Layered structure formation in the reaction-induced phase separation of epoxy/polysulfone blends

In an epoxy/polysulfone blend, the reaction-induced phase separation behavior and the final morphology were investigated. Three distinct morphological structures were obtained. Sea-island and nodular structures were observed at lower and higher polysulfone contents, respectively. A three-layered structure was obtained in the middle polysulfone concentration range. In order to understand the formation of three-layered structure, phase separation process was studied using time-resolved light scattering, phase-contrast optical microscope and scanning electron microscope. Bicontinuous structure formed uniformly in the whole sample at the beginning of phase separation. After the phase structure grew for a certain time, large domains formed and developed. Then, the large epoxy-rich domains gradually flew to the outer space of the sample film. This process assisted the formation of the three-layered structure. The mechanism of the formation of the three-layered structure was discussed based on the different viscoelastic properties of the components.     

In situ TPU/graphene nanocomposites: Correlation between filler aspect ratio and phase morphology

An in situ polymerization method to prepare thermoplastic polyurethanes (TPU)/graphene and TPU/graphite composites have been studied to clarify the influence of intrinsic filler properties and dispersion level on the morphology and properties of the TPU. Two types of graphene, one high-aspect ratio and one low, and graphite flake at various loadings were studied. Rotational rheology experiments on the suspensions of filler in polyol were used to characterize the agglomeration level of the filler after the dispersive mixing step and an effective aspect ratio reflective of the dispersion level was obtained. Variations in the glass transition temperature and thermal transitions of the TPU composites were related to the agglomeration level and intrinsic filler properties.     

Kinetics of demixing and remixing in poly(ethylene oxide)/poly(ether sulphone) blends as studied by modulated temperature differential scanning calorimetry

The phase diagram of a poly(ethylene oxide)/poly(ether sulphone) blend is constructed using modulated temperature DSC and optical microscopy. It includes the glass transition (T_g), melting point (T_m) and cloud point temperature (T_cl), which define the regions of interest in this work: demixing above T_cl, followed by remixing in the miscible melt region between T_cl and T_m or T_g. The width of T_g has to be taken into account to understand partial vitrification effects during phase separation at high temperatures. Dynamic rheometry provides complementary information about partial vitrification and devitrification. Excess contributions due to demixing and remixing on the time-scale of the modulation appear in the heat capacity in both non-isothermal and quasi-isothermal conditions. This apparent heat capacity signal is used to study the effects of composition of the blend and molecular weight of the constituents on the demixing and remixing kinetics and on the interrelation between both. Partial vitrification during demixing is important in this respect. Step-wise quasi-isothermal measurements show a time-independent excess heat capacity in between T_cl and the interference of vitrification.     

Rigid amorphous phase and low temperature melting endotherm of poly(ethylene terephthalate) studied by modulated differential scanning calorimetry

The rigid amorphous phase, the low temperature melting endotherm, and their development with thermal treatment in poly(ethylene terephthalate) (PET) were investigated by means of modulated differential scanning calorimetry. The differential of the reversing heat capacity and nonreversing heat flow signals were used to analyze the behavior of the glass transition and the low temperature melting endotherm. With increasing annealing time, the increment of the heat capacity at the glass‐transition temperature decreased and the increment of heat capacity at the annealing temperature increased. It was suggested that the origin of the low temperature melting endotherm mainly resulted from the transition of the rigid amorphous fraction for the PET used. The glasslike transition of the rigid amorphous fraction occurred between the glass transition and melting. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2779–2785, 2001     

Effect of small additions of Li2O on phase separation and crystallization of barium-silicate glasses

It is known that the addition of Li₂O to 33.3BaO-66.7SiO₂ glass, whose composition is the same as BaSi₂O₅, promotes crystallization of BaSi₂O₅. In this study, in order to clarify the effect of a smaller amount of Li₂O, xLi₂O-(30-x)BaO-70SiO₂[mol%] (x = 0, 0.2, 0.5) glasses were prepared. The main crystalline phases in the heat treatments near the maximum crystallization peak temperature, were high-BaSi₂O₅ and low-BaSi₂O₅ which transformed from high-BaSi₂O₅. It is found that the introduction of only 0.2 mol% and 0.5 mol% Li₂O significantly changes the crystallization behavior. In the composition without Li₂O, only high-BaSi₂O₅ was formed after heat treatment even for 24 h. For compositions containing Li₂O, low-BaSi₂O₅ was formed within 1 h of heat treatment. In these compositions, it is found that the addition of Li₂O enhances phase separation in the early stage of heat treatment, resulting in the formation of Si-rich droplet phases and Ba-rich phases. The composition of the Ba rich glass phase would be close to the stoichiometric composition of BaSi₂O₅, suggesting a significant change in crystallization behavior.     

Thermal properties measurements of renatured gelatin using conventional and temperature modulated differential scanning calorimetry

The thermal properties of amorphous gelatin films and gelatin films with renatured structural order were measured by using conventional and temperature modulated differential scanning calorimetry (DSC). Different amounts of gelatin structural order associated with a melting enthalpic change in the DSC measurement were prepared based on different gelatin drying conditions. Two consecutive heating and cooling DSC measurements on the gelatin films showed that there was no change in the glass‐transition temperature (T_g) for the amorphous gelatin but there was a decrease in the T_g for the structural gelatin on the second DSC scan. This decrease was attributed to the plasticizing effect from the release of originally hydrogen‐bonded water associated with the structural gelatin. In addition, a reversing endotherm observed upon melting of the structural gelatin during a temperature modulated DSC measurement indicated that the transition of bound water to free water occurred as the partial triple‐helix gelatin melted. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1795–1801, 2006     

Effect of poly(styrene‐co‐maleic anhydride) imidization on the miscibility and phase‐separation temperatures of poly(styrene‐co‐maleic anhydride)/poly(vinyl methyl ether) and poly(styrene‐co‐maleic anhydride)/ poly(methyl methacrylate) blends

The objective of this work was to study the miscibility and phase‐separation temperatures of poly(styrene‐co‐maleic anhydride) (SMA)/poly(vinyl methyl ether) (PVME) and SMA/poly(methyl methacrylate) (PMMA) blends with differential scanning calorimetry and small‐angle light scattering techniques. We focused on the effect of SMA partial imidization with aniline on the miscibility and phase‐separation temperatures of these blends. The SMA imidization reaction led to a partially imidized styrene N‐phenyl succinimide copolymer (SMI) with a degree of conversion of 49% and a decomposition temperature higher than that of SMA by about 20°C. We observed that both SMI/PVME and SMI/PMMA blends had lower critical solution temperature behavior. The imidization of SMA increased the phase‐separation temperature of the SMA/PVME blend and decreased that of the SMA/PMMA blend. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Epoxy/amine systems with monodisperse modifiers: thermodynamic analysis of the phase separation process taking the polymer polydispersity into account

Phase separation during polymerisation was studied by taking into account in the thermodynamic analysis the generated distribution of polymer species. A model system consisting of a diepoxide based on diglycidylether of bisphenol A, a diamine and castor oil as modifier was considered. One-and two-step polymerisation processes were simulated (in the two-step process a first step was carried out with an epoxy excess up to a particular conversion, stoichiometry was balanced and the reaction continued in a second step). A thermodynamic analysis for a monodisperse modifier-epoxy/amine system was performed taking the polydispersity of the polymer into account. It was shown that the cloud point conversion was decreased when the polymerisation was carried out in two steps. This effect was enhanced for lower stoichiometric ratios (higher epoxy excesses) and higher epoxy conversions in the first step. The dispersed phase became richer in low molecular weight species than the continuous one. In particular both monomers increased their concentration in the dispersed phase.     

Characterization of the cure of some epoxides and their sulphur-containing analogues with hexahydrophthalic anhydride by DSC and TGA

A series of curing reactions of epoxides and different substituted (1,3-oxo-thiolane-2-thione)s with hexahydrophthalic anhydride in the presence of 2,4,6-tri( dimethylaminomethyl) phenol have been characterized by nonisothermal and isothermal differential scanning calorimetry (DSC). The DSC method was employed to investigate the thermal behavior of the systems cured and to evaluate the short-term stability of one-pot compositions. It was found that the cure processes of novel sulphur analogues of epoxides were generally described through lower (absolute) values of enthalpy of curing; on the other hand, the cure onset and the peak maximum temperatures were considerably higher. To evaluate the thermal stability of the networks obtained, thermogravimetric analysis (TGA) was applied. Its use allowed us to observe that derivatives of (1,3-oxothiolane-2-thione)s were thermally more stable that their analogue epoxides (up to 25°C) and the degradation profiles depended on the steric hindrancesand interactions introduced by the substituents used. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 451–460, 1998     

Acceleration or retardation to crystallization if liquid-liquid phase separation occurs: Studies on a polyolefin blend by SAXS/WAXD, DSC and TEM

Blends of statistical copolymers containing ethylene/hexene (PEH) and ethylene/butene (PEB) exhibited the behavior of upper critical solution temperature (UCST). The interplay between the early and intermediate stage liquid-liquid phase separation (LLPS) and crystallization of the PEH/PEB 50/50 blend was studied by time-resolved simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. Samples were treated by two different quench procedures: in single quench, the sample was directly quenched from 160 °C to isothermal crystallization temperature of 114 °C; while in double quench, the sample was firstly quenched to 130 °C for 20 min annealing, where LLPS occurred, and then to 114 °C. It was found that in the early stage of crystallization, the integrated values of Iq² and crystallinity, X_c, in the double quench procedure were consistently higher than those in the single quench procedure, which could be attributed to accelerated nucleation induced by enhanced concentration fluctuations and interfacial tension. In the late stage of crystallization, some morphological parameters were found to crossover and then reverse, which could be explained by retardation of lamellar growth due to phase separation formed during the double quench procedure. This phenomenon was also confirmed by DSC measurements in blends of different compositions at varying isothermal crystallization temperatures. The crystal lamellar thickness determined by SAXS showed a good agreement with TEM observation. Results indicated that the early stage LLPS in the PEH/PEB blend prior to crystallization indeed dictated the resulting lamellar structures, including the average size of lamellar stack and the stack distribution. There seemed to be little variation of lamellar thickness and long period between the two quenching procedures (i.e., single quench versus double quench).     

Facile dispersion of exfoliated graphene/PLA nanocomposites via in situ polycondensation with a melt extrusion process and its rheological studies

This work attempted to improve the dispersion of graphene by coating poly(lactic acid) pellets with a masterbatch before melt processing. An in situ polycondensation reaction of lactic acid oligomer was utilized to prepare the masterbatch (MB) of exfoliated graphene (GR). MB dispersed composites of poly(lactic acid) (PLA) were fabricated by melt extrusion of MB‐coated PLA. One normal coated composite without MB coating (PLA‐M‐0.2GR) was fabricated for comparing properties. X‐ray diffraction, Raman spectroscopy, and morphological studies revealed better compatibility, dispersion, and interaction of GR for the diluted‐MB composite compared to the normal coated composite. The thermal stability, crystallization properties, and mechanical properties of the composites were examined, and the effect of short PLA chains in diluted‐MB composites was observed. The melt rheology nature of the composites was examined. Cole–Cole plots and Han plots suggested a uniform distribution of graphene. The sample PLA‐MB‐0.05GR showed improved modulus and elongation at break. It also showed better dispersion of GR, comparable thermal stability, good miscibility, good chain mobility, and high activation energy. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46476.     

集成橡胶SBR-IR-SBR和SBR-BR-SBR的玻璃化转变温度

考察了调制式差示扫描量热仪的实验影响因素及其对嵌段(丁苯共聚物-聚异戊二烯)集成橡胶(SBR—IR—SBR)和嵌段(丁苯共聚物-聚丁二烯)集成橡胶(SBR—BR—SBR)玻璃化转变温度的影响,并研究了SBR—IR—SBR和SBR—BR—SBR的动态黏弹性能。结果表明,SBR—IR—SBR和SBR—BR—SBR的玻璃化转变温度随着调制式差示扫描量热仪升温速率的增加而增加;SBR—IR—SBR和SBR—BR—SBR中均存在着明显的相分离结构;硫化后的SBR—IR—SBR更易于相分离。     

Real‐time temperature and photon transmission measurements for monitoring phase separation during the formation of poly(N‐isopropylacrylamide) gels

Phase separation during the formation of poly(N‐isopropylacrylamide) (PNIPA) hydrogels was investigated using real‐time photon transmission and temperature measurements. The hydrogels were prepared by free‐radical crosslinking polymerization of N‐isopropylacrylamide (NIPA) in the presence of N,N′‐methylenebisacrylamide (BAAm) as a crosslinker in an aqueous solution. The onset reaction temperature T₀ was varied between 20 and 28°C. Following an induction period, all the gelation experiments resulted in exothermic reaction profiles. A temperature increase of 6.5 ± 0.6°C was observed in the experiments. It was shown that the temperature increase during the formation and growth process of PNIPA gels is accompanied by a simultaneous decrease in the transmitted light intensities I_tr. The decrease in I_tr at temperatures below the lower critical solution temperature of PNIPA was explained by the concentration fluctuations due to the inhomogeneity in the gel network. At higher temperatures, it was shown that the gel system undergoes a phase transition via a spinodal decomposition process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3589–3595, 2002     

Reaction kinetics modeling and thermal properties of epoxy–amines as measured by modulated‐temperature DSC. II. Network‐forming DGEBA + MDA

Reaction‐induced vitrification takes place in the network‐forming epoxy–amine system diglycidyl ether of bisphenol A (DGEBA) + methylenedianiline (MDA) when the glass‐transition temperature (T_g) rises above the cure temperature (T_cure). This chemorheological transition results in diffusion‐controlled reaction and can be followed simultaneously with the reaction rate in modulated‐temperature DSC (MTDSC). To predict the effect of T_cure and the NH/epoxy molar mixing ratio (r) on the reaction rate in chemically controlled conditions, a mechanistic approach was used based on the nonreversing heat flow and heat capacity MTDSC signals, in which the reaction steps of primary (E_1OH = 44 kJ mol^?1) and secondary amine (E_2OH = 48 kJ mol^?1) with the epoxy–hydroxyl complex predominating. The diffusion factor DF as defined by the Rabinowitch approach expresses whether the chemical reaction rate or the diffusion rate determines the overall reaction rate. A model based on the free volume theory together with an Arrhenius temperature dependency was used to calculate the diffusion rate constant in DF as a function of conversion (x) and T_cure. The relation between x, r, and T_g, needed in this model, can be predicted with the Couchman equation. An experimental approximation for DF is the mobility factor DF* obtained from the heat capacity signal at a modulation frequency of 1/60 Hz, normalized for the effect of the reaction heat capacity in the liquid state and the change in C_p in the glassy region with x and T_cure. In this way, an optimized set of diffusion parameters was obtained that, together with the optimized kinetic parameters set, can predict the reaction rate for different cure schedules and for stoichiometric and off‐stoichiometric mixtures. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2814–2833, 2004     

In situ gasification and CO2 separation using chemical looping with a Cu-based oxygen carrier: Performance with bituminous coals

This paper is concerned with the chemical looping combustion of coal in a technique whereby the fuel is gasified in situ using CO₂ in the presence of a batch of supported copper oxide (the “oxygen carrier”) in a single reactor. As the metal oxide becomes depleted, the feed of fuel is discontinued, the inventory of fuel is reduced by further gasification and then the contents are re-oxidised by the admission of air to the reactor, to begin the cycle again. A catalyst support, impregnated with a saturated solution of copper and aluminium nitrates, acted as a durable oxygen carrier over numerous cycles of reduction and oxidation, using air as the oxidant. Two bituminous coals (Taldinskaya, Russia, and Illinois No. 5, USA) were investigated and compared with a lignite (Hambach, Germany). The lignite was highly reactive and was gasified completely by 15 mol% CO₂ in N₂ at 1203 K and 1 bar, so that there was no build up of char in the bed. The bituminous coals produced chars much less reactive than the lignite char, so that there was a steady accumulation of char in the bed with number of cycles, with the degree of accumulation being dependent on the reactivity of the char. Since the kinetics of gasification by CO₂ of the chars from either bituminous coal were slow, their rates were controlled by intrinsic chemical kinetics and were not affected by the ability of the oxygen carrier to alter the rates of external mass transfer when gasification is rapid. However, it is likely that rates of gasification in the presence of the carrier are still larger than in its absence, owing to the overall lower [CO] present in the bulk of the fluidised bed during chemical looping. At the temperature used, the carrier was cycling between Cu and Cu₂O, since CuO is only stable if the partial pressure of O₂ exceeds 0.03 bar at 1203 K. The CuO decomposes to Cu₂O and O₂ relatively rapidly at these temperatures, once the oxygen concentration is effectively zero. It was impossible to ascertain in our experiments whether the oxygen so generated, after the switching of the air for nitrogen before the start of the succeeding cycle of gasification, made any substantial difference to the reactivity of the char present in the bed. The rate of oxidation of the carrier was found to be much more rapid than the rate of oxidation of the inventory of char. This allows a preferential oxidation of the carrier and most likely accounts for why progressively less CO and CO₂ is produced during successive cycles with short periods of oxidation: the increasingly reduced carrier reacts more rapidly than the char. There was no obvious impact from the sulphur contained in the fuels, but longer-term testing is needed. No agglomeration between the carrier particles and the ash was observed, despite the high temperatures during oxidation.     

Reaction kinetics modeling and thermal properties of epoxy–amines as measured by modulated‐temperature DSC. I. Linear step‐growth polymerization of DGEBA + aniline

A mechanistic approach including both reactive and nonreactive complexes can successfully simulate both nonreversing (NR) heat flow and heat capacity (C_p) signals from modulated‐temperature DSC in isothermal and nonisothermal reaction conditions for different mixtures of diglycidyl ether of bisphenol A + aniline. The reaction of the primary amine with an epoxy–amine complex initiates cure (E_1A1 = 80 kJ mol^?1), whereas the reactions of the primary amine (E_1OH = 48 kJ mol^?1) and secondary amine (E_2OH = 48 kJ mol^?1) with an epoxy–hydroxyl complex are rate determining from about 2% epoxy conversion on. The reliability of the proposed mechanistic model was verified by experimental concentration profiles from Raman spectroscopy. When cure temperatures are chosen inside or below the full cure glass‐transition region, vitrification takes place partially or completely, respectively, as can be concluded from the magnitude of the stepwise decrease in C_p. The effect of the epoxy conversion (x) and mixture composition on thermal properties such as the glass‐transition temperature (T_g), the change in heat capacity at T_g [ΔC_p(T_g)], and the width of the glass transition region (ΔT_g) are considered. The Couchman relationship, in which only T_g and ΔC_p(T_g) of both the unreacted and the fully reacted systems are needed, was evaluated to predict the T_g– x relation by using simulated concentration profiles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:2798–2813, 2004     

Modulated temperature differential scanning calorimetry for examination of tristearin polymorphism: 2. Isothermal crystallization of metastable forms

The transformations of tristearin were examined by modulated temperature differential scanning calorimetry (MTDSC) in order to examine the utility of this technique. Tristearin has been used as a model polymorphic system, showing metastable phases and complicated transformation routes occuring at relatively slow rates. The β′-forms generated by thermal treatment under modulation do not differ significantly from those generated by the corresponding treatment without modulation. While the total heat flow thermograms are similar, the deconvoluted reversing component shows that annealing, especially at 63°C, has a significant effect on the crystal size and perfection of the solid phases formed. MTDSC also enables the melting of β′ to be separated from the simultaneous crystallization of the β form as evidenced in the c _p component. Quantitative interpretations about such systems cannot be drawn from MTDSC at this point in time.     

Construction of membrane formation system with low critical solution temperature for preparing hydrophilic polysulfone membrane via modified reverse thermally induced phase separation process

This paper presents a novel method to construct a membrane formation system featuring a low critical solution temperature (LCST) by incorporating hydroxy terminated hyperbranched polyester (HBPE) into polysulfone (PSF) casting solution. PSF membranes were developed by modified reverse thermally induced phase separation (m-RTIPS) process while the introduction of HBPE improved the hydrophilicity of the membrane. The critical properties of the flat-sheet PSF membranes were discussed in detail. The cloud point decreased as the HBPE concentration was increased. When membranes were prepared via m-RTIPS, the region of bicontinuous finger-like pores in the sublayer gradually broadened. The membranes showed better permeation properties, larger pore size, and better mechanical properties than those of the membranes prepared via non-solvent-induced phase separation (NIPS) process. Furthermore, no matter the enhanced hydrophilicity of membrane or m-RTIPS membrane-forming mechanism was beneficial to the anti-fouling properties. In general, the membrane MPSF-8-b had relatively high flux, good hydrophilicity and excellent mechanical properties at 0.8 wt.% HBPE content, and the pure water flux recovery of the membrane was increased to 55.2%.