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31st October 2019, Marl/Wallenhorst-Hollage

EP-SMC for volume production

The two companies developed a material that meets the requirements of modern lightweight construction and is suitable for use in large-volume manufacture. © Evonik

The two companies developed a material that meets the requirements of modern lightweight construction and is suitable for use in large-volume manufacture. © Evonik

Evonik, a leader in special chemistry, together with Lorenz Kunststofftechnik, a company active in semi-finished goods manufacture, R&D, customer- and component-specific material development, and thermoset recycling, have developed a Vestalite S epoxy hardener that is designed to meet all requirements for lightweight construction, including flame resistance. It also exhibits improved mechanical properties and is readily workable. This prototype epoxy SMC can be used instead of steel or aluminium in applications like battery housings and was presented at this year’s K-Messe.

“In the automotive industry, especially in lightweight construction for hybrids and electric vehicles, there is growing demand for components that are not just light, but also exhibit high stiffness and strength. Carbon-fibre reinforced plastics are often used in place of steel or aluminium in these cases. But these are expensive to manufacture and often cannot be produced in the high unit volumes required,” the company reports.

“Sheet-moulding compounds (SMCs) have been used for decades to make plastic components in large volumes, but until now have not been suitable for comparable lightweight construction purposes. One of the keys to lighter construction is the plastic. The epoxy resins typically used in carbon to give high strength and stiffness are hard to apply in SMCs and have therefore not been used in the automotive market.”

“But now, with Vestalite S, Evonik has succeeded in developing an epoxy hardener that eliminates these issues in compounds.”

Glass-fibre reinforced epoxy SMCs

Conventional SMCs made with polyester resins typically have mechanical properties like a bending strength of 200 MPa, flexural modulus of elasticity of 10,000 MPa and an impact resistance of 90 kJ/m2 at a density between 1.7 g/cm³ and 1.85 g/cm³.They are suitable for many uses in the electrical and automotive industries. However, in vehicle construction there is a growing need for low-density, and thereby low-mass, materials with better mechanical properties.

Together with Lorenz, a material has been developed that has a density of ≤ 1.7 g/cm³ and is very flame-resistant. © Lorenz Kunststofftechnik

Together with Lorenz, a material has been developed that has a density of ≤ 1.7 g/cm³ and is very flame-resistant. © Lorenz Kunststofftechnik

“SMCs with epoxy instead of polyester resins can deliver these requirements,” said Peter Ooms, Sales Director at Lorenz Kunststofftechnik. “But up until now these thermosets were difficult to work with and the mould material was hard to shape, which greatly restricted design freedom. Glass-fibre reinforced epoxy SMCs were impractical, and therefore never really reached market maturity for large series.”

For automotive applications requiring very light components, carbon is often used instead, but it is expensive. So Lorenz has a clear focus on glass fibre. “Glass-fibre reinforced epoxy SMCs have a similar strength to carbon fibre, but are 50% less expensive to make,” said Mr Ooms.

New development

A new glass-fibre reinforced epoxy SMC without the earlier material’s weaknesses could meet this demand, and Evonik’s newly developed hardener makes it possible. “Vestalite S is a diamine-based epoxy hardener that in conjunction with epoxy resins creates an SMC that is simple and quick to work with,” explained Dr Leif Ickert, in charge of Marketing Composites and Adhesives in the Crosslinkers division at Evonik Resource Efficiency.

Compounds with Vestalite S evince a high storage stability of the SMC mould material before hardening, while still permitting fast hardening in the manufacturing process, within three minutes. “What’s more, the flow and deformation properties of semifinished pieces in pressing are better, which enables higher component quality,” added Mr Ickert. SMCs with Vestalite S have no styrene emissions and only low VOC emissions, making them suitable for automotive interior components as well.

Evonik and the thermoset experts at Lorenz have been collaborating since 2018 on the development of this SMC. “With this collaboration, plus supplemental analyses and case studies, such as in the European research project Alliance, we want to show that our hardener can generate the desired properties in epoxy SMCs” said Mr Ooms.

www.lomix.de

www.evonik.de

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