Process for the preparation of reinforced cold-resistant puncture-resistant polyvinyl alcohol composite film

Abstract

The application belongs to the technical field of composite film preparation methods, and particularly relates to a preparation method of a reinforced anti-freezing and puncture-resistant polyvinyl alcohol composite film. After a rigid filler is dried, a surface modifier is added, and the modified rigid filler is obtained through stirring and activation treatment. The modified rigid filler is mixed with part of PVA and part of a mixed solvent, and a filler master batch is prepared through high-speed shearing and ultrasonic dispersion. A main plasticizer, an auxiliary compatibilizer, an anti-migration agent and a dynamic weak crosslinking agent are mixed and stirred to obtain a plasticizing and crosslinking premix system. The remaining PVA and the remaining mixed solvent are dissolved, and then the filler master batch and the plasticizing and crosslinking premix system are added, and a film-forming liquid is obtained through low-temperature stirring and intermittent shearing. The film-forming liquid is flow-coated, and then gradient drying, low-temperature annealing and cooling and stripping are performed to obtain the composite film. The raw materials include PVA 100 parts, rigid filler 5-20 parts, surface modifier, compound plasticizing and compatibilizing system, dynamic weak crosslinking agent 1-5 parts and mixed solvent 400-500 parts in terms of mass fraction.

Description

Technical Field

[0001] This invention belongs to the technical field of screening methods, and particularly relates to a method for preparing a reinforced, freeze-resistant and puncture-resistant polyvinyl alcohol composite film. Background Technology

[0002] Polyvinyl alcohol (PVA) film, due to its excellent film-forming properties, gas barrier properties, and biodegradability, has become an ideal alternative to traditional plastic films and is widely used in food packaging, cold chain transportation, and fresh food preservation. With the rapid development of the cold chain logistics industry, the performance requirements for packaging films are constantly increasing. Especially in low-temperature storage and transportation scenarios, films need to possess good freeze resistance and puncture resistance to resist the risk of brittleness in low-temperature environments and mechanical puncture damage during logistics, ensuring the integrity of the packaged contents.

[0003] Existing PVA films exhibit significant performance limitations at low temperatures. Their molecular chains tend to rigidify at low temperatures, leading to a substantial decrease in film toughness. After freeze-thaw cycles, they are prone to brittleness and deformation. Furthermore, the puncture strength of a pure PVA matrix is ​​low, failing to meet the mechanical protection requirements of logistics transportation. While the industry has modified PVA films by adding rigid fillers and plasticizers, these methods generally suffer from poor filler dispersion and insufficient interfacial compatibility with the PVA matrix. Unmodified fillers tend to agglomerate, forming stress concentration points that actually reduce the overall film performance. Simultaneously, single plasticizer systems are prone to plasticizer migration, causing rapid degradation of low-temperature toughness after long-term use, failing to achieve a synergistic improvement in both freeze resistance and puncture resistance.

[0004] Currently, there is still much room for optimization in the preparation process of PVA composite films. Traditional wet modification processes are prone to filler agglomeration, affecting the modification effect. Furthermore, the drying method after film formation is mostly isothermal drying, which can easily induce internal stress in the film and reduce structural stability. In addition, some preparation processes use strong crosslinking agents for crosslinking modification, which, while improving film strength, can lead to film embrittlement and further deteriorate low-temperature freeze resistance. Existing modification methods and preparation processes cannot simultaneously achieve the freeze resistance, puncture resistance, and structural stability of PVA composite films, failing to meet the practical application requirements of scenarios such as cold chain packaging. Therefore, developing an efficient and stable method for preparing enhanced freeze-resistant and puncture-resistant polyvinyl alcohol composite films has become a research focus and an urgent industry need. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned technical problems by providing a method for preparing an enhanced freeze-resistant and puncture-resistant polyvinyl alcohol composite film.

[0006] In view of this, the present invention provides a method for preparing a reinforced, freeze-resistant, and puncture-resistant polyvinyl alcohol composite film, comprising the following steps:

[0007] Step 1: After drying the rigid filler, add a surface modifier, and then stir and activate it to obtain the modified rigid filler;

[0008] Step 2: The modified rigid filler is mixed with part of PVA and part of mixed solvent, and the filler masterbatch is prepared by high-speed shearing and ultrasonic dispersion; the main plasticizer, auxiliary compatibilizer, anti-migration agent and dynamic weak crosslinking agent are mixed and stirred to obtain a plasticized crosslinking premix system;

[0009] Step 3: After dissolving the remaining PVA and the remaining mixed solvent, add the filler masterbatch and plasticized cross-linking premix system, and obtain the film-forming liquid by low-temperature stirring and intermittent shearing;

[0010] Step 4: After casting and coating the film-forming liquid, the composite film is obtained through gradient drying, low-temperature annealing, and cooling peeling.

[0011] The raw materials, by mass, include 100 parts PVA, 5-20 parts rigid filler, surface modifier, compound plasticizing compatibility system, 1-5 parts dynamic weak crosslinking agent, and 400-500 parts mixed solvent.

[0012] Preferably, in step four, the amount of surface modifier is 2-8% of the mass of the rigid filler, and the compound plasticizing and compatible system includes 3-5 parts of main plasticizer, 1-2 parts of auxiliary compatibilizer, and 0.5-1.5 parts of anti-migration agent.

[0013] Preferably, the degree of polymerization of the PVA is 1700-2400, and the degree of hydrolysis is 98-99%.

[0014] The rigid filler is nanocellulose, montmorillonite, or nanosilica, with a particle size of 50-200 nm.

[0015] Preferably, the surface modifier is a nonionic silane coupling agent or a polyol ester modifier, and the nonionic silane coupling agent is KH-550.

[0016] Preferably, in the compound plasticizing and compatibility system, the main plasticizer is glycerol or sorbitol, the auxiliary compatibilizer is tributyl citrate or acetylated tributyl citrate, and the anti-migration agent is PEG400-2000 or PPG1000, with a mass ratio of 3-5:1-2:0.5-1.5.

[0017] Preferably, the dynamic weak crosslinking agent is boric acid or citric acid.

[0018] Preferably, the mixed solvent is a mixture of water and ethanol in a volume ratio of 7:3 to 9:1.

[0019] Preferably, in step one, the drying temperature is 80℃ and the time is 3h, the stirring temperature is 70-75℃, the stirring speed is 2000rpm and the time is 45min, and the activation temperature is 90-95℃ and the time is 1.5h, and the whole process is carried out under nitrogen protection.

[0020] Preferably, in step two, the high-speed shearing speed is 10,000 rpm and the time is 20 min, the ultrasonic power is 400 W and the time is 30 min;

[0021] The stirring temperature of the plasticized crosslinking premix system was 50℃, the stirring speed was 400 rpm, and the stirring time was 25 min.

[0022] In step three, the PVA dissolution temperature is 60℃ and the time is 4 hours; the low-temperature stirring temperature is 60℃, the stirring speed is 600 rpm and the time is 1.5 hours; and the intermittent shearing speed is 11000 rpm, each time for 5 minutes, for a total of 3 times.

[0023] Preferably, in step four, the casting speed is 1.0 m / min and the thickness is 0.2 mm;

[0024] The gradient drying process was carried out at 40℃ for 1.5 hours, 60℃ for 1.5 hours, and 80℃ for 1 hour.

[0025] The low-temperature annealing temperature is 60-65℃ and the time is 3 hours.

[0026] The beneficial effects of this invention are as follows: Through scientific raw material system compatibility and structural design, the synergistic enhancement of the freeze resistance and puncture resistance of polyvinyl alcohol composite films is achieved. The rigid filler treated with surface modifier forms a rigid core and flexible shell structure, which not only fully utilizes the rigid support of the nanofiller to build a stable puncture-resistant skeleton, but also significantly improves the interfacial compatibility with the PVA matrix, fundamentally avoiding stress concentration problems. The compounded plasticizing and compatibility system, through the synergistic effect of each component, moderately disrupts the hydrogen bonds of PVA to improve low-temperature toughness, while effectively inhibiting plasticizer migration. Combined with the reversible dynamic bonds formed by the dynamic weak crosslinking agent, it ensures the structural stability of the film while avoiding embrittlement, allowing the film to maintain excellent mechanical properties in low-temperature environments.

[0027] This invention's innovative preparation process comprehensively solves the technical pain points of traditional preparation processes, such as filler agglomeration, excessive internal stress, and molecular chain damage, further enhancing the overall performance of the film. The dry stirring combined with low-temperature activation surface modification effectively improves the grafting efficiency of the modifier, while nitrogen protection prevents modifier oxidation. The staged pre-dispersion and low-temperature intermittent shearing blending process achieves uniform molecular-level dispersion of each component, avoiding secondary filler agglomeration and preventing excessive local crosslinking and PVA molecular chain breakage. The gradient drying and low-temperature annealing post-treatment process gradually removes the solvent and promotes molecular chain entanglement, significantly reducing internal stress in the film and significantly improving its structural stability and water resistance, ensuring performance retention during repeated use.

[0028] The polyvinyl alcohol composite film prepared by this invention possesses excellent low-temperature freeze resistance, high puncture resistance, and structural stability. Furthermore, all raw materials used are environmentally friendly, and the entire preparation process generates no harmful byproducts, perfectly aligning with the current trend of green and environmentally friendly industrial development. Compared to traditional modified PVA films, the overall performance of the product of this invention is significantly improved. The preparation process is clear, with controllable parameters, facilitating large-scale industrial production. It can be widely used in cold chain transportation, food preservation, and fresh produce packaging—fields with high requirements for low-temperature performance and mechanical protection of films—meeting practical industry application needs and possessing significant industrial application value and market development prospects. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0031] Raw material selection criteria

[0032] PVA matrix: PVA with a degree of polymerization of 1700-2400 and a degree of hydrolysis of 98-99% is selected to balance film-forming properties and mechanical strength. If the polymerization is too low, the strength will be insufficient, and if it is too high, it will be difficult to dissolve.

[0033] Rigid fillers: Select nano-cellulose, montmorillonite, and nano-silica with a particle size of 50-200nm. This particle size range can ensure high specific surface area and rigid support, and can also avoid agglomeration through modification. The dosage should be controlled at 5-20 parts. Too little will not form an effective puncture-resistant skeleton, while too much will easily lead to stress concentration.

[0034] Surface modifiers: nonionic silane coupling agents (such as KH-550) or polyol ester modifiers, which combine "hydroxyl reactivity" and "flexible segments", form a "rigid core-flexible shell" structure by grafting with hydroxyl groups on the filler surface. The dosage is 2-8% of the filler mass to ensure full coating and prevent the generation of free modifiers.

[0035] The compound plasticizing and compatibility system: the main plasticizer (glycerin, etc.) moderately disrupts the hydrogen bonds of PVA to improve low-temperature toughness; the auxiliary compatibilizer (tributyl citrate, etc.) constructs the interfacial bridge between PVA and the modified filler; the anti-migration agent (PEG400-2000) inhibits the migration of plasticizer. The three are mixed in a ratio of (3-5):(1-2):(0.5-1.5) to achieve a balance between toughening and strength.

[0036] Dynamic weak crosslinking agents: environmentally friendly crosslinking agents such as boric acid and citric acid form reversible dynamic bonds with PVA. The amount used is 1-5 parts. If the crosslinking is too low, the structure will be unstable; if it is too high, it will lead to embrittlement.

[0037] Mixed solvent: water / ethanol volume ratio 7:3-9:1, which ensures that PVA is fully dissolved and reduces the solvent evaporation rate, thus avoiding uneven film shrinkage.

[0038] Surface modification process: dry stirring and low-temperature activation to avoid filler agglomeration caused by wet modification, and nitrogen protection to prevent oxidation of the modifier and ensure grafting efficiency.

[0039] Staged pre-dispersion: The filler pre-dispersion is prepared into masterbatch through high-speed shearing and ultrasonic dispersion to avoid secondary agglomeration; plasticizing and cross-linking premixing and activation ensure that the components are uniformly integrated and avoid excessive local cross-linking.

[0040] Overall blending process: low-temperature stirring and intermittent shearing achieve molecular-level dispersion while avoiding the breakage of PVA molecular chains, thus ensuring the strength of the matrix.

[0041] Gradient molding and post-treatment: Gradient drying gradually removes the solvent and reduces internal stress; low-temperature annealing promotes molecular chain entanglement and improves structural stability.

[0042] Example 1;

[0043] Raw material composition (parts by mass): 100 parts PVA (degree of polymerization 1700, degree of hydrolysis 98%), 10 parts nanocellulose (particle size 50-100nm), 0.5 parts modifier KH-550 (5% of the mass of nanocellulose), 8 parts main plasticizer glycerin, 4 parts auxiliary compatibilizer tributyl citrate, 2 parts anti-migration agent PEG600, 2 parts dynamic crosslinking agent boric acid, and 400 parts mixed solvent (water: ethanol = 8:2).

[0044] Preparation steps:

[0045] (1) Dry nanocellulose at 80℃ for 3h, add KH-550, stir at 70℃ and 2000rpm for 45min, and activate at 90℃ for 1.5h to obtain modified nanocellulose;

[0046] (2) Modified nanocellulose was mixed with 15 parts PVA and 80 parts mixed solvent, sheared at 10000 rpm for 20 min, and sonicated at 400W for 30 min to obtain filler masterbatch; glycerol, tributyl citrate, PEG600 and boric acid were mixed and stirred at 50℃ and 400 rpm for 25 min to obtain plasticized cross-linking premix system.

[0047] (3) Dissolve the remaining PVA with 320 parts of mixed solvent at 60°C for 4 hours, add filler masterbatch and plastic crosslinking premix system, stir at 60°C and 600 rpm for 1.5 hours, and intermittently shear 3 times (5 min each time, 11000 rpm) to obtain film-forming solution;

[0048] (4) Cast coating at 1.0 m / min (thickness 0.2 mm), dry at 40℃ for 1.5 h, dry at 60℃ for 1.5 h, dry at 80℃ for 1 h, anneal at 60℃ for 3 h, cool and peel off to obtain composite film.

[0049] Performance testing: -30℃ impact strength 13.2kJ / m², puncture strength 8.5N, water absorption 12.3%, performance degradation rate after freeze-thaw cycle 6.2%.

[0050] Example 2;

[0051] Raw material composition (parts by mass): 100 parts PVA (degree of polymerization 2000, degree of hydrolysis 99%), 15 parts montmorillonite (particle size 100-150nm), 0.9 parts glyceryl triacetate (6% of the mass of montmorillonite) modifier, 10 parts sorbitol (main plasticizer), 5 parts tributyl acetyl citrate (auxiliary compatibilizer), 3 parts PPG 1000 (anti-migration agent), 3 parts citric acid (dynamic crosslinking agent), and 500 parts mixed solvent (water: ethanol = 9:1).

[0052] Preparation steps: Refer to Example 1, only adjust the modification temperature to 75°C, activation temperature to 95°C, and annealing temperature to 65°C.

[0053] Performance testing: -30℃ impact strength 14.5kJ / m², puncture strength 9.2N, water absorption 10.8%, performance degradation rate after freeze-thaw cycle 5.8%.

[0054] Comparative Example 1 (unmodified filler, single plasticizer);

[0055] Raw material composition: 100 parts PVA, 10 parts unmodified nanocellulose, 12 parts glycerol, 400 parts water. The preparation process is the same as in Example 1 (without modification steps, without auxiliary compatibilizers and anti-migration agents).

[0056] Performance testing: -30℃ impact strength 8.5kJ / m², puncture strength 5.2N, water absorption 23.5%, performance degradation rate after freeze-thaw cycle 25.3%.

[0057] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for preparing a reinforced, freeze-resistant, and puncture-resistant polyvinyl alcohol composite film, characterized in that: Includes the following steps: Step 1: After drying the rigid filler, add a surface modifier, and then stir and activate it to obtain the modified rigid filler; Step 2: The modified rigid filler is mixed with part of PVA and part of mixed solvent, and the filler masterbatch is prepared by high-speed shearing and ultrasonic dispersion; the main plasticizer, auxiliary compatibilizer, anti-migration agent and dynamic weak crosslinking agent are mixed and stirred to obtain a plasticized crosslinking premix system; Step 3: After dissolving the remaining PVA and the remaining mixed solvent, add the filler masterbatch and plasticized cross-linking premix system, and obtain the film-forming liquid by low-temperature stirring and intermittent shearing; Step 4: After casting and coating the film-forming liquid, the composite film is obtained through gradient drying, low-temperature annealing, and cooling peeling. The raw materials, by mass, include 100 parts PVA, 5-20 parts rigid filler, surface modifier, compound plasticizing compatibility system, 1-5 parts dynamic weak crosslinking agent, and 400-500 parts mixed solvent.

2. The method for preparing the enhanced freeze-resistant and puncture-resistant polyvinyl alcohol composite film according to claim 1, characterized in that: In step four, the amount of surface modifier used is 2-8% of the mass of rigid filler, and the compound plasticizing and compatibility system includes 3-5 parts of main plasticizer, 1-2 parts of auxiliary compatibilizer, and 0.5-1.5 parts of anti-migration agent.

3. The method for preparing the enhanced freeze-resistant and puncture-resistant polyvinyl alcohol composite film according to claim 1, characterized in that: The degree of polymerization of the PVA is 1700-2400, and the degree of hydrolysis is 98-99%. The rigid filler is nanocellulose, montmorillonite, or nanosilica, with a particle size of 50-200 nm.

4. The method for preparing the enhanced freeze-resistant and puncture-resistant polyvinyl alcohol composite film according to claim 1, characterized in that: The surface modifier is a nonionic silane coupling agent or a polyol ester modifier, and the nonionic silane coupling agent is KH-550.

5. The method for preparing the enhanced freeze-resistant and puncture-resistant polyvinyl alcohol composite film according to claim 1, characterized in that: In the compound plasticizing and compatibility system, the main plasticizer is glycerol or sorbitol, the auxiliary compatibilizer is tributyl citrate or acetylated tributyl citrate, and the anti-migration agent is PEG400-2000 or PPG1000, with a mass ratio of 3-5:1-2:0.5-1.

5.

6. The method for preparing the enhanced freeze-resistant and puncture-resistant polyvinyl alcohol composite film according to claim 1, characterized in that: The dynamic weak crosslinking agent is boric acid or citric acid.

7. The method for preparing the enhanced freeze-resistant and puncture-resistant polyvinyl alcohol composite film according to claim 1, characterized in that: The mixed solvent is a mixture of water and ethanol in a volume ratio of 7:3 to 9:

1.

8. The method for preparing the enhanced freeze-resistant and puncture-resistant polyvinyl alcohol composite film according to claim 1, characterized in that: In step one, the drying temperature is 80℃ and the time is 3 hours; the stirring temperature is 70-75℃ and the speed is 2000 rpm for 45 minutes; and the activation temperature is 90-95℃ for 1.5 hours. The entire process is carried out under nitrogen protection.

9. The method for preparing the enhanced freeze-resistant and puncture-resistant polyvinyl alcohol composite film according to claim 1, characterized in that: In step two, the high-speed shearing speed is 10,000 rpm and the time is 20 min, while the ultrasonic power is 400 W and the time is 30 min. The stirring temperature of the plasticized crosslinking premix system was 50℃, the stirring speed was 400 rpm, and the stirring time was 25 min. In step three, the PVA dissolution temperature is 60℃ and the time is 4 hours; the low-temperature stirring temperature is 60℃, the stirring speed is 600 rpm and the time is 1.5 hours; and the intermittent shearing speed is 11000 rpm, each time for 5 minutes, for a total of 3 times.

10. The method for preparing the enhanced freeze-resistant and puncture-resistant polyvinyl alcohol composite film according to claim 1, characterized in that: In step four, the casting speed is 1.0 m / min and the thickness is 0.2 mm; The gradient drying process was carried out at 40℃ for 1.5 hours, 60℃ for 1.5 hours, and 80℃ for 1 hour. The low-temperature annealing temperature is 60-65℃ and the time is 3 hours.

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