Enhanced Heat Resistance Research Articles

Constructing network structure of graphene nanoplatelets/carbon nanofibers in polystyrene and the resultant heat resistance, thermal and conductive properties

Polystyrene (PS) composites containing graphene nanoplatelets (GNPs) and carbon nanofibers (CNFs) were prepared through solution compounding processing. The results showed that more compact network structure was formed in the ternary PS/GNP/CNF composites, and the composites exhibited apparently enhanced heat resistance compared with the pure PS sample. Conductive properties measurements showed that largely reduced percolation threshold was achieved for the ternary PS/GNP/CNF composites. Furthermore, the PS/GNP/CNF composites had good thermal conductivity. At GNP content of 2 vol% and CNF content of 5.5 vol%, the thermal conductivity was enhanced to 1.12 W/mK, which was 522% higher than that of the pure PS sample. The potential application of the PS composites as the material of heat radiator was also evaluated, and the results showed that the composites exhibited excellent heat transferring ability. This work indicates that the PS/GNP/CNF composites may be used in the field relating to high temperature and load conditions.

Facile synthesis of fluorinated poly(arylene ether nitrile) and its dielectric properties

ABSTRACTA new class of specialty polymer, fluorinated poly(arylene ether nitrile) (PAEN‐F), was synthesized via the aromatic nucleophilic substitution reaction. Due to its rigid structure, PAEN‐F exhibited enhanced heat resistance and thermal stability. Consequently, the glass‐transition temperature and initial degradation temperature of PAEN‐F reached as high as 179°C and 554°C, respectively. PAEN‐F also showed excellent solubility in low‐boiling solvents owing to fluorine groups and the nonplanar structure in the repeat unit. Due to its strong 6F dipoles, PAEN‐F exhibited a high dielectric constant (ɛr) of 3.6, a high electrical breakdown strength of 346 MV/m, and a reasonably low dissipation factor (tan δ) of 0.014 at 25°C and 100 Hz. Therefore, this dipolar glass polymer is promising for high‐temperature and low‐loss electric energy storage applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46837.

Synthesis of Thermally Stable Reactive Polyurethane and Its Physical Effects in Epoxy Composites

A flame retardant polyol (EP-DOPO) with epoxy functional groups was synthesized by reacting a 1,6-hexanediol glycidyl ether with a flame retardant 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phospha-phenanthrene-10-oxide (DOPO). The polyurethane (EPPU) with enhanced heat resistance was prepared by the reaction of a polyol blend of EP-DOPO and polytetrahydrofuran (PolyTHF) at a ratio of 1:1 with isophorone diisocyanate. EPPU useful for the preparation of cables or coatings showed higher thermal decomposition temperature rather than that of reference polyurethane synthesized by the reaction between pure PolyTHF and isophorone diisocyanate by thermogravimetric analysis. Further study of the polyurethane as a toughening agent for epoxy polymers was carried out. Epoxy compositions consisting of bisphenol A epoxy resin and dicyandiamide as a hardener have a brittle property allowing crack propagation after cure. Polyurethane plays an important role as an impact modifier to prevent from cracks of epoxy polymers. Various contents of EPPU were added into epoxy compositions to measure the physical property changes of epoxy polymers. The tensile and flexural strengths of the cured specimen were compared with those of epoxy compositions including reference polyurethane. Furthermore, the crosslink density of the cured epoxy compositions was compared.

Organo-Mineral Composite Materials Based on Sodium Liquid Glass, Tolylene-2,4-diisocyanate, Epoxy Oligomer, and Polyisocyanate

Organo-mineral composite materials based on sodium liquid glass combined with tolylene-2,4-diisocyanate (TDI), polyisocyanate, and epoxy oligomer have been synthesized. When heated, the organic components of the composites form a polymer network through the trimerization reaction and TDI curing of the epoxy oligomer. The composite materials after heating to 130°C have a uniform structure. The resulting hybrid composite materials are not brittle and exhibit enhanced heat resistance as compared to common polyisocyanurate compositions. Hybrid composites can find wide application in various fields of engineering.

Synthesis of zinc sulfide nanoparticles and their incorporation into poly(hydroxybutyrate) matrix in the formation of a novel nanocomposite

In the present study, zinc sulfide (ZnS) nanoparticles (NPs) were successfully synthesized through a modified chemical precipitation protocol and then mediated into poly(hydroxybutyrate) (PHB) matrix to get ZnS/PHB nanocomposite. Mean diameter and zeta potential of ZnS NPs, as determined using dynamic light scattering technique (DLS), were observed to be 53 nm and −89 mV, respectively. The structural investigations performed using x-ray diffraction (XRD) technique depicted the phase purity of ZnS NPs exhibiting cubic crystal structure. Fourier transform infrared (FTIR) spectroscopic analysis was conducted to identify the presence or absence of bonding vibrational modes on the surface of synthesized single phase ZnS NPs. The FTIR analysis confirmed the metal to sulphur bond formation by showing the characteristic band at 1123 cm−1. The UV–vis absorption spectra of ZnS NPs confirmed the synthesis of particles in nanoscale regime showing a λmax of 302 nm. These NPs were then successfully incorporated into PHB matrix to synthesize ZnS/PHB nanocomposite. The synthesis of nanocomposite was confirmed by EDX analysis. The chemical bonding and structural properties of ZnS/PHB nanocomposite were determined by FTIR and XRD analysis, respectively. The FTIR analysis confirmed the synthesis of ZnS/PHB nanocomposite. Moreover, XRD analysis showed that structure of nanocomposite was completely controlled by ZnS NPs as pure PHB exhibited orthorhombic crystal structure while the nanocomposite demonstrated cubic crystal structure of ZnS. Thermal properties of nanocomposite were studied through thermogravimetric analysis revealing that the incorporation of ZnS NPs into PHB matrix lead to enhance heat resistance properties of PHB.

Aromatic Copolyether Ether Ketones Derived From Hydroquinone

Data are given on aromatic copolyether ether ketones obtained from aromatic diols, namely, hydroquinone and diphenylolpropane (Bisphenol A). The copolyethers were synthesized by high–temperature copolycondensation of the corresponding diols with 4,4'–difluorobenzophenol. The dependence of the rheological and thermochemical properties of the polymer samples on the mole ratio of the diphenols was studied for a broad range of monomer concentrations. Enhanced heat resistance along with decreased intrinsic viscosity and glassy point temperature were found for copolyether ether ketones with a greater content of hydroquinone.

Synthesis and Application of Pyrrolidone-containing Shale Inhibitors

New generation polyamine inhibitors are amino-terminated polyethers with excellent inhibiting capabilities; they play a key role in borehole stabilization and reservoir protection. However, polyamine inhibitors are limited by their poor thermal stability, which can be attributed to the presence of ether bonds in their molecular structures. We propose a three-step synthesis approach fora novel pyrrolidone-containing polyamine inhibitor (DYNP) by introducing N-vinyl-2-pyrrolidone (NVP) on divinyloxyethane. This polyamine inhibitor exhibits an optimized molecular structure and has enhanced heat resistance. Characterizations by infrared (IR) spectroscopy and evaluation tests demonstrate several advantages of DYNP inhibitors, including excellent inhibiting capability (superior to similar materials such as polyamines), improved heat resistance (reasonable stability at temperatures up to 240°C), and good compatibility with both fresh water and salt water drilling fluids. These can be attributed to the presence of considerable amounts of amino groups in the repeating unit of DYNP molecules. The DYNP inhibitor was applied in over 20 boreholes in tight oil blocks in Daqing Oilfield to relieve hydration of formations with high shale contents. For instance, drilling in the 2033.5m horizontal section of Dragon 2 borehole was smooth, with a borehole diameter expansion ratio below 10%.

Catalytic curing of epoxy–anhydride binders under the action of azo compounds

A series of azo compounds were studied by differential scanning calorimetry as catalysts of the reaction of UP-643 epoxy–novolac resin with various anhydrides. The latency of the catalysts was revealed. The principal possibility of making epoxy formulations with long pot life, from 10 to 30 days at room temperature, and curing at elevated temperatures to obtain network polymers and composites with high physicomechanical and thermomechanical characteristics was demonstrated. The polymers prepared in the presence of azo compounds with functional groups exhibit increased glass transition point and, correspondingly, enhanced heat resistance.

High-temperature chemical transformations of tetracarboxylic acid dianhydrides with aromatic diamines in rolivsan matrix

Thermochemical transformations of ternary thermosetting systems consisting of rolivsans, aromatic tetracarboxylic acid dianhydrides, and aromatic diamines were studied by dynamic mechanical and thermal analysis. The influence of the composition and curing conditions of these systems on the thermomechanical properties of new glassy network block copolymers exhibiting enhanced heat resistance was determined.

Influence of lactic acid and post-treatment recovery time on the heat resistance of Listeria monocytogenes

The aim of this study was to evaluate the effect of lactic acid (LA) with and without organic material at various post-treatment recovery times on the heat resistance of Listeria monocytogenes (Lm). LA decreased Lm numbers; however, the effect was remarkably attenuated by the presence of organic matter. Five strains of Lm were treated with LA and the listericidal effects were compared. The effect of LA varied depending on the strain, with ≥3.0% (w/w) LA required to kill the Lm strains in a short time. The heat resistance of Lm treated with LA was examined with respect to the time interval between the acid treatment and the subsequent manufacturing step. The heat resistance of Lm was shown to significantly increase during the post-treatment period. Heat tolerance (D value) increased up to 3.4-fold compared with the non-treated control bacteria. RNA sequencing and RT-PCR analyses suggested that several stress chaperones, proteins controlled by RecA and associated with high-temperature survival, were involved in the mechanism of enhanced heat resistance. These results are applicable to manufacturers when LA and heat treatment methods are utilized for the effective control of Lm in foods.

Chemical modification of rolivsans with epoxy resins

New glassy network copolymers exhibiting enhanced heat resistance were prepared by thermochemical transformations of rolivsans modified with small amounts (5 ± 3%) of epoxy resins. The influence of the composition of these copolymers on their thermomechanical properties was evaluated by performing dynamic mechanical and thermal analysis and by studying the temperature dependences of the ultimate strength at three-point bending.

Layer structure by shear-induced crystallization and thermal mechanical properties of injection-molded poly(l-lactide) with nucleating agents

A unique oscillation shear injection molding was utilized to investigate the crystallization of poly (l-lactide) (PLLA) under the coexistence of an intense shear flow and nucleating agents. The crystalline morphology and its distribution of injection-molded PLLA were probed by wide-angle X-ray diffraction, showing that an intense shear flow promotes the crystallization significantly, whereas the nucleation effect by nucleating agents is negligible. Additionally, applying an intense shear flow during injection molding processing at a low mold temperature makes PLLA form a crystalline layer structure, including skin, intermediate and core layers. Meanwhile, nucleating agents were found to play different roles in the crystallization of injection-molded PLLA under different processing conditions. The results of thermal mechanical property and Vicat softening temperature show the injection-molded PLLA sample with a thick crystalline layer structure has a greatly enhanced heat resistance property.

Enzyme-polymer hybrid nanogels fabricated by thiol-disulfide exchange reaction

In this paper a novel method for the fabrication of hybrid nanogels based on thiol-disulfide exchange reaction is reported. Poly(oligo(ethylene glycol) monomethyl ether methacrylate-co-di(ethylene glycol) methyl ether methacrylate-co-2-(2-pyridyldisulfide) ethyl methacrylate) (POEGMA-co-PDEGMA-co-PDSMA) was synthesized by reversible addition-fragmentation chain transfer polymerization. Pyridyl disulfide functionalized porcine pancreatic lipase (PPL-S-S-Py) was prepared by treatment of PPL with Traut’s reagent (2-iminothiolane) and 2,2′-dithiodipyridine. Upon addition of meso-2,3-dimercaptosuccinic acid into aqueous solutions of PPL-S-S-Py and POEGMA-co-PDEGMA-co-PDSMA, enzyme-polymer hybrid nanogels were prepared. The hybrid nanogels show thermal responsiveness. With an increase in the content of PPL in the nanogels, the lower critical solution temperature (LCST) shifts to the higher temperature. At a temperature below LCST, PPL molecules are in the shells of the nanogels, and at a temperature above LCST, PPL molecules are embedded inside the nanosized structures. The immobilized PPL show enhanced heat resistance and good reusability.

Induction of heat resistance in wheat seedlings by exogenous calcium, hydrogen peroxide, and nitric oxide donor: functional interaction of signal mediators

Functional interactions of calcium ions, hydrogen peroxide, and nitric oxide as signal mediators in root cells of wheat (Triticum aestivum L.) seedlings upon induction of their heat resistance was studied with use of inhibitor-based analysis. Treatment of the seedlings with hydrogen peroxide or a combination of calcium chloride with ionophore A23187 significantly increased their content of nitric oxide, which peaked 0.5–1 h after the start of the treatment. CaCl2 or exogenous NO donor (sodium nitroprusside, SNP) transitorily increased the hydrogen peroxide level in the roots. Seedlings pretreatments with calcium chelator (EGTA), blocker of Ca2+ channels (LaCl3), inhibitor of phospholipase C (neomycin), or antagonist of cyclic adenosine-5'-diphosphatribose formation (nicotinamide) more or less prevented the rise in the nitric oxide content in roots caused by exogenous H2O2; the SNP-induced rise in hydrogen peroxide was also damped down. However, the seedlings pretreatment with antioxidants ionol or dimethylthiourea did not hinder the increase in the NO level, which was caused by exogenous Ca2+. The inhibitors of NO synthase (NG-nitro-L-arginine methyl ester, L-NAME) or nitrate reductase (sodium tungstate) did not interfere in the accumulation of H2O2 in root tissues stimulated by exogenous calcium. Calcium antagonists diminished the seedlings heat resistance increased by hydrogen peroxide or SNP. Antioxidants and inhibitors of NO synthase or nitrate reductase weakened the calcium-stimulated enhancement in the seedlings heat resistance. It was concluded that calcium may activate NO- and H2O2-generating enzymatic systems as well as participate in the transduction of signals of these mediators into genetic apparatus and in the formation of physiological reactions underlying the enhanced heat resistance.

Enhanced Heat Resistance of Al-Cu-Mg Alloy by a Combination of Pre-stretching and Underaging

Enhanced heat resistance of Al-Cu-Mg alloy by employing a combined effect of pre-stretching and underaging has been characterized by thermal exposure, tensile testing, transmission electron microscopy (TEM) examination, and quantitative analysis. Tensile testing results showed that the samples subjected to both pre-stretching and underaging processing, presented a high tensile strength up to 440 MPa after thermal exposure at 200 °C for 500 h. This suggests that the long-time application temperature of Al-Cu-Mg alloys, which were normally applied at elevated temperature below 150 °C or even below 100 °C, can be raised to 200 °C by employing a combined effect of pre-stretching and underaging. TEM results showed that a fine and a narrow size distribution range of S′ phase was formed by the combined processing of pre-stretching and underaging, as compared to that without pre-stretching. Quantitative analysis results indicated that this narrow range of size distribution greatly reduced the growth rate of S′ phase during thermal exposure. It is suggested that this effect was ascribed to the Ostwald ripening mechanism.

Progress in improving high-temperature properties of thermosetting resins: development of the microheterogeneous model for the formation of crosslinked rolivsan-epoxy blends

Thermochemical transformations in blends of rolivsans (ROLs, i.e., compositions of (di)vinylaromatic ethers and thermosensitive (di)methacrylates) with epoxy resins were used to obtain new glassy heat resistant highly crosslinked ROLs/epoxy blends (block copolymers) which differ in composition, crosslink density, chemical, topological and morphological structure. The influence of the ROLs/epoxy blocks ratio in the blends and temperature-time regimes of curing on heat resistant properties of the materials was estimated by studying temperature dependences of breaking strength at three-point flexural test, dynamical elastic modulus, mechanical loss tangents (in dynamic mechanical analysis, DMA) and thermooxidative aging processes. Unusually high values of high temperature strength of the epoxy-modified ROLs were reached when using a new method for enhancing heat resistance and thermal stability of microheterogeneous network polymers (cured resins) consisting of highly crosslinked microdomains. These microdomains are weakly bound to each other by defective polymer interlayers. This method is illustrated by the example of transformations in ROLs/epoxy blends; it suggests (macro)molecular design and curing development. The method involves functionalization of microdomains, target delivery of epoxies into interlayers and carrying out high temperature chemical reactions in these interlayers. These reactions lead to additional crosslinking of supramolecular formations (highly crosslinked ROL microdomains) by epoxy bridges. The results obtained in the studies of structural transformations in rolivsans modified with epoxy resins were used as a basis for the new approach to enhancing heat resistance and thermal stability of thermosetting resins.

Optically active polyamidoimides based on amino acids containing cyclohexane fragment

New amino carboxylic acids containing a cyclohexane fragment and an L-leucine or L-valine fragment were synthesized. The reactions of the synthesized amino acids with 4,4′-oxydiphthalic anhydride gave in quantitative yields the dicarboxylic acids, which were converted to the corresponding dichlorides. Low-temperature polycondensation of the synthesized dichlorides with 4,4′-diaminodiphenyl ether yielded optically active polyamidoimides, which are soluble in various organic solvents and exhibit enhanced heat resistance. The structures of the synthesized monomeric compounds and polymers were confirmed by elemental analysis, IR and 1H NMR spectroscopy, and high-resolution mass spectrometry. Specific rotation angles of the synthesized amino carboxylic acids and polyamidoimides were determined.

Impact of Nanoparticles on Structure and Functional Properties of PBTG Biofilms

Biopolymer composites are required to enhance their mechanical properties and heat resistance for the industrial applications. Especially, the addition of nanoparticles in biopolymers can give various functionalities such as electrical, thermal and mechanical properties. In this study, the nanoparticles having functional characteristics were used to enhance heat resistance, tensile properties, and electrical conductivity of PBTG biofilms. Changes in tensile, crystalline and thermal properties of PBTG films with different additives (carbon black, sepiolite, zinc oxide, MWCNT) were investigated by the tensile tester and the instrument of XRD, DSC and TGA. As the results, Electrical conductivity of the biofilms was improved up to 10-5S/cm by adding MWCNT. And tensile modulus of PBTG biofilms with MWCNT was 1.37 times higher than the pure PBTG film. But their heat-resistance characteristics were not significantly affected by adding nanoparticles.

Flax fiber-reinforced polylactide stereocomplex composites with enhanced heat resistance and mechanical properties

Polylactide stereocomplex (sc-PLA) prepared by blending equivalent proportion of poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) and its composites reinforced with 10, 20, and 30% flax fibers were fabricated by melt compounding and followed by injection molding. The mechanical properties, crystallinity, cross-section morphology, and heat resistance of sc-PLA and flax/sc-PLA composites were compared. The results showed that homocrystallites (hc) and stereocomplex crystallites (sc) were formed simultaneously in sc-PLA and its composites, with a melting temperature at ∼170 and ∼210°C, respectively. The crystallinity and sc content of composite increased with the increasing content of the flax fibers. The sc content of 30% flax/sc-PLA composite could reach 98.4%, 32% higher than that of sc-PLA (66.4%). When compared with nonblended PLLA, heat resistance of sc-PLA increased slightly, but at the expense of mechanical properties. By the addition of flax fibers, the mechanical properties of flax/sc-PLA composite improved significantly. The highest tensile strength, Young's modulus, and notched Izod impact strength of flax/sc-PLA composite were 52.90 MPa, 6.42 GPa, and 5.27 kJ/m2, respectively, improved by 54, 132, and 343% when compared with sc-PLA. Moreover, the heat resistance of composite was also improved greatly by reinforcing with flax fibers. The Vicat softening temperature of 30% flax/sc-PLA composite could achieve 162.5°C, nearly 100°C higher than that of PLLA. POLYM. COMPOS., 38:472–478, 2017. © 2015 Society of Plastics Engineers

Application of impedance spectroscopy to study oxidized powders of titanium hydride

Results of studies of current-conducting properties of titanium hydride powders oxidized by air oxygen at different modes in order to form oxide and oxohydride coatings at the particles surface which enhance heat resistance of the hydride are presented. Method of impedance spectroscopy is used to determine contribution of resistance of the formed coatings and contribution of resistance of the grains of titanium hydride powders into the powder impedance. Method aspects of conducting measurements of the impedance of powder materials by stepwise sample compression are discussed. General approach to experimental data processing related to study of metal hydrides which contain shielding films of various chemical compositions at the particle surface is described.