1 Introduction
At present, the main raw material used in the preparation of cellulose ether is cotton, and its output is declining, and the price is also rising;
Moreover, commonly used etherifying agents such as chloroacetic acid (highly toxic) and ethylene oxide (carcinogenic) are also more harmful to the human body and the environment. Book
In this chapter, the pine cellulose with a relative purity of more than 90% extracted in the second chapter is used as the raw material, and sodium chloroacetate and 2-chloroethanol are used as substitutes.
Using highly toxic chloroacetic acid as etherifying agent, anionic carboxymethyl cellulose (CMC), non-ionic hydroxyethyl cellulose were prepared.
Cellulose (HEC) and mixed hydroxyethyl carboxymethyl cellulose (HECMC) three cellulose ethers. single factor
The preparation techniques of three cellulose ethers were optimized by means of experiments and orthogonal experiments, and the synthesized cellulose ethers were characterized by FT-IR, XRD, H-NMR, etc.
Fundamentals of cellulose etherification
The principle of cellulose etherification can be divided into two parts. The first part is the alkalization process, that is, during the alkalization reaction of cellulose,
Evenly dispersed in NaOH solution, pine cellulose swells violently under the action of mechanical stirring, and with the expansion of water
A large amount of NaOH small molecules penetrated into the interior of pine cellulose, and reacted with the hydroxyl groups on the ring of the glucose structural unit,
Generates alkali cellulose, the active center of the etherification reaction.
The second part is the etherification process, that is, the reaction between the active center and sodium chloroacetate or 2-chloroethanol under alkaline conditions, resulting in
At the same time, the etherifying agent sodium chloroacetate and 2-chloroethanol will also produce a certain degree of water under alkaline conditions.
The side reactions are resolved to generate sodium glycolate and ethylene glycol, respectively.
2 Concentrated alkali decrystallization pretreatment of pine cellulose
First, prepare a certain concentration of NaOH solution with deionized water. Then, at a certain temperature, 2g of pine fiber
The vitamin is dissolved in a certain volume of NaOH solution, stirred for a period of time, and then filtered for use.
Instrument Model Manufacturer
Precision pH Meter
Collector type constant temperature heating magnetic stirrer
Vacuum drying oven
Electronic balance
Circulating water type multi-purpose vacuum pump
Fourier Transform Infrared Spectrometer
X-ray diffractometer
Nuclear Magnetic Resonance Spectrometer
Hangzhou Aolilong Instrument Co., Ltd.
Hangzhou Huichuang Instrument Equipment Co., Ltd.
Shanghai Jinghong Experimental Equipment Co., Ltd.
METTLER TOLEDO Instruments (Shanghai) Co., Ltd.
Hangzhou David Science and Education Instrument Co., Ltd.
American Thermo Fisher Co., Ltd.
American Thermoelectric Switzerland ARL Company
Swiss company BRUKER
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Preparation of CMCs
Using pine wood alkali cellulose pretreated by concentrated alkali decrystallization as raw material, using ethanol as solvent and using sodium chloroacetate as etherification
CMC with higher DS was prepared by adding alkali twice and etherifying agent twice. Add 2g of pine wood alkali cellulose into the four-necked flask, then add a certain volume of ethanol solvent, and stir well for 30min
about, so that the alkali cellulose is fully dispersed. Then add a certain amount of alkali agent and sodium chloroacetate to react for a period of time at a certain etherification temperature
After time, a second addition of alkaline agent and sodium chloroacetate followed by etherification for a period of time. After the reaction is over, cool down and cool down, then
Neutralize with an appropriate amount of glacial acetic acid, then suction filter, wash and dry.
Preparation of HECs
Using pine wood alkali cellulose pretreated with concentrated alkali decrystallization as raw material, ethanol as solvent and 2-chloroethanol as etherification
The HEC with higher MS was prepared by adding alkali twice and etherifying agent twice. Add 2g of pine wood alkali cellulose into a four-necked flask, and add a certain volume of 90% (volume fraction) ethanol, stir
Stir for a period of time to fully disperse, then add a certain amount of alkali, and slowly heat up, add a certain volume of 2-
Chloroethanol, etherified at constant temperature for a period of time, and then added the remaining sodium hydroxide and 2-chloroethanol to continue etherification for a period of time. treat
After the reaction is completed, neutralize with a certain amount of glacial acetic acid, and finally filter with a glass filter (G3), wash, and dry.
Preparation of HEMCC
Using the HEC prepared in 3.2.3.4 as the raw material, ethanol as the reaction medium, and sodium chloroacetate as the etherifying agent to prepare
HECMC. The specific process is: take a certain amount of HEC, put it in a 100 mL four-necked flask, and then add a certain amount of volume
90% ethanol, mechanically stir for a period of time to make it fully dispersed, add a certain amount of alkali after heating, and slowly add
Sodium chloroacetate, the etherification at constant temperature ends after a period of time. After the reaction is completed, neutralize it with glacial acetic acid to neutralize it, then use a glass filter (G3)
After suction filtration, washing and drying.
Purification of cellulose ethers
In the preparation process of cellulose ether, some by-products are often produced, mainly the inorganic salt sodium chloride and some other
impurities. In order to improve the quality of cellulose ether, simple purification was carried out on the obtained cellulose ether. because they are in water
There are different solubility, so the experiment uses a certain volume fraction of hydrated ethanol to purify the prepared three cellulose ethers.
change.
Place the cellulose ether sample prepared with a certain quality in a beaker, add a certain amount of 80% ethanol that has been preheated to 60 ℃ ~ 65 ℃, and maintain mechanical stirring at 60 ℃ ~ 65 ℃ on a constant temperature heating magnetic stirrer for 10 ℃. min. Take the supernatant to dry
In a clean beaker, use silver nitrate to check for chloride ions. If there is a white precipitate, filter it through a glass filter and take the solid
Repeat the previous steps for the body part, until the filtrate after adding 1 drop of AgNO3 solution has no white precipitate, that is, the purification and washing are completed.
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into (mainly to remove the reaction by-product NaCl). After suction filtration, drying, cooling to room temperature and weighing.
mass, g.
Test and Characterization Methods for Cellulose Ethers
Determination of Degree of Substitution (DS) and Molar Degree of Substitution (MS)
Determination of DS: First, weigh 0.2 g (accurate to 0.1 mg) of the purified and dried cellulose ether sample, dissolve it in
80mL of distilled water, stirred in a constant temperature water bath at 30℃~40℃ for 10min. Then adjust with sulfuric acid solution or NaOH solution
pH of the solution until the pH of the solution is 8. Then in a beaker equipped with a pH meter electrode, use a standard solution of sulfuric acid
To titrate, under stirring conditions, observe the pH meter reading while titrating, when the pH value of the solution is adjusted to 3.74,
The titration ends. Note the volume of sulfuric acid standard solution used at this time.
Generation:
The sum of the upper proton numbers and the hydroxyethyl group
The ratio of the number of upper protons; I7 is the mass of the methylene group on the hydroxyethyl group
Intensity of the proton resonance peak; is the intensity of the proton resonance peak of 5 methine groups and one methylene group on the cellulose glucose unit
Sum.
The test methods described for the infrared characterization testing of the three cellulose ethers CMC, HEC and HEECMC
Law
3.2.4.3 XRD test
X-ray Diffraction Analysis Characterization Test of Three Cellulose Ethers CMC, HEC and HEECMC
the test method described.
3.2.4.4 Testing of H-NMR
The H NMR spectrometer of HEC was measured by Avance400 H NMR spectrometer produced by BRUKER.
Using deuterated dimethyl sulfoxide as solvent, the solution was tested by liquid hydrogen NMR spectroscopy. The test frequency was 75.5MHz.
Warm, the solution is 0.5mL.
3.3 Results and Analysis
3.3.1 Optimization of CMC preparation process
Using the pine cellulose extracted in the second chapter as the raw material, and using sodium chloroacetate as the etherifying agent, the method of single factor experiment was adopted,
The preparation process of CMC was optimized, and the initial variables of the experiment were set as shown in Table 3.3. The following is the HEC preparation process
In art, the analysis of various factors.
Table 3.3 Initial Factor Values
Factor Initial value
Pretreatment alkalizing temperature/℃ 40
Pretreatment alkalizing time/h 1
Pretreatment solid-liquid ratio/(g/mL) 1:25
Pretreatment lye concentration/% 40
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The first stage etherification temperature/℃ 45
First-stage etherification time/h 1
Second stage etherification temperature/℃ 70
Second stage etherification time/h 1
Base dosage in etherification stage/g 2
Amount of etherifying agent in etherification stage/g 4.3
Etherified solid-liquid ratio/(g/mL) 1:15
3.3.1.1 Influence of various factors on CMC substitution degree in pretreatment alkalization stage
1. The effect of pretreatment alkalization temperature on the substitution degree of CMC
In order to consider the effect of pretreatment alkalization temperature on the degree of substitution in the obtained CMC, in the case of fixing other factors as initial values,
Under the conditions, the effect of pretreatment alkalization temperature on CMC substitution degree is discussed, and the results are shown in Fig.
Pretreatment alkalizing temperature/℃
Effect of pretreatment alkalizing temperature on CMC substitution degree
It can be seen that the degree of substitution of CMC increases with the increase of the pretreatment alkalization temperature, and the alkalization temperature is 30 °C.
The above degrees of substitution decrease with increasing temperature. This is because the alkalizing temperature is too low, and the molecules are less active and unable to
Effectively destroy the crystalline area of cellulose, which makes it difficult for the etherifying agent to enter the interior of the cellulose in the etherification stage, and the degree of reaction is relatively high.
low, resulting in a lower degree of product substitution. However, the alkalization temperature should not be too high. As the temperature increases, under the action of high temperature and strong alkali,
Cellulose is prone to oxidative degradation, and the degree of substitution of the product CMC decreases.
2. Influence of pretreatment alkalinization time on CMC substitution degree
Under the condition that the pretreatment alkalization temperature is 30 °C and other factors are the initial values, the effect of pretreatment alkalization time on CMC is discussed.
The effect of substitution. Degree of substitution
Pretreatment alkalizing time/h
Effect of pretreatment alkalinization time on CMC substitution degree
The bulking process itself is relatively rapid, but the alkali solution needs a certain diffusion time in the fiber.
It can be seen that when the alkalization time is 0.5-1.5h, the substitution degree of the product increases with the increase of alkalization time.
The degree of substitution of the product obtained was the highest when the time was 1.5h, and the degree of substitution decreased with the increase of time after 1.5h. This can
It may be because at the beginning of alkalization, with the prolongation of alkalization time, the infiltration of alkali to cellulose is more sufficient, so that the fiber
The prime structure is more relaxed, increasing the etherifying agent and the active medium
Post time: Apr-26-2024