Study On Hetero-coagulation Process Of Poly (Tetrafluoroethylene) Latex Particles And Inorganic Particles

It is an important method to modify polytetrafluoroethylene (PTFE) by compositing PTFE with inorganic particles. In order to overcome the disadvantage of poor dispersion of inorganic particles in PTFE in the usual mechanical blending, a new method, in which PTFE latex particle were hetero-coagulated with inorganic particles, was developed to prepare modified PTFE. The hetero-coagulation of PTFE latex particles and carbon black particles under the function of coagulation agent, and hetero-coagulation of PTFE latex particles and Fe2O3 particles without coagulation agent, were investigated. The influences of inorganic particles characteristic, coagulation agent kinds, coagulation condition on hetero-coagulated particles size distribution and morphology was obtained. The mechanism of particle formation in the hetero-coagulation was discussed. The results would provide base for preparing modified PTFE by hetero-coagulation in industrial scale.Hetero-coagulation of PTFE latex particles and carbon black particles have been studied with different coagulation agent, such as A1(N03)3, CaCk and KC1. The influence of latex kinds, temperature, agitation speed on hetero-coagulation process were investigated. When the coagulation conditions and coagulation agent were same, PTFE latex with lower Zeta-potential could be easily coagulated. The diameter of hetero-coagulated particles increased and morphology was more irregular when temperature was increased. As agitation speed increased, the diameter of hetero-coagulated particle diameter decreased. SEM experiment showed that a hetero-coagulated particle was a carbon black covered by many PTFE latex particles. The composite particles prepared by this method were hydrophobic. The particle formation mechanism of composite particles was discussed.Hetero-coagulation of PTFE latex particles and Fe2O3 particles was carried out without coagulation agent. Effect of Fe2O3 particles charge, pH, Fe203/PTFE particle size ratio and Fe2O3 particle concentration on hetero-coagulation were investigated. The results showed that when charges of the two kinds of particles were opposite and the absolute value of Zeta-potential were approximate, PTFE latex particles and Fe2O3 particles were easily to hetero-coagulate. Through adding some cationic surfactant to adjust Zeta-potential of Fe2O3 particles, Fe2O3 particles with negative charge couldbecome positive and hetero-coagulate with PTFE to form hetero-coagulated particles. Zeta-potentials of the particles were related to pH. The relationship between pH of the dispersion medium and Zeta-potentials, and suitable pH for hetero-coagulation were obtained. Since Zeta-potentials of PTFE and 2# Fe2O3 were -46mV and 42.3mV, respectively, they would be hetero-coagulated easily. It is found that Zeta-potentials increased gradually from negative in process of hetero-coagulation of PTFE and nanometer Fe2O3 and Zeta-potentials was equal to that of distilled water when hetero-coagulation was finished, which indicated that Fe2O3 particles gradually deposited and adsorbed on PTFE particles in the hetero-coagulation process. Through observing the variation of particles size in the hetero-coagulation process, it found that hetero-coagulated particles were formed shortly after the mixing of two kinds particles.The morphology, composition and structure of PTFE/ Fe203 hetero-coagulated particles were studied. It found that morphology and structure of PTFE/ Fe2O3 particles varied with Fe2O3/PTFE particle size ratio. When Fe2O3/PTFE particle size ratio=7.54, the hetero-coagulated particle had core-shell structure with Fe2O3 particle in the core. When Fe2O3/PTFE particle size ratio=1.9, the hetero-coagulated particles were composed of irregular aggregates. The hetero-coagulated particles generated from hetero-coagulation of PTFE and nanometer Fe2O3 also had core-shell structure, but PTFE particle became the core. The hetero-coagulated particle was stable under ultrasonic function. The formation of hetero-coagulated particle undergoes three stages: the first...