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1.3 PHYSICAL SCIENCES
Ultraviolet (UV) fluorescent lamps are widely used in photopolymerisation processes. However, there a number of disadvantages to these lamps, namely, their intensity varies over time and has to be constantly monitored. This thesis is concerned with the possibility of replacing these lamps with UV Light Emitting Diodes (UV-LEDs). A number of emission characteristics of both the fluorescent lamp and the UV-LEDs were measured and compared to ensure that the optical properties of the UV-LEDs were equivalent to those of the lamps. From this study it was shown that the UV-LEDs have a quicker warm up time and exhibit a more stable output than the fluorescent lamps, while also emitting in the required region for photopolymerisation. The ability of each source to initiate photopolymerisation in a HEMA sample was then monitored using FTIR (Fourier Transform Infrared) and Raman spectroscopy and the percentage cure calculated. These studies proved that UVLEDs could produce a degree of cure that was comparable to that produced by the fluorescent lamp. The last section of the study was concerned with investigating how pulsed UV radiation affected the curing process and thus the mechanical properties of the final polymer. This work was performed using FTIR spectroscopy and Dynamic mechanical analysis (DMA). The study showed that the curing profiles and the mechanical properties of the polymer were not only affected by the irradiation wavelength but also by the duration of the pulsing. The findings of this thesis show that due to the inherent advantages that LEDs have over fluorescent lamps and the fact that they produce a comparable photopolymerisation as that achieved with the fluorescent lamps, LED photopolymerisation is a viable possibility in replacing fluorescent lamps in the manufacturing of biomaterials.
McDermott, S.: Investigation of UV-LED Initiated Photopolymerisation of Bio-compatible HEMA. Doctoral Thesis. Dublin Institute of Technology, 2008.