Circular building materials: Bio-cycle versus techno-cycle

In Pablo van der Lugt's vision of a more circular economy there are tremendous opportunities for smart biobased materials made from fast-growing resources. Head of sustainability at MOSO Innovation and Accsys Technology and guest lecturer at TU Delft he is specialising in biobased materials, environmental impact assessments, climate change mitigation, and Cradle to Cradle (C2C) implementation in the Built Environment.

Why should we prefer the bio-cycle over the techno-cycle?

From a general environmental point of view there are some clear benefits in using a material from the bio-cycle over a material from the techno-cycle:

–   renewable vs. non-renewable

–   low carbon footprint vs. high carbon footprint

–   biodegradable vs. non-biodegradable

Let’s zoom in on these points briefly.

Renewability

Bio-cycle 

If grown and managed sustainably (replanting after harvesting) and not overexploited, a bio-based material offers a constant supply of raw material suitable for many different applications, indefinitely. Furthermore, besides as feedstock for bio-based materials, the forest itself holds many other functions: recreation, flora and fauna (natural capital), oxygen production, fine-dust capture, water buffering, etc.

Techno-cycle 

By default, techno-cycle materials are non-renewable and thus finite, which particularly applies to resources with small reserves such as metals and oil-based building products such as bitumen and plastics. Furthermore, mining and oil drilling have a huge impact on eco-systems. 

Carbon footprint

Bio-cycle

Compared to techno-cycle materials, bio-based materials consume far less energy during production and, because of carbon sequestration during growth and possible energy production in the waste phase (replacing fossil fuels), in several cases can even be CO2 negative.

Techno-cycle

Techno-cycle materials often require huge amounts of energy to be processed into the final material, often using many (chemical) additives and catalysts. And although they may be recycled, this too requires a lot of energy (far more energy than growing and processing bio-based materials).

Waste

Bio-cycle

In general, bio-based materials pose less problems in the waste phase, as various recycling scenarios are possible following the cascading model (particle board, animal fodder, bio-energy, composting). One of the main benefits of bio-based materials such as wood is that they are easily workable and thus permit for flexibility in resizing in the end-of-life phase, which is in particular useful when working with large constructional elements (e.g. beams). 

Further, although it might feel counterintuitive, as long as a bio-based material has had a useful life that takes longer than the time to grow the material back (preferably further extended through cascading into lower value-added applications), it is actually a good thing to effectively utilize the stored solar energy by burning it for green energy production in special biomass energy plants.

Also, in the worst-case scenario of dumping the material, pure bio-based materials will eventually just serve as food for micro-organisms such as termites and fungi and will naturally degrade into biological nutrients, potentially providing no limitations in the waste phase. This is a crucial difference with materials from the techno-cycle.

Techno-cycle

Many techno-cycle material producers use the simple premise ‘easy to recycle thus sustainable’ to communicate their supposed green benefits, using another simple premise, ‘you don’t need to cut a tree/plant’, portraying bio-based materials as unsustainable. This is the world turned upside down. Not even mentioning the damage caused during extraction (#1) and the large carbon footprint (#2), also recycling requires a lot of energy, addition of virgin material, and often leads to a lower quality grade. Finally, even in the best-case scenario of multiple recycling rounds, at some point recycled materials need to be discarded and here is where the real problem with techno-cycle materials starts: they are not biodegradable and are either burned (mainly for plastics, leading to toxic emissions) or end up in landfills, or worse, in nature or the ocean.

Why are techno-cycle materials still used so often and are there bio-based materials that can compete in terms of performance?

Summarizing the key differences between bio-cycle materials vs. techno-cycle materials shows that if sustainability would be the only criterion, the choice would be easy and bio-based materials would be the only sensible choice.

However, in many cases materials from the techno-cycle are still used. Firstly, because usually societal costs related to the environmental damage or CO2 emissions (‘true costing’ or ‘carbon tax’) related to the production of techno-cycle materials are not included in the cost price, meaning that high volume techno-cycle industries can produce at reduced costs. Secondly, because in general the in-use performance of techno-cycle materials such as metals, concrete and glass are very high, with low variability in technical performance indicators such as durability and dimensional stability.

Nevertheless, there are many high-performance bio-based materials such as Accoya, that can easily meet technical requirements for many demanding applications indoors and outdoors (e.g. window frames, cladding, decking, flooring, insulation, etc.), and thus from a sustainability point of view deserve preference over alternatives from the techno-cycle. This does not mean we should abandon techno-cycle materials completely. Techno-cycle materials have an important role to play in industries where their unique properties are useful and bio-based materials cannot compete, such as high-tech industries (electronics, automotive, aerospace, weaponry, etc.).

Find out more in Pablo’s book: Booming Bamboo: the (re)discovery of a sustainable material with endless possibilities (2017)

Read our feature article on Transforming construction: Building the UK's circular economy.