How is Hydroxypropyl Methylcellulose (HPMC) produced?

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.

 

cellulsoe-ether-bag

 

I. How is HPMC produced?

 

Generally speaking, the production process of HPMC can be divided into two categories. First gas phase method. And the second liquid phase method.

 

1. 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.

 

2. Vapor phase method

 

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.

 

HPMC-raw-materials

 

II. About the four production formulations and processes of HPMC.

 

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.

 

  1. The slurry system consists of a mixture of crushed cellulose in the proportion of 80, sodium hydroxide in the proportion of 26, and toluene in the proportion of 950.

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.

 

  1. Under oxygen barrier conditions, crushed cellulose, 50% lye, propylene oxide, and chloromethane were added to the slurry tank in the ratio of 20:40:90:200. The slurry was pumped into the reactor at 1.7-1.9 MPa pressure and 80°C temperature under constant stirring for about 30 minutes each time. Then the slurry was conveyed to the washing and purification stage at 1.7-1.9 MPa pressure to get 27.5% methoxy (mass content) and 6.5% hydroxypropyl. The product was easily soluble in water with a viscosity of 14000 MPa.

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.

 

  1. Hydroxypropyl Methylcellulose products are required in some industries. Such as in the coating thickening industry, alcohol water-soluble hydroxypropyl methylcellulose products. It aims to avoid using methanol and dichloroethane.

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.

 

  1. This production process allows the dissolving of the hydroxypropyl methylcellulose product in anhydrous ethanol.

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.

 

III. HPMC can be used in what fields?

 

  1. Construction industry. As water retention agent and retarder for cement mortar to make mortar pumping. It can be used for plaster, gypsum, putty powder, or other construction materials.

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.

 

EIFS-additive-hpmc

  1. Ceramic manufacturing industry. It is widely used as a binder in the manufacture of ceramic products.

 

  1. Coating industry. As a thickener, dispersant, and stabilizer in the coating industry. It is compatible with water or organic solvents as a paint stripper.

 

  1. Ink printing. As a thickener, dispersant, and stabilizer in the ink industry, with good solubility in water or organic solvents.

 

  1. Plastics. As a moulding release agent, softening agent, lubricant, etc.

 

  1. Polyvinyl Chloride. It is used as a dispersant in the production of Polyvinyl Chloride. And it is the main auxiliary for the preparation of PVC by suspension polymerization.

 

  1. Other. It is also used in the leather paper products industry, fruit and vegetable preservation, textile industry, etc.

 

  1. Pharmaceutical industry. Coating materials, film materials, speed control polymer materials for slow-release formulations, stabilizers, suspension aid, tablet binder, and viscosity enhancer.

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