Fillers bound network

Carbon black is reinforced in polymer and mbber engineering as filler since many decades. Automotive and tmck tires are the best examples of exploitation of carbon black in mbber components. Wu and Wang [28] studied that the interaction between carbon black and mbber macromolecules is better than that of nanoclay and mbber macromolecules, the bound mbber content of SBR-clay nanocompound with 30 phr is still of high interest. This could be ascribed to the huge surface area of clay dispersed at nanometer level and the largest aspect ratio of silicate layers, which result in the increased silicate layer networking [29-32]. 

For silica in SBR, a polyacetylene coating gives the lowest filler-filler interaction, a good filler-polymer interaction, and the best dispersion compared to untreated and the other plasma-treated samples. However, for the stress-strain properties, the polythiophene-treated sample gives the best results. This shows the importance of sulfur moieties on the surface of the filler, which form a secondary network in the cured materials. In the blend of S-SBR and EPDM rubbers, the situation is less conclusive. The Payne effect, the bound rubber, and... 

Figure 10.11 The structure of an EPDM/N550 (phr=100) vulcanisate according to the results of NMR and extraction studies - (A) and mechanical data for the case of pure hydrodynamic reinforcement - (B) [62], The volume fraction of microphases/ components is given in vol.%. According to the NMR data, the total network density in the rubber phase, l/2Mc+e+ad, equals 425 mmol/kg, where subscripts c, e and ad stand for chemical crosslinks, chain entanglements and adsorption rubber-filler junctions. The density of the adsorption junctions in the loosely bound rubber, 1/...

H NMR transverse magnetisation relaxation experiments have been used to characterise the interactions between NR, isoprene rubber, BR, EPDM and polyethylacrylate rubbers with hydrophilic silica and silicas modified with coupling agents [124-129]. These studies showed that the physical interactions and the structures of the physical networks in rubbers filled with carbon black and rubbers filled with silicas are very similar. In both cases the principal mechanism behind the formation of the bound rubber is physical adsorption of rubber molecules onto the filler surface. 

The discussion in the Introduction led to the convincing assumption that the strain-dependent behavior of filled rubbers is due to the break-down of filler networks within the rubber matrix. This conviction will be enhanced in the following sections. However, in contrast to this mechanism, sometimes alternative models have been proposed. Gui et al. theorized that the strain amplitude effect was due to deformation, flow and alignment of the rubber molecules attached to the filler particle [41 ]. Another concept has been developed by Smith [42]. He has indicated that a shell of hard rubber (bound rubber) of definite thickness surrounds the filler and the non-linearity in dynamic mechanical behavior is related to the desorption and reabsorption of the hard absorbed shell around the carbon black. In a similar way, recently Maier and Goritz suggested a Langmuir-type polymer chain adsorption on the filler surface to explain the Payne-effect [43]. 

Fig. 11. The apparent number of elementary chain units ( ) between network junctions (line) and contribution in it from chemical (a) and adsorption (b) Junctions, and topological hindrances near the filler surface (c) as a function of the volume fraction of Aerosil (300 m g" ) in bound PDMS rubber [14] the apparent number of elementary chain units between transient entanglements is shown by an arrow the absolute error for the determination of the n value is shown by the dashed area...

In this paragraph we discuss briefly some common methods of investigating polymer-filler interactions other than by mechanical measurements involving the direct observation of reinforcement phenomena. These are primarily the adsorption of polymer from solution and from bulk. The latter is commonly referred to as bound rubber or carbon gel , whenever a coherent network of polymer and black is formed. 

This equation holds for a network in which the molecule is infinitely large (x 00) and the swelling is isotropic. Thus, for filled rubbers where the rubber is locally bound to the filler particles, the extent of... 

The data in Figure 2 clearly show that the phenolic model compounds studied here are more reactive than monomeric phenol under standard phenol formaldehyde reaction conditions. This is not surprising, since a wealth of literature shows the phenols substituted with electron donating groups are more reactive than unsubstituted phenol (12-14). However, it is particularly important for these complex phenolic-rich pyrolysis oils. These results suggest that the pyrolysis oil phenolic will react rapidly under standard cooking conditions and become covalently bound into the polymer networic. This means that the pyrolysis oils contribute to the strength of the network and do not simply act as fillers or extenders. 

Bound Rubber. The filler network is clearly evidenced by bound rubber measurements [115-117]. Bound rubber is a very specific measurement done on green mixes it consists of determining the part of rubber that can not be extracted by a good solvent [118]. A small part of rubber, previously weighted. 

The curing and dynamic properties of precipitated nano-silica on NR without and with the sulfur addition (NR with S), synthetic polyisoprene (IR), polybutadiene (BR) and SBR was investigated. Silica was treated with bis(3-triethoxysilylpropyl)tetrasulfane (TESPT) to form bonds at interfaces. Cure, Mooney viscosity, glass transition temperature, bound rubber, crosslink density and DMA were measured. The properties of silica-filled SBR and BR correlated with highest rolling resistance and SBR-silica correlated with best skid resistance. A Payne effect was observed in the loss modulus under some experimental conditions. In addition to possible filler de-agglomeration and network disruption, the nanoscale of the filler may have further contributed to the non-linear response typified by the Payne effect. ... 

In the scientific literature, nuclear magnetic resonance (NMR)," bound rubber measurements and glass transition (Tg) determination through calorimetric analysis are preferentially adopted for investigating the filler-rubber interaction, whereas microscopic analysis is in particular selected for assessing filler distribution and dispersion and for depicting the nature of the filler network. ... 

Most elastomers require reinforcing fillers to function effectively, and NMR has been used to characterize the structure of such composites as well. One examples is the adsorption of chains onto filler surfaces, -and the strong absorption of these chains into bound rubber —for example, PDMS immobilized onto high surface area silica. - Another example is the use of NMR to image the filler or polymer itself. ° NMR has also been used to study the phase separation and order of water molecules and silanol groups in polysiloxane networks and the activation of transport and local dynamics in polysiloxane-based salt-in-polymer electrolytes. ... 

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