The term hydroxypropyl methyl cellulose is not only a bit awkward to pronounce, but it is hard to understand its composition and use as mortar. About how it is formed, today, we will give you a lesson in popular language. explain.
Hydroxypropyl methyl cellulose is actually made of cotton. Of course, not just any cotton can be refined. Good cotton is needed. The production process is to first treat the cotton in lye and then It is pulverized, and then it is aged at 35 degrees, and then it is put into propylene oxide and methyl chloride and then processed. The first step is dehydration and crushing. Although this process seems more complicated, as long as you are proficient in the operation, you will not have this idea.
Regarding how to identify the quality of hydroxypropyl methylcellulose, in fact, the country does not yet have a hard indicator, because its product uses and auxiliary materials and additives are different, so the quality is not easy to check.
Cellulose ether was reported in 1905. It was prepared by Suida reacting alkali-swollen cellulose with dimethyl sulfate, but no isolated cellulose ether could be obtained at that time. In 1912, a patent for the preparation of cellulose ethers appeared. ; In 1927, the synthesis and separation of hydroxypropyl methyl cellulose were successful; in 1938, Dow Chem. realized the industrial production of methyl cellulose and “Methocel”; in 1948, large-scale hydroxypropyl methyl cellulose was carried out in the United States. Industrial production, and the production process reached maturity in 1960 to 1970.
The HPMC production companies currently compared in the world mainly include Dow Chemical Co., Hercules Co., and Clariant Co. in Germany. Japan’s Shin-Etsu Chemical Co. and South Korea’s Samsung Fine Chemical Co. (Samsung Fine Chemical Co.) have introduced technology and equipment from Dow Chemical Co. and German Loedige Co., respectively.
The production methods of hydroxypropyl methylcellulose can be divided into two categories: gas phase method and liquid phase method. At present, developed countries such as Europe, America and Japan adopt the gas phase process, using wood pulp as the raw material (cotton pulp is used in the production of high-viscosity products). The alkalization and etherification are carried out in the same reaction equipment. The main reaction is a horizontal reactor. The central horizontal stirring shaft and side rotating flying knife designed for the production of cellulose ether can obtain a good mixing effect. The reaction process adopts automatic control means, which can control temperature and pressure. After the reaction is completed, the excess methyl chloride and the by-product dimethyl ether enter the recovery system in gaseous form, and are recycled and reused separately. The purification treatment is carried out in a continuous rotary filter press. The crushing is carried out in the finished product crusher while drying to remove excess water. Auxiliary processes such as mixing and packaging are also completed under the automatic control system.
The gas-phase process has the following advantages: compact equipment, high single-batch output; lower reaction temperature than liquid-phase method, shorter reaction time than liquid-phase method; more accurate reaction control than liquid-phase method; no need for complex solvent recovery system; low labor cost , The labor intensity is small.
However, this process also has the following shortcomings: large investment in equipment and automatic control, high technical content, and large investment and construction costs; due to the high degree of automation, the requirements for the quality of the operators are high, and once a failure occurs, major accidents are prone to occur. If something goes wrong, the whole line will stop production.