阅读说明：本技术 一种基于纳米纤维素的可控雾度纳米纸及其制备方法 (Controllable haze nanometer paper based on nanometer cellulose and preparation method thereof ) 是由 刘德桃 苏灵峰 李映辉 徐科 欧阳豪 林美燕 于 2019-09-02 设计创作，主要内容包括：本发明公开了一种基于纳米纤维素的可控雾度纳米纸及其制备方法。该方法将绝干的植物纤维浸泡于纯水中充分吸水,然后在氢氧化钠水溶液中浸泡搅拌,加入异丙醇；过滤分离部分反应后的溶剂,控制纤维固含量为1％～2％,加入氯乙酸钠,保温,制得羧甲基纤维素钠包裹的纤维溶液；过滤纤维溶液,滤饼分散并过滤,滤饼烘干后变成纤维粉末,快速挤压制备纳米纤维粉末；纳米纤维粉末用纯水浸泡、洗涤、过滤,滤饼用纯水配置成固含量1％～5％的悬浮液,高压均质,得到纳米纤维素水溶液；将纳米纤维素水溶液与二甲基二烯丙基氯化铵混合,采用真空抽滤法制备复合材料纳米纸；本发明得到的纳米纸与普通纳米纸相比透过率高,雾度在大范围内可控。(The invention discloses a controllable haze nanopaper based on nano-cellulose and a preparation method thereof. Soaking completely dried plant fibers in pure water to fully absorb water, then soaking and stirring the plant fibers in a sodium hydroxide aqueous solution, and adding isopropanol; filtering and separating a part of reacted solvent, controlling the solid content of the fiber to be 1% -2%, adding sodium chloroacetate, and preserving heat to prepare a fiber solution coated by sodium carboxymethylcellulose; filtering the fiber solution, dispersing and filtering a filter cake, drying the filter cake to obtain fiber powder, and quickly extruding to prepare nano fiber powder; soaking the nano-fiber powder with pure water, washing, filtering, preparing a filter cake into a suspension with the solid content of 1-5% by using the pure water, and homogenizing under high pressure to obtain a nano-cellulose aqueous solution; mixing the nano-cellulose aqueous solution with dimethyl diallyl ammonium chloride, and preparing the composite nano-paper by adopting a vacuum filtration method; compared with the common nano paper, the nano paper obtained by the invention has high transmittance and controllable haze in a large range.)

1. A preparation method of controllable haze nanometer paper based on nanometer cellulose is characterized by comprising the following steps and process conditions:

1) completely absorbing water by soaking the completely dried plant fibers in pure water; soaking the plant fiber after water absorption in a sodium hydroxide aqueous solution, stirring, adding isopropanol, and uniformly stirring;

2) filtering and separating part of reacted solvent from the step 1) by using a metal filter screen, controlling the solid content of the fiber to be 1% -2%, adding sodium chloroacetate at the temperature of 60-65 ℃, and preserving heat to prepare a fiber solution coated by sodium carboxymethylcellulose;

3) filtering the fiber solution obtained in the step 2) by using a metal filter screen, dispersing and filtering a filter cake, drying the filter cake at 75-105 ℃ to obtain fiber powder, and quickly extruding to prepare nano fiber powder;

4) soaking the nanofiber powder obtained in the step 3) with pure water, washing and filtering, preparing a filter cake into a suspension with the solid content of 1% -5% by using the pure water, and homogenizing by using a high-pressure homogenizer with the homogenizing pressure of 15000-20000 psi to obtain a nanocellulose aqueous solution;

5) mixing the nano-cellulose aqueous solution obtained in the step 4) with dimethyl diallyl ammonium chloride, and preparing composite nano-paper by adopting a vacuum filtration method; controlling the mass ratio of the nano-cellulose to the dimethyl diallyl ammonium chloride to be 0.3-0.8: 1.

2. the method for preparing the nano-cellulose based haze controllable nano-paper according to claim 1, wherein the method comprises the following steps: the plant fiber is bleached pulp of softwood, hardwood and grass fibers.

3. The method for preparing the nano-cellulose based haze controllable nano-paper according to claim 1, wherein the method comprises the following steps: the temperature of the plant fiber soaked in the pure water is 20-30 ℃, and the time is 10-20 min.

4. The method for preparing the nano-cellulose based haze controllable nano-paper according to claim 1, wherein the method comprises the following steps: the mass ratio of the pure water and the oven-dried plant fibers in the step 1) is 2-5: 1; the oven-dry mass ratio of the sodium hydroxide to the plant fiber is 0.8-1.2: 1; the absolute dry mass ratio of the isopropanol to the plant fiber is 70-80: 1; the ratio of the total mass of the pure water and the water in the sodium hydroxide aqueous solution in the step 1) to the absolute dry mass of the plant fibers is 20-30: 1; soaking and stirring the plant fibers after water absorption in a sodium hydroxide aqueous solution for 10-60 s; the time for uniformly stirring in the step 1) is 50-70 min.

5. The method for preparing the nano-cellulose based haze controllable nano-paper according to claim 1, wherein the method comprises the following steps: the size of the meshes of the metal filter screen is 200-500 meshes; the heat preservation time is 60-180 min.

6. The method for preparing the nano-cellulose based haze controllable nano-paper according to claim 1, wherein the method comprises the following steps: the oven-dry mass ratio of the sodium chloroacetate to the wood fiber is 0.8-1.2: 1.

7. the method for preparing the nano-cellulose based haze controllable nano-paper according to claim 1, wherein the method comprises the following steps: in the step 3), dispersing and filtering the filter cake for 2-5 times by using isopropanol; the filtrate is reused after being purified; the transparent viscous substance on the inner wall of the container is dissolved by water to obtain the high-purity sodium carboxymethylcellulose by-product.

8. The method for preparing the nano-cellulose based haze controllable nano-paper according to claim 1, wherein the method comprises the following steps: soaking the nanofiber powder obtained in the step 4) in pure water, washing and filtering for 2-5 times, and purifying the collected solution to prepare a byproduct sodium carboxymethylcellulose; the mass ratio of the pure water for washing to the fiber powder is 10-25: 1; the homogenizing times of the high-pressure homogenizer are 3-6 times; the aperture of the high-pressure homogenizer is 60-90 microns.

9. The method for preparing the nano-cellulose based haze controllable nano-paper according to claim 1, wherein the method comprises the following steps: the mass concentration of the nano-cellulose in the mixed solution in the step 5) is lower than 5%.

10. A controllable haze nanopaper based on nanocellulose, characterized in that the nanopaper is prepared by the preparation method of any one of claims 1 to 9, the transparency of the nanopaper is higher than 78%, and the haze is controllable between 40% and 90%.

Technical Field

The invention relates to a nano paper, in particular to a controllable haze nano paper based on nano cellulose and a preparation method thereof.

Background

With the development of science and technology, the preparation method of nano-cellulose is diversified and mature, and nano-paper prepared in different ways is considered as a new material with high commercial value due to high transparency and low haze. However, there are limitations to the preparation of nanocellulose by either mechanical, chemical or biological methods. The mechanical method is most efficient in high-pressure homogenization treatment, but the high-pressure homogenization treatment has the problem that a homogenizing head is easily blocked, so that the production efficiency is greatly limited, mainly because the bonding force between cellulose macromolecular chains is too strong, the devillicate on the surface of macroscopic fiber is less and is not beneficial to devillicate brooming, the length and the diameter of the fiber are too large, and the agglomeration is easily generated before homogenization to block the homogenizing head, so that the fiber flocculation and the size of the macroscopic fiber need to be reduced through the combined action of mechanical pretreatment, chemical modification or biodegradation. The traditional industry uses chemical method, mechanical method, biological treatment method and other methods to pretreat the fiber, strives to reduce the problem of plug in the high-pressure homogenization process, and saves energy consumption and time, however, after the chemical pretreatment, the fiber after water washing and purification can not be directly ground, ultrasonically treated or sheared at high speed to obtain high-yield nano cellulose aqueous solution with lower energy consumption, and the nano cellulose aqueous solution prepared by adopting the suction filtration method has low efficiency and low haze.

At present, the preparation process of sodium carboxymethyl cellulose is mature, the fibrillation phenomenon on the surface of a fiber is removed by combining the preparation method of the sodium carboxymethyl cellulose, the sodium carboxymethyl cellulose is generated to wrap wood fibers, the arrangement of fibers in a crystalline region and an amorphous region of the cellulose is damaged by inward infiltration, the steric hindrance between cellulose macromolecular chains is increased, and the binding force between the cellulose macromolecular chains is reduced, so that the fiber with high brittleness and crystallinity is prepared, the brittleness of the fiber is further improved by washing and drying with isopropanol, the nano-fiber powder is directly obtained, and the nano-fiber powder is subjected to high-pressure homogenization treatment to obtain the nano-cellulose aqueous solution. The methods for preparing nanocellulose have been studied well, but these studies include other methods for preparing nanocellulose by carboxymethyl modification, which all use carboxymethyl cellulose with low substitution degree after water washing and purification or sodium salt thereof as a material, and prepare nanocellulose by mechanical treatment such as high-pressure homogenization. These washed fibers do not have high brittleness and are large in size, and the problem of clogging due to excessive size is caused by the fact that the fibers are completely homogenized under high pressure to make the fibers into nano-sized fibers, which is obviously not as efficient as nanofiber powder.

At present, a suction filtration mode is generally adopted for preparing nanopaper from nanocellulose obtained by different preparation methods, and the transparency and haze of the prepared nanopaper completely depend on the size of the nanocellulose or solid powder additionally added, such as Kim, Yujeong and the like [ Kim Y, Song Y, Kim h.preparation of transparent cellulose films with controlled haze using halloysite nanotubes, 2018,25(2): 1239-1248 ] by adding halloysite nanotubes (halloysite nanotubes) into the nanocellulose, the optical haze of the nanopaper is improved. Yang, Weisheng et al [ Yang W, Jiano L, Liu W, et al, management of high throughput and Hazy Cellulose Films Coating TEMPO-Oxidized Woodfibers, 9(1) ] transparent Films with high transparency (85%) and high haze (62%) were prepared by compounding micro-TEMPO nanocellulose with transparent Films by Coating and casting. Zhang, Zhao et al [ Zhang Z, Song F, Zhang M, et al, cellulose nanopaper with controllable optical haze and high affinity ultra-packaging for flexible optoelectronics, cellulose,2019,26(4): 1-8 ] by introducing a zinc (II) -terpyridine complex into TEMPO oxidized cellulose, the prepared nanopaper haze responds to the stimulus of a characteristic solvent of benzyl alcohol. Zhu, Hongli et al [ Hongli Z, Sepideh P, Colin P, et al.transmissive nanopaper with fibrous properties. nanoscale,2013,5(9): 3787-3792 ] obtain the relation between the transmission and scattering of light and the fiber size and the density of the nanopaper by mixing the nanocelluloses with different sizes, and obtain the theoretical calculation conclusion by simulation calculation. Tang, Hu et al [ Hu T, N ria B, Qi Z. ATransparent, Hazy, and Strong macromolecular Ribbon of organic cellulose fibers Bearing Poly (ethylene glycol). Advanced Materials,2015,27(12): 2070-2076 ] graft polyethylene glycol (PEG) on the surface of TEMPO oxidized fiber, the obtained nanopaper has Oriented wrinkle phenomenon, and the haze is greatly improved on the premise of a small reduction of transmittance. However, all of the above prior art methods require additional solid additives, or have particularly strict requirements on the size of nanofibers, or use solvents for the grafting reaction, and have the disadvantages of complicated process, high cost, and serious influence on the industrial application value.

Disclosure of Invention

The invention aims to solve the problems of the prior art, and provides the controllable haze nano paper which has the advantages that the raw materials can be repeatedly utilized, the yield of nano cellulose exceeds 80%, the problem of a plug in the high-pressure homogenization process is avoided, the transmittance is high, and the haze is controllable in a large range and is in the nano cellulose, and the preparation method thereof.

The invention relates to chemical modification and mechanical post-treatment of wood cellulose, and the prepared nano-cellulose aqueous solution is mixed with dimethyl diallyl ammonium chloride to prepare nano-paper. The preparation method comprises the steps of preparing sodium carboxymethyl cellulose on the surface of wood fibers, respectively obtaining byproducts sodium carboxymethyl cellulose and dried main product nano-fiber powder in a water phase and an alcohol phase, dispersing the nano-fiber powder in water, homogenizing under high pressure to obtain a nano-cellulose solution, regulating the aggregation form of the nano-cellulose aqueous solution by using dimethyl diallyl ammonium chloride, and controlling the efficiency of preparing nano-paper by suction filtration and the haze of the nano-paper. The dimethyl diallyl ammonium chloride adopted by the invention is a water-soluble solvent widely used in the papermaking industry, can be repeatedly used in water, can improve the preparation speed of the nano paper and the haze of the nano paper only by directly adding the dimethyl diallyl ammonium chloride into a nano cellulose aqueous solution, and is simple in method.

The purpose of the invention is realized by the following technical scheme:

a preparation method of controllable haze nanometer paper based on nanometer cellulose comprises the following steps and process conditions:

1) completely absorbing water by soaking the completely dried plant fibers in pure water; soaking the plant fiber after water absorption in a sodium hydroxide aqueous solution, stirring, adding isopropanol, and uniformly stirring;

2) filtering and separating part of reacted solvent from the step 1) by using a metal filter screen, controlling the solid content of the fiber to be 1% -2%, adding sodium chloroacetate at the temperature of 60-65 ℃, and preserving heat to prepare a fiber solution coated by sodium carboxymethylcellulose;

3) filtering the fiber solution obtained in the step 2) by using a metal filter screen, dispersing and filtering a filter cake, drying the filter cake at 75-105 ℃ to obtain fiber powder, and quickly extruding to prepare nano fiber powder;

4) soaking the nanofiber powder obtained in the step 3) with pure water, washing and filtering, preparing a filter cake into a suspension with the solid content of 1% -5% by using the pure water, and homogenizing by using a high-pressure homogenizer with the homogenizing pressure of 15000-20000 psi to obtain a nanocellulose aqueous solution;

5) mixing the nano-cellulose aqueous solution obtained in the step 4) with dimethyl diallyl ammonium chloride, and preparing composite nano-paper by adopting a vacuum filtration method; controlling the mass ratio of the nano-cellulose to the dimethyl diallyl ammonium chloride to be 0.3-0.8: 1.

to further achieve the object of the present invention, preferably, the plant fiber is bleached pulp of softwood, hardwood, and grass fibers.

Preferably, the temperature of soaking the plant fiber in pure water is 20-30 ℃, and the time is 10-20 min

Preferably, the mass ratio of the pure water and the oven-dried plant fibers in the step 1) is 2-5: 1; the oven-dry mass ratio of the sodium hydroxide to the plant fiber is 0.8-1.2: 1; the absolute dry mass ratio of the isopropanol to the plant fiber is 70-80: 1; the ratio of the total mass of the pure water and the water in the sodium hydroxide aqueous solution in the step 1) to the absolute dry mass of the plant fibers is 20-30: 1; soaking and stirring the plant fibers after water absorption in a sodium hydroxide aqueous solution for 10-60 s; the time for uniformly stirring in the step 1) is 50-70 min.

Preferably, the size of the meshes of the metal filter screen is 200-500 meshes; the heat preservation time is 60-180 min.

Preferably, the oven-dry mass ratio of the sodium chloroacetate to the wood fibers is 0.8-1.2: 1.

preferably, in the step 3), the filter cake is dispersed and filtered for 2-5 times by using isopropanol; the filtrate is reused after being purified; the transparent viscous substance on the inner wall of the container is dissolved by water to obtain the high-purity sodium carboxymethylcellulose by-product.

Preferably, soaking the nanofiber powder obtained in the step 4) with pure water, washing, filtering for 2-5 times, and purifying the collected solution to prepare a byproduct sodium carboxymethylcellulose; the mass ratio of the pure water for washing to the fiber powder is 10-25: 1; the homogenizing times of the high-pressure homogenizer are 3-6 times; the aperture of the high-pressure homogenizer is 60-90 microns.

Preferably, the mass concentration of the nano-cellulose in the mixed solution in the step 5) is less than 5%.

The solvent after the reaction in the step 2) of the method is the mixed solution of the sodium hydroxide aqueous solution and the isopropanol after the reaction in the step 1), and the fiber size is not changed due to the reaction, so that the fiber cannot pass through a metal filter screen, and the solvent and the fiber can be quickly separated.

In the step 3), the fiber powder obtained after drying is not uniform, a small part of the fiber is still slightly large in size, the dried fiber has high brittleness and is extremely easy to be completely crushed under the extrusion condition to obtain more fine powder, but the fiber cannot be crushed into powder if the fiber is not simply and quickly extruded before contacting water, so that part of the fiber is larger, and the subsequent preparation process is not favorable.

The preparation method of the controllable haze nanopaper based on the nanocellulose has the advantages that the transparency of the nanopaper is higher than 78%, and the haze is controllable between 40% and 90%.

The method is different from the traditional preparation method, after carboxymethyl modification is introduced, the modified fiber is dried in an alcohol phase and has high crystallinity and brittleness, the size is reduced to the nanometer level before high-pressure homogenization, the size of the modified fiber is smaller than that of the fiber modified by the traditional method, the energy consumption required by the high-pressure homogenization is lower, the yield of the prepared nano-cellulose aqueous solution is higher, and the efficiency of preparing nano-paper and the haze of the nano-paper can be improved and regulated after the obtained nano-cellulose aqueous solution is mixed with dimethyl diallyl ammonium chloride.

The invention introduces a preparation method of sodium carboxymethyl cellulose, so that the generated sodium carboxymethyl cellulose is wrapped on the surface of the fiber and penetrates inwards, the fiber can be separated in an alcohol phase and then dried to prepare nano fiber powder, and a by-product sodium carboxymethyl cellulose aqueous solution is collected in a water phase. The nanofiber powder prepared by the method can be homogenized under high pressure under ultrahigh concentration without risk of blockage (wood fibers are dried into nanofiber powder after chemical reaction and can be prepared into uniform suspension liquid after being washed and dispersed, precipitation and aggregation are avoided in a short time, the aperture of an effective processing round hole of a high-pressure homogenizer is 60-90 micrometers, the size of the dispersed nanofiber powder is smaller than that of the high-pressure homogenizing hole, the risk of blockage can be controlled to be the lowest), and the suction filtration rate and the haze of the nanopaper can be regulated and controlled after the nanofiber powder is mixed with dimethyl diallyl ammonium chloride according to different proportions.

The method comprises the steps of rapidly preparing a main product nano-cellulose aqueous solution and a byproduct sodium carboxymethyl cellulose through heterogeneous soluble etherification, and regulating the suction filtration speed of the nano-cellulose aqueous solution by using a chemical additive dimethyl diallyl ammonium chloride to obtain the haze controllable nano-paper. By the method, the prepared by-product sodium carboxymethylcellulose is dissolved in a water phase, and is separated and extracted by water; drying the main product fiber in an alcohol phase to obtain nano fiber powder, dissolving in water, and homogenizing under high pressure to obtain the nano cellulose water solution. The method provided by the invention is combined with a preparation method of sodium carboxymethylcellulose, so that the problems that the conventional chemical pretreatment fiber is too long, a homogenizer is blocked by high-pressure homogenization treatment to improve the production efficiency and yield of the nano-cellulose are solved, the prepared nano-cellulose aqueous solution is mixed with dimethyldiallylammonium chloride to regulate the pumping speed and the nano-paper haze, and the problems that the nano-cellulose pumping speed is low and the nano-paper haze is low are solved.

According to the method, after the chemical reaction is finished, the separation of the byproduct sodium carboxymethyl cellulose and the main product nano-fiber powder is controlled, isopropanol is firstly adopted for washing to separate the fibers from the sodium carboxymethyl cellulose, the nano-fiber powder is obtained after drying, and then the sodium carboxymethyl cellulose is collected by washing a reaction container with water.

According to the invention, the fiber surface and the devillicate fine fiber are modified into water-soluble sodium carboxymethyl cellulose, the sodium carboxymethyl cellulose insoluble in alcohol wraps the fiber and then penetrates inwards to fill fiber pores, and the redundant sodium carboxymethyl cellulose collects water in a system and adheres to the surface of a container, so that the reaction is stopped. Firstly, the fiber and the sodium carboxymethyl cellulose are separated by washing and filtering with isopropanol, the dried fiber and the sodium carboxymethyl cellulose are converted into nano fiber powder due to high crystallinity and brittleness, and the sodium carboxymethyl cellulose in the container can be completely collected after being dissolved by water. The surface of the nanofiber powder is exposed with pores and a large amount of devillicate brooming phenomenon after being washed and filtered, the nano-cellulose obtained after high-pressure homogenization is interacted with dimethyl diallyl ammonium chloride, the suction filtration speed is rapidly improved, and the haze of the obtained nano-paper is related to the addition amount of the dimethyl diallyl ammonium chloride.

Compared with the prior art, the invention has the following advantages:

1) the invention introduces a preparation method of improved carboxymethyl cellulose to assist in preparing nano cellulose, and comprises five steps of stirring, filtering, drying, crushing and homogenizing; the production period is short, fiber powder can be prepared within 2.5h, nano-cellulose can be prepared within 4h, and a byproduct carboxymethyl cellulose can be obtained; the yield is high, the fiber powder yield is more than 90 percent, and the nano-cellulose yield is 80 to 90 percent; the product has stable performance, the nano-fiber powder can be transported and stored, the size distribution of the fiber powder is concentrated, the yield of the high-pressure homogeneous nano-cellulose aqueous solution is stable, and the problem of a plug in the high-pressure homogeneous process is completely avoided.

2) The method is suitable for most plant fibers, only the fiber modification time and the water content of a system need to be changed, other variables do not need to be adjusted, the production flow is simplified, and the production difficulty is greatly reduced.

3) The nano-cellulose aqueous solution prepared by the method has good interaction with dimethyl diallyl ammonium chloride, and the nano-paper can be mixed according to different proportions, so that the production efficiency can be improved to different degrees, and nano-paper with different haze can be obtained, and the influence on the total light transmittance is small.

4) In order to reduce the generation of a byproduct carboxymethyl cellulose, wood fibers are soaked for absorbing water before use, and isopropanol is adopted to control alkalization reaction to be fixed on the cellulose in a non-crystallization area of micro-pores in the fibers.

5) The method can simultaneously prepare nano-cellulose powder, nano-cellulose aqueous solution and sodium carboxymethyl cellulose under mild conditions, controllably reduce the time for preparing nano-paper by suction filtration after adding dimethyldiallylammonium chloride, and simultaneously control the haze of the nano-paper.

Description of the drawings:

FIG. 1 is a graph comparing the fiber powder prepared in example 1 with wood fibers.

FIG. 2 is a surface topography SEM of the nanofiber powder washed with pure water in example 1, the surface containing a large number of nanopores and devillicates.

Fig. 3 is an AFM picture of the nanocellulose prepared in example 1.

FIG. 4 is a graph showing the phenomenon of light scattering in the nanopaper and the blank obtained in example 4 and example 6 without adding dimethyldiallylammonium chloride.

Detailed Description

For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings and examples, and it is intended that the scope of the present invention be limited not by the examples shown.

In the following examples, scanning electron microscope EVO 18 is adopted for characterization of the form of the washed nanofiber powder, atomic force microscope is adopted for characterization of the form of the nanocellulose, the haze and the transparency of the nanopaper are obtained by direct UV-Vis test, and the transmittance value and the haze value at 550nm of the nanopaper are read as reference values.