Defence of doctoral thesis: Abirami Senthil – Engineering Bioactive Cellulose Foams: Structure–Function Control through Enzymatic and Surface-Mediated Functionalization

Abstract:

As society moves toward reduced dependence on fossil-derived products, the role of materials has become increasingly important, particularly with respect to their sourcing, processing, and end-of-life management. In this context, biobased materials that are renewable, recyclable, and biodegradable are central to achieving climate neutrality targets. Cellulose is a strong candidate among biobased materials due to its wide availability, rapid renewability, and physicochemical properties that are well suited for material production. Traditionally, cellulose has been used in paper and board products and textile applications. However, recent developments have expanded its use through nano-reinforced and chemically modified systems designed for advanced applications such as active packaging, biomedical materials, and electronic components. This development is reflected not only by the rising interest but also through the growing global cellulose market valued at $200 billion. One class of materials that has gained attention in this context is foams. Conventional foams are commonly produced from fossil-derived polymers like polystyrene, which present environmental challenges related to recyclability, waste accumulation, and microplastic pollution. Cellulose-based foams offer a more sustainable alternative; however, native cellulose lacks intrinsic functionalities, which limits its use in many advanced applications, such as active packaging.

In this thesis, cellulose-based foams are developed by modifying cellulose fibers to impart bioactive properties. The modification strategies focus on bio-based approaches and the use of low-toxicity chemicals. Chemical and enzymatic surface modification routes are investigated, including lignin retention and coating strategies as well as laccase-assisted functionalization using ferulic acid. The work examines how cellulose fiber quality, surface modification strategies, and processing constraints collectively influence foam formation, stability, and functional performance. Foam descriptors relevant to both wet and dry states are used to assess structural robustness, while surface modification routes are evaluated in terms of their compatibility with foam processing and their interactions with different types of surfactants. In addition, the role of lignin structure is explored to assess how lignin-derived phenolic functionalities contribute to bioactive performance when incorporated into cellulose-based foams. The functional performance of the resulting foams is evaluated in terms of antioxidant activity, antibacterial activity, and moisture sorption behavior. For the different modification routes, antioxidant activity values expressed as IC50 in the range of 0.27-0.6 g/L, antibacterial growth resistance in the range of 13-73%, and reduced moisture sorption rates in the range of 0.5-1.4 x10-6 g/min are obtained. While maintaining foam structures with a wide range of density (11-75 kg/m3) and compression modulus (0.025-400 kPa). Finally, the transferability of foam formation and surface functionalization from laboratory scale to pilot scale is examined to assess the robustness of the developed approaches under less idealized processing conditions. The results demonstrate the key structural and functional characteristics that can be retained upon scale transition within the constraints considered in this work.

Overall, this thesis provides insight into how cellulose-based foams can be combined with chemo-enzymatic surface modification strategies to obtain active foams with defined functional properties while operating within material, processing, and sustainability-related constraints.

https://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-116716