The Importance of Water Retention of HPMC
April 24th 2024
This article mainly describes the four production technologies and formulas of HPMC. Hydroxypropyl Methylcellulose (HPMC) or Hypromellose is a water-soluble non-ionic cellulose ether polymer. With good performance of thickening, dispersion, emulsification, suspension, adsorption, surface activity, and water retention, our HPMC products are widely used in various fields, such as tile adhesives, gypsum-based products, cement mortar, paints and coatings, synthetic resins, ceramics, textiles, agriculture, and daily chemicals, etc.
According to different performance index requirements, production technologies and formulas of HPMC are also different. Below illustrates four production technologies and formulas of HPMC:
1. The first kind of production technologies and formulas of HPMC:
The slurry system consists of a mixture of pulverized cellulose mixed in a ratio of 80, NaOH in a ratio of 26, and toluene in a ratio of 950. If NaOH with a ratio of 106 is mixed into the slurry system at a concentration of 50% and heated for 30 minutes, methanol and water will be distilled off. Then, CH3X, with a ratio of 120 and propylene oxide with a ratio of 10 were added to the slurry system and reacted at a temperature of 60-120° C for 1.5 hours. The final product is soluble in water with a methyl substitution degree of 2.0 and a hydroxypropyl substitution of 0.1.
2. The second kind of production technologies and formulas of HPMC:
Under the condition of oxygen isolation, the crushed cellulose, 50% lye, propylene oxide, and methyl chloride should be added to the slurry tank in a ratio of 20:40:90:200. Under continuous stirring, pump the slurry into the reactor at a pressure of 1.7-1.9 MPa and a temperature of 80°C, and each stirring takes about 30 minutes. The slurry will then be conveyed to the washing and purification stage under a pressure of 1.7-1.9 MPa to obtain a 27.5% methoxy group (mass content) and a 6.5% hydroxypropyl group. The product is soluble in water with a viscosity of 14000Pa. S.
In a similar process, the crushed cellulose, 50% lye, propylene oxide and methyl chloride should be mixed into the slurry tank in a ratio of 20:36:90:130 witha pressure of 1.7-1.9 MPa and temperature of 80℃ into the reactor under continuous stirring, which takes about 30 minutes each time. The resulting product is soluble in methanol with 20.5% methoxy group (mass content) and 0.5% hydroxypropyl group.
3. The third kind of production technologies and formulas of HPMC:
For some particular industries, for example, production technologies and formulas of HPMC in the coating thickening industry, it is necessary to use alcohol-water co-soluble hydroxypropyl methyl cellulose (HPMC) products, which can avoid the use of methanol and dichloroethane. Alcohol-water co-soluble HPMC is an HPMC product with high hydroxypropyl content, which can also be used in tablets, various water-soluble coatings, and anhydrous alcohol solutions. Alcohol-water co-soluble HPMC has thermoplasticity and water-solubility. Its structural feature is that it contains 0.4-0.8 methyl DS and 1.5-1.8 hydroxypropyl MS, and the sum of methyl DS and hydroxypropyl MS must be more than 1.8.
The synthesis of alcohol-water co-soluble hydroxypropyl Methyl Cellulose requires that 1.54 units of propylene oxide and 0.4 to 0.8 parts of methyl chloride are mixed for etherification, and each part of cellulose corresponds to 0.35 to 0.4 parts of alkali.
4. The forth kind of production technologies and formulas of HPMC:
This production process allows the hydroxypropyl methyl cellulose product to be dissolved in absolute ethanol. First, pulverized refined cotton and NaOH aqueous solution with a 50% concentration should be prepared in a ratio of 20:14. Then, propylene oxide and methyl chloride should be added and mixed thoroughly in a ratio of 80:16. Next, the completely mixed paste should gradually be heated to 60℃ within 90min and then reacted for 5.5h. Finally, the final product can be obtained after unloading and post-processing. The degree of substitution of methyl is 0.58, and the hydroxypropyl group is 1.58.
The final product can be quickly dissolved in absolute ethanol to form a transparent, colorless, and viscous solution. It is also soluble in water, and the gel temperature in the water is 43℃. The product can be used as a water-soluble coating or a transparent and water-soluble film in pharmaceutical tablets.
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