In today’s consumerist society, the increasing demand for electronics has led to a surge in hazardous waste production. In lieu of the demand, Researchers have been searching for more ways to create green materials for use in electronic applications, in an effort to improve the environmental protection sustainability of electronic components. A team of Researchers from Istanbul, Turkey, have created a silk fibroin protein in hydrogel form, in a unique approach as an environmentally-friendly alternative to conventional polymers for lens applications in light-emitting diodes (LEDs).
Electronic waste (e-waste) is growing every day as the consumption of electronic devices is exponentially increasing around the world. As an example, the United States alone, only a few years ago, in 2011, produced over 2 million tonnes of e-waste with less than a quarter being recycled. This has since increased, and once the rest of the world has been factored in, there is a situation where this waste dumping becomes an unsustainable process.
Light-emitting diodes (LEDs), are one way of creating green electronic components, with their use now being apparent in energy-saving solid-state lighting (SSL) applications. Such approaches, using LEDs are known to reduce energy consumption by 50% every year and decrease carbon emission by 28 million tonnes per year against other light sources.
Unfortunately, despite their environmentally friendly nature, LEDs contain non-recyclable parts with the lens being one major component that fits this category. Within LEDs, the lens accounts for a large portion of the device, and with their standard composition containing epoxy resins and silicon-based polymers, new alternatives have been required which can be recycled and enhance the eco-friendliness of LED devices even more.
The Researchers have now created a biocompatible silk-hydrogel composed of cross-linked fibroin proteins topped with a poly(ester-urethane) coating. The Researchers fabricated crater and dome shaped lenses to control the spatial intensity profile and extract light on warm white LEDs.
The silk was extracted directly from the cocoons of worms and processed, rather than being purchased. Dialysis, centrifugation and wet chemical techniques were all used to create the silk fibroins, which were then solubilized into a stock type VI horseradish peroxidase solution and sonicated. Formation of hydrogels occurred upon addition of hydrogen peroxide post-sonication. 3 %wt was found to be ideal hydrogel concentration for LED applications.
To characterize the new environmentally friendly material, the Researchers used a combination of UV-Vis transmittance spectroscopy (Shimadzu UV-3600 - UV-VIS-NIR Spectrophotometer), optical CCD spectroscopy (CCS 220, Torlabs), modular spectroscopy (Ocean Optics, Torus) and Fourier-transform infrared spectroscopy (FTIR).
Both the concentration of the silk fibroin molecules and the cross-linking agent produced direct effects towards the optical properties on the hydrogel, where the spatial radiation was controlled by the crater and dome morphologies of the hydrogel.
The hydrogel showed a high light extraction efficiency greater than 0.95 when used in a warm white LED. The presence of the poly-urethane coating on the hydrogel was found to enhance the stability of the hydrogel three-fold, and the presence of an edible paraffin wax coating on the surface by more than three orders of magnitude. The coating helped to facilitate a high performance by significantly blocking the moisture vapor transmission.
Keeping in line with the rest of the materials in the lens, the coatings used were both biocompatible and biodegradable, with the paraffin wax extending the lifetime of the coating to 2 years and 341 days.
The Researchers have created an environmentally friendly material which could be used to replace conventional non-recyclable plastics currently found in modern-day electronics. The utilization and commercialization of these replacements would open the doors, to not only biodegradable LEDs, but to environmentally friendly electronics in general. Given the ease of synthesis, such components could become reality in the industrial sector and help in reducing the carbon footprint and waste produced by today’s consumerist society.
“Silk-hydrogel Lenses for Light-emitting Diodes”- Melikov R., et al, Scientific Reports, 2017, DOI:10.1038/s41598-017-07817-1