Biomass film and preparation method thereof

Abstract

The invention relates to a biomass film and a preparation method thereof. The biomass film comprises the following main components: cellulose derivatives (carboxymethyl cellulose, hydroxyethyl fibers, hydroxy propyl cellulose and the like), starch and derivatives thereof, a cationic amine high polymer, a cross-linking agent (fatty aldehydes, boric acid, borax, citric acid, epichlorohydrin and the like), nano cellulose and a plasticizer. And a coating mode is adopted for forming, so that quick and efficient roll-to-roll production and preparation can be realized. The biomass film has high strength, high modulus, high transparency and excellent degradability, recyclability and recyclability, and can be widely applied to the fields of packaging, circuit boards of electronic products, substrates of flexible electronic displays, disposable tableware, agriculture (mulching films, slow release of pesticides and chemical fertilizers and the like) and the like. In addition, the reaction process does not involve high-toxicity chemical preparations or harsh reaction conditions, and the method has the advantages of being simple and convenient in production process, low in cost, green, environmentally friendly and the like.

Description

Technical Field

[0001] The invention belongs to the field of biomass films and relates to a biomass film and a preparation method thereof. Background Art

[0002] Since its introduction, petroleum-based plastic products have provided great convenience for the development of human society with their advantages of light weight, high strength, excellent gas barrier and waterproof performance, and low cost. As of now, the total global plastic production has far exceeded 8 billion tons. Although petroleum-based plastic products are extremely convenient, their excellent stability has led to serious accumulation of plastic waste. Due to the lack of proper treatment technology, the residual plastic waste reaches hundreds of millions of tons every year. Plastic waste not only causes land environmental pollution, but also causes serious marine ecological pollution after entering the ocean. The decomposed microplastics are ingested by marine organisms and enter the human food chain, which also has adverse effects on human health. Although the recycling of petroleum-based plastic products is generally advocated at the social level, only 14% of plastic products can be recycled worldwide. Some researchers have developed alternative polymers such as polylactic acid (PLA), polyhydroxyalkanoates (PHA), polyhydroxybutyrate (PHB) and polybutylene succinate (PBS), but they generally have disadvantages such as complex production processes, high manufacturing costs and poor mechanical properties. In addition, their degradation requires specific humidity (95% RH) and temperature (58℃±2℃) conditions, making them difficult to promote and apply on a large scale.

[0003] Cellulose and starch are the most abundant natural polymers in nature. In recent years, research on them as biomass plastic substrates has also found that their films have certain mechanical properties and good barrier properties, and are considered to be one of the substitutes for traditional plastics. However, based on existing literature reports and patent publications, research on the preparation of biomass films using natural biomass materials has defects such as low transparency, low strength, and poor water resistance.

[0004] Cellulose is the largest polymer in nature. It is a natural resource with a wide range of sources, low price, renewable and degradable. However, it generally has the problem of low transparency in film formation. A variety of cellulose derivatives obtained by simple chemical modification can solve this problem well, but the film formation of cellulose derivatives generally has the problem of poor strength (<15MPa). In order to balance transparency and strength, the industry often uses a dissolution spinning process to dissolve cellulose and then prepare cellulose-based films, such as acetic acid and butyric acid reaction followed by acetone dissolution, or carbon disulfide / sodium hydroxide, copper ethylenediamine and other solvents to dissolve the fiber, or modified and dissolved in organic solvents (DMSO, DMF, N-methylmorpholine) and then washed and cross-linked. However, this process uses a large amount of highly toxic reagents and involves complex chemical reaction conditions, which does not meet the environmental protection requirements of biomass films. Similar to cellulose, starch and its derivatives are also natural polymers with huge reserves in nature. Its application research as degradable biomass films is more extensive. Thermoplastic starch can be obtained by adding plasticizers, which is a major branch of biomass films. Its film strength is high, but it is generally brittle and highly sensitive to moisture. Although starch films can maintain a certain toughness in the short term after plasticization, the brittleness caused by the need to use a large amount of plasticizers and the migration of plasticizers after a period of time still seriously limit the practical application of starch films. In addition, there are many reports on the study of cellulose, starch and its derivatives blended with other plastic-based materials to prepare composite plastic films, but due to the large doses of plastic components, it is still difficult to solve the problem of plastic degradation and recycling, and it cannot be classified as a degradable biomass film, so it will not be discussed here.

[0005] In general, exploring and developing a biomass film made of cellulose and starch is very necessary and of great significance for reducing the use of petrochemical plastics and reducing white pollution. Summary of the invention

[0006] The primary purpose of the present invention is to provide a biomass film obtained from biomass materials (cellulose derivatives, starch / starch derivatives, nanocellulose) and a preparation method thereof, wherein the cellulose derivatives and starch are covalently cross-linked, plasticized, and then coated on a substrate film and dried to form. The preparation method of the present invention uses simple and easily available raw materials, does not involve highly toxic agents or harsh chemical reaction conditions, and can use coating equipment to achieve large-scale "roll-to-roll" rapid production.

[0007] Another object of the present invention is to provide a biomass film obtained by the above-mentioned preparation method, which has the advantages of high transparency, high strength, water resistance and gas barrier, biodegradability and recyclability.

[0008] To achieve the above-mentioned object of the invention, the present invention provides the following solutions:

[0009] The first aspect of the present invention provides a method for preparing a biomass film, comprising the following steps:

[0010] After the cellulose derivative is dispersed in water, a cationic amine polymer solution is added and stirred for reaction. After the reaction is completed, it is blended with gelatinized starch, and then a cross-linking agent is added to blend for cross-linking reaction. After the reaction, nanocellulose and a plasticizer are added for plasticization to obtain a biomass plastic slurry. The coating is coated on a plastic substrate film, dried and peeled off to obtain a biomass film.

[0011] Preferably, the cellulose derivative is selected from one or more of carboxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose; the degree of substitution of the cellulose derivative is 0.5-2.5; and the cationic amine polymer is diluted with water to 0.1-10 wt % when used.

[0012] Preferably, the cationic amine polymer is selected from one or more of polyamide epichlorohydrin (12.5wt%-30wt%), polyacrylamide (Mw=800-1400w), and polyethyleneimine (Mw=1800-70000).

[0013] Preferably, the cationic amine polymer and the cellulose derivative are reacted at room temperature for 0.5-2 hours.

[0014] Preferably, the mass ratio of the cellulose derivative to the cationic amine polymer is 10:1 to 5:1.

[0015] Preferably, the starch is selected from one or more of natural starch and starch derivatives; the natural starch is selected from one or more of bean starch, corn starch, potato starch, and cassava starch; the starch derivative is selected from one or more of pregelatinized starch, oxidized starch, and esterified starch.

[0016] Preferably, the cross-linking agent is selected from one or more of fatty aldehydes, boric acid, borax, citric acid, and epichlorohydrin.

[0017] Preferably, the fatty aldehyde is selected from one or more of glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, adipaldehyde, suberaldehyde, glyceraldehyde and trichloroacetaldehyde.

[0018] Preferably, the mass ratio of the starch to the cross-linking agent is 10:1 to 5:3; the temperature of the cross-linking reaction is 60-100° C., and the time of the cross-linking reaction is 0.5-2 h.

[0019] Preferably, the mass ratio of the cellulose derivative to starch is 1:1 to 1:2.

[0020] Preferably, the plasticizer is selected from one or more of glycerol, ethylene glycol, polyethylene glycol, sorbitol, mannitol, urea, thiourea, formamide, N,N-dimethylformamide, diethyl phthalate, triacetin, and triethyl citrate.

[0021] Preferably, the plasticizing temperature is 25-90° C., and the plasticizing time is 0.5-12 h.

[0022] Preferably, the coating method is selected from one or more of air knife coating, blade coating, roller coating, slit coating and curtain coating.

[0023] Preferably, the plastic substrate is selected from one or more of polyethylene terephthalate (PET), high-density polyethylene (HDPE), polyvinyl chloride (PVC), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), and polyethylene (PE).

[0024] Preferably, the drying temperature is 25-105° C. and the drying time is 0.3-3 h.

[0025] The second aspect of the present invention provides a biomass film prepared according to the above preparation method.

[0026] Preferably, the biomass film comprises the following components in mass fractions: 20%-70% cellulose derivatives, 30-70% starch, 0-20wt% cationic amine polymers, 0-20wt% cross-linking agent, 0-5wt% nanocellulose, and 0-10wt% plasticizer.

[0027] The third aspect of the present invention provides the use of the biomass film prepared according to the above preparation method in packaging, electronic product circuit boards, flexible electronic display substrates, disposable tableware, and agriculture (such as mulch films, pesticide and fertilizer slow release, etc.).

[0028] A fourth aspect of the present invention provides a method for degradation and recycling of biomass film, comprising the following steps:

[0029] The prepared biomass film is immersed in water for more than 24 hours. After the hydrogen bond structure and the hemiacetal cross-linking structure in the film fail, the film absorbs water and softens. After stirring and dispersing at more than 1000rpm / min, the degradation of the biomass film material can be achieved to obtain a biomass film water dispersion, which can be used for secondary molding to prepare biomass film materials after concentration.

[0030] Compared with the prior art, the present invention has the following advantages and gain effects:

[0031] The present invention uses industrially modified cellulose derivatives, starch / starch derivatives, nanocellulose and other biomass materials as raw materials, and through blending, cross-linking and other mild reactions, through large-scale commercial production of "roll-to-roll" coating mode molding, to prepare high-strength, high-modulus, high-stability, high-transparency, degradable and recyclable biomass films. Compared with existing biomass film materials, the raw materials of the biomass film materials prepared by the present invention are more environmentally friendly, no highly toxic chemical reagents are involved in the preparation process, and the reaction conditions are mild. In addition, the problems of low film strength, poor water washing resistance of cellulose derivatives and large fragility and easy water absorption when starch is used in large doses in film materials are well solved. The "roll-to-roll" scraping molding method used is more efficient than traditional hot pressing molding and casting molding, and is more suitable for large-scale commercial production. Traditional papermaking coating equipment can be used to achieve rapid and large-scale preparation. Therefore, the biomass film prepared by the present invention has the advantages of high strength, high modulus, high transparency, high stability, simple preparation process, efficient gradual molding process, low cost and easy to achieve large-scale commercial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the tensile stress / strain curve of the biomass film of the present invention.

[0033] Figure 2 It is the light transmittance curve of the biomass film of the present invention.

[0034] Figure 3 This is a physical demonstration diagram of the biomass film of the present invention. DETAILED DESCRIPTION

[0035] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0036] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0037] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0038] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0039] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0040] Example 1

[0041] Biomass film, basis weight 60g / m 2 , ingredients: 50 parts of carboxymethyl cellulose, 50 parts of starch, 10 parts of polyamide epichlorohydrin, 10 parts of glutaraldehyde, 8 parts of glycerol, and 1 part of nanocellulose.

[0042] The preparation method is as follows:

[0043] After the cellulose derivative is dispersed in water, a 5 wt % polyamide epichlorohydrin solution is added and stirred, and the mixture is reacted at 35° C. for 1 hour; the gelatinized starch solution and carboxymethyl cellulose solution are blended, and glutaraldehyde is added and stirred for reaction at 60° C. for 1 hour; after the nanocellulose is added, the above biomass materials are blended evenly, and glycerol is added for plasticization at a temperature of 60° C. for 1 hour to obtain a biomass coating; the coating is applied on a PET substrate film, dried at 65° C., and then peeled off to obtain a biomass film.

[0044] The degree of substitution of the carboxymethyl cellulose in the above embodiment is 0.9, and the starch is corn starch;

[0045] Example 2

[0046] Biomass film, basis weight 60g / m 2 , ingredients: 40 parts of hydroxypropyl cellulose, 60 parts of starch, 5 parts of polyacrylamide, 15 parts of epichlorohydrin, 25 parts of sorbitol, and 3 parts of nanocellulose.

[0047] The preparation method is as follows:

[0048] After dispersing hydroxypropyl cellulose in water, add 1wt% polyethyleneimine solution and stir, and react for 1.5 hours at 25°C; blend the gelatinized starch solution with the cellulose derivative solution, add epichlorohydrin and stir for 0.5 hours at 90°C; after adding nanocellulose, blend the two biomass materials evenly and add sorbitol for plasticization at a temperature of 1.2 hours and 50°C to obtain a biomass coating; apply the coating on a HDPE substrate film, dry at 55°C and peel off to obtain a biomass film.

[0049] In the above embodiment, the degree of substitution of hydroxypropyl cellulose is 1.1; the starch is oxidized starch with an oxidation degree of 65%; the molecular weight of cationic polyacrylamide is 1200w;

[0050] Example 3

[0051] Biomass film, basis weight 60g / m 2 , ingredients: 30 parts of carboxymethyl cellulose, 5 parts of hydroxyethyl cellulose, 5 parts of hydroxypropyl cellulose, 60 parts of starch, 10 parts of polyethyleneimine, 10 parts of glyceraldehyde, 10 parts of N,N-dimethylformamide, and 5 parts of nanocellulose.

[0052] The preparation method is as follows:

[0053] After dispersing the cellulose derivative in water, add polyethyleneimine solution and stir, and react at 60°C for 0.8h; blend the gelatinized starch solution and cellulose derivative solution, add glyceraldehyde and stir at 90°C for 0.5h; add nanocellulose and evenly blend the two biomass materials, and after further reaction, add N,N-dimethylformamide for plasticization at 90°C for 0.5h to obtain a biomass coating; apply the coating on a PET substrate film, dry at 90°C and peel off to obtain a biomass film.

[0054] In the above embodiment, the degree of substitution of carboxymethyl cellulose is 1.4, the degree of substitution of hydroxyethyl cellulose is 1.2; the starch is pea starch; the molecular weight of polyethyleneimine is 70000;

[0055] Example 4

[0056] Biomass film, basis weight 60g / m 2 , Ingredients: 55 parts of carboxymethyl cellulose, 15 parts of hydroxypropyl cellulose, 5 parts of hydroxyethyl cellulose, 25 parts of starch, 10 parts of polyethyleneimine, 20 parts of borax, 8 parts of ethylene glycol, and 2 parts of nanocellulose.

[0057] The preparation method is as follows:

[0058] After the cellulose derivative is dried, the polyethylenimine solution is added and stirred, and the reaction is carried out at 90°C for 0.5h; the gelatinized starch solution is blended with the cellulose derivative solution, and after adding borax, the reaction is stirred at 75°C for 0.7h; after adding nanocellulose, the above two biomass materials are blended evenly, and after further reaction, ethylene glycol is added for plasticization, the plasticization temperature is 0.5h, and the plasticization temperature is 60°C to obtain a biomass coating; the coating is coated on a PVC substrate film, dried at 105°C and then peeled off to obtain a biomass film.

[0059] In the above embodiment, the degree of substitution of carboxymethyl cellulose is 1.0, the degree of substitution of hydroxypropyl cellulose is 1.9, and the degree of substitution of hydroxyethyl cellulose is 2.0; the starch is rice starch; and the degree of substitution of polyethyleneimine is 50000;

[0060] Example 5

[0061] Biomass film, basis weight 35g / m 2 , ingredients: 60 parts of hydroxyethyl cellulose, 40 parts of starch, 10 parts of polyacrylamide, 14 parts of citric acid, 5 parts of thiourea, and 4 parts of nanocellulose.

[0062] The preparation method is as follows:

[0063] After the cellulose derivative is dried, the polyacrylamide solution is added and stirred, and the reaction is carried out at 50°C for 1.3 hours; the gelatinized starch solution is blended with the cellulose derivative solution, and citric acid is added and stirred for reaction at 70°C for 0.9 hours; after adding nanocellulose, the above two biomass materials are blended evenly, and after further reaction, thiourea is added for plasticization, and the plasticization temperature is 0.8 hours and the plasticization temperature is 80°C to obtain a biomass coating; the coating is coated on a PS substrate film, dried at 45°C and then peeled off to obtain a biomass film.

[0064] The degree of substitution of hydroxyethyl cellulose in the above embodiment is 1.8, and the starch is pregelatinized starch;

[0065] Comparative Example 1

[0066] Biomass film, basis weight 60g / m 2 , ingredients: 1) 100 parts of carboxymethyl cellulose; 2) 100 parts of hydroxyethyl cellulose; 3) 100 parts of hydroxypropyl cellulose;

[0067] The preparation method is as follows:

[0068] After the cellulose derivative is dispersed in water, the coating is coated on a PET substrate film, dried at 65°C and then peeled off to obtain a biomass film.

[0069] The degree of substitution of carboxymethyl cellulose in the above comparative example is 1.4;

[0070] Comparative Example 2

[0071] Biomass film, basis weight 60g / m 2 , ingredients: 100 parts of starch.

[0072] The preparation method is as follows:

[0073] After the starch solution is gelatinized, it is coated on the PET substrate film, dried at 65°C and then peeled off to obtain a starch film.

[0074] The starch described in the above comparative example is corn starch;

[0075] Comparative Example 3

[0076] Biomass film, basis weight 60g / m 2 , ingredients: 70 parts of carboxymethyl cellulose, 30 parts of starch, and 2 parts of nanocellulose.

[0077] The preparation method is as follows:

[0078] After dispersing carboxymethyl cellulose in water, add the gelatinized starch solution and heat with stirring at 60°C for 1h; after adding nanocellulose, blend the two biomass materials evenly to obtain a biomass coating; the slurry coating is coated on a PET substrate film, dried at 65°C and peeled off to obtain a biomass film.

[0079] The degree of substitution of the carboxymethyl cellulose in the above comparative example is 1.4, and the starch is corn starch.

[0080] Comparative Example 4

[0081] Biomass film, basis weight 60g / m 2 , ingredients: 70 parts of carboxymethyl cellulose, 30 parts of starch, 10 parts of polyamide epichlorohydrin, 5 parts of glycerol, and 2 parts of nanocellulose.

[0082] The preparation method is as follows:

[0083] After dispersing carboxymethyl cellulose in water, add PAE solution and stir, and react at 35°C for 1 hour; add gelatinized starch solution and stir and heat at 60°C for 1 hour; after adding nanocellulose, blend the above two biomass materials evenly, add glycerol for further reaction and plasticize at a temperature of 0.5h and 60°C to obtain biomass coating; apply the coating on a PET substrate film, dry at 65°C and peel off to obtain a biomass film.

[0084] In the above comparative example, the degree of substitution of carboxymethyl cellulose is 1.4, and the starch is corn starch;

[0085] Comparative Example 5

[0086] Biomass film, basis weight 60g / m2 , ingredients: 70 parts of carboxymethyl cellulose, 30 parts of starch, 20 parts of glutaraldehyde, 5 parts of glycerol, and 2 parts of nanocellulose.

[0087] After the water-dispersed carboxymethyl cellulose is blended with the gelatinized starch solution, glutaraldehyde is added, and the reaction is stirred at 60°C for 1 hour; after adding nanocellulose, the above two biomass materials are blended evenly, and after further reaction, glycerol is added for plasticization, the plasticization temperature is 0.5h, and the plasticization temperature is 60°C to obtain a biomass coating; the coating is coated on a PET substrate film, dried at 65°C and then peeled off to obtain a biomass film.

[0088] The degree of substitution of the carboxymethyl cellulose in the above comparative example is 1.4, and the starch is corn starch.

[0089] Verification Example 1

[0090] The samples of Examples 1-5 and Comparative Examples 1-4 were respectively taken for performance tests, and the test results are shown in Table 1 below.

[0091] Table 1 Test parameters of samples

[0092]

[0093] Cellulose derivatives (Comparative Example 1) and starch (Comparative Example 2) are the more common biomass film substrates in recent years, but the film-forming strength of carboxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose materials is too low, and the film-forming brittleness of starch materials is too large. In addition, since both materials themselves contain a large number of hydrophilic functional groups such as hydroxyl groups, they are easily broken down by water after film formation. The above defects after film formation make it difficult to meet the performance requirements of biomass films.

[0094] As shown in Comparative Example 3, after blending cellulose derivatives with starch, the hydroxyl groups in the two and the carboxyl groups in the cellulose derivatives can undergo an esterification reaction under heating conditions to form ester bonds, and the adjacent hydroxyl groups between the molecules form a hydrogen bond structure, which increases the tensile stress of the film without affecting the transparency of the film. However, due to the low bonding density of the ester bond, the hydrogen bond structure is unstable and easily fails when exposed to water. After the film is exposed to water, the free hydroxyl groups in the cellulose derivatives and starch are rapidly hydrated, and the water molecules quickly enter the interior of the film, thereby destroying the hydrogen bond structure, which manifests itself as the dissolution of the film and the failure of strength on a macro scale. This is also well verified in the determination of the Cobb value (60s). The film dissolves during the test and it is difficult to determine the Cobb value. This also means that biomass films made solely of cellulose derivatives and starch still do not meet the water resistance requirements.

[0095] Cationic amine polymers are a commonly used wet strength grade in the papermaking field and have been widely studied and applied in improving the wet strength and dry strength of paper sheets. In Comparative Example 4, polyamide epichlorohydrin was added alone to improve the strength and water resistance of the biomass film. Judging from the test results, the tensile stress of the film has been further improved. The working principle of cationic amine polymers with cellulose derivatives and starch is as follows: 1) The cationic groups of the cationic amine polymers themselves make them positively charged. After being added to the system, the positive and negative charges on the non-ionic surfaces of cellulose derivatives and starch / starch derivatives combine to form ionic bonds, and can react with hydroxyl groups to form hydrogen bonds, so that the cellulose derivatives and starch form a co-crosslinked network, thereby improving the stability of the system; 2) Cationic amine polymers contain amino groups and other groups, and cellulose derivatives and starch / derivatives contain There are functional groups such as hydroxyl, aldehyde, and carboxyl groups. The active groups react with each other, so that the surface properties of the system after film formation are improved, the swelling ability of the film is reduced, and the water resistance of the film is improved; 3) During the heating process of film forming and drying, the amino groups of the cationic amine polymer react with the epoxy structure or carboxylic acid, aldehyde and other groups of the cross-linking agent to form new bonds, that is, the co-crosslinking between the cationic amine polymer molecules and the cross-linking agent forms a water-insoluble network structure, which wraps and fills in the system to prevent water molecules from entering the interior of the film, which is reflected in the further improvement of the strength and water resistance of the film. However, the test results of the Cobb value (60s) show that the water resistance of biomass films still has room for improvement. This is because cationic amine polymers, as macromolecular cross-linking agents, have limited cross-linking effects on molecular-level polyhydroxy materials such as starch and cellulose derivatives. The co-crosslinking density in the system is still difficult to meet the water resistance requirements of the system.

[0096] Fatty aldehydes, boric acid, borax, citric acid, epichlorohydrin and other cross-linking agents are common non-toxic small molecule cross-linking agents in the chemical industry and are widely used in starch sizing and wet strength improvement in the papermaking field. In Comparative Example 2, a cross-linking agent (glyoxal) is used alone as a cross-linking wet strength agent for the system. During the reaction, the cross-linking agent reacts with the hydroxyl groups on the molecular chains of cellulose derivatives and oxidized starch to produce hemiacetal, ester bonds, ether bonds, and hydrogen bond structures, realizing cross-linking reactions between cellulose derivative molecules, oxidized starch molecules, and between cellulose derivatives and oxidized starch. However, due to the short molecular chain of the cross-linking agent, a strong locking effect is formed on the long molecular chains of cellulose derivatives and oxidized starch after cross-linking, which seriously reduces the degree of freedom of the molecular chain, so that the strength of the film is significantly improved. However, due to the reduced degree of freedom of the molecular chain, the tensile strain of the film decreases seriously, and when folded in half or bent at a large angle, the stress concentration at the folding part is very likely to cause film bursting, which seriously limits the further application of the film.

[0097] Different from the above comparative examples, in Examples 1-5, the cellulose derivative is first blended with the cationic amine polymer solution, and the positively charged cationic amine polymer molecules are coated on the negatively charged cellulose derivative molecules by electrostatic adsorption to form a stable network structure, and then blended with the gelatinized oxidized starch. After adding a crosslinking agent for reaction, crosslinking between the oxidized starch and the cellulose derivative particles coated with the cationic amine polymer and between the oxidized starch molecules is further achieved. In this process, the flexible macromolecular cationic amine polymer molecules can react with the small molecular crosslinking agent to form a bond, which reduces the influence of the small molecular crosslinking agent on the molecular chain freedom, improves the tensile strain of the film, increases the film toughness, and is more resistant to folding. In addition, the multiple crosslinking system formed by the cationic amine polymer and the crosslinking agent increases the crosslinking density, increases the water resistance effect, and improves the tensile properties of the film.

[0098] In general, pure cellulose derivative films have low strength and are not water-resistant, while pure starch films are brittle and easily absorb water. After the two are blended into a film, the film strength is improved and the brittleness is reduced, but due to the rich hydroxyl groups in the material itself, there is still a problem of extremely easy water absorption. A single cross-linking system using cationic amine polymers or cross-linking agents alone cannot meet the film's water resistance requirements. This patent uses cellulose derivatives and starch as raw materials, and uses cationic amine polymers and cross-linking agents to prepare a biomass film with a multiple cross-linking system. While achieving high strength, high modulus, and high transparency, the film's water resistance is enhanced, meeting the application requirements of biomass films and providing new ideas for the preparation of biomass films.

[0099] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A biomass film, characterized in that: The biomass film comprises the following components in mass fractions: 20%-70% of cellulose derivatives, 30-70% of starch, 0-20wt% of cationic amine polymers, 0-20wt% of crosslinking agents, 0-5wt% of nanocellulose, and 0-10wt% of plasticizers.

2. The biomass film according to claim 1, characterized in that: The cellulose derivative is selected from one or more of carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose; the degree of substitution of the cellulose derivative is 0.5-2.5; the starch is selected from one or more of natural starch and starch derivatives; the natural starch is selected from one or more of bean starch, corn starch, potato starch, and cassava starch; the starch derivative is selected from one or more of pregelatinized starch, oxidized starch, and esterified starch.

3. The biomass film according to claim 1, characterized in that: The mass ratio of the cationic amine polymer to the cellulose derivative is 1:5 to 1:10; the cationic amine polymer is selected from one or more of polyamide epichlorohydrin, cationic polyacrylamide, and cationic polyethyleneimine.

4. The biomass film according to claim 1, characterized in that: The cross-linking agent is selected from one or more of fatty aldehydes, boric acid, borax, citric acid, and epichlorohydrin; The fatty aldehyde is selected from one or more of formaldehyde, glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, adipaldehyde, suberaldehyde, glyceraldehyde, and trichloroacetaldehyde; the mass ratio of the starch to the cross-linking agent is 10:1 to 5:

3.

5. The biomass film according to claim 1, characterized in that: The plasticizer is selected from one or more of glycerol, ethylene glycol, polyethylene glycol, sorbitol, mannitol, urea, thiourea, formamide, N,N-dimethylformamide, diethyl phthalate, triacetin, and triethyl citrate.

6. The method for preparing the biomass film according to any one of claims 1 to 5, characterized in that: The following steps are involved: After the cellulose derivative is dispersed in water, a cationic amine polymer solution is added and stirred for reaction. After the reaction is completed, it is blended with gelatinized starch, and then a cross-linking agent is added to blend for cross-linking reaction. After the reaction, nanocellulose and a plasticizer are added for plasticization to obtain a biomass plastic slurry. The coating is coated on a plastic substrate film, dried and peeled off to obtain a biomass film.

7. The preparation method according to claim 6, characterized in that: The coating method is selected from one or more of air knife coating, doctor blade coating, roller coating, slit coating and curtain coating.

8. The preparation method according to claim 6, characterized in that: The plastic substrate is selected from one or more of polyethylene terephthalate, high-density polyethylene, polyvinyl chloride, low-density polyethylene, polypropylene, polystyrene, and polyethylene.

9. The preparation method according to claim 6, characterized in that: The temperature of the cross-linking reaction is 60-100°C, and the time of the cross-linking reaction is 0.5-2h; The plasticizing temperature is 25-90°C and the plasticizing time is 0.5-12h; The drying temperature is 25-105° C. and the drying time is 0.3-3 h.

10. Application of the biomass film prepared according to the preparation method according to any one of claims 6 to 9 in packaging, electronic product circuit boards, flexible electronic display substrates, disposable tableware, and agriculture.

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