CN115449104A

CN115449104A - Preparation method of high-toughness uvioresistant wood cellulose membrane

Info

Publication number: CN115449104A
Application number: CN202211241262.8A
Authority: CN
Inventors: 刘琳; 沈荣盛; 王邓峰; 姚菊明
Original assignee: Zhejiang Sci Tech University ZSTU
Current assignee: Zhejiang Sci Tech University ZSTU
Priority date: 2022-10-11
Filing date: 2022-10-11
Publication date: 2022-12-09

Abstract

The invention discloses a preparation method of a high-strength and high-toughness uvioresistant wood cellulose membrane. The method comprises the steps of taking cellulose and lignin as raw materials, dissolving the cellulose and the lignin at a low temperature by utilizing a sodium hydroxide/urea system to obtain a lignin/cellulose solution, adding a cross-linking agent under the condition of an ice water bath after centrifugal deaeration, carrying out tape casting and film scraping, directly carrying out solidification forming in a solidification bath, and carrying out air drying at room temperature to prepare the regenerated lignin-cellulose composite membrane. The composite film prepared by the invention has good mechanical property and light transmittance, and excellent uvioresistant property; the cellulose and the lignin have wide sources and low prices, are easy to degrade and are harmless to the environment, so the material has good application prospects in the fields of energy storage, green packaging, electronic equipment and the like.

Description

Preparation method of high-strength and high-toughness uvioresistant wood cellulose membrane

Technical Field

The invention belongs to the field of natural polymers, and particularly relates to a high-toughness uvioresistant wood cellulose membrane and a preparation method thereof.

Background

In the context of global petrochemical energy shortage and increasingly stringent carbon emission policies, the high-valued utilization of biomass resources is attracting wide attention. Wherein cellulose and lignin are used as two types of biomass resources with the most abundant reserves in the nature, and the high-efficiency conversion and utilization of the cellulose and the lignin have important significance for the development of biological cycle economy. Cellulose film is one of the fastest developing and largest-demanded materials in recent years, is widely applied to the fields of packaging, agriculture, logistics, electronic components, military industry and the like, and researchers are struggling to develop environment-friendly materials prepared from lignocellulose in order to solve the problem of serious environmental pollution.

For example, patent CN110204748B reports a method for preparing a high-haze high-transmittance flexible cellulose film, which includes preparing TEMPO oxidized cellulose, adding deionized water to prepare an oxidized cellulose suspension, treating the suspension with ultrasonic waves, removing part of moisture in the suspension by rotary evaporation, and finally obtaining the high-haze high-transmittance flexible cellulose film by a solution casting method. The method has the characteristics of simple preparation process, low cost, easy operation and the like. In patent CN110240723B, a method for preparing an ultraviolet high-shielding cellulose membrane is reported, in which halloysite-cerium oxide nano hybrid and cellulose are respectively dispersed in water, and then the dispersion is dried to obtain the ultraviolet high-shielding cellulose membrane. The cellulose membrane has simple and easy preparation process and low cost of raw materials, and can be used in the fields of ultraviolet protection and the like. Patent CN112876744B discloses a method for enhancing mechanical properties of a nano cellulose membrane by using lignosulfonate, which comprises the steps of carrying out hydrothermal reaction on a mixed dispersion liquid of nano cellulose and lignosulfonate, washing and filtering a hydrothermal reaction product to obtain a sodium lignosulfonate modified nano cellulose composite membrane. According to the method, the nano cellulose membrane is modified by utilizing the lignosulfonate, so that the mechanical property of the nano cellulose membrane can be improved, and the application range of the nano cellulose membrane can be widened. Although there are a number of methods for preparing functional cellulose films, the above patents still have the following problems: (1) The prepared cellulose membrane has poor mechanical property, usually needs complex post-treatment and has great problem in practical application. (2) The prepared cellulose membrane is easy to decompose in water and has poor water stability, which greatly limits the application scene. (3) The preparation of the cellulose film with the ultraviolet resistance is mainly realized by adding an organic ultraviolet absorbent and an inorganic ultraviolet retarder. However, these functional fillers aggregate and migrate in the material, which impairs the properties of the material and also has a negative effect on human health or the environment.

Disclosure of Invention

In order to solve the problems of poor mechanical property, low water resistance, aggregation and migration of functional fillers and the like of a functional cellulose membrane, the wood is inspired from the structure of a tree, and is formed by tightly assembling cellulose, hemicellulose and lignin components in supermolecules, molecules, cells and other multi-scale dimensions, and has intramolecular and intermolecular covalent force and hydrogen bond network interaction, so that a typical hierarchical multi-level structure is presented. The cellulose linear molecules are assembled into micro-nano fibrils to endow the material with structural strength, and lignin serving as a binder component influences the spatial arrangement of cellulose. And lignin contains uv absorbing functional groups such as phenolic units, ketones and other chromophores. Besides ultraviolet absorption performance, the lignin has excellent oxidation resistance due to the free radical scavenging capacity of phenolic hydroxyl groups, and the thermal stability and oxidation resistance of the composite material can be improved.

Therefore, the invention designs a physical-chemical double-crosslinking method to prepare the lignocellulose membrane with excellent mechanical strength and ultraviolet blocking capability based on the technology of dissolving and regenerating cellulose in an alkaline urine solution. Due to the physical and chemical double-crosslinking effect, the problem of lignin migration is solved, the performance of the composite membrane is ensured, and the composite membrane has good application prospects in the fields of energy storage, green packaging, electronic equipment and the like.

The technical scheme adopted by the invention comprises the following steps:

1) Cellulose and lignin in a certain proportion are dissolved in 7wt% NaOH/12wt% urea solution, and the solution is subjected to centrifugal defoaming to obtain a light yellow lignin/cellulose solution.

2) Placing the lignin/cellulose solution prepared in the step 1) under the condition of ice-water bath, adding a certain proportion of cross-linking agent, reacting for 0.5-2 hours, pouring the solution on a glass plate, scraping the solution into a film by using a film coater, then placing the film into a coagulating bath for direct coagulation and forming, washing the film by using deionized water, and air-drying the film at room temperature to prepare the regenerated lignocellulose composite film.

The centrifugation condition of the step 1) is centrifugation for 15-30 min at 7200 r/min.

In the step 1): the mass ratio of the lignin to the cellulose is 1-5: 10; the mass ratio of the cellulose in the lignin/cellulose solution is 2-5 percent; the mass ratio of the lignin in the lignin/cellulose solution is 0.5-2%.

The lignin in the step 1) is one or more of alkali lignin, dealkalized lignin, enzyme lignin, sulfonated lignin and sulfate lignin, and the molecular weight is 1000-6000.

In the step 2), the cross-linking agent is epichlorohydrin, and the mass ratio of the cross-linking agent to the lignin/cellulose solution in the step 1) is 1-10: 100.

The coagulating bath is one of ethanol, glycol, sodium sulfate solution, sodium chloride, acetic acid, dilute sulfuric acid or dilute hydrochloric acid, the temperature of the coagulating bath is 10-60 ℃, and the coagulating time is 5-30 min.

Based on the designed functional cellulose composite membrane, the mechanical property, the light transmittance and the ultraviolet shielding property of the lignocellulose composite membrane are taken as main evaluation indexes, and the influence of the lignin type, the mass ratio of the lignin to cellulose, the coagulation bath type, the crosslinking time and other process factors on the performance of the lignocellulose composite membrane in a system is mainly considered.

The invention has the beneficial effects that:

the method is based on the fact that lignin mainly comes from byproducts of the pulping process, and a large amount of lignin cannot be reused every year, so that the environment is polluted; therefore, the lignin is recycled, so that the lignin not only has low-cost raw materials with abundant sources, but also can solve certain environmental problems, thereby realizing high-value utilization of byproducts in the paper industry. The beneficial effects are specifically that:

(1) The composite membrane prepared by the invention is realized by the physical and chemical double crosslinking of lignin and cellulose, the particle size of lignin particles on the surface of the membrane is uniform, the phenomenon of serious agglomeration is avoided, and the stable composite membrane can be effectively prepared;

(2) In the composite membrane prepared by the invention, the mechanical property and the thermal stability of the cellulose membrane are improved simultaneously by adding the lignin, and the composite membrane has high ultraviolet shielding rate, so that the multifunctional cellulose composite membrane is prepared by the invention;

(3) The preparation process of the composite film is simple and easy to implement, and complex processing equipment is not needed; the needed materials have wide sources and low price, and are easy to realize large-scale application;

(4) In the main raw materials used in the invention, lignin and cellulose are natural materials, so that high-value utilization of waste lignocellulose is realized, and the prepared membrane is biodegradable, and can effectively reduce environmental pollution.

Drawings

Fig. 1 is a digital photograph of a lignocellulose composite membrane of the present invention.

Fig. 2 is an SEM image of the lignocellulose composite membrane of the present invention.

FIG. 3 is a comparison of the lignocellulosic composite membrane of the present invention before and after 30 days of water immersion.

FIG. 4 is a water contact angle test of a lignocellulosic composite film of the present invention.

FIG. 5 shows the UV protection performance of the lignocellulose composite film of the invention.

Fig. 6 is a stress-strain curve of the lignocellulose composite membrane of the present invention.

Detailed Description

In order that those skilled in the art will better understand the invention, further details are provided below with reference to specific examples.

Example 1:

194g of a 7.0wt% aqueous solution of NaOH/12wt% urea was pre-cooled to-13 deg.C, and 6g of cellulose was weighed and dissolved in the above solution, followed by stirring to obtain a 3wt% cellulose mixed solution. The resulting solution was centrifuged and defoamed by a high-speed centrifuge at 8000 rpm for 15 minutes to obtain a transparent cellulose mixed solution. Under the condition of ice-water bath, 6g of epichlorohydrin is added for reaction for 1 hour. Setting the thickness of a BEVS1806 adjustable film coating device to be 0.6mm, casting a scraping film (in a hydrogel shape) on a glass plate, then placing the glass plate into an ethylene glycol coagulating bath at 25 ℃ for coagulating for 20 minutes, taking out the glass plate, and washing the glass plate by using distilled water. And finally, pasting the regenerated cellulose composite membrane on an acrylic plate and naturally airing to obtain the regenerated cellulose composite membrane. The breaking strength of the cellulose film in a dry state was 70MPa and the elongation at break was 7% as measured by a universal tester. The light transmittance of the cellulose membrane is measured by an ultraviolet spectrophotometer to be 90%, and the ultraviolet resistance effect of UVA reaches about 10%.

Example 2:

193g of a 7.0wt% NaOH/12wt% urea aqueous solution was pre-cooled to-13 ℃, and 1g of dealkalized lignin and 6g of cellulose were weighed and dissolved in the above solution, followed by stirring to obtain a 3wt% cellulose mixed solution. And (3) centrifuging and defoaming for 15 minutes at the rotating speed of 8000 rpm by using a high-speed centrifuge to obtain a transparent lignocellulose mixed solution. Under the condition of ice-water bath, 6g of epichlorohydrin is added for reaction for 1 hour. Setting the thickness of the film on a glass plate to be 0.6mm by using a BEVS1806 adjustable film coating device, carrying out tape casting and scraping, then placing the glass plate into an ethylene glycol coagulating bath at the temperature of 25 ℃ for coagulating for 20 minutes, taking out the glass plate, and washing the glass plate by using distilled water. And finally, pasting the composite membrane on an acrylic plate and naturally airing to obtain the regenerated lignin cellulose composite membrane. The breaking strength of the lignocellulose composite film in a dry state is 104MPa and the breaking elongation is 9 percent measured by a universal testing machine. The ultraviolet spectrophotometer is used for measuring that the light transmittance of the lignocellulose composite film is 70%, and the ultraviolet resistance effect of UVA reaches more than 80%.

Fig. 1 is a digital photograph of a lignocellulose composite film, and it can be seen that the composite film has better light transmittance.

Example 3:

192g of a 7.0wt% NaOH/12wt% urea aqueous solution was pre-cooled to-13 ℃ and 2g of dealkalized lignin and 6g of cellulose were dissolved in the solution, followed by stirring to obtain a 3wt% cellulose mixed solution. And (3) centrifuging and defoaming for 15 minutes at the rotating speed of 8000 rpm by using a high-speed centrifuge to obtain a transparent lignocellulose mixed solution. Under the condition of ice-water bath, 6g of epichlorohydrin is added for reaction for 1 hour. Setting the thickness of the film on a glass plate to be 0.6mm by using a BEVS1806 adjustable film coating device, carrying out tape casting and scraping, then placing the glass plate into an ethylene glycol coagulating bath at the temperature of 25 ℃ for coagulating for 20 minutes, taking out the glass plate, and washing the glass plate by using distilled water. And finally, pasting the composite membrane on an acrylic plate and naturally airing to obtain the regenerated lignin cellulose composite membrane. The breaking strength of the lignocellulose composite membrane in a dry state is 132MPa and the breaking elongation is 10 percent measured by a universal testing machine. The ultraviolet spectrophotometer is used for measuring that the light transmittance of the lignocellulose composite film is 60 percent, and the ultraviolet resistance effect of UVA reaches more than 90 percent.

Example 4:

190 g of an aqueous solution containing 7.0wt% of NaOH/12wt% of urea was pre-cooled to-13 ℃, and 4g of dealkalized lignin and 6g of cellulose were weighed and dissolved in the above solution, followed by stirring to obtain a 3wt% cellulose mixed solution. And (3) centrifuging and defoaming for 15 minutes at the rotating speed of 8000 rpm by using a high-speed centrifuge to obtain a transparent lignocellulose mixed solution. Under the condition of ice-water bath, 6g of epichlorohydrin is added for reaction for 1 hour. Setting the thickness of the film on a glass plate to be 0.6mm by using a BEVS1806 adjustable film coating device, carrying out tape casting and scraping, then placing the glass plate into an ethylene glycol coagulating bath at the temperature of 25 ℃ for coagulating for 20 minutes, taking out the glass plate, and washing the glass plate by using distilled water. And finally, pasting the composite membrane on an acrylic plate and naturally airing to obtain the regenerated lignin cellulose composite membrane. The breaking strength of the lignocellulose composite film in a dry state is 125MPa and the breaking elongation is 11 percent measured by a universal testing machine. The ultraviolet spectrophotometer is used for measuring the light transmittance of the lignocellulose composite film to be 55%, and the ultraviolet resistance effect of UVA reaches more than 95%.

Fig. 2 is an SEM image of the lignocellulose composite membrane, and it can be seen that many micro-nano particles appear on the surface of the cellulose membrane after lignin modification, which indicates that lignin particles are attached to the cellulose membrane.

Fig. 3 shows that the composite membrane still maintains a good state after being immersed in water for 30 days, and no lignin is precipitated, which illustrates that the problem of lignin migration and aggregation is effectively solved by the physical and chemical double crosslinking technology in the invention.

FIG. 4 is a water contact angle test of the lignocellulosic composite films of examples 1-4, showing that the water contact angle of the composite films increases as the amount of added lignin increases. This is mainly due to the fact that lignin is hydrophobic.

FIG. 5 shows the UV protection properties of the lignocellulosic composite films of examples 1-4, showing that the UV resistance of the composite films is increasing with the addition of lignin. This is mainly due to the fact that lignin contains uv-absorbing functional groups such as phenolic units, ketones and other chromophores.

Fig. 6 is a stress-strain curve of the lignocellulosic composite films of examples 1-4, and it can be seen that the breaking strength and elongation at break of the composite films are increasing with the increase of the lignin content in a certain range. This is because lignin has a rigid benzene ring structure, which increases the breaking strength, and because lignin fills the gaps between celluloses, which acts as a binder, the breaking elongation of the composite film also increases.

Note: the composite films were numbered ECF (example 1), ELCF-1 (example 2), ELCF-2 (example 3), ELCF-3 (example 4) with different amounts of added lignin.

Examples 5 to 8:

the dealkalized lignin in example 3 was replaced with any one of alkali lignin, enzymatic lignin, sulfonated lignin or sulfated lignin, and the rest of the conditions were the same as in example 3.

Examples 5-8 the results of the effect of lignin species on the performance of lignocellulosic composite membranes are shown in table 1.

TABLE 1 Effect of different lignins on lignocellulosic composite film Performance

The results in table 1 show that the lignin types all have certain influence on the performance of the composite membrane, and the influence on the performance of the composite membrane is different due to the difference of the structural units and the molecular weights of different lignins, wherein the composite membrane modified by the dealkalized lignin has the best comprehensive performance, and the composite membrane has higher breaking strength, breaking elongation, light transmittance and UVA-blocking.

Examples 9 to 13:

the same procedure as in example 3 was repeated except that the amount of epichlorohydrin used in example 3 was changed to 2g, 4g, 8g, 10g and 12 g.

The results of the impact of the amounts of epichlorohydrin used in examples 9-13 on the properties of the lignocellulosic composite films are shown in table 2.

TABLE 2 influence of the amount of epichlorohydrin on the properties of lignocellulosic composite films

From the results in table 2, it can be seen that, with the increase of the usage amount of epichlorohydrin, the mechanical properties of the composite film show a tendency of increasing first and then decreasing, which is greatly related to the crosslinking degree of the composite film. On the whole, the preferable range of the amount of the epichlorohydrin is 6-10 g.

Examples 14 to 18:

the coagulating bath in example 3 was changed to any one of ethanol, sodium sulfate solution, sodium chloride, acetic acid, dilute sulfuric acid or dilute hydrochloric acid, and the other conditions were the same as in example 3.

The results of the effect of coagulation bath type on the performance of lignocellulosic composite membranes of examples 14-18 are shown in table 3.

TABLE 3 influence of coagulation bath type on the performance of lignocellulosic composite membranes

As can be seen from the results in table 3, the types of the coagulation baths all have certain influence on the performance of the composite film, and the physical and chemical properties of different coagulation baths have different differences, so that the pore structure of the composite film after coagulation can be influenced, and the mechanical properties of the composite film can be influenced, wherein the composite film using ethylene glycol as the coagulation bath has the best comprehensive performance.

The above-described embodiments of the present invention are merely specific examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. It will be apparent to those skilled in the art that other variations on the foregoing description may be made. Any simple modifications, equivalent variations and improvements made to the above embodiments according to the technical and methodological principles of the invention are intended to be included within the scope of the claims.

Claims

1. The preparation method of the high-strength and high-toughness uvioresistant wood cellulose membrane is characterized by comprising the following steps of:

1) Dissolving cellulose and lignin in a certain proportion in 7wt% NaOH/12wt% urea solution, and centrifuging to remove gas to obtain light yellow lignin/cellulose solution;

2. The method for preparing the high-strength and high-toughness ultraviolet-resistant wood cellulose film according to claim 1, wherein the method comprises the following steps: the centrifugation condition of the step 1) is centrifugation for 15-30 min at 7200 r/min.

3. The preparation method of the high-strength and high-toughness ultraviolet-resistant lignocellulose membrane as recited in claim 1, wherein: in the step 1):

the mass ratio of the lignin to the cellulose is 1-5: 10;

the mass ratio of the cellulose in the lignin/cellulose solution is 2-5 percent;

the mass ratio of the lignin in the lignin/cellulose solution is 0.5-2%.

4. The method for preparing the high-strength and high-toughness ultraviolet-resistant wood cellulose film according to claim 1, wherein the method comprises the following steps: the lignin in the step 1) is one or more of alkali lignin, dealkalized lignin, enzyme lignin, sulfonated lignin and sulfate lignin, and the molecular weight is 1000-6000.

5. The method for preparing the high-strength and high-toughness ultraviolet-resistant wood cellulose film according to claim 1, wherein the method comprises the following steps: in the step 2), the cross-linking agent is epichlorohydrin, and the mass ratio of the cross-linking agent to the lignin/cellulose solution in the step 1) is 1-10: 100.

6. The preparation method of the high-strength and high-toughness ultraviolet-resistant lignocellulose membrane as recited in claim 1, wherein: the coagulating bath is one of ethanol, glycol, sodium sulfate solution, sodium chloride, acetic acid, dilute sulfuric acid or dilute hydrochloric acid, the temperature of the coagulating bath is 10-60 ℃, and the coagulating time is 5-30 min.