Characterisation of gamma‐irradiated polyetherimide films with infrared spectroscopy and thermally stimulated current measurements

The performance of insulators is usually affected by the presence of space charges. The evolution of these charges under applied constraints in many cases leads to the degradation of these materials. To evaluate the performance of an insulator it is necessary to study the evolution of the physical and chemical properties in the presence of space charges. In this paper, the effect of gamma irradiation on the space charge behaviour in polyetherimide (PEI; Ultem 1000) has been investigated at different radiation doses. Space charge measurements were made using thermally stimulated currents. Infrared spectroscopy characterisation was performed to investigate the effect of gamma irradiation on the physicochemical properties of PEI. The results obtained show minor differences in the infrared spectra, mainly in the 410 cm^?1 region. It is found that irradiation leads to a few structural changes in the material. The thermostimulated depolarisation current (TSDC) results show that β relaxations in PEI are affected by gamma irradiation. The activation energies of dipoles were calculated from the TSDC curves. Copyright © 2006 Society of Chemical Industry     

Investigation of electrical and optical properties of polyvinyl acetate doped with some polymers

Polyglycerol (PG) and polytriethanolamine(PTEA) have been prepared. The electrical resistivity (ρ) and the optical absorption of polyvinylacetate (PVAc) doped with polyglycerol (PG), polyaniline (PA), and polytriethanolamine (PTEA) have been studied. It was found that the conduction was mainly ionic in the temperature range from 20 to 120°C. The resistivity decreased with the increase of the dopant cocentration. The optical absorption spectra were determined in the wavelength range 400–2500 nm. The analysis of the absorption spectra showed that the intensity of the bands is remarkably affected by the dopant concentration. The optical energy gap of pure PVAc and the samples containing different dopants were estimated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1558–1563, 2002     

Effect of clay on the properties of poly(styrene‐co‐acrylonitrile)–clay nanocomposites

Clay‐dispersed poly(styrene‐co‐acrylonitrile) nanocomposites (PSAN) were synthesized by a free radical polymerization process. The montmorillonite (MMT) was modified by a cationic surfactant hexadecyltrimethylammonium chloride. The structures of PSAN were determined by wide‐angle X‐ray diffraction and FTIR spectroscopy. The dispersion of silicate layers in the polymer matrix was also revealed by transmission electron microscopy (TEM). It was confirmed that the clay was intercalated and exfoliated in the PSAN matrix. The increased thermal stability of PSAN with the addition of clay was observed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The dielectric properties of PSAN were measured in the frequency range 100 Hz to 1 MHz at 35–70°C. It was found that the dielectric constant from the dipole orientation had been suppressed due to the intercalation of clay. The dielectric loss is strongly related to the residual sodium content of clay, which increases as the sodium content increases by the addition of clay. Copyright © 2004 Society of Chemical Industry     

Tribological properties of micro‐ and nanoparticles‐filled poly(etherimide) composites

It has been found that nano‐ or microsized inorganic particles in general enhance the tribological properties of polymer materials. In the present study, 5 vol % nano‐TiO₂ or micro‐CaSiO₃ was introduced into a polyetherimide (PEI) matrix composite, which was filled additionally with short carbon fibers (SCF) and graphite flakes. The influence of these inorganic particles on the sliding behavior was investigated with a pin‐on‐disc testing rig at room temperature and 150°C. Experimental results showed that both particles could reduce the wear rate and the frictional coefficient (μ) of the PEI composites under the applied testing conditions. At room temperature, the microparticles‐filled composites exhibited a lower wear rate and μ, while the nano‐TiO₂‐filled composites possessed the lowest wear rate and μ at elevated temperature. Enhancement in tribological properties with the addition of the nano‐particles was attributed to the formation of transfer layers on both sliding surfaces together with the reinforcing effect. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1678–1686, 2006     

Preparation and characterization of acrylic latex/nano‐SiO2 composites

Acrylic/nano‐silica composite latexes were prepared by blending via high shear stirring (SS) or ball milling (BM) and in situ polymerization (IS). For comparison, composites filled with micro‐silica were also prepared. The mechanical and optical properties of the polymers formed by the composite latex filled with nano‐ or micro‐silica were investigated using an Instron testing machine, by dynamic mechanical analysis, ultraviolet–visible spectrophotometry and transmission electron micrography. The results showed that SS and BM methods could obtain better nanocomposite latex and polymers than the IS method, characterized by better dispersion of nanoparticles, higher tensile strength and T_g for SS and BM than for IS. The increase in absorbance and reduction in transmittance of UV (290–400 nm wavelength) were observed as nano‐silica content increased, whereas the UV absorbance or transmittance basically were kept unchanged for the composites filled with micro‐silica. © 2002 Society of Chemical Industry     

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     

Preparation and high oxygen‐enriching properties of cross‐linking polydimethylsiloxane/SiO2 nanocomposite membranes for air purification

Nanocomposite membrane based on polydimethylsiloxane (PDMS) and nanoscale SiO₂ particles were prepared by a convenient and mild sol–gel copolymerization of tetraethoxysilane as well as cross‐linking reaction. The oxygen‐enriching properties of cross‐linking PDMS/SiO₂ nanocomposite membranes containing different silica conversion and SiO₂ contents were investigated. The results showed that the nanocomposite membranes exhibited good membrane‐forming ability, superior mechanical properties, and high solvent resistance as well as excellent oxygen‐enriching properties for air purification. The oxygen‐enriching performance was regulated by the organic/inorganic ratio and silica conversion in the sol–gel synthesis process. Permeability and selectivity could increase simultaneously with the addition of nanoscale SiO₂. The oxygen permeation coefficient of the nanocomposite membrane increased to 680 Barrer and oxygen/nitrogen separation factor kept 3.0 or so, both higher than those of the corresponding pure PDMS membrane. The high oxygen‐enriching properties of the nanocomposite membranes arose from the introduction of SiO₂ particles, the sol–gel copolymerization, and cross‐linking method. © 2012 American Institute of Chemical Engineers AIChE J, 59: 650–655, 2013     

Characterization of SiO2 and Al2O3 incorporated PVdF‐HFP based composite polymer electrolytes with LiPF3(CF3CF2)3

Lithium fluoroalkylphosphate (LiPF₃(CF₃ CF₂)₃) based composite polymer electrolytes (CPE) have been prepared in the matrix of polyvinylidenefluoride‐hexafluoropropylene(PVdF‐HFP), using solvent casting technique. The membranes were gelled with ethylene carbonate and diethyl carbonate as a plasticizer and nanosized SiO₂ and nanoporous Al₂O₃ as fillers. These membranes were subjected to a.c. impedance, DSC, SEM, FTIR, and Fluorescence studies. The a.c. impedance studies and activation energy calculation reveal that 2.5 wt % fillers containing membranes only exhibit maximum conductivity for SiO₂ (1.16 mS cm^?1) and Al₂O₃ (0.98 mS cm^?1), compared to fillers free membranes and beyond 2.5 wt % of such fillers the conductivity tends to decrease. The enhancement of conductivity has been explained in terms of Vogel‐Tamman‐Fulcher (VTF) theory. Molecular interactions by FTIR and local viscosity environment by fluorescence studies have been investigated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of nano‐SiO2 reinforced alginate‐based nanocomposite films (II)

Crosslinked alginate‐based nanocomposites at different SiO₂ contents were prepared successfully by blending the nano‐SiO₂ solution into low concentration alginate solution (0.5 wt %), with the alginate concentration increased step by step to the resulted concentration, in this course glycerol was used as plasticizer and 5 wt % CaCl₂ as crosslinker. The combined effect of SiO₂ content (1.5–8 wt %) on the microstructural, physical, mechanical, and optical properties of the nanocomposite films were investigated. The results showed that tensile strength and elongation was improved by about 40.33% and 89%, respectively, upon increasing the SiO₂ content to 4.5 wt %. In addition, water vapor permeability and swelling degree decreased by 19% and 16% with increasing SiO₂ content up to 8 and 4.5 wt %, respectively with respect to pure crosslinked alginate film. Thermogravimetric analysis also revealed that nano‐SiO₂ can improve the thermal stability of sodium alginate films produced by this method. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45286.     

Preparation and property of raspberry‐like AS/SiO2 nanocomposite particles

Surfactant‐free poly(acrylonitrile‐co‐styrene)/silica (AS/SiO₂) nanocomposite particles was synthesized in the presence of cheap, commercially amorphous aqueous silica sol at ambient temperature. Thermogravimetric analysis (TGA) indicated silica contents ranging from 5 wt % to 29 wt %, depending on reaction conditions. Particle size distributions and morphologies were studied using dynamic light scattering (DLS) and transmission electron microscopy (TEM), which clearly showed that most of the colloidal nanocomposites comprised approximately spherical particle with raspberry‐like morphology and relatively narrow size distributions. The optical clarity of solution‐cast nanocomposite films was assessed using UV–vis spectrometer, with high transmission being obtained over the whole visible spectrum. Differential scanning calorimetry (DSC) studies showed that the glass transition temperature of AS/SiO₂ nanocomposites can be higher than the corresponding pure AS, resulting from the hydrophilicity of the nanometer silica. The robustness and simplicity of this method may make large‐scale manufacture of this nanocomposite possible. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 415–421, 2007     

Miscibility of polymer blends of poly(styrene‐co‐4‐hydroxystyrene) with bisphenol‐A polycarbonate

The miscibility of blends of bisphenol‐A polycarbonate (BAPC) and tetramethyl bisphenol‐A polycarbonate (TMPC) with copolymers of poly(styrene‐co‐4‐hydroxystyrene) (PSHS) was studied in this work. It has been demonstrated that BAPC is miscible with PSHS over a region of approximately 45–75 mol % hydroxyl groups in the copolymer. TMPC has a wider miscible window than BAPC when blended with PSHS. The blend miscibility was considered to be driven by the intermolecular attractive interactions between the hydroxyl groups of the PSHS and the π electrons of the aromatic rings of both polycarbonates (PCs). As the FTIR measurements showed, after blending of BAPC with PSHS, there is no visible shift of the carbonyl band of BAPC at 1774 cm⁻¹, whereas the stretching frequency of the free hydroxyl groups of the copoly‐ mers at 3523 cm⁻¹ disappeared. The large positive values of the segment interaction energy density parameter B_st‐HS calculated from the group contribution approach indicated that the intramolecular repulsive interaction may also have played a role in the promotion of the blend miscibility. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 639–646, 1999     

Study of viscoelastic properties of nanocomposites of SiO2–acrylonitrile–butadiene–styrene

Nanocomposites of acrylonitrile–butadiene–styrene (ABS) and nanosilica with different nanoparticle sizes and various loadings are prepared. Rheological experiments such as frequency sweep, strain sweep, and rotational test are performed to investigate the influence of nanoparticle loading and size on the viscoelastic properties of the nanocomposites. The results show that nanocomposites with higher filler loading and smaller particle size have both higher storage and loss moduli. Moreover, the results indicate that the storage modulus is more sensitive than loss modulus to filler loading and nanoparticle size. The smaller nanoparticles and higher filler loadings lead to the enhancement of nanoparticle surface area so that the viscoelastic properties are intensified through increase of polymer chain adsorption on nanoparticle, and creation of a network structure in the nanocomposites. The network structure causes changes to the rheological behavior of the nanocomposite such as solid‐like behavior in the low‐frequency region and reduction of the Newtonian region. The scanning electron microscopy micrographs revealed that the particle aggregates increase with particle size reduction and increasing nanoparticle content. We also used a nonlinear optimization to obtain the parameters of a multimode Maxwell model for low nanofiller content ABS/SiO₂ nanocomposites and found the relaxation times of the polymer chains increased with increasing nanoparticle content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Crystallization behavior and crystal structure of poly(ethylene‐co‐trimethylene terephthalate)s

A series of random copolymers were synthesized by the bulk polycondensation of dimethyl terephthalate with ethylene glycol (EG) and propane‐1,3‐diol (PDO) in various compositions. Their composition and thermal properties were investigated. The copolymers with 57.7 mol % or more PDO or 14.4 mol % or less PDO were crystallizable, but those with 36–46.2 mol % PDO were amorphous. The nonisothermal crystallization behavior was investigated with varying cooling rates by DSC. Poly(ethylene terephthalate) (PET) and poly(trimethylene terephthalate) (PTT) homopolymers have relatively lower activation energy than their copolymers. PET‐rich copolymers (EG > 85.9%) exhibited PET crystal structure, and exhibited no PTT crystal structure; and PTT‐rich copolymers (PDO > 41.7%) exhibited PTT crystal structure, and exhibited no PET crystal structure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Alumina‐filled polystyrene micro‐ and nanocomposites prepared by melt mixing with and without latex precompounding: Structure and properties

Alumina fillers were incorporated in polystyrene (PS) in 4.5 wt % by melt blending with and without latex precompounding. Latex precompounding was used for the latex‐mediated predispersion of the alumina particles. The related masterbatch was produced by mixing PS latex with water dispersible boehmite alumina in various particle sizes followed by drying. The dispersion of the alumina in the PS was studied by transmission and scanning electron microscopy (TEM and SEM, respectively). The mechanical and thermomechanical properties of the PS composites were determined in uniaxial tensile, dynamic‐mechanical thermal analysis (DMTA), and short‐time creep tests performed at various temperatures. In addition, the melt flow of the composites was characterized in a plate/plate rheometer. It was found that direct melt mixing of the alumina with PS resulted in micro‐, whereas the masterbatch technique in nanocomposites. The stiffness and resistance to creep (summarized in master curves) of the nanocomposites were improved compared to those of the microcomposites. The properties of the composites were upgraded by decreasing nominal size of the water dispersible alumina. The preparation technique and the size of the alumina particles affected the tensile strength, melt viscosity, and heat distortion temperature in lesser extent than the stiffness and thus compliance data. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Polymer gel electrolytes prepared from P(EG‐co‐PG) and their nanocomposites using organically modified montmorillonite

Polymer gel electrolytes were prepared by thermal crosslinking reaction of a series of acrylic end‐capped poly(ethylene glycol) and poly(propylene glycol) [P(EG‐co‐PG)] having various geometries and molecular weights. Acrylic end‐capped prepolymers were prepared by the esterification of low molecular weight (M_n: 1900–5000) P(EG‐co‐PG) with acrylic acid. The linear increase in the ionic conductivity of polymer gel electrolyte films was observed with increasing temperature. The increase in the conductivity was also monitored by increasing the molecular weight of precursor polymer. Nanocomposite electrolytes were prepared by the addition of 5 wt % of organically modified layered silicate (montmorillonite) into the gel polymer electrolytes. The enhancement of the ionic conductivity as well as mechanical properties was observed in the nanocomposite systems. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 894–899, 2004     

Study of relaxations in poly(methyl methacrylate)–magneto electrets by thermally stimulated depolarization current and surface‐charge‐decay mechanisms

The effect of the forming temperature and the magnetic field was investigated for the charge retention and stability of poly(methyl methacrylate) (PMMA)–magneto electret (ME) samples with thermally stimulated discharge currents (TSDCs) and a surface‐charge‐decay mechanism. The measurements were performed on a pristine PMMA sample with a thickness of 20 mm. The comparative studies of charge decay with TSDC indicated a strong resemblance between the results of the two techniques of MEs of PMMA and were characterized by two TSDC peaks, that is, an α peak at 110°C and a ρ peak at 160°C. The low‐temperature peak (i.e., the α peak) was associated with dipolar relaxation, and the high‐temperature peak (i.e., the ρ peak) was attributed to the self‐motion of space charges in PMMA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Carbon nanotube/graphene oxide‐added CaO‐B2O3‐SiO2 glass/Al2O3 composite as substrate for chip‐type supercapacitor

A CaO‐B₂O₃‐SiO₂ (CBS) glass/40 wt% Al₂O₃ composite sintered at 900°C exhibited a dense microstructure with a low porosity of 0.21%. This composite contained Al₂O₃ and anorthite phases, but pure glass sintered at 900°C has small quantities of wollastonite and diopside phases. This composite was measured to have a high bending strength of 323 MPa and thermal conductivity of 3.75 W/(mK). The thermal conductivity increased when the composite was annealed at 850°C after sintering at 900°C, because of the increase in the amount of the anorthite phase. 0.25 wt% graphene oxide and 0.75 wt% multi‐wall carbon nanotubes were added to the CBS/40 wt% Al₂O₃ composite to further enhance the thermal conductivity and bending strength. The specimen sintered at 900°C and subsequently annealed at 850°C exhibited a large bending strength of 420 MPa and thermal conductivity of 5.51 W/(mK), indicating that it would be a highly effective substrate for a chip‐type supercapacitor.     

Preparation and characterization of poly(styrene‐co‐butadiene) and polybutadiene rubber/clay nanocomposites

Poly(styrene‐co‐butadiene) rubber (SBR) and polybutadiene rubber (BR)/clay nanocomposites have been prepared. The effects of the incorporation of inorganically and organically modified clays on the vulcanization reactions of SBR and BR were analysed by rheometry and differential scanning calorimetry. A reduction in scorch time (t_s1) and optimum time (t₉₅) was observed for both the rubbers when organoclay was added and this was attributed to the amine groups of the organic modifier. However, t_s1 and t₉₅ were further increased as the clay content was increased. A reduction in torque value was obtained for the organoclay nanocomposites, indicating a lower number of crosslinks formed. The organoclays favoured the vulcanization process although the vulcanizing effect was reduced with increasing clay content. The tensile strength and elongation of SBR were improved significantly with organoclay. The improvement of the tensile properties of BR with organoclay was less noticeable than inorganic‐modified clay. Nevertheless, these mechanical properties were enhanced with addition of clay. The mechanical properties of the nanocomposites were dependent on filler size and dispersion, and also compatibility between fillers and the rubber matrix. Copyright © 2004 Society of Chemical Industry     

Modeling the stress‐relaxation behavior of wool fibers

The stress‐relaxation behavior of wool fibers after a pretreatment with a chemical solution is particularly important for evaluating the efficiency of the pretreatment. In this study, three viscoelastic models, including the Maxwell, two Maxwell unit, and modified two Maxwell unit models, were established first. To verify the feasibility of the models, stress‐relaxation experiments for wool fibers were performed. The wool fibers were pretreated with a sodium bisulfite solution (1 and 3%) at various temperatures (293, 298, 303, 308, 313, and 318 K). Then, the experimental values were fitted to the three models to obtain the rate constants of relaxation. The activation energy of the wool fibers was calculated with the Arrhenius equation. The results showed that the modified two Maxwell unit model provided the best fit for the experimental data of the wool fibers. The stress‐relaxation process of the wool fibers could be divided into two stages, a rapid stage followed by a slow stage. The rapid relaxation of stress was attributed to the weak bonds in the wool fibers, and the following slow relaxation stage was attributed to strong bonds. The Arrhenius equation could describe the stress‐relaxation process of the wool fibers very well. Furthermore, the activation energy decreased in the presence of sodium bisulfite. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of posttreatment on morphology and properties of poly(ethylene‐co‐vinyl alcohol) microporous hollow fiber via thermally induced phase separation

Poly(ethylene‐co‐vinyl alcohol) (EVOH) hollow fiber membranes were prepared by thermally induced phase separation (TIPS) process. Water, methanol, and acetone were used to extract the diluents in the fibers, respectively. Bigger shrinkage of fibers during extractant evaporation was observed when water or methanol was used. Their interaction parameters with EVOH were calculated via Hansen solubility, respectively. The mechanism of hollow fiber volume shrinkage was discussed. It was found that affinity of the extractant with polymer was the critical factor except for the surface tension of extractant. Through the X‐ray diffraction analysis during extraction and evaporation, the crystallization behavior of the polymer was studied. From the SEM photos, it was observed that the volume shrinkage was derived from the collapse of porous structure. The fiber sample extracted by acetone had similar morphology with the sample freeze‐dried. The gas and water permeability were also measured and the results were coincident with the morphology of fibers and shrinkage data. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4106–4112, 2007