How green is your carbon bike? And why your next one could be made from recycled carbon fibre

Carbon fibre is widely used in many industries due to its strength, light weight and resistance to stress and corrosion, but its durability means that once it's no longer needed, the material can remain without decomposing for a long time, so how green is your bike? We're talking about its environmental credentials rather than its colour, but you knew that. We spoke with industry experts to explore the fate of carbon fibre bikes and components at the end of their lifespan, and the likelihood of your next bike being made from recycled carbon. 

Despite cycling being greener than most other transport methods, the bike industry faces the same environmental challenges as any other global industry, particularly in terms of manufacturing processes, and there is growing concern for sustainability and eco-friendly practices in cycling. 

Carbon fibre is strong, lightweight, and can easily be moulded into different shapes, making it a widely sought-after material in bike manufacturing. It has transitioned from an exclusive choice for professionals to a more accessible and, at times, affordable option that appeals to many cyclists. 

This increase in carbon fibre usage has, however, resulted in the production of a significant amount of waste and a bike frame will not decompose when you dispose of it. Therefore, efforts to address and reduce this waste are crucial for maintaining sustainability in the cycling industry.

Environmental impact of carbon fibre

2023 Trek sustainability report carbon footprint of frame materials

As well as its widespread use in the cycling world, carbon fibre is used in various other industries, including aerospace, automotive, energy and marine. According to the UCI (Union Cycliste Internationale, cycle sport's world governing body), in 2021 the sports industry was the third largest user of carbon fibre worldwide, with most sports equipment using the material having an average lifespan of three years, and 90 per cent ending up in landfill at the end of its life.

Researchers from the University of Sydney say that carbon and glass fibre composites are expected to emerge as a significant global waste source by the end of this decade, with the total amount of such waste projected to reach 840,300 tonnes a year by 2050.

This raises a concern, and the consideration of what happens to a carbon fibre bike after it's finished with becomes a crucial aspect in addressing sustainability concerns. Historically, recycling the material has been complex, and while the need for action has increased, there are encouraging signs of positive change and innovative strides being made. 

> What is the carbon footprint of your bike?

While carbon fibre has a long lifecycle, its creation demands significant amounts of energy, making it more energy-intensive than materials such as aluminium and steel. For example, Giant says, "The manufacturing process [of high-end carbon fibre bikes] generates high carbon emissions at 50 kg CO2e/kg or more". 

CO2e (carbon dioxide equivalent) is a measurement used to compare the emissions from various greenhouse gases according to their global warming potential (GWP). The figure converts the amounts of other gases to an equivalent amount of carbon dioxide with the same global warming potential.

Trek released a sustainability report last year outlining the cost in carbon emissions of every bike showing that their most popular model, the Marlin, comes at a cost of 116 kg CO2e/kg which they are hoping to reduce by 30% to 81 kg CO2e/kg by 2032. 

As well as having a higher environmental cost during production, as previously mentioned, there are challenges to recycling carbon fibre. Aluminium and steel are both highly recyclable, with well-established, profitable systems that contribute to a reduced environmental impact.

However, there's growing interest in alternative materials such as BioFiber and flax fibres, which promise strength and stiffness comparable to carbon fibre but with reduced carbon footprints.

BioFiber, an all-natural composite, has gained attention for being used in high-end technologies such as those used by McLaren Racing in F1. Similarly, flax plant fibres have been utilised in the design of products like Hummingbird's foldable bike, with the flax model claimed to match the weight and strength of its carbon fibre counterpart. 

The process of recycling carbon fibre 

There are two main types of carbon fibre waste: virgin carbon-fibre offcuts that aren't needed in production, and carbon-fibre composites from bike frames and components at the end of their lives.

> Academics in Australia develop new way of recycling carbon-fibre waste

Recycling of end-of-life carbon fibre bike frames and components should be prioritised for a more circular economy, and this focus is essential due to the larger volume of waste generated compared to offcuts during production. However, Giant highlights the issue with this saying, "These products are sold globally and returning them to their production site for recycling is also energy-inefficient, so we will collaborate with local companies for the recycling process."

Trek announced the bike industry’s first carbon fibre recycling programme way back in 2011, and several companies have since announced their own recycling programmes, but untold thousands of carbon fibre bikes end up in landfill every year.

Most high-performance carbon bikes are made using thermoset carbon fibre composites, materials that, according to Giant, can only be recycled through pyrolysis or chemical methods. 

> What is an open mould bike frame?

Pyrolysis means subjecting carbon fibre composites to high temperatures in the absence of oxygen. At these temperatures, the resin matrix of the composite breaks down, leaving behind the carbon fibres. These carbon fibres can then be recovered and reused in various applications, which reduces the need for virgin carbon fibre production and minimises waste. 

Giant's current recycling process

However, these processes are energy-intensive and often result in a significant reduction in performance, so Giant is actively exploring alternative, lower-energy recycling methods such as microwave-pyrolysis and chemical solvolysis.

Hunt also explain the two options they've been utilising to help produce viable recyclable and recycled carbon fibre products. One option involves thermoplastic carbon, which allows for the melting of the resin, albeit with a slight increase in weight compared to thermoset products to achieve similar strength in impact testing.

Another option is the recovery of fibres from thermoset resins, as mentioned by Giant.

"A thermoset resin is much more mature for producing the highest strength-to-weight ratio products such as carbon fibre bike frames and rims," Hunt explains. 

The advantages of recycling carbon fibre

The two major advantages of recycling carbon fibre are the reduced environmental impact and resource conservation as we strive towards a more sustainable and circular approach to carbon fibre usage.

Recycling carbon fibre reduces the demand for virgin carbon fibre production which is energy-intensive and generates significant greenhouse gas emissions, and also reduces the need for raw material extraction. 

"Most of the environmental impact of products comes from the initial extraction and processing of raw materials needed to produce top-quality gear," writes Trek, so by recycling carbon fibre and repurposing it into new products, we can significantly reduce this initial impact. 

Another key advantage is waste reduction, and carbon fibre recycling minimises the volume of carbon fibre waste destined for landfill. 

Brands now publish annual CSR reports (corporate social responsibility) detailing their sustainability efforts, and with an increasing emphasis on environmental regulations and sustainability goals, recycling carbon fibre has become a focal point for many companies striving to contribute to a greener future. 

The challenges of recycling carbon fibre

> What the bike industry is doing, and what you can do to further reduce your carbon footprint as a cyclist

Recycling carbon fibre and incorporating recycled carbon fibre into components presents several challenges. One arises from the use of carbon fibre composites in complex structures, where carbon fibres are combined with a polymer matrix. Recovering carbon fibres from carbon fibre-reinforced composites (CFRC) is difficult, energy-intensive, and costly. 

Another significant challenge is maintaining the original performance of virgin carbon fibre, as recycling processes can reduce the strength and stiffness, leading to reduced performance. 

"Currently, most carbon fibre products are recycled through pyrolysis process into injection pellets with extremely short fibre," explains Giant. "It is both highly energy-intensive and leads to huge performance reduction." 

To address some of these challenges, both Hunt and Giant explore the possibility of utilising waste carbon fibres from elsewhere. 

"We've been looking into the opportunity to utilise mid-length fibres which are the by-product of larger original use industries such as aerospace as these mid-length fibres are suitable for some bicycle/component applications", Hunt explains. 

Despite these challenges, finding effective and efficient recycling methods for end-of-life composites is crucial for sustainable waste management, and Giant emphasises the importance of the manufacturer's involvement in the entire lifestyle of their products.

"We don't see the bikes at the end of life, so we don't have any control over what the owner does with the frame," Giant states.

This highlights a crucial gap in the current approach to sustainability in the cycling industry. 

Is recycled carbon fibre as good as virgin carbon fibre?

One of the main challenges of recycling carbon fibre is maintaining the original performance of virgin carbon fibre. According to a review published on carbon fibre recycling in PubMed, recycled carbon fibres generally exhibit a reduction in quality because the fibre length is significantly reduced. 

As demonstrated by Hunt's experience with carbon wheels, using thermoplastic carbon often means an increase in weight compared to standard carbon wheelsets to achieve equivalent strength levels. The weight penalty may not be substantial, but that's not the only factor that needs to be considered.

> Your complete guide to bike frame materials

Giant emphasises the importance of composite quality to achieve performance comparable to virgin carbon fibre composites and explains that they have developed their own process for handling recycled fibres in a structured manner.

"Our approach aims to create structural parts, effectively dealing with the messy recycled carbon fibres and achieving performance comparable to composites made of virgin carbon fibres," Giant explains. 

While recycled carbon fibre may exhibit differences in mechanical properties compared to virgin carbon fibre, Hunt and Giant show that strategic approaches to recycling and composite manufacturing can help minimise these differences and ensure optimal performance in recycled carbon fibre products. 

Could carbon fibre be recycled indefinitely in the future?

In the past, carbon fibre was challenging to recycle and the market wasn't ready to use recycled carbon fibre. However, significant progress has been made in the last decade, and we can anticipate further advancements in the next decade as well.  

While aerospace industries may lead in these developments initially, the bike industry could follow suit and both Giant and Hunt are optimistic about the potential for carbon fibre being recycled indefinitely in the future. 

Giant says, "[We intend] to recycle carbon composite parts multiple times. Eventually, the lowest-grade carbon fibre form (less than 1mm length) can be indefinitely recycled without a significant reduction in properties in certain applications."

Hunt says, "At the rate that we're seeing this technology develop, we think it is quite possible that we could see carbon fibre recycled indefinitely."

Will your next bike be recycled carbon fibre?

Establishing more robust recycling processes could prove to be one of the most effective strategies for mitigating the environmental impact of carbon fibre while meeting growing demands, and recycled content and the sustainability of carbon fibre are changing very quickly. 

This isn't a novel idea, and at the end of last year, New Zealand-based Vélos Advancements announced that they were taking pre-orders for their Holocene road bike. The Holocene frameset is 100% recycled carbon prepreg, rather than just a small proportion.

Brands are increasingly prioritising sustainability and industry experts like Hunt and Giant are optimistic about overcoming the challenges in the recycling processes of carbon fibre and offer hope for the indefinite recycling of carbon fibre.

Giant operates its own factories and explains that "significant quantities of testing frames (up to 25 tons) are generated each year during the production process. We are collaborating with partners to recycle them, aiming for 100% efficient reuse before 2030". 

Strategic approaches to recycling and composite manufacturing show promise in minimising performance differences and ensuring the viability of recycled carbon fibre products.

With commitments from industry players and ongoing technological advancements, the likelihood of your next bike being made from recycled carbon fibre is increasingly plausible, reflecting a broader movement towards sustainability in cycling and other sectors.

Would you consider choosing a bike made from recycled carbon fibre? Let us know in the comments section below...