Biodegradable antibacterial smart color-changing printing packaging materials and their preparation methods

Abstract

This invention relates to the field of color-changing printing and packaging materials technology, and particularly to a biodegradable, antibacterial, intelligent color-changing printing and packaging material and its preparation method. By weight, it comprises the following components: 63-67 parts of a blend of PLLA and PDLA, wherein the mass ratio of PLLA to PDLA is 70:30 to 90:10; 19-21 parts of a P(3HB-co-4HB) copolymer, wherein the molar ratio of 3HB to 4HB is 85:15 to 95:5; 17-18 parts of modified starch; 3.4-3.8 parts of surface-modified nano-silver; 7.7-8.3 parts of a pH-sensitive dye system; 8.0-8.6 parts of a silane coupling agent KH550; and 6.9-7.5 parts of kaolin. By controlling the stereoregularity and D-isomer content of PLLA and PDLA, the crystallinity and thermal stability of the material are improved through a stereocomposite effect.

Description

Technical Field

[0001] This invention relates to the field of color-changing printed packaging materials technology, and in particular to biodegradable antibacterial intelligent color-changing printed packaging materials and their preparation methods. Background Technology

[0002] With increasing environmental awareness and stricter food safety requirements, the development of bio-based smart packaging materials has become a current research hotspot. Among existing technologies, polylactic acid (PLA) is widely studied due to its good biocompatibility and processability. However, PLA has inherent defects such as high brittleness and poor thermal stability. Although blending modification can improve the performance of PLA to some extent, current modification methods often have trade-offs: toughening modification reduces the material's degradation performance, while improving degradation performance often sacrifices mechanical properties.

[0003] Furthermore, most smart packaging materials currently on the market use direct blending or loading of pH-sensitive dyes, a method that suffers from serious dye migration and shedding problems. Although some researchers have attempted to introduce pH-sensitive groups into polymer chains through chemical grafting, the demanding reaction conditions and complex processes make large-scale production difficult. At the same time, these materials often have slow pH responses and insufficient sensitivity, failing to meet practical application requirements.

[0004] Regarding antibacterial properties, current technologies often employ the simple method of adding nano-silver. However, due to the tendency of nano-silver to aggregate, its dispersibility and stability are poor, which not only affects the antibacterial effect but also leads to uneven material properties. Although some studies have improved the dispersibility of nano-silver through surfactants, this method introduces new compatibility issues, and the presence of surfactants may affect the food contact safety of the material.

[0005] A common problem in existing technologies is the lack of synergistic effects between functional components. For example, the addition of antibacterial agents may affect the responsiveness of pH-sensitive dyes, while the introduction of toughening agents may reduce the gas barrier properties of the material. This "one-for-one" phenomenon severely restricts the practical application of smart packaging materials. Summary of the Invention

[0006] To address the above problems, this invention provides a biodegradable, antibacterial, intelligent color-changing printing packaging material and its preparation method.

[0007] The purpose of this invention is to provide a biodegradable, antibacterial, intelligent color-changing printed packaging material, comprising the following components by weight:

[0008] 63-67 parts of a blend of PLLA and PDLA, wherein the mass ratio of PLLA to PDLA is 70:30 to 90:10;

[0009] 19-21 parts of P(3HB-co-4HB) copolymer, wherein the molar ratio of 3HB to 4HB is 85:15 to 95:5;

[0010] 17-18 parts modified starch;

[0011] 3.4-3.8 parts of surface-modified nano-silver;

[0012] 7.7-8.3 parts pH-sensitive dye system;

[0013] 8.0-8.6 parts of silane coupling agent KH550;

[0014] 6.9-7.5 parts kaolin.

[0015] Preferably, the blend of PLLA and PDLA has a D-isomer content of 0.5-2%, a stereoregularity of 98-99.5%, and a weight-average molecular weight of 100,000-150,000.

[0016] Preferably, the P(3HB-co-4HB) copolymer has a molecular weight distribution of 1.8-2.2 and a crystallinity of 55-65%.

[0017] Preferably, the modified starch comprises the following components by weight:

[0018] 21-23 parts corn starch, of which amylose content is 23-27%;

[0019] 6.5-7.5 parts of surface-modified nano-CaCO3 with a particle size of 40-60 nm;

[0020] 1.8-2.2 parts of hydroxymethyl cellulose, with a degree of substitution of 1.6-2.0;

[0021] 7.5-8.5 parts deionized water.

[0022] Preferably, the pH-sensitive dye system is composed of a copolymer obtained by free radical polymerization of the following monomers and Acid Violet 49 in a mass ratio of 3.5:1 to 4.5:1:

[0023] 43-47 parts styrene;

[0024] 33-37 parts acrylic acid;

[0025] 19-21 parts of 2-aminoethyl 2-methacrylate;

[0026] 0.45-0.55 AIBN.

[0027] The preparation method of the aforementioned biodegradable antibacterial smart color-changing printing packaging material includes the following steps:

[0028] (1) Preparation of modified starch:

[0029] a) Mix corn starch with deionized water at 115-120℃ and 0.18-0.22MPa, and stir at a rate of 210-230rpm for 33-37min.

[0030] b) Add surface-modified nano-CaCO3 and hydroxymethyl cellulose, heat to 135-145℃, and stir at 230-250 rpm for 38-42 min at 0.28-0.32 MPa.

[0031] (2) Preparation of surface-modified nano-silver:

[0032] a) Using 0.01-0.02 mol / L silver nitrate as raw material, and 0.5-1.0 wt% PVP as a protective agent, react at 78-82℃ for 28-32 min;

[0033] b) Add 2-3 wt% of mercaptosilane coupling agent KH590 and modify at 58-62℃ for 3.5-4.5 h;

[0034] (3) Preparation of pH-sensitive dye system:

[0035] Free radical polymerization was carried out at 73-77℃ and nitrogen protection with a stirring rate of 170-190 rpm for 5.5-6.5 h, followed by compounding with Acid Violet 49 at 48-52℃ for 1.8-2.2 h.

[0036] (4) Blending with matrix materials:

[0037] Under conditions of 175-185℃ and vacuum degree of -0.05 to -0.07MPa, modified PLA and modified PHA were stirred at a rate of 220-240rpm for 38-42min.

[0038] (5) Functional component combination:

[0039] Modified nano-silver, pH-sensitive dye system, coupling agent KH550, and kaolin were added sequentially, using a segmented heating program:

[0040] a) 180℃ to 200℃, heating rate 1.8-2.2℃ / min;

[0041] b) 200℃ to 250℃, heating rate 0.8-1.2℃ / min;

[0042] c) Keep warm at 240-260℃ for 28-32 minutes.

[0043] Preferably, the dispersion process in step (5) employs a shear control procedure:

[0044] The initial shear rate is 45-55 s⁻¹.

[0045] The termination shear rate is 190-210 s⁻¹.

[0046] The linear increase time was 14-16 min.

[0047] Preferably, the vacuum control procedure in step (5) is as follows:

[0048] The initial vacuum level was -0.018 to -0.022 MPa.

[0049] The final vacuum level is -0.058 to -0.062 MPa.

[0050] The vacuuming time is 18-22 minutes.

[0051] Preferably, the cooling procedure after step (5) is as follows:

[0052] Cooling rate: 2.8-3.2℃ / min, from 250℃ to 180℃;

[0053] Cooling rate from 180℃ to 100℃: 4.8-5.2℃ / min;

[0054] Natural cooling is used for temperatures below 100℃.

[0055] Preferably, the method for preparing the surface-modified nano-CaCO3 is as follows:

[0056] Nano-CaCO3 with a particle size of 40-60 nm and stearic acid with a mass fraction of 1.5-2.0% were stirred at 75-85 °C at a speed of 180-220 rpm for 1.8-2.2 h.

[0057] The present invention has the following beneficial effects:

[0058] Through molecular design and process innovation, the aforementioned technical challenges were ingeniously solved. First, by controlling the stereoregularity and D-isomer content of PLLA and PDLA, the crystallinity and thermal stability of the material were improved by utilizing the stereocomplex effect. At the molecular level, the two configurations of PLA molecular chains formed a stable stereocomplex crystal through stereoselective crystallization, which not only improved the material's strength but also significantly enhanced its heat resistance.

[0059] Secondly, the pH-sensitive copolymer developed in this invention has a unique molecular structure: the hydrophobic styrene units provide good matrix compatibility, while the acrylic acid and 2-methacrylate-2-aminoethyl ester units form a dynamic response network through hydrogen bonding. When the ambient pH changes, the protonation / deprotonation process causes a synergistic change in the copolymer chain conformation, thereby achieving a rapid and reversible color change response.

[0060] Of particular note is the breakthrough achieved in the surface modification of silver nanoparticles. Through chemical modification with a mercaptosilane coupling agent, an interface layer with a gradient transition structure was constructed on the surface of the silver nanoparticles. This interface design not only provides steric hindrance to prevent aggregation but also achieves strong interaction with the matrix through chemical bonding. Even more surprisingly, this surface-modified silver nanoparticle can synergistically interact with pH-sensitive dyes, enhancing the intensity of the color-changing signal through localized plasmon resonance.

[0061] At the process level, this invention establishes a precise temperature-shear coupling control system. Through programmed segmented heating and shear regulation, the directional arrangement and selective crystallization of multi-component systems are achieved. This process innovation not only optimizes the microstructure of the material but also significantly improves processing stability and reproducibility.

[0062] In summary, this invention, through multi-level molecular design and process innovation, achieves synergistic improvements in various material properties, successfully overcoming the bottlenecks of existing technologies. In particular, the groundbreaking progress achieved in degradation performance, antibacterial effects, and intelligent response has opened up new avenues for the development of bio-based intelligent packaging materials. These innovations not only solve long-standing technical problems in the industry but also bring about several unexpected synergistic effects, demonstrating the significant theoretical value and practical application prospects of this invention. Detailed Implementation

[0063] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0064] Example 1

[0065] This embodiment provides a biodegradable, antibacterial, and intelligent color-changing printing packaging material and its preparation method. In this embodiment, by optimizing the proportions of each component and the preparation process, the material achieves excellent biodegradability, antibacterial properties, and intelligent color-changing functions.

[0066] The packaging material, by weight, comprises the following components: 63 parts of a blend of PLLA and PDLA (mass ratio 70:30), 19 parts of a P(3HB-co-4HB) copolymer (molar ratio of 3HB to 4HB 85:15), 17 parts of modified starch, 3.4 parts of surface-modified nano-silver, 7.7 parts of a pH-sensitive dye system, 8.0 parts of silane coupling agent KH550, and 6.9 parts of kaolin. The PLLA and PDLA blend contains 0.5% D-isomers, has a stereoregularity of 98%, and a weight-average molecular weight of 100,000. The P(3HB-co-4HB) copolymer has a molecular weight distribution of 1.8 and a crystallinity of 55%.

[0067] The preparation method of this embodiment includes the following steps:

[0068] (1) Preparation of modified starch

[0069] First, 21 parts by weight of corn starch (amylose content 23%), 6.5 parts by weight of surface-modified nano-CaCO3 (particle size 40 nm), 1.8 parts by weight of hydroxymethyl cellulose (degree of substitution 1.6), and 7.5 parts by weight of deionized water were weighed. The corn starch and deionized water were mixed at 115°C and 0.18 MPa, and stirred at 210 rpm for 33 min. Then, the surface-modified nano-CaCO3 and hydroxymethyl cellulose were added, the temperature was raised to 135°C, and the mixture was stirred at 230 rpm for 38 min under a pressure of 0.28 MPa.

[0070] Preferably, in the preparation process of the modified starch, the surface modification of nano-CaCO3 is carried out by the following method: 40nm nano-CaCO3 and 1.5% stearic acid are stirred at 75°C at a rate of 180rpm for 1.8h. This modification process significantly improves the compatibility between nano-CaCO3 and the matrix.

[0071] (2) Preparation of surface-modified nano-silver

[0072] A 0.01 mol / L silver nitrate solution was used as the raw material, and 0.5 wt% PVP was added as a protective agent. The reaction was carried out at 78 °C for 28 min. Preferably, under these reaction conditions, the nano-silver particles obtained have a uniform size distribution, which is beneficial to improving the antibacterial properties of the material. Subsequently, 2 wt% of mercaptosilane coupling agent KH590 was added, and the mixture was modified at 58 °C for 3.5 h. Notably, the surface modification with the silane coupling agent significantly improved the dispersion stability of the nano-silver in the polymer matrix, thereby enhancing the long-lasting antibacterial properties of the material.

[0073] (3) Preparation of pH-sensitive dye system

[0074] Under nitrogen protection, 43 parts styrene, 33 parts acrylic acid, 19 parts 2-methacrylate-2-aminoethyl ester, and 0.45 parts AIBN were subjected to free radical polymerization for 5.5 h at 73 °C and a stirring rate of 170 rpm. In particular, the choice of this copolymer composition resulted in an ideal response sensitivity for the pH-sensitive dye. Subsequently, the obtained copolymer was compounded with Acid Violet 49 at a mass ratio of 3.5:1 at 48 °C for 1.8 h to obtain a functional component with excellent pH response properties.

[0075] (4) Blending of matrix materials

[0076] Modified PLA and modified PHA were stirred at 220 rpm for 38 min at 175℃ and a vacuum of -0.05 MPa. Notably, under these conditions, PLA and PHA formed an interpenetrating network structure, and this unique microstructure significantly improved the toughness of the material.

[0077] (5) Functional component compounding

[0078] A segmented heating program was used to sequentially add modified nano-silver, a pH-sensitive dye system, coupling agent KH550, and kaolin to the matrix material. Specifically:

[0079] a) First, raise the temperature from 180℃ to 200℃ at a rate of 1.8℃ / min;

[0080] b) Continue heating to 250℃, adjusting the heating rate to 0.8℃ / min;

[0081] c) Keep warm at 240℃ for 28 minutes.

[0082] During the dispersion process, programmed shear control was employed: the initial shear rate was 45 s⁻¹, the final shear rate was 190 s⁻¹, and the linear increase time was 14 min. Simultaneously, the vacuum control program was: initial vacuum level -0.018 MPa, final vacuum level -0.058 MPa, and evacuation time 18 min.

[0083] Finally, a segmented cooling process was adopted: the 250℃ to 180℃ segment was cooled at a rate of 2.8℃ / min, the 180℃ to 100℃ segment was cooled at a rate of 4.8℃ / min, and natural cooling was used below 100℃. It should be noted that this precisely controlled cooling process has a significant impact on the final crystallinity and mechanical properties of the material.

[0084] Preferably, the synergistic combination of the polymer matrix, functional filler, and their preparation process in this embodiment gives the material the following characteristics:

[0085] 1) By blending PLA / PHA and introducing modified starch, the biodegradability of the material was significantly improved while ensuring its mechanical properties.

[0086] 2) The combined use of nano-silver and pH-sensitive dyes not only endows the material with antibacterial properties, but also enables intelligent monitoring of food freshness.

[0087] 3) Synergistic modification of interfaces in multi-component systems effectively solves the compatibility problem that is common in composite materials.

[0088] Through the optimized component ratio and preparation process described above, the packaging material prepared in this embodiment exhibits excellent comprehensive performance. Specifically, the material achieves a biodegradability of 99.8%, an antibacterial rate of 90.0%, and a color difference ΔE*ab of 0.1 for its intelligent color-changing performance at 5°C, fully meeting relevant standard requirements.

[0089] Example 2

[0090] This embodiment also provides a biodegradable antibacterial smart color-changing printing packaging material and its preparation method. Compared with Example 1, this embodiment optimizes and adjusts the proportions of each component and the preparation process parameters, further improving the material performance.

[0091] The packaging material, by weight, comprises the following components: 65 parts of a blend of PLLA and PDLA (mass ratio 80:20), 20 parts of a P(3HB-co-4HB) copolymer (molar ratio of 3HB to 4HB 90:10), 17.5 parts of modified starch, 3.6 parts of surface-modified nano-silver, 8.0 parts of a pH-sensitive dye system, 8.3 parts of silane coupling agent KH550, and 7.2 parts of kaolin. The PLLA and PDLA blend contains 1.25% D-isomers, has a stereoregularity of 98.8%, and a weight-average molecular weight of 125,000. Preferably, the P(3HB-co-4HB) copolymer has a molecular weight distribution of 2.0 and a crystallinity of 60%.

[0092] The preparation method of this embodiment includes the following steps:

[0093] (1) Preparation of modified starch

[0094] First, 22 parts by weight of corn starch (25% amylose content), 7.0 parts by weight of surface-modified nano-CaCO3 (50 nm particle size), 2.0 parts by weight of hydroxymethyl cellulose (degree of substitution 1.8), and 8.0 parts by weight of deionized water were weighed. The corn starch and deionized water were mixed at 117.5 °C and 0.20 MPa, and stirred at 220 rpm for 35 min. Further, the surface-modified nano-CaCO3 and hydroxymethyl cellulose were added, the temperature was raised to 140 °C, and the mixture was stirred at 240 rpm for 40 min under 0.30 MPa pressure. Notably, this modification process significantly improved the compatibility of the starch with the polyester matrix.

[0095] Specifically, in the preparation of the modified starch, the surface modification of nano-CaCO3 is carried out by the following method: 50 nm nano-CaCO3 and 1.75% stearic acid are stirred at 80 °C at a rate of 200 rpm for 2.0 h.

[0096] (2) Preparation of surface-modified nano-silver

[0097] A 0.015 mol / L silver nitrate solution was used as the raw material, and 0.75 wt% PVP was added as a protective agent. The reaction was carried out at 80 °C for 30 min. Subsequently, 2.5 wt% mercaptosilane coupling agent KH590 was added, and the reaction was modified at 60 °C for 4.0 h. Preferably, by controlling the reaction conditions, nano-silver particles with uniform particle size and good dispersibility were obtained.

[0098] (3) Preparation of pH-sensitive dye system

[0099] Under nitrogen protection, 45 parts styrene, 35 parts acrylic acid, 20 parts 2-methacrylate-2-aminoethyl ester, and 0.50 parts AIBN were subjected to free radical polymerization for 6.0 h at 75 °C and a stirring rate of 180 rpm. Further, the resulting copolymer was compounded with Acid Violet 49 at a mass ratio of 4:1 at 50 °C for 2.0 h. This optimized formulation improved the color change sensitivity of the material.

[0100] (4) Blending of matrix materials

[0101] Modified PLA and modified PHA were stirred at 230 rpm for 40 min at 180 °C and a vacuum of -0.06 MPa. In particular, the selection of these process parameters is conducive to the formation of a stable blend system.

[0102] (5) Functional component compounding

[0103] Using an optimized segmented heating program, each functional component is added sequentially:

[0104] a) The temperature is increased from 180℃ to 200℃ at a rate of 2.0℃ / min;

[0105] b) Continue heating to 250℃ at a rate of 1.0℃ / min;

[0106] c) Keep warm at 250℃ for 30 minutes.

[0107] During the dispersion process, an improved shear control program was adopted: the initial shear rate was 50 s⁻¹, the final shear rate was 200 s⁻¹, and the linear increase time was 15 min. Simultaneously, the vacuum control program was: initial vacuum degree -0.020 MPa, final vacuum degree -0.060 MPa, and evacuation time 20 min.

[0108] Finally, an optimized cooling program is adopted: cooling at a rate of 3.0℃ / min from 250℃ to 180℃, cooling at a rate of 5.0℃ / min from 180℃ to 100℃, and natural cooling below 100℃.

[0109] Example 3

[0110] This embodiment provides a biodegradable antibacterial smart color-changing printing packaging material with further optimized component ratios and process parameters, and its preparation method. Compared with the previous two embodiments, this embodiment focuses on enhancing the antibacterial properties and pH response characteristics of the material.

[0111] The packaging material, by weight, comprises the following components: 66 parts of a blend of PLLA and PDLA (mass ratio 85:15), 20.5 parts of a P(3HB-co-4HB) copolymer (molar ratio of 3HB to 4HB 92:8), 18 parts of modified starch, 3.7 parts of surface-modified nano-silver, 8.2 parts of a pH-sensitive dye system, 8.5 parts of silane coupling agent KH550, and 7.4 parts of kaolin. The PLLA and PDLA blend contains 1.5% D-isomers, has a stereoregularity of 99%, and a weight-average molecular weight of 135,000. Notably, the P(3HB-co-4HB) copolymer has a molecular weight distribution of 2.1 and a crystallinity of 62%.

[0112] The preparation method of this embodiment includes the following steps:

[0113] (1) Preparation of modified starch

[0114] First, 22.5 parts by weight of corn starch (amylose content 26%), 7.2 parts by weight of surface-modified nano-CaCO3 (particle size 55 nm), 2.1 parts by weight of hydroxymethyl cellulose (degree of substitution 1.9), and 8.2 parts by weight of deionized water were weighed. The corn starch and deionized water were mixed at 118°C and 0.21 MPa, and stirred at 225 rpm for 36 min. Next, the surface-modified nano-CaCO3 and hydroxymethyl cellulose were added, the temperature was raised to 142°C, and the mixture was stirred at 245 rpm for 41 min under 0.31 MPa pressure.

[0115] Preferably, the surface modification of nano-CaCO3 is carried out by the following method: 55 nm nano-CaCO3 and 1.85% stearic acid are stirred at 82 °C at a rate of 210 rpm for 2.1 h.

[0116] (2) Preparation of surface-modified nano-silver

[0117] A 0.018 mol / L silver nitrate solution was used as the raw material, and 0.85 wt% PVP was added as a protective agent. The reaction was carried out at 81 °C for 31 min. Subsequently, 2.7 wt% mercaptosilane coupling agent KH590 was added, and the reaction was carried out at 61 °C for 4.2 h. This optimized process parameter significantly improved the dispersion stability of the nano-silver.

[0118] (3) Preparation of pH-sensitive dye system

[0119] Under strict nitrogen protection, 46 parts styrene, 36 parts acrylic acid, 20.5 parts 2-methacrylate-2-aminoethyl ester, and 0.52 parts AIBN were subjected to free radical polymerization for 6.2 h at 76 °C and a stirring rate of 185 rpm. Specifically, the resulting copolymer was compounded with Acid Violet 49 at a mass ratio of 4.2:1 at 51 °C for 2.1 h.

[0120] (4) Blending of matrix materials

[0121] Modified PLA and modified PHA were stirred at 235 rpm for 41 min at 182℃ and a vacuum of -0.065 MPa.

[0122] (5) Functional component compounding

[0123] An optimized segmented heating program was used to add each functional component sequentially:

[0124] a) The temperature is increased from 180℃ to 200℃ at a rate of 2.1℃ / min;

[0125] b) Continue heating to 250℃ at a rate of 1.1℃ / min;

[0126] c) Keep warm at 255℃ for 31 minutes.

[0127] During the dispersion process, a refined shear control program was adopted: the initial shear rate was 52 s⁻¹, the final shear rate was 205 s⁻¹, and the linear increase time was 15.5 min. Simultaneously, the vacuum control program was: initial vacuum degree -0.021 MPa, final vacuum degree -0.061 MPa, and evacuation time 21 min.

[0128] Finally, a three-stage cooling process is adopted: cooling from 250℃ to 180℃ at a rate of 3.1℃ / min, cooling from 180℃ to 100℃ at a rate of 5.1℃ / min, and natural cooling below 100℃.

[0129] Example 4

[0130] This embodiment demonstrates a biodegradable, antibacterial, intelligent color-changing printing and packaging material with optimized parameter ratios, and its preparation method. This embodiment places particular emphasis on the balance and synergy of various material properties.

[0131] The packaging material, by weight, comprises the following components: 67 parts of a blend of PLLA and PDLA (mass ratio 90:10), 21 parts of a P(3HB-co-4HB) copolymer (molar ratio of 3HB to 4HB 95:5), 18 parts of modified starch, 3.8 parts of surface-modified nano-silver, 8.3 parts of a pH-sensitive dye system, 8.6 parts of silane coupling agent KH550, and 7.5 parts of kaolin. Specifically, the PLLA and PDLA blend contains 2% D-isomers, has a stereoregularity of 99.5%, and a weight-average molecular weight of 150,000. The P(3HB-co-4HB) copolymer has a molecular weight distribution of 2.2 and a crystallinity of 65%.

[0132] The preparation method of this embodiment includes the following steps:

[0133] (1) Preparation of modified starch

[0134] First, 23 parts by weight of corn starch (amylose content 27%), 7.5 parts by weight of surface-modified nano-CaCO3 (particle size 60 nm), 2.2 parts by weight of hydroxymethyl cellulose (degree of substitution 2.0), and 8.5 parts by weight of deionized water were weighed. The corn starch and deionized water were mixed at 120°C and 0.22 MPa, and stirred at 230 rpm for 37 min. Further, the surface-modified nano-CaCO3 and hydroxymethyl cellulose were added, the temperature was raised to 145°C, and the mixture was stirred at 250 rpm for 42 min under 0.32 MPa pressure. Notably, these optimized process parameters resulted in the modified starch exhibiting the best toughening effect.

[0135] Specifically, the surface modification of nano-CaCO3 was performed by stirring 60 nm nano-CaCO3 with 2.0% stearic acid at 85 °C at a rate of 220 rpm for 2.2 h. This modification process significantly improved the surface activity of nano-CaCO3.

[0136] (2) Preparation of surface-modified nano-silver

[0137] A 0.02 mol / L silver nitrate solution was used as the raw material, and 1.0 wt% PVP was added as a protective agent. The reaction was carried out at 82 °C for 32 min. Preferably, 3.0 wt% mercaptosilane coupling agent KH590 was added, and the modification was carried out at 62 °C for 4.5 h. It is worth noting that the silver nanoparticles prepared under these conditions have the optimal particle size distribution and dispersion stability.

[0138] (3) Preparation of pH-sensitive dye system

[0139] Under strict nitrogen protection, 47 parts styrene, 37 parts acrylic acid, 21 parts 2-methacrylate-2-aminoethyl ester, and 0.55 parts AIBN were subjected to free radical polymerization for 6.5 h at 77 °C and a stirring rate of 190 rpm. Further, the resulting copolymer was compounded with Acid Violet 49 at a mass ratio of 4.5:1 at 52 °C for 2.2 h. These optimized process parameters resulted in the pH-sensitive dye system exhibiting the best response sensitivity.

[0140] (4) Blending of matrix materials

[0141] Modified PLA and modified PHA were stirred at 240 rpm for 42 min at 185 °C and a vacuum of -0.07 MPa. Specifically, these process conditions ensured thorough blending of the two polymers, resulting in an ideal interpenetrating network structure.

[0142] (5) Functional component compounding

[0143] A precisely controlled, segmented heating program is used to add each functional component sequentially:

[0144] a) The temperature is increased from 180℃ to 200℃ at a rate of 2.2℃ / min;

[0145] b) Continue heating to 250℃ at a rate of 1.2℃ / min;

[0146] c) Keep warm at 260℃ for 32 minutes.

[0147] During the dispersion process, an optimized shear control program was adopted: the initial shear rate was 55 s⁻¹, the final shear rate was 210 s⁻¹, and the linear increase time was 16 min. Simultaneously, the vacuum control program was: initial vacuum degree -0.022 MPa, final vacuum degree -0.062 MPa, and evacuation time 22 min.

[0148] Finally, a precisely controlled cooling program is employed: cooling from 250°C to 180°C at a rate of 3.2°C / min, cooling from 180°C to 100°C at a rate of 5.2°C / min, and natural cooling below 100°C.

[0149] The above four embodiments fully demonstrate the feasibility of the present invention and the optimization potential of its various technical parameters. It is worth noting that these embodiments cleverly achieve a synergistic effect among the various components of the material:

[0150] 1) The PLA / PHA blend system achieves an ideal compatible structure through precisely controlled process parameters;

[0151] 2) The introduction of modified starch not only improved the degradation performance of the material, but also played a toughening role;

[0152] 3) The combined use of nano-silver and pH-sensitive dyes produced an excellent synergistic effect, which not only ensured the antibacterial properties of the material, but also achieved a precise response to the pH of the environment.

[0153] 4) The multi-component system achieves good interfacial bonding through optimized process parameters.

[0154] The materials prepared in the above embodiments all exhibit excellent comprehensive performance and fully meet the relevant standard requirements. In particular, the formulation and process parameters in Example 4 achieve an optimal balance between antibacterial properties and intelligent color-changing function while maintaining high biodegradability.

[0155] Comparative Example 1

[0156] This comparative example serves as a reference to Example 1, primarily verifying the effect of nano-silver surface modification on the antibacterial properties of the material. While maintaining all other components and process parameters identical to those in Example 1, this comparative example uses unmodified nano-silver.

[0157] Specifically, the material comprises, by weight: 63 parts of a blend of PLLA and PDLA (other parameters are the same as in Example 1), 19 parts of P(3HB-co-4HB) copolymer, 17 parts of modified starch, 3.4 parts of unmodified nano silver, 7.7 parts of pH-sensitive dye system, 8.0 parts of silane coupling agent KH550, and 6.9 parts of kaolin.

[0158] In the preparation method, except for the preparation step of nano-silver, all other steps are the same as in Example 1. The nano-silver in this comparative example is prepared directly by chemical reduction: 0.01 mol / L silver nitrate solution is reduced at 78°C for 28 min, and only 0.5 wt% PVP is added as a protective agent, without surface modification.

[0159] Test results show that, due to the lack of surface modification, the dispersion of nano-silver in the matrix is ​​poor, and agglomeration is obvious. This directly leads to a significant decrease in the antibacterial properties of the material, with an antibacterial rate of only 75%, far lower than the 90.0% of Example 1. This result fully demonstrates the importance of surface modification in improving the dispersibility and antibacterial effect of nano-silver.

[0160] Comparative Example 2

[0161] This comparative example, Example 2, focuses on verifying the effect of the PLA / PHA blending ratio on the mechanical properties and degradation performance of the material.

[0162] This comparative example adjusts the mass ratio of PLA / PHA to 90:10 (much higher than the ratio in Example 2), and the specific components are: 85 parts of a blend of PLLA and PDLA, 10 parts of P(3HB-co-4HB) copolymer, 17.5 parts of modified starch, 3.6 parts of surface-modified nano silver, 8.0 parts of pH-sensitive dye system, 8.3 parts of silane coupling agent KH550 and 7.2 parts of kaolin.

[0163] The preparation method is basically the same as in Example 2, but in the matrix material blending step, due to the significant increase in PLA content, the temperature is increased to 185°C and the stirring time is extended to 45 min.

[0164] Test results showed that excessive PLA content led to material brittleness, reducing elongation at break by approximately 50%. Simultaneously, insufficient PHA content significantly reduced the material's biodegradation rate, with a 90-day degradation rate of only 85%, far below the design target. This fully demonstrates the rationality of the PLA / PHA ratio in this invention.

[0165] Comparative Example 3

[0166] This comparative example, Example 3, primarily verifies the effect of the copolymer composition of the pH-sensitive dye system on its color-changing properties. The proportions of the comonomers in this comparative example were adjusted to verify the rationality of the monomer ratios in the original scheme.

[0167] The specific components, by weight, include: 66 parts of a blend of PLLA and PDLA, 20.5 parts of P(3HB-co-4HB) copolymer, 18 parts of modified starch, 3.7 parts of surface-modified nano-silver, 8.2 parts of an improved pH-sensitive dye system (monomer ratio adjusted to: 55 parts styrene, 25 parts acrylic acid, 20.5 parts 2-methacrylate-2-aminoethyl ester), 8.5 parts of silane coupling agent KH550, and 7.4 parts of kaolin.

[0168] In the preparation method, except for the preparation of the pH-sensitive dye, all other steps are the same as in Example 3. The pH-sensitive dye was prepared under the same conditions, but due to the change in monomer ratio, the hydrophilicity of the resulting copolymer was significantly reduced. Test results show that due to the excessively high styrene content, the density of the pH-sensitive groups decreased, leading to a significant decrease in the pH response sensitivity of the material. The color difference ΔE*ab at 5°C was only 0.05, which cannot meet the requirements for rapid detection. This verifies the scientific validity of the monomer ratio in the original scheme of this invention.

[0169] Comparative Example 4

[0170] This comparative example, Example 4, focuses on verifying the comprehensive impact of modified starch composition on material properties. In this comparative example, the starch was not modified with nano-CaCO3; only ordinary starch and hydroxymethyl cellulose were used as a composite.

[0171] The material composition is as follows: 67 parts of PLLA and PDLA blend, 21 parts of P(3HB-co-4HB) copolymer, 18 parts of unmodified starch component (25 parts of ordinary corn starch, 2.2 parts of hydroxymethyl cellulose, and 8.5 parts of deionized water), 3.8 parts of surface-modified nano silver, 8.3 parts of pH-sensitive dye system, 8.6 parts of silane coupling agent KH550, and 7.5 parts of kaolin.

[0172] In the preparation method, the steps for preparing the modified starch are simplified as follows: corn starch and deionized water are mixed at 120°C, hydroxymethyl cellulose is added, and then stirred at 145°C. Test results show that due to the lack of reinforcement from nano-CaCO3, the mechanical properties of the material are significantly reduced, with tensile strength decreasing by approximately 30%. Simultaneously, the starch exhibits poor compatibility with the polyester matrix, resulting in significant phase separation, which not only affects the transparency of the material but also leads to uneven degradation.

[0173] Comparative Example 5

[0174] This comparative example, comparing Examples 1 and 4, verifies the influence of processing parameters on material properties. The component ratios are the same as those in Example 4, but the processing method is simplified.

[0175] The segmented heating process was eliminated during preparation, and the functional components were directly compounded at 250°C. A constant shear rate of 180 s⁻¹ was also used, eliminating programmed shear control. Other parameters were the same as in Example 4. Results showed that due to the lack of precise process control, the material exhibited significant thermal degradation, with a molecular weight reduction of approximately 20%. Furthermore, the uneven dispersion of the functional components led to significant fluctuations in both antibacterial and discoloration properties. This fully demonstrates the necessity of refined process control in this invention.

[0176] Comparative Example 6

[0177] This comparative example, Example 2, focuses on verifying the impact of filler type on the overall performance of the material. In this comparative example, kaolin was replaced with the same amount of talc.

[0178] In this material composition, except that 7.2 parts of kaolin were replaced with 7.2 parts of talc, the other components and their contents were exactly the same as in Example 2. The preparation method was also the same as in Example 2. Test results showed that although talc could play a certain reinforcing role, its gas barrier properties were reduced by about 40% due to its different plate-like structure compared to kaolin. Furthermore, talc has fewer functional groups on its surface, resulting in weaker interfacial bonding with the matrix, making it prone to forming micropores during degradation and affecting the material's service life.

[0179] Through the systematic study of the above six comparative examples, the innovation and superiority of this invention in the following aspects have been fully verified:

[0180] 1) Surface modification with nano-silver significantly improves antibacterial properties;

[0181] 2) The optimal PLA / PHA ratio achieves a balance between mechanical properties and degradation performance;

[0182] 3) The copolymer composition of pH-sensitive dyes plays a key role in the color change sensitivity;

[0183] 4) The synergistic effect of the modified starch components improves the overall performance of the material;

[0184] 5) Precise process control has a significant impact on material properties;

[0185] 6) Kaolin has unique advantages as a filler.

[0186] These results strongly support the inventiveness of the various technical features of this invention and demonstrate the scientific nature and advancement of the invention. It is important to emphasize that it is precisely the organic combination of these technical features that enables the material of this invention to exhibit excellent comprehensive performance. The applicant will design a series of test schemes to comprehensively evaluate the performance of the material of this invention. The test content will focus on the core innovations of the material, with a focus on verifying the synergistic effect of each component.

[0187] I. Degradation Performance Test

[0188] Based on the GB / T 20197-2006 standard, a systematic degradation performance evaluation scheme was designed. First, samples from Examples 1-4 and Comparative Examples 1-6 were cut into 100mm × 100mm × 0.2mm pieces, with five parallel samples per group. The samples were placed in an incubator, with the temperature controlled at 58±2℃ and the relative humidity at 85±5%. Preferably, samples were taken every 15 days to determine the mass loss rate, with continuous testing for 90 days. Specifically, the morphological changes during the degradation process were observed using a scanning electron microscope (SEM) at an operating voltage of 15kV and a vacuum degree of 10. -4 Pa. Furthermore, the molecular weight change was tracked and determined by gel permeation chromatography (GPC) with tetrahydrofuran as the mobile phase, a flow rate of 1 mL / min, and a column temperature of 35 °C.

[0189] The tests revealed that the samples in Examples 1-4 all exhibited uniform volumetric degradation characteristics, which is attributed to the good compatibility between the modified starch and the polyester matrix. Notably, the degradation rate after 90 days exceeded 99.8%, while in Comparative Example 2, due to insufficient PHA content, the degradation was uneven, and the degradation rate was only 85%.

[0190] II. Antibacterial Performance Test

[0191] A comprehensive antimicrobial performance evaluation system was designed based on the GB20123-2008 standard. The test strains selected were *Escherichia coli* (ATCC 25922), *Staphylococcus aureus* (ATCC 6538), and *Aspergillus niger* (ATCC 6275). First, the samples were cut into 25mm × 25mm pieces, sterilized with 75% ethanol, and then air-dried. The concentration of the inoculum was controlled at 1.5 × 10⁻⁶. 5 ~3×10 5 CFU / mL, inoculum size 0.2 mL. Bacteria were cultured at 37±1℃ for 24 h, and fungi were cultured at 28±1℃ for 72 h.

[0192] Test results showed that the materials in Examples 1-4 achieved inhibition rates of over 90% against the three microorganisms, mainly due to the uniform dispersion of the surface-modified silver nanoparticles. In contrast, Comparative Example 1, using unmodified silver nanoparticles, showed an inhibition rate of only 75% due to severe aggregation. Specifically, transmission electron microscopy (TEM) revealed that the surface-modified silver nanoparticles had uniform particle size and good dispersibility, which is key to achieving highly efficient antibacterial activity.

[0193] III. Intelligent Color-Changing Performance Test

[0194] A test scheme simulating real-world application scenarios for color-changing performance was designed. A spectrophotometer (D65 standard light source, 10° observation angle) was used to measure color difference, with sample sizes of 50mm × 50mm. Samples were placed in environments at 5℃, 15℃, and 25℃, with relative humidity controlled at 50±5%. The color difference value ΔE*ab was measured every 30 minutes, and observation continued for 4 hours. Simultaneously, buffer solutions with pH values ​​of 4.0, 5.0, 6.0, and 7.0 were used to evaluate pH response sensitivity.

[0195] Experimental results show that the materials in Examples 3 and 4 achieved significant color difference changes (ΔE*ab≥0.1) within 30 minutes at 5°C. However, in Comparative Example 3, due to the unreasonable copolymerization composition of the pH-sensitive dye, the response time was prolonged to over 2 hours. Furthermore, conformational changes of the pH-responsive groups were observed using in-situ ATR-FTIR spectroscopy, providing direct evidence for the response mechanism.

[0196] IV. Mechanical Properties and Structural Characterization

[0197] Based on a multi-scale characterization strategy, the mechanical properties and microstructure of the material were systematically evaluated. First, conventional mechanical property tests were conducted, including tensile, bending, and impact tests. Specifically, dynamic thermomechanical analysis (DMA) was used to investigate the dynamic mechanical behavior of the material in the range of -50 to 150 °C, with a heating rate of 2 °C / min and a frequency of 1 Hz.

[0198] Furthermore, the microstructure of the material was characterized using small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). The testing conditions were: Cu target, operating voltage 40 kV, current 30 mA, and scanning range 2θ = 0.5–40°. Scattering patterns were collected using a two-dimensional detector, and the crystal structure was analyzed using Lorentz correction. Simultaneously, the phase distribution of each component was observed using atomic force microscopy (AFM) in phase imaging mode, with a scanning size of 2 μm × 2 μm.

[0199] Experimental results show that the material in Example 4 exhibits the best balance of mechanical properties, which is attributed to the optimal PLA / PHA ratio and the toughening effect of the modified starch. SAXS results reveal a clear long-period structure, indicating an ordered arrangement of crystalline and amorphous regions. The AFM phase diagram visually demonstrates the uniform distribution of each component. In contrast, Comparative Example 4, due to the lack of nano-CaCO3 modification, shows poor interfacial bonding between the starch and the matrix, exhibiting significant phase separation.

[0200] Table 1. Test results of basic material properties

[0201]

[0202]

[0203] Table 2. pH response performance and gas barrier test results

[0204]

[0205]

[0206] Table 3. Characterization results of microstructure parameters

[0207]

[0208]

[0209] Based on the above test results, the present invention exhibits the following unexpected technical effects:

[0210] 1. Synergistic Effect: Example 4 exhibits the best overall performance, which stems from the synergistic effect of multiple innovations. In particular, the surface-modified silver nanoparticles not only provide excellent antibacterial properties (95.2% inhibition rate), but their uniformly dispersed nanoparticles also enhance compatibility, as evidenced by the significant increase in interfacial shear strength (15.2 MPa). This synergistic effect has not been reported in the prior art.

[0211] 2. Breakthrough in Structure-Performance Relationship: By precisely controlling the phase structure of the PLA / PHA blend system, excellent mechanical properties (tensile strength 47.8 MPa, elongation at break 275%) were achieved while maintaining high degradation performance (99.9%). This breaks the traditional understanding of the inverse relationship between degradability and mechanical properties. Microstructural analysis shows that this is due to the unique interpenetrating network structure and nanoscale phase separation morphology.

[0212] 3. Innovative Response Mechanism: The pH-sensitive dye system exhibits a rapid response (20 min) and precise sensitivity (0.1 pH unit) far exceeding expectations. In-depth research reveals that this stems from the concerted conformational change of copolymer segments, which not only accelerates the response speed but also improves signal accuracy. In particular, it maintains good responsiveness even at low temperatures (5°C) (ΔE*ab = 0.20), providing a new solution for cold chain monitoring.

[0213] 4. Breakthrough in Processing Technology: Through optimized segmented heating and programmed shear control, processing stability was significantly improved while enhancing material properties. This is reflected in a narrower nanoparticle size distribution (10-15 nm) and higher crystallinity (50.5%). In particular, this process optimization resulted in an unexpected improvement in gas barrier properties (oxygen permeability reduced to 62 cm⁻¹). 3 / m 2 ·24h·0.1MPa).

[0214] 5. Enhanced Environmental Adaptability: The multi-layered structural design of the modified starch not only provides excellent toughening but also endows the material with superior environmental adaptability. This is reflected in its wide glass transition temperature range and stable mechanical properties. In particular, the material maintains structural stability under cyclic temperature and humidity conditions, providing an important guarantee for practical applications.

[0215] In summary, Example 4 embodies the optimal technical solution of the present invention, and its superior performance stems from the organic unity of multiple technical innovations. These unexpected technical effects fully demonstrate the inventiveness of the present invention and provide new research ideas for the development of bio-based smart packaging materials.

[0216] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A biodegradable, antibacterial, intelligent color-changing printing packaging material, characterized in that, By weight, it includes the following components: 63-67 parts of a blend of PLLA and PDLA, wherein the mass ratio of PLLA to PDLA is 70:30 to 90:10; 19-21 parts of P(3HB-co-4HB) copolymer, wherein the molar ratio of 3HB to 4HB is 85:15 to 95:5; 17-18 parts modified starch; 3.4-3.8 parts of surface-modified nano-silver; 7.7-8.3 parts pH-sensitive dye system; 8.0-8.6 parts of silane coupling agent KH550; 6.9-7.5 parts kaolin; The modified starch comprises the following components by weight: 21-23 parts corn starch, of which amylose content is 23-27%; 6.5-7.5 parts of surface-modified nano-CaCO3 with a particle size of 40-60 nm; 1.8-2.2 parts of hydroxymethyl cellulose, with a degree of substitution of 1.6-2.0; 7.5-8.5 parts deionized water; The pH-sensitive dye system is composed of a copolymer obtained by free radical polymerization of the following monomers and Acid Violet 49 in a mass ratio of 3.5:1 to 4.5:1: 43-47 parts styrene; 33-37 parts acrylic acid; 19-21 parts of 2-aminoethyl 2-methacrylate; 0.45-0.55 AIBN; The preparation method of the aforementioned biodegradable antibacterial smart color-changing printing packaging material includes the following steps: (1) Preparation of modified starch: a) Mix corn starch with deionized water at 115-120℃ and 0.18-0.22MPa, and stir at a rate of 210-230rpm for 33-37min. b) Add surface-modified nano-CaCO3 and hydroxymethyl cellulose, heat to 135-145℃, and stir at 230-250 rpm for 38-42 min at 0.28-0.32 MPa. (2) Preparation of surface-modified silver nanoparticles: a) Using 0.01-0.02 mol / L silver nitrate as raw material, and 0.5-1.0 wt% PVP as a protective agent, react at 78-82℃ for 28-32 min; b) Add 2-3 wt% of mercaptosilane coupling agent KH590 and modify at 58-62℃ for 3.5-4.5 h; (3) Preparation of pH-sensitive dye system: Free radical polymerization was carried out at 73-77℃ and nitrogen protection with a stirring rate of 170-190 rpm for 5.5-6.5 h, followed by compounding with Acid Violet 49 at 48-52℃ for 1.8-2.2 h. (4) Blending of matrix materials: Under conditions of 175-185℃ and vacuum degree of -0.05 to -0.07MPa, modified PLA and modified PHA were stirred at a rate of 220-240rpm for 38-42min. (5) Functional component combination: Modified nano-silver, pH-sensitive dye system, coupling agent KH550, and kaolin were added sequentially, followed by dispersion. During dispersion, a programmed shear control and vacuum control program, along with a segmented heating program, were employed. a) 180℃ to 200℃, heating rate 1.8-2.2℃ / min; b) 200℃ to 250℃, heating rate 0.8-1.2℃ / min; c) Keep warm at 240-260℃ for 28-32 minutes.

2. The packaging material according to claim 1, characterized in that, The blend of PLLA and PDLA has a D-isomer content of 0.5-2%, a stereoregularity of 98-99.5%, and a weight-average molecular weight of 100,000-150,000.

3. The packaging material according to claim 1, characterized in that, The P(3HB-co-4HB) copolymer has a molecular weight distribution of 1.8-2.2 and a crystallinity of 55-65%.

4. The biodegradable antibacterial intelligent color-changing printing packaging material according to claim 1, characterized in that, The dispersion process in step (5) uses a shear control program: The initial shear rate is 45-55 s. -1 , The termination shear rate is 190-210 s. -1 , The linear increase time was 14-16 minutes.

5. The biodegradable antibacterial intelligent color-changing printing packaging material according to claim 1, characterized in that, The vacuum control procedure in step (5) is as follows: The initial vacuum level was -0.018 to -0.022 MPa. The final vacuum level is -0.058 to -0.062 MPa. The vacuuming time is 18-22 minutes.

6. The biodegradable antibacterial intelligent color-changing printing packaging material according to claim 1, characterized in that, The cooling procedure after step (5) is as follows: Cooling rate: 2.8-3.2℃ / min, from 250℃ to 180℃; Cooling rate from 180℃ to 100℃: 4.8-5.2℃ / min; Natural cooling is used for temperatures below 100℃.

7. The biodegradable antibacterial intelligent color-changing printing packaging material according to claim 1, characterized in that, The preparation method of the surface-modified nano-CaCO3 is as follows: Nano-CaCO3 with a particle size of 40-60 nm and stearic acid with a mass fraction of 1.5-2.0% were stirred at 75-85 °C at a speed of 180-220 rpm for 1.8-2.2 h.

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