Pyrolysis mechanism of Poly(lactic acid) for giving lactide under the catalysis of tin

On the Dendrite-Suppressing Effect of Laser-Processed Polylactic Acid-Derived Carbon Coated Zinc Anode in Aqueous Zinc Ion Batteries

A major bottleneck limiting the commercialization of aqueous zinc ion batteries (AZIBs) is dendrite formation on the zinc (Zn) anode during the plating/stripping process, which leads to rapid deterioration in performance and, consequently to the device failure. In this regard, researchers are trying to design more stable anodes toward suppressing dendrite formation. One possible solution to tackle this problem and to extend the cycling life of AZIBs is to modify the zinc anode surface by coating carbonaceous materials, enabling more controlled charge flux and uniform ion distribution. This work reports sustainable and bio-derived polylactic acid (PLA) as a coating layer on the zinc anode. Carbonizing this polymer under ambient conditions using a high-power nanosecond laser forms a carbon-coated zinc foil, which was directly utilized as the anode in aqueous zinc ion batteries. The fabricated laser-processed PLA-derived carbon-coated zinc anode demonstrated an extended cycling life of almost 1600 hours, significantly outperforming the bare zinc anode. A full aqueous zinc ion battery assembled from as-modified anode and as-prepared V2O5 nanofibers as cathode was able to deliver a specific capacity of 238 mAh g-1 at 1.0 A g-1 with a capacity retention of 70 % after 1000 cycles.

Depolymerization and Re/Upcycling of Biodegradable PLA Plastics

With the escalating utilization of plastic products, global attention has been increasingly drawn to environmental pollution and recycling challenges stemming from plastic waste. Against this backdrop, biodegradable plastics have emerged as viable alternatives owing to their sustainability and capacity for biodegradation. Polylactic acid (PLA) presently commands the largest market share among biodegradable plastics, finding extensive application in products such as thin films, medical materials, and biodegradable straws. However, the widespread adoption of PLA is hindered by challenges such as high cost, low recycling rates, and complete degradation to H2O and CO2 in natural conditions. Therefore, it is imperative and time-sensitive to explore solutions for the depolymerization and re/upcycling of PLA waste plastics. This review comprehensively outlines the current landscape of PLA recycling methods, emphasizing the advantages and significance of chemical re/upcycling. The subsequent exploration encompasses recent breakthroughs and technical obstacles inherent in diverse chemical depolymerization methods. Ultimately, this review accentuates the impediments and forthcoming possibilities in the realm of PLA plastics, emphasizing the pursuit of closed-loop recycling and upcycling.

Synthesis of L-Lactide from Lactic Acid and Production of PLA Pellets: Full-Cycle Laboratory-Scale Technology

Lactide is one of the most popular and promising monomers for the synthesis of biocompatible and biodegradable polylactide and its copolymers. The goal of this work was to carry out a full cycle of polylactide production from lactic acid. Process conditions and ratios of reagents were optimized, and the key properties of the synthesized polymers were investigated. The influence of synthesis conditions and the molecular weight of lactic acid oligomers on the yield of lactide was studied. Lactide polymerization was first carried out in a 500 mL flask and then scaled up and carried out in a 2000 mL laboratory reactor setup with a combined extruder. Initially, the lactic acid solution was concentrated to remove free water; then, the oligomerization and synthesis of lactide were carried out in one flask in the presence of various concentrations of tin octoate catalyst at temperatures from 150 to 210 °C. The yield of lactide was 67-69%. The resulting raw lactide was purified by recrystallization in solvents. The yield of lactide after recrystallization in butyl acetate (selected as the optimal solvent for laboratory purification) was 41.4%. Further, the polymerization of lactide was carried out in a reactor unit at a tin octoate catalyst concentration of 500 ppm. Conversion was 95%; Mw = 228 kDa; and PDI = 1.94. The resulting products were studied by differential scanning calorimetry, NMR spectroscopy and gel permeation chromatography. The resulting polylactide in the form of pellets was obtained using an extruder and a pelletizer.

Synthesis and Modeling of Poly(L-lactic acid) via Polycondensation of L-Lactic Acid

We present synthetic experiments of lactic acid (LA) polycondensation to produce poly(lactic acid) (PLA) as well as kinetic modeling calculations that capture the polymer molecular weight increase with time, given the initial concentrations. Tin-octoate-catalyzed polycondensation of (D,L)- or L-lactic acid was carried out in pre-dried toluene after azeotropic dehydration for 48-120 h at 130-137 °C. The polymerization was optimized by varying lactic acid and catalyst concentrations as well as the temperature. Gel permeation chromatography was used to experimentally follow the evolution of molecular weights and the products were characterized by NMR, TGA, DSC and IR. Under optimal conditions, PLLA with weight-average molecular weight (Mw) of 161 kDa could be obtained. The rate equations that describe polycondensation kinetics were recast in a condensed form that allowed very fast numerical solution and calculation of the number-average molecular weight with time. Deviations with respect to the experiment were minimized in a least-squares fashion to determine rate constants. The optimized kinetics parameters are shown to reproduce the experimental data accurately.

Sustainable Valorization of Bioplastic Waste: A Review on Effective Recycling Routes for the Most Widely Used Biopolymers

Plastics-based materials have a high carbon footprint, and their disposal is a considerable problem for the environment. Biodegradable bioplastics represent an alternative on which most countries have focused their attention to replace of conventional plastics in various sectors, among which food packaging is the most significant one. The evaluation of the optimal end-of-life process for bioplastic waste is of great importance for their sustainable use. In this review, the advantages and limits of different waste management routes-biodegradation, mechanical recycling and thermal degradation processes-are presented for the most common categories of biopolymers on the market, including starch-based bioplastics, PLA and PBAT. The analysis outlines that starch-based bioplastics, unless blended with other biopolymers, exhibit good biodegradation rates and are suitable for disposal by composting, while PLA and PBAT are incompatible with this process and require alternative strategies. The thermal degradation process is very promising for chemical recycling, enabling building blocks and the recovery of valuable chemicals from bioplastic waste, according to the principles of a sustainable and circular economy. Nevertheless, only a few articles have focused on this recycling process, highlighting the need for research to fully exploit the potentiality of this waste management route.

One-Pot Tandem Alcoholysis-Hydrogenation of Polylactic Acid to 1,2-Propanediol

The chemical recycling of end-of-life polylactic acid (PLA) plays roles in mitigating environmental pressure and developing circular economy. In this regard, one-pot tandem alcoholysis and hydrogenation of PLA was carried out to produce 1,2-propanediol, which is a bulk chemical in polymer chemistry. In more detail, the commercially available Raney Co was employed as the catalyst, and transformation was conducted in ethanol, which acted as nucleophilic reagent and solvent. Single-factor analysis and Box-Behnken design were used to optimize the reaction conditions. Under the optimized condition, three kinds of PLA materials were subjected to degradation. Additionally, 74.8 ± 5.5%, 76.5 ± 6.2%, and 71.4 ± 5.7% of 1,2-propanediol was yielded from PLA powder, particle, and straws, respectively, which provided a recycle protocol to convert polylactic acid waste into value-added chemicals.

The Chemical Recycling of Polyesters for a Circular Plastics Economy: Challenges and Emerging Opportunities

Whilst plastics have played an instrumental role in human development, growing environmental concerns have led to increasing public scrutiny and demands for outright bans. This has stimulated considerable research into renewable alternatives, and more recently, the development of alternative waste management strategies. Herein, the aim was to highlight recent developments in the catalytic chemical recycling of two commercial polyesters, namely poly(lactic acid) (PLA) and poly(ethylene terephthalate) (PET). The concept of chemical recycling is first introduced, and associated opportunities/challenges are discussed within the context of the governing depolymerisation thermodynamics. Chemical recycling methods for PLA and PET are then discussed, with a particular focus on upcycling and the use of metal-based catalysts. Finally, the attention shifts to the emergence of new materials with the potential to modernise the plastics economy. Emerging opportunities and challenges are discussed within the context of industrial feasibility.

Kinetic Study of Depolymerization of Lactic and Glycolic Acid Oligomers in the Presence of Oxide Catalysts

For glycolic acid oligomers (GAO): l-lactic acid oligomers (LAO) mixtures, as an example, it was shown that the nature of the active sites of the catalysts significantly affect the depolymerization process. So, ZnO, which has mainly basic sites, leads to the highest yield of cyclic diesters. On the contrary, depolymerization in the presence of acidic γ-Al₂O₃ and without a catalyst is characterized by lower diester yields due to the prevalence of a side polycondensation reaction. Using GAO:LAO mixtures, it was shown that in the case of three studied systems (with ZnO, γ-Al₂O₃, and without catalyst), mixed interactions occurred, including homo-paired and hetero-paired intermolecular interactions, as well as intramolecular interactions of oligomeric molecules. Kinetic models of the processes under study were determined by isoconversional thermal analysis. In the case of depolymerization of oligomers in the presence of ZnO, the kinetic model was between the kinetic models of the first (F1) and second (F2) orders, while in depolymerization in the presence of γ-Al₂O₃ and without a catalyst, the process was described by diffusion models such as the Jander equation (D3) and Zhuravlev, Lesokin, Tempelman equation (D5).