CN116079851B - Method for controllably removing lignin in wood and bamboo - Google Patents

Abstract

The invention discloses a method for controllably removing lignin in wood and bamboo, which comprises (1) preparing cellulose gel water: mixing cellulose with water, heating, and stirring uniformly to prepare cellulose gel water; (2) preparing composite gel water solution: dissolving a bleaching agent in cellulose gel water, and uniformly stirring at room temperature to obtain composite gel water; (3) Soaking the wood and bamboo in the composite gel water solution, and cleaning the soaked wood and bamboo with absolute ethyl alcohol to obtain wood and bamboo with controllable lignin removal. The technical problem that the traditional bleaching agent cannot bleach controllably is effectively solved, the bleaching agent is suitable for any wood and bamboo biomass material, controllable ordered bleaching of wood and bamboo from the surface to any inner thickness layer can be realized, and technical guarantee is provided for accurate functionalization of the surface of the wood and bamboo.

Description

A method for controllable removal of lignin in wood and bamboo materials

Technical Field

The invention relates to the technical field of materials, and in particular to a method for controllably removing lignin from wood or bamboo materials.

Background technique

Wood and bamboo materials are natural polymer composite materials composed of cellulose, hemicellulose and lignin. They are green and environmentally friendly, have a high strength-to-weight ratio, and have beautiful textures. They are widely used in the field of architecture and home furnishing. Especially in today's world, where green and sustainable development has become the theme of the times, the extensive application of renewable and degradable biomass resources represented by wood and bamboo materials to replace non-renewable and non-degradable petrochemical resources such as plastics is of great significance in promoting the sustainable development of human society. However, in some application scenarios, it is difficult to use wood and bamboo materials directly, and the surface of wood and bamboo materials needs to have functionality, such as wet stimulus responsiveness, surface flame retardancy, surface photoelectric and electromagnetic functions, etc., which can be cut and designed by exposing a certain amount of cellulose on the surface. At this time, it is necessary to controllably remove the lignin that affects the functional design.

Bleaching agents, such as sodium hypochlorite and hydrogen peroxide, are usually used to effectively remove lignin. However, it is difficult to controllably remove lignin in a layer of any thickness on the surface using these bleaching agents directly, which makes it difficult to design the functionalization of the surface of wood and bamboo materials. Therefore, developing a technical method for controllably and orderly removing lignin from the surface of wood and bamboo materials to any thickness layer inside is of great value for achieving efficient and high-value utilization of wood and bamboo resources.

Summary of the invention

In view of the above-mentioned prior art, the purpose of the present invention is to provide a method for controllably removing lignin from wood and bamboo materials. In order to solve the technical problem that the existing bleaching method is difficult to controllably remove lignin in a layer of any thickness on the surface, the present invention provides a method for controllably and orderly removing lignin from the surface of wood and bamboo materials to a layer of any thickness inside.

To achieve the above object, the present invention adopts the following technical solution:

The present invention provides a method for controllably removing lignin from wood and bamboo materials, comprising the following steps:

(1) preparing a cellulose gel aqueous solution: mixing cellulose and water, heating, and stirring to form a cellulose gel aqueous solution;

(2) preparing a composite gel solution: dissolving a bleaching agent in the cellulose gel solution, stirring the solution at room temperature to obtain a composite gel solution;

(3) soaking the wood and bamboo materials in the composite gel aqueous solution, and washing the soaked wood and bamboo materials with anhydrous ethanol to obtain the wood and bamboo materials with controllable removal of lignin.

Preferably, in step (1), the mass concentration of cellulose in the cellulose gel aqueous solution is 0.1-10%.

Preferably, in step (1), the heating temperature is 70-90°C.

Preferably, in step (1), the cellulose is one or more of cellulose nanofibers, cellulose nanocrystals, hydroxyethyl cellulose, and hydroxypropyl cellulose.

Preferably, in step (2), the volume fraction of the bleaching agent in the composite gel aqueous solution is 5-70%.

Preferably, in step (2), the bleaching agent is one or more of sodium hypochlorite, hydrogen peroxide, and sodium chlorite.

The cellulose gel aqueous composite bleaching agent can make full use of the high water absorption properties of cellulose itself and the rich network structure it forms, limit the contact speed between the bleaching agent and wood and bamboo materials, and thus controllably remove lignin from the surface to the inside, thereby achieving controllable bleaching of wood and bamboo materials.

Beneficial effects of the present invention:

The method for controllable and orderly removal of lignin of the present invention effectively solves the technical problem that traditional bleaching agents cannot achieve controllable bleaching, is applicable to any wood and bamboo biomass materials, and can achieve controllable and orderly bleaching of any thickness layer of wood and bamboo from the surface to the inside, providing technical guarantee for the precise functionalization of the surface of wood and bamboo materials.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1: Distribution curve from the wood surface to the inner thickness at different bleaching times.

Detailed ways

It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

As described in the background technology, in order to solve the technical problem that the existing bleaching method is difficult to controllably remove lignin in a layer of any thickness on the surface, based on this, the present invention provides a method for controllably removing lignin in wood and bamboo materials, comprising the following steps:

(1) Preparing a cellulose gel aqueous solution: mixing cellulose with water, heating to 70-90° C., and stirring evenly to prepare a cellulose gel aqueous solution, wherein the mass concentration of cellulose in the cellulose gel aqueous solution is 0.1-10%, and the cellulose is one or more of cellulose nanofibers, cellulose nanocrystals, hydroxyethyl cellulose, and hydroxypropyl cellulose.

(2) preparing a composite gel solution: dissolving a bleaching agent in a cellulose gel solution to obtain a composite gel solution, wherein the volume fraction of the bleaching agent in the composite gel solution is 5-70%, and the bleaching agent is one or more of sodium hypochlorite, hydrogen peroxide, and sodium chlorite.

(3) soaking the wood and bamboo materials in the composite gel aqueous solution, and washing the soaked wood and bamboo materials with anhydrous ethanol to obtain the wood and bamboo materials with controllable removal of lignin.

In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below in conjunction with specific embodiments.

The test materials used in the examples of the present invention are all conventional test materials in the art and can be purchased through commercial channels.

Example 1

A method for controllably removing lignin from wood and bamboo materials comprises the following steps:

(1) preparing a cellulose gel aqueous solution: mixing hydroxyethyl cellulose with water, heating to 80° C., and stirring evenly to prepare a cellulose gel aqueous solution with a mass fraction of 5%, which is transparent and viscous;

(2) preparing a cellulose/bleaching agent composite gel solution: adding a NaClO stock solution accounting for 20% of the volume of the gel solution to the hydroxyethyl cellulose gel solution obtained in step (1), stirring the mixture at room temperature to obtain a hydroxyethyl cellulose/NaClO composite gel solution;

(3) Place the wood and bamboo material on top of the composite gel solution so that the lower surface of the wood and bamboo material just contacts the gel solution and fixes this state. At this time, the lower surface will be bleached in an orderly manner at a rate of 0.2 mm/h at room temperature; after 5 hours of bleaching, the thickness of the wood surface layer that has been delignined (i.e., bleached) is about 1.0 mm. The thickness of the delignified layer can be determined by calculating the bleaching time.

The soaked wood and bamboo materials are cleaned with anhydrous ethanol to remove the residual bleaching agent inside, and finally the wood and bamboo materials with controllable removal of lignin are prepared.

Example 2

A method for controllably removing lignin from wood and bamboo materials comprises the following steps:

(1) preparing a cellulose gel aqueous solution: mixing nanocellulose with water, heating to 80° C., and stirring evenly to prepare a cellulose gel aqueous solution with a mass fraction of 1%, which is transparent and viscous;

(2) preparing a cellulose/bleaching agent composite gel solution: adding a NaClO stock solution accounting for 30% of the volume of the gel solution to the nanocellulose gel solution obtained in step (1), stirring evenly at room temperature to prepare a nanocellulose/NaClO composite gel solution;

(3) placing the wood and bamboo material on the composite gel solution so that the lower surface of the wood and bamboo material just contacts the gel solution and fixes the state, at which time the lower surface will be bleached in an orderly manner at a speed of 0.15 mm/h at room temperature;

The soaked wood and bamboo materials are cleaned with anhydrous ethanol to remove the residual bleaching agent inside, and finally the wood and bamboo materials with controllable removal of lignin are prepared.

Example 3

A method for controllably removing lignin from wood and bamboo materials comprises the following steps:

(1) preparing a cellulose gel aqueous solution: mixing nanocellulose, hydroxypropyl cellulose and water, heating to 80° C., stirring evenly, and preparing a composite cellulose gel aqueous solution with a mass fraction of 3%, which is transparent and viscous; wherein the nanocellulose accounts for 1% and the hydroxypropyl cellulose accounts for 2%;

(2) preparing a cellulose/bleaching agent composite gel solution: adding a hydrogen peroxide stock solution accounting for 40% of the volume of the gel solution to the composite cellulose gel solution obtained in step (1), stirring at room temperature to obtain a mixed cellulose/hydrogen peroxide composite gel solution;

(3) placing the wood and bamboo material on top of the composite gel solution so that the lower surface of the wood and bamboo material just contacts the gel solution and fixes this state. At this time, the lower surface will be bleached in an orderly manner at a rate of 0.1 mm/h at room temperature; by calculating the bleaching time, the thickness of the delignified layer can be determined;

The soaked wood and bamboo materials are cleaned with anhydrous ethanol to remove the residual bleaching agent inside, and finally the wood and bamboo materials with controllable removal of lignin are prepared.

Comparative Example 1

A method for removing lignin from wood and bamboo materials comprises the following steps:

(1) Prepare a 20% by volume NaClO aqueous solution and stir evenly at room temperature;

(2) Place the wood and bamboo material on top of the NaClO solution so that the lower surface of the wood and bamboo material just touches the NaClO solution and fixes this state. At this time, the lower surface will bleach in an uncontrollable manner at room temperature. The bleaching thickness can reach 1 to 2 mm or even greater than 3 mm within 1 hour. This is related to the anisotropic structure of the wood surface. It is greatly affected by the difference in the surface microstructure of the wood, making it difficult to controllably and orderly bleach lignin.

The soaked wood and bamboo materials are cleaned with anhydrous ethanol to remove the residual bleach inside, and finally the wood and bamboo materials with uncontrollable removal of lignin are prepared.

Experimental example

The distribution of lignin in the thickness direction of the wood in Example 1 after bleaching for 0.5 h, 0.7 h and 1.5 h was tested using a laser confocal microscope at a laser wavelength of 405 nm.

As shown in Figure 1, in the curve from left to right in the thickness direction of the wood, the fluorescence intensity reflected by lignin has obvious differences; after 0.5h of bleaching, about 0.1mm of lignin was removed from left to right in the thickness direction, and the acid-insoluble lignin content decreased by 3.7%; after 0.7h of bleaching, about 0.14mm of lignin was removed, and the acid-insoluble lignin content decreased by 5.1%; after 1.5h of bleaching, about 0.3mm of lignin was removed from left to right in the thickness direction, and the acid-insoluble lignin content decreased by 8.3%. It can be seen that under this condition, the lignin on the wood surface can be removed in an orderly manner, and the bleaching thickness can be controlled and customized.

The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (1)

1. A method for controllably removing lignin from wood and bamboo materials, comprising the following steps: (1) preparing a cellulose gel aqueous solution: mixing hydroxyethyl cellulose with water, heating to 80° C., and stirring evenly to prepare a cellulose gel aqueous solution with a mass fraction of 5%, which is transparent and viscous; (2) preparing a composite gel solution: adding a NaClO stock solution accounting for 20% of the volume of the gel solution to the hydroxyethyl cellulose gel solution obtained in step (1), stirring evenly at room temperature to prepare a hydroxyethyl cellulose/NaClO composite gel solution; (3) The wood and bamboo materials are placed on top of the composite gel solution so that the lower surface of the wood and bamboo materials just contacts the gel solution and the state is fixed. At this time, the lower surface will be bleached in an orderly manner at a rate of 0.2 mm/h at room temperature; after 0.5 h of bleaching, 0.1 mm of lignin is removed from left to right in the thickness direction, and the acid-insoluble lignin content is reduced by 3.7%; after 0.7 h of bleaching, 0.14 mm of lignin is removed, and the acid-insoluble lignin content is reduced by 5.1%; after 1.5 h of bleaching, 0.3 mm of lignin is removed from left to right in the thickness direction, and the acid-insoluble lignin content is reduced by 8.3%; The soaked wood and bamboo materials are washed with anhydrous ethanol to prepare wood and bamboo materials with controllable removal of lignin.