Polyurethaneurea Membranes Research Articles

Tuning the stiffness and stretchability of micro-scale-structured polymer membrane simultaneously by integrating mechanical modeling and spatiotemporal controllable photolithograph

Micro-scale structural polymer membranes with desired mechanical properties, such as modulus and stretchability, have extensive applications in repair scaffolds, stretchable electronic devices, etc., yet how to achieve the simultaneous tunability of high modulus (MPa-level) and excellent resilience in micron-scale polymer membrane remains challenge. In this work, based on the material-structure integrated design aided by mechanical modeling and photolithograph, a micro-scale-structured solid-state lithography polyurethane-urea (UVSLPU) membrane has been fabricated, achieving a wide range of controllability on elastic modulus of 25–55 MPa and stretchability of 2.7–7.6 by simultaneously controlling the exposure time and area. Based on the physical mechanism of solid-state lithography, a novel visco-hyperelastic constitutive model is developed to facilitate the quantitative tunning of the mechanical property of UVSLPU. According to the microstructure analysis, the model decomposes the free energy of UVSLPU into three components, including crosslinked network, free chains as well as dangling chains, and describes the influence of exposure time on their nonlinear evolutions through increasing chain density and reducing the number of Kuhn monomers per chain. The proposed model is validated through uniaxial tensile tests conducted at different strain rates and exposure conditions, and reveals the significant contribution of crosslinks and free chains in enhancing the modulus over exposure time. Then, by integrating constitutive modeling and spatiotemporal controllable photolithograph, the design and manufacture for the micro-scale-structured UVSLPU membrane achieving increasing stiffness without losing the stretchability is realized by precisely controlling the exposure area. This work offers a novel and efficient approach for the design and manufacture of micro-scale-structured membranes with desired mechanical properties.

Improved gas transport properties of polyurethane–urea membranes through incorporating a cadmium‐based metal organic framework

ABSTRACTThe increasing need for more efficient separation processes has motivated the development of polymer membranes that can provide fast and selective transport. In this work, cadmium‐based metal–organic framework (MOF) nanoparticles and a polyurethane–urea (PUU) elastomer were synthesized. New mixed‐matrix membranes (MMMs) were then fabricated from the nanoparticles and the PUU. SEM images verified that embedding the nanoparticles changes the morphology of the PUU and the nanoparticles disperse well in the PUU due to satisfactory compatibility of the polymer and nanoparticles. Fourier transform infrared spectroscopy and X‐ray diffraction analysis confirmed the dispersion of the nanoparticles in the soft segment of the PUU. With increased temperature, gas permeabilities of the MMMs improved but their sieving ability deteriorated. An MMM incorporating 2.5 wt % of the MOF showed a CO2 permeability of ~140 barrer and a CO2/N2 selectivity of ~30, which are 89 and 38% higher than those of the pristine membrane. Gas permeation tests showed that the higher CO2/N2 selectivity of the MMMs was due to improved solubility selectivity and the higher CO2 permeability was a result of improved CO2 diffusivity and solubility coefficients. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48704.

Divinyl benzene cross‐linked HTPB‐based polyurethaneurea membranes for separation of p‐/o‐xylene mixtures by pervaporation

AbstractCross‐linked hydroxy terminated polybutadiene (HTPB)‐based polyurethaneurea (PU), HTPB‐divinyl benzene (DVB)‐PU, was synthesized by a three‐step polymerization process. It was first used as membrane material to separate p‐/o‐xylene mixtures by pervaporation (PV). The effects of the content of cross‐linker DVB, feed concentration, and operating temperature on the PV performance of HTPB‐DVB‐PU membranes were investigated. The membranes demonstrated p‐xylene permselectivity as well as high total flux. The introduction of DVB significantly enhanced the temperature resistance ability of the HTPB‐DVB‐PU membranes. With increasing DVB content, the separation factor increased while the total flux decreased a little. The highest separation factor reaches 2.01 and the total flux is 33 g/m2h with feed concentration of 10 wt % p‐xylene at 30°C. These PV performances with increasing DVB content were explained in terms of the view point of chemical compositions and physical structures of the HTPB‐DVB‐PU membranes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

ZSM-5 filled polyurethaneurea membranes for pervaporation separation isopropyl acetate from aqueous solution

ZSM-5 filled hydroxyl terminated polybutadiene (HTPB)-based polyurethaneurea (PU) membranes, HTPB-PU/ZSM-5, were prepared by a two-step polymerization process, which were used as membrane material to recover aroma, isopropyl acetate (IPAC), from aqueous solution by pervaporation (PV). The membranes demonstrated high IPAC permselectivity and with the increase of ZSM-5 loading, the separation factor increased initially and then decreased, while the total flux demonstrated the similar variation until the ZSM-5 loading was 40 wt.%, at which it reached the lowest value. After that, it began to increase again. The HTPB-PU/ZSM-5 membranes containing 20 wt.% ZSM-5, HTPB-PU/ZSM-5-20, showed the highest separation factor. On the other hand, the separation factor and total flux of HTPB-PU/ZSM-5-20 membrane increased with the increase of feed concentration and temperature. The best separation factor and total flux reached 288.72 and 53.21 g m −2 h −1, respectively, at 60 °C when the feed concentration of IPAC is 0.39 wt.%.

Pervaporation Separation of p-/o-Xylene Mixtures Using HTPB-Based Polyurethaneurea Membranes

Hydroxy terminated polybutadiene (HTPB)-based polyurethaneurea membranes with and without cross-linkage were synthesized and first used as membrane material to separate p-/o-xylene mixtures by pervaporation. Compared with HTPB-PU (without cross-linkage) membranes, HTPB-DVB-PU (cross-linked HTPB-PU with divinyl benzene) membranes demonstrated a lower degree of swelling in xylene isomer solutions and noticeable improved separation factor of p-/o-xylene. On the other hand, the amount of p-xylene adsorbed in HTPB-DVB-PU membranes increased significantly rather than that of o-xylene. While the separation factor of p-/o-xylene increased but the total flux decreased with increasing DVB content, which can be ascribed to the improved chemical structure and more homogeneous chain structures of the HTPB-DVB-PU membranes. The p-xylene normalized permeation rate and separation factor of p-/o-xylene of HTPB-DVB-PU membrane reached 2.70 kgµm/m2h and 2.23, respectively, at a feed concentration of 10 wt% p-xylene at 30°C.

The effect of urethane and urea content on the gas permeation properties of poly(urethane-urea) membranes

The effect of urethane and urea contents on gas separation properties of the groups of polyurethane–urea membranes is studied. The membranes used in this study were prepared by polytetramethylene-glycol (PTMG) and isophorone diisocyanate (IPDI) prepolymers. The prepolymers were converted to final polymer using the designed proportion of 1,4-butane diol (BDO) and 1,4-butane diamine (BDA) as a chain extender. Five different BDO/BDA ratios were chosen in order to synthesize poly(urethane-urea)s with different urethane/urea linkage content. The prepared polymers were characterized and the permeability of gases through them was investigated. Results obtained by Fourier transform infrared spectrometer (FT-IR) and differential scanning calorimetery (DSC) indicate that by increasing the urea linkage in the polymers, the microphase separation of hard and soft segments increase. Study of the X-ray diffraction (WAXD) patterns confirmed that polyols may be arranged in small crystalline structures. Permeation measurements of polymers revealed that the permeability of gases decreases with increasing urethane content in the polymers and selectivity of gases decreases with increasing urea content. The solubility and diffusivity of gases indicate solubility domination of gas transport in these membranes. The results of permeability also show high amounts up to 128 Barrer (1 Barrer = 1 × 10 −10 [cm 3 (STP) cm/cm 2 s cm Hg]), and high selectivity for carbon dioxide with respect to nitrogen (CO 2/N 2: 27).

Pervaporative separation of furfural from aqueous solution using modified polyurethaneurea membrane

Hydroxy-terminated polybutadiene (HTPB) based modified polyurethaneurea membranes were prepared and used to study the furfural separation efficiency from dilute aqueous solution by pervaporation. The modification was done by incorporation of lithium chloride in the polymer matrix with subsequent leaching of the same in hot water, thereby creating pores on the membrane. The pervaporation performance of the synthesized membranes was studied with aqueous furfural solution as feed. The modified membrane was found to show a maximum furfural separation factor of 284 and a furfural flux of 41.5 g m − 2 h − 1 . The effects of membrane porosity, feed composition and temperature on the membrane performance were also studied. Pore flow model was used to predict the permeate flux and permeate composition for the porous polyurethaneurea membrane.

Cross-linked HTPB-based polyurethaneurea membranes for recovery of ethyl acetate from aqueous solution by pervaporation

Cross-linked hydroxy terminated polybutadiene (HTPB)-based polyurethaneurea (PU), HTPB–DVB–PU, was synthesized by a three-step polymerization process. It was firstly used as membrane material to recover aroma, ethyl acetate (EA), from aqueous solution by pervaporation (PV). The effects of the content of cross-linker DVB, EA concentration in feed, and operating temperature on the PV performance of HTPB–DVB–PU membranes were investigated. The membranes demonstrated high EA permselectivity as well as high total flux. The introduction of DVB significantly enhanced the temperature resistance ability of the HTPB–DVB–PU membranes. With increasing DVB content, the separation factor increased while the total flux decreased a little. The best PV performance, separation factor and total flux were 655 and 256 g/m 2 h, respectively with feed concentration of 2.5 wt% EA at 30 °C. These PV performances with increasing DVB content were explained in terms of the viewpoint of chemical compositions and physical structures of the HTPB–DVB–PU membranes.

Preparation and Pervaporation Performances of PEA‐based Polyurethaneurea and Polyurethaneimide Membranes to Benzene/Cyclohexane Mixture

Pervaporation is promising in the separation of benzene/cyclohexane mixture for the petrochemical industry. Two kinds of pervaporation membrane materials, including PEA‐based polyurethaneurea (PUU) and polyurethaneimide (PUI), were successfully synthesized from the same soft segment of poly(ethylene adipate)diol (PEA) and different hard segments via a two‐step method. The hard segment of PUU was prepared from toluene diisocyanate (TDI) and 4,4′‐diaminodiphenyl methane (MDA), while that of PUI was from 4,4′‐methylene‐bis(phenylisocyanate) (MDI) and pyromellitic dianhydride (PMDA). The structures and properties of PUU and PUI were characterized by means of FT‐IR, DSC and TGA. During the pervaporation experiment, the PUI membranes had a flux of 12.13 kg µm m−2 h−1 and separation factor of 8.25, while the PUU membranes had a flux of 26.35 kg µm m−2 h−1 and separation factor of 6.29 for 50 wt% benzene in the benzene/cyclohexane mixture at 40°C. The effects of the structures of hard segments on pervaporation performances were discussed. The investigation of the relationship in molecular structure and PV performances will be helpful for the choice and design of membrane materials in the separation of benzene/cyclohexane mixture.

Porous polyurethane urea membranes for pervaporation separation of phenol and chlorophenols from water

Abstract Porous hydrophobic polyurethane urea (PUU) membrane was prepared for pervaporation separation of phenol and two chlorophenols namely p-chlorophenol (PCP) and 2,4-dichlorophenol (DCP). Polyurethane urea was synthesized by reacting hydroxy terminated polybutadiene (HTPB) with 2,4-toluene diisocyanate (TDI) using oxydianiline (ODA) as chain extender. Porosity was generated in the dense PUU by incorporating lithium chloride (LiCl) during PUU formation and then leaching out LiCl after PUU membrane formation. Both the pore size and number of pores per unit area was found to increase with increase in amount of LiCl addition during synthesis of membrane. The porous PUU showed better pervaporation separation efficiency than the dense PUU. The porous polyurethane membranes performed separation of phenol and chlorophenols with separation factors ranging from about 570 to 1760 at total permeate fluxes of 7.7–14.1 kg/m2 h over feed concentrations of 1000–4000 ppm (0.1–0.4%, w/v) at 30 °C. Phenol and chlorophenol fluxes have been increased remarkably by incorporation of porosity in the membrane. But the separation factor has not been increased to the extent of increase in flux.

Separation of furfural from aqueous solution by pervaporation using HTPB-based hydrophobic polyurethaneurea membranes

Hydroxyterminated polybutadiene (HTPB) was reacted with 2,4-toluylene diisocyanate (TDI) in THF medium followed by the addition of a diamine chain extender, 4,4´-diaminodiphenyl sulfone (DADPS) to prepare polyurethaneurea (PUU). The prepared viscous polyurethaneurea solution was cast over a glass Petri dish to obtain polymer membrane. Pervaporative separation of furfural/water mixtures was performed by using prepared flat sheet hydrophobic polyurethaneurea membranes. The effect of feed composition on the membrane performance was described by the permeate flux of furfural and separation factor. The synthesized polyurethaneurea membrane was found to permeate furfural selectively with high separation factor for the organic component.

HTPB‐based polyurethaneurea membranes for recovery of aroma compounds from aqueous solution by pervaporation

AbstractHydroxyterminated polybutadiene (HTPB)‐based polyurethaneurea (PU), HTPB‐PU, was synthesized by two‐step polymerization and was firstly used as membrane materials to recover aroma, ethyl acetate (EA), from aqueous solution by pervaporation (PV). The effects of the number–average molecular weight (Mn) of HTPB, EA in feed, operating temperature, and membrane thickness on the PV performance of HTPB‐PU membranes were investigated. The membranes demonstrated high EA permselectivity as well as high EA flux. The DSC result showed two transition temperatures in the HTPB‐PU membrane and contact angle measurements revealed the difference of hydrophobicity of the membrane at both sides, which were induced by glass plate and air, respectively, due to movement of the soft hydrophobic polybutadiene (PB) segments in HTPB‐PU chains. Furthermore, the PV performance of the HTPB‐PU membrane with the hydrophobic surface facing the feed was much better than that with the hydrophilic surface. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 552–559, 2007

Pervaporative recovery of N-methyl-2-pyrrolidone from dilute aqueous solution by using polyurethaneurea membranes

Hydroxyterminated polybutadiene (HTPB)-based polyurethaneurea membranes were synthesized and used for pervaporative recovery of N-methyl-2-pyrrolidone (NMP) from dilute aqueous solution. The sorption of NMP in cross-linked polyurethaneurea membranes was found to vary with feed NMP concentration and soft segment content of the membrane. A linear sorption isotherm was observed. The effects of membrane soft segment content, feed NMP concentration, operating temperature and membrane thickness on the pervaporation performance of the synthesized polyurethaneurea membranes were studied. With decrease in soft segment content of the membrane, the permeation flux was observed to decrease slightly but the separation factor increased to some extent. With the increase in concentration of NMP in feed solution, permeation flux was found to improve significantly. Both the permeation flux and the separation factor for NMP were found to increase with increase in operating temperature. The activation energy for pervaporation of both NMP and water calculated from Arrhenius plot indicated that an increase in hard segment content imposed a restriction to the transport of the components through the membrane.

Synthesis and characterization of porous polyurethaneurea membranes for pervaporative separation of 4-nitrophenol from aqueous solution

Hydroxyterminated polybutadiene (HTPB) based porous polyurethaneurea (PUU) membranes were prepared. The porosity was developed by incorporation of lithium chloride into polymer matrix with subsequent leaching of the same in hot water. Scanning electron microscopic analysis of the prepared membrane surfaces was performed. The pervaporation performance of the synthesized membrane was studied with aqueous 4-nitrophenol solution as feed. The effects of various parameters on 4-nitrophenol separation factor and total as well as 4-nitrophenol flux were studied. Polyurethaneurea membrane was found to permeate 4-nitrophenol selectively with high separation factors for the organic component. Pore size and number of pores on the surface of the membrane were calculated from SEM image of the membranes. Effects of pore size and porosity on pervaporation flux were also investigated.

Separation of phenol from aqueous solution by membrane pervaporation using modified polyurethaneurea membranes

AbstractHydroxy‐terminated polybutadiene‐based porous and nonporous polyurethaneurea membranes were prepared and used to study the phenol separation efficiency from dilute aqueous solution. The porosity was developed by incorporation of lithium chloride in polymer matrix with subsequent leaching of the same in hot water. The porous membrane showed higher phenol flux over that of nonporous membrane. Permeate containing about 97 wt % phenol was obtained from feed containing 7 wt % phenol, when pervaporation was carried out with porous polyurethaneurea membrane at 75°C. The activation energies for diffusion, permeation, and pervaporation were calculated from Arrhenius plots. From the activation energy values, it was observed that the pervaporation process became easier with increased phenol concentration in the feed and porosity of the membrane used. The membrane boundary resistance was observed to decrease with increase in temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1857–1865, 2006

Microencapsulation of ammonium phosphate with a polyurethane shell. Part II. Interfacial polymerization technique

Combination of polyurethane and phosphate provides an efficient intumescent flame retardant (FR) system which is not permanent because of the water solubility and migration of phosphate. Microencapsulation has appeared as an alternative way to achieve the permanence of the intumescent flame retardant system. This work deals with the microencapsulation of di-ammonium hydrogen phosphate (DAHP) by polyurethane-urea membrane using an interfacial polymerization method. Chemical and physical structures of the DAHP microcapsules were characterized. According to the thermal degradation analysis, the DAHP microcapsules show characteristics of an intumescent system.

Separation of water and o-chlorophenol by pervaporation using HTPB-based polyurethaneurea membranes and application of modified Maxwell–Stefan equation

Hydroxyterminated polybutadiene (HTPB) was reacted with 2,4-toluylene diisocyanate (TDI) followed by the addition of 4,4′-diaminodiphenyl sulfone (DADPS) (diamine chain extender) to prepare polyurethaneurea (PUUSD). The prepared polyurethaneurea was cast over glass petridish to obtain polymer membrane. The pervaporation (PV) performance of the synthesized membrane was studied with aqueous o-chlorophenol solution as feed. The polyurethaneurea membranes were found to be selective towards aromatic component with separation factors >250. The total flux as well as those of the individual components was measured. The effects of various parameters, such as feed composition and temperature, membrane thickness on permeate flux and separation factor were determined. The activation energy for o-chlorophenol permeation, calculated from Arrhenius plot, indicated that an increase in hard segment content imposed a restriction to the transport of organic component. The dependencies of the pervaporation fluxes and the concentration of organic component in permeate on its concentration in the feed were established with the calculation based on modified Maxwell–Stefan equation. A very close agreement between experimental and theoretical fluxes was observed.

Separation of phenol from aqueous solution by pervaporation using HTPB-based polyurethaneurea membrane

Hydroxyterminated polybutadiene (HTPB)-based polyurethane and polyurethaneurea (PUUSD) membranes were synthesized using 4,4′-diaminodiphenylsulfone (DADPS) as chain extender at varying concentrations. The pervaporation (PV) performances of the synthesized membranes were studied with 3% phenol water mixture as feed. The feed solution may be considered as a representative of phenol containing industrial wastewater. The variation of phenol selectivity and flux and other membrane boundary parameters were monitored. The membranes were observed to demonstrate high phenol permselectivity but offered a lower flux than that provided by the other polymer membranes used so far for phenol–water separation. Polyurethaneurea synthesized with 50 mol% diamine concentration showed about 97% phenol selectivity in permeate when pervaporation was carried out at 60 °C. The activation energies of phenol permeation were calculated for all membranes from Arrhenius plots.

Separation of toluene/nitrogen through segmented polyurethane and polyurethane urea membranes with different soft segments

Segmented polyurethane and polyurethane urea, containing soft segments such as polydimethylsiloxane (PDMS), polytetramethylene oxide (PTMO), and polyethylene oxide-polypropylene oxide triblock copolymer (PEO–PPO–PEO), were synthesized with a wide range of monomer concentrations. Dense membranes with 30–40 μm in thickness prepared by casting 20 wt.% N, N-dimethylformamide (DMF) solutions onto glass plate were examined for the separation of toluene vapor from nitrogen stream. Equilibrium liquid sorption behaviors of synthetic membranes were carried out by determining the amount of liquid toluene absorbed in the films at 25 °C. The vapor permeability of toluene through the PTMO/PDMS based polyurethane urea membranes were higher than those measured in PEO–PPO–PEO based polyurethane membranes due to plasticization by toluene vapor. In the case of the PTMO/PDMS based polyurethane urea membranes, the permeability of nitrogen increased and then the toluene/N 2 selectivity was lowered relative to those for PEO–PPO–PEO based polyurethane membranes due to plasticization of polymer. Up to the feed-flow rate of 250 ml min −1, the toluene fluxes obtained in all the membranes showed a linear dependence on the saturated feed concentration. The polyurethane urea membranes containing PTMO/PDMS mixed soft segment performed best with toluene separation, with toluene/N 2 selectivity ranging from 70 to 140 and the pressure-normalized permeability as high as 17,500 Barrer when the saturated toluene feeds were operated at 25 °C and a downstream pressure of 0.5 cmHg.

Hydrophilic polyurethaneurea membranes: influence of soft block composition on the water vapor permeation rates

High molecular weight segmented polyurethaneurea (PUU) copolymers based on an aliphatic diisocyanate, bis(4-isocyanatocyclohexyl)methane and mixed hydrophilic and hydrophobic soft segments were prepared. Hydrophilic blocks consisted of poly(ethyleneoxide) (PEO) of molecular weight 1450 g/mol, whereas the hydrophobic blocks were poly(tetramethylene oxide) of molecular weight 2000 g/mol. Ethylene diamine was used as the chain extender. Hard segment contents of the copolymers were kept constant at 18%, whereas PEO contents were varied between 0% and 50% by weight. Water vapor permeation rates (WVPR) of thin films (23–178 μm) cast from dimethylformamide solutions were determined. In studies performed at 23°C and 50% relative humidity, the relationship between PEO content and WVPR followed an S-shaped curve. For copolymers containing up to about 15% by weight of PEO, WVPR were fairly low. This was followed by a region where WVPR increased continuously for membranes containing between 15% and 30% PEO. Further increase in PEO content above 30% did not influence the WVPR substantially. There was also a dramatic increase in WVPR with an increase in temperature from 23°C to 37°C. Activation energy of permeation was determined to be 91.5 kJ for PUU containing 22.0% by weight of PEO. Equilibrium water absorption levels of PUU containing different levels of PEO in their backbone structures followed a similar trend to that of WVPR. Hydrophilic PUUs showed good tensile properties and mechanical integrity even at very high levels of water absorption.