(649f) Reactive Extrusion Process and Elasticity in Sol Gel Polymers

Twin screw extruder (TSE) is a versatile melt mixing equipment for polymer processing especially in reactive extrusion, compounding, and in controlling sol gel process. The screw elements contribute to conveying and kneading enables optimizing dispersive and distributive mixing for reactive extrusion. The residence Time distribution (RTD), residence volume distribution (RVD) and residence rotation distribution (RRD) are powerful considerations in characterizing extruder performance. Residence Time Distribution can be predicted from input variables such as moisture content, screw speed, nozzle diameter and barrel temperature.  Increase of rotation speed results in significant increase of filler dispersion, whereas an increase of throughput resulted in worse dispersion. Beside these machine parameters, the design of the screw can further promote the filler dispersion especially when using distributive screw configurations containing mixing elements. Viscoelastic nature of the polymer must be taken into account in analyzing extrusion flows. The characteristic relaxation time λ of the polymer has proved to be the key quantity. When λ is small and viscous effects dominate, the RVD model approach is applicable. When λ is large, the elastic effects of the polymer may dominate under typical flow conditions.

Styrene acrylate and polyesters were reactive extruded in twin screw extruder Werner Pfleiderer 30mm Twin Screw Extruder, Type ZSK 30 and in Werner Pfleiderer ZSK 70, with organic peroxide as  cross-linker. The extrudates were crushed into small particles and they were compressed into discs which were characterized for dynamic viscoelastic modulus and complex viscosity using TA instrument of Rheometrics Spectrometer. The strain amplitude was kept at or below 1%.  Screw speeds, feed rate and barrel temperature were varied as processing variables while material variable was the variation in peroxide concentration that resulted in different concentration of gel in the composite. The results show that as the gel concentration is increased, Weissenberg number (Wi) increases Threshold in screw speed and peroxide concentration was investigated finding conditions when mixing was poor, had lower melt flow rate and when plug flow occurred.