Immobilization influence on the water sorption and diffusion in poly(3-hydroxybutyrate)

The temperature dependency of water vapor sorption and diffusion in poly(3-hydroxybutyrate) (PHB) was studied for the first time. Equilibrium sorption and diffusion kinetics were determined by a quartz McBain's vacuum microbalance technique in the temperature range of 303–333 K. A probability of water molecule interaction with the polymer matrix was analyzed for wet PHB films by FTIR spectroscopy technique. Sorption isotherms are interpreted as the solution of free water molecules estimated by the Flory–Huggins equation and the sorption of water molecules immobilized on the carbonyl groups of PHB. The immobilization effect was described by a Langmuir-type equation. The dependency of diffusivity on water concentration was described in the frames of Fujita's immobilization model in which the growing function D_w versus C_w characterized the filling degree of carbonyl groups as sites of immobilization in the polymer. Enthalpy of free water sorption (12 kJ/mol) and water immobilization (42 kJ/mol), as well as the activation energy of water diffusion coefficients (71 kJ/mol), in noncrystalline areas of PHB were determined. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 981–985, 1999     

Water sorption of poly(vinyl alcohol)/ poly(diallyldimethylammonium chloride) interpenetrating polymer network hydrogels

Temperature‐responsive interpenetrating polymer network (IPN) hydrogels constructed with poly(vinyl alcohol) and poly(diallyldimethylammonium chloride) using the sequential IPN method were studied. The characteristics of IPN hydrogels were investigated using the dynamic vapor sorption system. IPN hydrogels exhibited a relatively high sorption ratio, 180–360% at room temperature. The sorption ratio of hydrogels depended on temperature. Diffusion coefficients were calculated according to the Fickian Law at several temperatures. The apparent activation energy was 5.43 kJ mol^?1, which corresponds to typical diffusion processes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1389–1392, 2003     

Sorption studies of propylene in polypropylene. Diffusivity in polymer particles formed by different polymerization processes

Propylene was polymerized in gas phase and liquid phase by using a novel nonporous Ziegler–Natta‐catalyst system. The polymer particles formed at different polymerization times were used for sorption measurements. In both cases it was found that the effective diffusion coefficient is increasing with increasing size of polymer particles and the effective diffusion coefficients of polymer particles formed by liquid‐phase polymerization are larger than those of polymer particles produced by gas‐phase polymerization. The effective diffusion coefficients of polymer particles are in the range of 2 × 10^?11 to 1.6 × 10^?10 m²/s with activation energies from 34 to 22 kJ/mol. The analyzed polymer particles have average diameters between 250 and 875 μm. The solubility of propylene in polypropylene particles can be described by the law of Henry at conditions studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2642–2648, 2006     

Synthesis of Mo–W carbide via propane carburization of the precursor sulfide: Kinetic analysis

Thermogravimetric analysis (TGA) has been used to investigate the carburization kinetics of Mo–W sulfide using an H₂:C₃H₈ feed mixture. The effect of heating rate over the range 1–10 K min^?1 showed that up to four different carburized products may be formed but the critical (peak) temperature for formation of these species and the amount (peak height) of each species formed are highly dependent on the heating rate employed. The critical temperature increased linearly with heating rate for each of the four products. The four TGA peaks corresponding to the four phase transformation species are consistent with XRD identifiable species, namely; α‐Mo₂C, β‐Mo₂C, W and MoC_1?x. Isothermal conversion–time data at three different temperatures are described by a reaction‐controlled shrinking core model implicating a first‐order dependency on the H₂:C₃H₈ ratio. The reaction exhibited fractional order dependence on the metal sulfide concentration, the associated global activation energy estimated as 227 kJ mol^?1 is representative of a non‐catalytic gas–solid reaction. Copyright © 2004 Society of Chemical Industry     

Water sorption in amorphous poly(ethylene terephthalate)

The water sorption characteristics of poly(ethylene terephthalate) (PET) amorphous samples of 250 μm thickness have been studied at various temperatures in a saturated atmosphere. Concerning diffusivity, one can distinguish the following two domains characterized by distinct values of the activation energy: E_D ≈ 36 kJ mol⁻¹ at T > 100°C, and E_D ≈ 42 kJ mol⁻¹ at T < 60°C, with a relatively wide (60–100°C) intermediary domain linked to the glass transition of the polymer. The crystallization of this latter occurs in the time scale of diffusion above 80°C but doesn't change the Fickian character of sorption curves. The equilibrium concentration m_∞ is an increasing function of temperature, but the solubility coefficient S decreases sharply with this latter, with the apparent enthalpy of dissolution ΔH_s being of the order of −28 kJ mol⁻¹ at T < 80°C and −45 kJ mol⁻¹ at T > 80°C. Density measurements in the wet and dry states suggest that water is almost entirely dissolved in the amorphous matrix at T < 80°C but forms partially a separated phase at T > 80°C. Microvoiding can be attributed to crystallization-induced demixing. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1131–1137, 1999     

Reaction kinetics modeling and thermal properties of epoxy–amines as measured by modulated‐temperature DSC. I. Linear step‐growth polymerization of DGEBA + aniline

A mechanistic approach including both reactive and nonreactive complexes can successfully simulate both nonreversing (NR) heat flow and heat capacity (C_p) signals from modulated‐temperature DSC in isothermal and nonisothermal reaction conditions for different mixtures of diglycidyl ether of bisphenol A + aniline. The reaction of the primary amine with an epoxy–amine complex initiates cure (E_1A1 = 80 kJ mol^?1), whereas the reactions of the primary amine (E_1OH = 48 kJ mol^?1) and secondary amine (E_2OH = 48 kJ mol^?1) with an epoxy–hydroxyl complex are rate determining from about 2% epoxy conversion on. The reliability of the proposed mechanistic model was verified by experimental concentration profiles from Raman spectroscopy. When cure temperatures are chosen inside or below the full cure glass‐transition region, vitrification takes place partially or completely, respectively, as can be concluded from the magnitude of the stepwise decrease in C_p. The effect of the epoxy conversion (x) and mixture composition on thermal properties such as the glass‐transition temperature (T_g), the change in heat capacity at T_g [ΔC_p(T_g)], and the width of the glass transition region (ΔT_g) are considered. The Couchman relationship, in which only T_g and ΔC_p(T_g) of both the unreacted and the fully reacted systems are needed, was evaluated to predict the T_g– x relation by using simulated concentration profiles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:2798–2813, 2004     

Laboratory-scale coal reactivity testing for entrained gasification

A relatively simple and rapid micro-gasification test has been developed for measuring gasification reactivities of carbonaceous materials under conditions which are more or less representative of an entrained gasification process, such as the Shell coal gasification process. Coal particles of < 100 μm are heated within a few seconds to a predetermined temperature level of 1000–2000 °C, which is subsequently maintained. Gasification is carried out with either CO₂ or H₂O. It is shown that gasification reactivity increases with decreasing coal rank. The CO₂ and H₂O gasification reactions of lignite, bituminous coal and fluid petroleum coke are probably controlled by diffusion at temperatures 1300–1400 °C. Below these temperatures, the CO₂ gasification reaction has an activation energy of about 100 kJ mol^?1 for lignite and 220–230 kJ mol^?1 for bituminous coals and fluid petroleum coke. The activation energies for H₂O gasification are about 100 kJ mol^?1 for lignite, 290–360 kJ mol^?1 for bituminous coals and about 200 kJ mol^?1 for fluid petroleum coke. Relative ranking of feedstocks with the micro-gasification test is in general agreement with 6 t/d plant results.     

Effect of Temperature on Kinetics and Adsorption Profile of Endothermic Chemisorption Process: –Tm(III)–PAN Loaded PUF System

Abstract

The sorption behavior of 3.18×10^?6 mol l^?1 solution of Tm(III) metal ions onto 7.25 mg l^?1 of 1‐(2‐pyridylazo)‐2‐naphthol (PAN) loaded polyurethane foam (PUF) has been investigated at different temperatures i.e. 303 K, 313 K, and 323 K. The maximum equilibration time of sorption was 30 minutes from pH 7.5 buffer solution at all temperatures. The various rate parameters of adsorption process have been investigated. The diffusional activation energy (ΔE_ads) and activation entropy (ΔS_ads) of the system were found to be 22.1±2.6 kJ mol^?1 and 52.7±6.2 J mol^?1 K^?1, respectively. The thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) were calculated and interpreted. The positive value of ΔH and negative value of ΔG indicate that sorption is endothermic and spontaneous in nature, respectively. The adsorption isotherms such as Freundlich, Langmuir, and Dubinin–Radushkevich isotherm were tested experimentally at different temperatures. The changes in adsorption isotherm constants were discussed. The binding energy constant (b) of Langmuir isotherm increases with temperature. The differential heat of adsorption (ΔH_diff), entropy of adsorption (ΔS_diff) and adsorption free energy (ΔG_ads) at 313 K were determined and found to be 38±2 kJ mol^?1, 249±3 J mol^?1 K^?1 and –40.1±1.1 kJ mol^?1, respectively. The stability of sorbed complex and mechanism involved in adsorption process has been discussed using different thermodynamic parameters and sorption free energy.     

Surfactant (in situ)–Surfactant (Synthetic) Interaction in Na2CO3/Surfactant/Acidic Oil Systems for Enhanced Oil Recovery: Its Contribution to Dynamic Interfacial Tension Behavior

The effect of synthetic surfactant molecular structure on the dynamic interfacial tension (DIFT) behavior in Na₂CO₃/surfactant/crude oil was investigated. Three surfactants, a nonionic (iC₁₇(EO)₁₃), an alcohol propoxy sulfate (C_14–15(PO)₈SO₄), and sodium dodecyl sulfate (SDS) were considered in this study. Sodium tripolyphosphate (STPP) was added to ensure complete compatibility between brine and Na₂CO₃. In Na₂CO₃/iC₁₇(EO)₁₃/oil and Na₂CO₃/C_14–15(PO)₈SO₄/oil systems, a strong synergistic effect for lowering the dynamic interfacial tension was observed, in which the dynamic IFT are initially reduced to ultralow transient minima in the range 1.1 × 10^?3–6.6 × 10^?3 mNm^?1 followed by an increment to a practically similar equilibrium value of 0.22 mNm^?1 independent of Na₂CO₃ concentration (for iC₁₇(EO)₁₃) and to decreasing equilibrium values with increasing alkali concentrations (for C_14–15(PO)₈SO₄). The observed difference in the equilibrium IFT for the two systems suggest that in both systems, the mixed interfacial film is efficient in reducing the dynamic interfacial tension to ultralow transient minima (～10^?3 mNm^?1) but the mixed film soap‐iC₁₇(EO)₁₃ is much less efficient than the mixed film soap‐C_14–15(PO)₈SO₄ in resisting soap diffusion from the interface to the bulk phases. In both systems, the synergism was attributed, in part, to the intermolecular and intramolecular ion–dipole interactions between the soap molecules and the synthetic surfactant as well as to some shielding effect of the electrostatic repulsion between the carboxylate groups by the nearby ethylene oxide (13 EO) and propylene oxide (8 PO) groups in the mixed interfacial monolayer. SDS surfactant showed a much lower synergism relative to iC₁₇(EO)₁₃ and C_14–15(PO)₈SO₄, probably due to the absence of ion–dipole interactions and shielding effect in the mixed interfacial layer at the oil–water interface.     

Effect of moisture‐ingress on adhesion energy in a metal oxide‐polymer system

This work quantifies the damage caused by moisture in a metal coating system under extreme weathering conditions, using Variable Radius Roll Adhesion Test (VaRRAT). Interfacial toughness (adhesion energy) between the metal oxide and the polymer in painted steel panels, studied by using VaRRAT, is observed to fall with increasing temperature and time of exposure to moisture. Possible cause for irreversible loss in adhesion energy in the paint system is attributed to the sorption of free water at the metal oxide–polymer interface. Different failure responses were observed in two different paint–metal systems. Adsorption or diffusion in the Henry's mode is rate controlling in green paints as indicated by the low activation energy of 12 kJ mol^?1. The white samples showed a high activation energy of 30 kJ mol^?1, indicating a mixed process of diffusion as well as chemical to be rate determining. Different paint/binder ratios are responsible for the different responses of these samples. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Methyl,Ethyl, Propyl,Butyl: Futile But Not for Water,as the Correlation of Structure and Thermodynamic Signature Shows in a Congeneric Series of Thermolysin Inhibitors

Water is ubiquitously present in any biological system and has therefore to be regarded as an additional binding partner in the protein–ligand binding process. Upon complex formation, a new solvent‐exposed surface is generated and water molecules from the first solvation layer will arrange around this newly formed surface. So far, the influence of such water arrangements on the ligand binding properties is unknown. In this study, the binding modes of nine congeneric phosphonamidate‐type inhibitors with systematically varied, size‐increasing hydrophobic P₂′ substituents (from methyl to phenylethyl) addressing the hydrophobic, solvent‐exposed S₂′ pocket of thermolysin were analyzed by high‐resolution crystal structures and correlated with their thermodynamic binding profiles as measured by isothermal titration calorimetry. Overall, ΔΔG spreads over 7.0 kJ mol^?1, ΔΔH varies by 15.8 kJ mol^?1, and ?TΔΔS by 12.1 kJ mol^?1. Throughout the series, these changes correlate remarkably well with the geometric differences of water molecules arranged adjacent to the P₂′ substituents. Ligands with medium‐sized P₂′ substituents exhibit highest affinities, presumably because of their optimal solvation patterns around these complexes. The addition, removal, or rearrangement of even a single methyl group can result in a strong modulation of the adjacent water network pattern shifting from enthalpy to entropy‐driven binding. In conclusion, the quality of a water network assembled around a protein–ligand complex influences the enthalpy/entropy signature and can even modulate affinity to a surprising extent.     

Investigation of kinetics of 4‐methylpentene‐1 polymerization using Ziegler–Natta‐type catalysts

The kinetics of 4‐methylpentene‐1 (4MP1) polymerization by use of Ziegler–Natta‐type catalyst systems, M(acac)₃‐AlEt₃ (M = Cr, Mn, Fe, and Co), are investigated in benzene medium at 40°C. The effect of various parameters such as Al/M ratio, reaction time, aging time, temperature, catalyst, and monomer concentrations on the rate of polymerization and yield are examined. The rate of polymerization increased linearly with increasing monomer concentration with first‐order dependence, whereas the rate of polymerization with respect to catalyst concentration is found to be 0.5. For all cases, the polymer yield is maximum at an Al/M ratio of 2. The activation energies obtained from linear Arrhenius plots are in the range of 25.27–33.51 kJ mol^?1. It is found that the aging time to give maximum percentage yield of the polymer varies with the catalyst systems. Based on the experimental results, a plausible mechanism is proposed that envisages a free‐radical mechanism. Characterization of the resulting polymer product, for all the cases, through FTIR, ¹H‐NMR, and ¹³C‐NMR studies, showed isomerized polymeric structures with 1,4‐structure as dominant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2468–2477, 2003     

Non-isothermal crystallisation behaviour of fluorophlogopite/nepheline glass ceramics

Abstract

Fluorophlogopite/nepheline glass ceramics were formed from the system of SiO₂–Al₂O₃–MgO–K₂O–Na₂O–F, and the thermodynamic, crystallisation behaviour and microstructure were investigated using differential thermal analysis, X-ray diffraction, and scanning electron microscopy. It was found that fluorophlogopite crystals and nepheline crystals crystallised simultaneously, and bulk nucleation was the main crystallisation mechanism. Crystal growth was prone to follow the two-dimensional direction and controlled by diffusion. Activation energy for glass transition was 797·43 kJ mol^?1, and crystallisation activation energy was 433·16 kJ mol^?1.     

Toughening of cyanate ester resin by N‐phenylmaleimide–N‐(p‐hydroxy)phenyl‐maleimide–styrene terpolymers and their hybrid modifiers

N‐Phenylmaleimide–N‐(p‐hydroxy)phenylmaleimide–styrene terpolymer (HPMS), carrying reactive p‐hydroxyphenyl groups, was prepared and used to improve the toughness of cyanate ester resins. Hybrid modifiers composed of N‐phenylmaleimide–styrene copolymer (PMS) and HPMS were also examined for further improvement in toughness. Balanced properties of the modified resins were obtained by using the hybrid modifiers. The morphology of the modified resins depends on HPMS structure, molecular weight and content, and hybrid modifier compositions. The most effective modification of the cyanate ester resin was attained because of the co‐continuous phase structure of the modified resin. Inclusion of the modifier composed of 10 wt% PMS (M_w 136 000 g mol^?1) and 2.5 wt% HPMS (hydroxyphenyl unit 3 mol%, M_w 15 500 g mol^?1) led to 135% increase in the fracture toughness (K_IC) for the modified resin with a slight loss of flexural strength and retention of flexural modulus and glass transition temperature, compared with the values for the unmodified resin. Furthermore, the effect of the curing conditions on the mechanical and thermal properties of the modified resins was examined. The toughening mechanism is discussed in terms of the morphological and dynamic viscoelastic behaviour of the modified cyanate ester resin system. © 2001 Society of Chemical Industry     

Reaction kinetics modeling and thermal properties of epoxy–amines as measured by modulated‐temperature DSC. II. Network‐forming DGEBA + MDA

Reaction‐induced vitrification takes place in the network‐forming epoxy–amine system diglycidyl ether of bisphenol A (DGEBA) + methylenedianiline (MDA) when the glass‐transition temperature (T_g) rises above the cure temperature (T_cure). This chemorheological transition results in diffusion‐controlled reaction and can be followed simultaneously with the reaction rate in modulated‐temperature DSC (MTDSC). To predict the effect of T_cure and the NH/epoxy molar mixing ratio (r) on the reaction rate in chemically controlled conditions, a mechanistic approach was used based on the nonreversing heat flow and heat capacity MTDSC signals, in which the reaction steps of primary (E_1OH = 44 kJ mol^?1) and secondary amine (E_2OH = 48 kJ mol^?1) with the epoxy–hydroxyl complex predominating. The diffusion factor DF as defined by the Rabinowitch approach expresses whether the chemical reaction rate or the diffusion rate determines the overall reaction rate. A model based on the free volume theory together with an Arrhenius temperature dependency was used to calculate the diffusion rate constant in DF as a function of conversion (x) and T_cure. The relation between x, r, and T_g, needed in this model, can be predicted with the Couchman equation. An experimental approximation for DF is the mobility factor DF* obtained from the heat capacity signal at a modulation frequency of 1/60 Hz, normalized for the effect of the reaction heat capacity in the liquid state and the change in C_p in the glassy region with x and T_cure. In this way, an optimized set of diffusion parameters was obtained that, together with the optimized kinetic parameters set, can predict the reaction rate for different cure schedules and for stoichiometric and off‐stoichiometric mixtures. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2814–2833, 2004     

Application of nitrogen-enriched nanobiopolymer for the effective removal of Cr(VI) from tannery effluent

Nitrogen-enriched nanobiopolymer has been fabricated using (2,3-epoxypropyl) trimethylammonium chloride (EPTMAC) and explored for the removal of Cr(VI) from tannery effluent. The removal efficiency of nanobiopolymer was found to be 23.99 mg g^?1 (95.94%) under optimized conditions. The sorption data agrees well with the Langmuir and pseudo-second-order model. Equilibrium parameter (R_L) and sorption energy show the favorability and physical binding of Cr(VI) on the nanobiopolymer’s backbone. The values of ?G° (?7.84 kJ mol^?1), ?S° (65.97 J mol^?1K^?1) and ?H° (11.82 kJ mol^?1) reflect the feasible nature of the sorption process. Reusability study was also conducted to state the performance of the nanobiopolymer.     

Kinetic study of ytterbium(III) extraction from sulfate medium with Cyanex 923

The kinetics of ytterbium(III) extraction from sulfate medium with Cyanex 923 in heptane has been investigated with a constant interfacial cell with laminar flow, which aimed to identify the extraction regime, reaction zone and rate equations. It was found that the extraction rate of ytterbium(III) increased linearly with stirring speed and specific interfacial area. The activation energy E_a (9.56 kJ mol^?1), activation enthalpy ΔH^± (7.05 kJ mol^?1), activation entropy ΔS^±₂₉₈ (?0.31 kJ mol^?1) and Gibbs free energy of activation ΔG^±₂₉₈ (98.3 kJ mol^?1) were calculated from the dependence of extraction rate on temperature. The experiential rate equations were obtained by investigating the influence of the concentration of various species on the extraction rate. A diffusion regime has been deduced from evidence of the linear dependence of extraction rate on stirring speed and the low value of the activation energy. The liquid–liquid interface is most probably the reaction zone in view of the linear dependence of extraction rate on specific interfacial area, the high interfacial activity and low water‐solubility of extractant. Thus the mass transfer rate is controlled by interfacial film diffusion of species. Copyright © 2007 Society of Chemical Industry     

Molecular transport characteristics of a chlorosulfonated polyethylene geomembrane in the presence of aromatic esters

Results of a study on sorption and diffusion of chlorosulfonated polyethylene geomembrane with methyl benzoate, ethyl benzoate, methyl salicylate, iso-butyl salicylate, phenyl acetate, and diethyl phthalate in the temperature range 25–60°C are presented. A gravimetric sorption method is used to calculate the diffusion and permeation coefficients from the Fickian relationship. The diffusion results are dependent on penetrant–membrane interactions, temperature, and on penetrant concentration. The values of diffusion coefficients range from 0·02 × 10^?7 cm² s^?1 for diethyl phthalate at 25°C to 1·81 × 10^?7 cm² s^?1 for ethyl benzoate at 60°C. The activation energies for diffusion range from 21 to 50 kJ mol^?1. The values of heat of sorption ranged between 2·2 and 6·4 kJ mol^?1. Sorption results are also analyzed using a first-order sorption kinetic equation. Experimental results and calculated parameters are used to discuss the transport behavior. None of the esters used have shown any chemical attack toward the geomembrane.     

Sorption and diffusion of n-alkanes into bromobutyl rubber membranes

Sorption and diffusion of n-alkanes into bromobutyl rubber membranes were investigated in the temperature interval 25–60°C by a sorption gravimetric method. The Fickian diffusion equation was used to calculate the diffusion coefficients, which were dependent on the size of the alkanes, their interactions with the chain segments of the polymer and temperature. The diffusion coefficients varied from 0.34×10^?7 cm²/s (n-hexadecane) to 9.94×10^?7 cm²/s (n-hexane). The activation energy for diffusion varied from 14kJ/mol (n-hexane) heptane to 2.0kJ/mol for n-hexadecane. The sorption/swelling results are discussed in terms of first and second order kinetic equations. The molar mass between chain-entanglement-crosslinks was estimated from swelling data. The experimental and calculated results showed a systematic dependence on the increasing size of the alkanes. None of the solvents showed any degradative effects on the polymer.