Pultrusion with polyurethane (PU) resins offers enormous potential for the efficient mass production of composite sections

The trailblazing developments in PU pultrusion by Covestro and distinguished partners, KraussMaffei and the Institute of Plastics Processing at RWTH Aachen University, are pushing the boundaries of what has been historically possible and paving the way for new sustainable applications for our customers.

Pultrusion is a manufacturing process enabling the continuous manufacturing of composite sections and can offer widespread applications, but only under the right circumstances. But we’ve only scratched the surface; there is so much more potential in pultrusion that can be explored in the future.

Process and machine technology advances combined with innovations in chemistry were needed to support industrial-scale manufacturing for market segments to achieve huge efficiency, cost, performance and environmental benefits but have so far been unable to adopt pultrusion.

‘Groundbreaking creation’

“To support growing demand from our customers for a continuous, cost-effective and high-performance manufacturing process that would remain stable despite the workload and create better quality components, we have – with our partners – over the past few years, been focusing on optimizing the processes, technology and chemistry to improve the pultrusion process and component solutions it can offer,” says Benedikt Kilian, Project Manager for Pultrusion Process Development.

He adds: “We have been developing polyurethane resins to replace established materials for pultrusion, such as unsaturated polyester, epoxy and vinyl ester. These work smoothly together with the groundbreaking creation of the iPul machine, the first turnkey system to incorporate machine, process and dye technology all in a single source.

Jiangsu Top Composite Technology Co., Ltd.

“The iPul offers its customers central control of the discharge capacity and haul-off speed, which can be increased significantly – up to three meters per minute depending on the profile geometry, as well as more flexibility and precision than what is currently available.”

The polyurethane advantage

For pultrusion technology, polyurethane resin offers significant advantages over established materials. Its higher reactivity than epoxy resins, for example, as well as low viscosity and good fiber wetting supports faster processing speeds, which reduces manufacturing costs. The surface quality of its components is also better.

Mechanical properties, such as strength and stiffness, mean PU pultrudates are at least comparable to epoxy resins but superior to polyester resin systems.

One advantage, for example, is that wall thicknesses can be reduced, while fiber reinforcement perpendicular to the direction of the profile is usually not necessary, which again reduces manufacturing costs.

PU pultrudate’s good thermal insulating behavior, low thermal expansion and lightweight quality is another reason why they are ideal in many applications to replace materials, such as wood, PVC and metals, including steel and aluminium. Pultruded composite sections made with PU resins have for example, already proven successful in thermally insulating window frames.

Huge market potential

But this is the tip of the iceberg and already, we are seeing new market segments opening up. Profiles are being created for the new generation of Germany’s high-speed ICE trains, tram floors, pallets and for cable trays, which can be manufactured with Baydur® PUL more productively and efficiently in terms of cost and thinner than with unsaturated polyesters.

“We are very excited about the innovation potential of PU pultrusion and are currently looking at pultrusion of curved profiles, pultrusion with carbon fibres and significant further productivity gains through higher line speed,” says Claudio Pauler, PUR Marketing Manager EMEA, Covestro.

“The automotive sector is one industry that could massively benefit from tailormade pultruded solutions as it looks to reduce CO₂ emissions, and we look forward to working with clients in a great many new markets, including wind power, automotive and others, to support them with components that have better properties at comparable cost.”

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The Alchemy Team