HPMC (hydroxypropyl methylcellulose) is a commonly used polymer material widely used in construction, pharmaceuticals, food, daily chemicals and other fields. According to its solubility in water, it can be divided into cold water instant type and hot melt type. There are significant differences in the production process of these two types of HPMC.

(1), raw material processing
1. Cold water instant type
In the production process of cold water instant HPMC, the raw materials first need to be pretreated. Raw materials generally include cellulose, methanol, propylene oxide, methyl chloride, etc. The raw materials need to be finely crushed and mixed during the pretreatment process to ensure the uniformity and adequacy of the reaction. In particular, the treatment of cellulose requires strict drying and crushing to achieve a suitable particle size distribution.

2. Hot melt type
Hot-melt HPMC is similar to cold-water instant HPMC in terms of raw material processing, but has higher requirements for cellulose processing. Because hot-melt HPMC needs to react at high temperatures, the purity and particle size of cellulose have a more significant impact on the reaction process. It is usually necessary to use high-purity cellulose, and the particle size must be strictly controlled during the crushing process.

(2), synthesis reaction
1. Cold water instant type
The synthesis reaction of cold water instant HPMC is usually carried out at low temperature, generally controlled at 20-50 degrees Celsius. During the reaction process, cellulose is first pretreated under alkaline conditions to partially hydrolyze the cellulose molecular chains and generate free hydroxyl groups. Then, reactants such as methanol, propylene oxide and methyl chloride are added under stirring conditions to perform etherification reaction. The entire reaction process requires strict control of temperature and pH to ensure the uniformity and stability of the product.

2. Hot melt type
The synthesis reaction of hot-melt HPMC is carried out at high temperatures, generally 50-80 degrees Celsius or even higher. The reaction process is similar to the cold water instant type, but due to the faster reaction rate under high temperature conditions, more precise temperature control and reaction time are required. At high temperatures, the hydrolysis and etherification reactions of cellulose are more complete, and the molecular weight distribution of the product is more uniform.

(3) Post-processing process
1. Cold water instant type
After the synthesis reaction of cold water instant HPMC is completed, a series of post-processing processes are required. The first is a neutralization reaction to neutralize the alkaline substances in the reaction mixture. Filtration and washing are then performed to remove unreacted raw materials and by-products. The final step is drying and pulverizing. The product is dried to control the moisture content, and then pulverized to a suitable particle size to obtain the finished product HPMC.

2. Hot melt type
The post-treatment process of hot-melt HPMC is basically similar to that of cold-water instant HPMC. However, due to the high temperature used in the reaction process, the moisture content of the product is relatively low and the drying process is relatively simple. In addition, hot-melt HPMC needs to pay more attention to controlling the crushing temperature during the crushing process to prevent the degradation of product performance due to high temperature.

(4), performance and application
Cold water instant HPMC is widely used in fields that require rapid film formation or thickening, such as architectural coatings, emulsions, etc. due to its rapid dissolution in cold water. Its production process requirements are relatively high, especially the control of reaction conditions at low temperatures.

Hot-melt HPMC is more suitable for applications under high temperature conditions, such as tile adhesive, putty powder, etc., due to its excellent solubility in hot water. Its production process is relatively simple, but it has high requirements on the purity of raw materials and reaction temperature control.

The main difference in the production process between cold water instant-type and hot-melt HPMC is the difference in reaction temperature, which directly affects the differences in raw material processing, synthesis reaction process and post-treatment process. The cold water instant type needs to react at low temperature and has higher requirements for temperature and pH control, while the hot melt type reacts at high temperature and pays more attention to the purity of raw materials and the control of reaction temperature. The two are also different in specific application fields, and each plays an important role.