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Influence of the Cross‐linking Agent on the Gel Structure of Starch Derivatives
Author(s) -
Seidel Christian,
Kulicke WernerMichael,
Heß Christoph,
Hartmann Brigitte,
Lechner M. Dieter,
Lazik Waldemar
Publication year - 2001
Publication title -
starch ‐ stärke
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.62
H-Index - 82
eISSN - 1521-379X
pISSN - 0038-9056
DOI - 10.1002/1521-379x(200107)53:7<305::aid-star305>3.0.co;2-z
Subject(s) - self healing hydrogels , molar mass , chemistry , polymer , polymer chemistry , dynamic mechanical analysis , adipic acid , monomer , organic chemistry
Hydrogels were synthesized through cross‐linking of carboxymethyl starch (CMS; Degree of Substitution DS = 0.45) using polyfunctional carboxylic acids (malic, tartaric, citric, malonic, succinic, glutaric and adipic acid). The syntheses used a cross‐linking agent ratio (ratio of the number of cross‐linking agent molecules to the number of monomer units constituting the polymer) of F Z = 0.05. After cross‐linking the gels were dried, ground and then hydrogels of a polymer concentration of 4 mass‐% were produced. These CMS‐hydrogels were then rheologically characterized using dynamic oscillatory measurements. From measurements of the plateau region storage modulus G' P , the network parameters molar mass between two entanglement points M e ( M e ranging from 9.318 (citric acid) to 281.397 g/mol (tartaric acid)), the cross‐link density ν e and the distance between two entanglement points ξ were calculated. Using carboxylic acids without other functional groups, a maximum in gel sturdiness is found at a spacer length of two CH 2 ‐groups. The evaluation of the loss factor tan δ for the CMS‐hydrogels showed that values of tan δ = 0.2 varied only slightly with the frequency ω. Flow curves showed a pseudopIastic flow behavior for all CMS‐hydrogels (the shear viscosity η declining over five decades in the range of the shear rate γ of 10 −3 to 10 3 s −1 ) The different polyfunctional carboxylic acids have a strong influence on the sturdiness of the synthesized CMS‐hydrogels.