The Stability Of Non-aqueous Emulsion And Application In Synthesis Of Polimide Microspheres

Polyimide is one of the most promising high-performance polymeric materials possessing highly thermal stability,good mechanical properties,and low dielectric constants.Polyimide microspheres have characteristics of polymer microspheres and excellent performance of polyimide.In future,Polyimide microspheres will have broad application prospect in catalytic carrier,ion exchange,purification,aerospace materials,etc.Through earlier period exploration,the method of non-aqueous emulsion was put forward for preparation of polyimide microspheres.The method has some advantages:operation process simple,easy to operate,mild conditions.So it can prepare microspheres of high solid content and good dispersivity.However,the stability of non-aqueous emulsion was poor,PI microspheres were obtained having irregular sphere.Therefore,it is significant to study the stability of non-aqueous emulsions.In this paper,N’N-dimethylformamide as the dispersed phase and liquid paraffin as the continuous phase prepared non-aqueous emulsion system.Several factors influencing the stability of non-aqueous emulsions are investigated,such emulsion conditions,non-ion surfactant,ionic surfactant,polymers and inorganic particles and so on.The main contents and conclusions of this paper are as follows:（1）In order to make sure the optimal condition of preparation of non-aqueous emulsion system,the influence of the ratio of DMF and liquid paraffin,emulsion temperature,the amount of emulsifier was investigated.Emulsion stability was investigated by variation of emulsion volume fraction with time,hydrophile-lipophile balance,droplet diameter and stabilization time.Through these experiments,the best surfactant was found out.The results showed that the temperature was 50℃,VDMF:VLP=1:5,the amount of emulsifier was 10wt%;Comparing the stability of non-aqueous emulsion by Tween80,L64 and M-2070 with Span85 blends to prepare,the conclusion was:Span85+Tween80>Span85+M-2070>Span85+L64.The optimal mix surfactants was Span85 + Tween80 to stable the non-aqueous emulsion system,the ratio of mass was m（Span85）:m（Tween80）=2:1,stable time was more than 12 h,droplet size was 200 nm,the best HLB value was 6.2.（2）In the non-aqueous emulsion with the Span85 + Tween80 as blends surfactants,the ionic surfactant,polymer and mineral nutrients the effect on the stability of the emulsion was investigated,through the test of stability,Zeta electric potential and droplet size,to ensure the stability of the non-aqueous emulsion.The results showed that:anionic surfactant can increase the potential of emulsion particles,to strengthen the role of rejection between droplets,to promote the stability of non-aqueous emulsion system;Cationic surfactant increases the surface tension of the phase DMF,make the system stability worse;Polymer stabilizers reduced the non-aqueous emulsion density difference,viscosity difference,to enhance the stability of the non-aqueous emulsion system;In certain concentration range the inorganic salts solid grain of AlCl₃ solid particles can enhance the stability of the non-aqueous emulsion.（3）Polyimide microsphere is taken as mode for preparing in non-aqueous emulsion.The product was characterized by SEM,Particle size distribution.The results indicated that in the non-aqueous emulsion system,when emulsifiers were Span85 + Tween80 and Span85 + Tween80 + PVP respectively,PI microspheres were spherical neat and good scattered;Change the amount of blends emulsifier can control the PI microspheres of morphology and size.