Interpolymer complexation : a simple system to produce hydrogel and aerogel

Abstract

A model of interpolymer complex (IPC) hydrogel under physically crosslinked structure is proposed. The hydrogel prepared from the mixture of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) at various ratio by freezing-thawing proves to be an effective method. Freezing-drying of hydrogel is used as a procedure to convert hydrogel to aerogel. Heat treatment applied to hydrogel initiates the gel strength as clarified by thermogravimetry analysis. An increase of PVA crystallinity in IPC enhances the mechanical and thermal properties of the aerogel.

In this work, continuous froth flotation was developed to remove emulsified oil from industrial wastewater. Branched alcohol propoxylate sulfate sodium salt (C14-15(PO)5SO4Na), an extended surfactant, was used to form microemulsions with diesel oil. In the continuous froth flotation operation, the effects of operational parameters, including surfactant concentration, salinity, oil-to-water ratio, foam height, air flow rate and hydraulic retention time (HRT) were investigated to correlate the oil removal efficiency with interfacial tension (IFT) and foam characteristics. For the C14-15(PO)5SO4Na system, it was not possible to obtain both ultralow IFT and good foaming. Hence, sodium dodecyl sulfate (SDS) was added to enhance the foam stability. A maximum diesel oil removal of 96% was accomplished by this continuous froth flotation at 0.1 wt% C14-15(PO)5SO4Na, 0.5 wt% SDS, and 4 wt% NaCl. In order to improve the foam stability of the sole C14-15(PO)5SO4Na system without added SDS, colloidal gas aphron (CGA), which exhibits relatively high stability, was employed in a batch froth flotation unit. The effects of salinity, surfactant concentration, stirring speed, and stirring time were investigated for determining the optimum conditions of the CGA formation, which were further used for the froth flotation experiments. From the results, the use of CGA enhanced the separation performance of froth flotation. The highest diesel removed of 97% was achieved at an air flow rate of 0.30 l/min with the feed solution prepared under non-equilibrium and CGA conditions of 0.1 wt% C14-15(PO)5SO4Na. 3 wt% NaCl with a stirring speed of 5,000 rpm and a stirring time of 5 min.