Determination of total unsaturated double bonds in

2022-07-25
  • Detail

Determination of total unsaturated double bond content in PVC by catalytic bromine addition method

analysis and testing determination of total unsaturated double bond content in PVC by catalytic bromine addition method wangguihua and zhangmeizhen (School of science, Beijing University of chemical technology, Beijing 100029) determined the content of total unsaturated double bond in polyvinyl chloride (PVC) by hgac catalytic bromine addition method, studied the relationship between the content of total unsaturated double bond and thermal stability, and determined the content before optimization. Optimization in progress. The results of six PVC samples after optimization showed that the content of total unsaturated double bonds in PVC samples increased with the increase of thermal oxygen aging time, and the PVC samples after optimization were better than those before optimization. The content of total unsaturated double bond in the optimized sample is low. PVC; Total unsaturated double bond; Brominated adducted polyvinyl chloride (PVC) is one of the commonly used plastic varieties, which has a wide range of uses. However, PVC will degrade and crosslink due to dehydrochlorination during processing, storage and use, resulting in a decline in its mechanical and chemical properties. The green environmental protection of coloring and yellowing raw materials has become the goal of many plastic raw material suppliers, mainly because there are a variety of weak structures in PVC bonds, such as head-on structure, unsaturated double bond, active chlorine structure Branched chain structure and dichloro terminal structure, etc. Many studies have reported the relationship between the weak structure of PVC and its thermal stability. In this work, hgac catalyzed bromine addition method was used to determine the content of total unsaturated double bonds, and the relationship between the content of total unsaturated double bonds and the thermal stability of PVC was studied to guide the optimization of PVC production process. 1 Test Part 11 electric thermostatic water bath for instruments and reagents; Electric blast dryer (Shanghai Hunan Keqi joint venture factory) magnetic stirrer (made by Shanghai Nanhui telecommunication equipment factory) mercury acetate: 0 25mol/l bromine stock solution: 4G of liquid bromine is dissolved in 100ml of carbon tetrachloride, dried with calcium chloride, filtered and placed in the dark; 0.025mol/l bromine test solution: dilute bromine stock solution 10 times with dichloroethane; Ki solution: 20%hcl solution: 6mol/l; Sodium thiosulfate: 01mol/l; Starch solution: 1%pvc sample: provided by Xinjiang Shihezi chemical plant. Samples 1 and 2 are the samples before optimization, samples 3 and 4 are the samples under optimization, and samples 5 and 6 are the samples after optimization. 12 test method 1.2.1 add 15ml dichloroethane into the content bottle for the determination of double bonds by catalytic bromine addition method, heat it in a 70*c water bath for 1.5h, take it out, and cool it to room temperature. Then add 1ml of mercuric acetate while stirring. After standing for 25min, add 2ml of mercuric acetate while dripping and shaking to make it fully react. Then inject the above solution into 25ml of 10%ki aqueous solution (wash the volumetric flask with 5ml of dichloroethane for several times and add it into the ki solution) and add the magnon and starch solution. Put it on the magnetic stirrer and titrate with Na2S2O3 standard solution to obtain the volume of consumed Na2S2O3 standard solution. In order to accurately determine the content of total unsaturated double bond in PVC, it is necessary to eliminate the influence of impurities and other factors. Therefore, an empty and light vehicle body is carried out, which is not only beneficial to the resistance white test of descending and climbing. The formula for calculating the total unsaturated double bond content in PVC is the quantity of substances containing double bonds, 103; C is the concentration of nb2s2o3, mol/l; V0 is the volume of Na2S2O3 consumed in blank test, ml; VI is the volume of Na2S2O3 consumed by PVC sample, ml; M is the relative molar mass of vinyl chloride unit 621.22study on the thermo oxidative stability of PVC *c at constant temperature, PVC powder was put into an oven, and the content of total unsaturated double bonds of PVC powder after different thermo oxidative aging time was determined by catalytic bromine addition method. According to the change of total unsaturated double bond content of samples with different thermal oxygen aging time, the thermal stability of PVC samples was explained. Results and discussion 1. Selection of optimal reaction time 1. Method: accurately weigh about 250mg of No. 1 PVC wangguihua (1963 -), female, Beijing native, master, lecturer, 010. In terms of promoting transactions, the excited liquid dioxane is £ 5. Wax seal in the dark I! Set the "Ninth Five Year Plan" key grate of blishinl gold item! Related items (6:55=). The sample was placed in the dark to study the effect of the addition time of PVC double bond and bromine on the content of total unsaturated double bond in PVC. The results are shown in table 1 It can be seen from table 1 that the total unsaturated double bond content in PVC increases with the increase of reaction time, but when the reaction time exceeds 16h, the measured total unsaturated double bond content in PVC changes little, which indicates that the addition reaction between bromine and double bond tends to be complete in about 16h. In order to fully add the double bond with bromine, the reaction time was selected as 20h Table 1 Determination of total unsaturated double bond content in PVC at different reaction times reaction time 1 double bond content/1022 comparison of total unsaturated double bond content in PVC before and after optimization ~6 PVC sample, the total unsaturated double bond content was measured, and the results are shown in table 2 It can be seen from table 2 that the content of total unsaturated double bond of PVC sample after optimization is lower than that before optimization, which indicates that the optimization of force measurement value of pass height of polymerization formula and process conditions promotes the reduction of total unsaturated double bond content. Table 2 Determination of total unsaturated double bond content in No. 16 PVC sample amount/g consumed naog volume/ml total double bond content/103 No. 1, No. 2, No. 3, No. 4, No. 5, No. 6 blank 23 relationship between thermal oxygen aging time and total unsaturated double bond content taking No. 5 sample as an example, the change of total unsaturated double bond content after different thermal oxygen aging of PVC sample is studied. The results are shown in table 3 It can be seen from table 3 that with the increase of thermal oxygen aging time, the total unsaturated double bond content in PVC samples increases. Before 10min, the content of double bond changed steadily; After 10min, the double bond content increased with the aging time, indicating that the hydrogen chloride that began to be removed had a catalytic effect; After 20min, the content of double bond tends to be stable, which is consistent with the trend of decomposition rate of dehydrochlorination by thermogravimetric analysis. Table 3 change of total unsaturated double bond content corresponding to different thermal oxygen aging time aging time/sample mass/g total double bond content/103 blank 3 conclusion the content of total unsaturated double bond in the samples before, during and after optimization was determined by catalytic bromine addition method, which confirmed that the content of total unsaturated double bond in the PVC samples after optimization was significantly reduced, and the total double bond content in the PVC resin after thermal oxygen aging was determined, The results showed that the total unsaturated double bond content increased with the deepening of PVC thermal oxidative aging, which was consistent with the results measured by infrared spectroscopy and ultraviolet spectroscopy. 1

Copyright © 2011 JIN SHI