Document Type: Original research
Faculty of Polymer Engineering, Sahand University of Technology, P.O. Box: 51335-1996, Tabriz, Iran
Institute of Polymeric Materials, Sahand University of Technology, P.O. Box: 51335-1996, Tabriz, Iran
Laboratory runs can be minimized via experimental design which yields the optimum and best data regarding the independent parameters. In this research work, response surface methodology (RSM) based on a three-level central composite design (CCD) was utilized to optimize and evaluate the interactive effects of processing conditions for polymerization of 1,3-butadiene (Bd) diene monomer using Ziegler-Natta catalyst. The polybutadiene rubber (PBR) having different cis content and molecular weight was obtained. The catalyst components included neodymium versatate (NdV3) as catalyst, triethyl aluminum (TEAL) as cocatalyst or activator, and ethylaluminum sesquichloride (EASC) as chloride donor. For the modeling, three independent variables, namely monomer concentration (8-28 wt. %), reaction time (1.5-2.5 h), and reaction temperature (45-75 ºC) at three levels were selected to optimize the dependent variables or responses including monomer conversion, viscosity-average molecular weight and the cis isomer content of the obtained polymer. The interaction between three crucial parameters was studied and modeled. Quadratic models were obtained to relate process conditions to dependent variables. It was observed that the optimal conditions predicted by RSM were consistent with the experimental data. Statistical analysis demonstrated that concentration of monomer and time of reaction significantly affected cis content. Moreover, processing conditions to achieve the desired response variables were predicted and experimentally approved. The optimal reaction conditions derived from RSM are monomer concentration = 19 wt. %, polymerization time = 2 hours, and polymerization temperature = 50 ºC. Polymerization was carried out at optimum conditions. The appropriate level of dependent variables including 94.2% monomer conversion, 151812 g/mol viscosity-average molecular weight and 98.8 % cis content was acquired.