The purity of hydroxypropyl methylcellulose (HPMC) in building insulation mortar directly affects the quality of construction. In the HPMC production process, residual oxygen in the reactor leads to the degradation of HPMC and a decrease in molecular weight. However, the amount of residual oxygen is limited, and reconnecting the broken molecules is not difficult.

The manufacture of hydroxypropyl methylcellulose (HPMC) is mainly accomplished through three reactions: alkali treatment of cotton linters, hydroxypropylation, and methylation. Various technologies that have emerged in recent years have only focused on improving and refining each unit operation.
The production of hydroxypropyl methylcellulose uses chloromethane and propylene oxide as etherifying agents. The chemical reaction equation is: Rcell – OH (refined cotton) + NaOH (caustic soda) + CH3Cl (chloromethane) + CH2OCHCH2 (propylene oxide) → Rcell – O -CH2OHCH2 (hydroxypropyl methylcellulose) + NaCl (sodium chloride) + H2O (water). The principle of etherification synthesis of hydroxypropyl methylcellulose (HPMC) is not complicated, but the processes of alkalization, raw material crushing, etherification, solvent recovery, and centrifugal separation, as well as the etherification reaction under certain temperature and pressure conditions, require precise control. The reaction endpoint is determined by the required degree of etherification, followed by neutralization, washing, drying, and crushing to obtain the finished product. Each step involves a large number of technical key points and a wealth of knowledge. For different product varieties, the control conditions for each step, such as temperature, time, pressure, and material flow control, are crucial. Auxiliary equipment and control instruments are essential for ensuring stable product quality and a reliable production system.
The manufacturing process of hydroxypropyl methylcellulose (HPMC) generally uses a one-step slurry method. The general steps are as follows:
① Pre-treatment: Refined cotton is crushed into refined cotton blocks with a diameter of about 1-3 cm using an opening machine, and then enters a crusher, where it is rapidly sheared and crushed into refined cotton powder with a mesh size of 60-100.
② Alkalization: The crushed refined cotton powder is dispersed in 8-10 times the amount of mixed solvent, and the alkali reacts to produce alkali cellulose with chemical reaction activity. ③ Etherification: Alkali cellulose reacts with propylene oxide and methyl chloride in an etherification reaction. By controlling the reaction temperature, reaction time, and formula, the degree of methoxy and hydroxypropyl substitution is adjusted. The viscosity of the product is controlled by controlling the purity of the oxidant in the system and selecting refined cotton raw materials. A computer DCS control system is used to ensure stable product quality and reliable process characteristics.
④ Neutralization: After the reaction is complete, an acid is used to neutralize the remaining alkali, bringing the pH of the product to the specified standard.
⑤ Solvent Recovery: The neutralized mixture is heated, and the solvent is recovered through a condensation and cooling system. The recovered solvent is recycled.
⑥ Post-treatment: The desolventized compound is separated by a horizontal sedimentation centrifuge, then granulated, dried, homogenized, and packaged into the final product.
The purity of hydroxypropyl methylcellulose in building insulation mortar directly affects the quality of construction. In the production process of hydroxypropyl methylcellulose, residual oxygen in the reactor leads to the degradation of hydroxypropyl methylcellulose and a decrease in molecular weight. However, the amount of residual oxygen is limited, and reconnecting the broken molecules is not difficult. The water retention rate of hydroxypropyl methylcellulose is closely related to the hydroxypropyl content, but the entire reaction process also determines its water retention rate. The alkalization effect, the ratio of methyl chloride and propylene oxide, the concentration of alkali, and the ratio of water to refined cotton all determine the performance of the product.