Poly (Vinylidene Fluride) Membrane Preparation and Characterization: Effects of Mixed Solvents and PEG Molecular Weight

In this study, polyvinylidene fluoride (PVDF) ultrafiltration membranes were prepared via immersion precipitation method using a mixture of two solvents triethyl phosphate (TEP) and dimethylacetamide (DMAc), which had different affinities with the nonsolvent (water). Properties of the prepared membranes were characterized using scanning electron microscope (SEM) and contact angle and membrane porosity measurements. The prepared membranes were further investigated in terms of pure water flux and BSA rejection in cross flow filtration experiments. The results showed that by using a mixture of DMAc and TEP as solvent and changing the mixed solvent composition, membranes with different morphologies from sponge-like to macrovoid containing were obtained. Maximum flux of the prepared membranes with different solvent mixing ratios was obtained for the one with 60%wt TEP in the casting solution of PVDF/TEP-DMAc/ PEG which equals to 76.8 lm-2h-1. The effect of addition of polyethylene glycol with different molecular weight on morphology and performance of the membranes has also been discussed. </span

Synthesis of Polybutadiene Particles via Emulsion Polymerization: Effect of Emulsifier and Initiator Contents on the Reaction Kinetics and Latex’s Particle Size

Batch emulsion polymerization of butadiene was performed at 70°C in a Buchi reactor equipped with mechanical stirrer (300 rpm) in the presence of potassium persulfate (KPS), and disproportionate rosinate, potassium cation (DPR) as initiator and emulsifier, respectively. t-Dodecyl mercaptane was used as a chain transfer agent in polymerization reactions. Conversion was measured at various time intervals by gravimetry. Polymerization rate was then calculated from the slope of conversion versus time curves. Particle size and its distribution of the polybutadiene latex (PBL) were measured by dynamic light scattering (DLS) and scanning electron microscopy (SEM). Depending on the emulsion polymerization conditions, PBL latices were obtained with average particles’ diameter and particle size distribution in the range of 88.5-189 nm and 35-400 nm, respectively. The number of particles per unit volume of the continuous phase was calculated from the average particle size data, from which polymerization rate per particle or equally its number of growing chains per particle was evaluated. Results showed that by increasing the emulsifier concentration, the average particle size decreases while polymerization rate increases. Moreover, the number of growing chains per particle decreased slightly by increasing the emulsifier concentration. Unlike classic emulsion polymerization, particle size and polymerization rate were observed to be more or less independent of initiator concentration. The results obtained from investigation of the reaction trend showed that kinetics of the emulsion polymerization of butadiene follows case 1(n<<0/5) of the Smith-Ewart kinetics. The observed behaviour was attributed to the lower efficiency of initiator in the particle nucleation and growth processes