A highly transparent paper-based material and preparation method thereof

Abstract

The present invention relates to a highly transparent paper-based material and a preparation method thereof. The present invention provides a nanocellulose transparent paper with a high fiber aspect ratio, which comprises the following components by mass percentage: carboxyl-modified nanocellulose: 93% to 95%, filler 0 to 2%, and auxiliary agent 1 to 2%. The hydroxyl groups on the surface of nanocellulose are converted into carboxyl groups by TEMPO (2,2,6,6-tetramethyl-1-piperidinyl oxide) oxidation, which increases the negative charge density on the surface of cellulose, thereby enhancing the electrostatic repulsion between fibers and preventing the occurrence of agglomeration during the dispersion of nanocellulose. By introducing carboxyl groups on the surface of nanocellulose, a certain steric hindrance effect is formed, which limits the entry of water molecules into the amorphous region of cellulose and avoids hygroscopic expansion during papermaking. By controlling the oxidation reaction conditions, nanocellulose with a high aspect ratio is obtained, and a more dense and uniform fiber network structure can be formed when preparing a paper-based material, reducing the porosity and scattering center inside the material, thereby improving the light transmittance, and the transparency can reach 93%.

Description

Technical Field

[0001] The invention relates to the field of special paper manufacturing, in particular to a highly transparent paper-based material and a preparation method thereof. The paper-based material has high transparency and good mechanical properties. Background Art

[0002] Transparent paper is a type of specialty paper. It is usually made of plant-based cellulose nanofibers (such as Cellulose Nanofiber, referred to as CNF) as the main raw material. The fineness of these nanofibers is only one 20,000th of the diameter of a hair, giving transparent paper extremely high transparency. Due to its unique properties, transparent paper has shown broad application prospects in liquid crystal displays, lighting fixtures, solar cells, and replacing tablet computer display glass.

[0003] Although transparent paper has many advantages and application potential, there are still some problems to be solved in the production and application of transparent paper in the prior art. In particular, there is often a contradiction between the transparency and strength of transparent paper. How to improve the strength of paper while ensuring transparency is an important problem faced by the prior art. The prior art uses nanocellulose obtained by treating natural cellulose to manufacture transparent paper. Nanocellulose can form a tight network structure inside the paper, which significantly enhances the strength and toughness of the paper and ensures good quality transparency. However, nanocellulose itself is prone to form agglomerates during the dispersion process, and is prone to hygroscopic expansion during the preparation process, which ultimately affects the uniformity and transparency of the transparent paper. Summary of the invention

[0004] One of the purposes of the present invention is to provide a highly transparent paper-based material, wherein the hydroxyl groups on the surface of nanocellulose are converted into carboxyl groups by TEMPO oxidation, thereby increasing the negative charge density on the cellulose surface, thereby enhancing the electrostatic repulsion between fibers and preventing the occurrence of agglomeration during the dispersion of nanocellulose. By introducing carboxyl groups on the surface of nanocellulose, a certain steric hindrance effect is formed, which limits the entry of water molecules into the amorphous region of cellulose and avoids hygroscopic expansion during the papermaking process. By controlling the oxidation reaction conditions, nanocellulose with a high aspect ratio is obtained, and a more dense and uniform fiber network structure can be formed when preparing paper-based materials, reducing the porosity and scattering centers inside the material, thereby increasing the light transmittance, and the transparency can reach 95%.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solution: the highly transparent paper-based material comprises the following components by mass percentage: carboxyl-modified nanocellulose: 93% to 95%, filler 0 to 2%, and additive 1 to 2%.

[0006] In the above scheme, the carboxyl-modified nanocellulose is obtained by TEMPO oxidation of nanocellulose.

[0007] In the above solution, the filler is at least one of calcium carbonate, titanium dioxide and talc.

[0008] In the above scheme, the auxiliary agent is at least one of acrylic resin and polymethyl methacrylate.

[0009] In the above scheme, the highly transparent paper-based material comprises the following components by mass percentage: carboxyl-modified nanocellulose: 95%, filler 2%, and additive 1%.

[0010] In the above scheme, the aspect ratio of the carboxyl-modified nanocellulose fibers is 1:50-1:200.

[0011] Another object of the present invention is to provide a method for preparing the highly transparent paper-based material, the specific steps of which are:

[0012] S1: Preparation of carboxyl-modified nanocellulose, dispersing nanocellulose in deionized water to obtain a uniformly dispersed suspension, adding TEMPO / NaBr solution to the suspension, stirring sufficiently, slowly dropping NaClO solution, using 1 mol / L NaOH solution, maintaining the pH value of the reaction system at 10-11, and reacting at 0°C for 10 hours; after the reaction is completed, neutralizing the reaction solution with 1 mol / L HCl solution to neutrality, and filtering and washing the reaction solution with deionized water to obtain carboxyl-modified nanocellulose;

[0013] S2: Preparation of paper-based materials: dispersing carboxyl-modified nanocellulose, fillers and additives in appropriate amounts of water in proportion, performing ultrasonic dispersion for 2 hours and then filtering, and drying the filter cake in an oven at 30° C. for 2 hours to obtain the paper-based material.

[0014] In step S1, the mass ratio of nanocellulose, TEMPO, NaBr, and NaClO is 1:(0.01-0.02):(0.1-0.2):(5-10)

[0015] The beneficial effects brought about by the technical solution provided by the present invention include at least:

[0016] 1. The present invention converts the hydroxyl groups on the surface of nanocellulose into carboxyl groups through TEMPO (2,2,6,6-tetramethyl-1-piperidinyl oxide) oxidation, thereby increasing the negative charge density on the cellulose surface, thereby enhancing the electrostatic repulsion between fibers and preventing the occurrence of agglomeration during the dispersion of nanocellulose. By introducing carboxyl groups on the surface of nanocellulose, a certain steric hindrance effect is formed, which limits the entry of water molecules into the amorphous region of cellulose and avoids hygroscopic expansion during the papermaking process.

[0017] 2. By controlling the oxidation reaction conditions and adjusting the mass ratio of nanocellulose, TEMPO, NaBr, and NaClO to 1:(0.01-0.02):(0.1-0.2):(5-10), nanocellulose with a high aspect ratio was obtained. When preparing paper-based materials, a denser and more uniform fiber network structure can be formed, which reduces the porosity and scattering centers inside the material, thereby improving the light transmittance and achieving a transparency of 93%. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below.

[0019] The transparency of the following examples and comparative examples was measured according to the national standard GB / T 2410-2008; and the mechanical strength was measured using a tensile compression material testing machine (Instron 5565).

[0020] Example 1: Nanocellulose is dispersed in deionized water to obtain a uniform suspension. TEMPO / NaBr solution is added to the suspension. After sufficient stirring, NaClO solution is slowly added dropwise. The mass ratio of nanocellulose, TEMPO, NaBr, and NaClO is 1:0.01:0.1:5. A 1 mol / L NaOH solution is used to maintain the pH value of the reaction system at 10, and the reaction is carried out at 0°C for 10 hours. After the reaction is completed, the reaction solution is neutralized with a 1 mol / L HCl solution to neutralize the reaction solution, and the reaction solution is filtered and washed with deionized water to obtain carboxyl-modified nanocellulose.

[0021] Carboxyl modified nanocellulose, calcium carbonate and acrylic resin are dispersed in an appropriate amount of water at a mass ratio of 93:1:1, and filtered after ultrasonic dispersion for 2 hours. The filter cake is dried in an oven at 30°C for 2 hours to obtain the paper-based material. The fiber aspect ratio of the paper-based material is 50, the transparency is 89%, and the tensile strength is 201.3Mpa.

[0022] Example 2: Nanocellulose was dispersed in deionized water to obtain a uniform suspension. TEMPO / NaBr solution was added to the suspension. After sufficient stirring, NaClO solution was slowly added dropwise. The mass ratio of nanocellulose, TEMPO, NaBr, and NaClO was 1:0.02:0.2:10. A 1 mol / L NaOH solution was used to maintain the pH value of the reaction system at 10 and the reaction was carried out at 0°C for 10 hours. After the reaction was completed, the reaction solution was neutralized with a 1 mol / L HCl solution to neutralize the reaction solution. The reaction solution was filtered and washed with deionized water to obtain carboxyl-modified nanocellulose.

[0023] Carboxyl modified nanocellulose, titanium dioxide and acrylic resin are dispersed in a proper amount of water at a mass ratio of 95:2:1, and filtered after ultrasonic dispersion for 2 hours, and the filter cake is dried in an oven at 30°C for 2 hours to obtain the paper-based material. The fiber aspect ratio of the paper-based material is 200, the transparency is 93%, and the tensile strength is 233.1Mpa.

[0024] Example 3: Disperse nanocellulose in deionized water to obtain a uniform suspension, add TEMPO / NaBr solution to the suspension, stir thoroughly, and then slowly drop NaClO solution. The mass ratio of nanocellulose, TEMPO, NaBr, and NaClO is 1:0.01:0.2:5. Use 1 mol / L NaOH solution, keep the pH value of the reaction system at 10, and react at 0°C for 10 hours; after the reaction, neutralize the reaction solution with 1 mol / L HCl solution to neutrality, and filter and wash the reaction solution with deionized water to obtain carboxyl-modified nanocellulose;

[0025] Carboxyl modified nanocellulose, calcium carbonate and polymethyl methacrylate are dispersed in an appropriate amount of water at a mass ratio of 93:0:2, and filtered after ultrasonic dispersion for 2 hours. The filter cake is dried in an oven at 30°C for 2 hours to obtain the paper-based material. The fiber aspect ratio of the paper-based material is 135, the transparency is 90%, and the tensile strength is 214.5Mpa.

[0026] Comparative Example 1

[0027] The amounts of components and the preparation steps in Comparative Example 1 are basically the same as those in Example 1, except that the nanocellulose in Comparative Example 1 is not carboxylated. The fiber aspect ratio of the final paper-based material is 20, the transparency is 73%, and the tensile strength is 132.7 MPa.

[0028] Comparative Example 2

[0029] The dosage of each component and the preparation steps in Comparative Example 2 are basically the same as those in Example 1, except that NaOH is not used to adjust the pH of the reaction system in Comparative Example 2, and the reaction is carried out at room temperature for 20 hours; the fiber aspect ratio of the final paper-based material is 15, the transparency is 80%, and the tensile strength is 144.5 MPa.

[0030] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A highly transparent paper-based material, characterized in that: The following components are included by mass percentage: Carboxyl-modified nanocellulose: 93% to 95%, filler 0 to 2%, additive 1 to 2%; the carboxyl-modified nanocellulose is obtained by TEMPO oxidation of nanocellulose; the filler is at least one of calcium carbonate, titanium dioxide, and talc; the additive is at least one of acrylic resin and polymethyl methacrylate.

2. The highly transparent paper-based material according to claim 1, characterized in that The composition comprises the following components by mass percentage: carboxyl modified nanocellulose: 95%, filler 2%, auxiliary agent 1%; the aspect ratio of the carboxyl modified nanocellulose fiber is: 1:50-1:

200.

3. The method for preparing the highly transparent paper-based material according to claim 1, characterized in that: The specific steps are: S1: Preparation of carboxyl-modified nanocellulose, dispersing nanocellulose in deionized water to obtain a uniformly dispersed suspension, adding TEMPO / NaBr solution to the suspension, stirring sufficiently, slowly dropping NaClO solution, using 1 mol / L NaOH solution, maintaining the pH value of the reaction system at 10-11, and reacting at 0°C for 10 hours; after the reaction is completed, neutralizing the reaction solution with 1 mol / L HCl solution to neutrality, and filtering and washing the reaction solution with deionized water to obtain carboxyl-modified nanocellulose; S2: Preparation of paper-based materials: dispersing carboxyl-modified nanocellulose, fillers and additives in appropriate amounts of water in proportion, performing ultrasonic dispersion for 2 hours and then filtering, and drying the filter cake in an oven at 30° C. for 2 hours to obtain the paper-based material.

4. The method for preparing the highly transparent paper-based material according to claim 3, characterized in that: In the step S1, the mass ratio of nanocellulose, TEMPO, NaBr and NaClO is 1:(0.01-0.02):(0.1-0.2):(5-10).