Mixing of Rubber, Classic Rapra Reprints

Introducing the new 'Classic Rapra Reprint' Series. Mixing of Rubber is the first book in a series of Classic Rapra Reprints. We have searched our previously published and successful reference books, and found some real gems! The content is sure to be of interest to those in the Rubber Mixing Industry, both new to the industry and those more experience, all will benefit...

Since the discovery of vulcanisation in the nineteenth century, rubber has been a major industrial product. From its inception, the use of vulcanising agents, reinforcing fillers and other additives has been a major feature of the rubber industry. Innumerable articles and texts attest to the chemist's skill in balancing the chemical and physical properties of the manufactured products.

Mixing as a general operation may be considered as three basic processes occurring simultaneously. Simple mixing ensures that the mixture has a uniform composition throughout its bulk, at least when viewed on a scale large compared to the size of the individual particles. In the case of solids blending (Chapter 11), the particle size need not change, but the distribution of particles throughout the mixture approaches a random distribution. If the shear forces are sufficiently large, particles may fracture, as in dispersive mixing, and the polymer may flow, as in laminar mixing (Chapter 111). In both of these processes, the size of the original particles or fluid elements changes because of the mixing process. Then the properties of the mixture depending upon the size of the basic structures reached during mixing.

In the case of laminar mixing, the size may be the striation thickness of a hypothetical fluid element, which is inversely related to the total shear strain. If relatively strong particles, or aggregates of particles, are present, these must be reduced in size by the action of forces generated by flow in the mixer. Then the size is the actual additive particle size.

The relative balance between the importance of these three processes in determining the efficiency of mixing and the product quality depends upon the attraction between additive particles, the rubber flow properties, the geometry of the mixer and the operating conditions such as temperature, mixing time and rotor speed.
The interaction of operating conditions, raw material properties and the quality of mixing can be a formidable phenomenon to analyse. However, in many cases, a number of simplifying assumptions about the operation can be made.