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

The thermo-mechanical degradation during the multi-extrusion of unstabilized and stabilized polypropylene copolymer (cPP) was analyzed using the Chain Scission Distribution Function (CSDF) method. During the first extrusion of unstabilized cPP almost 60% of the initial polymeric chains were submitted to chain scission. The calculations using CSDF show a random chain scission process of chains with molecular weight below 100 kg.mol -1 , and above that a preferential chain scission process. When stabilized the cPP molecular weight is kept constant, even after four extrusions, independently of the stabilizers concentration used. Its chain scission is greatly reduced, only being noteworthy at high values of molecular weight, presenting in this case a preferential chain scission process. During extrusion the unstabilized cPP evolves Volatile Organic Compounds (VOC) due to the volatilization of low molecular weight oxidized chain segments. VOC's emissions are greatly reduced during the melt processing of stabilized cPP, even after multiple extrusions.

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In the past 15 years our research group has been creating new optical devices to characterize in real time the extrusion process. These detectors are made of a slit-die fitted at the extruder exit from where the molten polymer flows, with a pair of transparent windows that allows a light beam to pass orthogonally through the molten flow. Following the reduction of the transmitted light intensity one is able to quantify the turbidity, which is a function of the type, concentration and particle size and shape of the second phase present in the flow. By evaluating the scattering pattern of a laser beam (LALLS) it is possible to get information upon the morphology of the molten polymeric system in real time during the extrusion. With the interposition of a pair of crossed polarizers in the optical beam, rheopolarimetry, it is possible to evaluate quantitatively the flow birefringence, which is a function of the degree of the polymer matrix orientation. POLYM. ENG. SCI., 54:386-395, 2014. ª

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