Influence of FFF Process Conditions on the Thermal, Mechanical, and Rheological Properties of Poly(hydroxybutyrate-co-hydroxy Hexanoate)

Polyhydroxyalkanoates are natural polyesters synthesized by microorganisms and bacteria. Due to their properties, they have been proposed as substitutes for petroleum derivatives. This work studies how the printing conditions employed in fuse filament fabrication (FFF) affect the properties of poly(hydroxybutyrate-co-hydroxy hexanoate) or PHBH. Firstly, rheological results predicted the printability of PHBH, which was successfully realized. Unlike what usually happens in FFF manufacturing or several semi-crystalline polymers, it was observed that the crystallization of PHBH occurs isothermally after deposition on the bed and not during the non-isothermal cooling stage, according to calorimetric measurements. A computational simulation of the temperature profile during the printing process was conducted to confirm this behavior, and the results support this hypothesis. Through the analysis of mechanical properties, it was shown that the nozzle and bed temperature increase improved the mechanical properties, reducing the void formation and improving interlayer adhesion, as shown by SEM. Intermediate printing velocities produced the best mechanical properties.This work has received funding from the Basque Government through grant IT1503-22, the Gipuzkoa Provincial Council (Red I+D+i 2022-CIEN-000022-01), and the project National Centre of Competence in Polymer Materials and Technologies for the 21st Century no. TN02000051 (TA CR, Czech Republic)

Crystallization-Induced Gelling as a Method to 4D Print Low-Water-Content Non-isocyanate Polyurethane Hydrogels

[EN]The use of three-dimensional (3D) printable hydrogels for biomedical applications has attracted considerable attention as a consequence of the ability to precisely define the morphology of the printed object, allowing patients' needs to be targeted. However, the majority of hydrogels do not possess suitable mechanical properties to fulfill an adequate rheological profile for printability, and hence, 3D printing of cross-linked networks is challenging and normally requires postprinting modifications to obtain the desired scaffolds. In this work, we took advantage of the crystallization process of poly(ethylene glycol) to print non-isocyanate poly(hydroxyurethane) hydrogels with tunable mechanical properties. As a consequence of the crystallization process, the hydrogel modulus can be tuned up to 3 orders of magnitude upon heating up to 40 degrees C, offering an interesting strategy to directly 3D-print hydrogels without the need of postprinting cross-linking. Moreover, the absence of any toxicity makes these materials ideal candidates for biomedical applications.The authors acknowledge financial support from the European Commission through SUSPOL-EJD 642671 project. M.C.A. thanks the University of Birmingham for funding

Single-Ion Conducting Polymer Nanoparticles as Functional Fillers for Solid Electrolytes in Lithium Metal Batteries

[EN]Composite solid electrolytes including inorganic nanoparticles or nanofibers which improve the performance of polymer electrolytes due to their superior mechanical, ionic conductivity, or lithium transference number are actively being researched for applications in lithium metal batteries. However, inorganic nanoparticles present limitations such as tedious surface functionalization and agglomeration issues and poor homogeneity at high concentrations in polymer matrixes. In this work, we report on polymer nanoparticles with a lithium sulfonamide surface functionality (LiPNP) for application as electrolytes in lithium metal batteries. The particles are prepared by semibatch emulsion polymerization, an easily up-scalable technique. LiPNPs are used to prepare two different families of particle-reinforced solid electrolytes. When mixed with poly(ethylene oxide) and lithium bis(trifluoromethane)sulfonimide (LiTFSI/PEO), the particles invoke a significant stiffening effect (E' > 106 Pa vs 105 Pa at 80 °C) while the membranes retain high ionic conductivity (sigma = 6.6 * 10-4 S cm-1). Preliminary testing in LiFePO4 lithium metal cells showed promising performance of the PEO nanocomposite electrolytes. By mixing the particles with propylene carbonate without any additional salt, we obtain true single-ion conducting gel electrolytes, as the lithium sulfonamide surface functionalities are the only sources of lithium ions in the system. The gel electrolytes are mechanically robust (up to G' = 106 Pa) and show ionic conductivity up to 10-4 S cm-1. Finally, the PC nanocomposite electrolytes were tested in symmetrical lithium cells. Our findings suggest that all-polymer nanoparticles could represent a new building block material for solid-state lithium metal battery applications.L.P. has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska–Curie grant agreement no. 797295. P.S. has been funded by the SNSF (Swiss National Science Foundation) under project number P2FRP2_191846. J.R.L. and D.M. acknowledge the funding by the Basque Government (IT99-16). V.B. acknowledges support from the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract no. DE-AC05-00OR22725. A.S. acknowledges financial support for dielectric measurements and data discussions by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division

Crystallization-induced gelling as a method to 4D print low-water-content non-isocyanate polyurethane hydrogels

The use of three-dimensional (3D) printable hydrogels for biomedical applications has attracted considerable attention as a consequence of the ability to precisely define the morphology of the printed object, allowing patients’ needs to be targeted. However, the majority of hydrogels do not possess suitable mechanical properties to fulfill an adequate rheological profile for printability, and hence, 3D printing of cross-linked networks is challenging and normally requires postprinting modifications to obtain the desired scaffolds. In this work, we took advantage of the crystallization process of poly(ethylene glycol) to print non-isocyanate poly(hydroxyurethane) hydrogels with tunable mechanical properties. As a consequence of the crystallization process, the hydrogel modulus can be tuned up to 3 orders of magnitude upon heating up to 40 °C, offering an interesting strategy to directly 3D-print hydrogels without the need of postprinting cross-linking. Moreover, the absence of any toxicity makes these materials ideal candidates for biomedical applications

Controlling Associative Transcarbamoylation Reactions by Light in Dynamic Polyurethane Networks Using Reversible Spiropyran Photoswitches

Polyurethanes represent a versatile class of polymers and are one of the most employed in the thermoset market. However, due to their thermodynamically stable carbamate bond, they suffer from a lack of reprocessability, recyclability, and degradability, and are therefore usually discarded after use. Recently, transcarbamoylation in polyurethane thermosets has been demonstrated via associative exchange in the presence of a strong organic acid. Intending to introduce spatiotemporal control in the processability of polyurethane materials, in this work we investigate dynamic transcarbamoylation by the addition of a latent acidic catalyst into an aromatic and an aliphatic polyurethane network. We introduce three photoswitches based on merocyanine/spiropyran compounds which, upon exposure to visible light, undergo a reversible cyclization reaction, resulting in formation of strong acids. The use of such photoswitches prevents the presence of a permanent acidic species in the network, which would eventually lead to its degradation over time. Importantly, due to the reversible nature of the cyclization reaction, the release of the acidic catalyst is not permanent, as evidenced by stress relaxation measurements. Overall, the evidence of the light-induced, acid-catalyzed transcarbamoylation is supported by stress-relaxation, optical microscopy, and self-healing measurements

Synthesis of self-healable waterborne isocyanate-free poly(hydroxyurethane)-based supramolecular networks by ionic interactions

International audienc

Flow-induced crystallization of piezoelectric poly(L-lactide) fibers by a one-step melt-spinning process

Piezoelectric poly(L-lactide) (PLLA) fibers, exhibiting high molecular chain orientation, are promising for biomedical applications. Chain orientation decreases due to fast relaxation during melt-spinning process, which implies that a second process to induce piezoelectric chain morphology is usually necessary. This work introduces a one-step melt-spinning process of piezoelectric PLLA fibers, spun directly from the melt, employing a rheological guidance for the selection of the PLLA type and process parameters, based on Rouse's relaxation time. The chain orientation and the relaxation time increased with the optical purity and average molecular weight of PLLA. The reduction of extrusion temperature from 180 °C to 150 °C facilitated in a significant way the preservation of chain orientation, and the impact of the elongation rate was as well intensified. Combining high elongation rates of ≤ 29 s−1 and reduced extrusion temperature of 150 °C led to flow-induced crystallization of oriented crystals directly from melt in a single step. This fiber exhibited piezoelectric properties in form of a deflection of 1.9 ± 0.3 µm when applying an open-circuit voltage of 210 V. The piezoelectric response was similar to that of a fiber, melt-spun at high extrusion temperature of 180 °C, with additional post-annealing in a second step

Single–Ion Conducting Polymer Nanoparticles as Functional Fillers for Solid Electrolytes in Lithium Metal Batteries

Composite solid electrolytes including inorganic nanoparticles or nanofibers which improve the performance of polymer electrolytes due to their superior mechanical, ionic conductivity or lithium transference number are actively being searched for applications in lithium metal batteries. However, inorganic nanoparticles present limitations such as its tedious surface functionalization and agglomeration issues and poor homogeneity at high concentrations in polymer matrices. In this work, we report on polymer nanoparticles with lithium sulfonamide surface functionality (LiPNP) for application as electrolytes in lithium metal battery. The particles are prepared by semibatch emulsion polymerization, an easily up–scalable technique. LiPNPs are used to prepare two different families of particle reinforced solid electrolytes. When mixed with polyethylene oxide and lithium bis(trifluoromethane)sulfonimide (LiTFSI/PEO), the particles provoke a significant stiffening effect (E´ > 106 Pa vs. 105 Pa at 80 ºC) while retaining high ionic conductivity (σ = 6.6 × 10–4 S cm–1). Preliminary testing in LiFePO4 full cells, showed promising performance of the PEO nanocomposite electrolytes. By mixing the particles with propylene carbonate without any additional salt, we obtain true single ion conducting gel electrolytes as the lithium sulfonamide surface functionalities are the only sources of lithium ions in the system. The gel electrolytes are mechanically robust (up to G´ =106 Pa) and show ionic conductivity up to 10–4 S cm–1. Finally, the PC nanocomposite electrolytes were tested in symmetrical lithium cells. Our findings suggest that all–polymer nanoparticles could represent a new building block material for solid–state lithium metal battery applications

Self-healable dynamic poly(urea-urethane) gel electrolyte for lithium batteries

[EN] Self-healing materials are actively studied in order to extend the lifetime and performance of batteries. Dynamic covalent networks have recently emerged as one of the best self-healable materials which allow thermosets to be reprocessed and recycled. Among all the different exchangeable bonds studied over the last few years, hindered urea bonds appear to be one of the most feasible options to create self-healable materials due to their exchange activation at low temperatures. Although this chemistry is very popular in composite and coating applications, it has not been considered for designing self-healable materials for batteries. In this work we synthesize a membrane containing dynamic hindered urea crosslinking points by reacting tris[2-(isopropylamino)ethyl]amine with hexamethylene diisocyanate, followed by the addition of polyethylene glycol. It is proved that this newly designed material possesses self-healable properties and higher ionic conductivity than the commercially available liquid electrolyte embedded in a porous Celgard (R) 2500 separator. The polyurethane gel electrolyte shows very homogeneous Li plating and stripping in Li symmetrical cells and is also compatible with Li-mediated electrochemical ammonia synthesis approaches. Most importantly, after severely mechanically damaging the gel membrane, the polymer electrolyte shows great recovery of the electrochemical properties, experiencing more than 100 charge/discharge cycles (after cutting) at C/5 rate.This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 948769, project title: SuN2rise)