The project “Tubulyze” focused on developing a scalable extrusion process for coating titanium hollow bodies with a thin, homogeneous perfluorosulfonic acid (PFSA) membrane. A 16‑strand extruder equipped with a PFSA coating head was selected after a suitability assessment of an existing 16‑strand machine. The coating head was modified to accommodate vacuum chambers for 5 mm diameter tubes, enabling coating of tubes ranging from 4.5 mm to 5 mm in diameter. The process was shown to produce wall thicknesses between 0.1 mm and 0.05 mm while maintaining a vacuum of 0.5 bar, which was sufficient to achieve uniform coating without compromising the tube wall integrity. The system also allowed the introduction of hollow structures and post‑processing cutting of the coated tubes.

Extrusion trials on dummy titanium tubes supplied by the Friedrich‑Alexander‑University (FAU) demonstrated the feasibility of the coating process. The dummy tubes had an outer diameter of 5 mm and a length of 120–150 mm, with an internal porous structure. Process parameters such as temperature, withdrawal speed, vacuum strength (0.25–0.5 bar), alignment in the coating head, and the influence of porosity and ovality were systematically varied. The trials involved threading the tubes onto a guide rod, applying the PFSA coating under different vacuum strengths and wall thicknesses, measuring the minimal achievable coating thickness, assessing material penetration into the porous structure, and manually trimming the coated tubes. Results confirmed that 5 mm tubes could be coated with a uniform membrane thickness between 0.1 mm and 0.05 mm, without any holes or wall‑thickness variations. The coating distributed evenly across the tube surface and into the porous interior. Cutting the tubes at the ends was possible without damaging the membrane. Vacuum strength did not significantly affect penetration depth, as no notable difference was observed between 0.5 bar and 0.25 bar. Similar outcomes were obtained for 4.5 mm tubes and for dummy sets with varying porosity, indicating robustness of the process across different geometries and material characteristics.

Further extrusion experiments explored titanium hollow bodies of alternative geometries and loading conditions to optimize parameters. Two configurations were tested: tubes with a pin and adapters, and “rod” or “star” shapes without pins. The change in geometry was driven by evolving contact requirements in the cell design. Despite these changes, the existing extrusion equipment and vacuum tooling were reused, resulting in significant cost savings in tooling and vacuum equipment. The process remained stable, and the coating quality was maintained across the different geometries. The project also addressed practical aspects such as the need for modular tooling, the ability to adapt the extrusion line to new tasks, and the efficient use of resources, which contributed to keeping personnel and amortisation costs low.

The consortium comprised Uniwell Rohrsysteme GmbH & Co.KG, which led the extrusion development and tooling design; the Friedrich‑Alexander‑University (FAU), which supplied the titanium dummy bodies and provided technical expertise; the Hochschule für Angewandte Wissenschaften (HAW), which used the coated half‑cells for further testing; and Fumatech, which supplied the PFSA membrane material at no cost. The project was funded under the German Federal Ministry of Education and Research (BMBF) with the reference 03SF0564C, and ran from 2018/19 with a half‑year extension to compensate for delays caused by the COVID‑19 pandemic. The outcomes provide a process‑secure method for producing tubular PFSA membranes suitable for planar electrolyzer cells and potentially for sanitary product applications, thereby enhancing the competitiveness of the participating partners in the field of electrochemical energy conversion.