Low Strain Dynamic Properties of Filled Rubbers

Abstract

Carbon black does not exist as single spherical particles but forms itself into a rodlike primary structure. These rodlike structures then form into an aggregated secondary network. This secondary network is believed to be held together by Van der Waals-London attraction forces. The decrease in shear modulus of filled rubber vulcanizates with strain is due almost certainly to these secondary forces. Special mixing techniques such as attrition of the carbon black, increased time of mixing, or the addition of chemical promoters which aim at dispersing the carbon black within the mix better are shown to decrease the value of G′0−G′∞. The absence of any modulus change with strain for unfilled vulcanizates and secondly the little change observed in values of G′0−G′∞ with increasing vulcanization of the rubber when containing the same amount of carbon black confirms that the decrease in modulus with strain amplitude is in no way associated with the gum phase of the filled vulcanizate. The similarity in behavior of carbon black filled rubbers with clay/water and clay/rubber systems indicates that the decrease in modulus with amplitude is due to the breakdown of the three dimensional filler aggregates. A number of rheological studies on clay systems has confirmed that clay particles form into rigid three dimensional structures when dispersed in a medium. Evidence for the aggregated filler structure to be held together by Van der Waals-London attraction forces comes from the reasonable agreement between the experimental values for the forces required to breakdown the carbon black aggregates in paraffin oil and the forces calculated from Van den Tempel's model for flocculated solid particles in a liquid. The successful application of a domain model to the hysteretical behavior exhibited by carbon black filled vulcanizates at low strains indicates that the carbon black structure breaks down under stress but reforms to the original state when the stress is removed. This conclusion is also supported by the similarity in behavior between filled rubbers and a dendritic crystal structure of PBNA in rubber. Under the optical microscope the PBNA is seen to break down and reform under a stress-strain cycle. The breakdown and reformation of this secondary aggregated carbon black structure increases the hysteresis in filled rubber vulcanizates. Other sources of hysteresis include viscoelasticity of the polymer, crystallization, stress-softening, and changes in network structure (e.g., breakage of weak crosslinks). These mechanisms have been discussed in depth in previous publications. Recent work has shown, however, that the strength of a rubber is dependent on the combined effect of the different hysteretical mechanisms. The breakdown and reformation of the carbon black structure at low strains in filler reinforced rubbers therefore not only affects the heat build up, transmissibility, and fatigue behavior but also influences the failure properties of the filled vulcanizate.

Interactive effects between carbon allotrope fillers on the mechanical reinforcement of polyisoprene based nanocomposites

“…decreases with strain amplitude when the composites contain a carbon nanofiller and this decrease is particularly pronounced for composites with CNT as the nanofiller. As mentioned in the Introduction, nanofillers are known to promote a remarkable Payne effect [12]. Several models have been developed in order to explain such an effect on the basis of two main interpretations: the first one, related to the filler networking concept, assumes an agglomeration-deagglomeration process of the filler network above the filler percolation threshold [12,[32][33][34], the second one, related to filler-matrix interaction, assumes matrix-filler bonding and debonding mechanisms [35][36][37][38][39][40][41][42][43].…”

“…int (( nanofiller , ( CB ) is -0, that means there is interaction between the nanofiller and CB, what was named above as synergy. As a matter of fact, Equation (12) itself reveals the interaction between the two different fillers. In fact, Equation (12) shows that the modulus of the composite G!…”

“…As a matter of fact, Equation (12) itself reveals the interaction between the two different fillers. In fact, Equation (12) shows that the modulus of the composite G! c with both fillers can be obtained by multiplying the moduli of composites containing only one filler, as shown by Equation (14): (14) These comments concerning k factor are based on the collected experimental data and a more general validity (for other filler systems) has still to be demonstrated.…”

“…Reviews are available on polymer nanocomposites (PNC) based on these types of nanofillers [8][9][10][11]. In polymer melts and elastomers, the formation of networks at low nanofiller concentration leads to high values of the dynamic modulus at low strain amplitudes, that goes however along with a pronounced reduction as the strain amplitude increases, phenomenon known as Payne effect [12]. Most studies reported in literature refer to PNC made by a single type of carbon nanofiller in a neat polymer matrix.…”

Application of Acrylonitrile Butadiene Rubber for Management of Industrial Waste Silica

“…Therefore, it is essential to exploit new ways to enhance the ageing resistance and mechanical properties for NRL products. Further, such reinforcements are related to the secondary structure of filler particles (agglomerate) [16][17][18] and the rubber/ filler interactions [19][20][21]. Silica is also known as an effective filler of rubber reinforcement.…”