Macrodispersion Degree Elastomers

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Macrodispersion degree elastomers

Description of the macrodispersion of fillers

The dispersion of fillers in the rubber matrix of an elastomeric material is a crucial aspect in the characterisation of these materials, as it correlates very closely with mechanical and fracture mechanical properties [1].

To evaluate macrodispersion – i.e. the filler–filler interaction – the degree of macrodispersion D is used, which is also referred to as the dispersion coefficient or dispersion index.

Determination of material values using the gloss cut method

The experimental determination of the degree of macrodispersion can be carried out using the gloss cut method (for further methods, see elastomer dispersion filler) by determining the content of undispersed filler in accordance with ASTM D 2663 [2] and a method modified by Stump and Railsbach [3].

This method is also known as the UCB method (UCB = undispersed carbon black). In this reflected-light optical microscopy technique, the convex areas of the surface beneath which the filler particles are located appear dark, as they reflect light diffusely. In principle, the degree of dispersion reflects the projected area of the matrix excluding undispersed carbon black. Consequently, the fewer dark areas visible in a cross-sectional image produced using this method, the better the filler dispersion, as this indicates that few large agglomerates have been detected. The gloss sectioning method used enables the visualisation of filler agglomerates or aggregates with sizes from approximately 3–5 µm [3]. Figure 1 illustrates, by way of an example, how the areas of filler agglomerates are determined through image analysis. The area A_F determined in this way is directly incorporated into the calculation of the macrodispersion degree D according to Eq. (1), in proportion to the total area A₀. A degree of macrodispersion of 100 per cent means that no agglomerates larger than 5–6 µm were detectable in the image under consideration.

$D=\left(1-{\frac {{\frac {1}{n}}\sum _{i}^{n}(A_{F}\cdot \varphi _{MED})}{\varphi \cdot A_{0}}}\right)100\;\%$

(1)

where:	AF	–	surface area of the filler agglomerates,
	A0	–	total surface area under consideration (blue frame in Fig. 1),
	φ	–	mass content of filler,
	φMED	–	Mmedalia factor, which takes into account the volume of filler in the agglomerates; n-number of samples (here n = 6).

Fig. 1:

Example of the analysis of a light-microscopic image of a gloss cut to determine the degree of macrodispersion D [6]

Application of the degree of dispersion

The macrodispersion degree D, which is used to assess the macrodispersion of fillers in a rubber matrix, is a [[Material Parameter|parameter] frequently employed in processing and application engineering. Dispersion is regarded as a measure of mixing quality. It is significantly influenced by complex interactions at the interface between the rubber and the filler, as well as between the filler particles themselves [7].

See also

• Elastomers
• Elastomer dispersion filler
• Cross-linking elastomers
• Degree of cross-linking elastomers

References

[1]	Reincke, K.: Elastomere Werkstoffe – Zusammenhang zwischen Mischungsrezeptur, Struktur und mechanischen Eigenschaften sowie dem Deformations- und Bruchverhalten. Habilitation, Martin-Luther-Universität Halle-Wittenberg, Shaker Publishing (2016) (ISBN 978-3-8440-4637-3; see AMK-Library under B 2-2)
[2]	ASTM D 2663 (2014; reapproved 2025): Standard Test Methods for Carbon Black Dispersion in Rubber
[3]	Stumpe, N. A., Railsbach, H: E.: Carbon black dispersion – Photographic technique and rating system. Rubber World 151(1964) 41
[4]	Le, H. H., Ilisch, S., Kasiwal, G. R., Radusch, H.-J.: Thermogravimetrische Analyse an kautschuk-Füllstoff-Gel. Bestimmung dr phasenspezifischen Füllstoffverteilung in Kautschukblends. Kautsch.Gummi.Kunstst. (KGK) Mai (2007) 241–248
[5]	Schuster, R. H.: Kautschuk-Füllstoff-Wechselwirkungen und Füllstofftransfer in Verschnitten. Gummi Fasern Kunststoffe – GAK 49 (1996) 816–826
[6]	Ilisch, S., Thiele, S., Reincke, K., Le, H. H., Keller, M., Ferner, U., Radusch, H.-J., Grellmann, W.: SBR/BR-Komposite mit anorganischen Füllstoffen für rollwiderstandreduzierte Reifenmischungen. 14. Problemseminar Polymermischungen, September 14 and 15, 2011, Halle, Proceedings p. 47 und CD (ISBN 978-3-86829-391-3)
[7]	Ziegler, J.: Beeinflussung der Polymer-Füllstoff-Wechselwirkung durch Oberflächenmodifizierung von Füllstoffen. Dissertation (2004), Universität Hannover, see Deutsche Digitale Bibliothek (last accessed on August 11, 2026)