Alpha Relaxation Study of Poly(Vinyl Chloride Co-Vinylacetate-Co-2-Hydroxypropyl Acrylate)

By using thermally stimulated depolarization current (TSDC) technique, and coupling it with the thermal sampling (TS) method, the relaxation behavior of Poly(vinyl chloride-co-vinylacetate-co-2-hydroxypropyl acrylate) (PVVH) has been investigated in the vicinity of its glass transition temperature, T_g. The global TSDC spectra of amorphous PVVH with varying the poling field and poling temperature revealed the presence of two TSDC peaks. The first peak at about 347 K and is ascribed to the glass transition temperature and can be referred as α-relaxation. The second one is obtained in the temperature range 353–383 K and is attributed to the space charge relaxation and can be referred as ρ-relaxation. Fine structure of α-relaxation peak was obtained using the thermal sampling method. All the molecular parameters, such as activation energy (E_a) and preexponential factor (τ₀), have been estimated. In addition, the compensation law was found to be valid; and the compensation parameters such as compensation temperature (T_c) and compensation time (τ_c) have been determined.     

Thermal and structural characterization of the Bi2-xSmxSr2Ca2Cu3O10+δ glass-ceramic system

In this work, investigations on the crystallization and oxidization kinetics of the Sm substituted BiSrCaCuO glass-ceramic system were performed. It has been shown that the Sm ions changed the glassification properties of the BiSrCaCuO system. While fully glass samples were obtained for low Sm-substitution levels (x=0.2 and x=0.4), the Sm containing particles on the surface have grown especially at high Sm-substitution levels (x>0.6) and glassification problem increased. Nonisothermal crystallization kinetics including activation energy for crystallization, E_a, and Avrami parameter, n, of the samples prepared was investigated using differential thermal analysis (DTA) at four different uniform heating rates. The values of glass transition temperature and crystallization temperature exhibited compositional and heating rate dependence. E_a value of the samples showed an increase with increasing the Sm concentration. The Avrami parameter, n, was found approximately 4.5, suggesting the growth of small particles with an increasing nucleation rate. The calculated values of the oxidization rates and the activation energy for oxygen out-diffusion process, E, indicated that the oxygen deficiencies by the Sm substitution in the unit cell of BiSrCaCuO were formed and more oxygen atoms were absorbed to fill the oxygen deficiencies in the system.     

Polarization temperature effect on liquid–liquid transition and space charge detrapping behavior in atactic polystyrene by thermally stimulated depolarization current

Thermally stimulated depolarization current (TSDC) experiments were carried out to investigate the effect of polarization temperature (T _p) on liquid–liquid transition and space charge detrapping behavior in atactic polystyrene. Differential scanning calorimetry (DSC) measurement was applied as a complementary method. When T _p is 130 °C, there are four distinct peaks (α, ρ₁, LL, and ρ₂) showed in TSDC spectrum in the range of 30–200 °C. Compared with the result of DSC, TSDC spectrum show that peak α corresponds to glass transition, peak LL is related to liquid–liquid transition, and peak ρ₁ and peak ρ₂ belong to the space charge current peak. As T _p increases from 100 to 150 °C, the intensity of peak LL maximum increases and that of space charge peaks maxima decreases, which is attributed to different mechanism between liquid–liquid transition and space charge detrapping behavior. In addition, their corresponding characteristic parameters versus T _p are also analyzed in detail.     

Depolarization current in phenol-formaldehyde resin below the glass transition

A thermally stimulated depolarization (t.s.d.) current study of a novolac phenol-formaldehyde resin performed using electric poling at temperatures T ? T_g (T_g being the glass transition temperature which equals 323 ± 2 K) shows a continuous distribution of polarizability in the range from 295 to 323 K. The efficiency of poling is found to be dependent upon the physical ageing of resin. In addition to the known current peaks P₁ and P₂ which appear at T_m1 = (320 ± 2)K and T_m2 = (334 ± 6)K respectively, a new peak, P₀, is detected at T_m0 = (296 ± 1)K. P₀ appears reversibly with the same magnitude regardless of the electrical history of the resin or the physical ageing. The activation energy determined by the initial rise method and the whole curve integration method is found to be 500 and 570 kJ mol^?1, respectively. It is assumed that P₀ is caused by a discrete phase transition in the resin.     

Kinetic study of the polymerization of dimethyldiallylammonium chloride and acrylamide

The kinetics of the polymerization of dimethyldiallylammonium chloride (DMDAAC) and acrylamide (AM) with different monomer molar ratios initiated by an ammonium persulfate–sodium bisulfate redox complex in an aqueous solution were studied. The polymerization rate (R_p) equation, the activation energy (E_a), and the reactivity ratio were measured. The results show that when the n_DMDAAC:n_AM values were 1 : 9, 2 : 8, 3 : 7, 4 : 6, and 5 : 5, the copolymerization rate equation were R_p1 = k[M]^2.61[I_O]^0.51[I_R]^0.52, R_p2 = k[M]^2.70[I_O]^0.50[I_R]^0.53, R_p3 = k[M]^2.73[I_O]^0.50[I_R]^0.56, R_p4 = k[M]^2.77[I_O]^0.51[I_R]^0.59, and R_p5 = k[M]^2.84[I_O]^0.51[I_R]^0.61 (where [M] is the total monomer concentration, [I_O] is the oxidant concentration, and [I_R] is the reductant concentration), respectively when the temperature was 45°C. The E_a values were E_a1 = 79.10 kJ/mol, E_a2 = 81.39 kJ/mol, E_a3 = 85.15 kJ/mol, E_a4 = 88.88 kJ/mol, and E_a5 = 90.61 kJ/mol in the temperature range 35–55°C, respectively. The reactivity ratios of DMDAAC and AM were r_DMDAAC = 0.14 and r_AM = 6.11 when the temperature was 45°C. The structure of PDA was characterized by Fourier transform infrared spectroscopy and ¹H-NMR. The results of the kinetic parameters explained the differences in the copolymerization rate and intrinsic viscosity of PDA with different cationicities. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Assessing the variability of colour‐rendering indices using a random test‐colour method

This paper addresses the way in which the random selection of different sets of samples influences the values of two colour‐rendering indices analogous to the ones proposed by the International Commission on Illumination (CIE Publ. 13.3, 1995), R_a, and the Illuminating Engineering Society (IES Technical Memorandum TM‐30‐15, 2015), R_f. We report results found for 11 light sources, representative of current indoor and outdoor lighting, using a database with 12 123 spectral reflectance factors from real objects. For these 11 light sources, the differences between official R_a and R_f values and those computed using 100 iterations with 6000 random samples from our database proved to be in the range [?13, 2] and [?15, ?1], respectively, the highest differences corresponding to sources with narrow peaks in their spectral power distributions. For 100 random subsets of 10 samples from our database, the average standard deviations of the 11 light sources for indices analogous to R_a and R_f were 8 and 5 (or 2 and 1 using 110 samples) respectively. The standard deviations in computed R_a and R_f values, using subsets with different numbers of samples n, can be modelled as inversely proportional to the square root of n. We propose a method to estimate these standard deviations for n = 6000 using reduced sets of 10 spectral reflectance factors.     

Slow relaxations in semicrystalline poly(butylene succinate) below and above Tg

The slow molecular mobility in the amorphous part of the semi‐crystalline polymer poly(butylene succinate) (PBS) has been studied by the thermally stimulated depolarization current (TSDC) technique. Experiments were carried out in the temperature range, which includes the glassy state, the glass transformation region, and the rubber state. A broad and low intensity secondary relaxation was observed in the temperature region from ?140°C up to the glass transition region; the activation energy of the motional modes of this secondary relaxation was in the range between 35 and 55 kJ mol^?1. The glass transition temperature of PBS, provided by the TSDC technique, was T_g = ?40 °C, and the fragility index was found to be m = 43. The aging behavior of the main and of the secondary relaxations was analyzed. A strong relaxation above T_g was observed, whose molecular origin was discussed. The thermal behavior of the PBS was also characterized by differential scanning calorimetry. POLYM. ENG. SCI., 55:1873–1880, 2015. © 2014 Society of Plastics Engineers     

Cure Kinetics and Thermal Properties of Octa(aminophenyl)-POSS/Bromobisphenol A Epoxy Resin Nanocomposites

The tetrabromobisphenol A epoxy resin (TBBPAER) was synthesized and Octa(aminophenyl) polyhedral oligomeric silsesquioxane (OAP-POSS) was used as a curing reagent of TBBPAER. The cure kinetics, the glass transition temperature, and the flame resistance of OAP-POSS/TBBPAER nanocomposites were investigated. The results show that the curing reaction could be described by the autocatalytic ?esták-Berggren (S-B) model. The average activation energy E _a is 129.59 KJ/mol, the maximal mechanical loss temperature (T _p) is 166°C, when the molar ratio (N _s) of amino group to epoxy group is 0.5. The oxygen index for fire resistance is 46 ～ 49 for different amounts of OAP-POSS.     

Radiopaque epoxy resins

Transparent, X-ray contrast (radiopaque) epoxy resins were obtained by dissolving up to 25 wt % triphenylbismuth in the commercial epoxy resin prepolymers EPON-815, DER-330, DER-383, and DEN-431 which were then hardened with diethylenetriamine. The radiopacities of the mixtures were found to be proportional to the molar concentration of the radiopaque additive. The systems follow the relationship, R = R_o + (R_a ? R_o) V _a M_a where R, R_o, and R_a are the radiopacities of the mixture, the pure epoxy resin, and triphenylbismuth, respectively (expressed in mm aluminum/mm resin); M_a and V _a denote the molar concentration and molar volume of the bismuth compound. R_a for triphenylbismuth was found to be 7.4 ± 0.2 mm Al/mm resin; the average value of R_o for the four epoxies equals 0.16 ± 0.1 mm Al/mm resin. The amount of amine required to harden the radiopaque resins was far less for the epoxy novolac resin DEN-431 than for the three bisphenol-A based epoxies. The concentration of triphenylbismuth required to impart a radiopacity equivalent to that of aluminum measures 14.6 wt % in EPON-815, 14.8 wt % in DER-330, 14.9 wt % in DER-383, and 15.9 wt % in DEN-431. The radiopaque resins remain transparent indefinitely, even when exposed to water. © 1995 John Wiley & Sons, Inc.     

NEW-TPI thermoplastic polyimide: Structure and relaxation using SAXS and TSDC

The thermoplastic polyimide Regulus^TM NEW-TPI has been studied using small-angle X-ray scattering (SAXS) and thermally stimulated depolarization current (TSDC). SAXS was used to study the development of lamellar structure during isothermal or nonisothermal crystallization. The one-dimensional electron-density correlation function was used to determine structural parameters. The long period, lamellar thickness, and amorphous layer thickness increase as crystallization temperature increases from 300 to 360°C. By combining melting-point data with SAXS results, we report the side and fold surface free energies of NEW-TPI crystals, which are 29 ± 3 and 41 ± 3 erg/cm², respectively. Real-time SAXS was carried during nonisothermal cold-crystallization at 5°C/min. The long period decreases, while lamellar thickness, linear crystallinity, and interphase thickness increase, with increasing temperature. These changes are explained by a crystal-insertion model. TSDC was used as a more sensitive probe of the amorphous phase structure below 300°C. Both semicrystalline and amorphous NEW-TPI exhibit complex TSDC behavior. Above the glass transition, amorphous NEW-TPI has a strong TSDC peak attributed to short-range-ordered structures, which may serve as nucleation sites for subsequent crystallization. This peak was not seen in semicrystalline material. At the glass transition, both amorphous and semicrystalline NEW-TPI have a strong TSDC peak. In the semicrystalline polymer, relaxation of the amorphous dipoles is slightly restricted by the crystals, which results in a smaller relaxation peak and a shift to higher temperature. Below T_g, another TSDC peak occurs which is not due to dipolar relaxation. This peak is attributed to the combined effects of space charge, electrode type, ionizable species, and interfacial charges. © 1995 John Wiley & Sons, Inc.     

Thermoplastic urethane elastomers. II. Effects of variations in hard-segment concentration

The dynamic mechanical properties of thermoplastic urethane elastomers have been charac-terized for polymers composed of varying hard-segment concentrations and for two different molecular weight polyester diols as soft segments. The urethane polymers based on an 830 M?_n polycaprolactone diol exhibited a progressive increase in glass transition temperature at increased levels of hard segments. In contrast, a similar series of polymers prepared with a 2100 M?_n polycaprolactone diol as the soft segment maintained a relatively constant glass transition temperature. These differences are attributed to the relative degree of phase separation between the constitutive blocks of the copolymer. The polymers of both series possessed two lower-temperature, secondary relaxations, which are ascribed to methylene sequence mobility within the polycaprolactone units and to possible disruption of interfacial associations between the hard- and soft-segment structures.     

Annealing studies on a fully cured epoxy resin: Effect of thermal prehistory,and time and temperature of physical annealing

The dynamic mechanical behavior at about 1 Hz of a fully cured epoxy resin (maximum glass transition temperature, T_g∞, ca. 170°C) ahs been studied during and after isothermal annealing in terms of the influence of thermal prehistory, time of annealing, and temperature of annealing (T_a). Annealing temperatures ranged from T_g ? 15 to T_g ? 130°C. The rate of isothermal annealing was observed to decrease by a decade for each decade increase of annelaing time when the material was far from equilibrium. Annealing at high temperatures did not measurably affect the mateiral properties during cooling (for T ? T_a); similarly the effect of annealing at low temperatures was not measurale during heating (for T ? T_a).     

Radical polymerization of N-[(1-n-butoxycarbonyl)ethyl]maleimide

Poly(N-[(1-n-butoxycarbonyl)ethyl]maleimide) (PBAM) was synthesized by solution polymerization with 2,2′-Azobis(isobutylronitrile) (AIBN) as radical initiator. The resulting polymer(PBAM) was characterized by infrared spectroscopy (IR), themogravimetry (TG), and differential thermal analysis (DTA). The initial decomposition temperature of PBAM is 321.6°C; the glass transition temperature of PBAM was 240.5°C. The effects of solvent, temperature, initiator concentration ([I]), and monomer concentration ([BAM]) on polymerization were also discussed. The overall activation energy (E_a) of homopolymerization was determined (E_a = 93.5 kJ/mol). It was revealed that the rate of polymerization (R_p) can be expressed as R_p ∝ [I]^0.58[BAM]. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 424–427, 2001     

Optical absorption and thermally stimulated depolarization current studies of nickel chloride-doped poly(vinyl alcohol) irradiated with low-level fast neutron doses

The influence of neutron irradiation on ultraviolet/visible absorption and thermally stimulated depolarization current in nickel chloride–poly(vinyl alcohol) (PVA) cast films has been investigated. The spectral measurements indicate the responsibility of the Ni²⁺ ion in its octahedral symmetry. Dopant concentrations higher than 10 wt % Ni Cl₂ are found to make the samples more resistant to a degradation effect caused by neutron irradiation. The thermally stimulated depolarization currents (TSDC) of pure PVA revealed the existence of the glass transition T_g and space charge relaxation peaks, whereas doped-PVA samples show a new sub-T_g relaxation peak. A proposed mechanism is introduced to account for the neutron effects on both glass transition and space charge relaxation peaks. The peak positions, peak currents, and stored charges of the sub-T_g relaxation peak are strongly affected by both the concentration of the dopant and neutron exposure doses. © 1993 John Wiley & Sons, Inc.     

Influence of synthesis temperature on thermal properties of thermoplastic polyurethane prepared by torque rheometer

In this study, thermoplastic polyurethanes (TPUs) were obtained in a torque rheometer (an instrumented batch mixer) at 70, 80, and 90°C, and the thermal properties were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC results showed that the glass transition temperature (T_g) of the rubber phase is not affected by the synthesis temperature. The increase in synthesis temperature promoted side reactions, which modified the crystallization process and reduced nucleation and growth rate (k′) during the first stage of crystallization. From TGA analysis, it was observed that the TPU prepared at 70°C showed the highest activation energy (E_a) of decomposition, whereas the TPU synthesized at 80°C showed the lowest E_a values. The rigid‐phase decomposition mechanisms were mainly phase boundary controlled reaction (R_n) and random nucleation with one nucleus on the individual particle (F₁). These results show that side reactions (other than formation of urethane groups) could occur during the synthesis of polyurethane at temperatures lower than 100°C, and even a small amount of these side reactions influence the thermal properties. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Optical properties of alkali and alkaline-earth lead borate glasses doped with Nd<Superscript>3+</Superscript> Ions

Spectroscopic and physical properties of Nd³⁺-doped alkali lead borate glasses of type 20R ₂O · 30PbO · 49.5B₂O₃ · 0.5Nd₂O₃ (R = Li and K) and alkaline-earth lead borate glasses 20RO · 30PbO · 49.5B₂O₃ · 0.5Nd2O3 (R = Ca, Ba, and Pb) have been investigated. Optical absorption spectra have been used to determine the Slater-Condon (F₂, F₄, and F₆), spin orbit ξ_4f, and Racah parameters (E₁, E₂, and E₃). The oscillator strengths and the intensity parameters Ω₂, Ω₄, and Ω₆ have been determined by the Judd-Ofelt theory, which, in turn, provide the radiative transition probability (A), total transition probability (A _T ), radiative lifetime (τ _R ), and branching ratio (β _R , %) for the fluorescent levels. The lasing efficiency of the prepared glasses has been characterized by the spectroscopic quality factor (Ω₄/Ω₆), the value of which is in the range 0.2–1.5, typical of Nd³⁺ in different laser hosts. A red shift of the peak wavelength is observed upon addition of alkali or alkaline-earth oxides to the lead borate glass. A higher value of the W₂ parameter for potassium-doped glass indicates a higher covalency for this glass matrix. The relative intensity of the peaks ⁴I_9/2 → ⁴F_7/2, ⁴S_3/2 has also been studied. The text was submitted by the authors in English.     

Molecular motion in cured epoxy resin filled with mica flakes

Molecular motion in cured epoxy resin filled with mica flakes was investigated by dynamic mechanical and broad-line nuclear magnetic resonance measurements. Temperature dependences of dynamic modulus and tanδ were determined at 10 Hz for samples containing various amounts of filler. A primary dispersion temperature, T_∞, corresponding to the glass transition, shifts to higher temperature with increasing filler volume fraction V_f. The magnitudes of the slope parameters H_r (representing storage modulus E′ data below T_g) decreased with increasing V_f, but H_g (representing E′ data below T_g) remained nearly constant over the whole loading range studied here. NMR line shapes were observed over the temperature range from room temperature to about 200°C for unfilled and filled samples. Each sample showed a distorted line shape in the transition region where major narrowing occurs. The distorted line shape was decomposed into both broad and narrow components by Gaussian analysis. The temperature range where both components can be obtained becomes broader with increasing filler content. The possibility is set forth that the filler immobilizes the chain segments and causes a different distribution of local mobility around the junction point.     

Toughening of aromatic diamine-cured epoxy resins by modification with hybrid modifiers composed of N-phenylmaleimide–styrene copolymers and N-phenylmaleimide–styrene–p-hydroxystyrene terpolymers

Hybrid modifiers composed of N-phenylmaleimide–styrene copolymers (PMS), and N-phenylmaleimide–styrene–p-hydroxystyrene terpolymers (PMSH) containing pendent p-hydroxyphenyl groups as functionalities, were used to improve the toughness of bisphenol-A diglycidyl ether epoxy resin cured with p,p′-diaminodiphenyl sulphone. The hybrid modifiers were effective in toughening the epoxy resin. When using the modifier composed of 10 wt% PMS (M?_w 313000) and 2.5 wt% PMSH (2.5 mol% p-hydroxystyrene units, M?_w 316000), the fracture toughness (K_IC) for the modified resins increased 100% with no deterioration in the flexural properties and the glass transition temperature. The improvement in toughness of the epoxy resins was attained because of the co-continuous phase structure and the improvement in interfacial adhesion. The toughening mechanism is discussed in terms of the morphological characteristics of the modified epoxy resin systems.     

Viscoelastic properties and characterization of inorganic particulate‐filled polymer composites

To identify effects of glass bead (GB) content on the dynamic mechanical properties of filled low‐density‐polyethylene (LDPE) composites, the storage modulus, loss modulus, glass transition temperature, and mechanical damping of these composites were measured using a Du Pont dynamical mechanical analysis instrument in temperature range from ?150 to 100°C. It was found that the storage modulus increased nonlinearly with an increase of the GB volume fraction. On the basis of Eshelby's method and Mori's work, an equation describing the relationship between the relative storage modulus (E′_R) and filler volume fraction for polymeric composites was proposed, and the E′_R of LDPE/GB composites were estimated by means of this equation at temperatures of ?25, 0, and 25°C, and the calculations were compared with the experimental data, good agreement was showed between the predictions and the measured data. Furthermore, this equation was verified by the experimental from Al(OH)₃ filled EPDM composites at glassy state reported in a reference. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Temperature dependence of the dynamic electrical properties of Cu1+xMn1-xO2 (x = 0 and 0.06) crednerite materials

Polycrystalline samples of Cu_1+xMn_1-xO₂ (x?=?0 and 0.06) have been obtained by solid state reaction in silica tubes. Measurements of complex impedance (Z?=?Z′?+?iZ′′) at various temperatures T, between 30 °C and 120 °C and over the frequency range 100?Hz–2?MHz were performed. The frequency dependence of Z′′(f) exhibits a maximum which moves towards higher frequencies by increasing the temperature, proving thus the hopping of the charge carriers between the localized states is the dominant mechanism for the electrical conduction in the investigated samples. The barrier energy values were: 0.287?eV for CuMnO₂ and 0.208?eV for Cu_1.06Mn_0.94O₂.The conductivity spectrum, σ(f) follows the Jonscher universal law at each constant temperature. Based on the temperature and frequency dependencies of the electrical conductivity and using the variable-range-hopping (VRH) model, the frequency and temperature dependencies of the density of localized states near the Fermi level, N(E_F), the hopping distance, R and the hopping energy, W were computed. The results show that at constant frequency, N(E_F) does not depend on temperature for both samples. At constant temperature and frequencies up to 30?kHz, increasing the concentration of Cu ions leads to the decrease of R and W, whilst at high frequencies (over 100?kHz), R and W increase with the increase in the concentration of Cu ions.