Davide Rigo

Synthesizing biodegradable plastics which match the properties and performance of commercially available polymers is a timely challenge. In this study, we show how polyanhydrides are privileged reactive partners in polyesterification reactions with polyols, affording biodegradable polyesters with mechanical properties comparable to those of commercially available polymers, such as PVC, PS, and PE. The approach involves two steps: (i) converting (activating) dicarboxylic acids into polyanhydrides using non‐toxic isopropenyl acetate (iPAc) as the mediator under homo‐/hetero‐geneous catalysis and (ii) reacting polyanhydrides with polyols to yield thermoplastic and thermoset polyesters with tunable mechanical properties (9 examples; glass transition temperatures of 7°C–49°C, ultimate tensile strengths of 0.4–38 MPa, tensile moduli of 3–1300 MPa and elongations at break of 1%–178%). Our approach not only is carried out under milder conditions compared to conventional polycondensation methods but also is versatile and simple. The synthesized polymers may find applications as biodegradable packaging materials.

C–C bond cleavage is vital for breaking down resilient lignin and plastics. This review highlights current methods, mechanisms, promising strategies, and considerations to improve efficiency and guide future valorization.

Reactive extraction (REx) is a promising route to simultaneously fractionate and upgrade (functionalize) lignin under mild conditions. In this work, hydrothermally treated wood solids (T = 180 °C, t = 45 min, liquid-to-solid ratio = 1) were refluxed for 1 h using acetic acid, formic acid, and ethanol as solvent-reagents. In addition, Amberlyst 15 (Amb-15) was tested as a heterogeneous acid catalyst for REx. The design of the reaction setup allowed to minimize product losses, even when Amb-15 was used, which could be easily removed from the reaction mixture. The extracted lignins showed appreciable amounts of native linkages (28.8–46.4/100 Ar), molar masses of 2.8–13.7 kDa (Mw), and total hydroxy group contents of 4.6–5.8 mmol/g. HSQC NMR analysis proved the incorporation of ethoxy, acetyl, and formyl groups in the extracted lignins in 1.2–2.0/100 Ar, 39.2–39.4/100 Ar, and 12.6–15.4/100 Ar, respectively. The molar masses of the residual cellulosic solids ranged from DPw of 2900 to 1000, and 13C NMR solid-state and solution-state NMR analyses confirmed the functionalization of the residual cellulosic solids as well, though to a low extent.

Lignin and lignin–carbohydrate complexes (LCCs) were isolated using AquaSolv Omni (AqSO). The process involves hydrothermal treatment of wood followed by organic solvent extraction, using a sequential fractionation approach with water‐based alkaline (1 wt%), ethanol, and acetone solutions. This strategy allowed for isolating different lignin/LCCs fractions with varying structure and properties. The sequential fractionation approach provided fractions with wide variability of glass transition temperatures ranging from 94°C to 153°C, while demonstrating excellent antioxidant activity with a normalized radical scavenging index up to 13.2 mmol g ⁻¹ . The incorporation of different lignin/LCCs with high antioxidant activity into lignocellulosic film formulation at 1.5 wt%, in which lignin and cellulose were the sole components, demonstrated superior effectiveness in blocking over 90% of ultraviolet (UV) rays (sun protection factor = 6–12), yet maintaining a high transparency of the resulting film. This study underscores the versatility of lignin and its high potential for integration into applications where strong UV and antioxidant protection are concerned without posing any environmental concern.

Predicting the potential of newly designed cyclic monomers toward catalytic ring-opening polymerization (ROP) under mild conditions remains challenging and often only achieved after extensive empirical efforts. Here, we describe a computer-guided mechanistic model based on a widely applied N-heterocyclic organocatalyst (TBD) and a standard initiator (BnOH). The developed model allows to use two key parameters to predict the influence of the positional and functional substitution of five-, six- and seven-membered cyclic carbonates on their ROP potential to form polycarbonates. More specifically, the computed model determines the energy requirement (δE) of the key initiation and two following propagation steps for a large series of known and unknown cyclic carbonate monomers thereby extracting important trends in terms of the number, position and type of substituent present on the heterocyclic rings. It also provides an assessment of the relative thermodynamic stability (delta-GD) of the resting state prior to each of the propagation steps. In combination with the δE of the process, the probability of the ROP event for each monomer can be estimated. The computational data and model have been validated with a large number of reported experimentally data available for the TBD/BnOH-promoted ROP of various five-, six- and seven-membered cyclic carbonates, and are further complemented by a series of ROP experiments.

This study outlines a method for producing chemically recyclable crosslinked polyesters using renewable polyols—glycerol and sorbitol—combined with adipic acid (AA), which is transformed/activated into a polyanhydride mixture prior to use. A three‐step procedure has been designed: 1) an acid‐catalyzed reaction of AA with nontoxic isopropenyl acetate or acetic anhydride to form a crosslinking mixture (CLM) made of adipic‐acetic mixed polyanhydrides; 2) a solvent‐ and additive‐free process where glycerol or sorbitol, or a combination thereof, is reacted with the CLM to achieve a prepolymer, and 3) a casting/molding of the liquid viscous prepolymer to yield a thermoset as the end product. Different thermosets (eight examples) are prepared by changing the reagents ratio. These solids are thoroughly characterized by tensile tests, DMA, high‐resolution magic angle spinning and solid‐state NMR, thermal gravimetric analysis, DSC, and fourier transformed infra red (FT‐IR) spectroscopy. The formation of cross‐linked polyesters is confirmed in all cases, but mechanical properties varied significantly from one specimen to another. Interestingly, a tensile strength up to 18 MPa—approximately an order of magnitude higher than similar polymers—is achieved when sorbitol and the CLM are used in a 1:1 wt% ratio. The chemical recycle of the resulting polymers is achieved via methanolysis with quantitative recovery of the monomeric units.

The most widespread procedure to measure the antioxidant activity of lignin is via the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) assay. So far, different experimental procedures (i. e., different solvent, time, etc.) have been used to implement the DPPH methodology without estimating the effect of such modifications on the experimental procedure. To overcome this issue, the impact of the solvent, the time, and the type of substrate on the evaluation of the antioxidant activity (AoA) of lignin via the DPPH assay was investigated in this work. We found that multiple different parameters affect the evaluation of the AoA of lignin: i) the stability of the DPPH radical and the lignin solubility in a given solvent; ii) the importance of reaching steady state (the effect of time); iii) the background noise associated with lignin absorbance at λ=515 nm (used to monitor the DPPH radical scavenging); iv) lignin structure; v) providing a normalized radical scavenging index (nRSI); vi) comparing nRSI vs. inhibition percentage (IP) values. Overall, our investigation allowed us to provide guidelines on how to perform the DPPH assay for a more reliable evaluation of lignin AoA.

Lignin‐carbohydrate complexes (LCCs) present a unique opportunity for harnessing the synergy between lignin and carbohydrates for high‐value product development. However, producing LCCs in high yields remains a significant challenge. In this study, we address this challenge with a novel approach for the targeted production of LCCs. We optimized the AquaSolv Omni (AqSO) biorefinery for the synthesis of LCCs with high carbohydrate content (up to 60/100 Ar) and high yields (up to 15 wt %) by employing machine learning (ML). Our method significantly improves the yield of LCCs compared to conventional procedures, such as ball milling and enzymatic hydrolysis. The ML approach was pivotal in tuning the biorefinery to achieve the best performance with a limited number of experimental trials. Specifically, we utilized Bayesian Optimization to iteratively gather data and examine the effects of key processing conditions–temperature, process severity, and liquid‐to‐solid ratio–on yield and carbohydrate content. Through Pareto front analysis, we identified optimal trade‐offs between LCC yield and carbohydrate content, discovering extensive regions of processing conditions that produce LCCs with yields of 8–15 wt % and carbohydrate contents ranging from 10–40/100 Ar. To assess the potential of these LCCs for high‐value applications, we measured their glass transition temperature (T_g), surface tension, and antioxidant activity. Notably, we found that LCCs with high carbohydrate content generally exhibit low T_g and surface tension. Our biorefinery concept, augmented by ML‐guided optimization, represents a significant step toward scalable production of LCCs with tailored properties.