Fabrication of composite membranes for pervaporation of tetrahydrofuran-water: Optimization of intrinsic property by response surface methodology and studies on vulcanization mechanism by density functional theory

Abstract

Response surface methodology (RSM) optimized accelerator-to-sulfur (A/S) ratio was used to synthesize semi efficiently vulcanized styrene butadiene rubber (SBRSEV0) membrane possessing optimum balance between tensile strength (TS) and elongation at break (EAB). In addition, composite membranes, such as SBRSEV8, SBRSEV12 and SBRSEV24, were fabricated via incorporating 8, 12 and 24 wt% carbon black filler (CBF), respectively. The changes in physicochemical properties, as a result of crosslinking and CBF loading, were determined by analyzing CP MAS ¹³C-NMR, FTIR, TGA, DSC, XRD, FESEM-EDX and crosslink densities. Several bi-/poly-sulfidic products, formed by crosslinking precursors of SBR in accelerated sulfur vulcanization, were examined to ascertain the unambiguous reaction mechanism. In this regard, an extensive density functional theory (DFT) based optimization was conducted to apprehend the relative variation in stabilities of several mono-/poly-crosslinked configurations by measuring dipole moments and ground state energies. Moreover, intrinsic membrane properties, such as partial permeabilities and diffusion coefficients, were measured at varying conditions. RSM was employed to optimize membrane efficiency resulting from individual and/or interactive effects of input variables. For the first time, systematic three-stage RSM based optimization (i.e., TS/EAB, total flux (TF)/separation factor (SF) and partial permeabilities) was used to ensure excellent balance between TS/EAB (5.78 MPa/499.008% at 2.32 and 3.29 wt% of A and S, respectively), minimum TF/maximum SF (36.90 g m^–2 h^–1/202.46 at 35 °C, 0.97 wt% tetrahydrofuran (THF) and 24 wt% CBF) and minimum/maximum partial permeabilities of water/THF (2.94×10^–8/4.64×10^–8 Barrer at 35 °C, 0.97 wt% THF and 11.49 wt% CBF).