EFFECT OF HYDROPHOBICALLY MODIFIED COMB-LIKE POLYMER ON INTERFACIAL PROPERTIES OF COAL

Hydrophobically modified polymers are known to exhibit interesting interfacial properties and here surface modification of coal by a comb-type hydrophobic-hydrophilic copolymer (DAPRAL) was studied. Floatability tests revealed the coal to become more hydrophobic with increasing DAPRAL concentration regardless of its original floatability, suggesting that free segments of adsorbed polymer molecules can reorient with the hydrocarbon chains protruding into the gas phase. Zeta potential measurements at pH 3.5 and 7 showed the minimum DAPRAL concentrations needed to mask completely the surface charge of coal to correspond to those required to increase the coal floatability to the maximum. Hydrophobicity measured using a new reliable film-levitation technique also showed the coal to become more hydrophobic with increasing polymer concentration but only until a plateau is reached. Further increase in DAPRAL concentration caused a decrease in the hydrophobicity which is suggested to be due to the consumption of the hydrocarbon chains on unadsorbed polymer segments by the formation of micellar aggregates.