Preparation and nonisothermal crystallization behavior of polypropylene/layered double hydroxide nanocomposites

Polypropylene (PP)/layered double hydroxide (LDH) nanocomposites were prepared via melt intercalation using dodecyl sulfate anion modified LDH and maleated PP as compatibilizing agent. Evidently the interlayer anions in LDH galleries react with maleic anhydride groups of PP-g-MA and lead to a finer dispersion of individual LDH layers in the PP matrix. The nanostructure was characterized by XRD and TEM; the examinations confirmed the nanocomposite formation with exfoliated/intercalated layered double hydroxides well distributed in the PP matrix. The nonisothermal crystallization behavior of resulting nanocomposites was extensively studied using differential scanning calorimetry (DSC) technique at various cooling rates. In nonisothermal crystallization kinetics, the Ozawa approach failed to describe the crystallization behavior of nanocomposites, whereas the Avrami analysis and Jeziorny method well define the crystallization behavior of PP/LDH nanocomposite. Combined Avrami and Ozawa analysis (Liu model) also found useful. The results revealed that very small amounts of LDH (1%) could accelerate the crystallization process relative to the pure PP and increase in the crystallization rates was attributed to the nucleating effect of the nanoparticles. Polarized optical microscopy (POM) observations also support the DSC results. The effective crystallization activation energy was estimated as a function of the relative degree of crystallinity using the isoconversional analysis. Overall, results indicated that the LDH particles in nanometer size might act as nucleating agent and distinctly change the type of nucleation, growth and geometry of PP crystals.     

Structure–Property Correlation and Harvesting Power from Vibrations of Aerospace Vehicles by Nanocrystalline La–Pb(Ni1/3Sb2/3)–PbZrTiO3 Ferroelectric Ceramics Synthesized by Mechanical Activation

Nanostructured Pb_0.98La_0.02(Ni_1/3Sb_2/3)_0.05[(Zr_0.52Ti_0.48)_0.995]_0.95O₃ ferroelectric ceramic has been synthesized for the first time by columbite precursor method followed by mechanical activation (MA) from 5 to 40 h of dry oxide powders using high‐energy ball mill, thereby evading the calcination stage. Progressive perovskite phase formation and transformation by MA were investigated from X‐ray diffraction (XRD) analysis, indicating the noticeable presence of perovskite phase after 10 h of milling. Particle morphology of the powder was analyzed by HRTEM and correlated with activation time. Furthermore, the effect of activation time on microstructure and piezoelectric properties of the samples sintered at 1220°C were investigated. Compact microstructure, composition at morphotropic phase boundary, optimum tetragonality, and crystallinity obtained for the sintered samples resulted in best possible piezoelectric charge coefficient, d₃₃ (449 × 10^?12 C/N), piezoelectric voltage coefficient, g₃₃ (32 × 10^?3 m.V/N), and figure of merit for power harvesting, FoM_PH (14.4 × 10^?12 m‐V.C/N²), for 10 h of activation. The experimental data on output voltage in response to simulated random vibrations of aerospace vehicles measured in frequency band of 20–2000 Hz were also optimum for 10 h activation, which confirm the suitability of this composition for power‐harvesting applications.     

Synthesis,characterization, and performance evaluation of novel stabilized TDI‐based polyurethane coatings under accelerated weathering

Some toluene diisocyanate (TDI)‐based polyurethane resins (PURs) for coating applications were synthesized with castor oil and their performance was estimated under accelerated UV weathering with and without a novel UV absorber. Changes in physical properties, chemical structure, and color of the samples were monitored by mechanical property testing, FTIR spectroscopy, and colorimetry, respectively. A stable polyurethane coating was achieved at 0.5% concentration of additive in the host matrix. Mechanical properties were also retained as in the pristine PUR after mixing. Commercial Tinuvin P and benzotriazole‐based novel UV absorbers were found to improve the photoresistance of the PUR coating, and the highest efficiency of the novel UV absorber against weathering was estimated at 0.5 wt% concentration. J. VINYL. ADDIT. TECHNOL. 11:13–20, 2005. © 2005 Society of Plastics Engineers.     

Effect of La on piezoelectric properties of Pb(Ni1/3Sb2/3)O3–Pb(ZrTi)O3 ferroelectric ceramics

Piezoceramic compositions Pb_1?zLa_z(NiSb)_0.05[(Zr_0.52Ti_0.48)_1?Z/4]_0.95O₃ with Z = 0.01–0.05 were synthesized by mixed oxide route to study the effect of Lanthanum (La) on crystal structure, microstructure, piezoelectric and ferroelectric properties. Calcination was performed at 1,060 °C and sintering at 1,270 °C for 1 h. X-Ray diffraction pattern indicated the polycrystalline microstructure along with co-existence of tetragonal and rhombohedral perovskite phases. Dielectric constant ( $ K_{3}^{T} $ ) was increased whereas piezoelectric voltage constant (g ₃₃) was decreased with increase in lanthanum. Dense microstructure was observed for the composition containing 3 mol% of lanthanum. This was resulted in optimum piezoelectric charge constant (d ₃₃ = 468 × 10^?12 C/N), electromechanical coupling factor (k _p  = 0.68), remanent polarization (P _r = 24.65 μC/cm²) and displacement (D = 2,012 nm). Results indicated that the composition Pb_0.97La_0.03(NiSb)_0.05[(Zr_0.52Ti_0.48)_0.9925]_0.95O₃ could be suitable for actuator applications. The composition Pb_0.98La_0.02(NiSb)_0.05[(Zr_0.52Ti_0.48)_0.995]_0.95O₃ resulted into moderately high value of voltage constant (g ₃₃ = 39.3 × 10^?12 V m/N) and optimum value of Figure of Merit (d ₃₃ × g ₃₃ = 16.2 × 10^?12 C V m/N²) indicated the usefulness for sensor and power harvesting applications.     

Thermal,mechanical, and rheological characterization of polypropylene/layered double hydroxide nanocomposites

Polypropylene (PP)/organomodified layered double hydroxide (LDH) nanocomposites were prepared in order to examine the influence of LDH content on thermal, mechanical, and rheological properties. The nanostructure examinations by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the exfoliated/intercalated dispersion of LDH. Incorporation of the LDH resulted in a noteworthy improvement in the thermal stability of PP. It was shown that the addition of LDH contributed to the reinforcement effect by increasing the elastic modulus. The mechanical performance, as evaluated by stress–strain curves, reveal that PP/LDH hybrid materials showed significant contribution toward increment in elastic modulus, tensile strength but at the expense of impact strength. The rheological response showed a strong influence of LDH particles on the flow behavior of the PP/LDH melt which resulted in enhancement of storage, loss of moduli, and complex viscosity of nanocomposites. Therefore, the nanocomposites have higher moduli but better processibility compared with pure PP. Overall, the results indicated that the LDH particles in nanometer size might act as potential reinforcing agent for polypropylene. POLYM. ENG. SCI., 52:2006–2014, 2012. © 2012 Society of Plastics Engineers     

Facile In Situ Fabrication of Nanostructured Graphene–CuO Hybrid with Hydrogen Sulfide Removal Capacity

Nano-Micro Letters - A simple and scalable synthetic approach for one-step synthesis of graphene–CuO (TRGC) nanocomposite by an in situ thermo-annealing method has been developed. Using...