Foaming of polypropylene glycols and glycol/MIBC mixtures

The surface tension and foamability of a series of polypropylene glycols (PPG) with average molecular weights (MW) ranging from 200 to 2000 g mol−1 and hydrophilic-lipophilic balance (HLB) values ranging from 10.4 to 5.8 were compared to methyl isobutyl carbinol (MIBC), 4-methyl-2-pentanol (MW102 g mol−1 and HLB 6.1). Experiments were carried out using a modified Bikermann column in which the foam heights were determined at a range of gas flow rates and retention times were calculated at different foamer concentrations. These studies show the six-carbon polypropylene glycol (PPG400) with HLB value of 9.7 is an unusually strong frother. Since many industrial foamers/frothers commonly contain a mixture of chemical types, we have also studied the foaming behaviour of mixed systems of PPGs and MIBC at a range of concentrations. The foaming data indicated that a synergistic effect occurred for several of the mixed systems with differences in HLB values, which resulted in an increase in foam height compared to the performance of the individual systems. Dynamic surface tension measurements, determined in the short time span range of 0.1-10 s, correlated with the synergistic effect and it was found that the blended systems gave a higher dynamic surface tension gradient compared to the individual PPGs. It could be suggested that the mixed foamer (containing high HLB and low HLB value components) produce closed packed, molecular cohesive films at the air/solution interface giving greater surface elasticity, which appeared to increase foamability.