Environment-friendly furniture protective film and preparation method thereof

Abstract

The invention relates to the technical field of environment-friendly high polymer materials, in particular to an environment-friendly furniture protective film and a preparation method thereof. The technical problems that a traditional furniture protection film is insufficient in toughness and short in service life are solved. According to the protective film disclosed by the invention, a polylactic acid, polyhydroxyalkanoate and dimer fatty acid ester flexibilizer blending material is taken as a matrix, a cyanoethylation lignin-cellulose nanocrystal compound reinforcing agent is added to form a dense nano network, and a dynamic cross-linking agent containing disulfide bonds and a functional auxiliary agent are introduced. According to the invention, a solvent-free ultraviolet light / damp and hot dual-curing system is adopted for coating and curing to prepare the coating. The furniture protection film is excellent in mechanical property, toughness is remarkably improved, and the furniture protection film has multiple functions such as high barrier property and the like and has the self-repairing capacity and the full-life-cycle environment-friendly characteristic.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly polymer materials technology, specifically to an environmentally friendly furniture protective film and its preparation method. Background Technology

[0002] Furniture protective films are widely used to protect furniture surfaces from scratches, stains, and aging. Currently, most furniture protective films on the market are made of traditional plastic materials, such as PVC or polyester film, and are usually coated with acrylic adhesive. These traditional protective films have poor environmental performance and limited capabilities: First, petroleum-based materials such as PVC are not biodegradable, causing persistent environmental pollution after disposal; second, traditional protective films lack toughness and durability, easily cracking, tearing, or yellowing due to aging, requiring frequent replacement and having a short lifespan.

[0003] With increasing environmental awareness and stricter regulations, the development of green, biodegradable, and high-performance furniture protective films has become an urgent need. Polylactic acid (PLA) is a bio-based biodegradable polymer derived from renewable plant resources, possessing good mechanical strength and biocompatibility, and has attracted widespread attention in food packaging, daily necessities, and other fields. However, PLA is inherently brittle, with low impact strength and low elongation at break, making it difficult to meet the requirements of applications with high toughness. To improve the toughness of PLA, researchers have conducted numerous toughening modification attempts, including blending elastomers, plasticizers, or flexible copolymers. However, these toughening methods often have compatibility or durability issues: if the toughening component blended with PLA has poor compatibility, it will lead to a decrease in mechanical properties, while small-molecule plasticizers may migrate and volatilize, resulting in material performance degradation after long-term use. In addition, many toughening materials are not bio-based themselves, weakening the material's environmental friendliness. Furthermore, furniture is easily scratched, contaminated, or worn during transportation, storage, and use. Once the protective film is damaged, it is often difficult to repair, requiring replacement with a new film, increasing usage costs and material waste. The concept of self-healing materials has attracted attention in recent years; however, such dynamic self-healing networks have not yet been applied to thin film materials such as furniture protective films. How to introduce a reversible cross-linked network to achieve self-healing of minor scratches while ensuring the film's mechanical properties and transparency remains a technical challenge.

[0004] To solve the above problems, there is an urgent need to develop an environmentally friendly furniture protective film that simultaneously possesses high mechanical properties, high barrier properties, and self-healing functions. Summary of the Invention

[0005] The main objective of this invention is to provide an environmentally friendly furniture protective film and its preparation method, overcoming the shortcomings of existing furniture protective films, such as poor environmental performance, insufficient toughness, short service life, and lack of multifunctionality. This invention aims to prepare a furniture protective film with excellent mechanical properties, high barrier properties, multifunctional protection, and self-healing capabilities through innovative material combinations and processing methods, achieving more durable and effective green protection for furniture surfaces.

[0006] The specific technical solution is as follows: An environmentally friendly furniture protective film and its preparation method, comprising the following steps: S1: Take 100 parts of industrial lignin as a reference and dissolve it in 400 parts of ethanol-water mixed solvent with a volume ratio of 7:3. Add 10 parts of sodium hydroxide at room temperature, and add 30 parts of acrylonitrile dropwise while stirring. React at 60°C for 6 hours. After the reaction is complete, adjust the pH to neutral with dilute hydrochloric acid, then filter, and finally dry in a vacuum drying oven at 60°C for 24 hours. Grind and pass through a 200-mesh sieve to obtain cyanoethylated lignin. Mix cyanoethylated lignin with cellulose nanocrystals and add to an ethanol solution, and sonicate to form a suspension to prepare a cyanoethylated lignin-cellulose nanocrystal composite.

[0007] Furthermore, cyanoethylated lignin and cellulose nanocrystals are added to an ethanol solution at a mass ratio of 2:1, with a solid content of 1 wt%.

[0008] S2: Dissolve aromatic oil and wall material gelatin-gum arabic solution in deionized water at a mass ratio of 1:3, stir at 10000 rpm for 30 minutes to emulsify and form water-in-oil droplets; adjust pH to 3.5, keep warm at 60℃ for 2 hours, then cool to room temperature and filter to prepare microcapsule plant essential oil.

[0009] Furthermore, for mild aromatic oils, choose lavender oil or lemongrass oil.

[0010] S3: Prepare the following components: polylactic acid, poly(3-hydroxybutyric acid-co-3-hydroxyvalerate) (PHBV), dimer fatty acid ester toughening agent, and cyanoethylated lignin-vitamin nanocrystal composite reinforcing agent. After drying at 80℃ for 4 hours to remove moisture, add the mixture to a twin-screw extruder at 60 rpm for melt blending and extrusion. The discharged material is cooled, drawn into strands, and pelletized to prepare masterbatch.

[0011] Furthermore, the specific dosage of each component is as follows: 40-60 parts of polylactic acid as a baseline, 15-25 parts of poly(3-hydroxybutyric acid-co-3-hydroxyvalerate), 10-15 parts of dimer fatty acid ester toughening agent, and 4-6 parts of cyanoethylated lignin-vitamin nanocrystal composite reinforcing agent.

[0012] Furthermore, the temperatures of each zone of the extruder are set as follows: Zone 1: 170℃, Zone 2: 175℃, Zone 3: 180℃, and Zone 4: 175℃.

[0013] S4: Take 100 parts of the masterbatch prepared above as a reference, add it to a mixed solvent of ethyl acetate and dimethyl carbonate with a solid content of 25 wt% and a volume ratio of ethyl acetate to dimethyl carbonate of 1:1, and dissolve it by magnetic stirring at 50°C for 2 hours. After cooling to room temperature, add disulfide crosslinking agent, functional additive and temperature-responsive photoinitiator in sequence; stir at 50°C at 2000 rpm for 2 hours to mix the components evenly and prepare the coating liquid.

[0014] Furthermore, the amounts of the disulfide crosslinking agent, functional additives, and temperature-responsive photoinitiator are as follows: disulfide crosslinking agent: 1-3 parts of 2,2'-dithiodiethanol diacrylate and 0.3-0.5 parts of zinc acetylacetone; functional additives: 0.5-1.5 parts of nano-titanium dioxide, 0.4-0.6 parts of antistatic agent ST-3, and 0.5-1.5 parts of microcapsule plant essential oil; and temperature-responsive photoinitiator: 0.6-1.0 parts.

[0015] S5: The coating solution prepared above is uniformly coated onto a silicone release film using a doctor blade coating method to form a wet film. The film is allowed to stand at room temperature for 10 minutes, then placed in a forced-air oven at 40°C for 30 minutes to ensure complete evaporation of residual solvent. After drying, a dense solid film adhered to the release film is obtained. The dried film, along with the release film, is placed in a UV curing machine using a medium-pressure mercury lamp to initially form a cross-linked curing structure, followed by hydrothermal curing. After the hydrothermal treatment, the film is removed and cooled to room temperature to obtain the furniture protective film.

[0016] Furthermore, the parameters of the medium-pressure mercury lamp were set as follows: main wavelength 365nm, power 120W / cm, irradiation time 1 minute, and distance 15cm.

[0017] Furthermore, the damp heat curing parameters were set to a temperature of 60°C, a relative humidity of 65%–75%, and a placement time of 1 hour.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The main components of the protective film of this invention, such as polylactic acid, polyhydroxy fatty acid ester, modified lignin, cellulose nanocrystals, plant oil-based toughening agents, and plant essential oils, are all derived from renewable biomass or natural products. The preparation process uses low-toxicity solvents and solvent-free curing processes, with no emissions of volatile organic compounds, achieving environmental friendliness throughout the entire life cycle.

[0019] 2. This invention overcomes the brittleness of pure polylactic acid through the synergistic effect of toughening by blending with polyhydroxy fatty acid esters, plasticizing with dimer fatty acid esters, and dynamic cross-linking networks, exhibiting a balance between high strength and high toughness.

[0020] 3. This invention constructs a dense nano-network structure by combining cyanoethylated lignin and cellulose nanocrystals, and then combines it with the shielding effect of nano-titanium dioxide to give the protective film excellent barrier properties against oxygen, water vapor and ultraviolet rays. Moreover, the disulfide bonds in the dynamic cross-linked network can break and recombine under certain conditions, which can achieve self-repair properties and ultimately improve the service life of furniture.

[0021] 4. In addition to basic physical protection, the protective film of this invention integrates multiple practical functions. The film surface contains an antistatic agent, which effectively prevents static dust accumulation and keeps the furniture surface clean and shiny; the microcapsule plant essential oils dispersed in the film can slowly release natural fragrance, which can purify the air and repel insects and prevent mold. Attached Figure Description

[0022] Figure 1 This is a process flow diagram for preparing an environmentally friendly furniture protective film according to the present invention.

[0023] Figure 2 This is a scanning electron microscope image of the test in Experiment Example 1.

[0024] Figure 3 The graph shows a comparison of the mechanical property test results for Experiment Example 2.

[0025] Figure 4 This is a comparison chart of the barrier performance test results for Experiment Example 2.

[0026] Figure 5 This is a comparison chart of the self-healing efficiency test results for Experiment Example 3. Detailed Implementation

[0027] The following embodiments further explain and illustrate the technical solution of the present invention. It is particularly noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention. (See attached...) Figure 1 The image shows a process flow for preparing an environmentally friendly furniture protective film. The detailed preparation steps are as follows: 1. Raw material preparation 1.1 Preparation of cyanoethylated wood Take 100 parts of industrial lignin as a reference and dissolve it in 400 parts of ethanol-water mixed solvent with a volume ratio of 7:3. Add 10 parts of sodium hydroxide at room temperature, and add 30 parts of acrylonitrile dropwise while stirring. React at 60°C for 6 hours. After the reaction is complete, adjust the pH to neutral with dilute hydrochloric acid, then filter, and finally dry in a vacuum drying oven at 60°C for 24 hours. Grind through a 200-mesh sieve to prepare cyanoethylated lignin.

[0028] Acrylonitrile undergoes an addition reaction with the hydroxyl groups on the lignin molecule, introducing a -CH2CH2CN side chain.

[0029] 1.2 Preparation of cyanoethylated lignin-cellulose nanocrystal complex Weigh the cyanoethylated lignin prepared above and mix it with cellulose nanocrystals at a mass ratio of 2:1, with a solid content of 1wt%. Add the mixture to an ethanol solution and sonicate it to form a suspension. The sonication power is 600W and the sonication time is 30 minutes to allow the cyanoethylated lignin to be fully adsorbed and bound to the surface of the cellulose nanocrystals, thus preparing a cyanoethylated lignin-cellulose nanocrystal composite.

[0030] By cyanoethylating lignin and introducing –C≡N polar groups, the strong hydrogen bonds within the lignin macromolecule are weakened, improving its dispersibility and compatibility in the organic phase. Simultaneously, the aromatic structure of the lignin molecule is preserved, thus maintaining its excellent UV absorption and antioxidant properties. Cellulose nanocrystals are rigid, high aspect ratio whisker-like nanofibers hundreds of nanometers in length, rich in hydroxyl groups, which can form a tight bond with cyanoethylated lignin through hydrogen bonds and van der Waals forces. When cyanoethylated lignin-cellulose nanocrystals are dispersed in the matrix resin, the network structure formed by lignin and nanocrystals fills the polymer matrix, significantly improving the modulus and strength of the film material. Furthermore, it effectively blocks the diffusion of gas and liquid molecules through a "brick-wall" pathway, thereby endowing the protective film with high barrier properties and resistance to UV aging.

[0031] 2. Preparation of microencapsulated plant essential oils Aromatic oil and wall material gelatin-gum arabic solution were dissolved in deionized water at a mass ratio of 1:3. The mixture was stirred at 10,000 rpm for 30 minutes to emulsify and form water-in-oil droplets. The pH was adjusted to 3.5, and the mixture was kept at 60°C for 2 hours to allow the prepolymer to polymerize and deposit on the surface of the oil droplets to form capsule walls. After cooling to room temperature, the mixture was filtered to obtain microcapsule plant essential oil.

[0032] Microencapsulated plant essential oils can be selected from natural aromatic oils such as lavender oil or citronella oil. These oils are formed into microcapsules through in-situ polymerization and added to the coating solution. These microcapsules are evenly distributed and encapsulated within the protective film. When the film is subjected to friction or increased temperature, a small amount of essential oil is slowly released, not only giving the furniture a delicate natural fragrance but also providing additional protection by utilizing the antibacterial and insect-repellent properties of certain essential oils.

[0033] 3. Masterbatch blending Take 40-60 parts of polylactic acid as a reference, 15-25 parts of poly(3-hydroxybutyric acid-co-3-hydroxyvalerate) (PHBV), 10-15 parts of dimer fatty acid ester toughening agent, and 4-6 parts of cyanoethylated lignin-vitamin nanocrystal composite reinforcing agent. After drying the above components at 80℃ for 4 hours to remove moisture, add them to a twin-screw extruder. Set the temperatures of each zone of the extruder as follows: Zone 1 170℃, Zone 2 175℃, Zone 3 180℃, Zone 4 175℃, and the speed 60 rpm. Perform melt blending and extrusion. After cooling, stretching, and pelletizing, prepare masterbatch.

[0034] Poly(3-hydroxybutyric acid-co-3-hydroxyvalerate) copolyester (PHBV) provides higher ductility and biodegradability than polylactic acid (PLA). The dimer fatty acid ester toughening agent is prepared from natural vegetable oil fatty acid dimers and formed into saturated long-chain ester plasticizers through esterification or hydrogenation, exhibiting good compatibility and toughening effects. These three components are melt-blended to form a continuous matrix phase. The introduction of the polyhydroxy fatty acid ester and toughening agent effectively reduces the brittleness of the PLA matrix and improves elongation at break and impact toughness.

[0035] 4. Preparation of coating solution Take 100 parts of the prepared masterbatch as a reference and add it to a mixed solvent of ethyl acetate and dimethyl carbonate with a solid content of 25 wt% and a volume ratio of ethyl acetate to dimethyl carbonate of 1:1. Dissolve the masterbatch by magnetic stirring at 50°C for 2 hours. After cooling to room temperature, add the following components in sequence: disulfide crosslinking agent: 1-3 parts of 2,2'-dithiodiethanol diacrylate and 0.3-0.5 parts of zinc acetylacetonate; functional additives: 0.5-1.5 parts of nano titanium dioxide, 0.4-0.6 parts of antistatic agent, 0.5-1.5 parts of microcapsule plant essential oil, and 0.6-1.0 parts of temperature-responsive photoinitiator. Stir at 2000 rpm at 50°C for 2 hours to ensure uniform mixing of all components and prepare the coating solution.

[0036] The crosslinking agent includes disulfide-containing compounds and zinc acetylacetonate. The disulfide-bonded compounds are difunctional monomers with disulfide bond bridging. These compounds contain disulfide bonds that are easily broken and recombine under light or heating conditions, and also possess polymerizable functional groups. They can undergo free radical polymerization under the action of a UV photoinitiator to form a crosslinked network. After crosslinking, the disulfide bonds, as dynamically reversible bonds, can undergo breakage-recombination exchange under certain temperatures or specific triggering conditions, giving the crosslinked network topological rearrangement capabilities. Adding a small amount of zinc acetylacetonate as a catalyst helps lower the activation energy required for disulfide bond exchange, accelerating the dynamic rearrangement process. Furthermore, zinc acetylacetonate can coordinate with polar groups in the matrix, increasing the crosslinking density and stability of the network. In this invention, the introduction of this dynamic crosslinked network not only improves the toughness of the membrane material but, more importantly, endows it with self-healing capabilities: when fine scratches or cracks appear on the membrane surface, the disulfide bond dynamic network can reconnect the broken polymer chains under appropriate temperature or light conditions, achieving automatic repair of the damage.

[0037] Nano-titanium dioxide (particle size 30-40nm, surface treated with organosilanes to enhance hydrophobic dispersibility) serves as an inorganic shielding agent, which can improve the barrier properties and UV aging resistance of the membrane; the antistatic agent can avoid the impact on biodegradability, and its function is to reduce the static electricity accumulation on the membrane surface and prevent dust adsorption.

[0038] 5. Coating and curing The prepared coating solution was uniformly coated onto a silicone release film using a doctor blade coating method. After coating, the film was allowed to stand at room temperature for 10 minutes, and then dried in a forced-air oven at 40°C for 30 minutes to ensure that residual solvents were fully evaporated. After drying, a dense solid film adhered to the release film was obtained. The dried film, along with the release film, was placed in a UV curing machine using a medium-pressure mercury lamp with a main wavelength of 365nm, a power of 120W / cm, and irradiated for 1 minute at a distance of 15cm to initially form a cross-linked curing structure. Then, a hygrothermal curing process was performed. The UV-cured film was transferred to an incubator with heating and humidification functions and placed at 60°C and a relative humidity of 65%–75% for 1 hour. After the hygrothermal treatment, the film was removed and cooled to obtain the furniture protective film.

[0039] Under the action of temperature-responsive photoinitiators, ultraviolet light irradiation triggers a photocrosslinking reaction of disulfide-bonded compounds: the double bond groups in the disulfide compounds polymerize to form a three-dimensional network, and the disulfide bonds are introduced into the crosslinking points. Because the initiator has temperature-responsive characteristics, its activity is low at room temperature, which can prevent premature curing during coating and resting. When irradiated with ultraviolet light, the photoinitiator releases free radicals under the ultraviolet light and the resulting slight temperature rise, triggering the polymerization reaction and causing the coating to rapidly cure and form a pre-crosslinked solid film.

[0040] Moist heat curing promotes polymer chain movement and disulfide bond exchange reactions, causing rearrangement and further crosslinking of the previously formed crosslinked network, thus improving the density and uniformity of the network. On the other hand, this process is similar to heat post-treatment, which can eliminate the internal stress generated by UV rapid polymerization and induce appropriate crystallization of the polylactic acid / polyhydroxyalkanoate matrix, thereby comprehensively improving the mechanical and barrier properties of the film.

[0041] Example 1 Table 1 Raw Material Information Table: An environmentally friendly furniture protective film and its preparation method are as follows: S1: Take 100 parts of industrial lignin as a reference and dissolve it in 400 parts of ethanol-water mixed solvent with a volume ratio of 7:3. Add 10 parts of sodium hydroxide at room temperature, and add 30 parts of acrylonitrile dropwise while stirring. React at 60°C for 6 hours. After the reaction is complete, adjust the pH to neutral with dilute hydrochloric acid, then filter, and finally dry in a vacuum drying oven at 60°C for 24 hours. Grind through a 200-mesh sieve to prepare cyanoethylated lignin.

[0042] Weigh the cyanoethylated lignin prepared above and mix it with cellulose nanocrystals at a mass ratio of 2:1, with a solid content of 1wt%. Add the mixture to an ethanol solution and sonicate it to form a suspension. The sonication power is 600W and the sonication time is 30 minutes to allow the cyanoethylated lignin to be fully adsorbed and bound to the surface of the cellulose nanocrystals, thus preparing a cyanoethylated lignin-cellulose nanocrystal composite.

[0043] S2: Microcapsules were prepared by in-situ polymerization. Lavender oil and a gelatin-gum arabic solution were dissolved in deionized water at a mass ratio of 1:3, with the mass ratio of gelatin to gum arabic being 1:1. The mixture was stirred at 10,000 rpm for 30 minutes to emulsify and form water-in-oil droplets. The pH was adjusted to 3.5, and the mixture was kept at 60°C for 2 hours to allow the prepolymer to polymerize and deposit on the surface of the oil droplets to form capsule walls. After cooling to room temperature, the mixture was filtered to obtain microcapsule plant essential oil.

[0044] S3: Take 50 parts of polylactic acid as a baseline, 20 parts of poly(3-hydroxybutyric acid-co-3-hydroxyvalerate), 12 parts of dimer fatty acid ester toughening agent, and 5 parts of cyanoethylated lignin-vitamin nanocrystal composite reinforcing agent; after drying the above components at 80℃ for 4 hours to remove moisture, add them to a twin-screw extruder. Set the temperatures of each zone of the extruder as follows: Zone 1 170℃, Zone 2 175℃, Zone 3 180℃, Zone 4 175℃, and the speed 60 rpm for melt blending extrusion. After cooling, drawing into strands, and pelletizing, masterbatch is prepared.

[0045] S4: Take 100 parts of the masterbatch prepared above as a reference, add it to a mixed solvent of ethyl acetate and dimethyl carbonate with a solid content of 25 wt% and a volume ratio of ethyl acetate to dimethyl carbonate of 1:1, and dissolve it by magnetic stirring at 50°C for 2 hours. After cooling to room temperature, add the following in sequence: disulfide crosslinking agent: 2 parts of 2,2'-dithiodiethanol diacrylate and 0.4 parts of zinc acetylacetonate; functional additives: 1.0 part of nano titanium dioxide, 0.5 parts of antistatic agent ST-3, 1.0 part of microcapsule plant essential oil, and 0.8 parts of temperature-responsive photoinitiator; stir at 2000 rpm at 50°C for 2 hours to ensure uniform mixing of all components, and prepare the coating solution.

[0046] S5: The coating solution prepared above is uniformly coated onto a silicone release film using a doctor blade coating method. After coating, it is left to stand at room temperature for 10 minutes, and then the coated release film is placed in a forced-air drying oven at 40°C for 30 minutes to ensure that the residual solvent is fully evaporated. After drying, a solid film densely attached to the release film is obtained. The dried film and the release film are placed together in a UV curing machine, using a medium-pressure mercury lamp with a main wavelength of 365nm, a power of 120W / cm, and irradiated for 1 minute at a distance of 15cm to initially form a cross-linked curing structure. Then, a hygrothermal curing is performed. The UV-cured film is transferred to an incubator with heating and humidification functions and placed at 60°C and 70% relative humidity for 1 hour. After the hygrothermal treatment, it is taken out and cooled to obtain the furniture protective film.

[0047] Example 2 The preparation method is the same as in Example 1, but different: In step S2, lavender oil is replaced with lemongrass oil; In step S3, 40 parts of polylactic acid were taken as a reference, 15 parts of poly(3-hydroxybutyric acid-co-3-hydroxyvalerate), 10 parts of dimer fatty acid ester toughening agent, and 4 parts of cyanoethylated lignin-vitamin nanocrystal composite reinforcing agent were taken. In step S4, there are 1 part of 2,2'-dithiodiethanol diacrylate and 0.3 parts of zinc acetylacetonate; functional additives include: 0.5 parts of nano titanium dioxide, 0.4 parts of antistatic agent ST-3, 0.5 parts of microcapsule plant essential oil, and 0.6 parts of temperature-responsive photoinitiator. The relative humidity in step S5 is 65%.

[0048] Example 3 The preparation method is the same as in Example 1, but different: In step S3, 60 parts of polylactic acid were taken as a baseline, 25 parts of poly(3-hydroxybutyric acid-co-3-hydroxyvalerate), 15 parts of dimer fatty acid ester toughening agent, and 6 parts of cyanoethylated lignin-vitamin nanocrystal composite reinforcing agent were taken. In step S4, there are 3 parts of 2,2'-dithiodiethanol diacrylate and 0.5 parts of zinc acetylacetonate; functional additives include: 1.5 parts of nano titanium dioxide, 0.6 parts of antistatic agent ST-3, 1.5 parts of microcapsule plant essential oil, and 1.0 part of temperature-responsive photoinitiator. The relative humidity in step S5 is 75%.

[0049] Comparative Example 1 The preparation method of Example 1 was followed, but without the addition of cyanoethylated lignin and cellulose nanocrystals. All other steps were the same.

[0050] Comparative Example 2 The preparation method of Example 1 was followed, but without the addition of disulfide crosslinking agents: 2,2'-dithiodiethanol diacrylate and zinc acetylacetonate. All other steps were the same.

[0051] Comparative Example 3 The preparation method of Example 1 is followed, but without the addition of poly(3-hydroxybutyric acid-co-3-hydroxyvalerate) and dimer fatty acid ester toughening agents. All other steps are the same.

[0052] Comparative Example 4 The preparation method of Example 1 was followed, but instead of moisture curing, only UV curing was performed. All other steps were the same.

[0053] Experimental Example 1 The cyanoethylated lignin-cellulose nanocrystals prepared in Example 1 were observed using a scanning electron microscope. 1 mL of the cyanoethylated lignin-cellulose nanocrystal solution was diluted 10 times with anhydrous ethanol, then dropped onto a mica sheet and dried naturally at room temperature. Following this, gold sputtering was performed under vacuum with a sputtering thickness of 5 nm. The test parameters were: accelerating voltage 3-5 kV, working distance 5-8 mm, signal type secondary electron signal, and detector SE2. The test results are as follows: Figure 2 As shown.

[0054] The nanocrystals are coated with a layer of lignin, exhibiting a network-like aggregated structure. They are more uniformly dispersed in the polymer matrix. The nanofiber network composed of cellulose nanocrystals is coated with a layer of cyanoethylated lignin. The cellulose nanocrystals maintain their fibrous arrangement and network structure, but the surface of each fiber is slightly rougher and thicker due to the binding of lignin. Locally, granular attachments or coatings formed by lignin are visible, and no excessively aggregated large clusters have been observed. The presence of lignin not only imparts a new organic coating to the fiber surface but also forms bridges at fiber intersections, further consolidating the structure of the composite network and exerting a synergistic reinforcing effect.

[0055] Experiment Example 2 The environmentally friendly furniture protective films prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to comprehensive performance testing. Mechanical property testing: Elongation at break was determined according to standard ASTM D882-18 "Standard Test Method for Tensile Properties of Plastic Sheets"; Barrier performance testing: Oxygen transmission rate was determined according to ASTM D3985-24, "Standard Test Method for Determining Oxygen Transmission Rate of Plastic Films and Sheets Using Coulomb Sensors"; water vapor transmission rate was determined according to GB / T 1037-2021, "Determination of Water Vapor Transmission Performance of Plastic Films and Sheets - Cup Weight Gain and Weight Loss Method"; specific test comparison results are shown in Table 2. Figure 3 , Figure 4 As shown: Table 2 Comparison of Comprehensive Performance Test Results for Experiment Example 2: The comparison results show that Comparative Example 1, without the addition of cyanoethylated lignin and cellulose nanocrystals, exhibits extreme brittleness. Lacking the combined reinforcing agent of cyanoethylated lignin and cellulose nanocrystals, it cannot form an effective nano-network reinforcement structure, resulting in numerous internal defects, significantly deteriorated toughness, and the absence of a nano-network structure allows gas to easily diffuse through the matrix, leading to insufficient barrier properties. Comparative Example 2, without the addition of disulfide crosslinking agents, although reinforced with fillers, lacks a flexible crosslinking network to disperse stress. The toughening agent's effect on improving elongation is also limited, causing premature material breakage during stretching. Its barrier performance is close to that of Example 1, indicating that the contribution of the nanofiller network to barrier performance is independent of the crosslinking agent. Comparative Example 3, without the addition of poly(3-hydroxybutyric acid-co-3-hydroxyvalerate) and dimer fatty acid ester toughening agents, results in a lower elongation at break, but its barrier performance is acceptable. Comparative Example 4, without hygrothermal curing and only undergoing single UV curing, exhibits acceptable mechanical properties but slightly lower than Example 1. The lack of hygrothermal curing results in insufficient crosslinking density, leading to a network structure inferior to Example 1.

[0056] Experimental Example 3 The environmentally friendly furniture protective films prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to self-healing tests. Environmentally friendly furniture protective films prepared in Examples 1-3 and Comparative Examples 1-4 were prepared as samples. A scratch with a length of 1 cm and a depth of 70% of the film thickness was applied to the film surface using a scratch applicator. The initial morphology of the scratch was clearly photographed using an optical microscope, and its width W1 was measured. The sample with the scratch was placed in a constant temperature and humidity chamber and treated at 60°C and 70% relative humidity for 1 hour. After the sample was removed and cooled to room temperature, the scratch morphology was observed and photographed at the same position under a microscope, and the width W2 of the repaired scratch was measured. The repair efficiency was calculated according to the formula (W1-W2) / W1×100%. The specific results are shown in Table 3. Figure 5 As shown; Table 3. Comparison of test results for Experiment Example 3: The comparison results above show that in Comparative Example 1, after UV / humid heat curing, the material forms a certain cross-linking due to the presence of cross-linking agent, but lacks the synergy of fillers, resulting in reduced scratch self-healing efficiency. In Comparative Example 2, the scratches show no significant change and almost do not recover. This indicates that without a dynamic disulfide bond network, although the film material has good strength and barrier properties, it is extremely brittle and cannot be repaired once damaged, limiting its service life. In Comparative Example 3, due to the material's excessive hardness and brittleness, the scratches are difficult to close under heating conditions, showing only slight signs of healing. This comparison demonstrates that simply relying on polylactic acid with fillers and cross-linking is insufficient for toughening, and flexible components must be introduced to improve the matrix toughness. Comparative Example 4 does not undergo humid heat curing but only UV curing, resulting in a significantly lower repair efficiency than Example 1 because its internal dynamic cross-linking network has not been sufficiently optimized, leading to insufficient catalytic activity.

Claims

1. A method for preparing an environmentally friendly furniture protective film, characterized in that, The protective film is made of a blend of polylactic acid, polyhydroxy fatty acid ester and dimer fatty acid ester toughening agent as the matrix, with the addition of cyanoethylated lignin-cellulose nanocrystal composite reinforcing agent to form a dense nano network, and the introduction of dynamic crosslinking agent and functional additives containing disulfide bonds, and is coated and cured using a solvent-free ultraviolet light / humid heat dual curing system.

2. The method for preparing an environmentally friendly furniture protective film as described in claim 1, characterized in that, The specific steps include the following: S1: Dissolve lignin in an ethanol-water mixture, add sodium hydroxide at room temperature, add acrylonitrile dropwise with stirring, and react at 60°C for 6 hours; after the reaction is complete, adjust the pH to neutral with dilute hydrochloric acid, then filter, dry, grind and sieve to obtain cyanoethylated lignin; mix cyanoethylated lignin with cellulose nanocrystals and sonicate to form a suspension to prepare a cyanoethylated lignin-cellulose nanocrystal composite. S2: Dissolve aromatic oil and wall material gelatin-gum arabic solution in deionized water at a mass ratio of 1:3, stir at 10000 rpm for 30 minutes to emulsify and form water-in-oil droplets; adjust pH to 3.5, keep warm at 60℃ for 2 hours, then cool to room temperature and filter to prepare microcapsule plant essential oil; S3: Prepare the following components: polylactic acid, PHBV, dimer fatty acid ester toughening agent, cyanoethylated lignin-vitamin nanocrystal composite reinforcing agent. After drying at 80℃ for 4 hours to remove moisture, add them to a twin-screw extruder at 60 rpm for melt blending and extrusion. After cooling, stretching, and pelletizing, the output material is used to prepare masterbatch. S4: Take 100 parts of the masterbatch prepared in step S3 as a reference, add it to the ethyl acetate-dimethyl carbonate mixed solvent, and dissolve it by magnetic stirring at 50°C for 2 hours. After cooling to room temperature, add the disulfide bond crosslinking agent, functional additive and temperature-responsive photoinitiator in sequence; stir at 50°C at 2000 rpm for 2 hours to make the components mix evenly and prepare the coating liquid. S5: The coating liquid prepared in step S4 is uniformly coated onto the silicone release film using a doctor blade coating method to form a wet film. The film is left to stand at room temperature for 10 minutes. Then, the coated release film is dried at 40°C for 30 minutes. The dried film and the release film are placed together in a UV curing machine and a medium-pressure mercury lamp is used to form a cross-linked curing structure. Then, the film is subjected to humid heat curing. After the humid heat treatment is completed, the film is removed and cooled to room temperature to obtain the furniture protective film.

3. The method for preparing an environmentally friendly furniture protective film as described in claim 2, characterized in that, The cyanoethylated lignin and cellulose nanocrystals mentioned in step S1 are added to an ethanol solution at a mass ratio of 2:1, with a solid content of 1 wt%.

4. The method for preparing an environmentally friendly furniture protective film as described in claim 2, characterized in that, The aromatic oil mentioned in step S2 is selected from lavender oil or lemongrass oil.

5. The method for preparing an environmentally friendly furniture protective film as described in claim 2, characterized in that, The specific amounts of each component mentioned in step S3 are as follows: 40-60 parts of polylactic acid as a reference, 15-25 parts of PHBV, 10-15 parts of dimer fatty acid ester toughening agent, and 4-6 parts of cyanoethylated lignin-vitamin nanocrystal composite reinforcing agent.

6. The method for preparing an environmentally friendly furniture protective film as described in claim 2, characterized in that, The extruder described in step S3 has its temperature set as follows: Zone 1: 170°C, Zone 2: 175°C, Zone 3: 180°C, and Zone 4: 175°C.

7. The method for preparing an environmentally friendly furniture protective film as described in claim 2, characterized in that, The disulfide crosslinking agent, functional additive, and temperature-responsive photoinitiator mentioned in step S4 are used in the following amounts: disulfide crosslinking agent: 1-3 parts of 2,2'-dithiodiethanol diacrylate and 0.3-0.5 parts of zinc acetylacetone; functional additive: 0.5-1.5 parts of nano titanium dioxide, 0.4-0.6 parts of antistatic agent ST-3, and 0.5-1.5 parts of microcapsule plant essential oil. 0.6 to 1.0 parts of temperature-responsive photoinitiator.

8. The method for preparing an environmentally friendly furniture protective film as described in claim 2, characterized in that, The medium-pressure mercury lamp mentioned in step S5 has the following parameters: main wavelength 365nm, power 120W / cm, irradiation time 1 minute, and distance 15cm.

9. The method for preparing an environmentally friendly furniture protective film as described in claim 2, characterized in that, The parameters for the wet heat curing described in step S5 are set as follows: temperature 60°C, relative humidity 65%~75%, and placement time 1 hour.

10. An environmentally friendly furniture protective film prepared by the preparation method according to any one of claims 1-9, characterized in that, The environmentally friendly furniture protective film prepared has an elongation at break of over 95.3% and a repair efficiency of over 98.3%.

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