Thermal Stability Mechanism For Urea Derivatives As Thermal Stabllizers Of Poly(Vinyl Chloride)(PVC)

Polyvinyl chloride ( PVC ) is a kind of thermoplastic high polymer which is compound produced by polymerization reaction of monomer vinyl chloride and it is one of the earliest industrial polymer materials. After more than 100 years development, PVC has grown into one of the world's second largest production and most dynamic materials. However, PVC has many advantages, but there are fatal shortcomings of poor thermal stability, that is, it began to degrade when heating to 140?, and some of the traditional PVC thermal stabilizers in the degradation process will produce toxic residues, which may cause the environment problem. As public awareness of environmental issues is gradually improving, more and more researchers are beginning to turn their attention to the study of organic stabilizers now.In the first part, Hydroxyethylurea and 1,3-Diphenyl-2-thiourea(DFT) were synthesized successfully via a precipitation method, and characterized with 1H NMR spectra. They were investigated as thermal stabilizers for poly(vinyl chloride) (PVC)by torque rheometer, thermogravimetric analysis (TGA), congo red test, fourier transform infrared(FTIR) and exploring the possible thermal stability mechanism. In addition, 1,3-Diphenyl-2-thiourea (DFT) or hydroxyethylurea and calcium stearate(CaSt2) mixed at different mass ratios and then explored its thermal stability by discoloration test, the results show that this mixed thermal stabilizer greatly improved the thermal stability of PVC, especially the excellent initial color.In the second part, novel thiouracil thermal stabilizers for rigid(vinyl chlorid)(PVC), 6-methyl-2-thiouraci (6M2TU), 5-methyl-2-thiouraci (5M2TU) and 6-propyl-2-thiouraci (6P2TU) were synthesized successfully via a precipitation method, and characterized with 1H NMR spectra. Investigation of these thiouracil derivatives as thermal stabilizers for poly(vinyl chloride) (PVC) was measured by torque rheometer, thermogravimetric analysis (TGA), congo red test, fourier transform infrared(FTIR) and discoloration test. The results show that the thiouracil derivatives have strong ability to replace the labile chlorine atoms in PVC chains, but weak ability to absorb hydrogen chloride (HCl). Moreover, PVC using these thiouracil derivatives and calcium stearate (CaSt2) as a thermal stabilizer were compared with the same concentration of conventional Ca / Zn stabilizer thermal stability.In the third part, the organic compound 2-phenylindole, which is also a nitrogen atom structure, was selected as the research object. The thermal stability and possible mechanism of the PVC thermal stabilizer were investigated by the same method as the two parts above as well as its synergistic effect with the use of calcium stearate(CaSt2).