PH response type intelligent degradable packaging film as well as preparation method and application thereof

Abstract

The invention belongs to the field of intelligent degradable food packaging materials, and particularly relates to a pH response type intelligent degradable packaging film and a preparation method and application thereof. According to the invention, PBAT / PLA blended resin is used as a degradable matrix, a natural pH sensitive indicator alizarin is used as an intelligent response unit, no auxiliary component is added, and the high-performance pH response type intelligent degradable packaging film is prepared by controlling an alizarin solvent pre-dispersion-gradient mixing process and melt blending parameters. According to the invention, through collaborative proportion optimization of PBAT and PLA, the balance of flexibility and rigidity of the membrane is ensured, a uniformly dispersed microenvironment is provided for alizarin, and the core problem of agglomeration of alizarin in a hydrophobic matrix is solved. The packaging film can visually monitor the corruption degree of perishable food such as fresh chicken breast and aquatic products in real time through color change, the preparation process is simple, the cost is controllable, the safety is high, and a brand new technical path is provided for greenization and intelligentization of food packaging.

Description

Technical Field

[0001] This invention belongs to the field of intelligent biodegradable food packaging materials, specifically relating to a pH-responsive intelligent biodegradable packaging film, its preparation method, and its application. Background Technology

[0002] With the increasing global awareness of food safety and the deepening promotion of green and low-carbon development, food packaging materials that combine intelligent monitoring functions with biodegradability have become the core direction of industry development. Traditional food packaging materials are mostly made of polyethylene, polypropylene, etc., and their non-degradability has led to white pollution, which has become a serious environmental problem. While existing biodegradable packaging materials such as PBAT / PLA film have solved the environmental pollution problem, they have limited functionality and lack the ability to monitor food freshness in real time, making it difficult to meet consumers' dynamic needs for food safety.

[0003] pH-responsive smart packaging uses color changes in indicators to reflect the food spoilage process, making it a key technology for visually monitoring food freshness. Natural pH indicators, due to their high safety and environmental friendliness, are gradually replacing toxic chemically synthesized indicators in food packaging. Among them, alizarin (1,2-dihydroxyanthraquinone) possesses unique advantages such as sensitive response performance, a wide response range, excellent thermal stability, and significant color changes. It exhibits a significant color change when food spoilage produces volatile nitrogenous substances (such as TVB-N), leading to an increase in ambient pH, thus enabling visual monitoring of freshness.

[0004] CN115710409A describes the blown film formation of PBAT, PLA, and antibacterial agents, but it still falls short in monitoring food freshness. CN113150560A describes the preparation of films using a casting method by mixing gelatin, glycerin, and alizarin to obtain a film-forming solution. CN118667193A describes the preparation of pH-responsive food packaging films using a casting method by mixing starch, chitosan quaternary ammonium salt, pH-responsive agents, and plasticizers. However, these existing technologies are all still in the laboratory research stage and cannot directly meet the needs of large-scale industrial production, thus limiting their application and promotion in the actual market. Natural pH indicators are commonly used in laboratories, but due to their heat sensitivity, photosensitivity, and tendency to agglomerate, they are not currently used in industrial blown film production, limiting their application in real life.

[0005] Therefore, developing a food packaging film that achieves uniform dispersion of alizarin without additional auxiliary components, balances pH response sensitivity and environmental friendliness, and is suitable for industrial production is the key to breaking through existing technological bottlenecks. It has significant technological value and market significance for promoting the large-scale application of intelligent biodegradable packaging and filling the market gap for existing pH-responsive packaging films. Summary of the Invention

[0006] The purpose of this invention is to overcome the market gap for existing industrialized pH-responsive packaging films and to provide a pH-responsive smart biodegradable packaging film containing only a binary system of PBAT / PLA and alizarin, as well as its preparation method and application. By adjusting the alizarin solvent pre-dispersion-gradient mixing process and melt blending parameters, the invention achieves optimization of "uniform dispersion of indicator - sensitive pH response - suitable for industrial production". No auxiliary components need to be added, simplifying the system, reducing costs, and ensuring the biodegradability, pH stability and market applicability of the film.

[0007] The pH-responsive smart biodegradable packaging film provided by this invention has the following raw material composition by weight: Fully biodegradable resin: 93-99.7 parts, alizarin 0.3-7 parts.

[0008] The fully biodegradable resin is a mixture of PBAT and PLA in a mass ratio of (85-95):(5-15), with a preferred mass ratio of 95:5, at which point the membrane performance reaches the optimal balance. Too low an amount of alizarin will result in insufficient response sensitivity, while too high an amount will affect the membrane's mechanical properties and transparency. The optimal addition range is 0.3-1 parts, at which point the amount of fully biodegradable resin used is 99-99.7 parts.

[0009] The purity of alizarin used is preferably ≥98%.

[0010] The inventors further provided a method for preparing a pH-responsive smart biodegradable packaging film, the specific steps of which are as follows: 1. Preparation of alizarin dispersion: Weigh alizarin powder and add it to deionized water at a ratio of 1 g: 50-100 mL, preferably 1 g: 80 mL; ultrasonically disperse for 30-90 min to obtain a uniform alizarin dispersion.

[0011] 2. Preparation of high-concentration masterbatch: Weigh 10%-15% of the total mass of the biodegradable resin, pour all the alizarin dispersion into the above resin, mix evenly, and then add it to a mixer. Set the temperature to 150-160℃, the speed to 60-70 rpm, and the time to 5-10 min to mix until melted to obtain high-concentration masterbatch.

[0012] 3. Preparation of composite masterbatch: The remaining fully biodegradable resin and the high-concentration masterbatch obtained above are dried at 60-80℃ for 9-12 h. The dried material is added to a high-speed mixer and stirred at 3000-3500 rpm for 6-10 min. The stirred material is then poured into a twin-screw extruder. The five temperature ranges from the feed inlet to the die head are set sequentially as 145-165℃, 150-170℃, 155-175℃, 150-170℃, and 145-165℃, with a screw speed of 25-35 rpm. After melt blending, the material is extruded from the die head, air-dried, and then granulated in a pelletizer to obtain uniform composite masterbatch.

[0013] The fully biodegradable resin in the above two steps is a mixture of PBAT particles and PLA particles, with a mixing mass ratio of (85-95):(5-15), preferably 95:5, and the particle size of the resin particles is 2-4 mm.

[0014] 4. After drying the composite masterbatch obtained above at 60-70℃ for 9-12 h, it is fed into a single-screw extruder. The temperature range from the feed inlet to the die head is set sequentially as follows: 145-155℃, 150-160℃, 155-170℃, 150-165℃, and 145-160℃. The screw speed is 30-50 rpm. After melt extrusion, the material is blown into a film by a blown film machine to obtain a pH-responsive smart biodegradable packaging film with a thickness of 20-40μm. After cooling and setting, the film is wound up and stored at low temperature for later use.

[0015] The above steps, by employing solvent pre-dispersion, solved the problem of alizarin's tendency to agglomerate, resulting in a uniform final film without obvious particles.

[0016] The applications of the packaging film prepared above include, but are not limited to, visual monitoring and preservation packaging of the freshness of meat products such as fresh chicken breast, beef, and fish, or aquatic products such as shrimp, crab, and shellfish. Specifically, the degree of food spoilage can be visually indicated by changes in the film's color.

[0017] Compared with the prior art, the present invention has the following significant advantages: Compared to ordinary food packaging films, the pH-responsive intelligent biodegradable packaging film prepared in this invention exhibits superior intelligent response performance. It responds quickly to ammonia gas produced by food spoilage, with clear and uniform color changes, rapidly indicating early spoilage. It can be repeatedly used for packaging short-term stored foods. Simultaneously, through optimized synergistic ratios of PBAT and PLA, a uniformly dispersed microenvironment is provided for alizarin. The alizarin solvent pre-dispersion process disrupts the π-π stacking interactions between molecules, breaking the intermolecular forces and allowing alizarin to be uniformly dispersed as tiny particles within the PBAT / PLA matrix, thus solving the core problem of its aggregation in hydrophobic matrices. The resulting packaging film, as a food packaging material, combines biodegradability and safety. Alizarin is a natural extract, and both PBAT and PLA are food-contact grade biodegradable materials with no release of toxic or harmful substances, complying with GB 4806.7-2023 standards. Attached Figure Description

[0018] Figure 1 The images show the color changes of the ammonia-fumigated film surfaces of the responsive packaging films prepared in Examples 1-4 and Comparative Example 1. Figure 2 The graph shows the ammonia fumigation film sensitivity results of the responsive packaging films prepared in Examples 1-4 and Comparative Example 1; Figure 3 The ammonia-fumigated film color difference diagrams are shown for the responsive packaging films prepared in Examples 1-4 and Comparative Example 1. Figure 4 The graph shows the chicken preservation indication results of the responsive packaging films prepared in Examples 1-4 and Comparative Example 1; Figure 5 The graph shows the volatile basic nitrogen content of chicken meat in the responsive packaging films prepared in Examples 1-4 and Comparative Example 1. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to specific embodiments. These embodiments are only used to illustrate the technical solution of the present invention in more detail and should not be construed as limiting the scope of protection of the present invention.

[0020] Unless otherwise specified, all raw materials and reagents used in the following examples can be purchased commercially. The particle size of the resin particles in the PBAT / PLA blend is 2-4 mm.

[0021] Example 1: Preparation method of pH-responsive smart biodegradable packaging film First, prepare the alizarin dispersion: weigh 1.6 g of alizarin powder and add it to 120 mL of deionized water. Stir well and sonicate for 30 min to obtain the alizarin dispersion.

[0022] The specific steps for preparing a pH-responsive smart biodegradable packaging film are as follows: Weigh 50 g of PBAT / PLA blended resin with a mass ratio of 95:5 into a beaker, add all of the 120 mL alizarin dispersion obtained above into it, stir well, and then add it to a mixer. Set the temperature to 160 ℃, the speed to 60 rpm, and the time to 8 min to mix until melted to obtain high-concentration masterbatch. 380 g PBAT, 20 g PLA, and high-concentration masterbatch were dried in a blower dryer at 60 ℃ for 12 h. The dried material was then added to a high-speed mixer and stirred at 3000 rpm for 10 min. The stirred material was then poured into a twin-screw extruder, with the temperature settings from the feed inlet to the extruder die head being 165 / 170 / 175 / 170 / 165 ℃ sequentially, and the screw speed being 30 rpm. After being naturally air-dried at the outlet, the material was drawn into a pelletizer for pelletizing to obtain the composite masterbatch.

[0023] The composite masterbatch was dried in a forced-air dryer at 65℃ for 12 h, then fed into a single-screw extruder. The temperature was set to 155 / 160 / 170 / 165 / 160 ℃ and the screw speed was 40 rpm. The extruded masterbatch was blown into a packaging film with a thickness of 30±1 μm. The resulting pH-responsive smart biodegradable packaging film was stored in the dark at low temperature.

[0024] Example 2: Preparation method of pH-responsive smart biodegradable packaging film The specific steps for preparing alizarin dispersion are as follows: First, weigh 2.6 g of alizarin powder and add it to 240 mL of deionized water. After stirring evenly, sonicate for 45 min to obtain alizarin dispersion.

[0025] The preparation of pH-responsive smart biodegradable packaging film involves the following specific steps: Weigh 55 g of PBAT / PLA blended resin with a mass ratio of 95:5 into a beaker, add all of the 240 mL alizarin dispersion obtained above into it, stir well, and then add it to a mixer. Set the temperature to 155 ℃, the speed to 65 rpm, and the time to 5 min to mix until melted to obtain high-concentration masterbatch. 470.25 g PBAT, 24.75 g PLA, and high-concentration masterbatch were dried in a blower dryer at 60 ℃ for 12 h. The dried material was then added to a high-speed mixer and stirred at 3500 rpm for 8 min. The stirred material was then poured into a twin-screw extruder at a temperature of 160 / 165 / 170 / 165 / 160 ℃ and a screw speed of 30 rpm. After air drying at the outlet, the material was drawn into a pelletizer and pelletized to obtain composite masterbatch. The composite masterbatch was dried in a blower at 65 ℃ for 12 h and then added to a single-screw extruder at a temperature of 150 / 155 / 160 / 155 / 150 ℃ and a screw speed of 37 rpm to blow-dry a packaging film with a thickness of 33±1 μm. The resulting pH-responsive smart biodegradable packaging film was stored in the dark at low temperature.

[0026] Example 3: Preparation method of pH-responsive smart biodegradable packaging film The specific steps for preparing alizarin dispersion are as follows: First, weigh 4.6 g of alizarin powder and add it to 320 mL of deionized water. After stirring evenly, sonicate for 60 min to obtain alizarin dispersion.

[0027] The preparation of pH-responsive smart biodegradable packaging film involves the following specific steps: Weigh 60 g of PBAT / PLA blended resin with a mass ratio of 95:5 into a beaker, add all of the 320 mL alizarin dispersion obtained above into it, stir well, and then add it to a mixer. Set the temperature to 150 ℃, the speed to 65 rpm, and the time to 6 min to mix until melted to obtain high-concentration masterbatch. 513 g PBAT, 27 g PLA, and high-concentration masterbatch were dried in a blower dryer at 70 °C for 10 h. The dried material was then added to a high-speed mixer and stirred at 3500 rpm for 10 min. The stirred material was then poured into a twin-screw extruder at a temperature of 155 / 160 / 165 / 160 / 155 °C and a screw speed of 28 rpm. After air drying at the outlet, the material was drawn into a pelletizer and pelletized to obtain composite masterbatch. The composite masterbatch was dried in a blower at 65 °C for 12 h and then added to a single-screw extruder at a temperature of 145 / 150 / 155 / 150 / 145 °C and a screw speed of 38 rpm to form a packaging film with a thickness of 35 ± 1 μm. The resulting pH-responsive smart biodegradable packaging film was stored in the dark at low temperature.

[0028] Example 4: Preparation method of pH-responsive smart biodegradable packaging film The specific steps for preparing alizarin dispersion are as follows: First, weigh 3.75 g of alizarin powder and add it to 300 mL of deionized water. After stirring evenly, sonicate for 90 min to obtain alizarin dispersion.

[0029] The specific steps for preparing a pH-responsive smart biodegradable packaging film are as follows: Weigh 50 g of PBAT / PLA blended resin with a mass ratio of 95:5 into a beaker, add all of the 300 mL alizarin dispersion obtained above into it, stir well, and then add it to a mixer. Set the temperature to 160 ℃, the speed to 65 rpm, and the time to 10 min to mix until melted to obtain high-concentration masterbatch. 427.5 g PBAT, 22.5 g PLA, and high-concentration masterbatch were dried in a blower dryer at 65 ℃ for 10 h. The dried material was added to a high-speed mixer and stirred at 3500 rpm for 12 min. The stirred material was then poured into a twin-screw extruder at 145 / 150 / 155 / 150 / 145 ℃ and a screw speed of 28 rpm. After air drying at the outlet, the material was drawn into a pelletizer to obtain composite masterbatch. The composite masterbatch was dried in a blower at 65 ℃ for 12 h and then added to a single-screw extruder at 145 / 150 / 155 / 150 / 145 ℃ and a screw speed of 40 rpm to blow-dry a packaging film with a thickness of 37±1 μm. The resulting pH-responsive smart biodegradable packaging film was stored in the dark at low temperature.

[0030] Comparative Example 1 pH-responsive smart biodegradable packaging film was prepared using the same steps as in Example 1, except that alizarin dispersion was not added in Comparative Example 1, while the other steps were the same as in Example 1.

[0031] Experiment Example 1: pH Response Color Change Test Pipette 10 mL of 0.16 mol / L ammonia solution into a petri dish. Seal the pH-responsive smart biodegradable packaging film prepared in Examples 1-4 and Comparative Example 1 on the petri dish, cover it to prevent ammonia evaporation, take a picture every 4 minutes, and record the L using a colorimeter. * (Brightness), a * (Red-green hue), b * (Yellow-blue hue) and RGB (red-green-blue) values, and calculate the color difference ΔE and ammonia sensitivity S. RGB The results are shown Figure 1-3 .

[0032] The results showed that, among Examples 1-4, Example 4 exhibited the highest ammonia sensitivity and color difference, which continuously increased, indicating stable and most sensitive performance. Furthermore, it reached maximum dissolution without loss during dissolution. Therefore, the higher the concentration of alizarin within the packaging film, the more pronounced the film discoloration. With increasing ammonia fuming time, Examples 1-4 demonstrated a relatively rapid response to ammonia and significant color changes.

[0033] Experiment Example 2: Freshness Indication Test for Preserving Fresh Chicken Breast Fresh chicken breast was washed with sterile deionized water and dried with lint-free paper. It was then cut into approximately 40 g sample pieces. Each chicken breast sample was wrapped in the pH-responsive smart biodegradable packaging film prepared in Examples 1-4 and Comparative Example 1. The samples were placed in sterilized 90×10 mm plastic petri dishes and incubated at 25 ℃ for 3 days. The color change of the film was recorded daily by photographing. The results are shown below. Figure 4 The volatile basic nitrogen content of chicken breast was determined according to GB 5009.228-2016 standard, and the results are shown in the table below. Figure 5 .

[0034] Because food spoilage produces ammonia and amines, the more ammonia is produced during the preservation process, the more pronounced the color change of the film will be as the storage time increases. Figure 4 The results showed that the film color of Examples 1-4 became darker with increasing storage days, indicating that the film is suitable for chicken preservation and has an indicative function.

[0035] The national standard GB 2707-2016 stipulates that the volatile basic nitrogen content of fresh meat should be ≤15.00 mg / 100 g. On the first day, the meat packaged in Examples 1-4 and Comparative Example 1 exceeded the standard for fresh meat, and the packaging film of the examples showed a slight darkening in color. On the second day, the volatile basic nitrogen content was all above 25 mg / 100 g, and the color change of the packaging film of the examples was significant. Figure 4 Packaging film color and Figure 5 The results of volatile basic nitrogen content show that the color of the packaging film provided in this application is positively correlated with the degree of spoilage, which can more intuitively determine the freshness of food.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any equivalent substitutions or modifications made by those skilled in the art within the spirit and principle of the present invention without any creative effort should be included within the protection scope of the present invention.

Claims

1. A pH-responsive smart biodegradable packaging film, characterized in that, Its raw material composition by weight is as follows: fully biodegradable resin: 93-99.7 parts, alizarin: 0.3-7 parts; The fully biodegradable resin is a mixture of PBAT and PLA in a mass ratio of (85-95):(5-15).

2. The pH-responsive smart biodegradable packaging film according to claim 1, characterized in that, The mass ratio of PBAT to PLA is 95:5; the weight of alizarin is 0.3-1.0 parts.

3. The pH-responsive smart biodegradable packaging film according to claim 1, characterized in that, The thickness of the packaging film is 20-40 μm.

4. The pH-responsive smart biodegradable packaging film according to claim 1, characterized in that, The purity of the alizarin is ≥98%.

5. The method for preparing the pH-responsive smart biodegradable packaging film according to claim 1, characterized in that, Includes the following steps: (1) Preparation of alizarin dispersion: Weigh alizarin powder and add it to deionized water at a ratio of 1g: 50-100 mL; ultrasonically disperse for 30-90 min to obtain a uniform alizarin dispersion; (2) Preparation of high-concentration masterbatch: Weigh 10%-15% of the total mass of the biodegradable resin, pour all the alizarin dispersion into the above resin, mix evenly and then add it to the internal mixer, set the temperature to 150-160℃, the speed to 60-70 rpm, and the time to 5-10 min to internally mix until melted to obtain high-concentration masterbatch. (3) Preparation of composite masterbatch: The remaining amount of fully biodegradable resin and the high-concentration masterbatch obtained above are dried at 60-80℃ for 9-12 h. The dried material is added to a high-speed mixer and stirred at 3000-3500 rpm for 6-10 min. The stirred material is poured into a twin-screw extruder. The five temperature ranges from the feed inlet to the die head are set as 145-165℃, 150-170℃, 155-175℃, 150-170℃, and 145-165℃ respectively. The screw speed is 25-35 rpm. After melt blending, the material is extruded from the die head, air-dried, and then granulated by a pelletizer to obtain uniform composite masterbatch. (4) The composite masterbatch obtained above is dried at 60-70℃ for 9-12 h and then fed into a single screw extruder. The temperature range from the feed inlet to the die head is set to 145-155℃, 150-160℃, 155-170℃, 150-165℃, and 145-160℃ respectively, and the screw speed is 30-50 rpm. After the material is melt-extruded, it is blown into a film by a blown film machine to obtain a pH-responsive intelligent biodegradable packaging film. The film is cooled and shaped and then wound up.

6. The method for preparing the pH-responsive smart biodegradable packaging film according to claim 5, characterized in that, In step (1), the ratio of alizarin powder to deionized water is 1 g: 80 mL.

7. The method for preparing the pH-responsive smart biodegradable packaging film according to claim 5, characterized in that, The fully biodegradable resin in steps (2) and (3) is a mixture of PBAT particles and PLA particles with a mixing mass ratio of (85-95):(5-15) and a particle size of 2-4 mm.

8. The application of the pH-responsive smart biodegradable packaging film of claim 1 in the visualization monitoring of freshness and preservation packaging.

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