Polypropylene composite additive for manufacturing high-transparency and high-toughness food container cup

Abstract

The invention relates to a polypropylene composite additive for manufacturing a high-transparency and high-toughness food container cup, which belongs to the technical field of high polymer material modification, and effectively realizes the modification of a polypropylene material by compounding a transparent nucleating system and a compound toughening system and matching with a compatilizer, an antioxidant and a dispersing agent. The requirements of high transparency, high toughness and food contact safety can be met at the same time, and the effect is remarkable.

Description

Technical Field

[0001] This invention belongs to the field of polymer material modification technology, and particularly relates to polypropylene, specifically a composite additive for making food container cups with high transparency and high impact toughness. Background Technology

[0002] Polypropylene (PP), as one of the five major general-purpose materials, has advantages such as abundant supply, low price, non-toxicity, odorlessness, and ease of processing, and is widely used in the food packaging field. However, ordinary polypropylene materials have some inherent defects. On the one hand, its crystallization behavior leads to poor transparency of the products, affecting the appearance of food packaging. On the other hand, it lacks impact toughness at room temperature, especially at low temperatures, and is prone to brittle fracture, limiting its application in high-end food packaging.

[0003] However, many cup-shaped food packaging applications require high levels of transparency, high impact resistance, and food contact safety. Therefore, additives are often added to polypropylene materials to improve their performance. CN112480548A provides a high-impact abrasion-resistant polypropylene composite material using N,N-dimethylpropyl octadecylamide-modified nano-molybdenum disulfide as an abrasion-resistant additive, which effectively improves the material's abrasion resistance and impact toughness. However, this approach does not consider transparency requirements, and the added abrasion-resistant additive may further affect the material's light transmittance. Furthermore, its composition does not meet food contact safety requirements in the food industry. CN101817954A discloses a food-grade polypropylene composite material using calcium carbonate as a filler to reduce costs and improve degradation performance. However, this approach significantly reduces the material's transparency and offers limited improvement in toughness. CN113912941A relates to a polypropylene composite material for automotive transparent water bottles, which uses homopolymer polypropylene and random copolymer polypropylene as a blend, and adds ethylene-octene copolymer and ethylene-butene copolymer as toughening agents, giving the material good strength, stiffness, toughness, and light transmittance. However, automotive transparent water bottles are mainly used to store windshield washer fluid, coolant, etc., without considering food contact safety requirements. CN113980383A provides a polypropylene composition with high light transmittance and low-temperature toughness. By controlling the Mooney viscosity of ethylene copolymer elastomers and using one-dimensional inorganic fillers, the material achieves both high light transmittance and good low-temperature toughness. However, this technology is mainly aimed at automotive bumper applications and does not adequately consider food contact safety.

[0004] Therefore, existing technologies lack polypropylene materials and additives specifically designed for food container cups that can simultaneously meet the requirements of high transparency, high toughness, and food contact safety. Developing a polypropylene composite additive specifically designed for high-transparency and high-toughness food container cups has significant market value and technical importance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a polypropylene composite additive for manufacturing high-transparency and high-toughness food container cups, enabling polypropylene materials to simultaneously meet the requirements of high transparency, high toughness, and food contact safety.

[0006] The technical problem to be solved by the present invention is achieved through the following technical solution: A polypropylene composite additive for manufacturing high-transparency and high-toughness food container cups, comprising the following components by weight percentage: Transparent nucleating agent: 30-50%; Toughening agent: 20-40%; Compatibilizer: 10-20%; Antioxidant: 5-10%; Dispersant: 3-8%.

[0007] The transparent nucleating agent is a compound system of sorbitol-based nucleating agents and aromatic phosphate-based nucleating agents, with a mass ratio of (1-3):1. This compound nucleating agent system can work synergistically to significantly improve the transparency and surface gloss of polypropylene.

[0008] Optionally, the sorbitol nucleating agent is 1,3:2,4-di(3,4-dimethylbenzyl)sorbitol, and the aromatic phosphate nucleating agent is sodium 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate.

[0009] The toughening agent is a blend of hydrogenated styrene-butadiene-styrene block copolymer (SEBS) and ethylene-octene copolymer (POE) in a mass ratio of (0.5-2):1. This blended toughening system can improve toughness while minimizing the impact of pyrolysis on transparency.

[0010] The compatibilizer is maleic anhydride-grafted polypropylene (PP-g-MAH), with a grafting rate of 0.8-1.2%, which can improve the compatibility and dispersibility between the components.

[0011] The antioxidant is a compound system of hindered phenolic antioxidants and phosphite antioxidants, with a mass ratio of 1:(1-2), providing thermal and oxygen stability protection during processing and use.

[0012] Optionally, the hindered phenolic antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the phosphite antioxidant is tris(2,4-di-tert-butylphenyl)phosphite.

[0013] The dispersant is a compound system of fatty acid metal soap and polyethylene wax in a mass ratio of 1:(1-2), which helps to uniformly disperse the components in the polypropylene matrix. Optionally, the fatty acid metal soap is calcium stearate.

[0014] Based on the above components, the preparation method of the polypropylene composite additive includes the following steps: (1) Raw material pretreatment: Dry each component at 80-100 ℃ for 4-6 h to remove moisture; (2) Initial mixing: Add the transparent nucleating agent, toughening agent, compatibilizer, antioxidant and dispersant to a high-speed mixer according to the formula ratio, and mix at 500-1000 rpm for 8-15 min; (3) Melt blending: Melt blending: The mixed materials are added to a twin-screw extruder for melt blending. The temperature of each section of the extruder is set to 180-210 ℃ and the screw speed is 50-400 rpm. (4) Granulation: The extruded melt is granulated by an underwater pelletizing device to obtain composite additive particles with a particle size of 2-4 mm; (5) Packaging: The obtained composite additive granules are sealed and packaged.

[0015] In the above preparation method, during the extrusion stage of melt blending, the screw speed can be selected as a relatively low speed of 100-350 rpm, or an ultra-low speed of 20-50 rpm.

[0016] In this invention, the polypropylene composite additive can be used to prepare food container cups. Specifically, the composite additive is mixed with food-grade polypropylene resin at a weight ratio of (5-15):(95-85), and then the food container cups are made by injection molding or hot pressing.

[0017] Furthermore, the injection molding process parameters are: injection temperature 180-220 ℃, injection pressure 60-100 MPa, mold temperature 30-50 ℃, and cooling time 20-40 s.

[0018] Compared with the prior art, the present invention has the following advantages: (1) This application significantly reduces the crystal size of polypropylene through the synergistic effect of the composite nucleating agent system, thereby greatly improving the transparency and surface gloss of the product, so that the haze of the polypropylene material with 0.5 mm thickness using the additive can be reduced to below 12% and the light transmittance can reach more than 92%. (2) This application utilizes a SEBS / POE composite toughening system to significantly improve the impact toughness of the material while maintaining transparency, enabling the notched impact strength of the cantilever beam at room temperature to reach 15 kJ / m. 2 Above, the impact strength at -20℃ reaches 4.5 kJ / m.2 above; (3) The components of the additives in this application have good compatibility and dispersibility with the polypropylene matrix, do not affect the processing fluidity of the material, and can reduce the energy consumption during injection molding. (4) All components in the additives of this application comply with GB 9685-2016 standard for additives for food contact materials and articles, and can be used in food packaging containers; (5) The increased transparency of the polypropylene material with added additives in this application can reduce the wall thickness of the product while achieving the same visual effect and strength and toughness, thus saving materials and energy. Attached Figure Description Figure 1 This is a bar chart comparing the haze / transmittance of the embodiments and comparative food container cups of this application. Figure 2 Line graph showing the comparison of the normal / low temperature impact strength of food container cups in the embodiments and comparative examples of this application. Figure 3 This is a graph showing the relationship between the wall thickness of the food container cup in this application and the haze / impact strength. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0020] Example 1 A polypropylene composite additive for manufacturing high-transparency and high-toughness food container cups, comprising the following components by weight percentage: Transparent nucleating agent: 1,3:2,4-di(3,4-dimethylbenzyl)sorbitol: 20%; Sodium 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate: 10%; Toughening agent: Hydrogenated styrene-butadiene-styrene block copolymer: 12%; Ethylene-octene copolymer: 12%; Compatibilizer: Maleic anhydride-grafted polypropylene, grafting rate 1.0%:15%; Antioxidant: Pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]: 5%; Tris(2,4-di-tert-butylphenyl) phosphite: 10%; Dispersant: Calcium stearate: 8%; Polyethylene wax: 8%.

[0021] The preparation process of this auxiliary agent is as follows: (1) Dry each component at 90℃ for 5 h; (2) Add the dried components to a high-speed mixer and mix at 500-1000 rpm for 8-15 min; (3) Add the mixed material to the twin-screw extruder for melt blending. The temperatures of each section of the extruder are set sequentially from inlet to outlet: Zone 1 180-185 ℃, Zone 2 190-200 ℃, Zone 3 195-205 ℃, Zone 4 185-195 ℃, and the screw speed is 100-350 rpm. (4) The extruded melt is granulated by an underwater pelletizing device to obtain composite additive particles with a particle size of about 3 mm; (5) Seal and package the obtained composite additive granules.

[0022] The prepared composite additive granules were mixed with food-grade homopolymer polypropylene (melt flow rate 3 g / 10 min) at a weight ratio of 10:90, and then the mixture was injection molded into food container cups. The injection molding process parameters were: injection temperature 200℃, injection pressure 80 MPa, mold temperature 40℃, and cooling time 30 s.

[0023] In the melt blending step of this invention, the screw speed is a key parameter for controlling shear heat generation and dispersion effect. To protect heat-sensitive components and avoid degradation of toughening agent molecular chains, a lower screw speed is preferred, such as 100-350 rpm in this embodiment. For specific applications requiring extremely high thermal stability, an ultra-low speed process of 20-50 rpm can also be used. This process can maximally suppress shear heat generation and provide the mildest processing environment for the core auxiliary components, but it will correspondingly reduce production efficiency.

[0024] Example 2 A polypropylene composite additive for manufacturing high-transparency and high-toughness food container cups, comprising the following components by weight percentage: Transparent nucleating agent: 1,3:2,4-di(3,4-dimethylbenzyl)sorbitol: 15%; Sodium 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate: 15%; Toughening agent: Hydrogenated styrene-butadiene-styrene block copolymer: 16%; Ethylene-octene copolymer: 14%; Compatibilizer: Maleic anhydride-grafted polypropylene, grafting rate 1.0%:15%; Antioxidant: Pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]: 6%; Tris(2,4-di-tert-butylphenyl) phosphite: 6%; Dispersant: Calcium stearate: 7%; Polyethylene wax: 6%.

[0025] The preparation process is the same as in Example 1. The prepared composite additive is mixed with food-grade random copolymer polypropylene (melt flow rate 2 g / 10min) at a weight ratio of 8:92, and then food container cups are made by injection molding.

[0026] Example 3 A polypropylene composite additive for manufacturing high-transparency and high-toughness food container cups, comprising the following components by weight percentage: Transparent nucleating agent: 1,3:2,4-di(3,4-dimethylbenzyl)sorbitol: 25%; Sodium 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate: 10%; Toughening agent: Hydrogenated styrene-butadiene-styrene block copolymer: 15%; Ethylene-octene copolymer: 15%; Compatibilizer: Maleic anhydride-grafted polypropylene, grafting rate 1.0%:12%; Antioxidant: Pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]: 4%; Tris(2,4-di-tert-butylphenyl) phosphite: 8%; Dispersant: Calcium stearate: 6%; Polyethylene wax: 5%.

[0027] The preparation process is the same as in Example 1. The prepared composite additive is mixed with food-grade homopolymer polypropylene (melt flow rate 3 g / 10 min) at a weight ratio of 12:88, and then food container cups are made by injection molding.

[0028] Comparative Example A food container cup is made by simply mixing commercially available ordinary transparent polypropylene nucleating agent (phenyl phosphate, accounting for 30% of the total additives) and toughening agent (POE, accounting for 70% of the total additives) in a physical manner. The total amount of additives added is still less than 10% of the polypropylene resin. It is mixed with food-grade homopolymer polypropylene at a weight ratio of 10:90 and processed under the same process conditions.

[0029] Performance testing The performance of the food container cups prepared in Examples 1-3 and the comparative example was tested, and the results are shown in Table 1 below.

[0030] Table 1 Test Project Test Standards Example 1 Example 2 Example 3 Comparative Example Haze (0.5mm thickness) / % GB / T 2410-2008 10.5 11.2 9.8 16.8 transmittance / % GB / T 2410-2008 92.5 91.8 93.2 88.5 <![CDATA[Izod impact strength (23 °C) / (kJ / m 2 )]]> GB / T 1843-2008 16.2 15.8 16.8 12.5 <![CDATA[Izod impact strength (-20 °C) / (kJ / m 2 )]]> GB / T 1843-2008 4.8 4.6 5.2 3.2 Heat distortion temperature (0.45 MPa) / ℃ GB / T 1634.2-2019 87 86 88 84 Melt flow rate (230℃, 2.16kg) / (g / 10min) GB / T 3682.1-2018 2.8 3.2 2.5 3.5 <![CDATA[Hygiene performance (total migration amount) / (mg / dm 2 )]]> GB 31604.8-2016 2.5 2.8 2.3 3.2 Results Analysis The following analysis combines test data to examine Examples 1-3 and the comparative examples.

[0031] (1) Transparency analysis (haze & transmittance) All three examples exhibited significantly lower haze than the comparative example (16.8%) and higher light transmittance than the comparative example (88.5%), with Example 3 demonstrating the best transparency. (Comparative example...) Figure 1 As shown.

[0032] Since transparency is primarily determined by the type and combination effect of the "transparent nucleating agent," the comparative example uses a single phenyl phosphate nucleating agent, which improves crystallinity, but the resulting spherulites are not small enough and are unevenly distributed. When light passes through the material, strong light scattering occurs at the boundaries of these larger spherulites, leading to increased haze and decreased transmittance. The example uses a combination system of sorbitol-based (DMDBS) and aromatic phosphate (NA-11). These two nucleating agents work synergistically to provide denser nucleation sites, resulting in a large number of extremely small spherulites in polypropylene, much smaller than the visible light wavelength (380-780 nm). The optical fiber experiences almost no scattering and can transmit directly, thus achieving high transmittance and low haze. In Example 3, the total nucleating agent content is the highest (35%), and the proportion of sorbitol-based nucleating agents is even higher (25%). Sorbitol-based nucleating agents are generally superior to phosphate-based nucleating agents in providing high transparency, therefore, their higher proportion results in the optimal transparency effect.

[0033] (2) Toughness analysis All embodiments exhibited significantly higher impact strength at both room temperature and low temperatures compared to the comparative examples, with Example 3 demonstrating the best toughness, especially at low temperatures. (Comparative example...) Figure 2 As shown.

[0034] Since toughness is mainly determined by the type and formulation of toughening agents, compatibilizers are also crucial. In the comparative example, only POE was used as a toughening agent. POE is an excellent toughening agent, but its toughening effect diminishes at low temperatures, resulting in limited efficiency of a single toughening system. In the examples, a compound toughening system of SEBS and POE was used, supplemented with PP-g-MAH compatibilizer. POE, as a soft phase, primarily induces crazes and generates shear bands, absorbing a large amount of impact energy. SEBS's unique island structure can more effectively terminate crazes and crack propagation. The combination of SEBS and POE achieves a synergistic toughening effect. The hydrogenated saturated structure of SEBS results in excellent low-temperature performance, compensating for the shortcomings of POE at low temperatures. The maleic anhydride functional groups of PP-g-MAH can interact with the polar parts in SEBS and POE, while its polypropylene segments are completely compatible with the PP matrix. This greatly improves the interfacial adhesion between the elastomer dispersion phase and the PP matrix, ensuring that impact energy can be effectively transferred between the two phases, thereby fully realizing the toughening effect. In Example 3, the total toughening agent content was the highest (30%), and the ratio of SEBS to POE was 1:1. This balanced compound allowed it to exert the best synergistic toughening effect at both room temperature and low temperature.

[0035] (3) Heat resistance analysis (heat distortion temperature) The heat distortion temperature (HDT) of the embodiments was higher than that of the comparative examples.

[0036] HDT is primarily determined by the crystallization behavior of the matrix and the rigidity of the filler. In the comparative examples, although the nucleating agent increased crystallinity, the improvement in crystal perfection by a single nucleating agent system was limited. The efficient composite nucleating agent system used in the examples not only increased the number of crystal nuclei but also promoted the formation of a more perfect and regular crystal structure. This more perfect crystal has higher rigidity and stronger resistance to external forces, thus it is less prone to deformation when heated, resulting in an increase in HDT. SEBS and POE, as elastomers, slightly reduce HDT. For example, in Example 2, where the toughening agent content was the highest, its HDT was relatively slightly lower, but the positive effects of the nucleating agent far outweighed the negative effects of the elastomer, so the overall HDT was still improved.

[0037] (4) Processing fluidity analysis (melt flow rate) The comparative example showed the highest melt flow rate (MFR) and good fluidity, while the example showed a slightly lower MFR, but it was still within a good processable range.

[0038] In the comparative example, POE itself has excellent flowability, and the added nucleating agent is a small molecule, which plays a similar role to lubrication. Therefore, the MFR is the highest. In the example, the molecular chain entanglement of SEBS is strong, which will increase the melt viscosity to a certain extent, resulting in a decrease in MFR. High content of nucleating agent and dispersant may also have a slight impact on flowability. However, through formulation balancing, such as in Example 2, good processability can still be maintained. A moderate reduction in MFR is sometimes beneficial to the orientation and crystallization of molecular chains during injection molding, which is beneficial to the final performance.

[0039] (5) Health and safety performance analysis (total migration) The overall migration rates of the examples were all lower than those of the comparative examples, indicating that the replacement was safer and more stable.

[0040] In the comparative example, the use of highly migratory additives, such as certain small molecule additives, or poor compatibility between the additives and the matrix, may have led to their easy precipitation upon contact with the food simulant. In this example, the combined action of the PP-g-MAH compatibilizer and dispersant ensures that all additive components are more firmly bonded to the PP matrix, making migration difficult and exhibiting excellent compatibility. The selected SEBS, POE, nucleating agent, and antioxidant are all food-grade products with high molecular weight or stable structure, which are not easily migrated and are relatively stable. The high crystallinity and perfect crystal structure constitute a denser barrier, hindering the migration pathways of small molecules.

[0041] (6) Study on the relationship between product wall thickness and performance Supported by the excellent properties of polypropylene materials, the effects of thickness and haze / impact strength on food container cups were studied, such as... Figure 3 As shown.

[0042] The horizontal axis in the figure represents the product wall thickness of 0.3-0.8 mm, the left side of the vertical axis represents haze (%), and the right side represents impact strength (kJ / m). 2 Solid line (in this invention): When the wall thickness is reduced from 0.8 mm to 0.5 mm, the haze decreases from 12% to 9.8%, and the impact strength decreases from 16.8 kJ / m. 2 Reduced to 15.5 kJ / m 2 (Still meets requirements); Dashed line (comparative example): When the wall thickness is reduced from 0.8 mm to 0.5 mm, the haze increases from 16.8% to 20%, and the impact strength increases from 12.5 kJ / m 2 Reduced to 8 kJ / m 2 (Not meeting the requirements). Therefore, the present invention can reduce the wall thickness by 37.5%, achieving material / energy savings.

[0043] Therefore, the composite transparent nucleation system is the core key to achieving high transparency; the composite toughening system (SEBS / POE) + compatibilizer (PP-g-MAH) is the core key to achieving high toughness, and it has good compatibility with the nucleation system and does not affect transparency; the above two components, through scientific compounding with antioxidants and dispersants, achieve a balance and synergy of performance, and finally obtain an innovative material that simultaneously meets the four requirements of high transparency, high toughness, heat resistance and safety, successfully solving the contradiction that existing technologies represented by the comparative ratio cannot achieve.

Claims

1. A polypropylene composite additive for manufacturing high-transparency and high-toughness food container cups, characterized in that, It consists of the following components by weight percentage: 30-50% transparent nucleating agent; Toughening agent 20-40%; Compatibilizer 10-20%; Antioxidant 5-10%; Dispersant 3-8%; The transparent nucleating agent is a mixture of sorbitol-based nucleating agent and aromatic phosphate-based nucleating agent in a mass ratio of (1-3):1, and the toughening agent is a mixture of hydrogenated styrene-butadiene-styrene block copolymer and ethylene-octene copolymer in a mass ratio of (0.5-2):

1.

2. The composite additive according to claim 1, characterized in that: The sorbitol nucleating agent is 1,3:2,4-di(3,4-dimethylbenzyl)sorbitol, and the aromatic phosphate nucleating agent is sodium 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate.

3. The composite additive according to claim 1, characterized in that: The compatibilizer is maleic anhydride-grafted polypropylene with a grafting rate of 0.8-1.2%.

4. The composite additive according to claim 1, characterized in that: The antioxidant is a mixture of hindered phenolic antioxidant and phosphite antioxidant in a mass ratio of 1:(1-2). The hindered phenolic antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the phosphite antioxidant is tris(2,4-di-tert-butylphenyl)phosphite.

5. The composite additive according to claim 1, characterized in that: The dispersant, fatty acid metal soap, and polyethylene wax are compounded in a mass ratio of 1:(1-2), wherein the fatty acid metal soap is calcium stearate.

6. A method for preparing the composite additive as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Raw material pretreatment: Dry each component at 80-100 ℃ for 4-6 h to remove moisture; (2) Initial mixing: Add the transparent nucleating agent, toughening agent, compatibilizer, antioxidant and dispersant to a high-speed mixer according to the formula ratio, and mix at 500-1000 rpm for 8-15 min; (3) Melt blending: The mixed materials are added to a twin-screw extruder for melt blending. The temperature of each section of the extruder is set to 180-210 ℃ and the screw speed is 50-400 rpm. (4) Granulation: The extruded melt is granulated by an underwater pelletizing device to obtain composite additive particles with a particle size of 2-4 mm.

7. The method of preparing a criminal according to claim 6, characterized in that, In step (3), the screw speed during melt blending is 100-350 rpm.

8. The method of preparing a criminal according to claim 6, characterized in that, In step (3), the screw speed during melt blending is 20-50 rpm.

9. The application of a polypropylene composite additive as described in any one of claims 1-5 in the preparation of food container cups, characterized in that: The composite additive is mixed with food-grade polypropylene resin at a weight ratio of (5-15):(95-85), and then made into a food container cup by injection molding or hot pressing.

10. The application according to claim 9, characterized in that, The injection molding process parameters are: injection temperature 180-220℃, injection pressure 60-100 MPa, mold temperature 30-50℃, and cooling time 20-40 s.

Images