Thermal and dielectric properties of polycarbonatediol polyurethane

The dielectric relaxation behavior of segmented polyurethane has been studied using Broad‐Band Dielectric Spectroscopy in the frequency domain, 10^?2 to 10⁸ Hz, and in the temperature range of ?120 to 140°C. The spectra show three secondary processes (δ, γ, and β) followed by the α relaxation and conductive processes. The Havriliak‐Negami (HN) phenomenological equation was used in order to characterize all the processes. The δ, γ, and β relaxations are probably associated with (i) local motions of the main chain (ii) motions of the carbonate group in the soft phase and (iii) reorientational motions of water molecules. The microphase separated morphology associated with soft and hard domains is reflected in the dielectric spectra, at high temperatures, by the presence of the Maxwell‐Wagner‐Sillars (MWS) interfacial polarization process. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42007.     

Characterization of castor oil based polyurethane films prepared with N‐methyl‐2‐pyrrolidinone as a solvent

Molecular mobility in castor oil based polyurethane was investigated with thermally stimulated depolarization current (TSDC) measurements and alternating‐current (ac) dielectric relaxation spectroscopy. Three peaks could be observed in TSDC thermograms from 173 to 373 K. The relaxation located at 213 K could be attributed to the change in the molecular chain due to the interaction between the isocyanate and the solvent, and it was well fitted with the Vogel–Fulcher–Tammann equation. The other two peaks were located at 274 and 365 K and could be attributed to interfacial polarization and space charge, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 746–749, 2005     

Dielectric properties of C60 and Sc3N@C80 fullerenol containing polyurethane nanocomposites

Polymer–fullerene nanocomposites consisting of linear polyurethane (PU) chains crosslinked via increasing loadings of polyhydroxylated fullerenes (C₆₀ and Sc₃N@C₈₀, a metallic nitride fullerene) were prepared and characterized for their mechanical and dielectric properties using dynamic mechanical analysis (DMA) and broadband dielectric spectroscopy (BDS). Fullerene–polymer networks [C₆₀‐PU and Sc₃N@C₈₀‐PU] having high gel fractions, good mechanical properties and thermal stabilities were produced. Polyhydroxylated fullerenes C₆₀(OH)₂₉ and Sc₃N@C₈₀(OH)₁₈ were synthesized in high yield through a high‐speed vibration milling method and characterized using FTIR, matrix‐assisted laser desorption/ionization mass spectroscopy, and thermal gravimetric analysis. DMA of fullerene–PU networks indicates T_g ～ ?50°C, with a sub‐T_g relaxation due to local chain motions. BDS analyses of the fullerenes, before and after hydroxylation and before incorporation into the networks, revealed one relaxation and large real permittivity (ε′) values for C₆₀(OH)₂₉ relative to C₆₀. Analogous samples for Sc₃N@C₈₀ exhibit two relaxations, where the extra relaxation is attributed to motions of the cage‐encapsulated Sc₃N clusters. ε′ values for Sc₃N@C₈₀‐PU at a given frequency are higher than corresponding values for C₆₀‐PU, likely because of the rotationally mobile Sc₃N encapsulates. Surface and bulk resistivities of fullerene–PU networks were found to have a modest dependence on relative humidity. Capacitance versus voltage characteristics of the fullerene–PUs were also studied in the range of the applied dc bias voltage of ?30 to +30 v. It is generally concluded, based on all the evidence that this class of materials can be rendered quite polarizable and could be used as high dielectric permittivity materials in capacitance applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40577.     

Triglycine sulphate and its deuterated analog in polyurethane matrix for thermal/infrared detection: A comparison

Composites comprising of polycrystalline triglycine sulphate (TGS) or its deuterated analog (DTGS) in powder form dispersed in polyurethane (PU) are synthesized for pyroelectric sensor applications. TGS and DTGS have high pyroelectric coefficients, but are susceptible to humidity, and PU is inherently electroactive. So composites made of TGS or DTGS dispersed in PU can be expected to have high pyroelectric coefficient as well as immunity to humidity. Composites with inclusion volume fraction between 0 and 0.25 are prepared, and their dielectric, pyroelectric, and thermal properties measured. In general, deuteration leads to decrease in dielectric constant and specific heat, but increase in thermal conductivity. The pyroelectric coefficient and figures of merit get enhanced significantly with deuteration as well as inclusion volume fraction. Comparison with similar composites shows that these samples have the highest values for figures of merit, indicating their potential use as thermal/infrared detectors that are immune to humidity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42250.     

Synthesis and characterization of polyurethane anionomers

Un‐ionized polyurethane was obtained by the reaction of an isocyanate‐terminated urethane prepolymer, which was synthesized from 4,4′‐diphenylmethane diisocyanate and poly(oxytetramethylene)‐α,ω‐glycol, with 2,2‐bis(hydroxymethyl)propionic acid. A carboxylate‐based polyurethane anionomer was then derived from the polyurethane by the use of the sodium, potassium, or magnesium salt of acetic acid as a neutralizer. The ionomerization resulted in the following changes in the characteristics of the polyurethane: (1) an increase in the tensile strength, (2) a decrease in the glass‐transition temperature, (3) an increase in the wettability and hygroscopicity with respect to water, and (4) susceptibility to thermal decomposition. A sulfonate‐based polyurethane was also synthesized for comparison with the carboxylate‐based polyurethane. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2144–2148, 2005     

Enhanced microwave absorbing properties of lightweight films based on polyaniline/aliphatic polyurethane composites in X band

Polymer blends based on nanostructured polyaniline (PANI) doped with hydrochloric acid (HCl) and para‐toluene sulfonic acid (PTSA) introduced into aliphatic polyurethane matrix (PU) are synthesized to produce flexible thin composite films for microwave absorbers. The effects of dopant type, PANI content and film thickness on morphologies, dielectric and microwave absorption properties in the X‐band are studied. It reveals that real and imaginary parts of the complex permittivity are proportional to filler concentrations and type of doped PANI. The PANI‐PTSA/PU films show higher permittivity and better microwave absorbing properties than PANI‐HCl/PU for the same weight fraction of PANI. The minimum reflection loss RL_(dB) values for the PANI‐PTSA/PU are ?37 dB at (20% PANI and 11.6 GHz) and ?30 dB at (15% PANI and 11.3 GHz) for thicknesses of 1.2 and 1.6 mm, respectively. These high values of reflection losses make the obtained lightweight and flexible composites promising radar absorbing materials (RAM). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40961.     

Electrical ac and dc behavior of epoxy nanocomposites containing graphene oxide

This article deals with the investigation of electrical properties of epoxy‐based nanocomposites containing graphene oxide nanofillers dispersed in the polymer matrix through two‐phase extraction. Broadband dielectric spectroscopy and dc electrical conductivity as a function of electric field have been evaluated in specimens containing up to 0.5 wt % of nanofiller. Nanocomposites containing pristine graphene oxide do not show significant changes of electrical properties. On the contrary, the same materials after a proper thermal treatment at 135°C, able to provoke the in situ reduction of graphene oxide, exhibit higher permittivity and electrical conductivity, without showing large decrease of breakdown voltage. Moreover, a nonlinear behavior of the electrical conductivity is observed in the range of electric fields investigated, i.e. 2–30 kV mm^?1. A new relaxation phenomenon with a very low temperature dependence is also evidenced at high frequency in reduced graphene oxide composites, likely associated to induced polarization of electrically conductive nanoparticles. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41923.     

New compounds for production of polyurethane foams

A method of boroorganic compound preparation with boric acid, 1,3‐propanediol, 2,3‐butanediol, and 1,4‐butanediol is described in this article. The obtained compounds were characterized with respect to their usability as polyol components for the production of polyurethane (PUR) foams. New boroorganic compounds were applied as polyol components for the foaming of rigid PUR–polyisocyanurate (PIR) foams. The method of preparation, foaming parameters, and physicochemical properties of the PUR–PIR foams and their results are presented. Application of the prepared borates as polyol components in the production of foams had a favorable effect on the properties of the foams. The obtained rigid foams were characterized by lower brittleness, higher compressive strength, content of closed cells, and considerably reduced flammability in comparison with standard foams. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5918–5926, 2006     

Processing and tribology of thermoplastic polyurethane particulate composite materials

The processing, mechanical and tribological properties of wax containing thermoplastic polyurethane–filler composites were studied for different weight ratios of graphite, TiO₂, MoS₂, and ZrO₂ microparticles and SiO₂ nanoparticles. The composites were compounded by extrusion and processed by compression molding. The rheological, thermal, and mechanical properties were measured, and the wear characteristics were tested with ball-on-plate reciprocating tribometer tests under fixed friction conditions and then observed by scanning electron microscopy. Correlations between the friction, wear, and mechanical properties were observed, and their mechanisms are discussed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Structure and properties of polylactide toughened by polyurethane prepolymer

In this study, polyurethane prepolymer (PUP) was prepared by the reaction of Poly‐1,4‐butylene glycol adipate diol (PBA) and 4,4′‐Methylenedi‐p‐phenyl diisocyanate (MDI). The as‐prepared PUP was then blended with Polylactide (PLA), and the impact of the PUP on the blends regarding their structure and properties were thoroughly analyzed. Also, PLA was blended with PU powder without isocyanate groups (NCO) as an important control sample (PLAPW) to study the interface interaction of the blends. Obvious yield and neck stretch were obtained after the addition of PUP, and the elongation ratio at break increased from 2.9% to 231.5%. In contrast, the mechanical properties of PLAPW decreased significantly mainly due to the simple physical blending of the polymers without the formation of covalent bonds. Also, the results of the FTIR, SEM, DSC, and DMA analysis showed that the reactions of NCO groups in PUP with the terminal hydroxyl or carboxyl groups in PLA significantly improved the compatibility of the PUP and PLA blend. Compared to pristine PLA, the highest decomposition temperature of the PLA and PUP blend (PLAPU) increased from 359.3°C to 362.6°C. Additionally the thermal stability and mechanical properties of the blended materials were exceedingly improved even with only 5% of PUP in the blended materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42983.     

Effect of the hard‐segment structure on the dielectric relaxation of crosslinked polyurethanes

Two series of crosslinked polyurethanes based on poly(tetramethylene ether) glycol soft segments and hexamethylene diisocyanate/1,4‐butane diol and glycerin or castor oil as a hard segments were synthesized, and their dielectric properties were examined. We examined the influence of the structural heterogeneity of the copolymers (as a function of the quantity and structure of the hard segments and crosslinking density, as measured by comonomer composition), frequency, and temperature as experimental variables by observing changes in the dielectric behavior. Two relaxation peaks were observed in the temperature range of −30 to 40°C for polyurethanes with various hard‐segment contents. The dangling chains of the castor oil presented a plasticizing effect that was exerted during the relaxation processes, an effect that was studied. It was found that both the amount and the structure of the hard segment strongly affected the dielectric behavior. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Pulverized polyurethane foam particles reinforced rigid polyurethane foam and phenolic foam

Polyurethane consumption has been increasing in recent years, raising concerns about how to deal with the polymer waste. Post‐consumer rigid polyurethane foams or polyurethane foam scraps (PPU) ground into particles were utilized to strengthen mechanical properties of rigid polyurethane foam (PUF) and phenolic foam (PF). Viscosity of prepolymer with PUF was measured and PPU was well dispersed in prepolymer, as observed by optical microscope. Microstructures and morphologies of the reinforced foam were examined with scanning electron microscope (SEM) while cell diameter and density were measured by Scion Image software. Universal testing machine was employed to optimize compressive properties at various weight ratios of PPU. Both PUF and PF with 5 wt % PPU, respectively, exhibited considerable improvement in mechanical properties especially compressive property. The compressive modulus of PUF with 5 wt % PPU was 12.07 MPa, almost 20% higher than pure PUF while compressive strength of PF with 5 wt % PPU reached 0.48 MPa. The thermal stability of the reinforced foam was tested by thermal gravity analysis (TGA) and the result shows no obvious impact with PPU. The decomposition temperatures of PUF with PPU and PF with PPU were 280°C, because PPU has relatively weak thermal stability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39734.     

Thermoplastic vulcanizate nanocomposites based on thermoplastic polyurethane and millable polyurethane blends reinforced with organoclay prepared by melt intercalation technique: Optimization of processing parameters via statistical methods

Statistical approaches including Taguchi design of experiments (DOE), analysis of variance (ANOVA), and multiple linear regression analysis were employed to determine optimum processing conditions for successful preparation of a thermoplastic vulcanizate nanocomposite (TPVNC) based on thermoplastic polyurethane (TPU)/millable polyurethane (MPU) blend reinforced with an organoclay (TPU/MPU/organoclay = 50/50/3 wt/wt/wt) using an internal mixer. Total numbers of mixing layouts were designed by the application of Taguchi's orthogonal array (OA) methodology based on three parameters and three levels in the L₉ selector matrix model. Mechanical properties of all runs were measured and fitted into the statistical software to determine signal to noise (S/N) ratio. Ranks of the parameters were determined based on the delta statistics of the larger is better case of the S/N ratio. The ANOVA parameters were analyzed and percentage contribution of each factor, along with the correlation coefficient of each variable, was measured. The multiple linear regression models for each property were correlated with the parameters through mathematical equations. Fourier transform infrared (FTIR) analysis was performed to examine any interfacial interactions between polyurethane matrix and organoclay. X‐ray diffraction (XRD) analysis and field emission transmission electron microscope (FETEM) were employed to analyze the dispersion of organoclays in the polymer matrix. Field emission scanning electron microscope (FESEM) was employed to observe cryo‐fractured morphology. Dynamic mechanical analysis (DMA) and dynamic shear rheometer (DSR) were used to investigate dynamic mechanical properties and rheological properties of the trials, respectively. Based on all of these characterizations, an optimum processing condition was determined. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Weibull statistics in electrical aging of polyesterimide under AC voltage

This article is aimed at the investigation of electrical aging of polyesterimide under AC voltage using Weibull statistical analysis. It's shown that the time to breakdown characteristic (V–t) of polyesterimide includes two zones (segments of straight line). The first zone characterizes a statistical dispersion of the intrinsic defects of material. The second zone expresses the real aging of polymer. The variation of the slope of lifetime curve is attributed to the change in the degradation mechanism. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical properties of crosslinked polyurethane elastomers based on well‐defined prepolymers

This article presents research findings for selected mechanical properties of polyurethane elastomers. The studied elastomers were synthesized with the prepolymer‐based method with the use of controlled molecular weight distribution (MWD) urethane oligomers and with the classical single‐stage method. Prepolymers with defined MWDs were obtained with the use of a multistage method, that is, step‐by‐step polyaddition. To produce elastomers, isocyanate oligomers were then crosslinked with triethanolamine, whereas hydroxyl oligomers were crosslinked with 4,4′,4′′‐triphenylmethane triisocyanate (Desmodur RE). The tensile strength of the obtained elastomers ranged from 1.0 to 7.0 MPa, the ultimate elongation approached 1700%, the Shore A hardness varied from 40 to 93°, and the abrasion resistance index fell within 15–140. The effects of the types of raw materials used, the chemical structures, the production methods, and the supermolecular structures on the mechanical properties of the obtained polyurethane elastomers were examined. When the obtained findings were generalized, it was concluded that the structural changes in the polyurethanes, which were favorable for intermolecular interactions, improved the tensile strength, hardness, and abrasion resistance of the materials and impaired their ultimate elongation at the same time. More orderly supermolecular structures and, therefore, superior mechanical properties were found for polyurethane elastomers produced with the prepolymer method. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of pyridazine content and crosslinker structure on the properties of polyurethane elastomers

This article studies the development of a series of heterocyclic polyurethanes (PUs) with various pyridazine content and different crosslinker structure in their main chains. All of the isocyanate‐terminated PU prepolymers were prepared from poly(tetramethylene oxide) glycol of molecular weight 1400 (Terathane 1400) and 1,6‐hexamethylene diisocyanate. The properties of the obtained linear and crosslinked pyridazine‐based PU were compared with the properties of common PUs obtained by chain extension with 1,4‐butanediol. All the obtained PUs were characterized through spectral and thermal behavior. The pyridazine‐based PU showed improved thermal stability with 10% weight loss at temperatures above 370–400°C. With the increase of pyridazine content the values of Young's modulus are higher and the strain at break decreases. Increasing pyridazine content leads to increased films surface hydrophilicity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermoplastic polyurethane composites prepared from mechanochemically activated waste cotton fabric and reclaimed polyurethane foam

In this study, thermoplastic polyurethane (PU) composites were successfully prepared from waste cotton fabric (WCF) and reclaimed PU foam derived from the shoe manufacturing industry through melt mixing. A pan‐mill‐type mechanochemical reactor made in our laboratory was applied to determine the mechanochemical activation of WCF. The intramolecular and intermolecular hydrogen bonds of WCF could be broken up through pan milling because of the fairly strong shearing and squeezing forces. Moreover, the simultaneous reduction of particle size and the large increment of the specific surface area of pan‐milled WCF benefitted its dispersion and the interfacial adhesion with the PU matrix. Mechanochemically activated WCF could be used as a low cost but effective functional additive to enhance the melt processability and mechanical properties of PU/WCF composites. With the addition of 75‐phr WCF, the heat shrinkage of the melt‐reprocessed PU decreased sharply from its original 11.4 to 0.3%. Meanwhile, the tensile strength of the composites was enhanced from 10.3 to 23.2 MPa. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Shape‐memory behavior of thermally stimulated polyurethane for medical applications

Shape memory polymers (SMPs) have been of great interest because of their ability to be thermally actuated to recover a predetermined shape. Medical applications in clot extracting devices and stents are especially promising. We investigated the thermomechanical properties of a series of Mitsubishi SMPs for potential application as medical devices. Glass transition temperatures and moduli were measured by differential scanning calorimetry and dynamic mechanical analysis. Tensile tests were performed with 20 and 100% maximum strains, at 37 and 80°C, which are respectively, body temperature and actuation temperature. Glass transitions are in a favorable range for use in the body (35–75°C), with high glassy and rubbery shear moduli in the range of 800 and 2 MPa respectively. Constrained stress–strain recovery cycles showed very low hysteresis after three cycles, which is important to know for preconditioning of the material to ensure identical properties during applications. Isothermal free recovery tests showed shape recoveries above 94% for MP5510 thermoset SMP cured at different temperatures. One material exhibited a shape fixity of 99% and a shape recovery of 85% at 80°C over one thermomechanical cycle. These polyurethanes appear particularly well suited for medical applications in deployment devices such as stents or clot extractors. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3882–3892, 2007     

Synthesis and properties of nanosilica‐reinforced polyurethane for grouting

A polyurethane/nanosilica (PU/SiO₂) hybrid for grouting was prepared in a two‐step polymerization using poly(propylene glycol) diols as the soft segment, toluene 2,4‐diisocyanate (TDI) as the diisocyanate, 3,3′‐dichloro‐4,4′‐diaminodiphenylmethane (MOCA) as the chain extender, and acetone as the solvent. The size and dispersion of nanosilica, the molecular structure, mechanical properties, rheological behavior, thermal performance, and the UV absorbance characteristic of the PU/SiO₂ hybrid were investigated by transmission electron microscopy (TEM), FTIR, mechanical tests, viscometry, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and UV spectroscopy. Nanosilica dispersed homogeneously in the PU matrix. The maximum values of mechanical properties such as tensile strength, elongation break, and adhesive strength showed an addition of nanosilica of about 2 wt %. Resistance to both high and low temperatures was better than with PU. And the UV absorbance of the PU/SiO₂ hybrid increased in the range of 290–330 nm with increasing nanosilica content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4333–4337, 2006     

Synthesis of microsphere aluminum hypophosphite and its application in polyurethane elastomer

Microsphere aluminum hypophosphite (AHP) is prepared via the hydrothermal method and characterized by Fourier transform infrared spectrometry, X‐ray diffraction, and scanning electron microscopy. Then the hydrothermal AHP and the precipitation AHP are added to the polyurethane elastomer (PUE). The flame retardant properties, thermal stability, and mechanical properties of the PUE with different kinds of AHP added are studied. The results show that the hydrothermal AHP is microsphere with a uniform particle size of around 5 µm. The limited oxygen index of the PUE with the addition of 5% hydrothermal AHP increases to 28.5 vol %. Compared with the PUE including different kinds of AHP, the peak heat release rate of added hydrothermal AHP decreases by about 6%. Hydrothermal AHP could improve the char yield which provides better flame retardancy for PUE. Meanwhile, the hydrothermal AHP‐added PUE has better mechanical properties than that with precipitation AHP added. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42370.