| A novel reactive blending process was investigated to produce high performance poly(vinyl chloride)/thermoplastic polyurethane (PVC/TPU) blends of significant commercial utility. In this process, a high molecular weight TPU with poly(butylene adipate) (PBA) soft segments and 4,4 ′-diphenylmethane diisocyanate/1,4-butanediol (MDI/BDO) hard segments was polymerized in situ with PVC. More specifically, the process was broken down into two fundamental stages: the compounding and plasticization of PVC with PBA and BDO, and, upon adding MDI, the subsequent polymerization of TPU in situ with PVC to produce a PVC/TPU blend. A powerful, versatile characterization tool, Raman spectroscopy was used to elucidate the presence of intermolecular interactions in both stages of the PVC/TPU reactive blending process and measure the kinetics of TPU polymerization in situ with PVC.; Initially, model studies of the PVC/TPU reactive blending process were conducted on a batch internal mixer. In the first stage of the process, the TPU reactants PBA and BDO effectively functioned as plasticizers as they were completely miscible with PVC. In the second stage of the process, TPU polymerization in situ with PVC was accompanied by reaction induced PVC/TPU blend phase separation. Partially miscible, PVC/TPU blends were characterized by multi-phase morphologies at room temperature, with a broad distribution of phase sizes and compositions. In measuring their effect on reaction kinetics, both PVC and its tin mercaptide thermal stabilizer catalyzed TPU polymerization. In measuring some of their mechanical properties, PVC/TPU blends produced via reactive blending had comparable and even superior tensile properties to analogous PVC/TPU blends produced via melt blending.; Using information gleaned from the former model studies, the PVC/TPU reactive blending process was also conducted on a continuous, counter-rotating, intermeshing, twin screw extruder. In these reactive extrusion studies (REX), resultant PVC/TPU blends morphologies and tensile properties were similar to that observed in the model studies. Relative to the model studies, however, maintaining balanced stoichiometry, and thus polymerizing high molecular weight TPU in situ with PVC, was far more difficult. |
