A processing aid and its application in the preparation of polypropylene starch composite material and preparation method

Abstract

The present invention discloses a processing aid, its application in the preparation of polypropylene starch composite materials, and a preparation method, relating to the technical field of polypropylene modification. The processing aid not only improves the compatibility of polypropylene and starch but also promotes the refinement of polypropylene spherulites, thereby resolving the problems of low heat deformation temperature and poor toughness of polypropylene / starch composite materials. It also balances the toughness and thermal properties required for the application of polypropylene / starch composite materials in the field of disposable lunch boxes, thereby promoting the development of polypropylene / starch composite materials in the field of disposable lunch boxes.

Description

Technical Field

[0001] The invention relates to a processing aid and its application in the preparation of a polypropylene starch composite material and a preparation method, belonging to the technical field of polymer materials. Background Art

[0002] Polypropylene (PP) offers excellent processability and chemical stability, making it extremely difficult to degrade by air or microorganisms. Therefore, while maintaining performance, the addition of biodegradable starch to polypropylene composites imparts partial biodegradability, which has led to widespread application in disposable lunch boxes. However, the poor compatibility between polypropylene and starch severely impacts the performance of polypropylene / starch composites, making them difficult to meet the requirements of disposable lunch boxes. Therefore, improving the compatibility between polypropylene and starch is urgent.

[0003] Currently, this problem can be addressed through methods such as starch plasticization and the addition of compatibilizers. However, due to the inherently poor toughness of polypropylene, the addition of starch makes it even more difficult to achieve the toughness required for disposable lunch boxes. Therefore, in current industrial production, materials such as elastomers are the only way to ensure toughness. However, the addition of these materials compromises the heat distortion temperature (HDT), a crucial performance criterion for its application in disposable lunch boxes. Therefore, developing a processing aid that not only improves the compatibility between polypropylene and starch, but also simultaneously enhances toughness and thermal performance is crucial. Summary of the Invention

[0004] The present invention provides a processing aid and its use in the preparation of polypropylene / starch composite materials. The processing aid has a stable chemical structure during the processing of the composite material, and the ester bonds in its molecular chain can effectively plasticize starch, improving the compatibility between polypropylene and starch. The aluminum salt portion in the molecular chain can act as a nucleating agent, providing nucleation sites for polypropylene, promoting the refinement of its spherulites, and significantly improving the heat deformation temperature of the composite material. The long carbon chain structure can accelerate the rearrangement of the polypropylene molecular chain during processing, speeding up its crystallization rate, improving its molecular chain flexibility, and significantly improving the notched impact strength of the composite material.

[0005] The present invention provides a processing aid, which is obtained by the following preparation method, comprising: placing 39.8 g of bis[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide in 100 mL of dimethyl sulfoxide, adding 16 g of mandelic acid and 0.4 g of dodecylbenzenesulfonic acid, heating the system to 120° C., stirring at a speed of 1000 rpm for 8 hours, adding 25 g of ricinoleic acid to the system, continuing to stir at a speed of 1000 rpm for 4 hours, and removing the solvent by reduced pressure distillation after the reaction is completed. The obtained flaky solid is the processing aid.

[0006] The present invention also provides a method for preparing a polypropylene / starch composite material, which is characterized in that it comprises: placing starch in a high-speed stirrer and stirring, and when the temperature in the stirrer rises to 60-90°C, adding a processing aid, continuing stirring for 10 minutes, adding polypropylene and continuing stirring for 5 minutes, wherein the speed of the high-speed stirrer in the above process is 5000 rpm, and after stirring, melt-extruding and granulating the material, wherein the processing aid is the processing aid according to claim 1, and the amount of the processing aid is 1%-3% of the polypropylene / starch composite material.

[0007] The various reaction conditions and parameters in the preparation method of the processing aid described in the present invention are all optimal conditions verified by experiments.

[0008] The present invention also provides a method for preparing a polypropylene / starch composite material using a processing aid, characterized in that the processing aid is used in an amount of 1% to 3% of the polypropylene / starch composite material. The starch is stirred in a high-speed blender, and the processing aid is added when the blender temperature reaches 60-90°C.

[0009] Preferably, the amount of the processing aid is 2% of the polypropylene / starch composite material.

[0010] The amount of processing aid synthesized in the present invention must be appropriate. Too little addition will not achieve the desired effect, while too much addition will cause the processing aid to agglomerate, affecting its effect. The above addition amount is the optimal condition verified by experiments.

[0011] Preferably, in the preparation method, after adding starch, the temperature in the mixer is raised to 80° C. before adding the processing aid.

[0012] In this preparation method, the stirring temperature must be moderate when adding the processing aid. Temperatures that are too low will not achieve the desired effect, while temperatures that are too high will cause starch gelatinization, further deteriorating the interfacial compatibility between polypropylene and starch. The above temperatures are experimentally verified optimal conditions.

[0013] Compared with the prior art, the present invention has the following technical effects.

[0014] 1. The high content of ester bonds, long-chain fatty acid ester structures and hydroxyl groups in the molecular chain of the processing aid work together with starch during high-speed mixing, effectively plasticizing the starch, strengthening the interfacial compatibility between starch and polypropylene, improving the performance of the polypropylene / starch composite material, and improving the fluidity of the polypropylene / starch composite material during melt processing.

[0015] 2. The aluminum salt portion in the molecular chain of the processing aid can effectively provide nucleation sites for polypropylene during the processing of the polypropylene / starch composite material, promote the refinement of polypropylene spherulites, and thus significantly improve its heat deformation temperature.

[0016] 3. The long carbon chain structure in the molecular chain of the processing aid can play a lubricating role during the processing of polypropylene / starch composite materials, accelerate the rearrangement of polypropylene molecular chains, accelerate its crystallization rate, and improve its molecular chain flexibility, thereby significantly improving its toughness.

[0017] 4. The components of the processing aid are combined in the form of chemical bonds, which ensures that the chemical structure of the processing aid is stable during the processing process and the molecular segments of the components will not separate, thereby better improving the performance of the polypropylene / starch composite material. Specific implementation methods

[0018] To further clarify the technical problems, technical solutions, and beneficial effects to be solved by the present invention, the present invention is further described in detail below with reference to the following examples. It should be understood that the specific examples described herein are merely illustrative of the present invention and are not intended to limit the present invention. The polypropylene (brand: T30S), bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide (CAS: 13170-05-3), mandelic acid (CAS: 90-64-2), ricinoleic acid (CAS: 141-22-0), and dodecylbenzenesulfonic acid (CAS: 27176-87-0) used in the present invention are all commercially available. Example 1

[0019] 39.8 g of bis[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide was placed in 100 mL of dimethyl sulfoxide, and 16 g of mandelic acid and 0.4 g of dodecylbenzenesulfonic acid were added. The system was heated to 120°C and stirred at 1000 rpm for 8 h. Then, 25 g of ricinoleic acid was added to the system and the stirring was continued at 1000 rpm for 4 h. After the reaction was completed, the solvent was removed by distillation under reduced pressure to obtain a flaky solid which was the processing aid.

[0020] 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of the processing aid was added and stirring continued for 10 minutes. Then, 1000 g of polypropylene was added and stirring continued for 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the method specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1. Example 2

[0021] This example is basically the same as Example 1, except that this example uses the processing aid synthesized in Example 1 and the polypropylene / starch composite material in a mass ratio of 100:1 to prepare samples. The test data are shown in Table 1. Example 3

[0022] This example is basically the same as Example 1, except that this example uses the processing aid synthesized in Example 1 and the polypropylene / starch composite material in a mass ratio of 100:3 to prepare samples. The test data are shown in Table 1. Example 4

[0023] This embodiment is basically the same as embodiment 1, except that, in this embodiment, after starch is added, the processing aid is added when the temperature in the mixer rises to 60°C. Example 5

[0024] This embodiment is basically the same as embodiment 1, except that, in this embodiment, after starch is added, the processing aid is added when the temperature in the mixer rises to 90°C.

[0025] Comparative Example 1

[0026] Pure polypropylene was extruded and pelletized in a conventional twin-screw extruder. Samples were prepared and their notched impact strength was measured according to the method specified in GB / T 1843-2008. Samples were prepared and their heat deformation temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0027] Comparative Example 2

[0028] 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 1000 g of polypropylene was added and stirring continued for 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the method specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0029] Comparative Example 3

[0030] 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of bis(4-(1,1-dimethylethyl)benzoyloxy)aluminum hydroxide was added and stirring continued for 10 minutes. Then, 1000 g of polypropylene was added and stirring continued for 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the method specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0031] Comparative Example 4

[0032] 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of ricinoleic acid was added and stirring continued for 10 minutes. Then, 1000 g of polypropylene was added and stirring continued for 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the method specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0033] Comparative Example 5

[0034] 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of mandelic acid was added and stirring continued for 10 minutes. Then, 1000 g of polypropylene was added and stirring continued for 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the method specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0035] Comparative Example 6

[0036] 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of dodecylbenzenesulfonic acid was added and stirring continued for 10 minutes. Then, 1000 g of polypropylene was added and stirring continued for 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the method specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0037] Comparative Example 7

[0038] 39.8 g of bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide and 25 g of ricinoleic acid were physically mixed. 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of the physically mixed bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide and ricinoleic acid were added. Stirring was continued for 10 minutes. Then, 1000 g of polypropylene was added and stirred for 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the methods specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the methods specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0039] Comparative Example 8

[0040] 39.8 g of bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide and 16 g of mandelic acid were physically mixed. 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of the physically mixed bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide and mandelic acid were added. Stirring was continued for 10 minutes. Then, 1000 g of polypropylene was added and stirred for 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the methods specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the methods specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0041] Comparative Example 9

[0042] 39.8 g of bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide and 0.4 g of dodecylbenzenesulfonic acid were physically mixed. 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of the physically mixed bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide and dodecylbenzenesulfonic acid were added. Stirring was continued for 10 minutes. Then, 1000 g of polypropylene was added and stirred for another 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the methods specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the methods specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0043] Comparative Example 10

[0044] 25 g of ricinoleic acid and 16 g of mandelic acid were physically mixed. 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of the physically mixed ricinoleic acid and mandelic acid were added and stirring continued for 10 minutes. Then, 1000 g of polypropylene was added and stirring continued for 5 minutes. The high-speed blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the methods specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the methods specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0045] Comparative Example 11

[0046] 50 g of ricinoleic acid and 0.8 g of dodecylbenzenesulfonic acid were physically mixed. 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of the physically mixed ricinoleic acid and dodecylbenzenesulfonic acid was added and stirring continued for 10 minutes. Then, 1000 g of polypropylene was added and stirring continued for 5 minutes. The high-speed blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the methods specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the methods specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0047] Comparative Example 12

[0048] 48 g of mandelic acid and 1.2 g of dodecylbenzenesulfonic acid were physically mixed. 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of the physically mixed mandelic acid and dodecylbenzenesulfonic acid was added. Stirring was continued for 10 minutes. Then, 1000 g of polypropylene was added and stirred for another 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the methods specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the methods specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0049] Comparative Example 13

[0050] 39.8 g of bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide, 25 g of ricinoleic acid, and 16 g of mandelic acid were physically mixed. 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of the physically mixed bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide, ricinoleic acid, and mandelic acid were added. Stirring was continued for 10 minutes. Then, 1000 g of polypropylene was added and stirred for 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the methods specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the methods specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0051] Comparative Example 14

[0052] 39.8 g of bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide, 25 g of ricinoleic acid, and 0.4 g of dodecylbenzenesulfonic acid were physically mixed. 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of the physically mixed bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide, ricinoleic acid, and dodecylbenzenesulfonic acid was added. Stirring was continued for 10 minutes. Then, 1000 g of polypropylene was added and stirred for 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and tested for notched impact strength according to GB / T 1843-2008, and for heat distortion temperature (HDT) according to GB / T 1634-2019. The specific data are shown in Table 1.

[0053] Comparative Example 15

[0054] 39.8 g of bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide, 16 g of mandelic acid, and 0.4 g of dodecylbenzenesulfonic acid were physically mixed. 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of the physically mixed bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide, mandelic acid, and dodecylbenzenesulfonic acid were added. Stirring was continued for 10 minutes. Then, 1000 g of polypropylene was added and stirred for 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and tested for notched impact strength according to GB / T 1843-2008, and for heat distortion temperature (HDT) according to GB / T 1634-2019. The specific data are shown in Table 1.

[0055] Comparative Example 16

[0056] 25 g of ricinoleic acid, 16 g of mandelic acid, and 0.4 g of dodecylbenzenesulfonic acid were physically mixed. 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of the physically mixed ricinoleic acid, mandelic acid, and dodecylbenzenesulfonic acid was added. Stirring was continued for 10 minutes. Then, 1000 g of polypropylene was added and stirred for another 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the methods specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the methods specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0057] Comparative Example 17

[0058] 39.8 g of bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide, 25 g of ricinoleic acid, 16 g of mandelic acid, and 0.4 g of dodecylbenzenesulfonic acid were physically mixed. 1000 g of starch was stirred in a high-speed blender. When the blender temperature reached 80°C, 40 g of the physically mixed bis[4-(1,1-dimethylethyl)benzoyloxy]aluminum hydroxide, ricinoleic acid, mandelic acid, and dodecylbenzenesulfonic acid were added. Stirring was continued for 10 minutes. 1000 g of polypropylene was then added and stirred for 5 minutes. The blender speed was maintained at 5000 rpm throughout the entire process. After stirring, the material was melt-extruded and pelletized. Samples were prepared and their notched impact strength was measured according to the methods specified in GB / T 1843-2008. Samples were prepared and their heat distortion temperature (HDT) was measured according to the methods specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0059] Table 1 Test results of various embodiments and comparative examples

[0060] <![CDATA[Izod impact strength (KJ / m 2 )]]> HDT (℃) Example 1 3.79 103.2 Example 2 3.53 101.3 Example 3 3.61 101.7 Example 4 3.69 101.3 Example 5 3.51 101.9 Comparative Example 1 1.65 91.7 Comparative Example 2 1.33 86.6 Comparative Example 3 1.89 92.9 Comparative Example 4 2.14 94.8 Comparative Example 5 1.69 93.3 Comparative Example 6 1.92 94.3 Comparative Example 7 2.33 95.4 Comparative Example 8 2.07 94.1 Comparative Example 9 1.93 93.4 Comparative Example 10 2.19 95.1 Comparative Example 11 2.18 95.1 Comparative Example 12 1.73 93.7 Comparative Example 13 2.46 97.1 Comparative Example 14 2.36 95.9 Comparative Example 15 2.11 94.8 Comparative Example 16 2.23 95.6 Comparative Example 17 2.55 97.7

[0061] The experimental results in Table 1 show that the composite materials prepared by adding the processing aid prepared in accordance with the present invention to Examples 1-5 exhibit high notched impact strength and heat distortion temperature, fully meeting the requirements for use in disposable lunch boxes. Example 1, with a 2% addition level and a stirring temperature of 80°C, is optimal. Examples 2 and 3 demonstrate that either excessive or insufficient addition of the processing aid can reduce the notched impact strength and heat distortion temperature of the polypropylene / starch composite. Examples 4 and 5 demonstrate that the stirring temperature of the starch and processing aid is also a key parameter influencing the effectiveness of the processing aid. Excessively high stirring temperatures can cause starch gelatinization, impacting its effectiveness, while excessively low stirring temperatures can affect its plasticization. Therefore, a moderate stirring temperature is required to effectively utilize the processing aid. Compared to the pure polypropylene of Comparative Example 1 and the pure polypropylene / starch composite (1:1) of Comparative Example 2, the processing aid synthesized in accordance with the present invention significantly improves the notched impact strength and heat distortion temperature of the polypropylene / starch composite.

[0062] The processing aid prepared by the present invention is synthesized by chemical reaction so that each segment can function simultaneously, while Comparative Examples 3-17 are only single raw materials or simple mixtures of raw materials without chemical reaction, and the above functions cannot be fully exerted.

[0063] The addition of bis[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide in Comparative Example 3 acts as a polypropylene nucleating agent, refining spherulites and improving the composite's notched impact strength and heat distortion temperature. However, the compatibility of the polypropylene / starch substrate remains unchanged, resulting in a minimal improvement. The addition of ricinoleic acid, mandelic acid, and dodecylsulfonic acid in Comparative Examples 4, 5, and 6 improves the compatibility of polypropylene and starch by reacting with the hydroxyl groups on the starch molecular chains, improving the notched impact strength and heat distortion temperature of the polypropylene / starch composite, but the effect is limited. Furthermore, the long carbon chains of ricinoleic acid and dodecylsulfonic acid act as lubricants, resulting in the lowest notched impact strength and heat distortion temperature in Comparative Example 5. Furthermore, ricinoleic acid has a longer carbon chain than dodecylsulfonic acid, resulting in a superior notched impact strength and heat distortion temperature in Comparative Example 4 compared to Comparative Example 6.

[0064] Comparative Examples 7-12 are simple mixtures of two components. Due to the low content of dodecyl sulfonic acid, its role in the two-component physical mixtures of Comparative Examples 9, 11, and 12 is limited, so its effect is not significant. The results are essentially the same as those of Comparative Examples 3, 4, and 5. Comparative Example 7, which adds di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide and ricinoleic acid, can refine spherulites and lubricate, and improve the compatibility of polypropylene and starch. Therefore, the heat deformation temperature and notched impact strength of the polypropylene / starch composite are improved compared to Comparative Examples 9, 11, and 12. However, since it does not undergo a chemical reaction, it is less stable during processing than processing aids that undergo a chemical reaction, so its performance still lags significantly behind that of Examples 1-3. In comparison, Comparative Example 8, in which bis[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide and mandelic acid were added, failed to provide lubrication, and the system compatibility was relatively poor, resulting in a lower performance improvement than Comparative Example 7. Comparative Example 10, in which ricinoleic acid and mandelic acid were added, improved the compatibility between polypropylene and starch and provided a certain lubrication effect, but failed to refine the spherulites. Therefore, the improvement was lower than that of Comparative Example 7 but better than that of Comparative Example 8.

[0065] Comparative Example 13, which simultaneously added bis[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, ricinoleic acid, and mandelic acid, simultaneously improved compatibility, refined spherulites, and provided lubricity. Therefore, its effects were superior to those of Comparative Examples 3-12, which used single-component and two-component formulations. Furthermore, it was superior to Comparative Examples 14-16, which used a three-component mixture. However, without undergoing a chemical reaction, a stable chemical structure could not be formed, resulting in limited improvements compared to Examples 1-3. Furthermore, in Comparative Example 14, which simultaneously added bis[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, ricinoleic acid, and dodecylsulfonic acid; Comparative Example 15, which simultaneously added bis[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, mandelic acid, and dodecylsulfonic acid; and Comparative Example 16, which simultaneously added ricinoleic acid, mandelic acid, and dodecylsulfonic acid, the dodecylsulfonic acid content was relatively low, so its effect was not significant in the three-component physical mixtures of Comparative Examples 14-16. The effects are basically the same as those of Comparative Examples 7, 8 and 10.

[0066] Comparative Example 17, in which di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, ricinoleic acid, mandelic acid, and dodecylsulfonic acid were added simultaneously, exhibited multiple effects. Although the effect was the best compared to Comparative Examples 3-16, no chemical reaction occurred and no stable chemical structure was formed. Therefore, the improvement effect was still significantly lower than that of Examples 1-3.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of the present invention.

Claims

1. A processing aid, characterized in that: The preparation aid is obtained by the following preparation method, comprising: placing 39.8 g of bis[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide in 100 mL of dimethyl sulfoxide, adding 16 g of mandelic acid and 0.4 g of dodecylbenzenesulfonic acid, heating the system to 120° C., stirring at 1000 rpm for 8 hours, adding 25 g of ricinoleic acid to the system, continuing to stir at 1000 rpm for 4 hours, and removing the solvent by reduced pressure distillation after the reaction is completed. The obtained flaky solid is the processing aid.

2. Use of a processing aid according to claim 1 in the preparation of polypropylene / starch composite materials.

3. Use of a processing aid in the preparation of a polypropylene / starch composite material according to claim 2, characterized in that: The amount of the processing aid is 1%-3% of the polypropylene / starch composite material.

4. Use of a processing aid in the preparation of a polypropylene / starch composite material according to claim 3, characterized in that: The amount of the processing aid is 2% of the polypropylene / starch composite material.

5. A method for preparing a polypropylene / starch composite material, characterized in that: The starch is placed in a high-speed mixer and stirred. When the temperature in the mixer rises to 60-90°C, a processing aid is added and stirring is continued for 10 minutes. Polypropylene is added and stirring is continued for 5 minutes. The speed of the high-speed mixer is 5000 rpm during the above process. After stirring, the material is melt-extruded and granulated, wherein the processing aid is the processing aid according to claim 1, and the amount of the processing aid is 1%-3% of the polypropylene / starch composite material.