Thermostimulated current characterization of poly(ethersulfone)

Two thermal analysis techniques, differential scanning calorimetry (DSC) and thermostimulated currents, are used to characterize two Poly(ethersulfones) (PESs) obtained with the same process by two different manufacturers. The glass transition temperature observed by DSC is the same for both PESs and equal to 235°C. When PES samples are heated above the glass transition temperature (250–260°C), one initially white and opaque PES (B) looks transparent while the other one (A) stays in the initial stage. The PES B is visibly degraded upon increasing at a lower temperature than PES A. Below the glass transition temperature, two complex relaxation modes α and β situated at +170–175 and −120°C, respectively, are observed. The analysis of the fine structure shows that they are constituted of elementary processes characterized by relaxation times following compensation laws. For PES A at high temperatures the cooperative movements are precursors of the glass transition. For PES B a double compensation phenomena reveals the biphasic character of the vitreous phase. The comparison between the two PESs reveals different microstructures that could be due to different processing conditions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 320–325, 2000     

Molecular motions and transitions in a poly(p-hydroxystyrene) derivative

The dielectric relaxation mechanisms in a poly(p-hydroxystyrene) derivative have been studied by Thermally Stimulated Depolarization Currents (TSDC) in the temperature range between −160 and 130°C. A broad relaxation was observed at low temperatures, from −160 up to 0°C, which obeyed to the zero entropy approximation. In contrast, the glass transition relaxation showed the usual behavior, a strong departure to the zero entropy prediction. Both relaxations have been studied in detail by the technique of thermal sampling. The thermal behavior of this poly(p-hydroxystyrene) derivative was also studied by Differential Scanning Calorimetry in the temperature range between 20 and 200°C. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1921–1926, 1999     

Characterization of the relaxation transitions in toluene diisocyanate-based polyurethanes with poly(propylene glycol) as the soft segment by thermally stimulated current depolarization with relaxation mapping analysis

Thermal relaxation transitions of toluene diisocyanate (TDI)-based polyurethanes (PU) were characterized by the thermally stimulated current (TSC) technique with verification data from the relaxation mapping analysis (RMA) measurement. TDI-based PU elastomers with poly(propylene glycols) (PPG) as the soft segment and methylene-bis-orthochloroaniline (MOCA) as the hardener, showed three relaxation transitions, (1) a subglass transition (T_g) of the terminal groups occurred near −135°C; (2) the T_g; and (3) a global transition occurred above the T_g (assigned as T_global transition). The temperature of T_g of PU as expected was varied by the chain length and attributed by the motion of an urethanic chain dominated by the soft segment and may also associate in the cooperative movement with the hard segment. The T_global transition appearing above the T_g was identified and attributed to the global transition in the macromolecule scale and was supported by the tangent plot of the dynamic mechanical analyzer (DMA) measurement. The TSC measurement on thermal characteristic transitions of TDI-based PU provided a whole range of thermal transitions including a sub-T_g, the T_g (observed by DSC) to a global transition (may be observed by DMA) with the ease of sample preparation in one single measurement. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 527–545, 1999     

Compensation effect observed in thermally stimulated depolarization currents analysis of polymers

Thermally stimulated depolarization currents (TSDC) and differential scanning calorimetry (DSC) are performed on thermoplastic polyesters and dimethacrylate resins over temperature ranges covering the α and β relaxation regions. The noncooperative β relaxation is characterized by a continuous variation of activation energies as a function of temperature and follows the activated states equation with a zero activation entropy. The cooperative α relaxation shows a prominent maximum of the activation energies at the glass transition temperature. Compensation behavior is often observed by TSDC for many polymers in the glass transition temperature range. We show that this behavior is not systematic and that it appears for the α relaxation if the increase of the apparent activation enthalpy is strong and if the width of the glass transition is weak. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2716–2723, 1999     

Thermally stimulated current studies on molecular relaxation and blow moulding of poly(ethylene terephthalate)

The thermally stimulated current (TSC) technique has been used to investigate molecular relaxation in poly(ethylene terephthalate) (PET) films unstretched and biaxially stretched at 90 and 95 °C. Unstretched PET films show two peaks at 77 and 90 °C corresponding to α and ρ relaxation processes, respectively. The α relaxation is associated with the main glass transition of the material. The ρ peak with lower intensity is attributable to permanent dipoles. Both biaxially stretched samples show one TSC peak at 95 °C, supposed to correspond to ρ relaxation. The disappearance of the α peak, accompanied by the displacement of the ρ peak to higher temperature, is the result of the higher thermal stability of the permanent dipoles, which is strongly influenced by the stiffening of amorphous parts and the crystallization by stretching. In both stretched samples, the continuous distribution of pre-exponential factors over activation energies observed might correspond to a single relaxation mode. The kinematics of stretching PET has been discussed in terms of activation energy and temperature dependence of relaxation time. © 1999 Society of Chemical Industry     

Cooperative relaxations in amorphous polymers studied by thermally stimulated current depolarization

Thermally stimulated current depolarization (t.s.c.) was used to study the relaxations in amorphous polymers including poly (ethyl methacrylate) (PEMA), poly (methyl methacrylate) (PMMA), polystyrene (PS), polycarbonate (PC) and polyarylate (PAR) over temperature ranges covering the β and (glass transition) regions. A.c. dielectric was used to obtain activation energies (E_a) for PS and PC to verify the accuracy of those values determined by the t.s.c. thermal sampling method. At temperatures below the glass transition (T_g) the values of E_a were found to agree with those predicted using an activated states equation with a zero activation entropy. This is evidence of the localized, non-cooperative nature of the low temperature secondary β relaxations which are found to be characterized by a continuous variation of activation energies as a function of temperature. The measured values of E_a depart from the zero activation entropy curve and exhibit a prominent maximum at T_g. This behaviour is known to be due to an enhanced degree of cooperativity of segmental relaxations near T_g. The results indicate that the main advantage of the thermal sampling method is the high sensitivity and high temperature resolution for cooperative relaxations. For the polymers studied here, only PEMA and PMMA show a substantial population of cooperative relaxations more than 60°C below T_g. This is tentatively explained in terms of structural heterogeneity due to variable tacticity in the methacrylates. Compensation of the t.s.c. relaxation spectra plotted in Arrhenius or Eyring plots was found for all polymers to differing degrees. Some discussion of compensation is made in terms of independently measured values of the coefficient of thermal expansion.     

Characterization of structural heterogeneity of polyurethane coatings

The thermal analysis techniques—Differential Scanning Calorimetry and ThermoStimulated Current—have been used to characterize a polyurethane high solid coating. The glass transition temperature, as determined by DSC, is 60°C. Below this glass transition temperature, an α_sub dielectric relaxation mode has been observed; it corresponds to cooperative movements precursor of the glass transition. The α_ss dielectric relaxation mode, located at ≈ T_g has been attributed to movements of soft sequences of the amorphous phase liberated at the glass transition temperature. The analysis of the fine structure shows that they are constituted of elementary processes characterized by relaxation times following a compensation law. Above T_g, the α_hs dielectric relaxation of hard sequences has been shown. It corresponds to hard sequences hydrogen bonded in polyurethane. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2786–2790, 2001     

Relaxations in double base propellants

Double base propellants are composed of nitrocellulose(NC) plasticized with various amounts of nitroglycerine(NG). A series of propellants was made with NG contents of 10%, 35% and 60% by incorporating with solvents, extruding into cords and then drying. A study of relaxation behaviour of these propellants was made using dynamic mechanical analysis, thermomechanical analysis and differential scanning calorimetry (d.s.c.). Three relaxations were observed, one at about ?80°C designated γ, one in the temperature range ?10° to ?60°C designated β, and one above 35°C designated α. The γ relaxation is attributed to motion of the pendant nitrate side groups of NC. The β relaxation is attributed to motion of NC molecule side groups and associated NG molecules. It causes a peak in mechanical loss, and changes in modulus, thermal expansion and heat capacity. The β relaxation has previously been reported as the glass transition, but there is some doubt and this may be incorrect. The α relaxation occurs in the same temperature range as the glass transition reported in other plasticized cellulosic polymers, but it is unusual in that it involves a large change in modulus and mechanical loss, but no change in thermal expansion or heat capacity.     

Dielectric investigation of the molecular dynamics in blends: polymers with similar molecular architecture (TMPC/PC blend)

Broad band dielectric spectroscopy was used in the investigation of the molecular dynamics and compatibility of tetramethyl polycarbonate/polycarbonate (TMPC/PC) blends. Frequency scan measurements in the range 10^?2?10^?5 Hz were carried out in the temperature range 50–220°C for several blends with different compositions, namely, 0, 12.5, 25, 50, 75, 87.5 and 100 wt% of TMPC. The results obtained show that these two polymers are ideally compatible over the entire composition range. The blends reveal only one common glass process. The dielectric relaxation strength and the common glass transition temperature, T_g, were found to vary linearly with composition. Moreover, it was found, surprisingly, that blending has no effect on the distribution of relaxation times of the common glass process of the blends. Furthermore, neither the kinetics (relaxation frequency at a certain temperature) nor the distribution of relaxation times of the local process were influenced by blending. It is concluded that the polymeric chains of the different components are not miscible on a segmental level although the blend exhibits only one glass transition temperature.     

Effect of Method of Preparation on Molecular Packing of TMPC/PS Blends

Dielectric and differential scanning calorimetry measurements of polystyrene/tetramethyl polycarbonate (PS/TMPC) blends have been carried out for two series of samples prepared by a melt mixing method, using a Brabender, and a solvent casting method using methylene chloride. The dielectric measurements of the samples were carried out over wide ranges of temperature (50–220°C) and frequency (10^-2–10⁵Hz). The composition ratios of the samples measured were 12·5, 25, 50, 75 and 87·5wt% TMPC for solvent casting and 10, 25, 40, 50 and 60wt% TMPC for melt mixing. It has been found that melt mixing under the conditions used produces compatible blends for all the composition ratios measured without causing any pronounced degradation. The glass transition temperatures and dielectric relaxation behaviour of the blends prepared by the different methods showed differences in molecular packing and dynamics. The results obtained could be attributed to a variation in the size of structural units responsible for compatibility, which depended on the method of preparation. © of SCI.     

Effect of fillers on the relaxation behavior of chlorobutyl vulcanizates

The effect of addition of fillers (carbon black (CB), carbon silica dual phase filler (CSDPF), and nanoclays) on the relaxation behavior of chlorobutyl vulcanizates has been studied. The primary relaxation (α‐transition, the glass transition) was studied by dynamic mechanical analysis as a function of temperature (?60 to +100°C) and positron annihilation life time spectroscopy (?70 to +110°C). Irrespective of the filler and its loading, all the composites showed the glass transition temperature in the range of –29 to –33°C, which was explained on the basis of relaxation chain dynamics of polyisobutylene in the vicinity of fillers. The secondary relaxation (α* or β relaxation) was studied using dielectric relaxation spectra in the frequency range of 100–10⁶ Hz. Nanoclays had a profound influence on the secondary relaxation, whereas CSDPF and CB had a marginal effect. The nonlinear strain dependent dynamical parameters were also evaluated at double strain amplitudes of 0.07–5%. The nonlinearity in tan δ and storage modulus has been explained on the concept of filler–polymer interactions and the interaggregate attraction (filler networking). The “percolation limit” of the fillers in the composites has been studied by DC conductivity measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3161–3173, 2006     

Temperature dependence of the tensile properties of lignin/paper composites

The mechanical properties of dioxane lignin (DL)/paper and kraft lignin (KL)/paper composites were investigated as functions of temperature and strain rate. The tensile properties of the lignin/paper composites were governed by the viscoelastic properties of lignins used as a matrix. In the temperature dependence of the tensile properties, the strength of DL/paper composite decreased at 70° and 130°C at which the elongation had maxima. This behaviour was caused by the viscoelastic properties of DL having two relaxations in the primary dispersion region at 120° and 160°C. In the case of KL/paper composite, a drastic decrease in the strength and maximum of elongation were observed at the glass transition of KL (140°C). The strain rate dependence of the strength of DL/paper composite showed behaviour typical of viscoelastic materials. The strength increased with increase of the strain rate and then decreased after reaching a maximum, which showed a transition from a brittle to a ductile type of fracture.     

Enthalpy relaxation of photopolymerized multilayered thiol‐ene films

Multilayered thiol‐ene network films with two and three different components were fabricated by spin coating and photopolymerization. The distinctive glass transition temperatures of each layer component were observed at corresponding glass transition regions of each bulk sample. Sub‐T_g aging of 10‐, 21‐, and 32‐layered thiol‐ene films was investigated in terms of enthalpy relaxation. Enthalpy relaxation of each layer component occurred independently and presented the characteristic time and temperature dependency. Overlapped unsymmetrical bell‐shaped enthalpy relaxation distribution having peak maximum at T_g‐10°C of each layer component was observed, resulting in broad distribution of enthalpy relaxation over wide temperature range. In addition, enthalpy relaxation of each layer component in the multilayered thiol‐ene films was significantly accelerated comparing to that of bulk thiol‐ene samples. Dynamic mechanical thermal properties of multilayered thiol‐ene films also showed two and three separated glass transition temperature. However, for 32‐layered thiol‐ene film consisting of three different layer components, glass transition and damping region are overlapped and the width is extended more than 100°C. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal properties of gelatin films

Thermal properties of dehydrated ‘hot-cast’ gelatin films, obtained from hake skin, were studied using differential scanning calorimetry (d.s.c.) and thermal mechanical analysis (t.m.a.). Two glass transition temperatures, at 120°C and at 180°–190°C, were obtained. The low-temperature transition is assigned to the devitrification of blocks rich in α-amino acids, while the high-temperature transition is attributed to the devitrification of blocks rich in imino acids. For hydrated gelatins both transitions are shifted to lower temperatures. Differences in the behaviour of fish and mammalian gelatins were found. The influence of crosslinking with formaldehyde upon the thermal properties is analysed. The crosslinked fish gelatin devitrifies progressively in the 100°–200°C temperature range.     

Interfacial characteristics of poly(ε-caprolactone)-grafted-halloysites nanotubes bionanocomposites

Dielectric and thermal characterization of nanohybrid films based on poly(ε-caprolactone) biopolymer were investigated. Nano-composites samples with distinct loadings of halloysite nanotubes (HNT) were prepared by in situ Ring Opening Polymerisation of ε-caprolactone. The effect of the incorporated HNT on the molecular relaxation process and interfacial polarization of PCL was studied via broadband dielectric spectroscopy (BDS) on a frequency domain starting from 1E-1 to 1E6 Hz and at temperatures ranging from −70°C to 50°C. The BDS measurements revealed four significant dielectric processes α-primary relaxation attributed to glass transition, β-secondary relaxation and two interfacial polarizations due to the semi-crystalline character of PCL and the added HNT fillers. According to our results, the weight ratio of HNT ranging between 3% and 5% is recommended for achieving the highest performing nanocomposite that can be used in several applications.     

Phase segregation behavior in PE/DOP blends and glass‐transition temperatures of polyethylene

Phase segregation behavior in PEs/DOP blends, interactions between PEs and DOP, and glass‐relaxation transitions of PEs were investigated. FTIR, DSC, and TGA data demonstrated that molecular interactions were present between PEs and DOP. DMA data demonstrated that pure PEs each (except HDPE) exhibited two loss maxima at about ?20 and ?120°C but the PEs/DOP blends (including the HDPE/DOP blend) yielded one new loss maximum at about ?60°C. The glass‐relaxation transitions corresponding to the three loss maxima on the DMA curves were designated α (?20°C), β (?60°C), and γ (?120°C) transitions and were attributed to the relaxation of the amorphous phases in the interlamellar, interfibrillar, and interspherulitic regions, respectively, based on DMA, WAXD, SAXS, and POM measurements. The controversial T_g values of PEs and their origin were thus clarified in this study. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3591–3601, 2001     

Effect of carbon blacks on relaxation phenomenon of chlorobutyl vulcanizates

The effect of the types of carbon black on the physicomechanical, dynamic mechanical, and dielectric relaxation spectra in chlorobutyl vulcanizates was studied. The primary relaxation (α transition, the glass transition) was studied by dynamic mechanical analysis as a function of temperature (?60 to +100°C) and by positron annihilation lifetime spectroscopy (?70 to +100°C). Irrespective of the type of carbon black that was used, all composites showed glass‐transition temperatures in the range of ?29 to ?33°C, which was explained on the basis of the relaxation dynamics of polyisobutylene chains in the vicinity of the fillers. The secondary relaxation (α* or β relaxation) was studied using dielectric relaxation spectra in the frequency range of 100–10⁶ Hz. The nonlinear strain dependent dynamical parameters (Payne effect) were also evaluated at dynamic strain amplitudes of 0.07–5%. The nonlinearity in the tan δ and storage modulus was explained by the concept of filler–polymer interactions and the interaggregate attraction (filler networking). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1809–1820, 2006     

A relaxational and conductive study on two poly(ether imide)s

A study of the relaxations and the conductivity of poly(ether imide) (PEI) ULTEM 5000 was carried out. The results were compared with the ones obtained in a previous study of PEI ULTEM 1000. The glass transition temperature was determined by differential scanning calorimetry (DSC). Then, the relaxations of PEI ULTEM 5000 using the thermally stimulated depolarization current technique (TSDC) on conventionally polarized electrets were studied. Owing to the interesting structure indicated by this technique a more detailed analysis of the β relaxation was done using window polarization (WP). It was possible to isolate 7 subrelaxations that we related to their counterparts in PEI ULTEM 1000. WP was also used to compare, one by one, the other relaxations that both materials present. The analysis of the ρ relaxation showed that the space trapping capability is stronger in PEI ULTEM 5000. The role of conductivity was analyzed using open circuit polarized samples and, more quantitatively, using dielectric analysis (DEA) and the dielectric modulus formalism. DEA and dynamic mechanical thermal analysis (DMTA) were also used to obtain information about the polar relaxations, complementary to that obtained by TSDC. Copyright © 2004 Society of Chemical Industry     

Experimental Investigation on the Damping Behaviors of Epoxies with Different Epoxy Value

In this article, five different epoxies including a new kind of flexible epoxy having low glass transition temperatures (11 ～ 28°C) were prepared using polyamine as curing agent. Damping mechanical tests show that compared with other common available epoxies, the flexible epoxy has high loss factor over broad frequency and temperature range. Activation energy corresponding to glass transition process of different epoxies has been calculated from the temperature corresponding to tan δ_max values, obtained at different measurement frequencies. The maximum value of loss factor is 0.71 and the Tg varies from 11 to 28°C, indicating the flexible epoxy can be used as damping polymer materials in common temperature or frequency range.