A New Method For Assessing Mixing In Viscous Media And Its Application

Many important industrial operations take place in viscous media and the viscosity of system may increase by several orders of magnitude in some cases while the quality of local mixing can influent the structure of growing macromolecule.Though several chemical methods such as the competitive-consecutive reactions or the parallel competitive reactions have been proposed to measure the micromixing efficiency,most of the traditional methods are based on the systems of small molecule,can these methods reflect the behavior of viscous media such as polymeric system was not examined.Twin-screw extruders were widely used in polymer process and the mixing condition was used to be studied by residence time distribution by small molecule tracers,whether the small molecule can exactly reflect the flow of polymer was an unfathomed question.Find a new method to answer these questions and study on the mixing condition in TSE is a challenging fundamental research topic.A new macromolecular parallel competitive reaction system for assessing micromixing in viscous media was developed and a new kind of macromolecular tracer for study of RTD was synthesized.By these methods,mixing condition in TSE was studied.Most relevant results obtained in this work are summarized as follows.1 Tow kinds of new copolymers PS-co-TMI and PS-co-TMI-MAMA were synthesized.PS-co-TMI contain an isocyanate group which can react with many active groups,it can be used as intermediate to synthesize functional polymer such as PS-co-TMI-MAMA.PS-co-TMI-MAMA is a new kind of polymer which contain anthracene groups which can be easily examined by UV or fluorescence.It can be used as macromolecular tracers to assessing RTD.2 A new system of two parallel chemical reactions of macromolecule for assessing micromixing in viscous media has been developed.It's composed by the reaction between PS-co-TMI and MAMA and the reaction between PS-co-TMI andε-CL,where reaction between PS-co-TMI and MAMA is instantaneous reaction and reaction between PS-co-TMI andε-CL is slower.Micromixing condition in a tank was studied by this new system and the traditional iodide-iodate system,results indicated that the mixing condition improved with higher stirred speed and eddy engulfment is the key factor in micromixing of small molecule and diffusivity is major control step in macromolecular system.3 Reaction mechanism and kinetics of the reaction between PSt-co-TMI andε-caprolactam was studied by ¹³C NMR and FTIR.It indicated that reaction between PSt-co-TMI and CL is a reversible addition reaction resulted in PSt-co-TMI-CL.At 76.0℃～129.0℃and molar ratioε-CL/PS-co-TMI=2.62～82.7,the activation energy of positive reaction equal 82.2 kJ·mol^-1 with frequency factor equal 6.73×10⁸;the activation energy of negative reaction equal 117.8 kJ·mol^-1 with frequency factor equal 2.43×10¹².4 The macromolecular tracer PS-co-TMI-MAMA and competitive reaction system were used to assess micromixing condition in the twin-screw extruder..It indicated that micromixing is finished very quickly in the front of extruder and maintain stability at same operation conditions.For the transport elements at starve condition,micromixing improved at higher feed rate and lower screw speed,dimensionless RTD is almost independent of feed rate and screw speed.Fill degree is an important parameter which controls the micromixing in TSE and higher screw speed is helpful for micromixing at same fill degree.