A research project seeks to develop PLA-based materials for use in optical applications such as lights and headlights. The project, co-ordinated by the Aachen-Maastricht Institute for Biobased Materials (AMIBM, Maastricht / Netherlands; www.maastrichtuniversity.nl/research/aachen-maastricht-institute-biobased-materials), focuses on the use of PLA in conjunction with LEDs, including an investigation of the melting and crystallisation behaviour of the materials developed. German universities Paderborn University and Hamm-Lippstadt University of Applied Sciences are also contributing to the EUR 885,000 project, which is funded by the German Federal Ministry of Food and Agriculture.

PLA not only offers advantages in terms of sustainability, but it also has good optical properties for use in the visible electromagnetic spectrum, said Professor Klaus Huber from Paderborn University’s chemistry department. “Plus, the production capacities for PLA are huge. This makes it relatively price-competitive compared to conventional polymers,” he added.

The long service life of LEDs and the radiation emitted at the short-wave end of the visible spectrum place severe demands on optical materials, which requires the use of extremely durable materials. Until now, these products have been made mainly using PC and PMMA. The problem with PLA is that it softens at around 60 °C, while LED-based lights can reach temperatures of up to 80 °C. A further challenge is its crystallisation behaviour: at around 60 °C, crystallites form and can make the material cloudy. The scientists are working on either avoiding the formation of crystallites or replacing this process with controlled crystallisation so the dimensions of the particles do not interfere with the light.

The team is investigating the extent to which additives or irradiation of the samples improve material 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, ie precisely the processes that play a major role in determining the optical functionalities,” Huber said. The first results are expected at the end of 2022.

While calls for alternatives to petroleum-based plastic products are growing louder in scientific and political circles, currently the focus for bioplastics is on applications with relatively low material requirements and markets with high sales volumes, Huber noted. While some progress is being made in the field of optical materials, for example in the form of “modified PCs”, where isosorbide – a renewable resource – is used in the plastic as a second monomer, these materials are currently only rarely used in displays and optical films, he said. “This means that we need sustainable high-performance polymers with technical properties that are cost effective.”