Effect of carbon black addition and its phase selective distribution on the stress relaxation behavior of filled thermoplastic vulcanizates

The long term mechanical behavior of thermoplastic vulcanizates (TPV) based on polypropylene (PP) and ethylene propylene diene terpolymer (EPDM) and different types and concentrations of carbon black (CB) has been characterized by means of stress relaxation experiments. Evaluation of the relaxation curves was carried out using the two‐component model allowing a division of the initial stress into different stress components which are caused by different networks available in TPV. The discussion focussed on the background of the stress components, which are originated by the CB addition, the non‐relaxing stress components σ, and σ, as well as the relaxing stress components Δσ^{CB(polymer‐layer)} and Δσ^CB(network). It was found that the concentration and type of CB as well as the phase specific CB distribution strongly affect the non‐relaxing and relaxing stress components. Up to a CB concentration of 9% in the EPDM phase the composite behaves as a thermo‐rheologically simple material because the impact of CB addition on the α‐relaxation of the crystalline PP phase is still negligible. A master curve was created by the horizontal shift of the relaxing stress curves Δσ^Comp(t) to a reference curve. At higher local CB loadings the additional relaxation processes induced by CB addition overlap with the α‐relaxation, thus, no master curve could be made in that case. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Master curve of filler localization in rubber blends at an equilibrium state

In this study, the phase-specific localization of filler in NBR/NR blends was characterized by means of the selective extraction method and wetting concept. A strong dependence of silica localization on the filler loading was found. A model based on thermodynamic data was proposed for a quantitative prediction of filler localization in rubber blends. The filler localization can be described by a master curve demonstrating a characteristic behavior in dependence on the filler surface tension data of blend components and filler. The effect of filler loading on the silica localization is sufficiently explained by this model by taking into consideration the deactivation of the silanol groups on the silica surface by adsorbed curing additives. Using the master curve, the surface tension of filler affected by curing additives and silane addition can be estimated that may be useful for evaluation and comparison of the effect of different coupling agents. Surface tension values of different fillers were estimated by means of the master curve and they lie in the same order compared to those reported in literature. A potential transfer of filler within a rubber blend can be also quantitatively predicted.     

Effect of filler dispersion degree on the Joule heating stimulated recovery behaviour of nanocomposites

Composites based on highly branched ethylene-1-octene copolymer (EOC) and carbon black (CB) with different dispersion degree of CB were prepared. The method of the online measured electrical conductance/resistance was used to monitor the change of the electrical conductance/resistance of the composites during the preparation processes, i.e. mixing and cross-linking. It was found that the kinetics of thermally stimulated shape-memory recovery of CB filled EOC is strongly influenced by the filler dispersion degree, which actually affects the heat transfer in the composites. Using a special arrangement of experiments the Joule heating stimulated shape-memory behaviour was quantified. CB dispersion degree and related electrical resistivity determine the extent of the Joule heating stimulated shape-memory behaviour. Composite collected at the maximum in the online measured conductance–time characteristics showed the best shape-memory effect owing to the highest electrical conductivity in the solid state. The CB filled EOC showed a negative thermal coefficient of resistivity (NTC) effect, which accelerates the temperature increase and shape-memory recovery of the composites when applying a voltage.     

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.     

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     

Higher-order derivative spectrophotometry for studying and characterization of proteins and other native and synthetic macromolecules

Higher-order derivative spectrophotometry is very well adapted to the analytical chemistry of native and synthetic macromolecules. This is shown with the aid of some characteristic examples. The following ones have been described: The investigation of iso-forms of LDH, of myoglobins (whale and horse), of oligomer enzymes, the studying of the surroundings of the chromophores phe, tyr and trp in proteins, and of protein powder spectra; further spectra of nucleid acid, the quantitative estimation of monomers and additives in synthetic polymers, and the characterization of poly(vinyl pyrrolidons) of different molecular weights.     

Influence of carbon black properties on the Joule heating stimulated shape‐memory behavior of filledethylene‐1‐octene copolymer

The shape‐memory (SM) behavior of ethylene‐1‐octene copolymer (EOC) reinforced by carbon black (CB) was investigated. Two CB types, N110 and EC600, with different structure and specific surface area were used as conductive fillers. The mechanical tests showed that on addition of CB into EOC, modulus and strength increased significantly for both CB types but the elastic behavior stands on. The electrical resistivity decreases drastically with increasing CB content. The thermally stimulated SM recovery is deteriorated significantly because of the rigid CB network formed in EOC. With increasing temperature, the CB network gradually loses its rigidity, as the glassy polymer layers connecting the CB aggregates become softened. As a result, the samples with high CB content could recover nearly 100%. In this work, a sample preparation and a corresponding arrangement of experiment were introduced, which allows to quantify the Joule heating stimulated recovery behavior. EOC containing 17 wt% CB EC600 reaches a low resistivity of 8 Ω cm and shows good Joule heating stimulated SM recovery of up to 97% at a voltage of 15 V. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Effect of the cross‐linking process on the electrical resistivity and shape‐memory behavior of cross‐linked carbon black filled ethylene‐octene copolymer

The electrical resistance of carbon black (CB) filled ethylene‐octene copolymer (EOC) was monitored during the compression molding step by means of conductivity sensors. It increases strongly during the cross‐linking process due to the de‐agglomeration of CB aggregates. After completion of cross‐linking reaction CB aggregates reagglomerate causing a decay of resistance. The electrically stimulated shape‐memory (SM) behavior was found to be strongly dependent on the extent of electrical resistivity and the rigidity of CB network, which is formed during compounding and subsequent cross‐linking process. The effect of amount of peroxide and cross‐linking conditions like time and temperature on resistivity and the related SM behavior was characterized. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Silica Transfer in Ternary Rubber Blends: Calculation and Experimental Determination

A novel model is presented for predicting the phase selective filler localization in an equilibrium state for ternary rubber blends of SBR, NBR, and NR. It is based on surface tension data of the rubber components and the filler. Phase‐selective filler localization in ternary rubber blends is determined experimentally by means of FTIR spectroscopy on the basis of the wetting concept. It is found that by preparation of ternary blends with certain silica loadings, pre‐mixed in each blend phase using the masterbatch technology, silica transfer processes between blend phases take place until the equilibrium filler distribution is reached. The sequence of the silica transfer processes can be explained by taking into consideration the formation of a phase‐in‐phase morphology of the ternary blend.

     

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.