Advantages of HPMC in Construction Materials
December 26th 2024
Important factors affecting the quality indicators of hydroxypropyl methylcellulose: According to the product properties, reaction principles, and operating experience, factors such as the activity of the solvent and the degree of reaction directly affect the important quality indicators of the product.
1) The solvent is a catalyst in the reaction process. The activity of the solvent directly affects the important indicators of the product, such as viscosity, specific gravity, and pH value. Low solvent activity will lead to poor reaction of the material, low viscosity and specific gravity, and excessive pH value. According to the product properties, reaction principles, and operating experience, the activity of the solvent will decrease after a certain period of use. A small amount of new solvent is regularly added to the system to increase the activity of the solvent (try toluene/isopropanol ratio within a suitable range).
2) The degree of reaction directly determines the various indicators of the semi-finished product. The lack of reaction may lead to the possibility of failure of various indicators.
According to the product properties, reaction principles, and operating experience, the stirring frequency of the reactor is increased to 45HZ after the pressure alkali is adjusted, which increases the stirring frequency of the reactor and the stirring speed; the contact rate of the material is increased. The amount of solvent added to the system is 7300 kg, which increases the contact area of the material and makes the material more fully contacted and reacted.
1.Viscosity
According to the product properties, reaction principle, and operating experience, the viscosity is related to the polymerization degree of the raw material refined cotton, the sealing degree of the reactor, the feeding speed, the vacuuming speed, the nitrogen purity, and the feeding temperature.
Increasing viscosity:
1) Use cellulose raw materials with a high polymerization degree.
2) Add antioxidants.
3) Speed up the feeding speed, vacuum, exhaust air, and fill with nitrogen for protection.
Reducing viscosity:
1) Use cellulose raw materials with a low polymerization degree.
2) Add oxidants during the alkalization process or etherification process.
3) Reduce viscosity by radiation (reduce viscosity by destroying the molecular structure by external force).
2. Specific gravity
According to the product properties, reaction principle, and operating experience, the specific gravity is related to the total water content in the system, the proportion of caustic soda in the system, the degree of alkalization, the alkalization temperature, and the degree of alkalization.
1) The test report and experience determine the water content in the solvent, and the reactor operator determines it according to the turbidity of the solvent.
2) Adjust the amount of caustic soda from time to time according to the quality results of the semi-finished products.
3) Strictly abide by the operating procedures, dissolve the flake alkali well, and control the alkalization time and temperature (according to the product properties, reaction principle, and operating experience, the alkalization temperature is determined to be 20-23 degrees) to alkalize it.
4) The low bulk density of refined cotton will affect the contact between refined cotton and alkali, resulting in poor alkalization; the bulk density of refined cotton is above 150 to ensure that the refined cotton used meets the process requirements.
3. PH value
According to the product properties, reaction principle, and operating experience, the PH value is related to factors such as the degree of reaction and the concentration of acetic acid used for neutralization.
1) The alkalization reaction will not cause residual alkali to remain in the system after the reaction, which will lead to excessive PH; in order to avoid excessive PH due to abnormal reaction, the acetic acid can be adjusted accordingly according to experience.
2) The unqualified concentration of acetic acid used for neutralization will directly affect the neutralization effect and cause the PH value to exceed the standard. After discussion and decision by the cellulose workshop, the acetic acid concentration is 50% ± 1, and the batching area must be fully circulated before the workshop is hit.
3) Adjust the amount of acetic acid added for neutralization according to the change in the proportion of caustic soda in the system. In order to reduce the crystallization temperature of acetic acid, acetic acid, and mixed solvent are mixed and used in a ratio of 1:1, and the weight of mixed acetic acid controls the pH value.
4. Ash content
According to the product properties, reaction principles, and operating experience, the ash content is related to factors such as the raw materials used in the reaction, the amount of washing water added, and the hardness.
1) If the impurity content in the raw materials used is too high (such as high ash content in refined cotton, high content of acidic soda sodium carbonate, etc.), it will directly affect the ash content.
2) The amount of water used for washing directly affects the washing effect, and the amount of water used for washing is adjusted according to production needs. The hardness of the washing water also directly affects the washing effect. If the hardness of the washing water is too high, the washing effect will not be achieved.
5. Hydroxypropyl content
1) Change the amount of alkali used in the reaction system. The amount of alkali used in the cellulose alkalization process will directly affect the etherification efficiency of the product and the content ratio of the group. A high alkali concentration or increased amount of solid alkali added will increase the content. Suppose the concentration of the alkali solution is low or the amount of solid alkali added is reduced. In that case, the hydroxypropyl content of the product can be appropriately increased under the same process conditions. The hydroxypropyl content is inversely proportional to the alkali concentration, and the content is proportional to the alkali concentration.
2) Adjust the temperature change of the production process HPMC etherification stage is mainly the reaction of etherification and hydroxypropylation. The reaction conditions required for the two reactions are different, and the positive and negative reaction rates of the two reactions are also quite different.
3) The amount of etherifying agent added Under the conditions determined by the process conditions, the ratio of etherifying agents methyl chloride and propylene oxide to the two has a direct and obvious effect on the product and hydroxypropyl value.
6. Water retention rate, light transmittance, gel temperature, hydroxypropyl content, and ratio have a significant impact on the water solubility, water retention capacity, surface activity, and gel temperature of the product.
HPMC with high content and low hydroxypropyl content: good water solubility, surface activity, and low gel temperature. Properly increasing the hydroxypropyl content or decreasing the content can increase the gelation temperature. Still, if the hydroxypropyl content is too high, the gelation temperature will decrease, the water solubility and surface activity will deteriorate, and the solubility in organic solvents will increase.
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