Disclosure of Invention
Based on the above, in order to solve the problems that the preparation of the nano-cellulose in the prior art is not environment-friendly enough, equipment is easy to corrode, and the nano-cellulose is oxidized unevenly, the invention provides a preparation method of oxidized nano-cellulose, which has the following specific technical scheme:
a preparation method of oxidized nano-cellulose comprises the following steps:
crushing a cellulose raw material into fragments to obtain cellulose fragments;
adding cellulose fragments into an aqueous solution containing citric acid, then adding a solution containing polyalcohol and sulfuric acid, uniformly stirring, heating to 95-100 ℃, and standing for reaction for 3-5 hours to obtain a cellulose suspension;
carrying out suction filtration on the cellulose suspension under a vacuum condition, and recovering the citric acid to obtain cellulose pulp;
washing cellulose pulp with deionized water, and adjusting the pH value of the cellulose pulp to be neutral by using alkali liquor;
adding water into cellulose pulp, adjusting the solid content of the cellulose pulp to be 1-5% by mass, adding NaBr and TEMPO under the stirring condition, dropwise adding NaClO solution after uniform stirring, and controlling the pH of a reaction system to be 9.5-10.0 under the real-time monitoring of precise pH;
when the pH of the reaction system is stabilized at 9.5-10.0 within 15min, adding ethanol, and stopping the reaction to obtain cellulose pulp;
and adding deionized water into the cellulose pulp, carrying out suction filtration under a vacuum condition, and then washing until the pH value is neutral to obtain the oxidized nano cellulose.
Preferably, the cellulose fragments are less than 10mm in diameter and length.
Preferably, the polyol is one of ethylene glycol and glycerol.
Preferably, the content of sulfuric acid in the sulfuric acid solution is 30% by mass.
Preferably, the alkali content in the alkali liquor is 0.5-10% by mass percent.
Preferably, the addition amount of NaBr is as follows: 0.08g to 0.15g of NaBr was added to 1g of a cellulose raw material.
Preferably, the amount of TEMPO added is: 1g of cellulose raw material is added with 0.01g to 0.02g of TEMPO.
Preferably, the addition amount of the NaClO is as follows: 5mmol-12mmol of NaClO was added to 1g of the cellulose raw material.
Preferably, the citric acid in the citric acid aqueous solution accounts for 65-85% by mass.
Preferably, the cellulose fragments account for 3-10% of the aqueous solution of citric acid by mass percent.
In the scheme, the polyhydric alcohol is added under the catalysis of sulfuric acid, so that the reaction efficiency can be ensured, and side reactions in the reaction process can be inhibited; the preparation method disclosed by the invention is environment-friendly, equipment is not easy to corrode, the cost is lower, the yield of the cellulose in unit time can be ensured, and the production cost is further reduced; in addition, sodium hypochlorite solution is added to enable the reaction to be smooth, so that the oxidation of the nano-cellulose is more uniform, and oxidized nano-cellulose with better uniformity and quality is obtained.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to embodiments thereof. It should be understood that the detailed description and specific examples, while indicating the scope of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The preparation method of the oxidized nano-cellulose in one embodiment of the invention comprises the following steps:
crushing a cellulose raw material into fragments to obtain cellulose fragments;
adding cellulose fragments into an aqueous solution containing citric acid, then adding a solution containing polyalcohol and sulfuric acid, uniformly stirring, heating to 95-100 ℃, and standing for reaction for 3-5 hours to obtain a cellulose suspension;
carrying out suction filtration on the cellulose suspension under a vacuum condition, and recovering the citric acid to obtain cellulose pulp;
washing cellulose pulp with deionized water, and adjusting the pH value of the cellulose pulp to be neutral by using alkali liquor;
adding water into cellulose pulp, adjusting the solid content of the cellulose pulp to be 1-5% by mass, adding NaBr and TEMPO under the stirring condition, dropwise adding NaClO solution after uniform stirring, and controlling the pH of a reaction system to be 9.5-10.0 under the real-time monitoring of precise pH;
after the pH value of the reaction system is kept stable at 9.5-10.0 within 15min, adding ethanol, and stopping the reaction to obtain cellulose pulp;
and adding deionized water into the cellulose pulp, carrying out suction filtration under a vacuum condition, and washing until the pH value is neutral to obtain the oxidized nano cellulose.
In one embodiment, the preparation method further comprises the following steps: adding a proper amount of water into the oxidized nano-cellulose to ensure that the solid content of the oxidized nano-cellulose in the solution is 0.5-2% by mass, and homogenizing under high pressure to obtain the oxidized nano-cellulose suspension.
In one embodiment, the cellulose chips are less than 10mm in diameter and length.
In one embodiment, the polyol is one of ethylene glycol and glycerol.
In one embodiment, the sulfuric acid solution contains 30% of sulfuric acid by mass.
In one embodiment, the alkali content in the alkali liquor is 0.5-10% by mass percent.
In one embodiment, the addition amount of NaBr is: 0.08g to 0.15g of NaBr is added to 1g of the cellulose raw material.
In one embodiment, TEMPO is added in an amount of: 0.01g-0.02g TEMPO is added to 1g cellulose raw material.
In one embodiment, the addition amount of the NaClO is as follows: 5mmol-12mmol NaClO is added to 1g of the cellulose raw material.
In one embodiment, the citric acid in the aqueous solution of citric acid is 65-85% by mass.
In one embodiment, the cellulose fragments comprise 3-10% by mass of the aqueous solution of citric acid.
In one embodiment, the cellulose raw material is one or more of microcrystalline cellulose, bagasse pulp, wood pulp, straw pulp, cotton pulp and bamboo pulp.
In one embodiment, the cellulose material is one of wood flour treated by alkali or acid bleaching, bamboo flour treated by alkali or acid bleaching, and cotton fiber treated by alkali or acid bleaching.
In one embodiment, the high-pressure homogenizing pressure is 50MPa-150 MPa.
In one embodiment, the high-pressure homogenization is performed 1-10 times.
In one embodiment, the addition amount of the polyol is 1-10% of the aqueous solution of citric acid by mass percent.
In one embodiment, the addition amount of the sulfuric acid solution is 1-10% of the citric acid aqueous solution according to mass percentage.
In one embodiment, the alkali solution is sodium hydroxide or potassium hydroxide solution.
In the scheme, the polyhydric alcohol is added under the catalysis of sulfuric acid, so that the reaction efficiency can be ensured, and side reactions in the reaction process can be inhibited; the preparation method disclosed by the invention is environment-friendly and low in cost, and can ensure the yield of the cellulose in unit time, thereby being beneficial to reducing the production cost; in addition, sodium hypochlorite solution is added to enable the reaction to be smooth, so that the oxidation of the nano-cellulose is more uniform, and oxidized nano-cellulose with better uniformity and quality is obtained.
Embodiments of the present invention will be described in detail below with reference to specific examples.
Example 1
A preparation method of oxidized nano-cellulose comprises the following steps:
crushing the wood pulp board into wood pulp board fragments with the diameter and the length of less than 10mm by a crusher;
adding wood pulp board fragments into an aqueous solution of citric acid with the mass percent content of 80%, wherein the mass of the wood pulp board fragments accounts for 8% of the mass of the aqueous solution of the citric acid, adding glycol accounting for 10% of the mass of the aqueous solution of the citric acid, finally adding a sulfuric acid solution accounting for 5% of the mass of the aqueous solution of the citric acid, wherein the solid content of the added sulfuric acid solution accounts for 30% by mass, uniformly stirring, heating to 95 ℃, standing and reacting for 3 hours to obtain a cellulose suspension;
carrying out suction filtration on the cellulose suspension under a vacuum condition, and evaporating and recrystallizing filtrate at normal temperature or carrying out reduced pressure distillation to recover citric acid to obtain cellulose pulp;
washing cellulose pulp with deionized water, adjusting the pH value to be neutral by using a sodium hydroxide solution with the mass percent of 0.5%, sampling, measuring the solid content and calculating the cellulose yield;
adding a proper amount of water into cellulose pulp until the solid content is 3 percent by mass, continuously stirring the cellulose pulp by using a stirrer at room temperature, and sequentially adding NaBr (0.1 g.g) into the pulp-1Cellulose feedstock), TEMPO (0.015g.g-1Cellulose raw material), stirring uniformly, and then gradually dropwise adding NaClO (5mmol-1Cellulose feedstock), the entire reaction process was monitored in real time with a precision pH meter by adding 0.5mol.l-1NaOH solution controls the pH of the reaction system to be 9.5-10.0, and ethanol (1mL. g) is used when the pH of the reaction system is 9.5-10.0 and is not changed within 15min-1Cellulose raw material) and filtering the reaction solution by using a large amount of deionized water under a vacuum condition, and washing the reaction solution until the pH value is neutral to obtain oxidized nano-cellulose;
adding a proper amount of water into the oxidized nano-cellulose to ensure that the solid content of the oxidized nano-cellulose in the solution is 2% by mass, and homogenizing for 1 time under the homogenizing pressure of 100Mpa to obtain the oxidized nano-cellulose suspension.
Example 2:
a preparation method of oxidized nano-cellulose comprises the following steps:
crushing the straw pulp board into straw pulp board fragments with the diameter and the length of less than 10mm by a crusher;
adding straw pulp board fragments into a citric acid aqueous solution with the mass percentage content of 65%, wherein the mass of the straw pulp board fragments accounts for 10% of the mass of the citric acid aqueous solution, adding ethylene glycol with the mass of 1% of the mass of the citric acid aqueous solution, finally adding a sulfuric acid solution with the mass of 1% of the mass of the citric acid aqueous solution, wherein the solid content of the added sulfuric acid solution is 30%, uniformly stirring, heating to 100 ℃, standing and reacting for 5 hours to obtain a cellulose suspension;
carrying out suction filtration on the cellulose suspension under a vacuum condition, and evaporating and recrystallizing filtrate at normal temperature or carrying out reduced pressure distillation to recover citric acid to obtain cellulose pulp;
washing cellulose pulp with deionized water, adjusting the pH value to be neutral by using a sodium hydroxide solution with the mass percent of 5%, sampling, measuring the solid content and calculating the cellulose yield;
adding a proper amount of water into cellulose pulp until the solid content is 5 percent by mass, continuously stirring the cellulose pulp by using a stirrer at room temperature, and sequentially adding NaBr (0.2 g.g) into the pulp-1Cellulose feedstock), TEMPO (0.01g.g-1Cellulose raw material), stirring uniformly, and then gradually dropwise adding NaClO (10mmol-1Cellulose feedstock), the entire reaction process was monitored in real time with a precision pH meter by adding 0.5mol.l-1NaOH solution controls the pH of the reaction system to be 9.5-10.0, and ethanol (1mL. g) is used when the pH of the reaction system is 9.5-10.0 and is not changed within 15min-1Cellulose raw material) and filtering the reaction solution by using a large amount of deionized water under a vacuum condition, and washing the reaction solution until the pH value is neutral to obtain oxidized nano-cellulose;
adding a proper amount of water into the oxidized nano-cellulose to ensure that the solid content of the oxidized nano-cellulose in the solution is 1% by mass, and homogenizing for 10 times under the homogenizing pressure of 50Mpa to obtain the oxidized nano-cellulose suspension.
Example 3:
a preparation method of oxidized nano-cellulose comprises the following steps:
crushing the bamboo powder treated by the alkali liquor into bamboo powder fragments with the diameter and the length of less than 10mm by using a crusher;
adding bamboo powder chips into a citric acid aqueous solution with the mass percent of 75%, adding ethylene glycol with the mass percent of 5% of the citric acid aqueous solution into the bamboo powder chips, and finally adding a sulfuric acid solution with the mass percent of 5% of the citric acid aqueous solution into the bamboo powder chips, wherein the solid content of the added sulfuric acid solution is 30%, uniformly stirring, heating to 100 ℃, standing and reacting for 4 hours to obtain a cellulose suspension;
carrying out suction filtration on the cellulose suspension under a vacuum condition, and evaporating and recrystallizing filtrate at normal temperature or carrying out reduced pressure distillation to recover citric acid to obtain cellulose pulp;
washing cellulose pulp with deionized water, adjusting the pH value to be neutral by using a sodium hydroxide solution with the mass percent of 5%, sampling, measuring the solid content and calculating the cellulose yield;
adding a proper amount of water into cellulose pulp until the solid content is 5 percent by mass, continuously stirring the cellulose pulp by using a stirrer at room temperature, and sequentially adding NaBr (0.2 g.g) into the pulp-1Cellulose feedstock), TEMPO (0.01g.g-1Cellulose raw material), stirring uniformly, and then gradually dropwise adding NaClO (7mmol-1Cellulose feedstock), the entire reaction process was monitored in real time with a precision pH meter by adding 1mol-1NaOH solution controls the pH of the reaction system to be 9.5-10.0, and ethanol (1mL. g) is used when the pH of the reaction system is 9.5-10.0 and is not changed within 15min-1Cellulose raw material) and filtering the reaction solution by using a large amount of deionized water under a vacuum condition, and washing the reaction solution until the pH value is neutral to obtain oxidized nano-cellulose;
adding a proper amount of water into the oxidized nano-cellulose to ensure that the solid content of the oxidized nano-cellulose in the solution is 1% by mass, and homogenizing for 3 times under the homogenizing pressure of 100Mpa to obtain the oxidized nano-cellulose.
Example 4:
a preparation method of oxidized nano-cellulose comprises the following steps:
crushing the cotton fiber treated by the alkali liquor into cotton fiber fragments with the diameter and the length of less than 10mm by using a crusher;
adding cotton fiber fragments into an aqueous solution of citric acid with the mass percent of 85%, adding glycol with the mass percent of 6% of the aqueous solution of citric acid, finally adding a sulfuric acid solution with the mass percent of 7% of the aqueous solution of citric acid, stirring uniformly, heating to 98 ℃, standing and reacting for 4 hours to obtain a cellulose suspension;
carrying out suction filtration on the cellulose suspension under a vacuum condition, and evaporating and recrystallizing filtrate at normal temperature or carrying out reduced pressure distillation to recover citric acid to obtain cellulose pulp;
washing cellulose pulp with deionized water, adjusting the pH value to be neutral by using a sodium hydroxide solution with the mass percent of 5%, sampling, measuring the solid content and calculating the cellulose yield;
adding a proper amount of water into cellulose pulp until the solid content is 1 percent by mass, continuously stirring the cellulose pulp by using a stirrer at room temperature, and sequentially adding NaBr (0.2 g.g) into the pulp-1Cellulose feedstock), TEMPO (0.02 g.g)-1Cellulose raw material), stirring uniformly, and then gradually dropwise adding NaClO (12mmol-1Cellulose feedstock), the entire reaction process was monitored in real time with a precision pH meter by adding 2mol-1NaOH solution controls the pH of the reaction system to be 9.5-10.0, and ethanol (1mL. g) is used when the pH of the reaction system is 9.5-10.0 and is not changed within 15min-1Cellulose raw material) and filtering the reaction solution by using a large amount of deionized water under a vacuum condition, and washing the reaction solution until the pH value is neutral to obtain oxidized nano-cellulose;
adding a proper amount of water into the oxidized nano-cellulose to ensure that the solid content of the oxidized nano-cellulose in the solution is 1% by mass, and homogenizing for 5 times under the homogenizing pressure of 80Mpa to obtain the oxidized nano-cellulose suspension.
Comparative example 1:
a preparation method of oxidized nano-cellulose comprises the following steps:
crushing the wood pulp board into wood pulp board fragments with the diameter and the length of less than 10mm by a crusher;
adding wood pulp board fragments into an aqueous solution of citric acid with the mass percentage content of 80%, wherein the mass of the wood pulp board fragments accounts for 8% of the mass of the aqueous solution of the citric acid, adding a sulfuric acid solution with the mass of 5% of the mass of the aqueous solution of the citric acid, wherein the solid content of the added sulfuric acid solution accounts for 30% by mass, uniformly stirring, heating to 95 ℃, standing and reacting for 3 hours, and obtaining a cellulose suspension;
carrying out suction filtration on the cellulose suspension under a vacuum condition, and evaporating and recrystallizing filtrate at normal temperature or carrying out reduced pressure distillation to recover citric acid to obtain cellulose pulp;
washing cellulose pulp with deionized water, adjusting the pH value to be neutral by using a sodium hydroxide solution with the mass percent of 0.5%, sampling, measuring the solid content and calculating the cellulose yield;
adding a proper amount of water into cellulose pulp until the solid content is 3 percent by mass, continuously stirring the cellulose pulp by using a stirrer at room temperature, and sequentially adding NaBr (0.1 g.g) into the pulp-1Cellulose feedstock), TEMPO (0.015g.g-1Cellulose raw material), stirring uniformly, and then gradually dropwise adding NaClO (5mmol-1Cellulose feedstock), the entire reaction process was monitored in real time with a precision pH meter by adding 0.5mol.l-1NaOH solution controls the pH of the reaction system to be 9.5-10.0, and ethanol (1mL. g) is used when the pH of the reaction system is 9.5-10.0 and is not changed within 15min-1Cellulose raw material) and filtering the reaction solution by using a large amount of deionized water under a vacuum condition, and washing the reaction solution until the pH value is neutral to obtain oxidized nano-cellulose;
adding a proper amount of water into the oxidized nano-cellulose to ensure that the solid content of the oxidized nano-cellulose in the solution is 2% by mass, and homogenizing for 1 time under the homogenizing pressure of 100Mpa to obtain the oxidized nano-cellulose suspension.
The cellulose pulps obtained in the preparation process of examples 1 to 4 and comparative example 1 were examined, while the resulting oxidized nanocellulose suspensions were examined.
Wherein, the content determination of carboxylic acid: 0.1g of absolutely dry cellulose pulp or oxidized nano-cellulose suspension is uniformly dispersed in 55mL of deionized water, 5mL of KCl solution with the concentration of about 0.01mol/L is added, and after uniform dispersion, the pH value of the suspension is adjusted to 2.5-3.0 by using 0.1mol/L HCl solution. And (3) dripping 0.05mol/LNaOH standard solution into the solution successively at a dripping rate of 0.1mL/min, recording the conductivity change of each dripping by using a conductivity meter, drawing a curve graph according to data, and calculating the content of carboxylic acid according to the difference value of the V2 value at the end point of titration and the V1 value at the initial titration in the curve graph according to the following formula:
carboxylic acid content: [ COOH]=(CNaOHV2-CNaOHV1)/m(mmol/g)
The results obtained are shown in table 1 below.
Table 1:
as can be seen from the data analysis in Table 1 and the analysis in conjunction with FIGS. 1-3, the carboxylic acid content of the oxidized nanocellulose prepared by the present invention is high, specifically 0.8-1.5mmol/g, while the carboxylic acid content of the oxidized nanocellulose obtained in comparative example 1 without the treatment with the polyhydric alcohol is 0.2, which is significantly different from and inferior to examples 1-4; the oxidized nanocellulose prepared by the method is large in diameter and long in length, but the oxidized nanocellulose in comparative example 1 is degraded, so that the oxidized nanocellulose large in diameter and long in length cannot be obtained; the oxidized nanocelluloses prepared in examples 1 to 4 were high in yield and colorless and transparent oxidized nanocellulose was obtained, but the oxidized nanocellulose prepared in comparative example 1 was low in yield, dark in color, and easily oxidized into a darker product.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.