Novel approach in investigation of the poly(acrylic acid) hydrogel swelling kinetics in water

The swelling kinetics curves of structurally defined poly(acrylic acid) hydrogel in bidistilled water at temperatures: 25, 30, 35, 40, and 45°C were determined. The possibility of kinetically explaining the isothermal swelling process by applying the following models: reaction controlled by diffusion, first order chemical reaction kinetics, and second order chemical reaction kinetics, was investigated. It was found that kinetically explaining the swelling process using these methods was limited to only certain parts of the process. The swelling process in bidistilled water was described in full range assuming that the hydrogel's swelling rate was a kinetically controlled reaction by the rate of the movement of reactive interface of hydrogel. Based on that model, the kinetic parameters, activation energy (E_a) and preexponential factor (A), of the swelling process were determined to be E_a = 35 kJ/mol and lnA = 8.6. A possible mechanism of the investigated swelling process was discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The effects of the pH value of the swelling medium on the kinetics of the swelling of a poly(acrylic acid) hydrogel

The isothermal kinetics curves of the swelling of a poly(acrylic acid) hydrogel in buffer solutions of different pH values (5, 7, and 9) at temperatures ranging from 30 to 40°C were determined. The possibilities of applying the Fick kinetics model and the Peppas equation were examined. It was found that the applicability of these models were limited. The kinetics model of a first‐order chemical reaction was found to describe the swelling kinetics of the PAA hydrogel in all the investigated buffer solution at all the investigated temperatures. Swelling kinetics is determined by the rate of expansion of the network. The kinetic parameters (E_a, ln A) of the swelling of the PAA hydrogel in buffer solutions of different pH values were determined. The activation energy and the pre‐exponential factor of the swelling of the PAA hydrogel in buffer medium decreased with increasing pH value of the swelling medium. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Physical properties of hydrogels of poly(2‐hydroxyethyl methacrylate) and copolymers with mono‐methyl itaconate synthesized by bulk and solution polymerization

The physical properties found during the swelling process of poly(2‐hydroxyethyl methacrylate) (PHEMA) and of copolymers of HEMA with mono‐n‐methyl itaconate, synthesized by solution and bulk polymerization, are reported. The swelling kinetics were followed at four different temperatures (295, 300, 305 and 310 K). Experimental data follow second‐order swelling kinetics, from where the kinetic rate constant k_∞ and the swelling capacity at equilibrium W_∞ were calculated as a function of temperature. The kinetic rate constant obeys Arrhenius behaviour. The following network parameters were determined for the hydrogels: Young's moduli E, effective crosslinking density v_e, molar mass per crosslink M_C, volume fraction ϕ₂ and polymer‐liquid interaction parameter χ. © 2000 Society of Chemical Industry     

Evolution of Oxidative Values during Kinetic Studies on Olive Oil Oxidation in the Rancimat Test

A comparative study was carried out in order to evaluate the kinetics of the formation of a number of primary and secondary oxidation products during oxidation of olive oil in the Rancimat test at 100–130 °C. There were good correlations between the Rancimat index (OSI) and stability indices (IP) measured in the Rancimat test with no significant differences in kinetic parameters calculated from them. Mean values of the temperature coefficient, Q₁₀ number, activation energy (E_a), frequency factor (A), and free energy of activation (ΔG⁺⁺) for olive oil oxidation were calculated to be ?3.44 × 10^?2°C^?1, 2.21, 98.91 kJ/mol, 12.17 × 10¹² h^?1, and 128.25 kJ/mol, respectively. Each unit change in E_a was accompanied by an average 1.43 × 10¹² change in A, indicating a higher contribution for factor A than for E_a to the olive oil stability. The E_a and A correlated well with the values of enthalpy and entropy, respectively. The values of OSI or IP could be described well by the ΔG⁺⁺ values. Kinetic data indicated that olive oil stability is more affected by the indigenous antioxidants than by the fatty acid composition.     

Water Uptake Kinetics and Control Release of Agrochemical Fertilizers from Nanoclay-Assisted Semi-interpenetrating Sodium Acrylate-Based Hydrogel

Semi-interpenetrating composite hydrogels composed of poly(acrylic acid-co-sodium acrylate)/polyethylene glycol for the controlled release of fertilizers were synthesized by using nano-phyllosilicate. Hydrogel was characterized by infrared spectral analysis (Fourier transform infrared), X-ray diffraction, and scanning electron microscopy. The cross-link density (ρ_c), average molecular weight between cross-links (M_c), and the mesh size of the network (?) were also determined. The degree of neutralization of acrylic acid component has a positive impact in the swelling behavior of hydrogel, which was investigated through its swelling study and pH-oscillatory behavior. The dependency of synthesis parameters, pH and ionic strength on swelling characteristics were investigated. The type of the diffusion phenomena was investigated by calculating various kinetic parameters such as the diffusion coefficient, diffusion rate constant, swelling exponents, etc. The swelling ratio with varying synthetic parameters was recorded to investigate fourth-order factorial model. The model gives the idea of the effect of the independent parameters on the swelling ratio.     

Influence of poly(acrylic acid) xerogel structure on swelling kinetics in distilled water

Summary The basic structural properties of xerogels of crosslinked poly(acrylic acid) were defined and determined: xerogel density (ρ_xg), xerogel volume fraction in the equilibrium-swollen state (v₂), the number average molar mass between network crosslinks , the crosslink density (ρ_c) and the distance between macromolecular chains (d). A crosslinking ratio (X) increase leads to a linear increase in the values for ρ_xg and ρ_c, while the values and d decrease. The isothermal swelling kinetic curves of four samples of structurally different poly(acrylic acid) xerogels in bidistilled water at different temperatures ranging from 25 to 45 °C were determined. It is shown that isothermal kinetic swelling curves could not be described with the model of first-order reaction kinetics in entire. It was found that these curves could be described by the Johanson-Mampel-Avrami (JMA) equation. For all of the investigated xerogel samples, the initial swelling rate (v_in), effective reaction rate constant (k) and equilibrium swelling degree increased with swelling temperature increase. Based on the determined values of the v_in and k, the activation energy (E_a) and pre-exponential factor (lnA) were determined. It was concluded that the activation energy linearly increased with increasing distance between macromolecular chains (d) and molar mass between the network crosslinks . The relationship between the activation energy changes with pre-exponential factor (compensation effect) caused by xerogel structural properties was established. Isothermal swelling kinetics could be completely described by the kinetics of phase transition of the xerogel transformation from glassy to rubbery state, i.e. with the JMA kinetic equation.     

Kinetics study of isothermal nicotine release from poly(acrylic acid) hydrogel

The isothermal kinetic of the release of nicotine from a poly(acrylic acid) (PAA) hydrogel was investigated at temperature range from 26°C to 45°C. Specific shape parameters of the kinetic curves, the period of linearity and saturation time were determined. The change in the specific shape parameters of the kinetic curves with temperature and the kinetic parameters of release of nicotine E_a and ln A were determined. By applying the “model fitting” method it was established that the kinetic model of release of nicotine from the PAA hydrogel was [1 − (1 − α)^1/3] = k_Mt. The limiting stage of the kinetics release of nicotine was found to be the contracting volume of the interaction interface. The distribution function of the activation energy was determined and the most probable values of activation energies of 25.5 kJ mol⁻¹ and 35 kJ mol⁻¹ were obtained. Energetically heterogeneity of the interaction interface was explained by the existence of the two different modes of bonding the nicotine molecules onto the hydrogel network by hydrogen bond and electrostatic forces. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Tl(III) initiated polymerization of methyl methacrylate in micellar phase

The polymerization kinetics of methyl methacrylate (MMA) was studied, using Tl(III)‐cyclohexanone (CH) redox system as initiator, in the presence of emulsifier [i.e., sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and thallium triacetate (TX‐100)] over a temperature range of 25–45°C. The effect of various concentrations of MMA, Tl(III), cyclohexanone, H⁺, and varying ionic strengths on the rate of polymerization, rate of Tl(III) consumption (?R_Tl), and the percentage of monomer conversion were examined in the presence of 0.015M SDS. The kinetic results of polymerization in the absence and presence of 0.015M SDS were compared in terms of overall activation energy (E_a) for the process. The viscosity‐average molecular weight (M_V) of the polymers, obtained in the presence of varying concentrations of anionic surfactant (SDS), was also determined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2480–2485, 2004     

Swelling and Network Parameters of Oil Sorbers Based on Alkyl Acrylates and Cinnamoyloxy Ethyl Methacrylate Copolymers

Cinnamoyloxy ethyl methacrylate (CEMA) monomer was copolymerized with different monomer feed ratios of alkyl acrylate, such as dodecyl and octadecyl acrylate DDA and ODA, respectively. The monomers were copolymerized with different mole% to produce different compositions for each CEMA/alkylacrylate copolymer with low conversion. ¹HNMR was used to determine the copolymer compositions. The monomer reactivity ratios of each CEMA/alkylacrylate copolymer were determined using Fineman-Ross and Kelen-Tudos methods. CEMA was copolymerized with DDA or ODA and crosslinked using azobis isobutyronitrile (AIBN) as the initiator and 1% weight content of either 1,1,1-trimethylolpropane triacrylate (TPT) or 1,1,1-trimethylolpropane trimethacrylate (TPT_m) crosslinkers. The swelling parameters, such as the maximum oil absorbency (Q _max), characteristic oil sorbency (Q), characteristic swelling time (T), and swelling rate constant (k), were evaluated for the synthesized sorbers. The network parameters, such as the polymer solvent interaction (χ), effective crosslink density (υ _e), equilibrium modulus of elasticity (G _T), average molecular weight between crosslinks (M _c), and the theoretical crosslink density (υ _t), were determined and correlated with the structure of the synthesized sorbers.     

Studies of thermal,mechanical properties,and kinetic cure reaction of carboxyl-terminated polybutadiene acrylonitrile liquid rubber with diepoxy octane

Epoxy resins, despite their unique properties, have limitations in many applications due to their low fracture toughness. One of the most effective methods to overcome this limitation is to use toughening agents, such as carboxyl terminated poly butadiene-acrylonitrile (CTBN) in the epoxy matrix. CTBN can react with various compounds, such as epoxies. In this study, we investigated the severity of CTBN sedimentation with di epoxy octane (DEO) in the presence basis catalysts. The studied of the physical properties of the synthesized copolymer in the presence of pyridine compared to other catalysts increases mechanical properties (248.43% elongation, 0.63 MPa strength, and 32 hardness with Shore A) and decreases the glass transition temperature (−45.1) of the copolymer. Investigated the cure kinetics of the CTBN-DEO reaction was in the presence of pyridine using a nonisothermal technique of differential scanning calorimetry, and the curing kinetic parameters, such as activation energy (E_a), pre-exponential factor (A), and rate constant (k), were calculated by different kinetic methods. The obtained curing kinetic values with different kinetic methods are well-matched, the E_a values are in the range of 91.3–97.1 kJ.mol⁻¹ and the A values are in the range of 0.48 × 10¹¹–1.51 × 10¹¹ S⁻¹.     

Isoconversional and thermal methods of kinetic analysis of 2,4‐dihydroxybenzophenone copolymer resin

A copolymer (2,4‐DHBPOF) synthesized by the condensation of 2,4‐dihydroxybenzophenone and oxamide with formaldehyde in the presence of acid catalyst with varying the molar proportions of the reacting monomer. Composition of the copolymer has been determined by elemental analysis. The copolymer has been characterized by UV–visible, FTIR, and ¹H NMR spectroscopy. The morphology of synthesized copolymer was studied by scanning electron microscopy (SEM). The activation energy (E_a) and thermal stability calculated by using Sharp‐Wentworth, Freeman–Carroll, and Freidman's method. Thermogravimetric analysis (TGA) data were analyzed to estimate the characteristic thermal parameters. Freeman–Carroll and Sharp Wentworth methods have been used to calculate activation energy and thermal stability. The activation energy (E_a) calculated by using the Sharp‐Wentworth has been found to be in good agreement with that calculated by Freeman–Carroll method. Thermodynamic parameters such as free energy change (ΔF), entropy change (ΔS), apparent entropy change (S*), and frequency factor (Z) have also been evaluated based on the data of Freeman–Carroll method. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The effects of the synthesis parameters on the xerogels structures and on the swelling parameters of the poly(methacrylic acid) hydrogels

Poly(methacrylic acid) hydrogels were synthesized. The effects of the synthesis parameters: the neutralization degree of methacrylic acid and the concentrations of monomer, crosslinker and initiator on the xerogels structural properties: the xerogel density (ρ_xg), the number average molar mass between the network crosslinks (M_c), the crosslink degree (ρ_c), the number of elastically effective chains totally induced in a perfect network per unit volume (V_e), the distance between the macromolecular chains (ξ) and the equilibrium swelling degree (SD_eq) and the swelling kinetics was investigated. As the concentrations of crosslinker, monomer and initiator increase, the value of ρ_xg, ρ_c and V_e increases and decreases the value of M_c, ξ and SD_eq. With the increase in the neutralization degree of methacrylic acid, the values of ρ_xg, M_c, ξ, SD_eq increase, while the ρ_c and V_e decrease. The xerogels structural properties, SD_eq and swelling kinetic parameters are mainly in power law form functional relationships with the synthesis parameters as well as with the xerogels crosslinking degree.     

Comparison of the kinetics of conventional and microwave methyl methacrylate polymerization

A comparative investigation of the conventional and microwaves kinetics of methyl methacrylate (MMA) polymerization was performed. A method for determining the increase of the reaction rate in the microwave field (β) was presented. It was found that at all of the investigated temperatures and powers the polymerization rates increased in the presence of microwave energy by up to 8.9 times compared with conventional polymerization. Isothermal kinetics of the conventional MMA polymerization was investigated and its parameters were determined using isoconversion method. It was found that the calculated kinetics parameters changes complexly with degree of MMA conversion (α) and are in the mutual linear functional relationship, which is so called “compensation effect.” The complex changes of the kinetics parameters with α are explained with the postulated model for the mechanism of the MMA polymerization. The kinetics of the MMA polymerization under the microwave field (MWF) with different input power was investigated and its parameters were determined on the basis of the conversion‐temperature curves and Arrhenius equation. The values of the kinetics parameters for MMA polymerization in the MWF are dependent on α and are from 1.2 to 12 times lower than that for conventional MMA polymerization. A new method for the determination of activation energy (E_a) of the investigated process in the MWF was described. Decreased E_a value of the polymerization process in the MWF compared with the conventional polymerization is explained with the formation of the nonequilibrium energetic distribution of the reactants due to the rapid transfer of energy in the reaction system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1775–1782, 2007     

Nonisothermal decomposition kinetics of nylon 1010/POSS composites

The thermal stability of nylon 1010/polyhedral oligomeric silsesquioxane (POSS) composites prepared by melt blending was investigated with thermogravimetric analysis. The octavinyl POSS (vPOSS) and epoxycyclohexyl POSS (ePOSS) were used, and it was found that nylon/vPOSS composites have higher integral procedure decomposition temperature and char yield at 800°C than nylon/ePOSS composites. The Doyle–Ozawa (model‐free) and Friedman (model‐fitting) methods were used to characterize the nonisothermal decomposition kinetics of nylon 1010 and its composites. The activation energy (E_a), reaction order (n), and the natural logarithm of frequency factor of nylon 1010 were 267 kJ/mol, 1.0, and 47 min^?1, respectively, in nitrogen. After the addition of POSS, the E_a of nylon 1010 considerably increased, whereas n had less change. The E_a steadily increased with increasing conversion and with increasing heating rate. The lifetime of nylon 1010 and its composites decreased with increasing temperature. At a given temperature, POSS significantly prolonged the lifetime of nylon 1010. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Cardanol‐based novolac‐type phenolic resins. I. A kinetic approach

Novolac resins having two different mole ratios of cardanol‐to‐formaldehyde (1:0.6 and 1:0.8) were prepared by using aliphatic tricarboxylic acid as catalyst at four different temperatures ranging between 100 and 130°C with an interval of 10°C. The synthesized novolacs were confirmed by infrared spectroscopic analysis with the appearance of characteristic groups of the novolac resin. The reaction between cardanol (C) and formaldehyde (F) was found to follow second‐order rate kinetics as determined by two different approaches. The over all rate constant (k) increased with the increase of C/F molar ratio. Based on the value of k, various other kinetic parameters such as activation energy (E_a), change in enthalpy (ΔH), entropy (ΔS), and free energy (ΔG) of the reaction were also evaluated. The values of E_a and ΔH were found to be decreased with the increase of C/F molar ratio from 1:0.6 to 1:0.8. These values revealed the nature of the condensation reaction between cardanol and formaldehyde in presence of tricarboxylic acid catalysts. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:2730–2737, 2006     

Nonisothermal cure kinetics and diffusion effect of liquid-crystalline epoxy sulfonyl bis(1,4-phenylene)bis[4-(2,3-epoxypropyloxy)benzoate] resin with aromatic diamine

The curing kinetics of the liquid-crystalline epoxy resin sulfonyl bis(1,4-phenylene)bis[4-(2,3-epoxypropyloxy)benzoate] with 4,4′-diaminodiphenylsulfone was investigated by nonisothermal differential scanning calorimetry. The relationship between the apparent activation energy (E_a) and the conversion was determined, and the effects of the molecular structure and the order of liquid crystallinity on E_a are discussed in detail. Some parameters were evaluated with the autocatalytic kinetic model of the Šesták–Berggren (S–B) equation. The results show that there were some deviations of these simulation curves from the experimental curves at high heating rates and in the late stage of the curing reaction. The diffusion effect in the nonisothermal curing reaction is discussed, and a diffusion factor was proposed and introduced into the S–B equation. Then, a modified S–B equation was created, as follows: , where α is the conversion, t is the time, m and n are reaction orders, K is rate constant, C is the diffusion coefficient, and α_c is the critical conversion. The theoretical simulation curves agreed very well with the experimental data as determined with the modified S–B equation, which may be more useful for describing and predicting the nonisothermal curing reaction kinetics of epoxy resin. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Ionizable interpenetrating polymer networks of carboxymethyl cellulose and polyacrylic acid: Evaluation of water uptake

A semi interpenetrating polymer network (IPN) of carboxymethyl cellulose (CMC) and crosslinked polyacrylic acid (PAA) has been prepared and its water‐sorption capacity has been evaluated as a function of chemical architecture of the IPN, pH, and temperature of the swelling medium. The water uptake potential of the IPNs has also been investigated in inorganic salt containing aqueous solutions and simulated biological fluids. The IPN was characterized by IR spectral analysis, and the network parameters such as average molecular weight between crosslinks (M_c), crosslink density (q), and number of elastically effective chains (V_e) have been evaluated by water‐sorption measurements. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2054–2065, 2004     

Swelling Behaviour of Cured Urea–Formaldehyde Resin Adhesives with Different Formaldehyde to Urea Mole Ratios

As a part of understanding of the network structure of urea–formaldehyde (UF) resin adhesives, this study examined the swelling behaviour of cured UF resin adhesives with four different formaldehyde–urea (F/U) mole ratios, using Flory–Rehner thermodynamic theory and field emission-scanning electron microscopy (FE-SEM) to relate the swelling behaviour to consequently induce micromorphological changes. Cured UF resin films before and after acetone extraction were exposed to swelling in dimethyl sulphoxide at three different temperatures. For the first time, this study reported the experimentally determined swelling parameters, such as sol fraction (ω_sol), polymer volume fraction (φ_p), polymer–solvent interaction parameter (χ), and the number average molecular weight between cross-links (M_c), for cured UF resin adhesives. Both ω_sol and M_c decreased as the F/U mole ratio increased. But these values increased with an increase in the swelling temperature. The extraction resulted in negative ω_sol values, suggesting the removal of a scattered distribution of ω_sol in the cured UF resins. The micromorphology helped to explain the differences in the molecular integrity of the resins, indicating a close relationship between the swelling behaviour and the morphological changes after the swelling.     

Cure kinetics of the cardanyl acrylate–styrene system using isothermal differential scanning calorimetry

The curing kinetics of styrene (30 wt %) and cardanyl acrylate (70 wt %), which was synthesized from cardanol and acryloyl chloride, was investigated by differential scanning calorimetry under isothermal condition. The method allows determination of the most suitable kinetic model and corresponding parameters. All kinetic parameters including the reaction order, activation energy E_a and kinetic rate constant were evaluated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2034–2039, 2002     

Urethane reaction kinetics of butanediols catalyzed by Zr(acac)4

The urethane reaction of isocyanate was carried out with zirconium acetyl acetonate (Zr(acac)₄) as catalyst. 1,2‐Butanediol and 1,4‐butanediol were used as model compounds to investigate the reaction kinetics. It was shown that hydroxyl groups in 1,2‐butanediol appeared to have different reaction rate when reacting with phenyl isocyanate, which was labeled as k_fast and k_slow. It was very surprising that the reaction rate of 1,4‐butanediol (k_con) was very similar to the value of k_slow at the same temperature although there is only primary hydroxyl group in its molecule. Furthermore, activation energy (E_a), activation enthalpy (ΔH), and activation entropy (ΔS) for the reaction were calculated out, from which some catalytic properties of Zr(acac)₄ were revealed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013