Adhesion of elastomers: Dwell time effects

The strength of adhesion of elastomers to rigid substrates generally increases with time of contact. This effect has been studied for samples of butyl and chlorobutyl rubber adhering to some rigid substrates. The peel strength increased continuously over long periods of contact until in some cases failure became cohesive within the elastomer layer. At higher temperatures the strength increased more rapidly, consistent with the WLF relation governing molecular motions. It is postulated that slow molecular rearrangements occur at the interface and increase the bond strength. A criterion for the observed transition from interfacial to cohesive failure is suggested.     

ADHESION OF ELASTOMER LAYERS TO AN INTERPOSED LAYER OF FILLER PARTICLES

Adhesion of elastomers to filler particles was studied by interposing a single layer of particles between two layers of a crosslinked elastomer and peeling the sandwich apart. Carbon black particles increased the peel strength by up to 100% compared with autohesion of the elastomer layers. Silica particles also increased the adhesion, but by a smaller factor, and there were significant differences using different elastomers. Also, the strength of adhesion depended on the degree of crosslinking of the elastomer layers: at higher levels of crosslinking, both self-adhesion and adhesion to particles were reduced. Nevertheless, this simple experiment gives an indication of the relative strength of adhesion for different combinations of elastomer and reinforcing filler.     

Adhesion of elastomer layers to an interposed layer of filler particles

Adhesion of elastomers to filler particles was studied by interposing a single layer of particles between two layers of a crosslinked elastomer and peeling the sandwich apart. Carbon black particles increased the peel strength by up to 100% compared with autohesion of the elastomer layers. Silica particles also increased the adhesion, but by a smaller factor, and there were significant differences using different elastomers. Also, the strength of adhesion depended on the degree of crosslinking of the elastomer layers: at higher levels of crosslinking, both self-adhesion and adhesion to particles were reduced. Nevertheless, this simple experiment gives an indication of the relative strength of adhesion for different combinations of elastomer and reinforcing filler.     

EFFECT OF CURE RATE OF RUBBER COMPOUND ON THE ADHESION TO COPPER-PLATED STEEL CORD

Copper-plated steel cord was prepared and its adhesion properties to rubber compounds, which have different loading amounts of both sulfur and accelerator, were examined in comparison with brass-plated steel cord. The lower pullout force of copper-plated steel cord to the rubber compounds was shown compared with brass-plated steel cord. The copper-plated steel cord showed higher adhesion retention to rubber compounds than brass-plated steel cord against various hostile environments. The stability against both humidity aging and thermal aging, and the cause for the high adhesion retention of the copper-plated steel cord to rubber compounds, were discussed compared with those of the brass-plated steel cord. The pullout force of copper-plated steel cord to rubber compound is inversely correlated with cure rate after various aging treatments.     

EFFECTS OF SUBMICROMETER PARTICULATE SILICA ADDENDA ON THE ADHESION OF MICROMETER-SIZE PARTICLES TO A POLYESTER-COMPOSITE SUBSTRATE

The force needed to detach five sets of different size particles, having number-averaged diameters between 3.6 and 8.5 µm, from a composite substrate was measured using an ultracentrifuge. In addition to size variations, the asperity concentration for each size particle was adjusted by varying the silica concentration, adjusted so that the surface area concentration at each level was kept constant for the five sizes of particles. Due to the changing silica concentration and particle size, the charge per particle also varied. It was found that the detachment force appeared to be virtually independent of charge, with any correlation actually appearing slightly negative, if anything. However, the detachment force increased monotonically with increasing particle diameter and decreased monotonically with increasing silica concentration. Moreover, upon normalizing the detachment force to the particle diameter and the silica concentration to the surface area concentration of silica, it was found that the detachment force clustered into groups in which the force needed to separate the particle from the substrate depended only on the silica concentration. These results suggest that van der Waals interaction, rather than electrostatic forces, are the dominant mechanism controlling toner adhesion in this instance.     

INTERFACE/INTERPHASE ENGINEERING OF POLYMERS FOR ADHESION ENHANCEMENT: PART II. THEORETICAL AND TECHNOLOGICAL ASPECTS OF SURFACE-ENGINEERED INTERPHASE-INTERFACE SYSTEMS FOR ADHESION ENHANCEMENT

Part I of this paper reviewed the theoretical principles of the macromolecular design of polymer interface/interphase systems for obtaining maximum adhesion and fracture performance of adhesively bonded assemblies. In Part II a novel, relatively simple and industry-feasible technology for surface-grafting connector molecules is demonstrated and discussed in detail and supported by a range of experimental examples. It is shown, in agreement with contemporary theory, that the use of chemically attached graft chemicals of controlled spatial geometry and chemical functionality enables a significant increase in the strength and fracture energy of the interphase, to the point of cohesive fracture of the substrate, or that of an adjacent medium such as adhesive, elastomer, or other material. This occurs even after prolonged exposure of investigated systems to adverse environments such as hot water.     

INTERFACE/INTERPHASE ENGINEERING OF POLYMERS FOR ADHESION ENHANCEMENT: PART I. REVIEW OF MICROMECHANICAL ASPECTS OF POLYMER INTERFACE REINFORCEMENT THROUGH SURFACE GRAFTED MOLECULAR BRUSHES

This article reviews the theoretical principles of macromolecular design of interfaces between glassy polymers as well as those between rigid substrates and elastomers for maximizing adhesion and fracture performance of bonded assemblies. According to contemporary theories, macromolecular "connector molecules" grafted onto solid polymer surfaces effectively improve adhesion and fracture performance of interfaces between polymers by improving the interactions with adjacent materials through one or both of the following mechanisms: (1) interpenetration into adjacent polymeric phase, and (2) chemical reaction/crosslinking with the adjacent material.It is shown that the effectiveness of the interface reinforcement by surface-grafted connector molecules depends on the following factors: surface density of grafted molecules, length of individual chains of grafted molecules, and optimum surface density in relation to the length of connector molecules. The influence of the above-mentioned physico-chemical parameters of molecular brushes on the interphase-interface reinforcement is discussed and quantified by contemporary theories. Also, the optimum conditions for maximum adhesion enhancement are specified and verified by a range of experimental examples.Part II of this article demonstrates a novel and relatively simple, industry-feasible technology for surface grafting connector molecules and engineering of interface/interphase systems, which is discussed in detail and supported by a range of experimental examples. It is shown, in agreement with contemporary theories, that the use of chemically attached graft chemicals of controlled spatial geometry and chemical functionality enables a significant increase in the strength and fracture energy of the interphase, to the point of cohesive fracture of the substrate, or that of an adjacent medium such as adhesive, elastomer, or other material. This occurs even after prolonged exposure of investigated systems to adverse environments such as hot water.