Urethanes and polyurethanes from oxypropylated sugar beet pulp: I. Kinetic study in solution

Within the context of a study on the preparation and characterisation of polyurethanes based on oxypropylated sugar beet pulp (OSBP), used as the polyol, and conventional polyisocyanates, it was deemed necessary to carry out a preliminary study on the reactivity of the hydroxy functions borne by the grafted pulp. Aliphatic and aromatic mono-isocyanates, as well as an aromatic di-isocyanate, were tested in comparison with reference systems based on oligopropylene oxide glycols. The kinetics of all these reactions, carried out in different solvents, followed the classical second-order behaviour up to high conversions indicating that the use of OSBP-based polyol did not introduce any mechanistic anomaly. The influence of steric hindrance, associated with the position of the NCO group in the isocyanates used in this work was also assessed. When two such groups, possessing different accessibility, were made to react with OH functions, the second-order plot revealed two distinct slopes with a break around 50% conversion.