Analytical method for physicochemical properties of cellulose ether

The source, structure, properties and applications of cellulose ether were introduced. In view of the physicochemical property index test of cellulose ether industry standard, a refined or improved method was put forward, and its feasibility was analyzed through experiments.

Key words: cellulose ether; Physical and chemical properties; Analytical method; Experimental inquiry

Cellulose is the most abundant natural polymer compound in the world. A series of derivatives can be obtained by chemical modification of cellulose. Cellulose ether is the product of cellulose after alkalization, etherification, washing, purification, grinding, drying and other steps. The main raw materials of cellulose ether are cotton, kapok, bamboo, wood, etc., among which the cellulose content in cotton is the highest, up to 90 ~ 95%, is an ideal raw material for cellulose ether production, and China is a large country of cotton production, which also promotes the development of Chinese cellulose ether industry to a certain extent. At present, the production, processing and consumption of fiber ether are leading the world.

Cellulose ether in food, medicine, cosmetics, building materials, paper, and other industries have a wide range of applications. It has the characteristics of solubility, viscosity, stability, non-toxicity and biocompatibility. Cellulose ether test standard JCT 2190-2013, including cellulose ether appearance fineness, dry weight loss rate, sulfate ash, viscosity, pH value, transmittance and other physical and chemical indicators. However, when cellulose ether is applied to different industries, in addition to physical and chemical analysis, the application effect of cellulose ether in this system may be further tested. For example, water retention in the construction industry, mortar construction, etc.; Adhesives industry adhesion, mobility, etc.; Daily chemical industry mobility, adhesion, etc. The physical and chemical properties of cellulose ether determine its application range. Physical and chemical analysis of cellulose ether is essential for production, processing or use. Based on JCT 2190-2013, this paper proposes three refining or improving schemes for the physicochemical properties analysis of cellulose ether, and verifies their feasibility through experiments.

1. Dry weight loss rate

Drying weight loss rate is the most basic index of cellulose ether, also called moisture content, related to its effective components, shelf life and so on. The standard test method is oven weight method: About 5g samples were weighed and placed in a weighing bottle with a depth not exceeding 5mm. The bottle cap was put down in the oven, or the bottle cap was half-opened and dried at 105 ° C ±2 ° C for 2 h. Then the bottle cap was taken out and cooled to room temperature in the dryer, weighed, and dried in the oven for 30 min.

It takes 2 ~ 3 hours to detect the moisture content of a sample by this method, and the moisture content is related to other indexes and the preparation of the solution. Many indexes can only be carried out after the moisture content test is completed. Therefore, this method is not suitable in practical use in many cases. For example, the production line of some cellulose ether factories needs to detect the water content more quickly, so they may use other methods to detect the water content, such as rapid moisture meter.

According to the standard moisture content detection method, according to the previous practical experimental experience, it is generally required to dry the sample to constant weight at 105℃, 2.5h.

Test results of different cellulose ether moisture content under different test conditions. It can be seen that the test results of 135℃ and 0.5 h are closest to those of the standard method at 105℃ and 2.5h, and the deviation of the results of the rapid moisture meter is relatively large. After the experimental results came out, the two detection conditions of 135℃, 0.5 h and 105℃, 2.5 h of the standard method were continued to be observed for a long time, and the results were still not much different. Therefore, the test method of 135℃ and 0.5 h is feasible, and the moisture content test time can be shortened by about 2 h.

2. Sulfate ash

Sulfate ash cellulose ether is an important index, directly related to its active composition, purity and so on. Standard test method: Dry the sample at 105℃±2℃ for reserve, weigh about 2 g of sample into the crucible that has been burned straight and constant weight, put the crucible on the heating plate or electric furnace and slowly heat until the sample is completely carbonized. After cooling the crucible, 2 ml concentrated sulfuric acid is added, and the residue is moistened and heated slowly until white smoke appears. The crucible is put in the Muffle furnace and burned at 750 ° C ±50 ° C for 1 h. After burning, the crucible is taken out and cooled to room temperature in the dryer and weighed.

It can be seen that the standard method uses a large amount of concentrated sulfuric acid in the burning process. After heating, a large amount of volatilized concentrated sulfuric acid smoke. Even if it is operated in the fume hood, it will have a serious impact on the environment inside and outside the laboratory. In this paper, different cellulose ethers are used to detect ash in accordance with the standard method without adding concentrated sulfuric acid, and the test results are compared with the normal standard method.

It can be seen that there is a certain gap in the detection results of the two methods. Based on these original data, the paper calculates the gap multiple of the two in the approximate range of 1.35 ~ 1.39. That is to say, if the test result of the method without sulfuric acid is multiplied by the coefficient of 1.35 ~ 1.39, the ash test result with sulfuric acid can be roughly obtained. After the experimental results were released, the two detection conditions were compared for a long time, and the results remained roughly in this coefficient. It shows that this method can be used to test pure cellulose ether ash. If there are individual special requirements, the standard method should be used. Since the complex cellulose ether adds different materials, it will not be discussed here. In the quality control of cellulose ether, using the ash test method without concentrated sulfuric acid can reduce the pollution inside and outside the laboratory, reduce the experiment time, reagent consumption and reduce the possible accident hazards caused by the experiment process.

3, cellulose ether group content test sample pretreatment

Group content is one of the most important indexes of cellulose ether, which directly determines the chemical properties of cellulose ether. Group content test refers to the cellulose ether under the action of catalyst, heating and cracking in a closed reactor, and then the product extraction and injection into the gas chromatograph for quantitative analysis. The heating cracking process of group content is called pre-treatment in this paper. The standard pre-treatment method is: weigh 65mg dried sample, add 35mg adipic acid into the reaction bottle, absorb 3.0ml internal standard liquid and 2.0ml hydroiodic acid, drop into the reaction bottle, cover tightly and weigh. Shake the reaction bottle by hand for 30s, place the reaction bottle in a metal thermostat at 150℃±2℃ for 20min, take it out and shake it for 30S, and then heat it for 40min. After cooling to room temperature, the weight loss is required to be no more than 10mg. Otherwise, the sample solution needs to be prepared again.

The standard method of heating is used in the metal thermostat heating reaction, in actual use, the temperature difference of each row of metal bath is large, the results are very poor repeatability, and because the heating cracking reaction is more severe, often because the reaction bottle cap is not strict leakage and gas leakage, there is a certain risk. In this paper, through a long time test and observation, the pretreatment method is changed to: using glass reaction bottle, with butyl rubber plug tightly, and heat-resistant polypropylene tape wrapped the interface, then put the reaction bottle into a special small cylinder, cover tightly, finally put into the oven heating. The reaction bottle with this method will not leak liquid or air, and it is safe and easy to operate when the reagent is shaken well during the reaction. The use of electric blast drying oven heating can make each sample evenly heated, the result is good repeatability.

4. Summary

The experimental results show that the improved methods for detecting cellulose ether mentioned in this paper are feasible. Using the conditions in this paper to test the drying weight loss rate can improve the efficiency and shorten the testing time. Using no sulfuric acid test combustion ash, can reduce laboratory pollution; The oven method used in this paper as the pretreatment method of cellulose ether group content test can make the pretreatment more efficient and safe.