Composites of polyvinylidene fluoride (PVDF)/carbon nanofibers (CNFs) with different nanofiber contents were prepared by melt-blending using a twinscrew extruder by directly mixing CNFs with PVDF in the molten state. Fibers were extruded from the blended pellets. CNFs improved the nucleation efficiency of PVDF but the percent crystallinity decreased with increasing CNF concentration. X-ray diffraction results showed a change in the a phase, but the transition to the b phase did not occur. Dynamic mechanical analysis (DMA) indicated an improvement in storage modulus and reduced damping factor with increasing CNF concentration. A complementary improvement in mechanical properties was determined from tensile test results. Rheological measurements indicated increased storage modulus, loss modulus, and viscosity values with an increased percentage of CNFs in the PVDF.

ABSTRACT:The detrimental effect of cell adhesion on polymer surfaces has been a limiting factor in the medical deployment of many implants. We examined the potential to decrease cell proliferation while simultaneously increasing mechanical performance through Zn-Al layered double hydroxide (LDH) organically modified with ibuprofen dispersed in poly(L-lactic acid) (PLLA). These composites are commonly referred to as nanocomposites. The thermophysical and mechanical properties of the hybrids were studied with wide-angle X-ray diffraction (WAXD), transmission electron microscopy (TEM), differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, and tensile testing. The WAXD and TEM results indicated that intercalated and exfoliated nanocomposites were obtained. The storage modulus, tensile modulus, and ultimate tensile strength were improved. The LDH affected the cold crystallization and reduced the thermal stability of the neat PLLA. Smooth muscle cells were used for in vitro studies of the nanocomposites. It was found that the hybrids reduced cell proliferation, and the amount of cell reduction was related to ibuprofen release.

The effects of stress and temperature on the nonlinear creep behavior of linear low‐density polyethylene (LLDPE) nanocomposites reinforced with montmorillonite‐layered silicate (MLS) nanoclay and compatibilized with an amorphous maleated ethylene copolymer (amEP) is investigated. To study the effect of stress on the creep resistance of these materials, creep tests were conducted at different stress levels (10, 25, and 50% yield stress). The effect of temperature was examined by analyzing the creep and recovery of the films at temperatures in the range of −100 to 25°C. The individual creep compliance curves for each stress level and temperature were fitted to both the Burgers model and the Kohlrausch‐Williams‐Watts (KWW) function. The results indicate that modification of the polyethylene results in a suppression of relaxation times but the temperature trends are reversed below the β transition temperature. Filled systems exhibited a distribution in relaxation times whose trend matched the relaxation time trends in both Burger and KWW models. POLYM. ENG. SCI., 50:1633–1645, 2010. © 2010 Society of Plastics Engineers

The nonlinear time dependent creep of linear‐low density polyethylene (LLDPE) reinforced with montmorillonite layered silicate was investigated. A previous study related the time/stress dependence of creep compliance of the material at room temperature using the Burger and Kohlrausch‐Williams‐Watts models. Using both the creep and recovery compliance curves, we employ the Schapery formulation to study the relationship between deformation, time, stress, and temperature of LLDPE nanocomposites. Smooth mastercurves are constructed using time–temperature–stress superposition principles. The stress and temperature‐related creep constants and shift factors were determined for the material using the Schapery nonlinear viscoelastic equation. The prediction results confirm the enhanced creep resistance of nanofillers even at extended time scales and low temperatures. POLYM. ENG. SCI., 50:1646–1657, 2010. © 2010 Society of Plastics Engineers

Photovoltaic (PV) systems are well-known systems that convert solar energy into electrical energy. Increases in operating temperature induce a drop in conversion efficiency and, thus, in the output power produced by the panel. This paper investigates the effectiveness of using Phase Change Materials (PCMs) in cooling PV modules. Due to its high storage density with limited temperature fluctuations, the latent heat storage in a PCM is an important factor. This depends on the thermophysical properties of PCMs such as the melting point, specific heat capacity, latent heat, density, etc. This paper aims to make a comparison between four types of PCM with different melting points and physical properties. Indoor experimental studies were performed using five prototypes. A halogen lamp was used as a solar simulator to ensure that experiments were carried out under the same irradiance. The first prototype was the reference, which consisted of a PV panel, a stand, and an electric circuit without PCMs. Four other prototypes were investigated, consisting of a PV panel with a container added at the rear face, with each having different types of PCM: sodium sulfate decahydrate, sodium phosphate dibasic dodecahydrate, decanoic acid, and calcium chloride hexahydrate, respectively. The results clearly show the effect of PCMs’ properties on PV temperature profile and power generation.