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Título: Mechanisms of flocculation with poly(ethylene oxide) and novel cofactors : theory and experiment
Autores: Gaudreault, Roger
Fecha: 2003
Publicador: McGill University - MCGILL
Fuente:
Tipo: Electronic Thesis or Dissertation
Tema: Chemistry, Physical.
Descripción: In modern papermaking, the use of retention aids, which help to effectively incorporate fines and fillers into a sheet of paper, is widespread. Various single, dual and multi-component retention aid systems are available, one example of which is poly(ethylene oxide) and cofactor, the topic of this thesis. The mechanisms by which such systems function are still poorly understood, thus making the optimization of wet-end papermaking a complex problem. Without a knowledge of the basic mechanisms of these retention aids, costly trial-and-error runs have to be performed. The aim of this thesis is to use Molecular Mechanics (MM) and Semiempirical Molecular Orbital Theories to test the original ideas and theories, postulating that the association of PEO and cofactor is essential for the flocculation of cellulose fibre fines and that the driving force for association is hydrogen bonding. These theoretical methods provide structures and energies not easily obtainable from experiment, and predict properties and interactions that can be tested experimentally.
Gas phase calculations, using the PM3 Semiempirical Molecular Orbital Theory, of the interactions between non-ionic poly (ethylene oxide) (PEO), with three model cofactors, (gallic acid, beta-1-O-Galloyl-3,6-(R)-hexahydroxydiphenoyl-D-Glucose (corilagin) and 1,3,6-Tri-O-Galloyl-beta-D-Glucose (TGG)), showed that the delocalised molecular orbitals (DLMO), which describe the bonding between the n-mer (PEO)n and cofactors, cover the complete complexes. The DLMOs which cover R-OH···O or R-CH···O, traditionally considered as hydrogen bonds, show a distinct "pinch", a decrease of the electron density between the H···O atoms. Calculations of Gibbs free energy, entropy and enthalpy show that the PEO/cofactor complexes do not form at room temperature, because the loss of entropy exceeds the increase in enthalpy. Even though bond lengths, bond angles, DLMOs and electron densities for the PEO/cofactor complexes are consistent with the definition of hydrogen bonds, the number of intermolecular R-OH···O and R-CH···O bonds does not correlate with the enthalpy of association of the complexes, indicating that other interactions predominate in the bonding mechanism for this type of system. Moreover this thesis shows that the original idea that the main mechanism of complexation is hydrogen bonding, is incorrect.
Idioma: en