Recyclable and (Bio)degradable Polyesters in a Circular Plastics Economy

Polyesters carrying polar main-chain ester linkages exhibit distinct material properties for diverse applications and thus play an important role in today's plastics economy. It is anticipated that they will play an even greater role in tomorrow's circular plastics economy that focuses on sustainability, thanks to the abundant availability of their biosourced building blocks and the presence of the main-chain ester bonds that can be chemically or biologically cleaved on demand by multiple methods and thus bring about more desired end-of-life plastic waste management options. Because of this potential and promise, there have been intense research activities directed at addressing recycling, upcycling or biodegradation of existing legacy polyesters, designing their biorenewable alternatives, and redesigning future polyesters with intrinsic chemical recyclability and tailored performance that can rival today's commodity plastics that are either petroleum based and/or hard to recycle. This review captures these exciting recent developments and outlines future challenges and opportunities. Case studies on the legacy polyesters, poly(lactic acid), poly(3-hydroxyalkanoate)s, poly(ethylene terephthalate), poly(butylene succinate), and poly(butylene-adipate terephthalate), are presented, and emerging chemically recyclable polyesters are comprehensively reviewed.

Physicochemical Characterization and Finite Element Analysis-Assisted Mechanical Behavior of Polylactic Acid- Montmorillonite 3D Printed Nanocomposites

This work aims to improve the properties of poly(lactic acid) (PLA) for future biomedical applications by investigating the effect of montmorillonite (MMT) nanoclay on physicochemical and mechanical behavior. PLA nanocomposite filaments were fabricated using different amounts of MMT (1.0, 2.0, and 4.0 wt.%) and 2 wt.% Joncryl chain extenders. The 3D-printed specimens were manufactured using Fused Filament Fabrication (FFF). The composites were characterized by Gel Permeation Chromatography (GPC), Melt Flow Index (MFI), X-ray Diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The thermal properties were studied by means of Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Moreover, the hydrophilicity of the PLA/MMT nanocomposites was investigated by measuring the water contact angle. The mechanical behavior of the PLA/MMT nanocomposites was examined with nanoindentation, compression tests, and Dynamic Mechanical Analysis (DMA). The presence of Joncryl, as well as the pretreatment of MMT before filament fabrication, improved the MMT distribution in the nanocomposites. Furthermore, MMT enhanced the printability of PLA and improved the hydrophilicity of its surface. In addition, the results of nanoindentation testing coupled with Finite Element Analysis showed that as the MMT weight fraction increased, as well as an increased Young’s modulus. According to the results of the mechanical analysis, the best mechanical behavior was achieved for PLA nanocomposite with 4 wt.% MMT.

The Life Cycle Assessment for Polylactic Acid (PLA) to Make It a Low-Carbon Material

The massive plastic production worldwide leads to a global concern for the pollution made by the plastic wastes and the environmental issues associated with them. One of the best solutions is replacing the fossil-based plastics with bioplastics. Bioplastics such as polylactic acid (PLA) are biodegradable materials with less greenhouse gas (GHG) emissions. PLA is a biopolymer produced from natural resources with good mechanical and chemical properties, therefore, it is used widely in packaging, agriculture, and biomedical industries. PLA products mostly end up in landfills or composting. In this review paper, the existing life cycle assessments (LCA) for PLA were comprehensively reviewed and classified. According to the LCAs, the energy and materials used in the whole life cycle of PLA were reported. Finally, the GHG emissions of PLA in each stage of its life cycle, including feedstock acquisition and conversion, manufacturing of PLA products, the PLA applications, and the end of life (EoL) options, were described. The most energy-intensive stage in the life cycle of PLA is its conversion. By optimizing the conversion process of PLA, it is possible to make it a low-carbon material with less dependence on energy sources.

Adding Value in Production of Multifunctional Polylactide (PLA)-ZnO Nanocomposite Films through Alternative Manufacturing Methods

Due to the added value conferred by zinc oxide (ZnO) nanofiller, e.g., UV protection, antibacterial action, gas-barrier properties, poly(lactic acid) (PLA)–ZnO nanocomposites show increased interest for utilization as films, textile fibers, and injection molding items. The study highlights the beneficial effects of premixing ZnO in PLA under given conditions and its use as masterbatch (MB), a very promising alternative manufacturing technique. This approach allows reducing the residence time at high processing temperature of the thermo-sensitive PLA matrix in contact of ZnO nanoparticles known for their aptitude to promote degradation effects onto the polyester chains. Various PLA–ZnO MBs containing high contents of silane-treated ZnO nanoparticles (up to 40 wt.% nanofiller specifically treated with triethoxycaprylylsilane) were produced by melt-compounding using twin-screw extruders. Subsequently, the selected MBs were melt blended with pristine PLA to produce nanocomposite films containing 1–3 wt.% ZnO. By comparison to the more traditional multi-step process, the MB approach allowed the production of nanocomposites (films) having improved processing and enhanced properties: PLA chains displaying higher molecular weights, improved thermal stability, fine nanofiller distribution, and thermo-mechanical characteristic features, while the UV protection was confirmed by UV-vis spectroscopy measurements. The MB alternative is viewed as a promising flexible technique able to open new perspectives to produce more competitive multifunctional PLA–ZnO nanocomposites.