RE-PAD

So far, the raw materials in products like sanitary pads or tampons are subjected to thermal recovery after single use. This means they are burned at high temperatures, and the resulting heat generates steam, which drives turbines used for electricity generation and, in some areas, for district heating. Due to thermal losses and low efficiency, averaging just 50% in Germany, this process can be considered inefficient. Research on menstrual products showed the complex production processes for disposable pads. The material flows required to create layers of cotton, polyethylene, polypropylene, an adhesive matrix based on acrylic or silicone, and a superabsorbent polymer (SAP) matrix are highly complex. The energy required for the production and assembly of these components far exceeds that recovered through thermal recovery. Transport and raw material extraction are not included in this calculation. There is some research on the recovery of raw materials from diapers, which present similar problems, and also on the recovery of SAPs. Since SAPs can absorb up to 300 times their volume in liquid, recycling these materials is particularly challenging. Given that these issues could be most effectively addressed through systematic changes in waste recovery processes, which are difficult to implement within this semester project, I decided to design a reusable pad made from a single material. For silicone, which I chose in this case, there are no separate recycling processes in Germany. Silicone is often compared to plastics because both have a polymer structure, but silicone is sourced from sand and remains inert compared to plastics, which degrade into microplastics. Upon completing my project, I realized the oversight in not integrating the recycling of pad components from the beginning. The costs for chemical depolymerization of silicones are higher than those for producing new materials, making this process less attractive to manufacturers.

Because few large companies are interested in a closed-loop system, it would have been beneficial to incorporate this process through a service. After choosing this monomaterial, I attempted to design the replaceable absorbent core of the Re-Pad from the same material. In an experimental setup at the Bio-Lab of Burg Giebichenstein, the liquid absorption and release capacities of various open-cell medical foams were tested. The same amount of liquid was applied and then extracted by centrifugation. For cleaning the absorbent cores, silicone and PU foams pre-soaked in nutrient solutions with two different concentrations of Aliivibrio fischeri were cleaned and partially dried in a washing machine. Subsequent swab tests produced bacterial cultures observed over several days. The experiments showed that while silicone was easier to clean than PU foams, PU foams absorbed liquids better. The ease of handling the pad depends on the absorbent core’s capacity and secure attachment to clothing. Prof. Mareike Gast recommended consulting the company Gottlieb Binder GmbH & Co. KG, specialists in repositionable and reclosable fastening systems. Therefore, I could choose between silicone and plastic fasteners. The majority of the research for the semester project focused on proof of concept and the design of the stem cell donation process. References to papers and articles used are in the personal documentation. Without the detailed responses and assistance from Dr. Rachel W.S. CHAN from The University of Hongkong, I could not have continued the project. The discovery of endometrial stem cells in menstrual blood and their pluripotency only occurred in 2007, so there is little accessible scientific literature on collection, storage, and transport. Therefore, I contacted researchers for procedures.