Rubbery Materials Research Articles

Effect of sub-micron silica fillers on the mechanical performances of epoxy-based composites

Solid state thermo-mechanical properties, as well as low and large strain mechanical behaviour, of epoxy composites filled with sub-micron pyrogenic silica are discussed in this paper. The reinforcement mechanisms involved are investigated. Two distinct series of pyrogenic silica were used: hydrophilic silica with various specific surface areas and silica grafted with various organo-modifications. Furthermore, two series of networks, having either a high or low crosslink density, and resulting thus either in glassy or rubbery materials at room temperature, were considered. Dynamic mechanical analysis, uniaxial tensile tests and fracture mechanic tests were performed. All our results showed that pyrogenic silica leads to an improvement of network mechanical properties both in the glassy and rubbery states. The simultaneous increase of stiffness and toughness was observed, demonstrating the great potential of pyrogenic silica for the reinforcement of thermosetting systems. This exceptional behaviour has been interpreted in terms of the interactions and morphology developed.

EPDM/PP Thermoplastic Vulcanizates As Studied by Proton NMR Relaxation: Phase Composition, Molecular Mobility, Network Structure in the Rubbery Phase, and Network Heterogeneity

Proton solid-state NMR T2 relaxation analysis is used to study model oil-extended ethylene−propylene-diene rubber (EPDM) and thermoplastic vulcanizates (TPV) composed of polypropylene (PP), EPDM and oil. It is shown that the method allows selective characterization of crystalline and amorphous phases of PP, cross-linked EPDM, and oil in TPVs. The network density in the rubbery (EPDM) phase is determined in a wide range of the TPV compositions, as well as in the oil-extended EPDM vulcanizates containing different amount of oil. The entanglement density decreases with increasing oil content in oil-extended EPDM. This decrease can be described using a scaling approach. Molecular mobility of oil molecules decreases with increasing EPDM network density and is significantly lower than that of pure oil due to physical interactions with the host matrix. It is shown that the network density in the rubbery phase of TPV is composed of chemical cross-links, physical junctions at the EPDM/PP interface, and temporary and trapped chain entanglements. The density of chemical cross-links increases with the amount of cross-linker per weight unit of EPDM. The density of the physical junctions increases with increasing PP content. Crystallinity of PP in TPV is hardly affected by the TPV composition. A small fraction of oil molecules plasticizes the amorphous phase of PP and the plasticization effect is proportional to an oil:PP mass ratio in the TPV composition. Two NMR methods for improving the selectivity of the T2 relaxation analysis to different phases of TPV are evaluated. The methods are based on the inversion−recovery experiment and double-quantum (DQ) filtering of the decay of the transverse magnetization relaxation. The DQ filtered T2 relaxation experiment improves the selectivity of the method and could open new possibilities for characterization of the network heterogeneity in rubbery materials. Some relationships between the TPV composition, network density, and mechanical properties are shortly discussed.

An experimentalist's view of the physics of rubber elasticity

An experimentalist's view of the physics of rubber elasticity

Fine characterization of the ethylene and ethane sorption in poly(amide 12-block-tetramethylenoxide) copolymer/AgBF 4 membranes

Ethylene/ethane sorption characteristics were determined for dry Pebax™ (poly(amide 12-block-tetramethylenoxide) copolymer)/AgBF 4 membranes by using an electronic microbalance. The membranes containing 0.7 and 22 wt.% AgBF 4 showed a dual-mode sorption isotherm. The ethane isotherms for all the membranes were of the Henry-type, which is the normal sorption for gases in rubbery polymers. The abnormal presence of Langmuir sorption sites only for ethylene in the rubbery copolymer, never reported sofar, is attributed to the silver-based specific complexation sites. The silver salt which dissolved in limited amounts in the rubbery copolymer had a much smaller Langmuir sorption capacity than the salt that crystallized in the copolymer. The sorption kinetics indicate that the crystallized salt did adsorb slowly ethylene according to a zeroth-order kinetics, but not ethane. The gas uptake kinetics resulting from a step of the pressure surrounding the copolymer exhibited one stage for ethane but two stages for ethylene. For the latter, there was first a fast Fickian sorption stage, then a drift of the zeroth-order sorption of ethylene on salt crystals, which contributes for a large part to the total uptake. The zeroth-order sorption suggests that the sorbed ethylene amount in the second-stage is independent of the crystal-surface coverage. The value of the Fickian diffusion coefficient calculated by fitting the kinetics with a solution of the second Fick’s law was 5 × 10 −12 m 2/s for both ethylene (the first stage) and ethane, and is typical for small organic compounds in a rubbery material.

J-integral of a Penny-shaped Crack on the End of Stiff Cylindrical Cord Embedded in Rubbery Materials

The general purpose of this study is the determination of J-integral when dealing with fracture of a penny-shaped crack on the end of the stiff cylindrical cord embedded in rubber matrix. The dimensional analysis is applied to derive a general equation of J-integral, and then it is assumed that the equation of J-integral can be separated into the deformation and geometry functions, the validity of which is proved by using separation parameter. The J-integral is expressed in a multiplicative form in which the geometry calibration function (or factor) is introduced in order to take into account the finite dimensions. The values of the J-integral for the rubber-cord composites with various crack and specimen radius are obtained by using finite element analysis (FEA), and these results are used for concretely determining the geometry calibration function, which, in this work, is expressed in a polynomial form of fourth order. The deformation calibration function, which is a constant for a linear elastic materials, characterizing the large deformable nonlinear effect in rubbery materials is obtained by comparing the equation of J-integral with the ones for the linear elastic deformation. As we approach the infinitesimal strain, the value of the deformation calibration function comes close to the result of linear elastic fracture mechanics (LEFM).

Electron Beam Curing of Elastomers

Abstract Modification of thermoplastic and rubbery materials by electron beam (EB) radiation is a potential method for development of new polymers and composites. Irradiation of polymeric materials results in grafting and subsequently formation of a three dimensional network through the union of generated macro radicals. In the Green drive, i.e. to make the world pollution free, this technology takes an important position. Curing of a number of both non-polar and polar elastomers using an electron beam was carried out in our laboratory. The effects of irradiation dose in presence and absence of radiation sensitizer on the crosslinking and structure of ethylene propylene rubber, ethylene octene copolymer, nitrile, acrylic and fluorocarbon rubbers were investigated. An analysis of crosslink to scission ratio on the basis of Charlesby-Pinner Equation was done. Mechanical and dynamic mechanical properties showed that these improved with radiation dose and sensitizer level up to certain values, beyond which the properties deteriorated due to chain scission reactions. The properties of the vulcanizates were correlated with the structure. EB cured samples were compared with the samples having conventional crosslinks. Some applications of the electron beam curing are highlighted.

Palygorskite as an epoxy polymer reinforcement agent

Palygorskite, a silicate clay with a pleated 2:1 layered structure, has a lath-like particle morphology that makes it an attractive candidate for the formation of polymer nanocomposites. Here, we report the properties of palygorskite in pristine and silylated forms for the reinforcement of rubbery and glassy epoxy matrices. Three silylation reagents were used for surface modification of the mineral, namely, γ-aminopropyltrimethoxysilane (APTMS), N-dodecyltriethoxysilane (DTES), and 1,1,1,3,3,3-hexamethyldisilazane (HMSZ). The silylated palygorskite derivatives provided better dispersions in rubbery epoxy matrices than the pristine mineral, affording improvements in mechanical properties at low loadings levels of 2 and 5% (w/w). But at higher loadings where increases in the viscosity of the pre-polymer helps to stabilizes the mineral dispersion, little or no differences were observed for the reinforcement benefits provided by the pristine and silylated forms of palygorskite. Glassy epoxy nanocomposites formed from both pristine and silylated palygorskite exhibited marginal improvements in tensile properties regardless of the mineral loading level, suggesting that the tensile strength of the pleated sheet silicate may be approaching that of the polymer matrix.

Surface Energy for Creation of Multiple Curved Cracks in Rubbery Materials

A fracture parameter Mc is proposed for evaluation of the surface energy associated with the creation of multiple curved cracks in 2D rubbery solids under the action of large deformation. Based on the concept of the M-integral, the parameter is developed by performing the integration along a closed contour enclosing all the cracks and with respect to a reference coordinate system originated at the geometric center of all the crack tips. The integration is shown to be path-independent so that the complicated singular stress field in the near-tip areas need not be involved in the calculation. It is thus suggested that Mc be possibly used as a fracture parameter for describing the degradation of material and∕or structural integrity caused by irreversible evolution of multiple curved cracks in a rubbery media.

A test method to measure fatigue crack growth rate of rubbery materials

Crack growth characteristics of rubbery materials are an important factor determining the strength and durability of the materials. It is necessary to define the means of measuring the fatigue crack growth rate of rubbery materials. In this paper, a test method is introduced using a newly designed test machine. Measurements were made in order to characterize the fatigue crack growth behavior under repeated load expressed as a crack growth rate, i.e. crack length per cycle, as a function of the tearing energy, determined by a broad range of the strain energy density in a test piece of pure shear geometry. Measurements were also made to observe the effects of test temperature and loading frequency. A high speed CCD camera is utilized to allow in situ measurements following the path of the crack growth simultaneously. The power law dependency between crack growth rate and tearing energy was confirmed by the new test methodology. Comparison of the fatigue crack growth behavior between NR and SBR rubber compounds was made, and the exponent α values of the NR compound were found to be, in general, lower than those of the SBR compound, indicating that the NR compound is more resistant to fatigue crack growth than the SBR compound.

Carbon nanotubes as Raman sensors of vulcanization in natural rubber

A method has been developed to synthesize composites with cross-linked natural rubber (NR) and dispersed single-wall carbon nanotubes (SWNT). The mechanical response of the NR samples was observed to change as a function of the amount of sulfur used for cross-linking, based on the number density of cross-links resulting from the vulcanization process. The relationship between SWNTs D ∗ wavenumber shift and the amount of sulfur have been obtained by means of Raman spectroscopy. The cross-link densities of the NR and SWNT/NR samples have been calculated from uniaxial stress–strain measurements, and plotted as the function of the amount of added sulfur. Comparison of the results from mechanical measurements and Raman spectroscopic measurements showed that SWNT Raman sensors are sensitive to the cross-link density in natural rubber and can be used to evaluate the cross-linking process of rubbery materials.

Effect of a homogeneous magnetic field on the mechanical behavior of soft magnetic elastomers under compression

The mechanical properties of new magnetic composite materials were studied. The above materials represent rubbery silicon matrices filled with magnetic microparticles of metallic iron or magnetite. In homogeneous magnetic fields with an intensity of up to 0.4 T, the shear modulus of the composites was abnormally high (up to 10 000%). The variation of elastic properties of new materials on the type and volume content of the magnetic filler was investigated. In the presence of a sufficiently strong magnetic field, the above composites were shown to behave as elastoplastic materials with strengthening.

Fracture toughness of the epoxy/ATPEI-CTBN-ATPEI triblock copolymer/NMA blend system

The shortcoming of epoxy resin is the brittleness of this material though it shows excellent chemical, mechanical and electric properties. To improve fracture toughness of epoxy resin, rubbery materials that show high values in toughness but low values in glass transition temperature and mechanical properties, and thermoplastics that show high values in thermal and mechanical properties but relatively small increase in toughness were blended with epoxy. ATPEI-CTBN-ATPEI triblock copolymer, which consists of rubbery and thermoplastics blocks, was synthesized, and the triblock copolymer was blended with epoxy resin. The effects of parameters such as contents of the triblock copolymer, cure temperature, and contents of catalyst on the morphology of the blend systems were studied. From 30 wt% of the contents of the triblock copolymer, fracture toughness and impact energy absorption of the blend systems were increased significantly. This was due to the generation of nodular morphology in the system.

Novel Styrenic Thermoplastic Elastomers from Blends with Special Reference to Compatibilization and Dynamic Vulcanization

Abstract A thermoplastic elastomer (TPE) is a rubbery material with final properties and functional performance similar to those of a conventional vulcanized rubber at ambient temperature, yet it can be processed in a molten condition as a thermoplastic polymer at elevated temperature. The main objectives of the present investigation are: to prepare novel styrenic-based thermoplastic elastomers based on blends of a thermoplastic (polystyrene or styrene acrylonitrile) with a rubber (styrene butadiene or ethylene vinylacetate) and to investigate the interaction between various polymers with special reference to compatibilization via oxazoline-modified polystyrene or oxazoline-modified styrene acrylonitrile and dynamic vulcanization. Styrene acrylonitrile/ethylene vinylacetate blends are found to exhibit better overall properties, especially tensile strength, elongation at break and tension set. The solubility or interaction parameter and the morphology of the blends are the key parameters, which basically govern the final properties of blends. Physical properties of these blends have been correlated with the interaction parameter and final morphology.

Spherical Indentation Creep Following Ramp Loading

Elastic-viscoelastic correspondence, utilizing Boltzmann integral operators, was used to generate displacement–time solutions for spherical indentation testing of viscoelastic materials. Solutions were found for creep following loading at a constant loading rate and compared with step-loading solutions. Experimental creep tests were performed with different loading rate–peak load level combinations on glassy and rubbery polymeric materials. The experimental data were fit to the spherical indentation ramp–creep solutions to obtain values of shear modulus and time-constants; good agreement was found between the experimental results and known modulus values. A multiple ramp-and-hold protocol was examined for the measurement of creep responses at several loads (and depths) within the same test. Emphasis is given to the use of multiple experiments (or multiple levels within a single experiment) to test a priori assumptions made in the correspondence solutions regarding linear viscoelastic material behavior and the creep function.

Amorphous Polyethylene by Tandem Action of Cobalt and Titanium Single‐Site Catalysts

AbstractSummary: A variety of branched polyethylenes, spanning from semicrystalline LLDPE to completely amorphous, rubbery PE, was obtained from ethylene by homogeneous tandem catalysis using combinations of CoCl2(N) (1) (N = [1‐(6‐benzo[b]thiophen‐2‐yl‐pyridin‐2‐yl)‐ethylidlene)‐(2,6‐diisopropyl‐phenyl)‐amine) and [(η5‐C5Me4)SiMe2(tBuN)]TiCl2 (2) in the presence of MAO at 30 °C. The productivity reached a maximum of 4 570 kg PE (mol Ti · h)−1 at χCo = 0.50, yielding a rubbery material with d25 = 0.868 g · cm−3 and Tg = −55 °C.Conversion of ethylene into branched polyethylene using CoII iminopyridyl complex CoCl2(N) (1) and TiCl2[(η5‐C5Me4)SiMe2(tBuN)] (2).magnified imageConversion of ethylene into branched polyethylene using CoII iminopyridyl complex CoCl2(N) (1) and TiCl2[(η5‐C5Me4)SiMe2(tBuN)] (2).

Two new siloxanic proton-conducting membranes: Part I. Synthesis and structural characterization

The development of stable polymer electrolytes having good proton conductivity, low cost and operating at medium temperatures represent a crucial step in the evolution of polymer electrolyte fuel cells. We describe two new siloxanic proton-conducting membranes that were synthesized through a two-stage protocol. In the first stage, a poly(methyl hydrosiloxane) precursor ( P) bearing siloxane side chains with sulfonic acid groups was prepared. In the second step, the hydrolysis of pristine precursor or its derivative obtained by grafting siloxane chains on P yielded two types of membranes with the formulas {Si(CH 3) 3O[Si(CH 3)HO] 21.26 [Si(CH 3)((CH 2) 3SO 3H)O] 1.8 [Si(CH 3)((CH 2) 3Si(CH 3) 2O ) O] 14 Si(CH 3) 3} n ( A) and {Si(CH 3) 3O[Si(CH 3)HO] 21.26 [Si(CH 3)((CH 2) 3SO 3H)O] 1.8 [Si(CH 3)((CH 2) 3(Si(CH 3) 2O ) w ) O] v [Si(CH 3)((CH 2) 3Si(CH 3) 2O–) O] 14 − v Si(CH 3) 3} n ( B), with w = 20.31. Polymer membranes of A and B were prepared by means of a hot-pressing process at 80 °C and 10 t/cm 2. Scanning electron microscopy showed that A and B are rubbery materials with rough and transparent surfaces. Thermogravimetric investigations performed under air atmosphere disclosed that A and B are thermally stable up to at least 198 °C. DSC measurements yielded T g(s) of −44 and −60 °C for A and B, respectively. The polymers exhibit ionic exchange capacities of 0.33 ( A) and 0.15 meq/g ( B). FT-IR and FT-Raman investigations revealed that the polymers consist of reticulated siloxane networks with pendant silicone chains having sulfonic acid groups.

A Simple Pathway toward Quantitative Modification of Polybutadiene: A New Approach to Thermoreversible Cross-Linking Rubber Comprising Supramolecular Hydrogen-Bonding Networks

A commercial polybutadiene (PB) was modified by a simple three-step polymer analogous reaction (epoxidation, oxirane ring-opening, and sulfonyl isocyanate addition), and the degree of modification is quantitatively controlled by epoxidation reaction. Because of the introduction of sulfonyl urethane groups (−O−CO−NH−SO2−) which is prone to self-complementary thermoreversible supramolecular hydrogen-bonding (HB) networks, the PB was modified from a rubbery material to a thermoplastic elastomer. The modified rubbers were characterized by using 1H NMR, FTIR, DSC, and dynamic mechanical analyses. FTIR spectra showed a shift of SO stretching to lower frequency with increasing degree of modification as a result of the formation of HB complexes. DSC analysis showed that the crystalline melting was suppressed, and the glass transition was elevated to higher temperatures. From the dynamic mechanical analysis it revealed much clearer the crystallization suppression and the glass transition shifts. The changes in the...

High Internal Phase Emulsion Templating as a Route to Well‐defined Porous Polymers

AbstractFor Abstract see ChemInform Abstract in Full Text.

Finite strain behavior of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)-glycol (PETG)

Uniaxial and plane strain compression experiments are conducted on amorphous poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)-glycol (PETG) over a wide range of temperatures (25–110 °C) and strain rates (.005–1.0 s −1). The stress–strain behavior of each material is presented and the results for the two materials are found to be remarkably similar over the investigated range of rates, temperatures, and strain levels. Below the glass transition temperature ( θ g=80 °C), the materials exhibit a distinct yield stress, followed by strain softening then moderate strain hardening at moderate strain levels and dramatic strain hardening at large strains. Above the glass transition temperature, the stress–strain curves exhibit the classic trends of a rubbery material during loading, albeit with a strong temperature and time dependence. Instead of a distinct yield stress, the curve transitions gradually, or rolls over, to flow. As in the sub- θ g range, this is followed by moderate strain hardening and stiffening, and subsequent dramatic hardening. The exhibition of dramatic hardening in PETG, a copolymer of PET which does not undergo strain-induced crystallization, indicates that crystallization may not be the source of the dramatic hardening and stiffening in PET and, instead molecular orientation is the primary hardening and stiffening mechanism in both PET and PETG. Indeed, it is only in cases of deformation which result in highly uniaxial network orientation that the stress–strain behavior of PET differs significantly from that of PETG, suggesting the influence of a meso-ordered structure or crystallization in these instances. During unloading, PETG exhibits extensive elastic recovery, whereas PET exhibits relatively little recovery, suggesting that crystallization occurs (or continues to develop) after active loading ceases and unloading has commenced, locking in much of the deformation in PET.

Preparation of EPDM/synthetic montmorillonite nanocomposites by direct compounding

Elastomers are usually compounded with fillers such as carbon black or silica in order to improve their mechanical properties. The idea of using clays as fillers in a polymer matrix appeared in the 1950s, but not until 1990 did the Toyota group find that clay layers could be intercalated or exfoliated by polyamide-6 macromolecules [1]. Such composites can be expected to provide a very high interaction area between the filler and the polymer and as a consequence possess improved properties as compared to traditional reinforcing fillers. Many nanocomposites based on polymer/clay blends have been investigated using different polymers compounded in the melt such as polyamide-6 [1], polyethylene [2], polypropylene [3], poly(ethylene oxide) [4] and polystyrene [5]. However, relatively little attention has been paid to conventional rubbery materials. Such nanocomposites have been generally prepared by latex compounding [6, 7], solution blending [8, 9] or by using an appropriate vulcanization system [10], but no evidence of exfoliated rubber/clay nanocomposites prepared by direct compounding of the clay with the elastomer has been reported up to now in the litterature, except in the special case of silicone networks [11, 12]. Although thermoplastics are considered as rubbery when compounded in the melt, true elastomers at moderate temperature differ from melted thermoplastics by their high viscosity. This explains the complications to achieve clay exfoliation in elastomer matrices. The aim of this study is to define the main parameters controlling clay intercalation and exfoliation in an elastomer matrix, in order to prepare composites structured at the nanometer scale. Furthermore, we chose to respect three conditions: (1) no solvent use in the blend, (2) maximum exfoliation to a single layer level, (3) accurate understanding of the composite structure.