratio of the amount of oxidized intercalated graphite, water and N,N-dimethylformamide is 1g:(200-250)mL:(800-1000)mL.

[0011] Further, in A3, the mass ratio of the oxidized intercalated graphite, 1-ethyl-3-3-dimethylaminopropylcarbodiimide, and 4-dimethylaminopyridine is 1:(0.9-1.1):(0.9-1.1).

[0012] Furthermore, the phosphorus-nitrogen intumescent flame retardant is ammonium polyphosphate.

[0013] Furthermore, the dispersant stabilizer is tricresyl phosphate; the initiator is benzoyl peroxide; and the foaming agent is pentane.

[0014] Secondly, the present invention provides a graphite-grade expandable polystyrene bead, which is prepared by the above-described preparation method.

[0015] This application has the following beneficial effects: This invention uses intercalated-modified double-modified graphite and phosphorus-nitrogen intumescent flame retardant ammonium polyphosphate to prepare graphite-grade expandable polystyrene beads, which have both excellent thermal stability and flame retardancy, with an initial decomposition temperature of over 345.4℃ and a limiting oxygen index of over 42.1%.

[0016] The intercalated-modified graphite of this invention is prepared by surface modification of oxidized intercalated graphite with poly(1,3-propanediol succinate). In terms of thermal stability, the oxidative intercalation treatment introduces oxygen-containing groups, which partially destroy the quinone structure, thereby weakening its polymerization inhibition ability and improving its dispersibility. The poly(1,3-propanediol succinate) surface modification treatment can cover / shield the residual quinone groups or other polymerization inhibition groups on the graphite surface, further inhibiting its polymerization inhibition ability. In addition, the polyester layer can also enhance the compatibility between graphite and polymer matrix and reduce interface defects. The dual modification synergistically inhibits the polymerization inhibition effect, optimizes dispersibility, and synergistically improves thermal stability (initial decomposition temperature).

[0017] Regarding flame retardancy, oxidation intercalation treatment embeds perchlorate and nitric acid intercalators between graphite layers. These intercalators decompose at high temperatures, generating gases that cause expansion between the graphite layers, forming a loose, porous, expanded structure that blocks oxygen and heat transfer, inhibiting the combustion chain reaction. Surface modification treatment of poly(1,3-propanediol) succinate, containing numerous ester and carboxylic acid groups, undergoes ester bond breakage during high-temperature decomposition, releasing non-flammable gases such as CO2 and diluting the concentration of flammable gases. Oxidation intercalators, such as residual Mn2 in KMnO4, further enhance flame retardancy. + At high temperatures, it can catalyze the dehydration and char formation of poly(1,3-propanediol succinate), promote the formation of a dense char layer, synergistically construct a multi-layer barrier structure, and synergistically improve flame retardancy.

[0018] In addition, ammonium polyphosphate decomposes upon heating to produce polyphosphoric acid and polyphosphate, catalyzing the dehydration of poly(1,3-propanediol succinate) to char; simultaneously, it releases non-flammable gases such as NH3, which, together with the gases released from graphite, dilute the oxygen concentration; the acidic products of ammonium polyphosphate can also react with metal ions (Mn) in the graphite sheets. 2+ The reaction generates high-temperature resistant ceramic phases such as manganese phosphate, which enhances the thermal stability and density of the carbon layer, thereby achieving a multi-synergistic effect in improving flame retardancy. Attached Figure Description

[0019] Figure 1 A comparative trend chart of the initial decomposition temperature test data of the products obtained by Examples 1-5 and Comparative Examples 1-7 of this invention; Figure 2 A comparative trend chart of limiting oxygen index test data of the products obtained by Examples 1-5 and Comparative Examples 1-7 of the present invention. Detailed Implementation

[0020] The present application will be further described in detail below with reference to the embodiments.

[0021] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0022] Example 1: (1) The preparation method of oxide intercalated graphite is as follows: 1g of flake graphite is placed in a beaker, and 2.0g of concentrated nitric acid, 4.0g of perchloric acid and 0.2g of potassium permanganate are added to the beaker in sequence. The beaker is then sealed and placed in an ultrasonic environment at 28℃ (frequency 40kHz, power density 0.5W / cm). 2 The mixture was allowed to stand for 60 min; then, 2.0 g of glacial acetic acid was added dropwise to the beaker at a rate of 1 mL / min at 32 °C, and the mixture was allowed to stand for 30 min; the resulting product was then filtered, washed with water until the pH reached 7, and dried in an oven at 58 °C for 24 h to obtain intercalated graphite oxide. The flake graphite (fixed carbon content ≥99%), 50 mesh, was purchased from Qingdao Risheng Graphite Co., Ltd.

[0023] (2) The preparation method of intercalated-modified double-modified graphite is as follows: A1. The reactants 1,3-propanediol and succinic acid were placed in a three-necked flask at a molar ratio of 1:1.15. The polymerization inhibitor p-hydroxyanisole was added, with the mass of p-hydroxyanisole being 0.45% of the total mass of the reactants. The mixture was prepolymerized at 185°C for 1.6 h under nitrogen protection. Tetrabutyl titanate was added as a catalyst, with the mass of tetrabutyl titanate being 0.45% of the total mass of the reactants. The mixture was heated to 222°C under vacuum (≤100 Pa) and the reaction was continued for 2.5 h. The stirring rod phenomenon (the stirring rod phenomenon is considered to occur when the stirring rod torque increases to 5 times the initial value) was observed. The product was dissolved in chloroform, purified by precipitation with cold methanol, and then dried under vacuum at 48°C to obtain poly(1,3-propanediol succinate).

[0024] A2. Disperse oxidized intercalated graphite in water, sonicate for 1 hour, add N,N-dimethylformamide, and remove water under reduced pressure to obtain a graphite dispersion. The ratio of oxidized intercalated graphite, water, and N,N-dimethylformamide is 1 g: 220 mL: 900 mL.

[0025] A3. The poly(1,3-propanediol) succinate obtained in A1 was dissolved in the graphite dispersion obtained in A2. The mass ratio of poly(1,3-propanediol) succinate to intercalated graphite oxide was 12:1. After stirring at 200 rpm for 24 h at room temperature, 1-ethyl-3-3-dimethylaminopropylcarbodiimide and 4-dimethylaminopyridine were added as carboxyl activators to catalyze the esterification reaction. The mass ratio of intercalated graphite oxide, 1-ethyl-3-3-dimethylaminopropylcarbodiimide and 4-dimethylaminopyridine was 1:1:1. After stirring at room temperature for 72 h, ascorbic acid, a reducing agent, was added. The mass of ascorbic acid was 4 times that of intercalated graphite oxide. After reduction at 78 °C for 23 h, methanol was added for co-precipitation, and the mixture was dried to obtain intercalated-modified double-modified graphite.

[0026] (3) A process for preparing graphite-grade expandable polystyrene beads, comprising the following steps: S1. By weight, inject 200 parts of deionized water into the reactor, add 0.8 parts of the dispersion stabilizer tricresyl phosphate, stir at 240 rpm, then add 100 parts of styrene, 3.5 parts of intercalated-modified graphite, 0.32 parts of the initiator benzoyl peroxide and 1 part of the phosphorus-nitrogen intumescent flame retardant ammonium polyphosphate, continue stirring, heat to 88℃, maintain the temperature for 8 hours, polymerize to generate polymer particles, and obtain the particulate dispersion phase.

[0027] S2. Add 6 parts of foaming agent n-pentane to the particulate dispersion obtained in S1. The n-pentane is injected in liquid form at a pressure of 1 MPa through a high-pressure injector. The temperature is raised to 120°C and the reaction is continued for 5 hours. After cooling, the material is discharged, washed, and filtered to obtain graphite-grade expandable polystyrene beads.

[0028] Example 2: The difference between this example and Example 1 is as follows: (1) The preparation method of oxidized intercalated graphite is as follows: 1g of natural flake graphite is placed in a beaker, 1.7g of concentrated nitric acid, 3.5g of perchloric acid and 0.18g of potassium permanganate are added to the beaker and then sealed. The beaker is placed in an ultrasonic environment at 25°C and allowed to stand for 65min. Then, 1.8g of glacial acetic acid is slowly added to the beaker at 30°C and allowed to stand for 25min. The resulting material is then filtered, washed with water until the pH is 7, and then dried in an oven at 55°C for 24h to obtain oxidized intercalated graphite.

[0029] (2) The preparation method of intercalated-modified double-modified graphite is as follows: A1. The reactants 1,3-propanediol and succinic acid were placed in a three-necked flask at a molar ratio of 1:1.1. The polymerization inhibitor p-hydroxyanisole was added, with the mass of p-hydroxyanisole being 0.4% of the total mass of the reactants. The mixture was prepolymerized at 180°C for 1.8 h under nitrogen protection. Tetrabutyl titanate was added as a catalyst, with the mass of tetrabutyl titanate being 0.4% of the total mass of the reactants. The mixture was heated to 220°C under vacuum and reacted for another 2.78 h. When the "climbing rod" phenomenon occurred, the product was dissolved in chloroform, purified by precipitation with cold methanol, and then dried under vacuum at 45°C to obtain poly(1,3-propanediol succinate).

[0030] A2. Disperse oxidized intercalated graphite in water, sonicate for 1 hour, add N,N-dimethylformamide, and remove water under reduced pressure to obtain a graphite dispersion. The ratio of oxidized intercalated graphite, water, and N,N-dimethylformamide is 1 g: 200 mL: 800 mL.

[0031] A3. The poly(1,3-propanediol) succinate obtained in A1 was dissolved in the graphite dispersion obtained in A2. The mass ratio of poly(1,3-propanediol) succinate to intercalated graphite oxide was 10:1. After stirring at room temperature for 24 h, 1-ethyl-3-3-dimethylaminopropylcarbodiimide and 4-dimethylaminopyridine were added as carboxyl activators to catalyze the esterification reaction. The mass ratio of intercalated graphite oxide, 1-ethyl-3-3-dimethylaminopropylcarbodiimide, and 4-dimethylaminopyridine was 1:0.9:0.9. After stirring at room temperature for 72 h, ascorbic acid, a reducing agent, was added. The mass of ascorbic acid was 4 times that of intercalated graphite oxide. After reduction at 75 °C for 24 h, methanol was added for co-precipitation, and the mixture was dried to obtain intercalated-modified double-modified graphite.

[0032] Example 3: The difference between this example and Example 1 is as follows: (1) The preparation method of oxidized intercalated graphite is as follows: 1g of natural flake graphite is placed in a beaker, 1.8g of concentrated nitric acid, 3.8g of perchloric acid and 0.22g of potassium permanganate are added to the beaker and then sealed. The beaker is placed in an ultrasonic environment at 30°C and allowed to stand for 50min. Then, 2.2g of glacial acetic acid is slowly added to the beaker at 35°C and allowed to stand for 35min. The resulting material is then filtered, washed with water until the pH is 7, and then dried in an oven at 60°C for 24h to obtain oxidized intercalated graphite.

[0033] (2) The preparation method of intercalated-modified double-modified graphite is as follows: A1. The reactants 1,3-propanediol and succinic acid were placed in a three-necked flask at a molar ratio of 1:1.2. The polymerization inhibitor p-hydroxyanisole was added, with the mass of p-hydroxyanisole being 0.5% of the total mass of the reactants. The mixture was pre-polymerized at 190°C for 1.5 h under nitrogen protection. The catalyst tetrabutyl titanate was added, with the mass of tetrabutyl titanate being 0.5% of the total mass of the reactants. The mixture was heated to 225°C under vacuum and reacted for another 2.25 h. When the "climbing rod" phenomenon occurred, the product was dissolved in chloroform, purified by precipitation with cold methanol, and then dried under vacuum at 50°C to obtain poly(1,3-propanediol succinate). A2. Disperse oxidized intercalated graphite in water, sonicate for 1 hour, add N,N-dimethylformamide, and remove water under reduced pressure to obtain a graphite dispersion. The ratio of oxidized intercalated graphite, water, and N,N-dimethylformamide is 1 g: 250 mL: 1000 mL.

[0034] A3. The poly(1,3-propanediol) succinate obtained in A1 was dissolved in the graphite dispersion obtained in A2. The mass ratio of poly(1,3-propanediol) succinate to intercalated graphite oxide was 13:1. After stirring at room temperature for 24 h, 1-ethyl-3-3-dimethylaminopropylcarbodiimide and 4-dimethylaminopyridine were added as carboxyl activators to catalyze the esterification reaction. The mass ratio of intercalated graphite oxide, 1-ethyl-3-3-dimethylaminopropylcarbodiimide, and 4-dimethylaminopyridine was 1:1.1:1.1. After stirring at room temperature for 72 h, ascorbic acid, a reducing agent, was added. The mass of ascorbic acid was 4 times that of intercalated graphite oxide. After reduction at 80 °C for 22 h, methanol was added for co-precipitation, and the mixture was dried to obtain intercalated-modified double-modified graphite.

[0035] Example 4: The difference between this example and Example 1 is that: (3) A preparation process for graphite-grade expandable polystyrene beads includes the following steps: S1. By weight, inject 150 parts of deionized water into the reactor, add 0.5 parts of the dispersion stabilizer tricresyl phosphate, stir, then add 100 parts of styrene, 3.3 parts of intercalated-modified graphite, 0.3 parts of the initiator benzoyl peroxide and 0.9 parts of the phosphorus-nitrogen intumescent flame retardant ammonium polyphosphate, continue stirring, heat to 90℃, maintain the temperature for 8 hours, polymerize to generate polymer particles, and obtain the particulate dispersion phase.

[0036] S2. Add 5.6 parts of foaming agent n-pentane to the particulate dispersion obtained in S1, heat to 120℃, continue the reaction for 4.5h, cool, discharge, wash, and filter to obtain graphite-grade expandable polystyrene beads.

[0037] Example 5: The difference between this example and Example 1 is that: (3) A preparation process for graphite-grade expandable polystyrene beads includes the following steps: S1. By weight, inject 230 parts of deionized water into the reactor, add 1 part of the dispersion stabilizer tricresyl phosphate, stir, then add 100 parts of styrene, 3.8 parts of intercalated-modified graphite, 0.35 parts of the initiator benzoyl peroxide and 1.1 parts of phosphorus-nitrogen intumescent flame retardant ammonium polyphosphate, continue stirring, heat to 90℃, maintain the temperature for 8 hours, polymerize to generate polymer particles, and obtain the particulate dispersion phase.

[0038] S2. Add 6.2 parts of foaming agent n-pentane to the particulate dispersion obtained in S1, heat to 120℃, continue to react for 5.5h, cool, discharge, wash, and filter to obtain graphite-grade expandable polystyrene beads.

[0039] Comparative Example 1: The difference between this comparative example and Example 1 is that in the preparation process of graphite-grade expandable polystyrene beads, 3.5 parts of intercalated-modified double-modified graphite were replaced with 2.5 parts of flake graphite.

[0040] Comparative Example 2: The difference between this comparative example and Example 1 is that in the preparation process of graphite-grade expandable polystyrene beads, 3.5 parts of intercalated-modified double-modified graphite were replaced with 3.5 parts of flake graphite.

[0041] Comparative Example 3: The difference between this comparative example and Example 1 is that in the preparation process of graphite-grade expandable polystyrene beads, 3.5 parts of intercalated-modified double-modified graphite were replaced with 4.5 parts of flake graphite.

[0042] Comparative Example 4: The difference between this comparative example and Example 1 is that in the preparation process of graphite-grade expandable polystyrene beads, 3.5 parts of intercalated-modified double-modified graphite were replaced with 2.5 parts of intercalated-modified double-modified graphite.

[0043] Comparative Example 5: The difference between this comparative example and Example 1 is that in the preparation process of graphite-grade expandable polystyrene beads, 3.5 parts of intercalated-modified double-modified graphite were replaced with 4.5 parts of intercalated-modified double-modified graphite.

[0044] Comparative Example 6: The difference between this comparative example and Example 1 is that in the preparation process of graphite-grade expandable polystyrene beads, 3.5 parts of intercalated-modified double-modified graphite were replaced with 3.5 parts of oxidized intercalated graphite (i.e., the surface modification of poly(1,3-propanediol succinate) was removed).

[0045] Comparative Example 7: The difference between this comparative example and Example 1 is that in the preparation process of graphite-grade expandable polystyrene beads, 3.5 parts of intercalated-modified double-modified graphite were replaced with 3.5 parts of modified graphite (i.e., oxidized intercalated graphite was replaced with flake graphite).

[0046] Experimental Example: Test Subjects: Graphite-grade expandable polystyrene beads prepared in Examples 1-5 and Comparative Examples 1-7. Test Items: 1. Thermal stability - initial decomposition temperature; 2. Flame retardancy - limiting oxygen index. Test Results: See Table 1.

[0047]

[0048] Results Analysis: Analysis of Examples 1-5, combined with data from Table 1 and... Figures 1-2 As can be seen, the graphite-grade expandable polystyrene bead material prepared by the present invention (Examples 1-5) has an initial decomposition temperature of over 345.4℃ and a limiting oxygen index of over 42.1%, indicating that the product prepared by the present invention has both excellent thermal stability and flame retardancy.

[0049] Analysis of Example 1 and Comparative Examples 1-7, combined with data from Table 1 and Figures 1-2 By comparing Comparative Examples 1, 2, and 3, it can be seen that as the amount of graphite increases (from 2.5 parts to 3.5 parts and then to 4.5 parts), the flame retardancy (limiting oxygen index) of the graphite-grade expandable polystyrene beads does not change much, but the thermal stability (initial decomposition temperature) shows a significant downward trend.

[0050] This is because, in terms of flame retardancy, the flame retardant effect of ordinary flake graphite mainly relies on physical barriers, and a higher addition amount (usually >10%) is required to show an effective flame retardant effect. Variations in the addition amount of flake graphite within a very low range will not bring about a significant change in flame retardancy.

[0051] In terms of thermal stability, the graphite surface contains polymerization-inhibiting groups such as quinone groups, which have a strong inhibitory effect on the free radical polymerization reaction of styrene. The higher the graphite content, the more obvious the inhibitory effect on the polymerization reaction of styrene, the more obvious the inhibition of chain growth, and the lower the relative molecular mass of the product. With the increase of graphite addition, the initial decomposition temperature of the prepared graphite-containing expandable polystyrene shows a downward trend, and the thermal stability decreases.

[0052] By comparing Comparative Example 4, Example 1, and Comparative Example 5, it can be seen that preparing graphite into the intercalated-modified double-modified graphite of this invention can simultaneously improve the thermal stability (initial decomposition temperature) and flame retardancy (limiting oxygen index) of the prepared graphite-grade expandable polystyrene beads. However, regarding the improvement in thermal stability (initial decomposition temperature), the increase first increases and then decreases with the increase in the amount of intercalated-modified double-modified graphite (from 2.5 parts to 3.5 parts and then to 4.5 parts).

[0053] This is because, at low addition levels, dispersion is insufficient and interfacial interaction is limited, resulting in a weak effect on delaying the overall thermal decomposition path. At moderate addition levels, network formation occurs, significantly extending the diffusion path of volatiles during thermal decomposition. Furthermore, the intercalated structure and the polyester coating layer work together to better suppress heat and oxygen transfer, leading to a significant increase in the initial decomposition temperature. At excessive addition levels, agglomeration effects begin to appear, and the interface weakens. In summary, the improvement in thermal stability (initial decomposition temperature) of intercalated-modified graphite initially increases and then decreases with increasing dosage, essentially reflecting a dynamic interplay between dispersion, interfacial interaction, and agglomeration effects.

[0054] Comparing Comparative Examples 6 and 7, it can be seen that oxidative intercalation treatment of flake graphite alone can improve the thermal stability (initial decomposition temperature) and flame retardancy (limiting oxygen index) of the final graphite-grade expandable polystyrene beads; surface modification treatment of flake graphite with poly(1,3-propanediol succinate) alone can also improve the thermal stability (initial decomposition temperature) and flame retardancy (limiting oxygen index) of the final graphite-grade expandable polystyrene beads; and, oxidative intercalation treatment of flake graphite followed by surface modification treatment with poly(1,3-propanediol succinate) produces a synergistic effect, synergistically improving the thermal stability (initial decomposition temperature) and flame retardancy (limiting oxygen index) of the final graphite-grade expandable polystyrene beads.

[0055] This is because, in terms of thermal stability, the oxidative intercalation treatment introduces oxygen-containing groups, which partially destroy the quinone structure, weakening its polymerization inhibition ability and improving its dispersibility; the surface modification treatment of poly(1,3-propanediol succinate) can cover / shield the quinone or other polymerization inhibition groups remaining on the graphite surface, further inhibiting its polymerization inhibition ability. In addition, the polyester layer can also enhance the compatibility between graphite and the polymer matrix and reduce interface defects. The dual modification synergistically inhibits the polymerization inhibition effect, optimizes dispersibility, and synergistically improves thermal stability (initial decomposition temperature).

[0056] Regarding flame retardancy, oxidation intercalation treatment embeds perchlorate and nitric acid intercalators between graphite layers. These intercalators decompose at high temperatures, generating gases that cause expansion between the graphite layers, forming a loose, porous, expanded structure that blocks oxygen and heat transfer, inhibiting the combustion chain reaction. Surface modification treatment of poly(1,3-propanediol) succinate, containing numerous ester and carboxylic acid groups, undergoes ester bond breakage during high-temperature decomposition, releasing non-flammable gases such as CO2 and diluting the concentration of flammable gases. Oxidation intercalators, such as residual Mn2 in KMnO4, further enhance flame retardancy. + At high temperatures, it can catalyze the dehydration and charring reaction of poly(1,3-propanediol succinate), promoting the formation of a dense char layer and synergistically constructing a multi-layered barrier structure to enhance flame retardancy. Furthermore, ammonium polyphosphate decomposes upon heating to generate polyphosphoric acid and polyphosphate, catalyzing the dehydration and charring of poly(1,3-propanediol succinate); simultaneously, it releases non-flammable gases such as NH3, which, together with the gases released from graphite, dilute the oxygen concentration; the acidic products of ammonium polyphosphate can also react with metal ions (Mn) in the graphite sheets. 2+ The reaction generates high-temperature resistant ceramic phases such as manganese phosphate, which enhances the thermal stability and density of the carbon layer, thereby achieving a multi-synergistic effect in improving flame retardancy.

[0057] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0058] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A process for preparing graphite-grade expandable polystyrene beads, characterized in that, Includes the following steps: S1. By weight, inject 150-230 parts of deionized water into the reactor, add 0.5-1 parts of dispersant stabilizer, stir, then add 100 parts of styrene, 3.3-3.8 parts of intercalated-modified double-modified graphite, 0.3-0.35 parts of initiator and 0.9-1.1 parts of phosphorus-nitrogen intumescent flame retardant, continue stirring, heat to 86-90℃, maintain the temperature for 7-9 hours, and obtain particulate dispersed phase; S2. Add 5.6-6.2 parts of foaming agent to the particulate dispersion obtained in S1, heat to 120℃, continue the reaction for 4.5-5.5h, cool, discharge, wash, and filter to obtain graphite-grade expandable polystyrene beads. The intercalated-modified graphite is prepared by surface modification of oxidized intercalated graphite with poly(1,3-propanediol succinate).

2. The preparation process of graphite-grade expandable polystyrene beads according to claim 1, characterized in that, The preparation method of the intercalated-modified double-modified graphite is as follows: A1. Place the reactants 1,3-propanediol and succinic acid in a molar ratio of 1:(1.1-1.2) in a three-necked flask, add a polymerization inhibitor, and react at 180-190℃ for 1.5-1.8h under nitrogen protection; add a catalyst, and continue the reaction at 220-225℃ under vacuum for 2-3h; dissolve the product in chloroform, precipitate and purify with cold methanol, and then dry under vacuum at 45-50℃ to obtain poly(1,3-propanediol succinate); A2. Disperse intercalated graphite in water, sonicate, add N,N-dimethylformamide, remove water under reduced pressure to obtain graphite dispersion; A3. Dissolve the poly(1,3-propanediol succinate) obtained in A1 in the graphite dispersion obtained in A2. The mass ratio of poly(1,3-propanediol succinate) to oxidized intercalated graphite is (10-13):

1. After stirring at room temperature for 24 hours, add 1-ethyl-3-3-dimethylaminopropylcarbodiimide and 4-dimethylaminopyridine. After stirring for 72 hours, add a reducing agent and reduce at 75-80℃ for 22-24 hours. Then, pour in methanol to co-precipitate and dry to obtain intercalated-modified double-modified graphite.

3. The preparation process of graphite-grade expandable polystyrene beads according to claim 2, characterized in that, The preparation method of the oxide intercalated graphite is as follows: 1g of flake graphite is placed in a beaker, and 1.7-2.0g of concentrated nitric acid, 3.5-4.0g of perchloric acid and 0.18-0.22g of potassium permanganate are added to the beaker and then sealed. The beaker is placed in an ultrasonic environment at 25-30℃ and allowed to react for 50-65min. Then, 1.8-2.2g of glacial acetic acid is added to the beaker at 30-35℃ and allowed to react for 25-35min. The resulting material is then filtered, washed with water until the pH reaches 7, and then dried in an oven at 55-60℃ for 24h to obtain oxide intercalated graphite.

4. The preparation process of graphite-grade expandable polystyrene beads according to claim 2, characterized in that, In A1, the mass of the polymerization inhibitor is 0.4-0.5% of the total mass of the reactants.

5. The preparation process of graphite-grade expandable polystyrene beads according to claim 2, characterized in that, In A1, the mass of the catalyst is 0.4-0.5% of the total mass of the reactants.

6. The preparation process of graphite-grade expandable polystyrene beads according to claim 2, characterized in that, In A2, the ratio of the amount of oxidized intercalated graphite, water and N,N-dimethylformamide is 1g:(200-250)mL:(800-1000)mL.

7. The preparation process of graphite-grade expandable polystyrene beads according to claim 2, characterized in that, In A3, the mass ratio of the oxidized intercalated graphite, 1-ethyl-3-3-dimethylaminopropylcarbodiimide, and 4-dimethylaminopyridine is 1:(0.9-1.1):(0.9-1.1).

8. The preparation process of graphite-grade expandable polystyrene beads according to claim 1, characterized in that, The phosphorus-nitrogen intumescent flame retardant is ammonium polyphosphate.

9. The preparation process of graphite-grade expandable polystyrene beads according to claim 1, characterized in that, The dispersant and stabilizer is tricresyl phosphate; the initiator is benzoyl peroxide; and the foaming agent is pentane.

10. A graphite-grade expandable polystyrene bead, characterized in that, It is prepared using the preparation process of graphite-grade expandable polystyrene beads as described in any one of claims 1-9.

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