Analogy between adsorption and sorption:An elementary mechanistic approach.I.Monolayer adsorption and sorption without solvent cluster formation

The elementary mechanistic model of adsorption and sorption is based on a simple hypothesis:the adsorption sites are uniformly distributed on the surface of the pore walls in the adsorbent,the sorption sites are uniformly distributed in the volume of the polymer.In this first paper we will analyze the simple case where one solute mol-ecule is only allowed to occupy a single adsorption or sorption site.A common elementary occupation law of the free sites is assumed:the differential increase of the number of the adsorbed/sorbed molecules is proportional to the differential increase of the activity of the solute and the concentration of the free(non-occupied)sites in the solid.The proportionality coefficient is called affinity coefficient depending on the solid/solute couple and on the temperature and independent of the concentration of the solute.In adsorption the concentration of the free sites is a surface concentration on the pore walls and in sorption it is expressed by the molarity.The simple mono-layer adsorption law of Jovanovi?is obtained:n=n0(1?e?KP)where n is the number of moles adsorbed when the pressure is P. n0is the total number of adsorption sites and K the affinity coefficient for adsorption.The sorption law writes:a= 1k? ?1??]+1?rk ln?1+1r?1??]where?,r and k hold respectively for the volume fraction of the solvent in the polymer,for the ratio of the molar volumes of the solvent to the elementary polymer chain containing one single adsorption site and for the sorption affinity coefficient.The confrontation of these equations to experimental isotherms is satisfactory in comparison with the classical Langmuir and Flory-Huggins equations:the best results are obtained for adsorption of vapors on a 5A zeolite and for all analyzed sorption results.     

Transport of helium in polycarbonate membranes

The transport of helium in membranes of poly(bisphenol A carbonate-co-4,4′-(3,3,5-trimethylcyclohexylidene)diphenyl carbonate) (PBCDC) is reported. The experimental values of the diffusion and permeability coefficients, under the upstream pressure of 176 cmHg, are (10.9±0.7)×10⁻⁶ cm² s⁻¹ and 61.4±0.5 barrers, respectively, at 30°C. Both coefficients obey Arrhenius behavior with activation energies of 1.9 and 3.0 kcal mol⁻¹, respectively. The dynamics of helium in the membranes was simulated using the transition state approach (TSA). Very good agreement between the theoretical and experimental values of the diffusion coefficient was found. However, the simulated solubility coefficient is nearly one order of magnitude higher than the experimental value.     

Preparative fractionation and characterization of polycarbonate/eugenol-siloxane copolymers

Bisphenol-A polycarbonate/eugenol-siloxane copolymers were fractionated at the preparative scale by the continuous polymer fractionation (CPF) technique. It is the first example of copolymer fractionation by CPF. The distribution of siloxane species across the fractions was assessed for copolymers differing in initial siloxane concentration and block length. On- and off-line combinations of size exclusion chromatography and infrared spectroscopy were used to analyze chemical composition (CC) of the unfractionated samples across the molecular weight distribution enabling comparison with the fractions. A polycarbonate-siloxane copolymer containing 10 wt% of very short siloxane blocks (dp=2) was fractionated solely according to molecular weight (MW). By contrast, a copolymer containing 5 wt% siloxane blocks with a larger degree of polymerization (dp=23) was fractionated according to MW, as well as to CC. This ‘chemical drift’ effect for the larger siloxane block length can be ascribed to large solubility differences of low MW chains, which drastically vary in composition according to the (small) number of siloxane blocks they contain.     

Synthesis and flame retardancy of phosphorus containing polycarbonate

Novel P-containing copolycarbonate was prepared via melt polycondensation of diphenyl carbonate (DPC), bisphenol-A (BPA) and 2-(6-oxid-6H-dibenz〈;c,e〉〈1,2〉oxa-phosphorin-6-yl)-1,4-benzenediol (ODOPB). The copolycarbonates were characterized by infra-red spectra, reduced viscosity, and differential scanning calorimetry. The copolycarbonates with reduced viscosities of 0.21∼0.25 dL/g were obtained in quantitative yields. These phosphorus containing copolycarbonates have excellent thermal and flame retardant properties. Owing to the incorporation of the rigid structure of ODOPB and the pendant P group, the resulting phosphorus containing copolycarbonates exhibited better flame retardancy, higher char yield, higher degradation temperature and thermal stability than homopolymers of polycarbonate (PC). High LOI value and UL 94-VO rating could be achieved with a phosphorus content of as low as 0.75% for PC, and no fumes or toxic gas emissions were observed.     

Solubility and diffusion coefficient of supercritical-CO2 in polycarbonate and CO2 induced crystallization of polycarbonate

The solubility and diffusion coefficient of supercritical CO₂ in polycarbonate (PC) were measured using a magnetic suspension balance at sorption temperatures that ranged from 75 to 175 °C and at sorption pressures as high as 20 MPa. Above certain threshold pressures, the solubility of CO₂ decreased with time after showing a maximum value at a constant sorption temperature and pressure. This phenomenon indicated the crystallization of PC due to the plasticization effect of dissolved CO₂. A thorough investigation into the dependence of sorption temperature and pressure on the crystallinity of PC showed that the crystallization of PC occurred when the difference between the sorption temperature and the depressed glass transition temperature exceeded 40 °C (T − T_g ≥ 40 °C). Furthermore, the crystallization rate of PC was determined according to Avrami's equation. The crystallization rate increased with the sorption pressure and was at its maximum at a certain temperature under a constant pressure.     

Siloxane modification of polycarbonate for superior flow and impact toughness

Reactive modification of polycarbonate (PC) with a small amount of ultra-high molecular weight polydimethylsiloxane (PDMS) provides an effective route to a novel blend polymer with superior flow and excellent impact toughness. Low temperature impact toughness for such a blend was found to be comparable to polycarbonate copolymers made by interfacial copolymerization of bisphenol A and specialty silicones with phosgene. Interestingly, the blend also showed strong shear thinning behavior and a viscosity that is almost an order of magnitude lower than the starting PC resin. Analysis of the blend composition and blend morphology revealed the presence of both PC-PDMS copolymer and un-grafted siloxane as a dispersed phase in the polycarbonate matrix. The PC-PDMS copolymer provides a compatibilization effect for the stable sub-micron blend morphology in an otherwise immiscible PC-PDMS blend system. Improvement of low temperature ductility (e.g., at −40 °C) by PDMS was thus made possible. The lubricating effect from siloxane and the possibility of fibrillation flow at high shear stress are suspected to be the main reasons for high flow characteristics of these blends.     

Electrodeposition of cobalt based ferro-magnetic metal nanowires in polycarbonate films with cylindrical nanochannels fabricated by heavy-ion-track etching

Polycarbonate films of thickness 30 μm were irradiated with heavy ions by applying a flux of 10⁸ ions cm⁻² to produce straight tracks perpendicular to the film surface. The tracks were preferentially etched in 6 M aqueous solution of sodium hydroxide to prepare cylindrical nanochannels. The channel diameters were tuned between 200 and 600 nm by varying the etching time. Co₈₁Cu₁₉ alloy nanowires were electrodeposited potentiostatically, while Co/Cu multilayered nanowires, consisting of alternating Co and Cu layers with thickness 10 nm, were synthesized by means of a pulse plating technique in channels of length 30 μm and diameter 200 nm. Co₈₁Cu₁₉ alloy nanowires showed an anisotropic magnetoresistance effect of 0.6%, and the giant magnetoresistance of Co/Cu multilayered nanowires reached up to 8.0%.     

Crystallization of polycarbonate induced by spinodal decomposition in polymer blends

We found that amorphous polycarbonate (PC) can be crystallized in several minutes by blending poly(ethylene oxide) (PEO). When the blends were annealed in the two-phase region below the upper critical solution temperature, highly interconnected two-phase structure characteristic of the spinodal decomposition was developed and then the crystallization occurred in the PC-rich phase during the spinodal decomposition. As the molecular weight of PEO decreased, the crystallization rate decreased and the crystallizable temperature became narrower in spite of the acceleration of the polymeric segmental motion. These results suggest that the crystallization of the PC is not induced by the acceleration of the polymeric segmental motion, but by the up-hill diffusion of the liquid-liquid phase separation via spinodal decomposition. Owing to the competitive progress of the crystallization and the spinodal decomposition, the melting peak of the PC crystallites shifted to lower temperature with increasing annealing temperature.     

Thermally induced redistribution and degradation of bisphenol-A polycarbonate fractions in open and closed systems

Thermally induced chain-scission and redistribution reactions in as-polymerized and fractionated bisphenol-A polycarbonate (PC) materials made by melt-transesterification and interfacial polymerization were studied at temperatures between 200 and 300 °C in open systems, where volatile reaction products are continuously removed, and in closed systems, where these products are retained. Under the applied conditions, PC made via interfacial polymerization shows no measurable susceptibility towards redistribution. This is the result of an extremely low concentration of hydroxyl end-groups. Upon similar thermal treatment, PC made by melt-transesterification undergoes fast redistribution which leads to post-condensation in open systems and strong changes of molecular weight distributions (MWDs) for fractions in all cases. Redistribution effects were visualized through changes in the MWD of mixed fractions. The initial stages of redistribution were simulated using a Monte Carlo method based on a random sampling technique. From comparison between experimental and simulation results, it can be concluded that approximately half a percent of all carbonate linkages is involved in a redistribution reaction per minute at 250 °C for the studied samples.     

Morphology and properties of melt-spun polycarbonate fibers containing single- and multi-wall carbon nanotubes

Polycarbonate fibers based single wall and multi-wall nanotubes (SWNT and MWNT) were prepared by first dispersing the nanotubes via solvent blending and/or melt extrusion followed by melt spinning the composites to facilitate nanotube alignment along the fiber axis. Morphological studies involving polarized Raman spectroscopy and wide angle X-ray scattering using a synchrotron radiation source show that reasonable levels of nanotube alignment are achievable. Detailed transmission electron microscopy (TEM) investigations on the polymer-extracted composite fibers reveal that MWNT more readily disperse within the PC matrix and have higher aspect ratios than do SWNT; extraction of the polymer from the composite prior to TEM imaging helps overcome the common issue of poor atomic contrast between the CNT and the organic matrix. Stress-strain analysis on the composites fibers show that MWNT, in general, provide greater stiffness and strength than those based on SWNT. Despite significant reinforcement of the polycarbonate, the level of reinforcement is far below what could be achieved if the nanotubes were completely dispersed and aligned along the fiber axis as predicted by composite theory.     

High resolution,quasi-equilibrium sorption studies of molecular sieves

Argon, nitrogen, and neopentane adsorption isotherms from molecular sieves are recorded at 87 K, 77 K, and 273 K, respectively, by a quasi-equilibrium, high resolution gas sorption technique. The molecular sieves used in this study are alkali exchanged zeolite X, AlPO₄-11, AlPO₄-5, VPI-5, KL, CaA, ZSM-5, and ZSM-11. Little relation is observed between the transition pressure for microporous nitrogen adsorption and pore size. Small changes in the effective pore size resulting from variations in cation size are detected in the transition pressure for argon adsorption. Large shifts in the transition pressure for argon adsorption are found for the 10-, 12-, and 18-membered ring pores of AlPO₄-11, AlPO₄-5, and VPI-5, respectively. Argon adsorption combined with neopentane adsorption on microporous materials provides additional information regarding transitions in the isotherm that result from dual pore systems and effects that may be due to adsorbate packing. The step in the nitrogen isotherm atP/P ₀> 0.1 from ZSM-5 is not observed in the nitrogen isotherm from ZSM-11.     

Synthesis and characterization of transparent alumina reinforced polycarbonate nanocomposite

Transparent nanocomposite films were fabricated by blending a concentrated nanocomposite formed by in-situ polymerization of polycarbonate in the presence of alumina nanowhisker with a high molecular weight polycarbonate. Polycarbonate was grafted to the alumina nanowhisker surface to improve nanofiller dispersion and load transfer to polymer matrix. Fourier transform infrared spectroscopy confirmed the functionalization of the nanowhisker with polycarbonate. Samples produced using functionalized alumina exhibited improved dispersion compared to the raw alumina nanowhiskers in the PC. Functionalization of alumina nanowhisker enhanced tensile properties (Young’s modulus and tensile strength) relative to the pure polycarbonate and blends produced with raw alumina nanowhisker. Additionally, the nanocomposite formed using in-situ polymerization showed small decreases in transparency in the visual range compared to the base polymer with increased absorption in the UV range. The effect of reaction temperature during in-situ polymerization on the properties of the nanocomposite was investigated. Higher reaction temperature resulted in improved dispersion and sharp increases in tensile modulus and shear strength.     

Miscibility study of polycarbonate and SBS triblock copolymer blends

Polymer blends of Polycarbonate (PC) and Styrene-Butadiene-Styrene triblock (SBS) have been investigated. SBS copolymers have four different styrenic contents, three of which are linear SBS. PC and PS blends are partially miscible as revealed by dynamic mechanical analysis with two clear Tgs near 100–150°C. On the contrary, PC/SBS blends have only one Tg with a left shoulder. Based on the PS domain model of pure SBS, we suggest a micelle model based on the structure when the micelle and absorb PC in the PC/SBS blends. The micelle plays an important role in improving the miscibility. The proposed micelle model has been empolyed to interpret the testing results, such as toughness, impact strength, dynamic mechanical property and SEM morphologies. This proposed micelle model seems a worth-while method to explain the properties of partialtly miscible blends of PC and SBS.     

Polycarbonate and co-continuous polycarbonate/ABS blends: influence of specimen thickness

The influence of specimen thickness on the fracture behaviour of polycarbonate (PC) and co-continuous PC/ABS (50/50) blends was studied in single edge notch tensile tests at 1 m/s and different temperatures (−80 to 130 °C). Specimen thickness ranged from 0.1 to 8 mm. In the co-continuous PC/ABS blends the rubber concentration in the ABS was 0, 15 and 30 wt%. The change in fracture toughness was typified by the change in brittle-to-ductile transition temperature (T_bd).T_bd of pure PC depended strongly on specimen thickness, leading to very low transition temperatures for thin PC specimens. PC/ABS 0%, a 50/50 blend of PC and SAN (i.e. ABS without polybutadiene (PB)), was a brittle blend and showed a very high T_bd close to the T_g of SAN. T_bd did not seem to be influenced by specimen thickness. PC/ABS blends with 15 and 30% PB in ABS showed improved T_bd compared to PC/SAN and PC, indicating effective rubber toughening. T_bd decreased with decreasing thickness for PC/ABS specimens thicker than 1.5 mm. However, T_bd increased with decreasing thickness for specimens below 1.5 mm thickness. In thin specimens, the rubber-filled blend is less effective rubber toughening. The plane strain stress condition needed for rubber cavitation is apparently not present in thin specimens.     

Location-selective incorporation of multiwalled carbon nanotubes in polycarbonate microspheres

In this study, we describe a process to produce polycarbonate (PC) microspheres and incorporate multiwalled carbon nanotubes (MWCNTs) within them location-selectively. The process, an oil-in-water (O/W) emulsion method, entails the formation of an aqueous phase with poly(vinylpyrrolidone) (PVP) and a methylene chloride phase that dissolves PC. Uniform PC microspheres were prepared by forming a stable emulsion using a homogenizer and a steric stabilizer, PVP. With this process, MWCNTs can be location-selectively incorporated in PC microspheres to afford the required properties such as electrical conductivity and thermal stability. When MWCNTs were dispersed in an aqueous phase using PVP, they were incorporated only on the surface of the PC microspheres. However, PC microspheres incorporating MWCNTs inside them were fabricated when the MWCNTs were dispersed in methylene chloride by functionalizing them via alkylation.     

Comparative sorption equilibrium studies of toxic phenols on flyash and impregnated flyash

In the present study, the sorption of toxic phenols, which include phenol, o-cresol, m-cresol, p-cresol, o-nitrophenol, m-nitrophenol and p-nitrophenol, has been investigated. The influences of various factors, such as particle size, impregnation of flyash (IFA), pH and temperature on the sorption capacity have been studied. Equilibrium modelling has been carried out using Langmuir and Freundlich isotherm equations and constants have been calculated under different conditions. Thermodynamic studies have also been carried out and values of standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) calculated.     

Graphene-induced crystallinity of bisphenol A polycarbonate in the presence of supercritical carbon dioxide

Changes in the crystallinity of polycarbonate (PC) induced by the simultaneous presence of 0.5 wt% graphene nanoplatelets (GnP) and supercritical carbon dioxide (sc-CO₂) were examined by means of Raman spectroscopy, WAXS, SAXS and DSC. Composites were prepared by melt-mixing, compression-molding and dissolving sc-CO₂ at high pressure and temperature. It was found that dissolved CO₂ induced the formation of an ordered non-crystalline phase in PC during slow cooling under pressure. A fast depressurization and cooling did not cause such an effect in the resultant foams. GnP induced a higher crystallinity in PC, especially when combined with sc-CO₂, even during fast depressurization and cooling. Raman spectroscopy enabled to correlate changes in the PC vibration modes with the presence of ordered phases, as well as to detect interactions between GnP and PC. Additionally, evidence of GnP exfoliation in the composites could be explained by the intensity reduction of the (002) graphite diffraction peak.     

Thermal and mechanical properties of polyhedral oligomeric silsesquioxane (POSS)/polycarbonate composites

A series of composite materials were produced incorporating polyhedral oligomeric silsesquioxane (POSS) derivatives into polycarbonate (PC), by melt blending. Significant differences in compatibility were observed depending on the nano-scale filler's specific structure: trisilanol POSS molecules generally provided better compatibility with PC than fully-saturated cage structures, and phenyl-substituted POSS grades were shown to be more compatible with PC than fillers with other functional groups. Trisilanolphenyl-POSS/PC composites possess the best overall performance among the POSS materials tested. The high compatibility between the trisilanolphenyl-POSS and polycarbonate matrix results in generation of transparent samples up to 5 wt% POSS content. Slightly enhanced mechanical properties including tensile and dynamic mechanical modulus are observed with the increase of trisilanolphenyl-POSS loading at the cost of decreasing ductility of the nanocomposites. Importantly, upon orientation of the PC/POSS nanocomposite, crystallization of POSS within the oriented material results—this observation is consistent with a growing number of observations which suggest that ‘bottom-up’ formation of structures incorporating multiple POSS cages result from orientation of these nanocomposites, and that the hybrid organic-inorganic inclusions may be at the heart of observed nano-scale reinforcement.     

Polycarbonate and co-continuous polycarbonate/ABS blends: influence of notch radius

The influence of notch tip radius in the range of 1-0.002 mm was studied on polycarbonate (PC) and co-continuous PC/acrylonitrile-butadiene-styrene (ABS). Co-continuous PC/ABS blend was obtained by mixing PC and ABS containing 15% polybutadiene (PB) in a twin screw extruder. PC and PC/ABS specimens were injection moulded into test bars. A notch was milled-in, with notch tip radius of 1, 0.5, 0.25 and 0.1 mm. Very sharp notches with a radius of 0.015-0.002 mm were obtained with an Excimer LAZER. The specimens were tested by single edge notch tensile tests at 1 m/s (apparent strain rate 28.5 s⁻¹) and at different temperatures (−60 to 130 °C). Initiation and propagation phases of the fracture process were monitored and the brittle-ductile transition temperature (T_bd) determined. It appeared that the amount of deformation in the initiation phase of fracture was extremely sensitive to notch tip radius. Temperature measurements of the deformation zone showed that the size of the deformation zone decreased with decreasing notch radius. The T_bd of PC increased rapidly with decreasing notch radius, until the glass transition temperature was approached. Remarkably, for PC the notch sensitivity was strongest around the standard notch tip radius of 0.25 mm. This means that a small deviation of this standard notch leads to large deviations in the results. The PC/ABS blend was much less sensitive to notch tip radius and the T_bd was almost constant. Thus the sensitivity of PC to sharp defects can be neutralised by adding ABS.