Fillers loading

Surface Area. Surface area is the available area of fillers, be it on the surface or in cracks, crevices, and pores. The values obtained from different methods for measuring the surface area of a filler may vary significandy. These variations are because of the nature of the methods and in many instances yield information related to the heterogeneity of the surface. Understanding the surface area is important because many processing factors are dependent on the surface area, eg, ease of filler dispersion, rheology, and optimum filler loading. 

In modem industrial practice, compositions often contain pigments, reinforcements, rheological modifiers, surfactants, and other materials in addition to fillers. These materials can function synergisticaHy in the system. Hence, more complex models are needed to predict the optimal filler loading. ExceUent discussions of filler loading and selection in plastics are given (9,10). 

Filler loading Volume, parts Mooney viscosity Optimum cure (at 141°C), min Modulus (at 300%), MPa Tensde strength, MPa Elongation, % Hardness, Shore A NBS abrasion (ASTMD1630) Rebound, %... 

Another difference between hot and cold elastomeric SBR latices is that hot types are carried to < 90% conversion and not normally shortstopped. The cold latices are usually shortstopped at ca 60—80% conversion. Again the desired physical properties of the contained copolymer are responsible for these differences. Cold latices are used in applications where the modulus, eg, in foam, or retention of physical properties at high filler loadings, eg, in fabric backing, are required. The cold latices are generally suppHed at a higher soHds concentration than the hot series because of these uses. 

Low ionic impurity levels are imperative. In order to reduce the coefficient of thermal expansion of the final mol ding, and hence minimise stresses on the encapsulated siHcon chip, the highest possible filler loading is desired. This has to be balanced against the need to maintain as low a melt viscosity as possible to minimise the possibiHty of damage to the device during the encapsulation process. 

Figure 9 shows the variation of apparent viscosity with apparent shear stress. It is evident that the mixes are pseudoplastic in nature. Furthermore, as expected, viscosity increases with an increasing filler loading. 

Here 17 is the apparent viscosity at temperature T, R is the universal gas constant, and A is an empirical constant, called frequency factor for melt flow. The activation energy values for different systems and at different shear rates are summarized in Table 8. It is evident that activation energy for flow increases with filler loading, but it decreases with an increase in shear rate. 

The important yet unexpected result is that in NR-s-SBR (solution) blends, carbon black preferably locates in the interphase, especially when the rubber-filler interaction is similar for both polymers. In this case, the carbon black volume fraction is 0.6 for the interphase, 0.24 for s-SBR phase, and only 0.09 in the NR phase. The higher amount in SBR phase could be due to the presence of aromatic structure both in the black and the rubber. Further, carbon black is less compatible with NR-cE-1,4 BR blend than NR-s-SBR blend because of the crystallization tendency of the former blend. There is a preferential partition of carbon black in favor of cis-1,4 BR, a significant lower partition coefficient compared to NR-s-SBR. Further, it was observed that the partition coefficient decreases with increased filler loading. In the EPDM-BR blend, the partition coefficient is as large as 3 in favor of BR. 

Blend System (A/B) Blend Ratio Filler Loading (phr) Mixing Procedure Cb/C,... 

EUler Swelling is reduced by the use of high filler loadings, with less elastomer then available to absorb fluid. 

It has been well established that wear resistance of filled rubber is essentially determined by filler loading, filler morphology, and polymer-filler interaction. For fillers having similar morphologies, an increase in polymer-filler interaction, either through enhancement of physical adsorption of polymer chains on the filler surface, or via creation of chemical linkages between filler and polymer, is crucial to the enhancement of wear resistance. In addition, filler dispersion is also essential as it is directly related to the contact area of polymer with filler, hence polymer-filler interaction. 

Work done by L. Mullins on the prestressing of filler-loaded vulcanisates showed that such prestressing gives a stress-strain curve approaching that of an unfilled rubber. This work has thrown much light on so called permanent set and the theory of filler reinforcement. See Stress Softening. 

They may also act as reactive super plasticisers to increase rubber flow while increasing the mechanical properties of the rubber. Viscosity reduction or polymer solvation and higher filler loading can be accomplished with less plasticiser. Flow is achieved through molecular rearrangement and not average molecular weight reduction of the rubber. 

Very high oil loadings of aromatic oils can be compatible with some grades of CR. However, the level of the oil s aromaticity must be carefully considered, for although compatible with loadings of up to about 100 phr of oil, stickiness of the vulcanised surface can result in highly filler loaded compounds. This has been found to be overcome by the use of oils with lower compatibility, i.e., less aromaticity, and by the incorporation of small amounts of factice or SBR to assist... 

In general, tin compounds do not exhibit flame-retardant properties in halogen-free polymer systems, unless the composition contains a high inorganic filler loading. However, tin additives often act as smoke suppressants in non-halogenated polymers. 

Filled resins, 18 292 Filled silicone networks, 22 570-572 Filler hybrid preparation method, 13 539 Filler loading, 10 430, 457 Fillers, 10 430-434 11 301-321. See also Filled polymers applications of, 11 301-302 butyl rubber applications, 4 448-449... 

As impact modifiers and/or processing aids (permanent plasticizer), they improve economics by increasing filler loading without embrittlement to produce ... 

---