Formulation and characterisation of kappa-carrageenan gels with non-ionic surfactant for melting-triggered controlled release

Kappa carrageenan was identified as a possible gel for melting-triggered release at 30–40 °C with the inclusion of a non-ionic surfactant for use in detergency or food-related applications. The gel formulation was kappa carrageenan (0.6–3% w/w) and either Tween 20 or Dehypon LS 36: two different non-ionic surfactants (0–5% w/w). Rheology and micro differential scanning calorimetry (µDSC) found that the addition of either non-ionic surfactant had a significant increase in the gelling and melting temperatures, however the gelling and melting enthalpies remained unchanged with additional surfactant. Additionally, the elastic modulus, increased by up to an order of magnitude upon addition of the surfactant. Surface tension measurements showed that the critical micelle concentration of both non-ionic surfactants did not change with the addition of carrageenan, indicating no electrostatic interactions. The mechanism of interaction between carrageenan and non-ionic surfactants is suggested to be hydrophobic interactions leading to electrostatic shielding, which enhances carrageenan aggregation. Melting measurements of kappa-carrageenan gels with non-ionic surfactant proved that temperature-mediated release at 40 °C was achieved.