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 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 11). 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 depend 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.