Nanoclay exfoliation in rubber compounds characterized by online measurements of electrical conductance

A new method based on the online measured electrical conductance is presented for the characterization of the kinetics of dispersion of organoclay in a polar rubber matrix during melt mixing. The charge carriers available in the clay galleries become released as a result of the dispersion processes; thus, the conductance of the nanocomposites is altering during mixing. A coupled conductance/temperature sensor installed inside the mixing chamber enables the online measurement of the electrical conductance during mixing. The online measured conductance shows a characteristic chart correlating to the nanoclay dispersion process. To clarify the structural background of the conductance curve the kinetics of macro‐ and microdispersion of nanoclay have been investigated with the use of optical microscopy, small‐angle X‐ray diffraction (SAXS), and atomic force microscopy (AFM), as well as bound rubber measurements. A close correlation was found between the online conductance chart and the development of the clay dispersion. In the first mixing step, breakdown of agglomerates, diffusion of polymer chains into the galleries of the clay, wetting, and intercalation processes take place simultaneously. As a result, a significant increase of conductance is observed during this period. Subsequently, the intercalated structures undergo the exfoliation process, which causes a further but moderate increase of the electrical conductance. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Characterization of the effect of the filler dispersion on the stress relaxation behavior of carbon black filled rubber composites

In the present work a new evaluation method for the characterization of the stress relaxation behavior of rubber-carbon black (CB) composites is presented. Using the chart of the online measured electrical conductance received from the recording equipment in the mixing chamber different rubber-CB composites with well defined state of the CB network have been produced for the stress relaxation investigation. The development of CB dispersion degree and the rubber-layer bonded on the CB surface have been characterized systematically using the method of the online measured electrical conductance and the thermogravimetric analysis of rubber-filler gel. The analysis of the stress relaxation curves is based on the division of the initial stress into several stress components and the consideration of the structure of the composites as a combination of different networks. The contribution of the stress component to the corresponding network is the focus of the present work. Based on the systematic variation of material parameters and test conditions we could divide the applied stress into six stress components which are originated from the rubber matrix and CB. It is obvious that the debonding of the rubber-layer from the CB surface and the collapse of a part of the CB network can be described by the relaxing stress component Δσ^{CB(rubber-layer)} and Δσ^CB(network), respectively. The non-relaxing stress components σ_∞^{CB(rubber-layer)} and σ_∞^CB(network) are dependent on the amount of the time-stable bonding in the rubber-layer and the stable part of the CB network. The mechanical performance of the composites and especially the time and temperature dependent mechanical behavior could be specifically modified by CB addition.     

Electrically conductive carbon black (CB) filled in situ microfibrillar poly(ethylene terephthalate) (PET)/polyethylene (PE) composite with a selective CB distribution

In the present study, it was attempted to fabricate a new conductive carbon black (CB) filled poly(ethylene terephthalate) (PET)/polyethylene (PE) in situ microfibrillar composite with a lower percolation threshold through selectively localizing CB particles in the surfaces of the PET microfibrils. The CB particles were first mixed with PE matrix, and then PET was added into CB/PE compound. Subsequently, the CB/PET/PE composite was subjected to a slit die extrusion, hot stretch and quenching process to generate in situ PET microfibrils, in which CB particles moved to the surfaces of the PET microfibrils simultaneously. The morphological observation showed that the PET phases formed well-defined microfibrils, and CB particles did overwhelmingly localize in the surfaces of the PET microfibrils, which led to a very low percolation threshold, i.e., 3.8 vol%, and a good conductivity. The conductive network was built by the contact and overlapping of the CB particles coated PET microfibrils. In addition, the CB particles remaining in the PE matrix also contributed to the conductive paths, especially for the high CB loading filled microfibrillar composites. Because of the complexity of the distribution of CB particles, a high critical resistance exponent t (t = 6.4) exists in this conductive composite. To reveal the possibility of the migration of CB particles from PE to PET, the morphology of the CB/PET/PE composite mixed for different times was examined. It was found that, depending on the mixing time, the CB particles gradually migrated from the PE matrix to the surfaces at first, and then to the center of the PET phases. The preferable distribution of CB particles was originated from several factors including interfacial tension, viscosity, molecule polarity, and mixing process. Furthermore, during the mixing process of the CB/PET/PE composite, the migration of CB particles to PET phase from PE matrix led to the increase of both the viscosity ratio of the dispersed phase to the matrix and the volume of the dispersed phases, thus resulting in larger dispersed CB/PET composite phase particles.     

Carbon nanotubes/carbon black synergistic reinforced natural rubber composites

Abstract

Carbon black (CB) and carbon nanotubes (CNTs) filled natural rubber (NR) composites were prepared. In order to overcome the dispersion of CNTs in rubber matrix, the surface modification of CNTs with bis-(γ-triethoxysilylpropyl)-tetrasulphide (Si-69) was undertaken, and a two-step mixing process, i.e. the use of twin roll mill followed by mixing in a Haake Banbury mixer (TR-THM) was used. The structure and mechanical properties were investigated. The results show that the Si-69 treated CNTs (S-CNTs) were dispersed in the rubber matrix uniformly. Compared with CB/NR composites without CNTs, the S-CNTs/CB/NR composites have better mechanical properties. When the ratio of S-CNTs/CB/NR was 5 : 20 : 100, the tear strength was improved by ～60%, and the mechanical properties reached a maximum. Dynamical mechanical analysis (DMA) reveals that with increasing content of CNT, the elastic modulus of composites at room temperature increases, and the maximum loss tangent and the corresponding glass transition temperature of composites decrease.     

Chemical sensing materials. I. Electrically conductive SEBS copolymer systems

Chemical sensing materials based on conductive carbon black (CB) filled [styrene‐ethylene butylene‐styrene] triblock‐copolymers (SEBS) were investigated. Several types of SEBS copolymers were studied, differing in composition and melt viscosity. The sensing is based on electrical conductivity changes upon solvent sorption/desorption. Compression molding SEBS composites containing various amounts of CB were prepared. Their electrical conductivity was measured and samples containing CB, preferentially located in the continuous ethylene/butylene (EB) phase, at a level near the corresponding percolation threshold were used for the sensing experiments. The conductivity was measured during several exposure/drying cycles. Structure characterization included scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), and calorimetry (DSC). The SEBS composites exhibit large reversible changes in conductivity upon exposure to a limited number of solvents, e.g., acetone, n‐heptane, and air drying cycles. This behavior was related to the sorption kinetics, affected by the solvent characteristics (solubility parameter, polarity, molecular volume and vapor pressure). The samples' resistance tended to return to their initial value upon short drying of acetone, and longer drying of other studied solvents. The nature of the SEBS, the CB content, and mixing temperature are all significant parameters, determining the sample's structure and the resultant sensing property. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dynamics of migration and phase selective localization of nanoclay in HNBR/ENR blends

The phase specific selective localization and dynamics of migration of nanoclay in hydrogenated acrylonitrile butadiene rubber (HNBR)/epoxidized natural rubber (ENR) blend systems is investigated. The phase specific dispersion of clay particles is monitored through measuring the online measured electrical conductance (OMEC) during mixing by means of a sensor system installed inside the chamber of an internal mixer. The results of different characterization techniques, such as atomic force microscopy, transmission electron microscopy, and small angle X‐ray scattering have been used to understand and interpret the OMEC behaviors of nanoclay‐filled rubber compounds individually (HNBR and ENR) and their blend systems. The observed online conductance is ionic in nature that arises due to the release of surfactant molecules from the clay galleries. It is observed that the OMEC behavior depends mainly on two factors: the localization of nanoclay in specific phase of the blend system and on the gradual development of blend morphology. The OMEC behavior and the supported data from the microscopic methods, clearly reveal the migration of organoclay from the ENR to HNBR phase during the mixing process, particularly localizing near the interface of the blend. Further, the localization of organoclay is also evaluated by applying the surface tension measurements based model, which also predicts the favorable localization of organoclay in HNBR phase of the blend. The work clearly suggests the OMEC method to be a powerful online tool to monitor and control the nanoclay dispersion and localization in rubber based nanocomposites during the melt mixing process. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44074.     

Morphology development and compatibilization effect in nanoclay filled rubber blends

The present work introduces a new method for the characterization of morphology development and kinetics of nanoclay distribution in hydrogenated acrylonitrile butadiene rubber (HNBR)/natural rubber (NR) blends based on the measurement of electrical conductance during the mixing process. It was found that the online measurable electrical conductance of rubber-clay mixtures, which is originated from the release of the ionic surfactant from the nanoclay galleries during the mixing process depends on two factors: the phase specific localization of nanoclay and the change of the blend morphology. The former is due to the favorable interaction of nanoclay with one of the blend phases whereas the latter is caused by the compatibilization effect of nanoclay. It became obvious that the presence of clay influences the morphology of the blends drastically; a significant change from the co-continuous phase morphology into an island-matrix morphology was observed in HNBR/NR/clay nanocomposites. Thus, the method of the online conductance promises to be a powerful tool to study the nanoclay dispersion processes and to monitor the quality of rubber-nanoclay composites.     

Development and characterization of hydrocarbon polyol polyurethane and silicone magnetorheological polymeric gels

Magnetorheological polymeric gels (MRPG) have been developed for use in semi‐active magnetorheological fluid (MRF) dampers and other magnetorheological (MR) devices. The novel MRPGs are prepared by suspending iron particles in polymeric gels. Off‐state (i.e, no applied magnetic field) viscosity and settling behavior can be controlled through the selection of polymeric gels. In this study, tunable rheological properties were investigated with a piston‐driven flow type rheometer with a shear rate varying from 20 s^?1 to 6,000 s^?1. Silicone MRPG (with 84.5 wt % iron particles) has controllable viscosity and a high shear yield stress over a wide range of shear rates. Silicone MRPG (79.5 wt % iron particles) has the lowest viscosity of those studied. Polyurethane MRPG has the lowest settling rate. The order of addition of magnetic particles and polymer during the polymerization process affects the MRPG final off‐state apparent viscosity (80% increase in apparent viscosity for silicone MRPG polymerized after adding iron particles). This indicates that polymer gels modify the surface properties of the magnetic particles, causing interaction among particles. The dynamic shear yield stress is higher for fluids with better dispersion stability. Polyurethane MRPG, which has the lowest settling rate, has a high dynamic yield stress (23 kPa at 350 mT). Both dynamic and static shear stress values of the MRPGs were found to be similar in magnitude (5–8 kPa at 120 mT for silicone MRPG with 84.5 wt % iron particles and polyurethane MRPG), indicating that MRPGs can provide consistent performance in devices. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1176–1182, 2004     

Influence of liquid isoprene on rheological behavior and mechanical properties of polyisoprene rubber

Prevention of plasticizer leaching from polymers has been a difficult task. Conventional oily plasticizers (COPs) often migrate from rubber matrix, leading to a poor stability of rubber products and serious environmental problem during long‐term use. In the present study, liquid isoprene (LIP) with appropriate molecular weight and no migration was prepared by anionic polymerization. The effects of LIP on the comprehensive properties of carbon black filled polyisoprene rubber (CB/IR) composites were compared with those of one COP, naphthenic oil (NPO). The results showed that LIP reduced the Mooney viscosity and apparent viscosity, and improved the processability of CB/IR composites. LIP improved the mixing efficiency and the dispersion of the CB particles because its compatibility with CB/IR composites was higher than the compatibility of NPO and CB/IR composites. Furthermore, LIP did not migrate from the CB/IR composites because of its participation in the vulcanization reaction. Compared with CB/IR/NPO composites, CB/IR/LIP composites possessed higher mechanical properties, better aging resistance and long‐term dimensional stability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41485.     

Graphene/carbon black/natural rubber composites prepared by a wet compounding and latex mixing process

The extensively used latex mixing approach to prepare graphene can improve the graphene dispersion but meets some challenges in the preparation of high content carbon black filled rubber system like a rubber tire. Owing to the high melt viscosity of the rubber/graphene masterbatch, the dispersion of carbon black is not perfect during twin-roll mixing and some aggregates will be formed. Here we proposed a wet compounding process, combined with ultrasonically assisted latex mixing, named as the WCL method to prepare reduced graphene oxide/carbon black/natural rubber (rGO/CB/NR) composites. The morphological observations confirmed that both graphene and carbon black can be evenly dispersed in the rubber composites. The incorporation of rGO also improves the hardness, thermal conductivity and anti-aging properties of the composites. The rGO/CB/NR composites prepared by the WCL method possess better mechanical properties compared to conventional latex mixing. The entanglement-bound rubber tube model was utilised to understand the reinforcing mechanism.     

Design of sandwich structure conductive polypropylene/styrene-butadiene-styrene triblock copolymer/carbon black composites with inherent morphological tunability

The insulator-conductor transition of conductive polymer composites (CPCs) can be ascribed to the fabrication of conductive networks, and the morphology of conductive networks plays a significant role in the electrical conductivity. This study presents CPCs with inherent morphology tunability which can be controlled by kinetic methods (i.e., mixing procedures and sequences, and polymer melt viscosity). Polypropylene (PP)/styrene-butadiene-styrene block copolymer (SBS) (50/50, in volume)/10 phr (parts per hundred of the polymer matrix) conductive carbon black (CB) composites prepared by different compounding sequences (PP/CB composites mixed with SBS, SBS/CB composites mixed with PP, and PP/SBS blend mixed with CB) are named as PC₁₀S, SC₁₀P, and PSC₁₀. With the difference between the phase morphologies, distribution, and dispersion of CB, the PP/SBS/CB composites realize seven orders of magnitude difference in resistivity. The volume resistivity (ρ_v) of PC₁₀S SC₁₀P and PSC₁₀ are 1.57 × 10¹, 1.68 × 10², and 4.88 × 10⁸ Ω m, respectively.     

Epoxy resins toughened with in situ azide–alkyne polymerized polysulfones

To simultaneously improve the fracture toughness and heat resistance of a cured toughened epoxy resin along with a reduction in its viscosity during the mixing process, two novel polysulfone‐type polymers are synthesized via azide–alkyne polymerization for use as toughening agents. The epoxy resin toughened with these polymers by in situ azide–alkyne polymerization during the cure process, which shows excellent processibility and based on the significantly lower viscosity (61 and 62 cP) during epoxy mixing process than that of commonly commercial polyethersulfone (PES, 127,612 cP). The novel polysulfone‐type polymer toughened epoxy resin showed the advantage in excellent fracture toughness than the PES toughened epoxy. In addition, the glass transition temperature of the novel polysulfone‐type polymer toughened epoxy resin is similar to that of the neat one (～230 °C) and does not decrease, which implies excellent heat resistance of the toughened epoxy. These phenomena can be attributed to the formation of semi‐interpenetrating polymer networks comprising the epoxy network and the linear polysulfone‐type polymers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45790.     

Highly thermally conductive room‐temperature‐vulcanized silicone rubber and silicone grease

In this study, the effects of thermally conductive filler type (α‐Al₂O₃, SiC), volume fraction of the filler, and filler particle size distribution on the thermal conductivity and viscosity of room‐temperature‐vulcanized (RTV) silicone rubber and silicone grease were investigated. We were interested to find that silicone grease (or the RTV silicone rubber) had a maximum thermal conductivity (～1.48 W/mK) and a minimum viscosity (～3.4 × 10⁴ mPa s), with a definite total volume fraction of the filler (0.55) when the distribution of filler sizes (the number ratio of two different particles sizes, i.e., 0.8 and 6 μm) was 600–700. We were able to increase the thermal conductivity of the RTV silicone rubber and silicone grease beyond 2 W/mK by increasing the total volume fraction of the filler with adequate filler size distributions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2397–2399, 2003     

Effect of cavity pressure on crosslink density of injection moulded silicone rubber

Abstract

The effects of injection moulding conditions (temperatures 120 and 160°C, pressures from 5 to 50 MPa) on the crosslink density of the resulting parts (determined from equilibrium solvent swelling experiments) have been studied for an elastomer of the liquid silicone rubber type in which crosslinking results from platinum catalysed vinyl–silane addition. It was shown, unexpectedly, that a pressure increase leads to an increase in the cure rate, despite the unfavourable effect of pressure on viscosity.     

Selective wetting and dispersion of filler in rubber composites under influence of processing and curing additives

The present work highlighted the effect of commonly used processing and curing additives on the wetting and dispersion kinetics of filler like silica and carbon black (CB) in some examples using the methods like the wetting concept and online measured electrical conductance. The adsorption of additives and mono-functional silane on silica surface increases the wetting speed of silica in single compound of nitrile butadiene rubber (NBR), natural rubber (NR) and styrene butadiene rubber (SBR) compounds. In rubber blend, for instance NBR/NR, the extent of filler surface fraction wetted by each blend component is strongly dependent on the additive/silica and silane/silica ratio r. A model based on the surface tension data of rubber components and filler (Z-model) was used for prediction of the selective filler wetting at a thermodynamic equilibrium state. By combining the experimental results from the wetting concept and theoretical prediction from the Z-model the silica surface tension changed during mixing can be characterized. It quantitatively describes the deactivation of the silanol groups on the silica surface by adsorbed additives. The effect of adsorption of additives on filler dispersion was exemplarily demonstrated on CB filled SBR compounds by means of the method of online measured electrical conductance. The influence of additives on the CB dispersion in low styrene-content SBR mixtures is much more pronounced than that in high styrene-content SBR mixtures.     

The influence of viscosity on micromixing in turbulent flows

Viscosity has a negligible effect, if any, on macromixing parameters (e.g. velocity distribution and blending time when turbulent flow is fully developed). It does, however, influence micromixing parameters (e.g. Batchelor concentration microscale (νD²/ε)^1/4 and time constant for decay of fine-scale concentration fluctuations). The product distribution of two rapid, competitive, consecutive reactions (diazo coupling between 1-naphthol and diazotized sulphanilic acid) is sensitive to reagent concentration gradients on the molecular scale. It is shown that if all the independent micromixing parameters are kept constant, except the viscosity, the product distribution changes. The viscosity was varied by dissolving less than 0.5wt.% carboxymethyl cellulose (Hercules, type 7MF) in the aqueous reagent solutions. The viscosity then depends upon many factors (CMC concentration, temperature, shear rate, pH, chemical composition of the solution and mixing sequence during make-up of the solution), and CMC is not an ideal additive. Nothing better seems to be available. At least the spectrophotometric analytical method and the rate constants are unaffected by low CMC concentrations (0.5 wt.%). Three reactors (rotor---stator high intensity mixer, flow in a pipe, stirred tank) were operated in the turbulent flow regime. Increasing the viscosity caused more secondary product to be formed. This effect was described quantitatively by our earlier micromixing model.     

A molecular simulations study of the miscibility in binary mixtures of polymers and low molecular weight molecules

The miscibility behavior of binary mixtures of polymeric and low molecular weight molecules was studied using a combination of modified Flory-Huggins theory and molecular simulation techniques. Three different atomistic approaches were used to investigate the phase behavior and χ parameters of binary mixtures consisting of polymethyl methacrylate (PMMA) and 4-n-pentyl-4′-cyanobiphenyl (5CB). Binary mixtures of methyl methacrylate monomer/5CB and methyl methacrylate oligomer/5CB were also studied. As a first approach, a fast method that calculates the local interaction between a fragment of the polymer and the organic molecule and then extends it to determine the energy of mixing using an estimated coordination number was used. By using modified coordination numbers, we were able to extend this method to include cases where the polymer segment and the small molecules are slightly dissimilar in size. More detailed studies which take into account bulk effects were also carried out where the cohesive energies of the pure compounds were derived from molecular dynamics simulations and the interaction parameters were determined from the differences in the cohesive energies. The concentration and temperature dependence of the χ parameters was evaluated by calculating the energy of mixing from the differences in the cohesive energy densities of the mixed and demixed systems. The present study provides a detailed understanding of the miscibility of PMMA and 5CB as PMMA polymerizes from its monomer, and the results indicate that although methyl methacrylate and 5CB are completely miscible, 5CB is not miscible in PMMA even in small quantities.     

Real‐time property prediction for an industrial rubber‐mixing process with probabilistic ensemble Gaussian process regression models

In internal rubber‐mixing processes, data‐driven soft sensors have become increasingly important for providing online measurements for the Mooney viscosity information. Nevertheless, the prediction uncertainty of the model has rarely been explored. Additionally, traditional viscosity prediction models are based on single models and, thus, may not be appropriate for complex processes with multiple recipes and shifting operating conditions. To address both problems simultaneously, we propose a new ensemble Gaussian process regression (EGPR)‐based modeling method. First, several local Gaussian process regression (GPR) models were built with the training samples in each subclass. Then, the prediction uncertainty was adopted to evaluate the probabilistic relationship between the new test sample and several local GPR models. Moreover, the prediction value and the prediction variance was generated automatically with Bayesian inference. The prediction results in an industrial rubber‐mixing process show the superiority of EGPR in terms of prediction accuracy and reliability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41432.     

Dispersion,Mechanical and Thermal Properties of Epoxy Resin Composites Filled with the Nanometer Carbon Black

The nanometer carbon black (CB) was employed to prepare epoxy resin/carbon black (EP/CB) composites by blending-casting method. The different modified methods of silicone coupling agent were used to improve the dispersion of CB in epoxy resin. The mechanical and thermal properties of EP/CB composites were investigated. Experimental results showed that the mechanical properties increased at first, but decreased with excessive addition of CB. When the mass fraction of CB was 2%, the mechanical properties were maximum. The use of modified CB significantly enhanced the mechanical properties of the composites. For given CB loading, the CB modified by pretreatment method displayed better dispersion in the epoxy resin than that of the direct mixing method. SEM observation revealed that the tensile fracture surface of the composite filled with 2 wt% modified CB held more microcracks than that of 5 wt% modified CB, and the formed microcracks could consume more energy of rupture, finally to have better tensile strength. DSC analysis showed that the glass transition temperature (Tg) of the composites increased with the increasing mass fraction of CB.     

Waterborne latex coatings of color: II. Surfactant influences on color development and viscosity

A matrix of coating variables, nonassociative versus associative thickeners, different latex median particle sizes, individual surfactants and colorants [carbon black (CB), red, and yellow pigments], was examined for their influence on variances in coatings rheology and color development. Within the different coating groups, the variable of interest in this study was the surfactant added to the colorant formulation. In all three colorant formulations, sodium dodecyl sulfate (an anionic surfactant) provided poorer color development (CD) than in applied formulations containing an equivalent nonylphenol oxyethylene (EO) surfactant. In CB formulations, nonionic surfactants with higher EO content provide improved color development at low (2 mM) concentrations, but near equality in CD is achieved with low EO surfactants at higher concentrations. In contrast to CB formulations, red and yellow colorants exhibit good color development with high EO content nonionic surfactants only at low nonionic surfactants concentrations. This variance appears to be related to the interactions of surfactants with inorganic pigments (talc and laponite) in the colorant formulation. The coating’s rheology is related to latex, thickeners, and surfactant components of the paint, as has been noted in previous studies, but not to the nature of the color pigment. The viscosity of the hydroxyethyl cellulose (nonassociative type) and HEUR (associative type) thickened paint decreased with colorant addition due to dilution effects. There were no unusual deviations with the NP(EO)_x surfactants, except when a large hydrophobe nonionic surfactant [e.g., C₁₈H₃₇(EO)₁₀₀] is added. In HEC thickened coatings, the viscosity decreases when C₁₈H₃₇-(EO)₁₀₀ is in the colorant due to that surfactant inhibiting depletion flocculation. In the C₁₈H₃₇(EO)₁₀₀ coatings containing the HEUR thickener, significant increases in viscosity were observed, above the dilution values observed with the colorant addition. This is related to the viscosity maximum in the low concentration of HEUR with the C₁₈H₃₇(EO)₁₀₀ surfactant. Color development is independent of the viscosity profile of the coating. Presented in part at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 13–14, 2003 in Philadelphia, PA.