Although experts consider carbon fibres to be the most modern type of reinforcement for extremely lightweight composites, these products are finding it difficult to penetrate mass markets such as the automotive industry, the construction sector and other branches of industry that currently use glass fibres and natural fibres. A major reason for this is the high production costs for today’s carbon fibres. Only a considerable price reduction could help bring carbon fibres into more widespread use in these sectors.
Scientists at the Fraunhofer IAP plan to achieve this goal with their so-called ComCarbon technology. Their approach begins with the production of polyacrylonitrile (PAN) fibres, a precursor product for conventional carbon fibres, because this accounts for around half of the production costs. These so-called precursor fibres are not meltable, and they are therefore produced using the expensive solution-spinning process.
Around 60 of precursor costs saved
"We have developed an alternative PAN-based precursor technology that saves around 60 percent of the precursor costs. It is based on an inexpensive melt-spin process using special, meltable PAN copolymers that we developed especially for this purpose", explains Professor Johannes Ganster, head of the Biopolymers research division at the Fraunhofer IAP. "Once they are converted to an unmeltable state, these cost-effective precursor fibres can then be processed into carbon fibres in the same way as conventional precursors using the established production routes", says Ganster.
According to the IAP, several factors account for the economic and ecological advantages of melt-spinning over solution-spinning: No environmentally harmful solvents requiring costly recycling are involved, for example. According to the Institute, "eliminating solvents means that 100 percent of the melted material can be spun, which enables significantly higher spinning speeds." Precursor fibres must undergo stabilising and carbonising steps on the way to becoming carbon fibres. The melt-spun precursor fibres are converted into an unmeltable state for this purpose. As soon as this pre-stabilisation is complete, the multi-filament yarn is continuously conveyed into conventional stabilising furnaces and carbonised at temperatures up to 1,600 °C.