A new continuous fibre-reinforced thermoplastic composite (CFRTP) from Covestro is pushing boundaries. It can easily be manufactured in large quantities and is not brittle – unlike conventional synthetic resin composites

Going through hell to get to heaven

CFRTP composites from Covestro make mountain bikes safer

LIGHTWEIGHT, highly resilient and ideally also attractive to look at: These are the demands that enthusiastic cyclists make on the components of their bikes today. The challenge: the synthetic resin-carbon fibre composites that are in great demand in this scene may be light and chic – but the risk of breakage is always present. With its brand-new, lightweight CFRTP composites (continuous fibre-reinforced thermoplastic), Covestro opens up a new chapter: they can be processed in a novel process in just one step.

Previous restrictions on synthetic resin composites, such as the mass production capability and intrinsic brittleness of the material, could soon be a thing of the past thanks to CFRTPs. The impact-resistant matrix material polycarbonate further increases safety – and the popular carbon look is also included. Last but not least, CFRTP composites also increase the cost-effectiveness of production. Time for a change of guard in the bicycle sector!

Tours with adrenaline factor
When are mountain bike tours most beautiful? Of course: on the ups and downs! It goes without saying that not only all the driver’s senses are challenged as much as possible: The material also has to withstand enormous forces and shocks when shooting over roots and rocks, in tight hairpin curves and in hard landings after a jump.

This is reason enough for experienced developers such as Dr. Niccolo Pini, founder and managing director of next composites GmbH in Otelfingen, Switzerland (a company of Ensinger GmbH), to keep up with the latest materials that the market offers in order to achieve the best there is for the bikers. His latest highlight: a pedal crank made of CFRTP, the new high-performance composites in Covestro’s portfolio. The part is not only extremely light and robust, but also looks great due to the coveted carbon fibre optic. Thanks to the new manufacturing possibilities of next composites, it can be reproducibly and automatically produced – with all the advantages for component quality.

True engineering work
Get on your bike, get out of the exhaust fumes of city traffic, head down fast downhill over winding paths: For engineers, some mountain bike tours mean that the rider is in the sky while the material goes through hell. Of course, no one needs a breakdown when shooting at 50km/h, for example due to broken handlebars, frames or cranks.

“The development of components for mountain bikes is true engineering work,” explains Niccolo Pini of next composites. He is also a passionate cyclist who has been thrown out of the saddle several times while pursuing his hobby.

Material failure often has a very simple reason for Pini: poor workmanship due to manual labour. “Even for simple components such as a crank, you need sixty to seventy carbon fibre blanks in classic synthetic resin processing, which have to be aligned manually in the correct order and position. This is exhausting work that requires a lot of concentration. No wonder there are quality problems.” From the outside you can hardly see the black carbon part. But when it comes down to it, the break is there – and the driver goes over the handlebars.

The solution for Dr Pini is Covestro CFRTPs – continuous carbon fibres impregnated with the high-performance plastic polycarbonate. This new composite material offers enormous strengths thanks to the fibre reinforcement, but thanks to its thermoplastic matrix, it can be processed mechanically and significantly faster than epoxy-based systems. “Machines make mistakes less often,” says Pini. This means that problems with incorrectly laid carbon fibre sheets, which can lead to fractures later on, are remedied from the very beginning.

“In fact, the great strength of our CFRTP tapes is that they are not only able to absorb high forces thanks to the continuous carbon fibres,” adds Dr Michael Schmidt, who is one of two Co-CEOs of Covestro CFRTP, together with David Hartmann, “but that with their help, several conventional steps in the processing of previous carbon fibre thermoset composites can be combined in a single, fast process.” The tapes are automatically cut at precisely the required angle according to the mechanical requirements. They are then placed into a tool before the preform manufactured in this process is pressed in the next step.

High impact strength protects against fractures
In addition, there are considerable economic advantages in terms of post-treatment: traditionally manufactured composites made of synthetic resin and carbon fibre usually have to be laboriously treated with fillers, reground and polished in order to satisfy the aesthetic demands of the customers.

According to Pini, a “classic” carbon frame passes through up to 70 pairs of hands in the course of its manufacture. Approximately 120 working hours are required to bring the component so that it can be hung on the wall in the shop – and half of this time is needed for rework. With Covestro CFRTP, on the other hand, the component with a high-quality surface finish comes out of the machine practically ready for sale. And with a weight of 150 grams, the new crank is still incredibly light despite its load-bearing capacity – this is an important argument for the new material, according to Pini, especially when it comes to moving parts in bicycle construction.

The matrix material polycarbonate also offers clear advantages. “Thanks to its high fracture toughness, this plastic is ideal for such applications,” says Dr Pini. According to the composite expert, thermoset materials such as those often used in the manufacture of carbon fibre composites, on the other hand, tend to break brittle quickly in the event of blows – this is just not enough for the stresses and strains that mountain bikes are subject to in the fields and forests. Polycarbonate, on the other hand, is also able to withstand violent blows.

CFRTPs from Covestro are ‘Composites 2.0’
Another advantage: The toughness of the plastic material means that metal inlays, which are commonplace with synthetic resin composites, can be largely dispensed with when processing Covestro’s CFRTP tapes. Dr Pini and his colleagues simply cut their threads into the moulded crank – ready. At present, they only need a single inlay – and that too should soon be a thing of the past. “We are gradually approaching the goal of doing without aluminium inlays altogether,” says the manager, “in order to make the crank even lighter at the end.”

CFRTP is a new material whose maximum performance potential has yet to be explored by the engineers. In this way, Pini also takes the wind out of the sails of critics who did not have the best experiences with thermoplastic materials in bicycle construction in the 1990s: “With CFRTP, Covestro has practically reinvented carbon fibre composites!” The specialists of the plastics company are happy to pass on their knowledge: “We have received a competent answer to every question,” says the Swiss engineer.

Covestro is also proud of the project. “This was one of our first orders and the best opportunity for us to bring our unidirectional CFRTP tapes into a fascinating application,” says Dr Michael Schmidt.

“Covestro is also a very reliable consulting partner – and I have been working in this industry for 15 years,” says Dr Pini. No wonder that the committed bike fan is already thinking about further projects with the new material from the high-end materials factory in Leverkusen. Covestro also sees a whole range of new opportunities for CFRTP tapes – in addition to the sports sector, there are also opportunities in the automotive sector, electronics, medical technology and other sectors. The chances are good, because the demand for lightweight yet stable, cost-effective plastic components is growing worldwide.