Cryogenic mechanical behaviors of carbon nanotube reinforced composites based on modified epoxy by poly(ethersulfone)

Cryogenic mechanical properties are important parameters for epoxy resins used in cryogenic engineering areas. In this study, multi-walled carbon nanotubes (MWCNTs) were employed to reinforce diglycidyl ether of bisphenol F (DGBEF)/diethyl toluene diamine (DETD) epoxy system modified by poly(ethersulfone) (PES) for enhancing the cryogenic mechanical properties. The epoxy system was properly modified by PES in our previous work and the optimized formulation of the epoxy system was reinforced by MWCNTs in the present work. The results show that the tensile strength and Young’s modulus at 77 K were enhanced by 57.9% and 10.1%, respectively. The reported decrease in the previous work of the Young’s modulus of the modified epoxy system due to the introduction of flexible PES is offset by the increase of the modulus due to the introduction of MWCNTs. Meanwhile, the fracture toughness (K_IC) at 77 K was improved by about 13.5% compared to that of the PES modified epoxy matrix when the 0.5 wt.% MWCNT content was introduced. These interesting results imply that the simultaneous usage of PES and MWCNTs in a brittle epoxy resin is a promising approach for efficiently modifying and reinforcing epoxy resins for cryogenic engineering applications.     

Mechanical and thermal performance of distillers grains filled poly(butylene succinate) composites

The mechanical and dynamic mechanical properties, morphology, melting and crystallization behavior, as well as thermal stability of poly(butylene succinate)/distillers grains (PBS/DG) composites with different DG contents were investigated. The tensile modulus, crystallization rate, and crystallinity of PBS in the composites were efficiently enhanced in the presence of DG. The thermogravimetric analysis of the PBS/DG composites showed that their flame retardancy leveled up. The scanning electron microscopy analysis of the PBS/DG composites indicated that the DG was not damaged during the melt processing. These results supported the application of DG as fillers in polymer composites. Consequently, this study opened a new application of DG and has potential to decrease the cost of PBS-based materials with a variety of enhanced properties.     

PBS/PTMO嵌段共聚物的合成及表征

合成了以聚丁二酸丁二醇酯(PBS)为硬段,聚四氢呋喃醚(PTMO,分子量1000g/mol)为软段的可生物降解嵌段共聚物。采用核磁共振氢谱(1H-NMR)、傅立叶变换红外光谱(FT-IR)、差示扫描量热法(DSC)、偏光显微镜(POM)和原子力显微镜(AFM)对嵌段共聚物的结构、耐热性能、结晶形态和表面形貌进行了分析。结果表明,合成的目标产物为PBS/PTMO嵌段共聚物,随软段PTMO含量的增加,PBS硬段结晶温度和熔融温度降低,晶体尺寸变小;当PTMO质量分数低于50%,PTMO以非晶态形式存在时,PBS硬段晶体与PBS均聚物一样呈现环带球晶特征;当PTMO质量分数超过50%时,PBS晶体细小,无明显的环带球晶特征,且分散在非晶相中。     

Synthesis and characterization of polyester copolymers based on poly(butylene succinate) and poly(ethylene glycol)

A series of polyester copolymers was synthesized from 1,4-succinic acid with 1,4-butanediol and poly(ethylene glycol) through a two-step process of esterification and polycondensation in this article. The composition and physical properties of copolyesters were investigated via GPC, ¹HNMR, DSC and PLM. The copolymer composition was in good agreement with that expected from the feed composition of the reactants. The melting temperature (T_m), crystallization temperature (T_c), and crystallinity (X_c) of these copolyesters decreased gradually as the content of PEG unit increased. Otherwise, experimental results also showed that the contents of PEG in copolymers had an effect on the molecular weight, distribution, thermal properties, hydrolysis degradation properties, and crystalline morphology of polyester copolymers.     

Local thermal-mechanical analysis of ultrathin interfacially mixed poly(ethylene oxide)/poly(acrylic acid) layer-by-layer electrolyte assemblies

Ion conductivities of layer-by-layer (LBL) assemblies of solid thin film polyelectrolyte systems involving poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) were found to be a strong function of the number of bilayer stacks, n, with conductivities approaching 10^− 7 S/cm for n < 10, compared to 10^− 9 S/cm for n ≥ 10 and 10^− 10 S/cm for bulk PEO. Increased ion conductivity for low LBL stack numbers (n < 10) originated to part from an effective suppression of the PEO crystallization via PEO/PAA blending, which could be inferred from local glass transition temperature measurements involving shear modulation force microscopy. Another phenomenon responsible for high conductivity in thin films was found in the in-plane phase heterogeneity of PEO and PAA. Increased ion conductivity for larger LBL stacks (n ≥ 10) were attributed to low concentration autoblending caused by PEO-PAA hydrogen bonding, and an average layer thickness of noticeably less than 100 nm. The effect of interfacial constraints was evident in the degree of intermixing, addressed by a thin film extended Fox blend analysis, in the glass and melting transitions of PEO and PAA pure film components. While the glass transition value of PAA decreased by 55% to 46 °C for an 8 nm film, the melting transition for PEO decreased by 15% to 64 °C caused by surface tension effects.     

Dielectric characteristics of poly(N-vinylcarbazole) and its nanocomposites with ZnO and acetylene black

Dielectric constant and dielectric loss parameters of poly(N-vinylcarbazole) homopolymer and several nanocomposites of poly(N-vinylcarbazole) with ZnO were studied as a function of frequency. In the low frequency range (0–20 kHz) the dielectric constant values of the base polymer varied from ∼30 to ∼2, and the same for the composite varied from 8500 to 2000 (4.54), 5000 to 1000 (2.63) and 2000 to 500 (1.17), the figures in parenthesis denoting the ratio of ZnO:PNVC in the nanocomposites. Likewise, dielectric loss parameters were found to be (7–10 × 10⁻³) for the homopolymer and 4.0, 2.5 and 1.25 for the three PNVC–ZnO composites respectively. Notably, a mechanical mixture of ZnO and PNVC (1.17) exhibited much lower dielectric constant (400–25) and loss parameters (0.14–0.065). These features imply polarization was differently affected depending on factors such as grain size and grain-boundary interfaces being formed in these systems. Tan δ–temperature variation for the composites revealed the occurrence of a maximum between 60 and 70 °C. These features signified dipole group loss in the composite. Dielectric constant of a conducting nanocomposite of poly(N-vinylcarbazole) with acetylene black revealed very low negative value tending to zero at high frequency.     

Very-low temperature specific heat of Torlon

The specific heat of Torlon has been measured in the 0.15-4.2 K temperature range. Data below 1 K can be represented by c(T) = P₁T^1+δ + P₂T³, with P₁ = (5.41 ± 0.08)·10⁻⁶J K^−(2+δ) g⁻¹, P₂ = (2.82 ± 0.03) ·10⁻⁵JK⁻⁴g⁻¹ and δ = 0.28 ± 0.01, as predicted by the tunnelling theory. Above 1 K, the behaviour of c(T) is similar to that of other amorphous materials and can be expressed as: c(T) = P · T^Ω with P = (2.68 ± 0.07)·10⁻⁵JK^Ω+1g⁻¹ and Ω = 3.32 ± 0.02.     

Nickel (II) ions sensing properties of dimethylglyoxime/poly(caprolactone) electrospun fibers

A novel dimethylglyoxime (DMG)/poly(caprolactone) (PCL) blend was electrospun into fibers to serve as an optical sensor for the nickel detection based on the formation of a red Ni(DMG)₂ complex. DMG was mixed with PCL at 10, 20 and 30% (w/w) in a mixture of N, N-dimethylformamide (DMF) and dichloromethane (DCM) (50/50, v/v) prior electrospunning process. The best fibers were prepared under an electric field of 20 kV and a distance between needle and collector of 20 cm. From scanning electron microscopy (SEM), the average diameter of the fibers remained nearly constant with increasing amount of DMG. The optimum mass ratio of DMG and PCL was found to be 20:80 as it produced fibers with the smallest diameter distribution and the best sensing property. The formation of the Ni(DMG)₂ complex was confirmed by Fourier transform infrared spectroscopy (FT-IR). The colorimetric response of the PCL/DMG electrospun fibers were then tested against the nickel ions over a concentration range of 1-10 ppm using reflectance spectroscopy. Good linearity between the reflectance values at 547 nm and the concentrations was obtained (R² = 0.9925). These proposed DMG and PCL fibers could be used as the naked-eye sensor for nickel in waste water.     

微米六方BN-KH550/聚丁二酸丁二醇酯耐热性复合膜的制备及性能

为进一步改善聚丁二酸丁二醇酯(PBS)的力学性能和耐热性能,采用硅烷偶联剂KH550改性微米六方氮化硼(h-BN),对PBS进行共混改性,通过熔融共混与开炼压延工艺制备了具有较高耐热性的h-BN-KH550/PBS复合膜。对h-BN-KH550粒子结构和复合膜的力学性能、聚集态结构、断面形貌、结晶性能及热稳定性进行了测试和表征。结果表明:与PBS相比,h-BN-KH550/PBS复合膜的力学性能得到改善,当KH550与h-BN质量比为2∶50、h-BN-KH550与PBS质量比为3∶50时,综合力学性能最优;h-BN-KH550粒子可在PBS中均匀分散;在PBS结晶过程中,h-BN-KH550作为成核剂,使PBS的结晶速率加快,结晶度增大;h-BN-KH550/PBS复合膜的热稳定性显著提高,当h-BN-KH550与PBS质量比为3∶50时,复合膜热分解过程中质量损失为5%、10%、50%时的温度(T5d、T10d、T50d)和热分解峰值温度(Tp)分别提高了30.0、22.6、9.5和10.0℃。     

Effects of mesoscopic poly(3,4-ethylenedioxythiophene) films as counter electrodes for dye-sensitized solar cells

Counter electrode coated with chemically polymerized poly(3,4-ethylenedioxythiophene) (PEDOT) in a dye-sensitized solar cell (DSSC) was studied. The surface morphology and the nature of I⁻/I₃⁻ redox reaction based on PEDOT film were investigated using Atomic Force Microscopy and Cyclic Voltammetry, respectively. The performance of the DSSCs containing the PEDOT coated electrode was compared with sputtered-Pt electrode. We found that the root mean square roughness decreases and conductivity increases as the molar ratio of imidazole (Im)/EDOT in the PEDOT film increases. The DSSC containing the PEDOT coated on fluorine doped tin oxide glass with Im/EDOT molar ratio of 2.0, showed a conversion efficiency of 7.44% compared to that with sputtered-Pt electrode (7.77%). The high photocurrents were attributed to the large effective surface area of the electrode material resulting in good catalytic properties for I₃⁻ reduction. Therefore, the incorporation of a multi-walled carbon nanotube (MWCNT) in the PEDOT film, coated on various substrates was also investigated. The DSSC containing the PEDOT films with 0.6 wt.% of MWCNT on stainless steel as counter electrode had the best cell performance of 8.08% with short-circuit current density, open-circuit voltage and fill factor of 17.00 mA cm⁻², 720 mV and 0.66, respectively.     

Thermal stability and transport studies of (100 − 2x)TeO2-xAg2O-xWO3 (7.5 ≤ x ≤ 30) glass system

Differential scanning calorimetry (DSC), infrared (IR) and direct current (DC) conductivity studies have been carried out on (100 − 2x)TeO₂-xAg₂O-xWO₃ (7.5 ≤ x ≤ 30) glass system. The IR studies show that the structure of glass network consists of [TeO₄], [TeO₃]/[TeO₃₊₁], [WO₄] units. Thermal properties such as the glass transition (T_g), onset crystallization (T_o), thermal stability (ΔT), glass transition width (ΔT_g), heat capacities in the glassy and liquid state (C_pg and C_pl), heat capacity change (ΔC_p) and ratios C_pl/C_pg of the glass systems were calculated. The highest thermal stability (237 °C) obtained in 55TeO₂-22.5Ag₂O-22.5WO₃ glass suggests that this new glass may be a potentially useful candidate material host for rare earth doped optical fibers. The DC conductivity of glasses was measured in temperature region 27-260 °C, the activation energy (E_act) values varied from 1.393 to 0.272 eV and for the temperature interval 170-260 °C, the values of conductivity (σ) of glasses varied from 8.79 × 10⁻⁹ to 1.47 × 10⁻⁶ S cm⁻¹.     

Thermomechanical properties of poly(vinyl alcohol) plasticized with varying ratios of sorbitol

The objective of this work is to study the thermal and mechanical properties of films based on blends of poly(vinyl alcohol) (PVA) with different weight percent of sorbitol. Solid-state PVA/sorbitol polymer membranes were prepared by a solution casting method. The characteristic properties of these polymer membranes were examined by thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), nanoindentation methods and by Fourier Transform Infrared (FTIR) spectroscopy. It was found that the thermal properties (glass transition, T_g, melting point, T_m and decomposition temperature, T_d) for PVA blends showed a decrease proportional to the sorbitol concentrations. The hardness and elastic modulus obtained from nanoindentation test were also found to decrease with increase in plasticizer concentration. FTIR confirmed the reduction in hydrogen bonding between PVA chains in favour of formation new bonding between the plasticizer and the PVA chains.     

PBS合成用催化剂的研究概况

选择良好的催化剂对聚丁二酸丁二醇酯(PBS)的合成至关重要.对PBS的各种催化剂进行了归纳和总结,并重点介绍了催化机理,为PBS的催化合成提供了重要的参考.     

纳米氧化石墨烯/聚丁二酸丁二醇酯复合材料的制备与性能

以天然石墨为原料,利用改进的HUMMERS'法制备了氧化石墨烯(GO);采用原位复合方式制备了纳米氧化石墨烯/聚丁二酸丁二醇酯(GO/PBS)复合材料,并对其性能进行了研究。结果表明:适量GO的加入能更有效地加快GO/PBS复合材料的结晶速度;GO的加入,提高了GO/PBS复合材料的力学性能和酶降解速率;随着GO添加量的增加,复合材料晶体尺寸减小,GO起到了成核剂的作用。     

Morphological characterization and analytical application of poly(3,4-ethylenedioxythiophene)-Prussian blue composite films electrodeposited in situ on platinum electrode chips

Electrochemical in situ preparation and morphological characterization of inorganic redox material-organic conducting polymer coatings as thin films on platinum electrodes are presented. Composite inorganic-organic coatings consist of Prussian blue (PB) and [poly(3,4-ethylenedioxythiophene)] (PEDOT), and PEDOT organic polymers doped with ferricyanide (PEDOT-FeCN). The PEDOT coating deposited from an aqueous solution containing the 3,4-ethylenedioxythiophene monomer and LiClO₄ as supporting electrolyte was used as a “reference” material (PEDOT-ClO₄). The composite coatings were prepared by electrochemical methods on platinum electrode chips, which consist of a 150 nm Pt layer deposited on 100-oriented standard 3″ silicon wafers. Electrochemical behavior of the composite inorganic-organic coatings is based mainly on inorganic component redox reactions. Different surface properties of the composite materials were studied. Thus, the roughness of the deposited films was measured by both atomic force microscopy (AFM) and profilometry, leading to roughness values ranging from 3 nm to 217 nm for PEDOT-ClO₄, and PEDOT-FeCN and PEDOT-PB coatings, respectively. AFM and Scanning Electron Microscopy pictures were also produced to characterize the film morphologies, and revealed a granular pattern of the deposited inorganic component inside the organic polymer matrix. Moreover, the adhesion properties of the composites were studied by AFM and proved to be very different from one material to the other depending on the film structure. The electrochemical responses of these composite coatings to H₂O₂ reduction were also investigated using chronoamperometry. A linear response over a concentration range from 1 × 10^− 4 to 1 × 10^− 5 M and a detection limit of 10 μM were obtained.     

Thermomechanical and flexural properties of chopped silk fiber-reinforced poly(butylene succinate) green composites: effect of electron beam treatment of worm silk

The effect of electron beam treatment on the thermomechanical and flexural properties of chopped silk fiber-reinforced poly(butylene succinate) (PBS) green composites was studied for the first time in this work. The surface topological changes in worm silk fibers before and after the electron beam irradiation at various doses (5–100?kGy) were observed. Dynamic mechanical and flexural properties and thermal expansion behavior of neat PBS and silk/PBS green composites were investigated by means of dynamic mechanical analysis, three-point flexural test, and thermomechanical analysis. The irradiated silk/PBS composite result was compared with neat PBS and un-irradiated silk/PBS counterparts. It was concluded that use of electron beam irradiation at an appropriate dosage may contribute to an enhancement of the dynamic mechanical and flexural properties as well as to the thermodimensional stability of silk-based green composites. The result revealed that the property enhancement was most profound at the electron beam absorption dose of 20?kGy.     

四针状ZnO晶须改性对ZnO/聚丁二酸丁二醇酯复合材料性能的影响

以四针状ZnO晶须（T-ZnO_W）为填料,经过表面处理与聚丁二酸丁二醇酯（PBS）复合,采用熔融共混法制备了T-ZnOw/PBS复合材料。利用FTIR表征表面改性T-ZnO_W的结构,利用SEM观察改性T-ZnO_W和T-ZnO_W/PBS复合材料的形貌,利用XRD分析改性T-ZnO_W和复合材料的结晶性能,利用TG和DSC分析复合材料的热稳定性,利用拉伸试验研究复合材料的力学性能。研究结果表明：聚乙二醇2000（PEG2000）（P）、硬脂酸（S）和硅烷偶联剂（KH560）（K）三种不同改性剂中,硬脂酸对T-ZnO_W的改性效果最佳。经硬脂酸改性T-ZnO_W（ST-ZnO_W）,表面负载有机活性基团,表面粗糙度增加且与纯PBS之间界面结合力增强,使ST-ZnO_W/PBS复合材料的热稳定性和力学性能明显得到改善。热分解过程中质量损失10%的温度（T_d-10%）和最大热分解温度（T_d-max）较纯PBS分别提高了37.7℃和35.3℃;拉伸强度、断裂伸长率和弹性模量分别提高了17.7%、140.5%和95.4%。     

Polyethersulfone-expanded graphite nanocomposites: Charge transport and impedance characteristics

Polyethersulfone (PES)-expanded graphite nanocomposites have been prepared by solution blending route after sonicating expanded graphite in dichloromethane. It has been observed that ultrasonication results in nanosheets formation leading to a low percolation threshold of 3 wt.%. At 5 wt.% filler loading the conductivity is of the order of 10⁻² S/cm. Hopping type of charge transport occurs at 3.2 wt.% expanded graphite in PES below which capacitive effects couple. The effective dielectric constant at low frequency increases with filler concentration. Impedance measurement has been carried out to evaluate interfacial capacitance which, for 3.2 wt.% expanded graphite addition in PES, increases to 110 pF from 32 pF for 1 wt.% expanded graphite in the polymer. DSC analysis shows an increment of 12 °C in the T_g of PES with 3 wt.% expanded graphite suggesting interaction between the polymer and filler.     

微晶纤维素/聚丁二酸丁二醇酯复合材料的流变行为

采用熔融共混法制备了微晶纤维素/聚丁二酸丁二醇酯(MCC/PBS)复合材料,用高级毛细管流变仪和旋转流变仪分别测定复合材料的稳态流变性能和动态流变性能,研究了不同MCC含量、不同温度对复合材料流变行为的影响。结果表明,复合材料的黏度与剪切速率的流变曲线符合幂律流体的特征,可以用幂律模型对其进行拟合;复合材料的黏度与温度的关系可用Arrhenius方程对其进行描述。在线性黏弹区,复合材料的储能模量(G′)维持恒定,当应变(γ)超过临界值(γ_c)时,复合材料进入非线性黏弹区,出现了"Payne"效应,并且随着MCC含量的增加,γ_c下降。在角频率(ω)扫描范围内,复合材料的储能模量(G′)、损耗模量(G″)和复数黏度|η*|均随着MCC含量的增加而增大。在相同的MCC含量下,G″的值始终大于G′的值,损耗因子(tanδ)均大于1。在低频区,G′出现第二平台。MCC/PBS复合材料加工流变特性的研究,对指导MCC/PBS复合材料的成型加工具有一定的价值。