The biggest challenge when developing filtering face pieces (FFP) is to guarantee the required level of protection while keeping breathing resistance as low as possible. For instance, the FFP2 classification according to the DIN EN 149 standard requires that at an air flow rate of 95 l/min, particle penetration must not exceed 6% and breathing resistance must not exceed 2.4 mbar [1].

The aim of the research project SULA (“Sicherer und leichter atmen”, engl.: ‘safer and easier breathing’) is to significantly reduce both penetration and breathing resistance by improving the manufacture and processing of the nonwoven fabric. Expertise from industry (Reifenhäuser Reicofil, IMSTec) and application-oriented research (Fraunhofer ITWM) is being pooled to investigate the interaction of the individual processes and their effects on the product.

For a meltblown nonwoven to meet the specifications, the fibers are electrostatically charged. In this project, the focus is on the hydrocharging technology, which is applied already during fiber production and thus promises an even distribution of the electric charge in the nonwoven.

In Part 1 of the contribution, we aim to analyze the impact of various process parameters on the charging characteristics of nonwovens, particularly focusing on the differences between electrostatic charging and hydrocharging, as this is the main driver to reduce the pressure drop resulting in lower breathing resistance for the face mask.

To increase the productivity of the filter layer the Multi-Row process is in favor to the well-established Single-Row process. Nonwovens produced by these methods exhibit distinct permeabilities and charges, affecting the quality of FFP2 masks.

Our goal is to enhance our understanding of the positive effect of hydrocharging in comparison with electrostatic charging through simulation and to adapt the superior performance of the hydrocharged single row process to the multi row process with increased productivity.

The entire meltblown process, including hydrocharging, is complex. Therefore, we are starting with modeling and validating individual aspects of the process. Initially, the water nozzle was modeled in a static airflow, simulated, and its performance validated against the nozzle manufacturer's measurements. The simulation results closely matched the actual measurements, both in terms of droplet diameter distributions and velocities. Subsequently, we modeled the high-turbulence airflow without considering hydrocharging effects and validated this model using measurements of Reifenhäuser Reicofil. Later, we incorporated the interaction between water droplets and the airflow into the model and conducted further validations. We measured water quantities at various positions of the water nozzles behind the air jet and compared these with our simulation results.

In the next steps we want to include all the effects of Meltblown process to get insight into hydrocharging process. With this knowledge we want to optimize ...