Dielectric relaxation properties in polypropylene–polyurethane composites (original) (raw)
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Relaxation properties of some segmented polyurethane-CaCO3 composites. A Dielectric study
Journal of Polymer Science Part B: Polymer Physics, 1987
Dielectric relaxation in three segmented polyurethane-CaC03 composites was investigated between-7OOC and + 15OOC in the 300 Hz to 100 kHz frequency range. Two of the polymers contained a polyacetal-polyether soft segment, whereas the soft component of the third polymer was polypropylene oxide. The hard segments consisted of 4,4'-diphenyl methane diisocyanate in two cases and toluene-2,4-diisocyanate in the third case. In parallel studies two calorimetric relaxations, designated a and a', were observed for each sample and were determined to be glass transitions of the soft and hard segments, respectively. In general, the transition temperatures decrease with increasing filler content. High frequency, low temperature permittivities increase while low frequency, high temperature AC conductivities generally decrease with increasing filler content. The shift in the transition temperatures can be explained using the adsorption theory of filler-polymer interactions and the densities of the samples. The interfacial polarization mechanism becomes important only above the a' transition temperature and below 1 kHz. EXPERIMENTAL Three different classes of segmented polyurethanes with 0, 25, 40, and 60 vol% filler contents were synthesized and studied. The hard segment of the polymers designated A and B (Figure 1) contained 4,4'-diphenyl methane diisocyanate (MDI; Mobay Chemicals). The chain
Polymer …, 2011
Ternary hybrid composites composed of polyoxymethylene (POM), polyurethane (PU) and boehmite alumina nanoparticles were produced by melt blending with and without latex pre-compounding. PU latex pre-compounding was employed for the fine dispersion of both the PU and alumina particles within the POM matrix. In this study the electrical properties of the POM/PU/boehmite alumina nanocomposites were examined by means of broadband dielectric spectroscopy over a wide temperature (−100 to 150 • C) and frequency (10 −1 to 10 6 Hz) range. Data were analysed by means of the electric modulus formalism. The recorded relaxations include contributions from both polymers and the inorganic reinforcing phase. In the ternary hybrid systems five distinct relaxation processes were detected. Relaxations were assigned and interpreted by considering the morphology of the corresponding composite. In particular, they were attributed to the γ -mode of POM and/or of PU, the α-mode of PU, the α-mode of POM and to the interfacial polarization process. Finally, the dynamics of all the recorded processes are examined and discussed.
Dielectric relaxations of Acrylic-Polyurethane hybrid materials
Polymer, 2015
In this work we present a dielectric relaxation study of Acrilyc/Polyurethane polymers synthesized via miniemulsion photo-polymerization. Three different samples, both parts of the synthesized hybrid latex (SOL and GEL fractions) and a full acrylic sample as reference have been considered. Besides dielectric experiments using broadband Dielectric Spectroscopy (BDS) technique, complementary Differential Scanning Calorimetry measurements have been performed. The thermodynamic characterization outcomes evidence very similar characteristics of the glass transition phenomena among the investigated samples without any signature of melting/crystallization. However BDS experiments show three well resolved dielectric relaxation processes above Tg, two of them evidence marked differences among the samples. A detail study allows us to provide a molecular origin for these three dielectric relaxation processes in connection with the sample characteristics. In particular, our results show that the characterization of these hybrid Acrylic/PU by BDS can provide access to some of the structural features that would ultimately influence the adhesives properties.
Polymer, 1997
The dynamics of blends of poly(methylacrylate) (PMA)+ poly(4-hydroxystyrene) (P4HS) and poly(4hydroxystyrene-co-4-methoxystyrene) (MP4HS) have been studied by dielectric relaxation in the frequency range 20 < w/Hz < 105. The results have been analysed in terms of the Havriliak-Negami function plus a conductivity contribution. The time-temperature superposition principle breaks down for the blends, while it seems to be valid for PMA. The width of the relaxation region increases with the content of P4HS or MP4HS, in accordance with previous dynamic mechanical relaxation data. For a given composition, the data of the blends follow the scaling curve proposed by P. W. Dixon (Phys. Rev. Left., 1990, 42, 8179), however in the low frequency region each sample follows a different scaling curve, which slope is related to the c~ parameter of the Havriliak-Negami function. The increase of the width of the relaxation curves with decreasing the PMA content can be well correlated by the coupling model when a gaussian distribution of coupling parameters is taken into account. © 1997 Elsevier Science Ltd.
Dielectric Relaxation of Linear and Cross-Linked Polyurethane
Macromolecules, 2001
The dielectric relaxation is studied of linear and cross-linked polyurethane based on linear and three-armed star poly(propylene oxide), also called poly(propylene glycol). The dielectric relaxation of polyurethane melts and gels is indistinguishable if the density of urethane links is the same. The introduction of urethane links slows down the segmental relaxation of a number of segments adjacent to the links. The influence is much stronger on the dielectric relaxation than on the relaxation of the shear modulus. The relaxation of the end-to-end vector of the PPO precursors is not much influenced by endlinking at least as long as they are not strongly entangled.
New method to analyze dielectric relaxation processes: a study on polymethacrylate series
Polymer International, 2012
The relaxation properties of polymethacrylates of the n-alkyl series with n = l, 2 and 4 (poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA) and poly(n-butyl methacrylate) (PnBMA)) have been measured and analyzed in order to relate their properties to the size of the lateral side chains. The n-alkyl series has been regarded as a model system and was used in this work to test a graphical data analysis method. Essentially, four relaxation processes were detected in the three polymers: the γ , β, α and αβ relaxations, in increasing order of temperature. It was found that the γ relaxation has a low activation energy, of around 36.3-38.5 kJ mol −1 , independent of the side chain, exhibiting low entropy of activation values when referring to the Eyring description of the activation parameters. The β relaxation was found to be similar in PMMA and PEMA, showing an activation energy of 88.8 kJ mol −1 , increasing to 112.8 kJ mol −1 in PnBMA. The activation entropy was also found to be low for this relaxation, although greater than that for the γ relaxation. In contrast, the α relaxation is quite different in these polymers. We observed a gradual shift in the glass transition temperature towards lower temperatures as the side chain increases in length. The manner in which the α transition makes its way into the dielectric spectra is more abrupt in PMMA than in PnBMA, denoting a higher fragility in the former polymer. Finally, there is a significant difference in the coalescence scenarios of the α and β relaxations for temperatures higher than the glass transition temperature, where they give rise to the so-called αβ relaxation.
Thermal and dielectric properties of polycarbonatediol polyurethane
Journal of Applied Polymer Science, 2015
The dielectric relaxation behavior of segmented polyurethane has been studied using Broad-Band Dielectric Spectroscopy in the frequency domain, 10 22 to 10 8 Hz, and in the temperature range of 2120 to 140 C. The spectra show three secondary processes (d, c, and b) followed by the a relaxation and conductive processes. The Havriliak-Negami (HN) phenomenological equation was used in order to characterize all the processes. The d, c, and b 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.
Probing the dielectric response of polyurethane/alumina nanocomposites
Journal of Polymer Science Part B-polymer Physics, 2010
The dielectric properties of polyurethane (PUR) latexboehmite alumina nanocomposites were investigated by means of broadband dielectric spectroscopy in the temperature range À100 C to 70 C. The concentration of the filler (alumina) was kept constant at 10 phr for all specimens, whereas the mean particle diameter (namely 220, 90, and 25 nm) of the incorporated nanoparticles varied accordingly. For reasons of comparison, pure PUR was also examined. Four distinct relaxation modes were recorded in the spectra of all systems. They were attributed to interfacial polarization, glass transition (a-relaxation), local motions of polar side groups, and chain segments (b-relaxation and c-relaxation). All four relaxation processes exhibit a symmetric distribution of relaxation times, which in the case of interfacial polarization, becomes narrower. The intensity of interfacial polarization increases with the reduction of the mean particle diameter indicating enhanced interfacial area.
Polymer, 2001
Dielectric behaviour of poly(2-norbornyl methacrylate) (P2NBM) and poly(3-methyl-2-norbornyl methacrylate) (P3M2NBM) was studied. The effect of the methyl substituent on the norbornyl ring is to decrease the temperature of the dynamic glass transition about 50 K. Moreover, weak secondary relaxations are observed in the two polymers under study. The secondary process of P3M2NBM has been conveniently analysed in terms of the empirical Fuoss±Kirkwood (F±K) equation.
Dielectric relaxation spectroscopy in crosslinked polyurethanes based on polymer polyols
European Polymer Journal, 2000
This work deals with molecular mobility and microphase separation studies in blends of crosslinked polyurethanes and styrene-acrylonitrile (SAN), prepared by reactive blending, by means of dierential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS) techniques. The DRS techniques employed include broadband ac techniques, 10 À2 ±10 6 Hz, and thermally stimulated depolarization currents (TSDC) techniques, À180 to 308C. The results suggest, in agreement with each other by the dierent techniques, that SAN promotes the microphase separation between hard segment (HS) microdomains and soft segment (SS) microphase due to SAN±HS interactions, whereas SAN±SS interactions are weak. TSDC thermal sampling techniques show that a compensation law holds for the a relaxation associated with the glass transition of the SS microphase, with the compensation temperature being very close to the glass transition temperature. Analysis of the a relaxation in terms of fragility indicates that the systems under investigation are fragile. #