Rubber agglomerate

The formation of the steel/synthetic fibre/rubber agglomerates is a by-product of the milling process and in part the tyre manufacturing process. The steel belts used in auto... 

In a filled rubber, agglomeration of the particles produces a filler network, in addition to the network of covalently-bonded polymer chains. In fact, Reichert et al. [30] modeled the deformation of single network of filled rubber as a double network, adopting an approach similar to that used to analyze unfilled double networks [35-37]. This implies that double-network mbber reinforced with filler can be viewed as a composite of three distinct networks. 

Clarke,. 1. and Freakley, P.K., 1995. Modes of dispersive mixing and filler agglomerate size distributions in rubber compounds, Plast. Rubber Compos. Process. Appl. 24, 261-266. 

Prepare a saturated solution of sodium sulphide, preferably from the fused technical sodium polysulphide, and saturate it with sulphur the sulphur content should approximate to that of sodium tetrasulphide. To 50 ml. of the saturated sodium tetrasulphide solution contained in a 500 ml. round-bottomed flask provided with a reflux condenser, add 12 -5 ml. of ethylene dichloride, followed by 1 g. of magnesium oxide to act as catalyst. Heat the mixture until the ethylene dichloride commences to reflux and remove the flame. An exothermic reaction sets in and small particles of Thiokol are formed at the interface between the tetrasulphide solution and the ethylene chloride these float to the surface, agglomerate, and then sink to the bottom of the flask. Decant the hquid, and wash the sohd several times with water. Remove the Thiokol with forceps or tongs and test its rubber-like properties (stretching, etc.). 

FIGURE 19.1 Morphology of nano-filler in rubbery matrix Nano-particles are aggregated, and the aggregates also associate to give filler agglomerate in rubber. (From Kohjiya, S., Kato, A., Suda, T., Shimanuki, J., and Ikeda, Y., Polymer, Al, 3298, 2006. With permission.)... 

D-TEM gave 3D images of nano-filler dispersion in NR, which clearly indicated aggregates and agglomerates of carbon black leading to a kind of network structure in NR vulcanizates. That is, filled rubbers may have double networks, one of rubber by covalent bonding and the other of nanofiller by physical interaction. The revealed 3D network structure was in conformity with many physical properties, e.g., percolation behavior of electron conductivity. 

The most challenging part of rubber mixing is the dispersion of the filler The filler agglomerates have to be broken into smaller particles, the aggregates, but not completely to the level of primary particles. An optimal particle size distribution has to be achieved in order to obtain the best properties of the final rubber product [14]. 

Illustration Kinetics of dispersion the two-zone model. The models for agglomerate rupture when integrated with a flow model are useful for the modeling of dispersion in practical mixers, as was discussed for the case of drop dispersion. Manas-Zloczower, Nir, and Tadmor (1982), in an early study, presented a model for the dispersion of carbon black in rubber in a Banbury mixer (Fig. 34). The model is based on several simplifying assumptions Fragmentation is assumed to occur by rupture alone, and each rupture produces two equal-sized fragments. Rupture is assumed to occur... 

Manas-Zloczower, I., Nir, A., and Tadmor, Z., Dispersive mixing in internal mixers—a theoretical model based on agglomerate rupture. Rubber Chem. Tech 55, 1250-1285 (1982). 

The operation of processing rubber on a refiner, the object being to break down any agglomerates of compounding ingredients or to remove small particles of scorched rubber. Refining is one of... 

Removing foreign matter and agglomerates of compounding ingredients from rubber or rubber compound by passing it through a strainer. 

Incorporation - the carbon black is distributed into the rubber matrix but not into the desired state for complete reinforcement. At this stage of mixing the rubber penetrates the voids in the large agglomerates of carbon black. It is also at this stage that strong interaction between the rubber and black surface occurs in the case of small particle sized blacks with low structure, which makes the next step of dispersion difficult to achieve. 

Dispersion of soluble rhombic sulphur does not usually create problems in most polymers, but addition of the insoluble form can create problems of incorporation into the rubber compound due to insolubility in the rubber. The insoluble sulphur particles tend to agglomerate into small lumps, which cannot then be dispersed effectively. Various treated insoluble sulphur products are available which aid incorporation. 

In the early days of the rubber industry all mixing was carried out on two-roll mills. Now this situation only occurs occasionally, or when small or expensive batches of material are required, e.g., silicones or fluorocarbons. Mill mixing is an efficient method for breaking down agglomerates and, over a period of time, with good operatives, good homogeneity can be achieved. One batch, however, can take some 30-40 minutes to mix. 

These incorporate membranes fabricated from insoluble crystalline materials. They can be in the form of a single crystal, a compressed disc of micro-crystalline material or an agglomerate of micro-crystals embedded in a silicone rubber or paraffin matrix which is moulded in the form of a thin disc. The materials used are highly insoluble salts such as lanthanum fluoride, barium sulphate, silver halides and metal sulphides. These types of membrane show a selective and Nemstian response to solutions containing either the cation or the anion of the salt used. Factors to be considered in the fabrication of a suitable membrane include solubility, mechanical strength, conductivity and resistance to abrasion or corrosion. 

The dynamic response of polydimethylsiloxane (PDMS) reinforced with fused silica with and without surface treatment has been discussed in terms of interactions between the filler and polymer [54]. Since bound rubber measurements showed that PDMS chains were strongly attached to the silica surface, agglomeration due to direct contact between silica aggregates was considered an unlikely explanation for the marked increase in storage modulus seen with increasing filler content at low strains. Instead three types of flller-polymer-flller association were proposed which would cause agglomeration, as depicted in Fig. 15. 

Sometimes particles are encouraged to agglomerate to yield granules, for example, for pharmaceutical applications which may require the addition of liquids or other binders. In the ceramics, paint, plastics and rubber industries, however, reducing or eliminating agglomerate formation is of overriding importance. 

Studies on the kinetics of carbon black dispersion in various rubbers have been reported using a Brabender mixer fitted with cam-type rotors [110]. Dispersion rating, determined by visual inspection of photomicrographs, was found to depend strongly on mixing time. For an SBR emulsion, it was observed that there was an initial delay period where the carbon black agglomerates were thought to be fractured and incorporated into the rubber. Subsequently, the process of dispersion continued for a considerable time thereafter. 

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