Sodium and silver phosphate glasses doped with chlorides of Fe,Mn and Zn

A number of samples of sodium and silver phosphate glasses doped with various compositions of some transition metals viz. iron, manganese and zinc chlorides alongwith undoped samples of sodium and silver phosphate glasses were synthesized and characterized by X-ray diffraction, IR spectral, electrical conductivity and differential scanning calorimetry (DSC). The glass transition temperature (T _g) and crystallization temperature (T _c) values obtained from DSC curves were found to increase with increasing concentration of the dopant Fe/Mn/Zn chlorides in both sodium and silver phosphate glasses and the following sequence is observed: T _g(–FeCl₃)>T _g(–MnCl₂)>T _g(–ZnCl₂) T _c(–FeCl₃)>T _c(–MnCl₂)>T _c(–ZnCl₂) The increase in T _g and T _c values indicate enhanced chemical durability of the doped glasses. The electrical conductivity values and the results of FTIR spectral studies have been correlated with the structural changes in the glass matrix by the addition of different transition metal cations as dopants.     

A study on the glass transition behavior and morphology of semi-interpenetrating polymer networks

The epoxy resin/polyurethane semi-IPN was prepared and the glass transition behavior of the semi-IPN was discussed with DSC and DMA methods. The results show that the two glass transition temperatures (T_g) referring to epoxy resin and polyurethane respectively get closer. Between the two T_g there exists another T_g related to the interface between the two polymers. SEM indicates that this semi-IPN has a two-phase continuous structure which changes with different weight compositions. This is also proved by testing the Young's modulus. It is found that the IPN system has a cellular structure. Comparatively, the compatibility between the two polymers is the best when the weight ratio of EP/PU is 70/30. © 1996 John Wiley & Sons, Inc.     

The effect of stoichiometry on curing and properties of epoxy–clay nanocomposites

Epoxy–clay nanocomposites have been prepared with an organically modified montmorillonite. The epoxy network was based on diglycidyl ether of bisphenol A (DGEBA) cured with diaminodiphenylmethane (DDM). The stoichiometry DGEBA–DDM was varied, the molar ratio of amine hydrogen/epoxy groups, r, ranged from 0.85 to 1.15. The influence of stoichiometry on curing and properties of the nanocomposites was studied using differential scanning calorimetry, dynamic mechanical thermal analysis and X-ray diffraction. All nanocomposites had intercalated clay structures. The clays accelerated the curing reaction whose rate was also increased when increasing r. The heat of reaction, −ΔH (J/g epoxy), increased as r increased, reaching a constant value for r ≥ 1. In the presence of clays −ΔH was lower than in the neat DGEBA–DDM. The glass transition temperature (T _g) of the neat epoxy thermosets reached a maximum at r = 1; however, the nanocomposites showed the T _g maximum at 0.9 < r < 1. The presence of clay lowered the T _g for r > 0.94 and raised T _g for r ≤ 0.85. The elastic modulus of neat epoxy thermosets reached a maximum in the rubber state and a minimum in the glassy state at r = 1. The nanocomposites showed similar behavior, but the maximum and the minimum values of the elastic modulus were reached at stoichiometry r < 1. The comparison of the properties of neat epoxy with those of the nanocomposites varying the stoichiometry indicates that the clay itself induces stoichiometric changes in the system.     

Carbon nanotube–polyurethane shape memory nanocomposites with low trigger temperature

Ester-based polyurethane (PU) with low glass transition temperature was used to develop shape memory nanocomposites with low trigger temperature. Pristine carbon nanotubes (CNTs) and oxidized CNTs (ox-CNTs) were introduced by melt mixing to improve the mechanical and shape memory properties of the PU matrix. The dispersion of CNTs on the mechanical properties and shape memory behaviors of the nanocomposites were also investigated. The results show that better dispersion of ox-CNTs contributes to more stiffness effect below glass transition temperature (T_g) while lower storage modulus (E′) above T_g. The nanocomposites exhibit high shape fixity and recovery ratio above 98%. The ox-CNT/PU nanocomposite shows higher shape recovery ratio for the first cycle, faster recovery due to better dispersion of CNTs and have potential applications for controlling tags or proof marks in the area of frozen food. The trigger temperature can be tailored by controlling the T_g of the PU matrix or the content of the nanofillers.     

Uniaxial tensile tests and dynamic mechanical analysis of satin weave reinforced epoxy shape memory polymer composite

The utilization of epoxy shape memory polymer composite (SMPCs) as engineering materials for deployable structures has attracted considerable attention in recent decades due to high strength and satisfactory stiffness in comparison with shape memory polymers (SMPs). Knowledge of static and dynamic mechanical properties is essential for analyzing structural behavior and recovery properties, especially for new epoxy SMPCs. In this paper, a new weave reinforced epoxy shape memory polymer composite was prepared with satin weave technique and resin transfer molding technique. Uniaxial tensile tests and dynamic mechanical analysis were carried out to obtain basic mechanical properties and glass transition temperatures, respectively.The tensile strength and breaking elongation of warp specimens were comparable with those of weft specimens. The increment of elastic modulus and hysteresis loop areas became smaller with loading cycles, meaning that cyclic tests could obtain approximate stable mechanical properties. For dynamic mechanical properties, glass transition temperature (T_g) obtained from storage modulus curves was lower than that determined from tan delta curves and T_gs in the warp and weft directions were similar (29.4 °C vs 29.7 °C). Moreover, the storage modulus in response to T_g was two orders of magnitude less than that with respect to low temperature, which demonstrated the easy processibility of epoxy SMPCs near glass transition temperature. In general, this study could provide useful observations and basic mechanical properties of new epoxy SMPCs.     

Thermal stability and crystallization kinetics in superionic glasses using electrical conductivity–temperature cycles

The present work demonstrates application of electrical conductivity (σ)–temperature (T) cycles to investigate thermal properties viz., crystallization and glass transition kinetics in AgI–Ag₂O–V₂O₅–MoO₃ superionic glasses. The σ–T cycles are carefully performed at various heating rates, viz., 0.5, 1, 3, 5, and 7 K/min. The conductivity in Ag⁺ ion conducting glasses exhibit anomalous deviation from Arrhenius behavior near glass transition temperature (T _g) followed by a drastic fall at crystallization (T _c). The temperature corresponding to maximum rate of crystallization (T _p) is obtained from the derivative of σ–1/T plots. With increasing heating rates, the characteristic temperatures (T _g, T _p) are found to be shifting monotonically toward higher temperatures. Thus, activation energy of structural relaxation E _s, crystallization E _c and other thermal stability parameters have been obtained from σ–T cycles using Kissinger equation and Moynihan formulation. For a comparative study, these kinetics parameters have also been calculated from differential scanning calorimetry plots. The parameters obtained from both the methods are found to be comparable within experimental error.     

Use of dynamic mechanical thermal analysis (DMTA)

A Mark III DMTA (Polymer Laboratories, Loughborough, U.K.) was used to measure the glass transition temperatures (T _g) of a commercial cracker and its dough, each equilibrated to various water activities covering a range of 0.11–0.75 for the cracker and 0.11–0.90 for the cracker dough. DMTA measures the change in the elastic modulus (E′) and loss modulus (E″), as well as that in tanδ (E″/E′), with temperature. The change in the elastic modulus with temperature for the two systems followed a pattern similar to that found for complex food polymers (gluten, amylopectin), withT _g decreasing as moisture content increased. Baking did not change the location of the glass transition curve (T _g vs. moisture content); i.e. the curves for raw dough and baked finished product were somewhat superimposable, and similar to the published gluten curve, indicating that for this type of cracker containing ～5% sugars, the protein fraction is most responsible for theT _g curve.     

Thermal behavior of aromatic polyamic acids and polyimides containing oxadiazole rings

Two aromatic polyimides and the corresponding poly(amic acid)s, with oxadiazole and para/meta phenoxyphenylene rings in the backbone, were synthesized and the structure — thermal properties correlation was followed by dynamic mechanical analysis. Concerning the poly(amic acid)s, the glass transition domain was emphasized only for the compound with meta-oriented rings because the process of imidization takes place with increasing temperature. A multiplex experiment was performed to calculate the activation energy of the transition localized under 200°C. Consecutive heating-cooling-heating cycles were accomplished. All phenomena are discussed by cross-examination of the storage modulus (E′), loss modulus (E″) and loss factor tanδ variation with temperature.     

Thermal properties of lignin-and molasses-based polyurethane foams

Lignin-and molasses-based polyurethane (PU) foams with various lignin/molasses mixing ratios were prepared. The hydroxyl group in molasses and lignin is used as the reaction site and PU foams with various isocyanate (NCO)/the hydroxyl group (OH) ratios were obtained. Thermal properties of PU foams were investigated by differential scanning calorimetry (DSC), thermogravimetry (TG) and thermal conductivity measurement. Glass transition temperature (T _g) was observed depending on NCO/OH ratio in a temperature range from ca. 80 to 120°C and thermal decomposition temperature (T _d) from ca. 280 to 295°C. Mixing ratio of molasses and lignin polyol scarcely affected the T _g and T _d. Thermal conductivity of PU foams was in a range from 0.030 to 0.040 Wm⁻¹ K⁻¹ depending on mixing ratio of lignin and molasses.     

Glass transition, fragility, and structural features of amorphous nickel–tellurate–vanadate samples

The experimental FTIR spectra and DSC curves of the ternary 40TeO₂–(60?x)V₂O₅–xNiO glasses with 0 ≤ x ≤ 30 (in mol%) have been investigated. The glass transition properties that have been measured and reported in this paper, include the glass transition temperature (T _g), glass transition width (ΔT _g), heat capacity change at glass transition (ΔC _P) and Fragility (F). Thermal stability, fragility, and glass-forming tendency of these glasses have been estimated. Also, Poisson’s ratio (μ) and IR spectra of the presented systems have been investigated, to determine relationship between chemical composition and the thermal stability or to interpret the structure of glass. In addition, Makishima and Makenzie’s theory was applied for determination of Young’s modulus, bulk modulus, and shear modulus, indicating a strong relation between elastic properties and structure of glass. In general, results of this work show that glasses with x = 0 and 30 have the highest shear and young’s modulus which make them as suitable candidate for the manufacture of strong glass fibers in technological applications; but it should be mentioned that glass with x = 30 has higher handling temperature and super resistance against thermal shock.     

Comparative Studies on Thermomechanical Behavior of Veriflex®, a Shape Memory Polymer,for a Low Strain (ϵm = 70%): Laser Experiments

An interesting comparative case study on thermomechanical cycles including programming, cooling, unloading and heating to trigger the 1WE was done using Veriflex® at 62°C (T < T_g close to and below 5°C of T_g) and also at 72°C (T > T_g, close to and above 5°C of T_g) for slightly low strains (?_m = 70%) and the recovery time of 10 min. Accumulation of strain was estimated during the thermomechanical treatments for using both 70% strains at 62°C (T < T_g), as well as at 72°C (T > T_g). Recovery ratios for 70% strains at 62°C (T < T_g), as well as for 72°C (T > T_g) were also estimated. It turns out that programming, cooling, unloading and heating to trigger the 1WE causes an increase of irreversible strain and is associated with a corresponding decrease of the intensity of the 1WE, in particular, during the first thermomechanical cycles. A LSCM (Laser Scanning Confocal Microscopic) study shows very little change in surface structure which evolved during cycling up to 70% strains at 72°C (T > T_g).     

Calorimetric study of Diepoxide Chain-Extended Poly(Ethylene Terephthalate)

A series of chain-extended PET samples were obtained by the use of different amounts of a diepoxide as chain extender, which was prepared for this purpose. These samples exhibited different intrinsic viscosities and degrees of branching or cross-linking. The effects of this differentiation on the thermal properties were studied by differential scanning calorimetry. The thermal parameters studied were the glass transition temperature (T_g), the cold-crystallization temperature (T_cc), the melting temperature (T_m), the enthalpy (ΔH_m) and the degree of crystallinity. The data revealed that, the higher the quantity of chain extender or the chain extension time, the higher T_gand T_cc, but the lower T_mand ΔH_m, i.e. the more amorphous the chain-extended samples, as also shown by density measurements. This revised version was published online in July 2006 with corrections to the Cover Date.     

Water sorption and glass transition of freeze-dried camu-camu (myrciaria dubia (H.B.K.) Mc Vaugh) pulp

Differential scanning calorimetry (DSC) was used to determine phase transitions of freeze-dried camu-camu pulp in a wide range of moisture content. Samples were equilibrated at 25°C over saturated salt solutions in order to obtain water activities (a_w) between 0.11–0.90. Samples with a_w>0.90 were obtained by direct water addition. At the low and intermediate moisture content range, Gordon–Taylor model was able to predict the plasticizing effect of water. In samples, with a_w>0.90, the glass transition curve exhibited a discontinuity and T^’_g was practically constant (–58.8°C), representing the glass transition temperature of the maximally concentrated phase(T_g ).     

Mechanical properties and transition temperatures of crosslinked-oriented gelatin

 This second part of a systematic study of the properties of crosslinked-oriented gelatin involves the effects of orientation and water content on the glass transition temperature T _g and on the melting behavior. The samples were the same as those in the preceding study, and their transition temperatures were determined by both differential scanning calorimetry and dynamic mechanical thermal analysis. The crosslinked gelatin which had been room-conditioned showed two transition temperatures: the lower one was attributed to T _g of the water-plasticized gelatin, and the higher one was interpreted as T _g of dried gelatin superimposed by melting. A rather unusual situation arose because of the fact that the T _g and melting temperatures T _m (217 and 230 ^°C, respectively) are so similar. Using water as plasticizer not only decreases T _g but produces imperfect crystallites which melt below the T _g of the system. The presence of the amorphous phase in the glassy state would presumably make it essentially impossible to define a melting point or crystallization temperature in the normal manner, as an equilibrium between crystalline and amorphous phases. Received: 8 October 1996 Accepted: 2 November 1995     

Synthesis and characterization of poly(p-arylene sulfide ketone/Schiff base) copolymers

Poly(p-arylene sulfide ketone/Schiff base) copolymers(PASK/SB) were prepared by solution polycondensation of 4,4’-diflurobenzophenone(DFBP) and N-phenyl(4,4’-diflurodiphenyl) ketimine(DFBI) with sodium sulfide in the presence of sodium hydroxide under normal pressure.Elemental analyses,FT-IR,NMR,DSC,TGA and XRD were used to characterize the resultant copolymers.It was found that the copolymers had good thermal properties with glass transition temperature(T_g) of 155.0-172.0°C,melting temperature(T_m) of 298-344°C,5%weight loss temperatures(T_d) of 471.0-501.5°C.These copolymers were almost amorphous with the content of DFBI beyond 30%.The polymer with 100% DFBI had excellent solubility,and it could dissolve in some solvents such as tetrahydrofuran(THF) and N-methyl-2- pyrrolidone(NMP).The processability of polymers was improved.Meantime the viscosity of PASK made from hydrolysis of PASK/SB(H-PASK/SB) was greatly improved from 0.135 dL/g to 0.605 dL/g.     

Correlations between the morphology and the thermo-mechanical properties in poly(vinyl acetate)/epoxy thermosets

The mechanical properties of poly(vinyl acetate) (PVAc)/epoxy thermosets as a function of the PVAc content were investigated through dynamic mechanical thermal analysis from −100 to 220 °C and through tensile tests at room temperature. The morphology of the thermosets was examined by scanning electron microscopy. Cured PVAc/epoxy blends are phase separated, arising two phases that correspond to a PVAc-rich phase and to the epoxy rich-phase. The morphology evolves from nodular to inverted as the PVAc content increases. Intermediate compositions present combined morphologies, in which nodular and inverted regions are detected. The tensile properties at room temperature reveal that combined morphologies present the most ductile behaviour. The glass transition temperatures (T _g) of PVAc and of epoxy phases in the blends are different from those of the neat polymers. The profile of the loss modulus (E″)–temperature curves are correlated with the change in morphology that appears increasing the PVAc content. The storage modulus (E′)–temperature curves are highly dependent on the morphology of the samples. The E′-composition dependence is predicted using several models for two-phase composites. The low-temperature β-relaxation of the epoxy is slightly modified by the presence of PVAc. The activation energies of the α and β-relaxations are not dependent on the blend morphology.     

Synthesis,morphology, and viscoelastic properties of cyanate ester/polyhedral oligomeric silsesquioxane nanocomposites

Cyanate ester (PT‐15, Lonza Corp) composites containing the inorganic–organic hybrid polyhedral oligomeric silsesquioxane (POSS) octaaminophenyl(T₈)POSS [ 1 ; (C₆H₄NH₂)₈(SiO_1.5)₈] were synthesized. These PT‐15/POSS‐ 1 composites (99/1, 97/3, and 95/5 w/w) were characterized by X‐ray diffraction (XRD), transmission election microscopy (TEM), dynamic mechanical thermal analysis, solvent extraction, and Fourier transform infrared. The glass‐transition temperatures (T_g's) of the composite with 1 wt % 1 increased sharply versus the neat PT‐15, but 3 and 5 wt % 1 in these cyanate ester composites depressed T_g. All the PT‐15/POSS composites exhibited higher storage modulus (E′) values (temperature > T_g) than the parent resin, but these values decreased from 1 to 5 wt % POSS. The loss factor peak intensities decreased and their widths broadened upon the incorporation of POSS. XRD, TEM, and IR data were all consistent with the molecular dispersion of 1 due to the chemical bonding of the octaamino POSS‐ 1 macromer into the continuous cyanate ester network phase. The amino groups of 1 reacted with cyanate ester functions at lower temperatures than those at which cyanate ester curing by cyclotrimerization occurred. In contrast to 1 , 3‐cyanopropylheptacyclopentyl(T₈)POSS [ 2 ; (C₅H₉)₇(SiO_1.5)₈CH₂CH₂CH₂CN] had low solubility in PT‐15 and did not react with the resin below or at the cure temperature. Thus, phase‐separated aggregates of 2 were found in samples containing 1–10 wt % 2 . Nevertheless, the T_g and E′ values (temperature > 285 °C) of these composites increased regularly with an increase in 2 . © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3887–3898, 2005     

Curing behavior of epoxy resins with a series of novel curing agents containing 4,4′-biphenyl and varying methylene units

A new homologous series of curing agents (LCECAn) containing 4,4′-biphenyl and n-methylene units (n = 2, 4, 6) were successfully synthesized. The curing behaviors of a commercial diglycidyl ether of bisphenol-A epoxy (E-51) and 4,4′-bis(2,3-epoxypropoxy)biphenyl (LCE) by using LCECAn as the curing agent have been investigated by differential scanning calorimetry (DSC), respectively. The Ozawa equation was applied to the curing kinetics based upon the dynamic DSC data, and the isothermal DSC data were fitted using an autocatalytic curing model. The glass transition temperatures (T _g) of the cured epoxy systems were determined by DSC upon the second heating, and the thermal decomposition temperatures (T _d) were obtained by thermogravimetric (TG) analyses. The results show that the number of methylene units in LCECAn has little influence on the curing temperatures of E-51/LCECAn and LCE/LCECAn systems. In addition, the activation energies obtained by the dynamic method proved to be larger than those by the isothermal method. Furthermore, both the T _g and T _d of the cured E-51/LCECAn systems and LCE/LCECAn systems decreased with the increase in the number of methylene units in LCECAn.     

Thermal Methods Applied to the Glass Transition of Mixed Network AlPO4–BPO4–SiO2 Glasses

Glass transition effect of mixed network AlPO₄–BPO₄–SiO₂ glasses was studied. DTA/DSC and TMA measurements has been applied in the research. It has been found that glass transition effect has structurally sensitive properties. Glass transition temperature T _g, changes of specific heat (Δc _p)and thermal expansion coefficient (α) accompanying the process depend on the nature and the number of components forming the glassy framework. Character of chemical bonds combining them into the glass structure has an influence on the glass transition effect. Its course is dependent on the flexibility of the structure of glasses. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal properties of anhydride-cured bio-based epoxy blends

Epoxidized palm oil (EPO) (0–12 wt%) was added into petrochemical-based epoxy blends (diglycidyl ether of bisphenol-A (DGEBA)/cycloaliphatic epoxide resin/epoxy novolac resin) to develop a thermal curable bio-based epoxy system. The thermal behaviors of the EPO, epoxy blends (EB), and bio-based epoxy blends (EB/EPO) were characterized using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMT) and thermo-mechanical analysis (TM). The glass transition temperature (T _g) and storage modulus (E′) of the EB/EPO system was reduced with the increasing of the EPO loading. This is attributed to the plasticizing effect of the EPO. It was found that epoxy blends with higher loading of EPO possessed higher coefficient of thermal expansion (CTE) and tanδ value. This is due to the increase of the free volume and chain flexibility in the three-dimensional network of the epoxy blends. The internal thermal stresses of the EB/EPO were decreased as the increasing loading of EPO, owing to the reduction of crosslink density, modulus of elasticity, and T _g in the epoxy blends.