Processing And Kinetic Studies Of The Reactive Blends Of Polyvinyl Chloride And Thermoplastic Polyurethanes

Download or read book Processing and Kinetic Studies of the Reactive Blends of Poly(vinyl Chloride) and Thermoplastic Polyurethanes written by Johanna Baena and published by . This book was released on 2006 with total page 342 pages. Available in PDF, EPUB and Kindle. Book excerpt: A novel reactive blending process was investigated to produce poly(vinyl chloride)/thermoplastic polyurethane (PVC/TPU) blends of significant commercial interest. The reactive blending process took place in two stages. The thermally stabilized PVC was plasticized with the polyol monomers of TPU, and then the polyols reacted with diphenylmethane diisocyanate (MDI) to polymerize TPU in-situ with the PVC. In the first stage of the reactive blending, either a polyester or a polyether polyol and 1,4-butanediol (BDO), which forms the TPU's hard segment, were blended with PVC. The polyester polyols included poly(butylene adipate) (PBA), poly(hexamethylene adipate) (PHA) and poly(propylene adipate) (PPA), while the polyether polyol was poly (propylene glycol) (PPG). In the second stage of the reactive blending, several commercial MDIs, including 4,4'-diphenylmethane diisocyanate (SMDI), a mixture of 4,4'-diphenylmethane diisocyanate and 2,4'- diphenylmethane diisocyanate (LMDI), and carbodiimide Modified 4,4 Diphenylmetane Diisocyanate (CDMDI) were used. Initially, blends of PVC with the various polyols were prepared in a batch internal mixer. The PBA and PHA were partially miscible with the PVC in a wide range of compositions. The PPA turned out to be partially miscible with PVC only at high concentrations of PVC, and the polyether (PPG) was immiscible with PVC. The miscibility and resultant morphology of the blends were determined by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), respectively. The reactive blending studies were performed in both a batch internal mixer and a continuous counter-rotating intermeshing twin-screw extruder. The miscibility, morphology, and mechanical properties of the blends were determined by differential scanning calorimetry (DSC), Fourier transformed infrared (FTIR), scanning and transmission electron microscopy (SEM and TEM), and Instron tensile testing respectively. The study in the batch internal mixer revealed that PVC was miscible with the TPUs produced when the TPU was formed from the polyester polyols, i.e. PBA, PHA and PPA. TEM revealed that the PVC/TPU blends had a multiphase morphology at room temperature, with varying morphologies that depended on the monomers used. The mechanical properties of the reactive blends depended on the MDI used and they showed superior tensile properties than the analogous melt blends. The reactive extrusion (REX) in a continuous counter-rotating intermeshing twin-screw extruder was shown to improve the PVC/TPU (LMDI) properties compared to those obtained by a batch internal mixer. In REX a liquid MDI was required to assure accurate MDI feeding, given the difficulties in feeding SMDI, which dimerizes at room temperature. Additionally, the use of a liquid MDI provides the fulfillment of the stoichimetric ratio that is critical to obtaining high molecular weight polyurethane. The reactive blending studies with the different MDIs resulted in blends with different properties and phase morphology, but similar thermal properties. The kinetics of TPU polymerization was studied in a rheometer and in a home-made vessel under various conditions of shear and pressure, respectively. This study revealed that pressure had negligible effect on the polymerization under the conditions studied, but that the shear rate influenced the rate of TPU polymerization appreciably. The effect of different polyols (PBA and PHA) and a variety of MDIs (SMDI, LMDI and CDMDI) on the TPU polymerization was studied. It was observed that the kinetic parameters depended on the chemical structure, functionality and reactivity of the monomers. Lastly, the effect of the addition of the PVC on the kinetics of TPU polymerization was studied. It was observed that the PVC stabilizer works as a TPU polymerization catalyst. The kinetic equation obtained that includes the effects of temperature, pressure, and shear would be useful for applications in twin screw extruders.