1. Raw material requirements
The main raw material of high-viscosity hydroxypropyl methylcellulose (HPMC) is refined cotton, whose purity, moisture content and cellulose content directly affect the quality of the final product. Therefore, the requirements are:
Refined cotton: cellulose content ≥98%, ash content ≤0.1%, moisture content ≤5%.
Alkali solution (NaOH): concentration is controlled at 25% to 30%, and no excessive impurities are allowed.
Etherifying agent: propylene oxide (PO) and methyl chloride (MC) purity ≥99%, moisture content ≤0.2%.
Solvent: Use industrial grade isopropyl alcohol (IPA) or ethanol, which must be free of impurities and low in moisture.
2. Process control
The production process of HPMC mainly includes alkalization, etherification, neutralization, washing, drying and grinding, and each link needs to be strictly controlled.
(1) Alkalinization reaction
Use a closed reactor and add NaOH solution at low temperature (20 to 30°C) to fully swell the cellulose and improve the reaction activity.
The reaction time is controlled within 30 to 60 min to ensure sufficient alkalization and improve reaction efficiency.
(2) Etherification reaction
Reaction temperature: 50 to 80 °C, pressure 0.5 to 1.5 MPa.
Reaction time: 2 to 5 hours to ensure sufficient etherification and uniform molecular substitution.
The proportion of etherifying agent addition is strictly controlled. Usually, the molar ratio of propylene oxide (PO) to methyl chloride (MC) is 1.5 to 3 to ensure a moderate degree of substitution (DS 1.8 to 2.0).
(3) Neutralization and washing
Acetic acid or hydrochloric acid is used to neutralize the unreacted alkali, and the pH value is controlled between 6.0 and 8.0.
Wash with deionized water to remove inorganic salts and unreacted products, and wash until the conductivity is ≤50 μS/cm.
(4) Drying and crushing
Use low temperature (≤60 °C) vacuum drying or spray drying to reduce thermal degradation and improve product stability.
Grind to appropriate particle size (80-120 mesh) to ensure fluidity and dispersibility and avoid agglomeration. 
3. Product quality control
The quality of HPMC is mainly reflected in indicators such as viscosity, degree of substitution, water content, purity, etc., which require strict testing.
(1) Viscosity control
High viscosity HPMC requires a 2% aqueous solution viscosity ≥50,000 mPa·s (up to 200,000 mPa·s), which requires strict testing using a viscometer.
Influencing factors include degree of substitution, molecular weight, dissolution mode, etc., and process parameters need to be optimized during production.
(2) Degree of substitution (DS and MS)
Methoxy content: 19.0%-30.0%, hydroxypropoxy content: 4.0%-12.0%.
Substitution uniformity affects solubility and needs to be tested by nuclear magnetic resonance (NMR) or infrared spectroscopy (FTIR).
(3) Moisture and purity
Moisture content ≤5% to avoid agglomeration affecting fluidity.
Ash content (NaCl, Na2SO4, etc.) ≤1.0%, ensuring high purity.
4. Equipment and safety requirements
Production equipment must be alkali-resistant and corrosion-resistant (such as stainless steel or enamel reactor).
The production process must prevent leakage of etherifying agents, and be equipped with a closed circulation system and tail gas treatment devices (such as activated carbon adsorption).
The workshop is well ventilated, and operators must wear protective equipment to ensure safe production.
The production of high-viscosity HPMC requires strict control of raw material quality, process parameters and product testing to ensure that the performance of the final product is stable and meets application requirements.
Post time: Apr-15-2025