Browsing by Author "Saralegi, Ainara"
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- Flexible polyurethane foams based on 100% renewably sourced polyolsPublication . Ugarte, Lorena; Saralegi, Ainara; Fernández, Rocío; Martín, L.; Corcuera, Maria Angeles; Eceiza, ArantaxaSince polyol is one of the major components in polyurethane foam synthesis, introducing renewably sourced polyols in the foam formulation leads to materials with high renewable carbon content. A series of flexible polyurethane foams with variations in polyol composition were synthesized with castor oil based Lupranol Balance ® 50 polyether polyol and corn based polytrimethylene ether glycol mixtures. Water was used as the unique and eco-friendly blowing agent. The effect of the relative amount of each polyol on the structure and properties was analyzed by optical microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, tensile and compressive tests, dynamic mechanical analysis and atomic force microscopy. The average molecular weight and hydroxyl number of the polyol components showed to influence the foaming reaction and hence the structure and properties of the polyurethane foam. The newly developed peak force quantitative nano-mechanics technique was used to map the elastic modulus values of foam cell struts and it seemed to be adequate to assess the purity of the different phases.
- Spray drying as a viable process to produce nano-hydroxyapatite/chitosan (n-HAp/CS) hybrid microparticles mimicking bone compositionPublication . Ruphuy, Gabriela; Saralegi, Ainara; Lopes, José Carlos B.; Dias, Madalena M.; Barreiro, M.F.In this work nano-hydroxyapatite/chitosan (n-HAp/CS) hybrid microparticles were prepared by spray drying following a methodology where, in a first step, aqueous nanodispersions of n-HAp in the presence of chitosan were produced by fast stirring at pH values below and above chitosan pKa (5.5 and 7.0, respectively). The mixing system used allowed the production of homogeneous and stable nanodispersions, and the subsequent spray-dried microparticles, incorporating highly pure HAp nanoparticles of approximately 50 nm, were successfully produced without degrading the organic component, chitosan. Comparatively with the n-HAp/CS-7.0, the n-HAp/CS-5.5 dispersions were characterized by a lower particle size and a higher zeta potential, being then more stable. Differences in the spray-dried microparticles were also evident from a morphological point of view. HApCS-5.5 microparticles, which present an average size in volume of 15.8 μm and n-HAp crystals homogenously distributed, were found to be preferred over the HApCS-7.0 counterparts, which require an extra step in the productive process and presented a tendency to form large agglomerates. Both prepared hybrid particles presented similar composition to that one of natural bone (HAp/CS of 70/30) and no traces of KCl salts were observed if a washed n-HAp paste was used.
- Synthesis of waterborne polyurethane-urea dispersions with chain extension step in homogeneous and heterogeneous mediaPublication . Santamaria-Echart, Arantzazu; Fernandes, Isabel P.; Saralegi, Ainara; Costa, Mário Rui; Barreiro, M.F.; Corcuera, Maria Angeles; Eceiza, ArantaxaHypothesis: The possibility of tailoring the final properties of environmentally friendly waterborne polyurethane and polyurethane-urea dispersions and the films they produce makes them attractive for a wide range of applications. Both the reagents content and the synthesis route contribute to the observed final properties. Experiments: A series of polyurethane-urea and polyurethane aqueous dispersions were synthesized using 1,2-ethanediamine and/or 1,4-butanediol as chain extenders. The diamine content was varied from 0 to 4.5 wt%. Its addition was carried out either by the classical heterogeneous reaction medium (after phase inversion step), or else by the alternative homogeneous medium (prior to dispersion formation). Dispersions as well as films prepared from dispersions have been later extensively characterized. Findings: 1,2-Ethanediamine addition in heterogeneous medium leads to dispersions with high particle sizes and broad distributions whereas in homogeneous medium, lower particle sizes and narrow distributions were observed, thus leading to higher uniformity and cohesiveness among particles during film formation. Thereby, stress transfer is favored adding the diamine in a homogeneous medium; and thus the obtained films presented quite higher stress and modulus values. Furthermore, the higher uniformity of films tends to hinder water molecules transport through the film, resulting, in general, in a lower water absorption capacity.