Effect of steam on structure and mechanical properties of biomedical block copolymers

The Effect of Polyamide 11 on the Thermal Stability and Light Transmittance of Silicone-Based Thermoplastic Vulcanizates

The effect of polyamide 11 (PA11) on the thermal stability and light transmittance properties of silicone-based thermoplastic vulcanizates (TPVs) has been investigated. The blends were prepared through a dynamic vulcanization process by adding 15, 30, and 45 wt% PA11 to the silicon-based TPVs, respectively. The effect of PA11 on the dispersion of silicone rubber in the TPVs after dynamic vulcanization was characterized by a scanning electron microscope (SEM), the thermal stability of the compounds was evaluated through the changes in mechanical performance in the thermo-oxidative aging process, and the light transmittance of TPVs was measured by a haze meter. The results showed that adding PA11 to silicone-based TPVs caused a decrease in the size of the silicone rubber particles after dynamic vulcanization, resulting in improved dispersion. Due to this, by increasing the compatibility between the segments through silicone's effective dispersion, the amount of light absorption was reduced, and the amount of light transmittance was increased. Finally, according to the results of the thermal aging test, it was found that TPVs with 30 and 45 wt% PA11, respectively, showed outstanding thermal resistance after aging at 160 °C and 168 h and did not melt down.

Time-dependent mechanical behavior of partially oxidized polyvinyl alcohol hydrogels for tissue engineering

Polyvinyl alcohol (PVA) hydrogels are synthetic polymers which can be used as scaffolds for tissue engineering due to their biocompatibility and large water content. To improve their biodegradation properties, partial oxidation of PVA is achieved by means of different oxidizing agents, such as potassium permanganate, bromine and iodine. The effect of this process on hydrogels mechanical performance has not been fully investigated in view of tissue engineering applications. In this work, the time-dependent mechanical behavior of unmodified and partially oxidized PVA hydrogels is evaluated by means of uniaxial tensile and stress relaxation tests, to evaluate the effect of different oxidizing agents on the viscoelastic response. Tensile tests show an isotropic and almost-incompressible behavior, with a stiffness reduction after PVA oxidation. The time-dependent response of oxidized PVA is comparable to the one of unmodified PVA and is modeled as a quasi-linear viscoelastic behavior. Finite Element (FE) models of PVA samples are developed and numerical analyses are used to evaluate the effect of different strain rates on the mechanical response under uniaxial tension. This model can be exploited to predict the time-dependent mechanical behavior of partially oxidized PVA in tissue engineering application under tensile loading.

The Effect of SEBS/Halloysite Masterbatch Obtained in Different Extrusion Conditions on the Properties of Hybrid Polypropylene/Glass Fiber Composites for Auto Parts

Masterbatches from a linear poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) and halloysite nanotubes (HNT-QM) were obtained in different conditions of temperature and shear using two co-rotating twin-screw extruders. The influence of screw configuration and melt processing conditions on the morpho-structural, thermal and mechanical properties of masterbatches at macro and nanoscale was studied. A good dispersion of halloysite nanotubes and better thermal stability and tensile and nanomechanical properties were obtained at a lower temperature profile and higher screw speed. The effect of masterbatches, the best and worst alternatives, on the properties of a polypropylene (PP)–glass fiber (GF) composite was also evaluated. Double hardness, tensile strength and modulus and four times higher impact strength were obtained for PP/GF composites containing masterbatches compared to pristine PP. However, the masterbatch with the best properties led further to enhanced mechanical properties of the PP/GF composite. A clear difference between the effects of the two masterbatches was obtained by nanoindentation and nanoscratch tests. These analyses proved to be useful for the design of polymer composites for automotive parts, such as bumpers or door panels. This study demonstrated that setting-up the correct processing conditions is very important to obtain the desired properties for automotive applications.

Fabrication of silane-grafted graphene oxide and its effect on the structural, thermal, mechanical, and hysteretic behavior of polyurethane

Incorporation of nanofillers into polyurethane (PU) is a promising technique for enhancing its thermal and mechanical properties. Silane grafting has been used as a surface treatment for the functionalization of graphene oxide (GO) with numerous reactive sites dispersed on its basal plane and edge. In this study, amine-grafted GO was prepared using silanization of GO with (3-aminopropyl)triethoxysilane. The functionalized graphene oxide (fGO) was characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy. Next, it was introduced in PU fabricated using polycaprolactone diol, castor oil, and hexamethylene diisocyanate. The fGO-PU nanocomposites were in turn characterized by FT-IR, X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and a universal testing machine. The results obtained from these analyses showed changes in structural thermal properties, as well as improved thermal stability and mechanical properties because of the strong interfacial adhesion between the fGO and the PU matrix.

Heterogeneous ion exchange membranes based on thermoplastic polyurethane (TPU): effect of PSS/DVB resin on morphology and electrodialysis

In this research, novel heterogeneous cation exchange membranes based on thermoplastic polyurethane (TPU) have been prepared by the solution casting technique. The effects of incorporation level of sulfonated polystyrene divinyl-benzene (PSS/DVB) resin on water uptake, ion exchange capacity, membrane potential and salt extraction have been elucidated. Morphological and water uptake studies suggested a two-phase heterogeneous membrane morphology owing to the presence of hard and soft segments in the TPU backbone and swelling of PSS/DVB particles. This morphology was shifted to a semi-gelled morphology throughout the membrane bulk when resin loading exceeded 50 wt%. The physically cross-linked hard segments in the TPU backbone ensured a compact membrane morphology and prevented the formation of water channels. The membrane potential showed that increasing the resin content increased the membrane transport number (max. 0.95) up to 50 wt% resin loading and beyond this, the transport number started decreasing showing a pronounced effect of voids and water flow channels developing on excessive swelling. The permselectivity reached a maximum (up to 0.92) and salt extraction values also increased (by varying voltage) up to 50 wt% loading and started decreasing beyond this optimum content. This study shows successful development of low-cost heterogeneous cation exchange membranes based on TPU with acceptable electrochemical properties.

Facile Fabrication of Porous Conductive Thermoplastic Polyurethane Nanocomposite Films via Solution Casting

Porous conductive polymers are one of important materials, featuring lightweight, large specific surface area and high porosity. Non-solvent induced phase separation is widely employed to prepare porous polymer sheet materials. Through utilizing water vapor in ambient environment as the non-solvent, a facile approach was developed to produce porous conductive polymer nanocomposites using the conventional solution-casting method. Without using any non-solvent liquids, porous carbon nanofiber/thermoplastic polyurethane (CNF/TPU) nanocomposites were prepared directly by solution casting of their dimethylformamide (DMF) solutions under ambient conditions. The strength of the CNF framework played a key role in preventing the collapse of pores during DMF evaporation. The dependence of porous structures on CNF loading was studied by scanning electron microscopy and porosity measurement. The influence of CNF loading on the mechanical properties, electrical conductivity and piezoresistive behavior was explored.

Synthetic surgical meshes used in abdominal wall surgery: Part I-materials and structural conformation

Surgical implants are commonly used in abdominal wall surgery for hernia repair. Many different prostheses are currently offered to surgeons, comprising permanent synthetic polymer meshes and biologic scaffolds. There is a wide range of synthetic meshes currently available on the market with differing chemical compositions, fiber conformations, and mesh textures. These chemical and structural characteristics determine a specific biochemical and mechanical behavior and play a crucial role in guaranteeing a successful post-operative outcome. Although an increasing number of studies report on the structural and mechanical properties of synthetic surgical meshes, nowadays there are no consistent guidelines for the evaluation of mechanical biocompatibility or common criteria for the selection of prostheses. The aim of this work is to review synthetic meshes by considering the extensive bibliography documentation of their use in abdominal wall surgery, taking into account their material and structural properties, in Part I, and their mechanical behavior, in Part II. The main materials available for the manufacture of polymeric meshes are described, including references to their chemical composition, fiber conformation, and textile structural properties. These characteristics are decisive for the evaluation of mesh-tissue interaction process, including foreign body response, mesh encapsulation, infection, and adhesion formation. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 689-699, 2017.