A method for preparing a polylactic acid anti-fog film

Abstract

This invention discloses a method for preparing a polylactic acid (PLA) anti-fogging film, belonging to the field of plastic film preparation technology. The anti-fogging film is prepared by solution blending and coating of PLA as the matrix, polycaprolactone as the toughening agent, caprolactone-polyethylene glycol-caprolactone block copolymer as the compatibilizer, a compound of citric acid-bonded neodecanoic acid glycidyl ester and decaglycerol monolaurate as the hydrophilic agent, and dichloromethane as the solvent. The PLA film prepared by this invention has good anti-fogging properties and excellent mechanical properties, and is completely biodegradable. Its application in the food packaging field has significant economic value and social benefits.

Description

Technical Field

[0001] This invention belongs to the field of plastic film preparation technology, and specifically relates to a method for preparing polylactic acid antifog film. Background Technology

[0002] Polylactic acid (PLA) films possess advantages such as high transparency, high mechanical strength, biodegradability, good gas barrier properties, and good biocompatibility, and are gradually replacing traditional petroleum-based polyolefin films in food packaging, electronic product packaging, pharmaceutical packaging, and agricultural mulch films. However, when PLA films are used in food packaging, moisture evaporates from the packaged food over time and temperature changes. This moisture condenses on the inner surface of the PLA film, forming a water mist that severely affects the visual appeal of the packaged food. Furthermore, the rigid molecular structure of PLA results in poor toughness. Therefore, developing PLA films with excellent toughness and anti-fogging properties has become crucial for their widespread application in food packaging. Summary of the Invention

[0003] To address the shortcomings of current polylactic acid (PLA) films used in food packaging, such as poor toughness and anti-fogging properties, this invention provides a method for preparing a PLA anti-fogging film. The PLA film prepared by this invention exhibits good anti-fogging properties and superior mechanical properties, and is completely biodegradable. Its application in food packaging has significant economic and social benefits.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A polylactic acid antifog film is made by solution blending and coating, with polylactic acid as the matrix, polycaprolactone as the toughening agent, caprolactone-polyethylene glycol-caprolactone block copolymer as the compatibilizer, a compound of citric acid-bonded neodecanoic acid glycidyl ester and decaglycerol monolaurate as the hydrophilic agent, and dichloromethane as the solvent.

[0006] The preparation method of the polylactic acid antifog film specifically includes the following steps:

[0007] (1) Under a nitrogen atmosphere, 4-10 g of citric acid was added to 10-50 g of dioxane and magnetically stirred at 70-90 °C for 10-30 min. Then, 6-8 g of neodecanoic acid glycidyl ester and 0.4-1 g of triphenylphosphine were added and magnetically stirred at 80-100 °C for 3-5 h. After separation, purification and vacuum drying, citric acid-bonded neodecanoic acid glycidyl ester was obtained.

[0008] (2) Under a nitrogen atmosphere, 1~3 g of caprolactone and 3~6 g of polyethylene glycol were first magnetically stirred at 80~100 °C for 10~30 min, and then 0.02~0.08 g of tin isooctanoate was added. The mixture was then magnetically stirred at 120~140 °C for 6~10 h. After separation, purification and vacuum drying, caprolactone-polyethylene glycol-caprolactone block copolymer was obtained.

[0009] (3) Add polylactic acid, polycaprolactone, caprolactone-polyethylene glycol-caprolactone block copolymer, citric acid bonded neodecanoic acid glycidyl ester and decaglycerol monolaurate compound to dichloromethane in proportion, first stir magnetically at room temperature for 4-6 h, then sonicate at room temperature for 5-10 min to obtain coating mixture.

[0010] (4) The coating mixture is coated into a film at a speed of 5~10 mm / s and then air-dried to obtain the polylactic acid anti-fog film.

[0011] Further, the number average molecular weight of the polyethylene glycol in step (2) is 1000, 2000, 4000 or 6000.

[0012] Further, by weight, the amount of each material used in step (3) is: 3-5 parts of polylactic acid, 0.5-2 parts of polycaprolactone, 0.05-0.2 parts of caprolactone-polyethylene glycol-caprolactone block copolymer, and 0.2-0.4 parts of the compound of citric acid bonded neodecanoic acid glycidyl ester and decaglycerol monolaurate.

[0013] Furthermore, the weight ratio of citric acid-bonded neodecanoic acid glycidyl ester and decaglycerol monolaurate in the compound is 0.8:1.2~1.2:0.8.

[0014] The significant advantages of this invention are:

[0015] (1) The present invention uses caprolactone-polyethylene glycol-caprolactone block copolymer as a compatibilizer, which enables polycaprolactone, citric acid bonded neodecanoic acid glycidyl ester and decaglycerol monolaurate to be uniformly and stably dispersed in polylactic acid film. This is because the polyethylene glycol segments have good compatibility with polylactic acid, neodecanoic acid glycidyl ester and decaglycerol monolaurate, and the caprolactone segments have good compatibility with polycaprolactone. At the same time, neodecanoic acid glycidyl ester also has good compatibility with polylactic acid and decaglycerol monolaurate.

[0016] (2) Citric acid has abundant hydroxyl and carboxyl groups, making it a highly efficient hydrophilic agent with good hydrophilic and anti-fogging properties. However, the molecular structure of citric acid differs significantly from that of polylactic acid, polycaprolactone, and caprolactone-polyethylene glycol-caprolactone block copolymers. Therefore, citric acid is not easily and stably dispersed in polylactic acid films. This invention uses a chemical method to chemically bond citric acid with glycidyl neodecanoate. Through the compatibility between glycidyl neodecanoate and polylactic acid, polycaprolactone, and caprolactone-polyethylene glycol-caprolactone block copolymers, the uniform and stable dispersion of citric acid in polylactic acid films is promoted.

[0017] (3) Decaglycerol monolaurate has a polyhydroxy molecular structure, which makes it highly hydrophilic and provides excellent hydrophilic antifogging properties. However, the polyhydroxy molecular structure of decaglycerol monolaurate makes it prone to aggregation, making it difficult to disperse evenly in the polymer matrix and easy to be lost. In this invention, decaglycerol monolaurate and citric acid-bonded neodecanoic acid glycidyl ester are used in combination as two hydrophilic agents. Through the hydrogen bond interaction between the two hydrophilic agent molecules, the uniform and stable dispersion of decaglycerol monolaurate in polylactic acid film can be effectively promoted.

[0018] (4) The polylactic acid, polycaprolactone, caprolactone-polyethylene glycol-caprolactone block copolymer, citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate used in this invention are all non-toxic and biodegradable materials, which are environmentally friendly and pollution-free. Therefore, the polylactic acid antifog film prepared by this invention is an environmentally friendly polymer material that conforms to the national environmental protection concept and meets the requirements of sustainable development.

[0019] (5) Polycaprolactone, which is uniformly and stably dispersed in polylactic acid film, can endow polylactic acid film with excellent toughness. Citric acid bonded neodecanoic acid glycidyl ester and decaglycerol monolaurate can endow polylactic acid film with excellent hydrophilicity. Therefore, the polylactic acid film prepared by the present invention has good hydrophilicity and excellent mechanical properties. Its water contact angle is 9.8~16.9°, its anti-fogging failure time is 744~816 min, its tensile strength is 35.8~43.6 MPa, its elongation at break is 231~273%, and it is completely biodegradable. It is suitable for the food packaging field and has significant economic value and social benefits. Attached Figure Description

[0020] Figure 1 The infrared absorption spectrum of the citric acid-grafted neodecanoic acid glycidyl ester prepared in Example 1 is shown.

[0021] Figure 2 The infrared absorption spectrum of the caprolactone-polyethylene glycol-caprolactone block copolymer prepared in Example 1 is shown. Detailed Implementation

[0022] The specific steps of preparing a polylactic acid anti-fog film are as follows:

[0023] (1) Under a nitrogen atmosphere, 4-10 g of citric acid was first added to 10-50 g of dioxane and magnetically stirred at 70-90 °C for 10-30 min. Then, 6-8 g of neodecanoic acid glycidyl ester and 0.4-1 g of triphenylphosphine were added and magnetically stirred at 80-100 °C for 3-5 h. After separation, purification and vacuum drying at 60 °C for 24 h, citric acid-bonded neodecanoic acid glycidyl ester was obtained.

[0024] (2) Under a nitrogen atmosphere, 1~3 g of caprolactone and 3~6 g of polyethylene glycol were first magnetically stirred at 80~100 °C for 10~30 min, and then 0.02~0.08 g of tin isooctanoate was added. The mixture was then magnetically stirred at 120~140 °C for 6~10 h. After separation, purification and vacuum drying at 60 °C for 24 h, caprolactone-polyethylene glycol-caprolactone block copolymer was obtained.

[0025] (3) Add 3~5 g of polylactic acid, 0.5~2 g of polycaprolactone, 0.05~0.2 g of caprolactone-polyethylene glycol-caprolactone block copolymer, 0.2~0.4 g of citric acid-bonded neodecanoic acid glycidyl ester and decaglycerol monolaurate compound to 20~40 mL of dichloromethane, first stir magnetically at room temperature for 4~6 h, then sonicate at room temperature for 5~10 min to obtain coating mixture;

[0026] (4) The coating mixture is coated into a film at a speed of 5~10 mm / s and then air-dried to obtain the polylactic acid anti-fog film.

[0027] In step (2), the number average molecular weight of the polyethylene glycol is 1000, 2000, 4000 or 6000.

[0028] The weight ratio of citric acid-bonded neodecanoic acid glycidyl ester and decaglycerol monolaurate in the compound used in step (3) is 0.8:1.2~1.2:0.8.

[0029] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0030] Example 1

[0031] (1) Under a nitrogen atmosphere, 7 g of citric acid was first added to 30 g of dioxane, and the mixture was magnetically stirred at 80 °C for 20 min. Then, 7 g of glycidyl neodecanoate and 0.7 g of triphenylphosphine were added, and the mixture was magnetically stirred at 90 °C for 4 h. Afterward, the reaction mixture was first removed by rotary evaporation to remove dioxane, and then dissolved in dichloromethane. The supernatant was then rotary evaporated to remove dichloromethane. Later Citric acid-grafted neodecanoic acid glycidyl ester was obtained by vacuum drying at 60 ℃ for 24 h.

[0032] (2) Under a nitrogen atmosphere, 2 g of caprolactone and 4.5 g of polyethylene glycol with a number average molecular weight of 2000 were first magnetically stirred at 90 °C for 20 min, and then 0.05 g of tin isooctanoate was added. The mixture was magnetically stirred at 130 °C for 8 h. The reactants were dissolved in dichloromethane, precipitated with excess diethyl ether, washed with methanol, and vacuum dried at 60 °C for 24 h to obtain caprolactone-polyethylene glycol-caprolactone block copolymer.

[0033] (3) Add 4 g polylactic acid, 1 g polycaprolactone, 0.1 g caprolactone-polyethylene glycol-caprolactone block copolymer, 0.3 g citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate compound (the weight ratio of citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate used is 1:1) to 30 mL dichloromethane, first stir magnetically at room temperature for 5 h, and then sonicate at room temperature for 8 min to obtain the coating mixture;

[0034] (4) The coating mixture is coated into a film at a speed of 8 mm / s and then air-dried to obtain the polylactic acid anti-fog film.

[0035] Figure 1 The image shows the infrared absorption spectrum of the citric acid-grafted neodecanoic acid glycidyl ester prepared in this embodiment. As can be seen from the image, a peak at wavenumber 1697 cm⁻¹ can be clearly observed in the infrared spectrum of citric acid. -1 and 1747 cm -1 The vibrational absorption peak at the C=O group of the carboxyl group has a wavenumber of approximately 3500 cm⁻¹. -1 The vibrational absorption peak of the hydroxyl group is clearly visible in the infrared absorption spectrum of glycidyl neodecanoate at a wavenumber of 850 cm⁻¹. -1 and 910 cm -1 The characteristic absorption peak of the epoxy group at [location missing]. In the infrared spectrum of citric acid grafted neodecanoic acid glycidyl ester, except for [location missing] at wavenumber 850 cm⁻¹, [missing information]. -1 and 910 cm -1 Apart from the disappearance of the characteristic absorption peak of the epoxy group at the point, the characteristic absorption peaks of neodecanoic acid glycidyl ester and citric acid can be clearly observed, indicating that citric acid and neodecanoic acid glycidyl ester have successfully formed a chemical bond.

[0036] Figure 2 The image shows the infrared absorption spectrum of the caprolactone-polyethylene glycol-caprolactone block copolymer prepared in this embodiment. As shown in the figure, the infrared absorption spectrum of the caprolactone-polyethylene glycol-caprolactone block copolymer clearly shows a peak at wavenumber 3375 cm⁻¹. -1 The absorption peak of the hydroxyl stretching vibration at 2891 cm⁻¹ -1 and 2946 cm -1 The CH stretching vibration absorption peak at 1725 cm⁻¹ -1 The characteristic absorption peak of C=O at 1240 cm⁻¹ -1 The absorption peak of the COC stretching vibration of the caprolactone segment at 1106 cm⁻¹ -1 The absorption peak of CO stretching vibration of polyethylene glycol segments at the point of origin proves that the caprolactone-polyethylene glycol-caprolactone block copolymer was successfully prepared.

[0037] Example 2

[0038] (1) Under a nitrogen atmosphere, 7 g of citric acid was first added to 30 g of dioxane and stirred magnetically at 80 °C for 20 min. Then, 7 g of neodecanoic acid glycidyl ester and 0.7 g of triphenylphosphine were added and stirred magnetically at 90 °C for 4 h. After that, the reaction mixture was first removed by rotary evaporation to remove dioxane, then dissolved in dichloromethane and the supernatant was taken for rotary evaporation to remove dichloromethane. Finally, it was dried under vacuum at 60 °C for 24 h to obtain citric acid grafted neodecanoic acid glycidyl ester.

[0039] (2) Under a nitrogen atmosphere, 2 g of caprolactone and 4.5 g of polyethylene glycol with a number average molecular weight of 2000 were first magnetically stirred at 90 °C for 20 min, and then 0.05 g of tin isooctanoate was added. The mixture was magnetically stirred at 130 °C for 8 h. The reactants were dissolved in dichloromethane, precipitated with excess diethyl ether, washed with methanol, and vacuum dried at 60 °C for 24 h to obtain caprolactone-polyethylene glycol-caprolactone block copolymer.

[0040] (3) Add 4 g polylactic acid, 1 g polycaprolactone, 0.1 g caprolactone-polyethylene glycol-caprolactone block copolymer, 0.2 g citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate (the weight ratio of citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate is 1:1) to 30 mL dichloromethane, first stir magnetically at room temperature for 5 h, then sonicate at room temperature for 8 min to obtain the coating mixture;

[0041] (4) The coating mixture is coated into a film at a speed of 8 mm / s and then air-dried to obtain the polylactic acid anti-fog film.

[0042] Example 3

[0043] (1) Under a nitrogen atmosphere, 7 g of citric acid was first added to 30 g of dioxane and stirred magnetically at 80 °C for 20 min. Then, 7 g of neodecanoic acid glycidyl ester and 0.7 g of triphenylphosphine were added and stirred magnetically at 90 °C for 4 h. After that, the reaction mixture was first removed by rotary evaporation to remove dioxane, then dissolved in dichloromethane and the supernatant was taken for rotary evaporation to remove dichloromethane. Finally, it was dried under vacuum at 60 °C for 24 h to obtain citric acid grafted neodecanoic acid glycidyl ester.

[0044] (2) Under a nitrogen atmosphere, 2 g of caprolactone and 4.5 g of polyethylene glycol with a number average molecular weight of 2000 were first magnetically stirred at 90 °C for 20 min, and then 0.05 g of tin isooctanoate was added. The mixture was magnetically stirred at 130 °C for 8 h. The reactants were dissolved in dichloromethane, precipitated with excess diethyl ether, washed with methanol, and vacuum dried at 60 °C for 24 h to obtain caprolactone-polyethylene glycol-caprolactone block copolymer.

[0045] (3) Add 4 g polylactic acid, 1 g polycaprolactone, 0.1 g caprolactone-polyethylene glycol-caprolactone block copolymer, 0.4 g citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate compound (the weight ratio of citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate used is 1:1) to 30 mL dichloromethane, first stir magnetically at room temperature for 5 h, and then sonicate at room temperature for 8 min to obtain the coating mixture;

[0046] (4) The coating mixture is coated into a film at a speed of 8 mm / s and then air-dried to obtain the polylactic acid anti-fog film.

[0047] Example 4

[0048] (1) Under a nitrogen atmosphere, 4 g of citric acid was first added to 10 g of dioxane, and the mixture was magnetically stirred at 70 °C for 30 min. Then, 6 g of glycidyl neodecanoate and 0.4 g of triphenylphosphine were added, and the mixture was magnetically stirred at 80 °C for 5 h. Afterward, the reaction mixture was first removed by rotary evaporation to remove dioxane, and then dissolved in dichloromethane. The supernatant was then rotary evaporated to remove dichloromethane. Later Citric acid-grafted neodecanoic acid glycidyl ester was obtained by vacuum drying at 60 ℃ for 24 h.

[0049] (2) Under a nitrogen atmosphere, 1 g of caprolactone and 3 g of polyethylene glycol with a number average molecular weight of 1000 were first magnetically stirred at 80 °C for 30 min, and then 0.02 g of tin isooctanoate was added. The mixture was magnetically stirred at 120 °C for 10 h. The reactants were dissolved in dichloromethane, precipitated with excess diethyl ether, washed with methanol, and vacuum dried at 60 °C for 24 h to obtain caprolactone-polyethylene glycol-caprolactone block copolymer.

[0050] (3) Add 3 g polylactic acid, 0.5 g polycaprolactone, 0.05 g caprolactone-polyethylene glycol-caprolactone block copolymer, 0.2 g citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate compound (the weight ratio of citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate used is 0.8:1.2) to 20 mL dichloromethane, first stir magnetically at room temperature for 4 h, and then sonicate at room temperature for 5 min to obtain the coating mixture;

[0051] (4) The coating mixture is coated into a film at a speed of 5 mm / s and then air-dried to obtain the polylactic acid anti-fog film.

[0052] Example 5

[0053] (1) Under a nitrogen atmosphere, 10 g of citric acid was first added to 50 g of dioxane, and the mixture was magnetically stirred at 90 °C for 10 min. Then, 8 g of glycidyl neodecanoate and 1 g of triphenylphosphine were added, and the mixture was magnetically stirred at 100 °C for 3 h. After that, the reaction mixture was first removed by rotary evaporation to remove dioxane, and then dissolved in dichloromethane. The supernatant was then rotary evaporated to remove dichloromethane. Later Citric acid-grafted neodecanoic acid glycidyl ester was obtained by vacuum drying at 60 ℃ for 24 h.

[0054] (2) Under a nitrogen atmosphere, 3 g of caprolactone and 6 g of polyethylene glycol with a number average molecular weight of 4000 were first magnetically stirred at 100 °C for 10 min, and then 0.08 g of tin isooctanoate was added. The mixture was magnetically stirred at 140 °C for 6 h. The reactants were dissolved in dichloromethane, precipitated with excess diethyl ether, washed with methanol, and vacuum dried at 60 °C for 24 h to obtain caprolactone-polyethylene glycol-caprolactone block copolymer.

[0055] (3) Add 5 g polylactic acid, 2 g polycaprolactone, 0.2 g caprolactone-polyethylene glycol-caprolactone block copolymer, 0.4 g citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate compound (the weight ratio of citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate used is 1.2:0.8) to 40 mL dichloromethane, first stir magnetically at room temperature for 6 h, and then sonicate at room temperature for 10 min to obtain coating mixture;

[0056] (4) The coating mixture is coated into a film at a speed of 10 mm / s and then air-dried to obtain the polylactic acid antifog film.

[0057] Comparative Example 1

[0058] (1) Add 4 g of polylactic acid and 1 g of polycaprolactone to 30 mL of dichloromethane, stir magnetically at room temperature for 5 h, and then sonicate at room temperature for 8 min to obtain a coating mixture.

[0059] (2) The coating mixture is coated into a film at a speed of 8 mm / s and then air-dried to obtain the finished product.

[0060] Comparative Example 2

[0061] (1) Under a nitrogen atmosphere, 2 g of caprolactone and 4.5 g of polyethylene glycol with a number average molecular weight of 2000 were first magnetically stirred at 90 °C for 20 min, and then 0.05 g of tin isooctanoate was added. The mixture was magnetically stirred at 130 °C for 8 h. The reactants were dissolved in dichloromethane, precipitated with excess diethyl ether, washed with methanol, and vacuum dried at 60 °C for 24 h to obtain caprolactone-polyethylene glycol-caprolactone block copolymer.

[0062] (2) Add 4 g of polylactic acid, 1 g of polycaprolactone and 0.1 g of caprolactone-polyethylene glycol-caprolactone block copolymer to 30 mL of dichloromethane, first stir magnetically at room temperature for 5 h, and then sonicate at room temperature for 8 min to obtain a coating mixture.

[0063] (3) The coating mixture is coated into a film at a speed of 8 mm / s and then air-dried to obtain the finished product.

[0064] Comparative Example 3

[0065] (1) Under a nitrogen atmosphere, 7 g of citric acid was first added to 30 g of dioxane, and the mixture was magnetically stirred at 80 °C for 20 min. Then, 7 g of glycidyl neodecanoate and 0.7 g of triphenylphosphine were added, and the mixture was magnetically stirred at 90 °C for 4 h. Afterward, the reaction mixture was first removed by rotary evaporation to remove dioxane, and then dissolved in dichloromethane. The supernatant was then rotary evaporated to remove dichloromethane. Later Citric acid-grafted neodecanoic acid glycidyl ester was obtained by vacuum drying at 60 ℃ for 24 h.

[0066] (2) Add 4 g polylactic acid, 1 g polycaprolactone, 0.3 g citrate-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate (the weight ratio of citrate-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate is 1:1) to 30 mL dichloromethane, first stir magnetically at room temperature for 5 h, then sonicate at room temperature for 8 min to obtain the coating mixture;

[0067] (3) The coating mixture is coated into a film at a speed of 8 mm / s and then air-dried to obtain the finished product.

[0068] Comparative Example 4

[0069] (1) Under a nitrogen atmosphere, 2 g of caprolactone and 4.5 g of polyethylene glycol with a number average molecular weight of 2000 were first magnetically stirred at 90 °C for 20 min, and then 0.05 g of tin isooctanoate was added. The mixture was magnetically stirred at 130 °C for 8 h. The reactants were dissolved in dichloromethane, precipitated with excess diethyl ether, washed with methanol, and vacuum dried at 60 °C for 24 h to obtain caprolactone-polyethylene glycol-caprolactone block copolymer.

[0070] (2) Add 4 g polylactic acid, 1 g polycaprolactone, 0.1 g caprolactone-polyethylene glycol-caprolactone block copolymer, and 0.3 g decaglycerol monolaurate to 30 mL dichloromethane, first stir magnetically at room temperature for 5 h, and then sonicate at room temperature for 8 min to obtain the coating mixture.

[0071] (3) The coating mixture is coated into a film at a speed of 8 mm / s and then air-dried to obtain the finished product.

[0072] Comparative Example 5

[0073] (1) Under a nitrogen atmosphere, 7 g of citric acid was first added to 30 g of dioxane, and the mixture was magnetically stirred at 80 °C for 20 min. Then, 7 g of glycidyl neodecanoate and 0.7 g of triphenylphosphine were added, and the mixture was magnetically stirred at 90 °C for 4 h. Afterward, the reaction mixture was first removed by rotary evaporation to remove dioxane, and then dissolved in dichloromethane. The supernatant was then rotary evaporated to remove dichloromethane. Later Citric acid-grafted neodecanoic acid glycidyl ester was obtained by vacuum drying at 60 ℃ for 24 h.

[0074] (2) Under a nitrogen atmosphere, 2 g of caprolactone and 4.5 g of polyethylene glycol with a number average molecular weight of 2000 were first magnetically stirred at 90 °C for 20 min, and then 0.05 g of tin isooctanoate was added. The mixture was magnetically stirred at 130 °C for 8 h. The reactants were dissolved in dichloromethane, precipitated with excess diethyl ether, washed with methanol, and vacuum dried at 60 °C for 24 h to obtain caprolactone-polyethylene glycol-caprolactone block copolymer.

[0075] (3) Add 4 g polylactic acid, 1 g polycaprolactone, 0.1 g caprolactone-polyethylene glycol-caprolactone block copolymer, and 0.3 g citric acid-grafted neodecanoic acid glycidyl ester to 30 mL dichloromethane, first stir magnetically at room temperature for 5 h, and then sonicate at room temperature for 8 min to obtain the coating mixture.

[0076] (4) The coating mixture is coated into a film at a speed of 8 mm / s and then air-dried to obtain the finished product.

[0077] Comparative Example 6

[0078] (1) Under a nitrogen atmosphere, 2 g of caprolactone and 4.5 g of polyethylene glycol with a number average molecular weight of 2000 were first magnetically stirred at 90 °C for 20 min, and then 0.05 g of tin isooctanoate was added. The mixture was magnetically stirred at 130 °C for 8 h. The reactants were dissolved in dichloromethane, precipitated with excess diethyl ether, washed with methanol, and vacuum dried at 60 °C for 24 h to obtain caprolactone-polyethylene glycol-caprolactone block copolymer.

[0079] (2) Add 4 g polylactic acid, 1 g polycaprolactone, 0.1 g caprolactone-polyethylene glycol-caprolactone block copolymer, 0.3 g glycidyl neodecanoate and decaglycerol monolaurate (the weight ratio of glycidyl neodecanoate and decaglycerol monolaurate used is 1:1) to 30 mL dichloromethane, first stir magnetically at room temperature for 5 h, and then sonicate at room temperature for 8 min to obtain the coating mixture;

[0080] (3) The coating mixture is coated into a film at a speed of 8 mm / s and then air-dried to obtain the finished product.

[0081] Comparative Example 7

[0082] (1) Under a nitrogen atmosphere, 7 g of citric acid was first added to 30 g of dioxane, and the mixture was magnetically stirred at 80 °C for 20 min. Then, 7 g of glycidyl neodecanoate and 0.7 g of triphenylphosphine were added, and the mixture was magnetically stirred at 90 °C for 4 h. Afterward, the reaction mixture was first removed by rotary evaporation to remove dioxane, and then dissolved in dichloromethane. The supernatant was then rotary evaporated to remove dichloromethane. Later Citric acid-grafted neodecanoic acid glycidyl ester was obtained by vacuum drying at 60 ℃ for 24 h.

[0083] (2) Under a nitrogen atmosphere, 2 g of caprolactone and 4.5 g of polyethylene glycol with a number average molecular weight of 2000 were first magnetically stirred at 90 °C for 20 min, and then 0.05 g of tin isooctanoate was added. The mixture was magnetically stirred at 130 °C for 8 h. The reactants were dissolved in dichloromethane, precipitated with excess diethyl ether, washed with methanol, and vacuum dried at 60 °C for 24 h to obtain caprolactone-polyethylene glycol-caprolactone block copolymer.

[0084] (3) Add 4 g polylactic acid, 1 g polycaprolactone, 0.1 g caprolactone-polyethylene glycol-caprolactone block copolymer, 0.3 g citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate compound (the weight ratio of citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate used is 0.5:1.5) to 30 mL dichloromethane, first stir magnetically at room temperature for 5 h, then sonicate at room temperature for 8 min to obtain coating mixture;

[0085] (4) The coating mixture is coated into a film at a speed of 8 mm / s and then air-dried to obtain the finished product.

[0086] Comparative Example 8

[0087] (1) Under a nitrogen atmosphere, 7 g of citric acid was first added to 30 g of dioxane, and the mixture was magnetically stirred at 80 °C for 20 min. Then, 7 g of glycidyl neodecanoate and 0.7 g of triphenylphosphine were added, and the mixture was magnetically stirred at 90 °C for 4 h. Afterward, the reaction mixture was first removed by rotary evaporation to remove dioxane, and then dissolved in dichloromethane. The supernatant was then rotary evaporated to remove dichloromethane. Later Citric acid-grafted neodecanoic acid glycidyl ester was obtained by vacuum drying at 60 ℃ for 24 h.

[0088] (2) Under a nitrogen atmosphere, 2 g of caprolactone and 4.5 g of polyethylene glycol with a number average molecular weight of 2000 were first magnetically stirred at 90 °C for 20 min, and then 0.05 g of tin isooctanoate was added. The mixture was magnetically stirred at 130 °C for 8 h. The reactants were dissolved in dichloromethane, precipitated with excess diethyl ether, washed with methanol, and vacuum dried at 60 °C for 24 h to obtain caprolactone-polyethylene glycol-caprolactone block copolymer.

[0089] (3) Add 4 g polylactic acid, 1 g polycaprolactone, 0.1 g caprolactone-polyethylene glycol-caprolactone block copolymer, 0.3 g citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate compound (the weight ratio of citric acid-grafted neodecanoic acid glycidyl ester and decaglycerol monolaurate used is 1.5:0.5) to 30 mL dichloromethane, first stir magnetically at room temperature for 5 h, and then sonicate at room temperature for 8 min to obtain the coating mixture;

[0090] (4) The coating mixture is coated into a film at a speed of 8 mm / s and then air-dried to obtain the finished product.

[0091] The thickness of the films prepared in the group examples and comparative examples was tested using a micrometer screw gauge. Static water contact angle was tested according to GB / T30693-2014, and tensile strength and elongation at break were tested according to GB / T 1040.3-2006. At the same time, the long-term anti-fogging performance of the films was tested. The specific operation was as follows: 200 mL of deionized water was poured into a 250 mL flat-mouthed beaker, the film was fixed to the mouth of the beaker with a rubber band, and finally the beaker was placed in a 40 ℃ constant temperature water bath. Timing was started. When the area of ​​water droplets on the film at the mouth of the beaker exceeded 50%, the anti-fogging performance of the film was judged to have failed. The duration displayed by the timer was used to characterize the long-term anti-fogging performance of the film. The test results are shown in Table 1.

[0092] Table 1 Performance Test Results

[0093]

[0094] The test results from the examples and comparative examples show that the polylactic acid antifog film prepared in the examples has good antifog properties and excellent mechanical properties, with the polylactic acid antifog film prepared in Example 1 exhibiting the best performance in all aspects. In contrast, if caprolactone-polyethylene glycol-caprolactone block copolymer is used alone (Comparative Example 2), or a compound of citric acid-grafted glycidyl decanoate and decaglycerol monolaurate is used alone (Comparative Example 3), or only one of citric acid-grafted glycidyl decanoate and decaglycerol monolaurate is used (Comparative Examples 4 and 5), or a compound of ungrafted glycidyl decanoate and decaglycerol monolaurate is used (Comparative Example 6), or if the weight ratio of citric acid-grafted glycidyl decanoate and decaglycerol monolaurate in the compound differs significantly (Comparative Examples 7 and 8), it is impossible to obtain a polylactic acid antifog film that combines good antifog properties and excellent mechanical properties.

[0095] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a polylactic acid antifog film, characterized in that: Using polylactic acid as the matrix, polycaprolactone as the toughening agent, caprolactone-polyethylene glycol-caprolactone block copolymer as the compatibilizer, a compound of citric acid-bonded neodecanoic acid glycidyl ester and decaglycerol monolaurate as the hydrophilic agent, and dichloromethane as the solvent, the antifog film is prepared by solution blending and coating; specifically, it includes the following steps: (1) Under a nitrogen atmosphere, 4-10 g of citric acid was added to 10-50 g of dioxane and magnetically stirred at 70-90 °C for 10-30 min. Then, 6-8 g of neodecanoic acid glycidyl ester and 0.4-1 g of triphenylphosphine were added and magnetically stirred at 80-100 °C for 3-5 h. After separation, purification and vacuum drying, citric acid-bonded neodecanoic acid glycidyl ester was obtained. (2) Under a nitrogen atmosphere, 1~3 g of caprolactone and 3~6 g of polyethylene glycol were first magnetically stirred at 80~100 °C for 10~30 min, and then 0.02~0.08 g of tin isooctanoate was added. The mixture was then magnetically stirred at 120~140 °C for 6~10 h. After separation, purification and vacuum drying, caprolactone-polyethylene glycol-caprolactone block copolymer was obtained. (3) Add polylactic acid, polycaprolactone, caprolactone-polyethylene glycol-caprolactone block copolymer, citric acid bonded neodecanoic acid glycidyl ester and decaglycerol monolaurate compound to dichloromethane in proportion, first stir magnetically at room temperature for 4-6 h, then sonicate at room temperature for 5-10 min to obtain coating mixture. (4) The coating mixture is coated into a film and then air-dried to obtain the polylactic acid antifog film; The amounts of each material used in step (3) are: 3-5 parts of polylactic acid, 0.5-2 parts of polycaprolactone, 0.05-0.2 parts of caprolactone-polyethylene glycol-caprolactone block copolymer, and 0.2-0.4 parts of the compound of citric acid bonded neodecanoic acid glycidyl ester and decaglycerol monolaurate; The weight ratio of citric acid-bonded neodecanoic acid glycidyl ester and decaglycerol monolaurate in the compound is 0.8:1.2~1.2:0.

8.

2. The method for preparing the polylactic acid antifog film according to claim 1, characterized in that: The number average molecular weight of the polyethylene glycol in step (2) is 1000, 2000, 4000 or 6000.

3. A polylactic acid antifog film prepared by any of the methods described in claims 1 to 2.

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