Hydroxypropyl Methylcellulose, also known as HPMC. It is made from highly pure cotton cellulose. And it is etherified under alkaline conditions. HPMC has thickening ability, salt drainage, PH stability, and water retention. Besides, it has excellent stability and excellent film-forming properties. And it also has a wide range of enzyme resistance, dispersibility, and adhesion.
Hydroxypropyl Methylcellulose is soluble in water and most polar c and appropriate ratio of ethanol/water, propanol/water, dichloroethane, etc. It is insoluble in ether, acetone, and anhydrous ethanol. And it also dissolves in cold water into a clear or turbid colloidal solution. The aqueous solution has surface activity, high transparency, and stable performance.
Hydroxypropyl Methylcellulose has thermal gel properties, and the product's aqueous solution forms gel precipitation after heating. And then it dissolves after cooling. The gel temperature of different product specifications is different. The solubility varies with viscosity. The lower the viscosity, the greater the solubility and the different specifications of HPMC. Its properties have some differences. HPMC dissolved in water is not affected by PH value.
Generally speaking, the production process of HPMC can be divided into two categories. First gas phase method. And the second liquid phase method.
When using this method, the raw material is usually refined cotton. Then a joint crusher crushes it. Or fine cotton is alkalized and etherized with a binary mixture of organic solvents. The resulting mass is batch processed and pelletized at high temperatures.
The liquid-phase process has the following advantages.
First, the reaction process equipment's internal pressure is small. So the equipment pressure capacity requirements are low and less dangerous.
Second, cellulose is impregnated in the alkali solution to expand and fully alkalize uniform alkali cellulose. And the alkali solution to cellulose penetration swelling is better.
Third, the etherification reactor is small, and alkali cellulose can be uniform swelling. So the product quality is easy to control, can get the degree of substitution, and viscosity is more uniform. The products can be obtained with more uniform substitution and viscosity, and the varieties can be changed.
In this method, wood pulp is used as raw material. Alkalinization and etherification are carried out in the same reaction equipment. The reaction process is controlled by advanced automatic means, and the temperature and pressure can be controlled. After the reaction is completed, the excess chloromethane and by-product dimethyl ether enter the recovery system in gaseous form. And they are recycled separately.
The refining and purification process is carried out in a continuous rotary filter press. Crushing is performed in a high-efficiency finished product pulverizer. Besides, it is dried, a process that reduces any excess moisture. Besides, the auxiliary processes, such as mixing and packaging, are also fully automated.
According to different performance index requirements, the preparation process and technology of HPMC are also different. The following are examples of four types of HPMC production formulations and processes.
If the proportion of 106 sodium hydroxide at 50% concentration is mixed into the slurry system and heated for 30 minutes. Then methanol and water are evaporated. After that, 120 of CH3X and 10 of propylene oxide were added to the slurry system and reacted at a temperature of 60-120°C for 1.5 hours. The final product was readily soluble in water with a degree of methyl substitution of 2.0 and hydroxypropyl substitution of 0.1.
In the same way, the crushed cellulose, 50% alkali, propylene oxide, and chloromethane were mixed into the slurry tank in the ratio of 20:36:90:130 at a pressure of 1.7-1.9 MPa and a temperature of 80°C into the reactor under constant stirring, which took about 30 minutes each time. The resulting product is dissolved in methanol and contains 20.5% methoxy (by mass) and 0.5% hydroxypropyl.
Alcohol-water co-soluble HPMC is an HPMC product with high hydroxypropyl content. It can also be used in tablets, various water-soluble coatings, and anhydrous alcohol solutions.
Alcohol-water co-soluble HPMC is thermoplastic and water-soluble. Its structure is characterized by the presence of 0.4-0.8 methyl DS and 1.5-1.8 hydroxypropyl MS, and the sum of methyl DS and hydroxypropyl MS must be greater than 1.8. The synthesis of alcohol-water soluble Hydroxypropyl Methylcellulose requires the etherification of 1.54 units of propylene oxide mixed with 0.4-0.8 parts of chloromethane.
First, a 50% concentration of refined cotton powder and aqueous NaOH solution is prepared in a 20:14 ratio. Then propylene oxide and chloromethane were added and mixed fully in the ratio of 80:16. Then the completely mixed paste was warmed to 60°C over 90 min and reacted for 5.5 h. Finally, the final product was obtained after unloading and post-treatment. The degree of substitution is 0.58 for methyl and 1.58 for hydroxypropyl.
The final product dissolves rapidly in anhydrous ethanol. It forms a clear, colorless, viscous solution. It is also soluble in water and has a gel temperature of 43°C in water.
We have been developing new technologies and processes to meet the specific requirements of various fields. Such as exploring continuous production processes for HPMC. Besides Hydroxyalkyl Methylcellulose, other hybrid ethers have been developed. Three-group water-soluble hybrid ethers containing three substituents have been developed. They are alkyl, carboxymethyl, and hydroxyalkyl - for example, Hydroxypropyl Methylcellulose (HPMC).
Improved Zeisser methods or chromatographic techniques allow the analysis of its methoxy and hydroxyalkyl groups.
It is effective as an additive to adhesives to improve applicability and extend operability time. It can also reduce the amount of cement used for pasting tiles, and marble. As well as for plastic decorations and for pasting reinforcements. The water retention property of Hydroxypropyl Methylcellulose makes the paste not crack after application. Because it dries too fast and enhances the strength after hardening.