pH值对正十八烷微胶囊合成与性能的影响

Effects of pH on Synthesis and Properties of Microencapsulated n-Octadecane

研究了采用正十八烷为囊芯,三聚氰胺-甲醛为囊壁原位聚合法制备相变材料微胶囊过程中,乳液制备、预聚体制备和聚合过程中pH值对乳液和预聚体稳定性,以及微胶囊表面形貌和性能的影响.结果表明,pH值控制在6.5～9.0之间对乳液的稳定性影响很小.三聚氰胺-甲醛树脂预聚体在酸性条件下容易缩聚;预聚体分离时间随着pH值的升高而逐渐延长,随着保温温度的升高而缩短;在pH值较低时,部分甲醛残留在三聚氰胺-甲醛树脂中.缩聚体系中的pH值为4～5时,合成的微胶囊分散性好且呈球形,胶囊的热焓和耐热温度随pH值增大呈上升趋势.考虑到胶囊的分散性和合成周期,pH值最好控制在4～5.

The effects of pH on the emulsion and prepolymer solution stability, morphologies and properties of the microcapsules were studied in the fabrication of microencapsulated n-octadecane by in-situ polymerization of melamine-formaldehyde. The pH value in the range of 6. 5 -9. 0 does not significantly affect the stability of the emulsion. The prepolymer of melamine-formaldehyde is easy to polymerize in the acid solution, however, it is hard to polymerize in the alkaline solution. The separation time of the prepolymer solution is prolonged with the increase of pH value, and shortened with the increase of temperature. The residual formaldehyde exists in the melamine-formaldehyde polymer when the pH value is low. The microcapsules are perfect sphere and are dispersed well when the pH value of polymerization system is 4 - 5. Both the enthalpy and thermal stable temperature of the microcapsules increase with the rise of pH value; however, the pH value in the range of 4 - 5 is preferable due to the dispersity and reaction period of the microcapsules.