Bulk and Dispersed Phase Polymerization of Urethane in Twin Screw Extruders

Abstract

Abstract The bulk and dispersed phase polymerizations of urethane were investigated in a co-rotating twin screw extruder. The residence time has predominant influence on the bulk polymerization in twin screw extruders. Furthermore, the polyurethane polydispersity decreases going down the screws, as the result of the extent of the reaction and mixing in the extruder. As expected, the polyurethane polydispersity at the die exit of the extruder is close to the theoretical value (Ip = 2). In the case of urethane polymerization in molten polyethylene matrix, the residence time distributions showed that the two monomers (isocyanate and alcohols) have different behaviors in the extruder in presence of PE due to the solubility of isocyanate and non-solubility of alcohols in PE. Furthermore, this solubility phenomenon PE induces an imbalance stoichiometry which limits the degree of polymerization (molecular weight) and a broadening of the molecular weight distribution during the blending process in extruder. Slip phenomenon was also observed at the die because of the presence of polyurethane, with low molecular weights, at the sample surfaces. An in-situ pre-polymerizing step of isocyanate/alcohols tends to eliminate this phenomenon. Then, the aim of the present work was to study the formation of a polyethylene/polyurethane blend polymer via in situ polymerization of diols and diisocyanate monomers dispersed in a twin screw extruder.