Advanced Materials Forum III

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Authors: M. Isabel Pinto, Denise P. Queiroz, M. Helena Gil, Antonio Jorge Guiomar, Maria Norberta de Pinho
Abstract: The structural versatility of polyurethane based membranes is enhanced through the introduction of two soft segments to obtain new membranes with improved hemocompatibility. Crosslinked polyurethane/urea membranes with two soft segments were prepared by extending a polypropylene oxide-based tri-isocyanate terminated prepolymer (PU) with polybutadiene diol (PBDO). The ratio of PU to PBDO was 100/0 and 90/10. The membranes were characterised in terms of permeation towards O2 and CO2 and their hemocompatibility was evaluated through hemolysis and thrombosis experiments. It was found that the membrane with PBDO had the highest permeability to O2 and CO2 and it was non-hemolytic and less thrombogenic.
Authors: Veronica Santos, João P. Borges, Cláudia M.S. Ranito, Eduardo Pires, Hugo F. Araújo, António Marques, Luís Tomás, Elvira Fortunato, Rodrigo Martins, Yuri Nunes
Abstract: Total hip replacement is a common practice in every day clinical work. Artificial hip implants consist of a femoral component and an acetabular component. Nowadays the acetabular component is composed of a polymeric cup and a metallic shell. This study focuses the development of an innovative acetabular component substituting the metallic shell by a multilayer coating on the acetabular cup. A titanium coating was deposited onto ultra-high molecular weight polyethylene (UHMWPE) samples by physical vapour deposition (PVD), having an in situ pretreatment with argon ion bombardment in order to optimize the adhesive strength by surface modification, followed by the deposition of a thin film of hydroxyapatite (HA) using rf magnetron sputtering technique, at room temperature. Results obtained seem to indicate that these multilayer coatings can be a viable alternative to the metallic shell, leading to the substitution of a two part for a one part acetabular component.
Authors: Vitor Sencadas, M. Vitor Moreira, Senentxu Lanceros-Méndez, António Sergio Pouzada, Rinaldo Gregório Filho
Abstract: The α to β phase transformation of PVDF through the stretching process at different temperatures was investigated. The optimum stretching conditions were studied and characterised by infrared spectroscopy and differential scanning calorimetry. The maximum β−phase content was achieved at 80°C and a stretch ratio of 5. Accompanying the phase transformation, a orientation of the polymer chains and a packing of the crystalline structure is observed. The stretch ratio does not significantly affect the degree of crystallinity.
Authors: Gabriela Botelho, Arlete Queirós, Manuela A. Silva, Maria João Conceição
Abstract: The photodegradation of EPDM based on dicyclopentadiene was followed by FTIR spectroscopy and the main photo-oxidation products were identified by derivatization reactions. It could be found that the photodegradation is initiated at the diene with formation of α,β–unsaturated carbonyl compounds and is then propagated to the ethylene-propylene segments. The propagation reactions are accelerated and, hence, the rate of photodegradation increases with the diene content.
Authors: Marta M. D. Ramos, Helena M.G. Correia, Hugo Carmo
Abstract: Using a mesoscopic modelling approach, the authors performed computer experiments to study the influence of polymer density on bipolar charge evolution through thin layers of polydiacetylene (PDA) exhibiting specific microstructures. We found that the competition between charge transport, trapping and recombination within the polymer layer leads to several general trends, some of them being non-intuitive, as one varies polymer density. Our results show that polymer density mainly affects current and recombination efficiencies in the absence of defects or impurity states. The overall trends depend both on chain orientation relative to the electrodes and on the strength of the external applied electric field. These results suggest that adequate modelling of charge transport in electronic and optoelectronic devices based on conducting and semiconducting polymers, such as PDA, must include their structure and related key factors at mesoscopic scale. Such models provide the necessary knowledge-base to optimize the polymer film structure for electronic applications.
Authors: Joanna Ryszkowska, Monika Bil, Piotr Woźniak, Małgorzata Lewandowska, Krzysztof Jan Kurzydlowski
Abstract: Segmented polyurethanes (PUR) based on poly(ε-caprolactone)diol (PCL) as soft segments and cycloaliphatic diisocyanate were obtained. Two different types of catalysts were used for synthesis: dibutyltin dilaurate (DBTDL) and iron (III) acetylacetonate Fe(acac)3. Structure, thermal analysis, water absorption of obtained polyurethanes were studied. Polyurethanes catalyzed by Fe(acac)3 have lower glass transition temperature (Tg2) and melting temperature (Tm2) of hard domains in comparison with polyurethanes synthesized with DBTDL. Amount of absorbed water is in the range of 1,0-2,0% and is higher for PUR catalyzed by DBTDL. SEM observations show that type of catalyst used in synthesis affect structure of polyurethanes. Biological test XTT was done in order to determine influence of various metallic compounds used as catalyst on viability of human bone cell culture. The XTT results indicate no influence on viability of human osteoblasts cultured on the obtained PUR.
Authors: Nuno Correia, João C. Bordado, João Pires, Manuela B. Carvalho, Ana P. Carvalho, Moisés Pinto
Abstract: A flexible foam was developed based on polymeric diphenylmethane diisocyanate (MDI) to be used as support for pre-synthesized adsorbent additives (activated carbon) for air-conditioning filters that provide air purification and improve indoor air quality. Foam for air purification filters must be an open cell foam with low density, air permeability and the adsorbents must retain indoor air pollutants, such as volatile organic compounds (VOCs). To achieve the right structural characteristics different polyether polyols, catalysts and surfactants were used and several tests of pressure drop, apparent volume, real volume and densities were performed. Another aspect that was studied in this work was the adsorption capacity of several activated carbons and the foam matrix influence in the adsorption. For that purpose room temperature adsorption isotherms of toluene, which is a probe of noxious aromatic VOCs, were determined and compared. For scale up purpose, rise time curves of the foams were measured. This study was made at different starting temperatures and with different types and quantities of catalyst. The relationships rise time/starting temperature and rise time/quantity of catalyst were obtained and expressed in equations.
Authors: Wei Ping Jia, José Valdemar Fernandes
Abstract: Sequences of fatigue-tension tests were performed on copper polycrystal sheet, with 32µm mean grain size. The effect of strain path change on subsequent reloading yield stress as well as work hardening rate has been investigated. Dislocation microstructure was observed by transmission electron microscopy after mechanical tests. Under present conditions, it was found that fatigue prestraining caused the increase of reloading yield stress, larger amplitude of strain path change resulted in higher reloading yield stress and lower work hardening rate. Reloading tensile curves are independent of predeformation plastic strain amplitudes in both cases. Many isolated dislocation lines between cell walls have been detected for Φ=0° case when the subsequent tension strain amount is 5%, this can be well understood from the microscopic dislocation slip mechanisms. When the reloading tension tests have been done until rupture, dislocation structures become typical of monotonic tension without preloading. The correlation of mechanical properties and microstructural observations was discussed in this paper.
Authors: Ana Vera Machado, Isabel Neves, Gabriela Botelho, P. Rebelo
Abstract: Commercial samples of high density polyethylene were decomposed over faujasites (FAU) type zeolites (Y-type) using thermal gravimetric analysis (TGA). The catalytic activity and behavior of the FAU-zeolites catalysts were determined. It was found that the degradation temperature of polymer strongly depends on the catalytic acidity of the zeolites. HY zeolite was identified as the most active catalyst due to its strong acidity. The results showed that the activation energy decrease with the amount of catalyst added.
Authors: Artur J.M. Valente, Hugh D. Burrows, Victor M.M. Lobo
Abstract: The interaction between sodium dodecyl sulfate (SDS) and blends of polyaniline (PANi) and cellulose acetate (CA) is discussed. The diffusion coefficients of SDS in the blends show that the transport process is accompanied by interactions between the diffusant and the polymeric matrix. In the visible absorption spectrum, the interaction between SDS and CA-PANi blends results in a red shift of the maximum absorption wavelength. This behaviour is explained on the basis of alterations in the lamellar phase of the polymer upon SDS sorption. The interactions between SDS and the blend film are of the Langmuir-type. These blends also show an interesting selective behaviour to SDS with respect to a set of similar surfactants.

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