Tire cord adhesion—A TEM study

Abstract

AbstractTire cords are commonly bonded to the rubber by means of resorcinol–formaldehyde–latex (RFL) adhesives. Modified systems involving compatible first dip resins or RFL additives are required for standard polyester (PET) cords. The tire composite contains several interfaces at which adhesive failure can be initiated. However, very little is known about the interfaces between the various materials. This paper describes a method which allows ultrathin sectioning and thereby TEM studies of cord sections embedded in rubber. The studies were performed on model samples produced in the laboratory as well as cord sections cut from commercial tires. The TEM micrographs clearly demonstrate the pronounced capillary flow of the RFL solution from outer fiber surfaces to fiber interstices. This flow leads to either no RFL or very thin RFL layers at the outer filament surfaces of the cord even in the case of high RFL levels (6%) and double dipping of the RFL. A qualitative relationship between adhesion and RFL surface coverage has been demonstrated. The RFL interface to rubber, to a second RFL dip, or to predips of other adhesives is generally very distinct and its texture similar to that of the bulk RFL. Also, no evidence for diffusion of either the predip or RFL components into the fiber surface could be found. This indicates that only limited interdiffusion of the polymeric materials of RFL and rubber phases takes place. Texture differences in the RFL and rubber phases between the various tires can be used to characterize the type of system used.