Use of dye-containing polymeric microcapsules for the determination of shear stresses in polymeric systems during compounding (internal batch mixer, single screw extruder).

摘要

The primary objective of this research is to determine the rupture response of two polymeric microcapsules, which contain a visibly detectable dye, in both an internal batch mixer (IBM) and a single screw extruder (SSE) under a variety of well controlled processing conditions. The two polymeric microcapsules examined, CM511 and CM567, have average diameters of 36 and 48 microns respectively. Their rupture response is examined in both a single polymer melt, polystyrene (PS) and a multiple polymer (PS/poly(methyl methacrylate) (PMMA) system. The degree of rupture is determined using ultraviolet/visible spectroscopy and colorimetric analysis of pressed out films for the PS and PS/PMMA respectively. Optical microscopy (OM) is also used to verify conclusions made from these studies. The average shear stress value in the IBM is determined using torque rheometry equations found in the literature which convert the IBM mixing torque to a bulk average shear stress value. Shear stress values in the SSE are determined using equations developed for flow in a parallel plate geometry.; It is observed that the CM567 microcapsule begins to rupture at a shear stress value of 100 kPa and achieves complete rupture at a shear stress level of 230 kPa. In the case of the CM511, complete rupture is not observed over the shear stress range investigated.; At shear stress values between 130 and 190 kPa, the time for both microcapsules to achieve a steady state breakup value is on the order of four to five minutes. This time period is independent of the magnitude of the stress environment and the size of the microcapsule used in this work.; Finally, it is also observed that the microcapsules can provide insight into the nature of the melting mechanism in the compression zone of the SSE as the temperature in this zone is manipulated.