Preparation of Ultra High Molecular Weight Polyethylene Using Ziegler-Natta Catalyst System: Optimization of Parameters by Response Surface Methodology

The ultra-high molecular weight polyethylene (UHMWPE) was prepared using titanium tetrachloride (TiCl4) supported by MgCl2 (ethoxide type), accompanied by triisobutylaluminium (TIBA) as co-catalyst. These all constituted the Ziegler–Natta catalytic system. MgCl2 is one of the best supports for Ziegler-Natta catalyst in order to increase its yield.In the present study, the process variables were investigated through response surface methodology (RSM) to optimize the productivity of the catalyst and also the molecular weight of the polymer. Taking this into consideration a three-level Box-Behnken design for three factors with temperature (X1), monomer pressure (X2), and [Al]/[Ti] molar ratio (X3) as the independent variables were selected. Different molar ratio of [Al]/[Ti] is achieved by changing the amount of the co-catalyst.The dependent variables were productivity and molecular weights of the prepared polymers. Specifically, using these three parameters at three levels including 50, 60, and 70°C for temperature; 4, 6, and 8 bar for pressure; and 150, 250, and 350 for [Al]/[Ti] molar ratio. The RSM yielded optimum reaction conditions equal to: temperature of 55°C, pressure of 8 bar, and [Al]/[Ti] molar ratio of 230. Under these optimum conditions, the productivity and molecular weight were 2628 g PE/mmolTi.h and 5.09×106 g/mol, respectively.