Hydroxypropylmethylcellulose at the air-water interface: dynamic of adsorption and films rheology

PÉREZ, OSCAR E; CARRERA-SÁNCHEZ, CECILIO; PÉREZ, OSCAR E; PILOSOF, ANA MR.

Montevideo, Urugüay

Congreso; XIII Seminario Latinoamericano y del Caribe de Ciencia y Tecnología de Alimentos; 2004

Universidad de la República

Hidroxypropylmethylcellulose (HPMC), a water soluble polymer used in food, ceramic processing, cosmetics and pharmaceutical for drug-delivery systems, is able to adsorb at interfaces and stabilize foams and emulsions. The objective of the present work was to characterize the behaviour of three different commercial HPMC at the interface from a kinetic and rheological point of view. The HPMCs studied were E4M, E50LV and F4M from Methocel Dew Chem-Colorcon SA. The concentration of HPMC varied between 10-4 and 1% w/w. Temperature, pH and ionic strength were maintained constant at 20ºC, 7 and 0.05 M respectively. The dynamic of adsorption and the rheological parameters, the viscoelastic modulus (E) with its elastic (Ed) and viscous component (Ev) and the relative viscoelasticity (tan d) of the films were determined in an automatic drop tensiometer. E4M diffused an order of magnitude faster than the other types of HPMCs. E4M could have a more appropriate chemical structure to get the interface in short periods of time in spite of being more viscous. Differences between the three gums were also found in the unfold and rearrangement rates. E4M and F4M showed a transition from a more expanded structure (Structure I) to a more condensed structure (Structure II) at a surface pressure of 20 mN/m, and collapsed at 29.4 and 27 mN/m. However, E50LV did not show such structural transitions and collapsed at 32 mN/m. The evolution of the elastic component of the modulus over adsorption time was related to the structural changes of HPMC. At the pseudo-equilibrium E50LV films showed the less solid character, and E4M showed de highest. It could be concluded that HPMCs films showed different interfacial characteristics depending on the structure acquired at interface which is related to the molecular characteristics.