Preparation And Research Of Phenol/Formaldehyde Microspheres Via Water/’Water’ System

Polymer microspheres have been a hot topic in recent years because of their special performance and application. As one of them, phenolic resin microspheres have a wide application in advanced coating, precursor reinforcement of carbon foam, lightweight adhesive thermal ablation on aircraft materials. But the preparation methods of phenolic microspheres are restricted to oil-soluble mediums which must involve organic solvent. In this research, phenol/formaldehyde microspheres are successfully prepared in such water/’water’system in presence of acid catalyst, which was expected to enrich the polymerization method of step polymerization. Furthermore, the mechanism of microsphere formation in such new system is firstly studied. Main works are as follows.Ammonium sulfate solution with HEC was employed as’water’ phase and the mixture of phenol/formaldehyde/H2SO4was called water phase to prepare phenol/formaldehyde resin microspheres. The homogeneous and stable microspheres with rather smooth surface were prepared under proper condition. FTIR spectrum and NMR spectrum were used respectively to confirm the phenolic composition and chemical structure of microspheres. The result showed that the molecule structure of microspheres was branched.Based on above research, the mechanism and process of microspheres formation was studied via a series of dynamic research. The effects of reaction time on particle size and particle size distribution of phenolic microspheres and content of free formaldehyde in the system under different conditions including monomer ratio and amount of AS or HEC were studied. In the mean while, the change of SEM photographs and statuses of system were characterized as an aid. The mechanism was finally decided as dispersion polymerization after excluding the possibility of emulsion polymerization and suspension polymerization via change the loading way of monomers.The reactions were conducted at different conditions and the effects of these reaction parameters on particle sizes, particle size distribution and morphology of microsphere were investigated. The results showed that phenolic microspheres had perfect morphology. Furthermore, the particle size of microspheres obviously increased with the reaction time and amount of AS increasing, while decreased as the amount of HEC increasing. However, The PDI value varied narrowly in a small range under different conditions, which kept constantly around1.1.The study results are expected to enrich the method of preparing phenolic microspheres for industries, and the studied on the mechanism and process of microspheres formation are expected to be a instruction to following researches.