Properties of Rubber Crumb

In Europe, the Comite Europeen de Normalisation (CEN) technical committee TC 366 (Project Committee - Tyre recycling) published a Technical Specification (TS), CEN/TS 14243 2010 in 2010 that provides a definition for the categories of materials that are produced from end-of-life tyres based on their dimensions or impurities. This publication also provides test methods for the determination of the dimensions of the materials produced from all categories of end-of-life tyres, at all stages within the treatment process, as well as for the determination of impurities. It also describes test methods for the collection of samples, and for the preparation of representative samples based on a sampling plan for the purpose of determining dimensions and impurities. It does not cover the following technical areas  

American standards that address the general properties of rubber crumb include ASTM D-5603 (Classification for Rubber Compounding Materials - Recycled Vulcanisate Particulate Rubber). This standard has sections covering the classification of rubber crumb into six classes - (1) to (6) - covering the determination of mesh size, the determination of bulk density and other key properties. 

As described in the sections above, once a grinding process (ambient, cryogenic or water jet) has produced crumb it is sieved, which produces a nominal size, e.g., 40 mesh (equivalent to 400 pm). 

However, another important property of the crumb will be its particle size distribution. This can be determined using ASTM D-5644 (Standard Test Methods for Rubber Compounding Materials - Determination of Particle Size Distribution of Recycled Vulcanisate Particulate Rubber). Two different methods are described in this standard, Methods A and B  

Method B also differs from Method A in that it is an ultrasonic technique and the use of this technology addresses the problems that may be caused by tackiness and the static electrical forces that recycled rubber particles may exert on each other to form agglomerates. The problem of agglomeration can be particularly prevalent for particles that are 80 mesh or finer. The use of ultrasonic agitation eliminates the formation of agglomerate by dispersing the particles. 

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