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Fernanda M B Coutinho - One of the best experts on this subject based on the ideXlab platform.

  • degradation profiles of cast films of polyurethane and poly urethane Urea aqueous dispersions based on hydroxy terminated polybutadiene and different diisocyanates
    Polymer Degradation and Stability, 2003
    Co-Authors: Thais L Alves, Fernanda M B Coutinho, Marcia C Delpech, Antonio A Ferreira
    Abstract:

    Abstract New formulations of waterborne polyurethanes (wPU) and poly(urethane-Urea)s (wPUU) were produced based on hydroxy-terminated polybutadiene (HTPB), poly(propylene glycol) (PPG), dimethylolpropionic acid (DMPA), and three different types of aliphatic diisocyanates—isophorone diisocyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (HMDI) and hexamethylene diisocyanate (HDI)—and the aromatic tolylene diisocyanate (TDI). Three types of chain extender were used in some of the formulations: ethylene glycol (EG), forming polyurethanes, and hydrazine (HYD) or ethylenediamine (EDA), resulting in poly(urethane-Urea)s. In the formulations, HTPB content and NCO/OH ratio were varied. The thermal stability of the materials, obtained as cast films prepared from aqueous dispersions was evaluated by thermogravimetry (TG). It was observed that initial degradation temperatures were above 200 °C, with two- or three-step degradation profiles. An increase in HTPB content, the presence of Urea linkages, and HMDI as diisocyanate in the formulations led to materials with higher thermal stability. DTG curves exhibited stages not perceptible in the curves of weight loss, which were mainly influenced by the differences in the formulations.

  • waterborne anionic polyurethanes and poly urethane Urea s influence of the chain extender on mechanical and adhesive properties
    Polymer Testing, 2000
    Co-Authors: Marcia C Delpech, Fernanda M B Coutinho
    Abstract:

    Abstract Polyurethane and poly(urethane-Urea) aqueous dispersions based on 4,4′-dicyclohexylmethane diisocyanate (H12MDI), poly(propylene glycol) (PPG) and dimethylolpropionic acid (DMPA) were synthesized. Three types of chain extenders were used, hydrazine (HYD) and ethylenediamine (EDA), producing poly(urethane-Urea)s and ethylene glycol (EG), polyurethanes. The dispersion was performed before or after the chain extension reaction, depending on the extender employed. The dispersions were prepared with and without the addition of acetone after the prepolymer synthesis and neutralization steps. The length of soft segment and NCO/OH ratio were varied. Some mechanical properties of cast films obtained from the aqueous dispersions, the characteristics of coating application on a wood surface and their adhesive properties were evaluated.

  • waterborne anionic polyurethanes and poly urethane Urea s influence of the chain extender on mechanical and adhesive properties
    Polymer Testing, 2000
    Co-Authors: Marcia C Delpech, Fernanda M B Coutinho
    Abstract:

    Abstract Polyurethane and poly(urethane-Urea) aqueous dispersions based on 4,4′-dicyclohexylmethane diisocyanate (H12MDI), poly(propylene glycol) (PPG) and dimethylolpropionic acid (DMPA) were synthesized. Three types of chain extenders were used, hydrazine (HYD) and ethylenediamine (EDA), producing poly(urethane-Urea)s and ethylene glycol (EG), polyurethanes. The dispersion was performed before or after the chain extension reaction, depending on the extender employed. The dispersions were prepared with and without the addition of acetone after the prepolymer synthesis and neutralization steps. The length of soft segment and NCO/OH ratio were varied. Some mechanical properties of cast films obtained from the aqueous dispersions, the characteristics of coating application on a wood surface and their adhesive properties were evaluated.

Alex J Hsieh - One of the best experts on this subject based on the ideXlab platform.

  • dissipative particle dynamics simulation of microphase separation in polyurethane Urea nanocomposites
    Polymer, 2020
    Co-Authors: Yelena R Sliozberg, Alex J Hsieh, Jeffrey L Gair
    Abstract:

    Abstract Vertically aligned carbon nanotube reinforced segmented poly(urethane-Urea) (PUU) polymer nanocomposites (A-CNT/PUU PNCs) have been synthesized and proven to be potential candidates for novel materials with high mechanical strength, toughness, and thermal energy dissipation. It has been experimentally observed that incorporation of A-CNTs could induce interface-mediated nanophases of PUU along the A-CNTs axes. Here, we employed dissipative particle dynamics (DPD) computer simulations to elucidate the nature of the filler and matrix relationship in polyurethane composites at a molecular level. Diamine and diisocyante, the constituents of hard segments (domains), were found to have a propensity to adsorb onto the CNTs. This phenomenon is presumably facilitated by their greater thermodynamic compatibility with CNTs than the soft segments. Additionally, increasing the polymer's effective density leads to a rise in thermodynamic incompatibility of the polymer blocks. Hard domain aggregation around the CNTs' axes and between CNTs was also found to increase the conformational entropy. At the higher CNT loading, when the inter-CNT spacing becomes comparable with the distance between hard domain clusters, these domains form nanophase columns. Finally, simulation results agree with our previous PUU experimental data.

  • strong process structure interaction in stoveable poly urethane Urea aligned carbon nanotube nanocomposites
    Composites Science and Technology, 2018
    Co-Authors: Alex J Hsieh, Jeffrey L Gair, Robert H Lambeth, Daniel P Cole, Dale L Lidston, Itai Y Stein, Estelle Kalfoncohen, Hugh A Bruck
    Abstract:

    Abstract The exceptional static and dynamic physical properties of poly(urethane-Urea) (PUU) elastomers make them prime candidates for impulsive loading structural applications, such as blast protection coatings. Since the theoretical physical properties of carbon nanotubes (CNTs) are among the best for any currently known material, a number of previous studies explored the use of CNTs as nanoscale fillers to enhance the properties of PUU nanocomposites. However, due to the challenges inherent in dispersing CNTs in a PUU matrix and the resulting random orientation of the CNTs, these previous works observed marginal improvements in physical properties, and were unable to establish clear structure-property relations. Here, we report the synthesis of aligned-CNT (A-CNT) reinforced PUU polymer nanocomposites (A-PNCs) by infusing A-CNT forests with a stoveable PUU, and establish process-structure-property relations that quantify the contribution of CNT confinement on the PUU mechanical response. This stoveable process was achieved using blocked isocyanate which prevented polymerization until the blocks were removed with heat. PUUs of two distinct compositions were explored: one with 40 wt% hard-segment content (PUU211) and the other with 66 wt% hard-segment content (PUU541). Thermogravimetric analysis indicates that A-CNTs enhance the thermal stability of the hard-segment phase in PUU A-PNCs at 340 °C by up to 45% over the baseline PUUs. Atomic force microscopy reveals that the elongated nanophase hard-segment formations along the CNT axis observed only in the nanocomposites were of similar characteristic size to the average inter-A-CNT spacing (∼70 nm), indicating a strong influence of A-CNTs on the size and orientation of hard-segment nanophases, as corroborated via small angle X-ray scattering. Nanoindentation testing reveals that PUU A-PNCs possess significant elastic anisotropy, and exhibit enhanced longitudinal effective indentation moduli of ∼460 MPa (>3 × that of the PUU211 baseline) and ∼1350 MPa (∼1.5 × that of the PUU541 baseline) for PUU211 and PUU541 nanocomposites, respectively. This difference in magnitude of CNT reinforcement efficacy indicates that CNT confinement leads to significant hard-segment re-organization in the PUU211 A-PNCs, whereas the interconnected network of hard-segments in the PUU541 is affected by CNT templating to a lesser extent. Dynamic nanoindentation testing results are consistent with these interpretations, where longitudinally-loaded PUU211 A-PNCs are found to exhibit a >3 × enhancement in storage modulus at 1 Hz of ∼730 MPa, whereas the longitudinally-loaded PUU541 A-PNCs exhibit a slightly enhanced storage modulus enhancement at 1 Hz of 2190 MPa (∼1.5 × that of the PUU541 baseline). Reinforcement of PUUs with A-CNTs is a promising way to tune the physical properties of the PNCs; higher A-CNT packing densities, where the inter-CNT spacing could approach the nanophase characteristic diameter, could further enhance the PUU performance in ballistic protection applications.

  • molecular influence in high strain rate microparticle impact response of poly urethane Urea elastomers
    Polymer, 2017
    Co-Authors: David Veysset, Alex J Hsieh, Steven E Kooi, Keith A Nelson
    Abstract:

    Abstract The dynamic deformation response of select model poly(urethane Urea) elastomers (PUU) at high strain rates is investigated via an all-optical laser-induced projectile impact test (LIPIT). LIPIT measurements allow the direct visualization of the impact of micro-projectiles (silica spheres) on substrates and in-situ characterization, including depth of penetration and the extent of rebound of the micro-projectiles. PUUs are proven to be robust and the silica spheres are observed to rebound from them upon impact. In addition, for PUUs a strong correlation was noted between the coefficient of restitution and the maximum depth of penetration. Also, the coefficient of restitution data is comparable to that of glassy polycarbonate (PC), which is in great contrast to the comparison of the corresponding ambient storage modulus data obtained via dynamic mechanical analysis at 1 Hz. We hypothesize that high-rate deformation-induced glass transition is a plausible molecular relaxation mechanism towards macroscopic, dynamic stiffening/strengthening in PUUs.

  • dynamics of supersonic microparticle impact on elastomers revealed by real time multi frame imaging
    Scientific Reports, 2016
    Co-Authors: David Veysset, Alex J Hsieh, Steven E Kooi, A A Maznev, Kevin A Masser, Keith A Nelson
    Abstract:

    Understanding high–velocity microparticle impact is essential for many fields, from space exploration to medicine and biology. Investigations of microscale impact have hitherto been limited to post–mortem analysis of impacted specimens, which does not provide direct information on the impact dynamics. Here we report real–time multi–frame imaging studies of the impact of 7 μm diameter glass spheres traveling at 700–900 m/s on elastomer polymers. With a poly(urethane Urea) (PUU) sample, we observe a hyperelastic impact phenomenon not seen on the macroscale: a microsphere undergoes a full conformal penetration into the specimen followed by a rebound which leaves the specimen unscathed. The results challenge the established interpretation of the behaviour of elastomers under high–velocity impact.

  • influence of microstructure on micro nano mechanical measurements of select model transparent poly urethane Urea elastomers
    Polymer, 2013
    Co-Authors: Kenneth E Strawhecker, Alex J Hsieh, Tanya L Chantawansri, Ilke Z Kalcioglu, Krystyn J Van Vliet
    Abstract:

    Morphology of 4,4 0 -dicyclohexylmethane diisocyanateepoly(tetramethylene oxide) (PTMO)ediethyl toluenediamine based poly(urethane Urea) (PUU) elastomers is investigated by atomic force micros- copy (AFM) and compared with elastic modulus data measured from AFM-enabled indentation, dynamic nanoindentation (nanoDMA), and dynamic mechanical analysis (DMA). These measurements highlight the effect of altering the molecular weight (Mw) of PTMO, which is used as a soft segment (SS), on the microstructure. In particular, at SS Mw 2000 g/mol, a strong microphase-separated morphology is observed, whereas a phase-mixed dominated microstructure is noted in PUU with SS Mw of 1000 and 650 g/mol. These observations are also consistent with DMA tan d results. Furthermore, instrumented impact indentation is also utilized for elucidation of dynamic damping characteristics in these PUUs. Published by Elsevier Ltd.

C Cor E Koning - One of the best experts on this subject based on the ideXlab platform.

  • property profile of poly urethane Urea dispersions containing dimer fatty acid sugar and amino acid based building blocks
    European Polymer Journal, 2014
    Co-Authors: Yingyuan Y Li, Bart A. J. Noordover, C Cor E Koning, Ratm Rolf Van Benthem
    Abstract:

    The understanding of the polymer composition–properties relationship is of great importance to improve the mechanical properties of bio-based polyurethanes containing long chain fatty acid derivatives. In this work, water-borne poly(urethane Urea) dispersions containing dimer fatty acid-based diisocyanate (DDI), ethyl ester l-lysine diisocyanate (EELDI), 1,4:3,6-dianhydro-d-glucitol (isosorbide, IS) and dimethylolpropionic acid (DMPA) residues were prepared. The investigation focuses on the thermal and mechanical properties of these dispersion-cast films as well as on the morphology in correlation with the polymer composition. Significant dependencies of these properties and the morphology on the polymer composition are observed. By partially replacing the flexible DDI with the rigid EELDI as well as by increasing the isosorbide contents in the monomer feed, the Tg as measured by DSC was significantly enhanced from 18 to 58 °C (1st Tg) and to above 70 °C (2nd Tg). As evidenced from the DSC, AFM and FT-IR measurements, the H-bonds-induced micro-phase separation was influenced by the polymer composition. The observed improved phase mixing at relatively high EELDI-to-DDI ratio was related to the increased EELDI content and the corresponding urethane/Urea bonds. The viscoelastic behavior of these dispersion-cast films showed a strong dependence on the ratio of the flexible DDI to the rigid EELDI and were less dependent on the IS and DMPA contents.

  • chain extension of dimer fatty acid and sugar based polyurethanes in aqueous dispersions
    European Polymer Journal, 2014
    Co-Authors: Bart A. J. Noordover, Van Ratm Rolf Benthem, C Cor E Koning
    Abstract:

    Abstract The chain extension process of renewable waterborne polyurethane dispersions (WBPUDs) prepared from a dimer fatty acid-based diisocyanate (DDI) and isosorbide (IS), using dimethylolpropionic acid (DMPA) as the internal dispersing agent, was investigated. Ethylene diamine (EDA), adipic dihydrazide (ADH) and water were evaluated as chain extenders. Other variables such as the chain extension temperature, the sequence of addition of the chain extender with respect to the dispersion step and the utilization of a catalyst (triethylamine, TEA) were investigated as well. It was found that EDA extended the NCO-functional prepolymer chains at both 30 and 50 °C, independent of the moment of its addition. A limited extent of chain extension by ADH was observed, which was thought to be caused by the low solubility of ADH in the solvent 2-butanone, used for the prepolymer synthesis. ADH chain extension only took place after removal of the 2-butanone. Water chain extension was observed at temperatures ranging from 50 °C to 70 °C. A good balance was found at 50 °C, where a stable dispersion with a relatively high molecular weight, a small particle size and a narrow particle size distribution were obtained. The usage of TEA during the dispersion process promoted the water chain extension reaction, however, at the cost of dispersion stability. An increased DMPA level has shown to improve the dispersion stability. Dispersion-cast poly(urethane Urea) films were found to be thermally stable up to 249 °C (5 wt% mass loss) and had Tg values around room temperature.

Garth L Wilkes - One of the best experts on this subject based on the ideXlab platform.

  • a comparative study of the structure property behavior of highly branched segmented poly urethane Urea copolymers and their linear analogs
    Polymer, 2005
    Co-Authors: Jignesh P Sheth, Serkan Unal, Timothy Edward Long, Emel Yilgor, Iskender Yilgor, Frederick L Beyer, Garth L Wilkes
    Abstract:

    Abstract The solid-state structure–property behavior of highly branched segmented poly(urethane Urea) (PUU) copolymers and their linear analog was investigated. A limited study of their solution rheological behavior was also undertaken. The linear PUUs were synthesized by the two-step prepolymer method, whereas the oligomeric A2+B3 methodology was utilized to synthesize the highly branched materials. The soft segments (SS) were either poly(tetramethylene oxide) (PTMO) or poly(propylene oxide) (PPO). All copolymers utilized in this study, with one exception, contained 28 wt% hard segment (HS) content. DMA, SAXS, and AFM studies indicated that the linear as well as the highly branched PUUs were microphase separated. The SS Tg of the highly branched PUUs was nearly identical to that of their respective linear analogs. However, the linear copolymers exhibited broader and less temperature sensitive rubbery plateaus, both attributed to one or both of two reasons. The first is better hydrogen bonding organization of the HS phase as well as greater HS lengths than in the highly branched analogs. The second parameter is that of a potentially higher chain entanglement for the linear systems relative to the branched analogs. Tapping-mode AFM phase images confirmed the microphase morphology indicated by SAXS and DMA. Ambient temperature strain-induced crystallization was observed in the PUU based on PTMO 2040 g/mol at a uniaxial strain of ca. 400%, irrespective of the chain architecture. Stress–strain, stress relaxation, and mechanical hysteresis of the highly branched copolymers were in general slightly poorer than that of their linear analogs. Ambient temperature solution viscosity of the highly branched materials in dimethyl formamide was substantially lower that that of the linear samples of nearly equal molecular weight.

  • structure property relationships of poly urethane Urea s with ultralow monol content poly propylene glycol soft segments iii influence of mixed soft segments of ultralow monol poly propylene glycol poly tetramethylene ether glycol and tri propylene g
    Journal of Applied Polymer Science, 2003
    Co-Authors: Matthew J Osickey, Bruce D Lawrey, Garth L Wilkes
    Abstract:

    Recent advances in the catalyst technology associated with the production of poly(propylene glycol) (PPG) have allowed for the fabrication of ultralow monol content PPG macrodiols (Acclaim™ polyols), which are highly bifunctional and can be produced in substantially higher molecular weights and with narrower molecular weight distributions than previously possible. These factors have enabled the preparation of higher value elastomers and may allow for the first manufacture of economically attractive PPG-based poly(urethane-Urea) (PUU) fibers. In the past, many performance polyurethane and PUU elastomers used poly(tetramethylene ether glycol) (PTMEG) for the soft segments either alone or in combination with other macrodiols. The work presented here details the investigation of the morphological features of PUU systems with mixed soft segments of PPG, PTMEG, and a low molecular analog of PPG, tri(propylene glycol) (TPG) in an effort to ascertain the influence of structural features on the mechanical and thermal properties of the elastomers. Also of interest was whether the incorporation of PPG and TPG would either prohibit or greatly hinder the formation of strain-induced PTMEG crystallites. It was found that, even when only 60 wt % of the soft segments consisted of PTMEG, those soft segments were still able to undergo recognizable strain-induced crystallization as detected by wide-angle X-ray scattering. It was also seen that, as the ratio of PPG to PTMEG was varied, there were systematic changes in the soft segment glass transition and cold crystallization characteristics. Inclusion of PPG and TPG resulted in PTMEG's diminished ability to undergo cold and strain-induced crystallization, as seen with differential scanning calorimetry and wide-angle X-ray scattering. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3520–3529, 2003

  • structure property relationships of poly urethane Urea s with ultra low monol content poly propylene glycol soft segments i influence of soft segment molecular weight and hard segment content
    Journal of Applied Polymer Science, 2002
    Co-Authors: Matthew J Osickey, Bruce D Lawrey, Garth L Wilkes
    Abstract:

    Structure–property relationships in poly(urethane Urea)s synthesized with ultra-low monol content poly(propylene glycol) soft segments were investigated as soft segment molecular weight (2000, 4000, and 8000 g/mol) and hard segment content (6.3 and 9.0 wt %) were varied. Morphological features such as interdomain spacing and interphase thickness were quantified and revealed with small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). The thermal and mechanical behavior was assessed with a dynamic mechanical analyzer (DMA) and by differential scanning calorimetry (DSC) and stress-strain tests. Hard segment content, over the limited range studied, had little effect on the morphology and soft segment thermal and mechanical properties. The molecular weight of the soft segments had considerably more influence on the morphology and mechanical properties. Increasing soft segment molecular weight resulted in greater interdomain spacings, as shown by SAXS, and a noticeable change in the structure, as shown by AFM. Additionally, as soft segment molecular weight decreased the soft segment glass transition broadened and rose to higher temperatures. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 229–243, 2002; DOI 10.1002/app.10168

Chuhyung Chen - One of the best experts on this subject based on the ideXlab platform.

  • study on the morphology and permeation property of amine group contained polyurethanes
    Polymer, 1998
    Co-Authors: Liang Siong Teo, Jen Feng Kuo, Chuhyung Chen
    Abstract:

    The better CO2 affinity reagents, N-methyldiethanolamine (MDEA) and tetraethylenepentamine(TEPA), were used as chain extenders to prepare MDEA-extended polyurethanes, TEPA- and MDEA/TEPA (11 by mole)-extended poly(urethane-Urea)s. 4,4′-diphenylmethane diisocyanate (MDI) and poly(ethylene glycol) (PEG) of molecular weights (MW) 400 and 600 were used as hard and soft segments, respectively. The effects of the chain extenders and PEG MW on the mode of urethane moiety association and the polymer thermal transition properties were studied using differential scanning calorimetry, Fourier Transform infrared spectrophotometry (FTi.r.) and the deconvolute technique on the FTi.r. bands due to stretching vibrations of carbonyl and NH groups. The new chain extenders caused the polymers to have less ordered urethane hard segment domains and a lower T2. They also caused an increase in the number of hard segments found in soft segment domains and a higher Tgs, compared with typical 1,4′-butandiol-extended polyether polyurethanes. The larger MW PEG improved phase separation and exhibited a lower Tgs. The polymers were prepared as gas separation membranes for various gases such as He, H2, O2, N2, CH4 and CO2. The steady state permeability (Pi), diffusivity (Di) and solubility (Si) of the gases permeated through the polymer membranes were determined using Barrer's high vacuum technique and the time lag method. Polymer membranes having PEG soft segments of MW600 showed quite promising performance (Pi, αij = PiPj) for permeation of industrially interesting gas pairs such as CO2CH4, HeCH4, H2N2, andO2N2. The relation of permeation properties to the molecular properties of the penetrant gases as well as the polymer structure is discussed. The separation mechanism of the gas pairs is also discussed.

  • fourier transform infrared spectroscopy study on effects of temperature on hydrogen bonding in amine containing polyurethanes and poly urethane Urea s
    Macromolecules, 1997
    Co-Authors: Liang Siong Teo, Chuhyung Chen, Jen Feng Kuo
    Abstract:

    Three types of amine-containing polyurethanes and poly(urethane−Ureas), N-methyldiethanolamine (MDEA) and/or tetraethylenepentamine (TEPA) as the chain extender and poly(ethylene glycol) of MW 400 as the soft-segment component, have been studied by FTIR. The hydrogen bonding in hard and soft segments was examined for the extent of phase separation, and the microstructure was evidenced by differential scanning calorimetry (DSC). The temperature effects on the hydrogen bonding were also investigated. They show a significant amount of hydrogen bonding between the hard and soft segments. It indicates that there exists a large amount of partial phase mixing of hard and soft segments compared to the conventional polyurethanes. The bulky CH3 groups of MDEA in hard segments restrict the hydrogen bonding within the hard segments, while the TEPA-containing urethane−Urea polymers have more distinct phase separation. However, all of the polymers studied are amorphous materials such that the dissolved soft segments in...

  • fourier transform infrared spectroscopy study on effects of temperature on hydrogen bonding in amine containing polyurethanes and poly urethane Urea s
    Macromolecules, 1997
    Co-Authors: Chuhyung Chen
    Abstract:

    Three types of amine-containing polyurethanes and poly(urethane−Ureas), N-methyldiethanolamine (MDEA) and/or tetraethylenepentamine (TEPA) as the chain extender and poly(ethylene glycol) of MW 400 as the soft-segment component, have been studied by FTIR. The hydrogen bonding in hard and soft segments was examined for the extent of phase separation, and the microstructure was evidenced by differential scanning calorimetry (DSC). The temperature effects on the hydrogen bonding were also investigated. They show a significant amount of hydrogen bonding between the hard and soft segments. It indicates that there exists a large amount of partial phase mixing of hard and soft segments compared to the conventional polyurethanes. The bulky CH3 groups of MDEA in hard segments restrict the hydrogen bonding within the hard segments, while the TEPA-containing urethane−Urea polymers have more distinct phase separation. However, all of the polymers studied are amorphous materials such that the dissolved soft segments in...