Van Krevelen Method Research Articles

Thermal analysis study of imidazolinium and some benzimid azolium salts by TG

The imidazolinium and benzimidazolium bromide salts with pentafluor substituents on N atom were synthesized. The structures of imidazolinium and benzimidazolium bromide salts obtained were conformed by 1H and 13C NMR, 19F NMR and elemental analysis. It was found that pyrolytic decomposition occurs with melting in salts. The imidazolinium and benzimidazolium bromide salts were studied by TG-DTG and DTA from ambient temperature to 1000°C in nitrogen atmosphere. The decomposition occurred mainly in one stage and the values of activation energy E, frequency factor A, reaction order n, enthalpy change ΔH#, entropy change ΔS# and Gibbs free energy ΔG#, of the thermal decomposition were calculated by means of Coats-Redfern (CR), MacCallum-Tanner (MC) and van Krevelen (vK) methods. The activation energy value obtained by CR and MC methods were in good agreement with each other while those obtained by vK were found to be 10–12 kJ mol−1 larger.

Thermal degradation kinetics of poly(imide-silica) hybrid films. I. Nanocomposites prepared from HFPA and bis(4-amino phenyl) ether by sol–gel process

Degradation kinetics of poly(imide-silica) hybrid films based on 4-4′-(hexafluro isopropylidene) bis(phthallic anhydride) and bis(4-aminophenyl) ether were investigated by thermogravimetric analysis TGA and DTG. The results indicated that the presence of inorganic content influence the mechanism of degradation of organic phase. Energy of activation of degradation for the hybrids with varying inorganic content was determined by the Flynn-Wall-Ozawa, pseudo first-order, van Krevelen methods. Although the values of Ea calculated by using various methods are different, there is a similar change trend of Ea between those methods. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Thermal stability and corrosion resistance of polysiloxane coatings on 2024-T3 and 6061-T6 aluminum alloy

Hybrid coatings based on polydimethylsiloxane-cured organically modified silicate were synthesized through a sol–gel technique. Amino-terminated siloxane, 3-glycidoxypropyltrimethoxysilane and tetraethoxysilane were used as precursors for the hybrid coatings. These hybrid films were deposited via spin coating onto an aluminum alloy to improve the corrosion protection. The effects induced by the different molar ratio of silane on the chain dynamics, thermal stability and corrosion performance of the coated samples were investigated. The rotating-frame spin-lattice relaxation times and scale of the spin-diffusion path length indicated that the configuration of the hybrid films was highly crosslinked and dense. The thermal stability and the apparent activation energy, evaluated by van Krevelen's method, of the hybrid coatings depended on the molar ratio of silane. Potentiodynamic analysis revealed that the hybrid films provided good barrier and corrosion protection in comparison with untreated aluminum alloy substrates.

Synthesis and characterization of polydimethylsiloxane-cured organically modified silicate hybrid coatings

Hybrid coatings based on polydimethylsiloxane-cured organically modified silicate were synthesized through a sol–gel technique. Amino-terminated siloxane, 3-glycidoxypropyltrimethoxysilane and tetraethoxysilane were used as precursors for the hybrid coatings. These hybrid films were deposited via spin coating onto an aluminum alloy to improve the corrosion protection. The effects induced by the different chain lengths of siloxane on the chain dynamics, thermal stability and corrosion performance of the coated samples were investigated. The rotating-frame spin–lattice relaxation times and scale of the spin-diffusion path length indicated that the configuration of the hybrid films was highly crosslinked, dense and adhered to the aluminum alloy substrates. The thermal stability and the apparent activation energy, evaluated by van Krevelen's method, of the hybrid coatings depended on the siloxane chain length. Potentiodynamic analysis revealed that the hybrid films provided exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates.

Swelling behavior and solubility parameter of sulfonated poly(ether ether ketone)

AbstractThe solubility parameter of sulfonated poly(ether ether ketone) (SPEEK) was investigated. SPEEK exhibited two solubility parameters, 26.4 and 35.7 J1/2 cm−3/2, and was similar in that respect to Nafion, which has two cohesive energy densities. The theoretical solubility parameter of SPEEK, 26.1 J1/2 cm−3/2, was determined with van Krevelen's method and corresponded to the experimental value. The theoretical volume fraction of SPEEK in the solvent was determined with Flory's equation. The trend of the theoretical volume fraction of SPEEK fit quite well with the experimental results when the solubility parameter of the solvent was lower than 35 J1/2 cm−3/2. A significant deviation of the experimental volume fraction of SPEEK with the high solubility parameter resulted from the presence of sulfonic acid groups. SPEEK in the sodium form exhibited similar solvent absorption in comparison with SPEEK in the acid form. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3128–3134, 2006

Some aspects of the ozone degradation of poly(vinyl alcohol)

Poly(vinyl alcohol) (PVAL) forms a strong hydrogen-bond complex with ozone. The interaction energy is of the order of 47.3 kJ/mol as calculated from the blue shift undergone by the ozone absorption band in the UV after its complexation with PVAL. This fact may have many important practical implications in the application of PVAL in wastewater treatment both in terms of O 3 dissolution and persistence in water. Furthermore, PVAL is easily biodegradable but it is also slowly degraded by ozone. It is shown by viscometry, electrical conductimetry and by pH measurements that PVAL is degraded by ozone attack with extensive chain breaking. By FT-IR spectroscopy it has been shown that the final product is a PVAL oligomer with numerous ketonic groups along the main oligomer backbone and with carboxylic end groups. A mechanism of ozone degradation of PVAL has been presented and discussed. The chain scission is based on the ozone oxidation of the alcoholic groups of PVAL with formation of ketonic groups which in turn are the source of a keto–enol tautomerism which leads to random chain scission by further O 3 attack. Viscometric measurements show that the main viscosity drop of PVAL is achieved when a nominal stoichiometric ratio of O 3/PVAL < 0.05 is reached which means one ozone molecule for every >20 PVAL monomeric units. For comparison PVAL has been oxidized also with paraperiodic acid. Ozonized PVAL has been studied by thermal analysis (TGA, DTG and DTA) in comparison to a reference untreated PVAL under N 2. The oxidation of PVAL causes its complete amorphization since the crystalline melting point of PVAL at 235 °C is no longer detectable in the case of ozonized PVAL. In any case ozonized PVAL shows a better thermal stability which can be confirmed for instance by a higher maximum decomposition rate temperature as measured by DTG. This result is in agreement with theoretical calculations made by group increments according to Van Krevelen's method which predicts a higher decomposition temperature for a PVAL having ketonic groups in place of alcoholic moieties in the main polymer backbone.

Characterization and corrosion resistance of organically modified silicate/MO2 (M = Zr, Ti, or Ce) hybrid coatings on a 6061‐T6 aluminum alloy

AbstractHybrid coatings based on organically modified silicate (Ormosil)/ZrO2 (0–1.0 wt %) and Ormosil/MO2 (M = Ti or Ce) were synthesized through a sol–gel technique. Tetraethylenepentamine, 3‐glycidoxypropyltrimethoxysilane, tetraethoxysilane, and MO2 (M = Zr, Ti, or Ce) metallic particle were used as precursors for the hybrid coatings. These hybrid films were deposited via spin coating onto an aluminum alloy to improve the corrosion protection. The effects induced by the ZrO2 content and the metallic particle type on the chain dynamics, thermal stability, and corrosion performance of the coated samples were investigated. The rotating‐frame spin–lattice relaxation times and scale of the spin–diffusion path length indicated that the configuration of the hybrid films was highly crosslinked and dense and adhered to the aluminum alloy substrates. The thermal stability and the apparent activation energy, evaluated by van Krevelen's method, of the hybrid coatings depended on the ZrO2 content and on the metallic particle type. Potentiodynamic and salt‐spray analysis revealed that the hybrid films provided exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 335–342, 2006

Estimation of Thermal Parameters of Halogenated Polymers Based on Group Additive Methods

The thermal parameters such as, glass transition temperature (Tg), crystalline melting point (Tm), initial thermal degradation temperature (Td,0), and coefficient of thermal expansion (Eg) of some halogenated polymers have been estimated employing two different relations such as the Van Krevelen method and the Askadskii method based on the group additive principle. The estimated parameters were compared with the experimental values. The estimated thermal parameters by the Van Krevelen method are found to be more accurate, rapid, and simple than the Askadskii method, except for a crystalline melting point.

A graph-structural method for prediction of polymer properties

Group contribution methods have been widely used for the estimation and prediction of properties of a great variety of chemical compounds and mixtures of compounds. In this paper, the glass transition temperature of polymers is evaluated by a second-order group contribution method previously developed by Ourique and Silva Telles (1997). From a total of 1018 polymers in the data base, 923 are selected as the training set to which group and interacting group contributions are assigned. The remaining 95 polymers are used as the validation set. Results are compared to the ones obtained by application method of Van Krevelen method's to the same data base.

The influence of guaifenesin and ketoprofen on the properties of hot-melt extruded polyethylene oxide films.

Films containing polyethylene oxide (PEO) and a model drug, either guaifenesin (GFN) or ketoprofen (KTP), were prepared by hot-melt extrusion. The thermal properties of the hot-melt extruded films were investigated using differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) was used to examine the surface morphology of the films, and wide angle X-ray diffraction (XRD) was used to investigate the crystalline properties of the polymer, drugs and physical mixtures as well as the solid state structure of the films. The stability of the polymer was studied using gel permeation chromatography. The mechanical properties, including percent elongation and tensile strength of the films, were determined on an Instron according to American Society for Testing Materials (ASTM) procedures. The Hansen solubility parameter was calculated using the Hoftyzer or van Krevelen method to estimate the likelihood of drug--polymer miscibility. Both GFN and KTP were stable during the extrusion process. Melting points corresponding to the crystalline drugs were not observed in the films. Crystallization of GFN on the surface of the film was observed at all concentrations studied, however KTP crystallization did not occur until reaching the 15% level. Guaifenesin and ketoprofen were found to decrease drive load, increase PEO stability and plasticize the polymer during extrusion. The Hansen solubility parameters predicted miscibility between PEO and KTP and poor miscibility between PEO and GFN. The predictions of the solubility parameters were in agreement with the XRD and SEM results. The percent elongation decreased with increasing GFN concentrations and significantly increased with increasing levels of KTP. Both GFN and KTP decreased the tensile strength of the extruded film.

A thermoanalytic and kinetic study of sunflower oil

Recently, thermoanalytic methods have frequently been used in the characterization of oils and fats. In this work, thermoanalytic and kinetic parameters of sunflower oils, with and without antioxidants, were evaluated using thermogravimetry / derivative thermogravimetry and differential scanning calorimetry. The thermogravimetric profiles for the sunflower oils had similar characteristics, showing a level stretch indicative of stability up to about 200ºC. Thermal decomposition of these oils occurred in three stages, related to the decomposition of polyunsaturated, monounsaturated and saturated fatty acids, respectively. DSC curves show two events that characterize the polymerization and decomposition of triglycerides. The heat capacities of the sunflower oils, obtained by DSC, showed a good correlation and were dependent on the composition of fatty acids. The kinetic parameters, obtained by non isothermal thermogravimetry by the Coats and Redfern, Madhusudanan, Horowitz and Metzger and Van Krevelen methods, were dependent on the antioxidant used. Increasing the frying time produced a decrease in the onset of thermal decomposition temperature in the sunflower oils analyzed.

Prediction of plugging effect of biopolymers using their glass transition temperatures

In this paper, it was demonstrated that the two main transition temperatures, i.e., the glass-rubber transition temperature ( T g) and the crystalline melting temperature ( T m) of biopolymers, can be correlated with their chemical structure by means of the van Krevelen's method based on additive group-contributions. Five different biopolymers, namely polyhydroxybutyrate (PHB), chitosan, polyglutamic acid (PGA), guar gum and xanthan, were studied. The transition temperatures of these five biopolymers were predicted using the above method. In this paper, the ratio, T g/ T m, was calculated to be 0.62, which is close to the value first reported to be 0.66. The data calculated were in agreement with the experimental data of other laboratories. It was shown that PHB had the lowest T g and T m, and xanthan had the highest T g and T m. Also, from a previous study, PHB had the highest permeability reduction factor (i.e., best plugging effect), and xanthan had the lowest permeability reduction factor (i.e., worst plugging effect). This means that at low T g and T m the biopolymer has a glassy behavior, which makes it a good plugging agent (in this case PHB).

Organic-Inorganic Hybrid Materials X: Characterization and Degradation of Hydroxyl-Containing Fluorinated Polyimide-Silica Hybrids

Hydroxyl-containing fluorinated polyimide-silica hybrid materials (FPI-SiO 2 ) were obtained using the sol-gel technique by polycondensation of tetramethoxysilane (TMOS) in 3-aminopropylmethyl diethoxysilane (APrMDEOS)-terminated amic acid solution. Infrared, 29 Si-, and 13 C-NMR spectroscopy and thermogravimetric analysis (TGA) were used to study hybrids containing various proportions of TMOS. The microstructure and chain mobility of the hybrids was investigated by spin-lattice relaxation time in rotating frame ( T^{H}_{1\\rho} ) measurements. The apparent activation energy (E a ) for degradation of the hybrids was studied by Friedman and van Krevelen methods.

Effect of phenolic phosphite antioxidant on the thermo-oxidative degradation of PMMA

A novel high molar mass phenolic phosphite antioxidant, tetrakis-(2,5-di- tert-butyl-4-hydroxyphenyl)-2,5-di- tert-butyl-hydroquinonediyl diphosphite (2P5B), was prepared and characterized by IR, 31P NMR, FAB-MS and thermogravimetric analysis (TGA). The effect of 2P5B content on the thermal properties of poly(methyl methacrylate) (PMMA) was studied by TGA, differential scanning calorimetry (DSC), and oxidative induction time (OIT). 0.5 wt.% of the novel phenolic phosphite antioxidant retarded the 10% weight loss temperature and reduced the maximum rate of weight loss. The stabilized-PMMA showed a clear OIT onset that increased with increasing 2P5B content. The apparent activation energies for initial thermo-oxidative degradation, evaluated by van Krevelen method, of the stabilized-PMMA were less than that of antioxidant free PMMA. Hence, it seems reasonable that the PMMA was degraded easily as the 2P5B antioxidant was consumed.

Organic–inorganic hybrid materials XI. Characterization and degradation of hydrogen-bonded acidic fluorinated poly(siloxane-amideimide-silica) hybrids

Hydrogen-bonded acidic fluorinated poly(siloxane-amideimide-silica) hybrid materials (FPSAI–SiO 2) were obtained using the sol-gel technique by polycondensation of tetramethoxysilane (TMOS) in diethoxysilane-terminated amic acid solution. IR, 29Si- and 13C-NMR spectroscopy and thermogravimetric analysis (TGA) were used to study hybrids containing various proportions of TMOS. The abundant Q 4 structures implied that in the absence of HCl the degree of condensation of TMOS was enhanced by hydrogen-bonded acidic fluorinated poly(siloxane amideimide). The microstructure and chain mobility of the hybrids were investigated by measurements of the spin-lattice relaxation time in the rotating frame ( T H 1ρ) and the time constant for energy exchange between 1H and 29Si spin systems ( T SiH). The results suggested that the rate of polarization transfer in FPSAI–SiO 2 hybrids was dependent on the local motion. On the other hand, the spin-diffusion path length ( L) in FPSAI–SiO 2 hybrids was around 3.6 nm. The apparent activation energy ( E a) for degradation of the hybrids was studied by the van Krevelen method. The E a values of the FPSAI–SiO 2 hybrids in thermal degradation decreased with increasing silica content, whereas those for thermo-oxidative degradation were almost unchanged.

Organic-inorganic hybrid materials. V. Dynamics and degradation of poly(methyl methacrylate) silica hybrids

Poly(methyl methacrylate)–silica hybrid materials (PMMA–SiO2) were prepared by in situ polycondensation of alkoxysilane in the presence of trialkoxysilane-functional PMMA. Infrared, differential scanning calorimetry, 29Si and 13C nuclear magnetic resonance spectroscopy, and thermogravimetric analysis were used to study the PMMA–SiO2 hybrids. The effects of the content and kind of the alkoxysilane on the dynamics and stability of the PMMA–SiO2 hybrids were investigated in this study.The dynamics of SiO2within hybrids were investigated with 29Si–1H cross-polarization. The spin-diffusion path length was on a nanometer scale estimated with the spin–lattice relaxation time in the rotating frame (T). The apparent activation energies for the degradation of the hybrids under air and nitrogen were evaluated by the van Krevelen method. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1972–1980, 2000

Organic–inorganic hybrid materials3 Characterization and degradation of poly(imide–silica) hybrids doped with LiCF 3SO 3

Lithium salts-containing hybrids were prepared by hydrolysis-condensation of tetramethoxysilane (TMOS) in solution in N, N-dimethylacetamide(DMAc) containing 10 wt% trifluoromethanesulfonate (LiCF 3SO 3) and (3-aminopropyl)methyl diethoxysilane (APrMDEOS) terminated amic acid. Infrared (IR), 29Si and 13C CP/MAS nuclear magnetic resonance (NMR) spectroscopy, thermo-mechanical analysis (TMA), and thermogravimetric analysis (TGA) were used to study various hybrids. The spin–spin relaxation time T 2 of the hybrid was studied to probe the role of the salt. The apparent activation energy E a for degradation of hybrids in air was evaluated by the van Krevelen method.

Organic-inorganic hybrid materials. II. Chain mobility and stability of polysiloxaneimide-silica hybrids

Polysiloxaneimide–silica hybrid materials (PSI-SiO2) were obtained using the sol–gel technique by polycondensation of tetramethoxysilane (TMOS) in a polyamic acid solution. IR, 29Si- and 13C-NMR spectroscopy, and thermogravimetric analysis were used to study hybrids containing various proportions of TMOS and hydrolysis ratios. The morphology, dynamics, and thermal stability of the hybrids were investigated. The chain mobility of the hybrids was investigated by spin–spin relaxation time (T2) measurements. The apparent activation energy (Ea) for degradation of the hybrids in air was studied by the van Krevelen method. The T2 value was independent of the silica content whereas that of the Ea decreased as silica content increased. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 965–973, 2001

Organic-Inorganic Hybrid Materials 8: Stability of Poly (Methyl Methacrylate) in Pmma-SiO2 Hybrids

Poly(methyl methacrylate) modified silica hybrid materials (PMMA-SiO2 hybrids) were prepared by in situ polycondensation of alkoxysilane in the presence of trialkoxysilane-functional poly(methyl methacrylate), The thermal stabilities and apparent activation energies E a for the thermal and thermo-oxidative degradations of these samples were studied by thermo-gravimetric analysis (TGA), The effects of alkoxysilane content and atmosphere on the stability of the PMMA moiety were investigated in this study. The values of E a were evaluated by van Krevelen method.

Organic-inorganic hybrid materials. I. Characterization and degradation of poly(imide-silica) hybrids

Poly(imide–silica) hybrid materials with covalent bonds were prepared by (3-aminopropyl)methyldiethoxysilane (APrMDEOS) terminated amic acid, water, and tetramethoxysilane (TMOS) via a sol–gel technique. Infrared (IR), 29Si and 13C CP/MAS nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis (TGA) were used to study hybrids containing various proportions of TMOS and hydrolysis ratios. The microstructure and chain mobility of hybrids were investigated by proton spin–spin relaxation T2 measurements. The apparent activation energy Ea for degradation of hybrids in air was studied by the van Krevelen method. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2275–2284, 1999