The labor-intensive dip process can be avoided when the components of the adhesive system are added directly to the rubber mixture. Highly dispersed silica is used to activate the reaction, and hexamethylenetetramine or hydroxyl methyl derivatives are employed as formaldehyde donors. The reaction between fiber and matrix takes place according to the mechanism described above. This method has the disadvantage that the adhesion promoter will be contained throughout the matrix, which may impair mechanical and dynamic properties.
When high adhesion performance is required, a combination of adhesion-promoted textiles and adhesion-promoted rubber mixtures has proven to be very useful, provided that other desired properties, such as dynamic resistance or resistance to aging, are not too much impaired [58].