Using straw cellulose as raw material, it was modified by etherification. Through the single factor and rotation test, the optimal conditions for the preparation of carboxymethyl cellulose were determined to be: etherification time 100min, etherification temperature 70℃, NaOH dosage 3.2g and monochloroacetic acid dosage 3.0g, the maximum substitution The degree is 0.53.
Key words: CMC cellulose; monochloroacetic acid; etherification; modification
Carboxymethyl cellulose is the most produced and sold cellulose ether in the world. It is widely used in detergent, food, toothpaste, textile, printing and dyeing, paper making, petroleum, mining, medicine, ceramics, electronic components, rubber, Paints, pesticides, cosmetics, leather, plastics and oil drilling, etc., known as “industrial monosodium glutamate”. Carboxymethyl cellulose is a water-soluble cellulose ether derivative obtained by chemically modifying natural cellulose. Cellulose, the main raw material for the production of carboxymethyl cellulose, is one of the most abundant natural renewable resources on the earth, with an annual production of hundreds of billions of tons. my country is a large agricultural country and one of the countries with the most abundant straw resources. Straw has always been one of the main living fuels for rural residents. These resources have not been rationally developed for a long time, and less than 2% of agricultural and forestry wastes such as straw are used in the world every year. Rice is the main economic crop in Heilongjiang Province, with a planting area of more than 2 million hm2, an annual output of 14 million tons of rice, and 11 million tons of straw. Farmers generally burn them directly in the field as waste, which is not only a huge waste of natural resources, but also causes serious pollution to the environment. Therefore, realizing the resource utilization of straw is the need of the sustainable development strategy of agriculture.
1. Experimental materials and methods
1.1 Experimental materials and equipment
Straw cellulose, self-made in the laboratory; JJ～1 type electric mixer, Jintan Guowang Experimental Instrument Factory; SHZW2C type RS—A vacuum pump, Shanghai Pengfu Electromechanical Co., Ltd.; pHS-3C pH meter, Mettler-Toledo Co., Ltd.; DGG-9070A electric heating constant temperature drying oven, Beijing North Lihui Test Instrument Equipment Co., Ltd.; HITACHI-S ~ 3400N scanning electron microscope, Hitachi Instruments; ethanol; sodium hydroxide; chloroacetic acid, etc. (the above reagents are analytically pure).
1.2 Experimental method
1.2.1 Preparation of carboxymethyl cellulose
(1) The preparation method of carboxymethyl cellulose: Weigh 2 g of cellulose into a three-necked flask, add 2.8 g of NaOH, 20 mL of 75% ethanol solution, and soak in alkali in a constant temperature water bath at 25°C for 80 min. Stir with a mixer to combine well. During this process, cellulose reacts with alkaline solution to form alkali cellulose. In the etherification stage, add 10 mL of 75% ethanol solution and 3 g of chloroacetic acid to the three-necked flask reacted above, raise the temperature to 65-70° C., and react for 60 minutes. Add alkali for the second time, then add 0.6g NaOH to the above reaction flask to keep the temperature at 70°C, and the reaction time is 40min to obtain crude Na—CMC (sodium carboxymethylcellulose).
Neutralization and washing: add 1moL·L-1 hydrochloric acid, and neutralize the reaction at room temperature until pH=7~8. Then wash twice with 50% ethanol, then wash once with 95% ethanol, filter with suction, and dry at 80-90°C for 2 hours.
(2) Determination of the degree of sample substitution: acidity meter determination method: Weigh 0.2g (accurate to 0.1mg) of the purified and dried Na-CMC sample, dissolve it in 80mL distilled water, stir it electromagnetically for 10min, and adjust it with acid or alkali The solution brought the pH of the solution to 8. Then titrate the test solution with sulfuric acid standard solution in a beaker equipped with a pH meter electrode, and observe the indication of the pH meter while titrating until the pH is 3.74. Note down the volume of sulfuric acid standard solution used.
1.2.2 Single factor test method
(1) The effect of the amount of alkali on the degree of substitution of carboxymethyl cellulose: carry out alkalization at 25 ℃, alkali immersion for 80 minutes, the concentration in ethanol solution is 75%, control the amount of monochloroacetic acid reagent 3g, etherification temperature is 65 ~70°C, the etherification time was 100 minutes, and the amount of sodium hydroxide was changed for the test.
(2) The effect of the concentration of ethanol solution on the degree of substitution of carboxymethyl cellulose: the amount of fixed alkali is 3.2g, alkaline immersion in a constant temperature water bath at 25°C for 80min, the concentration of ethanol solution is 75%, the amount of monochloroacetic acid reagent is controlled at 3g, etherification The temperature is 65-70°C, the etherification time is 100min, and the concentration of the ethanol solution is changed for the experiment.
(3) The effect of the amount of monochloroacetic acid on the degree of substitution of carboxymethyl cellulose: fix at 25°C for alkalization, soak in alkali for 80 minutes, add 3.2g of sodium hydroxide to make the concentration of the ethanol solution 75%, ether The temperature is 65~70°C, the etherification time is 100min, and the amount of monochloroacetic acid is changed for experiment.
(4) Effect of etherification temperature on the degree of substitution of carboxymethyl cellulose: fix at 25°C for alkalization, soak in alkali for 80 minutes, add 3.2g of sodium hydroxide to make the concentration of ethanol solution 75%, etherification temperature The temperature is 65~70℃, the etherification time is 100min, and the experiment is carried out by changing the dosage of monochloroacetic acid.
(5) Effect of etherification time on the degree of substitution of carboxymethyl cellulose: fixed at 25°C for alkalization, added 3.2g of sodium hydroxide, and soaked in alkali for 80min to make the concentration of the ethanol solution 75%, and controlled monochlor The dosage of acetic acid reagent is 3g, the etherification temperature is 65~70°C, and the etherification time is changed for experiment.
1.2.3 Test plan and optimization of carboxymethyl cellulose
On the basis of the single factor experiment, a quadratic regression orthogonal rotation combined experiment with four factors and five levels was designed. The four factors are etherification time, etherification temperature, the amount of NaOH and the amount of monochloroacetic acid. The data processing uses SAS8.2 statistical software for data processing, which reveals the relationship between each influencing factor and the degree of substitution of carboxymethyl cellulose. inner law.
1.2.4 SEM analysis method
The dried powder sample was fixed on the sample stage with conductive glue, and after vacuum spraying gold, it was observed and photographed under a Hitachi-S-3400N Hitachi scanning electron microscope.
2. Results and analysis
2.1 Effect of single factor on degree of substitution of carboxymethyl cellulose
2.1.1 The effect of the amount of alkali on the degree of substitution of carboxymethyl cellulose
When NaOH3.2g was added to 2g cellulose, the substitution degree of the product was the highest. The amount of NaOH is reduced, which is not enough to form the neutralization of alkaline cellulose and etherification agent, and the product has a small degree of substitution and low viscosity. On the contrary, if the amount of NaOH is too much, the side reactions during the hydrolysis of chloroacetic acid will increase, the consumption of etherifying agent will increase, and the product viscosity will also decrease.
2.1.2 Effect of concentration of ethanol solution on degree of substitution of carboxymethyl cellulose
Part of the water in the ethanol solution exists in the reaction medium outside the cellulose, and the other part exists in the cellulose. If the water content is too large, CMC will swell in water to form jelly during etherification, resulting in very uneven reaction; if the water content is too small, the reaction will be difficult to proceed due to the lack of reaction medium. Generally, 80% ethanol is the most suitable solvent.
2.1.3 Effect of the dosage of monochloroacetic acid on the degree of substitution of carboxymethyl cellulose
The amount of monochloroacetic acid and sodium hydroxide is theoretically 1:2, but in order to move the reaction to the direction of generating CMC, ensure that there is a suitable free base in the reaction system, so that the carboxymethylation can proceed smoothly. For this reason, the method of excess alkali is adopted, that is, the molar ratio of acid and alkali substances is 1:2.2.
2.1.4 Effect of etherification temperature on degree of substitution of carboxymethyl cellulose
The higher the etherification temperature, the faster the reaction rate, but the side reactions are also accelerated. From the perspective of chemical balance, rising temperature is unfavorable to the formation of CMC, but if the temperature is too low, the reaction rate is slow and the utilization rate of etherifying agent is low. It can be seen that the optimum temperature for etherification is 70°C.
2.1.5 Effect of etherification time on degree of substitution of carboxymethyl cellulose
With the increase of etherification time, the degree of substitution of CMC increases, and the reaction speed is accelerated, but after a certain time, the side reactions increase and the degree of substitution decreases. When the etherification time is 100min, the degree of substitution is maximum.
2.2 Orthogonal test results and analysis of carboxymethyl groups
It can be seen from the variance analysis table that in the primary item, the four factors of etherification time, etherification temperature, the amount of NaOH and the amount of monochloroacetic acid have a very significant impact on the degree of substitution of carboxymethyl cellulose (p<0.01) . Among the interaction items, the interaction items of etherification time and the amount of monochloroacetic acid, and the interaction items of etherification temperature and the amount of monochloroacetic acid had a very significant effect on the degree of substitution of carboxymethyl cellulose (p<0.01). The order of influence of various factors on the degree of substitution of carboxymethyl cellulose was: etherification temperature>the amount of monochloroacetic acid>etherification time>the amount of NaOH.
After the analysis of the test results of the quadratic regression orthogonal rotation combination design, it can be determined that the optimal process conditions for carboxymethylation modification are: etherification time 100min, etherification temperature 70℃, NaOH dosage 3.2g and monochloroacetic acid The dosage is 3.0g, and the maximum degree of substitution is 0.53.
2.3 Microscopic performance characterization
The surface morphology of cellulose, carboxymethyl cellulose and cross-linked carboxymethyl cellulose particles was studied by scanning electron microscopy. The cellulose grows in a strip shape with a smooth surface; the edge of carboxymethyl cellulose is rougher than that of the extracted cellulose, and the cavity structure increases and the volume becomes larger. This is because the bundle structure becomes larger due to the swelling of carboxymethyl cellulose.
3. Conclusion
3.1 Preparation of carboxymethyl etherified cellulose The order of importance of the four factors affecting the degree of substitution of cellulose is: etherification temperature > monochloroacetic acid dosage > etherification time > NaOH dosage. The optimal process conditions of carboxymethylation modification are etherification time 100min, etherification temperature 70℃, NaOH dosage 3.2g, monochloroacetic acid dosage 3.0g, and maximum substitution degree 0.53.
3.2 The optimal technological conditions of carboxymethylation modification are: etherification time 100min, etherification temperature 70℃, NaOH dosage 3.2g, monochloroacetic acid dosage 3.0g, maximum substitution degree 0.53.