An oil-proof packaging material for food contact paper and a preparation process thereof

Abstract

The present application relates to the technical field of food packaging materials, and particularly relates to an oil-proof packaging material for food contact paper and a preparation process thereof. The oil-proof packaging material for food contact paper is prepared by the following steps: preparing a citraconic acid fermentation liquor, preparing methyl succinic acid by hydrogenation reaction of the citraconic acid, and preparing the oil-proof packaging material for food contact paper. The present application realizes the full-chain green preparation from straw to bio-based methyl succinic acid, and produces degradable polymer particles on the basis. The bio-based methyl succinic acid endows the oil-proof packaging material for food contact paper with the characteristics of renewability and biodegradability, helps to solve the problem of plastic pollution, and in terms of material performance, the introduction of bio-based monomers can optimize the polymer chain structure, improve the barrier effect of the film on oil, make the film thinner and tougher, and thus improve the oil-proof capacity.

Description

Technical Field

[0001] This invention relates to the field of food packaging materials technology, specifically to an oil-resistant packaging material for food contact paper and its preparation process. Background Technology

[0002] With increasing global concern about plastic pollution, the food packaging industry is facing an urgent need to transform towards green and sustainable practices. This is especially true for oil-resistant packaging materials, which fall into two categories: traditional plastic packaging, whose raw materials largely rely on petroleum-based polymers that are difficult to degrade in the natural environment, placing a long-term burden on the ecosystem; and paper-based packaging, which achieves oil resistance and barrier properties by adding a biodegradable polyester coating to the surface of the paper base. This biodegradable polyester coating is formed by polymerizing monomers; for example, current technology typically uses succinic acid and butanediol as monomers to synthesize polyester, which is then applied to the paper base surface to achieve oil resistance. Furthermore, due to the regular chain structure of the polyester synthesized from succinic acid and butanediol, it not only has oil resistance but also good biodegradability.

[0003] However, because the polyester chain structure synthesized from butanediol and succinic acid is relatively regular, its chain segment movement is also relatively easy. As a result, although it can block the penetration of large molecule oils, its ability to block small molecule oils is limited. Moreover, the overly regular chain structure can also cause the material to be brittle and lack toughness. At the same time, it does not adhere well to the surface of paper products, causing the polyester layer on the surface of the base paper to easily fall off.

[0004] In view of this, the present invention prepares a novel bio-based monomer and biodegradable polyester that are derived from biomass materials and endow the materials with high strength, high toughness and intrinsic high barrier properties, and uses them in oil-proof packaging materials for food contact paper. Thus, an oil-proof packaging material for food contact paper and its preparation process have been developed to solve the problems that the prior art has not solved. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide an oil-resistant packaging material for food contact paper and its preparation process.

[0006] A process for preparing an oil-resistant packaging material for food contact paper includes the following steps: S1: Preparation of itaconic acid fermentation broth Add water, corn steep liquor, ammonium sulfate and magnesium sulfate heptahydrate to the sugar solution, then heat and cool to obtain a culture medium. Inoculate the Aspergillus terrestris seed liquid into the culture medium. After fermentation, add methionine dropwise and continue fermentation. After fermentation is completed, remove solids by centrifugation and filtration, and then purify the fermentation broth with resin to obtain itaconic acid fermentation broth. S2: Preparation of methylsuccinic acid by hydrogenation of itaconic acid The itaconic acid fermentation broth was dissolved in anhydrous ethanol and then added to a reactor. 5-8% (by mass) of nickel skeletal catalyst was then added. The air inside the reactor was purged with hydrogen, and then hydrogen was introduced again to bring the pressure inside the reactor to 8.08 × 10⁻⁶. 5 Pa, stir, heat, and after the reaction time, stop heating and wait for the pressure to drop to 1.01 × 10⁻⁶. 5 Pa, remove the reaction solution, let stand, filter to recover the catalyst, and then distill the filtrate under reduced pressure to obtain bio-based methyl succinic acid; S3: Preparation of oil-resistant packaging materials for food contact paper Bio-based methyl succinic acid and 1,4-butanediol were added to a reactor, followed by p-toluenesulfonic acid and triphenyl phosphite. Under nitrogen protection, the temperature was gradually increased for 3-5 hours. Subsequently, the reaction was carried out under vacuum with stirring. The product was extruded, granulated, and dried to obtain biodegradable polymer granules. The biodegradable polymer granules were added to a single-screw extruder and extruded into a film. The film was then pressed onto the surface of pretreated base paper with a pressure of 5-15 N / m to obtain an oil-proof packaging material for food contact paper.

[0007] Furthermore, step S1 specifically includes the following steps: Add water to the sugar solution to adjust the concentration to 40-44 g / L, then add 10-20 g / L corn steep liquor, 2-4 g / L ammonium sulfate and 0.5-1.5 g / L magnesium sulfate heptahydrate. Then adjust the pH to 2.5-3 with 1M HCl. Then heat at 121-125℃ for 20-30 min and cool to 34-37℃ to obtain the culture medium. Inoculate the Aspergillus terreus seed culture into the culture medium at an inoculation rate of 9.8-10.2% (v / v), stir on a shaker at 200-220 r / min at 34-37℃, and ferment for 60-70 h. Then, add methionine dropwise at a rate of 3-4 mL / s to a concentration of 0.5-1.5 g / L. Fermentation continued for 72-80 hours. After fermentation, solids were removed by centrifugation and filtration, and the fermentation broth was purified with resin to obtain itaconic acid fermentation broth.

[0008] Furthermore, the preparation method of the sugar solution in step S1 specifically includes the following steps: Straw was soaked in a 2-4% (w / v) NaOH solution at 30-40℃ for 12-14 hours, followed by steam explosion to obtain straw residue. High-purity water at 50-60℃ was added to the reactor, and the straw residue was divided into three portions, accounting for 30-50%, 20-30%, and 20-50% of the total mass of straw residue, respectively. The straw residue accounting for 30-50% of the total mass was mixed with high-purity water at 50-60℃ at a ratio of 1g:(1-1.2)mL. Mix the liquid and water, adjust the pH to 4.8-5, add 10 CBU / g of cellulase (based on straw residue as dry substrate), and hydrolyze for 12-20 hours. Then add 20-30% of the total straw residue, adjust the pH to 4.8-5, and add 10 CBU / g of cellulase (based on straw residue as dry substrate) to hydrolyze for 12-20 hours. Finally, add the remaining straw residue and repeat the above process. Finally, raise the temperature to 80-85℃ and hold for 20-30 minutes to obtain the sugar solution.

[0009] Furthermore, step S3 specifically includes the following steps: Bio-based methyl succinic acid and 1,4-butanediol were added to a reactor at a molar ratio of 1:(1-1.5). Then, 0.3-0.5% of p-toluenesulfonic acid and 0.2-0.4% of triphenyl phosphite were added to the reactor. Under nitrogen protection, the temperature was gradually increased to 190-200℃ and the reaction was carried out for 3-5 hours. Subsequently, the reaction was carried out under vacuum stepwise. Then, the mixture was stirred at 500-600 r / min for 1.5-3 hours. The product was extruded, granulated, and dried in hot air at 80-90℃ for 6-8 hours to obtain biodegradable polymer granules. The biodegradable polymer granules are dried in a dehumidifying dryer at 70-80℃ for 6-7 hours, added to a single-screw extruder, and extruded into a film. The film is then pressed onto the surface of a pretreated base paper with a pressure of 5-15 N / m to obtain an oil-proof packaging material for food contact paper.

[0010] Furthermore, the preparation of the pretreated base paper in step S3 is specifically as follows: Soy protein isolate was dispersed in deionized water to prepare a 5-10% (w / w) solution. The pH of the system was adjusted to 9-10 with NaOH solution while stirring at 100-120 rpm. The solution was then preheated at 50-60℃ for 20-30 min to obtain the protein solution. Alkenyl succinic anhydride was added dropwise to the protein solution, and the reaction was stirred continuously for 2-3 hours at 50-60℃ and pH 8-9. Then, 1,2-epoxyoctadecane was added to the protein solution, the pH of the reaction system was adjusted to 9-10, the temperature was raised to 65-75℃, and the reaction was stirred continuously for 2-3 hours under these conditions to obtain the modified protein solution. Cool the modified protein solution to 40-50℃, add PVA solution, the ratio of PVA solution to raw soybean protein is 1:1, gently stir and mix at this temperature for 1-2 hours to make it uniformly mixed, adjust the final pH value to neutral, and obtain the protein-based coating solution. Preheat the base paper to 50-60℃, then apply the protein-based coating solution to the surface of the base paper with a coating thickness of 50-70μm. Then heat the base paper to 100-120℃ to obtain the pretreated base paper.

[0011] Furthermore, the volume ratio of alkenyl succinic anhydride, protein solution and 1,2-epoxyoctadecane is (1-1.2):100:(0.5-0.9).

[0012] Furthermore, the melt temperature of the single-screw extruder is 170-190℃.

[0013] Furthermore, the base paper is any one of food-grade kraft paper, tracing paper, or silicone paper.

[0014] Furthermore, the specific steps of the vacuum stepwise reaction in step S3 are as follows: turn on the vacuum system, reduce the absolute pressure of the system to 4900-5100 Pa within 30-60 min, and at the same time raise the material temperature to 230-240℃ and maintain it for 1-2 h. Continue to increase the vacuum degree, reduce the absolute pressure to 80-100 Pa within 30 min, maintain the temperature at 240-250℃, and stir at a speed of 500-600 r / min for 1.5-3 hours.

[0015] An oil-proof packaging material for food contact paper is prepared by the above-mentioned preparation process for oil-proof packaging material for food contact paper.

[0016] The present invention has the following advantages: 1. This invention achieves a fully green, end-to-end production process from straw to bio-based methyl succinic acid, and uses this as a basis to produce biodegradable polymer particles. Bio-based methyl succinic acid imparts renewable and biodegradable properties to oil-resistant packaging materials for food contact paper, helping to solve the problem of plastic pollution. Furthermore, in terms of material properties, the introduction of bio-based monomers optimizes the polymer chain structure, improves the film's barrier effect against grease, and makes the film thinner and tougher. Specifically, compared to succinic acid used in existing technologies, bio-based methyl succinic acid carries a methyl side chain on its main chain. When this monomer participates in polycondensation, this methyl side chain... The methyl group is permanently introduced into the generated polyester macromolecular chain. As a sterically hindered group, the methyl group directly hinders the internal rotation of the single bond it is in, thereby increasing the local rigidity of the polymer backbone. This reduces the mobility of the chain segments at room temperature. The more rigid chain segments require a larger free volume and higher energy to undergo cooperative rearrangement, which sets a higher kinetic energy barrier for small molecule diffusion, thereby enhancing the toughness of the material. In addition, the methyl group is a strongly hydrophobic group. Its uniform distribution in the molecular chain enhances the intrinsic oleophobicity of the entire polymer matrix at the molecular level, thereby improving the oil-repellent ability.

[0017] 2. In the process of producing itaconic acid by Aspergillus terrestris fermentation, this invention adds methionine, using it as a key metabolic precursor and regulator. Firstly, methionine is a highly efficient sulfur source for cysteine ​​synthesis. The key enzymes in itaconic acid synthesis can be activated and their activity and metabolism accelerated by supplementing with methionine. Furthermore, methionine can be converted into S-adenosylmethionine, which acts as a major methyl donor participating in global cellular metabolic regulation, helping to redirect carbon flux from cell growth to the product synthesis pathway. Therefore, adding methionine dropwise in the later stages of fermentation is a precise metabolic engineering strategy aimed at specifically addressing the coenzyme bottleneck in itaconic acid synthesis, optimizing metabolic flow, thereby maximizing the conversion efficiency of the target product and increasing the yield of itaconic acid.

[0018] 3. This invention involves dual chemical modification of soybean protein with alkenyl succinic anhydride and octadecyl oxide, synergistically blended with PVA, significantly improving its performance as a paper binder. The alkenyl succinic anhydride undergoes an acylation reaction with the protein's amino groups under pH 8-9 conditions, covalently grafting long-chain alkyl groups, endowing the material with inherent hydrophobicity. Subsequently, octadecyl oxide further reacts with the protein under alkaline conditions, introducing longer hydrophobic chains and increasing the density of intermolecular crosslinks, thereby enhancing the coating's density and chemical stability. Finally, PVA forms an interpenetrating network with the modified protein through hydrogen bonds, effectively improving film brittleness and enhancing flexibility and adhesion. When the protein-based coating liquid prepared in this way is coated onto food paper, its covalently grafted hydrophobic alkyl chains effectively block oil penetration and water vapor diffusion, providing excellent oil and water resistance. Furthermore, the reinforcing effect of the crosslinking network and PVA significantly improves the paper's tensile strength and folding endurance. Simultaneously, the coating possesses thermoplasticity, enabling heat sealing of the paper, making the surface coating of the food contact paper oil-proof packaging material less prone to peeling. Attached Figure Description

[0019] Figure 1 This is a process flow diagram for preparing the oil-resistant packaging material for food contact paper according to the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention.

[0021] Example 1: A preparation process for an oil-resistant packaging material for food contact paper, such as... Figure 1 As shown, it includes the following steps: S1: Preparation of itaconic acid fermentation broth Straw was soaked in a 2% (w / v) NaOH solution at 30°C for 12 hours, followed by steam explosion to obtain straw residue. High-purity water at 50°C was added to the reactor, and the straw residue was divided into three portions, accounting for 30%, 20%, and 50% of the total straw residue mass, respectively. The straw residue accounting for 30% of the total straw residue mass was mixed with high-purity water at 50°C at a material-to-liquid ratio of 1g:1mL, and the pH was adjusted to 4.8. Cellulase at a concentration of 10 CBU / g based on the straw residue as dry substrate was added, and enzymatic hydrolysis was carried out for 12 hours. Then, straw residue accounting for 20% of the total straw residue mass was added, the pH was adjusted to 4.8, and cellulase at a concentration of 10 CBU / g based on the straw residue as dry substrate was added, and enzymatic hydrolysis was carried out for 12 hours. Finally, the remaining straw residue was added, and the above process was repeated. The temperature was raised to 80°C and held for 20 minutes to obtain a sugar solution. Add water to the sugar solution to adjust the concentration to 40 g / L, then add 10 g / L corn steep liquor, 2 g / L ammonium sulfate and 0.5 g / L magnesium sulfate heptahydrate, then adjust the pH to 2.5 with 1 M HCl, then heat at 121 °C for 20 min and cool to 34 °C to obtain the culture medium. Aspergillus terrestris seed culture was inoculated into the culture medium at an inoculation rate of 9.8% (v / v). The mixture was stirred on a shaker at 200 r / min at 34 °C for 60 h. Methionine was added dropwise at a rate of 3 mL / s to a final concentration of 0.5 g / L. Fermentation was then continued for another 72 h. After fermentation, solids were removed by centrifugation and filtration. The fermentation broth was then purified with resin to obtain itaconic acid fermentation broth.

[0022] S2: Preparation of methylsuccinic acid by hydrogenation of itaconic acid The itaconic acid fermentation broth was dissolved in anhydrous ethanol and then added to a reactor. 5% (by mass) of nickel skeletal catalyst was then added. The air inside the reactor was purged with hydrogen, and then hydrogen was introduced again to bring the pressure inside the reactor to 8.08 × 10⁻⁶. 5 Pa, stir, heat, and after the reaction time, stop heating and wait for the pressure to drop to 1.01 × 10⁻⁶. 5 Pa, remove the reaction solution, let stand, filter to recover the catalyst, and then distill the filtrate under reduced pressure to obtain bio-based methyl succinic acid.

[0023] S3: Preparation of oil-resistant packaging materials for food contact paper Bio-based methyl succinic acid and 1,4-butanediol were added to a reactor in a 1:1 molar ratio. Then, 0.3% p-toluenesulfonic acid and 0.2% triphenyl phosphite were added to the reactor. Under nitrogen protection, the temperature was gradually increased to 190°C and reacted for 3 hours. Subsequently, the vacuum system was gradually turned on, and the absolute pressure of the system was steadily reduced to 4900 Pa within 30 minutes, while the material temperature was raised to 230°C and maintained for 1 hour. The vacuum degree was further increased, and the absolute pressure was reduced to 80 Pa within 30 minutes. The temperature was maintained at 240°C, and the mixture was stirred at 500 r / min for 1.5 hours. The product was extruded, granulated, and dried in hot air at 80°C for 6 hours to obtain biodegradable polymer granules. Soy protein isolate was dispersed in deionized water to prepare a 5% (w / w) solution. The pH of the system was adjusted to 9 with NaOH solution while stirring at 100 rpm, and then preheated at 50°C for 20 min to obtain the protein solution. Alkenyl succinic anhydride was added dropwise to the protein solution, and the reaction was carried out with stirring for 2 hours at 50°C and pH 8. Then, 1,2-epoxy octadecane was added to the protein solution, the pH of the reaction system was adjusted to 9, the temperature was raised to 65°C, and the reaction was carried out with stirring for 2 hours to obtain a modified protein solution. The volume ratio of alkenyl succinic anhydride, protein solution and 1,2-epoxy octadecane was 1:100:0.5. The modified protein solution was cooled to 40°C, and PVA solution was added. The ratio of PVA solution to the original soybean protein was 1:1. The mixture was gently stirred and mixed at this temperature for 1 hour to ensure uniform mixing. The final pH value was adjusted to neutral to obtain the protein-based coating solution. Food-grade kraft paper is preheated to 50°C, and then a protein-based coating solution is applied to the surface of the food-grade kraft paper with a coating thickness of 50μm. The food-grade kraft paper is then heated to 100°C to obtain pretreated base paper. The biodegradable polymer granules were dried in a dehumidifying dryer at 70°C for 6 hours, then fed into a single-screw extruder with a melt temperature of 170°C. The granules were extruded into a film and pressed onto the surface of a pretreated base paper with a pressure of 5 N / m to obtain an oil-resistant packaging material for food contact paper.

[0024] Example 2: A preparation process for an oil-resistant packaging material for food contact paper, such as... Figure 1 As shown, it includes the following steps: S1: Preparation of itaconic acid fermentation broth Straw was soaked in a 3% (w / v) NaOH solution at 35°C for 13 hours, followed by steam explosion to obtain straw residue. High-purity water at 55°C was added to the reactor, and the straw residue was divided into three portions, accounting for 50%, 20%, and 30% of the total mass of straw residue, respectively. The straw residue accounting for 50% of the total mass of straw residue was mixed with high-purity water at 55°C at a material-to-liquid ratio of 1g:1.1mL, and the pH was adjusted to 4.9. Cellulase with 10 CBU / g calculated based on the straw residue as dry substrate was added, and enzymatic hydrolysis was carried out for 16 hours. Then, straw residue accounting for 20% of the total mass of straw residue was added, the pH was adjusted to 4.9, and cellulase with 10 CBU / g calculated based on the straw residue as dry substrate was added, and enzymatic hydrolysis was carried out for 16 hours. Finally, the remaining residue was added, and the above process was repeated. Finally, the temperature was raised to 83°C and held for 25 minutes to obtain a sugar solution. Add water to the sugar solution to adjust the concentration to 42 g / L, then add 15 g / L corn steep liquor, 3 g / L ammonium sulfate and 1 g / L magnesium sulfate heptahydrate, then adjust the pH to 2.7 with 1.1 M HCl, then heat at 123 °C for 25 min and cool to 35 °C to obtain the culture medium. Aspergillus terrestris seed culture was inoculated into the culture medium at an inoculation rate of 10% (v / v). The mixture was stirred on a shaker at 210 r / min at 35°C for 65 h. Methionine was added dropwise at a rate of 3 mL / s to a concentration of 1 g / L. Fermentation was then continued for 76 h. After fermentation, solids were removed by centrifugation and filtration. The fermentation broth was then purified with resin to obtain itaconic acid fermentation broth.

[0025] S2: Preparation of methylsuccinic acid by hydrogenation of itaconic acid The itaconic acid fermentation broth was dissolved in anhydrous ethanol and then added to a reactor. Next, 6% (by mass) of nickel skeletal catalyst was added. The air inside the reactor was purged with hydrogen, and then hydrogen was introduced again to bring the pressure inside the reactor to 8.08 × 10⁻⁶. 5 Pa, stir, heat, and after the reaction time, stop heating and wait for the pressure to drop to 1.01 × 10⁻⁶. 5 Pa, remove the reaction solution, let stand, filter to recover the catalyst, and then distill the filtrate under reduced pressure to obtain bio-based methyl succinic acid.

[0026] S3: Preparation of oil-resistant packaging materials for food contact paper Bio-based methyl succinic acid and 1,4-butanediol were added to a reactor at a molar ratio of 1:1.2. Then, 0.4% p-toluenesulfonic acid and 0.3% triphenyl phosphite were added to the reactor. Under nitrogen protection, the temperature was gradually increased to 195°C and reacted for 4 hours. Subsequently, the vacuum system was gradually turned on, and the absolute pressure of the system was steadily reduced to 5000 Pa within 45 minutes. At the same time, the temperature of the material was raised to 235°C and maintained for 1.5 hours. The vacuum degree was further increased, and the absolute pressure was reduced to 90 Pa within 30 minutes. The temperature was maintained at 245°C, and the mixture was stirred at 550 r / min for 2 hours. The product was extruded, granulated, and dried in hot air at 85°C for 7 hours to obtain biodegradable polymer granules. Soy protein isolate was dispersed in deionized water to prepare an 8% (w / w) solution. The pH of the system was adjusted to 9.5 with NaOH solution while stirring at 110 rpm, and then preheated at 55°C for 25 min to obtain the protein solution. Alkenyl succinic anhydride was added dropwise to the protein solution, and the reaction was carried out with stirring for 2.5 hours at 55°C and pH 8.5. Then, 1,2-epoxy octadecane was added to the protein solution, the pH of the reaction system was adjusted to 9.5, the temperature was raised to 70°C, and the reaction was carried out with stirring for 2.5 hours to obtain a modified protein solution. The volume ratio of alkenyl succinic anhydride, protein solution and 1,2-epoxy octadecane was 1.1:100:0.7. The modified protein solution was cooled to 45°C, and PVA solution was added. The ratio of PVA solution to the original soybean protein was 1:1. The mixture was gently stirred and mixed at this temperature for 1.5 hours to ensure uniform mixing. The final pH value was adjusted to neutral to obtain the protein-based coating solution. Food-grade kraft paper is preheated to 55°C, and then a protein-based coating solution is applied to the surface of the food-grade kraft paper with a coating thickness of 60μm. The food-grade kraft paper is then heated to 110°C to obtain pretreated base paper. The biodegradable polymer granules were dried in a dehumidifying dryer at 75°C for 6.5 hours, then fed into a single-screw extruder with a melt temperature of 180°C. The granules were extruded into a film and pressed onto the surface of a pretreated base paper at a pressure of 10 N / m to obtain an oil-resistant packaging material for food contact paper.

[0027] Example 3: A preparation process for an oil-resistant packaging material for food contact paper, such as... Figure 1 As shown, it includes the following steps: S1: Preparation of itaconic acid fermentation broth Straw was soaked in a 2-4% (w / v) NaOH solution at 40°C for 14 hours, followed by steam explosion to obtain straw residue. High-purity water at 60°C was added to the reactor, and the straw residue was divided into three portions, accounting for 50%, 30%, and 20% of the total mass of straw residue, respectively. The straw residue accounting for 50% of the total mass of straw residue was mixed with high-purity water at 60°C at a material-to-liquid ratio of 1g:1.2mL, and the pH was adjusted to 5. Cellulase with 10 CBU / g calculated based on the straw residue as dry substrate was added, and enzymatic hydrolysis was carried out for 20 hours. Then, straw residue accounting for 30% of the total mass of straw residue was added, the pH was adjusted to 5, and cellulase with 10 CBU / g calculated based on the straw residue as dry substrate was added, and enzymatic hydrolysis was carried out for 20 hours. Finally, the remaining residue was added, and the above process was repeated. Finally, the temperature was raised to 85°C and held for 30 minutes to obtain a sugar solution. Add water to the sugar solution to adjust the concentration to 44 g / L, then add 20 g / L corn steep liquor, 4 g / L ammonium sulfate and 1.5 g / L magnesium sulfate heptahydrate, then adjust the pH to 3 with 1.2 M HCl, then heat at 125 °C for 30 min and cool to 37 °C to obtain the culture medium. Aspergillus terrestris seed culture was inoculated into the culture medium at an inoculation rate of 10.2% (v / v). The mixture was stirred on a shaker at 220 r / min at 37 °C for 70 h. Methionine was added dropwise at a rate of 4 mL / s to bring the concentration to 1.5 g / L. Fermentation was then continued for another 80 h. After fermentation, the solids were removed by centrifugation and filtration. The fermentation broth was then purified with resin to obtain itaconic acid fermentation broth.

[0028] S2: Preparation of methylsuccinic acid by hydrogenation of itaconic acid The itaconic acid fermentation broth was dissolved in anhydrous ethanol and then added to a reactor. Next, 8% (by mass) of nickel skeletal catalyst was added. The air inside the reactor was purged with hydrogen, and then hydrogen was introduced again to bring the pressure inside the reactor to 8.08 × 10⁻⁶. 5 Pa, stir, heat, and after the reaction time, stop heating and wait for the pressure to drop to 1.01 × 10⁻⁶. 5 Pa, remove the reaction solution, let stand, filter to recover the catalyst, and then distill the filtrate under reduced pressure to obtain bio-based methyl succinic acid.

[0029] S3: Preparation of oil-resistant packaging materials for food contact paper Bio-based methyl succinic acid and 1,4-butanediol were added to a reactor at a molar ratio of 1:1.5. Then, 0.5% p-toluenesulfonic acid and 0.4% triphenyl phosphite were added to the reactor. Under nitrogen protection, the temperature was gradually increased to 200°C and reacted for 5 hours. Subsequently, the vacuum system was gradually turned on, and the absolute pressure of the system was steadily reduced to 5100 Pa within 60 minutes. At the same time, the temperature of the material was raised to 240°C and maintained for 2 hours. The vacuum degree was further increased, and the absolute pressure was reduced to 100 Pa within 30 minutes. The temperature was maintained at 250°C and stirred at 600 r / min for 3 hours. The product was extruded, granulated, and dried in hot air at 90°C for 8 hours to obtain biodegradable polymer granules. Soy protein isolate was dispersed in deionized water to prepare a 10% (w / w) solution. The pH of the system was adjusted to 10 with NaOH solution while stirring at 120 rpm, and then preheated at 60°C for 30 min to obtain the protein solution. Alkenyl succinic anhydride was added dropwise to the protein solution, and the reaction was carried out with stirring for 3 hours at 60°C and pH 9. Then, 1,2-epoxy octadecane was added to the protein solution, the pH of the reaction system was adjusted to 10, the temperature was raised to 75°C, and the reaction was carried out with stirring for 3 hours to obtain a modified protein solution. The volume ratio of alkenyl succinic anhydride, protein solution and 1,2-epoxy octadecane was 1.2:100:0.9. The modified protein solution was cooled to 50°C. The ratio of PVA solution to raw soybean protein was 1:1. The mixture was gently stirred and mixed at this temperature for 2 hours to ensure uniform mixing. The final pH value was adjusted to neutral to obtain the protein-based coating solution. Food-grade kraft paper is preheated to 60°C, and then a protein-based coating solution is applied to the surface of the food-grade kraft paper with a coating thickness of 70μm. The food-grade kraft paper is then heated to 120°C to obtain pretreated base paper. The biodegradable polymer granules were dried in a dehumidifying dryer at 80°C for 7 hours, then fed into a single-screw extruder with a melt temperature of 190°C. The granules were extruded into a film and pressed onto the surface of a pretreated base paper at a pressure of 15 N / m to obtain an oil-resistant packaging material for food contact paper.

[0030] Comparative Example 1: Compared with Example 1, the difference of Comparative Example 1 is that the bio-based methyl succinic acid in step S3 is replaced by industrial succinic acid, while the other steps remain unchanged. This is referred to as Comparative Example 1.

[0031] Comparative Example 2: Compared with Example 1, Comparative Example 2 differs in that the methionine in step S1 is replaced with glutamic acid by mass, while the other steps remain unchanged. It is referred to as Comparative Example 2.

[0032] Comparative Example 3: Compared with Example 1, Comparative Example 3 differs in that the 1,2-epoxyoctadecane in step S3 is replaced by an alkenyl succinic anhydride by mass, while the other steps remain unchanged. This is referred to as Comparative Example 3.

[0033] Comparative Example 4: Compared with Example 1, Comparative Example 4 differs in that the alkenyl succinic anhydride in step S3 is replaced by 1,2-epoxy octadecane by mass, while the other steps remain unchanged. This is referred to as Comparative Example 4.

[0034] The oil penetration resistance of the food contact paper oil-resistant packaging materials of Examples 1-3, Comparative Examples 1 and 3-4 was tested using the method recorded in GB / T22805.1-2008 "Determination of Grease Resistance of Paper and Paperboard". The oil penetration resistance of the packaging materials was demonstrated by the grease penetration time in an environment of 26°C and 55%RH. The results are shown in Table 1.

[0035] The conversion rate of sugar solution to itaconic acid fermentation broth in step S1 of Examples 1-3 and Comparative Example 2 was calculated. The specific calculation method was itaconic acid fermentation broth mass / sugar solution mass * 100%. The results are shown in Table 2.

[0036] The peel strength of the surface coating of the food contact paper oil-proof packaging material of Examples 1-3 and Comparative Examples 3-4 was tested using the method recorded in GB / T34444-2017 "Determination of interlayer peel strength of paper and paperboard". The results are shown in Table 3.

[0037] Table 1 (Unit: h)

[0038] Table 2 (Unit: %)

[0039] Table 3 (Unit: N / 15mm)

[0040] As can be seen from Table 1, the permeation time of Examples 1-3 increased slightly, indicating good process repeatability. The permeation time of the comparative example in which bio-based methyl succinic acid was replaced with succinic acid decreased to 24.2 h, indicating that although the polyesters of industrial succinic acid and 1,4-butanediol have similar chemical structures, the lack of side methyl branches from itaconic acid leads to a decrease in performance. The combination of 1,2-epoxyoctadecane and alkenyl succinic anhydride also has a synergistic effect on the barrier of oils.

[0041] As can be seen from Table 2, the conversion rate of Examples 1-3 is about 22.6%, while Comparative Example 2 replaces methionine with glutamic acid. Glutamic acid does not contain sulfur, which shows that methionine, as a sulfur source / methyl donor, has a significant impact on the carbon flux of itaconic acid, thus affecting the conversion rate of itaconic acid.

[0042] As shown in Table 3, the peel strength of Examples 1-3 is above 2.91 N / 15 mm, while that of Comparative Examples 3-4 is 1.45 N / 15 mm and 1.59 N / 15 mm, respectively. The peel strength test is conducted at the three-phase interface of the "degradable polymer / protein layer / paper base". After the absence of 1,2-epoxyoctadecane, the crosslinking density of the protein layer decreases, the cohesive strength decreases, and the failure surface during peeling changes from the "polyester-protein interface" to the "inside the protein layer", thus exhibiting a significant decrease in peel strength.

[0043] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims. Parts not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A preparation process for an oil-resistant packaging material for food contact paper, characterized in that, Specifically, the following steps are included: S1: Preparation of itaconic acid fermentation broth Add water, corn steep liquor, ammonium sulfate and magnesium sulfate heptahydrate to the sugar solution, then heat and cool to obtain a culture medium. Inoculate the Aspergillus terrestris seed liquid into the culture medium. After fermentation, add methionine dropwise and continue fermentation. After fermentation is completed, remove solids by centrifugation and filtration, and then purify the fermentation broth with resin to obtain itaconic acid fermentation broth. S2: Preparation of methylsuccinic acid by hydrogenation of itaconic acid The itaconic acid fermentation broth was dissolved in anhydrous ethanol and then added to a reactor. 5-8% (by mass) of nickel skeletal catalyst was then added. The air inside the reactor was purged with hydrogen, and then hydrogen was introduced again to bring the pressure inside the reactor to 8.08 × 10⁻⁶. 5 Pa, stir, heat, and after the reaction time, stop heating and wait for the pressure to drop to 1.01 × 10⁻⁶. 5 Pa, remove the reaction solution, let stand, filter to recover the catalyst, and then distill the filtrate under reduced pressure to obtain bio-based methyl succinic acid; S3: Preparation of oil-resistant packaging materials for food contact paper Bio-based methyl succinic acid and 1,4-butanediol were added to a reactor, followed by p-toluenesulfonic acid and triphenyl phosphite. Under nitrogen protection, the temperature was gradually increased for 3-5 hours. Subsequently, the reaction was carried out under vacuum with stirring. The product was extruded, granulated, and dried to obtain biodegradable polymer granules. The biodegradable polymer granules were added to a single-screw extruder and extruded into a film. The film was then pressed onto the surface of pretreated base paper with a pressure of 5-15 N / m to obtain an oil-proof packaging material for food contact paper.

2. The preparation process of the oil-resistant packaging material for food contact paper according to claim 1, characterized in that, Step S1 specifically includes the following steps: Add water to the sugar solution to adjust the concentration to 40-44 g / L, then add 10-20 g / L corn steep liquor, 2-4 g / L ammonium sulfate and 0.5-1.5 g / L magnesium sulfate heptahydrate. Then adjust the pH to 2.5-3 with 1M HCl. Then heat at 121-125℃ for 20-30 min and cool to 34-37℃ to obtain the culture medium. Inoculate the Aspergillus terreus seed culture into the culture medium at an inoculation rate of 9.8-10.2% (v / v), stir on a shaker at 200-220 r / min at 34-37℃, and ferment for 60-70 h. Then, add methionine dropwise at a rate of 3-4 mL / s to a concentration of 0.5-1.5 g / L. Fermentation continued for 72-80 hours. After fermentation, solids were removed by centrifugation and filtration, and the fermentation broth was purified with resin to obtain itaconic acid fermentation broth.

3. The preparation process of the oil-resistant packaging material for food contact paper according to claim 2, characterized in that, The preparation method of the sugar solution in step S1 specifically includes the following steps: Straw was soaked in a 2-4% (w / v) NaOH solution at 30-40℃ for 12-14 hours, followed by steam explosion to obtain straw residue. High-purity water at 50-60℃ was added to the reactor, and the straw residue was divided into three portions, accounting for 30-50%, 20-30%, and 20-50% of the total mass of straw residue, respectively. The straw residue accounting for 30-50% of the total mass was mixed with high-purity water at 50-60℃ at a ratio of 1g:(1-1.2)mL. Mix the liquid and water, adjust the pH to 4.8-5, add 10 CBU / g of cellulase (based on straw residue as dry substrate), and hydrolyze for 12-20 hours. Then add 20-30% of the total straw residue, adjust the pH to 4.8-5, and add 10 CBU / g of cellulase (based on straw residue as dry substrate) to hydrolyze for 12-20 hours. Finally, add the remaining straw residue and repeat the above process. Finally, raise the temperature to 80-85℃ and hold for 20-30 minutes to obtain the sugar solution.

4. The preparation process of the oil-resistant packaging material for food contact paper according to claim 1, characterized in that, Step S3 specifically includes the following steps: Bio-based methyl succinic acid and 1,4-butanediol were added to a reactor at a molar ratio of 1:(1-1.5). Then, 0.3-0.5% of p-toluenesulfonic acid and 0.2-0.4% of triphenyl phosphite were added to the reactor. Under nitrogen protection, the temperature was gradually raised to 190-200℃ and the reaction was carried out for 3-5 hours. Subsequently, the reaction was carried out under vacuum stepwise. Then, the mixture was stirred at 500-600 r / min for 1.5-3 hours. The product was extruded, granulated, and dried in hot air at 80-90℃ for 6-8 hours to obtain biodegradable polymer granules. The biodegradable polymer granules are dried in a dehumidifying dryer at 70-80℃ for 6-7 hours, added to a single-screw extruder, and extruded into a film. The film is then pressed onto the surface of a pretreated base paper with a pressure of 5-15 N / m to obtain an oil-proof packaging material for food contact paper.

5. The preparation process of the oil-resistant packaging material for food contact paper according to claim 4, characterized in that, The preparation of the pretreated base paper in step S3 is specifically as follows: Soy protein isolate was dispersed in deionized water to prepare a 5-10% (w / w) solution. The pH of the system was adjusted to 9-10 with NaOH solution while stirring at 100-120 rpm. The solution was then preheated at 50-60℃ for 20-30 min to obtain the protein solution. Alkenyl succinic anhydride was added dropwise to the protein solution, and the reaction was stirred continuously for 2-3 hours at 50-60℃ and pH 8-9. Then, 1,2-epoxyoctadecane was added to the protein solution, the pH of the reaction system was adjusted to 9-10, the temperature was raised to 65-75℃, and the reaction was stirred continuously for 2-3 hours under these conditions to obtain the modified protein solution. Cool the modified protein solution to 40-50℃, add PVA solution, the ratio of PVA solution to raw soybean protein is 1:1, gently stir and mix at this temperature for 1-2 hours to make it uniformly mixed, adjust the final pH value to neutral, and obtain the protein-based coating solution. Preheat the base paper to 50-60℃, then apply the protein-based coating solution to the surface of the base paper with a coating thickness of 50-70μm. Then heat the base paper to 100-120℃ to obtain the pretreated base paper.

6. The preparation process of the oil-resistant packaging material for food contact paper according to claim 5, characterized in that, The volume ratio of alkenyl succinic anhydride, protein solution and 1,2-epoxyoctadecane is (1-1.2):100:(0.5-0.9).

7. The preparation process of the oil-resistant packaging material for food contact paper according to claim 4, characterized in that, The melting temperature of a single-screw extruder is 170-190℃.

8. The preparation process of the oil-resistant packaging material for food contact paper according to claim 5, characterized in that, The base paper can be any one of food-grade kraft paper, tracing paper, or silicone paper.

9. The preparation process of the oil-resistant packaging material for food contact paper according to claim 4, characterized in that, The specific steps of the vacuum stepwise reaction in step S3 are as follows: turn on the vacuum system, reduce the absolute pressure of the system to 4900-5100 Pa within 30-60 min, and at the same time raise the material temperature to 230-240℃ and maintain it for 1-2 h. Continue to increase the vacuum degree, reduce the absolute pressure to 80-100 Pa within 30 min, maintain the temperature at 240-250℃, and stir at a speed of 500-600 r / min for 1.5-3 hours.

10. An oil-resistant packaging material for food contact paper, characterized in that, It is prepared by the preparation process of the food contact paper oil-proof packaging material according to any one of claims 1-9.

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