Climate Friday | Glass – The recyclable material we’re not recycling

14 July 2021

15th May 2020


Glass is an example of a material which has the potential to be endlessly recycled without degrading in quality. But in our latest Climate Friday post, Associate Director Simon Pierce and Engineer Rafailia Ampla explain that getting waste glass back into the float line is not as simple as we might hope.

“Much of today’s architectural demand is for highly transparent, low-iron glass, and as a consequence a lot of the glass being removed from existing buildings has a higher iron content than the float material currently being produced. As such, producers have struggled to achieve greater than 40% recycled content on their lines while maintaining the optical quality we demand. Even then, the majority of recycled content is in off-cuts (known as pre-consumer cullet) produced during processing of the float glass, rather than glass taken off a building at end-of-life (post-consumer cullet).

This ‘contamination’ challenge is compounded by the way we have used glass compositely with other materials – laminating glass plies with interlayers or assembling insulating glass units (IGUs) using butyl, poly-sulphide and structural silicone products. Separating such intricately bonded materials creates a huge economic barrier to fully dismantling and recycling the constituent parts.

But there is hope. Progress is being made on material separation techniques such as delaminating glass plies without breaking the glass, allowing it to be reused directly. Several initiatives to extract most of the glass from existing IGUs have seen recycled content in the UK float lines jump by 10% – although there are concerns regarding further metal contamination from that extraction process.

We need to push ourselves further on this. To fully apply circular economy principles to glass, we need to be able to recycle (not down-cycle) all the material and get to a place where the recycled content of float glass is 100%.

How can this be done? Should we look to increase the iron-content in glass and accept the visual differences? What might it take to avoid using liquid-applied adhesives and commercially produce fully demountable glass assemblies that overcome the resultant warranty issues? How can we realistically transition from where we are today to achieve a cradle-to-cradle approach to the glass industry?

While these questions cannot be answered immediately, we cannot do this in isolation. We need to collectively develop the mechanisms and mindset to collaborate across the whole industry – manufacturers, contractors, consultants, developers, and end-users alike. We need to lead our institutions in this direction, holding ourselves and each other accountable, creating shared platforms that champion the cross-disciplinary innovation our industry desperately needs to rise to this challenge.”