Gelation and Properties of Chemically Crosslinked Gel of Polyvinyl Alcohol
| Autor: | Mei-Shan Hu, 胡美山 |
|---|---|
| Rok vydání: | 1999 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 87 The purpose of this study is focused on the preparation of polyvinyl alcohol gels, their gel properties, and microstructure of those gels. The chemically crosslinked gel of polyvinyl alcohol polymer with boric acid, added as a crosslinking agent, was made with a mixture of dimethyl sulfoxide and water. The polyvinyl alcohol polymer with four kinds of degree of polymerization (P) (1700, 2000, 2400 and 2600) was used in this study. From the experimental results, the viscosity of polyvinyl alcohol solution is found to increase not only with the increment of boric acid content, but also with the temperature in the range of 70 ℃ ∼ 100 ℃, although the viscosity is increased in the range of 30 ℃ ∼ 70 ℃. The gelation temperatures are between —15 ℃ and 70 ℃. It is found that the gelation time is decreased with the decreasing of gelation temperature. As the gelation temperature is below 0 ℃, the gels are nearly transparent, and also the polyvinyl alcohol concentration is independent of gelation temperature. Moreover, the minimum requirement of polyvinyl alcohol concentration to form a gel is proportional to P-0.5. On the contrary, as the gels were formed above 0℃ the gels were opaque (milky white). The transmission of the visible light to gels was decreased with the increment of gelation temperature. However, the light transmission of gel was increased with an increment of polyvinyl alcohol concentration. The thermal and dynamic modulus properties of polyvinyl alcohol gels were measured by a differential scanning calorimeter and a dynamic mechanical thermoanalyst, respectively. Results show that an increment of polyvinyl alcohol polymer concentration, or boric acid content to the gel makes an increasing of gel to sol transition temperature, endothermic enthalpy and dynamic modulus. The maximum values of gel to sol transition, endothermic enthalpy and dynamic modulus happen at the volume ratio 6:4 of dimethyl sulfoxide to water, which is independent on the polyvinyl alcohol polymer and boric acid content. According to the modified Eldrige-Ferry theory for thermoreversible gel, it is found that both of gel to sol transition temperature and endothermic enthalpy vs. polyvinyl alcohol content could be superimposed with respect to the boric acid content. We also evaluate the values of Young''s modulus of polyvinyl alcohol gel, E, E*, and the elastic parameters, C1 and C2 of Mooney-Rivlin equation, according to the Hooks law and the theory of rubber elasticity, respectively. Based on these, the polyvinyl alcohol gel behaves a good rubber-like elastic behavior. As seen from the wide angle X-ray diffraction patterns, it exhibits crystal in gel. The morphology of the gel is significantly influenced by the liquid —liquid phase separation, as observed from the scanning electronic microscope. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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