Over the past few years, polymer composites have slowly started to come in to their own. Composite materials combine very good mechanical properties with low weight and are in huge demand in many different application fields, especially where lightweighting is a key concern. In lightweight design in the automotive and aviation industries, for example, the use of composite materials can significantly affect fuel consumption. According to experts, every 100 kilograms of weight saved in a car equates to a saving of 0.3 to 0.5 liters of fuel per 100 kilometers. In wind turbines, composites guarantee enormous stability and make bigger and, thus, more-efficient energy plants possible.
However, the production of composites is still complex and costly, forming an obstacle to the full-scale adoption of these materials. For composites to become truly competitive, both the manufacturing process and manufacturing speed need to be addressed.
To that end, specialty chemicals giant Evonik (Essen, Germany) has been working on an innovative development, called hybrid polymer systems, that will facilitate the bulk production of composites, according to the company.
In a composite material, it is the polymer that mainly determines its processing properties. Thermosetting plastics have very good mechanical properties but require longer processing times compared with thermoplastic materials. Thermoplastic polymers are easy to process, quick to reshape and to recycle, but rarely demonstrate the excellent mechanical properties of thermosetting plastics. There is a reason for the very different properties: Polymer chains in thermosetting plastics are cross-linked; in thermoplastics, they are not. This chemical crosslinking process is irreversible.
Now, Evonik has developed hybrid polymer systems that combine the easy processability that is characteristic of thermoplastic polymers with the excellent mechanical properties of thermosetting plastics. How?
Working in collaboration with Karlsruhe Institute of Technology in Germany, the company has developed a process that uses a special Diels-Alder reaction as a chemical switch, which allows them to crosslink without the use of catalysts in a completely reversible process. Heating causes de-crosslinking and allows the system to be reshaped. During the cooling phase, the crosslink is created again and its shape becomes stabile. Material properties are maintained even with repeated heating and cooling.
Since 2014, Evonik has successfully demonstrated the new technology at pilot plants at its Marl, Germany, site. The material concept of hybrid polymer systems has, indeed, been shown to save time and cost in manufacturing composites.
"Our technology will help to significantly reduce manufacturing costs for composites," Chief Innovation Officer Ulrich Küsthardt declared with conviction. "We want to contribute to leading the way to bulk production of composites," he added.
Evonik already offers numerous innovative products for composites and is seeking to continue strengthening its position in this growth market.
The company is aiming for sales in the lower triple-digit million-euro range in the composites market in the medium term. For the market of carbon fiber–reinforced plastics alone, CCeV, a network of companies and research institutes in the fiber composites field, is expecting stable annual growth of 9% on average by 2020.
"We're cooperating closely with suppliers of semi-finished products, plant producers and processing companies of fiber-reinforced plastics to develop appropriate processing chains for our hybrid polymers," explains Sandra Reemers, head of Evonik's Composites Project House. "We aim at offering system solutions that enable an efficient production process for semi-finished products as well as final parts."
A select number of potential customers have already received samples for testing. The first hybrid polymer systems are expected to be ready for market in 2018.