Browsing by Subject "Gelation"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Publication
    Open Access
    Associative phenomena in galactomannan-deacetylated xanthan systems
    (Elsevier, 2001-09-30) Milas, Michel; Rinaudo, Marguerite; Goycoolea Valencia, Francisco Martín; Biología Celular e Histología
    The interaction between mesquite seed galactomannan (MSG; D-mannose to D-galactose ratio (M/G) ~1.1) and deacetylated xanthan (DX) in 5 mM NaCl leading to synergistic gel formation at 25 °C was investigated and compared with the far more studied system made of xanthan and locust bean gum (LBG; M/G ~3.5). Rheology and differential scanning calorimetry were used to measure temperatures of gel formation and transition enthalpy as a function of polymer composition, while circular dichroism was used to probe the conformation of DX in the LBG– DX system. MSG and DX associate at 25 °C with a well defined stoichiometry of 0.6:1.0 (w/w) at low ionic strength favouring the disordered coil state of DX. When LBG was used in place of MSG in water or 5 mM NaCl, two types of mechanisms of interpolymeric association are envisaged.
  • Thumbnail Image
    Publication
    Open Access
    Kinetics of gelation and thermal sensitivity of N-Isobutyryl Chitosan hydrogels
    (American Chemical Society, 2005-06-25) Félix, Leticia; Hernández, Javier; Argüelles Monal, Waldo M.; Goycoolea Valencia, Francisco Martín; Biología Celular e Histología
    N-Acylation of chitosan with carboxylic anhydrides in dilute acetic acid/methanol has been a well documented strategy to selectively modify chitosan. Although this reaction is known to lead to irreversible gel formation, the kinetics and mechanism of this process have not so far been addressed. To this purpose, gel formation during the N-isobutyrylation of chitosan was investigated as a function of the reaction stoichiometry (R), chitosan concentration, and temperature by small deformation oscillatory rheology. Gel formation follows closely the chemical reaction and it proceeds predominantly under second-order kinetics as established from the dependence of critical gel time, tgel, on R and concentration. The activation energy value derived from tgel vs 1/T data (Ea ) 68.29 ( 1.80 kJ/mol) was almost identical to values reported for the chitosan N-acetylation reaction in previous studies. An excess isobutyric anhydride is suggested to be necessary for nucleation and hydrophobic association. The potential application of N-isobutyrylchitosan (NIBC) hydrogels in the design of thermally sensitive materials is also demonstrated.