Structure and properties of polyethylene ionomer based nanocomposites

Li and Zn ionomers of poly(ethylene‐co‐methacrylic acid) were modified by two organically modified montmorillonites by melt mixing. In the nanocomposites (NCs), the increase in the loss tangent main peak temperature indicated a reduction in the mobility of the long‐chain segments containing neutralized acid groups. The stack compaction observed by wide‐angle X‐ray scattering and transmission electron microscopy in the Cloisite 30B based NCs was attributed to the partial degradation of the surfactant and to the irreversible character of the ion‐exchange process of the ammonium cation of the surfactant with the Li cation. The considerable dispersion that occurred in the poly(ethylene‐co‐methacrylic acid) zinc salt (PEMA–Zn)/Cloisite 20A (20A) NCs was attributed to the high volume of the surfactant, which reduced undesired interactions between the inorganic clay surface and the ionomer. The ductile nature of the matrix remained in all of the NCs, and the increase in the modulus of elasticity of the PEMA–Zn/20A NCs reached a value five times greater than that of the PEMA–Zn matrix. The results suggest that this ionomer is suitable for use both as a matrix for 20A NCs and as a compatibilizer of polyolefin‐based NCs with 20A. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Viscoelastic and thermal properties of woven‐sisal‐fabric‐reinforced natural‐rubber biocomposites

Textile–rubber biocomposites were prepared by the reinforcement of natural rubber with woven sisal fabric. The viscoelastic properties of the composites were analyzed at different frequencies. Sisal fabric was subjected to different chemical modifications, such as mercerization, silanation, and thermal treatment, and the influences of the modifications on the dynamic mechanical properties were analyzed. The storage modulus was found to increase with reinforcement of natural rubber with woven sisal fabric. The chemical modification of the sisal fabric resulted in a decrease in the storage modulus. The damping factor was found to decrease with chemical treatment, and the gum compound exhibited maximum damping characteristics. The thermal stabilities of the composites were also analyzed by thermogravimetric studies. Scanning electron microscopy studies were performed to evaluate the morphology of the fabric–matrix interface.© 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Replication characterization of microribs fabricated by combining ultraprecision machining and microinjection molding

This article aims to investigate the effects of five processing parameters and two geometric factors on replication quality of the microribs, as well as determination of the processing condition when different materials were used. Specifically, the considered parameters include barrel temperature, mold temperature, injection velocity, holding pressure, holding time, aspect ratio, and location of the microribs. The experiment results showed a considerable difference in replicated height of molded microribs with polymethylmethacrylate and polypropylene. Among the processing parameters, the barrel temperature and injection velocity significantly affected replication quality, whereas the holding pressure and holding time appeared to have little influence for both materials. The mold temperature was found to be a sensitive parameter only for polymethylmethacrylate. As for geometric factors, both aspect ratio and location of the microribs played important roles in achievable replication. In addition, simulation results showed good prediction on the trend of how process parameters affect replication, with a small amount of over prediction. POLYM. ENG. SCI., 50:2021–2030, 2010. © 2010 Society of Plastics Engineers     

Uncertainty determination methodology, sampling maps generation and trend studies with biomass thermogravimetric analysis

This paper investigates a method for the determination of the maximum sampling error and confidence intervals of thermal properties obtained from thermogravimetric analysis (TG analysis) for several lignocellulosic materials (ground olive stone, almond shell, pine pellets and oak pellets), completing previous work of the same authors. A comparison has been made between results of TG analysis and prompt analysis. Levels of uncertainty and errors were obtained, demonstrating that properties evaluated by TG analysis were representative of the overall fuel composition, and no correlation between prompt and TG analysis exists. Additionally, a study of trends and time correlations is indicated. These results are particularly interesting for biomass energy applications.     

International society of sports nutrition position stand: caffeine and performance

Background

We compared Glycine Propionyl-L-Carnitine (GlycoCarn^®) and three different pre-workout nutritional supplements on measures of skeletal muscle oxygen saturation (StO₂), blood nitrate/nitrite (NOx), lactate (HLa), malondialdehyde (MDA), and exercise performance in men.

Methods

Using a randomized, double-blind, cross-over design, 19 resistance trained men performed tests of muscular power (bench press throws) and endurance (10 sets of bench press to muscular failure). A placebo, GlycoCarn^®, or one of three dietary supplements (SUPP1, SUPP2, SUPP3) was consumed prior to exercise, with one week separating conditions. Blood was collected before receiving the condition and immediately after exercise. StO₂ was measured during the endurance test using Near Infrared Spectroscopy. Heart rate (HR) and rating of perceived exertion (RPE) were determined at the end of each set.

Results

A condition effect was noted for StO₂ at the start of exercise (p = 0.02), with GlycoCarn^® higher than SUPP2. A condition effect was also noted for StO₂ at the end of exercise (p = 0.003), with SUPP1 lower than all other conditions. No statistically significant interaction, condition, or time effects were noted for NOx or MDA (p > 0.05); however, MDA decreased 13.7% with GlycoCarn^® and increased in all other conditions. Only a time effect was noted for HLa (p < 0.0001), with values increasing from pre- to post-exercise. No effects were noted for HR, RPE, or for any exercise performance variables (p > 0.05); however, GlycoCarn^® resulted in a statistically insignificant greater total volume load compared to the placebo (3.3%), SUPP1 (4.2%), SUPP2 (2.5%), and SUPP3 (4.6%).

Conclusion

None of the products tested resulted in favorable changes in our chosen outcome measures, with the exception of GlycoCarn^® in terms of higher StO₂ at the start of exercise. GlycoCarn^® resulted in a 13.7% decrease in MDA from pre- to post-exercise and yielded a non-significant but greater total volume load compared to all other conditions. These data indicate that 1) a single ingredient (GlycoCarn^®) can provide similar practical benefit than finished products containing multiple ingredients, and 2) while we do not have data in relation to post-exercise recovery parameters, the tested products are ineffective in terms of increasing blood flow and improving acute upper body exercise performance.     

Dynamic mechanical analysis of oil palm microfibril‐reinforced acrylonitrile butadiene rubber composites

The dynamic mechanical properties of microfibers of oil palm‐reinforced acrylonitrile butadiene rubber (NBR) composites were investigated as a function of fiber content, temperature, treatment, and frequency. The storage modulus (E′) was found to increase with weight fraction of microfibrils due to the increased stiffness imparted by the strong adhesion between the polar matrix and the hydrophilic microfibrils. The damping properties were found to decrease with increase in fiber loading. As the fiber content increases, the damping nature of the composite decreases because of the increased stiffness imparted by the natural fibers. By steam explosion method (STEX), microfibrils are separated from fibers. Natural fibers were undergone treatment such as mercerization, benzoylation, and silane treatment. The NBR is modified by the addition of resorcinol‐hexa‐hydrated silica (HRH) bonding agent. Also dicumyl peroxide (DCP) is used as an alternating vulcanizing agent in the system. In the case of composites containing chemically modified fibers, storage modulus were found to increase. Cole–Cole analysis was made to study the phase behavior of the composite samples. Activation energy for the relaxation processes in different composites was calculated. Morphological studies using scanning electron microscopy of tensile fracture surfaces of treated and untreated composites indicated better fiber matrix/adhesion in the case of treated microfibril‐reinforced composites. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

A simple method to measure phase difference between sinusoidal signals

In this paper, a novel and simple method to measure the phase difference between two sinusoidal signals is presented. Basically, the method consists of subtracting two sinusoidal signals with same frequencies and measuring the resulting signal amplitude: this amplitude being a minimum whenever there is a coincidence between both signal phases. In order to test this method, an adjustable phase reference signal has been generated using a direct digital synthesizer device. Employing this reference signal, it can be demonstrated that the phase difference between two signals can be evaluated with errors smaller than 0.3° for signals with frequencies up to 1.25 MHz.     

Optical add-drop multiplexers based on the antisymmetric waveguide Bragg grating

A novel optical add-drop multiplexer (OADM) based on a null coupler with an antisymmetric grating was designed and experimentally demonstrated. The antisymmetric grating exclusively produces a reflection with mode conversion in a two-mode waveguide. This improves the performance compared with previous demonstrations that used tilted Bragg gratings. Our design minimizes noise and cross talk produced by reflection without mode conversion. In addition, operational bandwidth and, versatility are improved while the compactness and simplicity of the null coupler OADM are maintained.     

Redundant binary partial product generators for compact accumulation in Booth multipliers

The use of signed-digit number systems in arithmetic circuits has the advantage of constant time addition. When signed-digit number systems are used in binary, they are referred as redundant binary. Here, we present a new encoding technique for generating redundant binary partial products for a multiplier, without using any additional hardware. We express each normal binary partial product in one's complement form, with an extra bit denoting the sign bit. The proposed redundant binary partial product generator (RBPPG) achieves the highest reduction in the number of partial products (75%) for a radix-4 multiplier. The carry-free nature of redundant binary adders is exploited to add the extra bits with the partial products, without using any extra adder stages. The new partial product generation (PPG) technique is shown to improve the speed of multipliers, with the least number of adder stages, irrespective of the multiplier size.     

Hierarchical adaptive nanostructured PVD coatings for extreme tribological applications: the quest for nonequilibrium states and emergent behavior

Adaptive wear-resistant coatings produced by physical vapor deposition (PVD) are a relatively new generation of coatings which are attracting attention in the development of nanostructured materials for extreme tribological applications. An excellent example of such extreme operating conditions is high performance machining of hard-to-cut materials. The adaptive characteristics of such coatings develop fully during interaction with the severe environment. Modern adaptive coatings could be regarded as hierarchical surface-engineered nanostructural materials. They exhibit dynamic hierarchy on two major structural scales: (a) nanoscale surface layers of protective tribofilms generated during friction and (b) an underlying nano/microscaled layer. The tribofilms are responsible for some critical nanoscale effects that strongly impact the wear resistance of adaptive coatings. A new direction in nanomaterial research is discussed: compositional and microstructural optimization of the dynamically regenerating nanoscaled tribofilms on the surface of the adaptive coatings during friction. In this review we demonstrate the correlation between the microstructure, physical, chemical and micromechanical properties of hard coatings in their dynamic interaction (adaptation) with environment and the involvement of complex natural processes associated with self-organization during friction. Major physical, chemical and mechanical characteristics of the adaptive coating, which play a significant role in its operating properties, such as enhanced mass transfer, and the ability of the layer to provide dissipation and accumulation of frictional energy during operation are presented as well. Strategies for adaptive nanostructural coating design that enhance beneficial natural processes are outlined. The coatings exhibit emergent behavior during operation when their improved features work as a whole. In this way, as higher-ordered systems, they achieve multifunctionality and high wear resistance under extreme tribological conditions.