A preparation method of anti-aging PP injection-molded food packaging material

Abstract

The present invention relates to the technical field of polymer materials, and in particular to a method for preparing an anti-aging PP injection-molded food packaging material. The method first synthesizes 4-amino-2-hydroxy-1-acetonaphthone through a nitration-reduction reaction, and then reacts with a terminal olefinic polyalkylene isocyanate to generate a low-polarity anti-UV oxidant containing a long-chain alkyl group; then, an active amino group is introduced through Michael addition and deprotection of N-Boc-ethylenediamine to obtain a modified anti-UV oxidant; finally, under nitrogen protection, the material is chemically bonded with maleic anhydride-grafted PP, and injection molded after melt blending with a nucleating agent, a toughening agent, and a lubricant. The resulting material imparts anti-aging ability through the naphthyl ring ketone-enol interconversion mechanism and free radical capture ability in the anti-UV oxidant. At the same time, the polarity matching between the anti-UV oxidant and PP is achieved by relying on the long-chain alkyl group, and the chemical bonding effect significantly inhibits migration, meeting the long-term safety protection requirements of food packaging.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to a method for preparing an anti-aging PP injection-molded food packaging material. Background Art

[0002] Polypropylene (PP), a common material in food packaging, faces significant industry concerns regarding its anti-aging performance and migration safety. Traditional anti-aging modification methods often rely on physical blending to add UV inhibitors and antioxidants. However, these technologies fail to address compatibility challenges through molecular polarity matching. Firstly, the polarity difference between small molecule antioxidants and the PP matrix is ​​significant. Without optimizing polarity matching through methods such as adjusting alkyl chain length, the antioxidants easily separate from the PP during use, directly leading to a decrease in UV protection efficiency. Secondly, this polarity mismatch exacerbates the dissolution and migration of the antioxidants, exceeding the 0.01mg / kg safety threshold specified in GB 9685-2016.

[0003] Although some existing studies have introduced polar groups to improve interfacial interactions by grafting maleic anhydride onto PP (PP-g-MAH), the polarity of the antioxidant has not been specifically designed. The polar groups (such as hydroxyl and amino groups) in the antioxidant have not been adjusted by long-chain alkyl chains, resulting in polarity conflicts with the PP matrix after grafting. For example, when an unpolarized UV inhibitor is blended with PP-g-MAH, the interfacial polar groups are unevenly distributed, resulting in a significant interfacial energy difference, which in turn increases the migration of the antioxidant. Furthermore, existing technologies fail to combine polarity matching with chemical bonding techniques, primarily relying on physical dispersion. Phase separation caused by polarity differences during long-term use can accelerate the precipitation of the antioxidant, failing to meet the long-term anti-aging requirements of food packaging. Summary of the Invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a method for preparing an anti-aging PP injection-molded food packaging material.

[0005] Based on the above objectives, the present invention provides a method for preparing an anti-aging PP injection-molded food packaging material, comprising the following steps:

[0006] (1) In a reaction vessel, 1-acetyl-2-naphthol is added to acetic acid, cooled to 0-5°C, and then nitric acid is added dropwise. After the addition is complete, the mixture is returned to room temperature and reacted for 2-3 hours. The reaction solution is added to 0-5°C ice water, and a large amount of solid precipitation is observed. The obtained solid is filtered, washed, and dried, and then added to methanol. 5% palladium carbon is added, and the pH is adjusted to 3-4 with a 1 mol / L hydrochloric acid solution. The mixture is replaced with hydrogen three times and reacted at room temperature for 3-4 hours. The filtrate is then filtered to obtain a filtrate. After concentration under vacuum, the filtrate is washed, dried, and recrystallized from a methanol / water mixed solution to obtain 4-amino-2-hydroxy-1-naphthone. The chemical reaction equation is as follows:

[0007] Formula (1), When 1-acetyl-2-naphthol reacts with nitric acid, the hydroxyl group at position 2 of the naphthalene ring acts as a directing group to activate the naphthalene ring. Although the acetyl group at position 1 also acts as a directing group, the hydroxyl group has a stronger activation effect. In addition, the acetyl group produces steric hindrance at position 1, making it difficult to replace position 3. However, position 4 has little steric hindrance and is the α position of the naphthalene ring with a high electron cloud density. Therefore, the nitro group selectively replaces the nitro group at position 4, and the product is catalyzed by H NMR confirmed the structure. The amino group in the product acts as an active group and can react with the isocyanate group in the subsequent step. The keto configuration in the molecular structure relies on the conjugated system constructed by the naphthalene ring. Under ultraviolet light, it absorbs light energy and is excited to a high-energy state. At this time, protons migrate rapidly through the intramolecular hydrogen bond network, prompting the keto configuration to be converted into a high-energy enol intermediate. The enol structure releases the absorbed light energy as heat energy through a non-radiative transition process and returns to the ground state keto configuration. Through this keto-enol dynamic conformational conversion cycle, effective absorption and energy dissipation of ultraviolet light are achieved, thereby exerting an anti-ultraviolet aging effect. The chemical process diagram of the conformational transition is as follows:

[0008] Formula (2), At the same time, the hydroxyl group at position 2 in the product acts as a hydrogen donor, providing hydrogen atoms to free radicals (such as R·) by breaking the OH bond, terminating the oxidation chain reaction and generating stable ROOH and phenoloxy radicals. Specifically, the phenoloxy radical generated is stabilized by the resonance effect of the large π conjugated system of the naphthalene ring, avoiding further oxidation reactions.

[0009] (2) The terminal olefin polyalkylene isocyanate, the general structural formula is: CH2=CH-(CH2) n-NCO, wherein n=7-9 and 4-amino-2-hydroxy-1-acetonapthone are added to tetrahydrofuran, cooled to 0-5°C, stirred and reacted for 1-3 hours, then returned to room temperature, stirred and reacted for 8-10 hours, added to ether, filtered and collected the precipitate, washed, and dried to obtain a low-polarity UV antioxidant. The chemical reaction equation is:

[0010] Formula (3), The structure of the product was confirmed by H NMR. The introduction of long-chain alkyl groups reduced the overall polarity of the compound. When subsequently grafted onto maleic anhydride-grafted PP materials, the "like dissolves like" principle was used to reduce interfacial tension during grafting, avoiding uneven dispersion or phase separation due to polarity differences. This allowed the UV antioxidant to be evenly distributed within the PP matrix. The low-polarity structure reduced the migration or precipitation of the UV antioxidant within the PP matrix. The entanglement of the long-chain alkyl groups with the PP molecular chains formed steric hindrance, stabilizing the UV protection mechanism of the keto-enol conformational transition and extending the material's anti-aging time.

[0011] (3) Add a low-polarity UV-resistant oxidant, N-Boc-ethylenediamine and a catalyst to anhydrous methanol, stir and react at room temperature for 1-2 hours, then heat to 35-45°C and react for 4-6 hours. Remove methanol by distillation under reduced pressure, add dichloromethane and stir for 10-20 minutes, then wash with 0.1 mol / L hydrochloric acid and saturated sodium bicarbonate, dry the organic phase with anhydrous sodium sulfate, and obtain a low-polarity UV-resistant oxidant containing an amino protecting group after column chromatography gradient elution. The chemical reaction equation is:

[0012] Formula (4), The structure of the product was confirmed by H NMR. The protected amino group was reintroduced into the molecular structure through the Michael addition reaction between the amino group and the double bond, providing active reaction sites for the final grafting of the maleic anhydride-grafted PP material.

[0013] (4) Add a low-polarity UV oxidant containing an amino protecting group to dichloromethane, cool to 0°C while stirring, and add trifluoroacetic acid dropwise for 1-2 hours. After the addition is complete, return to room temperature, react for 2-4 hours, filter, and wash the obtained solid with ethyl acetate. After drying, add it to deionized water, adjust the pH to 8-9 with saturated sodium bicarbonate, filter, and wash and dry the obtained solid to obtain a modified UV oxidant. The chemical reaction equation is:

[0014] Formula (5), The product was characterized by H NMR, and the amino protecting group was removed to obtain the active reaction site;

[0015] (5) Under nitrogen protection, add maleic anhydride grafted PP into xylene, heat to 90-110℃, stir for 1-2h, then add modified UV oxidant, heat to 130-140℃, react for 3-5h, cool to room temperature, add methanol, wash and dry the precipitate to obtain anti-aging PP. The chemical reaction diagram is as follows:

[0016] Formula (6), The product was characterized by FTIR infrared spectroscopy;

[0017] (6) The anti-aging PP is pre-dehydrated in a vacuum at 70-80°C for 3-5 hours, then mixed evenly with a nucleating agent, a toughening agent and a lubricant and added to a twin-screw extruder. After melt extrusion, it is sent to an injection molding machine, and the mold cavity is filled by injection molding. After cooling and shaping, the mold is opened to obtain the anti-aging PP injection-molded food packaging material.

[0018] Preferably, the weight ratio of 1-acetyl-2-naphthol, acetic acid, nitric acid, 0-5°C ice water, methanol, and 5% palladium on carbon in (1) is 1:4-6:1.2-2:6-10:4-6:0.01-0.03.

[0019] Preferably, the methanol / water mixed solution in (1) is a mixture of methanol and water in a weight ratio of 3:2.

[0020] Preferably, the weight ratio of the (2) mid-terminal alkenyl polyalkylene isocyanate, 4-amino-2-hydroxy-1-acetonaphthone, tetrahydrofuran and diethyl ether is 1.2-1.6:1:8-12:10-20.

[0021] Preferably, the weight ratio of the (3) small to medium polar anti-ultraviolet oxidant, N-Boc-ethylenediamine, catalyst, anhydrous methanol and dichloromethane is 1:0.6-0.8:0.01-0.03:8-12:8-12.

[0022] Preferably, the catalyst in (3) is diazabicyclic DBU.

[0023] Preferably, the column chromatography gradient elution in (3) refers to the volume ratio of dichloromethane to methanol in each step of the eluent being successively from 1:0, 20:1 to 9:1.

[0024] Preferably, the methanol / water mixed solution in (3) refers to a mixture of methanol and water in a weight ratio of 3:2.

[0025] Preferably, the weight ratio of the low-polarity anti-ultraviolet oxidant containing an amino protecting group, trifluoroacetic acid, dichloromethane and deionized water in (4) is 1:2-3:8-12:10-20.

[0026] Preferably, the weight ratio of the modified anti-ultraviolet oxidant, maleic anhydride grafted PP, xylene and methanol in (5) is 0.1-0.2:1:8-12:10-14.

[0027] Preferably, the weight ratio of the anti-aging PP, nucleating agent, toughening agent and lubricant in (6) is 1:0.001-0.003:0.005-0.01:0.001-0.003.

[0028] Preferably, the nucleating agent in (6) is one or more of organic phosphates, sorbitol benzyl derivatives, and sodium benzoate.

[0029] Preferably, the toughening agent in (6) is one or more of dioctyl phthalate, dibutyl phthalate, and triphenyl phosphate.

[0030] Preferably, the lubricant in (6) is one or more of stearic acid, butyl stearate, and ethylene bisstearamide.

[0031] Preferably, the parameters of each zone of the twin-screw extruder in (6) are: feeding section: 180-200°C, plasticizing section: 220-240°C, homogenizing section: 210-230°C, metering section: 200-220°C, discharging section: 190-210°C, screw aspect ratio of 30:1, rotation speed of 400-600rpm, and head temperature of 210-230°C.

[0032] Preferably, the parameters of the injection molding machine in (6) are: mold temperature 60-70°C, injection pressure 80-120 MPa, injection speed 30-80 mm / s, holding pressure 60-100 MPa, and holding time 15-25 s.

[0033] Beneficial effects of the present invention:

[0034] 1. The present invention constructs a dual anti-aging mechanism by modifying the keto-enol conformational conversion of the naphthalene ring structure in the anti-ultraviolet oxidant and coordinating with the aromatic hydroxyl functional group. The material can simultaneously inhibit molecular chain breakage and oxidative yellowing under ultraviolet irradiation and thermal oxygen environment. The anti-aging ability under outdoor exposure conditions is higher than that of traditional anti-aging processes, and the long-term storage requirements of food can be met without frequent replacement of packaging.

[0035] 2. This invention eliminates the risk of additive migration from a molecular design perspective by modifying the amino group in the UV antioxidant to form a covalent bond with PP, and using long-chain alkyl groups with n=7-9 to adjust polarity matching. The migration levels in water, acid, alcohol, and oil-based food simulants meet the stringent migration requirements of food safety standards such as GB 9685-2016.

[0036] 3. The present invention introduces long-chain alkyl groups and rigid molecular groups, such as naphthalene rings, into the PP molecular chain through a covalent grafting structure to synergistically enhance heat resistance, thereby increasing the Vicat softening temperature of the anti-aging PP material and enabling it to withstand high-temperature sterilization and hot filling processes. At the same time, through crystallization optimization, a balance between strength and toughness is achieved, meeting the actual requirements of food packaging for impact resistance and bending resistance.

[0037] 4. The present invention adjusts the polarity of the anti-UV agent through terminal olefin polyalkylene isocyanate, greatly reducing the solubility parameter difference between it and PP, fundamentally solving the problems of anti-aging agent agglomeration and phase separation caused by polarity mismatch in traditional technologies, improving the uniformity of the material microstructure, and avoiding the attenuation of mechanical properties and the decline of anti-aging efficiency caused by defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The H NMR spectrum of 4-amino-2-hydroxy-1-acetonaphthone prepared in Preparation Example 2 of the present invention;

[0039] Figure 2 This is the H NMR spectrum of the low-polarity UV antioxidant prepared in Preparation Example 2 of the present invention;

[0040] Figure 3 This is the H NMR spectrum of the low-polarity UV antioxidant containing an amino protecting group prepared in Preparation Example 2 of the present invention;

[0041] Figure 4 This is the H NMR spectrum of the modified ultraviolet oxidant prepared in Preparation Example 2 of the present invention;

[0042] Figure 5 This is the FTIR infrared spectrum of the anti-aging PP prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0043] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0044] The main sources of raw materials used in the present invention are as follows:

[0045] 1-Acetyl-2-naphthol was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. with a purity of 98%; terminal olefin polyalkylene isocyanate, with the general structural formula: CH2=CH-(CH2) n -NCO, where n = 7-9, was purchased from Hefei Shenghang Pharmaceutical Technology Co., Ltd. with a purity of 98%; N-Boc-ethylenediamine was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. with a purity of 98%; maleic anhydride-grafted PP was purchased from Beijing Pulihongbin Chemical Materials Co., Ltd. with a melt index (190°C / 325gr) of 10 g / 10 min and a Vicat softening point of 147°C.

[0046] Preparation Example 1: The specific preparation process of the modified anti-ultraviolet oxidant includes the following steps:

[0047] (1) In a reaction vessel, 10 g of 1-acetyl-2-naphthol was added to 40 g of acetic acid, and the temperature was lowered to 0°C. 12 g of nitric acid was then added dropwise. After the addition was complete, the temperature was restored to room temperature and the reaction was carried out for 2 h. The reaction solution was added to 60 g of 0°C ice water. The obtained solid was filtered, washed, and dried, and then added to 40 g of methanol. 0.1 g of 5% palladium carbon was added, and the pH was adjusted to 3 with a 1 mol / L hydrochloric acid solution. The gas was replaced with hydrogen three times and the reaction was carried out at room temperature for 3 h. The filtrate was then filtered to obtain a filtrate. After concentration under vacuum, the filtrate was washed, dried, and recrystallized from a methanol / water mixed solution (methanol and water were mixed in a weight ratio of 3:2) to obtain 4-amino-2-hydroxy-1-naphthyl acetonide.

[0048] (2) 9.6g of terminal olefin polyalkylene isocyanate, structural formula: CH2=CH-(CH2) n -NCO, wherein n=7 and 8g of 4-amino-2-hydroxy-1-acetonapthone are added to 64g of tetrahydrofuran, cooled to 0°C, stirred and reacted for 1h, then returned to room temperature, stirred and reacted for 8h, added to 80g of ether, filtered and collected the precipitate, washed, and dried to obtain a low-polarity anti-ultraviolet oxidant;

[0049] (3) 10 g of a low-polarity UV antioxidant, 6 g of N-Boc-ethylenediamine and 0.1 g of DBU were added to 80 g of anhydrous methanol, stirred at room temperature for 1 h, then heated to 35 °C and reacted for 4 h. Methanol was removed by distillation under reduced pressure, 80 g of dichloromethane was added and stirred for 10 min, and then washed with 0.1 mol / L hydrochloric acid and saturated sodium bicarbonate. The organic phase was dried over anhydrous sodium sulfate and eluted by column chromatography with a gradient elution. The volume ratio of dichloromethane to methanol in each step of the eluent was changed from 1:0, 20:1 to 9:1, to obtain a low-polarity UV antioxidant containing an amino protecting group.

[0050] (4) 10 g of a low-polarity anti-ultraviolet oxidant containing an amino protecting group was added to 80 g of dichloromethane, and the temperature was lowered to 0°C while stirring. 20 g of trifluoroacetic acid was added dropwise for 1 hour. After the addition was completed, the mixture was returned to room temperature and reacted for 2 hours. The solid was filtered and washed with ethyl acetate. After drying, the solid was added to 100 g of deionized water, and the pH was adjusted to 8 with saturated sodium bicarbonate. The solid was filtered and washed and dried to obtain a modified anti-ultraviolet oxidant.

[0051] Preparation Example 2: The specific preparation process of the modified anti-ultraviolet oxidant includes the following steps:

[0052] (1) In a reaction vessel, 10 g of 1-acetyl-2-naphthol was added to 50 g of acetic acid, cooled to 3°C, and then 16 g of nitric acid was added dropwise. After the addition was complete, the temperature was restored to room temperature and the reaction was carried out for 2.5 h. The reaction solution was added to 80 g of 3°C ice water. The obtained solid was filtered, washed, and dried, and then added to 50 g of methanol. 0.2 g of 5% palladium carbon was added, and the pH was adjusted to 3.5 with a 1 mol / L hydrochloric acid solution. The hydrogen was replaced three times and the reaction was carried out at room temperature for 3.5 h. The filtrate was then filtered to obtain a filtrate. After concentration under vacuum, it was washed, dried, and recrystallized from a methanol / water mixed solution (methanol and water were mixed in a weight ratio of 3:2) to obtain 4-amino-2-hydroxy-1-naphthyl acetonide.

[0053] (2) 11.2g of terminal olefin polyalkylene isocyanate, structural formula: CH2=CH-(CH2) n -NCO, wherein n=8 and 8g of 4-amino-2-hydroxy-1-acetonapthone were added to 80g of tetrahydrofuran, cooled to 3°C, stirred and reacted for 2h, then returned to room temperature, stirred and reacted for 9h, added to 120g of ether, filtered and collected the precipitate, washed, and dried to obtain a low-polarity anti-ultraviolet oxidant;

[0054] (3) 10 g of a low-polarity UV antioxidant, 7 g of N-Boc-ethylenediamine and 0.2 g of DBU were added to 100 g of anhydrous methanol, stirred at room temperature for 1.5 h, then heated to 40 °C and reacted for 5 h. Methanol was removed by distillation under reduced pressure, 100 g of dichloromethane was added and stirred for 15 min, and then washed with 0.1 mol / L hydrochloric acid and saturated sodium bicarbonate. The organic phase was dried over anhydrous sodium sulfate and eluted by column chromatography with a gradient elution. The volume ratio of dichloromethane to methanol in each step of the eluent was changed from 1:0, 20:1 to 9:1, to obtain a low-polarity UV antioxidant containing an amino protecting group.

[0055] (4) 10 g of a low-polarity anti-ultraviolet oxidant containing an amino protecting group was added to 100 g of dichloromethane, and the mixture was cooled to 0°C while stirring. 25 g of trifluoroacetic acid was added dropwise for 1.5 h. After the addition was complete, the mixture was returned to room temperature and reacted for 3 h. The solid was filtered and washed with ethyl acetate. After drying, the solid was added to 150 g of deionized water, and the pH was adjusted to 8.5 with saturated sodium bicarbonate. The solid was filtered and washed and dried to obtain a modified anti-ultraviolet oxidant.

[0056] Preparation Example 3: The specific preparation process of the modified anti-ultraviolet oxidant includes the following steps:

[0057] (1) In a reaction vessel, 10 g of 1-acetyl-2-naphthol was added to 60 g of acetic acid, and the temperature was lowered to 5°C. 20 g of nitric acid was then added dropwise. After the addition was complete, the temperature was restored to room temperature and the reaction was carried out for 3 h. The reaction solution was added to 100 g of 5°C ice water. The obtained solid was filtered, washed, and dried, and then added to 60 g of methanol. 0.3 g of 5% palladium carbon was added, and the pH was adjusted to 4 with a 1 mol / L hydrochloric acid solution. The gas was replaced with hydrogen three times and the reaction was carried out at room temperature for 4 h. The filtrate was then filtered to obtain a filtrate. After concentration under vacuum, the filtrate was washed, dried, and recrystallized from a methanol / water mixed solution (methanol and water were mixed in a weight ratio of 3:2) to obtain 4-amino-2-hydroxy-1-naphthyl acetonide.

[0058] (2) 12.8g of terminal olefin polyalkylene isocyanate, structural formula: CH2=CH-(CH2) n -NCO, wherein n=9 and 8g of 4-amino-2-hydroxy-1-acetonapthone were added to 96g of tetrahydrofuran, cooled to 5°C, stirred and reacted for 3h, then returned to room temperature, stirred and reacted for 10h, added to 160g of ether, filtered and collected the precipitate, washed, and dried to obtain a low-polarity anti-ultraviolet oxidant;

[0059] (3) 10 g of a low-polarity UV antioxidant, 8 g of N-Boc-ethylenediamine and 0.3 g of DBU were added to 120 g of anhydrous methanol, stirred at room temperature for 2 h, then heated to 45 °C and reacted for 6 h. Methanol was removed by distillation under reduced pressure, 120 g of dichloromethane was added and stirred for 20 min, and then washed with 0.1 mol / L hydrochloric acid and saturated sodium bicarbonate. The organic phase was dried over anhydrous sodium sulfate and subjected to gradient elution by column chromatography. The volume ratio of dichloromethane to methanol in each step of the eluent was adjusted from 1:0, 20:1 to 9:1, to obtain a low-polarity UV antioxidant containing an amino protecting group.

[0060] (4) 10 g of a low-polarity anti-ultraviolet oxidant containing an amino protecting group was added to 120 g of dichloromethane, and the mixture was cooled to 0°C while stirring. 30 g of trifluoroacetic acid was added dropwise for 2 h. After the addition was complete, the mixture was returned to room temperature and reacted for 4 h. The solid was filtered and washed with ethyl acetate. After drying, the solid was added to 200 g of deionized water, and the pH was adjusted to 8-9 with saturated sodium bicarbonate. The solid was filtered and washed and dried to obtain a modified anti-ultraviolet oxidant.

[0061] Comparative Preparation Example 1: The difference between Comparative Preparation Example 1 and Preparation Example 2 is that 1-acetyl-2-naphthol is directly used as an anti-ultraviolet oxidant without any modification.

[0062] Comparative Preparation Example 2: The difference between Comparative Preparation Example 2 and Preparation Example 2 is that the terminal olefin polyalkylene isocyanate with the structural formula: CH2=CH-(CH2) n-NCO, where n=8, is replaced by terminal olefin polyalkylene isocyanate, with the structural formula: CH2=CH-(CH2) n -NCO, where n=6.

[0063] Comparative Preparation Example 3: The difference between Comparative Preparation Example 3 and Preparation Example 2 is that the terminal olefin polyalkylene isocyanate with the structural formula: CH2=CH-(CH2) n -NCO, where n=8, is replaced by terminal olefin polyalkylene isocyanate, with the structural formula: CH2=CH-(CH2) n -NCO, where n=4.

[0064] Comparative Preparation Example 4: The difference between Comparative Preparation Example 4 and Preparation Example 2 is that the terminal olefin polyalkylene isocyanate with the structural formula: CH2=CH-(CH2) n -NCO, where n=8, is replaced by terminal olefin polyalkylene isocyanate, with the structural formula: CH2=CH-(CH2) n -NCO, where n=10.

[0065] Comparative Preparation Example 5: The difference between Comparative Preparation Example 5 and Preparation Example 2 is that the terminal olefin polyalkylene isocyanate with the structural formula: CH2=CH-(CH2) n -NCO, where n=8, is replaced by terminal olefin polyalkylene isocyanate, with the structural formula: CH2=CH-(CH2) n -NCO, where n=12.

[0066] Comparative Preparation Example 6: The difference between Comparative Preparation Example 5 and Preparation Example 2 is that steps (3) and (4) are omitted, and the low-polarity anti-UV oxidant obtained in step (2) is the modified anti-UV oxidant.

[0067] Example 1: A specific preparation method of an anti-aging PP injection-molded food packaging material, comprising the following steps:

[0068] (1) Under nitrogen protection, 1 kg of maleic anhydride grafted PP was added to 8 kg of xylene, heated to 90 ° C, stirred for 1 hour, and then 100 g of the modified anti-ultraviolet oxidant prepared according to Preparation Example 1 was added, heated to 130 ° C, reacted for 3 hours, cooled to room temperature, and 10 kg of methanol was added. The obtained precipitate was washed and dried to obtain anti-aging PP;

[0069] (2) 1 kg of anti-aging PP was pre-dehydrated in a vacuum at 70 ° C for 3 h, then mixed evenly with 1 g of nucleating agent, 5 g of toughening agent and 1 g of lubricant and added to a twin-screw extruder. The feeding section of the twin-screw extruder was 180 ° C, the plasticizing section was 220 ° C, the homogenizing section was 210 ° C, the metering section was 200 ° C, the discharging section was 190 ° C, the screw aspect ratio was 30:1, the speed was 400 rpm, and the head temperature was 210 ° C. After melt extrusion, it was sent to the injection molding machine. The mold temperature of the injection molding machine was 60 ° C, the injection pressure was 80 MPa, the injection speed was 30 mm / s, the holding pressure was 60 MPa, and the holding time was 15 s. After injection molding, the mold cavity was filled, and the mold was opened after cooling and shaping to obtain anti-aging PP injection molding food packaging material.

[0070] Example 2: A specific preparation method of an anti-aging PP injection-molded food packaging material comprises the following steps:

[0071] (1) Under nitrogen protection, 1 kg of maleic anhydride grafted PP was added to 10 kg of xylene, heated to 100 ° C, stirred for 1.5 hours, and then 150 g of the modified anti-ultraviolet oxidant prepared according to Preparation Example 2 was added. The temperature was raised to 135 ° C, reacted for 4 hours, cooled to room temperature, and 12 kg of methanol was added. The obtained precipitate was washed and dried to obtain anti-aging PP;

[0072] (2) 1 kg of anti-aging PP was pre-dehydrated in a vacuum at 75 ° C for 4 h, then mixed evenly with 2 g of nucleating agent, 7 g of toughening agent and 2 g of lubricant and added to a twin-screw extruder. The feeding section of the twin-screw extruder was 190 ° C, the plasticizing section was 230 ° C, the homogenizing section was 230 ° C, the metering section was 210 ° C, the discharging section was 200 ° C, the screw aspect ratio was 30:1, the speed was 500 rpm, and the head temperature was 220 ° C. After melt extrusion, it was sent to the injection molding machine. The mold temperature of the injection molding machine was 65 ° C, the injection pressure was 100 MPa, the injection speed was 55 mm / s, the holding pressure was 80 MPa, and the holding time was 20 s. After injection molding, the mold cavity was filled, and the mold was opened after cooling and shaping to obtain anti-aging PP injection molded food packaging material.

[0073] Example 3: A specific preparation method of an anti-aging PP injection-molded food packaging material, comprising the following steps:

[0074] (1) Under nitrogen protection, 1 kg of maleic anhydride grafted PP was added to 12 kg of xylene, heated to 110 ° C, stirred for 2 h, and then 200 g of the modified anti-ultraviolet oxidant prepared according to Preparation Example 3 was added. The temperature was raised to 140 ° C, reacted for 5 h, cooled to room temperature, and 14 kg of methanol was added. The obtained precipitate was washed and dried to obtain anti-aging PP;

[0075] (2) 1 kg of anti-aging PP was pre-dehydrated in vacuum at 80 ° C for 5 h, then mixed evenly with 3 g of nucleating agent, 10 g of toughening agent and 3 g of lubricant and added to a twin-screw extruder. After melt extrusion, it was sent to an injection molding machine. The feeding section of the twin-screw extruder was: 200 ° C, the plasticizing section was: 240 ° C, the homogenizing section was: 230 ° C, the metering section was: 220 ° C, the discharging section was: 210 ° C, the screw aspect ratio was 30:1, the speed was 600 rpm, and the head temperature was 230 ° C. After melt extrusion, it was sent to the injection molding machine. The mold temperature of the injection molding machine was 70 ° C, the injection pressure was 100 MPa, the injection speed was 80 mm / s, the holding pressure was 100 MPa, and the holding time was 25 s. After injection molding, the mold cavity was filled, and the mold was opened after cooling and shaping to obtain anti-aging PP injection molded food packaging material.

[0076] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that the modified anti-ultraviolet oxidant prepared according to the preparation method of Comparative Preparation Example 1 is used.

[0077] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that the modified anti-ultraviolet oxidant prepared according to the preparation method of Comparative Preparation Example 2 is used.

[0078] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the modified anti-ultraviolet oxidant prepared according to the preparation method of Comparative Preparation Example 3 is used.

[0079] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that the modified anti-ultraviolet oxidant prepared according to the preparation method of Comparative Preparation Example 4 is used.

[0080] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that the modified anti-ultraviolet oxidant prepared according to the preparation method of Comparative Preparation Example 5 is used.

[0081] Comparative Example 6: The difference between Comparative Example 6 and Example 2 is that the modified anti-ultraviolet oxidant prepared according to the preparation method of Comparative Preparation Example 6 is used.

[0082] Comparative Example 7: The difference between Comparative Example 7 and Example 2 is that the maleic anhydride-grafted PP is replaced by PP.

[0083] Comparative Example 8: The difference between Comparative Example 8 and Example 2 is that the modified anti-ultraviolet oxidant is replaced by a common commercial anti-ultraviolet agent such as UV326 and an antioxidant such as Irganox 168, which are melt-blended with maleic anhydride-grafted PP, and then a nucleating agent, a toughening agent and a lubricant are added. The mixture is then extruded through a twin-screw extruder and injection molded to obtain a food packaging material.

[0084] Performance testing:

[0085] 1. Mechanical Properties Test: The food packaging materials prepared in Examples 1-3 and Comparative Examples 1-8 were prepared into specimens of uniform size. Tensile strength and elongation at break were tested at room temperature using a universal material testing machine at a tensile rate of 50 mm / min. The experimental results are shown in Table 1.

[0086] 2. Vicat Softening Temperature Test: The food packaging materials prepared in Examples 1-3 and Comparative Examples 1-8 were prepared into uniformly sized specimens and tested according to the test method specified in GB / T 1633-2000. The test methods used were: a load of 50 N, a heating rate of 50°C / h, an indenter tip radius of 0.1 mm, and an indentation force accuracy of ±1%. The experimental results are shown in Table 1.

[0087] 3. UV aging resistance test: The food packaging materials prepared in Examples 1-3 and Comparative Examples 1-8 were prepared into samples of uniform size. After drying, the samples were placed in a UV aging test chamber (irradiance 0.68 W / m², temperature 60°C, humidity 50%) and irradiated for 500 h. The CIELAB color value of the coating was measured before and after the test using a colorimeter, and the CIELAB color value change ΔE was calculated. The smaller the ΔE, the better the UV resistance of the coating. The experimental results are shown in Table 1.

[0088] 4. Antioxidant performance test: The food packaging materials prepared in Examples 1-3 and Comparative Examples 1-8 were prepared into uniform-sized samples. After drying, they were placed in an oven (80°C, 72 hours) to simulate an oxidative environment. The tensile strength and elongation at break after aging were measured, and the performance retention rate was calculated. , the experimental results are shown in Table 1.

[0089] 5. Migration and dissolution test: According to GB31604.19-2016 "General Rules for Migration Tests of Food Contact Materials and Articles" and GB5009.156-2016 "General Rules for Pretreatment Methods for Migration Tests of Food Contact Materials and Articles", by simulating food contact conditions, the material is exposed to different types of food simulants to measure the migration amount of the anti-ultraviolet oxidant and evaluate its safety. The simulants are deionized water, simulated aqueous foods (such as beverages, soups), 3% acetic acid solution, simulated acidic foods (such as vinegar, juice), 10% ethanol solution, simulated low-alcohol Refined foods (such as beer and yogurt) and n-hexane simulate oily foods (such as cooking oil and meat). The food packaging materials prepared in Examples 1-3 and Comparative Examples 1-8 were washed with deionized water, dried, and cut into 50 mm × 50 mm × 2 mm specimens. The specimens and the corresponding simulants were placed in a glass container, sealed, and subjected to a constant temperature treatment according to the above-mentioned national standard test method. After the test, the simulant solution was collected and filtered through a 0.45 μm filter membrane. The filtrate was analyzed for composition by HPLC, and the migration amount was calculated. The experimental results are shown in Table 1.

[0090] Table 1 Performance test results

[0091]

[0092] Performance Analysis:

[0093] The experimental data in Table 1 show that the comprehensive performance of the food packaging materials prepared using the present invention in Examples 1-3 is superior to that of Comparative Examples 1-8, with Example 2 demonstrating the most outstanding performance. In terms of mechanical properties, the materials exhibit excellent toughness and strength; a Vicat softening temperature of 163°C, significantly higher than the comparative example, demonstrating outstanding high-temperature resistance; a ΔE after UV aging of only 1.1, demonstrating excellent color stability; and in antioxidant testing, tensile strength retention reached 95% and elongation at break retention reached 93%, demonstrating minimal performance degradation. Furthermore, migration in various simulants was extremely low, demonstrating optimal overall performance.

[0094] From the perspective of mechanical properties, this may be because Example 2 constructs a "covalent bond-physical entanglement" composite reinforcement network in the PP matrix through chemical grafting: the amino group of the modified anti-ultraviolet oxidant and the anhydride group of the maleic anhydride grafted PP form covalent crosslinks, which significantly enhances the interaction force between the molecular chains, improves the stress transfer efficiency during stretching, and significantly improves the mechanical properties compared to the control example. At the same time, the n=8 long-chain alkyl introduced by the terminal olefin polyalkylene isocyanate is entangled with the PP molecular chain to form a toughening structure similar to a "molecular rope". When the material is stretched, the alkyl chain segment can absorb energy by slipping to avoid brittle fracture. This synergistic effect of "rigid crosslinking + flexible entanglement" makes Example 2 have both high strength and high toughness.

[0095] From the perspective of Vicat softening temperature, this may be because the modified anti-ultraviolet oxidant in Example 2 forms a covalent amide bond through the amino group and the anhydride group of maleic anhydride grafted to PP, building a three-dimensional chemical cross-linking network between the PP molecular chains. The bond energy of this covalent bond is much higher than the van der Waals force, which significantly increases the movement resistance of the molecular chain. When the temperature rises, the covalent cross-linking network needs to absorb more heat energy to destroy the interaction between the chains, thereby increasing the Vicat softening temperature. The FTIR spectrum shows that Example 2 has a 3D chemical cross-linking network at 1650 cm -1The obvious characteristic peak of amide bond appears at , confirming the formation of covalent bond; secondly, the naphthalene ring in the modified anti-ultraviolet oxidant is a planar conjugated system, and its rigid planar structure is grafted onto the PP chain as a "molecular reinforcing block". The π-π conjugation effect of the naphthalene ring significantly increases the rigidity of the molecular chain. Higher temperature is required to overcome the electron delocalization of the conjugated system and cause segment slip, resulting in an increase in the Vicat temperature; then, the n=8 long-chain alkyl group introduced by the terminal olefin polyalkylene isocyanate affects the crystallization of the PP molecular chain, and promotes the formation of fine and uniform β-crystal of PP through the "molecular chain entanglement-nucleation synergy" mechanism. The melting point of β-crystal is higher than that of α-crystal. At the same time, the entanglement of the alkyl chain and PP forms physical cross-linking points, which further enhances the rigidity of the crystalline region and makes the material more difficult to undergo plastic deformation during heating; finally, chemical grafting eliminates the phase interface defects between the anti-ultraviolet agent and the PP matrix, avoiding the weak points of thermal deformation caused by phase separation in the comparative example.

[0096] From the perspective of anti-ultraviolet and anti-oxidation properties, the excellent anti-ultraviolet oxidation performance of Example 2 is derived from the "light energy dissipation-free radical capture-structural stabilization" trinity protection system constructed by the modified anti-ultraviolet oxidant at the molecular level. The naphthalene ring in the molecular structure of the modified anti-ultraviolet oxidant realizes ultraviolet light energy dissipation through keto-enol interconversion. When irradiated with ultraviolet light, the naphthalene ring absorbs light energy and is excited to a high energy state. The keto carbon group at position 1 migrates through the intramolecular hydrogen bond network, promoting the conversion of the keto configuration into an enol intermediate, which releases energy in the form of heat through non-radiative transition and returns to the ground state. At the same time, the large π-conjugated system of the naphthalene ring stabilizes the excited-state intermediate, preventing light-induced PP chain breakage. Furthermore, the hydroxyl group acts as a hydrogen donor, providing hydrogen atoms to free radicals (such as R·) by breaking the OH bond, terminating the oxidative chain reaction and generating stable ROOH and phenoloxy radicals. This is stabilized by the resonance effect of the naphthalene ring. Finally, the modified UV antioxidant forms a three-dimensional crosslinked network through covalent bonds between the amino groups and the PP, allowing the UV antioxidant to be present in the PP matrix as a "molecular anchor," avoiding the shortened aging time caused by UV antioxidant migration during physical blending. Furthermore, the entanglement of the n=8 long-chain alkyl group with the PP molecular chain stabilizes the keto-enol conformational transition of the naphthalene ring. The co-crystallized structure formed by the alkyl chain and the PP further reduces crystal defects, blocks oxygen diffusion pathways, and structurally slows the oxidation process. This multi-layered protection mechanism ensures that Example 2 maintains excellent performance stability in UV and oxidative environments.

[0097] From the migration and dissolution test, it can be seen that in Example 2, a covalent amide bond is formed between the modified anti-UV oxidant and the anhydride group of the maleic anhydride grafted PP. The bond energy is higher than the van der Waals force, and the anti-UV oxidant is fixed on the PP molecular chain. This chemical bonding prevents the anti-UV oxidant from escaping from the PP matrix by diffusion, and the migration amount is greatly reduced compared with the control ratio of physical blending, verifying the inhibitory effect of covalent bonds on migration; secondly, the n=8 long-chain alkyl introduced in Example 2 optimizes the polarity matching between the anti-UV oxidant and PP through the "like dissolves like" principle. Its non-polar long chain reduces the polarity of the anti-UV oxidant, matches the polarity of PP, and significantly reduces the dissolution tendency of the anti-UV oxidant in polar solvents. In n-hexane, the interaction between the alkyl chain and n-hexane may promote However, the entanglement of the alkyl chain and the PP molecular chain forms a steric hindrance, which hinders the diffusion of the anti-UV agent into the solvent, so that the migration amount in n-hexane is also within the safe level for food packaging materials; then, the entanglement of the long-chain alkyl group and the PP molecular chain promotes the improvement of PP crystallinity, and the formed small and uniform β-crystal has a tighter molecular stacking structure, which reduces the intermolecular gaps and forms a physical barrier to block the migration path of the anti-UV agent; finally, chemical bonding fixes the spatial position of the anti-UV agent, the alkyl chain regulates its interaction with the solvent, and the crystalline structure consolidates the barrier effect from a macroscopic perspective. The synergy of these multiple mechanisms enables the anti-UV agent to maintain a low migration state in various food simulants. Even in the most polar 3% acetic acid, the migration amount is far below the safety threshold of 0.01 mg / kg specified in GB 9685-2016.

[0098] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing an anti-aging PP injection-molded food packaging material, characterized in that: The following steps are involved: (1) In a reaction vessel, 1-acetyl-2-naphthol is added to acetic acid, cooled to 0-5°C, and then nitric acid is added dropwise. After the addition is complete, the mixture is returned to room temperature and reacted for 2-3 hours. The reaction solution is added to 0-5°C ice water, and a large amount of solid precipitation is observed. The obtained solid is filtered, washed, and dried, and then added to methanol. 5% palladium carbon is added, and the pH is adjusted to 3-4 with a 1 mol / L hydrochloric acid solution. The mixture is replaced with hydrogen three times and reacted at room temperature for 3-4 hours. The filtrate is then filtered to obtain a filtrate, which is concentrated under vacuum, washed, dried, and then recrystallized from a methanol / water mixed solution to obtain 4-amino-2-hydroxy-1-naphthone. (2) The terminal olefin polyalkylene isocyanate, the general structural formula is: CH2=CH-(CH2) n -NCO, wherein n=7-9 and 4-amino-2-hydroxy-1-acetonapthone are added to tetrahydrofuran, cooled to 0-5°C, stirred and reacted for 1-3 hours, then returned to room temperature, stirred and reacted for 8-10 hours, added to diethyl ether, filtered and collected the precipitate, washed, and dried to obtain a low-polarity anti-ultraviolet oxidant; (3) Add a low-polarity UV-resistant oxidant, N-Boc-ethylenediamine and a catalyst to anhydrous methanol, stir and react at room temperature for 1-2 hours, then heat to 35-45°C, react for 4-6 hours, remove methanol by distillation under reduced pressure, add dichloromethane and stir for 10-20 minutes, then wash with 0.1 mol / L hydrochloric acid and saturated sodium bicarbonate, dry the organic phase with anhydrous sodium sulfate, and elute by column chromatography gradient elution to obtain a low-polarity UV-resistant oxidant containing an amino protecting group; (4) Add a low-polarity UV antioxidant containing an amino protecting group to dichloromethane, cool to 0°C while stirring, and add trifluoroacetic acid dropwise for 1-2 hours. After the addition is complete, return to room temperature, react for 2-4 hours, filter, and wash the obtained solid with ethyl acetate. After drying, add it to deionized water, adjust the pH to 8-9 with saturated sodium bicarbonate, filter, wash, and dry the obtained solid to obtain a modified UV antioxidant. (5) Under nitrogen protection, add maleic anhydride grafted PP into xylene, heat to 90-110 ° C, stir for 1-2 hours, then add modified anti-ultraviolet oxidant, heat to 130-140 ° C, react for 3-5 hours, cool to room temperature, add methanol, wash the obtained precipitate, and dry it to obtain anti-aging PP; (6) The anti-aging PP is pre-dehydrated in a vacuum at 70-80°C for 3-5 hours, then mixed evenly with a nucleating agent, a toughening agent and a lubricant and added to a twin-screw extruder. After melt extrusion, it is sent to an injection molding machine, and the mold cavity is filled by injection molding. After cooling and shaping, the mold is opened to obtain the anti-aging PP injection-molded food packaging material.

2. The method for preparing the anti-aging PP injection-molded food packaging material according to claim 1, characterized in that: In the (1), the weight ratio of 1-acetyl-2-naphthol, acetic acid, nitric acid, 0-5°C ice water, methanol, and 5% palladium carbon is 1:4-6:1.2-2:6-10:4-6:0.01-0.03, and the methanol / water mixed solution refers to a mixture of methanol and water in a weight ratio of 3:

2.

3. The method for preparing the anti-aging PP injection-molded food packaging material according to claim 1, characterized in that: The weight ratio of the (2) mid-terminal alkenyl polyalkylene isocyanate, 4-amino-2-hydroxy-1-acetonaphthone, tetrahydrofuran and diethyl ether is 1.2-1.6:1:8-12:10-20.

4. The method for preparing the anti-aging PP injection-molded food packaging material according to claim 1, characterized in that: The (3) small and medium polar anti-ultraviolet oxidant, N-Boc-ethylenediamine, catalyst, anhydrous methanol and dichloromethane are in a weight ratio of 1:0.6-0.8:0.01-0.03:8-12:8-12, and the catalyst refers to diazabicyclic DBU.

5. The method for preparing the anti-aging PP injection-molded food packaging material according to claim 1, characterized in that: The gradient elution of column chromatography in (3) refers to the volume ratio of dichloromethane to methanol in the eluent of each step being successively from 1:0, 20:1 to 9:

1.

6. The method for preparing the anti-aging PP injection-molded food packaging material according to claim 1, characterized in that: The (4) contains a low polarity UV antioxidant containing an amino protecting group, trifluoroacetic acid, dichloromethane and deionized water in a weight ratio of 1:2-3:8-12:10-20.

7. The method for preparing the anti-aging PP injection-molded food packaging material according to claim 1, characterized in that: The modified anti-ultraviolet oxidant, maleic anhydride grafted PP, xylene and methanol in (5) are in a weight ratio of 0.1-0.2:1:8-12:10-14.

8. The method for preparing the anti-aging PP injection-molded food packaging material according to claim 1, characterized in that: The weight ratio of the anti-aging PP, nucleating agent, toughening agent and lubricant in (6) is 1:0.001-0.003:0.005-0.01:0.001-0.003, the nucleating agent refers to one or more of organic phosphates, sorbitol benzyl derivatives and sodium benzoate, the toughening agent refers to one or more of dioctyl phthalate, dibutyl phthalate and triphenyl phosphate, and the lubricant refers to one or more of stearic acid, butyl stearate and ethylene bisstearamide.

9. The method for preparing the anti-aging PP injection-molded food packaging material according to claim 1, characterized in that: The parameters of each zone of the twin-screw extruder in (6) are as follows: feeding section: 180-200°C, plasticizing section: 220-240°C, homogenizing section: 210-230°C, metering section: 200-220°C, discharging section: 190-210°C, screw aspect ratio of 30:1, rotation speed of 400-600rpm, and head temperature of 210-230°C.

10. The method for preparing the anti-aging PP injection-molded food packaging material according to claim 1, characterized in that: The parameters of the injection molding machine in (6) are: mold temperature 60-70°C, injection pressure 80-120 MPa, injection speed 30-80 mm / s, holding pressure 60-100 MPa, and holding time 15-25 s.

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