Scientists want to develop visible radiation-resistant bioplastics for optical applications

Photo Credit: Adobe Stock/Mikhail

Scientists from three German universities are working to develop new bio-plastics for optical applications such as headlights, lenses, reflectors and light guides – and the catch is, they want the material to stand up to emitted radiation at the short-wave end of the visible spectrum.

 The researchers are from Paderborn University, Hamm-Lippstadt University of Applied Sciences and the Aachen-Maastricht Institute for Biobased Materials (AMIBM), and they note that up until now, these products have been made from petroleum-based plastics like polycarbonate and polymethyl methacrylate (PMMA). But the German scientists want to create a non-petroleum-based alternative.

“Currently, the focus is on applications with rather low material requirements and markets with high sales volumes,” said Professor Klaus Huber from the Department of Chemistry at Paderborn University, who is leading the project at the university. “Some progress is being made in the field of optical materials. For example, in the form of ‘modified polycarbonates’, whereby isosorbide – a renewable resource – is used in the plastic as a second monomer. These materials are used in displays and optical films – though at the moment only very rarely.”

The scientists’ aim is to use a specific raw material from the bio-plastics family as an optical material in lights and headlights, and polylactide – also known as Polylactic acid or PLA – has emerged as a suitable candidate. “[It] not only offers advantages in terms of sustainability, but is also has very good optical properties for use in the visible area of the electromagnetic spectrum,” Huber said. “Plus, the production capacities for polylactide are huge. This makes it relatively price-competitive compared to conventional polymers.”

Research is initially being conducted into the use of PLA in conjunction with LEDs, well-known as an efficient and environmentally-friendly light source. “In particular the extremely long service life and the radiation emitted at the short-wave end of the visible spectrum, i.e. the high blue component of LED light, place extreme demands on optical materials,” Huber said. This means that extremely durable materials need to be used. But the problem is that PLA softens at around just 60°C, while LED-based lights can reach temperatures of up to 80°C when in use. A further challenge is its crystallisation behaviour – at around 60°C, crystallites form that make the material cloudy. The scientists are working on either avoiding the formation of crystallites altogether or replacing this process with controlled crystallisation, whereby only crystallites with dimensions that do not interfere with the light are formed.

“The project aims to make it possible to use PLA in high-performance technical lighting applications for the very first time, specifically as a lens material in bike headlights,” Huber said. “To this end, we’re working closely with the company Busch und Müller in Meinerzhagen. Other lighting companies, including Hella in Lippstadt, are also interested in the progress we’re making and are seeing a growing need for the use of sustainable solutions in their products. In Lippstadt, we’re using specially developed equipment to investigate the resistance of the polylactides developed in the project to short-wave visible radiation.”

In Paderborn, the focus is on determining the molecular nature of the polylactides to be used, with a view to the subsequent use of the material. In particular, the researchers are investigating the melting and crystallisation behaviour of the materials developed – Huber is investigating the extent to which additives or irradiation of the samples improve this behaviour with regard to the desired optical properties. “The work is being carried out using a small-angle light scattering system built especially for this purpose and enables us to investigate crystal growth and the melting process of crystals, i.e. precisely the processes that play a major role in determining the optical functionalities,” Huber said.

In addition to scientific and technical findings, the project is expected to provide significant economic stimuli. A sustainable optical bio-plastic with competitive properties will improve the competitiveness of light manufacturers and automotive suppliers. The project will also train early-career researchers and junior academics for positions in industry and research institutions.

The team anticipates to have the first results at the end of 2022.