Estudio cinético de la síntesis en masa de poliuretanos de 1,6-hexamtilen diisocianato y distintos glicoles de baja masa molecular

Los poliuretanos (PU) segmentados presentan tal versatilidadque permiten diseñar materiales con distintas propiedadesmecánicas, tales como alta elasticidad, resilienciay alta tenacidad de fractura. El estudio sistemático de lamorfología y propiedades de distintos bloques de poliuretanopermite entender su contribución en las propiedadesfinales de los PU sintetizados a partir de distintos bloques.En este trabajo se estudia la cinética de síntesis en masade poliuretanos formados a partir de 1,6-hexametilen diisocianato(HDI) y cinco distintos glicoles de baja masa molecularque difieren en su estructura y composición química:1,4-butanodiol (BD), etilenglicol (EG), propilenglicol (PPgli),N-metil dietanolamina (MDEA) y 3-metil 1,5-pentanodiol(3MPD). También se discute algunos aspectos morfológicosde los PUs formados a partir de estos dioles. La exotermicidadde la reacción estequiométrica entre el HDI y losglicoles sigue el orden MDEA > PPgli > EG > BD > 3MPD.Las velocidades de reacción siguen aproximadamente elorden MDEA > PPgli > BD > 3MPD > EG. La diferenciaentre el orden de exotermicidad y de cinética de curadoparecen ser influidas por las viscosidades de los glicolesasí como por las características de los PU formados

Polyurethane wood adhesives prepared from modified polysaccharides

This study investigated the performance of polyurethane adhesives prepared with various combinations of wheat starch that had been modified by isophorone diisocyanate (MS), two polyol types (1,3-propanediol (PD) and glycerol (Gly)), native wheat starch (NS), and 4,4′-diphenylmethane diisocyanate (pMDI) at a NCO:OH weight ratio of 1:1. Two more adhesives were also synthesized with NS, PD, or Gly and pMDI blends and served as controls. The thermal behavior of the adhesives before and after the curing process, as well as their rheological performance and lap shear strength, were analyzed. Differential scanning calorimetry (DSC) showed a reduction in curing temperature and heat by adding MS. The thermal stability of the cured adhesives was slightly increased by MS addition. The viscosity of the adhesives that contained MS substantially increased at a linear ascendant ramp of shear, while the controls exhibited relatively low viscosity during the whole shear rate spectrum from 0.1 to 100 s−1. The tensile shear strength of wood veneers was also significantly increased by the incorporation of MS under both dry and wet measuring conditions. The maximum dry shear strength was obtained for the adhesive with Gly polyol and a higher content of MS and was comparable to the control adhesive with pMDI

Microwave-assisted extraction of cellulose nanocrystals from almond (Prunus amygdalus) shell waste

Almond (Prunus amygdalus) is one of the most common tree nuts on a worldwide basis. This nut is highly regarded in the food and cosmetic industries. However, for all these applications, almonds are used without their shell protection, which is industrially removed contributing approximately 35-75% of the total fruit weight. This residue is normally incinerated or dumped, causing several environmental problems. In this study, a novel cellulose nanocrystal (CNCs) extraction procedure from almond shell (AS) waste by using microwave-assisted extraction was developed and compared with the conventional approach. A three-factor, three-level Box–Behnken design with five central points was used to evaluate the influence of extraction temperature, irradiation time, and NaOH concentration during the alkalization stage in crystallinity index (CI) values. A similar CI value (55.9 ± 0.7%) was obtained for the MAE process, comprising only three stages, compared with the conventional optimized procedure (55.5 ± 1.0%) with five stages. As a result, a greener and more environmentally friendly CNC extraction protocol was developed with a reduction in time, solvent, and energy consumption. Fourier transform infrared (FTIR) spectra, X-ray diffractogram (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) images, and thermal stability studies of samples confirmed the removal of non-cellulosic components after the chemical treatments. TEM images revealed a spherical shape of CNCs with an average size of 21 ± 6 nm, showing great potential to be used in food packaging, biological, medical, and photoelectric materials. This study successfully applied MAE for the extraction of spherical-shaped CNCs from AS with several advantages compared with the conventional procedure, reducing costs for industry.This work was supported by Conselleria de Educación (Spain) (APOSTD/2016/093 Postdoctoral Research Training Grant), the Spanish Ministry of Economy, Industry and Competitiveness (MAT2017-84909-C2-1-R), and the University of the Basque Country (UPV/EHU) (GIU18-216)

Effect of the catalyst system on the reactivity of a polyurethane resin system for RTM manufacturing of structural composites

The high versatility of polyurethanes (PU’s) is encouraging the development of new formulations for new appli cations, like their use as a matrix for structural composites. PU’s based technology offers some advantages, such as fatigue resistance and fast curing cycles. However, their high reactivity hinders some manufacturing processes like Resin Transfer Moulding (RTM). This work aimed to achieve a PU resin (PUR) formulation with the required latency and reactivity for the RTM. For this purpose, different catalytic systems based on an epoxide and LiCl were investigated. The reactivity of the systems was evaluated through Differential Scanning Calorimetry (DSC) and rheology tests, and the curing reaction and viscosity were modelled. Furthermore, the RTM process of a representative composite part was simulated. Results demon strated the processability improvements when the LiCl was incorporated into the isocyanate component of the formulation combined with a monool or a diol. It was observed that these combinations contribute to the encapsulation of the LiCl between the as formed urethane groups by hydrogen bonding, providing the desired latency and acting as a delayed action catalyst. Once the reaction started and the encapsulation was deactivated, an alkoxide was formed to act as a catalyst. En capsulation was more effective with the diol, providing a higher latency.We gratefully acknowledge the Basque Government for the fi nancial support through the ELKARTEK 2020 (ProjectAVAN SITE New generation of sustainable composites for advanced manufacturing KK2020/00019) program. The authors also ac knowledge the University of the Basque Country (UPV/EHU) in the frame of GIU18/216 Research Group and the Macrobe havior-Mesostructure-Nanotechnology SGIker unit

Advances in waterborne polyurethane and polyurethane-urea dispersions and their eco-friendly derivatives: a review

Polyurethanes and polyurethane-ureas, particularly their water-based dispersions, have gained relevance as an extremely versatile area based on environmentally friendly approaches. The evolution of their synthesis methods, and the nature of the reactants (or compounds involved in the process) towards increasingly sustainable pathways, has positioned these dispersions as a relevant and essential product for diverse application frameworks. Therefore, in this work, it is intended to show the progress in the field of polyurethane and polyurethane-urea dispersions over decades, since their initial synthesis approaches. Thus, the review covers from the basic concepts of polyure-thane chemistry to the evolution of the dispersion’s preparation strategies. Moreover, an analysis of the recent trends of using renewable reactants and enhanced green strategies, including the current legislation, directed to limit the toxicity and potentiate the sustainability of dispersions, is described. The review also highlights the strengths of the dispersions added with diverse renewable additives, namely, cellulose, starch or chitosan, providing some noteworthy results. Similarly, dispersion’s potential to be processed by diverse methods is shown, evidencing, with different examples, their suitability in a variety of scenarios, outstanding their versatility even for high requirement applications.This research was funded by the University of the Basque Country (UPV/EHU) (GIU18/216 Research Group), the Spanish Ministry of Science, Innovation and Universities and European Union (MICINN/EU/FEDER) (MAT2016-76294-R and PID2019-105090RB-I00). Also, the Foundation for Science and Technology (FCT, Portugal) funded by financial support by national funds FCT/MCTES to CIMO (UIDB/00690/2020). National funding by FCT- Foundation for Science and Technology, through the institutional scientific employment program-contract with I.F.info:eu-repo/semantics/publishedVersio

Copolímeros de poliuretano do tipo poli[(hexametileno-carbamato- butanodiol)-co-(carbonato-co-éster)]

Los poliuretanos segmentados termoplástico elastoméricos (PUSTE) comprenden una familia de materiales muy versátiles debido a su su potencial empleo en diversos campos tales como biomedicina. Entre los PUSTE los formados por policarbonatos dioles y diisocianatos alifáticos son especialmente atractivos debido a su bioestabilidad y biocompatibilidad. En este trabajo se presentan los resultados del análisis morfológico y conducta mecánica de una familia de PUSTEs formados por 1,6-hexametilen diisocianato (HDI), 1,4-butanodiol (BD) y un copolímero cauchoso de policaprolactona y polihexametilen carbonato diol, PCL-b-PHMC-b-PCL, sintetizados con distinta relación entre bloques rígidos (HDI-BD) y copolímero cauchoso.Segmented thermoplastic polyurethane elastomers (PUSTE) comprise a family of very versatile materials with large potential for their applicability in different fields such as biomedicine. Among the PUSTEs the ones formed by polycarbonates diols and aliphatic diisocyanates are especially attractive due to their bioestability and biocompativility. In this work we present the results of morphological and mechanical characterization of different PUSTEs formed by 1,6-hexamethyene diisocyanate, 1,4-butanediol and a copolymer of polycaprolactone and polyhexamethylene carbonate diol, PCL-b-PHMC-b-PCL, synthesized with different ratios between rigid (HDI-BD) segments and the rubbery copolymer.Os poliuretanos segmentados termoplástico elastoméricos (PUSTE) compõem uma família de materiais versátil devido ao seu potencial uso em diversas áreas tais como biomedicina. Entre o PUSTE aqueles formaram por policarbonato dióis e diisocianatos alifáticos são especialmente atraentes porque seu biostability e biocompatibilidade. Este trabalho apresenta os resultados da análise morfológica e comportamento mecânico de uma família de PUSTEs é composto por 1,6-hexametilen diisocianato (HDI), 1,4-butanodiol (BD) e um copolímero de policaprolactona e polihexametilen carbonato de diol, PCL-b-PHMC-b-PCL, sintetizado com proporção diferente de copolímero de cauchoso de blocos rígida (HDI-BD)

Development of a Novel Biobased Polyurethane Resin System for Structural Composites

Polyurethanes are gaining increasing interest for their use as structural components subjected to cyclic loads, such as leaf springs. Thermoset polyurethane (PUR) based technology offers some advantages, such as fatigue resistance, low viscosity, and fast curing. However, current PUR formulations present two major drawbacks: their petrochemical origin and high reactivity. The aim of this work was to develop a novel biobased PUR (BIO-PUR) with the required mechanical properties and processability for manufacturing structural composites by resin transfer moulding (RTM). For this purpose, a high functionality and high hydroxyl index castor-oil-based polyol was used combined with a biobased glycerol (BIO-Gly) to increase the crosslinking density and improve the final properties of the BIO-PUR. The viscosity and reactivity of the different systems were studied by means of rheology tests and differential scanning calorimetry (DSC). Thermal and mechanical properties were studied by dynamic mechanical analysis (DMA) and flexural tests. Furthermore, the RTM process of a representative part was simulated and validated through the manufacturing and testing of plates. The properties of the BIO-PUR resin systems were strongly influenced by the addition of biobased glycerol and its effect on the crosslinking density. The combination of a high functionality and hydroxyl index biobased polyol with the biobased glycerol resulted in a high-performance BIO-PUR with the required reactivity and final properties for structural applications.This research was funded by the Basque Government through the ELKARTEK 2021 (Project NEOMAT KK-2021/00059) and in the frame of Grupos Consolidados (IT-1690-22) and by the University of the Basque Country (UPV/EHU) in the frame of GIU18/216 Research Group

Copolímeros de poliuretano do tipo poli[(hexametileno-carbamato- butanodiol)-co-(carbonato-co-éster)]

Los poliuretanos segmentados termoplástico elastoméricos (PUSTE) comprenden una familia de materiales muy versátiles debido a su su potencial empleo en diversos campos tales como biomedicina. Entre los PUSTE los formados por policarbonatos dioles y diisocianatos alifáticos son especialmente atractivos debido a su bioestabilidad y biocompatibilidad. En este trabajo se presentan los resultados del análisis morfológico y conducta mecánica de una familia de PUSTEs formados por 1,6-hexametilen diisocianato (HDI), 1,4-butanodiol (BD) y un copolímero cauchoso de policaprolactona y polihexametilen carbonato diol, PCL-b-PHMC-b-PCL, sintetizados con distinta relación entre bloques rígidos (HDI-BD) y copolímero cauchoso.Segmented thermoplastic polyurethane elastomers (PUSTE) comprise a family of very versatile materials with large potential for their applicability in different fields such as biomedicine. Among the PUSTEs the ones formed by polycarbonates diols and aliphatic diisocyanates are especially attractive due to their bioestability and biocompativility. In this work we present the results of morphological and mechanical characterization of different PUSTEs formed by 1,6-hexamethyene diisocyanate, 1,4-butanediol and a copolymer of polycaprolactone and polyhexamethylene carbonate diol, PCL-b-PHMC-b-PCL, synthesized with different ratios between rigid (HDI-BD) segments and the rubbery copolymer.Os poliuretanos segmentados termoplástico elastoméricos (PUSTE) compõem uma família de materiais versátil devido ao seu potencial uso em diversas áreas tais como biomedicina. Entre o PUSTE aqueles formaram por policarbonato dióis e diisocianatos alifáticos são especialmente atraentes porque seu biostability e biocompatibilidade. Este trabalho apresenta os resultados da análise morfológica e comportamento mecânico de uma família de PUSTEs é composto por 1,6-hexametilen diisocianato (HDI), 1,4-butanodiol (BD) e um copolímero de policaprolactona e polihexametilen carbonato de diol, PCL-b-PHMC-b-PCL, sintetizado com proporção diferente de copolímero de cauchoso de blocos rígida (HDI-BD)

Green nanocomposites from Salvia-based waterborne polyurethane-urea dispersions reinforced with nanocellulose

Waterborne polyurethane-urea (WBPUU) dispersions, products having none or low contents of organic solvents, depending on the used synthesis process, can provide suitable environmentally-friendly strategies to prepare novel materials. Moreover, waterborne systems enable the incorporation of aqueous dispersible nanoentities and soluble additives, which provides a strategy to design versatile functional materials with tailored properties. Having demonstrated in previous work the bacteriostatic properties of a 3 wt% Salvia-based WBPUU against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, this work is focused in the preparation of Salvia-based WBPUU added with cellulose nanocrystals (CNC) tackling the preparation of functional green nanocomposite films with increased mechanical properties. Through this strategy, nanocomposites loaded with 1, 3 and 5 wt% of CNC were prepared, showing an effective CNC incorporation avoiding agglomerates. CNC addition is able to modulate soft and hard phase's segregation, inducing enhanced mechanical stiffness, together with improved deformability, while retarding thermomechanical instability to higher temperatures.Financial support from the University of the Basque Country (UPV/ EHU) (GIU18/216 Research Group), the Spanish Ministry of Economy and Competitiveness (MINECO) (MAT2016-76294-R). Foundation for Science and Technology (FCT, Portugal) for financial support by national funds FCT/MCTES to CIMO (UIDB/00690/2020). National funding by FCT- Foundation for Science and Technology, through the institutional scientific employment program-contract with I.P. Fernandes. We also wish to acknowledge the “Macrobehaviour-Mesostructure- Nanotechnology” SGIker units from the UPV/EHU, for their technical supporinfo:eu-repo/semantics/publishedVersio

Bacterial-cellulose-derived carbonaceous electrode materials for water desalination via capacitive method: The crucial role of defect sites

Electrosorptive desalination is a very simple and appealing approach to satisfy the increasing demand for drinking water. The large-scale application of this technology calls for the development of easy-to-produce, cheap and highly performing electrode materials and for the identification and tailoring of their most influential properties, as well. Here, biosynthesised bacterial cellulose is used as a carbon precursor for the production of three-dimensional nanostructures endowed with hierarchically porous architecture and different density and type of intrinsic and hetero-atom induced lattice defects. The produced materials exhibit unprecedented desalination capacities for carbon-based electrodes. At an initial concentration of 585 mg L−1 (10 mmol L−1), they are able to remove from 55 to 79 mg g−1 of salt; as the initial concentration rises to 11.7 g L−1 (200 mmol L−1), their salt adsorption capacity reaches values ranging between 1.03 and 1.35 g g−1. The results of the thorough material characterisation by complementary techniques evidence that the relative amount of oxygenated surface functional species enhancing the electrode wettability play a crucial role at lower NaCl concentrations, whereas the availability of active non-sp2 defect sites for adsorption is mainly influential at higher salt concentrations.L.U., M.A.C. and A.E. gratefully thank GIU18/216 - UPV/EHU Research Group for the financial support to their work