阅读说明：本技术 一种基于不同分子量多糖的高强度湿度响应纳米纤维素膜 (High-strength humidity response nano cellulose membrane based on polysaccharides with different molecular weights ) 是由 龙柱 孟亚会 于 2021-01-14 设计创作，主要内容包括：本发明公开了一种基于不同分子量多糖的高强度湿度响应纳米纤维素膜,属于功能材料领域。本发明所述的多糖/CNC彩虹膜,其组分包括纳米纤维素CNC、多糖,其中多糖的分子量为182-70000；多糖和CNC的质量比为0～60：100；但多糖的用量不为0。本发明的多糖/CNC彩虹膜的拉伸强度达到30MPa以上,可以高达67.3MPa；断裂伸长率在0.38％以上,可以达到6.75％。且本发明的多糖/CNC彩虹膜具有湿度响应功能,而且具有湿度相应的可逆稳定性能,反复10次,湿度响应性能没有太大的变化。(The invention discloses a high-strength humidity-response nano cellulose membrane based on polysaccharides with different molecular weights, and belongs to the field of functional materials. The polysaccharide/CNC rainbow film comprises the components of nano-cellulose CNC and polysaccharide, wherein the molecular weight of the polysaccharide is 182-70000; the mass ratio of polysaccharide to CNC is 0-60: 100, respectively; but the amount of polysaccharide used is not 0. The tensile strength of the polysaccharide/CNC rainbow film reaches more than 30MPa and can reach 67.3 MPa; the elongation at break is more than 0.38 percent and can reach 6.75 percent. The polysaccharide/CNC rainbow film has a humidity response function, has reversible stability corresponding to humidity, and does not change greatly in humidity response performance after being repeated for 10 times.)

1. A polysaccharide/CNC rainbow film is characterized in that the components comprise nano-cellulose CNC and polysaccharide, wherein the molecular weight of the polysaccharide is 182-70000; the mass ratio of polysaccharide to CNC is 0-60: 100, respectively; but the amount of polysaccharide used is not 0.

2. The polysaccharide/CNC rainbow film of claim 1, wherein the molecular weight of said polysaccharide is 182-.

3. The polysaccharide/CNC rainbow film of claim 1 or 2, wherein the mass ratio of polysaccharide to CNC is 10-40: 100.

4. a method of preparing the polysaccharide/CNC iris lactea of any one of claims 1 to 3, comprising the steps of:

(1) carrying out acidolysis on microcrystalline cellulose to obtain a nano cellulose suspension; then concentrating to obtain nano cellulose concentrated solution;

(2) adding polysaccharide into the nano-cellulose concentrated solution, and uniformly mixing to obtain a film forming solution;

(3) casting the film-forming solution into a film, and drying to obtain a CNC rainbow film;

wherein the molecular weight of the polysaccharide is 182-70000; the mass ratio of the polysaccharide to the CNC is 0-60: 100, but the amount of polysaccharide used is not 0.

5. The method as claimed in claim 4, wherein the acid hydrolysis in the step (1) is carried out by adding microcrystalline cellulose into sulfuric acid solution, and the mass-to-volume ratio of the cellulose nanocrystal CNC to the sulfuric acid solution is 10-20 g: 100mL, the concentration of the sulfuric acid solution is 60-65 wt%.

6. The method according to claim 4 or 5, characterized in that the concentration of the nano-cellulose CNC suspension of step (1) is 0.4-0.8 wt%.

7. The process according to any one of claims 4 to 6, wherein the nanocellulose concentrate of step (1) has a solids content of 2.6 to 2.8 wt.%.

8. The method according to any one of claims 4 to 7, wherein the step (3) of casting the film-forming solution into a polytetrafluoroethylene disk with a thickness of 50 to 60 μm.

9. Use of the polysaccharide/CNC iridescent film according to any of the claims 1 to 3 in the fields of decorative coatings, optical and humidity sensing, anti-counterfeiting and the like.

10. A moisture sensor comprising the polysaccharide/CNC iridescent film of any one of claims 1-3.

Technical Field

The invention relates to a high-strength humidity-response nano cellulose membrane based on polysaccharides with different molecular weights, belonging to the field of functional materials.

Background

Bright structural colors are present in many animals and plants in nature, such as: bird feathers, butterfly wings, shells, pollen fruits, etc., which are also called iridescent colors, are generated by light interference in the nano-scale periodic multilayer structure on their surfaces. Many scientists are working on materials with this structural color. Among them, nanocellulose crystals (CNC) can produce similar photonic structure colors.

Cellulose is the most abundant biopolymer in nature and is available from a variety of natural sources. Cellulose Nanocrystals (CNC) produced by cellulose hydrolysis have sulfate half-ester groups on the surface, and this electrostatic repulsion of surface charges allows CNC to form stable dispersions in water, thus imparting unique self-assembly properties to CNC. CNC displays a chiral structure due to the D-glucose unit in cellulose. During slow evaporation of the CNC suspension, the CNC spontaneously organizes into chiral nematic liquid crystal structures and after the film is completely dried, the chiral nematic structures are completely retained. The chiral nematic phase has a helical structure and exhibits a left-handed chiral structure, in which the CNC is arranged along one guide axis, each of which is slightly rotated from one layer to the next along the helical axis, and the vertical distance required for the guide axis to complete a 180 ° rotation is called the pitch (p). When the wavelength of the incident light matches the pitch of the CNC film, the light is selectively reflected, resulting in coloration of the material. Therefore, the CNC can be subjected to color control by adjusting the pitch size (such as methods of adding electrolyte, ultrasonic treatment, ionic strength, drying temperature and the like).

Disclosure of Invention

[ problem ] to

Recently, low cost photonic materials produced by biopolymer self-assembly have received increasing attention in the materials community. Due to the biodegradability, low cost, non-toxicity and biocompatibility of biomass materials, many photonic structures with optical response have been produced using a variety of biomass materials. However, there are some limitations to this. Such as: cellulose-based photonic structures can provide bright colors, but they are generally very brittle; the addition of polymers to CNC can improve mechanical properties, but at higher additive levels (40-50%) it tends to destroy the chiral structure, induce crystallization, induce large scale phase separation, increase optical losses and thus destroy the structural color. Therefore, a delicate balance between chirality and mechanical strength should be considered in selecting a suitable polymer as an additive for CNC films. The chiral nematic structure of CNC can be preserved if the polymer is compatible with CNC and does not interfere with the CNC's self-assembly.

Usually biopolymers (such as polysaccharides) are used as the main composite and CNC is used as reinforcing agent. However, biocomposites rarely have CNC as the major component of the composite, with biopolymers as additives. And there are few reports on the effect of polysaccharides of different molecular weights on the mechanical properties and humidity responsiveness of CNC films.

[ solution ]

In order to solve at least one problem, the CNC rainbow film with good mechanical property, humidity sensitivity and adjustable color is prepared by using CNC as a base material and glucan with different molecular weights as an additive. The CNC rainbow film has potential application value in the fields of decorative coating, optical and humidity sensing, anti-counterfeiting and the like.

The invention provides a polysaccharide/CNC rainbow film, which comprises the components of nano-cellulose CNC and polysaccharide, wherein the molecular weight of the polysaccharide is 182-70000; the mass ratio of polysaccharide to CNC is 0-60: 100, respectively; but the amount of polysaccharide used is not 0.

In one embodiment of the present invention, the molecular weight of the polysaccharide is 182-.

In one embodiment of the invention, the mass ratio of the polysaccharide to the CNC is 10-40: 100.

in one embodiment of the invention, the polysaccharides are dextrans of different molecular weights.

A second object of the present invention is a method for preparing a polysaccharide/CNC rainbow film, comprising the steps of:

(1) carrying out acidolysis on microcrystalline cellulose to obtain a nano cellulose suspension; then concentrating to obtain nano cellulose concentrated solution;

(2) adding polysaccharide into the nano-cellulose concentrated solution, and uniformly mixing to obtain a film forming solution;

(3) casting the film-forming solution into a film, and drying to obtain a CNC rainbow film;

wherein the molecular weight of the polysaccharide is 182-70000; the mass ratio of the polysaccharide to the CNC is 0-60: 100, but the amount of polysaccharide used is not 0.

In one embodiment of the present invention, the molecular weight of the polysaccharide is 182-; the mass ratio of polysaccharide to CNC is 10-40: 100.

in one embodiment of the invention, the acidolysis in the step (1) is performed by adding microcrystalline cellulose into a sulfuric acid solution, and the mass-to-volume ratio of the cellulose nanocrystal CNC to the sulfuric acid solution is 10-20 g: 100mL, the concentration of the sulfuric acid solution is 60-65 wt%.

In one embodiment of the invention, the concentration of the nano-cellulose CNC suspension in the step (1) is 0.4-0.8 wt%.

In one embodiment of the present invention, the solid content of the nano-cellulose concentrated solution in the step (1) is 2.6-2.8 wt%.

In one embodiment of the present invention, the step (2) of uniformly mixing is performed by uniformly stirring at room temperature.

In one embodiment of the present invention, the step (3) of casting the film-forming solution into a teflon disc, wherein the thickness of the film-forming solution is 50 to 60 μm.

In one embodiment of the present invention, the drying in step (3) is performed at room temperature (20-30 ℃) for 10-30 h.

The third purpose of the invention is the application of the polysaccharide/CNC rainbow film in the fields of decorative coating, optical and humidity sensing, anti-counterfeiting and the like.

It is a fourth object of the present invention to provide a moisture sensor comprising the polysaccharide/CNC rainbow film of the present invention.

In one embodiment of the invention, the polysaccharide/CNC rainbow film serves as part of the moisture response in the moisture sensor.

[ advantageous effects ]

(1) The preparation process of the polysaccharide/CNC rainbow film is simple and easy to operate.

(2) The invention adopts polysaccharides with different molecular weights as the reinforcing agent, is green and environment-friendly, can improve the mechanical property of the film, can also carry out color regulation and control, and endows the nano cellulose film with different colors.

(3) The polysaccharide/CNC rainbow film has a humidity response function, has reversible stability corresponding to humidity, and does not change the humidity response performance too much after repeating for 10 times.

(4) The tensile strength of the polysaccharide/CNC rainbow film reaches more than 30MPa and can reach 67.3 MPa; the elongation at break is more than 0.38 percent and can reach 6.75 percent.

Drawings

FIG. 1 is a UV-Vis spectrum of a polysaccharide/CNC rainbow film with different molecular weights; wherein (a) is Glucose; (b) is Glu-2000; (c) is Glu-20000; (d) is Glu-70000.

Figure 2 is a scanning electron microscope with different molecular weight polysaccharide/CNC iridescent films.

FIG. 3 is a UV-Vis spectrum of a polysaccharide/CNC rainbow film with different molecular weights under different humidity conditions; wherein (a) is Glucose; (b) is Glu-2000; (c) is Glu-20000; (d) is Glu-70000.

FIG. 4 is a graph of response membrane cycling stability for polysaccharide/CNC rainbow films with different molecular weights; (a) is Glucose; (b) is Glu-2000; (c) is Glu-20000; (d) is Glu-70000.

Detailed Description

The following description of the preferred embodiments of the present invention is provided for the purpose of better illustrating the invention and is not intended to limit the invention thereto. The polysaccharides used in the examples were all dextrans.

The test method comprises the following steps:

tensile strength and elongation at break: the composite films were tested for mechanical strength using a BZ2.5/TNIS Zwick materials tester (Zwick, Germany) at 25 ℃ and a humidity RH of 60%. The samples were 15X 100mm in size, 50mm in grip, 50mm in draw speed, and tested at least 5 times per sample.

Example 1

A method of preparing a polysaccharide/CNC iridescent film comprising the steps of:

(1) placing 11g of microcrystalline cellulose into 100mL of 64 wt% sulfuric acid solution for acidolysis to obtain 0.4 wt% nanocellulose suspension; then evaporating at room temperature to obtain a nano-cellulose concentrated solution with the solid content of 2.6 wt% (the amount of nano-cellulose crystal CNC in the concentrated solution is 1 g);

(2) adding polysaccharide into the nano-cellulose concentrated solution, stirring at room temperature (25 ℃) and 300rpm for 60min, and uniformly mixing to obtain a film forming solution; wherein the addition amount of the polysaccharide is 10, 20, 30, 40, 50 and 60 wt% of the CNC; the molecular weight of the polysaccharide is 0, 180, 2000, 20000 and 70000 respectively;

(3) casting the film forming liquid in a polytetrafluoroethylene disc, and drying for 24 hours at room temperature (25 ℃) to obtain a polysaccharide/CNC rainbow film (the thickness is 55 +/-3 mu m), wherein the marks are respectively 10% Glucose, 20% Glucose, 30% Glucose, 40% Glucose, 50% Glucose and 60% Glucose; 10% Glu-2000, 20% Glu-2000, 30% Glu-2000, 40% Glu-2000, 50% Glu-2000, 60% Glu-2000; 10% Glu-20000, 20% Glu-20000, 30% Glu-20000, 40% Glu-20000, 50% Glu-20000, 60% Glu-20000; 10% Glu-70000, 20% Glu-70000, 30% Glu-70000, 40% Glu-70000, 50% Glu-70000, 60% Glu-70000.

The polysaccharide/CNC rainbow film obtained in example 1 was tested for polysaccharide content and the effect of polysaccharides of different molecular weights on the color of the rainbow film using an ultraviolet-visible spectrophotometer, and the test results are shown in table 1 and fig. 1, as can be seen from table 1 and fig. 1: with the increase of the polysaccharide content, the reflectance spectrum of the rainbow film gradually red-shifts, because the polysaccharide content increases, taking up more free space between CNC layers, resulting in an increase in CNC layer spacing, which in turn red-shifts the reflectance spectrum. The reflectance spectrum of the rainbow film gradually blueshifts as the molecular weight of the polysaccharide increases. When the mass fractions of polysaccharides in the iridescent film are the same, the larger the molecular weight of the polysaccharides is, the smaller the number of moles of the polysaccharides contained in the iridescent film system is, and the free space between CNC layers is occupied, so that the spacing between the CNC layers is reduced, and further the blue shift of the reflection spectrum is realized.

Table 1 maximum spectral change of uv-visible spectrum with different molecular weight polysaccharide/CNC iridescent films.

The polysaccharide/CNC rainbow film obtained in example 1 was observed for microstructure of the film using a scanning electron microscope, as shown in fig. 2. As can be seen from fig. 2: with the increase of the molecular weight of the polysaccharide, the microstructure of the rainbow film is changed, and the interlayer spacing of the CNC is increased from 168nm to 275 nm. This result is consistent with the reflectance spectrum.

The polysaccharide/CNC rainbow film obtained in example 1 was measured for strength using a universal material tester, and the influence of polysaccharide content and polysaccharides of different molecular weights on the mechanical properties of the rainbow film was investigated. The mechanical properties of the rainbow film are shown in table 2. As can be seen from table 2: as the molecular weight of the polysaccharide decreases, the tensile strength of the rainbow film decreases and the elongation at break increases, because the mobility of the polysaccharide with a smaller molecular weight in the CNC film is greater, so that the movement between CNC molecules in the rainbow film increases, resulting in an increase in the elongation at break of the CNC rainbow film. When the polysaccharide molecules are larger, the tensile strength of the rainbow film increases with increasing polysaccharide content, which is due to increased hydrogen bonding between the polysaccharide and the CNC, resulting in increased tensile strength of the CNC rainbow film. When the polysaccharide content is more than 40 wt%, it is difficult to measure by the in-plane tensile test since the rainbow film is too brittle.

TABLE 2 mechanical Properties of polysaccharide/CNC Iris films with different molecular weights

Note: in the table "-" means that the film was too brittle to be tested at all.

Example 2 humidity response Properties of polysaccharide/CNC Iris film

Adding saturated salt solution CaCl₂、K₂CO₃And NaCl solution and distilled water in a closed vessel to control different humidity conditions (50% RH, 70% RH, 85% RH, 98% RH);

then, 30% Glucose, 30% Glu-2000, 30% Glu-20000, and 30% Glu-70000 obtained in example 1 were cut into 2 cm. times.2 cm, placed in the above-mentioned closed vessel, and then sealed.

The reflectance spectra of the polysaccharide/CNC rainbow film were tested under different humidity conditions and the results are shown in fig. 3 and table 3, as can be seen from fig. 3 and table 3: with the increase of the relative humidity from 50% to 98%, the reflectance spectra of the rainbow film of 30% Glucose, 30% Glu-20000 and 30% Glu-70000 all show a red shift.

Table 3 maximum spectral change of uv-vis spectra with different molecular weight polysaccharide/CNC iridescent films under different humidity conditions.

Example 3 cycling stability of humidity response

A reflection spectrum of a film was recorded by placing a 2cm × 2 cm-sized polysaccharide/CNC rainbow film of 30% Glucose, 30% Glu-20000, and 30% Glu-70000 under a humidity condition of 50% RH, and then, by placing the film under a humidity condition of 98% RH. The above operations are repeated for more than ten times circularly.

The cycle stability of the rainbow film tested is shown in figure 4. As can be seen from fig. 4: the change of the reflectance spectrum of the polysaccharide/CNC iridescent film in the multiple cycle response is particularly small within 10 cycles under the conditions of 30% and 95% relative humidity, indicating that the polysaccharide/CNC iridescent film has good reversible stability.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.