Equilibrium Swelling Data Research Articles

Solvent polarity impacts the sorption kinetics and tensile properties of carbon black filled elastomers

Room temperature sorption kinetics is conducted on semi-crystalline ethylene-co-butyl acrylate (EBA) polymer samples filled with different contents of carbon black (CB) in polar (ethanol) or non-polar (toluene) solvents. Equilibrium swelling data obtained by solvent uptake measurements are found to decrease as the CB content increases. This is due to the increase of the crosslink density and tortuosity inside the EBA/CB samples. The preferential area occupied by the solvent molecules in the samples is determined by analyzing the behavior of the wetting coefficient. Higher equilibrium uptake and faster solvent penetration are observed for toluene compared to the case of ethanol. Billmeyer's approach, that is phenomenologically sound and insightful while mathematically straightforward to implement, is applied where the specific parameters of this approach are determined from experiments. Subsequently, the transport mechanisms are discussed using the Peppas-Sahlin and Berens-Hopfenberg relaxation-diffusion models. A significant drop in the tensile properties is observed in the swollen samples compared to their dry counterparts. Furthermore, the sorption data and the mechanical response are found to be well correlated. Additionally, the stress-strain curves of the swollen and dry samples under large deformation are analyzed with the Haward-Thackray model by considering microstructure characteristics (CB content, strain hardening modulus, entanglement, cross-linking degree and polymer-solvent interaction).

Swelling of Random Copolymer Networks in Pure and Mixed Solvents: Multi-Component Flory–Rehner Theory

A generalized extension of Flory-Rehner (FR) theory is derived to describe equilibrium swelling of polymer networks, including copolymers with two or more chemically distinct repeat units, in either pure or mixed solvents. The model is derived by equating the chemical potential of each solvent in the liquid and gel phases at equilibrium, while assuming the deformation of the network chains is affine. Simplifications of the model are derived for specific cases involving homopolymer networks, copolymer networks, pure solvents, and binary solvent mixtures. With reasonable assumptions, the number of polymer-solvent interaction parameters that must be determined by experiments can be reduced to two effective parameters (θ1 and θ2), which describe the net interactions between water/copolymer (θ1) and ethanol/copolymer (θ2), respectively. Experimental measurements of the swelling of random copolymer networks of n-butyl acrylate and 2-hydroxyethyl acrylate in water, ethanol, and a 100 g/L ethanol/water mixture are utilized to validate the model. For a random copolymer network, θ1 and θ2 can be obtained by fitting the three-component FR model to equilibrium swelling data obtained in the pure solvents. Predicted solvent volume fractions for swelling in water-ethanol mixtures obtained by inserting fitted values of θ1 and θ2 into the four-component FR model are in reasonable agreement with experimental measurements.

Charge density dependence of elasticity of anionically modified N,N-dimethylacrylamide-based gels with (meth)acrylic acid segments: An insight by quantitative analysis of electrostatic contributions

Swollen state properties of modified polyelectrolyte gels with anionic species is highly dependent on the effective charge density distributions as well as the interactions between the mobile and immobile groups. A more systematic and comparative study of the role of structure and content of the anionic comonomers has been made on poly(N,N-dimethylacrylamide) PDMAAm-based hydrogels attention being focused on their Gaussian elasticity and corresponding swollen state properties. A thermodynamic framework for interpreting gel-swelling model was presented to describe the aqueous equilibrium swelling properties of a series of weakly ionic polyelectrolyte hydrogels based on acidic comonomers; acrylic acid (AAc), methacrylic acid (MAAc), sodium acrylate (NaA) and a base monomer DMAAm as well as the effect of ionizable groups on their resulting mechanical properties. The introduction of the electrostatic interactions decreased the elastic modulus of ionic PDMAAm hydrogels and cryogels. The model predicts well the effect of the gel charge density on the elasticity; however, the correlation of the obtained results with the equilibrium swelling data suggests that a change of the gel microstructure with electrostatic interactions is the responsible of the observed background effect. Although the ionizable functional groups of AAc and MAAc display weak anionic polyelectrolyte characteristics, the swelling ratio is enhanced with respect to homopolymeric PDMAAm, increasing in the order DMAAm<MAAc<AAc<NaA.

NEW INSIGHTS INTO RUBBER NETWORK STRUCTURE BY A COMBINATION OF EXPERIMENTAL TECHNIQUES

ABSTRACTRobust quantitative cross-link density characterization becomes necessary for the complete understanding of the structure and optimization of final properties of rubber compounds for industrial applications. A combination of different experimental techniques have been used to establish the quantitative consistency on the correlations between the results obtained by the individual methods within a reliable unique (physically based) platform reclined on the concept of rubber elasticity that considers the impact of entanglements in technical rubbers. The contribution of cross-links and elastically active entanglements to mechanical properties has been quantified by the analysis of uniaxial stress–strain measurements by means of the extended tube model of rubber elasticity. In a complementary manner, rubber network structure has also been investigated by state-of-the-art multiple-quantum low-field NMR experiments and classical T1 and T2 relaxation measurements. In addition, equilibrium swelling data were analyzed by the classical phantom and Flory–Rehner limits as well as by applying the theoretical approach proposed by Helmis, Heinrich, and Straube that takes into account topological constraints during swelling. Correlations among these complementary techniques have been reported, and the interpretation of the obtained differences is addressed. The baseline study focuses on unfilled NR, setting the basis for the investigation of unfilled SBR matrices and filled rubbers.

Effect of nature of chemical crosslinker on swelling and solubility parameter of a new stimuli-responsive cationic poly(N-acryloyl-N′-propyl piperazine) hydrogel

New stimuli-responsive cationic hydrogels based on N-acryloyl-N′-propyl piperazine (AcrNPP) were prepared using two types of chemical crosslinkers, viz., N,N-methylene bisacrylamide (Mba) and 1,4-butanediol diacrylate (Bda), respectively. The solubility parameter of the hydrogels was evaluated by equilibrium swelling experiment in a series of twelve solvents with well-distributed range of solubility parameters. The hydrogels exhibited maximum equilibrium swelling ratio in 1-butanol. The experimental swelling data were analyzed by two methods, (1) non-linear curve fitting and (2) least-square regression to determine the solubility parameter of the hydrogels. The solubility parameter determined by the two methods was in the range 11.45–11.85 (cal cm−3)1/2. The solubility parameter of the hydrogel containing the hydrophilic crosslinker (Mba) was higher than the hydrogel with a hydrophobic crosslinker (Bda), in all cases. This showed that the nature of chemical crosslinker influences the swelling and thus the solubility parameter of the hydrogels. The partial solubility parameter of the hydrogels related to the cohesive energy was evaluated by plotting the equilibrium swelling data against dispersion forces, polar forces, and hydrogen bonding. It was observed that both polar forces and hydrogen bonding play an important role in the swelling of these cationic hydrogels. The solubility parameter and the related forces were also estimated theoretically using group contribution methods and compared with the experimental results.

A green approach to prepare silver nanoparticles loaded gum acacia/poly(acrylate) hydrogels

In this work, gum acacia (GA)/poly(sodium acrylate) semi-interpenetrating polymer networks (Semi-IPN) have been fabricated via free radical initiated aqueous polymerization of monomer sodium acrylate (SA) in the presence of dissolved Gum acacia (GA), using N,N′-methylenebisacrylamide (MB) as cross-linker and potassium persulphate (KPS) as initiator. The semi-IPNs, synthesized, were characterized by various techniques such as X-ray diffraction (XRD), thermo gravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The dynamic water uptake behavior of semi-IPNs was investigated and the data were interpreted by various kinetic models. The equilibrium swelling data were used to evaluate various network parameters. The semi-IPNs were used as template for the in situ preparation of silver nanoparticles using extract of Syzygium aromaticum (clove). The formation of silver nanoparticles was confirmed by surface plasmon resonance (SPR), XRD and transmission electron microscopy (TEM). Finally, the antibacterial activity of GA/poly(SA)/silver nanocomposites was tested against E. coli.

A quantitative analysis of alginate swelling

The swelling behavior of physically cross-linked polysaccharides is not fully understood despite its significance in many applications such as drug delivery. In this study the swelling behavior of three types of alginate were characterized experimentally at various calcium concentrations. Additionally, equilibrium swelling data was analyzed in terms of Flory and rubber elasticity theories, which were developed for chemically cross-linked networks. This analysis suggested that these theories are not applicable for alginate. In particular, an increase in the number of monomeric units between cross-links was observed at a higher calcium concentration, whereas the theory predicts the opposite. The kinetics of the swelling process was also analyzed experimentally and theoretically. The experimental data was found to obey second-order kinetics. Moreover, a decrease in the swelling rate constant with elevated calcium concentration was observed. Lastly, it is indicated that the unusual swelling behavior of alginate could be attributed to a lateral chain association.

Study on Kinetics of Natural Rubber Vulcanization by S/La(DiPDP) 3

Abstract Kinetics of natural rubber (NR) vulcanization by lanthanum O, O'-diisopropyldithiophosphate [La(DiPDP) 3] was studied. La(DiPDP) 3 had remarkable accelerating effect on the vulcanization of NR. The rate constant k 6 of the reaction that turned polysulphidic cross-links into the modified main chain was higher than that of desulfuration reaction of polysulfidic cross-links ( k 3). The activation energies ( E a2, E a3, and E a6) of the formation, desulfuration, and decomposition of polysulfidic cross-links were 87.57, 102.34, and 95.01 kJ · mol −1, respectively. Activation energy ( Ea 5) of the reaction that turned the cross-link precursors into the modified main chain was 82.67 kJ · mol −1. It could be concluded that the proportion of polysulphidic cross-links was higher than mono- and di-sulphidic cross-links during induction and curing periods, mono- and di-sulphidic cross-links increased as curing temperature rose. In the temperature range of 140 ∼ 160 °C, the amounts of polysulphidic cross-links were similar. However, over 160 °C, mono- and di-sulphidic cross-links increased rapidly. Moreover, cross-link density of the vulcanizates was determined from the equilibrium-swelling data. A chemical probe detected the concentration of polysulphidic cross-links of vulcanizates. The change trend of the results predicated from equation corresponded to that of the experimental results.

Modification of rubber by iodoform

AbstractThe activity of iodoform (CHI3) toward unsaturated rubbers was examined. Special attention was devoted to cis‐1,4‐(poly)isoprene (IR). The thermal decomposition of CHI3 was studied by ion mass spectroscopy, and the obtained data were used for the identification of pyrolysis products of CHI3 vulcanizates by pyrolytic gas chromatography. The kinetics of the chemical crosslinking of rubber were studied with a cure meter. The changes observed in the chemical structure of rubber were explained on the basis of 13CNMR and Fourier transform infrared spectroscopy, differential scanning calorimetry, equilibrium swelling, and chemical microanalysis data. Apart from crosslinking, a simultaneous modification of the rubber macromolecules took place, specifically the cis–trans isomerization of IR. This resulted in a significant increase in the rubber hardness, especially after a postheat treatment accompanied by oxidation. CHI3–IR vulcanizates behaved like thermoplastics because of the presence of a trans‐1,4 phase, as confirmed by dynamic mechanical thermal analysis. The structure of the macromolecules treated with CHI3 and its effect on the physical properties of the material were compared with those of peroxide–IR vulcanizates. The influence of the modification on the surface energy, bacteriostaticity, and mechanical properties of the vulcanizates was examined. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 177–189, 2007

Synthesis and characterization of novel dendritic (arborescent, hyperbranched) polyisobutylene–polystyrene block copolymers

AbstractThe synthesis of novel arborescent (arb; randomly branched, “tree‐like,” and often called “hyperbranched”) block copolymers comprised of rubbery polyisobutylene (PIB) and glassy polystyrene (PSt) blocks (arb‐PIB‐b‐PSt) is described. The syntheses were accomplished by the use of arb‐PIB macroinitiators (prepared by the use of 4‐(2‐methoxyisopropyl) styrene inimer) in conjunction with titanium tetrachloride (TiCl4). The effect of reaction conditions on blocking of St from arb‐PIB was investigated. Purified block copolymers were characterized by 1H NMR spectroscopy and Size Exclusion Chromatography (SEC). arb‐PIB‐b‐PSt with 11.7–33.8 wt % PSt and Mn = 468,800–652,900 g/mol displayed thermoplastic elastomeric properties with 3.6–8.7 MPa tensile strength and 950–1830% elongation. Samples with 26.8–33.8 wt % PSt were further characterized by Atomic Force Microscopy (AFM), which showed phase‐separated mixed spherical/cylindrical/lamellar PSt phases irregularly distributed within the continuous PIB phase. Dynamic Mechanical Thermal Analysis (DMTA) and solvent swelling of arb‐PIB‐b‐PSt revealed unique characteristics, in comparison with a semicommercial PSt‐b‐PIB‐b‐PSt block copolymer. The number of aromatic branching points of the arb‐PIB macroinitiator, determined by selective destruction of the linking sites, agreed well with that calculated from equilibrium swelling data of arb‐PIB‐b‐PSt. This method for the quantitative determination of branching sites might be generally applicable for arborescent polymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1811–1826, 2005

Influence of Novel Electron Beam Modified Surface Treated Dual Phase Filler on Rheometric and Mechanical Properties of Styrene Butadiene Rubber Vulcanizates

Abstract Rheometric and mechanical properties, hysteresis and swelling behavior of the Styrene-Butadiene Rubber vulcanizates (SBR) filled with unmodified and novel electron beam modified surface treated dual phase fillers were investigated. Scorch time increases for these modified filler loaded vulcanizates due to introduction of quinone type oxygen on the surface. Electron beam modification of dual phase filler in the absence of trimethylol propanetriacrylate (TMPTA) or triethoxysilylpropyltetrasulphide (Si-69) significantly improves the modulus of the SBR vulcanizates, whereas the values of tensile strength and elongation at break drop. However, presence of TMPTA or silane slightly increases the modulus with significant improvement in tensile strength. This effect is more pronounced at higher loading of these modified fillers in SBR vulcanizates. These variations in modulus and tensile strength are explained by the equilibrium swelling data, Kraus plot and a new mathematical model interpreting the polymer-filler interaction. Hysteresis loss ratio of SBR vulcanizates loaded with irradiated fillers in absence and presence of TMPTA or silane increases due to highly aggregated structure of the filler.

Monte Carlo Simulation of the Effect of Entanglements on the Swelling and Deformation Behavior of End-Linked Polymeric Networks

The effect of entanglements on deformation properties of end-linked networks was investigated using Monte Carlo simulations. Model tetrafunctional networks were prepared by cross-linking precursor monodisperse chains in the framework of the bond fluctuation model (BFM). The degree of entanglement in these networks was tuned by changing the precursor chain lengths (N = 20 and 50-mers) and the initial polymer concentration (Φ0). Continuum-space simulations of isotropic swelling and uniaxial deformation were carried out in isobaric and isostress ensembles, respectively. Both equilibrium swelling and force-strain data indicated that elastic forces are enhanced in more entangled networks. The effect of Φ0 on the equilibrium swelling and on the elastic modulus was analyzed with the help of scaling theory and the Rubinstein and Panyukov model, respectively; our results are shown to be consistent with reported experimental data. Our results indicate that the effect of entanglements on the network elastic response is the largest at small extension and decreases with strain at higher extensions (supporting an entanglement-slippage scenario).

Investigations on the addition of styrene butadiene rubber in natural rubber and dichlorocarbene modified styrene butadiene rubber blends

This paper focuses on the use of styrene butadiene rubber (SBR) as a viscosity modifier in novel blends of natural rubber (NR) and dichlorocarbene modified styrene butadiene rubber (DCSBR). The processing characteristics, vulcanisation kinetics, stress-strain behaviour, mechanical properties and low temperature transition of the blends have been examined in order to analyse the influence of SBR in the blends. The change in cross-link density values from stress strain behaviour and equilibrium swelling data has been correlated with the technological properties of the blends. The excellent mechanical properties and the increased cross-link density in blends in the presence of 5—10 phr of styrene butadiene rubber reveals the viscosity modifying action of SBR in NR/DCSBR blends. The variation in viscosities of these blends with the addition of SBR is reflected in the DSC thermograms. The resulting blends show very high resistance to thermal ageing as compared to those without SBR.

Characterization of polyimide gels crosslinked with hexamethylene diisocyanate

Characterization of the crosslinked structure has been carried out for soft polyimide gels prepared from a soluble high-performance fluorine-containing polyimide consisting of 4,4′-(hexafluoro-isopropylindene)diphthalic anhydride and 3,3′-dihydroxy-4,4′-diaminobiphenyl crosslinked with hexamethylene diisocyanate. Weight-average molecular weight (Mw=9.28×104), second and third virial coefficients (A2=0.82×10−3molml/g2, A3=6.42×10−3molml2/g3) of the linear polyimide in N-methylpyrrolidone at 24°C were determined by a static laser light scattering measurement. The average molecular weight between crosslinking points Mc, was calculated based on both swelling and viscoelastic measurements of the polyimide gels. As for the equilibrium swelling data, a concentration-dependent form of the Flory–Huggins parameter (i.e. χ=χ1+χ2φ) has been applied to calculate the Mc. The values of Mc from equilibrium swelling and viscoelastic measurement have been found to be in agreement. By comparing Mc with the results of 1H-NMR, the percentages of effective and ineffective linkages have been evaluated quantitatively for all the polyimide gels. It has been found that the elastically effective crosslinking is less than 20%. Results from classical and improved Flory–Rehner theory have been compared and we believe that the improved theory gives a more reasonable description of Mc at higher crosslink density.

Swelling behavior of pervaporation membranes in ethanol-water mixtures

Novel hydrophobic composite membranes made of crosslinked poly(dimethylsiloxane) and poly(methyl hydrogen siloxane) (PDMS–PMHS) with various amounts of catalyst were prepared. Pervaporation experiments with water–ethanol mixtures revealed that an optimum ratio of catalyst to polymer base existed. Both swelling behavior and dynamic–mechanical properties of these silicone films were studied. The swelling experiments in different mixtures of ethanol and water determined that ethanol is preferentially sorbed and that the membranes are only capable to absorb a limited quantity of solvent. Equilibrium swelling data were also used in combination with the analysis of the viscoelastic relaxation of the swollen samples to obtain the dependence of the dynamic–mechanical properties of the silicone films on the quantity of permeants sorbed into the membrane. It was observed that the permselective parameters were related with the mobility of the chains and the free volume. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1424–1433, 2000

Model networks based on `endlinking' processes: synthesis, structure and properties

The present review comprises five main sections. The first section is devoted to the synthesis by `endlinking' processes of homogeneous model networks of well-defined architectures, which can be characterized by their structural parameters. In most of the methods developed in our Institute over the past two decades, linear polymer `precursor' chains, fitted at both chain ends with reactive groups, are first synthesized. Under selected experimental conditions, the addition of an appropriate compound to this α, ω-functional polymer, allows the formation of model networks, provided no `syneresis' has occurred. In such a way, various polymer `precursors' of known molar mass and narrow polymolecularity have been used, such as `living' poly(styrene), poly(isoprene), poly(alkyl methacrylates), poly(2-vinylpyridine), as well as poly(dimethylsiloxane), poly(ethylene oxide) and poly(1,3-dioxolane), which become the elastic chains of the model networks. Among all these materials, `labeled' model networks with deuterated molecules are of great interest, since they allow one to perform small-angle neutron scattering experiments, as is described in the second section of the review. `Labeled' poly(styrene) and poly(dimethylsiloxane) have been used to characterize the spacial distributions of the crosslinks and the conformations of elastic chains in the dry, the equilibrium swollen and uniaxially stretched states. As shown in the third section, uniaxial deformation and equilibrium swelling data are compared with those arising from rubber elasticity theories and from swelling equations. Alternately, interpretation of the experimental data based on `scaling' concepts is developed using the analogy between semidilute solutions and permanent model networks swollen to equilibrium in a `good' solvent. In the fourth section, it is shown that the use of branching theories allows one to evaluate the number of effective crosslinks, as well as the extent of the reaction, knowing experimentally the amount of the sol-fraction in the network. The theories of the equilibrium elastic response of a collection of ν network chains have been tested using equilibrium swelling and elastic modulus data obtained from poly(ethylene oxide) model networks. Systematic departures from the predictions of the classical theories of rubber elasticity are observed. However, satisfactory agreement between theory and experiments is found by the introduction of two additional contributions to the elastic free energy, namely the limitation of free fluctuations of the junctions and the entanglement effect. In the last section, a new approach based on rheology, kinetics and branching theory is developed. In these studies, poly(urethane) model networks are used. The rheological behavior of the reaction medium is evaluated by measuring the storage and the loss moduli at various stages of the process, over a wide range of oscillatory shear frequencies. For stoichiometric systems, at a given conversion (determined by Fourier transform infra-red spectroscopy), the two moduli become congruent and proportional to the root square of the frequency over the entire frequency range. The method used allows one to determine precisely the time at which crosslinking occurs (gel point). This experimental value is in excellent agreement with that arising from branching theory.

The effect of crosslinking on mechanical properties of ldpe filled with organic fillers

AbstractMechanical properties of low density polyethylene filled with various organic fillers were investigated. Different effect of different fillers on the properties was observed and the effect of crosslinking of these materials is also different. Fine anisotropic fillers behave similarly as inorganic fillers. The effect of crosslinking is the highest for composites containing large particulate fillers like beech wood flour. The effects are discussed in terms of mechanical behaviour and crosslinking degree determined from extraction or equilibrium swelling data. A formation of covalent bonds between the filler surface and polymeric matrix is proposed as a result of crosslinking.

Dependency of swelling on the length of subchain in poly(N,N-dimethylacrylamide)-based gels

The equilibrium swelling degree of poly(N,N-dimethylacrylamide) (polyDMAAm)-based gels in water was systematically studied with various initial monomer (cm) and cross-linker (cxl) concentrations, and as a function of initial concentration of fully ionized co-monomer, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). Proportionality of the length of a subchain (N) in the gels to [cxl(cm+cxl)]−1 was revealed, both theoretically and experimentally. Equilibrium swelling data indicate non-Gaussian elasticity of the gel network.

Interpretation of equilibrium swelling data on model networks using affine and ‘phantom’ network models

Well-defined polystyrene model networks and poly(dimethylsiloxane) model networks have been synthesized by endlinking processes under standard conditions. The networks have been swollen to equilibrium in appropriate swelling solvents. The experimental swelling data have been compared with those arising from the affine model and the ‘phantom’ model. The results obtained allow us to calculate the interaction parameter between the swelling solvent and the network. This coefficient strongly depends upon several structural parameters, such as the functionality of the crosslinks, the molar mass of the elastic chains, the polymer volume fraction upon crosslinking and the nature of the swelling solvent. In most cases, satisfactory agreement has been found between experiment and theoretical expectations.

Characterization of crosslinking of random polymer network by rheological and equilibrium swelling data

AbstractThe transesterification reaction in the molten state of ester groups of ethylene vinyl acetate (EVA) copolymers and ethylene acrylic ester (EMA) copolymers has been used to crosslink the chains of this polymeric system. The relative EVA copolymers (or EMA copolymers) concentration dependence of the network formation by co‐crosslinking of EVA/EMA miscible blends has been assessed. EVA/EMA networks were characterized by swelling experiments, rheological measurements, and determination of the extent of the reaction through a chromatographic technique. All results can be compared in a master curve. The influence of the polydispersity and the microstructure of EVA and EMA samples was put in evidence. On the other hand, a scaling law (v2∼Mc−3/5) was observed in agreement with predictions of the Flory‐Rhener expression. © 1994 John Wiley &amp; Sons, Inc.