SynopsisThe action of hydrogen peroxide and sodium hydroxide independently as well as in combination together with satbilizer formulation-consisting of magnesium sulphate (5 g/L), ethylenediamine tetraacetic acid (2 g/L), gluconic acid (2 g/L), and nonionic/anionic wetting agent (1.5 g/L)--on poly(viny1 alcohol) (PVA) was investigated at 30°C and 95°C. The effect of sodium hydroxide (5-25 g/L) alone was to bring about an enhancement in the viscosity of PVA most probably due to gel formation. The latter was favored at higher sodium hydroxide concentrations and longer duration (30 min) of treatment. The opposite holds true when hydrogen peroxide (35% w/v) was used alone at concentrations ranging from 2 to 20 mL/L. The viscosity of PVA decreased as the hydrogen peroxide concentration increased. Nevertheless, hydrogen peroxide alone could not cause complete dissolution of PVA even at 95°C for 30 min. On the other hand, complete dissolution of PVA could be achieved under the influence of stabilized alkaline solutions of hydrogen peroxide at 95°C in less than 10 min. It was postulated that, under the conditions used, oxidation of PVA by hydrogen peroxide prevailed over gel formation under the influence of sodium hydroxide.

The natural log of critical micelle concentration (CMC) values obtained from the natural log discontinuities in surface tension‐concentration relationships, through the least‐squares regression analysis, were plotted against the respective hydrophile‐lipophile balance (HLB) values of four groups of ethoxylated octylphenol‐, dodecylphenol‐, tetradecylphenol‐ and hexadecylphenol‐formal‐dehyde polymeric surfactants. The obtained HLB‐CMC relationship for the investigated compounds can be represented satisfactorily by the linearized equation In (CMC) = a—b (HLB). Values of the two constants a (intercept) and b (slope) for 16 of these compounds were determined at 28, 38, 48 and 58°C, using the least‐squares regression analysis of data. The study revealed that both a and b values increase with increasing number of carbon atoms in the ethoxylates of polymeric compounds having a linear alkyl chain. The influence of branching is reflected in the values of a and b of the compounds having a branched dodecyl chain. The most striking feature of the obtained equation is that the CMC decreases with increasing HLB (negative slope). This observation is contrary to what is generally expected for both ionic and nonionic surfactants.

The interfacial tensions (IFT) of four low molecular weight groups of ethoxylated octylphenol‐, dodecylphenol‐, tetradecylphenol‐ and hexadecyl‐phenol—formaldehyde polymeric surfactants were determined using the spinning drop method. Some noteworthy features of the interfacial behaviour of dilute aqueous solutions of 16 of these compounds and homologous hydrocarbons are discussed. An important feature is that these surfactants behave similarly to monomeric ones in their hydrocarbon scan, that is they have a minimum IFT value against a particular member of a homologous hydrocarbon series. The magnitudes of the tension at minimum (γmin) values obtained in this study are of the order of ‘ultralow’ (10−2‐10−3 mNm−1). The nmin values of these polymeric nonionic surfactants decrease with increasing hydrophilicity, that is decrease with the increase of ethylene oxide units condensed per mole of alkylphenol unit in the polymeric surfactants studied. In this case, the downward shift in nmin is smaller and apparently not linearly related to the number of EO units. Increasing the hydrophobicity of these polymeric nonionics, that is increasing the length of the alkyl chain from C8 to C16, resulted in an increase in the nmin values obtained. For each of the investigated groups, the lowest γmin values are obtained with polymeric surfactants having the highest EO content. The optimum low tension performance occurs at the low end of the equivalent alkane carbon number scale (at EACNs below 6). Under the influence of added electrolytes these EACNs were shifted to higher values.