Volume 37, Issue 1

After a short discussion of various shape memory related phenomena and the basic working mechanisms behind the shape memory effect (SME) in polymeric shape memory materials (SMMs), standard techniques and procedures to characterize these types of materials are reviewed in details (including the concerns in the selection of testing methods and parameters). Although the focus of this paper is on the heating-responsive SME, important issues in the chemo-responsive SME are addressed. Furthermore, some other shape memory related phenomena, such as various kinds of temperature memory effect (TME), and multiple-SME etc., and optimization of the shape memory performance of a shape memory polymer (SMP) via tailoring the programming parameters are included.

Epoxy resin/montmorillonite nanocomposites were obtained via in situ intercalative polymerisation. The polymer matrix consists of anhydride-cured epoxy, and the choice of catalyst allows exchange reactions without depolymerisation. This makes the resin insoluble and reprocessable at the same time and potentially recyclable. In this study, reprocessing of the nanocomposites was done by mechanical grinding and re-welding by compression moulding at high temperature, similarly to thermoplastics. The effect of this process on the level of clay dispersion is discussed. Nanocomposite superstructures were imaged by means of transmission electron microscopy, and montmorillonite interlayer spacings were estimated by small angle X-ray scattering. The thermomechanical and combustion properties of the nanocomposites were investigated by means of dynamic mechanical thermal analysis, thermogravimetric analysis and cone calorimetry. The material tensile complex modulus E * was improved by nanocomposite formation, also after the glass transition occurred. Flammability of the material was moderately affected by the dispersed clay.

Inorganic montmorillonite (MMT)/poly(vinylidene fluoride) nanocomposites were prepared by two methods: co-precipitation and solution casting. The effect of preparation methods and thermal treatment on crystalline phase was investigated by Fourier transform infrared spectroscopy and differential scanning calorimetry tests. The isothermal crystallization process was observed with polarized optical microscopy. It was found that the solution-casting method was more effective than the co-precipitation method in inducing the polar phase in the melt-isothermal crystallization process. The addition of inorganic MMT by the solution-casting method without further thermal treatment promoted the β-phase crystallization. The inorganic MMT significantly improved the γ phase of the solution-cast samples in the melt-recrystallization process. The degree of dispersion of inorganic MMT influenced the relative content of the polar phase and the crystallinity of the samples in the same crystallization conditions, i.e. the preparation method and the thermal treatment. The effect of dispersion on crystallization kinetics was also studied to verify the enhancement of finely dispersed nanolayer clusters on the γ phase.

Natural rubber (NR)/montmorillonite (MMT) nanocomposites compatibilized with epoxidized natural rubber (ENR) were produced by latex compounding method. The effects of ENR as a compatibilizer on NR/MMT nanocomposites were investigated. The addition of ENR brought intercalation or exfoliation of the clay, which improved the clay dispersion in the rubber matrix, as characterized by X-ray diffraction (XRD) and transmission electronic microscopy (TEM). The interfacial interaction of ENR with MMT was investigated by Fourier transform infrared spectroscopy (FTIR). The vulcanization was hindered by the incorporation of ENR, while the mechanical performances, thermal stability and ageing resistance were improved. The glass transition temperature and storage modulus increased with ENR loading, which was corroborated by dynamic mechanical analysis (DMA).

In this study, poly( p -phenylene sulfide) (PPS) nanofiber sheets were fabricated by winding PPS nanofibers onto a spool. Previously, PPS nanofibers have been prepared by irradiating a PPS fiber with a CO 2 laser while drawing it at supersonic speeds by single-fiber injection through an orifice. Here, we incorporated the nanofibers obtained into large nanofiber sheets and determined their mechanical properties. Supersonic air was introduced into a vacuum chamber through eight fiber injection orifices to obtain large PPS nanofiber sheets. The nanofibers were collected for 10 min, producing a rectangle sheet with dimensions of 17 cm×18 cm, a thickness of 70 μm, and an average fiber diameter of 700 nm. The dependence of the sheet’s mechanical properties on winding speed was investigated in the machine direction (MD) and traverse direction (TD) at four winding speeds.

In the current research, poly(phenylene ether-ether sulfone) (PEES)-co-poly vinyl pyrrolidone (PVP) nanofiltration membranes were prepared by a casting solution technique using N -methyl-2-pyrrolidone (NMP) as a solvent. The ethanol was used as fixed additive for better dispersion of iron oxide nanoparticles into the membranes structure. The effect of iron oxide nanoparticle concentration in the casting solution on the membrane performance/properties was studied. The membrane pure water flux, permeated flux, salt rejection, water content, tensile strength and membrane porosity were studied. Scanning electron microscopy (SEM) analysis was also used for the membrane morphology characterization. The results revealed that water content increased from 70.25% for bare PEES to about 83.25% for the membrane filled with 0.05 wt.% nanoparticles. SEM images showed that the membrane structure changed and turned from sponge shape to finger like. The results showed that porosity was increased from 55.92% for PEES one to 69.65% for M3. Additionally, the maximum value of flux was obtained for M3. Moreover, rejection was improved by the addition of nanoparticles into the casting solution compared to the unfilled one. Obtained results showed more appropriate performance for the modified membrane filled with 0.05 wt.% iron oxide nanoparticles compared to other prepared membranes.

Polyethersulfone (PES) is among the most interesting materials for membranes preparation, thanks to its outstanding properties, coupled to compatibility with several additives and the facility to be solubilized in several solvents. In this work, flat sheet membranes were prepared by the non-solvent induced phase separation (NIPS) technique, using PES as polymer and polyvinyl pyrrolidone (PVP, 10 kDa) as additive. Preparation and casting conditions were varied and membranes with tailored morphology and properties were obtained. The main objective was to investigate the relationship between selected preparation conditions and membrane features. This may help to understand how to tailor membrane morphology and properties depending on the desired application.

Pure and Cu 2+ -doped polyvinyl chloride (PVC) polymer films were prepared using the solution cast technique. Investigations were conducted using DSC, TGA, XRD, FT-IR, UV–Vis, SEM and EPR. Differential scanning calorimetry studies suggested that the Cu 2+ samples have higher values of the glass transition ( T g ) temperature, and thermo gravimetric studies show that weight loss of polymer film indicates the improved thermal stability of the polymer film. The features of the complexation of the polymer films were studied by X-ray diffraction. FT-IR spectra exhibits the bands in three regions, which are attributed to C–Cl, C–C and numerous CH groups of stretching and bending vibrations. The absorption spectra have been recorded in the wavelength range 200–900 nm. The absorption edge, direct bandgap, indirect bandgap and urbach energy have been evaluated. Film morphology was examined by scanning electron microscopy. XRD, DSC and SEM reveal the amorphous nature and surface morphology of polymer films, respectively. Electron paramagnetic resonance studies were used to calculate the number of spins and paramagnetic susceptibility as a function of dopant concentration, all the Cu 2+ -doped PVC samples exhibit signal with g values g ⊥ =2.176 and g || =2.254. The observed variation in the EPR signal intensity is due to variation in the dopant concentration.

Hollow glass microspheres (HGMs)/epoxy syntactic foam reinforced by multiwalled carbon nanotubes (MWCNTs) was prepared in this study. The effect of MWCNTs on the density, mechanical properties and water absorption of HGMs/epoxy syntactic foam was investigated. Because of the low density and low content of MWCNTs, the density of HGMs/epoxy syntactic foam does not change much with adding MWCNTs. In addition, the compression strength of HGMs/epoxy is enhanced by 17–25% when adding 0.3 wt% MWCNTs. The fracture surfaces of specimens were examined with scanning electron microscopy (SEM), and results indicated that the bridging effect of MWCNTs is the reinforcement mechanism. Analyzing the water absorption testing results, it is concluded that MWCNTs may decrease the water absorption content due to the hydrophobicity. Bigger inorganic ions in salt water could prevent the water diffusion, which results in a decrease of water absorption. In addition, the water absorption rate decreases with the extension of testing time.

The process of electrospinning is utilized with different approaches including conventional electrospinning, extrusion electrospinning, and electroblowing to form nanofibrous meshes and composites. Here, we report on the quality and properties of spatially graded polycaprolactone (PCL) and nano-hydroxyapatite (nHA) composite meshes fabricated with multiple-spinneret electrospinning. The composite meshes were characterized in terms of the amount of spatially allocated nHA concentration across the mesh, fiber diameter, porosity, pore size, and hydrophilicity of meshes. Results show that linearly and continuously varying nHA concentration distribution, i.e. graded structure, can be accomplished across the mesh thickness using multiple-spinneret electrospinning, which is in accordance with the change of mineral concentration observed in native tendon-bone interface. Furthermore, incorporation of nanoparticles into nanofibers led to increased fiber diameter as depicted by a shift in fiber diameter distribution, a significant increase in mean fiber diameter from 361±9 nm to 459±21 nm, and an increase in contact angle from 120.01±2.77° to 115.24±1.17°. These findings suggest that the composite meshes formed in this study could serve as model systems to be used as scaffolds in tendon-bone tissue engineering application in particular, and for other tissue-tissue interfaces in a broader context.