Environment-friendly furniture protective film and preparation method thereof

Abstract

This invention relates to the field of environmentally friendly polymer materials technology, specifically to an environmentally friendly furniture protective film and its preparation method. It aims to solve the technical problems of insufficient toughness and short service life of traditional furniture protective films. The protective film of this invention uses a blend of polylactic acid, polyhydroxyalkanoates, and dimer fatty acid esters as a matrix, adds cyanoethylated lignin-cellulose nanocrystal composite reinforcing agents to form a dense nano-network, and introduces dynamic crosslinking agents and functional additives containing disulfide bonds. This invention employs a solvent-free ultraviolet light / humid heat dual curing system for coating and curing. The furniture protective film of this invention exhibits excellent mechanical properties, significantly improved toughness, high barrier properties, and multiple functions, as well as self-healing capabilities and environmentally friendly characteristics throughout its entire life cycle.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmentally friendly polymer materials, and particularly relates to an environmentally friendly furniture protective film and a preparation method thereof. BACKGROUND

[0002] Furniture protective films are widely used for furniture surface protection to prevent scratches, stains and aging. The furniture protective films on the market at present are mostly made of traditional plastic materials such as polyvinyl chloride or polyester film, and are usually coated with an acrylic adhesive. Such traditional protective films have poor environmental friendliness and performance limitations during use. First, petroleum-based materials such as PVC are not biodegradable and will cause persistent environmental pollution after being discarded. Second, the traditional protective films have insufficient toughness and durability, are prone to cracking, tearing or yellowing, and need to be frequently replaced, with a short service life.

[0003] With the improvement of environmental awareness and the tightening of supervision, it is an urgent need to develop green and degradable furniture protective films with excellent performance. Polylactic acid is a biobased degradable polymer made from renewable plant resources, has good mechanical strength and biocompatibility, and is widely concerned in the fields of food packaging, daily necessities and the like. However, polylactic acid has inherent brittleness, low impact strength and low elongation at break, and is difficult to meet the requirements of applications with high toughness. In order to improve the toughness of polylactic acid, researchers have made a lot of attempts for toughening modification, including blending elastomers, plasticizers or flexible copolymers and the like. However, the above-mentioned toughening means often has compatibility or durability problems: if the toughening components blended with polylactic acid have poor compatibility with polylactic acid, the mechanical properties will be reduced, and small molecule plasticizers may migrate and volatilize, and the material performance will be attenuated after long-term use. In addition, many toughening materials are not biobased, which weakens the environmental friendliness of the material. In addition, furniture is easily scratched, stained or worn during transportation, storage and use, and once the surface of the protective film is damaged, it is often difficult to repair and can only be replaced with a new film, which increases the use cost and material waste. The concept of self-repairing material has attracted attention in recent years, however, so far such dynamic self-repairing network has not been applied to thin film materials such as furniture protective films. It is a technical challenge to introduce a reversible crosslinking network while ensuring the mechanical properties and transparency of the film, and to realize the self-healing of slight scratches.

[0004] In order to solve the above-mentioned problems, it is urgent to develop an environmentally friendly furniture protective film with high mechanical properties, high barrier properties and self-repairing function. SUMMARY

[0005] The main purpose of the present application is to provide an environmentally friendly furniture protection film and its preparation method, in order to overcome the defects of poor environmental protection, insufficient toughness, short service life and lack of multifunctionality of the furniture protection film in the prior art. The present application aims to prepare a furniture protection film with excellent mechanical properties, high barrier, multi-functional protection and self-repairing ability by innovative material combination and process means, to realize more durable and effective green protection of the furniture surface.

[0006] The specific technical solutions are as follows:

[0007] An environmentally friendly furniture protection film and its preparation method, comprising the following steps:

[0008] S1: Take industrial lignin 100 parts 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 drop 30 parts of acrylonitrile under stirring, react at 60℃ for 6 hours; after the reaction is completed, adjust the pH to neutral with dilute hydrochloric acid, then perform suction filtration, and finally dry in a 60℃ vacuum drying oven for 24 hours, grind through a 200 mesh sieve, obtain cyanoethylated lignin, mix cyanoethylated lignin and cellulose nanocrystals into an ethanol solution, and ultrasonically form a suspension to prepare a cyanoethylated lignin-cellulose nanocrystal compound.

[0009] Further, the amount of cyanoethylated lignin and cellulose nanocrystals is 2:1 by mass ratio of cyanoethylated lignin and cellulose nanocrystals added to the ethanol solution, and the solid content is 1wt%.

[0010] S2: Dissolve the aromatic oil and the gelatin-arabic gum solution as wall material in deionized water at a mass ratio of 1:3, stir at a speed of 10000 rpm for 30 minutes to form water-in-oil emulsion droplets; adjust the pH to 3.5, incubate at 60℃ for 2 hours, then cool to room temperature and filter to prepare microcapsule plant essential oil.

[0011] Further, the micro-aromatic oil is selected from lavender oil or citronella oil.

[0012] S3: Prepare the components: polylactic acid, poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid)(PHBV), dimer fatty acid ester toughening agent, cyanoethylated lignin-cellulose nanocrystal compound reinforcing agent, and add them into a twin-screw extruder after drying at 80℃ for 4 hours to remove moisture, at a speed of 60 revolutions per minute, melt blend and extrude. The discharged material is cooled, drawn, and granulated to prepare a master batch.

[0013] Further, the specific amount of each component is as follows: polylactic acid 40-60 parts as a reference, poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) 15-25 parts, dimer fatty acid ester toughening agent 10-15 parts, and cyanoethylated lignin-cellulose nanocrystal compound reinforcing agent 4-6 parts.

[0014] Further, the temperature settings of the extruder zones are one zone 170℃, two zone 175℃, three zone 180℃, and four zone 175℃.

[0015] S4: Take 100 parts of the prepared master batch as a reference, add it into ethyl acetate-dimethyl carbonate mixed solvent, the solid content is 25wt%, the volume ratio of ethyl acetate to dimethyl carbonate is 1:1, dissolve under magnetic stirring at 50℃ for 2 hours, cool to room temperature, then add disulfide crosslinking agent, functional additives and temperature responsive photoinitiator in sequence; stir at 2000 rpm for 2 hours at 50℃ to make the ingredients evenly mixed, and prepare a coating liquid.

[0016] Further, the amount of disulfide crosslinking agent, functional additives and temperature responsive photoinitiator is respectively: disulfide crosslinking agent, the amount of 2,2'-dithiodiethanol diacrylate is 1-3 parts, and the amount of zinc acetylacetone is 0.3-0.5 parts; the amount of functional additives is: the amount of nano-titanium dioxide is 0.5-1.5 parts, the amount of antistatic agent ST-3 is 0.4-0.6 parts, and the amount of microcapsule plant essential oil is 0.5-1.5 parts; the amount of temperature responsive photoinitiator is 0.6-1.0 parts.

[0017] S5: The prepared coating liquid is uniformly coated on a silicon release film by using a doctor blade coating method to form a wet film, and then the coated release film is placed in a forced air oven at 40℃ for drying for 30 minutes to ensure that the residual solvent is fully volatilized. After drying, a solid-state film is obtained, which is densely attached to the release film. The dried film together with the release film is placed in an ultraviolet curing machine, a medium pressure mercury lamp is used to preliminarily form a crosslinked and cured structure, and then wet heat curing is performed. After the wet heat treatment is completed, the cooled to room temperature to prepare a furniture protective film.

[0018] Further, the parameters of the medium pressure mercury lamp are set as follows: the main wavelength is 365 nm, the power is 120 W / cm, the irradiation time is 1 minute, and the distance is 15 cm.

[0019] Further, the parameters of the wet heat curing are set as follows: the temperature is 60℃, the relative humidity is 65%-75%, and the placement time is 1 hour.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] 1. The main components of the protective film of the present application, such as polylactic acid, polyhydroxyalkanoate, modified lignin, cellulose nanocrystal, plant oil-based toughening agent, and plant essential oil, are all derived from renewable biomass or natural products, and low-toxicity solvents and solvent-free curing processes are used in the preparation process, without organic volatile emissions, realizing environmental friendliness in the whole life cycle.

[0022] 2.The invention overcomes the brittleness of pure polylactic acid by the synergistic effect of polyhydroxyalkanoate blending toughening, dimeric fatty acid ester plasticizing and dynamic crosslinking network, and shows a balance of high strength and high toughness.

[0023] 3.The invention constructs a dense nanometer network structure by cyanoethylation of lignin and cellulose nanocrystals, and cooperates with the shielding effect of nanometer titanium dioxide, so that the protective film has excellent barrier properties to oxygen, water vapor and ultraviolet light, and the disulfide bond in the dynamic crosslinking network can break and recombine under certain conditions, so that the self-repairing property can be realized, and finally the service life of the furniture is improved.

[0024] 4.The protective film of the invention integrates a variety of practical functions in addition to the basic physical protection. The surface of the film material contains an antistatic agent, which effectively prevents static dust accumulation and keeps the surface of the furniture clean and bright; the dispersed microcapsule plant essential oil in the film can slowly release natural fragrance, and has the functions of air purification and insect and mildew prevention. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The invention is a preparation process flow chart of an environmentally friendly furniture protective film.

[0026] Figure 2 The invention is a scanning electron microscope image for experimental example 1.

[0027] Figure 3 The invention is a comparison chart of mechanical property test results of experimental example 2.

[0028] Figure 4 The invention is a comparison chart of barrier property test results of experimental example 2.

[0029] Figure 5 The invention is a comparison chart of self-repairing efficiency test results of experimental example 3. DETAILED DESCRIPTION

[0030] The following examples further explain and illustrate the technical solutions of the invention. It is particularly pointed out that each specific embodiment is a specific embodiment and explanation of the technical solution, and should not be regarded as a limitation on the protection scope of the invention. Those skilled in the art still have the right to modify the technical solutions of these examples, to equivalently replace part or all of the technical features, and these modifications or replacements do not change the essence of the corresponding technical solution, and do not make the essence of the corresponding technical solution deviate from the scope of the technical solution described in the invention. As shown in the accompanying drawings, Figure 1 The invention is a preparation process flow chart of an environmentally friendly furniture protective film, and the detailed preparation steps are as follows:

[0031] 1.Raw material preparation

[0032] 1.1 Preparation of cyanoethylated wood

[0033] Take 100 parts of industrial lignin as a reference, 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 drop 30 parts of acrylonitrile under stirring, react at 60°C for 6 hours; after the reaction is completed, adjust the pH to neutral with dilute hydrochloric acid, then perform suction filtration, and finally dry in a vacuum drying oven at 60°C for 24 hours, grind through a 200 mesh sieve, to prepare cyanoethylated lignin.

[0034] Acrylonitrile reacts with the hydroxyl groups on the lignin molecule to introduce a -CH2CH2CN side chain.

[0035] 1.2 Preparation of cyanoethylated lignin-cellulose nanocrystal composite

[0036] Take the cyanoethylated lignin prepared above and mix it with cellulose nanocrystals at a mass ratio of 2:1, with a solid content of 1 wt%, add an ethanol solution, and ultrasonicate to form a suspension, with an ultrasonic power of 600W and an ultrasonic time of 30 minutes, so that the cyanoethylated lignin is fully adsorbed and combined on the surface of the cellulose nanocrystals, to prepare a cyanoethylated lignin-cellulose nanocrystal composite.

[0037] By cyanoethylation of lignin, -C≡N polar groups are introduced, which on the one hand weaken the strong hydrogen bonding within the lignin macromolecule, improving its dispersibility and compatibility in organic phase, and on the other hand retain the aromatic structure in the lignin molecule, thus still having excellent ultraviolet absorption and antioxidant properties. Cellulose nanocrystals are a kind of whisker-like nanofibers with a length of hundreds of nanometers and high rigidity and aspect ratio, with a surface rich in hydroxyl groups, which can form a tight combination with cyanoethylated lignin through hydrogen bonding and van der Waals forces. When the cyanoethylated lignin-cellulose nanocrystal is 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, and effectively blocking the diffusion of gas and liquid molecules through the "brick wall" path, thus imparting high barrier and ultraviolet aging resistance to the protective film.

[0038] 2. Preparation of microcapsulated plant essential oil

[0039] Take the aromatic oil and the gelatin-arabic gum solution as wall material, dissolve them in deionized water at a mass ratio of 1:3, stir at a speed of 10000 rpm for 30 minutes to emulsify and form water-in-oil droplets; adjust the pH to 3.5, incubate at 60°C for 2 hours to allow the pre-polymer to polymerize and deposit on the surface of the oil droplets to form a capsule wall, cool to room temperature, and then filter to prepare a microcapsulated plant essential oil.

[0040] The microencapsulated plant essential oil can be selected from natural aromatic oils such as lavender oil or citronella oil, etc. and added to the coating liquid by forming microcapsules through in-situ polymerization. These microcapsules are uniformly distributed in the protective film and remain encapsulated, slowly releasing a small amount of essential oil when the film is subjected to friction or temperature rise, not only imparting a delicate natural fragrance to the furniture, but also providing additional protection to the furniture by utilizing the antibacterial and insect-repellent properties of certain essential oils.

[0041] 3. Masterbatch blending

[0042] Take 40-60 parts of polylactic acid as a reference, 15-25 parts of poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV), 10-15 parts of dimer fatty acid ester toughening agent, and 4-6 parts of cyano-ethylated lignin-cellulose nanocrystal composite reinforcing agent. After drying at 80°C for 4 hours and dehumidifying, the above components are added to a twin-screw extruder. The temperature of each zone of the extruder is set to 170°C for zone 1, 175°C for zone 2, 180°C for zone 3, and 175°C for zone 4, with a rotation speed of 60 revolutions per minute. The material is melt blended and extruded. The output is cooled, drawn, and granulated to obtain the masterbatch.

[0043] Poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) copolyester (PHBV) provides higher ductility and biodegradability than polylactic acid; dimer fatty acid ester toughening agent is prepared from natural plant oil fatty acid dimers, esterified or hydrogenated to form saturated long-chain ester plasticizers, which have good compatibility and toughening effect. The above three components form a continuous matrix phase through melt blending, and the introduction of polyhydroxyalkanoate and toughening agent effectively reduces the brittleness of the polylactic acid matrix, improves the elongation at break and impact toughness.

[0044] 4. Coating liquid preparation

[0045] Take 100 parts of the masterbatch prepared above as a reference and add it to a mixture of ethyl acetate-dimethyl carbonate solvent, with a solid content of 25wt%, a volume ratio of ethyl acetate to dimethyl carbonate of 1:1, and magnetic stirring at 50°C for 2 hours. After cooling to room temperature, add 1-3 parts of disulfide crosslinking agent 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, 0.5-1.5 parts of microencapsulated plant essential oil, and 0.6-1.0 parts of temperature-responsive photoinitiator; stir at 2000 rpm for 2 hours at 50°C to mix the components uniformly, and prepare the coating liquid.

[0046] The cross-linking agent includes a disulfide bond-containing compound and zinc acetylacetonate. The disulfide bond compound is a difunctional monomer with a disulfide bond bridge, which contains a disulfide bond in the molecule that is easy to break and recombine under light or heating conditions, and has a polymerizable functional group that can undergo free radical polymerization under the action of a UV photoinitiator to form a cross-linked network. After cross-linking, the disulfide bond acts as a dynamic reversible bond and can break and recombine under certain temperature or specific triggering conditions, allowing the cross-linked network to have topological rearrangement capability. Adding a small amount of zinc acetylacetonate as a catalyst helps to reduce the activation energy required for disulfide bond exchange and accelerate the dynamic rearrangement process. In addition, zinc acetylacetonate can also form coordination with polar groups in the matrix, increasing the cross-linking density and stability of the network. In the present application, the introduction of this dynamic cross-linked network not only improves the toughness of the film material, but more importantly, it gives the film material self-repairing ability: when a fine scratch or crack appears on the film surface, the disulfide bond dynamic network can reconnect the polymer chains at the broken section at an appropriate temperature or under light, achieving automatic repair of the damage.

[0047] Nanometer titanium dioxide (particle size 30-40 nm, surface treated with organosilane to enhance hydrophobic dispersibility) as an inorganic shielding agent can improve the barrier property and UV aging resistance of the film; the antistatic agent can avoid affecting biodegradability, and its role is to reduce the accumulation of static electricity on the film surface to prevent dust adsorption.

[0048] 5. Coating, film formation and curing

[0049] The coating solution prepared above is uniformly coated on a silicon 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 oven at 40°C for drying for 30 minutes to ensure that the residual solvent is fully volatilized. After drying, a solid thin film is obtained which is densely attached to the release film, and the dried film together with the release film is placed in a UV curing machine, using a medium pressure mercury lamp, setting the main wavelength at 365 nm, the power at 120 W / cm, irradiating for 1 minute at a distance of 15 cm, to initially form a cross-linked and cured structure, and then wet heat curing is performed. The film subjected to UV curing is moved into a culture box with heating and humidifying functions, and is placed at 60°C and a relative humidity of 65%-75% for 1 hour; after the wet heat treatment is completed, it is taken out and cooled to prepare a furniture protective film.

[0050] Under the action of the temperature-responsive photoinitiator, ultraviolet irradiation will initiate the photocrosslinking reaction of the disulfide bond-containing compound: the double bond groups in the disulfide bond compound polymerize to form a three-dimensional network, and the disulfide bond is introduced into the cross-linking point. Because the initiator has temperature response characteristics, its activity is low at room temperature, which can avoid premature curing during coating and standing; when ultraviolet irradiation occurs, the photoinitiator releases free radicals under the condition of ultraviolet light and the slight temperature rise generated thereby, triggering the polymerization reaction and causing the coating to rapidly cure and form a solid film, forming a preliminarily cross-linked solid film.

[0051] The moisture heat curing promotes the movement of polymer chain segments and disulfide bond exchange reactions, rearranges and further crosslinks the previously formed crosslinked network, and improves the density and uniformity of the network. On the other hand, the process is similar to thermal post-treatment, which can eliminate the internal stress generated by ultraviolet rapid polymerization and induce moderate crystallization of the polylactic acid / polyhydroxyalkanoate matrix, thereby comprehensively improving the mechanical and barrier properties of the film.

[0052] Example 1

[0053] Table 1: Raw material information table

[0054]

[0055] An environmentally friendly furniture protective film and a preparation method thereof are as follows:

[0056] S1: Take 100 parts of industrial lignin as a reference and dissolve it in 400 parts of an ethanol-water mixed solvent with a volume ratio of ethanol to water of 7:3. Add 10 parts of sodium hydroxide at room temperature, and drop 30 parts of acrylonitrile under stirring. React at 60°C for 6 hours. After the reaction is completed, adjust the pH to neutral with dilute hydrochloric acid, then perform suction filtration, and finally dry in a vacuum drying oven at 60°C for 24 hours. Grind through a 200-mesh sieve to prepare cyanoethylated lignin.

[0057] Weigh the cyanoethylated lignin prepared above, mix it with cellulose nanocrystals at a mass ratio of 2:1, and add an ethanol solution with a solid content of 1wt%. Then, ultrasonic treatment is performed to form a suspension liquid, with an ultrasonic power of 600W and an ultrasonic time of 30 minutes. In this way, the cyanoethylated lignin is fully adsorbed and combined on the surface of the cellulose nanocrystals, and a cyanoethylated lignin-cellulose nanocrystal compound is prepared.

[0058] S2: Microcapsules are prepared by in-situ polymerization. Lavender oil and a gelatin-arabic gum solution are dissolved in deionized water at a mass ratio of 1:3, and the mass ratio of gelatin to arabic gum is 1:1. Stirring is performed at a speed of 10000 rpm for 30 minutes to form water-in-oil droplets. The pH is adjusted to 3.5, and the pre-polymer is allowed to polymerize and deposit on the surface of the oil droplets to form a capsule wall at 60°C for 2 hours. After cooling to room temperature, filtration is performed to prepare microcapsulated plant essential oil.

[0059] S3: Take 50 parts of polylactic acid as a reference, 20 parts of poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid), 12 parts of dimer fatty acid ester toughening agent, and 5 parts of cyanoethylated lignin-cellulose nanocrystal compound reinforcing agent. After drying at 80°C for 4 hours to remove moisture, the above components are added to a twin-screw extruder. The temperature of each zone of the extruder is set as follows: Zone 1: 170°C, Zone 2: 175°C, Zone 3: 180°C, and Zone 4: 175°C. The rotation speed is 60 revolutions per minute. The material is melt blended and extruded. After cooling and drawing, the material is cut into granules to prepare a master batch.

[0060] S4: Take the above prepared master batch 100 parts as a reference, add ethyl acetate-dimethyl carbonate mixed solvent, solid content 25wt%, the volume ratio of ethyl acetate and dimethyl carbonate is 1:1, dissolve at 50℃ under magnetic stirring for 2 hours, cool to room temperature, then add disulfide crosslinking agent: 2,2'-dithiodiethanol diacrylate 2 parts and zinc acetylacetone 0.4 parts; functional additives: nano titanium dioxide 1.0 parts, antistatic agent ST-3 0.5 parts, microcapsule plant essential oil 1.0 parts and temperature responsive photoinitiator 0.8 parts; stir at 50℃ at a speed of 2000rpm for 2 hours to make the ingredients evenly mixed, and prepare a coating liquid.

[0061] S5: The above prepared coating liquid is uniformly coated on a silicon release film by using a doctor blade coating method. After coating, it is placed at room temperature for 10 minutes, and then the coated release film is placed in a forced air oven at 40℃ for drying for 30 minutes to ensure that the residual solvent is fully volatilized. After drying, a solid film is obtained which is densely attached to the release film. The dried film together with the release film is placed in a UV curing machine, using a medium pressure mercury lamp with a main wavelength of 365nm and a power of 120W / cm, irradiated for 1 minute at a distance of 15cm, to preliminarily form a crosslinked and cured structure, and then wet heat curing is performed. The UV cured film is moved into a incubator with heating and humidifying functions, and placed at 60℃ and a relative humidity of 70% for 1 hour. After wet heat treatment, it is cooled and removed to prepare a furniture protective film.

[0062] Example 2

[0063] Reference to the preparation method of Example 1, but different from:

[0064] In step S2, the lavender oil is replaced with citronella oil;

[0065] In step S3, take polylactic acid 40 parts as a reference, poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) 15 parts, dipoly fatty acid ester toughening agent 10 parts, and cyanoethylated lignin-cellulose nanocrystal composite reinforcing agent 4 parts;

[0066] In step S4, 2,2'-dithiodiethanol diacrylate 1 part and zinc acetylacetone 0.3 parts; functional additives: nano titanium dioxide 0.5 parts, antistatic agent ST-3 0.4 parts, microcapsule plant essential oil 0.5 parts and temperature responsive photoinitiator 0.6 parts;

[0067] In step S5, the relative humidity is 65%.

[0068] Example 3

[0069] Reference to the preparation method of Example 1, but different from:

[0070] In step S3, 60 parts of polylactic acid is taken as a reference, 25 parts of poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid), 15 parts of dimer fatty acid ester toughening agent, and 6 parts of cyanoethylated lignin-cellulose nanocrystal composite reinforcing agent are added.

[0071] In step S4, 3 parts of 2,2'-dithiodiethanol diacrylate and 0.5 parts of zinc acetylacetonate are added; functional additives: 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 parts of temperature-responsive photoinitiator.

[0072] In step S5, the relative humidity is 75%.

[0073] Comparative Example 1

[0074] The preparation method of Reference Example 1 is used, but no cyanoethylated lignin and cellulose nanocrystals are added. The remaining steps are the same.

[0075] Comparative Example 2

[0076] The preparation method of Reference Example 1 is used, but no disulfide crosslinking agent: 2,2'-dithiodiethanol diacrylate and zinc acetylacetonate are added. The remaining steps are the same.

[0077] Comparative Example 3

[0078] The preparation method of Reference Example 1 is used, but no poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) and dimer fatty acid ester toughening agent are added. The remaining steps are the same.

[0079] Comparative Example 4

[0080] The preparation method of Reference Example 1 is used, but no humid heat curing is performed, only single ultraviolet curing is performed. The remaining steps are the same.

[0081] Experimental Example 1

[0082] The cyanoethylated lignin-cellulose nanocrystal prepared in Example 1 is observed by scanning electron microscope, 1 mL of cyanoethylated lignin-cellulose nanocrystal solution is diluted 10 times with anhydrous ethanol, then dropped on a mica sheet, dried at room temperature under natural air, then sprayed with gold under vacuum, the spraying thickness is 5 nm, the test parameters are acceleration voltage 3-5 kv, working distance 5-8 mm, signal type is secondary electron signal, and the probe is SE2. The test results are shown in Figure 2 .

[0083] The nanowhisker surface can be covered with a layer of lignin material in a network-like aggregation structure; the cellulose nanocrystals can be more uniformly dispersed in the polymer matrix, and the nanofiber network composed of cellulose nanocrystals is covered with a layer of cyanoethylated lignin; the cellulose nanocrystals still maintain a fibrous arrangement and network structure, but the surface of each fiber is slightly rough and thickened due to the combination of lignin, and local granular attachments or coatings formed by lignin can be seen, and no more than aggregated large clusters are seen. The presence of lignin not only gives the fiber surface a new organic coating, but also forms a bridge at the intersection of the fibers, further consolidating the structure of the composite network and playing a synergistic reinforcing role.

[0084] Experimental Example 2

[0085] The environmentally friendly furniture protection films prepared in Experimental Examples 1-3 and Comparative Examples 1-4 were tested for comprehensive performance,

[0086] Mechanical property test: the elongation at break was determined according to the standard ASTM D882-18 "Standard Test Methods for Tensile Properties of Plastics Sheeting";

[0087] Barrier property test: oxygen transmission rate was determined according to the standard ASTM D3985-24 "Standard Test Methods for Measuring the Oxygen Transmission Rate of Plastics Films and Sheeting Using a Coulometric Sensor"; water vapor transmission rate was determined according to the standard GB / T 1037-2021 "Determination of Water Vapor Transmission Properties of Plastics Films and Sheeting Cup Method for Gain and Loss in Weight"; the specific test comparison results are shown in Table 2, Figure 3 , Figure 4

[0088] Table 2 Comparison of comprehensive performance test results of Experimental Example 2

[0089]

[0090] ​From the above comparison results, it can be seen that in Comparative Example 1, no cyanethylated lignin and cellulose nanocrystals are added; the brittleness is extremely great, there is no cyanethylated lignin and cellulose nanocrystal complex reinforcing agent, an effective nanometer network reinforcing structure cannot be formed, there are many defects in the material, the toughness is significantly deteriorated, and there is no nanometer network structure, gas is easy to diffuse through the matrix, and the barrier ability is insufficient; in Comparative Example 2, no disulfide crosslinking agent is added, although there is filler reinforcement, there is no flexible crosslinking network to disperse stress, and the effect of the toughening agent on improving the elongation rate is also limited, the material breaks prematurely during stretching, and in terms of barrier performance, it is close to the level of Example 1, indicating that the contribution of the nanofiller network to the barrier is independent of the presence of the crosslinking agent; in Comparative Example 3, no poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) and dipoly fatty acid ester toughening agent is added, resulting in a low elongation at break, but the barrier performance is still acceptable; in Comparative Example 4, no hydrothermal curing is performed, only single ultraviolet curing is performed, the mechanical properties are acceptable but slightly lower than those of Example 1, and the lack of hydrothermal curing and insufficient crosslinking density result in a network structure that is not as good as that of Example 1.

[0091] Experimental Example 3

[0092] The environmentally friendly furniture protection films prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to self-repairing tests. The environmentally friendly furniture protection films prepared in Examples 1-3 and Comparative Examples 1-4 were respectively prepared as samples, a scratch with a length of 1 cm and a depth of 70% of the film thickness was applied on the surface of the film using a scratch tester, the initial morphology of the scratch was clearly photographed using an optical microscope, and the width W1 was measured. The sample with the scratch was placed in a constant temperature and humidity chamber, and was treated at 60°C and 70% relative humidity for 1 hour. After taking out the sample and cooling to room temperature, the scratch morphology was observed and photographed under the microscope at the same position, the repaired scratch width W2 was measured, and the repair efficiency was calculated according to the formula: repair efficiency=(W1-W2) / W1x100%. The specific results are shown in Table 3, Figure 5

[0093] Table 3: Comparison of test results of Experimental Example 3

[0094]

[0095] ​From the above comparison results, in Comparative Example 1, after UV / hygrothermal curing, due to the presence of crosslinking agent, the material forms a certain crosslinking, but lacks the synergy of fillers, and the scratch self-repairing efficiency is reduced; in Comparative Example 2, the scratch has no obvious change and almost no recovery, thus it can be seen that without the dynamic network of disulfide bond, although the film material has good strength and barrier, it is extremely brittle and cannot be repaired once damaged, and the service life is limited; in Comparative Example 3, due to the fact that the material is too hard and brittle, the scratch is also difficult to close under heating conditions, and only has weak healing signs. This comparison shows that simply relying on polylactic acid and fillers and crosslinking is insufficient in toughening, and a flexible component must be introduced to improve the toughness of the matrix; in Comparative Example 4, no hygrothermal curing is performed, only single UV curing is performed, and the repair efficiency will be significantly lower than that of Example 1, because the internal dynamic crosslinking network is not fully optimized and the catalytic activity is insufficient.

Claims

1. A method for preparing an environmentally friendly furniture protection film, characterized in that, The protective film is prepared by using a polylactic acid, polyhydroxyaliphatic ester and dimer fatty acid ester toughener blended material as a matrix, adding a cyanoethylated lignin-cellulose nanocrystal compounded reinforcing agent to form a dense nanometer network, introducing a dynamic crosslinking agent containing a disulfide bond and a functional additive, and using a solvent-free ultraviolet light / humidity dual curing system for coating and curing. The method comprises the following specific steps, S1: dissolving lignin in an ethanol-water mixed solvent, adding sodium hydroxide at room temperature, adding acrylonitrile dropwise under stirring, and reacting at 60°C for 6 hours; after the reaction is completed, the pH is adjusted to neutral with dilute hydrochloric acid, then filtration and drying are performed, grinding and sieving are performed, cyanoethylated lignin is obtained, the cyanoethylated lignin is mixed with cellulose nanocrystals, and a suspension is formed by ultrasonic treatment to prepare a cyanoethylated lignin-cellulose nanocrystal compounded reinforcing agent; S2: dissolving aromatic oil and wall material gelatin-arabic gum solution in deionized water at a mass ratio of 1:3, stirring at a speed of 10,000 rpm for 30 minutes to form water-in-oil emulsion droplets, adjusting the pH to 3.5, and incubating at 60°C for 2 hours, then cooling to room temperature and filtering to prepare microcapsule plant essential oil; S3: preparing components: polylactic acid, PHBV, dimer fatty acid ester toughener, and cyanoethylated lignin-cellulose nanocrystal compounded reinforcing agent, adding them into a twin-screw extruder after drying at 80°C for 4 hours to remove moisture, melting and blending extrusion at a speed of 60 revolutions per minute, and cooling, drawing, and granulating the discharged material to prepare a master batch; S4: taking 100 parts of the master batch prepared in step S3 as a reference, dissolving it in an ethyl acetate-dimethyl carbonate mixed solvent at 50°C for 2 hours under magnetic stirring, then cooling to room temperature, and sequentially adding a disulfide crosslinking agent, a functional additive, and a temperature-responsive photoinitiator; stirring at a speed of 2,000 rpm at 50°C for 2 hours to uniformly mix the components, and preparing a coating liquid; S5: uniformly coating the coating liquid prepared in step S4 on a silicon release film to form a wet film, standing at room temperature for 10 minutes, then drying the coated release film at 40°C for 30 minutes, placing the dried film together with the release film in an ultraviolet curing machine, using a medium-pressure mercury lamp to form a crosslinked and cured structure, and then performing humidity curing; after the humidity treatment is completed, cooling to room temperature, and preparing a furniture protective film.

2. The method for preparing an environmentally friendly furniture protective film according to claim 1, wherein the cyanoethylated lignin and cellulose nanocrystals in step S1 are added to an ethanol solution at a mass ratio of 2:1, and the solid content is 1 wt%.

3. The method for preparing an environmentally friendly furniture protective film according to claim 1, wherein the aromatic oil in step S2 is lavender oil or citronella oil.

4. The method for preparing an environmentally friendly furniture protective film according to claim 1, wherein ​ ​ The components in step S3, the specific amount is 40-60 parts of polylactic acid as a reference, PHBV 15-25 parts, 10-15 parts of dimer fatty acid ester toughening agent, 4-6 parts of cyanoethylated lignin-cellulose nanocrystal composite reinforcing agent.

5. The preparation method of the environmentally friendly furniture protection film according to claim 1, characterized in that, The extruder in step S3 is set to have a temperature of 170℃ in the first zone, 175℃ in the second zone, 180℃ in the third zone, and 175℃ in the fourth zone.

6. The preparation method of the environmentally friendly furniture protection film according to claim 1, characterized in that, The disulfide crosslinking agent, functional additives, and temperature-responsive photoinitiator in step S4 are used in the following amounts: 1-3 parts of 2,2'-dithiodiethanol diacrylate, 0.3-0.5 parts of zinc acetylacetonate; 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 0.6-1.0 parts of temperature-responsive photoinitiator. The disulfide crosslinking agent, functional additives, and temperature-responsive photoinitiator in step S4 are used in the following amounts: 1-3 parts of 2,2'-dithiodiethanol diacrylate, 0.3-0.5 parts of zinc acetylacetonate; 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 0.6-1.0 parts of temperature-responsive photoinitiator.

7. The preparation method of the environmentally friendly furniture protection film according to claim 1, characterized in that, The medium-pressure mercury lamp in step S5 is set to have a main wavelength of 365nm, a power of 120W / cm, an irradiation time of 1 minute, and a distance of 15cm.

8. The preparation method of the environmentally friendly furniture protection film according to claim 1, characterized in that, The humid heat curing in step S5 is set to have a temperature of 60℃, a relative humidity of 65%-75%, and a placement time of 1 hour.

9. The environmentally friendly furniture protection film prepared by the preparation method according to any one of claims 1-8, characterized in that, The prepared environmentally friendly furniture protection film has an elongation at break of 95.3% or more and a repair efficiency of 98.3% or more.

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