A Study of Structure-Property Relations in Rigid Polyurethane Foams

In this thesis, the relationship between the chemical structure of reactants, the processing of the foam and the resultant morphology of water blown rigid polyurethane foam have been studied. Chemical variations were systematically made and the morphology and diffusion properties of the foam investigated. The chemical variations include polyol arm length, polyol/monol content, water level, type of catalysts and type of isocynates. Various techniques were employed throughout the study: adiabatic temperature rise method to analyse the reaction kinetics, Fourier Transform Infra Red spectroscopy to simultaneously monitor polymerization and microphase separation behaviour, static small angle x-ray scattering, environmental scanning electron microscopy and interference optical microscopy to characterize the final foam morphology and gravimetry diffusion measurements to assess the CO2 diffusion coefficient of the water blown rigid polyurethane foams.
The findings have highlighted the dependence of chemical formulations on morphology which in turn determined the observed diffusional property. Shorter polyol arm length, least amount of monol and higher isocynate functionality resulted in smaller cell diameter, thinner cell membrane and higher concentration of hydrogen bonded urea. These in effect gave rise to a denser, rigid structure characterized by a higher value of fractal dimension. A higher fractal dimension value would indicate a lower diffusion coefficient signifying a better thermal insulation property.