Injection and injection compression molding of ultra‐high‐molecular weight polyethylene powder

Ultra‐high‐molecular weight polyethylene (UHMWPE) powder was processed using injection molding (IM) with different cavity thicknesses and injection‐compression molding (ICM). The processing parameters of feeding the powders were optimized to ensure proper dosage and avoid jeopardizing the UHMWPE molecular structure. Dynamic mechanical analysis (DMA) and Fourier‐transform infrared spectroscopy tests confirmed that the thermal and oxidative degradations of the material were avoided but crosslinking was induced during melt processing. Tensile tests and impact tests showed that the ICM samples were superior to those of IM. Increased cavity thickness and ICM were helpful for reducing the injection pressure and improving the mechanical properties due to effective packing of the material. Short shot molding showed that the UHMWPE melt did not exhibit the typical progressive and smooth melt front advancements. Due to its highly entangled polymer chains structure, it entered the cavity as an irregular porous‐like structure, as shown by short shots and micro‐computed tomography scans. A delamination skin layer (around 300‐μm thick and independent of cavity thickness) was formed on all IM sample surfaces while it was absent in the ICM samples, suggesting two different flow behaviors between IM and ICM during the packing phase. POLYM. ENG. SCI., 59:E170–E179, 2019. © 2018 Society of Plastics Engineers     

The copper sulfide coating on polyacrylonitrile with a chelating agent of ethylenediaminetetraacetic acid by an electroless deposition method and its EMI shielding effectiveness

In this study, a copper sulfide layer was instantaneously coated on the polyacrylonitrile (PAN) by an electroless plating method with the reduction agents NaHSO₃ and Na₂S₂O₃·5H₂O and a chelating agent (ethylenediaminetetraacetic acid, EDTA). A variety of concentrations of EDTA was added to obtain the anchoring effect and chelating effect in the electroless plating bath. The mechanism of the Cu_{x(x = 1, 2)}S growth and the electromagnetic interference shielding effectiveness (EMI SE) of the composite were studied. It was found that the vinyl acetate was residual in PAN substrate would be purged due to the swelling effect by EDTA solution. Then, the anchoring effect occurred due to the hydrogen bonding between the pits of PAN substrate and the chelating agent. Consequently, the copper sulfide layer deposited successfully by the electroless plating reacted upon EDTA. The swelling degree (S_d) was proposed and evaluated from the FTIR spectra. The relationship between swelling degree of the PAN composite and EDTA concentration (C) is expressed as follows: S_d = 0.13 + 0.90 × e^(?15.15C). On the other hand, the FESEM micrograph showed that the average thickness of copper sulfide increased from 76 to 383 nm when the concentration of EDTA increased from 0.00 to 0.20M. For this reason, the EMI SE of the composites increased from 10–12 dB to 20–23 dB. The GIA‐XRD and laser Raman analysis indicated that the deposited layer consisted of CuS and Cu₂S. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of alkyl group on the chain extension of phosphites in polylactide

Polylactide (PLA), which is synthesized from natural resources and can degrade easier, possesses high mechanical strength, so it is a reasonable substitute for petroleum‐based plastics. Phosphites can increase the stability of PLA through chain extension with the hydroxyl and carboxyl groups simultaneously. But there are few reports on the structural effects of phosphites on the chain extension of PLA. In this article, three kinds of phosphites with different amounts of aryl and alkyl groups were used as chain extenders in PLA and were compared in detail. The molecular weights, complex viscosities, and storage moduli of virgin PLA and PLA stabilized by three different phosphites were characterized by gel permeation chromatography and rheometry. The results show that the presence of alkyl groups is not beneficial for chain extension, as the more alkyl groups there are, the worse the chain extension is. Regarding the three phosphite chain extenders added to PLA—triphenylphosphite (TPP), diphenylisooctylphosphite (PTC), and phenyldiisooctylphosphite (PDOP)—the number of alkyl groups in them can be ranked as follows: PDOP > PTC > TPP. Since PDOP had the most alkyl groups, the chain extension of PDOP was the weakest. In addition, the product, which was formed due to the chain extension of PLA and TPP, had some plastication, thus enabling PLA to move more freely and making it easier to process. J. VINYL ADDIT. TECHNOL., 25:144–148, 2019. © 2018 Society of Plastics Engineers     

Study of injection molded microcellular polyamide‐6 nanocomposites

This study aims to explore the processing benefits and property improvements of combining nanocomposites with microcellular injection molding. The microcellular nanocomposite processing was performed on an injection‐molding machine equipped with a commercially available supercritical fluid (SCF) system. The molded samples produced based on the Design of Experiments (DOE) matrices were subjected to tensile testing, impact testing, Dynamic Mechanical Analysis (DMA), and Scanning Electron Microscope (SEM) analyses. Molding conditions and nano‐clays have been found to have profound effects on the cell structures and mechanical properties of polyamide‐6 (PA‐6) base resin and nanocomposite samples. The results show that microcellular nanocomposite samples exhibit smaller cell size and uniform cell distribution as well as higher tensile strength compared to the corresponding base PA‐6 microcellular samples. Among the molding parameters studied, shot size has the most significant effect on cell size, cell density, and tensile strength. Fractographic study reveals evidence of different modes of failure and different regions of fractured structure depending on the molding conditions. Polym. Eng. Sci. 44:673–686, 2004. © 2004 Society of Plastics Engineers.     

Estimation of left ventricular end-diastolic pressure with the difference in pulmonary venous and mitral A durations is limited when mitral E and A waves are overlapped

Previous studies showed that difference in pulmonary venous and mitral A-wave durations can be used for the estimation of left ventricular end-diastolic pressure, which is based on the assumption that the pulmonary venous A wave and mitral A wave start with the beginning of left atrial contraction. It is also assumed that the mitral A wave ends with the end of left atrial contraction. These assumptions may not be correct if left atrial contraction occurs before the early left ventricular filling is completed. Adequate Doppler mitral inflow and pulmonary venous flow signals were obtained simultaneously with left ventricular pressures at the cardiac catheterization laboratory in 50 patients who showed separated E and A waves in mitral inflow. After heart rate was increased by right atrial pacing to make the mitral E and A waves overlap, Doppler and hemodynamic measurements were repeated. When E and A waves are separated, pulmonary A-wave duration exceeding mitral A-wave duration has a sensitivity of 67% and specificity of 85% in the prediction of elevated left ventricular end-diastolic pressure (>/=20 mm Hg), whereas the pulmonary A wave ending later than mitral A wave has a sensitivity of 83% and a specificity of 45%. When the mitral E and A waves are overlapped, the pulmonary A wave ending later than mitral A wave is better for the prediction of elevated left ventricular end-diastolic pressure (sensitivity 55%, specificity 75%) than pulmonary A-wave duration exceeding mitral A-wave duration (sensitivity 9%, specificity 96%). However, overall, both methods are limited for clinical use.     

Activation of alpha 2-adrenoceptors causes inhibition of calcium channels but does not modulate inwardly-rectifying K+ channels in caudal raphe neurons

Many neurotransmitter receptors that interact with pertussis toxin-sensitive G proteins, including the alpha 2-adrenergic receptor, can modulate both voltage-dependent calcium channels and G protein-coupled inwardly-rectifying K+ channels. Serotonergic neurons of the medulla oblongata (nucleus raphe obscurus and nucleus raphe pallidus), which provide a major projection to sympathetic and motor output systems, receive a catecholaminergic input and express alpha 2-adrenergic receptors. Therefore, we tested the effects of norepinephrine on voltage-dependent calcium channels and G protein-coupled inwardly-rectifying K+ channels in neonatal raphe neurons using whole-cell recording in a brainstem slice preparation. Calcium channel currents were inhibited by norepinephrine in the majority of raphe neurons tested (88%) and in all identified tryptophan hydroxylase-immunoreactive (i.e. serotonergic) neurons. When tested in the same neurons, the magnitude of calcium current inhibition by norepinephrine (approximately 25%) was less than that induced by 5-hydroxytryptamine (approximately 50%). The norepinephrine-induced calcium current inhibition was mediated by alpha 2-adrenergic receptors; it was mimicked by UK 14304, an alpha 2-adrenergic receptor agonist and blocked by idazoxan, an alpha 2-adrenergic receptor antagonist, but not affected by prazosin or propanolol (alpha 1 and beta adrenergic antagonists, respectively). Calcium current inhibition by norepinephrine was essentially eliminated following application of omega-Conotoxin GVIA and omega-Agatoxin IVA, indicating that norepinephrine modulated N- and P/Q-type calcium channels predominantly. Calcium current inhibition by norepinephrine was voltage-dependent and mediated by pertussis toxin-sensitive G proteins. Thus, as expected, alpha 2-adrenergic receptor activation inhibited N- and P/Q-type calcium currents in medullary raphe neurons via pertussis toxin-sensitive G proteins. In parallel experiments, however, we found that norepinephrine had no effect on G protein-coupled inwardly-rectifying K+ channels in any raphe neurons tested, despite the robust activation of those channels in the same neurons by 5-hydroxytryptamine. Together, these data indicate that alpha 2-adrenergic receptors can modulate N- and P/Q-type calcium channels in caudal medullary raphe neurons but do not couple to the G protein-coupled inwardly-rectifying K+ channels which are also present in those cells. This is in contrast to the effect of 5-hydroxytryptamine1A receptor activation in caudal raphe neurons, and indicates a degree of specificity in the signalling by different pertussis toxin-sensitive G protein-coupled receptors to voltage-dependent calcium channels and G protein-coupled inwardly-rectifying K+ channels even within the same cell system.     

Whole-body and pinhole bone scintigraphic manifestations of Reiter''s syndrome: distribution patterns and early and characteristic signs

The characteristic whole-body and pinhole scintigraphic manifestations of osteo-enthesopathy and arthropathy in Reiter's syndrome (RS) are described, with an emphasis on early diagnosis. We analysed 59 sets of whole-body and pinhole bone scintigrams of 59 patients with RS. The population comprised 47 men and 12 women with an age range from 15 to 53 years (mean=29.4). Bone scintigraphy was carried out 2-2.5 h after intravenous injection of technetium-99m hydroxydiphosphonate using a single-head gamma camera (Siemens Orbiter Model 6601) with a low-energy high-resolution and a 4-mm pinhole collimator for whole-body and pinhole scintigraphy, respectively. In total 262 lesions of osteo-enthesopathy and arthritis were detected on 59 whole-body scintigrams, an incidence of 4.4 lesions per patient. As anticipated, the lesional distribution was asymmetrical: 68% were in the lower limb skeleton and 32% in the axial and upper limb skeleton. Pinhole bone scintigraphy, applied selectively to one region of interest in each case, enabled us to accurately diagnose arthritis and osteo-enthesopathy. It was noteworthy that osteo-enthesopathy, alone or in combination with arthritis, occurred in 78.9%, and had a strong predilection for the foot bones, especially the calcaneus (25. 6%). Pinhole scintigraphy detected enthesopathy in the absence of radiographic alteration in 14.1% of cases and portrayed characteristic signs of RS in 6.9%. Whole-body bone scintigraphy augmented with pinhole scintigraphy was found to be useful in order to panoramically display the systemic involvement pattern, to assess the characteristic bone and articular alterations and to detect early signs of RS.     

Phytotoxicity and cytotoxicity of the fumonisin C and P series of mycotoxins from Fusarium spp. fungi

Fumonisin C (FC) and P (FP) are two recently identified series of sphingosine-analog mycotoxins, for which biological activities have not previously been reported. FC1, FC2 and OH-FC1 (1 microM) exhibited strong phytotoxicity comparable to the standard FB1 in duckweed (Lemna pausicotata L.) cultures, whereas FC3 and FC4 were moderately phytotoxic. Conversely, FP1 exhibited weak phytotoxicity only at higher concentrations (> or =10 microM). These mycotoxins exhibited a similar pattern of cytotoxicity with FB1-sensitive cultured mammalian cell lines, H4TG and MDCK.     

Injection molding of delamination‐free ultra‐high‐molecular‐weight polyethylene

When ultra‐high‐molecular‐weight polyethylene (UHMWPE) in powder form is injection molded, the so‐called delamination layering occurs near the skin of the parts. This layering defect hampers UHMWPE's superior wear resistance property and part surface quality. The delamination layer was caused by a combination of excessive shear stress near the part surface and high degree of molecular entanglement of UHMWPE. A mold insulation method that delays the rapid cooling of UHMWPE to reduce the shear stress and improve the polymer chain “interdiffusion” across the entangled chain bundles was used to eliminate the delamination layer. When the insulation layer thickness and mold temperature were optimized, the delamination layer was eliminated completely while still maintaining a reasonable cooling/cycle time. The delamination‐free parts were found to regain UHMWPE's superior impact resistance and tensile properties. POLYM. ENG. SCI., 59:2313–2322, 2019. © 2019 Society of Plastics Engineers