Co-reporter:Hee Jeung Oh, James E. McGrath, Donald R. Paul
Journal of Membrane Science 2017 Volume 524() pp:257-265
Publication Date(Web):15 February 2017
DOI:10.1016/j.memsci.2016.11.036
•Sulfonated polysulfone membranes were prepared by solvent-free, melt extrusion using poly(ethylene glycol) (PEG) plasticizers.•PEG can be water extracted after melt extrusion.•A Fickian model was used to analyze the kinetic desorption of PEG materials from the extruded films.•The diffusion coefficients of the PEG materials follow the Arrhenius equation.Disulfonated poly(arylene ether sulfone)s (BPS) random copolymers have been used as membranes for purifying water and generating electricity. These membranes can be prepared by solvent-free, melt extrusion using a proper plasticizer. Poly(ethylene glycol), PEG, materials are used as plasticizers to extrude thin, single layer BPS membranes and need to be extracted from the films before their use as membranes. Since PEG materials are water soluble, they can, in principle, be water extracted after melt extrusion. Experimental and theoretical studies of several factors influencing the diffusion of PEG from these films are needed in order to optimize this route to membrane preparation. The rate of PEG extraction is affected by the molecular weight (M̅n) and concentration (wt%) of PEG in the extruded BPS-20K/PEG films, as well as the temperature. When the early time approximation and complete solution of a Fickian model were used to analyze the kinetic desorption of PEG materials from the extruded films, they were found to describe the data. The diffusion coefficients of the PEG materials determined from this analysis correlated well with temperature and follow the Arrhenius equation.
Co-reporter:Rajkiran R. Tiwari, Jianyong Jin, B.D. Freeman, D.R. Paul
Journal of Membrane Science 2017 Volume 537(Volume 537) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.memsci.2017.04.069
•Pure gas permeability was measured for thick and thin films of PIM-1 at a fixed temperature of 35 °C.•Effect of post processing treatment, casting solvent, film thickness and molecular weight were studied.•Chloroform cast thin films have higher permeability and selectivity than ortho-dichlorobenzene cast thin films of PIM-1.•Aging effects are much more dominant than CO2 plasticization in thin films compared to thick films.•CO2 sorption in thin films decreases with increase in the aging time and decrease in the molecular weight of PIM-1.Physical aging of both thick and thin films of “high free-volume” glassy polymer, PIM-1 (polymer with intrinsic microporosity) was studied by monitoring changes in pure gas permeability of O2, N2 and CH4 at a fixed temperature of 35 °C. Permeability of PIM-1 is very sensitive to film thickness, post-treatment (methanol soak, water soak or dried) and casting solvent (chloroform and ortho-dichlorobenzene). Thin films of PIM-1 undergo accelerated aging, leading to initial permeability lower by an order of magnitude compared to thick films. The relative permeability for thin films of PIM-1 was decreased by 67% compared to 53% decrease for thick films at 1000 h of aging due to the higher aging rates in thin films. The effect of casting solvent (vapor pressure and boiling point) is more pronounced on aging and selectivity of thin films with initial permeability almost two times higher for the film casted from chloroform (CHCl3) compared to that prepared from ortho-dichlorobenzene (o-DCB) solvent. The effect of casting solvent on the initial permeability is less prominent for thick films. The film thickness, casting solvent and CO2 exposure protocols also have significant effect on the absolute CO2 permeability and plasticization behavior of both thick and thin films. The thin films undergo significant increase in the relative permeability upon plasticization compared to thick films and permeability was found to increase even during CO2 depressurization. The long time, constant pressure CO2 exposure study revealed dominant aging effect in thin film where aging overcomes the CO2 plasticization effect just within 1.2 min of the CO2 exposure compared to 10 h for thick film. The ellipsometry measurements showed that the CO2 solubility in thin films decreases with increases in the aging time and temperature, and with decrease in the molecular weight. A strong correlation was observed for the Langmuir sorption capacity, CH' and solubility at infinite dilution, S0 with the aging time, temperature and molecular weight of PIM-1.
Co-reporter:Hee Jeung Oh, Jaesung Park, Sebnem Inceoglu, Irune Villaluenga, Jacob L. Thelen, Xi Jiang, James E. McGrath, Donald R. Paul
Polymer 2017 Volume 109() pp:106-114
Publication Date(Web):27 January 2017
DOI:10.1016/j.polymer.2016.12.035
•Sulfonated polysulfone thin film membranes were prepared by solvent-free melt extrusion.•Melt extrusion in this study did not change the chemical structures and compositions of the extruded BPS/PEG films.•Some melt processed BPS/PEG films were opaque due to surface roughness.•The factors leading to film opacity such as phase separation, crystallization and micro-voids were not found.In this study, we discuss a new membrane formation route for preparing sulfonated polysulfone desalination membranes by solvent-free melt processing. Single-layer membranes composed of a 20 mol% disulfonated poly(arylene ether sulfone) random copolymer (BPS-20K) and poly(ethylene glycol) (PEG) plasticizers were successfully prepared by using melt extrusion. The chemical integrity of the components in the BPS-20K/PEG membranes was maintained after the extrusion process, as confirmed by 1H NMR and FT-IR analysis. Although some of the films appeared opaque after extrusion, this was found to be due to surface roughness. Other factors that might lead to film opacity, such as phase separation, crystallization, or micro-voids, were not found.
Co-reporter:Michele Galizia, Zachary P. Smith, Giulio C. Sarti, Benny D. Freeman, Donald R. Paul
Journal of Membrane Science 2015 Volume 475() pp:110-121
Publication Date(Web):1 February 2015
DOI:10.1016/j.memsci.2014.10.009
•Hydrogen and helium solubility isotherms in glassy and rubbery polymers can be correctly described by Lattice fluid models.•The He/H2He/H2 solubility selectivity can be correctly predicted for glassy and rubbery polymers suitable for membrane-based gas separations.•The isosteric heat of sorption and its dependence on the penetrant concentration can be correctly predicted.Hydrogen sorption isotherms in selected glassy and rubbery polymers, available over a wide range of temperatures (−20 to 70 °C) and pressures (0–60 atm) have been modeled and correlated using equilibrium and non-equilibrium thermodynamic models based on the lattice fluid theory. A good representation of the experimental data can be obtained for the systems considered over the whole range of pressures and temperatures inspected by using just one fitting parameter, under the fundamental assumption that hydrogen behaves as a non-swelling penetrant. The theoretical estimates of infinite dilution solubility coefficients are in excellent agreement with the experimental data. Remarkably, the model analysis allows a reliable estimate of the isosteric heat of sorption and its dependence on the hydrogen concentration over the whole range of pressures considered. A similar theoretical analysis has been performed by considering the helium sorption data available at 35 °C for a series of polymers considered for membrane-based gas separations. Finally, He/H2 solubility–selectivity at 35 °C has been correctly predicted: as expected, the glassy Teflon® AF-series perfluorinated copolymers display a higher He/H2 solubility selectivity compared to the hydrocarbon-based polymers.
Co-reporter:Rajkiran R. Tiwari, Zachary P. Smith, Haiqing Lin, B.D. Freeman, D.R. Paul
Polymer 2015 Volume 61() pp:1-14
Publication Date(Web):20 March 2015
DOI:10.1016/j.polymer.2014.12.008
•We report CO2 permeability, diffusivity and solubility in thin films of “high free-volume” glassy perfluoropolymers.•Perfluoropolymers show less CO2 plasticization than other glassy polymers used for gas separations.•Strong linear correlation exists between Langmuir sorption parameter, CH′ and (Tg-35) °C.•The decrease in the film thickness in the presence of CO2 correlate well with the observed CO2 permeability for AF 2400.Carbon dioxide (CO2) plasticization and sorption effects in both thick and thin films of “high free-volume” glassy perfluoropolymers were studied by monitoring CO2 permeability and by observing changes in the film thickness and refractive index with ellipsometry measurements. The film thickness, aging time, thermal history and CO2 exposure protocols have significant effect on the absolute CO2 permeability and plasticization behavior of both thick and thin films. The extent of CO2 plasticization increases as film thickness decreases and as the aging time is increased. The as-cast films showed higher plasticization compared to films which were annealed above Tg; however, the CO2 permeability of both the as-cast and annealed films continuously decreased during the depressurization step unlike other glassy polymers. In general, the various CO2 exposure protocols revealed lower CO2 plasticization for perfluoropolymers compared to other reported glassy polymers. The extent of CO2 sorption obtained from the ellipsometry measurements was found to decrease with the decrease in the excess volume and increase in the aging time for perfluoropolymers; in addition, the structural differences among the various glassy polymers resulting in different polymer–gas interactions also affects the overall sorption characteristics. The lower plasticization in perfluoropolymers compared to Matrimid was also confirmed from the smaller percent increase observed for the experimental diffusion coefficient compared to the theoretically predicted diffusion coefficient from the dual sorption-mobility model. The Langmuir sorption parameter, CH′, and solubility at infinite dilution, S0, obtained from fitting dual sorption-mobility model to sorption data, showed an excellent linear correlation with (Tg-35) °C. The CO2 diffusivity and permeability data obtained for thin films of various glassy polymers also showed a strong correlation with free volume. The somewhat unusual behavior of thin films of AF 2400 in comparison to other glassy polymers studied to date is believed to be related to the low cohesive energy density expected of perfluorinated structures and its high free volume resulting from the bulky dioxole comonomer.
Co-reporter:S.K. Peddini, C.P. Bosnyak, N.M. Henderson, C.J. Ellison, D.R. Paul
Polymer 2014 Volume 55(Issue 1) pp:258-270
Publication Date(Web):14 January 2014
DOI:10.1016/j.polymer.2013.11.003
Because of the exceptionally high modulus and aspect ratios of multiwall carbon nanotubes (MWCNT), there has been much interest in using them as reinforcing agents for polymer composites. However, the commercial implementation of such nanocomposites has generally met with very limited success owing to poor dispersion of the MWCNT in the polymer matrix. A strategy that overcomes many of these difficulties is described here with a view towards incorporating MWCNT with carbon black or silica for improved elastomer performance in such applications as tires. Key issues are control of the MWCNT surface functionality for proper individual tube dispersion, their aspect ratio for a balance of mechanical performance versus melt processability and an appropriate masterbatch concentration for ease of further formulation by rubber goods manufacturers. Styrene-butadiene rubber (SBR), commonly used as a tread stock for tires, is employed here as the matrix for creation of a masterbatch with oxidized MWCNT (12.3–15 wt.%). Masterbatch rheology is necessary to understand how to achieve good dispersion and conformation of the MWCNT in the final product. Rheological characterization of the masterbatch nanocomposites and their dilutions over shear rate ranges relevant for processing will be described. Scanning transmission electron microscopy (STEM) investigations have revealed that this process produces good dispersion of the MWCNT's in the SBR matrix. The distribution of diameters, contour lengths, and end-to-end distances of the MWCNT in these formulations has also been determined. Effective tube aspect ratios for the nanocomposites with various MWCNT loadings were estimated by analysis of the rheological data for uncured specimens and the dynamic mechanical properties of cured composites using the Guth–Gold–Smallwood theory. These materials do not show a high level of electrical conductivity as might be expected from a percolation concept, signifying excellent tube dispersion and formation of a bound rubber layer on the discrete MWCNT.
Co-reporter:Hee Jeung Oh, Benny D. Freeman, James E. McGrath, Chang Hyun Lee, Donald R. Paul
Polymer 2014 Volume 55(Issue 1) pp:235-247
Publication Date(Web):14 January 2014
DOI:10.1016/j.polymer.2013.11.041
One route to melt processing of high glass transition temperature polyelectrolytes, such as disulfonated poly(arylene ether sulfone) (BPS), involves mixing a plasticizer with the polymer. In this study, poly(ethylene glycol) (PEG) was used as a plasticizer for BPS. BPS and PEG are miscible, and the effect of PEG molecular weight (in the range of 200–600 g/mol) and concentration on the Tg of BPS/PEG blends was investigated. As PEG molecular weight decreases and concentration increases, the blend Tg is depressed significantly. Based on isothermal holds in a rheometer at various temperatures and times, the PEG materials considered were thermally stable up to 220 °C for 10 min in air or 250 °C for at least 10 min under a nitrogen atmosphere, which is long enough to permit melt extrusion of such materials.
Co-reporter:Grant T. Offord, Shannon R. Armstrong, Benny D. Freeman, Eric Baer, Anne Hiltner, Donald R. Paul
Polymer 2014 Volume 55(Issue 5) pp:1259-1266
Publication Date(Web):10 March 2014
DOI:10.1016/j.polymer.2014.01.030
Multilayered gas separation membranes with alternating layers of β crystalline polypropylene and PEBAX copolymers were produced via coextrusion and biaxial stretching for potential applications in modified atmosphere packaging. The number of layers and PEBAX compositions were varied to study the effect of various membrane configurations on pore formation in the polypropylene layers, which ideally serve as a mechanical support for the selective PEBAX layers. Gas permeabilities of multilayered films were compared to control PEBAX films using a simple model, which allowed inferences about the completeness of pore formation to be drawn. Preliminary results show that increasing the layer count degrades membrane throughput and separation capability, while varying PEBAX composition results in a tradeoff between these properties.
Co-reporter:Hee Jeung Oh, Benny D. Freeman, James E. McGrath, Christopher J. Ellison, Sue Mecham, Kwan-Soo Lee, Donald R. Paul
Polymer 2014 Volume 55(Issue 6) pp:1574-1582
Publication Date(Web):24 March 2014
DOI:10.1016/j.polymer.2014.02.011
Disulfonated poly(arylene ether sulfone) (BPS) random copolymers, prepared from a sulfonated monomer, have been considered for use as membrane materials for various applications in water purification and power generation. These membranes can be melt-processed to avoid the use of hazardous solvent-based processes with the aid of a plasticizer, a low molecular weight poly(ethylene glycol) (PEG). PEG was used to modify the glass transition temperature and melt rheology of BPS to enable coextrusion with polypropylene (PP). Our previous paper discussed the miscibility of BPS with PEG and the influence of PEG on the glass transition of BPS. In this study, the rheological properties of disulfonated poly(arylene ether sulfone)s plasticized with poly(ethylene glycol) (PEG) are investigated to identify coextrusion processing conditions with candidate PPs. The effects of various factors including PEG molecular weight, PEG concentration, temperature and BPS molecular weight on blend viscosity were studied. The rheological data effectively lie on the same master curve developed by Bueche and Harding for non-associating polymers such as poly(methyl methacrylate) (PMMA) and polystyrene (PS). Although sulfonated polysulfone contains ionic groups, the form of its viscosity versus shear rate (or frequency) behavior appears to be dominated by the relaxation of polymer entanglements.
Co-reporter:Huan Wang, Tai-Shung Chung, Donald R. Paul
Journal of Membrane Science 2014 458() pp: 27-35
Publication Date(Web):
DOI:10.1016/j.memsci.2014.01.066
Co-reporter:Rajkiran R. Tiwari, Zachary P. Smith, Haiqing Lin, B.D. Freeman, D.R. Paul
Polymer 2014 Volume 55(Issue 22) pp:5788-5800
Publication Date(Web):23 October 2014
DOI:10.1016/j.polymer.2014.09.022
•We report physical aging in thin films of “high free-volume” glassy perfluoropolymers.•Due to stable permeation performance, perfluoropolymers can be potential materials for gas separation applications.•Teflon AF undergo rapid initial aging resulting in apparent lower aging compared to Hyflon AD for the same aging time.•The (P1000h/P1h) ratio showed a stronger correlation with (Tg−35) °C than with FFV.Physical aging of both thick and thin films of “high free-volume” glassy perfluoropolymers was studied by monitoring changes in pure gas permeability of O2, N2 and CH4. All permeability measurements were done at a fixed temperature of 35 °C for more than 1000 h of aging. Two grades of perfluoropolymers, Teflon AF and Hyflon AD, having different comonomer structures but with similar comonomer ratios were studied to understand the effect of comonomer type and content on the aging behavior. The effect of casting process (solution vs. spin coating) and solvent type (vapor pressure and boiling point) had a significant effect on the absolute permeability of both thick and thin films; however, the aging rates were more affected by thickness and solvent type rather than the casting process for similar thicknesses. After 1000 h of aging, the relative permeability for thin films of Teflon AF 2400 was decreased by 27% compared to only 10% for thick films prepared from Novec 7500 solvent. Teflon AF, which has a higher fractional free volume (FFV) than Hyflon AD, is believed to undergo significant aging well before the initial permeability measurement could be made (after ∼ 1 h of aging) and, therefore, Teflon AF materials showed a lower decrease in relative permeability compared to Hyflon AD for the same aging time. The comonomer type and content has a significant effect on the permeability; the initial absolute oxygen permeability for AF 2400 was an order of magnitude higher compared to AD 60. The physical aging of thin films of the various glassy perfluoropolymers was also tracked by recording changes in the refractive index and thickness with time by ellipsometry. The ellipsometry data also confirmed higher aging rates in Hyflon AD compared to Teflon AF materials. The volumetric aging rate, obtained from the change in the refractive index using the Lorentz–Lorenz equation, and the permeability reduction rate from the (P1000h/P1h) ratio showed an excellent linear correlation. The (P1000h/P1h) ratio also showed a stronger correlation with (Tg−35) °C than with FFV.
Co-reporter:P. Li, T.S. Chung, D.R. Paul
Journal of Membrane Science 2014 450() pp: 380-388
Publication Date(Web):
DOI:10.1016/j.memsci.2013.09.030
Co-reporter:Jianzhong Xia, Tai-Shung Chung, D.R. Paul
Journal of Membrane Science 2014 450() pp: 457-468
Publication Date(Web):
DOI:10.1016/j.memsci.2013.09.047
Co-reporter:Huan Wang, Tai-Shung Chung, D.R. Paul
Journal of Membrane Science 2014 450() pp: 308-312
Publication Date(Web):
DOI:10.1016/j.memsci.2013.09.006
Co-reporter:Cher Hon Lau, Pei Li, Fuyun Li, Tai-Shung Chung, Donald R. Paul
Progress in Polymer Science 2013 Volume 38(Issue 5) pp:740-766
Publication Date(Web):May 2013
DOI:10.1016/j.progpolymsci.2012.09.006
This paper reviews the material design and fabrication of a class of membranes where some larger molecules can permeate faster than smaller ones, or so-called reverse-selective membranes, for conventional gas or vapor separation applications. The main requirements for a good reverse-selective gas or vapor separation membrane are high permeability, good separation capability, stable performance and sufficient mechanical properties to withstand the harsh environments in commercial separation processes. High permeability in reverse-selective membranes is achieved by tuning the fractional free volume (FFV) content, i.e., free spaces for penetrant diffusion, while facilitating preferential interaction between functional moieties of the membrane material and penetrant molecules to enhance penetrant sorption, and suppressing crystallinity where applicable. The separation capabilities of these membranes are generally controlled by the preferential sorption of larger condensable penetrants over smaller penetrants rather than size-selective diffusion common for conventional gas separation polymers. Reverse-selective gas separation membranes have attracted much attention owing to their advantages for certain commercial gas separation applications. This review summarizes the different aspects of polymeric reverse-selective gas separation membranes reported in the literature and comments briefly on their commercialization potential.
Co-reporter:Pei Li, T.S. Chung, D.R. Paul
Journal of Membrane Science 2013 Volume 432() pp:50-57
Publication Date(Web):1 April 2013
DOI:10.1016/j.memsci.2013.01.009
Gas transport properties of PIM-1, i.e., the first “polymer with intrinsic microporosity,” at 25 °C and different pressures were systematically studied. Permeability coefficients of 10 gases including He, H2, N2, O2, CH4, CO2, C2H4, C2H6, C3H6 and C3H8 were conducted at 25 °C for five different upstream pressures (from 1 to 10 atm). The C2 and C3 hydrocarbons exhibited serious plasticization responses while the permeability coefficients of He, H2, O2, N2, CH4 and CO2 decreased with the trans-membrane pressure as expected from the dual-mobility model. Sorption isotherms of all 10 gases were also determined using a dual-volume sorption cell at 25 °C up to a maximum pressure of 27 atm. The sorption isotherms followed the dual-mode sorption model. The logarithm of the solubility coefficients increased linearly with the critical temperature of the gas and the slope of this plot (0.018) was found to be comparable with values reported for other glassy polymers. Diffusion coefficients were calculated from the permeability and solubility data; the values for He, H2, O2, N2, CH4 and CO2, increased with pressure as predicted by the dual-mobility model while those of the C2 and C3 hydrocarbon gases increased more strongly because of plasticization. Parameters from the dual mobility model, DD and DH, were significantly higher and their ratio, DH/DD was significantly smaller than those of previously reported polymers.Highlights► Sorption isotherms for various gases in PIM-1 were measured. ► Permeability coefficients for various gases in PIM-1 were measured. ► Results were analyzed by the dual-mode model for glassy polymers.
Co-reporter:Donald R. Paul (Editor)
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 51) pp:18121-18122
Publication Date(Web):December 26, 2013
DOI:10.1021/ie403658e
Co-reporter:Geoffrey M. Geise, Carl L. Willis, Cara M. Doherty, Anita J. Hill, Timothy J. Bastow, Jamie Ford, Karen I. Winey, Benny D. Freeman, and Donald R. Paul
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 3) pp:1056
Publication Date(Web):April 5, 2012
DOI:10.1021/ie202546z
Suspension-phase neutralization of an acid-form sulfonated styrenic pentablock copolymer was used to prepare aluminum cross-linked polymer films. Aluminum neutralization was confirmed by 27Al solid state NMR, and the aluminum-neutralized polymer resisted ion exchange to the sodium counterion form when the polymer was soaked in 1 mol/L sodium chloride for 30 days. The effects of aluminum neutralization on polymer morphology, mechanical properties, water and salt transport properties, and free volume were explored. The primary spacing of the morphology, as measured by small-angle X-ray scattering (SAXS), decreased upon neutralization of the sulfonated polymer. The hydrated aluminum-neutralized polymer was mechanically stronger than the non-neutralized polymer, but the dry aluminum-neutralized polymer was more brittle than the non-neutralized polymer. Neutralization of the polymer’s sulfonic acid functionality resulted in a 5.5-fold decrease in water uptake. This water uptake decrease upon aluminum neutralization resulted in a decrease, relative to the non-neutralized polymer, in water and sodium chloride permeability and water vapor transport rate. These decreases in transport rates and water uptake were consistent with one another, based on an analysis of changes in free volume of the material upon aluminum neutralization. Sodium chloride permeability of the aluminum-neutralized polymer was less dependent on salt concentration than that of the non-neutralized polymer, which is consistent with neutralization of the polymer’s charged sulfonate groups. Aluminum neutralization increased the polymer’s water/sodium chloride permeability selectivity because of a 1.8-fold increase in the material’s diffusion selectivity. Free volume element size, characterized by ortho-positronium lifetime, decreased upon aluminum neutralization in both dry and hydrated film samples.
Co-reporter:Thomas M. Murphy, B.D. Freeman, D.R. Paul
Polymer 2013 Volume 54(Issue 2) pp:873-880
Publication Date(Web):24 January 2013
DOI:10.1016/j.polymer.2012.12.010
Co-reporter:Grant T. Offord, Shannon R. Armstrong, Benny D. Freeman, Eric Baer, Anne Hiltner, John S. Swinnea, Donald R. Paul
Polymer 2013 Volume 54(Issue 10) pp:2577-2589
Publication Date(Web):26 April 2013
DOI:10.1016/j.polymer.2013.03.026
Microporous polymer membranes were fabricated by extrusion, thermal annealing, and subsequent biaxial stretching of β nucleated isotactic polypropylene. Fabrication conditions were optimized based on prior studies so that the influence of annealing on the precursor film crystallinity and the pore formation in such films upon stretching could be investigated. Annealing perfected the crystalline structure of these materials, as evidenced by thermal and x-ray techniques. A mechanism detailing the annealing and pore formation process during biaxial stretching is presented. An appropriate metric was developed to relate the crystallinity of the precursor films to the porosity of the films after biaxially stretching. The porosity developed in biaxially stretched films increased substantially when its precursor was annealed near the melting temperature of β crystalline material, enabling the production of high permeability microporous membranes.
Co-reporter:Grant T. Offord, Shannon R. Armstrong, Benny D. Freeman, Eric Baer, Anne Hiltner, Donald R. Paul
Polymer 2013 Volume 54(Issue 11) pp:2796-2807
Publication Date(Web):9 May 2013
DOI:10.1016/j.polymer.2013.03.050
Microporous polymer membranes were produced from β nucleated isotactic polypropylene using a solvent-free process involving extrusion and biaxial stretching. Pore formation, previously shown to depend upon the quantity of perfected β crystalline material in the film, was found to also depend upon stretching temperature. The pore structure of membranes produced under a variety of processing conditions was investigated by SEM, flow porometry, and gas permeation techniques. The mechanism of gas transport through the membrane was determined using permeability experiments and the film pore size distribution. Gas permeability was correlated with film porosity and compared to the permeability of an array of porous polypropylene films. High quality microporous membranes were produced without the use of the strict process control required for traditional extruded films, and such membranes exhibit performance comparable to commercially available Celgard films. This process flexibility provides an avenue toward coextruded composite membranes for a range of high-value applications.
Co-reporter:C.B. Bucknall, D.R. Paul
Polymer 2013 Volume 54(Issue 1) pp:320-329
Publication Date(Web):8 January 2013
DOI:10.1016/j.polymer.2012.11.019
The stress-field model introduced in Part 1 is used to analyse the effects of rubber particle size D and volume fraction ϕϕ on impact behaviour. The model is refined by including energy released from the matrix during rubber particle cavitation, and interactions between cavitated rubber particles, porous shear bands, and crazes, in the later stages of energy absorption. The analysis shows that with increasing ϕϕ, critical stresses for rubber particle cavitation increase slightly, while yield stresses and craze formation stresses fall substantially, and craze stability increases. Particle morphology and particle–matrix adhesion also affect the locations of the brittle-ductile (BD) transition, which is caused by cavitation resistance in very small particles, and the ductile-brittle (DB) transition, which is due essentially to failure of crazes initiated from larger particles. Comparisons of model predictions with Izod data provide further insight into the ways in which large porous plastic zones develop ahead of notch tips.
Co-reporter:Geoffrey M. Geise, Benny D. Freeman, Donald R. Paul
Journal of Membrane Science 2013 427() pp: 186-196
Publication Date(Web):
DOI:10.1016/j.memsci.2012.09.029
Co-reporter:J.L. Osborne, I.C. Sanchez, D.R. Paul
Journal of Membrane Science 2013 442() pp: 27-30
Publication Date(Web):
DOI:10.1016/j.memsci.2013.03.051
Co-reporter:Rajkiran R. Tiwari;Douglas L. Hunter
Journal of Polymer Science Part B: Polymer Physics 2013 Volume 51( Issue 12) pp:952-965
Publication Date(Web):
DOI:10.1002/polb.23289
ABSTRACT
Coefficients of linear thermal expansion (CTE) for poly(propylene)/ poly(propylene)-grafted-maleic anhydride/montmorillonite ethylene-co-octene elastomer (PP/PP-g-MA/MMT/EOR) blend nanocomposites were determined as a function of MMT content and various PP-g-MA/organoclay masterbatch ratios. The nanocomposites were prepared in a twin-screw extruder at a fixed 30 wt % elastomer, 0–7 wt % MMT content, and various PP-g-MA/organoclay ratio of 0, 0.5, 1.0, and 1.5. The organoclay dispersion facilitated by the maleated PP helps to reduce the size of the dispersed phase elastomer particles in the PP matrix. The elastomer particle size decreased significantly as the PP-g-MA/organoclay ratio and MMT content increased; the elastomer particles viewed // to flow direction (FD) are smaller and less deformed compared to those viewed // to transverse direction (TD). The elastomer particle shape based on the view along the three orthogonal directions of the injection molded sample is similar to a prolate ellipsoid. The CTE decreased significantly in the FD and TD, whereas a slight increase is observed in the normal direction in the presence of MMT and PP-g-MA. The Chow model based on a two population approach showed better fit to experimental CTE when the effect of MMT and elastomer are considered individually. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B Polym. Phys. 2013, 51, 952–965
Co-reporter:Y. T. Sung;P. D. Fasulo;W. R. Rodgers;Y. T. Yoo;Y. Yoo;D. R. Paul
Journal of Applied Polymer Science 2012 Volume 124( Issue 2) pp:1020-1030
Publication Date(Web):
DOI:10.1002/app.35147
Abstract
The morphology, tensile, impact properties, and thermal expansion behavior of polycarbonate (PC)/acrylonitrile-styrene-butadiene (ABS)/talc composites with different compositions and mixing sequences were investigated. From the studies of morphology of the PC/ABS/talc composites, it was observed that some talc particles were located in both the PC and the ABS phases of the blend but most were at the interface between the PC and ABS phases for every mixing sequence. Aspect ratios of the talc particles determined by TEM image analysis reasonably matched values computed from tensile modulus using composite theory. The thermal expansion behavior, or CTE values, was not significantly influenced by the mixing sequence. The impact strength of the PC/ABS/talc composites depended significantly on the mixing sequence; a premix with PC gave the poorest toughness. The molecular weight of the PC in PC/talc composites was found to be significantly decreased. It appears that the impact strength of the PC/ABS/talc composites is seriously compromised by the degradation of the PC caused by talc. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Co-reporter:Rajkiran R. Tiwari;Douglas L. Hunter
Journal of Polymer Science Part B: Polymer Physics 2012 Volume 50( Issue 22) pp:1577-1588
Publication Date(Web):
DOI:10.1002/polb.23154
Abstract
PP/PP-g-MA/MMT/EOR blend nanocomposites were prepared in a twin-screw extruder at fixed 30 wt % elastomer and 0 to 7 wt % MMT content. Elastomer particle size and shape in the presence of MMT were evaluated at various PP-g-MA/organoclay masterbatch ratios of 0, 0.5, 1.0, and 1.5. The organoclay dispersion facilitated by maleated polypropylene serves to reduce the size of the elastomer dispersed phase particles and facilitates toughening of these blend nanocomposites. The rheological data analysis using modified Carreau-Yasuda model showed maximum yield stress in extruder-made nanocomposites compared with nanocomposites of reactor-made TPO. Increasing either MMT content or the PP-g-MA/organoclay ratio can drive the elastomer particle size below the critical particle size below which toughness is dramatically increased. The ductile-brittle transition shift toward lower MMT content as the PP-g-MA/organoclay ratio is increased. The D-B transition temperature also decreased with increased MMT content and masterbatch ratio. Elastomer particle sizes below ∼1.0 μm did not lead to further decrease in the D-B transition temperature. The tensile modulus, yield strength, and elongation at yield improved with increasing MMT content and masterbatch ratio while elongation at break was reduced. The modified Mori-Tanaka model showed better fit to experimental modulus when the effect of MMT and elastomer are considered individually. Overall, extruder-made nanocomposites showed balanced properties of PP/PP-g-MA/MMT/EOR blend nanocomposites compared with nanocomposites of reactor-made TPO. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012
Co-reporter:Daniel R. Dreyer, Daniel J. Miller, Benny D. Freeman, Donald R. Paul, and Christopher W. Bielawski
Langmuir 2012 Volume 28(Issue 15) pp:6428-6435
Publication Date(Web):April 4, 2012
DOI:10.1021/la204831b
Herein we propose a new structure for poly(dopamine), a synthetic eumelanin that has found broad utility as an antifouling agent. Commercially available 3-hydroxytyramine hydrochloride (dopamine HCl) was polymerized under aerobic, aqueous conditions using tris(hydroxymethyl)aminomethane (TRIS) as a basic polymerization initiator, affording a darkly colored powder product upon isolation. The polymer was analyzed using a variety of solid state spectroscopic and crystallographic techniques. Collectively, the data showed that in contrast to previously proposed models, poly(dopamine) is not a covalent polymer but instead a supramolecular aggregate of monomers (consisting primarily of 5,6-dihydroxyindoline and its dione derivative) that are held together through a combination of charge transfer, π-stacking, and hydrogen bonding interactions.
Co-reporter:Thomas M. Murphy, D.S. Langhe, M. Ponting, E. Baer, B.D. Freeman, D.R. Paul
Polymer 2012 Volume 53(Issue 18) pp:4002-4009
Publication Date(Web):17 August 2012
DOI:10.1016/j.polymer.2012.07.012
Recent studies of physical aging in confined polymer glasses have revealed that aging behavior in confinement often differs from bulk behavior. This study used DSC to characterize physical aging and structural relaxation in bulk polysulfone (PSF) and co-extruded multilayered films of PSF and an olefin block copolymer (OBC) that have average PSF layer thicknesses of 640 nm, 260 nm, and 185 nm. The films were aged isothermally at 170 °C, and the recovered enthalpy upon reheating was measured over time. The films with 640 nm and 260 nm PSF layers had aging rates very similar to that of bulk PSF, while the film with 185 nm PSF layers had an aging rate slightly greater than the bulk value. The cooling rate dependence of the limiting fictive temperature (Tf′) in multilayered and bulk PSF samples was also characterized. Values of Tf′ were similar for all films at each cooling rate. The results of this work are in general agreement with our previous gas permeation aging study of multilayered PSF films aged at 35 °C, in which the effect of layer thickness on aging behavior was minimal. This stands in contrast to studies with thin, freestanding PSF films, which exhibit accelerated aging relative to bulk and have aging rates that depend strongly on film thickness.Graphical abstract
Co-reporter:M.W. Spencer, M.D. Wetzel, C. Troeltzsch, D.R. Paul
Polymer 2012 Volume 53(Issue 2) pp:569-580
Publication Date(Web):24 January 2012
DOI:10.1016/j.polymer.2011.12.013
The effects of the degree of neutralization of the acid groups and, to some extent, the precursor melt index on the thermal, rheological, and mechanical properties of two series of poly(ethylene-co-methacrylic acid) (EMAA) ionomers, one based on sodium (Na+) cations and one based on potassium cations (K+), were examined. Differential scanning calorimetry (DSC) and modulus results indicate that the secondary crystallization of the ionomers is generally completed 21 days after melt processing. DSC results indicate that the extent of crystallization increases with increasing neutralization level. The mechanical relaxation seen by dynamic mechanical analysis (DMA) in the vicinity of the secondary crystal melting point shifts to higher temperatures as the neutralization level increases. The rheological properties increase with decreasing precursor melt index and with increasing neutralization level to a lesser extent. The ionomer modulus and yield strength increase with increasing neutralization level up to 40% neutralization and then plateau or slightly decrease with further neutralization. The plateaus/maxima may be the result of an optimal spacing of alkaline ions and carboxyl groups within ionic groups at neutralization levels near 33%. The elongation at break and the Izod impact strength decrease with increasing neutralization. The modulus, yield stress, and impact strength are generally lowest for the ionomers with the highest precursor melt index.
Co-reporter:M.W. Spencer, M.D. Wetzel, C. Troeltzsch, D.R. Paul
Polymer 2012 Volume 53(Issue 2) pp:555-568
Publication Date(Web):24 January 2012
DOI:10.1016/j.polymer.2011.12.016
Nanocomposites were prepared by melt blending various sodium (Na+) and potassium (K+) ionomers formed from poly(ethylene-co-methacrylic acid) and the M2(HT)2 organoclay formed from montmorillonite (MMT). The effects of the neutralization level of the acid groups and the precursor melt index on the morphology and properties of the nanocomposites were evaluated using stress-strain analysis, wide angle X-ray scattering (WAXS), and transmission electron microscopy (TEM) coupled with particle analysis. The aspect ratio generally increases as the neutralization level increases, except for Na+ ionomer nanocomposites with neutralization levels >50%. It appears from both WAXS and TEM analyses that Na+ ionomer nanocomposites have higher levels of MMT exfoliation and particle orientation in the flow direction than K+ ionomer nanocomposites. DSC results indicate that the level of crystallinity in the Na+ ionomers generally increases slightly with MMT addition, while the crystallinity in the K+ ionomers decreases slightly with MMT addition. The relative modulus of K+ ionomer nanocomposites increases as the degree of neutralization increases. The relative moduli of Na+ ionomer nanocomposites are higher than the relative modulus of K+ ionomer nanocomposites, likely due to the increased crystallinity of the Na+ ionomers and the decreased crystallinity of the K+ ionomers upon addition of MMT, the higher exfoliation levels measured by the aspect ratios and the particle densities, and the higher particle orientation indicated by TEM and WAXS. The relative modulus generally increases as the aspect ratio increases. The elongation at break generally decreases as the MMT content increases and as the neutralization level increases for both ionomer types. The fracture energy of most of the ionomers increases with the addition of MMT, reaches a maximum between 2.5 and 5 wt% MMT, and then decreases upon further MMT addition.
Co-reporter:Kevin K. Tung, R.T. Bonnecaze, B.D. Freeman, D.R. Paul
Polymer 2012 Volume 53(Issue 19) pp:4211-4221
Publication Date(Web):31 August 2012
DOI:10.1016/j.polymer.2012.07.028
Butadiene-containing polymers such as styrene-butadiene-styrene (SBS) block copolymers are of a potential use as oxygen scavenging polymers (OSP) in barrier applications. To evaluate their use in such applications, oxygen uptake was measured for films made of an SBS copolymer and four cobalt catalyst loadings with various thicknesses. The oxygen uptake was found to be kinetically limited for thin films while diffusion controls the uptake at long times for thick films. The thickness of the oxidized region at long oxidation times is termed the critical thickness Lc and was quantified by various analyses. Thin films (i.e.,L ≤ 2Lc) oxidize fully and homogeneously, whereas heterogeneous oxidation typically occurs in thicker films (i.e., L > 2Lc). A thin film model was used to extract the reaction rate parameters and a stoichiometric oxidation coefficient that describe oxygen uptake in the absence of diffusion limitation. An approximate moving-boundary model was developed to describe thick film oxidation behavior at long times and was found to be in semi-quantitation agreement with the measured uptake.Graphical abstract
Co-reporter:Jianzhong Xia, Tai-Shung Chung, Pei Li, Norman R. Horn, D.R. Paul
Polymer 2012 Volume 53(Issue 10) pp:2099-2108
Publication Date(Web):25 April 2012
DOI:10.1016/j.polymer.2012.03.009
Industrial gas separation membranes have selective dense layers with thicknesses around 100 nm. It has long been assumed that these thin layers have the same properties as thick (bulk) films. However, recent research has shown that thin films with such thickness experience accelerated physical aging relative to bulk films and, thus, their permeation properties can differ significantly from the bulk. Thin films made from Extem® XH 1015, a new commercial polyetherimide, have been investigated by monitoring their gas permeability. The permeability of the thin films is originally greater than the thick films but eventually decreases well below the permeability of the thick film. The CO2 plasticization of Extem thin films is explored using a series of exposure protocols that indicate CO2 plasticization is a function of film thickness, aging time, exposure time, pressure and prior history.
Co-reporter:Rajkiran R. Tiwari, D.R. Paul
Polymer 2012 Volume 53(Issue 3) pp:823-831
Publication Date(Web):2 February 2012
DOI:10.1016/j.polymer.2011.12.029
Izod impact strength was determined as a function of temperature for polypropylene (PP)/ethylene-co-octene elastomer (EOR) blends and nanocomposites to determine the effect of PP molecular weight, elastomer MFI, EOR octene content and MMT content on the ductile-brittle (D-B) transition temperature. The D-B transition temperature decreases with increased molecular weight of the PP (H = high, M = medium and L = low) and the addition of MMT. The D-B transition temperature also decreases as the elastomer particle size is decreased, and at a fixed elastomer particle sizes, the D-B transition varies as H-PP< M-PP< L-PP. The H-PP based materials show a smaller decrease in the D-B transition temperature compared to L-PP based materials in the presence of MMT. Elastomers having a melt flow index (MFI) in the range of 0.5–1.0 showed a significant decrease in the D-B transition temperature for both L-PP and H-PP nanocomposites. The D-B transition temperature also decreases with increasing octene content of the elastomer.
Co-reporter:Geoffrey M. Geise, Linda P. Falcon, Benny D. Freeman, Donald R. Paul
Journal of Membrane Science 2012 s 423–424() pp: 195-208
Publication Date(Web):
DOI:10.1016/j.memsci.2012.08.014
Co-reporter:Norman R. Horn and D. R. Paul
Macromolecules 2012 Volume 45(Issue 6) pp:2820-2834
Publication Date(Web):March 6, 2012
DOI:10.1021/ma300177k
Our previous publications have demonstrated that thin glassy polymer films respond to highly sorbing penetrants, such as CO2, quite differently than thick films. These studies focused on CO2 permeation behavior and revealed that, for thin films, CO2 permeability at constant CO2 pressure goes through a maximum followed by a continual decrease in permeability owing to physical aging. So far, thick and thin glassy polymer films have been compared in the context of permeability, but lack of substantial means of obtaining thin film sorption data has prevented adequate comparison of thick and thin films in the context of gas solubility. In this paper, spectroscopic ellipsometry is used to obtain simultaneously the film thickness and CO2 sorption capacity for thin glassy polymer films. This allows a more comprehensive look at CO2 permeability, sorption, and diffusivity as a function of both CO2 pressure and exposure time. The evidence reported here suggests that thin film sorption behavior is substantially different than that of thick film counterparts. Partial molar volume is determined from sorption-induced swelling data. Fractional free volume and diffusivity are calculated as a function of CO2 pressure. Dual sorption model parameters are presented for Matrimid thin films for different aging times. Dynamic ellipsometry experiments show that refractive index minima, fractional free volume maxima, and CO2 diffusivity maxima correlate well with observed CO2 permeability maxima observed for thin Matrimid films. The results support the claim that plasticization and physical aging are competing processes but that aging dominates over long time scales. The CO2 diffusivity behavior over time is most affected by the competing effects of plasticization and aging, and the evolution of CO2 diffusivity is shown to be the main contributing factor to changes in CO2 permeability at constant pressure.
Co-reporter:Brandon W. Rowe, Lloyd M. Robeson, Benny D. Freeman, Donald R. Paul
Journal of Membrane Science 2011 Volume 366(1–2) pp:436
Publication Date(Web):1 January 2011
DOI:10.1016/j.memsci.2010.10.008
Co-reporter:M.W. Spencer, D.L. Hunter, B.W. Knesek, D.R. Paul
Polymer 2011 Volume 52(Issue 23) pp:5369-5377
Publication Date(Web):27 October 2011
DOI:10.1016/j.polymer.2011.09.034
A silanized organoclay (s-M2(HT)2) was prepared by reaction of trimethoxyphenyl silane with an organoclay with a M2(HT)2 surfactant structure. Nanocomposites were formed from polypropylene (PP) and a blend of PP and maleic anhydride-grafted polypropylene (PP-g-MA) and the M2(HT)2 and s-M2(HT)2 organoclays by melt processing to explore the extent of exfoliation and the mechanical properties. Wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM) coupled with detailed particle analysis were used to determine the effect of the organoclay used and the PP-g-MA compatibilizer on exfoliation and mechanical, rheological, and thermal expansion properties. The PP/s-M2(HT)2 nanocomposites have higher particle densities than the PP/M2(HT)2 nanocomposites though the aspect ratio remains the same. Platelet dispersion is significantly improved by using PP-g-MA compatibilizer for both organoclays. The rheological properties and the relative modulus improve for the PP/s-M2(HT)2 nanocomposites but not to the same degree as either organoclay in a PP-g-MA compatibilized matrix. The thermal expansion properties, however, are not improved by using the s-M2(HT)2 organoclay. The s-M2(HT)2 organoclay is less prone to agglomeration during extrusion than the M2(HT)2 organoclay.
Co-reporter:Thomas M. Murphy, D.S. Langhe, M. Ponting, E. Baer, B.D. Freeman, D.R. Paul
Polymer 2011 Volume 52(Issue 26) pp:6117-6125
Publication Date(Web):13 December 2011
DOI:10.1016/j.polymer.2011.10.061
The physical aging of polymers in confined environments has been an area of intensive study in recent times. The rate of physical aging in thin films of many polymers used in gas separation membranes is dependent on film thickness and accelerated relative to bulk. In this study, the physical aging of polymer films with alternating glassy polysulfone and rubbery polyolefin layers was monitored by measuring the gas permeability of O2 and N2 as a function of aging time at 35 °C. The alternating layer structures were formed by a melt co-extrusion process. The polysulfone layers have thicknesses ranging from 185 to 400 nm, and the overall thicknesses of the films are on the order of 80–120 μm. The aging of freestanding thin films of polysulfone is rapid and exhibits clear thickness dependence, whereas the aging of multilayered films was observed to be similar to bulk and showed no dependence on layer thickness. At 1000 h of aging time, a 400 nm freestanding PSF film decreased in O2 permeability by 35%, whereas on average the bulk and multilayered films only experienced a decline of 10–15%. A slight increase in O2/N2 selectivity for the multilayered films was observed over the course of aging.
Co-reporter:M.W. Spencer, D.R. Paul
Polymer 2011 Volume 52(Issue 21) pp:4910-4919
Publication Date(Web):29 September 2011
DOI:10.1016/j.polymer.2011.08.042
The modulus and coefficient of thermal expansion (CTE) of polypropylene-based nanocomposites and blends were predicted using various composite theories and compared to experimental results. The Mori–Tanaka and Chow model predictions best match the previously reported experimental trends, though the Chow model underestimates the CTE in the normal direction (ND). Of the various ternary-phase approaches used to predict the modulus and CTE of thermoplastic polyolefin (TPO) nanocomposites, a multiplicative approach wherein the contribution of the clay is calculated first and the nanocomposite is then considered to be the matrix for the elastomer blend best matches the experimental trends. The models better capture the effects of the MMT than those of the ethylene–octene elastomer, EOR. A different model predicting the effect of the MMT tactoids on the experimental TPO gives rather good quantitative agreement between the predicted and experimental values of modulus and CTE for TPO nanocomposites.
Co-reporter:Rajkiran R. Tiwari, D.R. Paul
Polymer 2011 Volume 52(Issue 21) pp:4955-4969
Publication Date(Web):29 September 2011
DOI:10.1016/j.polymer.2011.08.019
PP/PP-g-MA/MMT/elastomer nanocomposites were prepared in a twin-screw extruder at fixed 30 wt% elastomer and 0–7 wt% MMT content. The ratio of maleated polypropylene, PP-g-MA and organoclay was maintained at 1. Elastomer particle size and shape in the presence of MMT were evaluated for three different molecular weight grades of polypropylene (PP) and five different ethylene-co-octene elastomers (EOR) with different melt flow index (MFI) and octene contents. The MMT particles are located exclusively in the PP phase in the PP/PP-g-MA/MMT/EOR nanocomposites as seen from TEM images. Injection molded nanocomposite samples show significant decreases in elastomer particle size and increases in elastomer aspect ratio and particle density compared to as-extruded or pelletized samples. The elastomer particle size decreased significantly with increased MMT content and the molecular weight of PP. Low molecular weight PP based nanocomposite showed a greater reduction in elastomer particle size compared to medium and high molecular weight PP based nanocomposites. Elastomers having MFI in the range of 0.5–1.0 gave minimum elastomer particle sizes in the PP/PP-g-MA/MMT/EOR nanocomposite. The elastomer particles were deformed during injection molding leading to an increase in their aspect ratio. The nanocomposites containing high octene content elastomer gave smaller elastomer particle size and higher elastomer aspect ratios compared to nanocomposites containing low octene content elastomer.
Co-reporter:Rajkiran R. Tiwari, D.R. Paul
Polymer 2011 Volume 52(Issue 4) pp:1141-1154
Publication Date(Web):17 February 2011
DOI:10.1016/j.polymer.2011.01.019
The effect of organically modified clay on the morphology, phase stability and mechanical properties of polypropylene (PP) and polystyrene (PS) blends was studied using three molecular weight grades of PP. Maleated polypropylene was used, at a PP-g-MA/organoclay ratio of 1, to preferentially promote dispersion of the organoclay in the PP matrix. The MMT content was fixed at 3 wt% based on the PP/PP-g-MA/MMT phase and the PS content was varied from 0–100 wt% in the blend. All blends were processed using a twin screw extruder. The organoclay resides in the PP phase and at the PP/PS interface. The dispersed PS particle size is significantly reduced by the presence of MMT, with maximum decrease observed for the low viscosity PP compared to its blend without MMT. The blends with MMT did not show any change in onset of co-continuity, though MMT shifts the phase inversion composition toward lower PS contents. The phase stability of the blend was significantly improved by the presence of MMT; for blends annealed at 210 °C for 2 h the dispersed phase particle size increased by as much as 10x without MMT with little change was noted with MMT present in the blend. The tensile modulus of blends improved with the addition of MMT at low PS contents. Blends based on the highest molecular weight grade PP showed increase in the tensile yield stress up to 40 wt% PS in the absence of MMT. The tensile strength at break for blend increased slightly with MMT while elongation at break and impact strength decreased in the presence of MMT. Surface energy analysis model was used to predict the orientation and equilibrium position of the clay platelet at the interface based on the surface energies.
Co-reporter:Youngjae Yoo, M.W. Spencer, D.R. Paul
Polymer 2011 Volume 52(Issue 1) pp:180-190
Publication Date(Web):7 January 2011
DOI:10.1016/j.polymer.2010.10.059
Nylon 6 composites containing both an organoclay and glass fibers as fillers were prepared by melt processing. The aspect ratios of the glass fibers and the clay platelets were determined by electron microscopy techniques. The aspect ratio of each type of filler decreased as filler loading increased. A two particle population model for the tensile modulus was constructed based on the Mori–Tanaka composite theory. The experimental levels of reinforcement appear to be reasonably consistent with model predictions when changes in particle aspect ratios are accounted for. The tensile strength increases and elongation at break decreases as the content of either filler increases according to expected trends. Izod impact strength increased with glass fiber content but decreased with clay content.
Co-reporter:Lili Cui, Wulin Qiu, D.R. Paul, W.J. Koros
Polymer 2011 Volume 52(Issue 24) pp:5528-5537
Publication Date(Web):10 November 2011
DOI:10.1016/j.polymer.2011.10.008
Co-reporter:Norman R. Horn, D.R. Paul
Polymer 2011 Volume 52(Issue 24) pp:5587-5594
Publication Date(Web):10 November 2011
DOI:10.1016/j.polymer.2011.10.004
Co-reporter:Rajkiran R. Tiwari, D.R. Paul
Polymer 2011 Volume 52(Issue 24) pp:5595-5605
Publication Date(Web):10 November 2011
DOI:10.1016/j.polymer.2011.10.002
Room temperature Izod impact strength was determined for polypropylene (PP)/ethylene-co-octene elastomer (EOR) blends and nanocomposites, containing organoclays based on montmorillonite (MMT), at fixed elastomer content of 30 wt% and 0–7 wt% MMT. A ratio of maleated polypropylene, PP-g-MA to organoclay of unity was used as a compatibilizer in the nanocomposites. The organoclay serves to reduce the size of the EOR dispersed phase particles and facilitates toughening. The Izod impact strength is also influenced by the molecular weight of PP, elastomer octene content, elastomer MFI in addition to MMT content. Nanocomposites based on a low molecular weight polypropylene (L-PP) containing a higher octene content elastomer showed higher impact strength at lower MMT contents compared to those based on a low octene content elastomer. The effect of elastomer octene content on impact strength of high molecular weight polypropylene (H-PP) nanocomposites is not so significant. Elastomers having a melt flow index (MFI) in the range of 0.5–1.0 showed significant improvement in the impact strength of L-PP based nanocomposites. Most H-PP/EOR blends gave ‘super-tough’ materials without MMT and maintain this toughness in the presence of MMT. The critical elastomer particle size below which the toughness is observed is reduced by decreasing the octene content of the elastomer. For the similar elastomer particle sizes in nanocomposites, the impact strength varies as H-PP > M-PP > L-PP. The tensile modulus and yield strength improved with increasing MMT content; however, elongation at break was reduced. The extruder-made TPO showed a good-balance of properties in the presence of MMT compared to reactor-made TPO having similar modulus and elastomer content.
Co-reporter:Norman R. Horn, D.R. Paul
Polymer 2011 Volume 52(Issue 7) pp:1619-1627
Publication Date(Web):23 March 2011
DOI:10.1016/j.polymer.2011.02.007
Recent studies have shown that thin glassy polymer films undergo physical aging more rapidly than thick films. This suggests that thickness may also play a role in the plasticization and conditioning responses of thin glassy films in the presence of highly-sorbing penetrants such as CO2. In this paper, a carefully designed systematic study explores the effect of thickness on the CO2 plasticization and conditioning phenomena in Matrimid®, a polyimide commonly used in commercial gas separation membranes. Thin films are found to be more sensitive than thick films to CO2 exposure, undergoing more extensive and rapid plasticization at any pressure. The response of glassy polymers films to CO2 is not only dependent on thickness, but also on aging time, CO2 pressure, exposure time, and prior history. Finally, thin films experiencing constant CO2 exposure for longer periods of time exhibit an initial large increase in CO2 permeability, which eventually reaches a maximum, followed by a significant decrease in permeability for the duration of the experiment. Thick films, in contrast, do not seem to exhibit this trend for the range of conditions explored.
Co-reporter:Lili Cui, Wulin Qiu, D.R. Paul, W.J. Koros
Polymer 2011 Volume 52(Issue 15) pp:3374-3380
Publication Date(Web):7 July 2011
DOI:10.1016/j.polymer.2011.05.052
The aging behaviors, as judged by gas permeability, of two glassy 6FDA-based polyimides, 6FDA-DAM and 6FDA-mPDA, in thick and thin film forms are reported. Their O2 and N2 gas permeabilities were monitored over several thousands of hours. In general, the properties of these thin films deviate dramatically from their bulk behavior, by showing much more rapid decrease in gas permeability and increase in selectivity. Owing to the high free volume, the 6FDA-DAM thin films have very high permeability at the very early aging time, followed by an order of magnitude decrease in permeability relative to the initial value over the course of 1000 h of aging. On the other hand, a thick 6FDA-DAM polymer film maintained a high permeability over thousands of hours of aging. 6FDA-mPDA thin films have moderate aging rates comparable to thin films made from other polyimides such as Matrimid®. Effect of PDMS coating on gas permeability and aging was examined using a few 6FDA-mPDA thin film membranes and was found to be insignificant.
Co-reporter:G.M. Geise, B.D. Freeman, D.R. Paul
Polymer 2010 Volume 51(Issue 24) pp:5815-5822
Publication Date(Web):12 November 2010
DOI:10.1016/j.polymer.2010.09.072
Water and salt transport properties were determined in a family of sulfonated pentablock copolymers to characterize their potential as chlorine-tolerant desalination membrane materials. The degree of sulfonation, block molecular weight, and casting conditions can be independently varied to tune the transport properties of these materials. Data for water uptake, water permeability, salt permeability, and apparent surface charge are presented. Apparent diffusion coefficients of water in these materials were calculated using the solution-diffusion theory. Generally speaking, water sorption, water diffusivity, water permeability, and salt permeability increase with increasing degree of sulfonation. As ion exchange capacity increases from 0.4 to 2.0 meq/g (dry polymer), water uptake values vary between 21% and 118%, and water permeability values, in units of cm2 s−1, vary over 4 orders of magnitude. Salt permeability depends on both the upstream sodium chloride concentration, between 0.01 and 1.0 mol L−1, and the degree of sulfonation. Both water permeability and salt permeability are sensitive to the conditions used when casting the polymer films. Apparent surface charge, as characterized by zeta potential, has been shown to be related to the fouling tendency of several membrane materials. In these materials, zeta potential is most negative in samples with low levels of sulfonation and is near neutral in samples with the highest level of sulfonation.
Co-reporter:M.W. Spencer, Lili Cui, Youngjae Yoo, D.R. Paul
Polymer 2010 Volume 51(Issue 5) pp:1056-1070
Publication Date(Web):2 March 2010
DOI:10.1016/j.polymer.2009.12.047
Nanocomposites formed from blends of high density polyethylene (HDPE) and maleic anhydride-grafted high density polyethylene (HDPE-g-MA) and M2(HT)2 organoclay were melt processed to explore the extent of exfoliation and the mechanical properties. Wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM) coupled with detailed particle analysis were used to determine the effect of HDPE-g-MA content and organoclay content on exfoliation and mechanical properties. As the HDPE-g-MA content increases, the global average particle aspect ratio initially increases drastically, reaches a maximum, and slightly decreases. The fraction of single platelets, however, increases at a steady rate for nanocomposites with HDPE-g-MA contents ≥25%. Relative modulus initially improves with increased levels of HDPE-g-MA, and then levels off with greater HDPE-g-MA content. Izod impact strength reaches a maximum at low HDPE-g-MA levels, decreases below the value for the pure HDPE nanocomposite, and levels off at higher HDPE-g-MA content. A composite model based on the Mori–Tanaka theory was developed to treat organoclay tactoids and single platelets as two separate types of fillers. This model gives rather good quantitative agreement between the predicted values of modulus calculated from the TEM results and that measured experimentally.
Co-reporter:Youngjae Yoo, Rajkiran R. Tiwari, Young-Tai Yoo, Donald R. Paul
Polymer 2010 Volume 51(Issue 21) pp:4907-4915
Publication Date(Web):1 October 2010
DOI:10.1016/j.polymer.2010.08.036
An amorphous polyamide (a-PA) was blended with an ethylene-1-octene (EOR) elastomer with organoclays present to control the elastomer particle size. Four different organoclays, M3(HT)1, M2(HT)2, M1H1(HT)2, and (HE)2M1T1 and two different mixing protocols were used to investigate the effect of the organoclay structure and mixing protocol on the morphology and properties of the resulting blends. Wide angle X-ray scattering, transmission electron microscopy, and stress-strain behavior were used to evaluate the degree of exfoliation of the organoclays and the morphology of the elastomer particles for these blends. A detailed particle analysis was made to provide a quantitative assessment of elastomer particle size. The size and shape of the elastomer particles were dramatically affected by the amount of organoclay but the organoclay type and the mixing protocol led to slight differences. Broadly speaking, most of the MMT platelets are well exfoliated in the a-PA phase, but some locate at the interface and tend to envelop the EOR phase. The mechanical properties were not significantly affected by the organoclay type or the mixing protocol. While the organoclays reduced the EOR particles to size range where toughness might be expected, all blends proved to be brittle. A clear trade-off was observed between the Izod impact strength and tensile modulus for these blends containing organoclays.
Co-reporter:Brandon W. Rowe, Benny D. Freeman, D.R. Paul
Polymer 2010 Volume 51(Issue 16) pp:3784-3792
Publication Date(Web):22 July 2010
DOI:10.1016/j.polymer.2010.06.004
The physical aging behavior of thin glassy polysulfone (PSF) films (∼125 nm) with different previous histories was tracked using gas permeability measurements. The initial states of these materials were modulated by thermal annealing at fixed temperatures below the glass transition or by exposure to high pressure (800 psig (56.2 bara)) CO2 for various times. Regardless of the previous history, the nature of the aging response in these samples was consistent with the aging behavior of an untreated film that was freshly quenched from above Tg, i.e., permeability decreased and pure gas selectivity increased with aging time. However, the extent of aging-induced changes in transport properties of these materials depended strongly on previous history. The aging behavior was described using Struik’s aging model by allowing the initial conditions to depend on each sample’s previous history.
Co-reporter:Youngjae Yoo, Lili Cui, P. J. Yoon and D. R. Paul
Macromolecules 2010 Volume 43(Issue 2) pp:615-624
Publication Date(Web):December 15, 2009
DOI:10.1021/ma902232g
The effects of addition of an organoclay on the morphology and the mechanical properties of blends of an amorphous polyamide (a-PA) and an elastomer (with and without grafted maleic anhydride) prepared via melt processing are reported. Transmission electron microscopy (TEM) and wide-angle X-ray scattering (WAXS) were employed to obtain a detailed quantitative analyses of the morphology of the elastomer particles for these nanocomposites containing 80 wt % a-PA and 20 wt % elastomer. Stress−strain diagrams and impact strength were measured as a function of organoclay content for blends containing maleated and unmaleated elastomer. It is clear that the addition of organoclay to blends can be an effective way for reducing elastomer particle size and enhancing stiffness when the elastomer is not maleated; however, for this system, toughness is not improved in spite of these morphological changes. Blends based on the maleated elastomer give a more beneficial balance of toughness versus stiffness.
Co-reporter:Geoffrey M. Geise;Hae-Seung Lee;Daniel J. Miller;Benny D. Freeman;James E. McGrath
Journal of Polymer Science Part B: Polymer Physics 2010 Volume 48( Issue 15) pp:1685-1718
Publication Date(Web):
DOI:10.1002/polb.22037
Abstract
Two of the greatest challenges facing the 21st century involve providing sustainable supplies of clean water and energy, two highly interrelated resources, at affordable costs. Membrane technology is expected to continue to dominate the water purification technologies owing to its energy efficiency. However, there is a need for improved membranes that have higher flux, are more selective, are less prone to various types of fouling, and are more resistant to the chemical environment, especially chlorine, of these processes. This article summarizes the nature of the global water problem and reviews the state of the art of membrane technology. Existing deficiencies of current membranes and the opportunities to resolve them with innovative polymer chemistry and physics are identified. Extensive background is provided to help the reader understand the fundamental issues involved. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010
Co-reporter:Brandon W. Rowe, Lloyd M. Robeson, Benny D. Freeman, Donald R. Paul
Journal of Membrane Science 2010 360(1–2) pp: 58-69
Publication Date(Web):
DOI:10.1016/j.memsci.2010.04.047
Co-reporter:M.C. Ferrari, S. Carranza, R.T. Bonnecaze, K.K. Tung, B.D. Freeman, D.R. Paul
Journal of Membrane Science 2009 Volume 341(1–2) pp:1
Publication Date(Web):30 September 2009
DOI:10.1016/j.memsci.2009.05.054
Co-reporter:L.M. Robeson, B.D. Freeman, D.R. Paul, B.W. Rowe
Journal of Membrane Science 2009 Volume 341(1–2) pp:178-185
Publication Date(Web):30 September 2009
DOI:10.1016/j.memsci.2009.06.005
A large database of permeability values for common gases (He, H2, O2, N2, CO2 and CH4) has been employed in the following correlation: Pj=kPin where Pi and Pj are the permeabilities of gases i and j; the indices are chosen such that the value of n is >1.0. The plots of log Pi versus log Pj show linear behavior over nine orders of magnitude implying solution–diffusion behavior persists over the entire range of permeabilities existing in known dense polymeric materials. The scatter of data around the linear correlation for each gas pair was modest over the entire range of permeability. It was found that n correlates with the kinetic diameter of the specific gases of the pair by a relationship: n − 1∼(dj/di)2 − 1 in agreement with theory. Correlations exist between n and k for the noted relationship and nu and ku of the upper bound relationship of Pi=kuαijnu where αij = Pi/Pj. The experimental values of n − 1 enable the determination of a new set of kinetic diameters showing excellent agreement between theory and experimental results. The value of 1/k was found to be virtually an exact fit with the relationship developed by Freeman in predicting the value of ku for the upper bound relationship using the new set of kinetic diameters where the calculations were constrained to minimize the error in (n − 1) = (dj/di)2 − 1. The significance of these results includes a new set of kinetic diameters predicted by theory and agreeing with experimental data with accuracy significantly improved over the zeolite determined diameters previously employed to correlate diffusion selectivity in polymers. One consequence of this analysis is that the kinetic diameter of CO2 is virtually identical to that of O2. Additionally, the theoretical relationship developed by Freeman for the upper bound prediction is further verified by this analysis which correlates the average permeability for polymeric materials as compared to the few optimized polymer structures offering upper bound performance.
Co-reporter:M.C. Ferrari, S. Carranza, R.T. Bonnecaze, K.K. Tung, B.D. Freeman, D.R. Paul
Journal of Membrane Science 2009 Volume 329(1–2) pp:183-192
Publication Date(Web):5 March 2009
DOI:10.1016/j.memsci.2008.12.030
The oxygen barrier behavior of polymer films can be significantly improved by incorporating particles of an oxygen-scavenging polymer, e.g., those based on butadiene containing an appropriate catalyst, in a matrix of a barrier polymer like poly(ethylene terephthalate) or polystyrene. This paper develops a mathematical model for predicting the transient barrier properties of such blend films. The analysis uses a “shrinking core” model for oxygen consumption by the particles and treats oxygen diffusion in the matrix polymer by a one-dimensional approximation. Scavenging can extend the time lag for the transient permeation by factors of thousands. A key point of the analysis is the calculation of the flux of oxygen exiting the downstream surface of the film for times of the order of the time lag and less using realistic geometrical and physical parameters.
Co-reporter:Brandon W. Rowe, Steven J. Pas, Anita J. Hill, Ryoichi Suzuki, Benny D. Freeman, D.R. Paul
Polymer 2009 50(25) pp: 6149-6156
Publication Date(Web):
DOI:10.1016/j.polymer.2009.10.045
Co-reporter:Brandon W. Rowe, Benny D. Freeman, Donald R. Paul
Polymer 2009 50(23) pp: 5565-5575
Publication Date(Web):
DOI:10.1016/j.polymer.2009.09.037
Co-reporter:Lili Cui, Jason E. Bara, Yefim Brun, Youngjae Yoo, P.J. Yoon, D.R. Paul
Polymer 2009 50(11) pp: 2492-2502
Publication Date(Web):
DOI:10.1016/j.polymer.2009.03.036
Co-reporter:Lili Cui, Christina Troeltzsch, P. J. Yoon and D. R. Paul
Macromolecules 2009 Volume 42(Issue 7) pp:2599-2608
Publication Date(Web):March 10, 2009
DOI:10.1021/ma900105w
Nanocomposites were prepared by melt blending a series of sodium ionomers formed from poly(ethylene-co-methacrylic acid) and the M2(HT)2 organoclay. The effects of the degree of neutralization of the acid groups on the morphology and properties of the nanocomposites were evaluated using stress−strain analysis, wide-angle X-ray scattering (WAXS), and transmission electron microscopy coupled with particle analysis. The organoclay exfoliation improves progressively as the neutralization level of the sodium ionomers increases. It seems that the ionic units on polymer chains provide a more favorable interaction between the polymer matrix and organoclay than acid units. Predictions of the tensile modulus of the nanocomposites by the Halpin−Tsai equations capture some of the experimental trends, but the absolute values do not agree well with the experimental observations.
Co-reporter:B.S. Kirkland, R. Clarke, D.R. Paul
Journal of Membrane Science 2008 Volume 324(1–2) pp:119-127
Publication Date(Web):31 October 2008
DOI:10.1016/j.memsci.2008.07.001
Modified atmosphere packaging, MAP, employs gas permeable membranes to achieve the specific atmosphere needed to prolong the shelf-life of produce; commercial implementation of this concept is growing for small, disposable retail packages. Membrane technology can also be used to create appropriate atmospheres in reusable large-scale bulk containers for storage and shipping of produce. However, this approach would be more viable if a versatile system were available that could accommodate the requirements of different types of produce without altering the hardware, i.e., one membrane system could be used to create different compositions of oxygen and carbon dioxide, depending on what produce is being shipped or stored at a given time. A scheme is proposed here that uses a selective membrane and a non-selective membrane acting in parallel. The relative amount of gas exchange through the non-selective membrane can be adjusted by varying the volumetric air feed rate to its upstream surface; this will, in turn, adjust the steady-state composition of the gas around the produce. A quantitative model for this scheme and sample calculations are presented to illustrate the concept and how to design such a system where the atmosphere created can be set to the desired range by adjusting the air feed rate.
Co-reporter:Donald R. Paul
Materials Today 2007 Volume 10(1–2) pp:55
Publication Date(Web):January–February 2007
DOI:10.1016/S1369-7021(06)71795-3
Fillers used in polymer composites range from nanosized particles to macroscale fibers, and a new volume aims to cover them all.
Co-reporter:R.K. Shah;D.L. Hunter;D.R. Paul;F. Chavarria
Polymer Engineering & Science 2007 Volume 47(Issue 11) pp:1847-1864
Publication Date(Web):28 SEP 2007
DOI:10.1002/pen.20894
Nylon 6 (PA-6) organoclay nanocomposites were prepared by melt processing using three different twin screw extruders (TSEs). The effect of mixing conditions, feed port location, residence time, and number of extrusion passes on the morphology and mechanical properties of the nanocomposites were examined. Wide-angle X-ray scattering, transmission electron microscopy (TEM), and mechanical property data are reported. Particle analyses were performed on the TEM images to quantitatively characterize the extent of exfoliation. The amount of shear and the mixing conditions created by TSEs have a significant effect on the morphology and properties of PA-6 nanocomposites. Morphology and mechanical property results show that (1) melting the polymer before coming into contact with the organoclay followed by a low level of shear and (2) maintaining a medium level of shear throughout the extruder with a longer residence time lead to extremely high platelet dispersion and matrix reinforcement for PA-6 nanocomposites. Nanocomposites formed in a DSM microcompounder showed similar morphologies and modulus trends as those obtained with conventional TSEs; thus, this microcompounder is a good alternative for nanocomposite research especially when only small amounts of material are available. POLYM. ENG. SCI., 47:1847–1864, 2007. © 2007 Society of Plastics Engineers
Co-reporter:Y. Huang;D. R. Paul
Journal of Polymer Science Part B: Polymer Physics 2007 Volume 45(Issue 12) pp:1390-1398
Publication Date(Web):25 APR 2007
DOI:10.1002/polb.21173
The effects of polymer molecular weight and temperature on the physical aging of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is examined. Gas permeability and refractive index were monitored during the aging process for PPO film samples at three aging temperatures below the glass transition temperature. Comparisons between the two samples of PPO that differ widely in molecular weight reveal an insignificant difference, which support the notion that above a critical molecular weight range there is little influence on aging rate. Increased temperature, over the limited range of 35–55 °C, results in higher aging rates for films made from both PPO materials. The rate of aging decreases strongly with increasing film thickness over the range examined, ∼0.4–25 μm. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1390–1398, 2007
Co-reporter:J.H. Kim, W.J. Koros, D.R. Paul
Journal of Membrane Science 2006 Volume 282(1–2) pp:21-31
Publication Date(Web):5 October 2006
DOI:10.1016/j.memsci.2006.05.004
The changes in permeability of He, O2, N2, CH4 and CO2 through thin films (∼350 nm) of 6FDA-based polyimides with and without DABA units in the chain were monitored as a function of aging time at 35 °C using different methodologies that varied the exposure of these films to CO2. A pulse of CO2 exposure after aging causes the permeability of each gas to increase; the change is greater the larger the probe gas molecule. Continuous exposure to CO2 over 100 h leads to a larger increase in permeability than periodic CO2 exposure over the same period, but the trends are basically similar for the two cases. After a CO2 pulse, the permeability relaxes and approaches the aging response established prior to CO2 exposure. The change in refractive index for CO2 exposed films is consistent with the change in gas permeability in most regards; however, the recovery of refractive index following CO2 exposure is somewhat less than observed by permeability. Periodic exposure to CO2 during aging seems to retard the decline in gas permeability with the effect being greater for larger probe molecules. An increase in CO2/CH4 and O2/N2 selectivities with aging was observed for thin films that were never exposed to CO2 while these selectivities decrease with aging when periodic exposure to CO2 was imposed.
Co-reporter:J.H. Kim, W.J. Koros, D.R. Paul
Journal of Membrane Science 2006 Volume 282(1–2) pp:32-43
Publication Date(Web):5 October 2006
DOI:10.1016/j.memsci.2006.05.003
The changes in permeability of N2, O2, He, CH4 and CO2 of thin films (∼300 nm) of crosslinked and uncrosslinked 6FDA-based polyimides with DABA units in the chain were monitored as a function of aging time at 35 °C. The crosslinked polyimides have significantly lower permeability than the corresponding uncrosslinked material. Over about 2000 h of aging, the oxygen permeability decreased by two- to three-fold depending on the polymer structure. The changes in density for the crosslinked and uncrosslinked polyimides with aging time were calculated from refractive index measurements made by ellipsometry using the Lorentz–Lorenz equation. An excellent correlation between the volumetric aging rate and the permeability reduction rate is observed for these polyimides and other glassy polymers. On a relative basis, it seems that the crosslinked polyimide films show slightly higher or about the same aging rates than uncrosslinked polyimide films. Periodic exposure to CO2 has a significant effect on the permeability and selectivity and how they change with physical aging for the uncrosslinked polyimides but the effects for crosslinked films are much less. Thus, crosslinking appears to be a viable strategy for mitigating the plasticization or conditioning effects of CO2 exposure.
Co-reporter:Rhutesh K. Shah;D. R. Paul;Kelly L. Williams;Bernard Bauman;Lili Cui
Journal of Applied Polymer Science 2006 Volume 102(Issue 3) pp:2980-2989
Publication Date(Web):23 AUG 2006
DOI:10.1002/app.24586
We present a novel approach to improving organoclay exfoliation in a nonpolar matrix, polyethylene. High-density polyethylene (HDPE) particles were modified by exposure to a reactive gas atmosphere containing F2 and O2. This treatment was aimed at increasing the polarity of the polymer with the formation of carboxyl, hydroxy, and ketone functionalities on the particle surface. The surface-treated high-density polyethylene (ST-HDPE) particles were then melt-mixed with an appropriate organoclay to form nanocomposites. Transmission electron microscopy (TEM), wide-angle X-ray scattering, stress–strain analysis, and Izod impact measurements were used to evaluate the nanocomposite morphology and physical properties. These data were compared to those of equivalent nanocomposites prepared from unmodified HDPE and high-density polyethylene grafted with maleic anhydride (HDPE-g-MA). The nanocomposites prepared from the ST-HDPE particles exhibited much better properties and organoclay dispersion than those prepared from unmodified HDPE. The level of reinforcement observed in ST-HDPE-based nanocomposites was comparable to, if not better than, that seen in HDPE-g-MA-based nanocomposites. However, a comparison of the TEM micrographs suggested better organoclay exfoliation in HDPE-g-MA than the current version of ST-HDPE. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2980–2989, 2006
Co-reporter:D.R. Paul, Q.H. Zeng, A.B. Yu, G.Q. Lu
Journal of Colloid and Interface Science 2005 Volume 292(Issue 2) pp:462-468
Publication Date(Web):15 December 2005
DOI:10.1016/j.jcis.2005.06.024
Understanding the interlayer swelling and molecular packing in organoclays is important to the formation and design of polymer nanocomposites. This paper presents recent experimental and molecular simulation studies on a variety of organoclays that show a linear relationship between the increase of d-spacing and the mass ratio between organic and clay. A denser molecular packing is observed in organoclays containing surfactants with hydroxyl–ethyl units. Moreover, our simulation results show that the head (nitrogen) groups are essentially tethered to the clay surface while the long hydrocarbon chains tend to adopt a layering structure with disordered conformation, which contrasts with the previous assumptions of either the chains lying parallel to the clay surface or being tilted at rather precise angles.Molecular simulations show that the alkyl chains of organoclay surfactants pack in a disordered conformation but with a tendency for layering. The measured and calculated gallery spacings increase in proportion to the mass of the surfactant consistent with a given mass density of the confined organic material with good agreement between experiment and simulation.
Co-reporter:S. Matsui, D.R. Paul
Journal of Membrane Science 2004 Volume 235(1–2) pp:25-30
Publication Date(Web):1 June 2004
DOI:10.1016/j.memsci.2003.12.020
A new model for pervaporation of binary mixtures through rubbery polymeric membranes is proposed. The model deals with the inherent problem of plasticization in a very simple, but physically realistic manner, and consequently contains fewer parameters than prior models; thus, concentration profiles can be computed from a minimum of experimental results for pervaporation and sorption. Results from a series of ionically crosslinked poly(n-alkyl acrylate) membranes and toluene/i-octane binary mixtures are used to test the model. The model reasonably represents experimental results for pervaporative transport of toluene/i-octane mixtures through these membranes. Concentration profiles for the penetrants across the membranes are calculated from the model using experimental results and parameters obtained in the fitting process.
Co-reporter:Wenyuan Xu, Donald R Paul, William J Koros
Journal of Membrane Science 2003 Volume 219(1–2) pp:89-102
Publication Date(Web):15 July 2003
DOI:10.1016/S0376-7388(03)00188-1
Pervaporation (PV) separation of toluene/iso-octane mixtures via copolyimide membranes containing 3,5-diaminobenzoic (DABA) was investigated. Incorporation of the DABA units promotes segmental packing, reduces membrane swelling, and improves membrane selectivity and durability. The material containing 60% DABA-based repeat units provides a normalized flux of 1 kg μm/m2 h and a selectivity of 90 for the toluene/iso-octane (50/50 wt.%) system at 100 °C. The improvement in pervaporation selectivity, relative to the polymer without DABA, is mainly due to the increase in diffusivity selectivity; however, favorable toluene/iso-octane solubility selectivity also contributes significantly as well. A correlation of the pervaporation performance with the intrinsic fractional free volume (FFV) of the glassy polymer is observed and explained in terms of the downstream conditions present in pervaporation. The pervaporation performance of the current polyimides is compared with other materials reported in the literature. Relationships between polymer structure and transport are established.
Co-reporter:D.R. Paul, R. Clarke
Journal of Membrane Science 2002 Volume 208(1–2) pp:269-283
Publication Date(Web):1 October 2002
DOI:10.1016/S0376-7388(02)00303-4
The freshness of fruits and vegetables can be prolonged by storage in an optimum atmosphere of oxygen and carbon dioxide that slows the respiratory process. The technology known as modified atmosphere packaging (MAP) seeks to create such an environment passively during shipping, storage, and marketing of produce. It is shown here that the combination of a high flux membrane (selective permeation of gases) patch with perforations (or holes that provide non-selective permeation of gases) in the package film offer a versatile route to create whatever oxygen and carbon dioxide environment may be needed for a given product. Detailed mathematical models are developed here for describing and designing such systems. Particular attention is devoted to the steady-state analysis where produce respiration is balanced by transport into and out of the package. The perforations serve the dual function of allowing convective flow of gases to prevent package volume shrinkage and non-selective permeation of gases to adjust the ratio of CO2/O2 transport. Detailed predictive models for both functions are developed.
Co-reporter:Z. Mogri;D. R. Paul
Journal of Polymer Science Part B: Polymer Physics 2001 Volume 39(Issue 10) pp:979-984
Publication Date(Web):27 MAR 2001
DOI:10.1002/polb.1074
The water-vapor permeability of poly(octadecyl acrylate) (PA-18) was measured as a function of temperature in the region traversing its melting point (50 °C). The molten-state permeability of PA-18 is comparable to that of shorter side-chain methacrylate polymers. Water permeability in the semicrystalline state of PA-18 is similar to that of polyethylene at comparable crystallinity levels. The permeation switch, or change in permeability with the traversing of the melting point, for water is discussed in the context of previous results for other penetrants in this and other side-chain crystalline polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 979–984, 2001
Co-reporter:Cher Hon Lau, Pei Li, Fuyun Li, Tai-Shung Chung, Donald R. Paul
Progress in Polymer Science (May 2013) Volume 38(Issue 5) pp:740-766
Publication Date(Web):1 May 2013
DOI:10.1016/j.progpolymsci.2012.09.006
This paper reviews the material design and fabrication of a class of membranes where some larger molecules can permeate faster than smaller ones, or so-called reverse-selective membranes, for conventional gas or vapor separation applications. The main requirements for a good reverse-selective gas or vapor separation membrane are high permeability, good separation capability, stable performance and sufficient mechanical properties to withstand the harsh environments in commercial separation processes. High permeability in reverse-selective membranes is achieved by tuning the fractional free volume (FFV) content, i.e., free spaces for penetrant diffusion, while facilitating preferential interaction between functional moieties of the membrane material and penetrant molecules to enhance penetrant sorption, and suppressing crystallinity where applicable. The separation capabilities of these membranes are generally controlled by the preferential sorption of larger condensable penetrants over smaller penetrants rather than size-selective diffusion common for conventional gas separation polymers. Reverse-selective gas separation membranes have attracted much attention owing to their advantages for certain commercial gas separation applications. This review summarizes the different aspects of polymeric reverse-selective gas separation membranes reported in the literature and comments briefly on their commercialization potential.
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-benzoxazolediylphenyleneoxyphenylene]](http://img.cochemist.com/ccimg/133600/133515-46-5_b.png)
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1,4-phenylene)oxy-1,4-phenylenecarbonyl-1,4-phenylene]](http://img.cochemist.com/ccimg/87800/87781-17-7.png)
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1,4-phenylene)oxy-1,4-phenylenecarbonyl-1,4-phenylene]](http://img.cochemist.com/ccimg/87800/87781-17-7_b.png)
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