High-performance bioinspired materials have shown rapid development over the last decade. Examples are brick-and-mortar hierarchical structures, which are often achieved via solvent evaporation. Although good properties are claimed, most systems are composed of stacked or intercalated platelets. Exfoliation is a crucial step to give ultimate anisotropic properties, e.g., thermal, mechanical, and barrier properties. We propose a general framework for all the various types of micro-scale structures that should be distinguished for 2D filler nanocomposites. In particular, the exfoliated state is systematically explored by the immobilization of montmorillonite platelets via (gelatin) hydrogelation. Scattering techniques were used to evaluate this strategy at the level of the particle dispersion and the regularity of spatial arrangement. The gelatin/montmorillonite exfoliated nanostructures are fully controlled by the filler volume fraction since the observed gallery d-spacings perfectly fall onto the predicted values. Surprisingly, X-ray analysis also revealed short- and quasi long-range arrangement of the montmorillonite clay at high loading.

@en

The urgent need to address sustainability within material science, driven by global environmental concerns over pollution, climate change, and resource scarcity, has led to a growing interest in bio-based materials. This thesis explores the potential of biopolymers as alternatives to non-renewable resources, specifically the ones derived from renewable and residual sources. The biomacromolecules can be harvested from plants, algae, microorganisms, and animal products; or extracted from the process waste of agricultural and urban cycles. In particular, the high stiffness (Young's modulus) exhibited by certain biopolymers, often surpassing that of standard engineering polymers, motivates this investigation. The biopolymers' uncontrolled chemical structure and morphology still inhibit their application in many industries. Inspired by the unique structures, properties, and functions found in biological systems, this research aimed to develop (solid-state) structureproperty relationships for relevant biopolymer systems aiming at predicting final material properties (physicochemical, thermal, mechanical, barrier). The focus on structure-property guidelines is brought about by systematic investigations of the intricate architecture and interactions found in biopolymers and bioinspired nanocomposites. The ultimate goal is to design bio-based materials with superior performance, such as lightweight, high stiffness and strength, and functionality, while at a competitive cost and sustainability. @en

Tailoring the order in hierarchical structures is a key goal of bioinspired nanocomposite design. Recently, nacre-like materials have been developed by solvent evaporation methods that are scalable and attain advanced functionalities. However, understanding the alignment mechanisms of 2D fillers, nanosheets, or platelets remains challenging. This work explores possible pathways for nanocomposite ordering via orientation distribution functions. We demonstrate how the immobilization of 2D materials via (pseudo)network formation is crucial to alignment based on evaporation. We show a modified affine deformation model that describes such evaporative methods. In this, a gel network develops enough yield stress and uniformly deforms as drying proceeds, along with the immobilized particles, causing an in-plane orientation. Herein, we tested the dominance of this approach by using a thermo-reversible gel for rapid montmorillonite (MMT) particle fixation. We researched gelatin/MMT as a model system to investigate the effects of high loadings, orientational order, and aspect ratio. The nacre-like nanocomposites showed a semiconstant order parameter (⟨P₂⟩ ∼ 0.7) over increasing nanofiller content up to 64 vol % filler. This remarkable alignment resulted in continuously improved mechanical and water vapor barrier properties over unusually large filler fractions. Some variations in stiffness and diffusion properties were observed, possibly correlated to the applied drying conditions of the hybrid hydrogels. The affine deformation strategy holds promise for developing next-generation advanced materials with tailored properties even at (very) high filler loadings. Furthermore, a gelling approach offers the advantages of simplicity and versatility in the formulation of the components, which is useful for large-scale fabrication methods.

@en

Biopolymers are abundant, renewable, and biodegradable resources. However, bio-based materials often require toughening additives, like (co)polymers or small plasticizing molecules. Plasticization is monitored via the glass transition temperature versus diluent content. To describe this, several thermodynamic models exist; nevertheless, most expressions are phenomenological and lead to over-parametrization. They also fail to describe the influence of sample history and the degree of miscibility via structure-property relationships. We propose a new model to deal with semi-compatible systems: the generalized mean model, which can classify diluent segregation or partitioning. When the constant k_GM is below unity, the addition of plasticizers has hardly any effect, and in some cases, even anti-plasticization is observed. On the other hand, when the k_GM is above unity, the system is highly plasticized even for a small addition of the plasticizer compound, which indicates that the plasticizer locally has a higher concentration. To showcase the model, we studied Na-alginate films with increasing sizes of sugar alcohols. Our k_GM analysis showed that blends have properties that depend on specific polymer interactions and morphological size effects. Finally, we also modeled other plasticized (bio)polymer systems from the literature, concluding that they all tend to have a heterogeneous nature.

@en

Wastewater solids could be an attractive source of secondary raw cellulose, mainly originating from toilet paper. Cellulose can be recovered through sieving of raw wastewater, return sludge, or excess sludge. In particular, a large fraction of cellulose (13–15%) can be found in the excess sludge of the aerobic granular sludge produced by the Nereda® wastewater technology. A cellulose extraction method was developed during this study, allowing the recovery of a pulp with over 86 wt% purity. The wastewater derived cellulose fibres could be an excellent source for production of recovered cellulose nanocrystals (rCNC). Several pre-treatment steps needed in cellulose nanocrystals (CNC) production from wood pulp are already performed in the production of toilet paper. Here, the technical feasibility of such rCNC is studied. As reference materials, microcrystalline cellulose and toilet paper were also used. The rCNC were obtained by acid hydrolysis, with yields of ∼30 wt% (pulp basis). The wastewater-based material was rod-like, with high aspect ratio (10–14), crystallinity (62–68%), and chemical structure similar to commercial CNC. The yield of rCNC per gram of cellulose recovered from the influent was 22%, while for excess sludge cellulose it was less (4%). Bio-nanocomposites of rCNC and alginate were also investigated. At 50 vol% loading of rCNC, there was a 50% relative increase in stiffness (18 GPa) compared to matrix (12 GPa). The characterization of rCNC and positive impact in composite materials confirms a suitable quality of wastewater derived CNC. Ultimately, the nanocellulose is a tangible example that recovery of high-end products from wastewater is possible, in line with a circular economy.

@en

Background
Face masks, also referred to as half masks, are essential to protect healthcare professionals working in close contact with patients with COVID-19-related symptoms. Because of the Corona material shortages, healthcare institutions sought an approach to reuse face masks or to purchase new, imported masks. The filter quality of these masks remained unclear. Therefore, the aim of this study was to assess the quality of sterilized and imported FFP2/KN95 face masks.

Methods
A 48-minute steam sterilization process of single-use FFP2/KN95 face masks with a 15 minute holding time at 121°C was developed, validated and implemented in the Central Sterilization Departments (CSSD) of 19 different hospitals. Masks sterilized by steam and H2O2 plasma as well as new, imported masks were tested for particle filtration efficiency (PFE) and pressure drop in a custom-made test setup.

Results
The results of 84 masks tested on the PFE dry particle test setup showed differences of 2.3±2% (mean±SD). Test data showed that the mean PFE values of 444 sterilized FFP2 face masks from the 19 CSSDs were 90±11% (mean±SD), and those of 474 new, imported KN95/FFP2 face masks were 83±16% (mean±SD). Differences in PFE of masks received from different sterilization departments were found.

Conclusion
Face masks can be reprocessed with 121 °C steam or H2O2 plasma sterilization with a minimal reduction in PFE. PFE comparison between filter material of sterilized masks and new, imported masks indicates that the filter material of most reprocessed masks of high quality brands can outperform new, imported face masks of unknown brands. Although the PFE of tested face masks from different sterilization departments remained efficient, using different types of sterilization equipment, can result in different PFE outcomes.@en

Cellulose is a biopolymer commonly used as a renewable constituent in the production of green materials. Wastewater solids can be an attractive source of cellulose, mainly originating from toilet paper. Cellulosic solids can be recovered (i) through sieving before the sewage treatment - resulting in a Fine Sieve Fraction (FSF), or (ii) after biological treatment in the waste sludge – such as in Nereda® Excess Sludge (NES). Its recovery and valorisation into high-end bio-based products, such as crystalline nanocellulose, could improve the techno-economic feasibility of cellulose recovery from wastewater. A cellulose extraction method from wastewater solids was developed during this project. Reference materials (microcrystalline cellulose and toilet paper) and wastewater-extracted cellulosic pulps were studied for the production of cellulose nanocrystals (CNCs). CNCs were prepared by controlled acid hydrolysis followed by centrifugation, filtration, dialysis, neutralisation and ultrasonication. A detailed protocol for CNCs isolation from toilet paper and wastewater-recovered pulps can be found in the appendix section. CNCs could be extracted at around 30 % yield (g g pulp-1). FSF showed to be an attractive source of nanocellulose since the yield per g FSF was 22 %, while for NES it was only 4 %. The wastewater-CNCs presented rod-like morphology with high aspect ratio (10 – 14), crystallinity (62 – 68 %), and chemical structure very similar to commercially available CNCs. However, there is still great extent for improvements since impurities might be still present and the isolation process needs reproducibility and optimization. Bionanocomposites consisting of CNCs (commercial and lab-made) and alginate materials were investigated by measuring the stiffness of freestanding films. A 50 % loading of commercial-CNCs reinforced alginate films by a factor of 1.6 (19 GPa). For the same loading, CNCs isolated from toilet paper and FSF reinforced alginate by a factor of 1.8 and 1.5 (22 – 18 GPa) respectively. Both characterisation results and reinforcement efficiency of CNCs isolated from toilet paper and wastewater-recovered pulps confirm the good quality of this potential product. Furthermore, we have observed changes in the nematic-isotropic phase diagram of CNCs in alginate suspensions. We developed a model hypothesizing that an alginate-shell decorates the CNCs rods increasing its volume fraction and allowing the nematic phase to appear at lower concentrations. The model was highly representative to the experimental data. Lastly, the market relevance of wastewater-CNCs is discussed together with a research outlook.