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In the present work, different ferrite-type nanoparticles (Ni0.5Zn0.5Fe2O4, NiFe2O4 and Fe3O4) were incorporated into an epoxy resin to obtain composites loaded with 20 and 40 wt% of filler. The morphology of these monolayered composites was investigated by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), which allow identifying a fractal structure of the ferrite-based filler with rough surface. The electromagnetic properties of the monolayer composites with 1 mm thickness were evaluated by the transmission line method in X-band (8.2–12.4 GHz), whose better response in terms of reflection loss was obtained for the composite filled with Ni0.5Zn0.5Fe2O4. Epoxy-based composites containing 20 and 40 wt% of Ni0.5Zn0.5Fe2O4 in the form of plaques were arranged in two types of three-layered structures: (i) stacked monolayers and (ii) low dielectric spacer sandwiches between monolayers (air, honeycomb and foam), whose structure sequence was built based on the reflectivity simulation. The best system, designed by mathematical simulation and experimental results, consisted of ER/NiZn(40)–honeycomb–ER/NiZn(20) arrangement, which presented RL of around − 40 dB at a frequency of 8.75 GHz. Broadband with > 90% attenuation (minimum of − 10 dB) with band width of around 1.2 GHz and minimum RL ≈ 20 dB (Eabs ≈ 99%) was achieved for both three-layered structures contain in PU foam or honeycomb as low dielectric spacer. The ferrite-based multilayer structures with only 6 mm of thickness constitute promising absorbing materials for applications in both civil and military fields.

This article presents a review of the split Hopkinson pressure bar uses on evaluation of polymer composites ballistic material’s dynamic mechanical properties A small introduction concerning the equipment is given, followed by a summarization of the most recent published studies relating to dynamic compressive tests used to study dynamic properties of ballistic polymeric composites such as Young's modulus, maximum stress, strain at maximum stress, tenacity and maximum strain, as well as the sensitivity of these properties to changes in the applied strain rate.

Cornstarch was processed on an extruder with glycerol and different contents of urea giving rise to samples named as SGU-0, SGU-1, SGU-5, and SGU-10. The gelatinization enthalpy ΔHgel, calculated by DSC, indicated that the mixture of glycerol and urea seems to better plasticize the starch than glycerol alone. XRD was used to identify the changes in the crystal structure of native starch after extrusion processing. XRD diffractograms indicated the presence of both residual native crystallinity and processing-induced crystallinity. The morphology observed by SEM was compatible with the presence of residual crystals and recrystallization, as suggested by XRD analysis. SAXS experiments pointed out the minute amount of B-type crystallites in the samples with urea, probably due to the hydrophilic character of urea, which contributes to starch hydration.

The development of impact resistant hybrid composites for ballistic applications is a recent trend. The increased energy absorption and reduced weight are some of the advantages for using these composites. Hybrid composites constituted of ultra-high molecular weight polyethylene (UHMWPE) laminates and aramid fiber fabrics were obtained by autoclave molding. The dynamic compression test was performed using a Split Hopkinson pressure bar with a standard deformation rate. The V50 ballistic limit test was carried out following the military standard MIL-STD-662F. The ballistic table NIJ Standard 0108.01 was taken as a reference and 9 mm Luger FMJ and .44 Mag Lead SWC EXPP ammunition were used. The dynamic-mechanical properties of the hybrid composites were evaluated. The composites exhibited an areal density of 5.30 ± 0.05 kg.m−2, meeting the required criteria in NIJ 0108.01. The V50, maximum stress, tenacity, storage modulus and tan delta peak height depended on the proportion of UHMWPE used in the hybrid composites: the best results were obtained for the composites with 75% UHMWPE and 25% aramid.

Polystyrene (PS) was blended with shape memory polyurethanes (SMPU). Styrene blocks were grafted onto PU chains during SMPU synthesis to yield a modified SMPU with a higher affinity towards PS. Furthermore, blends containing a compatibilizer, poly (styrene-co-maleic anhydride) (SMA), were also prepared by melt mixing the components. The non-compatibilized blends display phase separated structures with PS rich and SMPU rich phases, which were less evident in blends prepared with either the modified SMPU or SMA compatibilizer. The elastic storage modulus of PS was less affected when blended with SMPU in samples containing modified SMPU with styrene grafts. The impact strength of the blends with higher contents of SMPU modified with styrene blocks (25 and 50 wt.%), after shape recovery, was higher than the impact strength of neat PS. The incorporation of shape memory polymers into a brittle polymer matrix is a potential strategy to improve the toughness by external stimuli.

This study focused on evaluating mechanical and dynamic-mechanical properties of polyaramid/vinyl ester composites, as a function of the fiber content. Furthermore, split Hopkinson pressure bar technique and V50 Ballistic limit tests were performed. Composites were prepared by resin transfer molding (RTM) with different fiber content, samples being identified as AD4, AD5 and AD6 (with 4, 5 and 6 polyaramid layers, respectively). Initially, fiber, void and matrix contents were calculated and statistically analyzed, in different regions of the composites. Mechanical and dynamical mechanical properties of the composites were improved by using higher fiber content. For example, impact strength of AD6 composite was 35% higher than AD4. Moreover, increase in the fiber content promoted an increase in tenacity and stress of the composites, in the same strain rate. Velocity limit in AD6 sample was estimated in ballistics tests and it was concluded that the composite obtained could accomplish the level I requisites of ballistic protection with V50 of 304 m.s−1.

In this work, it has been reported the preparation of catalytic systems based on chemically modified niobium oxides and different polymer matrices, polypropylene (PP), poly(3-hydroxibutyrate) (PHB) and polyurethane (WPU). The efficiency of systems as photocatalytis was investigated. Materials prepared from various polymer matrices showed distinct photocatalytic activities. The systems based on PHB matrix and niobium oxihydroxide presenting the best performance among the studies systems, ~ 90% dye removal at 60 min. The results of systems characterization by Scanning Electron Microscopy (SEM), Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) analysis technical have showed that nanoparticles size, their dispersion in the polymeric matrix and interaction polymer-inorganic particles are responsible by changing photocatalysis process. However, for the PHB, structure parameters of matrix are important. The synchrotron radiation was used to investigate the macromolecular structure of the pure polymers and after the incorporation of niobium nanoparticles.

Collagen is an important biomaterial because it has many applications in the biomedical sector. However, the high hydrophilicity of collagen (COL) leads to easy swelling. Thus, controlling this property is highly desirable. In this work, cellulose nanocrystals (CNCs) dispersed in glycerol (GLI) were incorporated in the matrix collagen to tailor the hydrophilicity and mechanical properties. Study of the hydrophilicity of the bio-based nanocomposite was evaluated by contact angle measurement and thermogravimetric analysis. Mechanical analyses showed that CNCs are excellent reinforcing fillers to the collagen matrix. Synchrotron small-angle X-ray scattering was employed to investigate the nanostructures of COL/GLI/CNC nanocomposites and CNC water dispersion. CNC in concentrations up to 1 wt% presents an intermediate shape between a rod and a plane with a 9.34-nm radius of gyration (R g). Bio-based nanocomposites present two different structural levels with two types of particles with very different R gs. At the intermediate power-law regime, a large-scale mass fractal aggregate is observed. In the high-power-law regime, it is observed scattering from primary particles smaller than 1 nm. As the CNC concentration increases, the original particle distorts from a rod to a plate. The cytotoxicity assay indicates that the collagen and nanocomposites did not affect the cell viability of rat calvarial cells in vitro.

In this work, the effect of synthesizing shape memory polyurethanes in aqueous dispersions instead of in organic solvents on the structure and properties of the obtained polymers was investigated. Shape memory polyurethanes based on polycaprolactone diol and isophorone diisocyanate were synthesized by two routes: (1) aqueous dispersion (PU/SMWATER) and (2) dissolution in THF (PU/SMTHF). The samples were analyzed by infrared spectroscopy (FTIR), X-ray diffraction (XRD), static light scattering (SLS), atomic force microscopy (AFM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and mechanical tests. The aqueous dispersion method led to the production of polyurethanes with a higher degree of phase separation and a higher degree of crystallinity. The morphology of the obtained polyurethanes demonstrated that PU/SMWATER displays a structure with better defined phase separated domains. The polyurethanes exhibited similar average molar masses, soft segment glass transitions (Tgs) and mechanical properties. The lower degrees of phase separation and crystallinity of the PU/SMTHF led to lower values for the shape memory properties (shape recovery ratio (Rr)). The observed changes in the structure of the polyurethanes due to the replacement of organic solvent by an aqueous dispersion during their syntheses confirmed the preparation of shape memory polyurethanes with enhanced shape memory properties. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

In this study a novel approach for improving the photo-stabilization of polymers by incorporation of nanoparticles of a new niobium compound is reported. For the first time, this approach uses the electronic properties of niobium oxyhydroxide to absorb UV light efficiently to avoid the decomposition of the polymers. The innovative results of this work consist of preparing nanoparticles of niobium oxyhydroxide and its modification by treatment with hydrogen peroxide to alter their ability to absorb radiation and act as a photo-stabilizer for preventing polypropylene degradation. Synchrotron radiation was employed: (i) to explore the niobium nanoparticle form and (ii) to investigate the macromolecular structure of neat PP and PP/Nb compounds before and after degradation. The results from this research study using FTIR-ATR, DSC and microscopies, as TEM, SEM and OM, indicate that the incorporation of niobium oxyhydroxide nanoparticles into the PP matrix provides stability against the action of ultraviolet radiation.

Ultra-high molecular weight polyethylene samples were submitted to dynamical compressive test in a split Hopkinson Pressure Bar. Three thickness/diameter ratio (0.11, 0.44 and 0.64) and two strain rates (3250 s-1 and 6500 s-1) were used to understand how the test set-up influences the stress equilibrium and the constancy of strain rate during the impact. Concepts of stress equilibrium, constancy of strain rate, dynamical stressstrain curves and dynamical mechanical properties of the material were evaluated. All studied samples achieved stress equilibrium, but the samples with smaller ratio achieved it more easily. Nevertheless, samples with the smallest ratio were not able to achieve strain rate constancy. Additionally, dynamical stress-strain curves were plotted to investigate the mechanical properties of this material at high strain rates. T-tests pointed out that the properties are controlled by the strain rate rather than by the specimen’s thickness/diameter ratio.

Polyurethane waterborne synthesis was performed using a two-step method, commonly referred to as a prepolymer method. Nanocomposites based on waterborne polyurethane and cellulose nanocrystals were prepared by the prepolymer method by altering the mode and step in which the nanofillers were incorporated during the polyurethane formation. The morphology, structural, thermal, and mechanical properties of the resulting nanocomposite films were evaluated by Fourier transform infrared spectroscopy (FTIR), small angle X-ray scattering (SAXS), scanning electron microscopy (SEM), and tensile tests. FTIR results indicated that the degree of interaction between the nanofillers and the WPU through hydrogen bonds could be controlled by the method of cellulose nanocrystal incorporation. Data obtained from SAXS experiments showed that the cellulose nanocrystals as well as the step of the reaction in which they are added influenced the morphology of the polyurethane. The reinforcing effect of CNCs on the nanocomposites depends on their morphology.

Waterborne Polyurethanes (PUs) are a family of polymers that contains urethane linkages synthesized in an aqueous environment and are thus free of organic solvents. Recently, waterborne PUs have been extensively studied for biomedical applications because of their biocompatibility. The present work investigates the following: (1) the impact on electrical performance of electrode materials (platinum and silicon) modified chemically by a layer of waterborne PU, and (2) the behavior of rat cardiac fibroblasts and rat cardiomyocytes when in contact with an electrode surface. Diisocyanate and poly(caprolactone diol) were the main reagents for producing PUs. The electrochemical impedance of the electrode/electrolyte interface was accessed by electrochemical impedance spectroscopy. The cellular viability, proliferation, and morphology changes were investigated using an MTT assay. Cardiomyocyte adherence was observed by scanning electron microscopy. The obtained surface was uniform, flat, and transparent. The film showed good adhesion, and no peeling was detected. The electrochemical impedance decreased over time and was influenced by the ionic permeability of the PU layer. The five samples did not show cytotoxicity when in contact with neonatal rat cells.

In this work, the idea of modulating the shape memory properties of polyurethanes by changing their macromolecular architecture through the incorporation of polystyrene-based moieties was investigated. To study these effects, poly(styrene-co-maleic anhydride) (SMA) was incorporated during the synthesis of PU as a potential chain extender. Two sample groups were produced: (i) PU, produced with hydrazine as a chain extender and (ii) PUSMA, produced with the addition of SMA instead of hydrazine. The results suggest that the SMA incorporation in the PUSMA chains occurred by the reaction between NCO groups of the PU and maleic anhydride (MA) of the SMA. The presence of SMA was useful in modulating the structure of PU by reducing the soft segment crystallinity and molar mass. These changes in the structure and macromolecular architecture due to the presence of SMA moieties in PU chains led to pronounced improvements in strength, toughness, and the shape recovery ratio. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44471.

In this work, we propose the use of shape-memory polymer as an anchoring system for a bladder sensor. The anchoring system was designed from a biomedical biodegradable water-based poly(ester-urethane) produced in an aqueous environment by using isophorone diisocyanate/hydrazine (hard segment) and poly(caprolactone diol)/2,2-bis (hydroxymethyl) propionic acid (soft segment) as the main reagents. Tensile strength and elongation-at-break deterioration upon degradation in synthetic urine were investigated. In-body shape recovery was simulated and measured in synthetic urine. Results indicated that shape recovery can occur at body temperature and expulsion of the sensor by the body along with urine may occur through the combined effect of urine hydrolytic attack and compression exerted by the bladder walls.

Five series of segmented polyurethanes with different hard segment content were prepared by the prepolymer mixing method. The nano-morphology of the obtained polyurethanes and their microphase separation were investigated by infrared spectroscopy (FTIR), modulated differential scanning calorimetry (MDSC) and small-angle X-ray scattering (SAXS). Although highly hydrogen bonded segments were formed, high hard segment contents led to the presence of elevated degree of phase mixture and reduced the chain mobility, decreasing the hard domain precipitation and the soft segment crystallization. The applied techniques were able to show that the hard-segment content and the hard-segment interactions were the two controlling factors for determining the structure of segmented polyurethanes.

The relationship between shape-memory behavior and structure was studied using three series of poly(ester-urethanes) with varying amounts of hard segment. The materials were designed to display a three-phase structure consisting of a disperse phase of crystallites and hard domains embedded in an amorphous matrix based on soft segment. Structure and thermal properties of the resultant materials were investigated using techniques such as modulated differential scanning calorimetry (MDSC), dynamic mechanical analysis (DMA) and small angle X-ray scattering (SAXS). The results revealed morphological changes in the materials during a low temperature shape-memory cycle. To study shape recovery, a deformed specimen was evaluated on a heating stage mounted at the SAXS beamline. Furthermore, to study the effect of temperature during recovery, the specimens were subjected to different thermo-cycles. Under each set of conditions, the phase morphology and composition were investigated. Temporary shape was stored by the metastable structure formed during deformation. The recovery was triggered by the melting of crystallites and hydrogen bonding between hard domains. The recovery process was divided into three stages. Bulk incompatibility and entropic recovery determined the final polyurethane morphology.

Three series of shape memory poly(ester–urethane) with varying hard-segment contents were synthesized. The materials were designed to display a three-phase structure consisting of a disperse phase formed by crystallites and hard domains embedded in an amorphous matrix. The initial undeformed morphology was investigated using techniques such as modulated differential scanning calorimetry, Fourier transform infrared spectroscopy, and wide angle X-ray scattering. These techniques were used to determine the phase separation, hydrogen-bonding structure, and crystalline fraction of the specimens prior to thermo-mechanical treatments. The obtained information was correlated with small angle X-ray scattering investigations of morphological changes that occurred during shape memory cycling. The deformation cycle led to the formation of an oriented nanostructure derived from chain alignment. The nanostructure recovered was observed to be triggered by the melting of the crystallites and bulk incompatibility. A relationship between the ability of the studied poly(ester–urethane) specimens to recover their original shape and their original nanostructure was determined.

In recent years, there has been increased interest in biodegradable polyurethanes for use in regenerative medicine because of their versatility and biocompatibility. Nevertheless, these polymers are usually produced using organic solvents that can lead to the release of toxic components. In this work, polyurethane/montmorillonite nanocomposites were designed to work as guided tissue regeneration membranes to treat periodontal diseases. Polyurethanes were synthesized in an aqueous environment. The composition, morphology, and mechanical properties of the biomaterials were evaluated. The cellular viability, proliferation, and morphology changes of rat culture cementoblasts were also investigated using a montmorillonite assay. Small-angle X-ray scattering, X-ray diffraction, and infrared spectroscopy results showed that the degree of clay delamination within the polymer was able to tailor the phase morphology of the polymer, the chemical aspects of the surface, the mechanical properties, and the kinetics of hydrolysis of the materials. The produced scaffolds provided a good environment for the adhesion and proliferation of cementoblasts and thus can be considered suitable biomaterials for participating in procedures associated with periodontal regeneration. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

There is great economical interest in the workability prediction of a material during sheet metal forming. This type of processing involves complex sequences of stress and strain states, and the material workability cannot be evaluated through simple procedures such as tension testing. Under these circumstances, various mechanical tests have been proposed in order to analyze sheet forming. There is also an increasing interest in the description of this process through numerical approaches such as finite element analysis (FEA), which allows the evaluation of the mechanical damage of the material employing various ductile fracture criteria. The present paper presents a comparison between the mechanical damage measured experimentally during the Marciniak test of a steel sheet and the damage predicted by FEA. No clear relationship between the two approaches was found and the FEA results display a fairly high dispersion. It is concluded that the various mechanical damages calculated in the FEA are not directly connected to the experimental damage associated with pore opening and measured through metallographic techniques.

Gas tungsten arc welding is fundamental in those applications where it is important to control the weld bead shape and the metallurgical characteristics. This process is, however, of low productivity, particularly in the welding of large components. The activated flux TIG (ATIG) welding process, developed by the Paton Welding Institute in the 1960s, is now considered as a feasible alternative to increase the process productivity. ATIG welding uses a thin layer of an active flux that results in a great increase in weld penetration. This effect is, generally, connected to the capture of electrons in the outer parts of the arc by elements of high electronegativity, which constrict the arc causing an effect similar to that used in plasma arc welding. Generally, the literature does not present the flux formulations for ATIG welding, the few formulations that were found to have a complex nature. The present work evaluates the use of ATIG welding for the austenitic stainless steels with fluxes of only one major component. The changes in weld geometry were compared to variations in the electrical signals from the arc and the arc shape. The effect of the flux on the weld microstructure was also studied. The results indicate that even the very simple flux that was used can greatly increase the penetration of the weld bead.