In‐line turbidity monitoring of the second phase droplets deformation during extrusion

Abstract

The dispersion and deformation of the second phase during extrusion of polymer mixtures were in real‐time characterized using an in‐line turbidimeter. Three polymer mixtures with constant concentration but very different viscosity ratios (1/4, 1, and 4) were reprocessed up to three times in a twin‐screw extruder. After that they were processed again, having the extruder exit being blocked by an on/off valve, which controls the hold‐on and discharge. The melt turbidity, a variable dependent of the droplets size and shape, was recorded during processing and controlled die‐head pressure discharge. The deformation of the droplets is high and reversible in mixture having viscosity ratio close to 1, indicating no droplet breakup and/or coalescence. In contrast, for high viscosity ratios and high matrix elasticity a hysteresis is formed during deformation/recovery of the droplets. POLYM. ENG. SCI., 53:2422–2428, 2013. © 2013 Society of Plastics Engineers

In-line optical techniques to characterize the polymer extrusion

“…b). This arrangement is fully explained in previous publications . Figure b shows schematically the design of the light‐scattering device developed in our group.…”

“…Finally, an on‐off valve, operated by a lever with two states: opened/closed, i.e., allowing flow/no flow of the extruder output was mounted ahead the slit‐die during some experimental procedures with two main objectives: first it can be set closed to assess the optical influence of the glass windows on the base‐line of the detector's signal for the rheo‐polarimetry measurements ; still having it set closed leads the extruder to “mimic” a torque‐rheometer. Second, when it is set opened the optical monitoring of the processed polymeric system can be taken in real time during the discharge of the material . A detail of the on‐off valve is shown in Fig.…”

“…After cycling for nine minutes, the valve was opened and the discharge of the polymer mixture started, based on a methodology previously devised : the discharge die‐head pressure is set by the software running a PID controller to vary cyclically in a ramp profile from zero to 2.07 MPa. While the molten polymer mixture is discharged, the response from the optical detector was recorded, corresponding to the turbidity of the molten flow, which is dependent on the size and shape of the second phase droplets.…”

“…This article deals with the use of in‐line optical detectors based on visible‐light stimulus and procedures developed in our research group to monitor the extrusion of multiphase polymeric systems. When studying morphology development of polymer mixtures the flow type plays a critical role in determining whether or not drop breakup is possible.…”

“…Migler et al found coexistence between large aspect ratio strings and ellipsoidal droplets mildly deformed in the slit‐die land for PE/PS mixture by visible‐light microscopy visualizations; they also showed the depth dependence of the morphology. Recently, Zborowski and Canevarolo proposed an in‐line procedure to probe the deformation/recovery phenomena of disperse phase droplets in PP/PS dilute mixtures by turbidity in a slit‐die attached to a twin‐screw extruder.…”