Tennis is a globally admired sport with a huge fan following. And as all things human, it generates waste. I am an avid tennis player and wanted to explore how the game could be made more sustainable and environmentally friendly. I evaluated a key component of the game, the tennis racquet and its strings and found that a single shop in Singapore, restrings about 400 racquets every month, generating about 4,800 meters of waste string each month. The global annual production of tennis racquets is seven million. If each racquet were to be restrung once every year, 84 thousand kilometers of string would be required, which is enough to circumnavigate the planet twice. Burning this can release around 800 tons of carbon-dioxide into the atmosphere.

Through my research, I identified that tennis strings could be recycled and used as 3D printing filaments, thereby extending the lifecycle of the string, and making the sport more environmentally sustainable. The basic premise of my hypothesis is that both 3D printing filaments and tennis strings have similar physical and chemical properties which make the used strings suitable for this alternative method of recycling.

I compared tennis strings made from Nylon (Nylon 6,6) and Polyester against literature available for 3D printing filaments made from Poly-lactic Acid (PLA), ABS, PETG TPU, PEEK for parameters across strength, durability, flexibility, heat resistance, chemical resistance and water resistance. I also compared the chemical compatibility of Nylon, Polyester and PLA with common chemicals against available literature. I identified common uses of each type of 3D printing material to test for suitability of applications of the recycled tennis strings. I focused my further study and experiments to find the possibility of replacing PLA filament, typically used to print prototypes or aesthetically appealing products, with ‘used’ Nylon or Polyester tennis strings. I conducted experiments to compare nylon and polyester strings against PLA 3D printing filament for evaluating the temperature range at which extrusion, a key process of 3D printing, is possible. 

Due to the COVID pandemic lockdown, I had no access to a laboratory, and I designed my own experiment setup using a digital multimeter with temperature probe and soldering irons as the heat source. I ran the experiment several times to get meaningful results. I observed that the Polyester string softened and began to flow similar to the PLA filament. 

My study shows that Polyester is a potential candidate for replacement of PLA. I believe that as 3D printing gains wide acceptance, a critical feedstock for this can be provided by the sporting industry. This will make the sport more sustainable and benefit our planet. While I studied tennis strings, the methods presented are applicable to other racquet sports like squash and badminton.