Preparation process of bio-based packaging plate

Abstract

The invention discloses a preparation process of a bio-based packaging plate, and relates to the field of bio-based packaging materials, and the bio-based packaging plate comprises the following raw materials by weight: 70-80 parts of polylactic acid, 15-25 parts of PBS, 10-15 parts of modified CNC, 5-7 parts of an anti-aging agent, and 2-3 parts of a flame retardant. The bio-based packaging plate is obtained by mixing bio-based polyester, namely polylactic acid, PBS, modified CNC, an anti-aging agent and a flame retardant and then performing hot press molding. The modified CNC has good biodegradability and thermal stability, the hygroscopicity is weakened, and the mechanical strength of the packaging plate is better improved; phosphite ester with high hydrolysis resistance in the anti-aging agent and phenothiazine synergistically improve the aging resistance of the packaging plate.

Description

Technical Field

[0001] The present invention relates to the field of bio-based packaging materials, and in particular to a preparation process of a bio-based packaging board. Background Art

[0002] Bio-based packaging materials, with their environmentally friendly, lightweight, and processable advantages, are seeing increasing application in food, logistics, construction, and other fields. Polylactic acid (PLA), an aliphatic bio-based polyester, can be produced through anaerobic fermentation of agricultural products such as wheat. It completely avoids petroleum-based products, making it a green and sustainable polymer and a key research target for biodegradable packaging materials. However, the poor mechanical properties of biodegradable materials like PLA limit their application.

[0003] Nanocomposite modification is considered an effective approach to improving the properties of biodegradable polymers. Cellulose nanocrystals (CNCs) are considered the most promising reinforcing filler due to their high specific surface area, high reactivity, high strength, and biodegradability. However, CNCs suffer from insufficient thermal stability and a low glass transition temperature (approximately 150-200°C). They are prone to thermal decomposition during packaging sheet processing (such as hot pressing and injection molding) or high-temperature use. Furthermore, CNCs are highly hygroscopic, negatively impacting the mechanical properties of packaging materials.

[0004] During long-term use, biodegradable materials such as PLA will be affected by aging such as oxidation, which will lead to a decrease in molecular weight and the material becoming yellow and brittle. The antioxidant capacity can be significantly improved by adding antioxidants. Phosphite antioxidants are a type of auxiliary antioxidant that decomposes hydroperoxides. However, the relative volume of the P atom in the phosphite structure is relatively large. When affected by the electron delocalization effect in the environment, it is easily hydrolyzed when in contact with nucleophilic reagents such as water. The hydrolytic stability of phosphite antioxidants is poor, which limits their application in biodegradable packaging materials such as PLA.

[0005] Therefore, suitable modification methods are needed to improve the thermal stability and hygroscopicity of cellulose nanocrystals (CNCs), enhance the hydrolytic stability of phosphite antioxidants, and apply them to bio-based packaging boards to obtain bio-based packaging boards with better mechanical properties, aging resistance and other properties. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a preparation process of a bio-based packaging board.

[0007] The purpose of the present invention can be achieved through the following technical solutions: The preparation of the bio-based packaging board comprises the following steps: Step S1, weighing 70-80 parts of polylactic acid, 15-25 parts of PBS, 10-15 parts of modified CNC, 5-7 parts of antioxidant, and 2-3 parts of flame retardant for standby use; Furthermore, the flame retardant is pyromellitic dianhydride; Step S2, stirring and mixing polylactic acid and PBS at 150-160° C. for 35-40 minutes, then adding modified CNC, antioxidant, and flame retardant and continuing to stir and mix for 1-1.5 hours to obtain a mixture, and hot-pressing the mixture to obtain a sheet-like bio-based packaging board; Furthermore, the conditions for the hot pressing molding are a temperature of 180-200° C. and a pressure of 10-20 MPa; The preparation of the modified CNC comprises the following steps: Step A1, adding microcrystalline cellulose (MCC) to a sulfuric acid solution, stirring at 40-50°C in a protective gas atmosphere for 2-2.5 hours, adding deionized water and stirring for 5-10 minutes to obtain a suspension, washing with deionized water, centrifuging, adjusting the pH of the suspension to neutral, and drying to obtain product 1; Furthermore, the ratio of microcrystalline cellulose, sulfuric acid solution, and deionized water in the suspension is 9.5-10 g: 1-1.5 mL: 20-25 mL; the mass fraction of the sulfuric acid solution is 50-60%; and the solution used to adjust the pH is a 0.1 mol / L sodium hydroxide solution. During the reaction of step A1, cellulose nanocrystals (CNC), i.e., product 1, are prepared by an acid hydrolysis process; Step A2, adding product 1 to acetone and ultrasonically dispersing for 30-35 minutes, then adding DMF and stirring at 60-65°C for 20-25 minutes, then heating to 80-85°C, adding a catalyst and stirring for 1-1.5 hours, adding anhydride and continuing to stir for 4-4.5 hours, cooling, washing with anhydrous ethanol and deionized water alternately, and drying to obtain product 2; Furthermore, the usage ratio of product 1, acetone, DMF, catalyst, and acid anhydride is 5-6 g: 30-35 mL: 35-40 mL: 0.05-0.07 g: 15-18 g; the acid anhydride is tricyclo[3.2.2.02,4]non-8-ene-6,7-dicarboxylic anhydride, and the catalyst is p-dimethylaminopyridine; During the reaction of step A2, product 1, namely cellulose nanocrystal (CNC), is modified with anhydride to obtain CNC containing a spirotricyclic ring and surface carboxylation, namely product 2; Step A3, adding product 2 to DMF, adding dichlorothionyl with stirring, and stirring at 45-50° C. for 5-5.5 hours to obtain product 3; mixing 1,4-dihydroxy-2,3-naphthalenedicarboxylic acid, pyridine, triethylamine, and dimethyl sulfoxide to obtain a mixed solution a; mixing product 3 and dimethyl sulfoxide to obtain a mixed solution b; adding the mixed solution b dropwise to the mixed solution a in an ice-water bath, raising the temperature to 45-50° C. after the addition, stirring and reacting for 9-9.5 hours, extracting, drying, and distilling to obtain modified CNC; Furthermore, the amount ratio of product 2, DMF, and dichlorothionyl is 7-8 g: 90-100 mL: 25-27 g; the amount ratio of 1,4-dihydroxy-2,3-naphthalenedicarboxylic acid, pyridine, triethylamine, and dimethyl sulfoxide in the mixed solution a is 21.5-22 g: 0.04-0.06 g: 10.5-11 g: 70-80 mL; the amount ratio of product 3 and dimethyl sulfoxide in the mixed solution b is 7.5-8.5 g: 110-115 mL; the amount ratio of the mixed solution a to the mixed solution b is 50-55 mL: 120-130 mL; During the reaction of step A3, the carboxyl group in product 2 reacts with thionyl chloride to generate product 3 containing an acyl chloride; the acyl chloride in product 3 reacts with the phenolic hydroxyl group of 1,4-dihydroxy-2,3-naphthalenedicarboxylic acid to obtain a modified CNC containing an ester group, a spirotricyclic ring, and o-naphthalenedicarboxylic acid; The preparation of the antioxidant comprises the following steps: Step B1, after pentaerythritol and toluene are mixed, phosphorus trichloride and triethylamine are added at 15-20°C, stirred for 35-40 minutes, heated to 50-55°C, stirred for 5-5.5 hours, and distilled under reduced pressure at 65-70°C to obtain product a; p-nitrobenzyl alcohol, toluene, and product a are mixed, triethylamine is added, and stirred at 35-40°C for 1-1.5 hours, then heated to 55-60°C and stirred for 6-6.5 hours, cooled, washed, and distilled under reduced pressure to obtain product b; Furthermore, the usage ratio of pentaerythritol, toluene, phosphorus trichloride, and triethylamine is 15-17 g: 200-250 mL: 42-44 g: 25-26 g; the usage ratio of p-nitrobenzyl alcohol, toluene, product a, and triethylamine is 31-33 g: 170-180 mL: 28-30 g: 20-22 g; During the reaction of step B1, pentaerythritol reacts with phosphorus trichloride to generate dibasic phosphite chloride, i.e., product a; p-nitrobenzyl alcohol reacts with the phosphite chloride of product a to generate a phosphite containing a large sterically hindered dibasic nitro group, i.e., product b; Step B2: Add product b to DMF, heat to 50-55°C, start reflux stirring, add hydrosulfite, and stir for 1-1.5 hours to obtain product c; mix epichlorohydrin, product c, tetrabutylammonium bromide, and toluene, reflux and stir at 100-110°C for 3-3.5 hours, cool, add alkali solution and stir for 5-5.5 hours to obtain product d; Furthermore, the dosage ratio of product b, DMF, and sodium hydrosulfite is 55.5-56.5 g: 210-220 mL: 40-42 g; the dosage ratio of epichlorohydrin, product c, tetrabutylammonium bromide, toluene, and alkali solution is 38-40 g: 53-55 g: 3-4 g: 160-170 mL: 40-50 mL; and the alkali solution is a sodium hydroxide solution with a mass fraction of 40-45%; During the reaction of step B2, the nitro group of product b is reduced to an amino group, namely product c; epichlorohydrin and the amino group of product c undergo ring opening and ring closing to obtain a phosphite substituted with a large steric group containing an epoxy group, namely product d; Step B3, mixing the product d, 10H-phenothiazine-2-amine, and dimethyl sulfoxide, and stirring the mixture at 80-85° C. for 12-12.5 hours to obtain an antioxidant; Furthermore, the usage ratio of product d, 10H-phenothiazine-2-amine, and dimethyl sulfoxide is 92-94 g: 43-45 g: 270-280 mL; During the reaction of step B3, the epoxy group of product d reacts with the primary amino group of 10H-phenothiazine-2-amine to obtain an antioxidant containing hydroxyl, phenothiazine, and phosphite.

[0008] Beneficial effects of the present invention: The present invention discloses a preparation process of a bio-based packaging board, wherein the bio-based packaging board is obtained by hot-pressing a mixture of bio-based polyester, i.e., polylactic acid, PBS, modified CNC, an antioxidant, and a flame retardant.

[0009] The modified CNC is obtained by introducing ester groups, spirotricyclic rings, and o-naphthalenedicarboxylic acid (O-naphthalenedicarboxylic acid) into CNC. The ester groups, similar to the PLA molecular chain structure, enhance the compatibility of the modified CNC in the matrix. The spirotricyclic rings are highly hydrophobic, reducing the hygroscopicity of the modified CNC, thereby improving its hygroscopicity. The cyano groups in O-naphthalenedicarboxylic acid (O-naphthalenedicarboxylic acid) enhance the hydrogen bond crosslinking network in the modified CNC through self-crosslinking and intermolecular crosslinking, thereby improving the thermal stability of the modified CNC. The cyano groups in O-naphthalenedicarboxylic acid can also crosslink with PLA, further improving the compatibility of the modified CNC with the matrix. In addition, the ester substituent introduced on the spirotricyclic rings after the grafting of tricyclo[3.2.2.02,4]non-8-ene-6,7-dicarboxylic anhydride onto cellulose nanocrystals also stabilizes the spirocyclic ring structure. The modified CNC exhibits good biodegradability, thermal stability, and reduced hygroscopicity, further enhancing the mechanical strength of the packaging board.

[0010] The antioxidant contains hydroxyl groups, phenothiazine, and phosphite. During the preparation of the antioxidant, the phosphorus atoms in the phosphite are replaced with sterically hindered pentaerythritol ether and phenoxy ether structures, which weaken the effects of nucleophiles such as water, enhance the hydrolysis resistance of the phosphite, and better exert its antioxidant effect of decomposing hydroperoxides. Phenothiazine can capture free radicals and inhibit the initial stage of the oxidation reaction, making it a free radical scavenging antioxidant. It works in synergistically with chain-terminating phosphite antioxidants to improve the antioxidant efficiency of the matrix in stages. The hydroxyl groups enhance hydrogen bonding between the antioxidant and PLA, thereby enhancing the dispersion of the antioxidant in the matrix. The improved hydrolysis resistance of the phosphite and phenothiazine synergistically enhance the aging resistance of the packaging board. DETAILED DESCRIPTION

[0011] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0012] Example 1 A modified CNC, the preparation of which comprises the following steps: Step A1. Add microcrystalline cellulose (MCC) (supplier: Merck) to a sulfuric acid solution, stir at 40°C for 2 hours under a nitrogen atmosphere, add deionized water and stir for 5 minutes to obtain a suspension, wash three times with deionized water, centrifuge, adjust the pH to neutral, and dry to obtain product 1. The ratio of microcrystalline cellulose, sulfuric acid solution, and deionized water in the suspension is 9.5 g:1 mL:20 mL; the mass fraction of the sulfuric acid solution is 50%; and the solution used for pH adjustment is 0.1 mol / L sodium hydroxide solution. Step A2, adding product 1 to acetone and ultrasonically dispersing for 30 minutes, then adding DMF and stirring at 60°C for 20 minutes, then heating to 80°C, adding p-dimethylaminopyridine and stirring for 1 hour, adding tricyclo[3.2.2.02,4]non-8-ene-6,7-dicarboxylic anhydride and continuing to stir for 4 hours, cooling, washing with anhydrous ethanol and deionized water alternately 6 times, and drying to obtain product 2; the usage ratio of product 1, acetone, DMF, p-dimethylaminopyridine, and tricyclo[3.2.2.02,4]non-8-ene-6,7-dicarboxylic anhydride is 5g:30mL:35mL:0.05g:15g; Step A3, product 2 was added to DMF, and dichlorothionyl was added under stirring, and stirred at 45 ° C for 5 hours to obtain product 3; 1,4-dihydroxy-2,3-naphthalenedicarboxylic acid, pyridine, triethylamine, and dimethyl sulfoxide were mixed to obtain a mixed solution a; product 3 and dimethyl sulfoxide were mixed to obtain a mixed solution b; mixed solution b was added dropwise to the mixed solution a under an ice-water bath, and after the addition, the temperature was raised to 45 ° C, stirred for reaction for 9 hours, extracted, dried, and distilled to obtain modified C NC; the dosage ratio of product 2, DMF, and dichlorothionyl is 7g:90mL:25g; the dosage ratio of 1,4-dihydroxy-2,3-naphthalenedicarboxylic acid, pyridine, triethylamine, and dimethyl sulfoxide in mixed solution a is 21.5g:0.04g:10.5g:70mL; the dosage ratio of product 3 and dimethyl sulfoxide in mixed solution b is 7.5g:110mL; the dosage ratio of mixed solution a and mixed solution b is 50mL:120mL.

[0013] Example 2 A modified CNC, the preparation of which comprises the following steps: Step A1. Add microcrystalline cellulose (MCC) (supplier: Merck) to a sulfuric acid solution, stir at 5°C under a nitrogen atmosphere for 2.3 hours, add deionized water and stir for 8 minutes to obtain a suspension, wash three times with deionized water, centrifuge, adjust the pH to neutral, and dry to obtain product 1. The ratio of microcrystalline cellulose, sulfuric acid solution, and deionized water in the suspension is 9.8 g:1.3 mL:23 mL; the mass fraction of the sulfuric acid solution is 55%; and the solution used for pH adjustment is 0.1 mol / L sodium hydroxide solution. Step A2, product 1 was added to acetone and ultrasonically dispersed for 33 minutes, then DMF was added and stirred at 63°C for 23 minutes, then the temperature was raised to 83°C, p-dimethylaminopyridine was added and stirred for 1.3 hours, tricyclo[3.2.2.02,4]non-8-ene-6,7-dicarboxylic anhydride was added and stirring was continued for 4.3 hours, and after cooling, the mixture was washed alternately with anhydrous ethanol and deionized water, and dried to obtain product 2; the dosage ratio of product 1, acetone, DMF, p-dimethylaminopyridine, and tricyclo[3.2.2.02,4]non-8-ene-6,7-dicarboxylic anhydride was 5.5 g:33 mL:38 mL:0.06 g:16.5 g; Step A3, product 2 was added to DMF, and dichlorothionyl was added under stirring, and the mixture was stirred at 48 ° C for 5.3 hours to obtain product 3; 1,4-dihydroxy-2,3-naphthalenedicarboxylic acid, pyridine, triethylamine, and dimethyl sulfoxide were mixed to obtain a mixture a; product 3 and dimethyl sulfoxide were mixed to obtain a mixture b; the mixture b was added dropwise to the mixture a in an ice-water bath, and after the addition, the temperature was raised to 48 ° C, and the reaction was stirred for 9.3 hours, and the modified product was extracted, dried, and distilled to obtain the modified product. CNC; the dosage ratio of product 2, DMF, and dichlorothionyl is 7.5 g:95 mL:26 g; the dosage ratio of 1,4-dihydroxy-2,3-naphthalenedicarboxylic acid, pyridine, triethylamine, and dimethyl sulfoxide in mixed solution a is 21.8 g:0.05 g:10.8 g:75 mL; the dosage ratio of product 3 and dimethyl sulfoxide in mixed solution b is 8.0 g:113 mL; the dosage ratio of mixed solution a and mixed solution b is 53 mL:125 mL.

[0014] Example 3 A modified CNC, the preparation of which comprises the following steps: Step A1. Add microcrystalline cellulose (MCC) (supplier: Merck) to a sulfuric acid solution, stir at 50°C for 2.5 hours under a nitrogen atmosphere, add deionized water and stir for 10 minutes to obtain a suspension. Wash with deionized water, centrifuge, adjust the pH of the suspension to neutral, and dry to obtain product 1. The ratio of microcrystalline cellulose, sulfuric acid solution, and deionized water in the suspension is 10 g:1.5 mL:25 mL; the mass fraction of the sulfuric acid solution is 60%; and the solution used for pH adjustment is 0.1 mol / L sodium hydroxide solution. Step A2: Product 1 was added to acetone and ultrasonically dispersed for 35 minutes. DMF was then added and stirred at 65°C for 25 minutes. The temperature was then raised to 85°C, p-dimethylaminopyridine was added and stirred for 1.5 hours, tricyclo[3.2.2.02,4]non-8-ene-6,7-dicarboxylic anhydride was added and stirring was continued for 4.5 hours. After cooling, the mixture was washed alternately with anhydrous ethanol and deionized water, and dried to obtain product 2. The usage ratio of product 1, acetone, DMF, p-dimethylaminopyridine, and acid anhydride was 6 g:35 mL:40 mL:0.07 g:18 g. Step A3, product 2 was added to DMF, and dichlorothionyl was added under stirring, and stirred at 50 ° C for 5.5 hours to obtain product 3; 1,4-dihydroxy-2,3-naphthalenedicarboxylic acid, pyridine, triethylamine, and dimethyl sulfoxide were mixed to obtain a mixture a; product 3 and dimethyl sulfoxide were mixed to obtain a mixture b; the mixture b was added dropwise to the mixture a under an ice-water bath, and after the addition, the temperature was raised to 50 ° C, and the reaction was stirred for 9.5 hours, and then extracted, dried, and distilled to obtain Modified CNC; the dosage ratio of product 2, DMF, and dichlorothionite is 8 g:100 mL:27 g; the dosage ratio of 1,4-dihydroxy-2,3-naphthalenedicarboxylic acid, pyridine, triethylamine, and dimethyl sulfoxide in mixed solution a is 22 g:0.06 g:11 g:80 mL; the dosage ratio of product 3 and dimethyl sulfoxide in mixed solution b is 8.5 g:115 mL; the dosage ratio of mixed solution a and mixed solution b is 55 mL:130 mL.

[0015] Example 4 An antioxidant, the preparation of which comprises the following steps: Step B1, after pentaerythritol and toluene are mixed, phosphorus trichloride and triethylamine are added at 15°C, stirred for 35 minutes, heated to 50°C, stirred for 5 hours, and distilled under reduced pressure at 65°C to obtain product a; p-nitrobenzyl alcohol, toluene, and product a are mixed, triethylamine is added, and stirred at 35°C for 1 hour, then heated to 55°C and stirred for 6 hours, cooled, washed, and distilled under reduced pressure to obtain product b; the amount ratio of pentaerythritol, toluene, phosphorus trichloride, and triethylamine is 15g:200mL:42g:25g; the amount ratio of p-nitrobenzyl alcohol, toluene, product a, and triethylamine is 31g:170mL:28g:20g; Step B2, adding product b to DMF, heating to 50 ° C, turning on reflux stirring and adding sodium hypochlorite, stirring and reacting for 1 hour to obtain product c; mixing epichlorohydrin, product c, tetrabutylammonium bromide, and toluene, reflux stirring and reacting at 100 ° C for 3 hours, cooling, adding alkali solution and stirring for 5 hours to obtain product d; the amount ratio of product b, DMF, and sodium hypochlorite is 55.5g:210mL:40g; the amount ratio of epichlorohydrin, product c, tetrabutylammonium bromide, toluene, and alkali solution is 38g:53g:3g:160mL:40mL; the alkali solution is a sodium hydroxide solution with a mass fraction of 40%; Step B3: Mix product d, 10H-phenothiazine-2-amine, and dimethyl sulfoxide, and stir the mixture at 80°C for 12 hours to obtain an antioxidant; the dosage ratio of product d, 10H-phenothiazine-2-amine, and dimethyl sulfoxide is 92 g:43 g:270 mL.

[0016] Example 5 An antioxidant, the preparation of which comprises the following steps: Step B1, after pentaerythritol and toluene are mixed, phosphorus trichloride and triethylamine are added at 17°C, stirred for 37 minutes, heated to 53°C, stirred for 5.3 hours, and distilled under reduced pressure at 68°C to obtain product a; p-nitrobenzyl alcohol, toluene, and product a are mixed, triethylamine is added, and stirred at 38°C for 1.3 hours, then heated to 58°C and stirred for 6.3 hours, cooled, washed, and distilled under reduced pressure to obtain product b; the amount ratio of pentaerythritol, toluene, phosphorus trichloride, and triethylamine is 16g:220mL:43g:25.5g; the amount ratio of p-nitrobenzyl alcohol, toluene, product a, and triethylamine is 32g:175mL:29g:21g; Step B2, product b was added to DMF, the temperature was raised to 53 ° C, reflux stirring was started, and sodium hydroxide was added, and the reaction was stirred for 1.3 hours to obtain product c; epichlorohydrin, product c, tetrabutylammonium bromide, and toluene were mixed, refluxed and stirred at 105 ° C for 3.3 hours, and after cooling, alkali solution was added and stirred for 5.3 hours to obtain product d; the amount ratio of product b, DMF, and sodium hydroxide was 56.0 g:215 mL:41 g; the amount ratio of epichlorohydrin, product c, tetrabutylammonium bromide, toluene, and alkali solution was 39 g:54 g:3.5 g:165 mL:45 mL; the alkali solution was a sodium hydroxide solution with a mass fraction of 43%; Step B3: Mix product d, 10H-phenothiazine-2-amine, and dimethyl sulfoxide, and stir the mixture at 83°C for 12.3 hours to obtain an antioxidant; the dosage ratio of product d, 10H-phenothiazine-2-amine, and dimethyl sulfoxide is 93 g:44 g:275 mL.

[0017] Example 6 An antioxidant, the preparation of which comprises the following steps: Step B1, after pentaerythritol and toluene are mixed, phosphorus trichloride and triethylamine are added at 19°C, stirred for 40 minutes, heated to 55°C, stirred for 5.5 hours, and distilled under reduced pressure at 70°C to obtain product a; p-nitrobenzyl alcohol, toluene, and product a are mixed, triethylamine is added, and stirred at 40°C for 1.5 hours, then heated to 60°C and stirred for 6.5 hours, cooled, washed, and distilled under reduced pressure to obtain product b; the amount ratio of pentaerythritol, toluene, phosphorus trichloride, and triethylamine is 17g:250mL:44g:26g; the amount ratio of p-nitrobenzyl alcohol, toluene, product a, and triethylamine is 33g:180mL:30g:22g; Step B2, adding product b to DMF, heating to 55 ° C, turning on reflux stirring and adding sodium hypochlorite, stirring and reacting for 1.5 hours to obtain product c; mixing epichlorohydrin, product c, tetrabutylammonium bromide, and toluene, reflux stirring and reacting at 110 ° C for 3.5 hours, cooling, adding alkali solution and stirring for 5.5 hours to obtain product d; the amount ratio of product b, DMF, and sodium hypochlorite is 56.5g:220mL:42g; the amount ratio of epichlorohydrin, product c, tetrabutylammonium bromide, toluene, and alkali solution is 40g:55g:4g:170mL:50mL; the alkali solution is a sodium hydroxide solution with a mass fraction of 45%; Step B3: Mix product d, 10H-phenothiazine-2-amine, and dimethyl sulfoxide, and stir the mixture at 85°C for 12.5 hours to obtain an antioxidant; the dosage ratio of product d, 10H-phenothiazine-2-amine, and dimethyl sulfoxide is 94 g:45 g:280 mL.

[0018] Example 7 A bio-based packaging board, the preparation of which comprises the following steps: Step S1, weighing 70 parts of polylactic acid (supplier: Anhui Fengyuan Biotechnology Co., Ltd.), 15 parts of PBS (supplier: Jinan Quanxing New Materials Co., Ltd.), 10 parts of modified CNC, 5 parts of antioxidant, and 2 parts of flame retardant for standby use; the flame retardant is pyromellitic dianhydride; Step S2: polylactic acid and PBS are stirred and mixed at 150° C. for 35 minutes, and then the modified CNC obtained in Example 1, the antioxidant obtained in Example 4, and pyromellitic dianhydride are added and stirred and mixed for 1 hour to obtain a mixture, and the mixture is hot-pressed to obtain a sheet-like bio-based packaging board; the hot-pressing conditions are a temperature of 180° C. and a pressure of 10 MPa.

[0019] Example 8 A bio-based packaging board, the preparation of which comprises the following steps: Step S1, weighing 75 parts of polylactic acid (supplier: Anhui Fengyuan Biotechnology Co., Ltd.), 20 parts of PBS (supplier: Jinan Quanxing New Materials Co., Ltd.), 13 parts of modified CNC, 6 parts of antioxidant, and 2.5 parts of flame retardant for standby use; the flame retardant is pyromellitic dianhydride; Step S2: polylactic acid and PBS are stirred and mixed at 155° C. for 38 minutes, and then the modified CNC obtained in Example 2, the antioxidant obtained in Example 5, and pyromellitic dianhydride are added and stirred and mixed for 1.3 hours to obtain a mixture, and the mixture is hot-pressed to obtain a sheet-like bio-based packaging board; the hot-pressing conditions are a temperature of 190° C. and a pressure of 15 MPa.

[0020] Example 9 A bio-based packaging board, the preparation of which comprises the following steps: Step S1, weighing 80 parts of polylactic acid (supplier: Anhui Fengyuan Biotechnology Co., Ltd.), 25 parts of PBS (supplier: Jinan Quanxing New Materials Co., Ltd.), 15 parts of modified CNC, 7 parts of antioxidant, and 3 parts of flame retardant for standby use; the flame retardant is pyromellitic dianhydride; Step S2: polylactic acid and PBS are stirred and mixed at 160° C. for 40 minutes, and then the modified CNC obtained in Example 3, the antioxidant obtained in Example 6, and pyromellitic dianhydride are added and stirred and mixed for 1.5 hours to obtain a mixture, and the mixture is hot-pressed to obtain a sheet-like bio-based packaging board; the hot-pressing conditions are a temperature of 200° C. and a pressure of 20 MPa.

[0021] Comparative Example 1 Compared with Example 9, the tricyclo[3.2.2.02,4]non-8-ene-6,7-dicarboxylic anhydride in the preparation process of modified cellulose nanocrystals was replaced with 4-methylphthalic anhydride, and the rest was exactly the same as Example 9 to prepare a bio-based packaging board.

[0022] Comparative Example 2 Compared with Example 9, the 1,4-dihydroxy-2,3-naphthalenedicononitrile in the preparation process of modified cellulose nanocrystals was replaced with 4,5-dihydroxy-1,2-benzenedicononitrile, and the rest was exactly the same as Example 9 to prepare a bio-based packaging board.

[0023] Comparative Example 3 Compared with Example 9, the product a in the preparation process of the antioxidant was replaced with a-chloromethyl acrylate, and the rest was exactly the same as Example 9 to prepare a bio-based packaging board.

[0024] Comparative Example 4 Compared with Example 9, the 10H-phenothiazine-2-amine in the preparation process of the antioxidant was replaced with p-aminodiphenylamine, and the rest was exactly the same as Example 9 to prepare a bio-based packaging board.

[0025] The bio-based packaging board prepared by the present invention is further tested for its effectiveness, and the test results are described below.

[0026] The obtained bio-based packaging board was made into standard specimens according to ASTM-D638-22. The tensile strength and elongation at break were tested using a universal tensile machine at a tensile speed of 50 mm / min. The average value of 5 specimens was tested. The obtained bio-based packaging board was made into standard impact specimens with a V-notch according to GB / T1043.1-2008. After being kept at room temperature for 24 hours, the notched impact strength was tested using an impact tester at a test temperature of 25°C. The average value of 10 standard impact specimens was tested. Water immersion treatment: The obtained bio-based packaging board was immersed in deionized water for 3 days and then dried. The tensile strength retention rate after water immersion was tested according to ASTM-D638-22; Water immersion + aging treatment: The obtained bio-based packaging board was immersed in deionized water for 3 days and then dried. 2 Treat for 360 hours under the conditions of , and test the notched impact strength; The results are recorded in Table 1; Table 1: Test results

[0027] According to the data in Table 1, the bio-based packaging board of the present invention has excellent mechanical strength and aging resistance. Comparison of Example 9 with Comparative Example 1 shows that replacing tricyclo[3.2.2.02,4]non-8-ene-6,7-dicarboxylic anhydride with 4-methylphthalic anhydride during the preparation of modified cellulose nanocrystals reduces the hydrophobicity of the benzene ring in 4-methylphthalic anhydride compared to the spirotricyclic ring in tricyclo[3.2.2.02,4]non-8-ene-6,7-dicarboxylic anhydride, enhancing the hygroscopicity of the cellulose nanocrystals. The tensile strength of the packaging board decreases significantly after water immersion, and the notched impact strength decreases somewhat after water immersion and aging. Comparison of Example 9 with Comparative Example 2 shows that when 1,4-dihydroxy-2,3-naphthalenedicononitrile in the preparation process of modified cellulose nanocrystals is replaced with 4,5-dihydroxy-1,2-benzenedicononitrile, the thermal stability of 4,5-dihydroxy-1,2-benzenedicononitrile is weakened compared to 1,4-dihydroxy-2,3-naphthalenedicononitrile. The tensile strength and elongation at break of the packaging board obtained by hot pressing are reduced, and the tensile strength of the packaging board after water immersion is reduced more. The notched impact strength and the notched impact strength after water immersion and aging treatment are reduced. Comparison of Example 9 with Comparative Example 3 shows that when product a in the preparation process of the antioxidant is replaced with a-chloromethyl acrylate, the steric hindrance of the phosphite substituent is reduced and the hydrolytic stability is weakened, resulting in a decrease in the tensile strength after water immersion and a decrease in the notched impact strength after water immersion and aging treatment. Comparison of Example 9 with Comparative Example 4 shows that when the product e in the antioxidant preparation process is replaced with p-aminodiphenylamine, the hydrophobicity of diphenylamine compared to phenothiazine decreases, and the synergistic antioxidant activity with phosphite also decreases, resulting in a decrease in the tensile strength after water immersion and a greater decrease in the notched impact strength after water immersion and aging treatment.

[0028] The above content is merely an example and explanation of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A process for preparing a bio-based packaging board, characterized by: The steps include: Step S1, weighing 70-80 parts of polylactic acid, 15-25 parts of PBS, 10-15 parts of modified CNC, 5-7 parts of antioxidant, and 2-3 parts of flame retardant for standby use; Step S2: After mixing polylactic acid and PBS, modified CNC, an antioxidant, and a flame retardant are added and the mixture is continued to be mixed to obtain a mixture, and the mixture is hot-pressed to obtain a sheet-like bio-based packaging board.

2. The process for preparing a bio-based packaging board according to claim 1, characterized in that: The flame retardant is pyromellitic dianhydride; and the conditions for the hot pressing molding are a temperature of 180-200° C. and a pressure of 10-20 MPa.

3. The process for preparing a bio-based packaging board according to claim 1, characterized in that: The preparation of the modified CNC comprises the following steps: Step A1, adding microcrystalline cellulose to a sulfuric acid solution, stirring under a protective gas atmosphere, adding deionized water and stirring to obtain a suspension, and post-treating to obtain product 1; Step A2, adding product 1 to acetone for ultrasonic dispersion, then adding DMF with stirring, then heating, adding a catalyst and anhydride, reacting and post-processing to obtain product 2; Step A3: Product 2, DMF, and dichlorothionyl are mixed and stirred to obtain product 3; 1,4-dihydroxy-2,3-naphthalenedicarboxylic acid, pyridine, triethylamine, and dimethyl sulfoxide are mixed to obtain a mixed solution a; product 3 and dimethyl sulfoxide are mixed to obtain a mixed solution b; mixed solution b is added dropwise to mixed solution a in an ice-water bath, reacted, and post-treated to obtain modified CNC.

4. The process for preparing a bio-based packaging board according to claim 3, characterized in that: In step A1, the ratio of microcrystalline cellulose, sulfuric acid solution, and deionized water in the suspension is 9.5-10 g: 1-1.5 mL: 20-25 mL; the mass fraction of the sulfuric acid solution is 50-60%; and the solution used for adjusting the pH in the post-treatment is a 0.1 mol / L sodium hydroxide solution.

5. The process for preparing a bio-based packaging board according to claim 3, characterized in that: In step A2, the usage ratio of product 1, acetone, DMF, catalyst, and acid anhydride is 5-6 g: 30-35 mL: 35-40 mL: 0.05-0.07 g: 15-18 g; the acid anhydride is tricyclo[3.2.2.02,4]non-8-ene-6,7-dicarboxylic anhydride, and the catalyst is p-dimethylaminopyridine.

6. The process for preparing a bio-based packaging board according to claim 3, characterized in that: In step A3, the amount ratio of product 2, DMF, and dichlorothionyl is 7-8 g: 90-100 mL: 25-27 g; the amount ratio of 1,4-dihydroxy-2,3-naphthalenedicarboxylic acid, pyridine, triethylamine, and dimethyl sulfoxide in the mixed solution a is 21.5-22 g: 0.04-0.06 g: 10.5-11 g: 70-80 mL; the amount ratio of product 3 and dimethyl sulfoxide in the mixed solution b is 7.5-8.5 g: 110-115 mL; the amount ratio of the mixed solution a and the mixed solution b is 50-55 mL: 120-130 mL.

7. The process for preparing a bio-based packaging board according to claim 1, characterized in that: The preparation of the antioxidant comprises the following steps: Step B1, pentaerythritol and toluene are mixed, phosphorus trichloride and triethylamine are added, and the mixture is stirred and heated to obtain product a; p-nitrobenzyl alcohol, toluene, and product a are mixed, triethylamine is added, and the mixture is heated to obtain product b; Step B2, adding product b to DMF, heating and reflux stirring, adding hydrosulfite, and reacting to obtain product c; mixing epichlorohydrin, product c, tetrabutylammonium bromide, and toluene, reacting and cooling, and then adding alkali solution to react to obtain product d; Step B3: mixing the product d, 10H-phenothiazine-2-amine and dimethyl sulfoxide, and reacting them to obtain an antioxidant.

8. The process for preparing a bio-based packaging board according to claim 7, characterized in that: In step B1, the usage ratio of pentaerythritol, toluene, phosphorus trichloride, and triethylamine is 15-17 g: 200-250 mL: 28-30 g: 40.5-41 g; the usage ratio of p-nitrobenzyl alcohol, toluene, product a, and triethylamine is 31-33 g: 170-180 mL: 28-30 g: 20-22 g.

9. The process for preparing a bio-based packaging board according to claim 7, characterized in that: In step B2, the amount ratio of product b, DMF, and hydrosulfite is 55.5-56.5g:210-220mL:40-42g; the amount ratio of epichlorohydrin, product c, tetrabutylammonium bromide, toluene, and alkali solution is 38-40g:53-55g:3-4g:160-170mL:40-50mL; and the alkali solution is a sodium hydroxide solution with a mass fraction of 40-45%.

10. The process for preparing a bio-based packaging board according to claim 7, characterized in that: In step B3, the usage ratio of product d, 10H-phenothiazine-2-amine, and dimethyl sulfoxide is 92-94 g: 43-45 g: 270-280 mL.

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