The Study On The Methods For The Characterization Of Segment Structures In PVC Chains

The studies of the methods for the segment structures in PVC chains and the relationship between structure and performance are foundation of materials design and modification,not only in theoretical research,but in application.Most of the applied methods for the segment structures in PVC chains now are for the pre-treated PVC in which the content of the defect structures in PVC chains has been enchanced,but it is poor when the methods are used for the commericial PVC in which the content of the defect structures in commercial PVC resins is very low.The paper focus on the segment structures in PVC chains and is conducted to build more systematic and accurate analysis methods for the segment structures in PVC chains.Base on this and in order to build the relationship between the defect structure and materials performance for a theoretical support of PVC quality-control and modification,the unsaturated structures and oxygen-containing group models are built to study the relationship between the unsaturated structures and thermal properties,oxygen-containing group and thermal properties.The specific work includes the following aspects:1 the methods for the segment structures in PVC chains?1?In order to improve the testing accuracy of bromine addition to determine the total unsaturation in commercial PVC chains,the experiment was conducted with the combination technology of heating and ultrasonic treatment and under a closed container for titration process.The result showed that the total unsaturation in commercial PVC chains is about3.1028/1000VC and the relative deviation is less than 2%.?2?In order to improve the resolution and testing accuracy of UV-visible spectrophotometry?UV-Vis?to determine the conjugated polyene structures?CPS?in commercial PVC chains,a solution method with the 1,2-dichloroethane as solvent was proposed.The result showed that the resolution is largely influenced by the vinyl chloride structure unit concentration(C_vc)and the best resolution of spectrum was obtained at 0.08mol/L of C_vc.The number of CPS in PVC chains would not be more than 1/1000 and the relative standard deviation?RSD?of the conjugated polyene structures is less than 6%.?3?In order to assess the method of the X-Ray photoelectron spectroscopy?XPS?to determinate the oxygen-containing groups in commercial PVC chains,the thermal degradation of the commercial PVC resin was conducted at 190?and in different atmosphere for different time and the obtained samples were analyzed by XPS.The result showed that the XPS was sensitive to oxygen.The oxygen-containing groups consisted of-C-O?-OH and-C=O and their amount showed obvious change with different thermal degradation time.?4?In order to assess the method of the phenolysis to determinate the labile chlorine in commercial PVC chains,the standard curve was conducted with different concentration of phenol in THF and after phenolysis reaction,the PVC sample in THF was determinated with the aid of UV-visible spectrophotometry.The result showed that the labile chlorine in commercial PVC chains,Cl_L%,is about 0.1657 and the relative deviation is less than 7%.?5?In order to assess the method of the FT-infrared spectrometer?FT-IR?to determinate the carbonyl group in PVC chains,the thermal degradation of the commercial PVC resin was conducted at 120?and in different atmosphere for 10d and the obtained samples were analyzed by FT-IR.The carbonyl index?CI?was obtained by using the result of the height of the band at 1735 cm^-1divided by the 1429 cm^-1band.The result showed that the method is poor for the commercial PVC resin in which the amount of carbonyl group is very low but the sensitivety of the method is high for the thermal degradation PVC samples.?6?In order to assess the method of the nuclear magnetic resonance spectra?NMR?to determinate the unsaturation and configuration structures in PVC chains,the thermal degradation of the commercial PVC resin was conducted at 190?and in oxygen atmosphere for 40 min and the obtained samples were analyzed by NMR.The result showed that the method is poor for the commercial PVC resin in which the amount of the unsaturation group is very low,but the sensitivety of the method is high for the thermal degradation PVC samples in which the amount of the unsaturation group is higher,and the result was influenced by the scans times and magnet strength.?7?In order to assess pH meter method to determinate the thermal property of the commercial PVC resin,the evolved hydrogen chloride was deteriminated by a pH meter for the commercial PVC resin during thermal degradation at a certain temperature with the high pure nitrogen as carrier gas and the effect of temperature and gas flow were also investigated.The result was influenced by the temperature and gas flow and the data decreased with the temperature and gas flow increasing,respectively.The relative deviation is less than 6%.2 build structure models and the relationship between the structures and thermal propertyIn order to build the relationship between the unsaturated structures and thermal property,oxygen-containing group and thermal property,and study the mechanism of the thermo-oxidative degradation,the experiment focus on the segment structures in commercial PVC chains and is conducted to built the unsaturated structures and oxygen-containing groups model by treating the commercial PVC resin at 200?and 120?under nitrogen/oxygen atmosphere,and then the structures and thermal stability were analyzed with the aid of TGA,XPS and FT-IR.The result showed that the thermal property was greatly influenced by the oxygen-containing group,but the unsaturated structures.The thermo-oxidative degradation mechanism was that the methylene or methane structure in PVC chains was attacked by the oxygen molecular,then the carbonyl group was produced and the chains were broken.