Development and characterization of PEEK/carbon nanotube composites

New poly(ether ether ketone) (PEEK) based composites have been fabricated by the incorporation of single-walled carbon nanotubes (SWCNTs) using melt processing. Their structure, morphology, thermal and mechanical properties have been investigated. Scanning electron microscopy observations demonstrated a more uniform distribution of the CNTs for samples prepared following a processing route based on polymer ball milling and CNT dispersion in ethanol media. Thermogravimetric analysis indicated a remarkable improvement in the thermal stability of the matrix by the incorporation of SWCNTs. Differential scanning calorimetry showed a decrease in the crystallization temperature with increasing SWCNT content, whilst no significant changes were observed in the melting of the composites. The crystallite size determined by X-ray diffraction decreased at high SWCNT loading, which is attributed to the spatial limitations on crystal growth by confinement within the CNT network. Dynamic mechanical analysis revealed an increase in the storage moduli, hence in the rigidity of the systems, with increasing SWCNT content. Their addition shifts the glass transition peak to higher temperatures due to the restriction in chain mobility imposed by the CNTs. Higher thermal stability and mechanical strength were found for composites with improved dispersion of the SWCNTs.     

Epoxidized linolenic acid salts as multifunctional additives for the thermal stability of plasticized PVC

Calcium and zinc salts of epoxidized linolenic acid were synthesized and used as multifunctional additives, to minimize or prevent the reaction of epoxidized soybean oil (ESO) with liberated hydrochloric acid (HCl) during the thermal degradation of poly(vinyl chloride) (PVC) in particular. These metal epoxy salts were incorporated as thermal stabilizers for both diisodecyl phthalate and ESO–plasticized PVC blends that underwent thermal degradation studies at 170°C. The overall performance of these metal epoxy salts was examined by thermal gravimetric analysis and visual color retention of the PVC blends. The weight loss profiles of the metal salt stabilized PVC were comparable to those of blends containing metal stearates. There were, however, vast improvements in color retention of the plasticized PVC using these novel additives. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41736.     

Prediction of enteric methane output from milk fatty acid concentrations and rumen fermentation parameters in dairy cows fed sunflower, flax, or canola seeds

Milk fatty acid (FA) composition has been suggested as a means of predicting enteric methane (CH₄) output in lactating dairy cattle because of the common biochemical pathways among CH₄, acetate, and butyrate in the rumen. Sixteen lactating Holstein cows were used in a Latin square design with four 28-d periods. All diets contained steam-rolled barley, a pelleted supplement, barley silage [45% of dietary dry matter (DM)] and 3.3% added fat (DM basis) from 1 of 4 sources: calcium salts of long-chain FA (palm oil; control) or crushed oilseeds from sunflower, flax, or canola. The objectives of this study were to (1) compare the effect of diets on milk FA profile; (2) model CH₄ production from milk FA composition, intake, and rumen fermentation variables; and (3) test the applicability of CH₄ prediction equations reported in previous studies. Methane (g/d) was measured in chambers (2 animals/chamber) on 3 consecutive days (d 21–23). The test variables included total DM intake (DMI, kg/d; d 21–23), forage DMI (kg/d; d 21–23), milk yield (kg/d; d 21–23), milk components (d 18–21), milk FA composition (% total FA methyl esters; d 18–21), rumen volatile FA (mol/100 mol; d 19–21), and protozoal counts (d 19–21), and were averaged by chamber and period to determine relationships between CH₄ and the test variables. Milk trans(t)10-, t11-18:1, and cis(c)9t11-18:2 were greater for sunflower seeds compared with the other diets. Forage DMI (correlation coefficient, r = 0.52; n = 32), DMI (r = 0.52; n = 32), and rumen acetate + butyrate:propionate (r = 0.72; n = 16) were positively related to CH₄ (g/d), whereas rumen propionate (r = 0.63; n = 16), milk c9-17:1 (r = 0.64; n = 32), and c11-18:1 (r = 0.64; n = 32) were negatively related to CH₄. The best regression equation (coefficient of determination = 0.90; n = 16) was CH₄ (g/d) = −910.8 (±156.7) × milk c9-17:1 + 331.2 (±88.8) × milk 16:0 iso + 0.0001 (±0.00) × total entodiniomorphs + 242.5 (±39.7). Removing rumen parameters from the model also resulted in a reasonably good estimate (coefficient of determination = 0.83; n = 32) of CH₄. Stepwise regression analysis within diets resulted in greater coefficient of determination and lower standard error values. Predictions of CH₄, using equations from previous studies for the data set from this study, resulted in a mean overestimation ranging from 19 to 61% across studies. Thus, milk FA alone may not be suitable for developing universal CH₄ prediction equations.     

Synthesis of polyethylene using ultrasonic energy with a metallocene catalyst

Ethylene polymer was synthesized by the treatment of a metallocene catalyst Zr(CP)₂Cl₂ solution with ultrasonic energy. Ultrasonic energy irradiation was used to change the polymer structure of the formed polymer. Different ultrasonic energy irradiation times were applied to the metallocene catalyst solution. The ultrasonic energy had an effect on the average molecular weight, molecular weight distribution, and polymer productivity. A lower average molecular weight and a narrower molecular weight distribution were produced with a longer ultrasonic irradiation time. The polymer productivity was almost constant when the metallocene catalyst was treated with ultrasonic energy. Finer polyethylene particles were produced with longer ultrasonic irradiation times. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 756–759, 2006     

Substrate Temperature Dependent Surface Morphology and Photoluminescence of Germanium Quantum Dots Grown by Radio Frequency Magnetron Sputtering

The visible luminescence from Ge nanoparticles and nanocrystallites has generated interest due to the feasibility of tuning band gap by controlling the sizes. Germanium (Ge) quantum dots (QDs) with average diameter ~16 to 8 nm are synthesized by radio frequency magnetron sputtering under different growth conditions. These QDs with narrow size distribution and high density, characterized using atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) are obtained under the optimal growth conditions of 400 °C substrate temperature, 100 W radio frequency powers and 10 Sccm Argon flow. The possibility of surface passivation and configuration of these dots are confirmed by elemental energy dispersive X-ray (EDX) analysis. The room temperature strong visible photoluminescence (PL) from such QDs suggests their potential application in optoelectronics. The sample grown at 400 °C in particular, shows three PL peaks at around ~2.95 eV, 3.34 eV and 4.36 eV attributed to the interaction between Ge, GeO_x manifesting the possibility of the formation of core-shell structures. A red shift of ~0.11 eV in the PL peak is observed with decreasing substrate temperature. We assert that our easy and economic method is suitable for the large-scale production of Ge QDs useful in optoelectronic devices.     

Soft-templating pathway to create nanostructured Mg–Al spinel as high-temperature absorbent for SO2

Interest in reducing SO₂ emission from the fluid catalytic cracking (FCC) crude oil has been encouraging the development of new materials to achieve such goal. The nanostructured Mg–Al spinel (MgAl₂O₄) was prepared by co-precipitation and post hydrothermal treatment in the presence of glucose and followed by elimination of the organic components by calcination at 700 °C for 3 h. Physical and chemical properties were characterized by XRD, N₂ sorption, TG, FTIR, SEM, and TEM methods. Mesoporous nanostructured MgAl₂O₄ with a high surface area of 324 m² g^?1 were obtained. The organic components contributed to the development of mesoporosity, functioning as a soft template. SO₂ adsorption tests showed that the nanostructured MgAl₂O₄ had a 51.58 % increase of SO₂ sorption capacity than MgAl₂O₄ prepared without glucose. These results showed that the nanostructured MgAl₂O₄ is a promising candidate as catalyst for flue gas desulfurization in FCC process. Three kinetic models were also applied to analyze the SO₂ adsorption kinetics; the pseudo-second order kinetic model fit well with a correlation coefficient (R²) of 0.991 for nanostructured MgAl₂O₄.     

KINETICS OF THE COMPLEXATION OF UO2(NO3)2 WITH TRIBUTYL PHOSPHATE (TBP) IN XYLENE#

ABSTRACT

The kinetics of ligand exchange between bulk solution TBP and uranyl nitrate bound TBP in o-xylene has been investigated by ³¹P dynamic NMR spectroscopy. First order ligand exchange rate constant, k, and the activation energy for the uranyl nitrate-TBP system were determined from plots of transverse relaxation rates (In (l/τ)) versus reciprocal temperature (1/T). Using the Eyring equation, the average values of activation enthalpy, δH^* (30.8±5.1 kJ-mole^?1), and activation entropy, δS^* (-109±19 J/mol-K) have been calculated. The negative entropy of activation value indicates an increase in order on proceeding from the reactants to the activated complex. Therefore, an associative mechanism may be proposed for the ligand exchange reaction between UO₂(NO₃)₂ TBP2 and TBP. Equilibration of the extractant phase with 1.0 M HC1 did not change the ligand exchange rate constants or the activation parameters appreciably. These results are discussed in comparison with previous reports on TBP exchange rates for this system.