Processing aid, application of processing aid in preparation of polypropylene starch composite material and preparation method of processing aid

Abstract

The invention discloses a processing aid and application thereof in preparation of a polypropylene starch composite material and a preparation method, and relates to the technical field of polypropylene modification. The processing aid not only improves the compatibility of polypropylene and starch, but also promotes the spherocrystal refinement of polypropylene, solves the problems of low thermal deformation temperature and poor toughness of the polypropylene / starch composite material, and balances the toughness and thermal properties required by the application of the polypropylene / starch composite material in the field of disposable meal boxes. Therefore, the development of the polypropylene / starch composite material in the field of disposable meal boxes is promoted.

Description

Technical Field

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

[0002] Polypropylene (PP) has excellent processability and chemical stability, and is extremely difficult to be degraded by air or microorganisms. Therefore, on the basis of ensuring performance, adding biodegradable starch to give polypropylene composite materials partial degradability has been widely used in the field of disposable lunch boxes. However, the poor compatibility between polypropylene and starch will have a serious impact on the performance of polypropylene / starch composite materials, making it difficult to meet the requirements of disposable lunch boxes. Therefore, it is urgent to improve the compatibility between polypropylene and starch.

[0003] At present, this problem can be solved by methods such as starch plasticization and adding compatibilizers. However, due to the poor toughness of polypropylene itself, it is even more difficult to meet the requirements of disposable lunch boxes after adding starch. Therefore, in the current industrial production, only elastomers and other materials can be added to the system to ensure the toughness of the material. However, after adding this type of material, its heat deformation temperature is difficult to take into account, and the heat deformation temperature is also an important indicator for its application in the field of disposable lunch boxes. Therefore, it is particularly important to develop a processing aid that can not only improve the compatibility between polypropylene and starch, but also improve its toughness and thermal properties at the same time. Summary of the invention

[0004] The present invention provides a processing aid and its application in the preparation of a polypropylene / starch composite material. The processing aid has a stable chemical structure during the processing of the composite material, and the ester bond in the molecular chain can effectively plasticize starch and improve the compatibility between polypropylene and starch. The aluminum salt part in the molecular chain can act as a nucleating agent to provide nucleation sites for polypropylene, promote its spherulite refinement, and greatly improve the thermal deformation temperature of the composite material. The long carbon chain structure can accelerate the rearrangement of the polypropylene molecular chain during the processing, accelerate its crystallization rate, improve its molecular chain flexibility, and greatly improve 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 di[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 reaction for 8 h, adding 25 g of ricinoleic acid to the system, continuing to stir at a speed of 1000 rpm for reaction for 4 h, and removing the solvent by reduced pressure distillation after the reaction is completed, and the obtained flaky solid is the processing aid.

[0006] The present invention also provides a method for preparing a polypropylene / starch composite material, characterized in that it comprises: placing starch in a high-speed stirrer and stirring, when the temperature in the stirrer rises to 60-90°C, adding a processing aid, continuing stirring for 10 min, adding polypropylene and continuing stirring for 5 min, the speed of the high-speed stirrer in the above process is 5000 rpm, and 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.

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

[0008] The present invention also provides an application of a processing aid in the preparation of a polypropylene / starch composite material, characterized in that the amount of the processing aid is 1%-3% of the polypropylene / starch composite material. The starch is stirred in a high-speed stirrer, and when the temperature in the stirrer rises to 60-90°C, the processing aid is added.

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

[0010] The amount of the processing aid synthesized in the present invention must be appropriate. Too little addition will not achieve the expected effect, and 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 the 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. Too low a temperature will not achieve the desired effect, and too high a temperature will cause starch gelatinization, further deteriorating the interfacial compatibility between polypropylene and starch. The above temperature is the optimal condition verified by experiments.

[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 structure and hydroxyl groups in the molecular chain of the processing aid work together with starch during high-speed mixing, effectively plasticizing starch, strengthening the interfacial compatibility of 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 part 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 in 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 greatly 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, and the molecular segments of each component will not separate, thereby better improving the performance of the polypropylene / starch composite material. Specific implementation methods

[0018] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention is further described in detail in conjunction with the embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. The polypropylene (brand: T30S), di[4-(1,1-dimethylethyl)benzoyl-oxy]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 in the art. Example 1

[0019] 39.8 g of di[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 reduced pressure distillation to obtain a flaky solid which was the processing aid.

[0020] 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g of the processing aid was added and the stirring was continued for 10 min. Then 1000 g of polypropylene was added and the stirring was continued for 5 min. The speed of the high-speed mixer was 5000 rpm in the above process. After stirring, the material was melt-extruded and granulated. The sample was prepared and its notched impact strength was measured according to the method specified in GB / T 1843-2008, and the sample was prepared and its heat deformation 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 embodiment is basically the same as Embodiment 1, except that this embodiment uses the processing aid synthesized in Embodiment 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 embodiment is basically the same as Embodiment 1, except that this embodiment uses the processing aid synthesized in Embodiment 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 After pure polypropylene was extruded and granulated in a conventional twin-screw extruder, samples were prepared and the notched impact strength was measured according to the method specified in GB / T 1843-2008. Samples were prepared and the heat deformation temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0026] Comparative Example 2 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 1000 g of polypropylene was added and stirred for 5 min. The speed of the high-speed mixer was 5000 rpm in the above process. After stirring, the material was melt-extruded and granulated. Samples were prepared and their notched impact strength was measured according to the method specified in GB / T 1843-2008, and samples were prepared and their heat deformation temperature (HDT) was measured according to the method specified in GB / T1634-2019. The specific data are shown in Table 1.

[0027] Comparative Example 3 1000 g starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide was added and stirred for 10 min. Then 1000 g polypropylene was added and stirred for 5 min. The speed of the high-speed mixer was 5000 rpm. After stirring, the material was melt-extruded and granulated. The samples were prepared and the notched impact strength was measured according to the method specified in GB / T 1843-2008. The samples were prepared and the heat deformation temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0028] Comparative Example 4 1000 g starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g ricinoleic acid was added and stirred for 10 min. Then 1000 g polypropylene was added and stirred for 5 min. The speed of the high-speed mixer was 5000 rpm. After stirring, the material was melt-extruded and granulated. Samples were prepared and notched impact strength was measured according to the method specified in GB / T 1843-2008. Samples were prepared and heat deformation 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 5 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g of mandelic acid was added and stirred for 10 min. Then 1000 g of polypropylene was added and stirred for 5 min. The speed of the high-speed mixer was 5000 rpm. After stirring, the material was melt-extruded and granulated. The samples were prepared and the notched impact strength was measured according to the method specified in GB / T 1843-2008. The samples were prepared and the heat deformation temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0030] Comparative Example 6 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g of dodecylbenzene sulfonic acid was added and stirred for 10 min. Then 1000 g of polypropylene was added and stirred for 5 min. The speed of the high-speed mixer was 5000 rpm. After stirring, the material was melt-extruded and granulated. The samples were prepared and the notched impact strength was measured according to the method specified in GB / T 1843-2008. The samples were prepared and the heat deformation 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 7 39.8 g of di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide and 25 g of ricinoleic acid were physically mixed. 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g of physically mixed di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide and ricinoleic acid were added, and stirring continued for 10 min. Then 1000 g of polypropylene was added and stirring continued for 5 min. The speed of the high-speed mixer was 5000 rpm during the above process. After stirring, the material was melt-extruded and granulated. Samples were prepared and notched impact strength was measured according to the method specified in GB / T 1843-2008, and samples were prepared and heat deformation temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0032] Comparative Example 8 39.8 g of di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide and 16 g of mandelic acid were physically mixed. 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g of physically mixed di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide and mandelic acid were added, and stirring continued for 10 min. Then 1000 g of polypropylene was added and stirring continued for 5 min. The speed of the high-speed mixer was 5000 rpm in the above process. After stirring, the material was melt-extruded and granulated. Samples were prepared and their notched impact strength was measured according to the method specified in GB / T 1843-2008, and samples were prepared and their heat deformation temperature (HDT) was measured according to the method specified in GB / T1634-2019. The specific data are shown in Table 1.

[0033] Comparative Example 9 39.8 g of di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide and 0.4 g of dodecylbenzenesulfonic acid were physically mixed. 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g of physically mixed di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide and dodecylbenzenesulfonic acid were added, and stirring continued for 10 min. Then 1000 g of polypropylene was added and stirring continued for 5 min. The speed of the high-speed mixer during the above process was 5000 rpm. After stirring, the material was melt-extruded and granulated. Samples were prepared and their notched impact strength was measured according to the method specified in GB / T 1843-2008, and 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.

[0034] Comparative Example 10 25 g of ricinoleic acid and 16 g of mandelic acid were physically mixed. 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g of ricinoleic acid and mandelic acid after physical mixing were added, and stirring continued for 10 min. Then 1000 g of polypropylene was added and stirring continued for 5 min. The speed of the high-speed mixer was 5000 rpm in the above process. After stirring, the material was melt-extruded and granulated. The sample was prepared and its notched impact strength was measured according to the method specified in GB / T 1843-2008, and the sample was prepared and its heat deformation 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 11 50 g of ricinoleic acid and 0.8 g of dodecylbenzene sulfonic acid were physically mixed. 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g of ricinoleic acid and dodecylbenzene sulfonic acid after physical mixing were added, and stirring was continued for 10 min. Then 1000 g of polypropylene was added and stirring was continued for 5 min. The speed of the high-speed mixer was 5000 rpm in the above process. After stirring, the material was melt-extruded and granulated. The sample was prepared and its notched impact strength was measured according to the method specified in GB / T 1843-2008, and the sample was prepared and its heat deformation temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0036] Comparative Example 12 48 g of mandelic acid and 1.2 g of dodecylbenzene sulfonic acid were physically mixed. 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g of mandelic acid and dodecylbenzene sulfonic acid after physical mixing were added, and stirring was continued for 10 min. Then 1000 g of polypropylene was added and stirring was continued for 5 min. The speed of the high-speed mixer was 5000 rpm in the above process. After stirring, the material was melt-extruded and granulated. The sample was prepared and its notched impact strength was measured according to the method specified in GB / T 1843-2008, and the sample was prepared and its heat deformation 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 13 39.8 g of di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, 25 g of ricinoleic acid and 16 g of mandelic acid were physically mixed. 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g of physically mixed di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, ricinoleic acid and mandelic acid were added, and the stirring was continued for 10 min. Then 1000 g of polypropylene was added and the stirring was continued for 5 min. The speed of the high-speed mixer was 5000 rpm in the above process. After stirring, the material was melt-extruded and granulated. The sample was prepared and its notched impact strength was measured according to the method specified in GB / T 1843-2008, and the sample was prepared and its heat deformation temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0038] Comparative Example 14 39.8 g of di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, 25 g of ricinoleic acid and 0.4 g of dodecylbenzenesulfonic acid were physically mixed. 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g of physically mixed di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, ricinoleic acid and dodecylbenzenesulfonic acid were added, and the stirring was continued for 10 min. Then 1000 g of polypropylene was added and the stirring was continued for 5 min. The speed of the high-speed mixer was 5000 rpm in the above process. After stirring, the material was melt-extruded and granulated. The sample was prepared and its notched impact strength was measured according to the method specified in GB / T 1843-2008, and the sample was prepared and its heat deformation temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0039] Comparative Example 15 39.8 g of di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, 16 g of mandelic acid and 0.4 g of dodecylbenzenesulfonic acid were physically mixed. 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80°C, 40 g of physically mixed di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, mandelic acid and dodecylbenzenesulfonic acid were added, and the stirring was continued for 10 min. Then 1000 g of polypropylene was added and the stirring was continued for 5 min. The speed of the high-speed mixer was 5000 rpm in the above process. After stirring, the material was melt-extruded and granulated. The sample was prepared and its notched impact strength was measured according to the method specified in GB / T 1843-2008, and the sample was prepared and its heat deformation temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0040] Comparative Example 16 25 g of ricinoleic acid, 16 g of mandelic acid and 0.4 g of dodecylbenzene sulfonic acid were physically mixed. 1000 g of starch was placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g of ricinoleic acid, mandelic acid and dodecylbenzene sulfonic acid after physical mixing were added, and the stirring was continued for 10 min. Then 1000 g of polypropylene was added and the stirring was continued for 5 min. The speed of the high-speed mixer was 5000 rpm in the above process. After stirring, the material was melt-extruded and granulated. The sample was prepared and its notched impact strength was measured according to the method specified in GB / T 1843-2008, and the sample was prepared and its heat deformation temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0041] Comparative Example 17 39.8 g of di[4-(1,1-dimethylethyl)benzoyl-oxy]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 placed in a high-speed mixer and stirred. When the temperature in the mixer rose to 80 °C, 40 g of physically mixed di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, ricinoleic acid, mandelic acid and dodecylbenzenesulfonic acid were added, and the stirring was continued for 10 min. Then 1000 g of polypropylene was added and the stirring was continued for 5 min. The speed of the high-speed mixer was 5000 rpm in the above process. After stirring, the material was melt-extruded and granulated. The sample was prepared and its notched impact strength was measured according to the method specified in GB / T 1843-2008, and the sample was prepared and its heat deformation temperature (HDT) was measured according to the method specified in GB / T 1634-2019. The specific data are shown in Table 1.

[0042] Table 1 Test results of various embodiments and comparative examples <![CDATA[Notched 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 According to the experimental results in Table 1, after adding the processing aid prepared by the present invention to Examples 1-5, the notched impact strength and heat deformation temperature of the composite material are relatively high, which can fully meet the use in the field of disposable lunch boxes. Among them, Example 1, in which the addition amount is 2% and the temperature when the processing aid is added and stirred is 80 ° C, is the best. Example 2 and Example 3 illustrate that too much or too little addition of the processing aid will reduce the notched impact strength and heat deformation temperature of the polypropylene / starch composite material. Example 4 and Example 5 illustrate that the temperature when starch and the processing aid are stirred is also an important parameter affecting the effect of the processing aid. Too high a temperature during stirring will cause starch gelatinization and affect the effect, and too low a temperature during stirring will affect the plasticization effect of starch. Therefore, the temperature during stirring needs to be moderate in order to more effectively exert the effect of the processing aid. Compared with the pure polypropylene of Comparative Example 1 and the pure polypropylene / starch composite material (1:1) of Comparative Example 2, it is shown that the processing aid synthesized by the present invention has the effect of significantly improving the notched impact strength and heat deformation temperature of the polypropylene / starch composite material.

[0043] The processing aid prepared by the present invention is synthesized by chemical reaction so that each segment can play a role at the same time, while Comparative Examples 3-17 are only single raw materials or simple mixtures of raw materials without chemical reaction, so the above effects cannot be fully exerted.

[0044] Among them, the di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide added in Comparative Example 3 can act as a polypropylene nucleating agent to refine spherulites and improve the notched impact strength and heat deformation temperature of the composite material, but the compatibility of the polypropylene / starch substrate has not changed, so the improvement effect is not obvious. The ricinoleic acid, mandelic acid and dodecyl sulfonic acid added in Comparative Examples 4, 5 and 6 can improve the compatibility of polypropylene and starch by reacting with the hydroxyl groups on the starch molecular chain, and can improve the notched impact strength and heat deformation temperature of the polypropylene / starch composite material, but the effect is limited. At the same time, the long carbon chain structure of ricinoleic acid and dodecyl sulfonic acid can play a lubricating role, so the notched impact strength and heat deformation temperature of Comparative Example 5 are the lowest. In addition, the carbon chain length of ricinoleic acid is greater than that of dodecyl sulfonic acid, so the notched impact strength and heat deformation temperature of Comparative Example 4 are better than those of Comparative Example 6.

[0045] Comparative Examples 7-12 are simple mixtures of two components. Among them, due to the low content of dodecyl sulfonic acid, its role in the two-component physical mixture of Comparative Examples 9, 11, and 12 is limited, so its role is not obvious. The effects are basically the same as those of the corresponding Comparative Examples 3, 4, and 5. Comparative Example 7, which adds di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide and ricinoleic acid, can play a role in refining spherulites and lubrication, and improve the compatibility of polypropylene and starch. Therefore, the heat deformation temperature and notched impact strength of the polypropylene / starch composite material are better than those of Comparative Examples 9, 11, and 12, but because it does not undergo a chemical reaction, it is less stable during the processing than the processing aid that undergoes a chemical reaction, so its performance is still far behind that of Examples 1-3. Compared with the above, Comparative Example 8, in which di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide and mandelic acid are added, cannot play a lubricating role, and the compatibility of the system is relatively poor, so the performance improvement is lower than that of Comparative Example 7. Although Comparative Example 10, in which ricinoleic acid and mandelic acid are added, can improve the compatibility between polypropylene and starch and provide a certain lubricating effect, it cannot play a role in refining spherulites, so the improvement effect is lower than that of Comparative Example 7 but better than that of Comparative Example 8.

[0046] Comparative Example 13, in which di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, ricinoleic acid and mandelic acid are added simultaneously, has the effects of improving compatibility, refining spherulites and providing lubricity. Therefore, its effect is better than that of Comparative Examples 3-12 of single component and two components. At the same time, it is better than Comparative Examples 14-16 of three-component mixing. However, it has not undergone a chemical reaction and cannot form a stable chemical structure, and the improvement compared with Examples 1-3 is still limited. In addition, Comparative Example 14, in which di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, ricinoleic acid and dodecyl sulfonic acid are added simultaneously, Comparative Example 15, in which di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, mandelic acid and dodecyl sulfonic acid are added simultaneously, and Comparative Example 16, in which ricinoleic acid, mandelic acid and dodecyl sulfonic acid are added simultaneously, due to the low content of dodecyl sulfonic acid, it plays a limited role in the three-component physical mixture of Comparative Examples 14-16, so its role is not obvious. The effects are basically the same as those of Comparative Examples 7, 8 and 10.

[0047] Comparative Example 17 in which di[4-(1,1-dimethylethyl)benzoyl-oxy]aluminum hydroxide, ricinoleic acid, mandelic acid and dodecyl sulfonic acid are added simultaneously has multiple effects. Although the effect is the best compared with Comparative Examples 3-16, it has not undergone a chemical reaction and has not formed a stable chemical structure. Therefore, the improvement effect is still significantly different from that of Examples 1-3.

[0048] 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 principle of the present invention should be included in the scope of the present invention.

Claims

1. A processing aid, characterized in that: The preparation method comprises the following steps: placing 39.8 g of di[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 the system at a speed of 1000 rpm for 8 h, adding 25 g of ricinoleic acid to the system, continuing to stir the system at a speed of 1000 rpm for 4 h, 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 a polypropylene / starch composite material.

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

4. The 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 min. Polypropylene is added and stirring is continued for 5 min. The speed of the high-speed mixer is 5000 rpm in 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.