Molecularly Mixed Composite Membranes for Gas Separation Based on Macrocycles Embedded in a Polyimide.

Polyimides are a polymer class that has been extensively investigated as a membrane material for gas separation owing to its interesting permselective properties in a wide range of operation temperatures and pressures. In order to improve their properties, the addition of different filler types is currently studied. p-tert-Butylcalix[n]arene macrocycles (PTBCs) with different cavity sizes (PTBC4, PTBC6, PTBC8) were used as fillers in a commercial thermoplastic polyimide, with a concentration in the range 1-9 wt%, to develop nanocomposite membranes for gas separation. The selected macrocycles are attractive organic compounds owing to their porous structure and affinity with organic polymers. The nanocomposite membranes were prepared in the form of films in which the polymeric matrix is a continuous phase incorporating the dispersed additives. The preparation was carried out according to a pre-mixing approach in a mutual solvent, and the solution casting was followed by a controlled solvent evaporation. The films were characterized by investigating their miscibility, morphology, thermal and spectral properties. The gas transport through these films was examined as a function of the temperature and also time. The results evidenced that the incorporation of the chosen nanoporous fillers can be exploited to enhance molecular transport, offering additional pathways and promoting rearrangements of the polymeric chains.

Effects of Horseback Riding on the Postural Control of Autistic Children: A Multiple Baseline Across-subjects Design.

The aim of this research was to study the effect of a horseback-riding programme on postural control in a group of autistic children (ASD). Nine children aged 9 to 12 years participated in this study through a multiple baseline across subjects design. The whole programme took place over nine months. Participants followed a previously developed specific horseback-riding programme, consisting of 45-minute sessions held twice a week for at least three months. To evaluate postural control, the average velocity of the centre of pressure displacement was measured by means of a posturographic platform. Results indicated that this intervention with horses had a positive effect on the postural control in children with ASDs.

Temperature Responsive Copolymers Films of Polyether and Bio-Based Polyamide Loaded with Imidazolium Ionic Liquids for Smart Packaging Applications.

Temperature-responsive materials are highly interesting for temperature-triggered applications such as drug delivery and smart packaging. Imidazolium Ionic Liquids (ILs), with a long side chain on the cation and a melting temperature of around 50 °C, were synthetized and loaded at moderate amounts (up to 20 wt%) within copolymers of polyether and a bio-based polyamide via solution casting. The resulting films were analyzed to assess their structural and thermal properties, and the gas permeation changes due to their temperature-responsive behavior. The splitting of FT-IR signals is evident, and, in the thermal analysis, a shift in the glass transition temperature (Tg) for the soft block in the host matrix towards higher values upon the addition of both ILs is also observed. The composite films show a temperature-dependent permeation with a step change corresponding to the solid-liquid phase change in the ILs. Thus, the prepared polymer gel/ILs composite membranes provide the possibility of modulating the transport properties of the polymer matrix simply by playing with temperature. The permeation of all the investigated gases obeys an Arrhenius-type law. A specific permeation behavior, depending on the heating-cooling cycle sequence, can be observed for carbon dioxide. The obtained results indicate the potential interest of the developed nanocomposites as CO2 valves for smart packaging applications.

Polyether Block Amide as Host Matrix for Nanocomposite Membranes Applied to Different Sensitive Fields.

The cornerstones of sustainable development require the treatment of wastes or contaminated streams allowing the separation and recycling of useful substances by a more rational use of energy sources. Separation technologies play a prominent role, especially when conducted by inherently environmentally friendly systems such as membrane operations. However, high-performance materials are more and more needed to improve the separative performance of polymeric materials nanocomposites are ideally suited to develop advanced membranes by combining organic polymers with suitable fillers having superior properties. In this area, polyether block amide copolymers (Pebax) are increasingly adopted as host matrices due to their distinctive properties in terms of being lightweight and easy to process, having good resistance to most chemicals, flexibility and high strength. In this light, the present review seeks to provide a comprehensive examination of the progress in the development of Pebax-based nanocomposite films for their application in several sensitive fields, that are challenging and at the same time attractive, including olefin/paraffin separation, pervaporation, water treatment, flexible films for electronics, electromagnetic shielding, antimicrobial surfaces, wound dressing and self-venting packaging. It covers a wide range of materials used as fillers and analyzes the properties of the derived nanocomposites and their performance. The general principles from the choice of the material to the approaches for the heterogeneous phase compatibilization as well as for the performance improvement were also surveyed. From a detailed analysis of the current studies, the most effective strategies to overcome some intrinsic limitations of these nanocomposites are highlighted, providing guidelines for the correlated research.

La integración sensorial y su importancia en el aprendizaje de los niños con trastorno de espectro autista / Sensory integration and its importance in learning for children with autism spectrum disorder

Resumen La integración sensorial se apoya en múltiples antecedentes teóricos que justifican su importancia para poder integrar la información que procede de los diferentes sentidos y desarrollar una respuesta adaptada al entorno. Así también, la literatura científica ha demostrado que existe una estrecha relación entre la integración sensorial y el aprendizaje. El objetivo de este artículo es abordar el concepto de integración sensorial y su influencia en el aprendizaje, en especial, de los niños con Trastorno de Espectro Autista. La metodología utilizada ha sido mediante una revisión bibliográfica de tipo narrativa, orientada por el objetivo de la investigación. Las bases de datos consultadas han sido: Web of Science, SCOPUS, Dialnet y RedaLyC. Y los principales descriptores han sido Integración Sensorial, Aprendizaje y Trastorno de Espectro Autista (TEA). Los resultados obtenidos apoyan la idea de que los niños con TEA suelen presentar dificultades en este proceso de integración sensorial, siendo ésta la causa explicativa de algunos de los problemas de aprendizaje y conducta que presentan. Se espera que a partir de este trabajo se potencie una toma de conciencia de la necesidad de considerar este aspecto durante el diagnóstico y/o la intervención para así favorecer una auténtica inclusión de los niños con TEA en la sociedad.

Abstract Sensory integration is supported by multiple theoretical backgrounds that justify its importance in order to integrate the information coming from the different senses and to develop an adapted response to the environment. Scientific literature has also shown that there is a close relationship between sensory integration and learning. The aim of this article is to address the concept of sensory integration and its influence on learning, especially in children with Autism Spectrum Disorder (ASD). The methodology used was a narrative literature review, guided by the aim of the research. The databases consulted were: Web of Science, SCOPUS, Dialnet and RedaLyC. The main descriptors used were Sensory Integration, Learning and ASD. The results obtained support the idea that children with ASD often present difficulties in this sensory integration process, and that this is the explanatory cause of some of the learning and behavioural problems they present. It is hoped that this work will raise awareness of the need to consider this aspect during diagnosis and/or intervention in order to favour the genuine inclusion of children with ASD in society.

EVA Films Loaded with Layered Double Hydroxide (LDH) Modified with Methacrylic Anion: Effect of the Nanohybrid Filler on the Photodegradation Phenomena.

The photo-oxidative studies of ethylene vinyl acetate copolymer (EVA) matrix, filled with Layered Double Hydroxide (LDH) modified with methacrylic anion (MA), were herein reported, together with gas permeation tests. The formulation of nano-hybrid LDHs was characterized using X-ray diffractometry (XRD) and thermogravimetric analysis (TGA), demonstrating the partial intercalation of the 30% of MA anion between the LDH's galleries. The as-modified filler was introduced into an EVA matrix by mechanical milling, producing free-standing films subjected to accelerated aging. Fourier transform infrared spectroscopy (FT-IR) results suggested that the nanohybrid presence determined a stabilizing effect up to 45 days of UV irradiation, especially if compared to the EVA/LDH references for all formulated EVA hybrid nanocomposites. Conversely, the presence of nanohybrid in the matrix did not significantly change the thermal stability of EVA samples. The dispersion of modified MA-LDH in the EVA matrix produces defect-free samples in the whole range of investigated loadings. The samples show a slight decrease in gas permeability, coupled with a substantial stabilization of the original CO2/O2 selectivity, which also proves the integrity of the films after 30 days of UV irradiation.

Hollow Fiber Polyimide Membranes Prepared in a Triple Orifice Spinneret: Effect of a Reduced Water Activity in the Bore Fluid on the Gas Separation Performance.

Polyimide-based hollow fibers were spun using a triple orifice spinneret in order to apply them in gas separation. The membrane structure was tailored producing a porous external layer and a thin internal skin layer, that controlled the gas transport. The measurement of gas permeation rates and the morphological analysis were combined to obtain information on the performance of the membranes. The aim was to tune the inner top layer and investigate the role of the bore fluid on the gas permeation properties of the membranes. The bore fluid composition was explored by using water mixtures containing the solvent used for preparing the dope solution or a salt in order to reduce the water activity in the inner coagulant, but also a low amount of a crosslinker for improving the gas selectivity. The change of the dope flow-rate was also analyzed. At moderate dope flow-rates, the use of a saline water solution as bore fluid is more effective in enhancing the membrane gas selectivity with respect to a bore fluid containing certain amounts of solvent. This option represents a green approach for the preparation of the membrane. The behavior of the prepared hollow fibers over time (physical aging) in gas permeation was discussed.

A Review of the Recent Progress in the Development of Nanocomposites Based on Poly(ether-block-amide) Copolymers as Membranes for CO2 Separation.

An inspiring challenge for membrane scientists is to exceed the current materials' performance while keeping the intrinsic processability of the polymers. Nanocomposites, as mixed-matrix membranes, represent a practicable response to this strongly felt need, since they combine the superior properties of inorganic fillers with the easy handling of the polymers. In the global strategy of containing the greenhouse effect by pursuing a model of sustainable growth, separations involving CO2 are some of the most pressing topics due to their implications in flue gas emission and natural gas upgrading. For this purpose, Pebax copolymers are being actively studied by virtue of a macromolecular structure that comprises specific groups that are capable of interacting with CO2, facilitating its transport with respect to other gas species. Interestingly, these copolymers show a high versatility in the incorporation of nanofillers, as proved by the large number of papers describing nanocomposite membranes based on Pebax for the separation of CO2. Since the field is advancing fast, this review will focus on the most recent progress (from the last 5 years), in order to provide the most up-to-date overview in this area. The most recent approaches for developing Pebax-based mixed-matrix membranes will be discussed, evidencing the most promising filler materials and analyzing the key-factors and the main aspects that are relevant in terms of achieving the best effectiveness of these multifaceted membranes for the development of innovative devices.

Heterogenized Imidazolium-Based Ionic Liquids in Pebax®Rnew. Thermal, Gas Transport and Antimicrobial Properties.

Imidazolium-based ionic liquids (ILs) have interesting antimicrobial activity and their inclusion in a flexible film is ideal to take advantage of their properties in practical applications. Poly(ether-block-amide) (Pebax®Rnew) films were prepared by solution casting, loading two synthetized ILs (1-hexadecyl-3-methylimidazolium dimethyl-5-sulfoisophthalate [Hdmim][DMSIP], IL1 and 1-octyloximethyl-3-methylimidazolium hexafluorophosphate [OOMmim][PF6], IL2) up to 5 wt.%. The ILs were characterized by 1H NMR and MALDI-TOF spectroscopy. The films were investigated for miscibility, morphology, wettability, spectral properties and gas transport. The films display a good thermal stability (>200 °C). Differential scanning calorimetry (DSC) proves phase separation in the blends, that is consistent with FTIR analysis and with the island-like surface morphology observed in the micrographs. Gas permeability tests revealed that the IL-loaded films are dense and poreless, keeping the selectivity of the polymer matrix with a somewhat lessened permeability owing to the impermeable ILs crystals. The film antimicrobial activity, evaluated against Gram-negative and Gram-positive bacterial strains, was correlated to the structure of the incorporated ILs. The smaller IL2 salt did not modify the hydrophobic nature of the neat polymer and was readily released from the films. Instead, IL1, having a longer alkyl chain in the cation, provided a promising antimicrobial activity with a good combination of hydrophilicity, permeability and thermal stability.

Effect of Bridgehead Methyl Substituents on the Gas Permeability of Tröger's-Base Derived Polymers of Intrinsic Microporosity.

A detailed comparison of the gas permeability of four Polymers of Intrinsic Microporosity containing Tröger's base (TB-PIMs) is reported. In particular, we present the results of a systematic study of the differences between four related polymers, highlighting the importance of the role of methyl groups positioned at the bridgehead of ethanoanthracene (EA) and triptycene (Trip) components. The PIMs show BET surface areas between 845-1028 m2 g-1 and complete solubility in chloroform, which allowed for the casting of robust films that provided excellent permselectivities for O2/N2, CO2/N2, CO2/CH4 and H2/CH4 gas pairs so that some data surpass the 2008 Robeson upper bounds. Their interesting gas transport properties were mostly ascribed to a combination of high permeability and very strong size-selectivity of the polymers. Time lag measurements and determination of the gas diffusion coefficient of all polymers revealed that physical ageing strongly increased the size-selectivity, making them suitable for the preparation of thin film composite membranes.

Effect of Physical Aging on Gas Transport in Asymmetric Polyimide Hollow Fibers Prepared by Triple-Orifice Spinneret.

The systematic evaluation of the gas transport properties related to differences in the history of the samples is a useful tool to appropriately design a membrane-based gas separation system. The permeation rate of six pure gases was measured over time in asymmetric hollow-fiber (HF) samples, that were prepared according to the non-solvent-induced phase separation in different operation conditions, in order to identify their response to physical aging. Four types of HFs having a different structure were analyzed, comparing samples spun in a triple-orifice spinneret to HFs prepared using a conventional spinneret. A generalized gas permeance decline, coupled to a maintained permselectivity for the different gas pairs, was observed for all HFs. Instead, H2/N2 permselectivity values were enhanced upon aging. Cross-linked hollow-fiber samples showed a marked size-sieving behavior that favored the separation of small species, e.g., hydrogen, from other larger species and a good stability over time. Some HFs, post-treated using different alcohols, presented a permeance decay independently on the alcohol type and a greater selectivity over time.

Enhancing Gas Permeation Properties of Pebax® 1657 Membranes via Polysorbate Nonionic Surfactants Doping.

Composite membranes were prepared by co-casting, incorporating two nonionic surfactants in a poly(ether-block-amide), Pebax® 1657 up to 50 wt %. These polysorbate nonionic surfactants contain many ethylene oxide units and are very CO2-philic agents; thereby, they can be exploited as membrane additives for gas separation involving carbon oxide. Dynamic light scattering analysis proved a higher stability of additionated Pebax® 1657 solutions with respect to those containing only the copolymer. Scanning electron microscopy showed a regular membrane morphology without pores or defects for all investigated samples. If on the one hand the addition of the additive has depressed the mechanical properties, on the other, it has positively influenced the gas transport properties of Pebax® 1657 films. CO2 permeability increased up to two or three times after the incorporation of 50 wt % additive in copolymer matrix, while the selectivity was not significantly affected. The effect of temperature on permanent gas transport properties was studied in the range of 15-55 °C.

Effect of the Post-Spinning Solvent Exchange on the Performance of Asymmetric, Polyimide Hollow Fibers Prepared by Using a Triple-Orifice Spinneret.

Hollow fibers (HFs) are widely applied in different membrane operations, particularly in gas separation. The present work investigates the effect of post-spinning treatment on the gas transport properties of polyimide-based HFs. The membranes were spun by using both a conventional spinneret and a triple-orifice spinneret. A systematic analysis was carried out by considering different alcohols as the first fluid for the solvent exchange, with or without n-hexane as a second fluid. The HFs were characterized by exploring the change of the morphology and the permselective properties as a consequence of the operation conditions for spinning and post-treatments. According to the morphology, for a specific hollow fiber type, an optimal post-treatment was identified. The HFs prepared with the triple-orifice spinneret, using a solvent-rich shell fluid, can take advantage of the post-treatment using larger alcohols, while smaller alcohols should be preferred for the conventional spun HFs that present inside-outside double skin layers.

Ball Milling to Produce Composites Based of Natural Clinoptilolite as a Carrier of Salicylate in Bio-Based PA11.

Antimicrobial packaging systems are recognized as effective approaches to prolong food shelf life. In this context, Bio-based PA11 loaded with a food-grade zeolite were prepared using ball milling technology in the dry state. Zeolite was filled with sodium salicylate, as an antimicrobial agent, and incorporated into the polymer matrix (~50 wt % of salicylate) at different loadings (up to 10 wt %). Structural characterization and an analysis of the physical properties (thermal, barrier, mechanical) were conducted on the composites' films and compared with the unfilled PA11. The successful entrapment of the antimicrobial molecule into the zeolite's cavities was demonstrated by the thermal degradation analysis, showing a delay in the molecule's degradation. Morphological organization, evaluated using SEM analysis, indicated the homogeneous distribution of the filler within the polymer matrix. The filler improves the thermal stability of PA11 and mechanical properties, also enhancing its barrier properties against CO2 and O2. The elongated form of the zeolite particles, evaluated through SEM analysis, was used to model the permeability data. The controlled release of salicylate, evaluated as a function of time and found to depend on the filler loading, was analyzed using the Gallagher‒Corrigan model.

Influence of the Preparation Method and Photo-Oxidation Treatment on the Thermal and Gas Transport Properties of Dense Films Based on a Poly(ether-block-amide) Copolymer.

Dense films based on the hydrophobic Pebax®2533 were prepared by using solution casting in different solvents as well as compression molding and subjected to photo⁻aging under ultraviolet (UV) irradiation. The influence of the preparation method, including the casting solvents, as well as the UV irradiation time selected to treat the samples, were evaluated in terms of permeation rates of pure gases (CO2, N2, O2, CH4, He, and H2). The transport data were correlated with the microstructure and surface properties by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), as well as water contact angle measurements. The obtained results showed that a controlled photo-oxidation process reduces the hydrophobicity of the Pebax®2533 films, increasing their permeability without compromising their integrity.

Polymer ultrapermeability from the inefficient packing of 2D chains.

The promise of ultrapermeable polymers, such as poly(trimethylsilylpropyne) (PTMSP), for reducing the size and increasing the efficiency of membranes for gas separations remains unfulfilled due to their poor selectivity. We report an ultrapermeable polymer of intrinsic microporosity (PIM-TMN-Trip) that is substantially more selective than PTMSP. From molecular simulations and experimental measurement we find that the inefficient packing of the two-dimensional (2D) chains of PIM-TMN-Trip generates a high concentration of both small (<0.7 nm) and large (0.7-1.0 nm) micropores, the former enhancing selectivity and the latter permeability. Gas permeability data for PIM-TMN-Trip surpass the 2008 Robeson upper bounds for O2/N2, H2/N2, CO2/N2, H2/CH4 and CO2/CH4, with the potential for biogas purification and carbon capture demonstrated for relevant gas mixtures. Comparisons between PIM-TMN-Trip and structurally similar polymers with three-dimensional (3D) contorted chains confirm that its additional intrinsic microporosity is generated from the awkward packing of its 2D polymer chains in a 3D amorphous solid. This strategy of shape-directed packing of chains of microporous polymers may be applied to other rigid polymers for gas separations.

The influence of few-layer graphene on the gas permeability of the high-free-volume polymer PIM-1.

Gas permeability data are presented for mixed matrix membranes (MMMs) of few-layer graphene in the polymer of intrinsic microporosity PIM-1, and the results compared with previously reported data for two other nanofillers in PIM-1: multiwalled carbon nanotubes functionalized with poly(ethylene glycol) (f-MWCNTs) and fused silica. For few-layer graphene, a significant enhancement in permeability is observed at very low graphene content (0.05 vol.%), which may be attributed to the effect of the nanofiller on the packing of the polymer chains. At higher graphene content permeability decreases, as expected for the addition of an impermeable filler. Other nanofillers, reported in the literature, also give rise to enhancements in permeability, but at substantially higher loadings, the highest measured permeabilities being at 1 vol.% for f-MWCNTs and 24 vol.% for fused silica. These results are consistent with the hypothesis that packing of the polymer chains is influenced by the curvature of the nanofiller surface at the nanoscale, with an increasingly pronounced effect on moving from a more-or-less spherical nanoparticle morphology (fused silica) to a cylindrical morphology (f-MWCNT) to a planar morphology (graphene). While the permeability of a high-free-volume polymer such as PIM-1 decreases over time through physical ageing, for the PIM-1/graphene MMMs a significant permeability enhancement was retained after eight months storage.

Highly Permeable Benzotriptycene-Based Polymer of Intrinsic Microporosity.

A novel polymer of intrinsic microporosity (PIM) was prepared from a diaminobenzotriptycene monomer using a polymerization reaction based on Tröger's base formation. The polymer (PIM-BTrip-TB) demonstrated an apparent Brunauer, Emmet, and Teller (BET) surface area of 870 m2 g-1, good solubility in chloroform, excellent molecular mass, high inherent viscosity and provided robust thin films for gas permeability measurements. The polymer is highly permeable (e.g., PH2 = 9980; PO2 = 3290 Barrer) with moderate selectivity (e.g., PH2/PN2 = 11.0; PO2/PN2 = 3.6) so that its data lie over the 2008 Robeson upper bounds for the H2/N2, O2/N2, and H2/CH4 gas pairs and on the upper bound for CO2/CH4. On aging, the polymer demonstrates a drop in permeability, which is typical for ultrapermeable polymers, but with a significant increase in gas selectivities (e.g., PO2 = 1170 Barrer; PO2/PN2 = 5.4).

Carbon nanotube- and carbon fiber-reinforcement of ethylene-octene copolymer membranes for gas and vapor separation.

Gas and vapor transport properties were studied in mixed matrix membranes containing elastomeric ethylene-octene copolymer (EOC or poly(ethylene-co-octene)) with three types of carbon fillers: virgin or oxidized multi-walled carbon nanotubes (CNTs) and carbon fibers (CFs). Helium, hydrogen, nitrogen, oxygen, methane, and carbon dioxide were used for gas permeation rate measurements. Vapor transport properties were studied for the aliphatic hydrocarbon (hexane), aromatic compound (toluene), alcohol (ethanol), as well as water for the representative samples. The mechanical properties and homogeneity of samples was checked by stress-strain tests. The addition of virgin CNTs and CFs improve mechanical properties. Gas permeability of EOC lies between that of the more permeable PDMS and the less permeable semi-crystalline polyethylene and polypropylene. Organic vapors are more permeable than permanent gases in the composite membranes, with toluene and hexane permeabilities being about two orders of magnitude higher than permanent gas permeability. The results of the carbon-filled membranes offer perspectives for application in gas/vapor separation with improved mechanical resistance.

Enhancement of CO2 Affinity in a Polymer of Intrinsic Microporosity by Amine Modification.

Nitrile groups in the polymer of intrinsic microporosity PIM-1 were reduced to primary amines using borane complexes. In adsorption experiments, the novel amine-PIM-1 showed higher CO2 uptake and higher CO2/N2 sorption selectivity than the parent polymer, with very evident dual-mode sorption behavior. In gas permeation with six light gases, the individual contributions of solubility and diffusion to the overall permeability was determined via time-lag analysis. The high CO2 affinity drastically restricts diffusion at low pressures and lowers CO2 permeability compared to the parent PIM-1. Furthermore, the size-sieving properties of the polymer are increased, which can be attributed to a higher stiffness of the system arising from hydrogen bonding of the amine groups. Thus, for the H2/CO2 gas pair, whereas PIM-1 favors CO2, amine-PIM-1 shows permselectivity toward H2, breaking the Robeson 2008 upper bound.