Polyurethane Molecules Research Articles

Simulation of polyurethane/activated carbon surface interactions

The influence of interfacial structure on interfacial properties between activated carbon filler and surrounding organic matrix of composites has been studied by infrared and NMR spectroscopy. Urea, semicarbazide and ethylurethane, component parts of polyurethane, have been used as organic model compounds in order to predict the interactions between the activated carbon surface and polar groups of real polyurethane molecule. It was shown that organic matrix/activated carbon interphase presented a region where the filler and matrix phases were chemically and/or physically combined. The spectra of the organic matrix undergo significant changes with increase of carbon content. Due to the surface reactive functionalities the activated carbon is considered not only as filler, influenced on the sorption properties of the composition, but also as a physicochemical modifier of the polyurethane matrix.

Enhanced mechanical and dielectric properties of poly(vinylidene fluoride)/polyurethane/multi-walled carbon nanotube nanocomposites

Multi-walled carbon nanotubes (MWNTs) nanocomposites with the polymer matrix composed of blends of poly(vinylidene fluoride) (PVDF) and polyurethane (PU) were prepared via functionalization of 3,4,5-triflouroaniline (TFA) on MWNTs. The MWNTs/polymer nanocomposites showed a dominantly enhanced elongation due to incorporation of PU molecules in PVDF matrix and the improved MWNTs dispersion in the polymer matrix resulting from functionalization of MWNTs with TFA. The functionalization of TFA on MWNTs was confirmed by the measurements of Raman, FT-IR spectra, SEM, and TEM images. In addition, the dielectric constant of nanocomposites increased with an increase of TFA-functionalized MWNTs in PVDF/PU/MWNTs nanocomposites. The polymer blend nanocomposites incorporating MWNTs may be available as an alternative potential route for the actuator materials.

Mechanical behavior of shape memory fibers spun from nanoclay-tethered polyurethanes

This study examined the effect of nanoclays on the shape memory behavior of polyurethane (PU) in fibrous form. A cation was introduced into the PU molecules to disperse the organo-nanoclay (MMT) into poly(e- caprolactone) (PCL)-based PU (PCL-PU). The MMT/PCL-PU nanocomposites were then spun into fibers through melt-processing. The shape memory performance of the spun fibers was examined using a variety of thermomechanical tests including a new method to determine the transition temperature of shape memory polymers. The MMTs showed an improved the fixity strain rate of the MMT/PCL-PU fibers but a slight decrease in their recovery strain rate. This was explained by the limited movement of PU molecules due to the presence of nanoclays. The shape memory performance of the MMT/PCL-PU fibers was not enhanced significantly by the nanoclays. However, their recovery power was improved significantly up to a strain of approximately 50%.

Thermal and structural characterization of quasi-nanometer zirconium carbon/polyurethane composites prepared under roller pressure

In this study, we use quasi-nanometer zirconium carbon (ZrC) to compose with polyurethane (PU) resin under roller pressure to study the interaction between the ZrC particle and PU molecules in the composite films, and find that the values of tensile strength, modulus, energy at break, Tm of soft-segment, and Tg of soft-segment, and weight percentage of char yield are increased, and elongation and char yield temperature are decreased with the increase of ZrC composed in PU, as this composed amounts are lower than 2.5%. The infrared spectroscopic spectra and wide angle X-ray diffraction patterns reveal that the ether and ester groups of PU polymer can interact with ZrC to lower the interlayer distance of the crystal of PU polymer in composites. We assure that the interaction between the particles of ZrC and PU under roller pressure is in preparation process and account that the interaction between the particle and PU molecule will be an important factor to evaluate whether the particle in the composite is even and perfect. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 191–197, 2006

Effect of Quasi-nanometer zirconium carbide on the physical characterization of zirconium carbide/polyurethane composite films irradiated under ultraviolet light

We used quasi-nanometer zirconium carbide (ZrC) and a polyurethane (PU) resin under roller pressure to form a composite film and found that the tensile strength at break, elongation at break, and modulus gradually decreased with increasing ultraviolet (UV)-irradiation time for films of both PU and the PU/ZrC composite. However, this phenomenon was significantly higher for the PU film than for the ZrC/PU composite film. The construction of the PU film changed after UV irradiation, but that of the PU/ZrC composite film was almost unchanged. The degradation of PU molecules occurred in the absence of ZrC particles after irradiation with UV light but almost did not occur in the presence of ZrC particles. This was confirmed with Fourier transform infrared spectroscopy and gel permeation chromatography analyses. It was suggested that polymer radicals which formed through the photooxidation of UV irradiation and free radicals which formed through the photoreduction of nanometer ZrC/UV irradiation interacted to form a dead polymer to stop the degradation; simultaneously, the chemical bonding between polymer molecules could be re-formed from free radicals created by photooxidation and photoreduction and thus reduce the mobility of PU molecules, thereby raising the glass-transition and melting temperatures of the soft segment. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4842–4849, 2006

Effects of NCO/OH molar ratio on structure and properties of graft-interpenetrating polymer networks from polyurethane and nitrolignin

A series of graft-interpenetrating polymer networks (graft-IPNs) with different NCO/OH molar ratio was synthesized from castor oil-based polyurethane (PU) and nitrolignin (NL) by changing the content of 1,4-butanediol as chain-extender. The effects of NCO/OH molar ratio on the morphology and properties of the PU–NL films (UL) were investigated by infrared, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry, dynamic mechanical analysis, and tensile test. WAXD patterns showed that all the UL films were nearly amorphous. With an increase in NCO/OH molar ratio, the glass transition temperature (Tg), the stiffness and tensile strength (σb) increased, while the breaking elongation (εb) and strain recoverability (Re) decreased. The UL films with 1.20 of NCO/OH molar ratio exhibited the maximum value of tensile strength (σb=30.2MPa;εb=152%). 2.8wt% NL plays an important role in the simultaneous enhancement of σb and εb of the UL films. Solid-state 13C nuclear magnetic resonance (13C NMR) showed that the introduction of NL into PU restricted the motion of PU molecules, indicating a relatively high cross-link network structure in the UL films. Therefore, a relatively great network structure like a star by grafting with multi-PU networks on a NL molecule as the graft-IPNs model was deduced in this work.

Thermal and Mechanical Properties of Polyurethanes Derived from Fractionated Kraft Lignin.

Polyurethane (PU) sheets were prepared from fractionated kraft lignin (KL) samples having molecular weights (MW's) of 1420 and 860, polyethylene glycol having a MW of 400 (PEG 400) and diphenylmethane diisocyanate (MDI). KL contents in weight %, in a mixture of KL and PEG 400, were varied from 10 to 50%. The thermal and mechanical properties of PU's were studied by thermogravimetry (TG), differential scanning calorimetry (DSC) and tensile tests. The thermal decomposition temperatures slightly decreased with increasing KL contents. The glass transition temperatures (Tg's) increased, the temperature range of glass transition (ΔT) increased, and the heat capacity difference between the glass and rubbery states at Tg's (ΔCp) decreased, with increasing KL contents. Tensile properties such as strength at break (σ), elongation at break (ε), and Young's modulus (E) were measured at 25°C. The obtained results were highly dependent on the state, i.e. the glassy state and the rubbery state. The effect of molecular weight of KL on thermal degradation and tensile properties was not prominent. However, Tg's apparently increased with decreasing molecular weights of KL when the same amounts in weight % of KL were introduced into PU molecules.

Interfacial interactions and the polymer/polyurethane bond

AbstractLap shear measurements of adhesion in joints of polymers bonded with polyurethane adhesives varied significantly with time at elevated temperature. The effect has been linked with the ability of polyurethane molecules to restructure in response to the orienting strength of substrate surfaces, as defined by their non‐dispersive surface energy component. Acid/base interactions at the polymer/adhesive interface further affect the bond strength, increasing this important property when acid/base pairs are located at the interface, and diminishing the variable when acid/base interactions are absent.

The effect of hard segment structure on rheological properties of solutions of segmented polyurethanes

Segmented polyurethanes based on polypropylene glycol, butane diol and a mixture of (diphenylmethane diisocyanate)/(toluene diisocyanate) (MDI/TDI) were prepared and characterized. Soft segment concentration was kept constant at 50% in all polymers but the structure of the hard segment was varied by using MDI/TDI ratios from zero to pure MDI. The aim of the work was to examine solution properties as a function of the polymer composition and also the stability of polyurethane solutions in dimethylformamide. Polyurethane solutions exhibited Newtonian behaviour up to rather high concentrations of 30%. No structure formation, due to association of polyurethane molecules through hydrogen bonding, was observed in DMF up to concentrations >70%. Ageing of polyurethane solutions, manifested as decrease of viscosity with time, was observed only with two high molecular samples. Solubility of the polymer increased and rigidity decreased with increasing TDI/MDI ratio. Activation energy for viscous flow increased with solution concentration and rigidity of the hard segment.

Domain structure of Vitur T-0533 segmented polyurethane

A combination of low-angle and high-angle X-ray diffraction, H→D isotopic exchange and differential scanning calorimetry has been used to study the domain structure in Vitur T-0533 films. The changes in the characteristics of the domain structure of the film have been analysed to take account of their history. By studying the temperature dependence of the accessibility of the segmented polyurethane molecules to D 2O, information could be obtained about the proportion of only slightly ordered formations and strong rigid-chain formation (domains) throughout the entire polymer volume.

Mechanism of thermal degradation of polyurethane based on MDI and propoxylated trimethylol propane

AbstractThe various pathways of degradation of polyurethane based on MDI and propoxylated trimethylol propane were studied from the analysis of degradation gases sampled at various temperatures during the heating rise. From the beginning of degradation (250°C) to 400°C, we suggest that the main mechanism is the fracture of the polyurethane molecule into primary amine, carbon dioxide, and propenyl ether, the last leading to propene. Beyond this temperature, the mechanism may be reduced to a depolymerization process followed by radical breakdown of the polyol chain and by stripping and rearrangement of simple radicals, all of these giving the gaseous species obtained.

Synthesis of phosphorus-containing dihydrazides and polyurethanes from them

From phosphonic acid esters and hydrazine hydrate, phosphorus-containing dihydrazides have been synthesized with two reactive amino groups; from them, polyurethanes have been prepared. It is shown that the introduction of phosphorus into the polyurethane molecules leads to improvement of physical and mechanical properties, to a large reduction in losses during combustion and to an improvement in capacity to absorb water.

Effects of lithium bromide on the gel‐permeation chromatography of polyester‐based polyurethanes in dimethylformamide

AbstractThe hydrodynamic volume changes of the polyester‐based polyurethanes, as dimethylformamide solutions with and without lithium bromide, were studied. Gel‐permeation chromatographic (GPC) and intrinsic viscosity techniques were employed as methods for characterization. Decreases in intrinsic viscosity as well as dramatic changes in the GPC chromatograms were observed. These observations are explained by the polarity of these polyester‐based polyurethane molecules and the resulting characteristics of molecular expansion, association, and polymer–column interaction normally associated with polyelectrolytes.