Characterization of microporous ECTFE membranes exposed to different liquid media and ?-radiation and nanoparticle microfiltration through such membranes

Microporous polymeric membranes are used in a variety of applications for separations, purification as well as barrier function. A major application is for microfiltration (MF). Changes in the properties of MF membranes exposed to acids, bases and organic solvents are of interest in semiconductor processing as well as in membrane contactor applications. Microfiltration membranes used for sterilization in beverage, biotechnology and pharmaceutical industries are sterilized by gamma radiation among others. Irradiation-induced degradation in membrane properties should be known. A variety of fluoropolymer-based microporous membranes are available with varying properties. Ethylene chlorotrifluoroethylene (ECTFE) membranes are a new addition and are of potential interest. Microporous membranes of ECTFE membranes subjected to caustic soaking, organic solvent soaking and γ-irradiation were characterized extensively and compared with widely-used polyvinylidene fluoride (PVDF) membranes for selected properties. ECTFE membrane swellings by seven solvents including tri-n-octylamine (TOA) were much larger than those of nonporous ECTFE films. Scanning electron microscopy (SEM), atomic force microscopy (AFM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) indicated significant defects in TOA-soaked membranes. Bubble-point-pressure (BPP) based maximum pore diameters of selected solvent-soaked ECTFE membranes are in good agreement with the pore size distribution estimated from AFM. Fourier transform infrared and Raman spectroscopies were used to study the solvent-membrane interactions: TOA introduced C-H stretching and deformation. Thermogravimetric analysis (TGA) and DSC confirmed TOA presence in membrane pores. Solvents tetrahydrofuran, toluene, acetonitrile and TOA decreased Young’s modulus by 6 to 30%. ECTFE membranes resisted plasticization by these solvents: glass transition temperature variations were limited. In TOA-treated membranes, XRD indicated more significant defects in PVDF membranes. Treatment with NaOH solutions showed no effect on contact angle and BPP. Only 3M caustic solution reduced liquid entry pressure by 13.8 kPag. ECTFE membranes showed greater hydrophobicity, stronger wetting resistance and better ability to maintain hydrophobicity vis-à-vis PVDF membranes. ECTFE membranes subjected to γ-radiation (up to 45 kGy) showed almost no effect on morphology, porosity and Young’s modulus. Slight variations were observed in BPP, melting enthalpy obtained via DSC and energy loss measured in dielectric relaxation spectroscopy. The solvent resistance of ECTFE membranes, especially to TOA, is important especially in membrane solvent extraction in the presence of diluents e.g., xylene. Many characterization techniques were employed to study solvent-treatment effects on ECTFE membranes exposed to ethanol, xylene, xylene80/TOA20 and pure TOA. Membrane-surface roughness of virgin, ethanol-soaked and TOA-soaked membranes indicated: TOA-soaked membranes were the roughest, followed by ethanol-soaked and virgin ones. Bubble-point-pressure based maximum pore diameters (dmax) of solvent-treated membranes were: dmax, TOA \u3e dmax, Xylene/TOA \u3e dmax, Xylene \u3e dmax, Ethanol \u3e dmax, Virgin. In FTIR and Raman spectra, TOA introduced extra peaks contributing to C-H stretching and deformation. Raman spectra of xylene80/TOA20-soaked membrane were a combination of those of xylene and TOA. The presence of a large amount of diluent reduces the impact of TOA on ECTFE membranes. In dead-end MF, fouling mechanisms behaved differently for virgin and TOA-soaked membranes; filtrate particle size distributions agreed well with estimated pore sizes. The values of permeance (kg/m2-s-kPa) determined from the slope of the linear plot of filtration flux vs. the applied pressure difference across the membrane, were 0.39, 0.23 and 0.03 for methanol, ethanol and 2-propanol, respectively. In cross-flow MF using silica nanoparticles suspended in 25% ethanol solution, Particle agglomerates having less than 100 nm size can pass through the membrane; some fouling was observed. The governing fouling mechanisms for tests operated using 3.8 ppm at 6.9 kPag (1 psig) and 13.8 kPag (2 psig) were pore blocking; for tests conducted using 3.8 ppm at 27.6 kPag (4 psig ) and 1.9 ppm at 6.9, 13.8 and 27.6 kPag (1, 2 and 4 psig), the mechanism was membrane resistance controlled. Less particles got embedded in membrane pores in experiments operated using suspensions with lower concentrations or higher concentrations with a higher transmembrane pressure. This is in good agreement with the values of the shear rate in the pore flow and SEM images of the membrane after MF

Long-term effects of thermal variation on the performance of Balanced Twisted Pair Cabling

Remote powering over the Ethernet (including PoE, PoE+ and PoE++) is currently trending as a cost-effective option to power networked devices using balanced twisted pair cabling. As technology advances and Ethernet penetration grows, more devices are deployed, thereby increasing the cabling density to support these devices. Power delivery through Ethernet cables has numerous benefits, including cost and space saving. However, concurrent high-power transmission and installation conditions could induce local heating, and thus, thermal variation may occur in the cable bundles, and these can be exacerbated by the installation conditions, and sometimes by extreme weather conditions. Over a long time, all these could modify the cable properties, thus affecting the performance of the cabling system and thereby impacting the Ethernet signal integrity. Although Joule heating of the cable bundle is primarily assumed to be concomitants of current transmission through the cable, several fundamental questions around these processes are not yet fully answered. They include: Do cable heating and thermal variations influence the designed transmission parameters of the cable? If yes, how can the cause(s) and effects be accurately measured and reliably validated? In answering some of these questions, a series of experiments were developed and adopted to (1) assess cable bundle heating (2) assess the performance of Balanced Twisted Pair cables subject to repeated thermal variation, both within the specified operating range and beyond to account for the situations where high temperature and localised heating might stress the cables beyond the designed or expected levels (3) assess the performance of Ethernet cable dielectrics to understand some of the root causes of Ethernet cable performance degradation. The outcome of the research showed that high power (100 watts) deployment over bundled and insulated unshielded Ethernet cables triggered an extremely high-temperature increase (~ 1400C) that resulted in mechanical failure of the cables’ dielectrics and a short circuit between the copper conductors of the cables. Larger cable conductor size, screening of the twisted pair along with Fluoropolymers as the conductor insulation helped the shielded cables not to reach a point of failure when tested in the insulated environments and at high power levels even though there was a temperature rise on the cables. Moreover, repeated resistive and non- resistive heating have adverse effects on the electrical properties and transmission parameters of Balanced Twisted Pair cables, most notably in the first few cycles. The impact was more pronounced during the cooling phase than the heating phase. Also, the thermal impact was more accentuated in insulated operating condition than in ventilated operating condition. The electrical length of the cable measured by the tester decreased by 0.7 m 5 due to the effect of repeated non-resistive heating in an insulated environment and at a high temperature of ~1200C but decreased by 0.4 m with ~700C in a similar insulated environment. Phase drifts in Balanced Twisted Pair cables were observed to be dependent on the combined effects of mechanical dimension, dielectric constant and frequency. Thermal variation caused a phase change in the Return Loss (RL) signal from 630 to 900, from 900 to 1350 and from 1350 to 3150 respectively. The RL performance of Category 6 U/UTP CoMmunications Plenum rated (CMP) cable failed at 200C and recovered at 230C initially, but after the electrical length of the cable had decreased, subsequent failure and recovery temperatures accelerated towards higher temperature (400C). Similarly, the transition temperatures of the bandwidth of the cavity loaded with the Fluorinated Ethylene Propylene (FEP) from the Category 6 U/UTP CMP cable accelerated during the prolonged thermal cycling. The maximum reduction in the RL value of Category 6A F/UTP cable due to the 40 thermal cycles conducted was observed to be 5 % per degree, whereas the maximum Insertion Loss (IL) increase was 5.8 % per degree. Moreover, for the 24 thermal cycles conducted on Category 6 U/UTP CMP cable, an increase in IL of ~8.3 % per degree was observed while RL decreased by ~6.8 % per degree. Using the Features Selective Validation technique, the comparison between the baseline performance and long-term performance of Category 6A F/UTP permanent link (PL) showed a fair agreement, which implies degradation in the performance of the cable. Furthermore, results showed that impedance varied significantly along the length of the cable due to localised heating of the cable. The impedance along the unheated sides of the cable reverted at every 2 (0.4 m) and 4 (0.2 m) but the impedance profile of the heated middle portion of the cable varied significantly. The results of the Scanning Electron Microscope revealed the deformation in the conductor insulation of a twisted pair sample. Furthermore, the adhesion of the twisted pair conductor insulation to its copper conductor was also observed to be affected near the end of the twisted pair sample. Connector impedance mismatch was observed to be severe on the split pair pins (pair 3,6) than other pairs in the cable. The connector impedance mismatch also dominated the Near End Crosstalk (NEXT) loss at frequencies around 35 MHz. The repeated heating of the cable to a higher temperature of 1200C caused the loss of the PL at room temperature and a DC contact resistance issue which of course resulted in poor intra-pair resistance unbalance between the split pair. The Transverse Conversion Loss (TCL) and Equal Level Transverse Conversion Transfer Loss (ELTCTL) of Category 6 U/UTP CMP PL revealed some imbalances in the structure of the twisted pairs. Also, the equivalent differential mode noise voltages for the TCL values of the cable revealed a voltage spike following the decrease in the electrical length of the cable. More also, Crosstalk performance between the longest and shortest pair in the Category 6A 6 F/UTP cable was also observed to be better due to the heating of the cable in comparison to the crosstalk loss measured due to the cooling of the cable. Crosstalk performance of the portion insulated cables was initially worse during the first few heating and cooling cycles but improved afterwards. In addition, crosstalk, which was not initially present at the reference plane of the permanent link, was observed to increase rapidly from the point where the electrical length decreased. The increase in temperature to ~650C caused an accentuated frequency shift in the resonance of the FEP, which is the probable cause of the immediate performance degradation of the Category 6 U/UTP CMP cable. The dielectric constant of the extracted FEP rod sample from Category 6 U/UTP CMP cable increased as a consequence of prolonged thermal cycling, particularly during the cooling phase, which also suggests the root cause of the poor RL performance observed during the cooling phase. The increased loss tangent of the FEP during thermal cycling also indicates that IL performance degradation of the Ethernet cables will increase during the heating and cooling process in Ethernet cables. Also, on a long-term, IL performance will drift due to thermal cycling. Furthermore, various signal phase transitions were recorded during the heating and cooling of the cable and its dielectric due to the different behaviour of the molecular transitions. As a result, an echo of RL was measured during the transition between the intermittent and prolonged thermal cycling of the cable, of which can be correlated to the spurious resonance, observed in the resonance of the FEP sample during the transition period. Thus, it could be inferred that immediate and longterm effects of thermal variation influence the designed electrical properties and transmission parameters of Balanced Twisted Pair cables. Also, an immediate and long-term effect of thermal variation on the conductor insulation of the cable has a direct effect on the performance of Balanced Twisted Pair Cables