To obtain optimum performance from Zonyl® MP1500 as a reinforcing additive in elastomer formulations, sufficient shear must be applied during the mixing step to deform the very small particles of Zonyl® resin into ribbons or platelets. If reinforcement in the final product is less than expected, it is most likely due to insufficient shear during mixing.
To ensure sufficient shear during mixing, particularly if the uncured elastomer has a low viscosity, the best procedure is to first prepare a masterbatch of a very high concentration of Zonyl® MP1500 in the base elastomer that can later be let down with the additional base elastomer to achieve the desired level of Zonyl® MP1500 in the final formulation. The concentrated masterbatch should contain as high a level of Zonyl® MP1500 as practical. Typically, the masterbatch should contain from at least 50% to 80% Zonyl® MP1500. Any fillers such as carbon black that will be in the final let down formulation should also be included in the masterbatch since this increases the viscosity of the rubber stock during mixing. Generally, the higher the Mooney Viscosity of the base elastomer, the easier it will be to achieve adequate shear during mixing. Reinforcing filler such as carbon black raises the Mooney Viscosity of the rubber base stock and is desirable in the concentrated masterbatch.
Zonyl® MP1500 should be added to and mixed into the base elastomer using a Banbury mixer or a two-roll rubber mill, using the same procedure as is used for other fillers. The exception is that high shear must be maintained.
On a two-roll mill, the masterbatch should be compounded using as tight a nip setting as possible during incorporation of the Zonyl® MP1500. The usual folding-in procedure and cigar rolling should be done, again with as tight a nip as possible. The fully compounded masterbatch should then be sheeted out and used as a compounding ingredient in the final composition.