CN114539800A - A kind of preparation method and application of high toughness and high transparency heat-sealable cellulose film - Google Patents

Abstract

The invention belongs to the field of preparation of heat-sealable packaging materials, and particularly relates to a preparation method of a high-toughness high-transparency heat-sealable cellulose film, which comprises the following steps: (1) dissolving cellulose: preparing a chloride solution, adding plant fibers and dissolving the plant fibers after the chloride solution is in a transparent solution state at a proper temperature; (2) blending: adding a plasticizer after the plant fibers are dissolved to fully blend the plant fibers; (3) coating a film; (4) solvent replacement: immersing the film into a coagulating bath for organic solvent replacement after film coating so as to keep the residual salt amount in a fixed concentration range; (5) and (5) air drying. The cellulose membrane prepared by the method can be completely degraded, has good biocompatibility, presents the characteristics of high transparency and high toughness, can be thermally bonded at relatively low temperature, and expands the application scenes of the cellulose membrane in different industries such as food, cosmetics and the like.

Description

A kind of preparation method and application of high toughness and high transparency heat-sealable cellulose film

technical field

The invention belongs to the field of preparation of heat-sealable packaging materials, in particular to a preparation method of a high-toughness and high-transparency heat-sealable cellulose film.

Background technique

In the context of the accelerated national plastic ban and carbon reduction actions, packaging materials such as plastics have been gradually banned due to the depletion of petroleum resources, serious environmental pollution and non-degradable reasons. Countries around the world are actively looking for an alternative to plastic. Degradable material. As a class of natural polymer materials with a wide range of sources, good biocompatibility and degradability, cellulose plays an important role in many green and renewable energy sources. The annual global natural output can reach 150 billion tons. The tightly bound hydrogen bonds between the molecular chains lead to the fatal defects of cellulose being insoluble and having no melting point. These two "fatal" defects directly limit the acceleration of the industrialization of cellulose products, and more severely limit the use of cellulose films as packaging. Substitute materials for heat-sealable plastics, therefore, heat-seal modification of cellulose films has always been a hot work in the packaging industry.

At present, the preparation of a heat-sealable cellulosic film is usually carried out by a coating method. Xue Mengqing of Donghua University and others immersed the Lyocell cellulose membrane prepared from waste cotton in solutions such as silane coupling agent and dichloromethane to modify it. Although they obtained a heat-sealable cellulose membrane, the process of immersion It is equivalent to adding a layer of coating on the surface of the cellulose film. The role of the coating makes the Lyocell cellulose film heat-sealable. The cellulose film itself does not have heat-sealability. Therefore, the disadvantage of preparing the heat-sealable cellulose film by the coating method is that the process flow is more complicated than direct blending, and in order to make the surface coating heat-sealable, polyester, etc. are often used for environmental protection. Hazardous Materials. Residues of polyester and other materials on the surface of packaging materials will limit its application in industries such as food, cosmetics, and daily necessities. Therefore, the direct blending of the cellulose film with environmentally friendly substances can be truly valuable to realize the heat-sealable modification of the cellulose film.

The patent document with the application number of 202110402446.7 discloses a production method of heat sealable food packaging paper, which adopts the method of film transfer sizing to apply a surface sizing agent with waterproof, oil-proof and heat-sealing properties to the paper The surface production of heat-sealable food packaging paper, although the product bag or box-making method is realized by heat-sealing machine, but the steps are cumbersome, not completely degradable, and still need to be further improved.

SUMMARY OF THE INVENTION

Based on the above-mentioned shortcomings and deficiencies in the prior art, one of the objectives of the present invention is to at least solve one or more of the above-mentioned problems existing in the prior art. In other words, one of the objectives of the present invention is to provide one of the aforementioned requirements A preparation method of a high toughness and high transparent heat-sealable cellulose film.

In order to achieve the above-mentioned purpose of the invention, the present invention adopts the following technical solutions:

A preparation method of a high-toughness and high-transparency heat-sealable cellulose film, comprising the following steps:

(1) Put the plant cellulose in the salt solution and stir to dissolve;

(2) Prepare a plasticizer, and blend it with a cellulose solution to obtain a mixed solution;

(3) Pour the mixed solution into the film maker, and scrape and coat the film on the glass plate;

(4) Put it in a coagulation bath after scraping, and replace the organic solvent to control the residual salt mass ratio of the cellulose film;

(5) Air-drying the cellulose film replaced in step (4) to form a film.

As a preferred solution, the residual salt mass ratio is 20-30%, and the residual salt mass ratio refers to the ratio of the final salt mass to the original added salt mass.

As a preferred solution, the plant fibers include one or more of cotton, flax, wood pulp, and bagasse.

As a preferred solution, the salt solution is a chloride salt solution.

As a preferred solution, the chloride salt solution is a chloride salt solution capable of dissolving cellulose, including a zinc chloride solution or a ferric chloride solution.

As a preferred solution, the mass of cellulose in the step (1) is 1-2.5% relative to the mass ratio of the solvent, preferably the mass of cellulose is 0.4-1.0g, the mass fraction of salt solution is 70%-80%, and the temperature is 70-80%. 90°C.

As a preferred solution, the plasticizer in the step (2) includes an alcohol with a water-retaining effect, and also an alcohol with a water-absorbing effect.

As a preferred solution, the alcohol with water retention effect includes glycerol, the alcohol with water absorption effect includes any one of sorbitol, pentaerythritol, and xylitol, and the glycerol has a quality of any one of sorbitol, pentaerythritol, and xylitol. The ratio is 1:(0.5-1), and the mass ratio of the sum of the two relative to the cellulose solution is 10-20%.

As a preferred solution, the thickness of the film maker in the step (3) is 250-750 μm, preferably 250 μm, 500 μm, and 750 μm; the coagulation bath in the step (4) adopts any one of ethanol, methanol, and acetone. One, the volume is 500-900mL, and the time is 35-40 min;

As a preferred solution, the air-drying film-forming environment temperature in the step (5) is 15-20°C, and the humidity is 40-60%.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The high-toughness and high-transparency heat-sealable cellulose film prepared by the present invention is completely degradable.

(2) The plasticizer used is bio-friendly, non-toxic and harmless.

(3) The process flow of cellulose film preparation is simpler than the coating method. The prepared heat-sealable cellulose film has high toughness and high transparency, and can be heat-sealed at about 100°C, which realizes the direct sealing of cellulose film. The heat-sealing property is conducive to expanding the application market of cellulose film in the fields of food, cosmetics and packaging.

Description of drawings

Fig. 1 is the scanning electron microscope picture of the cross-section of two cellulose films bonding place of the embodiment of the present invention 1;

2 is a physical comparison diagram of the heat-sealable cellulose film of Example 1 of the present invention and the non-heat-sealable cellulose film of Comparative Example 1 after hot pressing.

Detailed ways

In order to more clearly illustrate the embodiments of the present invention, some embodiments of the present invention are described in the following description. Obviously, for those of ordinary skill in the art, other implementations can also be obtained according to these embodiments without creative effort.

In the heat-sealable cellulose film prepared by the invention, the inventor accidentally discovered the defect that the solution after dissolving cellulose could not be completely removed after film formation, and skillfully converted the salt solution that could not be removed into a solution under the action of heat. Heat seal inducer. When a chloride salt solution and a plasticizer are used to dissolve cellulose to form a film, such as a zinc chloride solution, although a certain amount of zinc ions will remain in the cellulose film, it is inseparable from a certain concentration of zinc ions. The presence of water, and the plasticizer has the effect of water retention and water absorption, it is the presence of the plasticizer that makes the residual zinc ion concentration reach a certain value. Therefore, under the synergistic effect of the plasticizer and the residual salt solution, when the residual zinc ion concentration reaches a certain value, even the cellulose film that has formed a film can return to the sol state again under the action of heat. glued together.

The specific steps of a method for preparing a high-toughness and high-transparency heat-sealable cellulose film are as follows:

(1) Dissolve a certain quality of plant fiber in a certain concentration of chloride salt solution, and stir at a constant speed at a certain temperature to dissolve until it is in a transparent light yellow viscous state;

(2) Prepare a certain proportion of mixed plasticizer, stir and mix at a certain temperature to a flowing state, and blend with the cellulose solution in an appropriate proportion to obtain a mixed solution;

(3) Pour the mixed solution into the film maker for film coating, select the appropriate thickness for the film maker, and scrape and coat the film on the glass plate;

(4) Immediately after scraping, it is placed in a certain volume of coagulation bath, and the organic solvent is replaced for an appropriate time;

(5) Replace the organic solvent in step (4), and continue to replace the organic solvent in a certain volume for an appropriate time, so that the residual salt content of the cellulose membrane is within a certain range;

(6) The cellulose membranes subjected to organic solvent replacement in steps (4) and (5) are placed in a suitable environment for air-drying to form a membrane.

In the present invention, the above steps (4) and (5) can also be carried out for an appropriate time to replace the organic solvent, so that the residual salt content of the cellulose film is within a certain range;

Effect of salt solution: Cellulose cannot be dissolved in water or in organic solvents. A high concentration of chloride salt solution can break a large number of hydrogen bonds within and between molecules of cellulose and dissolve cellulose.

Organic solvents, such as ethanol, methanol, and acetone, are used in the coagulation bath to replace zinc chloride from the membrane, and these organic solvents are volatile. After air-drying, only fibers and some residual residues remain in the cellulose membrane. Salt.

Plasticizers include alcohols with water-retaining effect, such as glycerol, and alcohols with water-absorbing effect, such as sorbitol, pentaerythritol, and xylitol.

Example 1:

The preparation method of the high-toughness and high-transparency heat-sealable cellulose film of the present embodiment includes:

(1) Dissolve 0.8 g of cotton fiber in a solution of 70% zinc chloride by mass, and stir at a constant speed at 90 °C to dissolve until it is in a transparent pale yellow viscous state;

(2) The mass ratio of glycerol and sorbitol is 2:1, the mass ratio of the total amount of glycerol and sorbitol to the cellulose film solution system is 15%, and the mixture is stirred and mixed at 90 °C until it is in a flowing state, and mixed with cellulose. The solution is blended to obtain a mixed solution;

(3) Pour the mixed solution into the film maker for film coating. The film maker is selected with a thickness of 750 µm, and the film is formed by scraping on the glass plate;

(4) Immediately after scraping, put it into 500 mL of ethanol for 30 min of organic solvent replacement;

(5) Replace the organic solvent in step (4), and continue to replace the organic solvent in 250 mL of ethanol for 8 min, so that the residual salt mass ratio of the cellulose membrane is 24%;

(6) The cellulose film after the organic solvent replacement in steps (4) and (5) is placed in an environment with a temperature of 15 °C and a humidity of 40% to be air-dried to form a film.

Example 2:

(1) Dissolve 0.8 g of flax fiber in a zinc chloride solution with a mass fraction of 70%, and stir at a constant speed at 70 °C to dissolve until it is in a transparent pale yellow viscous state;

(2) The mass ratio of glycerol and sorbitol is 2:1, and the mass ratio of the total amount of glycerol and sorbitol to the cellulose film solution system is 10%. Stir and mix at 80 °C to a flowing state, and mix with cellulose. The solution is blended to obtain a mixed solution;

(3) Pour the mixed solution into the film maker for film coating. The film maker is selected with a thickness of 250 µm, and the film is formed by scraping on the glass plate;

(4) Immediately after scraping, put it into 500 mL of organic ethanol for 30 min of organic solvent replacement;

(5) Replace the organic solvent in step (4), and continue to replace the organic solvent in 250 mL of ethanol for 5 min, so that the residual salt mass ratio of the cellulose membrane is 30%;

(6) The cellulose film after the organic solvent replacement in steps (4) and (5) is placed in an environment with a temperature of 15 °C and a humidity of 40% to be air-dried to form a film.

Example 3:

(1) Dissolve 0.8 g of wood pulp fibers in a 90% ferric chloride solution, and stir at a constant speed at 90 °C to dissolve until a transparent pale yellow viscous state;

(2) The mass ratio of glycerol and sorbitol is 1:1, and the mass ratio of the total amount of glycerol and sorbitol to the cellulose film solution system is 15%. Stir and mix at 90 °C to a flowing state, and mix with cellulose. The solution is blended to obtain a mixed solution;

(3) Pour the mixed solution into a film maker for film coating. The film maker is selected with a thickness of 500 µm, and the film is formed by scraping and coating on a glass plate;

(4) Immediately after scraping, it was placed in 800 mL of ethanol, and the organic solvent was replaced for 40 min, so that the residual salt mass ratio of the cellulose film was 28%;

(5) The cellulose film after the organic solvent replacement in step (4) is placed in an environment with a temperature of 20 °C and a humidity of 50% to be air-dried to form a film.

Example 4:

(1) Dissolve 0.4 g of bagasse fiber in a ferric chloride solution with a mass fraction of 70%, and stir at a constant speed at 70 °C to dissolve until it is in a transparent pale yellow viscous state;

(2) The mass ratio of glycerol and sorbitol is 2:1, and the mass ratio of the total amount of glycerol and sorbitol to the cellulose film solution system is 20%. Stir and mix at 70 °C to a flowing state, and mix with cellulose. The solution is blended to obtain a mixed solution;

(3) Pour the mixed solution into the film maker for film coating. The film maker is selected with a thickness of 200 µm, and the film is formed by scraping on the glass plate;

(4) Immediately after scraping, put it into 500 mL of ethanol for 30 min of organic solvent replacement;

(5) Replace the organic solvent in step (4), and continue to replace the organic solvent in 300 mL of ethanol for 10 min, so that the residual salt mass ratio of the cellulose membrane is 20%;

(6) The cellulose film after the organic solvent replacement in steps (4) and (5) is placed in an environment with a temperature of 20 °C and a humidity of 40% to be air-dried to form a film.

Example 5:

(1) Dissolve 0.6 g of cotton fiber in a 90% zinc chloride solution, and stir at a constant speed at 90 °C to dissolve until it is in a transparent, pale yellow and viscous state;

(2) The mass ratio of glycerol and sorbitol is 2:1, the mass ratio of the total amount of glycerol and sorbitol to the cellulose film solution system is 15%, and the mixture is stirred and mixed at 90 °C until it is in a flowing state, and mixed with cellulose. The solution is blended to obtain a mixed solution;

(3) Pour the mixed solution into the film maker for film coating. The film maker is selected with a thickness of 750 µm, and the film is formed by scraping on the glass plate;

(4) Immediately after scraping, put it into 500 mL of ethanol for 30 min of organic solvent replacement;

(5) Replace the organic solvent in step (4), and continue to replace the organic solvent in 400 mL of ethanol for 5 min, so that the residual salt mass ratio of the cellulose membrane is 20%;

(6) The cellulose film after the organic solvent replacement in steps (4) and (5) is placed in an environment with a temperature of 15 °C and a humidity of 60% to be air-dried to form a film.

Comparative Example 1:

The difference between the cellulose film of Comparative Example 1 and Example 1 is:

In step (5), replace the organic solvent in step (4), and continue to replace the organic solvent in 1000 mL of ethanol for 30 min, that is, remove the residual salt in the membrane as much as possible, so that the residual salt mass ratio of the cellulose membrane is 5 %;

Other steps and process parameters are the same as in Example 1.

Comparative Example 2:

The difference between the cellulose film of Comparative Example 2 and Example 1 is:

In step (5), replace the organic solvent in step (4), and continue to replace the organic solvent in 800 mL of ethanol for 30 minutes, that is, remove the residual salt in the membrane as much as possible, so that the residual salt mass ratio of the cellulose membrane is 10 %;

Other steps and process parameters are the same as in Example 1.

Comparative Example 3:

The difference between the cellulose film of Comparative Example 3 and Example 1 is:

In step (5), replace the organic solvent in step (4), and continue to replace the organic solvent in 500 mL of ethanol for 30 minutes, that is, remove the residual salt in the membrane as much as possible, so that the residual salt mass ratio of the cellulose membrane is 15 %;

Other steps and process parameters are the same as in Example 1.

Comparative Example 4:

The difference between the cellulose film of Comparative Example 4 and Example 1 is:

In step (5), replace the organic solvent in step (4), and continue to replace the organic solvent in 100 mL of ethanol for 5 min, so that the residual salt mass ratio of the cellulose membrane is 40%;

Other steps and process parameters are the same as in Example 1.

Comparative Example 5:

The difference between the cellulose film of Comparative Example 4 and Example 1 is:

In step (5), the organic solvent in step (4) is not replaced, so that the residual salt mass ratio of the cellulose membrane is 45%;

Other steps and process parameters are the same as in Example 1.

The conditions of the cellulose films prepared in Examples 1 to 5 and Comparative Examples 1 to 5 are summarized in Table 1 below.

Table 1

In the above embodiment, the residual salt only refers to the chloride salt, and the residual amount is determined according to the mass loss in the thermogravimetric analysis test (TGA). value.

The residual salt mass ratio refers to the ratio of the final salt mass to the original added salt mass.

The cross section of the high-toughness, high-transparency heat-sealable cellulose film of the present embodiment after bonding is observed by field emission scanning electron microscope (FE-SEM), and is tested by universal testing machine (ASTM), ultraviolet-visible spectrophotometry (UV- vis) and differential scanning calorimetry (DSC) to characterize the mechanical properties, transparency and melting point of the cellulose films as shown in Table 2.

Table 2

In Table 1, when the solvent replacement is carried out in Examples 1-5, the volume of the second solvent replacement is within 250mL-400mL, and the time is within 5-10min; accordingly, if only one solvent replacement is used, the volume Within 500-800mL, the time is within 35-40min, so that the residual salt mass ratio of the cellulose film is within the range of 20-30%, creating conditions for the cellulose film to return to the viscous state of the sol under heating. bonding. As shown in Figure 1, the layers in the cross-sectional SEM image are dense, and no obvious cracks are found, indicating the excellent adhesion between the films.

As can be seen from Comparative Examples 1-5, the heat-sealing properties of the heat-sealable cellulose film of Comparative Example 1, as shown in Figure 2, under the action of hot-pressing, the cellulose film at the hot-pressing place was broken, and no adhesion was observed. Traces; by controlling the amount of solvent, when the residual salt mass ratio is below 20% (such as Comparative Examples 1, 2, 3), due to the low concentration of residual zinc ions, it cannot be used as a solvent at a certain temperature, and it is not sticky. However, when the residual salt mass ratio is above 30% (such as Comparative Examples 4 and 5), the film cannot be formed due to excessive residual zinc ions and too much moisture.

As can be seen from Table 2, the test results of the universal testing machine in Examples 1-5 show that the tensile elongation of the cellulose film can reach 50%;

The UV-Vis spectrophotometry test results show that the transparency of the cellulose film can reach 90%; the differential scanning calorimeter test results show that the minimum melting point of cellulose can be reduced to 90°C. As shown in FIG. 2 , the heat-sealable cellulose film of this embodiment can be adhered and subjected to a certain external force after being hot-pressed. On the other hand, the tensile elongation of Comparative Examples 1-5 was relatively low, and no melting point was detected. Therefore, under the action of hot pressing, the cellulose film at the hot pressing position was broken, and no adhesive trace was found.

To sum up, the residual salt-induced high-toughness and high-transparency heat-sealable cellulose film of the embodiment of the present invention not only has the ability to achieve thermal bonding at a relatively low temperature, but also exhibits a high-toughness and high-transparency state. It is completely degradable in the environment, non-toxic and harmless, which increases the substitution of cellulose film for plastics, and also expands the application scenarios of cellulose film in food, cosmetics, packaging and other fields.

Since there are many embodiments of the solution of the present invention, and the experimental data of each embodiment is huge and numerous, it is not suitable to enumerate and describe one by one here, but the content to be verified in each embodiment and the final conclusion obtained are close. Therefore, the verification contents of each embodiment will not be described one by one here, and only embodiments 1-5 are used as representatives to illustrate the advantages of the application of the present invention.

The above is only a detailed description of the preferred embodiments and principles of the present invention. For those of ordinary skill in the art, according to the technical concept provided by the present invention, there will be changes in the specific implementation, and these changes will also It should be regarded as the protection scope of the present invention.

Claims (10)

1. A preparation method of a high-toughness high-transparency heat-sealable cellulose film is characterized by comprising the following steps:

(1) putting plant cellulose into a salt solution, and stirring for dissolving;

(2) preparing a plasticizer, and blending the plasticizer and a cellulose solution to obtain a mixed solution;

(3) pouring the mixed solution into a film making device, and blade-coating a glass plate to make a film;

(4) scraping and coating, then placing into a coagulating bath, carrying out organic solvent replacement, and controlling the residual salt mass ratio of the cellulose membrane;

(5) and (4) air-drying the cellulose membrane replaced in the step (4) to form a membrane.

2. The method for preparing the high-toughness high-transparency heat-sealable cellulose film according to claim 1, wherein the mass ratio of the residual salt is 20-30%, and the mass ratio of the residual salt is the ratio of the mass of the final salt to the mass of the original salt.

3. The method for preparing the high-toughness high-transparency heat-sealable cellulose film according to claim 2, wherein the plant fiber comprises one or more of cotton, flax, wood pulp and bagasse.

4. The method for preparing a high-toughness high-transparency heat-sealable cellulose film according to claim 1, wherein the salt solution is a chloride solution.

5. The method for preparing a high-toughness high-transparency heat-sealable cellulose film according to claim 4, wherein the chloride solution is a chloride solution capable of dissolving cellulose, and comprises a zinc chloride solution or a ferric chloride solution.

6. The method for preparing a high-toughness high-transparency heat-sealable cellulose film according to claim 1, wherein the cellulose in step (1) is in a mass ratio of 1-2.5% relative to the solvent, the salt solution is in a mass fraction of 70-80%, and the temperature is 70-90 ℃.

7. The method for preparing a high-toughness high-transparency heat-sealable cellulose film according to claim 1, wherein the plasticizer in step (2) comprises an alcohol having a water-retaining effect and an alcohol having a water-absorbing effect.

8. The process for producing a high tenacity highly transparent heat-sealable cellulose film according to claim 7, wherein said alcohol having a water-retaining effect comprises glycerin, said alcohol having a water-absorbing effect comprises any one of sorbitol, pentaerythritol and xylitol, the mass ratio of said glycerin to any one of sorbitol, pentaerythritol and xylitol is 1 (0.5-1), and the mass ratio of the sum of both is 10-20% with respect to the cellulose solution.

9. The method for preparing a high-toughness high-transparency heat-sealable cellulose film according to claim 1, wherein the thickness of the film-making device in the step (3) is 250-750 μm; the coagulating bath in the step (4) adopts any one of ethanol, methanol and acetone, the volume is 500-900 mL, and the time is 35-40 min.

10. The method for preparing a high-toughness high-transparency heat-sealable cellulose film according to claim 1, wherein the air-drying and film-forming environment in step (5) has a temperature of 15-20 ℃ and a humidity of 40-60%.

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