| Summary: | Rigid polystyrene and polyurethane plastic foams are extensively used as insulating
materials in many important energy saving applications due to their extremely efficient
thermal insulating and good mechanical properties. A critical foam component responsible
for this superior performance is the chlorofluorocarbon (CFC) blowing agent, which has a
much lower thermal conductivity than air and when trapped within the foam cells serves as
the insulating gas. Over time, the CFC gas slowly diffuses out of the cells and causes a
gradual decrease in the foam's thermal resistance. There has long been a need for a reliable
and fast method for estimating the long-term thermal performance of foams, especially since
recent environmental concerns require the fast development of new foam products with
CFC replacements.
The 1 9F NMR microscopic imaging technique described in this thesis is
demonstrated to be a non-destructive, efficient and reliable method for the investigation of
fluorinated blowing agents in various foams. Detailed studies of polystyrene foams made
with CFC, HCFC and HFC blowing agents show that 1 9F NMR microscopic imaging
technique is ideally suited for monitoring the spatial distribution of gaseous blowing agents
in foams and that it can yield a quantitative description of the distribution of cell gas in
foams as a function of time and temperature as well as other factors. There is no other
technique available which is able to directly measure and monitor the spatial distribution of
the concentrations of blowing gases inside foams. A detailed investigation on the measurement of the diffusion coefficients of the
blowing gases in polystyrene foams shows that a one-dimensional imaging experiment can
be used to obtain the quantitative spatial distribution of blowing gases in foams as functions
of time and temperature. The diffusion coefficients for different sample geometries can be
simply determined by fitting theoretical model calculations to the experimental data and
results obtained from both ambient temperature and elevated temperatures. The technique
makes it possible to predict long-term foam insulation performance and will provide
valuable information for improving foam formulation and manufacturing methods.
Fast MAS high resolution 1 9F solid-state NMR spectroscopy has been used to
investigate the effects of the dissolved blowing gas components in the polymer matrix. It is
demonstrated that it is possible to detect and quantify the blowing gas dissolved in the solid-phase
in polystyrene foam systems. The results are presented for different blowing gases in
various PS foams and the effect of the dissolved gas on the diffusion process is also
discussed.
Both the imaging and solid-state NMR experiments are extended to various
polyurethane foam systems to investigate the diffusion process of blowing gases as well as
the effect of the dissolved gas components. The results show a significant contribution from
the dissolved component to the diffusion of the gaseous component in PU foams in the
accelerated aging process. The theoretical models were therefore modified in order to
address such an effect. Satisfactory results are obtained and the diffusion coefficients
determined. Foam systems which had been post-treated with a second blowing gas were also
investigated to probe the outward and inward diffusion processes using the above
techniques. The results are presented as functions of time and temperature. The diffusion
coefficients determined for each gas in the opposing diffusion processes are presented. === Science, Faculty of === Chemistry, Department of === Graduate
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