An important aspect before large-scale production and application of bioplastics such as polylactic acid (PLA), is the need to close the life cycle of the material to reduce the need for first-generation biomass and to prevent waste accumulation in the environment. In this work, starting from a high-mass linear commercial PLA, a depolymerization route based on a bulk alcoholysis reaction in the molten state was developed. For this purpose two polyalcohols, pentaerythritol and dipentaerythritol, and an environmentally friendly catalyst, i.e., zinc stearate, were utilized. The formation and specific polyalcohol dependent structure of star-shaped oligomers characterized by a low glass transition temperature was confirmed by spectroscopical and thermal analysis. Indeed, 1H NMR characterization evidenced that the most effective polyalcohol was pentaerythritol, which at the highest concentration in the reaction mixture, namely 10 wt.-%, allowed most of the hydroxyl groups to react, resulting in a system with a Tg of about 20 °C, which was much lower than that of the starting linear polymer, characterized by a Tg of about 60 °C. Moreover, GPC as well as DSC analysis in particular demonstrated the active role of zinc stearate in the transesterification reaction, as the samples prepared without adding the catalyst to the reaction mixture showed a modest reduction in Tg and molecular weight, which decreased from 92,000 g⋅mol−1 to 1700 g⋅mol−1 for the starting linear polymer and the resulting oligomer, respectively, in the case of the sample prepared with the highest amount of PE and with the addition of zinc stearate.The films produced from the star-shaped PLA oligomers were characterized by poor mechanical properties, but the high concentration of alcohol-functionalities could make them applicable in various polymer formulations. The star-shaped polymers were thereby blended with a multifunctional epoxide from renewable sources. The reactivity and compatibility of the two components was proved along with the specific role of zinc stearate remaining from the alcoholysis, in promoting the reaction between the two compounds. Indeed, the produced materials proved to be homogeneous, manageable and also completely enzymatically degradable.

Cationic photopolymerization offers a significant advantage over radical polymerization due to its resistance to oxygen inhibition and superior dimensional stability during the crosslinking process. In this study, we aim to advance the development of bio-based monomers for cationic photopolymerization by synthesizing oxetane-functionalized derivatives of adipic, itaconic, and citric acids. These three renewable acids were chosen for their multifunctionality and availability. The synthesized monomers, bis((3-methyloxetan-3-yl)methyl) adipate (BOA), bis((3-methyloxetane-3-yl)methyl) itaconate (BOI), and tris((3-methyloxetane-3-yl)methyl) citrate (TOC), were fully characterized using nuclear magnetic resonance (NMR). Fourier transform infrared (FTIR) spectroscopy and photo differential scanning calorimetry (photo-DSC) were employed to monitor the oxetane ring-opening reaction kinetics and to determine the degree of conversion, revealing high reactivity in all monomers, reaching nearly complete conversion within 90 s. The mechanical properties of the UV-cured films were assessed by dynamic mechanical thermal analysis (DMTA) and gel content measurements. Results indicated that the BOI-based films exhibited higher glass transition temperatures (Tg) and crosslinking densities compared to BOA- and TOC-based films. The findings demonstrate the potential of bio-based oxetane monomers to produce UV-curable materials with acceptable thermomechanical properties, offering a sustainable alternative to petroleum-derived precursors.

Accelerated production of recyclable and biodegradable polymers is crucial in combating the socioeconomic and environmental issues connected to traditional plastics. While renewable diacids have been in the spotlight for the generation of biobased polyesters with tailored properties by varying the alkyl chain length, capitalizing on diols from biomass for this purpose is underexplored and has mainly focused on linear and branched shorter chain alcohols. Here, we explored the potential of two (-)-alpha-pinene-derived diols (PDOs) as building blocks to generate biobased polyesters harboring bicyclic ring structures in their backbones that can mimic aromatic fossil-based plastics' properties. We demonstrate a concise synthesis of two novel unsymmetrical chiral PDOs on the 20-40 g scale, together with eight structurally differing heat-resistant polyesters, as reflected by high glass transition (T g ) temperatures (90 and 121 degrees C) for two of the polymers. The stereochemistry of PDO-derived polyesters is guided by intramolecular hydrogen bonding made possible by the protruding rings and the polyester backbone. Most of the synthesized polyesters (five) in this study showed potential as adhesives based on the analysis of tensile strength and adhesive properties on paper boards. The steric hindrance of the intact bicyclic alpha-pinene ring structure protruding from the backbone of the polymers can also aid in the degradation process, manifested by facile chemical recycling of these polyesters under mild conditions to recover both monomers. Finally, our results show how the generated rigid polymers are susceptible to enzymatic degradation by PETase and cutinase without any chemical pretreatment. Our results illuminate the potential of expanding the current scope of biobased monomers to bicyclic diols to generate biomaterials with tailor-made properties.

A series of cellulose networks are designed by reversibly crosslinking amino-functionalized 2-hydroxyethyl cellulose (HEC-NH2) with different amounts of vanillin dimer (VA-CHO). The Schiff base reaction between amino-and aldehyde groups creates networks (SBHEC) bridged with crosslinks containing dynamic imine groups. These SBHEC networks can be hot pressed to flexible films with good thermal stability and solvent resistance, including notable stability in water, opposite to water-soluble HEC and HEC-NH2. Compared to HEC-NH2, the cross-linked SBHEC networks exhibit higher glass transition temperatures, elastic modulus, and tensile stress at break, and slightly reduced tensile strain at break. Reprocessing of the SBHEC networks is achieved through hot pressing under facile conditions, leading to good recovery of mechanical properties. Furthermore, the materials can be chemically recycled in a closed-loop by imine-hydrolysis under acidic conditions at room temperature. This releases the original building blocks HEC-NH(2 )and VA-CHO, which can be recured to produce new SBHEC. This work highlights the potential of dynamic covalent cellulose networks as mechanically and chemically recyclable materials, contributing to the development of closed-loop recycling systems.

The growing emphasis on sustainable development has underscored the importance of replacing petroleum-based resources with bio-based alternatives and integrating covalent adaptable networks (CANs) as recyclable adhesives. However, combining a green synthesis process with rapid recycling capabilities remains a significant challenge. In this work, commercially available organosolv lignin (OL) was acrylated and subsequently cured with pentaerythritol triacrylate (PTA) and poly (propylene glycol) bis (2-aminopropyl ether) 400 (PEA D400) through a click reaction, specifically Aza-Michael addition, to fabricate CANs featuring dual dynamic bonds (hydroxyl-ester and β-amino ester). The thermodynamic and mechanical properties of the networks were tuned by varying the acrylated lignin-to-PTA ratio. These materials demonstrated adhesive properties on various substrates with shear strengths above 1.5 MPa on wood, aluminum, polycarbonate, and more. The incorporation of dual dynamic bonds facilitated rapid stress relaxation within 3 min at 160 °C. Leveraging these dynamic features, both uncured and cured resins could be swiftly re-bonded with a 10-minute hot pressing post-failure. Additionally, adhesive layers could be peeled and rebonded within 5 min at elevated temperatures, achieving adhesion strengths up to 2.1 times that of the original samples. Furthermore, the photothermal properties of lignin enabled light-controlled healing, highlighting its potential for on-demand adhesive applications. This work presents an eco-friendly and sustainable strategy for the challenges of adhesive recovery.

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.

Recycling of polymer composites by melt-extrusion has been limited to reinforced thermoplastics. Here, we demonstrate several melt-extrusion recycling cycles for glass fiber-reinforced elastomers cross-linked with a reversible cross-linker (SS). In comparison, reinforced elastomers lacking reversible cross-linking (CC) exhibited clogging during successive melt-extrusion recycling. Furthermore, commercially available starting materials, such as maleated polypropylene (PPgMA), maleated ethylene propylene rubber (EPRgMA), and short-cut glass fibers, were utilized. We showed that when tetrasulfide functionalized glass fibers (SGF) were embedded in SS cross-linked composites (CompSS-SGF), disulfide exchange reactions were further activated. This was manifested in the high tensile strength of 10 MPa and 220% elongation, which were remarkably higher than the 6 MPa and 17% elongation of CC cross-linked composites (CompCC-SGF). Moreover, the higher interactions of CompSS-SGF contributed to at least a 25% increase in tensile strength and storage modulus and a 36% increase in creep resistance compared to composite counterparts prepared with as-received glass fibers (CompSS-AGF) or clean glass fibers (CompSS-CGF). Additionally, the disulfide exchanges in CompSS-SGF possibly contributed to a approximate to 10% higher tensile strength after recycling. This simple up-scalable approach opens new avenues for the development of fiber-reinforced cross-linked elastomers with facile processability, higher dimensional stability, and up-scalable recycling processes.

Hierarchical porous, bioactive, and biocompatible scaffolds with customizable multi-functionality are promising alternatives for autografts and allografts in bone tissue engineering. Combining high internal phase emulsion (HIPE) templating with additive manufacturing provides possibilities to produce such multiscale porous scaffolds. 3D printing of HIPE remains a challenging task due to the intense phase separation under high shear extrusion and reported printability (Pr) of either less than or greater than 1. Tuning viscoelastic properties of emulsion is therefore required to achieve a Pr approximate to 1. This study addresses these issues by preparing Pickering HIPEs using dual networks with synergistic viscous and elastic properties, stabilized by Cloisite 30B interphase. This configuration enhances viscoelasticity and achieves Pr values close to 1 (0.98-1.02). The printed scaffolds exhibit trabecular bone-like, hierarchical interconnected porosity (77%-86%). Computational simulations accurately predict the mechanical, biological, and degradation behavior. Functionalization with Cissus quadrangularis bioactivates the scaffolds, demonstrates in vivo biocompatibility, promotes MC3T3-E1 adhesion, and proliferation, accelerates osteogenesis, and reduces oxidative stress compared to neat PCL scaffolds. This work introduces a facile strategy for "engineering printability" to produce regenerative materials with hierarchical design and holds the potential for developing optimized bone tissue engineering scaffolds.

Lignin, traditionally considered a low-value byproduct of the pulp and paper industry, has gained significant attention in recent years as a sustainable precursor for the development of functional materials. This paradigm shift is driven by recent studies exploring the structure–property–performance relationships of lignin-based functional materials, which have provided valuable insights for selective chemical functionalization or pretreatment of lignin. Furthermore, the use of complementary analytical techniques has helped to shed light into lignin’s complex and heterogeneous structure, opening new avenues for chemical modification. Finally, the emergence of colloidal lignin nanoparticles (LNPs) over the past decade has significantly contributed to the advancement and potential applications of lignin-based functional materials in diverse fields, including drug delivery and complex supramolecular systems.

Epoxy resins play a crucial role in several industrial applications. However, their irreversible crosslinked structure and need for precursors from fossil-fuels provide sustainability issues. This study explores the synthesis of bio-based epoxy vitrimers using glycidylated derivatives of gallic acid (GGA) and tannic acid (GTA) as eco-friendly alternatives. ATR-FTIR and NMR spectroscopies confirmed the successful glycidylation reaction. The thermal curing of epoxy monomers with Vitrimax imine T130 was performed after thoughtful DSC and TGA analyses, achieving reprocessable and thus recyclable materials. Indeed, thanks to the covalent adaptable networks (CANs) based on imine bonds the reprocessing of polyphenols-based composites was possible by hot-pressing their powders after a grinding step. Carbon nanotubes (CNT) were introduced into natural polyphenol-based materials at 1 and 2 wt% contents to improve electrical conductivity and piezoresistive properties. Thermomechanical performance of the bio-based composites was assessed as a function of CNT content, measuring a glass transition temperature of approximately 60 °C. Electrical conductivity measurements revealed an outstanding capability of polyphenols-based composites to conduct electricity with a percolation threshold at 1 wt% of CNT, reaching a maximum of 0.1 S/m and 0.4 S/m for GGA and GTA, respectively. Moreover, unlike systems with 1 wt%, the composites with 2 wt% of CNT exhibited significant Joule heating capabilities reaching 60 °C by just applying about 50 V. Finally, strain-sensing tests demonstrated the electromechanical responsiveness of the composites, showing outstanding gauge factors of 89 and 17 with the GGA_1CNT and GTA_1CNT, respectively, highlighting their potential in structural health monitoring (SHM) applications. This work underscores the feasibility of electrically conductive natural polyphenol-based composites as sustainable, recyclable, and multifunctional alternatives to conventional epoxy systems.