Method for modifying polypropylene waste plastic and application thereof

Abstract

The application discloses a method for modifying polypropylene waste plastics and application thereof, and belongs to the technical field of environmental pollution control. The method comprises the following steps: mixing crushed polypropylene waste plastics with glycidyl methacrylate modified sodium alginate, and reacting for 2h-8h under the mechanical mixing effect; filtering out the modified waste plastics, and vacuum drying to obtain the modified polypropylene waste plastics. The method for modifying polypropylene waste plastics provided by the application is grafted and modified for the polypropylene waste plastics through mechanochemistry, the C-C bond of the polypropylene is directly activated by mechanical force (such as shearing, ball milling and the like) to make the C-C bond break and generate macromolecular free radicals. Under the action of the mechanical force, the polypropylene waste plastics are grafted and modified by the glycidyl methacrylate modified sodium alginate, the efficient persulfate activation of the polypropylene is realized, and the oxidative degradation of the polypropylene is promoted. The method can be carried out at room temperature and in a solvent-free condition, and is efficient, rapid, green and environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of environmental pollution control technology, specifically to a method for modifying polypropylene waste plastics and its application. Background Technology

[0002] With the continuous growth in the consumption of plastic products, the world faces increasingly severe pressure from plastic pollution and waste plastic disposal. Among the many types of plastics, polyolefins, such as polyethylene (PE) and polypropylene (PP), account for half of the total plastic production due to their excellent performance and low cost, and are therefore the most significant component of waste plastics. Traditional waste plastic treatment methods mainly include landfill, incineration, and mechanical recycling. Landfill occupies a large amount of land resources and may cause long-term environmental risks; incineration can recover energy but poses a risk of producing harmful gases; while conventional mechanical recycling is currently the most widely used physical recycling method.

[0003] Because polyolefin materials undergo aging processes such as molecular chain breakage, molecular weight reduction, and functional group changes during repeated processing and use, the mechanical and processing properties of recycled materials deteriorate significantly, severely limiting the application scope and economic value of recycled plastics. One of the most effective ways to upgrade recycling is to modify and graft inert polyolefin molecular chains to introduce polar functional groups, fundamentally improving their properties.

[0004] Currently, existing grafting technologies include melt grafting, solution grafting, solid-phase grafting, radiation grafting, and plasma grafting. Melt grafting is the most common industrial method, typically carried out at high temperatures in a twin-screw extruder. Its challenge lies in its heavy reliance on chemical initiators; however, residual stabilizers, antioxidants, and other impurities in waste plastics can quench free radicals, severely depleting the initiator and leading to low grafting efficiency and serious side reactions (such as cross-linking, gelation, or degradation). Furthermore, the high temperature process accelerates the thermal aging of the material. Solution grafting, while producing uniform reactions, requires large amounts of organic solvents, resulting in long processes, high energy consumption, complex post-processing, and significant costs and environmental pollution risks. Solid-phase grafting involves reactions at temperatures below the material's melting point, avoiding a molten state; however, the reaction is extremely slow, and the degree of reaction is severely limited by the diffusion rate of monomers and initiators within the solid particles, making uniform grafting difficult. Radiation grafting utilizes high-energy rays to initiate the reaction, requiring no chemical initiators and producing uniform grafting sites. However, it involves significant equipment investment, poses safety and protection challenges with the radiation source, and high-energy rays can also cause random breakage of the polymer backbone, leading to a reduction in material properties. Plasma grafting is a surface modification technique that uses plasma to activate the surface of an object, generating active sites for grafting. It has minimal impact on the bulk properties of the material. However, the modified layer produced by this technique is extremely thin (typically only nanometer-scale), and the equipment is expensive, making continuous production difficult. It is limited to the preparation of high-value-added specialty surface materials. Summary of the Invention

[0005] The purpose of this invention is to provide a method for modifying polypropylene waste plastics and its application. Efficient depolymerization of polypropylene is a key step in realizing resource utilization, but it is usually limited by its chemically inert structure and complex depolymerization products. This invention solves the problem that the modification and grafting of polyolefin molecular chains (polypropylene) requires high conditions and is difficult.

[0006] This invention is achieved through the following technical solution: This invention provides a method for modifying waste polypropylene plastics, comprising the following steps: After crushing the waste polypropylene plastic, it was mixed with glycidyl methacrylate-modified sodium alginate and reacted for 2 to 8 hours under mechanical mixing. The waste plastic modified material is filtered out and then vacuum dried to obtain the modified polypropylene waste plastic.

[0007] More specifically, in the method for modifying polypropylene waste plastics, the particle size range of the crushed polypropylene waste plastics is 0.1 mm to 10 mm.

[0008] Further specifying, in the method for modifying polypropylene waste plastic, the mass ratio of the polypropylene waste plastic to the glycidyl methacrylate-modified sodium alginate is 100:(30~70).

[0009] Further specifying, in the method for modifying polypropylene waste plastics, the preparation of the glycidyl methacrylate-modified sodium alginate includes: Glycidyl methacrylate and sodium alginate were added to water and mixed evenly. The mixture was reacted at 50℃~70℃ for 1h~5h to obtain the glyceryl methacrylate-modified sodium alginate.

[0010] Further specifying, in the method for modifying polypropylene waste plastic, the mass ratio of glycidyl methacrylate to sodium alginate is 1.5:(0.1~0.5).

[0011] More specifically, in the method for modifying polypropylene waste plastics, the concentration of sodium alginate is 5 g / L to 25 g / L.

[0012] More specifically, in the method for modifying polypropylene waste plastics, the mechanical mixing method includes: planetary milling, ball milling, vibratory milling, or stirred milling.

[0013] More specifically, in the method for modifying polypropylene waste plastics, the mechanical mixing method is ball milling.

[0014] More specifically, in the method for modifying polypropylene waste plastics, the ball milling conditions include: a rotation speed of 500 rpm to 700 rpm and a ball milling time of 2 h to 6 h.

[0015] This invention provides the application of the above-mentioned method for modifying polypropylene waste plastics in waste plastic recycling.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention provides a method for modifying polypropylene waste plastics. Through mechanochemical graft modification, the method directly activates the C-C bonds in polypropylene using mechanical forces (such as shearing and ball milling), causing them to break and generate large molecular free radicals. Under the action of mechanical forces, the polypropylene waste plastics are grafted with sodium alginate modified with glycidyl methacrylate, achieving efficient persulfate activation of polypropylene and promoting its oxidative degradation. This method can be carried out at room temperature under solvent-free conditions, and the reaction is highly efficient, rapid, and environmentally friendly.

[0017] The method for modifying waste polypropylene plastics provided by this invention utilizes mechanical force (such as shearing, ball milling, etc.) to directly activate the C-C bonds of polypropylene, causing them to break and generate large molecular free radicals. This eliminates the need for traditional chemical initiators, fundamentally avoiding the inefficiency caused by impurity quenching in the waste material. Mechanical force simultaneously achieves strong mixing and mass transfer, ensuring uniform grafting and significantly improving the compatibility of waste plastics with polar materials, thus opening up new pathways for their high-value applications.

[0018] The method for modifying waste polypropylene provided by this invention utilizes sodium alginate (SA), a sodium salt of a localized anionic polysaccharide composed of β-D-mannuronic acid (M) and α-L-guluronic acid (G), which exhibits good biocompatibility and biodegradability. Its use in polypropylene grafting will not have adverse environmental impacts. Glycidyl methacrylate is used to modify sodium alginate, which is then grafted onto polypropylene under mechanical force. This introduces both C-OH and C=O functional groups into the polypropylene structure. The introduction of these bifunctional groups activates the polypropylene's structure and enables efficient persulfate activation during the advanced persulfate oxidation process, generating free radicals to achieve the oxidative degradation of polypropylene.

[0019] The method for modifying polypropylene waste plastics provided by this invention effectively enhances the chemical activity of the polymer, constructs target sites, and improves product selectivity by grafting polypropylene waste plastics with mechanochemical methods. This is beneficial for the efficient depolymerization of polypropylene and is of great significance for realizing the resource utilization of polyolefins. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 The modified polypropylene waste plastic provided in Example 1 of the present invention and the infrared spectrum of the polypropylene waste plastic; Figure 2 The thermogravimetric curves of the modified polypropylene waste plastics and polypropylene waste plastics prepared in Examples 1-5 of Test 3 of this invention are shown. Figure 3 The diagram shows the TOC values ​​of the degradation solutions of modified polypropylene waste plastics and polypropylene waste plastics and sodium alginate-grafted polypropylene waste plastics obtained in Examples 1-5 of Test 4 of this invention. Figure 4 This diagram shows the percentage of hydroxyl and carbonyl functional group products in the modified polypropylene waste plastics and polypropylene waste plastic degradation products prepared in Examples 1-5 of Test 5 of this invention. Wherein, PP-MSA -8% corresponds to the result of Example 1; PP-MSA-12.8% corresponds to the result of Example 2; PP-MSA-13.7% corresponds to the result of Example 3; PP-MSA-18% corresponds to the result of Example 4; PP-MSA-28% corresponds to the result of Example 5; PP-MSA represents the modified polypropylene waste plastic provided by the present invention; PP represents polypropylene waste plastic; PP-SA represents sodium alginate grafted polypropylene waste plastic. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. The illustrative embodiments and descriptions of this invention are for explanation only and are not intended to limit the invention. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0022] To address the challenges and high requirements of existing technologies for modifying and grafting polyolefin molecular chains (polypropylene), the following technology is proposed: A method for modifying waste polypropylene plastics includes the following steps: After crushing the waste polypropylene plastic, it was mixed with glycidyl methacrylate-modified sodium alginate and reacted for 2 to 8 hours under mechanical mixing. The waste plastic modified material is filtered out and then vacuum dried to obtain the modified polypropylene waste plastic.

[0023] This invention provides a method for modifying polypropylene waste plastics. Through mechanochemical graft modification, the method directly activates the C-C bonds in polypropylene using mechanical forces (such as shearing and ball milling), causing them to break and generate large molecular free radicals. Under the action of mechanical forces, the polypropylene waste plastics are grafted with sodium alginate modified with glycidyl methacrylate, achieving efficient persulfate activation of polypropylene and promoting its oxidative degradation. This method can be carried out at room temperature under solvent-free conditions, and the reaction is highly efficient, rapid, and environmentally friendly.

[0024] The method for modifying waste polypropylene plastics provided by this invention utilizes mechanical force (such as shearing, ball milling, etc.) to directly activate the C-C bonds of polypropylene, causing them to break and generate large molecular free radicals. This eliminates the need for traditional chemical initiators, fundamentally avoiding the inefficiency caused by impurity quenching in the waste material. Mechanical force simultaneously achieves strong mixing and mass transfer, ensuring uniform grafting and significantly improving the compatibility of waste plastics with polar materials, thus opening up new pathways for their high-value applications.

[0025] The method for modifying waste polypropylene provided by this invention utilizes sodium alginate (SA), a sodium salt of a localized anionic polysaccharide composed of β-D-mannuronic acid (M) and α-L-guluronic acid (G), which exhibits good biocompatibility and biodegradability. Its use in polypropylene grafting will not have adverse environmental impacts. Glycidyl methacrylate is used to modify sodium alginate, which is then grafted onto polypropylene under mechanical force. This introduces both C-OH and C=O functional groups into the polypropylene structure. The introduction of these bifunctional groups activates the polypropylene's structure and enables efficient persulfate activation during the advanced persulfate oxidation process, generating free radicals to achieve the oxidative degradation of polypropylene.

[0026] Sodium alginate was modified with glycidyl methacrylate and then grafted onto waste polypropylene plastics. The introduced C-OH and C=O functional groups enhance the activation of persulfate. Specifically, the C=O structure can donate electrons to the persulfate molecule to generate a free radical, transforming it into CO. This CO radical then abstracts hydrogen from the polymer matrix to generate C-OH, which in turn can donate H to further evolve into the C=O structure, further activating the persulfate. Furthermore, this bifunctional group can be effectively recycled, achieving highly efficient synergistic activation. When applied to the persulfate oxidation process, it can also effectively improve the selectivity of oxygen-containing products.

[0027] More specifically, the particle size range of the crushed polypropylene waste plastic is 0.1mm to 10mm. It can be 0.1mm, 0.5mm, 1mm, 2mm, 5mm, 10mm, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] More specifically, the mass ratio of the polypropylene waste plastic to the glycidyl methacrylate-modified sodium alginate is 100:(30~70). This can be 100:30, 100:40, 100:50, 100:60, 100:70, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The more glycidyl methacrylate-modified sodium alginate added, the higher the grafting rate. However, a higher grafting rate is not always better. An excessively high grafting rate not only results in smaller molecules generated from polypropylene degradation, leading to further mineralization into CO2 and other low-value small molecules, but also results in excessive consumption of grafting reagents, thus increasing modification costs. When the mass ratio of polypropylene waste plastic to glycidyl methacrylate-modified sodium alginate is 100:(30~70), the grafting rate ranges from 8% to 28%. Controlling the grafting rate within this range helps convert polypropylene into more valuable soluble organic matter without increasing excessive carbon emissions.

[0029] More specifically, the preparation of the glycidyl methacrylate-modified sodium alginate includes: Glycidyl methacrylate and sodium alginate were added to water and mixed evenly. The mixture was reacted at 50℃~70℃ for 1h~5h to obtain the glyceryl methacrylate-modified sodium alginate.

[0030] Further specified, the mass ratio of the glycidyl methacrylate to the sodium alginate is 1.5:(0.1~0.5), which can be 1.5:0.1, 1.5:0.2, 1.5:0.3, 1.5:0.4, 1.5:0.5, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Further specified, the concentration of sodium alginate is 5 g / L to 25 g / L. It can be 5 g / L, 10 g / L, 15 g / L, 20 g / L, 25 g / L, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] More specifically, the mechanical mixing method includes: planetary milling, ball milling, vibratory milling, or stirred milling.

[0033] More specifically, the mechanical mixing method is ball milling. Ball milling, with relatively low impact energy and a relatively long reaction time, can effectively refine particles while maintaining the structural integrity of the mixture to the greatest extent. The continuous and uniform mechanical energy input of ball milling creates ideal conditions for mechanical alloying and mechanochemical reactions, enabling the uniform composite of components at the atomic scale.

[0034] More specifically, the ball milling conditions include: a rotation speed of 500 rpm to 700 rpm and a ball milling time of 2 h to 6 h.

[0035] To further illustrate the present invention, the following describes a method for modifying polypropylene waste plastics and its application in conjunction with embodiments. However, it should be understood that these embodiments are implemented under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating procedures. They are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention. The scope of protection of the present invention is not limited to the following embodiments.

[0036] Example 1: The method for modifying polypropylene waste plastics provided in this embodiment specifically includes the following steps: Step 1: Add 1.5g glycidyl methacrylate (GMA) and 100mg sodium alginate (SA) to 20mL of aqueous solution, mix with a stirrer, react for 1 hour, and control the temperature at 50℃ to obtain glycidyl methacrylate modified sodium alginate (MSA).

[0037] Step 2: Put the waste polypropylene plastic into a blender and crush it. Take 100mg of PP waste plastic sample and 30mg of glycidyl methacrylate modified sodium alginate (MSA) and put them into a 100mL zirconium dioxide ball milling jar. Add 16 zirconium dioxide grinding balls with a diameter of 10mm into the jar. Set the ball milling time to 2 hours and the ball milling speed to 700rpm.

[0038] Step 3: After ball milling, filter out the PP waste sample, wash it, and place it in an oven for vacuum drying for 12 hours to obtain modified PP waste plastic (PP-MSA).

[0039] Example 2: The method for modifying polypropylene waste plastics provided in this embodiment specifically includes the following steps: Step 1: Add 1.5g glycidyl methacrylate (GMA) and 200mg sodium alginate (SA) to 20mL of aqueous solution, mix with a stirrer, react for 3 hours, and control the temperature at 60℃ to obtain glycidyl methacrylate modified sodium alginate (MSA).

[0040] Step 2: Put the waste polypropylene plastic into a blender and crush it. Take 100mg of PP waste plastic sample and 50mg of glycidyl methacrylate modified sodium alginate (MSA) and put them into a 100mL zirconium dioxide ball milling jar. Add 16 zirconium dioxide grinding balls with a diameter of 10mm into the jar. Set the ball milling time to 4h and the ball milling speed to 600rpm.

[0041] Step 3: After ball milling, the PP waste sample is filtered out, cleaned, and placed in an oven for vacuum drying for 12 hours to obtain modified PP waste plastic (PP-MSA).

[0042] Example 3: The method for modifying polypropylene waste plastics provided in this embodiment specifically includes the following steps: Step 1: Add 1.5g glycidyl methacrylate (GMA) and 500mg sodium alginate (SA) to 20mL of aqueous solution, mix with a stirrer, react for 5 hours, and control the temperature at 70℃ to obtain glycidyl methacrylate modified sodium alginate (MSA).

[0043] Step 2: Put the waste polypropylene plastic into a blender and crush it. Take 100mg of PP waste plastic sample and 70mg of glycidyl methacrylate modified sodium alginate (MSA) and put them into a 100mL zirconium dioxide ball milling jar. Put 16 zirconium dioxide grinding balls with a diameter of 10mm into the jar, set the ball milling time to 6h and the ball milling speed to 500rpm.

[0044] Step 3: After ball milling, filter out the PP waste sample, wash it, and place it in an oven for vacuum drying for 12 hours to obtain modified PP waste plastic (PP-MSA).

[0045] Test 1: The modified polypropylene waste plastic (PP-MSA) obtained in Example 1 and polypropylene waste plastic (PP) were subjected to infrared spectroscopy detection. The results are shown in the figure. Figure 1 As shown.

[0046] Figure 1 The results showed that the infrared spectrum of modified PP waste plastic (PP-MSA) at 1630 cm⁻¹ -1 1734cm -1 And 3450cm -1 A new peak appeared, indicating that carbonyl and hydroxyl groups were successfully grafted onto PP.

[0047] The modified polypropylene waste plastics obtained in Examples 2 and 3 were subjected to infrared spectroscopy analysis, and the positions of the characteristic peaks on their spectra were similar to those in Examples 2 and 3. Figure 1 Consistent, both at 1630 cm in the spectrum. -1 1734cm -1 And 3450 cm -1 A new peak appeared, indicating that carbonyl and hydroxyl groups were successfully grafted onto PP as well.

[0048] Example 1: The method for modifying polypropylene waste plastics provided in this example specifically includes the following steps: Step 1: Add 1.5g glycidyl methacrylate (GMA) and 200mg sodium alginate (SA) to 20mL of aqueous solution, mix with a stirrer, react for 3 hours, and control the temperature at 60℃ to obtain glycidyl methacrylate modified sodium alginate (MSA).

[0049] Step 2: Put the waste polypropylene plastic into a blender and crush it. Take 100mg of PP waste plastic sample and 30mg of glycidyl methacrylate modified sodium alginate (MSA) and put them into a 100mL zirconium dioxide ball milling jar. Add 16 zirconium dioxide grinding balls with a diameter of 10mm into the jar. Set the ball milling time to 4h and the ball milling speed to 600rpm.

[0050] Step 3: After ball milling, the PP waste sample is filtered out, cleaned, and placed in an oven for vacuum drying for 12 hours to obtain modified PP waste plastic (PP-MSA).

[0051] Example 2: The method for modifying polypropylene waste plastics provided in this example has the same steps as in Example 1, except that in step 2, the amount of glycidyl methacrylate-modified sodium alginate (MSA) is 40 mg.

[0052] Example 3: The method for modifying polypropylene waste plastics provided in this example has the same steps as in Example 1, except that in step 2, the amount of glycidyl methacrylate-modified sodium alginate (MSA) is 50 mg.

[0053] Example 4: The method for modifying polypropylene waste plastics provided in this example has the same steps as in Example 1, except that in step 2, the amount of glycidyl methacrylate-modified sodium alginate (MSA) is 60 mg.

[0054] Example 5: The method for modifying polypropylene waste plastics provided in this example has the same steps as in Example 1, except that in step 2, the amount of glycidyl methacrylate-modified sodium alginate (MSA) is 70 mg.

[0055] Test 2: The modified polypropylene waste plastic (PP-MSA) and polypropylene waste plastic (PP) obtained in Examples 1-5 were subjected to infrared spectroscopy analysis. The positions of the characteristic peaks on the spectra were similar to those of the modified polypropylene waste plastic (PP). Figure 1 Consistent, both at 1630 cm in the spectrum. -1 1734cm -1 And 3450 cm -1 A new peak appeared, indicating that carbonyl and hydroxyl groups were successfully grafted onto PP as well.

[0056] Test 3: The modified polypropylene waste plastic (PP-MSA) and polypropylene waste plastic (PP) obtained in Examples 1-5 were used as test samples for thermogravimetric analysis (TGA). Approximately 15 mg of the test sample was weighed and placed in the crucible of the thermogravimetric analyzer. The nitrogen flow rate was set to 50 mL / min, the heating rate to 10 °C / min, and the temperature was increased from room temperature to 600 °C. The sample was held at 600 °C for 10 minutes. After the test, the mass loss was calculated using software, and the thermogravimetric curve is shown below. Figure 2 As shown.

[0057] The modified polypropylene waste plastic (PP-MSA) and polypropylene waste plastic (PP) obtained in Examples 1-5 were used as test samples to calculate the weight loss rate (grafting rate) within the temperature difference range using the following formula: ; Where W(loss) represents the total weight loss of the sample under the temperature difference range; W(toal) represents the total mass of the sample under the temperature difference range. The weight loss point of the sample is affected by temperature; it will pyrolyze when the temperature reaches the pyrolysis temperature of the sample. The pyrolysis temperature of polypropylene is 360℃. The weight loss temperature of modified polypropylene waste plastic (PP-MSA) will be earlier due to the grafting of new functional groups. Therefore, the temperature difference range is from the weight loss temperature of modified polypropylene waste plastic (PP-MSA) to the weight loss temperature of polypropylene waste plastic (PP) (360℃). The weight loss rate occurring within this temperature difference range is also the grafting rate. The weight loss rate was calculated using the above formula, and the results are shown in Table 1.

[0058] Table 1

[0059] Table 1 and Figure 2 The results show that the initial degradation temperatures of the modified polypropylene waste plastics (PP-MSA) prepared in Examples 1-5 are different, and are affected by the amount of glycidyl methacrylate-modified sodium alginate added; the more added, the lower the initial degradation temperature. Similarly, the calculated weight loss rate (grafting rate) is affected by the amount of glycidyl methacrylate-modified sodium alginate added; the more added, the higher the grafting rate.

[0060] Test 4: The modified polypropylene waste plastic (PP-MSA) obtained in Examples 1-5 was subjected to a hydrothermal degradation reaction with polypropylene waste plastic (PP) (reaction conditions: 20 mg pp, 20 mL 0.2 M sodium persulfate solution, 160℃, 12 hours). After the hydrothermal degradation reaction was completed, the degradation solution was collected and filtered to remove solid impurities. 1 mL of the filtrate was taken and diluted 50 times with water, and the TOC of the diluted degradation solution was tested. Sodium alginate-grafted polypropylene waste plastic was obtained as a control group according to the method provided in Example 1, and the total organic carbon (TOC) content of the degradation solution was tested. The results are shown in Table 2 and... Figure 3 As shown.

[0061] Table 2

[0062] Table 2 and Figure 3 The results showed that the TOC value of sodium alginate-grafted polypropylene waste plastic (PP-SA) was slightly higher than that of the original polypropylene waste plastic (PP), indicating that the ball milling reaction of sodium alginate and PP may have changed the structure of polypropylene, but the degree of modification was relatively mild.

[0063] The TOC of modified polypropylene waste plastic (PP-MSA) was significantly higher than that of undiluted polypropylene waste plastic (PP), and the TOC value varied with different grafting ratios: the TOC value gradually increased with increasing grafting ratio. This indicates that the introduction of functional groups provides polypropylene with more reaction sites, making its molecular chains more susceptible to oxidation and degradation, accelerating the degradation reaction, and thus improving degradation efficiency.

[0064] Test 5: The degradation solution was also analyzed by GC-MS: After filtering to remove solid impurities, 2 ml of the hydrolyzed degradation solution was added to 4 ml of dichloromethane solvent and thoroughly mixed. After mixing, the solution was allowed to stand and separate into layers. The lower layer was collected and transferred to a gas chromatograph vial. An appropriate temperature program was set in the experiment, with an initial temperature of 25℃ and a rate of 10℃ per minute, eventually reaching 280℃. The sample was detected by mass spectrometry, generating chromatograms and mass spectra. By comparing with a database and combining the peak areas in the chromatograms, the structure and content of the compounds were analyzed and determined. The inventors found that most of the degradation products also contained hydroxyl and carbonyl functional groups. The proportion of products containing hydroxyl and carbonyl groups was calculated, and the results are shown in Table 3. Figure 4 As shown.

[0065] Table 3

[0066] Table 3 and Figure 4The results showed that the modified PP waste plastic (PP-MSA) exhibited better selectivity than the original polypropylene (PP) product. This was attributed to the modification of sodium alginate with glycidyl methacrylate through hydroxyl and carbonyl grafting, which significantly increased the number of products containing hydroxyl and carbonyl functional groups. As the grafting rate increased, the proportion of products containing these functional groups in the modified sample gradually rose, indicating that the modified PP waste plastic structure contains hydroxyl and carbonyl functional groups, which effectively enhances the polymer's chemical activity, constructs targeting sites, improves product selectivity, and facilitates the efficient depolymerization of polypropylene.

[0067] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for modifying waste polypropylene plastics, characterized in that, Includes the following steps: After crushing the waste polypropylene plastic, it was mixed with glycidyl methacrylate-modified sodium alginate and reacted for 2 to 8 hours under mechanical mixing. The waste plastic modified material is filtered out and then vacuum dried to obtain the modified polypropylene waste plastic.

2. The method for modifying polypropylene waste plastics according to claim 1, characterized in that, The particle size range of crushed polypropylene waste plastic is 0.1mm~10mm.

3. The method for modifying polypropylene waste plastics according to claim 1, characterized in that, The mass ratio of the polypropylene waste plastic to the glycidyl methacrylate-modified sodium alginate is 100:(30~70).

4. The method for modifying polypropylene waste plastics according to claim 1 or 3, characterized in that, The preparation of the glycidyl methacrylate-modified sodium alginate includes: Glycidyl methacrylate and sodium alginate were added to water and mixed evenly. The mixture was reacted at 50℃~70℃ for 1h~5h to obtain the glyceryl methacrylate-modified sodium alginate.

5. The method for modifying polypropylene waste plastics according to claim 4, characterized in that, The mass ratio of glycidyl methacrylate to sodium alginate is 1.5:(0.1~0.5).

6. The method for modifying polypropylene waste plastics according to claim 5, characterized in that, The concentration of sodium alginate is 5 g / L to 25 g / L.

7. The method for modifying polypropylene waste plastics according to claim 1, characterized in that, The mechanical mixing methods include: planetary milling, ball milling, vibratory milling, or stirred milling.

8. The method for modifying polypropylene waste plastics according to claim 7, characterized in that, The mechanical mixing method is ball milling.

9. The method for modifying polypropylene waste plastics according to claim 8, characterized in that, The ball milling conditions include: a rotation speed of 500 rpm to 700 rpm and a ball milling time of 2 h to 6 h.

10. The application of the method for modifying polypropylene waste plastics according to any one of claims 1-9 in waste plastic recycling.

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