Department Seminar 2025-Dr. Varvara Apostolopoulou-Kalkavoura (CelluCircle AB (CEO/CTO))

Abstract

My research journey focuses on developing and characterizing sustainable, high-performance materials based on cellulose nanomaterials (CNMs), integrating both fundamental materials science and applied circular economy principles. The initial investigation centered on engineering CNM-based foams and aerogels as fossil-free alternatives for thermal management. A novel enclosed cell was developed to accurately measure thermal conductivity under controlled humidity and temperature, demonstrating the highly anisotropic thermal properties of ice-templated cellulose nanofibrils (CNF) foams. Specifically, the thermal conductivity perpendicular to the CNF fibrils in anisotropic foam structures achieved levels comparable to superinsulation, a phenomenon mathematically modeled using the interfacial thermal resistance approaches to elucidate heat transfer mechanisms. During my postdoctoral studies my focus shifted toward circularity and upcycling post-consumer textiles which are also rich in cellulose. A big part of my work involved developing sustainable protocols for extracting high-quality cellulose nanocrystals (CNCs) and CNFs from textile waste using different chemical pathways. In many cases the extracted nanomaterials were used in foam fabrication. The chemical groups grafted on the cellulose backbone, the structure of foams, the drying method and the packing of nanoparticles were some of the features investigated and analyzed.
A key achievement of my research journey is the patented process for converting blended cotton and PET fabrics into functional 3D-printable filaments after combined chemical and mechanical fibrillation of the cotton component. The process yields also other products such as PET fibers and nanocellulose. These innovations are currently being commercialized through the spin-off company CelluCircle, where the work is being scaled up, bridging fundamental materials chemistry with industrial sustainability.
In conclusion, my research work provides critical insights into the relationship between nanocellulose colloids, moisture interactions, and thermal performance, while establishing scalable methods for converting textile waste into high-value materials.

Speakers Short CV

Dr. Varvara Apostolopoulou-Kalkavoura is a highly accomplished executive and researcher with a robust academic foundation, holding a PhD in Materials Chemistry from Stockholm University (SU), M.Sc. in Sustainable Technology (KTH) and Diploma in Chemical Engineering (NTUA). After her PhD, she was postdoctoral researcher at Stockholm University and visiting researcher at EMPA research institute in Switzerland (Swiss Federal Laboratories for Materials Science and Technology). Her scientific career is distinguished by a deep expertise in developing fossil-free, high-performance materials, specifically through pioneering research on converting nanocellulose colloids into nanocellulose-based foams for thermal management and, most notably, the innovative upcycling of post-consumer textiles into functional products like 3D printable filaments, which resulted in a patent and over 20 peer-reviewed articles. Demonstrating a successful transition from academia to industry leadership, she has progressed rapidly at the SU spin-off CelluCircle AB, serving as the Chief Technology Officer (CTO) before being appointed Chief Executive Officer (CEO) in August 2025, where she is responsible for R&D strategy, budget management, lab development, and leading EU projects, complementing her strong experience in supervision and teaching, success in securing research grants, and proven administrative and public communication skills.