Dielectric Relaxations and Conductivity of Crosslinked PVA/SSA/GO Composite Membranes for Fuel Cells

[EN] Composite membranes obtained from Poly(vinyl Alcohol) (PVA) with sulfosuccinic acid (SSA) as crosslinking agent, and two different proportions of graphene oxide (GO), were prepared to be used in Proton Exchange Membrane Fuel Cells (PEMFCs). The superficial micrographs from transmission electron microscopy (TEM) confirmed a good dispersion of GO. Fourier Transform Infrared spectroscopy (FTIR) was used to evaluate the final chemical structure. Differential Scanning Calorimetry (DSC) showed that glass transition and crystalline phase were not present in the cross-linked PVA/SSA/GO composites membranes. Thermogravimetric analysis (TGA) demonstrated that the addition of GO reduced the moisture content and increased the thermal stability of the membranes. The electrical properties of PVA/SSA and PVA/SSA/GO composite membranes and the effect of GO concentration were evaluated by means of dielectric spectra in a broad range of temperatures and frequencies. The dielectric permittivity of these membranes was significantly promoted at low filler concentration due to an interfacial polarization effect. From the analysis of the dielectric relaxation spectrum, it can be deduced that the origin of the associated molecular movements is intramolecular and occurs in the working range of the PMEFC. In addition, the direct current conductivity, the protonic conductivity, and the polarization currents were correlated to the power produced in a hydrogen monocell. It was observed that low and no high GO concentrations of filler in PVA/SSA composite membranes enhanced their performance. The systematic characterization procedure based on the study of dielectric spectra and conductivity allowed to establish a potential approach to control the addition of GO in the design of other composite membranes for PEMFC with improved properties.The authors would like to thank Dr. Roberto Teruel Juanes and Dr. Victor Saenz de Juano for their advice in the treatment of results. The authors are also thankful to Generalitat Valenciana and the European Social Fund for the Santiago Grisolia scholarship, GRISOLIA/2013/031, and the Spanish Ministry of Science and Innovation for the concession of Research Project ENE2014-53734-C2-1-R.González-Guisasola, C.; Ribes-Greus, A. (2018). Dielectric Relaxations and Conductivity of Crosslinked PVA/SSA/GO Composite Membranes for Fuel Cells. Polymer Testing. 67:55-67. https://doi.org/10.1016/j.polymertesting.2018.01.024S55676

Valorization of cotton residues for production of bio-oil and engineered biochar

[EN] Cotton seed was submitted to fast pyrolysis in a fixed bed reactor and the liquid and solid products were characterized applying several techniques. The detailed chemical composition of the bio-oil was investigated using GC × GC/TOFMS combined with software tools and retention index. A total of 257 compounds were tentatively identified with 168 were confirmed by LTPRI. The most abundant compounds identified in the cotton seed bio-oil were nitrogenous (56 compounds) and phenolic (42 compounds) what distinguishes this bio oil from others, produced from various sources of biomass. The higher heating values of cotton seed and bio-oil were 19.34 MJ kg ¿1 and 34.25 MJ kg ¿1 respectively and demonstrating the feasibility of the use of cotton seed in its natural form for energy generation or as a secondary source once a bio-oil with these characteristics would be a suitable candidate for use in boilers for heating purposes or chemical extraction. The biochar had a significant carbon content and a high heating value (22.12 MJ kg ¿1), making it attractive for fuel applications. The activation methods used were able to improve the physical and chemical characteristics of the biochar, as demonstrated by methylene blue adsorption tests. The maximum adsorption capacity of NaOH-activated biochar was 23.82 mg g ¿1 while that of K2CO3-activated biochar was 332.40 mg g ¿1.The authors would like to thanks the support of Brazilian Coordenaçao de Aperfeicoamento de Pessoal de Nivel Superior(CAPES, scholarships for the first author-Finance code 001) and EBW thorn Project Euro-Brazilian Windows Erasmus Mundus Program (scholarships for the first author).Primaz, CT.; Ribes-Greus, A.; Jacques, RA. (2021). Valorization of cotton residues for production of bio-oil and engineered biochar. Energy. 235:1-11. https://doi.org/10.1016/j.energy.2021.12136311123

Thermo-oxidative characterisation of the residues from persimmon harvest for its use in energy recovery processes

[EN] The residues from the harvest of persimmon fruit will be thermally valorised by means of high temperature reactions within a spouted bed reactor. With the aim to obtain valuable information for the design of the device, the thermo-chemical processes were simulated by multi-rate linear non-isothermal Thermogravimetric Analysis (TGA) using O-2 as carrier gas. In addition, a set of analyses were carried out using Ar as carrier gas in order to evaluate the influence of the atmosphere (oxidative or inert conditions) on the decomposition of the samples evaluating the reactions of pyrolysis. The release of gases was monitored by Evolved Gas Analysis (EGA) with in-line Fourier Transformed Infrared (FT-IR) analysis. The thermochemical reaction was mathematically described through the definition of the main kinetic parameters: activation energy (Ea), pre-exponential factor (In A) and model and order of reaction (n). The so-called kinetic triplet was calculated through the application of a methodology based on complementary isoconversional methods. These results will be the initial parameters that will help design the Spouted Bed Reactor and it is envisaged that they will be used in computer simulation software to achieve a better understanding of the process to obtain the optimum operational parameters. (C) 2016 Published by Elsevier B.V.Moliner, C.; Aguilar, A.; Bosio, B.; Arato, E.; Ribes-Greus, A. (2016). Thermo-oxidative characterisation of the residues from persimmon harvest for its use in energy recovery processes. Fuel Processing Technology. 152:421-429. https://doi.org/10.1016/j.fuproc.2016.07.008S42142915

Long-term properties and end-of-life of polymers from renewable resources

The long-term properties and end-of-life of polymers are not antagonist issues. They actually are inherently linked by the duality between durability and degradation. The control of the service-todisposal pathway at useful performance, along with low-impact disposal represents an added-value. Therefore, the routes of design, production, and discarding of bio-based polymers must be carefully strategized. In this sense, the combination of proper valorisation techniques, i.e. material, energetic and/ or biological at the most appropriate stage should be targeted. Thus, the consideration of the end-of-life of a material for a specific application, instead of the end-of-life of a material should be the fundamental focus. This review covers the key aspects of lab-scale techniques to infer the potential of performance and valorisation of polymers from renewable resources as a key gear for sustainability

Suitability of Blends from Virgin and Reprocessed Polylactide: Performance and Energy Valorization Kinetics

A blending strategy of virgin and reprocessed polylactide may be postulated as an alternative to reduce the material cost at industrial level, and as a valorization route to plastic waste management of production scraps. The performance of blends prepared from virgin polylactide and polylactide mechanically reprocessed up to two cycles (PLA-V/R) was assessed in terms of thermo-oxidative stability, morphology, viscoelasticity and thermal kinetics for energetic valorization. PLA-V/R blends showed appropriate thermo-oxidative stability. The amorphous nature of polylactide was preserved after blending. The viscoelastic properties showed an increment of the mechanical blend effectiveness, which suggested the feasibility of using PLA-V/R blends under similar mechanical conditions to those of virgin PLA goods. Finally, it was shown that the energetic valorization of PLA-V/R blends would result in a more feasible process, due to the lower required activation energy, thus highlighting the advantages of the energetic demand for the process. In conclusion, PLA-V/R blends showed similar processability, service performance and valorization routes as virgin PLA and therefore could be relevant in the sustainable circular industry of bioplastics

Analysis of Poly(thiourethane) Covalent Adaptable Network through Broadband Dielectric Spectroscopy

[EN] The dielectric spectra of the poly(thiourethane) network, HDI-S3, have been analyzed to know the nature and the cooperativity of each of the six dielectric processes observed. At low temperatures, ¿1, ¿2, and ß dielectric relaxations were attributed to noncooperative local motions in the glassy state, in which apparent activation energies are 30, 36, and 60 kJ·mol¿1, respectively. At higher temperatures, three dielectric relaxations are observed (¿Tg, ¿*, ¿). The ¿Tg relaxation is attributed to the glass transition, and it is overlapped with the ¿* relaxation. The molecular origin of ¿* relaxation is associated with the bond exchange reaction. Finally, the ¿ relaxation is ascribed to the heterogeneity of the sample although its origin is uncertain. The DC conductivity (¿DC) is found to be an appropriate variable to analyze the bond exchange reaction. Accordingly, the HDI-S3 has a molecular exchange mechanism of dissociative nature.The authors would like to thank the support of the European Union through the European Regional Development Funds (ERDF) and the Spanish Ministry of Science and Innovation for the research projects POLYELMETH (PID2020-116322RB-C31) and MCIN/AEI/10.13039/201100011033, which financed the PID2020/115102RB-C21 project, and the Generalitat de Catalunya for the 2017-SGR-77. This study forms part of the Advanced Materials programme and was supported by MCIN with funding from European Union NextGenerationEU (PRTR-C17.11) and by Generalitat Valenciana.Pascual-Jose, B.; De La Flor, S.; Serra, A.; Ribes-Greus, A. (2023). Analysis of Poly(thiourethane) Covalent Adaptable Network through Broadband Dielectric Spectroscopy. ACS Applied Polymer Materials. 5(2):1125-1134. https://doi.org/10.1021/acsapm.2c01543112511345

Thermal analysis as a quality tool for assessing the influence of thermo-mechanical degradation on recycled poly(ethylene terephthalate)

Mechanical recycling of poly(ethylene terephthalate) (PET) was simulated by multiple processing to assess the effects of thermo-mechanical degradation, and characterized using rheological and thermal analysis techniques. Thermo-mechanical degradation under repeated extrusion induces chain scission reactions in PET, which result in a dramatic loss in the deformation capabilities and an increase in the fluidity of the polymer under reprocessing, reducing its recycling possibilities after four extrusion cycles. Multiple reprocessing severely affects the storage modulus and the microstructure of recycled PET, both in the amorphous and crystalline regions. Multimodal melting behavior is observed for reprocessed PET, indicating heterogeneous and segregated crystalline regions. A deconvolution procedure has been applied to individually characterize each crystalline population in terms of lamellar thickness distribution and partial crystallinity. Thermal analysis techniques such as differential scanning calorimetry (DSC) and dynamic-mechanical analysis (DMA) have proved to be suitable techniques for the quality assessment of recycled PET, giving unequivocal information about its degree of degradation compared to the common technological measurements of melt-mass flow rate (MFR) or oxidative stability (TOx)

Material valorisation of amorphous polylactide. Influence of thermo-mechanical degradation on the morphology, segmental dynamics, thermal and mechanical performance

This paper reports the effects of multiple mechanical recycling on the structure and properties of amorphous polylactide (PLA). The influence of the thermo-mechanical degradation induced by means of five successive injection cycles was initially addressed in terms of macroscopic mechanical properties and surface modification. A deeper inspection on the structure and morphology of PLA was associated to the thermal properties and viscoelastic behaviour. Although FT-IR analysis did not show significant changes in functional groups, a remarkable reduction in molar mass was found by viscometry. PLA remained amorphous throughout the reprocessing cycles, but the occurrence of a cold-crystallization during DSC and DMTA measurements, which enthalpy increased with each reprocessing step, suggested chain scission due to thermo-mechanical degradation. The effect of chain shortening on the glass-rubber relaxation studied by DMTA showed an increase in free volume affecting the segmental dynamics of PLA, particularly after the application of the second reprocessing step, in connection to the overall loss of performance showed by the remaining properties

Thermal analysis applied to the characterization of degradation in soil of polylactide: II. On the thermal stability and thermal decomposition kinetics

The disposal stage of polylactide (PLA) was assessed by burying it in active soil following an international standard. Degradation in soil promotes physical and chemical changes in the polylactide properties. The characterization of the extent of degradation underwent by PLA was carried out by using Thermal Analysis techniques. In this paper, studies on the thermal stability and the thermal decomposition kinetics were performed in order to assess the degradation process of a commercial PLA submitted to an accelerated soil burial test by means of multi-linear-non-isothermal thermogravimetric analyses. Results have been correlated to changes in molecular weight, showing the same evolution as that described by the parameters of thermal stability temperatures and apparent activation energies. The decomposition reactions can be described by two competitive different mechanisms: Nucleation model (A2) and Reaction Contracting Volume model (R3). The changes in the kinetic parameters and kinetic models are in agreement with the calorimetric and dynamic-mechanical-thermal results, presented in the Part I of the study

Performance of polyester-based electrospun scaffolds under in vitro hydrolytic conditions: From short-term to long-term applications

The evaluation of the performance of polyesters under in vitro physiologic conditions is essential to design scaffolds with an adequate lifespan for a given application. In this line, the degradation-durability patterns of poly(lactide-co-glycolide) (PLGA), polydioxanone (PDO), polycaprolactone (PCL) and polyhydroxybutyrate (PHB) scaffolds were monitored and compared giving, as a result, a basis for the specific design of scaffolds from short-term to long-term applications. For this purpose, they were immersed in ultra-pure water and phosphate buffer solution (PBS) at 37 °C. The scaffolds for short-time applications were PLGA and PDO, in which the molar mass diminished down to 20% in a 20-30 days lifespan. While PDO developed crystallinity that prevented the geometry of the fibres, those of PLGA coalesced and collapsed. The scaffolds for long-term applications were PCL and PHB, in which the molar mass followed a progressive decrease, reaching values of 10% for PCL and almost 50% for PHB after 650 days of immersion. This resistant pattern was mainly ascribed to the stability of the crystalline domains of the fibres, in which the diameters remained almost unaffected. From the perspective of an adequate balance between the durability and degradation, this study may serve technologists as a reference point to design polyester-based scaffolds for biomedical applications