Propylene glycol alginate (PGA) gelled foams: A systematic study of surface activity and gelling properties as a function of degree of esterification

Abstract

A series of propylene glycol alginates (PGA) with degrees of esterification (D.E.) in the range of 32–93% were investigated with respect to surface activity and gelling potential. The surface tension measurements revealed increasing surface activity with increasing contents of propylene glycol groups. The rheological characterization of the PGA series calcium gels uncovered that the gelling potential of the PGAs was surprisingly well conserved even at intermediate degrees of esterification, assumed to reflect heterogeneity in the esterification pattern. For the PGAs of highest degree of esterification the assumed electrostatic point associations combined with hydrogen bonding lead to the rapid formation of weak gels. The rheological properties of high D.E. PGA solutions could be easily modified through the addition of sodium chloride and urea. Self-supporting, heterogeneous and stable PGA and PGA/unmodified alginate gelled foams were prepared applying the internal setting method and characterized with respect to mechanical properties and density. Increasing foamability and corresponding decrease in densities of the gelled foams and their mechanical strength was observed with increasing D.E..