BEHAVIOUR OF HYDROXYPROPYLMETHYLCELLULOSE OF DIFFERENT MOLECULAR STRUCTURE AND WATER AFFINITY AT THE AIR -WATER INTERFACE.

PÉREZ, OSCAR E; CARRERA-SÁNCHEZ, CECILIO; RODRÍGUEZ-PATINO, JUAN M; PILOSOF, ANA MR.

Mar del Plata, Argentina

Congreso; IX International Symposium on the Properties of Water.; 2004

Universidad de Buenos Aires, Comité permanente ISOPOW

Hydroxypropylmethycellulose (HPMC) is a water-soluble non-ionic macromolecule derived from cellulose. It is quite interesting for food, pharmaceutical and cosmetic use, mainly for controlled release.  HPMC gums exhibit surface activity due to varying ratios of hydroxypropyl to methoxyl substitution. The objective of present work was to evaluate the impact of the degree and type of substitution and water affinity of different HPMC gums on the structure and dynamics of formation of the air-water film. The HPMC used were E4M, E50LV and F4M from Methocel Dow-Chem.- Colorcon SA. The concentration of gums were varied within 10-4 and 1% wt and temperature and pH were kept constant at  20 ºC and  pH 7 respectively. Information about the structure of the air- water interface was obtained from the measurement of the surface pressure (p) vs. area (A) isotherrm, performed on fully automated Wihelmy-type film balance (KSV 3000, Finland). The film elasticity (E) was derived from p-A isotherms, as E = -A.(dp/dA). The rheological parameters of the film, surface dilatational modulus (G*) with its elastic and viscous components (G´ and G´´), and loss angle tangent (tan d) were obtained by sinusoidal periodic compressions and expansions. The dynamics of adsorption and the film structure development were monitored simultaneously in a automatic drop tensiometer. HPMC gums showed different behaviours according to their molecular differences and affinities for water (i.e. viscosity). E4M showed the highest interfacial activity at any concentration at equilibrium and was able to increase surface pressure at a concentration as low as 5. 10-7%. The elasticity of the films as a function of p could be related to molecular structural arrangements adopted by the gums at the interface. E4M showed a more complex structure than the other gums. The dynamics of adsorption indicated that E4M resulted to have the faster adsorption rate. Although  F4M formed the most elastic films due to a higher content of methyl groups in the molecule which favour the formation of hydrophobic bonds at the interface.   Keywords: Hydroxypropylmethylcellulose, interface, dynamic of adsorption, rheological parameters of films.