INVESTIGADORES
PEREZ Oscar Edgardo
capítulos de libros
Título:
Behaviour of hydroxypropylmethylcellulose of different molecular structure and water affinity at the air-water interface.
Autor/es:
PÉREZ, OSCAR E; CARRERA-SÁNCHEZ, CECILIO; RODRÍGUEZ-PATINO, JUAN M; PILOSOF, ANA MR
Libro:
Water properties of food, pharmaceutical, and biological materials.
Editorial:
CRC, Taylor & Francis Group
Referencias:
Lugar: Boca Ratón, USA; Año: 2005; p. 455 - 461
Resumen:
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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.