Views: 0 Author: Site Editor Publish Time: 2023-05-12 Origin: Site
Abstract: This paper introduces the application of domestic hydroxypropyl methylcellulose to replace imported hydroxypropyl methylcellulose in the polymerization of high-degree polyvinyl chloride, and investigates the effect of two kinds of hydroxypropyl methylcellulose on high-degree polyvinyl chloride. The impact of various indicators of vinyl resin. The results show. It is feasible to replace imported hydroxypropyl methylcellulose with domestic hydroxypropyl methylcellulose.
Key words:hydroxypropyl methylcellulose; high degree of polymerization polyvinyl chloride; small test; polymerization; localization
High degree of polymerization PVC resin refers to PVC resin with an average degree of polymerization of more than 1700 or a slight crosslinking structure between molecules, among which the most common is PVC resin with an average degree of polymerization of 2500. Compared with ordinary PVC resin, high-polymerization PVC resin has high resilience, small compression set, heat resistance, aging resistance, fatigue resistance and wear resistance. It is an ideal rubber substitute and can be used in automotive sealing strips, wires and cables, Medical catheters, etc.
The production method of high-polymerization PVC is mainly suspension polymerization. In the production of suspension method, dispersant is an important auxiliary agent, and its type and dosage will directly affect the particle shape, particle size distribution, plasticizer absorption, etc. of the finished PVC resin. Commonly used dispersion systems are polyvinyl alcohol systems and hydroxypropyl methylcellulose and polyvinyl alcohol composite dispersion systems, and domestic manufacturers mostly use the latter.
1. Main raw materials and specifications
The domestic hydroxypropyl methylcellulose selected in this paper is consistent with the imported hydroxypropyl methylcellulose, which provides a premise for the substitution test in this paper.
2. Test content
2.1 Preparation of hydroxypropyl methylcellulose solution
Take a certain amount of deionized water, put it in a container and heat it to 70°C, gradually add hydroxypropyl methylcellulose under constant stirring, the cellulose floats on the water surface at first, and then is gradually dispersed until it is evenly mixed Cool the solution down and bring to volume.
2.2 Test method
On the 10 L small-scale test device, use imported hydroxypropyl methylcellulose to conduct a benchmark test to determine the basic formula of the small test; use domestic hydroxypropyl methylcellulose to replace imported hydroxypropyl methylcellulose for testing; The PVC resin products produced by different hydroxypropyl methylcellulose were compared to study the feasibility of replacing domestic hydroxypropyl methylcellulose. According to the results of the small test, the production test is carried out.
2.3 Test steps
Before the reaction, clean the polymerization kettle, close the bottom valve, add a certain amount of desalted water, and then add a dispersant; close the lid of the kettle, vacuumize after passing the nitrogen pressure test, and then add vinyl chloride monomer; after cold stirring, add initiator agent; use circulating water to raise the temperature in the kettle to the reaction temperature, and add ammonium bicarbonate solution in time during this process to adjust the pH of the reaction system
value; when the reaction pressure drops to the pressure specified by the formula, add a terminator and a defoamer, discharge the material, centrifuge and dry to obtain the finished PVC resin, and take a sample for analysis.
2.4 Analytical method
According to the relevant test methods in the enterprise standard Q3I/0116000823C002--2018, the viscosity number, apparent density, volatile matter (including water) of the finished PVC resin and the plasticizer absorption of 100 g PVC resin are tested and analyzed; The average particle size of the PVC resin is tested by an instrument; the morphology of the PVC resin particles is observed by an electron scanning microscope.
3. Results and Discussion
3.1 Comparative analysis of different batches of PVC resin quality in small-scale polymerization
Test each batch of small-scale finished PVC resin.
The apparent density, viscosity number, and plasticizer absorption of the PVC resin obtained by using different cellulose are relatively close; the average particle size of the resin product obtained by using the domestic hydroxypropyl methylcellulose formula is slightly smaller.
From the SEM electron microscope images of PVC resin products obtained by using different hydroxypropyl methylcellulose, it can be seen that the surface structure and morphology of PVC resin particles that should be produced when different cellulose dispersants are relatively similar.
In summary, it can be seen that the domestic hydroxypropyl methylcellulose tested in this paper has the feasibility of replacing imported hydroxypropyl methylcellulose.
3.2 Comparative analysis of the quality of high-polymerization PVC resin in production test
Due to the high cost and risk of the production test, the complete replacement plan of the small test test cannot be directly applied, so the plan to gradually increase the proportion of domestic hydroxypropyl methylcellulose in the formula is adopted.
Gradually increase the use of domestic hydroxypropyl methylcellulose, until domestic hydroxypropyl methylcellulose completely replaces imported hydroxypropyl methylcellulose in various batches of tests, the plasticizer absorption of PVC resin, the apparent The main indicators such as density have no obvious fluctuations, indicating that the domestic hydroxypropyl methylcellulose selected in this paper can replace imported hydroxypropyl methylcellulose in production.
The test of domestic hydroxypropyl methylcellulose on a 10 L small test device shows that it is feasible to replace imported hydroxypropyl methylcellulose; the results of productive substitution tests show that domestic hydroxypropyl methylcellulose is used for In the production of PVC resin, there is no significant difference in the main quality indicators of the finished PVC resin and imported hydroxypropyl methylcellulose. At present, the price of domestic cellulose in the market is lower than that of imported cellulose. Therefore, if domestic cellulose is used in production, the cost of production aids can be significantly reduced.