Murphy, Shona (2011)
M.Res. thesis, University of Birmingham.
Investigation into the crystallisation kinetics and melting point depression of poly(L-lactideco-meso-lactide) with approximately 3.3% D-lactide content (PLA 3051D) was undertaken. The rate of crystallisation was too slow for a crystallisation exotherm to be detected by the DSC, therefore hot-stage microscopy was used as an alternative method to characterise the crystallisation behaviour. Light intensity with time during isothermal crystallisation of a thin polymer film (<15μm) was measured. The results were normalised in order to calculate crystallisation half-life (t0.5). From half-life calculations, the optimal crystallisation temperature was found to be 118°C. By replacing the light dependant resistor with a digital camera, the diameter growths of individual spherulites could be measured minute-by-minute. Using the results obtained through hot-stage microscopy, re-processing of PLA could be carried out to restore the original crystallinity at Tmax 118°C. Plots showing % crystallinity with storage time at 118°C indicated a storage time of 2 hours was required to restore the crystallinity to 40%. Studies using the high pressure DSC found that with increasing CO2 pressure up to 60 bar, the melting point decreased from 152 to 142°C . An alternative biodegradable polymer, polycaprolactone CAPA 6800 was investigated with high pressure DSC as a comparison polymer to polylactic acid. Similarly to PLA, the melting point of PCL showed a significant reduction (55 to 40°C) when soaked with increasing pressures of CO2.
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