2014-07

Macromolecules (القضية : 16) (الحجم : 47)

Membrane gas separations require materials with high permeability and good selectivity. For glassy polymers, the gas transport properties depend strongly on the amount and distribution of free volume, which may be enhanced either by engineering the macromolecular backbone to frustrate packing in the solid state or by thermal conversion of a soluble precursor to a more rigid structure of appropriate topology. The first approach gives polymers of intrinsic microporosity (PIMs), while the second approach is used in thermally rearranged (TR) polymers. Recent research has sought to combine these approaches, and here a new range of thermally rearrangeable PIM-polyimides are reported, derived from dianhydrides incorporating a spiro center. Hydroxylfunctionalized polyimides were prepared using two different diamines: 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (bisAPAF) and 4,6-diaminoresorcinol (DAR). Thermal treatment at 450 °C under N2 for 1 h yielded polybenzoxazole (PBO) polymers, which showed increased permeability, compared to the precursor, in membrane gas permeation experiments. A polymer based on DAR (PIM-PBO-3) exhibited a CO2/N2 selectivity of 30 as prepared, higher than the values of 21−23 obtained for polymers derived from bisAPAF with the same dianhydride (PIM-PBO-1).

2012-07

Iraq. J of Polymers (القضية : 2) (الحجم : 16)

In this work peppermint stem (PMS) was collected from Baghdad area, which is a wild plant, dried and ground to particle size 200-500µm, then washed repeatedly with plenty of deionized water to remove all soluble materials. The peppermint stem powder was then grafted with acrylic acid (GPMS) and characterized by FTIR and thermal analysis. The PMS and GPMS were used for removal of Ni(II) ions from aqueous solution. Adsorption of Ni(II) ions onto PMS and GPMS were found to be pH dependent and maximum removal of Ni(II) ions were obtained at pH 7. The adsorption kinetic data of Ni(II) onto PMS and GPMS were best fitted with the Pseudo-second-order kinetic model. The equilibrium data were also fitted well with the Langmuir and Freundlich isotherm models. From RL values, it was concluded that the adsorption of Ni(II) onto PMS and GPMS were favored. The activation energy Ea of the adsorption process was determined and found to be 7.7 KJ mol-1 for the adsorption of Ni(II) onto PMS reflecting the physisorption process and that for the adsorption of Ni(II) onto GPMS was 70.3 KJ mol-1 indicate that the adsorption may be chemical in nature.