engleski

Structural and Thermal Behavior of Biopolymer/Surfactant Complexes

Structural characteristic and thermal stability of a series of dodecylammonium carrageenates (abbreviated as (DDA)KC, (DDACl)2IC and (DDACl)3LC) formed by stoichiometric complexation of dodecylammonium chloride and differently charged carrageenans (with ideally one, two or three sulfate groups, k-, i- and λ -carrageenan, respectively) were investigated. FTIR investigations confirmed the electrostatic and hydrogen bond interactions between the dodecylammonium and carrageenan species. XRD analysis revealed the formation of a surfactant bilayered structure with irregular conformations of dodecylammonium chains in conjunction with the carrageenan chains. Slightly enhanced local ordering of dodecylammonium chains within (DDACl)2IC can be explained with sulfate groups symmetrically located on the both side of polysaccharide backbones and bonded paraffin chains. Location of one or three sulfate groups in the k- and λ -carrageenan backbones induced asymmetric binding of paraffin layers to sulfate groups and greater disordering inside a bilayer. Complexation of carrageenans with DDACl affected their thermal behavior. All (DDA)nCAR were less thermally stable, i.e. the temperature of their initial decomposition was lower than that of parent compounds. Microscopic observation confirmed that the melting occurs just in the beginning of their decomposition. Common characteristics of (DDA)nCAR DSC heating curves are expressed exothermic transitions and smaller molar enthalpy change associated with decomposition/melting than for parent compounds.

biopolymers; surfactants; complexes; thermal properties

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