Isothermal Melt Crystallization Kinetics for Poly(Trimethylene Terephthalate)/Poly(Butylene Terephthalate) Blends

The kinetics of isothermal melt crystallization of poly(trimethylene terephthalate) (PTT)/poly(butylene terephthalate) (PBT) blends were investigated using differential scanning calorimetry (DSC) over the crystallization temperature range of 184–192°C. Analysis of the data was carried out based on the Avrami equation. The values of the exponent found for all samples were between 2.0 and 3.0. The results indicated that the crystallization process tends to be two‐dimensional growth, which was consistent with the result of polarizing light microscopy (PLM). The activation energies were also determined by the Arrhenius equation for isothermal crystallization. The values of ΔE of PTT/PBT blends were greater than those for PTT and PBT. Lastly, using values of transport parameters common to many polymers (U*=6280 J/mol, T _∞=T _g – 30), together with experimentally determined values of T _m ⁰ and T _g, the nucleation parameter, K _g, for PTT, PBT, and PTT/PBT blends was estimated based on the Lauritzen–Hoffman theory.     

Properties of Poly(butylene terephthalate)/Bisphenol A Polycarbonate Blends Toughening with Epoxy-Functionalized Acrylonitrile–Butadiene–Styrene Particles

Glycidyl methacylate functionalized acrylonitrile–butadiene–styrene particles (ABS-g-GMA) prepared via an emulsion polymerization method were used to toughen poly(butylene terephthalate) (PBT)/bisphenol A polycarbonate (PC) blends. DMA results showed PBT was partially miscible with PC and the addition of ABS-g-GMA improved the miscibility between PBT and PC. DSC tests further testified that the introduction of ABS-g-GMA improved the miscibility of PBT and PC according to the T_m depression criterion. SEM displayed a very good dispersion of ABS-g-GMA particles in the PBT/PC blends and the dispersed phase size of PC decreased due to the compatibilization effect of ABS-g-GMA. The mechanical properties showed that the addition of 10 wt% ABS-g-GMA was sufficient to induce a super-tough fracture behavior to the PBT/PC blends and a notched impact strength of more than 1000J/m was achieved. The Vu-Khanh test showed that stable crack propagation took place for PBT/PC blends with the addition of ABS-g-GMA and led to ductile failure.     

Nanocomposites based on polymer blends: enhanced interfacial interactions in polycarbonate/ethylene-propylene copolymer blends with multi-walled carbon nanotubes

In this article, the phase separation in the melt blended polycarbonate (PC) and ethylene propylene copolymer (EPC) has been studied with dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM). Two glass transition temperatures on the tan δ curves were detected. This confirms the immiscibility of PC and EPC phases. Different content of multi-walled carbon nanotubes (MWCNTs) were added to the PC/EPC blends and the interfacial adhesion between MWCNTs and PC/EPC blend were shown using transmission electron microscopy (TEM). The MWCNTs were located in the PC phase and at the interfaces of PC and EPC phases. Moreover, the storage modulus (E′) of polymer blends was changed by the increasing content of EPC elastomer and MWCNTs. The value of E′ of PC decreased with an incorporation of EPC. While, along with an addition of MWCNTs in the PC/EPC blends an increase of E′ was visible. The strong interfacial interactions between the matrix and MWCNTs played the main role in increasing the values of the E′ of the nanocomposites.     

Effect of proton irradiation on the physical properties of PC/PBT blends

Samples from polycarbonate/poly (butylene terephthalate) (PC/PBT) blends film have been irradiated using different fluences (1?×?10¹⁵– 5?×?10¹⁷ H⁺/cm²) of 1?MeV protons at the University of Surrey Ion Beam Center, UK. The structural modi?cations in the proton irradiated samples have been studied as a function of fluence using different characterization techniques such as X-ray diffraction and UV spectroscopy. The results indicate that the proton irradiation reduces the optical energy gap that could be attributed to the increase in structural disorder of the irradiated samples due to crosslinking. Furthermore, the color intensity ΔE, which is the color difference between the non-irradiated sample and those irradiated with different proton fluences, increased with increasing the proton fluence up to 5?×?10¹⁷ H^+/cm², convoyed by an increase in the red and yellow color components. In addition, the resultant effect of proton irradiation on the thermal properties of the PC/PBT samples has been investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). It is found that the PC/PBT decomposes in one weight loss stage. Also, the variation of transition temperatures with proton fluence has been determined using DSC. The PC/PBT thermograms were characterized by the appearance of two endothermic peaks due to the glass transition and melting temperatures. The melting temperature of the polymer, T_m, was investigated to probe the crystalline domains of the polymer, since the proton irradiation destroys the crystalline structure so reducing the melting temperature.     

Thermally Stimulated Depolarization Current and Thermal Analysis Studies of Gamma Irradiated Lithium‐Salt/Polymer Electrolyte Blends

Thermally stimulated depolarization current (TSDC) and thermal analysis studies of gamma irradiated LiOH/PVA blends were done. To study the mechanisms of conduction and TSDC in poly(vinyl alcohol) (PVA) and LiOH/PVA blends, short circuit TSDC at a polarizing temperature 353 K with a polarizing field of 3 kV cm^?1 have been analyzed in the temperature range 300–410 K. Two peaks are evident from the global TSDC measurements on the pure PVA homopolymer. Meanwhile, in all blended samples; there is only one broad peak with a shoulder on the high temperature side due to the relaxation of the poly‐blend system. The temperature dependence, 300–408 K, of the current density (J) for pure PVA and its blended samples has been studied. It was observed that J values increase dramatically with increasing temperature (in the low temperature region from 300–340 K) owing to the formation of local ordered regions in the otherwise disordered amorphous matrix of PVA. Further increase in the temperature caused a marginal increase in J values. The temperature dependence of the specific heat for all samples was measured. A linear increase of C _p was observed with an increase in temperature, which is ascribed to the increase in lattice vibration of linear macromolecules and consequently, increases in the number of internal degree of freedom of phonons.     

Morphology,miscibility and mechanical properties of PMMA/PC blends

This study deals with some results on morphology, miscibility and mechanical properties for polymethyl methacrylate/polycarbonate (PMMA/PC) polymer blends prepared by solution casting method at different concentration between 0 and 100 wt%. Dynamic storage modulus and tan δ were measured in a temperature range from 30 to 180°C using dynamical mechanical analyzer (DMA). The value of the storage modulus was found to increase with the addition of the PC in the matrix. Transition temperature of pure PMMA and pure PC is found to be 83.8 and 150°C, respectively. The result shows that the two polymers are miscible for whole concentration of PC in PMMA. The distribution of the phases in the blends was studied through scanning electron microscopy (SEM). Also the mechanical properties like elongation at break and fracture energy of the PMMA/PC blends increase with the increase in concentration of PC in PMMA.     

Etude de la relaxation dipolaire dans le Ce2(S04)3·9H2O(9D2O) monocristallin

We report in this article the resolution of TSDC (Thermally Stimulated Depolarization Current) spectra and the relaxation parameters of Ce₂(SO₄)₃· 9H₂O(9D₂O) single crystals, for two typical orientations parallel and perpendicular to C₆, symmetry axes The TSDC peaks obtained show a nonDebye type of behavior Calculation of the dipolar relaxation parameters was achieved by fitting the experimental curves to a general order kinetic equation This method allows us to describe the nonDebye-type of behavior of the TSDC peaks on the basis of dipolar interactions during the relaxation process The three different kinds of electric dipoles leading to the three experimentally observed TSDC peaks are ascribed to three different configurations of hydrogen bonds.     

Ageing exploration of the energy landscape of a glass by the TSDC technique

Different thermal treatments were used in order to follow the structural relaxation of m-toluidine by thermally stimulated depolarization currents (TSDC) in the sub-T _g temperature region. In some of these thermal treatments, the ageing time, t _a, and the probing (or polarization) time, t _P, are varied independently in order to allow a clear understanding of the exploration of the energy landscape which occurs as a consequence of the structural relaxation. The TSDC results show that ageing induces a shift to higher temperatures of the TSDC peaks, in a way similar to that observed in the calorimetric heat capacity overshoot. More importantly, TSDC results show that ageing induces a decrease of the activation energies with regard to the window defined by the probing time and a sharpening of the energy distribution of the modes of motion that are present in the glass, in the studied sub-T _g temperature region.     

Crystallization Behavior of Poly(Trimethylene Terephthalate)/Polycarbonate Blends

The crystallization behavior of poly(trimethylene terephthalate (PTT) in compatibilized and uncompatibilized PTT/polycarbonate (PC) blends are investigated in the research reported in this paper. The differential scanning calorimetry (DSC) results showed that the crystallization behaviors of PTT/PC blends were very sensitive to PC content. The onset (T_ci) and the peak (T_c) crystallization temperatures shifted to lower temperatures whereas the area of the exotherm decreased quickly as the PC content was increased. The Avrami exponent, n, decreased from 4.32 to 3.61 as the PC content was increased from 0 to 20 wt %, and the growth rate constant, Z _c , decreased gradually as well. This suggests that the nucleation mechanism exhibits the tendency of changing gradually from a thermal nucleation to an athermal mode although the growth mechanism still remains three‐dimensional. When epoxy (2.7 phr) was added as a compatibilizer during melt blending, the T_ci and T_c shifted slightly to higher temperature (≤2°C), and the crystallization enthalpy, however, exhibited an increased crystallinity with the exception of the 90/10/2.7 phr PTT/PC/Epoxy. This suggests that the epoxy make a positive contribution to the PTT crystallization. Moreover, the influences of epoxy on the crystallization behaviors of PTT/PC blends are related to the epoxy content. By contrast, the compatibilizer of ethylene‐propylene‐diene copolymer graft glycidyl methacrylate (EPDM‐g‐GMA, ≤6.3 phr) had little effect on the crystallization behavior of PTT/PC blends. For PTT/PC/Epoxy (2.7 phr) blends, the Avrami exponent, n, decreased to near 3, while the growth rate constant, Z _c , increased slightly as PC content was increased from 0 to 20 wt %. It is suggested that epoxy accelerated the process of the nucleation mechanism changing from thermal nucleation to an athermal mode. The EPDM‐g‐GMA had little effect on the nucleation mode and spherical growth mechanism. The PTT spherulite morphologies in PTT/PC blends were very sensitive to blend composition. Completely different morphologies were observed in pure PTT, PTT/PC, PTT/PC/Epoxy, and PTT/PC/EPDM‐g‐GMA blends.     

Activation Energy for the Glass Transition of a Confined Elastomer in HDPE/PP Blends

Blends of two highly crystalline polymers containing an elastomer were prepared to study the glass transition of the confined elastomer. The polymers chosen were high density poly ethylene (HDPE), polypropylene (PP), and two elastomers of a different nature: natural number (NR) and EPDM. The dynamic mechanical analyzer (DMA) technique was used to analyze the storage modulus of blends with elastomer content from 0% to 30% by weight, with the remainder made up of equal amounts of HDPE and PP, and blends with 10% of the elastomer, but varied ratios of polyolefins. We used the differentiation modification of the Arrhenius method in the kinetic analysis assuming an n‐order relaxation mechanism, which allowed detecting the percolation threshold of NR. Results indicate that both temperature and activation energy for glass transition (T _g ) are dependent on the types of polymers in the blend and blend composition. The T _g and E values of the unblended elastomers are higher than those in blends; this behavior is associated with the elastomer confinement and blend morphology.     

Thickness dependence of elastic modulus of polycarbonate interphase

The oligomer of bis-phenol A (oligo-PC) with M _w = 1300 and bis-phenol A polycar-bonate (PC) with M _w = 20 000 were deposited onto E-glass surface using SiCl₄ as the grafting and cross-linking agent. Thickness of the deposited layers was varied from 30 to 10⁶ nm and the layers were investigated as prepared and after thermal annealing at 245°C for 10 min in the air. Vibrational piezoelectric resonator technique and the speed of Rayleigh wave measurement were used to determine elastic moduli of the ultra thin layers deposited on flat E-glass substrate as a function of their thickness. In all cases, increase of the Young modulus of the interphase, E _i, with decreasing layer thickness, t _i, was observed. At a given thickness, the E _i of PC layer was significantly lower than that for the oligo-PC layer. Thermal annealing of the deposited PC layer resulted in a significant increase of its E _i compared to the as received layer. No significant change was observed for oligo-PC interphases. Increase of the shear strength of the interface, τ _a, with reducing interphase thickness, t _i, was observed. The observed increase of E _i with the decreasing t _i was ascribed to the reduction of the molecular mobility of chains near solid surface compared to their mobility in the bulk. Most probably, the observed increase of E _i after thermal annealing of PC was caused by rearrangement of both segment density distribution in individual PC coils near the solid surface and cooperative rearrangements of multiple PC chains. Since the oligomers attached to the surface attained presumably more regular extended conformations with lower conformation entropy compared to the PC random coils, the effect of thermal annealing was negligible. In agreement with theoretical predictions, increase of E _i at the same extent of interfacial interactions resulted in the observed increase of the τ _a measured using the single embedded fiber test.     

Dielectric relaxation properties of tysonite-type solid solutions La1−xBaxF3−x

Dielectric relaxation properties of solid solutions La_1?xBa_xF_3?x (x ? 0105) have been studied by thermally stimulated depolanzation current (TSDC)- and a c. dielectric loss (DL) techniques.For x < 30 × 10^?3 the dielectric spectra show a relaxation peak which is ascribed to a simple associate of a substitutional dopant ion and a fluoride ion vacancy (Ba_LaV_F)^x in nearest-neighbour position, the vacancy being confined to the B sublattice For x values of about 1.3 × 10^?2 a relaxation peak appears which is tentatively attributed to a similar type of defect associate with the vacancy now confined to the A sublattice of the tysonite anion array One broad relaxation peak dominates the TSDC and DL spectra over the whole concentration range This peak is due to the relaxation of macroscopic space charge, i e ionic conductivity The low-temperature ion conductivity has been determined for several solid solutions, and extrapolates to the high-temperature conductivity determined previously with impedance spectroscopy Below liquid-nitrogen temperature three relaxations are observed, and ascribed to electronic transitions in cenum impurities. A computer programme has been developed to analyse TSDC relaxation peaks, taking dipole-dipole interactions into account Relaxation parameters and dipole concentrations are presented.     

Space charge analysis in enamelled wires by using thermally stimulated depolarization current (TSDC)

This paper reports on measurements of thermally stimulated depolarization current (TSDC) that is applied to characterize changes in the large motors and generators enamelled wires that have been exposed to aging under steep-front pulse voltage waveforms. The thermoelectrets are prepared at various polarizing fields, E_P, and measurements of TSDC are carried out both as a function of time and temperature over the range of 23–200 °C. In addition, various TSDC parameters such as activation energy, ?_a, characteristic relaxation time, τ and the released charge, Q during the relaxation process have been determined by applying initial rise method. The experimental results for TSDC spectra of wire specimens have shown that the total stored charge in the insulation bulk increases significantly, as the number of insulation layers increases on the wire. The reason for such a higher concentration of trapped charges is more likely due to the presence of a broad distribution of the traps, which are occupied by the injected charges.     

Surface spin-glass-like behavior of monodispersed superparamagnetic Mn0.5Zn0.5Fe2O4 magnetic fluid

Zero field cooled dc-magnetization measurements of monodispersed Mn_0.5Zn_0.5Fe₂O₄ nanoparticles dispersed in kerosene exhibit two transitions at low temperatures. These transitions correspond to (i) the superparamagnetic to blocked superparamagnetic and (ii) the blocked superparamagnetic to surface spin-glass like/quantum superparamagnetic state upon lowering the temperature. The existence of a disorder surface is confirmed by recording small-angle neutron scattering data below and above the Curie temperature. Magnetic relaxation analysis shows a plateau at low temperature (below 5 K) with a slight minimum at 3 K, which is a characteristic of the surface spin-glass-like state. This is analyzed considering the energy distribution n(E)∼1/E. The existence of surface disorder dominates at low temperature and mimics the transition from superparamagnetic to quantum superparamagnetic states.     

Effect of Polarization Temperature on the Chain Segment Motion and Space Charge Detrapping in Polyamide 610 Film Electrets

The effect of polarization temperature on the chain segment motion and charge trapping and detrapping in polyamide 610 films has been investigated by means of thermally stimulated depolarization current (TSDC) and wide-angle X-ray diffraction (WAXD). A small part of the amorphous phase of quenched polyamide 610 changes into the crystalline state with increasing polarization temperature. There are three current peaks (named α, ρ₁, and ρ₂ peak, respectively) in the TSDC spectra. The α peak corresponds to the glass transition, the ρ ₁ peak is attributed to space charge trapped in the amorphous phase, and interphase between crystalline and amorphous phases, and the ρ ₂ peak originates from space charge trapped in the crystalline phase. By analyzing the characteristic parameters of these peaks, it was found that the increase of polarization temperature induced a decrease of the chain segment mobility and promoted the creation of structural traps in polyamide 610. The decrease of the chain segment mobility in the amorphous phase made the intensity of the α peak weak and the activation energy increased. The higher the polarization temperature, the higher the degree of crystallinity and the more charge carriers trapped in the crystalline phase. So, the increase of polarization temperature made the intensity of the ρ ₂ peak strong and increased the stability of trapped charge in the crystalline phase. The increase of polarization temperature also made the intensity of the ρ ₁ peak strong and decreased the stability of trapped charge in the amorphous phase and interphase.     

Effects of Montmorillonite on the Nonisothermal Crystallization Behavior of the Poly(trimethylene terephthalate)/Polypropylene/Montmorillonite Nanocomposites

Organic montmorillonite (MMT) reinforced poly(trimethylene terephthalate) (PTT)/ polypropylene (PP) nanocomposites were prepared by melt blending. The effects of MMT on the nonisothermal crystallization of the matrix polymers were investigated using differential scanning colorimetry (DSC) and analyzed by the Avrami equation. The DSC results indicated that the effects of MMT on the crystallization processes of the two polymers exhibited great disparity. The PTT's crystallization was accelerated significantly by MMT no matter whether PTT was the continuous phase or not, but the thermal nucleation mode and three-dimensional growth mechanism remained unchanged. However, in the presence of MMT, the PP's crystallization was slightly retarded with PP as the dispersed phase, and was influenced little with PTT as the dispersed phase. When the MMT content was increased from 2_wt% to 7_wt%, the crystallization of the PTT phase was slightly accelerated, whereas the crystallization of the PP phase was severely retarded, especially at lower temperatures. Moreover, the nucleation mechanism for the PP's crystallization changed from a thermal mode to an athermal one. In the polypropylene-graft-maleic anhydride (PP-g-MAH) compatibilized PTT/PP blends, with the addition of 2_wt% MMT during melt blending, the T _c (PTT) shifted 7.8°C to lower temperature and had a broadened exotherm, whereas the T _c (PP) shifted 17.1°C to higher temperature, with a narrowed exotherm. TEM analysis confirmed that part of the PP-g-MAH was combined with MMT during blending.     

Study of thermal currents in powder β-spodumene ceramics doped with Cuo, FeO and TiO2

Ternary-phase ceramic system of Li₂O Al₂O₃ 4SiO₂ doped with CuO, FeO and TiO₂ has been prepared and subjected to dc electrical conductivity and thermally stimulated depolarization current (TSDC) measurements as a function of temperature (30-250 °C) and field strength. The electrical conductivity results are explained by assuming both ionic and electronic conduction mechanisms coexist with different contributions over the whole temperature range of experiments. TSDC spectra have been found to be characterized by a broad intense relaxation peak, which can be attributed to an ionic charge polarization. The broad relaxation transitions are apparently a result of the nonuniform nature of this process. Activation energies are calculated for both dc electrical conductivity and TSDC according to Arrhenius equation and initial rise method, respectively.     

The determination of the glass transition temperature by thermally stimulated depolarization currents. Comparison with the performance of other techniques

Several experimental techniques are currently used for the determination of the glass transition temperature, T_g. Thermally stimulated depolarization currents (TSDC) is a thermal analysis technique whose experimental results display a very clean glass transition signature and that, nevertheless, is seldom used as a technique for T_g determination. In the present work we explain how to get the glass transition temperature from TSDC data, and we compare the values obtained for a vast number of glass forming systems (with T_gs in a wide range between ?145 and +180 °C and fragilities between m = 15 and m = 100), with the values obtained by differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS). We conclude that the T_g determination by TSDC is direct, accurate and reproducible and that the obtained values correlate very well with those obtained by DSC and DRS. This general survey thus suggests TSDC as a valuable alternative technique for determining T_g.     

TSDC studies of the effects of plasticizer and water on the sub-T g relaxations of an epoxy resin system

The sub-glass-transition-temperature (sub-T _g relaxations of an epoxy resin system based on diglycidyl ether of bisphenol-A (DGEBA) and cured with triethylenetetramine (TETA) were investigated by means of the thermally stimulated depolarization current (TSDC) technique in the temperature range 77 K to 300 K. Three relaxation regions were observed: the γ relaxation at about 150 K, the β relaxation at 160 K to 200 K and the ω relaxation at 240 K to 270 K. The plasticization effect on the aforementioned relaxations of a plasticizer chemically connected to the epoxy resin network was investigated. The amount of plasticizer (commercial name THIOCOL LP3) was varied between 0% and 60% by weight of the epoxy. The broad range of the β relaxation reflects the heterogeneous structure of the material. The activation energies of the γ and β relaxations were calculated using the thermal sampling technique. Physical aging strongly influenced the TSDC thermogram of the ω relaxation, indicating phase separation during the aging procedure. Water effects were systematically investigated from dry samples to water-saturated samples (water content, 2.5%). In all specimens, water induced plasticization, which is expressed by the shifting of the β relaxation toward lower temperatures. The mode of water absorption (immersion in water or exposure to humid environment) also influenced the evolution of the ω relaxation.     

Thermal behavior of gamma-irradiated low-density polyethylene/paraffin wax blend

The thermal properties of low-density polyethylene (LDPE)/paraffin wax blends were studied using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and melt flow index (MFI). Blends of LDPE/wax in ratios of 100/0, 98/2, 96/4, 94/6, 92/8, 90/10 and 85/15 (w/w) were prepared by melt-mixing at the temperature of 150°C. It was found that increasing the wax content more than 15% leads to phase separation. DSC results showed that for all blends both the melting temperature (T_m) and the melting enthalpy (ΔH_m) decrease linearly with an increase in wax content. TGA analysis showed that the thermal stability of all blends decreases linearly with increasing wax content. No clear correlation was observed between the melting point and thermal stability. Horowitz and Metzger method was used to determine the thermal activation energy (E_a). MFI increased exponentially by increasing the wax content. The effect of gamma irradiation on the thermal behavior of the blends was also investigated at different gamma irradiation doses. Significant correlations were found between the thermal parameters (T_m, ΔH_m, T₅%, E_a and MFI) and the amount of wax content and gamma irradiation.