Starling Cycles’ First Carbon Fibre Frame

But wait a minute, doesn’t Starling only makes steel bikes? And didn’t I always say carbon bikes are rubbish?! 

Yes, we only make steel bikes.  But no, I never said carbon is rubbish, it’s just that having worked in aerospace and seen carbon manufacture to the highest level, I don’t believe current carbon manufacturing methods for bikes offer anywhere near the kind of quality I’m used to. 

But this project offered an opportunity to try and change that… So why not?

The idea of the project was to use braided thermoplastic tubes with novel design lugs. The thermoplastic has several advantages over traditional epoxy-based carbon fibres:

• Firstly, thermoplastic is much tougher against impact damage than epoxy.  Many people are not aware, but with an epoxy composite you can take an impact that shows no damage on the outside, but there could be significant internal damage within the laminate that risks the integrity of the structure.  This is not a problem with thermoplastic based composite where the internal damage is much less likely to occur due to high plasticity of the material.
  
  
• Secondly, the thermoplastic can be reformed, which means it is much more amenable to repairs.  Whereas epoxy is quite often restricted to ‘cosmetic’ repairs.  
  
  
• The ability of the thermoplastic to be reformed means that, although it can’t be recycled (I’ll come onto this in a moment) it can be repurposed in a much easier way.  For example, old frames could be returned to the manufacturer and the tubes cut out and reformed into a smaller frame size.  Theoretically, you could heat up a thermoplastic composite and remove the plastic matrix and retrieve the carbon fibres.  But realistically, this would use significant amount of energy and reduce the properties of both materials.
  
  
  • As an aside, we need to be super careful when using the term, ‘recycled’, to me it is a cycle than can continue for ever. Steel for example, can be recycled.  It can infinitely be melted down and reformed into pristine new material.  Noting some super high grade steel do require pristine ore.  
  • Plastic cannot be recycled, there is always a degradation in quality with each cycle.  The life may only be three or so cycles.  This is not recycling, just reusing.  
  • Epoxy Carbon fibre can never be recycled, as much as some people will try to tell you it can.  Currently, as best it can be chopped up and maybe used as filler in short strand plastics.  Mostly it is chopped up and used a filler, or mug coaters.  And this one short reuse with much degraded qualities is about as far as you can go.
    
    
• Thermoplastic composite require much less energy to manufacture than epoxy composites.  The time to heat for epoxies to cure and therefore the energy requirements are much more.
  
  
• The solution being worked on also offers significant quality benefits and ability for mid-process inspection.  This means manufacturing scrap rate will be significantly reduced.  I’ve heard up to 50% for some epoxy carbon frames, i.e. the piles of frames going into the sea we have all seen.