A method for preparing a polylactic acid composite paper

Abstract

This invention relates to the field of paper technology and discloses a method for preparing polylactic acid (PLA) composite paper. The invention involves extruding fluorinated PLA, hot-pressing it into a film, and then hot-pressing it onto the surface of paper to form a PLA composite paper-plastic material with excellent mechanical properties, showing significant improvements in tensile strength and elongation at break. The hydroxyl groups in the fluorinated PLA film, as well as the fluorinated groups containing low surface energy, interact with the cellulose hydroxyl groups in the paper, causing the hydrophilic groups of the PLA to bond inwards with the paper, while the low surface energy fluorinated segments face outwards. This forms a hydrophobic and oleophobic layer on the paper surface, significantly improving the paper's oil resistance and water contact angle, exhibiting excellent water and oil repellency.

Description

Technical Field

[0001] This invention relates to the field of paper technology, specifically to a method for preparing polylactic acid composite paper. Background Technology

[0002] Combining paper with polymer plastics yields high-performance paper-plastic composites, widely used in packaging, printing, and other fields. Improving the mechanical strength, water and oil repellency, and other properties of paper-plastic composites is of great significance. Common polymer plastics used in paper-plastic composites include polyethylene, polypropylene, and polylactic acid. Coating the paper surface with oil-repellent modifiers can enhance the paper's hydrophobic and oil-repellent properties.

[0003] Polylactic acid (PLA) is simple to prepare, non-toxic, environmentally friendly, biodegradable, and widely used. Patent application CN117947656A discloses a biodegradable film paper with good waterproof and oil-resistant properties, obtained by using a film-forming agent, cellulose derivatives, and glycerin as an oil-resistant adhesive, and PLA and dichloromethane as a waterproof adhesive. However, this patent does not significantly improve the tensile strength, elongation at break, and other mechanical properties of the paper. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a waterproof and oil-resistant polylactic acid composite paper.

[0005] Technical solution: A method for preparing polylactic acid composite paper:

[0006] (1) Add the double-epoxy polylactic acid to the solvent, stir to dissolve, then add 2,2'-bis(trifluoromethyl)diaminobiphenyl, stir to react, reflux during the reaction, add ethanol to the solution to precipitate the precipitate, filter, wash with ethanol, and dry to obtain fluorinated polylactic acid.

[0007] (2) Fluorinated polylactic acid and plasticizer are added to a twin-screw extruder, extruded, granulated, and then the granules are hot-pressed into a film by a hot press to obtain a fluorinated polylactic acid film.

[0008] (3) Pass the fluorinated polylactic acid film into a hot press and hot press the paper surface to obtain polylactic acid composite paper.

[0009] Preferably, the solvent is dichloromethane, trichloromethane, or toluene.

[0010] Preferably, in (1), the mass of 2,2'-bis(trifluoromethyl)diaminobiphenyl is 0.6-0.9% of the mass of the di-terminated epoxy polylactic acid.

[0011] Preferably, the reaction in (1) is carried out at 40-90℃ for 12-36h.

[0012] Preferably, the plasticizer in (2) is triphenyl phosphite, poly(1,2-propanediol adipate) or triacetin.

[0013] Preferably, (2) the temperature of the first to fifth stages of the twin-screw extruder is 145-180℃ and the screw speed is 150-200r / min; the temperature of the hot press is 175-180℃, the pressure is 10-15MPa, and the time is 10-20min.

[0014] Preferably, (3) the temperature during hot pressing is 150-160℃, the pressure is 10-15MPa, and the time is 2-5min.

[0015] Preferably, the preparation method of polylactic acid with two epoxy groups is as follows: polylactic acid with a carboxyl group is added to thionyl chloride, and an acyl chloride reaction is carried out at 60-70°C for 3-5 hours under a nitrogen atmosphere. The product is concentrated under reduced pressure and added to dichloromethane. Glycidyl chloride and triethylamine are added, and an esterification reaction is carried out at 20-25°C for 18-24 hours. Ethanol is added to the solution to precipitate the precipitate. After filtration, the precipitate is washed with ethanol and dried to obtain polylactic acid with two epoxy groups.

[0016] Preferably, the mass percentages of glycidol and triethylamine are 0.3-0.4% and 0.5-0.8% of the mass of carboxyl-terminated polylactic acid, respectively.

[0017] Technical Effects: This invention utilizes the reaction of carboxyl-terminated polylactic acid with thionyl chloride and glycidyl chloride to obtain bi-epoxy-terminated polylactic acid, which then undergoes a ring-opening polymerization reaction with the amino group of 2,2'-di(trifluoromethyl)diaminobiphenyl to obtain fluorinated polylactic acid. After extrusion and hot pressing, a fluorinated polylactic acid film is obtained, which is then hot-pressed onto the surface of paper to form a polylactic acid composite paper-plastic composite material with excellent mechanical properties, showing significant improvement in tensile strength and elongation at break.

[0018] The fluorinated polylactic acid film of the present invention contains hydroxyl groups and fluorinated groups with low surface energy. The hydroxyl groups interact with the cellulose hydroxyl groups in the paper, causing the hydrophilic groups of polylactic acid to bond inward with the paper, and the fluorinated low surface energy segments to face outward, thereby forming a hydrophobic and oleophobic layer on the paper surface, which significantly improves the oil resistance and water contact angle of the paper and exhibits excellent waterproof and oil-proof performance. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] 30g of dried and dehydrated lactic acid was added to a flask and reacted at 100℃ for 2 hours under 0.098 MPa, followed by 2 hours at 120℃. Then, 1.75g ​​of succinic anhydride and 0.15g of stannous octoate were added, and the reactions were carried out sequentially at 140℃ for 2 hours, 160℃ for 2 hours, and 170℃ for 2 hours. After cooling, the product was discharged to obtain carboxyl-terminated polylactic acid. The structural formula is:

[0021]

[0022] Example 1

[0023] (1) 50g of carboxyl-terminated polylactic acid was added to 500mL of thionyl chloride. The acyl chloride reaction was carried out at 60℃ for 5h under a nitrogen atmosphere. The product was concentrated under reduced pressure and added to 700mL of dichloromethane, along with 0.18g of glycidyl and 0.4g of triethylamine. Esterification was carried out at 20℃ for 24h. Ethanol was added to the solution to precipitate the precipitate. After filtration, the precipitate was washed with ethanol and dried to obtain di-epoxy-terminated polylactic acid. The reaction formula is:

[0024]

[0025] (2) 50g of di-epoxy polylactic acid was added to chloroform solvent and stirred until dissolved. Then, 0.3g of 2,2'-bis(trifluoromethyl)diaminobiphenyl was added, and the mixture was stirred at 60℃ for 24h. During the reaction, the mixture was refluxed, and ethanol was added to the solution to precipitate the precipitate. After filtration, the precipitate was washed with ethanol and dried to obtain fluorinated polylactic acid. The reaction formula is:

[0026]

[0027] (3) Fluorinated polylactic acid and plasticizer triphenyl phosphite are added to a twin-screw extruder. The temperatures of sections 1-5 are 145℃, 170℃, 180℃, 175℃ and 175℃ respectively. The screw speed is 150r / min. The material is extruded and granulated. Then the granules are hot-pressed into a film by a hot press. The temperature is controlled at 180℃, the pressure is 10MPa and the time is 20min to obtain a fluorinated polylactic acid film.

[0028] (4) Pass the fluorinated polylactic acid film into a hot press and hot press the paper surface to composite it. Control the temperature at 155℃, the pressure at 10MPa, and the time at 5min to obtain polylactic acid composite paper.

[0029] Example 2

[0030] (1) 50g of carboxyl-terminated polylactic acid was added to 600mL of thionyl chloride and acyl chloride reaction was carried out at 70℃ for 3h under nitrogen atmosphere. The product was concentrated under reduced pressure and added to 800mL of dichloromethane. 0.2g of glycidyl and 0.4g of triethylamine were added and esterification reaction was carried out at 20℃ for 24h. Ethanol was added to the solution to precipitate the precipitate. After filtration, the precipitate was washed with ethanol and dried to obtain double-epoxy-terminated polylactic acid.

[0031] (2) Add 50g of dichloromethane solvent to dichloromethane, stir to dissolve, then add 0.45g of 2,2'-bis(trifluoromethyl)diaminobiphenyl, stir at 40℃ for 36h, reflux during reaction, add ethanol to the solution to precipitate, filter, wash with ethanol, dry to obtain fluorinated polylactic acid.

[0032] (3) Fluorinated polylactic acid and plasticizer triacetin are added to a twin-screw extruder. The temperatures of sections 1-5 are 145℃, 170℃, 180℃, 175℃ and 175℃ respectively. The screw speed is 200r / min. The material is extruded and granulated. Then the granules are hot-pressed into a film by a hot press. The temperature is controlled at 175℃, the pressure is 15MPa and the time is 10min to obtain a fluorinated polylactic acid film.

[0033] (4) Pass the fluorinated polylactic acid film into a hot press and hot press the paper surface to composite it. The temperature is controlled at 160℃, the pressure is 15MPa, and the time is 2min to obtain polylactic acid composite paper.

[0034] Example 3

[0035] (1) 50g of carboxyl-terminated polylactic acid was added to 600mL of thionyl chloride and acyl chloride reaction was carried out at 60℃ for 4h under nitrogen atmosphere. The product was concentrated under reduced pressure and added to 600mL of dichloromethane. 0.15g of glycidyl and 0.25g of triethylamine were added and esterification reaction was carried out at 20℃ for 24h. Ethanol was added to the solution to precipitate the precipitate. After filtration, the precipitate was washed with ethanol and dried to obtain double-epoxy-terminated polylactic acid.

[0036] (2) Add 50g of double-epoxy polylactic acid to toluene solvent, stir to dissolve, then add 0.38g of 2,2'-bis(trifluoromethyl)diaminobiphenyl, stir and react at 90℃ for 12h, add ethanol to the solution to precipitate the precipitate, filter, wash with ethanol, and dry to obtain fluorinated polylactic acid.

[0037] (3) Fluorinated polylactic acid and plasticizer triphenyl phosphite are added to a twin-screw extruder. The temperatures of sections 1-5 are 145℃, 170℃, 180℃, 175℃ and 175℃ respectively. The screw speed is 200r / min. The material is extruded and granulated. Then the granules are hot-pressed into a film by a hot press. The temperature is controlled at 180℃, the pressure is 15MPa and the time is 10min to obtain a fluorinated polylactic acid film.

[0038] (4) Pass the fluorinated polylactic acid film into a hot press and hot press the paper surface to composite it. The temperature is controlled at 160℃, the pressure is 10MPa, and the time is 5min to obtain polylactic acid composite paper.

[0039] Example 4

[0040] (1) Add 50g of carboxyl-terminated polylactic acid to 500mL of thionyl chloride and carry out acyl chloride reaction at 65℃ for 3h under nitrogen atmosphere. Concentrate the product under reduced pressure and add it to 600mL of dichloromethane. Add 0.15g of glycidyl and 0.25g of triethylamine and carry out esterification reaction at 25℃ for 18h. Add ethanol to the solution to precipitate the precipitate. After filtration, wash with ethanol and dry to obtain double-epoxy-terminated polylactic acid.

[0041] (2) Add 50g of di-epoxy polylactic acid to chloroform solvent, stir to dissolve, then add 0.45g of 2,2'-bis(trifluoromethyl)diaminobiphenyl, stir and react at 60℃ for 36h, reflux during reaction, add ethanol to the solution to precipitate the precipitate, filter, wash with ethanol, dry to obtain fluorinated polylactic acid.

[0042] (3) Fluorinated polylactic acid and plasticizer poly1,2-propanediol adipate are added to a twin-screw extruder. The temperatures of sections 1-5 are 145℃, 170℃, 180℃, 175℃ and 175℃ respectively. The screw speed is 150r / min. The material is extruded and granulated. Then the granules are hot-pressed into a film by a hot press. The temperature is controlled at 180℃, the pressure is 15MPa and the time is 15min to obtain a fluorinated polylactic acid film.

[0043] (4) Pass the fluorinated polylactic acid film into a hot press and hot press the paper surface to composite it. Control the temperature at 150℃, the pressure at 15MPa, and the time at 3min to obtain polylactic acid composite paper.

[0044] Comparative Example 1

[0045] (1) Add polylactic acid and plasticizer triphenyl phosphite to a twin-screw extruder. The temperatures of sections 1-5 are 145℃, 170℃, 180℃, 175℃, and 175℃, respectively. The screw speed is 150r / min. Extrusion and granulation are carried out. Then, the granules are hot-pressed into a film by a hot press. The temperature is controlled at 180℃, the pressure is 10MPa, and the time is 20min to obtain a polylactic acid film.

[0046] (2) Pass the polylactic acid film into a hot press and hot press the paper surface to composite it. Control the temperature at 155℃, the pressure at 10MPa, and the time at 5min to obtain polylactic acid composite paper.

[0047] Comparative Example 2

[0048] (1) Add the double-terminated epoxy polylactic acid (prepared according to the method of Example 1) and the plasticizer triphenyl phosphite to a twin-screw extruder. The temperatures of sections 1-5 are 145℃, 170℃, 180℃, 175℃, and 175℃, respectively. The screw speed is 150r / min. Extrusion and granulation are carried out. Then, the granules are hot-pressed into a film by a hot press. The temperature is controlled at 180℃, the pressure is 10MPa, and the time is 20min to obtain a polylactic acid film.

[0049] (2) Pass the polylactic acid film into a hot press and hot press the paper surface to composite it. Control the temperature at 155℃, the pressure at 10MPa, and the time at 5min to obtain polylactic acid composite paper.

[0050] Comparative Example 3

[0051] (1) 50g of double-epoxy polylactic acid (prepared according to the method of Example 1) was added to chloroform solvent, stirred and dissolved, and then 0.3g of 4,4'-diaminobiphenyl was added. The mixture was stirred and reacted at 60°C for 24h. During the reaction, the mixture was refluxed and ethanol was added to the solution to precipitate the precipitate. After filtration, the precipitate was washed with ethanol and dried to obtain modified polylactic acid.

[0052] (2) Modified polylactic acid and plasticizer triphenyl phosphite are added to a twin-screw extruder. The temperatures of sections 1-5 are 145℃, 170℃, 180℃, 175℃ and 175℃ respectively. The screw speed is 150r / min. The material is extruded and granulated. Then the granules are hot-pressed into a film by a hot press. The temperature is controlled at 180℃, the pressure is 10MPa and the time is 20min to obtain a polylactic acid film.

[0053] (3) Pass the polylactic acid film into a hot press and hot press the paper surface to composite it. Control the temperature at 155℃, the pressure at 10MPa, and the time at 5min to obtain polylactic acid composite paper.

[0054] Paper without heat-pressed polylactic acid film was used as a blank control.

[0055] Mechanical properties were determined using a tensile strength tester. Paper samples were 100mm × 15mm in size, and each sample was tested three times; the average value was taken.

[0056] The oil resistance of polylactic acid composite paper was tested according to Tappi T559cm-02, the method for testing the oil resistance of paper and paperboard. The test solution was a mixture of castor oil, toluene, and n-heptane in a volume ratio of 1.5:1:1.

[0057] The water contact angle of polylactic acid composite paper surface was tested using a water contact angle tester. Each sample was tested 5 times and the average value was taken.

[0058] Table 1 Performance Tests of Polylactic Acid Composite Paper

[0059]

[0060] The blank control paper, which was not heat-pressed with polylactic acid film, showed a tensile strength and elongation at break of only 3.14 kN / m and 6.7%, respectively. It had an oil resistance rating of ≤1, was highly absorbent, easily wetted, and did not exhibit a water contact angle.

[0061] Each embodiment utilizes a fluorinated polylactic acid film to hot-press and laminate the paper surface, forming a paper-plastic composite material with better mechanical properties. The tensile strength and elongation at break are significantly improved. Furthermore, the hydroxyl groups of the fluorinated polylactic acid film, as well as the fluorinated groups containing low surface energy, interact with the cellulose hydroxyl groups in the paper, causing the hydrophilic groups of polylactic acid to bond inward with the paper, while the low surface energy fluorinated segments face outward. This forms a hydrophobic and oleophobic layer on the paper surface, significantly improving the paper's oil resistance and water contact angle, exhibiting excellent waterproof and oil-repellent properties.

[0062] The polylactic acid in Comparative Example 1 and the polylactic acid with double epoxy groups in Comparative Example 2 do not contain hydroxyl groups, resulting in lower bonding strength with paper. The tensile strength and elongation at break of the resulting paper-plastic composite material are lower than those in the examples. Furthermore, the polylactic acid in both examples does not contain fluorinated groups with low surface energy, resulting in lower oil resistance and water contact angle of the paper compared to the examples, and poor water and oil resistance.

[0063] Comparative Example 3 uses double-terminated epoxy polylactic acid and 4,4'-diaminobiphenyl to react and obtain modified polylactic acid containing hydroxyl groups but not containing low surface energy fluorinated groups. The oil resistance and water contact angle of the paper are lower than those of the examples, and the water and oil resistance performance is poor.

[0064] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing polylactic acid composite paper, characterized in that, The preparation method is as follows: (1) Add the double-epoxy polylactic acid to the solvent, stir to dissolve, then add 2,2'-bis(trifluoromethyl)diaminobiphenyl, stir to react, reflux during the reaction, add ethanol to the solution to precipitate the precipitate, filter, wash, and dry to obtain fluorinated polylactic acid. (2) Fluorinated polylactic acid and plasticizer are added to a twin-screw extruder, extruded, granulated, and then the granules are hot-pressed into a film by a hot press to obtain a fluorinated polylactic acid film. (3) Pass the fluorinated polylactic acid film into a hot press and hot press the paper surface to obtain polylactic acid composite paper; The preparation method of the double-epoxy polylactic acid is as follows: add carboxyl-terminated polylactic acid to thionyl chloride, carry out acyl chloride reaction in nitrogen atmosphere, concentrate the product under reduced pressure, add dichloromethane, add glycidyl and triethylamine, carry out esterification reaction, add ethanol to the solution to precipitate the precipitate, filter, wash, and dry to obtain double-epoxy polylactic acid. The glycidyl ether and triethylamine are respectively 0.3-0.4% and 0.5-0.8% of the mass of the carboxyl-terminated polylactic acid.

2. The method for preparing polylactic acid composite paper according to claim 1, characterized in that, The solvent in (1) is dichloromethane, trichloromethane or toluene.

3. The method for preparing polylactic acid composite paper according to claim 1, characterized in that, The mass of 2,2'-bis(trifluoromethyl)diaminobiphenyl in (1) is 0.6-0.9% of the mass of polylactic acid with two-terminal epoxy groups.

4. The method for preparing polylactic acid composite paper according to claim 1, characterized in that, The reaction in (1) is carried out at 40-90℃ for 12-36 hours.

5. The method for preparing polylactic acid composite paper according to claim 1, characterized in that, The plasticizer in (2) is triphenyl phosphite, poly(1,2-propanediol adipate) or triacetin.

6. The method for preparing polylactic acid composite paper according to claim 1, characterized in that, The temperature of sections 1-5 of the twin-screw extruder (2) is 145-180℃, and the screw speed is 150-200r / min; the temperature of the hot press is 175-180℃, the pressure is 10-15MPa, and the time is 10-20min.

7. The method for preparing polylactic acid composite paper according to claim 1, characterized in that, The temperature during hot pressing (3) is 150-160℃, the pressure is 10-15MPa, and the time is 2-5min.

8. The method for preparing polylactic acid composite paper according to claim 1, characterized in that, In the preparation method of the double-terminated epoxy polylactic acid, the acyl chloride reaction is carried out at 60-70℃ for 3-5 hours; the esterification reaction is carried out at 20-25℃ for 18-24 hours.

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