Preparation method of a colored reusable time-temperature indicator

Abstract

The present invention discloses a method for preparing a colorful, reusable time-temperature indicator. The method is characterized by first synthesizing different types of furfural-based dyes, then using amphiphilic polymers, polymethyl methacrylate, and the furfural-based dye to self-assemble in a solution to form a microcapsule emulsion. The microcapsule emulsion is then dispersed in a polyvinyl alcohol solution, dried under natural conditions, and subjected to light treatment to obtain a colorful, reusable time-temperature indicator. The preparation method of the present invention has the advantages of a wide range of raw materials, a simple process, and high efficiency. The resulting time-temperature indicator has the characteristics of high accuracy, reusability, stable properties, and no toxic effects.

Description

Technical Field

[0001] The invention specifically relates to a preparation method of a colored reusable time-temperature indicator, and belongs to the technical field of food intelligent packaging. Background Art

[0002] During long-distance transportation of fresh and cooked food, temperature fluctuations inevitably lead to the proliferation of microorganisms (such as Salmonella and Bacillus cereus), causing spoilage. Once these spoiled foods reach the market and are consumed by consumers, they can cause a range of health problems, ranging from nausea, vomiting, abdominal pain, and diarrhea to life-threatening consequences. Therefore, to protect consumer health and food safety, researchers have developed advanced materials—time-temperature indicators (TTIs)—that change color based on temperature and time. By observing the color changes of TTIs in real time, we can directly understand the state of food and ensure consumer health. This technology provides the food industry with a simple and effective way to monitor and assess the freshness and safety of food.

[0003] Chinese patent CN202011323959.0 discloses a multiple pH printing ink type time temperature indicator and its preparation method. The patent uses raw materials such as anthocyanins, curcumin, phenol red, methyl red and bromothymol blue to change the color of the pattern by the change in the freshness of the food in the packaging, thereby solving the problem that the traditional liquid time temperature indicator is not obvious in the real-time monitoring process. However, this TTI indicator substance is exposed to the external environment without effective protection, and is prone to leakage and failure due to the influence of the external environment, resulting in failure of the indication. Chinese patent CN201911064417.3 discloses a Pickering emulsion-based indicator and its preparation method. The TTI uses oil particles to control the stability of the emulsion and can accurately monitor the storage temperature of food. However, the TTI does not have rich colors and is inconvenient to use. It is impossible to directly observe the color changes of the TTI with the naked eye and obtain relevant indicative information. Summary of the Invention

[0004] The present invention aims to address the deficiencies of the prior art and provides a method for preparing a colorful, reusable time-temperature indicator. The method first uses furfural as a raw material to synthesize a furfural-based dye with photochromic properties. Then, using polyvinyl alcohol as an amphiphilic molecule, the organic phase is dispersed into a water-dispersible emulsion. Next, the emulsion is evenly mixed with a polyvinyl alcohol solution, coated on a mold, and naturally dried, thereby preparing a novel, colorful, reusable time-temperature indicator. The present invention uses two furfural-based dyes of different colors and composites them to form a new intermediate color. After the TTI is activated by a light source, the color gradually transitions from a single base color of red to the intermediate color. The color change during this transition process gives the TTI a colorful color characteristic.

[0005] The present invention provides a method for preparing a colored reusable time-temperature indicator, which is characterized by comprising the following steps, wherein the fractions of the materials used are all weight fractions:

[0006] (1) Preparation of 5-(furan-2-methylene)-1,3-dimethylpyrimidine-2,4,6-trione:

[0007] 1.9 parts of furfural, 3.0-3.1 parts of 1,3-dimethylpyrimidine-2,4,6-trione, 0.21 parts of (L)-proline and 39.7 parts of dichloromethane were added to a round-bottom flask, and the mixture was stirred at room temperature for 20 hours. The reaction product was then subjected to column chromatography and vacuum distillation to obtain 5-(furan-2-methylene)-1,3-dimethylpyrimidine-2,4,6-trione;

[0008]

[0009] (2) Preparation of 4-(furan-2-methylene)-2-phenyl-5-trifluoromethylpyrazol-3-one: 1.9 parts of furfural, 2.0-2.1 parts of 2-phenyl-5-trifluoromethylpyrazol-2-one, 0.21 parts of (L)-proline and 39.7 parts of dichloromethane were added to a round-bottom flask and stirred at room temperature for 20 hours. The reaction product was then subjected to column chromatography and vacuum distillation to obtain 4-(furan-2-methylene)-2-phenyl-5-trifluoromethylpyrazol-3-one;

[0010]

[0011] (3) Preparation of furfural-based dye I:

[0012] 0.10 parts of 4-(furan-2-methylene)-2-phenyl-5-trifluoromethylpyrazol-3-one and 0.043 parts of 2-methylindole were dissolved in 1.06 parts of dichloromethane, a small amount of catalyst was added dropwise, and the mixture was stirred at room temperature for 1 hour. The solvent was then removed from the reaction product by vacuum distillation, and the product was ground with ether, filtered, and collected to obtain a furfural-based dye.

[0013]

[0014] (4) Preparation of furfural-based dye II:

[0015] 0.14 parts of 5-(furan-2-methylene)-1, 3-dimethylpyrimidine-2, 4, 6-trione and 0.044 parts of diethylamine were dissolved in 1.06 parts of dichloromethane, a small amount of catalyst was added dropwise, and the reaction was stirred at room temperature for 1 hour. The solvent was then removed by distillation under reduced pressure from the reaction product, which was then ground with ether, filtered, and collected to obtain a furfural-based dye.

[0016]

[0017] (5) Preparation of furfural-based microcapsules I:

[0018] 0.50 parts of polymethyl methacrylate were dissolved in 13.78 parts of dichloromethane, 0.030 parts of furfural-based dye I were added to 0.88 parts of lauric acid, and then 15 parts of 1 wt% polyvinyl alcohol were added together, followed by homogenization, vacuum drying, centrifugation, and freeze drying to finally obtain furfural-based dye microcapsules I;

[0019] (6) Preparation of furfural-based microcapsules II:

[0020] 0.50 parts of polymethyl methacrylate were dissolved in 13.78 parts of dichloromethane, 0.030 parts of furfural-based dye II were added to 0.88 parts of lauric acid, and 15 parts of 1 wt% polyvinyl alcohol were added together, followed by homogenization, vacuum drying, centrifugation, and freeze drying to finally obtain furfural-based dye microcapsules II;

[0021] (7) Preparation of time-temperature indicator:

[0022] 0.015 parts of furfural-based dye microcapsules I and 0.015 parts of furfural-based dye microcapsules II were added to 6 parts of 20 wt% PVA solution and dried naturally at room temperature for 24 h to allow water to evaporate on the plate.

[0023] The method for preparing a colored reusable time-temperature indicator is characterized in that the alkylamine compound is diethylamine, methylindoline, or 4-methoxy-N-methylaniline.

[0024] The method for preparing a colored reusable time-temperature indicator is characterized in that the catalyst used in step (3) is 1, 1, 1, 3, 3, 3-hexafluoro-2-propanol, 2, 3, 4, 5, 6-pentafluorophenol, 2, 2, 3, 3-tetrafluoro-1-propanol, pentafluorobenzyl alcohol, 2, 2, 2-trifluoroethanol, 3, 3, 4, 4, 5, 5, 5-heptafluoropentan-2-ol, or high-fluorinated tert-butanol.

[0025] The method for preparing a colored reusable time-temperature indicator is characterized in that the weight-average molecular weight of the polyvinyl alcohol is 27,000-35,000.

[0026] Compared with the prior art, the present invention has the following positive effects:

[0027] (1) Wide range of raw materials and higher safety: The raw material furfural used in the present invention is derived from corn cobs, dried bagasse, rice husks, etc., which are abundant and easily available. The furfural-based color-changing dye is encapsulated in polymer microcapsules. The polymethyl methacrylate and polyvinyl alcohol used in the microcapsules are non-toxic to the human body, which has higher safety and can effectively prevent the possibility of dye leakage.

[0028] (2) Reusable and stable properties: The TTI prepared by the present invention can be recycled and can still maintain its original performance after multiple uses, and its physical and chemical properties are stable.

[0029] (3) TTI is thin, sensitive and fold-resistant: The TTI prepared by the present invention is thin, transparent, resistant to bending and folding, has good mechanical properties, and can be applied to the surfaces of various objects as the use environment changes.

[0030] (4) TTI has diverse colors and obvious indicating effects: The TTI prepared by the present invention has significant color changes before and after being affected by temperature, and has great potential for meeting the application of food safety indicators in real life. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the NMR spectrum of the product of formula III;

[0032] Figure 2 This is the NMR image of the product formula V;

[0033] Figure 3 is the nuclear magnetic resonance image of the product formula VII;

[0034] Figure 4 is the nuclear magnetic resonance image of the product formula IX;

[0035] Figure 5 This is the absorbance change diagram of the time-temperature indicator before and after illumination;

[0036] Figure 6 Reuse recovery degree for temperature indicator. DETAILED DESCRIPTION

[0037] The present invention is described in detail below through examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art in this field can make some non-essential improvements and adjustments based on the contents of the above invention, which still fall within the scope of protection of the present invention. Example 1

[0038] (1) Preparation of 5-(furan-2-methylene)-1,3-dimethylpyrimidine-2,4,6-trione:

[0039] 1.9 parts of furfural, 3.0-3.1 parts of 1,3-dimethylpyrimidine-2,4,6-trione, 0.21 parts of (L)-proline and 39.7 parts of dichloromethane were added to a round-bottom flask, and the mixture was stirred at room temperature for 20 hours. The reaction product was then subjected to column chromatography and vacuum distillation to obtain 5-(furan-2-methylene)-1,3-dimethylpyrimidine-2,4,6-trione;

[0040] (2) Preparation of 4-(furan-2-methylene)-2-phenyl-5-trifluoromethylpyrazol-3-one:

[0041] 1.9 parts of furfural, 2.0-2.1 parts of 2-phenyl-5-trifluoromethylpyrazol-2-one, 0.21 parts of (L)-proline and 39.7 parts of dichloromethane were added to a round-bottom flask and stirred at room temperature for 20 hours. The reaction product was then subjected to column chromatography and reduced pressure distillation to obtain 4-(furan-2-methylene)-2-phenyl-5-trifluoromethylpyrazol-3-one;

[0042] (3) Preparation of furfural-based dye I:

[0043] 0.10 parts of 4-(furan-2-methylene)-2-phenyl-5-trifluoromethylpyrazol-3-one and 0.043 parts of 2-methylindole were dissolved in 1.06 parts of dichloromethane, a small amount of catalyst was added dropwise, and the mixture was stirred at room temperature for 1 hour. The solvent was then removed from the reaction product by vacuum distillation, and the product was triturated with ether, filtered, and collected to obtain furfural-based dye I.

[0044] (4) Preparation of furfural-based dye II:

[0045] 0.14 parts of 5-(furan-2-methylene)-1, 3-dimethylpyrimidine-2, 4, 6-trione and 0.044 parts of diethylamine were dissolved in 1.06 parts of dichloromethane, a small amount of catalyst was added dropwise, and the mixture was stirred at room temperature for 1 hour. The solvent was then removed by distillation under reduced pressure from the reaction product, which was then ground with ether, filtered, and collected to obtain furfural-based dye II.

[0046] (5) Preparation of furfural-based microcapsules I:

[0047] 0.50 parts of polymethyl methacrylate were dissolved in 13.78 parts of dichloromethane, 0.030 parts of furfural-based dye I were added to 0.88 parts of lauric acid, and then 15 parts of 1 wt% polyvinyl alcohol were added together, followed by homogenization, vacuum drying, centrifugation, and freeze drying to finally obtain furfural-based dye microcapsules I;

[0048] (6) Preparation of furfural-based microcapsules II:

[0049] 0.50 parts of polymethyl methacrylate were dissolved in 13.78 parts of dichloromethane, 0.030 parts of furfural-based dye II were added to 0.88 parts of lauric acid, and 15 parts of 1 wt% polyvinyl alcohol were added together, followed by homogenization, vacuum drying, centrifugation, and freeze drying to finally obtain furfural-based dye microcapsules II;

[0050] (7) Preparation of time-temperature indicator:

[0051] 0.015 parts of furfural-based dye microcapsules I and 0.015 parts of furfural-based dye microcapsules II were added to 6 parts of 20 wt% PVA solution and dried naturally at room temperature for 24 h to allow water to evaporate on the plate. Example 2

[0052] (1) Preparation of 5-(furan-2-methylene)-1,3-dimethylpyrimidine-2,4,6-trione:

[0053] 1.9 parts of furfural, 3.0-3.1 parts of 1,3-dimethylpyrimidine-2,4,6-trione, 0.21 parts of (L)-proline and 39.7 parts of dichloromethane were added to a round-bottom flask, and the mixture was stirred at room temperature for 20 hours. The reaction product was then subjected to column chromatography and vacuum distillation to obtain 5-(furan-2-methylene)-1,3-dimethylpyrimidine-2,4,6-trione;

[0054] (2) Preparation of (Z)-4-(furan-2-methylene)-2, 5-diphenyl-3-pyrazol-3-one:

[0055] 1.9 parts of furfural, 1.9-2.0 parts of 2,5-diphenyl-3-pyrazol-3-one, 0.21 parts of (L)-proline, and 39.7 parts of dichloromethane were added to a round-bottom flask, and the mixture was stirred at room temperature for 20 hours. The reaction product was then purified by column chromatography and vacuum distillation to obtain (Z)-4-(furan-2-methylene)-2,5-diphenyl-3-pyrazol-3-one;

[0056] (3) Preparation of furfural-based dye I:

[0057] 0.10 parts of (Z)-4-(furan-2-methylene)-2, 5-diphenyl-3-pyrazol-3-one and 0.043 parts of 2-methylindole were dissolved in 1.06 parts of dichloromethane, a small amount of catalyst was added dropwise, and the mixture was stirred at room temperature for 1 hour. The solvent was then removed from the reaction product by vacuum distillation, and the product was triturated with diethyl ether, filtered, and collected to obtain furfural-based dye I.

[0058] (4) Preparation of furfural-based dye II:

[0059] 0.14 parts of 5-(furan-2-methylene)-1, 3-dimethylpyrimidine-2, 4, 6-trione and 0.044 parts of diethylamine were dissolved in 1.06 parts of dichloromethane, a small amount of catalyst was added dropwise, and the mixture was stirred at room temperature for 1 hour. The solvent was then removed by distillation under reduced pressure from the reaction product, which was then ground with ether, filtered, and collected to obtain furfural-based dye II.

[0060] (5) Preparation of furfural-based microcapsules I:

[0061] 0.50 parts of polymethyl methacrylate were dissolved in 13.78 parts of dichloromethane, 0.030 parts of furfural-based dye I were added to 0.88 parts of lauric acid, and 15 parts of 1 wt% polyvinyl alcohol were added together, followed by homogenization, vacuum drying, centrifugation, and freeze drying to obtain furfural-based dye microcapsules.

[0062] (6) Preparation of furfural-based microcapsules II:

[0063] 0.50 parts of polymethyl methacrylate were dissolved in 13.78 parts of dichloromethane, 0.030 parts of furfural-based dye II were added to 0.88 parts of lauric acid, and 15 parts of 1 wt% polyvinyl alcohol were added together, followed by homogenization, vacuum drying, centrifugation, and freeze drying to finally obtain furfural-based dye microcapsules;

[0064] (7) Preparation of time-temperature indicator:

[0065] 0.015 parts of furfural-based dye microcapsules I and 0.015 parts of furfural-based dye microcapsules II were added to 6 parts of 20 wt% PVA solution and dried naturally at room temperature for 24 h to allow water to evaporate on the plate. Example 3

[0066] (1) Preparation of 5-(furan-2-methylene)-1,3-dimethylpyrimidine-2,4,6-trione:

[0067] 1.9 parts of furfural, 3.0-3.1 parts of 1,3-dimethylpyrimidine-2,4,6-trione, 0.21 parts of (L)-proline and 39.7 parts of dichloromethane were added to a round-bottom flask, and the mixture was stirred at room temperature for 20 hours. The reaction product was then subjected to column chromatography and vacuum distillation to obtain 5-(furan-2-methylene)-1,3-dimethylpyrimidine-2,4,6-trione;

[0068] (2) Preparation of (Z)-4-(furan-2-methylene)-2,5-diphenyl-2,4-pyrazol-3-one:

[0069] 1.9 parts of furfural, 1.9-2.0 parts of 2,5-diphenyl-3-pyrazol-3-one, 0.21 parts of (L)-proline, and 39.7 parts of dichloromethane were added to a round-bottom flask, and the mixture was stirred at room temperature for 20 hours. The reaction product was then purified by column chromatography and vacuum distillation to obtain (Z)-4-(furan-2-methylene)-2,5-diphenyl-3-pyrazol-3-one;

[0070] (3) Preparation of furfural-based dye I:

[0071] 0.10 parts of (Z)-4-(furan-2-methylene)-2, 5-diphenyl-3-pyrazol-3-one and 0.043 parts of 2-methylindole were dissolved in 1.06 parts of dichloromethane, a small amount of catalyst was added dropwise, and the mixture was stirred at room temperature for 1 hour. The solvent was then removed from the reaction product by vacuum distillation, and the product was triturated with ether, filtered, and collected to obtain furfural-based dye I.

[0072] (4) Preparation of furfural-based dye II:

[0073] 0.14 parts of 5-(furan-2-methylene)-1, 3-dimethylpyrimidine-2, 4, 6-trione and 0.043 parts of 2-methylindole were dissolved in 1.06 parts of dichloromethane, a small amount of catalyst was added dropwise, and the mixture was stirred at room temperature for 1 hour. The solvent was then removed by distillation under reduced pressure from the reaction product, which was then ground with ether, filtered, and collected to obtain furfural-based dye II.

[0074] (5) Preparation of furfural-based microcapsules I:

[0075] 0.50 parts of polymethyl methacrylate were dissolved in 13.78 parts of dichloromethane, 0.030 parts of furfural-based dye I were added to 0.88 parts of lauric acid, and 15 parts of 1 wt% polyvinyl alcohol were added together, followed by homogenization, vacuum drying, centrifugation, and freeze drying to obtain furfural-based dye microcapsules.

[0076] (6) Preparation of furfural-based microcapsules II:

[0077] 0.50 parts of polymethyl methacrylate were dissolved in 13.78 parts of dichloromethane, 0.030 parts of furfural-based dye II were added to 0.88 parts of lauric acid, and 15 parts of 1 wt% polyvinyl alcohol were added together, followed by homogenization, vacuum drying, centrifugation, and freeze drying to finally obtain furfural-based dye microcapsules;

[0078] (7) Preparation of time-temperature indicator:

[0079] 0.015 parts of furfural-based dye microcapsules I and 0.015 parts of furfural-based dye microcapsules II were added to 6 parts of 20 wt% PVA solution and dried naturally at room temperature for 24 h to allow water to evaporate on the plate.

Claims

1. A method for preparing a colored reusable time-temperature indicator, characterized in that The method comprises the following steps, wherein all materials are by weight: (1) Preparation of 5-(furan-2-methylene)-1,3-dimethylpyrimidine-2,4,6-trione: 1.9 parts of furfural, 3.0-3.1 parts of 1,3-dimethylpyrimidine-2,4,6-trione, 0.21 parts of (L)-proline and 39.7 parts of dichloromethane were added to a round-bottom flask, and the mixture was stirred at room temperature for 20 hours. The reaction product was then subjected to column chromatography and vacuum distillation to obtain 5-(furan-2-methylene)-1,3-dimethylpyrimidine-2,4,6-trione; ; (2) Preparation of 4-(furan-2-methylene)-2-phenyl-5-trifluoromethylpyrazol-3-one: 1.9 parts of furfural, 2.0-2.1 parts of 2-phenyl-5-trifluoromethylpyrazol-2-one, 0.21 parts of (L)-proline and 39.7 parts of dichloromethane were added to a round-bottom flask and stirred at room temperature for 20 hours. The reaction product was then subjected to column chromatography and reduced pressure distillation to obtain 4-(furan-2-methylene)-2-phenyl-5-trifluoromethylpyrazol-3-one; ; (3) Preparation of furfural-based dye I: 0.10 parts of 4-(furan-2-methylene)-2-phenyl-5-trifluoromethylpyrazol-3-one and 0.043 parts of 2-methylindole were dissolved in 1.06 parts of dichloromethane, a small amount of catalyst was added dropwise, and the mixture was stirred at room temperature for 1 hour. The solvent was then removed from the reaction product by vacuum distillation, and the product was ground with ether, filtered, and collected to obtain a furfural-based dye. ; (4) Preparation of furfural-based dye II: 0.14 parts of 5-(furan-2-methylene)-1,3-dimethylpyrimidine-2,4,6-trione and 0.044 parts of diethylamine were dissolved in 1.06 parts of dichloromethane, a small amount of catalyst was added dropwise, and the mixture was stirred at room temperature for 1 hour. The solvent was then removed from the reaction product by vacuum distillation, and the product was ground with ether, filtered, and collected to obtain a furfural-based dye. ; (5) Preparation of furfural-based microcapsules I: 0.50 parts of polymethyl methacrylate were dissolved in 13.78 parts of dichloromethane, 0.030 parts of furfural-based dye I were added to 0.88 parts of lauric acid, and then 15 parts of 1 wt% polyvinyl alcohol were added together, followed by homogenization, vacuum drying, centrifugation, and freeze drying to finally obtain furfural-based dye microcapsules I; (6) Preparation of furfural-based microcapsules II: 0.50 parts of polymethyl methacrylate were dissolved in 13.78 parts of dichloromethane, 0.030 parts of furfural-based dye II were added to 0.88 parts of lauric acid, and 15 parts of 1 wt% polyvinyl alcohol were added together, followed by homogenization, vacuum drying, centrifugation, and freeze drying to finally obtain furfural-based dye microcapsules II; (7) Preparation of time-temperature indicator: 0.015 parts of furfural-based dye microcapsules I and 0.015 parts of furfural-based dye microcapsules II were added to 6 parts of 20 wt% PVA solution and dried naturally at room temperature for 24 h to allow water to evaporate on the plate.

2. The method for preparing a colored reusable time-temperature indicator according to claim 1, characterized in that The catalyst used in step (3) is one of 1, 1, 1, 3, 3, 3-hexafluoro-2-propanol, 2, 3, 4, 5, 6-pentafluorophenol, 2,2, 3, 3-tetrafluoro-1-propanol, pentafluorobenzyl alcohol, 2, 2, 2-trifluoroethanol, 3, 3, 4, 4, 5, 5, 5-heptafluoropentan-2-ol, and high-fluorinated tert-butanol.

3. The method for preparing a colored reusable time-temperature indicator according to claim 1, characterized in that The weight average molecular weight of the polyvinyl alcohol is 27,000-35,000.

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