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Contributed talk

The effect of high intensity irradiance on the durability of polymer compounds

Jörg Meyer, Hochschule Hamm-Lippstadt, 59063 Hamm, Germany
M. Sc. Nico Schmidt, University of Applied Sciences Hamm-Lippstadt, 59063 Hamm, Germany
Dr. Frank Tappe, University of Applied Sciences Hamm-Lippstadt, 59063 Hamm, Germany
Prof. Dr. Sabine Fuchs, University of Applied Sciences Hamm-Lippstadt, 59063 Hamm, Germany

Today semiconductor based light sources, especially light-emitting diodes (LEDs), have found widespread use in automotive exterior lighting and general lighting as well. The industry witnesses a very fast development of such lamps, radiative flux and light output are increasing at high rates, as well as wall plug efficiencies and color quality. It may therefore be expected that the market penetration of these light sources will increase further.

While there is great potential for the lighting industry with respect to the reduction of energy consumption and increased lifetime of the novel luminaires, there are also great challenges, among which much shorter product development and innovation cycles, long-term stability of the devices, and the avoidance of obsolescence play important roles. In this respect, the durability, especially of polymer based luminaire components, is of major importance. This is notably true for those materials which form the optical system of the lighting fixtures, viz. reflectors, lenses and windowpanes. Additionally, the use of sustainable materials is desirable to fully leverage the promise of environmentally friendly lighting solutions.

The optical properties of transparent Poly(lactid acid) (PLA) and PLA-blends and the effect of high intensity irradiance, thermal load and the combination of both on the stability of injection molded PLA were investigated. Mechanical and optical properties as well as the temporal evolution of these properties were monitored in several aging studies. It is demonstrated that the presence of oxygen and/or atmospheric humidity has a major influence on aging effects.

Along with standard analyses (TGA, DSC, GPC, UV-vis and IR-Spectroscopy, REM etc.) dedicated equipment is build up for materials characterization, this includes a Small Angle Light Scattering setup for dynamic molecular microstructure assessment and test benches for accelerated lifetime measurements. The technological goal of these investigations is to demonstrate the applicability of biobased polymers, namely PLA, for optical components. The scientific goal is to correlate morphological, i.e., microscopic, material properties to macroscopic material properties, inter alia by investigating crystallization processes via Small Angle Light Scattering (SALS).

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