Preparation and Characterization of Poly(ethylene oxide)/Graphene Nanocomposites from an Aqueous Medium

The nanocomposite films of a functionalized graphene sheet (FGS) and poly(ethylene oxide) (PEO) were cast from the physical blend of an aqueous FGS dispersion assisted by sodium dodecyl sulfate and an aqueous PEO solution. The thermal properties observed by differential scanning calorimetry suggested that FGS had a nucleating effect on the PEO crystallization. However, we found FGS actually hindered the growth of PEO crystals. The dynamic mechanical properties indicated that FGS effectively reinforced the matrix PEO. The FGS also efficiently improved the electric conductivity of PEO. With the addition of 2 parts of FGS per 100 parts of PEO, the conductivity was increased by more than 10³-fold from that of pristine PEO.     

Miscibility and Crystallization Behavior of Poly (Ethylene Terephthalate)/Phosphate Glass Hybrids

Fundamental studies on miscibility and crystallization behavior of poly (ethylene terephthalate) (PET) and inorganic phosphate glass (Pglass) hybrids were conducted. The Flory–Huggins interaction parameter (χ) value of ?0.075 for the PET/Pglass hybrids was obtained using the Nishi–Wang equation, demonstrating that the Pglass and PET components were miscible in the melt state. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the phase separation occurred during quenching from the melt. The phase boundaries between PET and Pglass were blurred, which indicated partial compatibility of the components in the solid state. Contact angle measurements indicated the interfacial tension of PET/Pglass hybrids was 1.5 mN/m, and the work of adhesion was 78.0 mN/m at 28 °C. Based on the Hoffman–Lauritzen theory, the nucleation constant (K_g) and fold surface free energy (σ_e) of PET/Pglass hybrids were less than those of neat PET.     

富勒烯C60的近共振非线性光学响应

利用锁模Ｎｄ：ＹＡＧ激光器的５０ｐｓ和信频光输出对Ｃ_（６０）甲苯溶液及Ｃ_（６０）膜进行了时间分辨简并回波混频测量．从溶液及膜都观察到一个很快的非线性光学响应．而一个较长寿命的成分仅在溶液中见到．由实验结果可以推算得Ｃ_（６０）的近共振三阶非线性光学极化率为（３．６±１．４）×１０（－１０）ｅｓｕ．     

Crystallization Behavior of Poly(Trimethylene Terephthalate)/Polycarbonate Blends

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

Rheological Behavior of Blends of Poly(Phenylene Sulfide) with a Thermotropic Liquid Crystalline Aromatic Poly(Ether Ester)

A new type of thermotropic liquid crystalline aromatic poly(ether ester) (PEE) was prepared from 1,3-bis(4′-carboxyphenoxy)benzene, 1,4-diacetoxybenzene, and p-acetoxybenzoic acid through a melt transesterification process. The rheological behavior of blends of poly(phenylene sulfide) (PPS) with PEE was studied using a high-pressure capillary rheometer with the shear rate range of 50 s^?1 to 3000 s^?1. The results show that according to the range of shear rate, the flow curves of PEE/PPS blends can be divided into three zones: a first shear-thinning zone (n < 1, “n” represents non-Newtonian indexes), a shear-thickening zone (n > 1), and a second shear-thinning zone (n < 1), and the former two zones are more obvious with the increase of PEE content or elevated temperature. In the second shear-thinning zone, the PPS melt is close to a Newtonian fluid at high temperature and high shear rate; meanwhile the non-Newtonian behavior of the PPS melt at high temperature is enhanced with the addition of PEE. The apparent viscosity of PPS melts sharply dropped after adding PEE, especially at relatively low temperature and low shear rate. The curve of apparent viscosity vs. shear rate starts to flatten out after adding PEE, suggesting that the addition of PEE lowers the sensitivity of PPS to shear rate. As the content of PEE increases, the activation energy of the viscous flow, ΔE_η, of PPS decreases, which means that adding PEE weakens the temperature sensitivity of the apparent viscosity of the PPS melt. It can clearly be seen that the addition of PEE is beneficial to the processing of PPS.     

Influence of Polycarbonate on the Crystallization Behavior of Poly(Trimethylene Terephthalate)/Polycarbonate Blends

To determine the factors influencing the retardation of the crystallization of poly(trimethylene terephthalate) (PTT) when PTT is blended with polycarbonate (PC), different PTT/PC blends were prepared via the melt mixing method. The relationships between the crystallization behavior and blend composition, as well as the phase morphology, were investigated. The results showed that the predominant reason for the retardation in crystallization is due to the PC content and phase morphology. The PC influences the crystallization of PTT via two methods. First, it retards PTT crystallization. Secondly, the PC exhibits a nucleation effect on the PTT crystallization which is, however, much weaker compared to the negative effect PC exerts with regards to PTT crystallization. When the processing temperature and shear rate remains unchanged, the two effects of PC determine the crystallization behavior of the blend. The phase morphology, which is strongly dependent on the mixing temperature and the shear rate, and which is also related to mixing time, had an appreciable impact on PTT crystallization. In the case of similar adhesion with the interface, a finer PC phase domain would show a slightly stronger nucleation effect on PTT crystallization.     

Microstructures and Mechanical Properties of Poly(Trimethylene Terephthalate)/Maleic Anhydride Grafted Poly(Ethylene-octene)/Polypropylene Blends

A range of blends based on 70 wt% of poly(trimethylene terephthalate) PTT with 30 wt% dispersed phase were produced via melt blending. The dispersed phase composition was varied from pure maleic anhydride grafted poly(ethylene-octene) (POE-g-MA) over a range of POE-g-MA:polypropylene (PP) ratios. The micromorphology and mechanical properties of the ternary blends were investigated. The results indicated that the domains of the POE-g-MA are dispersed in the PTT matrix, and at the same time the POE-g-MA encapsulate the PP domains. The interfacial reaction between the hydroxyl-end group of PTT and maleic anhydride (MA) during melt blending changes the formation from “isolated formation” to “capsule formation,” where the PP domains are encapsulated by POE-g-MA. Compared to the PTT/POE-g-MA blends, mechanical properties of ternary blends, such as tensile strength and Young's modulus, were improved significantly.     

Nonisothermal Crystallization of Recycled Poly(Ethylene Terephthalate)/Poly(Ethylene Octene) Blends

Recycled poly(ethylene terephthalate) (r-PET) was blended with poly(ethylene octene) (POE) and glycidyl methacrylate grafted poly(ethylene octene) (mPOE). The nonisothermal crystallization behavior of r-PET, r-PET/POE, and r-PET/mPOE blends was investigated using differential scanning calorimetry (DSC). The crystallization peak temperatures (T _p ) of the r-PET/POE and r-PET/mPOE blends were higher than that of r-PET at various cooling rates. Furthermore, the half-time for crystallization (t _1/2 ) decreased in the r-PET/POE and r-PET/mPOE blends, implying the nucleating role of POE and mPOE. The mPOE had lower nucleation activity than POE because the in situ formed copolymer PET-g-POE in the PET/mPOE blend restricted the movement of PET chains. Non-isothermal crystallization kinetics analysis was carried out based on the modified Avrami equation, the Ozawa equation, and the Mo method. It was found that the Mo method provided a better fit for the experimental data for all samples. The effective energy barriers for nonisothermal crystallization of r-PET and its blends were determined by the Kissinger method.     

Miscibility and Isothermal Crystallization Behavior of Poly (Butylene Succinate-co-Adipate) (PBSA)/Poly (Trimethylene Carbonate) (PTMC) Blends

Poly(butylene succinate-co-adipate) (PBSA)/poly (trimethylene carbonate) (PTMC) blend samples with different weight ratios were prepared by solution blending. The morphologies after isothermal crystallization and in the melt were observed by optical microscopy (OM). Differential scanning calorimetry (DSC) was used to characterize the isothermal crystallization kinetics and melting behaviors. According to the OM image before and after melting, it was found that the blends formed heterogenous morphologies. When the PTMC content was low (20%), PBSA formed the continuous phase, while when the PTMC contents was high (40%), PBSA formed the dispersed phase. The glass transition temperatures (T_g) of the blends were determined by DSC and the differences of the T_g values were smaller than the difference between those of pure PBSA and PTMC. In addition, the equilibrium melting points were depressed in the blends. According to these results, the PBSA/PTMC blends were determined as being partially miscible blends. The crystallization kinetics was investigated according to the Avrami equation. It was found that the incorporation of PTMC did not change the crystallization mechanism of PBSA. However, the crystallization rate decreased with the increase of PTMC contents. The change of crystallization kinetics is related with the existences of amorphous PTMC, the partial miscibility between PLLA and PTMC, and the changes of phase structures.     

On the Supermolecular Structure of Fullerene C60 Solutions

Small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) techniques were used for investigation of fullerene C₆₀ solutions in toluene and p‐xylene. On all SAXS curves, intensity decreases to some constant value of I_C with increase of scattering angle. The value of I_C depends on concentration non‐monotonically: it first slightly increases, then drops sharply to some minimal value, and then increases again. A qualitative explanation of such dependence is offered. It is supposed that the presence of fullerene C₆₀ in solution suppresses thermal fluctuations of density in the solvent. In combination with the X‐ray data the results obtained for solutions of fullerene C₆₀ by various others techniques (calorimetry, densimetry, etc.) are discussed. Possible models of a supermolecular structure of fullerene C₆₀ solutions in good solvents are considered.     

Phase Ordering and Crystallization Kinetics in Ultrathin Poly(ethylene oxide)/Poly(methyl methacrylate) Blend Films

Crystallization in ultrathin Poly(Ethylene Oxide)/Poly(Methyl Methacrylate) (PEO/PMMA) blend films with thickness of ca. 10 nm was investigated by means of microscopic and in situ spectroscopic methods. It was revealed that the blend films undergo a phase ordering in a humid atmosphere before or during crystallization, with PEO de-mixing with PMMA and segregating to the free film interface on the PMMA layer. The de-mixed PEO chains crystallize into a fractal-like morphology by a diffusion-limited process, and the crystal growth is 1-dimensional with Avrami exponent n ≈ 1, resulting in flat-on crystal lamellae with the PEO chains oriented normal to the film plane.     

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

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

电场作用下C60富勒烯二聚体分子的几何构型与失效

采用分子力学与量子力学相结合的方法,模拟了电场作用下C60富勒烯二聚体(2C60)分子的几何构型与失效行为,讨论了三种不同方向外加电场对2C60分子几何变形、构型失效、电荷分布与极化偶极矩的影响,并与电场作用下C60富勒烯分子的几何变形与失效行为进行了对比.研究结果表明,2C60分子的几何变形与失效行为与外加电场的方向密切相关.当外加电场与2C60分子的桥接C-C键平行时,2C60分子很容易发生失效,且失效形式也十分独特.     

Synthesis of Poly(butylene terephthalate)/Attapulgite Nanocomposites by In-Situ Polymerization and Its Crystallization Behavior

Poly(butylene terephthalate) (PBT)/attapulgite (AT) nanocomposites were prepared via in-situ polymerization without pre-modification of AT. By this method, PBT chains were successfully grafted onto the surface of AT, which was confirmed by Fourier transform infrared spectroscopy and thermogravimetric analysis. Scanning electron microscope examination indicated the uniform dispersion of AT nanoparticles in PBT matrix. The crystallization behavior of PBT/AT nanocomposites was investigated by X-ray diffraction patterns, differential scanning calorimetry, and step-scan differential scanning calorimetry. The non-isothermal crystallization processes were analyzed with the Avrami, Ozawa, and Mo methods. Crystallization activation energies of the samples were also determined by the Kissinger method. The results indicated that AT could act as a heterogeneous nucleating agent in PBT crystallization and lead to an acceleration of crystallization, while AT also acted as a physical hindrance to retard the transport of polymer chains to the growing crystals.     

Influence of Reactive Compatibilizer on the Morphology,Rheological, and Mechanical Properties of Recycled Poly(Ethylene Terephthalate)/Polyamide 6 Blends

Recycled poly(ethylene terephthalate) (R-PET) and virgin polyamide 6 (PA6) blends compatibilized with glycidyl methacrylate grafted poly(ethylene-octene) (POE-g-GMA) were melt blended. The morphological, rheological and mechanical properties of the prepared blends were investigated by scanning electron microscopy, rheology, and an electromechanical testing instrument, respectively. All of the blends showed a droplet dispersion type morphology, and the PA6 particle size decreased with increase in the POE-g-GMA concentration. The storage modulus (G′), loss modulus (G′′), and complex viscosity (η*) of the blends significantly increased at low frequency with the addition of POE-g-GMA. In addition, ‘‘Cole-Cole’’ plots showed that the elasticity of the blends was also increased by raising the compatibilizer dosage. It was also found that 10 wt% of POE-g-GMA caused 88.46 and 171.05% increments in Charpy impact strength and elongation at break with only a 21.66% decrement in tensile strength.     

Isothermal Crystallization Kinetics and Melting Behavior of Poly(ethylene terephthalate)/Attapulgite Nanocomposites Studied by Step-scan DSC

The crystallization kinetics of poly(ethylene terephthalate)/attapulgite (AT) nanocomposites and their melting behaviors after isothermal crystallization from the melt were investigated by DSC and analyzed using the Avrami method. The isothermal crystallization kinetics showed that the addition of AT increased both the crystallization rate and the isothermal Avrami exponent of PET. Step-scan differential scanning calorimetry was used to study the influence of AT on the crystallization and subsequent melting behavior in conjunction with conventional DSC. The results revealed that PET and PET/AT nanocomposites experience multiple melting and secondary crystallization processes during heating. The melting behaviors of PET and PET/AT nanocomposites varied in accordance with the crystallization temperature and shifted to higher temperature with the increase of AT content and isothermal crystallization temperature. The main effect of AT nanoparticles on the crystallization of PET was to improve the perfection of PET crystals and weaken its recrystallization behavior.     

Isothermal Crystallization and Subsequent Melting Behavior of Poly(ethylene terephthalate)/Silica Nanocomposites

The crystallization process of poly(ethylene terephthalate)/silica nanocomposites were investigated by differential scanning calorimetry (DSC) and then analyzed using the Avrami method. The results indicated that the crystallization of pure poly(ethylene terephthalate) (PET) was fitted for thermal nucleation and three‐dimensional spherical growth throughout the whole process, whereas the crystallization of PET/silica nanocomposites exhibits two stages. The first stage corresponds to athermal nucleation and three‐dimensional spherical growth, and the second stage corresponds to recrystallization caused by the earlier spherulites impingement. The crystallization rate increases remarkably and the activation energies decrease considerably when silica nanoparticles are added. The subsequent melting behavior of the crystallized samples shows that the melting point (T _m) of nanocomposites is higher than that of pure PET, which might be caused by two factors: (1) The higher melting point might be due to some hindrance to the PET chains caused by the nanoparticles at the beginning of the melting process; (2) it might also be the case that more perfect crystals can be formed due to the higher crystallization temperatures and lower activation energies of PET/silica nanocomposites.     

The Peculiar Temperature Response of Dynamic Rheological Behaviors of Poly (Vinyl Chloride)/trioctyl Trimellitate (100/70) System

The dynamic rheological behavior, application of time-temperature superposition (TTS) and the failure mechanism of TTS are studied for the poly(vinyl chloride) (PVC)/trioctyl trimellitate (TOTM) (100/70) system. The Arrhenius equation, Williams–Landel—Ferry (WLF) equation, mathematical non-linear fitting and manual shift are applied to TTS fitting. For the PVC/TOTM (100/70) system, none of those methods can give well-superimposed master curves with either single horizontal shift or two-dimensional (horizontal and vertical) shift. The failure reason is attributed to the thermorheological complexity of the PVC/TOTM (100/70) system. Curves of the storage modulus versus the frequency can be well fitted with an empirical equation (G′=G′₀+Kω ⁿ ) usually used to describe filled polymer systems, indicating the multilevel flowing unit characteristic in this system. With the increase of test temperature, the structure of the PVC/TOTM (100/70) system changes and an apparent transition appears in the rheological behavior. Differential scanning calorimetry (DSC) results reveal that for the PVC/TOTM (100/70) system there are microcrystallites present below 220°C, but above the rheological transition temperature (190°C) the bulk of the microcrystallites melted, which corresponds to the appearance of viscous flow participating in the rheological behavior. It verifies the fact that the gel networks crosslinked by microcrystallites dominate the rheological behavior below the transition temperature in the PVC/TOTM (100/70) system. The quantity of microcrystallites remaining in the melt determines the perfection of the physical gel networks. With the increase of test temperature, the microcrystallites melted gradually and the gel networks are broken up.     

Effects of Polymer Bridging and Electrostatics on the Rheological Behavior of Aqueous Colloidal Dispersions†

Effects of a low molecular weight physically adsorbed polyethylene oxide (PEO) and the range of the electrostatic repulsion on the rheological behavior of silica dispersions (as a model system) has been investigated. Particular attention is given to the evolution of the rheological behavior with increasing the polymer concentration in the system and also effectiveness of the polymer as a dispersant under extreme conditions (high ionic strength). Results indicate that at small separation distances and low polymer coverage, the polymer chains are long enough to adsorb on the surface of two particles simultaneously causing bridging flocculation in the system and hence increasing the viscosity and linear viscoelastic functions of the dispersion. A significant increase was observed in the viscosity of the dispersion at salt concentrations high enough to eliminate electrostatics between the particles. Under these conditions,the viscosity of the system increased significantly when PEO was added to the dispersion showing that at high electrolyte concentrations, a neutral polymer such as PEO is not able to stabilize the system.     

Isothermal Crystallization and Melting Behavior of Composites Composed of Poly(L-lactic Acid) and Poly(glycolic Acid) Fibers

Several composites of poly (L-lactic acid) (PLLA) with poly (glycolic acid) (PGA) fibers were prepared. The isothermal crystallization kinetics and melting behavior of PLLA and all of the composites were characterized by using differential scanning calorimetry. The experimental data were processed by using the Avrami equation. The relative parameters, such as the Avrami exponent and half-time crystallization, revealed that PGA fibers had positive effects on the crystallization of PLLA, but these effects had only a minimal dependence on the PGA fiber content. Moreover, at low isothermal crystallization temperatures (85°C～110°C), recrystallization during the heating scan was observed, which could lower the melting point of the samples to a certain extent.