Surface aspects of discolouration in Bisphenol A Polycarbonate (BPA-PC), used as lens in LED-based products |
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| Affiliation: | 1. 3 Philips Lighting, Miribel, France;2. Philips Lighting, High Tech Campus, Eindhoven, The Netherlands;3. Delft University of Technology, Delft, The Netherlands;1. Faculty of Biomedical Engineering, Amirkabir University of Technology, 424 Hafez Ave., Tehran, Iran;2. Materials Science and Engineering Department, Sharif University of Technology, Azadi Ave., Tehran, Iran |
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| Abstract: | The surface-related reactions during discolouration of Bisphenol A Polycarbonate (BPA-PC), used as LED lens plates, under thermal stress are studied. X-ray photoelectron spectroscopy (XPS) has been used to monitor the changes in the surface chemistry of BPA-PC plates over a temperature range of 100–140 °C for a period up to 3000 h. Increasing time under thermal stress is associated with the discolouration, and increase in the yellowing index (YI) of PC plastic lens. The XPS results show that discolouration is associated with oxidation at the surface, finding a significant increase in the signal ratio O1s/C1s in the XPS spectra of degraded specimens. During thermal ageing, the C H concentration decreases and new oxide features C O and OCO form, with the latter being a support for oxidation at the surface being a major reaction during discolouration. Results also show that irradiation with blue light during thermal ageing accelerates the kinetics of discolouration and the increased O1s/C1s ratio in XPS spectra. |
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| Keywords: | Bisphenol A Polycarbonate (BPA-PC) XPS Discolouration LED lens |
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