In situ fourier‐transform infrared spectra analysis of hydrogen bond in polypropylene/chlorinated polypropylene/polyaniline composite

The previous studies suggest that hydrogen bond between chlorinated polypropylene (CPP) and polyaniline (PANI) plays a prominent role in the decision of polypropylene/CPP/PANI composites' electric property. In situ Fourier‐transform infrared spectra were employed to detect and identify the relationship between the hydrogen bond and the temperature. Two kinds of hydrogen bond were carefully studied in the nitrogen–hydrogen bond (N? H) stretching, sulfur–oxygen double bond (S?O) stretching, and carbon–chlorine bond (C? Cl) stretching regions, using an iterative least‐squares computer program to obtain the best fit of spectra. The ratio of absorptivity coefficients and the mole fraction of the “free” and two kinds of H‐bonded N? H were calculated. There exists an apparent turning point in the curves of the relationship between the fraction of two kinds of H‐bonded N? H and temperature. This phenomenon also exists in the S?O stretching region, and the turning point is at about 60°C. The mole fraction of H‐bonded C? Cl decreases, and that of “free” C? Cl increases with increasing temperature. The enthalpy gap between the H‐bonded N? H…O?S and the H‐bonded N? H…Cl?C dissociation was also obtained as 23.2 KJ/mol. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Thermooxidative degradation behavior of poly(silphenylene–siloxane)s

Copolymers of poly(silphenylene–siloxane) with dimethylsiloxane and diphenylsiloxane with various end groups were synthesized through an Si? H/Si? OR polycondensation process. The thermooxidative degradation behaviors of the copolymers were investigated by thermogravimetric analysis and IR spectrometry techniques. All of the polymers were characterized by a two‐step mass loss. The first one, which peaked at 510–545°C in differential thermogravimetric curves, was mostly caused by the main‐chain depolymerization, whereas the second one, which reached its maximum around 650°C, was caused by side‐group oxidation and Si? C bond scission. The main‐chain depolymerization occurred over a temperature range of some 470–580°C, whereas Si? C bond scission and side‐group oxidation occurred over a temperature range of about 585°C to above 720°C. The incorporation of phenyl groups in the end groups greatly retarded the temperature for the degradation onset of the main chain to 120°C higher. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

FTIR study of poly(propylene carbonate)/bisphenol A blends

A systematic investigation by FTIR spectroscopy was undertaken on blends of poly(propylene carbonate) (PPC) and bisphenol A (BPA). It provided direct evidence of the hydrogen bond (H‐bond) between BPA O? H groups and PPC C?O groups. Using a curve‐fitting method, qualitative as well as quantitative information concerning this H‐bond interaction was obtained. The inter‐H‐bond in PPC/BPA blends was weaker than the self‐H‐bond in BPA. The absorptivities of the free and the H‐bonded C?O groups were nearly equal. The fraction of H‐bonded C?O in the blends increased with BPA content and leveled off at a value close to 40 %. Finally, FTIR–temperature measurements of pure PPC and a representative blend were reported: by monitoring the peak areas of C?O absorptions, the dissociation of the inter‐H‐bonds and the thermal degradation of PPC were observed. It revealed that the presence of BPA clearly retarded the thermal degradation of PPC. Copyright © 2004 Society of Chemical Industry     

Effect of doping polyacrylic acid with some dopants as studied by different techniques

The molecular weight of polyacrylic acid (PAA) was determined by a viscometric method using NaNO₃ as solvent at 30°C. The specific electric conductivities (σ) of PAA as well as PAA doped with carbon black (CB), chromium oxide (Cr₂O₃), and cupferron with different concentrations (from 0.25 to 1 wt %) were measured at a temperature range 360–400 K. IR spectra of some polymers were determined and it was shown that when PAA was doped with 0.5 wt % CB, a C? O? C band appeared at 775–875 cm^?1. The positron annihilation lifetime (PAL) spectra in PAA doped with the above‐mentioned dopants were measured as a function of their concentrations. It was observed that the short lifetime intensity I₁ decreased, whereas the intermediate lifetime intensity I₂, which is related to the conductivity of the material, increased with increasing the wt % of Cr₂O₃ and cupferron as well as at low concentrations of CB. These results are discussed in terms of the conducting island model. It was found that there were distinct positive relationships between σ and I₂. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 877–883, 2002; DOI 10.1002/app.10381     

Influence of hydrogen donors on peroxide‐initiated melt grafting of vinylsilane to poly(ethylene‐co‐vinyl acetate)

A technique has been examined for reducing the extent of crosslinking resulting from 1,1‐di(t‐butylperoxy)‐3,3,5‐trimethylcyclohexane (L‐231) initiating melt grafting of vinyltriethoxysilane (VTEOS) onto poly(ethylene‐co‐vinyl acetate) (EVA). Using measurements of crosslink density and VTEOS conversion, a standard of selectivity for the EVA/VTEOS/L‐231 system at 145 °C was defined and used to assess the influence of a range of additives (0.25 mol per mole VTEOS). The data indicated that compounds such as 4‐nonene, N,N‐dimethylaniline, and cumene improve reaction selectivity, whereas dodecane and cyclohexyl acetate have no effect. A strong correlation between the minimum C? H bond dissociation energy and the influence of a given compound is evident, suggesting that a labile C? H bond is the key element of an effective additive. A mechanism of additive function on the basis of hydrogen atom donation is proposed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2397–2402, 2002     

Thermodynamic functions of ionization of pentafluorobenzoic acid in dilute aqueous solutions

The thermodynamic functions of ionization of pentafluorobenzoic acid in aqueous solutions have been evaluated from the conductimetrically determined thermodynamic dissociation constants, over the temperature range of 5°C–45°C. The pK_a values, only, may be calculated over this temperature range using the equation     

IN-SITU FT-IR SPECTROSCOPIC STUDIES OF FUEL CELL ELECTRO-CATALYSIS: FROM SINGLE-CRYSTAL TO NANOPARTICLE SURFACES

The work presented in this article shows the power of the variable temperature, in-situ FT-IR spectroscopy system developed in Newcastle with respect to the investigation of fuel cell electro-catalysis. On the Ru(0001) electrode surface, CO co-adsorbs with the oxygen-containing adlayers to form mixed [CO + (2 × 2)–O(H)] domains. The electro-oxidation of the Ru(0001) surface leads to the formation of active (1 × 1)–O(H) domains, and the oxidation of adsorbed CO then takes place at the perimeter of these domains. At 20°C, the adsorbed CO is present as rather compact islands. In contrast, at 60°C, the CO_ads is present as a relatively looser and weaker adlayer. Higher temperature was also found to facilitate the surface diffusion and oxidation of CO_ads. No dissociation or electro-oxidation of methanol was observed at potentials below approximately 950 mV; however, the Ru(0001) surface at high anodic potentials was observed to be very active. On both Pt and PtRu nanoparticle surfaces, only one linear bond CO adsorbate was formed from methanol adsorption, and the PtRu surface significantly promoted both methanol dissociative adsorption to CO and its further oxidation to CO₂. Increasing temperature from 20° to 60°C significantly facilitates the methanol turnover to CO₂.     

Kinetic mechanism on Thermal Degradation of a Nitrate Ester Propellant

The thermal degradation of a double-base propellant has been studied to elucidate the rate-determining steps and the kinetic mechanism in a wide range of temperatures (60°C–200°C) by using modified Taliani test, thermogravimetry (TG), and temperature-varied Abel (TVA) test. The results indicate that the degradation process consists of two major reactions, homolysis and autocatalysis, depending on temperature and total pressure due to evolved gases. The activation energy for the homolysis was obtained to be 35–37 kcal/mol from Taliani and TVA tests, which fall in the range of the bond dissociation energy of the weakest bonds RO–NO₂. The activation energy for the autocatalysis was determined to be 46–49 kcal/mol from Taliani and TG methods. Those values observed for the two key reactions are totally opposite to reported values in the earlier literature. The temperature dependence of the reaction rates obtained in this study implies that the homolysis is the rate-determining step in the lower temperature range, the autocatalysis in the higher temperature range.     

Electrical properties of poly(butylene terephthalate)

Direct current (dc) and alternating current (ac) electrical properties of semicrystalline poly(butylene terephthalate) (PBT) are investigated as a function of temperature and frequency. Dc electrical conductivity measurements have been performed over the temperature range ?75°C to 130°C and point out an essentially ionic mechanism of charge transport. Charge carriers are identified in protons supplied by ionization of carboxyl end-groups after dissociation of the existing hydrogen bonds. Dielectric constant and loss factor have been measured over the temperature range ?100°C to 130°C and over the frequency range 10^?6 to 10⁶ Hz. Together with de measurements, they allow the detection of the α glass-rubber and the β subglass relaxation processes, as well as an interfacial polarization of the Maxwell–Wagner–Sillars type. Finally, the contour map of loss factor, summarizing the overall dielectric behavior of the polymer, is reported and discussed for electrical applications of PBT.     

X‐ray Diffraction Study of the Effect of High‐Temperature Heat Treatment on the Microstructural Stability of Third‐Generation SiC Fibers

Third‐generation SiC fibers [High Nicalon S (HNS) and Tyranno SA3 (Ty–SA3)] were studied by X‐ray diffraction and transmission electron microscopy (TEM) after heat treatments in neutral atmosphere up to 1900°C. The microstructural changes in both materials were determined using a modified Hall–Williamson method introducing an anisotropy parameter taking into account the high density of planar defects. HNS fibers exhibit significant modifications in the coherent diffraction domains (CDD) size, which drastically increases from 24 to 70 nm in the range 1600°C–1900°C. TEM observations support these results. The residual microstrain values decrease from 0.0015 to 0.0005 between 1750°C and 1850°C. Similarly, the anisotropy parameter significantly decreases in the same temperature range. Concerning the Ty–SA3 fibers, no evolution in terms of CDD size and residual microstrain was observed. However, the anisotropy parameter decreases at 1800°C. TEM observations did not show noticeable grain growth. The grain size was found to be larger than the CDD and the planar defects density to decrease at high temperature. In both types of fibers, the CDD sizes are similar for the highest temperature heat treatments.     

Thermal degradation kinetics of para‐substituted poly (styrene peroxide)s in solution

The thermal degradation of three polymeric peroxides of styrene monomers with substituents in the para position was studied at various temperatures (65, 75, 85, and 95°C). A continuous distribution model was used to evaluate the rate coefficients for the random‐chain and chain‐end scission degradation from the evolution of molecular weight distributions with time. The activation energy determined from the temperature dependence of the rate coefficients was in the range 18–22 kcal mol^?1. This result suggests that the thermal degradation of polyperoxide is controlled by the dissociation of the O—O bonds in the polymer backbone. The thermal stability for poly(p‐methylstyrene peroxide) lies in between that of poly(p‐tert‐butylstyrene peroxide) (highest) and poly(p‐bromostyrene peroxide) (lowest). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 957–961, 2002     

Effect of ring size on the oxidizability of lactams

The initial stage of oxidation of lactams was studied in the temperature range 70–120°C. It was found that pyrrolidone and piperidone are oxidized essentially more easily than the seven-, eight-, nine- and thirteen-membered lactams as well as linear N-alkylamides. The high oxidizability of the five- and six-membered lactams may be attributed to the easier homolytic splitting of the N-vicinal C? H bond and to the different reactivity of lactam radicals in the propagation step of the chain oxidation.     

Chitosan functionalization with a series of sulfur‐containing α‐amino acids for the development of drug‐binding abilities

Chitosan (Chi; 0.5 g) in 69.66 mM aqueous acetic acid was mixed with 312.4 mM methionine (methi) at 0.01 mL/s to disperse and cause optimum collisions for supporting condensation reactions through ? NH₂ of Chi and ? COOH groups of methi. The functionalized chitosan (f‐Chi) product with methi developed an amide bond, which was represented as methi‐functionalized chitosan [Chi–NH? C(?O)–methi]. Both the 1‐Ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide (EDC) and Dean–Stark methods were followed for Chi functionalization. Sulfonation with chlorosulfonic acid in a dimethylformamide medium was conducted at 90 °C and 750 rpm with an approximately 72% yield. The Chi–NH? C(?O)–methi was characterized by ¹H‐NMR spectroscopy and Fourier transform infrared stretching frequencies. The onset temperature of 280 °C recorded by thermogravimetric analysis/differential scanning calorimetry analysis, confirmed the high stability of the covalent bonds in Chi–NH? C(?O)–methi. The synthesis was repeated with other series members of sulfur (S) atoms containing α‐amino acids: homocysteine, ethionine, and propionine. The shielding of terminal ? CH₃ was enhanced on elongation of the terminal alkyl chain in the case of propionine. The peak for the ? NH₂ of Chi at a δ value of 4.73 ppm shifted to 5.36 ppm in Chi–NH? C(?O)–methi because of the involvement of ? NH₂ in ? NH? C(?O)? . Theoretically, the value of ? NH₂ of Chi was 5.11 ppm, with a difference of 0.38 ppm as compared to the experimentally determined value of 4.73 ppm. Additionally, a new peak at a δ value of 3.26 ppm also confirmed Chi functionalization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46000.     

Formation of poly(butylene terephthalate): Secondary reactions studied by model molecules

The secondary reactions occurring in the formation poly(butylene terephthalate), leading to thermal degradation (in the temperature range 210°–280°C) or giving rise to tetrahydrofuran (in the temperature range 160°–190°C) have been kinetically studied with the aid of model molecules: 1,4-butylene dibenzoate and 4-hydroxybutyl benzoate. Some kinetic parameters have been determined; the effect of temperature and of catalysts and stabilizers has been considered and a mechanism is proposed for the formation of tetrahydrofuran from hydroxyl end groups.     

Flexible TiO2 ceramic fibers near-infrared reflective membrane fabricated by electrospinning

Titanium oxide is a potential high temperature reflective material due to its high melting point, large refractive index, and suitable band gap. The flexible TiO₂ ceramic fibers membrane was successfully fabricated by sol–gel method using the polyacetylacetonetitanium (PAT) as the precursor. In order to obtain high-quality TiO₂ fibers, the PAT precursor with good stability and good spinnability was optimized by adjusting the molar ratio of acetylacetone to Ti to 1:1. The TiO₂ fibers heat-treated at 700?°C had a diameter of 400–500?nm. The crystal phase of TiO₂ fibers was anatase, and the surface of fibers was smooth without obvious defects. In addition, the TiO₂ ceramic fibers membrane heat-treated at 700?°C had good flexibility and tensile strength, and the average reflectance in the wavelength range of 500–2500?nm was up to 91.3%. The fibers membrane exhibits a significant reflection effect in the practical experiments and maintained good morphology of the fibers after 1200?°C test.     

Dissociation of Basal Dislocations in 4H–SiC Single Crystals Deformed Around the Transition Temperature

The dislocation microstructure was studied in 4H–SiC samples plastically deformed by basal slip activation around the transition temperature (1000°C–1100°C). Dissociation of basal dislocations takes place over a wide temperature range (800°C–1300°C), but its influence on dislocation motion is different in the high‐ and low‐temperature regimes due to the difference in mobility of partials. Consequently, this material exhibits a completely different mechanical behavior below and above its transition temperature, indicating a change in the deformation mechanism. In this work, the dislocation microstructure was studied around the transition temperature at which both mechanisms are still operative, thus providing a richer number of different configurations generated by dissociation of basal dislocations. They were observed and analyzed by means of the complementary use of weak‐beam dark‐field imaging and high‐resolution transmission electron microscopy. Firstly, 3C band nucleation in the 4H–SiC matrix was identified and its appearance discussed from an energy standpoint. Secondly, the attractive interaction between partials in dipoles and the difference in mobility between the leading and the trailing partial have remarkable effects on the dissociation width, and explain the absence of work hardening above the transition temperature.     

Effect of thermal aging on electrical conductivity of the 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid‐doped polyaniline fiber

The thermal characteristics of inherently conductive polyaniline (PANi) fiber have been studied using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Fibers show five major weight losses at ∼100°C, 165°C, 215°C, 315°C, and 465°C, which are associated with the removal of moisture, residual solvent, decompositions of the sulfonic acid and degradation of PANi fiber, respectively. The 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPSA) that dopes the PANi (in fiber form) performs two‐stage decompositions. The conductivity of the drawn fibers aged at 50°C, 100°C, 150°C, and 190°C under vacuum for various periods of time decreases, particularly at temperatures higher than 100°C. The reduction in conductivity of the fiber aged at temperatures lower than 100°C is mainly due to the evaporation of the residual solvent (15–20% in the as‐spun fiber). Further decrease in conductivity of the fiber aged at temperatures higher than 100°C is caused by the decomposition of the dopant AMPSA. The temperature‐dependent conductivity of the fiber was measured at 15 K (−258.5°C) to 295 K (21.5°C). The conductivity of both aged and un‐aged fibers is all temperature activated, however, the conductivity of the un‐aged fibers is higher than that of the aged fibers. Although a negative temperature coefficient was observed in the temperature range from 240 K (–24.5°C) to 270 K (–3.5°C) for the un‐aged fibers, it was disappeared when the fibers were thermal aged at 100°C for 24 h in vacuum oven. These results indicate that the residual solvent trapped inside the fiber enhanced the electrical conductivity of the fibers and its “metallic” electrical conductivity at temperatures ∼263 K (–10°C). © 2001 John Wiley & Sons, Inc. † J Appl Polym Sci 79: 2503–2508, 2001     

Durable flame resistance via reaction of cotton cellulose bearing aromatic amino groups with tetrakis(hydroxymethyl)phosphonium chloride

Chemically modified cotton fabric samples having different amounts of aromatic amino groups were prepared. These modified samples were reacted with tetrakis(hydroxymethyl)phosphonium chloride (THPC) under a variety of conditions using the pad-dry–thermofixation technique. The extent of the reaction (expressed as %P) was dependent of the degree of chemical modification of cotton, temperature and time of heating, and pH of the treating bath as well as incorporation of Lyofix CHN (N-methylol finishing agent), MgCl₂·6H₂O (catalyst), and urea at various concentrations. THPC did react with the modified cotton having a nitrogen content over a range of 0.4%–1.3% even in the absence of catalyst at a temperature as low as 30°C for 10 min to impart durable flame resistance to cotton. Increasing the temperature up to 80°C enhanced considerably the extent of reaction; he latter remained practically constant upon further increase in temperature. The reaction was favored in acidic media (pH 4–6), whereas alkaline media (pH 9–11) inhibited it. Incorporation of Lyofix CHN (9%), MgCl₂6H₂O (1%), and urea (5%) along with THPC (25%) in the treating bath required a curing temperature of 120°C and a curing time of 5 min to achieve a fabric containing as much as 2.7% phosphorus with excellent durable flame resistance. A tentative mechanism of the reaction between THPC and the modified cotton was also elicited.     

Dynamic mechanical and impact properties of PP/SEBS blend

Studies on impact behaviour of the blend of isotactic polypropylene (PP) with styrene-b-ethylene-co-butylene–b-styrene triblock copolymer (SEBS) in the composition range 0–25 wt % SEBS at three temperatures, viz., ambient, ?30°C, and ?190°C, are presented. Dynamic mechanical properties on a torsion pendulum in the temperature range ?100?100°C are also studied for this blend at various compositions. Scanning electron microscopic studies of the impact-fractured surfaces are presented to illustrate the differences in the mode of fracture at the three temperatures of impact tests. Choice of the three temperatures for impact tests was such that the effect of shear yielding mechanism of toughening of PP at ambient temperature remains suppressed at ?30°C, whereas at the lowest temperature (i.e., ?190°C) the elastomeric role of the inclusion SEBS is suppressed. The observed considerably large difference in impact toughening at ambient temperature and at ?;30°C seems not entirely accountable by the prevalence of shear yielding or crazing mechanisms in the respective temperature regions. A third mechanism, viz., viscoelastic energy dissipation, is invoked to account for the observed large difference of impact toughening at these two upper temperatures. Correlation of peak area of dynamic mechanical loss peaks occurring below the impact test temperature with the impact strength is also shown. This suggests greater significance of viscoelastic energy dissipation mechanism in the toughening of this blend at ambient temperature than at ?30°C.     

Succinoylation of wheat straw hemicelluloses with a low degree of substitution in aqueous systems

The reaction of wheat straw hemicelluloses with succinic anhydride in aqueous alkaline systems was studied. The products showed a rather low degree of substitution, ranging from 0.017 to 0.21. The effects of reaction times of 0.5–16 h, temperatures of 25–45°C, and molar ratios of succinic anhydride to anhydroxylose units in hemicelluloses of 1:5–1:1 on the succinoylation yield and degree of substitution were examined. With the reaction kept within a pH range of 8.5–9.0, a temperature range of 25–28°C, a reaction duration of 1–2 h, and a 1:1 molar ratio of succinic anhydride to hemicelluloses were preferred. The structure of the resulting polymers was determined with Fourier transform infrared and ¹H‐ and ¹³C‐NMR spectroscopy, which indicated monoester substitution. The thermal stability of the esterified polymer increased with chemical modification. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 757–766, 2002