Flexural and tensile moduli of polypropylene nanocomposites and comparison of experimental data to Halpin‐Tsai and Tandon‐Weng models

This research focuses on the reinforcing efficiency of nanomateterials and the role of the reinforcement's dispersion and orientation on the nanocomposite's flexural and tensile moduli. Polypropylene‐based composites reinforced with (i) exfoliated graphite nanoplatelets, xGnP?, (ii) vapor grown carbon fibers, (iii) PAN‐based carbon fibers, (iv) highly structured carbon black and (v) montmorillonite clay were fabricated by extrusion and injection molding. It was found that graphite platelets are the best reinforcement in terms of flexural modulus whereas PAN‐based carbon fibers cause the largest improvement in the tensile modulus. The difference in the reinforcing efficiency during the flexural and tensile testing is attributed to (i) the degree of fiber alignment along the flow direction during injection molding, which is higher in the thinner tensile specimens than in the flex specimens; and (ii) the different deformation modes of the two tests. The importance of good dispersion of the reinforcements within the polymer matrix and of perfect contact between the two phases is emphasized comparing the experimental modulus data to theoretical predictions made using the Halpin‐Tsai and the Tandon‐Weng models. POLYM. ENG. SCI., 47:1796–1803, 2007. © 2007 Society of Plastics Engineers     

Effect of Cu Content on the Structure,and Performance of Substoichiometric Cr–N Coatings

Cu–Cr–N coatings with Cu contents between 3 and 65 at.%, Cu/Cr ratios in the 0.04–4.5 range and 21–27 at.% N, synthesized by twin electron-beam Physical Vapor Deposition at 450 °C, were investigated and compared against substoichiometric Cr–N reference samples. The main objective of this study is to study the influence of Cu on the structure, and the subsequent effects on the mechanical properties, room (22 °C) and high temperature (500 and 840 °C) tribological performance of Cu–Cr–N coatings. Using X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and scanning electron microscopy, in combination with nanoindentation mechanical property measurements and laboratory-controlled ball-on-disc sliding experiments, it is shown that Cu–Cr–N coatings with low Cu content (3 at.%) possess sufficient wear resistance for high-temperature demanding tribological applications. The lubricious effect of oxide formation at high temperatures is also evaluated.     

Micromorphology,composition and origin of the orange patina on the marble surfaces of Propylaea (Acropolis,Athens)

This paper is an attempt to contribute to the discussion started in the 1980s and continuing until today, on the origin of orange-brown patinas observed on marble surfaces. SEM and XRD were used in the study of the orange-brown patina growing at the east stoa of Propylaea, at the Acropolis of Athens. The patina consists of an extremely compact, homogenous, 500-microm-thick layer, mainly of hydroxyapatite. The outer part (50 microm) of the layer presents an orange colour attributed to iron in clay particles, which were deposited on the surface of the patina and have gradually been diffused in the bulk. The interface between the phosphatic layer and the marble is very uneven and full of cavities colonised by microorganisms. The phosphatic layer penetrates into the grain boundaries and fills the empty space between the grains. The presence of biological attack at the interface causes progressive erosion and detachment of both the patina and the marble. The minimum presence of oxalates, the absence of microorganisms or remnants of them in the phosphatic layer, the homogeneity and compactness of the patina, give evidence against the theory of biogenic origin. It is suggested that the layer originates from an artificial coating deliberately applied onto the marble surface for protective or aesthetic reasons, when the marble had already been weathered. Possible manmade pastes are suggested.     

Optical properties of aerosol over a South European urban environment

Aerosol optical depths (AODs) and single scattering albedos (SSAs) were derived from in situ aircraft measurements of scattering and absorption coefficients at 550 nm. These values were compared to the AODs and SSAs derived from the sun photometer (CIMEL) data of the Aerosol Robotic Network (AERONET) site, in Thessaloniki, Greece, between 18 and 21 July 2006. The aircraft-obtained AODs were lower than the corresponding columnar values. However, aircraft SSAs were found to be in good agreement with the columnar values retrieved from the CIMEL. Aircraft aerosol size distributions measured by means of an optical particle counter (OPC) were also in good agreement with the respective distributions derived from the AERONET site. Filter samples were collected on board the aircraft at different altitudes, to provide detailed information on the chemical composition of tropospheric aerosol. The concentrations of identified chemical species were used to calculate particle refractive indices (RIs) for comparison with the AERONET calculated values.     

Nanocrystalline Fe‐Ni alloy/polyamide 6 composites of high mechanical performance made by ultrasound‐assisted master batch technique

The focus of this study is to improve the dispersion state of nanocrystalline (nc) Fe‐Ni particles in polyamide 6 (PA6) matrix and the filler‐matrix interfacial interactions to provide Fe‐Ni alloy/PA6 nanocomposites of remarkable mechanical performance for engineering applications. nc Fe₄₀Ni₆₀ particles were chemically synthesized. Then Fe₄₀Ni₆₀/PA6 nanocomposites of various nanofiller loading were prepared by compounding via a newly modified master batch technique called ultrasound assisted master batch (UMB), followed by injection molding (IM). Their mechanical properties, morphology and structural parameters were characterized and compared with the corresponding properties of Fe₄₀Ni₆₀/PA6 nanocomposites made by solution mixing (SM) and IM. The study reveals that the UMB process is more cost effective and time efficient, simpler and easier to scale up compared with the SM process. In addition, UMB nanocomposites exhibit superior mechanical properties and distinctive morphology compared with the corresponding SM ones. Moreover, structural analyses indicate that physical structural changes occurred in PA6 due to presence of alloy particles are affected differently by the different compounding methods, profound understanding of such phenomenon is focused throughout the article. These distinctive advantages recommend that UMB technique can be of great potential in commercial production of polymer nanocomposites (PNCs). It is concluded that the sonication of nc Fe₄₀Ni₆₀ particles in dilute polymer solution during UMB compounding, a new step that is incorporated for the first time in the master batch process, is mainly responsible for the good wetting between nanoparticles and polymer chains, strong filler‐matrix interactions and consequently the remarkable mechanical performance of UMB PNCs. POLYM. COMPOS., 35:2343–2352, 2014. © 2014 Society of Plastics Engineers     

Tribological Study Comparing PAG and POE Lubricants Used in Air-Conditioning Compressors under the Presence of CO2

Polyalkylene glycol (PAG) and polyolester (POE) synthetic lubricants are good candidates for air-conditioning systems that work with alternative refrigerants such as carbon dioxide (CO₂). Both synthetic lubricants are widely used in air-conditioning compressors and have been optimized for use with hydrofluorocarbon (HFC) refrigerants. However, it is still not clear which lubricant is more suitable for use in compressors operating with CO₂ as a refrigerant. This study compares the performance of PAG and POE lubricants of the same viscosity (ISO VG 68) used in air-conditioning compressors. The materials used were Al390-T6 disks and hardened steel SAE 52100 pins. The tests were performed using a high pressure tribometer (pin-on-disk configuration) in the presence of CO₂. The results showed that scuffing and wear resistance of Al390-T6 tested with PAG were superior compared to the samples tested with the POE lubricant. Chemical analysis using X-ray photoelectron spectroscopy showed that PAG tends to promote the formation of carbonate layers on the surface, leading to improvement in the tribological performance of the interface.     

Comparative study of the release kinetics of osmotically active solutes from hydrophobic elastomeric matrices combined with the characterization of the depleted matrices

The release process of three osmotically active solutes with various solubilities in water (NaCl, CsNO₃, and CsCl) from silicone rubber matrices is presented. The kinetics of release for different initial loads of the salts were supplemented by measurements of the kinetics of concurrent water uptake. To gain insight on the relevant non‐Fickian transport mechanisms, the morphology, the diffusion and sorption properties and the physicochemical state of water in the salt‐depleted matrices were studied. In addition, both salt‐loaded and salt‐depleted matrices were characterized with respect to their mechanical properties. The combined information, derived from these techniques, supported the operation of a release mechanism carried out through the formation of microscopic cracks, interconnecting the permanently formed cavities inside the matrices. The results indicate that these microscopic cracks may have healed upon drying. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of exfoliated graphite nanoplatelets on the mechanical and viscoelastic properties of poly(lactic acid) biocomposites reinforced with kenaf fibers

The focus of this study is to explore synergy between nanomaterials such as exfoliated graphite nanoplatelets (xGnP) and micro-size reinforcements such as kenaf natural fibers, in poly(lactic acid) based composites. The nano-biocomposites are made by melt-mixing followed by injection molding. Prior to melt-mixing the kenaf fibers were coated with the xGnP using sonication. The reinforcement content used in the study was up to 5 wt% and up to 40 wt% for xGnP and kenaf fibers, respectively. The flexural strength and modulus and the viscoelastic properties such as storage modulus were determined. It was found that addition of 5 wt% xGnP did not increase the viscosity of the polymer melt, enhanced the flexural modulus by 25–30% at any fiber loading used but did not increase the strength, indicating insufficient load transfer at the polymer-xGnP or xGnP-kenaf interface. Finally, addition of xGnP had a positive effect on the heat distortion temperature but only at higher fiber loadings.     

Low cholesterol along with inflammation predicts morbidity and mortality in hemodialysis patients

Low and not high cholesterol seems to predict high mortality in hemodialysis (HD) patients. The confirmation of this reverse epidemiology as well as its possible interconnection with the increased inflammatory activity observed in this population is being explored in the present study. A group of 136 HD patients was prospectively studied for 2 years, and cardiovascular disease (CVD) as well as all-cause mortality and morbidity were recorded. Baseline lipid profile, inflammatory status, and patients' characteristics were studied as potential survival and hospitalization predictors. During the 24-month follow-up, 21 deaths (52.4% due to CVD) and 38 hospitalizations (55.3% due to CVD) were recorded. In multivariate Cox regression analysis, decreased interleukin-10 (IL-10) and decreased total serum cholesterol (TChol) were the only independent predictors of CVD mortality while C-reactive protein and decreased TChol predicted all-cause mortality. Interleukin-10 at baseline was 11.29 ± 21.49 vs. 5.51 ± 4.57 pg/mL (P<0.018) and TChol 167.37 ± 47.84 vs.122.04 ± 26.48 mg/dL (P<0.000) in survivors vs. nonsurvivors from CVD, while C-reactive protein at baseline was 9.37 ± 11.54 vs. 23.15 ± 18.76 mg/L (P<0.000) and TChol 169.26 ± 46.42 vs. 133.26 ± 46.33 mg/dL (P<0.003) in survivors vs. nonsurvivors from any cause of death. Using the same method of statistical analysis, IL-6 and decreased soluble gp130 (sgp130)—an antagonist of IL-6 action—were found to be the only independent prognostic factors for hospitalization due to CVD while decreased soluble gp130 remained the sole predictor of hospitalization due to any cause. In conclusion, reverse epidemiology regarding cholesterol is confirmed in the present study. Furthermore, inflammatory activity also predicts, independently of or in conjunction with low-cholesterol, CVD and all-cause morbidity and mortality in HD patients.     

Synergistic effect of graphite nanoplatelets and glass fibers in polypropylene composites

In this study, polypropylene (PP) composites reinforced with short glass fibers (GF) and exfoliated graphite nanoplatelets were obtained by melt compounding followed by injection molding. Morphological observations and quasi‐static tensile tests were carried out in order to investigate how the morphology and the mechanical properties of the composites were affected by the combined effect of two fillers of rather different size scales (i.e., micro‐ and nanoscale). The results indicate that the dispersion of the nanofiller in the PP matrix promoted the formation of a stronger interface between the matrix and GF, as indicated by the increase of the interfacial shear strength determined by the single‐fiber microdebonding test. Concurrently, a significant improvement of the tensile modulus and impact strength of the composites was observed, with small changes in the processability of hybrid composites compared to that of GF composites, as confirmed by rheological measurements. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41682.