Polymer-filler Interaction Research Articles

Influence of carbon black/silica ratio on the physical and mechanical properties of composites based on epoxidized natural rubber

The aim of the present paper is to investigate how carbon black/silica ratio influences the curing characteristics, mechanical and dynamic properties of composites based on epoxidized natural rubber (Epoxyprene 25). The data obtained show that the composites, containing carbon black and silica at a 30:40, 20:50, and 10:60 ratio have the best complex of parameters (cure characteristics, mechanical and dynamic properties). That is probably due to the intermingling of carbon black and silica particles what leads to the formation of hydrogen bonds between the silanol groups of silica particles. As a result, silica particles aggregate less and the filler disperses better in the rubber matrix. On the other hand, the presence of a silane coupling agent and the polar character of epoxidized natural rubber predetermine the stronger polymer–filler interaction.

Prediction of the viscoelastic response of filler network in highly nanofilled polymer composites

An accurate prediction of any process is the key to the control of that system. Modeling the rheological properties of nanocomposites would provide us a pattern for prediction of their properties as a function of process and material variables. In this study, the focus is to model and investigate the behavior of highly nanofilled systems, which is controlled by the filler–polymer and filler–filler interactions. In these systems, particles attract each other and form a network, which has a viscoelastic response to the applied stress or strain. Due to the filler–polymer interaction, polymer chains are adsorbed on the filler surface to create a secondary network, parallel with the filler–filler network. The third network in the system is the network of free polymer chains around the adsorbed ones. In this work, the behavior and contribution of these networks in the highly nanofilled systems are described. Furthermore, the relaxation time and the modulus of the filler network are estimated as a function of particle size and concentration. It is observed that the relaxation time and modulus of the filler network are increased with a reduction in particle size and an increase in particle concentration. For studying the parameters of the model, polymer adsorbed layer and available surface area of particles are estimated from the density of the nanocomposites.

Polymer–filler interactions in a tire compound reinforced with silica

Elastomers, usually, are reinforced with reinforcing filler in order to improve their mechanical properties like tensile strength and abrasion resistance. The efficiency of this reinforcement is correlated with different factors like filler structure, surface area, and polymer–filler interactions. This study presents a methodology to quantify the bound rubber attached to the reinforcing filler silica using the thermogravimetric analyzer. Three typical rubber compounds used in tread tire were studied. In the samples tested, the silica content was kept constant, varying only the percentage of the coupling agents. Considering the results of the thermal analysis, physical, mechanical, and rheological tests, the thermogravimetric analysis has proved to be a very useful technique in evaluating the interaction of filler and polymer.

Equilibrium and dynamical properties of polymer chains in random medium filled with randomly distributed nano-sized fillers.

The effect of randomly distributed nano-sized fillers on the equilibrium and dynamical properties of linear polymers is studied by using off-lattice Monte Carlo simulation. Lennard-Jones interactions between polymers and fillers are considered. Results show that the statistical dimensions and dynamical diffusion of polymer are dependent on the polymer-filler interaction strength εpf. The mean square radius of gyration 〈RG(2)〉 shows a minimum at a critical polymer-filler interaction εpf*. The value of εpf* decreases with the increase in the polymer length or the concentration of fillers. The exponent ν in 〈RG(2)〉 ∼ N(2ν) is a typical value of self-avoiding walking chain at small εpf but it increases sharply to a bigger value at εpf > εpf*. The mean square displacement decreases with the increase in εpf. Moreover, the normal diffusion of the polymer at weak interactions changes to subnormal diffusion at moderate and strong attractions. We find that polymers diffuse in dilute filler regions at weak attraction and diffuse in dense filler regions at strong attraction.

Effect of a silica nanofiller on the structure, dynamics and thermostability of LDPE in LDPE/silica nanocomposites

Study of molecular interactions and dynamics in LDPE–silica nanocomposites using FTIR spectroscopy.

Monte Carlo simulation of the structure of mono- and bidisperse polyethylene nanocomposites

The structure of bidisperse polyethylene (PE) nanocomposite mixtures of 50:50 (by mole) of long and short chains of C160H322/C80H162 and C160H322/C40H82 filled with spherical nanoparticles were investigated by a coarse-grained, on lattice Monte Carlo method using rotational isomeric state theory for short-range and Lennard-Jones for long-range energetic interactions. Simulations were performed to evaluate the effect of wall-to-wall distance between fillers (D), polymer-filler interaction (w) and polydispersity (number of short chains in the mixture) on the behavior of the long PE chains. The results indicate that long chain conformation statistics remain Gaussian regardless of the effects of confinement, interaction strength and polydispersity. The various long PE subchain structures (bridges, dangling ends, trains, and loops) are influenced strongly by confinement whereas monomer-filler interaction and polydispersity did not have any impact. In addition, the average number of subchain segments per filler in bidisperse PE nanocomposites decreased by about 50% compared to the nanocomposite system with monodisperse PE chains. The presence of short PE chains in the polymer matrix leads to a reduction of the repeat unit density of long PE chains at the interface suggesting that the interface is preferentially populated by short chains.

COMBINED DIELECTRIC AND MECHANICAL INVESTIGATION OF FILLER NETWORK PERCOLATION BEHAVIOR, FILLER–FILLER CONTACT, AND FILLER–POLYMER INTERACTION ON CARBON BLACK–FILLED HYDROGENATED ACRYLONITRILE–BUTADIENE RUBBER

ABSTRACTThe filler network percolation behavior, filler–filler contact, and filler–polymer interaction of carbon black (CB)–filled hydrogenated acrylonitrile–butadiene rubber were investigated with the combination of dielectric and mechanical properties, by means of changing CB concentration, CB-specific surface area, cycling deformation for vulcanizates, and rotation speed of rotors in the internal mixer during the mixing process. A dielectric relaxation spectrometer was used to determine the percolation threshold of the CB network, which was made up of filler–filler contact, combined with the percolation theory. Dynamic mechanical analysis and a universal testing machine were employed to observe the filler–filler contact and filler–polymer interaction. The filler–filler bonds were determined by analysis of the Arrhenius plot on the basis of temperature sweep. The filler–polymer interaction and filler–filler contact were determined by hysteresis loss dependence and analysis of the reinforcement factor on the basis of strain sweep and quasi-static stress–strain behavior. The model of variable network density proposed by Maier and Goritz was applied to explain the contribution of stable and unstable bonds, which constituted the filler–polymer interaction, to storage modulus. The results showed that the percolation threshold of the filler network increased with an increase in rotation speed and a decrease in CB-specific surface area, which indicated that the filler–filler contact was affected by increasing rotation speed to some degree. Cycling deformation did not obviously affect the percolation threshold. This means that the filler–filler contact was not obviously affected by cycling deformation. However, the filler–polymer interaction was weakened by this procedure, according to careful investigation for the variation of some mechanical properties. We found new interesting correlations between the macroscopic mechanical properties and CB concentration. The molecular nature of these findings was discussed, combined with the overlap model and traditional molecular slip theory.

Polymer-Filler Interphase Dynamics and Reinforcement of Elastomer Nanocomposites

The effect of polymer-filler interaction on interphase dynamics between filler particles in elastomer nanocomposites and the mechanisms of rubber reinforcement by carbon black (CB) are investigated with different techniques. To determine how polymer-filler interface influences the properties of the system, CB black was modified with the ionic liquid (IL) 1-allyl-3-methylimidazolium chloride (AMIC) and mixed with different, more or less, polar elastomers. For typical diene-elastomers (EPDM, SBR), this modification leads to a decreased polymer-filler coupling strength due to the coverage of active sites at the CB surface by AMIC. This is demonstrated by evaluating the energy site distribution from static gas adsorption isotherms with the polymer analogues gas 1-Butene. However, an improvement of polymer filler coupling was determined in the case of saturated, polar rubbers (HNBR) due to attractive dipolar interactions between the polar units of the polymer and the strongly adsorbed IL at the CB surface. The different couplings affect the polymer-filler interphase dynamics between filler particles, which determines the properties of the filler network and filler-filler bonds. To describe the effect of CB surface modification quantitatively, the Dynamic Flocculation Model (DFM) has been used to calculate polymer- and filler-specific material parameters from cyclic stress-strain measurements. The fitted data deliver a coherent picture of filler-filler- and polymer-filler couplings showing a characteristic dependence on rubber polarity. A confirmation of the effect of surface modification on the strength of filler-filler bonds is obtained by nonequilibrium molecular dynamics (MD) simulations of bond rupture under tension. They also provide indications for a glassy-like behavior of strongly confined polymer layers between attractive walls.

Properties of PVDF-MCM41 Nanocomposites Studied by Dielectric, Raman and NMR Spectroscopy

To obtain information on the polymer-inorganic filler interactions and on the confinement effect of polymer chains we studied the properties of solution-cast poly(vinylidene fluoride)-MCM41 molecular sieve nanocomposites. The dielectric response of the nanocomposites was found to be determined generally by the response of the polymer matrix, whereas the polymer-filler interactions resulted in an increase of the relaxation rates of the local mode and segmental motions in the amorphous phase of the poly(vinylidene fluoride) matrix. The effect has been related to a reduction of intermolecular correlations between the segments and was confirmed by the dispersion of 1H spin-lattice relaxation times in PVDF-MCM41 composites. Moreover, the relaxometry experiments have shown that the dynamics of poly(vinylidene fluoride) chains confined to MCM41 molecular sieve channels can be described by tube/reptation model proposed by De Gennes, Doi and Edwards.

Functionalized graphene oxide/polyimide nanocomposites as highly CO2-selective membranes

The design of highly CO2-selective membranes by incorporating low amounts (0.25–0.75 wt%) of functionalized graphene oxide (F-GO) nanosheets (polyethylene glycol functionalized and aminated GOs) into an Ultem® 1000 polyetherimide (PEI) is presented. Structural and morphological analysis of the membranes by infrared spectroscopy, X-ray diffraction, differential scanning calorimetry and scanning electron microscopy revealed strong interfacial interactions between the F-GO nanosheets and PEI. The CO2/CH4 separation performance of the membranes was discussed in terms of filler-polymer interfacial interactions and free volume characteristics. The origins of free volume are proposed to be different for GO/PEI and F-GO/PEI membranes: free volume is mainly located at the GO-PEI interface of the GO/PEI membranes while distributed within interphase regions formed around the F-GO nanosheets in the F-GO/PEI ones. These different free volume localizations resulted in distinct gas separation properties of the membranes. The membranes containing aminated-GO showed outstanding CO2/CH4 selectivities up to 142, due to the activation of multi-permselectivity mechanism in the PEI membrane by addition of the aminated nanosheets. The promising potential of F-GOs in CO2 removal is highlighted by comparing the CO2/CH4 separation performance of the F-GO/PEI membranes with that of other nanocomposites of PEI.

Tailoring Dispersion and Interaction of MWNT in Polymer Nanocomposites, Using Triton X-100 as Nonionic Surfactant

This study reports an investigation on the effect of non-ionic surfactant (Triton X-100) on the dispersion of multiwalled carbon nanotubes (MWNTs) inside the polymer matrix. Adsorption of triton X-100 to the MWNTs was confirmed through FTIR. A reduced bundling of MWNT fibrils were noticed in Triton X-100 modified MWNTs (Tr-MWNTs). The polymer nanocomposites were prepared via melt blending technique. The optimization of loading ratio of the MWNTs and Tr-MWNTs was carried out on the basis of mechanical properties. Dynamic mechanical analysis exhibited the much uniform dispersion of the Tr-MWNT inside polymer matrix as compared to that of MWNTs. A faster rate of crystallization was noticed in case of MWNT reinforced nanocomposites, however, a strong filler-polymer interaction could be seen in case of Tr-MWNT filled nanocomposites. Optical microscopic analysis exhibited similar effect of MWNT and Tr-MWNT on the spherulite size of the polymer.

Mechanical Property Improvement of Poly(Butylene Succinate) by Reinforcing with Modified Fumed Silica

Fumed silica particles (SiO2) were directly added into poly (butylene succinate) (PBS) by melt mixing process. The effects of amount of fumed silica particles on mechanical properties of PBS/fumed silica composites, those are tensile strength, tensile modulus, impact strength as well as flexural strength, were investigated. It was found that the mechanical properties decreased with increasing fumed silica loading (0-3 wt%). In order to increase polymer-filler interaction, fumed silica was treated with 3-glycidyloxypropyl trimethoxysilane (GPMS), and its structure was analyzed by FT-IR spectrophotometry. The PBS/modified was found to possess better tensile strength, tensile modulus, impact strength and flexural strength that those of PBS/fumed silica composites.

Dielectric properties of modified graphene oxide filled polyurethane nanocomposites and its correlation with rheology

This study aims at investigating the dynamic mechanical, dielectric and rheological properties of reinforced polyurethane (PU) nanocomposites containing hydrophilic graphene oxide (GO) and/or hydrophobic modified graphene oxide (mGO) sheets. The organic modification of GO was performed with 4,4′-methylenebis (phenyl isocyanate) (MDI) and the samples were prepared by solvent mixing. We found that addition of mGO provides a more significant increase in the dielectric permittivity as compared to the addition of GO. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) spectroscopy demonstrate the more effective dispersion of thin exfoliated sheets of mGO in the PU matrix as compared to unmodified GO. This qualitative morphology observation is correlated with the quantitative results inferred from the dynamic mechanical analysis, rheology and dielectric studies. The viscoelastic Payne effect is noticed for all nanocomposites and the filler–filler and polymer–filler interactions are studied by applying the Kraus and Maier and Goritz models. The non-linear viscoelastic behavior of the PU nanocomposites is in good agreement with the Maier and Goritz model, which includes the effects of the adsorption/desorption of PU chains on the filler surface. The observed results underline the possibilities of PU composites with organically modified GO sheets in capacitor applications.

Dynamic mechanical and dielectric relaxation studies of chlorobutyl elastomer nanocomposites

Primary and secondary relaxation behavior of chlorobutyl elastomer nanocomposites have been studied as a function of variation in nanographite loading in the temperature range from −100°C to +100°C and in the frequency range of 100–106 Hz respectively. The effect of nanographite loadings on glass transition temperature was marginal for all the composites in the narrow range of −10°C to 10°C. The nonlinearity in tan δ and storage modulus has been explained on the concept of filler–polymer interaction and aggregation of nanographites. The effect of variation in nanographite loadings on the dielectric relaxation such as complex and real parts of impedance was distinctly visible. The electric modulus formalism has been utilized to further investigate the conductivity and relaxation phenomenon. The frequency dependence of electrical conductivity has been investigated using percolation theory. The phenomenon of percolation in the composites has been discussed based on the measured changes in electrical conductivity. The percolation threshold as studied by electrical conductivity occurred in the vicinity of 4–6 phr of nanographite loading. Cole–Cole, Nyquist plots, and Argand diagram confirm the existence of non-Debye/nonlinear relationship. Scanning electron microscopic images show agglomeration of the nanographite and formation of a continuous network structure.

Influence of various nanoparticle shapes on the interfacial chain mobility: a molecular dynamics simulation.

To fully understand the polymer-filler interfacial interaction mechanism, we use a coarse-grained molecular dynamics simulation to mainly investigate the interfacial dynamic properties by tuning the polymer-filler interaction, temperature, chain length, volume fraction of filler, and size and shape of filler. The polymer beads around the filler exhibit an obvious layering behavior and a gradient of polymer dynamics is observed for systems filled with three kinds of fillers (spherical, rod-like and sheet-like). By analyzing the dynamics of the interfacial beads in the first adsorbed layer, we find that the mobility of interfacial beads becomes greater at lower polymer-filler interaction strength and higher temperature. The adsorption/desorption dynamics of interfacial beads decreases with the increase of the chain length, and then becomes nearly unchanged when the chain length exceeds the entanglement molecular weight. It is found that the influence of the different size of nanospheres on the mobility of interfacial beads is just induced by the curvature. However, for systems filled with nanorods and nanosheets, besides the curvature, the force exerted on the polymer beads also plays an important role. For systems filled with three kinds of fillers, the mobility of interfacial beads is the slowest for the nanosheet filled system and only in this case the "glassy layer" exists for strongly attractive interfacial interaction. By comparing the dynamics of the adsorbed polymer beads for three different shapes of filler, it is concluded that it is the total force exerted on the polymer beads by the filler that determines the mobility of the interfacial beads. In short, this work could provide valuable information on the fundamental understanding of polymer-filler interfacial behavior, especially for systems filled with fillers of different shapes.

Flocculation and Viscoelastic Behaviour in Carbon Black-Filled Natural Rubber

The process of particulate flocculation in natural rubber melts and subsequently crosslinked samples is investigated using carbon blacks of varying surface free energy, surface area and morphology. The surface free energies are varied via thermal treatment of the carbon blacks (graphitization). Reduction in surface free energy of the particulates accelerates the flocculation processes in the melt as measured by rheological experiments and reduces the percolation volume fraction threshold as determined by D/C conductivity measurements. The consequent effects on amplification of the small strain storage moduli of the crosslinked compounds are dramatic. Reduced polymer–filler interactions result in both an increased small strain modulus versus the unmodified carbon black-filled materials and an increased mechanical fragility of the fractal networks. Examination of the dynamic elastic moduli of crosslinked carbon black-filled samples loaded at volume fractions below the onset of network development reveal a significant temperature dependence isolated at the filler–rubber interface.

Synthesis and Characterization of Poly Chloromethylstyrene TiO2-Nanocomposite Through a Simple Method via Reversible Addition-Fragmentation Transfer Polymerization

Due to the strong tendency of nanoparticles such as metal oxides to agglomerate, homogeneous dispersion of these materials in a polymeric matrix is extremely challenging. In order to overcome this problem and to enhance the filler-polymer interaction, this study focused on living polymerization that was initialized from the surface of titanium fillers. A new method for synthesizing TiO2/polymer nanocomposites was found with a good dispersion of the nanofillers by using the RAFT agent, 4-cyano-4-[(phenyl carbon tool) solfanylvaleric acid. This RAFT agent has an available carboxyl group to anchor onto TiO2 nanoparticles, and an S = C (C6H5) moiety for subsequent RAFT polymerization of 4-chloromethyl styrene (PCMS) to form n-TiO2/4-chloromethyl styrene nanocomposites. The functionalization of n-TiO2 was determined by FTIR and partitioning studies, the livings of the polymerization were verified using GPC, while the dispersion of the inorganic filler in the polymer was studied using electron microscopy, FTIR and thermal analysis.

Effects of stretch induced softening to the free recovery behavior of shape memory polymer composites

During a cyclic tension test, many elastomeric materials exhibit an appreciable softening in their mechanical properties resulting from the previous stretch, known as the Mullins effect. This paper explores the influence of the stretch induced softening effect to the free recovery behavior of an acrylate shape memory polymer (SMP) composite by incorporating carbon black (CB) as filler materials. The observed softening effect in this SMP composite is considered to be a consequence of stretch induced alternation of filler–polymer interactions inside the composite. Further experiments find that a larger prior stretch gives a larger increase in material softening, which in turn decreases the shape recovery speed. To capture the experimental observations, a multi-branch one dimensional (1D) model is applied, where the modulus in the equilibrium branch is modeled to decrease with stretching deformation following a damage-like softening function. It is found that the loss in modulus due to softening consequently reduces the driving force for recovery and thus results in a slow recovery. Parametric studies further demonstrate that the discounted shape recovery speed will finally reach a saturated level when gradually increasing the programmed strain level in a shape memory cycle.

The effect of coupling agents on silicate-based nanofillers/carbon black dual filler systems on the properties of a natural rubber/butadiene rubber compound

Nanofillers have been introduced a few years ago, but their application in elastomers is still a challenge. With the existing rubber processing equipment and constraints of rubber mixing, dispersion of nanofillers is difficult. The processability and performance of compounds containing plate- or tube-like silicates in a blend with conventional fillers, such as carbon black (CB), are investigated, and the effect of surface modification of the nanofillers is studied. Processing is facilitated by the replacement of CB by the nanofillers, but curing efficiency is reduced. The dispersion of the fillers is improved with the addition of nanofillers. The dynamic properties of the cured composite material are affected, giving the composite material lower hysteresis, while the mechanical properties are merely affected by the addition of nanofillers. Additionally, the filler–polymer interaction is increased. The addition of a compatibilizing and coupling agent, a silane, has only a minor effect and does not improve processing and properties significantly for these combined filler systems.

Hugoniot-based equations of state for two filled EPDM rubbers

Particle-filled elastomers are commonly used as engineering components due to their ability to provide structural support via their elastic mechanical response. Even small amounts of particle fillers are known to increase the mechanical strength of elastomers due to polymer-filler interactions. In this work, the shock response of two filled (SiO2 or silica and KevlarTMfillers) ethylene-propylene-diene (EPDM) rubbers were studied using single and two-stage gas gun-driven plate impact experiments. Hugoniot states were determined using standard plate impact methods. Both filled-EPDM elastomers exhibit high compressibility under shock loading and have a response similar to adiprene rubber.