Used tennis strings were processed into a new sheet material, which was then used across circular economy activations around the Championships. Three distinct behaviours under heat. Of three processes tested, one worked.
Wimbledon · The Championships · London, UK · 2022 · Sport and live events · Design; Consultancy
Used tennis strings are a waste stream nobody has a route for. They are thin, mixed polymer and produced in quantity at a single venue each summer. The question put to Pie Factory was whether they could be turned into a usable material rather than disposed of, and if so by what process. This was research and development, not a build. The output needed to be a sheet material with predictable behaviour, suitable for use in circular economy activations around the Championships.
The work began with characterising the material. The strings are mostly nylon. Some contain, or are coated with, PVDF, polyvinylidene fluoride. That mix is the whole problem: a recycling process that assumes one polymer will not behave predictably on a feedstock that contains two. Heating the strings identified three distinct behaviours. Normal string melts homogeneously. A second type, referred to as twister string, delaminates when heated and separates rather than fusing. A third, referred to as foamy string, foams up under heat. Three processes were then tested against that feedstock. Extrusion was found to be impossible with the sample. Moulding works, but only on a single material type, which means sorting the feedstock first. Sheet pressing proved the most forgiving: it tolerates mixed behaviour in the input and still produces a usable panel. Sheet pressing became the route. The strings were processed into a new sheet material on that basis, and the resulting material was then used across circular economy activations around the Championships. Two of the three processes tested did not give a workable route, and that is recorded because it is the useful part of the finding.
The PVDF. A feedstock that is mostly nylon but partly fluoropolymer has no single melt window, so any process relying on uniform melting is unreliable before it starts. Extrusion failed on that basis with the sample tested. Moulding only works if the feedstock is sorted to one material type, which adds a sorting step. Sheet pressing was chosen because it is the process least sensitive to that variation, not because it is the best process in the abstract.
This was a materials research and development project and it was not carbon measured. No impact report exists, so this page carries no figures. What the project produced is a finding and a material. The finding: used tennis strings are mostly nylon, some containing or coated with PVDF, with three distinct behaviours under heat; extrusion is not viable on that feedstock; moulding requires a single material type; sheet pressing is the most forgiving process. The material: a new sheet pressed from the strings, subsequently used across circular economy activations around the Championships. No mass of strings processed is published, because the only figure on file sits in a proposal scope line rather than a delivery record.