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Effect of Filler Properties on Elastomer Performance
The influence of the filler physical properties on reinforcement and other important properties is a very complex subject as they interact with one another. The general trends are summarized in very simple form in Table 1 below. This shows that the best reinforcement is achieved by small particle size, high structure, strong filler/polymer interaction, and good dispersion. Only a few filler types are able to achieve this, notably carbon blacks, synthetic silicas when used with coupling agents such as organosilanes, and precipitated calcium carbonates with unsaturated carboxylated polymer coupling agents.
Some examples of the importance of the various effects follow.
Some Effects of Particle Size
Table 2 exemplifies how tensile strength and abrasion resistance vary with carbon black primary particle size. This is a based on data in a sulfur cured SBR compound.
Some Effects of Filler Dispersion
Table 3 shows how various filled elastomer properties develop as a function of dispersion. This study was achieved by measuring dispersion and property profile of a compound as a function of mixing time.
This study did not consider the effect of the actual size or nature of the poorly dispersed material. This was investigated in detail in the classic studies by Boonstra and Medalia (1963) who found that particles become detrimental at a size of about 1 pm. They found little further effect of size above this critical value, but did find that properties deteriorated further as the hardness of the particles increased. The most sensitive property to poor dispersion in both studies was found to be abrasion
Table 1 The direction and magnitude of the effects of the main filler properties on those of filled elastomers (adapted from (Boonstra 1975))
Notes: + and ++ mean increase in that property and — and perty and++ mean increasedo not mean that the change is beneficial or detrimental. This depends very much on the application. For instance, high hysteresis is good for sound damping, but bad where heat build-up has to be avoided
Table 2 The effect of carbon black primary particle size on tensile sand laboratory abrasion resistance in a sulfur cured SBR compound (adapted from (Boonstra 1975))
Table 3 Development of dispersion and properties during compound mixing (adapted from (Boonstra 1975))
resistance. Even trace amounts of grit (a few 100 ppm) was found to cause a detectable loss in performance in fatigue tests and are thus important in some critical applications, notably tires.
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