Preparation method of recyclable high-bending-resistance polystyrene material

Abstract

The invention belongs to the technical field of recycling of high polymer materials, and particularly relates to a preparation method of a recyclable high-bending-resistance polystyrene material. According to the present invention, the recycled polystyrene material with high bending resistance is prepared by using the recycled polystyrene material as the main matrix, carrying out maleic anhydride grafting modification in the double screw extruder, adding the composite modifier, and carrying out the one-step reaction extrusion method, such that the mechanical property of the recycled polystyrene material is significantly improved; especially, the bending strength of the polystyrene recycled material is improved. The bending strength of the recyclable high-bending-resistance polystyrene material can be recovered to be close to the level of a new polystyrene material and even exceed the level of the new polystyrene material, an effective and environment-friendly way is provided for high-value utilization of waste polystyrene, and the requirements of circular economy and sustainable development are met.

Description

Technical Field

[0001] This invention belongs to the field of polymer material recycling and reuse technology, specifically relating to a method for preparing recyclable high flexural strength polystyrene material. Background Technology

[0002] Polystyrene (PS) and its polystyrene foam (PSF) are widely used in packaging, construction, disposable tableware, and household goods due to their advantages such as light weight, low cost, thermal insulation, and good processability. Waste polystyrene is extremely difficult to degrade in the natural environment, causing long-term pollution to soil and water bodies; while incineration releases harmful gases. Therefore, recycling and reusing waste polystyrene is not only an urgent need to solve environmental pollution, but also an important way to achieve sustainable resource utilization and develop a circular economy.

[0003] Currently, the recycling of waste polystyrene mainly relies on physical recycling, which involves processes such as washing, crushing, and melt granulation to regenerate it into plastic granules. However, during repeated processing and use, the molecular chains of polystyrene degrade, leading to a decrease in the molecular weight of the recycled polystyrene (RPS) and a significant reduction in its mechanical properties (such as tensile strength, impact strength, and flexural strength), thus limiting its application in high-value-added products. (See Appendix of this invention.) Figure 1 As shown, the flexural strength of recycled polystyrene obtained through conventional physical recycling is much lower than that of virgin polystyrene.

[0004] To improve the performance of recycled plastics, blending modification or chemical modification methods are commonly used. Maleic anhydride (MA) is a commonly used polar monomer and grafting agent that can be attached to the non-polar polymer backbone through free radical grafting reactions, thereby improving the compatibility and mechanical properties of the material. For example, Chinese patent application CN115124792A (A method for preparing maleic anhydride-toughened modified polystyrene / polypropylene composite material) discloses a method for improving the compatibility of polystyrene / polypropylene blends using maleic anhydride, demonstrating that the addition of MA can significantly improve the tensile strength and elongation at break of the composite material. Furthermore, research by Graziano et al. (Enhancing the mechanical, morphological, and rheological behavior of polyethylene / polypropylene blends with maleic anhydride-grafted polyethylene) also shows that maleic anhydride grafts can act as reactive compatibilizers, effectively improving the mechanical properties of polyethylene / polypropylene blends. These studies provide a theoretical basis for modifying recycled polystyrene with maleic anhydride. However, existing technologies mostly focus on improving the compatibility of polymer blend systems or have relatively complex processes, such as the two-step extrusion method mentioned in Chinese patent application CN103396644A (a polyolefin / polystyrene blend-based wood-plastic composite material and its preparation method). There is a lack of an industrialized method that is simple to process and can efficiently restore the mechanical properties of recycled polystyrene. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a simple, low-cost, and environmentally friendly method for preparing recyclable high-flexural-strength polystyrene materials. This invention uses recycled polystyrene as the main matrix, and through graft modification with maleic anhydride in a twin-screw extruder, while simultaneously adding a composite modifier, a one-step reactive extrusion method is used to obtain recyclable high-flexural-strength polystyrene materials. This method can effectively repair and improve the flexural strength of recycled polystyrene, restoring the flexural strength of the recyclable high-flexural-strength polystyrene materials to levels close to, or even exceeding, those of virgin polystyrene.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a recyclable high flexural strength polystyrene material includes the following steps: Step 1: Mix the recycled polystyrene, maleic anhydride, initiator, and composite modifier to obtain a mixture. Step 2: Add the mixture to a twin-screw extruder, melt-extrude, cool, and pelletize to obtain recyclable high flexural strength polystyrene material.

[0007] Preferably, in step one, the mass ratio of recycled polystyrene, maleic anhydride, initiator, and composite modifier is 100:(0.5-2.5):(0.05-0.25):(1-3).

[0008] Preferably, the number average molecular weight of the recycled polystyrene material in step one is 30,000-40,000.

[0009] Preferably, the initiator in step one includes dicumyl peroxide (DCP).

[0010] Preferably, the composite modifier in step one is prepared by the following steps: S1. Disperse nano-calcium carbonate in ethanol, add γ-mercaptopropyltrimethoxysilane (silane coupling agent KH590), add ammonia water dropwise to adjust the pH value to 9.5-10.5, react, filter, wash and dry to obtain mercapto-modified nano-calcium carbonate. S2. SBS (styrene-butadiene-styrene block copolymer) is dissolved in tetrahydrofuran (THF), and then a photoinitiator and mercapto-modified nano-calcium carbonate are added. After the reaction is completed, the product is precipitated, filtered, washed, and dried to obtain the composite modifier.

[0011] Preferably, in S1, the mass ratio of nano-calcium carbonate, ethanol, and γ-mercaptopropyltrimethoxysilane is 1:(15-25):(0.6-1), and the reaction conditions are 1.5-2.5 h at a temperature of 45-55 °C.

[0012] Preferably, in S2, the mass ratio of SBS, tetrahydrofuran, photoinitiator and mercapto-modified nano-calcium carbonate is 5:(10-20):(0.04-0.06):(0.6-1), and the reaction conditions are: under nitrogen protection, at room temperature, and under ultraviolet light irradiation at a wavelength of 350 nm for 1-2 hours.

[0013] Preferably, the photoinitiator comprises dimethyl benzoate (DMPA).

[0014] Preferably, in step two, the temperature of melt extrusion is 190-210℃.

[0015] Preferably, in step two, the screw speed during extrusion is 250-350 r / min.

[0016] Preferably, in step two, a rotary cutter is used for pelletizing, and the rotary cutter rotates at a speed of 180-220 r / min.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: In this invention, waste polystyrene recycled material is used as the main raw material, realizing the recycling of resources, reducing environmental pollution, and conforming to the concept of green and sustainable development. In this invention, the flexural strength of recycled polystyrene is significantly improved by grafting maleic anhydride, solving the key problem of poor mechanical properties of recycled materials and broadening their application fields. The organic-inorganic composite modifier prepared by adding nano-calcium carbonate and SBS through a grafting reaction can further improve the flexural strength of recycled polystyrene. The modification process not only introduces polar groups, but also increases the molecular weight of the recycled material to a certain extent and reduces its polydispersity, thus improving the material's performance at the molecular level. Using a twin-screw extruder as the reaction and processing equipment, the mixing, grafting, and extrusion granulation can be completed in one step. The process is short, easy to operate, and conducive to large-scale industrial production. Moreover, there is no need to add expensive compatibilizers or plasticizers, resulting in lower production costs. Attached Figure Description

[0018] Figure 1 A comparison chart of the flexural strength test results of virgin polystyrene and recycled polystyrene. Figure 2 These are test diagrams of the bending performance of the recyclable high bending resistance polystyrene materials prepared in Examples 1-5 of this invention; Figure 3 The images show the infrared spectra of the recycled polystyrene material in this invention and the maleic anhydride-grafted recycled polystyrene material prepared in Example 6. Detailed Implementation

[0019] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0020] Example 1 This embodiment discloses a method for preparing a recyclable high-bending-strength polystyrene material, including the following steps: Step 1: Dry the recycled polystyrene material in a vacuum drying oven at 100℃ for 1 hour. Take 100 parts of the dried recycled polystyrene material, 0.5 parts of maleic anhydride, 0.05 parts of dicumyl peroxide, and 1 part of composite modifier and mix them to obtain a mixture. The composite modifier is prepared by the following steps: S1. Disperse nano-calcium carbonate in ethanol, add γ-mercaptopropyltrimethoxysilane, the mass ratio of nano-calcium carbonate, ethanol and γ-mercaptopropyltrimethoxysilane is 1:20:0.8, add 25wt% ammonia water to adjust the pH to 10, react at 50℃ for 2h, after the reaction is completed, filter, wash with ethanol 3 times, and place in a vacuum drying oven at 50℃ to dry to constant temperature to obtain mercapto-modified nano-calcium carbonate; S2. SBS was dissolved in tetrahydrofuran, and then benzoin dimethyl ether and mercapto-modified nano-calcium carbonate were added. The mass ratio of SBS, tetrahydrofuran, benzoin dimethyl ether and mercapto-modified nano-calcium carbonate was 5:15:0.05:0.8. The reaction was carried out under nitrogen protection, at room temperature, and under ultraviolet light irradiation at a wavelength of 350 nm for 1.5 h. After the reaction was completed, the reaction mixture was added to 10 times the mass of n-hexane to precipitate. The precipitate was filtered and washed three times with ethanol. Then it was placed in a vacuum drying oven at 50 °C and dried to a constant temperature to obtain the composite modifier. Step 2: Add the mixture to a twin-screw extruder, melt extrude, cool and pelletize to obtain recyclable high flexural strength polystyrene material; The melt extrusion temperature is 200℃, the screw speed during extrusion is 300r / min, and the pelletizing is performed using a roller cutter with a speed of 200r / min.

[0021] Example 2 This embodiment discloses a method for preparing a recyclable high-bending-strength polystyrene material, including the following steps: Step 1: Dry the recycled polystyrene material in a vacuum drying oven at 100℃ for 1 hour. Take 100 parts of the dried recycled polystyrene material, 1 part of maleic anhydride, 0.1 parts of dicumyl peroxide, and 1.5 parts of composite modifier and mix them to obtain a mixture. The preparation method of the composite modifier is the same as in Example 1; Step 2: Add the mixture to a twin-screw extruder, melt extrude, cool and pelletize to obtain recyclable high flexural strength polystyrene material; The melt extrusion temperature is 200℃, the screw speed during extrusion is 300r / min, and the pelletizing is performed using a roller cutter with a speed of 200r / min.

[0022] Example 3 This embodiment discloses a method for preparing a recyclable high-bending-strength polystyrene material, including the following steps: Step 1: Dry the recycled polystyrene material in a vacuum drying oven at 100°C for 1 hour. Take 100 parts of the dried recycled polystyrene material, 1.5 parts of maleic anhydride, 0.15 parts of dicumyl peroxide, and 2 parts of composite modifier and mix them to obtain a mixture. The preparation method of the composite modifier is the same as in Example 1; Step 2: Add the mixture to a twin-screw extruder, melt extrude, cool and pelletize to obtain recyclable high flexural strength polystyrene material; The melt extrusion temperature is 200℃, the screw speed during extrusion is 300r / min, and the pelletizing is performed using a roller cutter with a speed of 200r / min.

[0023] Example 4 This embodiment discloses a method for preparing a recyclable high-bending-strength polystyrene material, including the following steps: Step 1: Dry the recycled polystyrene material in a vacuum drying oven at 100℃ for 1 hour. Take 100 parts of the dried recycled polystyrene material, 2 parts of maleic anhydride, 0.2 parts of dicumyl peroxide, and 2.5 parts of composite modifier and mix them to obtain a mixture. The preparation method of the composite modifier is the same as in Example 1; Step 2: Add the mixture to a twin-screw extruder, melt extrude, cool and pelletize to obtain recyclable high flexural strength polystyrene material; The melt extrusion temperature is 200℃, the screw speed during extrusion is 300r / min, and the pelletizing is performed using a roller cutter with a speed of 200r / min.

[0024] Example 5 This embodiment discloses a method for preparing a recyclable high-bending-strength polystyrene material, including the following steps: Step 1: Dry the recycled polystyrene material in a vacuum drying oven at 100℃ for 1 hour. Take 100 parts of the dried recycled polystyrene material, 2.5 parts of maleic anhydride, 0.25 parts of dicumyl peroxide, and 3 parts of composite modifier and mix them to obtain a mixture. The preparation method of the composite modifier is the same as in Example 1; Step 2: Add the mixture to a twin-screw extruder, melt extrude, cool and pelletize to obtain recyclable high flexural strength polystyrene material; The melt extrusion temperature is 200℃, the screw speed during extrusion is 300r / min, and the pelletizing is performed using a roller cutter with a speed of 200r / min.

[0025] Example 6 This embodiment discloses a method for preparing maleic anhydride-grafted polystyrene material, including the following steps: Step 1: Dry the recycled polystyrene material in a vacuum drying oven at 100°C for 1 hour. Take 100 parts of the dried recycled polystyrene material, 0.5 parts of maleic anhydride, and 0.05 parts of dicumyl peroxide and mix them to obtain a mixture. Step 2: Add the mixture to a twin-screw extruder, melt extrude, cool and pelletize to obtain maleic anhydride-grafted polystyrene material; The melt extrusion temperature is 200℃, the screw speed during extrusion is 300r / min, and the pelletizing is performed using a roller cutter with a speed of 200r / min.

[0026] Performance testing (1) Infrared spectroscopy was performed on the recycled polystyrene material and the maleic anhydride-grafted polystyrene material prepared in Example 6. The results are as follows: Figure 3 As shown, in the infrared spectrum, 1740 cm⁻¹ -1 The appearance of the ester bond peak confirms the successful grafting of maleic anhydride.

[0027] (2) GPC tests were performed on virgin polystyrene, recycled polystyrene, and the maleic anhydride-grafted polystyrene material prepared in Example 6 to determine the molecular weight distribution of the polymer materials. The results are shown in Table 1. Table 1 As shown in Table 1, compared with virgin polystyrene, the number-average molecular weight (Mn) and weight-average molecular weight (Mw) of recycled polystyrene decreased significantly, while the polydispersity index (PDI) increased significantly. This confirms that the recycling process led to polymer degradation, molecular chain breakage, and a wider molecular weight distribution. After the modification treatment in Example 6, the Mn value of the composite material increased significantly from 33605 to 46650, which is very close to the level of virgin material. At the same time, its PDI value decreased from 2.37 to 1.79, even better than that of virgin material. This result indicates that the MA grafting reaction not only introduces polar groups into the polystyrene molecular chain, but may also promote the reconnection or crosslinking of some broken molecular chains through free radical reactions, playing a role in "repairing" the molecular structure, thereby fundamentally improving the macroscopic mechanical properties of the material.

[0028] (3) The virgin polystyrene, recycled polystyrene, and the recyclable high-bending-strength polystyrene material prepared in Examples 1-5 were melted separately. The melts were injection molded to obtain polystyrene samples. The temperature of the injection melt was 210°C, the mold temperature was 105°C, the injection pressure was 35 MPa, and the injection time was 10 s. The bending strength of the polystyrene samples was measured. The results of the bending strength measurements of the polystyrene samples made from virgin polystyrene and the polystyrene samples made from recycled polystyrene are as follows: Figure 1 As shown, the flexural strength test results of polystyrene samples made from recyclable high-flexural-strength polystyrene materials prepared in Examples 1-5 are as follows. Figure 2 As shown. From Figure 1 The test results show that after the recycling process, the flexural strength of polystyrene decreased from approximately 50 MPa in virgin material to approximately 45 MPa, indicating a significant performance degradation. This is mainly due to the breakage of polymer molecular chains caused by heat, oxygen, and shear during the recycling process. Figure 2 The test results show that the flexural strength of the composite material continuously increases with the increase of maleic anhydride and composite modifier dosage. This indicates that the grafting reaction of maleic anhydride can effectively improve the mechanical properties of recycled polystyrene. The introduction of maleic anhydride forms polar groups on the molecular chain, enhancing intermolecular forces and thus improving the overall strength and stiffness of the material. Similarly, the organic-inorganic composite modifier prepared by the grafting reaction of nano-calcium carbonate and SBS can also improve the mechanical properties of recycled polystyrene, further enhancing its flexural strength.

[0029] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a recyclable high-bending-strength polystyrene material, characterized in that, Includes the following steps: Step 1: Mix the recycled polystyrene, maleic anhydride, initiator, and composite modifier to obtain a mixture. Step 2: Add the mixture to a twin-screw extruder, melt-extrude, cool, and pelletize to obtain recyclable high flexural strength polystyrene material.

2. The method for preparing a recyclable high-bending-strength polystyrene material according to claim 1, characterized in that, In step one, the mass ratio of recycled polystyrene, maleic anhydride, initiator, and composite modifier is 100:(0.5-2.5):(0.05-0.25):(1-3).

3. The method for preparing a recyclable high-bending-strength polystyrene material according to claim 1, characterized in that, The number average molecular weight of the recycled polystyrene material in step one is 30,000-40,000.

4. The method for preparing a recyclable high-bending-strength polystyrene material according to claim 1, characterized in that, The initiator in step one includes dicumyl peroxide.

5. The method for preparing a recyclable high-bending-strength polystyrene material according to claim 1, characterized in that, The composite modifier in step one, It is prepared by the following steps: S1. Disperse nano-calcium carbonate in ethanol, add γ-mercaptopropyltrimethoxysilane, and adjust the pH value to 9.5-10.5 by adding ammonia dropwise. After the reaction is completed, filter, wash, and dry to obtain mercapto-modified nano-calcium carbonate. S2. Dissolve SBS in tetrahydrofuran, then add a photoinitiator and mercapto-modified nano-calcium carbonate, react, and after the reaction is complete, precipitate, filter, wash, and dry to obtain the composite modifier.

6. The method for preparing a recyclable high-bending-strength polystyrene material according to claim 4, characterized in that, In S1, the mass ratio of nano-calcium carbonate, ethanol, and γ-mercaptopropyltrimethoxysilane is 1:(15-25):(0.6-1), and the reaction conditions are 1.5-2.5 h at 45-55 °C.

7. The method for preparing a recyclable high-bending-strength polystyrene material according to claim 4, characterized in that, In S2, the mass ratio of SBS, tetrahydrofuran, photoinitiator and mercapto-modified nano-calcium carbonate is 5:(10-20):(0.04-0.06):(0.6-1), and the reaction conditions are: under nitrogen protection, at room temperature, and under ultraviolet light irradiation at a wavelength of 350 nm for 1-2 hours.

8. The method for preparing a recyclable high-bending-strength polystyrene material according to claim 1, characterized in that, In step two, the temperature of melt extrusion is 190-210℃.

9. The method for preparing a recyclable high-bending-strength polystyrene material according to claim 1, characterized in that, In step two, the screw speed during extrusion is 250-350 r / min.

10. The method for preparing a recyclable high-bending-strength polystyrene material according to claim 1, characterized in that, In step two, a rotary cutter is used to cut the pellets, and the rotary cutter rotates at a speed of 180-220 r / min.

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