Functional Cellulose for Rubber Engineering
Short Glance on the Rubber Market
The world of rubber is vast and expanding. In 2019 the market size stood at ~41 billion $, with a forecasted growth of 5.3% annually until 2027. Key drivers are automotive and industrial applications, using the toughness, tear resistance and low temperature suitability of rubber grades.
A basic differentiation is made between natural rubbers, produced from the rubber tree, consisting mainly of isoprene polymer and synthetic rubber. The first of those was chloroprene (invented in the 1930s), best known probably from diving suits, with better resistance to corrosion, burning and degradation.
Nowadays, a wide variation of rubber types like nitriles, silicones, styrene-butadienes, butyls, EPDMs and more allow for careful material selection for each application.
Cellulose Functionality in Elastomers
Following our blog, you might have read some articles about plastic-fiber composites already. In addition, rubbers have been used as matrices for natural fiber fillers for many years. Similar to nonpolar polyolefins, the matrix fiber interaction of rubber and cellulose fillers is very weak. Hence, the fibers cannot be seen as a classical reinforcement for rubber composites. In spite of this, for applications like tubes or gaskets, cellulose fibers ranging from 300 µm to 1000 µm have reinforcing impact when the fiber orientation is vertical to the extrusion direction.
Furthermore, celluloses enhance transmission belts due to friction and noise reduction and stabilize the essential cord layer during production. Also tennis balls, shoes and more are target fields for rubber composites.
Rubber formulations are complex systems with manifold interactions of their components. Therefore, the underlying mechanisms of those effects can often only be assumed. One theory for reinforcement is, that cellulose fibers stop cracks and fissures forming in the rubber matrix due to their missing interaction. They 'block' the continuation of a crack, thus improving the service life.
TPE-Composites – What’s That?
In thermoplastic elastomers (TPE) advantages of elastic rubber and easily processable thermoplastics come together. In contrast to classic elastomers, the polymer chains are not chemically linked, and can be molten again. They consist of blends or copolymers of thermoplastic and elastomeric components, but are no substitute to elastomers, as they do not match all material qualities.
Cellulose-TPE composites are a possible road to improve the heat stability of the materials, research along these lines shows however, that improved mechanical properties only come with compatibilizers.
If you are interested natural fiber solutions for your rubber applications, just give us a heads up!
