(283i) The Solid State Shear Extrusion Process Optimization for Cross-Linked Polymers

Developing a commercial technique to produce fine particles with proper physical and chemical properties from cross-linked polymers is one of the challenge areas in particle technology. The Solid State Shear Extrusion (SSSE) process is one of the mechanical techniques for pulverization that has been used for reducing the size of cross-linked polymers. The process involves extrusion of material at high shear and normal stresses. Here we focus on optimizing this process for cross-linked natural rubber in different combinations of temperatures and rotating speeds of the screw (which is proportional to shear forces) to get insight into the pulverization mechanism. The produced Particle Size Distribution (PSD) was found to be strongly dependent on the rotating speed. For a given residence time the average PSD increases with increasing rotation speed because of the decreasing residence time. It was also observed that, in order to pulverize a cross-linked polymer, the process should be operated in a particular range of temperature in order to minimize the viscous property of the polymer and maximize its elastic property. The cross-linked polymer that undergoes the pulverization process dictates this particular range of temperature. The average particle size versus the applied average temperature in the process showed a non-monotonic change in natural rubber. This non-monotonic behavior might be caused by competition between the energetic elasticity and the entropic elasticity of the natural rubber. In other words, in a low temperature range, the entropic elasticity is the dominator and, by increasing the temperature, the energetic elasticity becomes the dominator.