Flame retardancy and mechanical properties of pet‐based composites containing phosphorus and boron‐based additives

Flame retardancy of poly(ethylene terephthalate), PET, was improved using different flame retardant additives such as triphenylphosphate, triphenylphosphine oxide, zinc borate, and boron phosphate (BP). Composites were prepared using a twin screw extruder and subsequently injection molded for characterization purposes. The flame retardancy of the composites was determined by the limiting oxygen index (LOI) test. Smoke emission during fire was also evaluated in terms of percent light transmittance. Thermal stability and tensile properties of PET‐based composites were compared with PET through TGA and tensile test, respectively. The LOI of the flame retardant composites increased from 21% of neat PET, up to 36% with the addition of 5% BP and 5% triphenyl phosphate to the matrix. Regarding the smoke density analysis, BP was determined as an effective smoke suppressant for PET. Enhanced tensile properties were obtained for the flame retardant PET‐based composites with respect to PET. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42016.     

Bilirubin levels in subarachnoid clot and effects on canine arterial smooth muscle cells

BACKGROUND AND PURPOSE: Previous studies have suggested that bilirubin is a potential contributor to cerebral vasospasm. The purpose of this investigation was to determine whether bilirubin accrues in subarachnoid clot, whether its vasoconstrictive effect could involve a direct action on arterial smooth muscle cells, and, if so, whether bilirubin affects their Ca2+ uptake. METHODS: Subarachnoid clots were analyzed for bilirubin using high-performance liquid chromatography. The length and 45Ca2+ uptake of vascular smooth muscle cells enzymatically dissociated from canine carotid arteries were measured before and after exposure to bilirubin solution. Additional experiments were conducted on cultured smooth muscle cells from canine basilar artery and on ATP-depleted cardiac myocytes. RESULTS: Mean +/- SE bilirubin concentration in experimental clot was 263 +/- 35.7 mumol/L. Vascular smooth muscle cells exposed to bilirubin showed progressive shortening (P < .01) and an increased uptake of 45Ca2+ (P < .001). Contraction was prevented by Ca(2+)-free media but not by verapamil. Experiments with heart myocytes showed that bilirubin caused an increased uptake of 45Ca2+ but not of [14C]sucrose. CONCLUSIONS: The results indicate that bilirubin accrues in subarachnoid clot, that it exerts a direct constrictive effect on arterial smooth muscle cells, and that this effect is associated with an increased uptake of Ca2+. Studies on heart myocytes suggest that the Ca2+ uptake induced by bilirubin could be due to a selective increase in membrane permeability to Ca2+.     

Short glass fiber reinforced ABS and ABS/PA6 composites: Processing and characterization

In this study acrylonitrile‐butadiene‐styrene (ABS) terpolymer was reinforced with 3‐aminopropyltrimethoxysilane (APS)‐treated short glass fibers (SGFs). The effects of SGF concentration and extrusion process conditions, such as the screw speed and barrel temperature profile, on the mechanical properties of the composites were examined. Increasing the SGF concentration in the ABS matrix from 10 wt% to 30 wt% resulted in improved tensile strength, tensile modulus and flexural modulus, but drastically lowered the strain‐at‐break and the impact strength. The average fiber length decreased when the concentration of glass fibers increased. The increase in screw speed decreased the average fiber length, and therefore the tensile strength, tensile modulus, flexural modulus, and impact strength were affected negatively and the strain‐at‐break was affected positively. The increase in extrusion temperature decreased the fiber length degradation, and therefore the tensile strength, tensile modulus, flexural modulus, and impact strength increased. At higher temperatures the ABS matrix degraded and the mechanical strength of the composites decreased. To obtain a strong interaction at the interface, polyamide‐6 (PA6) at varying concentrations was introduced into the ABS/30 wt% SGF composite. The incorporation and increasing amount of PA6 in the composites broadened the fiber length distribution (FLD) owing to the low melt viscosity of PA6. Tensile strength, tensile modulus, flexural modulus, and impact strength values increased with an increase in the PA6 content of the ABS/PA6/SGF systems due to the improved adhesion at the interface, which was confirmed by the ratio of tensile strength to flexural strength as an adhesion parameter. These results were also supported by scanning electron micrographs of the ABS/PA6/SGF composites, which exhibited an improved adhesion between the SGFs and the ABS/PA6 matrix. POLYM. COMPOS. 26:745–755, 2005. © 2005 Society of Plastics Engineers     

Viscoelasticity and high buckling stress of dense carbon nanotube brushes

We report on the mechanical behavior of a dense brush of small-diameter (1-3 nm) non-catalytic multiwall (2-4 walls) carbon nanotubes (CNTs), with ∼10 times higher density than CNT brushes produced by other methods. Under compression with spherical indenters of different radii, these highly dense CNT brushes exhibit a higher modulus (∼17-20 GPa) and orders of magnitude higher resistance to buckling than vapor phase deposited CNT brushes or carbon walls. We also demonstrate the viscoelastic behavior, caused by the increased influence of the van der Waals’ forces in these highly dense CNT brushes, showing their promise for energy-absorbing coatings.     

Microcompounding of organoclay–ABS/PA6 blend‐based nanocomposites

In this study, acrylonitrile–butadiene–styrene (ABS) and polyamide‐6 (PA6) were blended in the presence of an olefin‐based compatibilizer and organoclays. The effects of ABS to PA6 ratio, clay content, and screw speed of the microcompounder were examined by performing morphological (i.e., XRD, SEM, and TEM) and tensile tests. The average aspect ratio of the clay platelets after processing was obtained by applying semiautomatic image analysis method. SEM analysis showed that addition of the compatibilizers to the ABS/PA6 blend system resulted in a decrease in diameter of dispersed phase when one of the phases was continuous. The addition of 5 wt% compatibilizer altered the dispersed morphology to cocontinuous morphology when the weight percentage of ABS was equal to that of PA6. The results of XRD analysis implied that clays were exfoliated in the presence of PA6. It was observed in TEM micrographs that clays were selectively dispersed in PA6 phase. Aspect ratio of the platelets increased as the PA6 content increased. Moduli of the nanocomposites were improved by enriching blend with PA6 and increasing screw speed. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Effect of mechanical depoling on piezoelectric properties of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–<Emphasis Type="Italic">x</Emphasis>BaTiO<Subscript>3</Subscript> in the morphotropic phase boundary region

The effect of mechanical stress on the direct piezoelectric properties of pre-poled (1 ? x)(Na_0.5Bi_0.5)TiO₃–xBaTiO₃ (NBT–xBT) in the range 4% ≤ x ≤ 13% was studied in situ using a mechanical load frame. Prior to mechanical loading, compositions near the morphotropic phase boundary (MPB, x = 6–7% BT) exhibited enhanced ferroelectric and piezoelectric properties compared to compositions further from the MPB. Specifically, the lowest ferroelectric coercive field and highest piezoelectric coefficient within this composition range occur at x = 7% BT. During mechanical compression, the MPB compositions exhibited the lowest depoling stress. The results demonstrate that, while favorable piezoelectric and ferroelectric properties can be obtained at compositions near the MPB, these compositions are also the most susceptible to the effects of mechanical depoling. Ferroelastic domain wall motion is suggested as the primary factor that may be responsible for these behaviors.     

Effect of anisotropy on stresses in rotating discs

Stresses and deformations resulting from centrifugal forces in rotating specially orthotropic circular plates are determined. The classical laminated plate theory is employed in the analysis, and the results are presented in a manner which illustrates the effect of anisotropy. The plate is assumed to be rigidly fixed to a concentric rod allowing no deformation in its central region. The outer boundary is either free of any constraints or the plate is placed in a stiff casing which prevents radial deformation. A stiffness ratio, which is defined as the ratio of circumferential stiffness to radial stiffness, is used as the parameter to indicate the degree of anisotropy. Having a stiffness ratio greater than one eliminated the stress build-up on the boundaries. Higher stiffness ratios reduced the compressive stresses which began to occur near the outer boundary when the boundary was restrained from radial expansion, thus contributing to stability against local buckling. The results of Tsai-Wu failure analysis also showed that the choice of a stiffness ratio higher than one gives higher resistance against ply failure in tension.     

Impact essential work of fracture toughness of ABS/polyamide-6 blends compatibilized with olefin based copolymers

The impact fracture toughness of acrylonitrile-styrene-butadiene/polyamide-6 (ABS/PA6) blends compatibilized with 5% by weight carbon monoxide modified ethylene-n butyl acrylate-maleic anhydride (EnBACO-MAH) or ethylene-methyl acrylate-glycidyl methacrylate (EMA-GMA) copolymers were examined as a function of blend ratio by standard Charpy tests, Essential Work of Fracture (EWF) Methodology and fracture surface morphologies. The samples were first processed in twin-screw extruder and they were subsequently injection moulded. The incompatibilized blends and neat-PA6 fractured in brittle manner, whereas compatibilized blends fractured in ductile manner. The EWF values yielded a maximum when weight percentages of ABS and PA6 were equal to each other. The values obtained in the case of EnBACO-MAH were higher than that of EMA-GMA regardless of blend composition in EWF tests. The trend of impact strengths observed in standard notched Charpy impact tests was in accordance with that of EWF values of blends. The morphology of the ABS/PA6 blends exhibited differences as a function of the component ratio and compatibilizer type. These differences in topology of the fracture surfaces of the blends were utilized to understand the deformation mechanism, and to correlate the fracture toughness values of the blends.     

Anisotropic etching of SiC whiskers

We have demonstrated a method of producing nanoplatelets or complex well-ordered nanostructures from silicon carbide (SiC) whiskers. Preferential etching of SiC whiskers in a mixture of hydrofluoric and nitric acids (3:1 ratio) at 100 degrees C results in the selective removal of cubic SiC and the formation of complex structures resembling a pagoda architecture. Possible mechanisms governing selective etching are discussed. Reproducible results on SiC whiskers manufactured in different laboratories suggest that the self-patterning phenomena are common in SiC whiskers, and the same electroless etching procedure can be used to synthesize various complex nanostructures from more conventional nano- and microscale objects for use as building blocks in the fabrication of sensors, cellular probes, and electronic, optoelectronic, electromechanical, and other devices.     

Nucleation and growth of graphene/Mo2C heterostructures on Cu through CVD

We investigated the chemical vapor deposition synthesis of Mo₂C/graphene heterostructures on a partially wetted liquid copper surface, studied the morphology of resulting phases using electron and optical microscopy, and determined the rate-limiting step for the growth of Mo₂C on graphene. The morphology of the Mo₂C crystals varied from the center to the edge of the copper substrate because of the change in the Mo diffusion pathways owing to the variation in the thickness of the Cu substrate. Thin, hexagonal-shaped crystals of Mo₂C were found in the central region, where Cu is the thickest. In addition, the growth pressure substantially affects the nucleation and growth kinetics of both Mo₂C and graphene. At high pressures (750 Torr), the graphene layer fully covered the Cu surface and Mo₂C crystals formed with a regular shape, while at low pressures (5 Torr), the nucleation of both domains was suppressed, leading to the evolution of Mo₂C crystals with irregular shapes. The activation energy for the growth of Mo₂C on graphene was calculated to be 3.76 ± 0.3 eV, and the diffusion of Mo to the Cu surface through uncovered Cu or graphene vacancies/defects was determined to be the rate-limiting step.