Para-aramid fibres have a highly crystalline structure, high strength, high modulus, excellent stability at elevated temperatures and good resistance to some solvents (see table 1). Pulp fibres have an average length from 0,7 mm to less than 2 mm and a specific surface area from 5 m2/g to 8 m2/g.
Aramid fibres, as other fibres, improve dimensional stability and green strength before curing, and mechanical properties of the vulcanizates. But the incorporation of high surface area additives is difficult to achieve and only a few compounders are able to disperse pulp into rubber.
To facilitate the dispersion, it is possible to pre-open the pulp by high shear mixing techniques, wet and pre-disperse it.
RheinChemie patented some masterbatches of Twaron Pulp that are easier to mix into the rubber compound. They are available for EPDM, NR, BR, CR, NBR and silicone. Dupont offers a patented composite of Kevlar Pulp and elastomer : The " Kevlar Engineered elastomer ". Results from Table 2 show the effectiveness of a good dispersion and the high anisotropy in machine direction (MD) of vulcanizates reinforced with a moderate quantity of pulp (10 phr).
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