Cellulose acetate (CA) is an established commercial material based on an inherently biodegradable biobased resource, cellulose. However, chemical modification through acetylation to obtain thermoplastic properties significantly limits the biodegradation rate, making deacetylation the rate-determining step for subsequent biodegradation. We developed an innovative approach by immobilizing lipase (IL) enzymes on cellulose nanocrystals (CNCs), and embedding the resulting CNC-IL into CA films to accelerate the biodegradation of CA. This offers a platform for controlling and accelerating the degradation of CA, as demonstrated by significantly enhanced degradation rates under self-degradation and enzymatic degradation in aqueous medium, including artificial seawater, and under simulated industrial composting conditions. We also explored the underlying mechanisms by detailed characterization of the degradation process in different degradation environments, demonstrating that the enzyme-embedded approach and utilization of CNCs as an immobilization matrix holds significant promise for catalyzing the biodegradation process by initiating self-degradation from inside the polymer material. This approach thus holds promise in accelerating the degradation process and ensuring degradation even under less favorable environmental conditions.

Zeolites are a group of crystalline aluminosilicates with exchangeable cations and molecular-dimensioned micropores, which have successfully been applied to transform biomass and waste into biofuels. Herein, the effectiveness of acidic H-zeolites in biomass transformation and chemical valorization is demonstrated. In this process, the Br & oslash;nsted/Lewis acid sites in zeolites catalyze the transition of carbohydrates into valuable chemicals. beta-glucan polymer extracted from the lichen Usnea was catalytically converted into value-added molecules, such as glucose monomers. Particular challenges to elucidate the zeolite-catalyzed beta-glucan conversion to glucose were addressed, namely: (i) water as the solvent, ii) hydrolysis of the biopolymer in an ionic liquid of 1-Butyl-3-vinylimidazolium bromide ([BVinIm]Br), and iii) reaction time of 30, 60, 120, and 240 min. Effective hydrolysis of beta-glucan was achieved by H-zeolites (H-Beta, H-Mordenite, and H-ZSM-5), and the formed glucose was quantified through the dinitrosalicylic acid (DNS) method. Finally, applying H-zeolites as heterogeneous catalysts to prove the chemical recyclability of flexible films based on beta-glucan was demonstrated as a step forward in integrating biopolymer-based materials into the circular economy.

Four biobased ester and ester-imine photocurable resins were formulated and evaluated for printability by digital light processing 3D printing. The resin formulations consisted of methacrylated eugenol alone or in combination with methacrylated poly(hydroxybutyrate)-oligomers and/or methacrylated vanillin-derived Schiff-base monomers. It was not possible to print methacrylated eugenol alone into coherent thermosets, likely due to the lower reactivity of the allyl-double bond. However, in combination with the other building blocks methacrylated eugenol improved the printability, although some over-curing phenomena were registered especially for the resins composed of methacrylated eugenol and methacrylated poly(hydroxybutyrate)-derived oligomers. The three formulations that were successfully printed to coherent thermosets were further evaluated for their solvent resistance, thermal and mechanical properties, reprocessability and biodegradability under simulated industrial composting conditions. The reprocessing experiments documented the synergic effect of ester and imine dynamic covalent bonds in favoring the preservation of the elastic modulus of the thermosets; while an evidently higher deterioration of the mechanical properties was registered for the ester-thermosets. The biodegradation studies highlighted a clear correlation between the biodegradation rate and the chemical structure of the thermosets, with the aliphatic components and ester and imine bonds increasing the thermosets' susceptibility to the biodegradation under simulated industrial composting conditions.

Environmental pollution by release of nondegradable textile fibers and single-use fabrics, such as face masks, is a serious threat. Replacement of electrospun polypropylene fabrics with materials that have a better environmental degradation profile is therefore of interest. Here, a strategy is presented through carbon dot (CD) modification of cellulose acetate (CA) mats produced by a one-step electrospinning process. The mats were carefully characterized for their physicochemical properties and screened for any antioxidant or antibacterial properties before they were subjected to aging under UV irradiation or soil burial. Typically, the degree of substitution (DS) of CA needs to be under 2 for any significant biodegradation to take place. It was therefore of interest to notice that some deacetylation took place already during electrospinning as the initial DS of 2.2, as determined by nuclear magnetic resonance spectroscopy (NMR), decreased to 2.0 and 1.8 for CA and CD-modified CA (CA-CD), respectively. After 30 days of soil burial or 7 days of UV irradiation, the DS of CA-CD had further decreased to 1.1 and 0.9, while the corresponding values for plain CA were 1.5 and 1.8. CD modification thus significantly catalyzed the deacetylation process, helping to overcome the bottleneck of CA biodegradation. The degradation of the mats was supported by other physicochemical changes, such as decreased water contact angle and molecular weight values. It was further shown that degradation during soil burial was significantly faster for the electrospun mats compared to the corresponding CA and CA-CD films, which could be due to the combination of larger surface area and the deacetylation that took place during electrospinning, making the electrospun mats more susceptible to subsequent biodegradation. However, the catalyzing effect of CD was observed even for the film samples, leading to somewhat lower DS and higher mineralization as determined by CO₂ release.

Fungal mycelium is emerging as a source for sustainable bio-based materials. Fungal biomass of Aspergillus oryzae was prepared by cultivation on bread waste hydrolysate to valorize this abundant food waste. Chitin-glucan-rich alkali-insoluble material (AIM) was isolated from fungal biomass, formed into hydrogels, and wet spun into monofilaments. AIM in the form of fungal microfibers containing 0.09 g polymer of glucosamine (GlcN)/g AIM was subjected to freeze-thaw and deacetylation treatments to increase the amount of GlcN. The GlcN fraction was 0.19 and 0.34 g polymer of GlcN/g AIM, for AIM subjected to deacetylation (AIM-DAC) and freeze-thaw cycles and deacetylation (AIM-FRTH-DAC), respectively. The increased GlcN fraction enabled the formation of hydrogels via the protonation of amino groups after the addition of lactic acid. Morphological differences in the hydrogels included aggregation of the fungal microfibers in the AIM-DAC hydrogel, whereas the microfibers in the AIM-FRTH-DAC hydrogel had a porous and interconnected network. Rheological assessment revealed shear thinning behavior and gel properties of the produced hydrogels. Wet spinning of the hydrogels resulted in monofilaments with tensile strengths of up to 70 MPa and 12 % elongation at break. This demonstrates promising avenues for biomaterial development from fungal cell walls containing chitin-glucan via food waste valorization.

Embedding immobilized lipase (IL) enzymes into polycaprolactone (PCL) matrix was demonstrated as a promising route to faster biodegradable and chemically recyclable PCL products. Furthermore, the materials could be thermally processed by extrusion and 3D printed by fused filament fabrication technique. The embedded-enzymes were shown to effectively accelerate the degradation of PCL under simulated industrial composting conditions and in aqueous solution in combination with external enzymes. To reveal deeper insights into the underlying mechanisms, the biodegradation kinetic parameters governing organic carbon (OC) mineralization were calculated. Furthermore, the concept of biodegradation half-life (B1/2) was introduced and correlated with the organic carbon (OC) mineralization rate of enzyme-embedded PCL films and filaments, especially under thermophilic composting conditions. This sheds light on how the incorporation of immobilized enzymes into PCL facilitates the degradation process. Furthermore, the feasibility of enzyme-catalyzed chemical recycling under mild conditions followed by enzyme-catalyzed repolymerization was demonstrated. The applied material design principle holds promise for addressing the pressing challenges associated with plastic waste, when moving forward towards a more sustainable and environmentally conscious future.

Rice husk (RH), an abundant agricultural residue, was successfully chemically modified and used as a component in reprocessable and biodegradable epoxy thermosets. First, RH was subjected to alkaline treatment to increase the cellulose content followed by succinylation and curing with trimethylolpropane triglycidyl ether to form the thermoset films. The chemical structure of the different intermediates and thermosets was confirmed by Fourier transform infrared spectroscopy. The developed thermoset films had good solvent resistance against common organic solvents and good thermal stability as measured by thermogravimetry with peak temperatures of 347–387 ℃, char residues of 16–20% and limiting oxygen index values of 24–26%, respectively. The films could be thermally reprocessed by hot-pressing with excellent recovery of the mechanical properties (92–96% recovery of tensile stress). Furthermore, 80–84% biodegradation during 150 days under mesophilic home composting conditions was demonstrated by cumulative CO<inf>2</inf> evolution. These results indicate promising potential for the developed RHs thermosets as replacements for petroleum-based plastics in e.g. packaging and agricultural applications.

The current study aimed at the valorization of bread waste in a fungal biorefinery for the recovery of protein hydrolysate for food applications and monofilaments for medical textile applications. Rhizopus delemar was cultivated on bread waste in a 1 m³airlift bioreactor to obtain fungal biomass. The protein hydrolysate was isolated as a soluble fraction after a mild enzymatic treatment of fungal biomass with a protease enzyme. The recovered protein hydrolysate was rich in eight essential amino acids and showed foaming and emulsion properties. The fungal microfibers rich in chitin and chitosan were recovered as an insoluble fraction of fungal biomass during the protease treatment process. A hydrogel of the fungal microfibers was wet-spun to monofilaments, which showed high elongation at break. In in vitro scratch assay, the monofilaments demonstrated significant improvements of the rate of cell migration and wound closure compared to viscose fibers (which are commonly used in wound healing dressings). Furthermore, fungal biomaterials in the form of microfibers, hydrogel, and monofilaments showed excellent biocompatibility against fibroblast cells and significantly enhanced cell growth at higher concentrations (above 500 μg/mL). This work suggests a sustainable approach to using abundant food wastes to create value-added products for food and medical textile applications.

This review presents an overview of recent scientific developments and innovations aiming to integrate biodegradable polyesters into the circular economy. We especially concentrate on the development of different end-of-life management options for biodegradable polyesters including mechanical, chemical and organic recycling (composting or biodegradation in specified environments). Polymer materials in general are crucial for sustainable development, but we need to rethink and redesign to incorporate them in circular material flows. Biodegradable polyesters have all the prerequisites to become fully compatible with the principles of the circular economy. The development of polyesters with balanced material properties, ment routes will be a step forward to reduce and eliminate plastic waste accumulation.

A green strategy that significantly accelerates the biodegradation rate of cellulose acetate (CA) by triggering deacetylation was demonstrated. Lipase isolated from Candida rugosa was immobilized on CA particles (immobilized lipase (IL)) by a physical entrapment method and further incorporated in CA films. After 40 days of aging in contact with external enzymes (lipase and cellulase), the number-average molecular weight (Mn) of CA/IL 5% decreased by 88%, while the Mn of CA only exhibited a 48% reduction. Fourier transform infrared and nuclear magnetic resonance spectroscopy of CA/IL 5% indicated significant deacetylation, which was further supported by the decrease of the water contact angle from 59 to 16°. These drastic changes were not observed for CA. Similar differences in the degradation rate were observed during aging under simulated composting conditions. After 180 days of simulated composting, traces of CA/IL 5% were barely observable, while large pieces of CA still remained. This could open the door to modified lignocellulose materials with retained biodegradability, also reducing the requirements for the degradation environment as the process is initiated from inside of the material.