Gideon Analytical Laboratories performed thermal mechanical analysis TMA and differential thermal analysis (DSC) on two plastics which compose the encapsulation of Unity LEDs. TMA is a measurement of a change of a dimension or a mechanical property when it is subjected to a temperature regime. DSC is a technique for quantitatively analyzing the chemical composition of a substance by observing its thermal behavior while being heated. The samples were disassembled and separated into three items to analyze; the white casing, the clear resin, and the clear core material.
The DSC was run using a TA Instruments DSC2920. The temperature program was a ramp at 20°C/min from room temperature to 360°C for the white case and to 250°c for the clear insert. The analysis was carried out under a purge of nitrogen gas. The TMA analysis was carried out using a TA Instruments TMA2940 with normal expansion probe. The furnace purge was helium at 90 ml/min. The temperature program was an equilibration at -20°C followed by a ramp at 5°C/min to 300°C. The second heat was a ramp from -20°C to 300°C. The force was 0.05 N plus an added static weight of 5 g for a total force of 0.1N. The added thermal mass was used in the TMA furnace to provide increased thermal stability.
The samples were analyzed by DSC to determine the presence of any crystalline melting points. All samples were carried through two heats with rapid cooling after the first heat to improve the appearance of any Tg transitions. The white casing DSC results were consistent with a semicrystalline polymer having a standard melt peak at 325°C. The melt transition showed a double peak in the second heat and this was due to crystal reorganization. The white casing material was shrinking once 50C was reached. This could have caused cracks. The DSC for the clear resin resulted in some interesting findings. The offset at 85°C in the first heat may be a result of relaxation and not a Tg. The second heat showed an apparent Tg at 155°C.
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