Adhesion Interphase Research Articles

ADHESION OF STEEL CORD WITH CU-ZN-FE COATING IN COBALT-FREE COMPOUND

ABSTRACT The adhesion of steel cord with Cu-Zn-Fe coating in a cobalt-free skim compound in hot and humid conditions was investigated and compared with the current adhesion system consisting of brass-coated steel cord in cobalt-containing skim compound. Standard adhesion tests showed that the adhesion retention of Cu-Zn-Fe–coated cord in a cobalt-free compound was significantly improved with respect to current adhesion system. Advanced characterization of adhesion interphases by field emission scanning electron microscopic examination of cord-compound cross sections and X-ray photoelectron spectroscopy depth profiling revealed that incorporating the Fe element into the coating significantly reduces the dezincification of the metallic coating and prevented excessive growth of adhesion interphase. This results in high adhesion retention of Cu-Zn-Fe–coated steel cord in cobalt-free compound. Furthermore, a hypothesis was proposed to explain how the Fe element decreases the dezincification of the metallic coating in hot and humid conditions. Because Cu-Zn-Fe–coated cord eliminates the need for cobalt salts in the compound, using this cord in cobalt-free compounds generates a completely cobalt-free solution to tackle adhesion degradation and health risks of the current adhesion system.

Mechanism of weak bond formation in CFRP epoxy adhesion joints

Saltwater contamination, such as human factored sweat dew and breath moisture, is studied to explain the mechanisms of weak bond formation in carbon fiber reinforced plastics (CFRP) epoxy adhesive joints. First, a mechanism of epoxy ring consumption by is proposed to explain the reduction of covalent bond density at the adhesion interphase in a function form of pH alkaline drift. Second, a double cantilever beam test (DCB test) is applied to saltwater-polluted CFRP adhesion samples to prove the formation of the contamination-triggered weak bonds. Applying the data to the function, the thickness of the contamination layer is estimated to imply that adhesive flow in the adhesion process dissipates the layer to make the weak bond formation a statistical phenomenon.

On characterizing microscopically the adhesion interphase for the adhesion between metal and rubber compound Part III. Effect of brass-plating amount for brass-plated steel cord

Three kinds of brass-plated steel cords with different brass-plating amounts from 2.62 to 5.01 g/kg were prepared and their adhesion properties to rubber compounds were studied. Adhesion properties decreased with the increase in the brass-plating amount from 2.62 to 3.88 g/kg. Furthermore as the increase of brass-plating amount over 3.88%, adhesion property increased. The strong adhesion of brass-plated steel cord with low brass-plating amount to the rubber was shown not only after curing but also after hostile aging treatments. The good adhesion stability against humidity aging of adhesion property for brass-plated steel cord with low brass-plating amount to rubber compound was discussed in terms of the formation and growth of adhesion interphase determined by AES depth profile. The good adhesion stability of brass-plated cord with low brass-plating amount can be resulted from the suppression of the excessive growth of copper sulfide and the inhibition of dezincification due to the low brass-plating amount.

On characterizing microscopically the adhesion interphase for the adhesion between metal and rubber compound Part II. Effect of copper content for brass-plated steel cord

Three brass-plated steel cords with different copper contents from 51.4 to 75.5% were prepared and their adhesion properties to rubber compound were examined. Adhesion properties improved with the decrease in the copper content. The high adhesion of brass-plated steel cord with low copper content to the rubber was obtained after cure and after hostile aging treatments. The stability against humidity aging and the cause for the high adhesion of the brass-plated steel cord with low copper content were discussed in conjunction with the formation and growth of adhesion interphase determined by Auger electron spectroscopy depth profile. The excellent adhesion stability of brass-plated cord with low copper content can be explained by the suppression of the excessive growth of copper sulfide and the inhibition of dezincification due to the low copper content.

On characterizing microscopically the adhesion interphase for the adhesion between metal and rubber compound part I. Effect of hexamethoxymethylmelamine in rubber compound

The adhesion between hexamethoxymethylmelamine (HMMM)-containing rubber compounds and brass-plated steel cords was studied to understand the role of HMMM as an adhesion promoter. No improvement in adhesion after cure was shown with loading of HMMM in the range 1.3–5.2 phr, while enhancement of adhesion retention after humidity aging was observed with loading of HMMM in the range 1.3–5.2 phr. The adhesion interphase between the brass-plated steel cord and the rubber compound subjected to humidity-aging treatment showed using Auger electron spectroscopy (AES) stabilized depth profile by HMMM incorporation as loading of HMMM, resulting in enhancement of adhesion retention.

Enhancing the Adhesion Retention by Controlling the Structure of the Adhesion Interphase between Rubber Compound and Metal. Part II. Effect of Zinc Borate

The adhesion between zinc borate-containing rubber compounds and brass-plated steel cords was studied to understand the role of zinc borate as an adhesion promoter. No improvement in adhesion after cure was shown with loading of zinc borate in the range 0.5–2 phr, while enhancement of adhesion retention after humidity aging was observed with loading of zinc borate in the range 0.5–2 phr. The adhesion interphase between the brass-plated steel cord and the rubber compound subjected to humidity aging treatment showed, using AES, a stabilized depth profile by a moderate loading of zinc borate, resulting in enhancement of adhesion retention. For the high loading of zinc borate, copper sulfide layer and zinc oxide layer grew excessively in the adhesion interphase under humidity aging.

Photoelectron spectroscopic studies of the interfacial reaction between glass and commercial adhesive

AbstractThe valence band and core‐level photoelectron spectroscopy [using X‐ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS)] were used to probe the interfacial reaction between glass and a commercial adhesive (Loctite). The interaction was investigated by comparing experimental valence band spectra with spectra calculated for various possible interaction schemes. The valence band spectrum for the interfacial region between the glass and the adhesive was obtained using difference spectra on a thin film of adhesive on glass. This film was sufficiently thin that the adhesion interphase could be directly probed. Chemical interaction occurs at the interface as evidenced by the fact that the spectrum for the interfacial region could not be represented by the addition of the spectrum of the glass alone and the adhesive alone. The XPS valence band spectrum and the UPS spectrum showed that the shallow top surface layer is very much enriched in acrylic acid, which is a minor component in the adhesive. When the Loctite adhesive was coated on glass, the C1s and O1s regions of the adhesion interface region showed evidences of new chemistry at the adhesive–glass interface. The possible reactions were evaluated by comparison of the experimental spectra with calculated ones based on different models using ab initio molecular orbital calculations. The experimental spectra are well represented by models where the acrylic acid of the surface region of the adhesive reacts with the glass, suggesting chemical interaction occurred at the adhesion interphase. Copyright © 2009 John Wiley & Sons, Ltd.

Enhancing the Adhesion Retention by Controlling the Structure of the Adhesion Interphase Between Rubber Compound and Metal. Part I. Effect of Cobalt Salt

The adhesion between cobalt salt-containing rubber compounds and brass-plated steel cords was studied to understand the role of cobalt salt as an adhesion promoter. An improvement in adhesion was shown with the low loading of cobalt salt in the range 0.5–1 phr, while a significant decline in adhesion was observed with high loading at 2 phr and a long aging time of 15 days under humidity aging. The adhesion interphase between the rubber compound and the brass-plated steel cord studied using Auger electron spectroscopy (AES) showed stable depth profile by cobalt salt incorporation at low loading, resulting in the enhancement of the adhesion retention. For the high loading of cobalt salt, adhesion interphase grew excessively, especially ZnO layer formed under humidity aging, which resulted in reduced adhesion.

Adhesion Between Rubber Compounds Containing Various Adhesion Promoters and Brass-Plated Steel Cords. Part II. Effect of Accelerator Loading in Rubber Compounds

The adhesion property between rubber compounds containing different types of adhesion promoters (resinous adhesion promoter (methylene donor/acceptor), cobalt salt and zinc borate) and loading amounts of accelerator and brass-plated steel cord was investigated to understand the effect of accelerator loading in rubber compounds on their adhesion characteristics to the brass-plated steel cords. The adhesion property of the rubber compounds to brass-plated steel cord was largely dependent on the type of adhesion promoter and the loading amount of accelerator in the rubber compounds. Among the various adhesion promoters incorporated, zinc borate showed the largest enhancement of adhesion properties after cure. For the rubber compounds containing zinc borate, pull-out force increased two times with increasing loading amount of accelerator from 0.4 to 1.6 phr. But for the rubber compounds containing either resinous adhesion promoter or cobalt salt, pull-out force decreased slightly with increasing loading amount of accelerator. For cobalt salt incorporated, interfacial failure between adhesion interphase and rubber compound after humidity aging occurs dominantly, whereas a cohesive failure occurs dominantly in the weak boundary layer closely adjacent to the adhesion interphase for both resinous adhesion promoter and zinc borate. Adhesion property was interpreted in terms of the interphases between the rubber compounds and the brass-plated steel cords studied using Auger electron spectroscopy. Suppression of dezincification was observed for a high loading of the accelerator in the rubber compounds.

Application of a nonlinear boundary condition model to adhesion interphase damage and failure

In an earlier paper [J. Sadler, B. O'Neill, and R. Maev, J. Acoust. Soc. Am. 118, 51-59 (2005)], a set of generalized boundary conditions were proposed, based on a thin layer (thickness << wavelength) model of the acoustic interface. In this paper, the model is extended to cover the more pathological nonlinearity of the adhesion interphase-that is, the critically important thin layer where bonds are formed between adhesive and substrate. First, the boundary conditions are shown to be sufficiently general to cope with all manner of interphase nonlinearity, including unilateral cases such as clapping or slipping. To maintain this generality, an analytic time domain solution is proposed based on expansion in terms of the layer thickness rather than the conventional expansion in terms of harmonics. Finally, the boundary conditions are applied to an interphase failure model based upon basic continuum damage mechanics principles. It is proposed that such a model, which can predict the evolution of the interphase damage under stressful conditions, may allow a proper prediction of the ultimate adhesion strength based on nonlinear parameters measured nondestructively with ultrasound.

Adhesion between rubber compounds and ternary-alloy-coated steel cords, Part I: effect of cobalt plating amount in ternary-alloy-coated steel cords

The adhesion between a rubber compound and ternary-alloy-coated steel cords with different cobalt plating amounts (0, 2 and 4 wt%) was investigated to understand the role of cobalt in stabilizing adhesion to the rubber compound. The adhesion property of ternary alloy coated steel cords to the rubber compound did show significant enhancement after cure for the ternary alloy coated steel cord with 2 wt% cobalt plating. Further increase of cobalt plating in ternary-alloy-coated steel cord was responsible for the poor adhesion to the rubber compound. An improvement in adhesion durability after aging in various hostile environments was shown for the ternary-alloy-coated steel cord with 2 wt% cobalt plating. The interphase between the ternary-alloy-coated steel cords and the rubber compound studied using AES showed a stable adhesion interphase by optimum cobalt plating, resulting in enhancement of adhesion retention.

Adhesion of rubber compounds to nano-copper-coated iron plates as studied by AES depth profiles

Three nano-copper-coated iron plates with different thicknesses of the copper coating from 29 to 56 nm were prepared by sputtering and their adhesion properties to rubber compounds were examined. At the optimum cure of rubber, the nano-copper-coated iron plate with thick copper coating (56 nm) showed the best adhesion to rubber compound, whereas the thin copper coating (29 nm) showed the best adhesion to rubber compound at overcure. This may be explained as follows: at optimum cure, diffusion of iron to the copper surface in the adhesion interphase is dominant, whereas copper sulfide formation in the adhesion interphase is dominant at overcure. This fact was confirmed by Auger electron spectroscopy (AES) depth profiles of adhesion interphases using Ar+ ion sputtering.

Effects of cure levels on adhesion between rubber and brass in the composites made up of rubber compound and brass-plated steel cord

The adhesion between rubber compound and brass-plated steel cord of rubber-brass composites with different cure levels was investigated in relation to the formation and growth of their adhesion interphase examined with AES spectroscopy. The optimum-cured adhesion sample showed a maximum pullout force, but the pullout forces of samples under-cured and over-cured were low. The adhesion property of under-cured adhesion samples enhanced with humidity aging due to further curing of rubber and supplementary growth of the adhesion interphase. Cure level exhibiting good adhesion was discussed based on the composition and structure of the adhesion interphase and the crosslinking density of the rubber layer attached to the interphase.

Boric acid ester as an adhesion promoter for rubber compounds to brass-plated steel cord

The adhesion between a boric acid ester (BAE) containing rubber compound and a brassplated steel cord was investigated to understand the role of BAE as an adhesion promoter. An improvement in adhesion was shown with the low loading of BAE in the range 0.5-1 phr, while significant decline of adhesion was not observed with high loading at 2 phr and a long aging time of 15 days. The interphase between the brass plated steel cord and the rubber compound studied using Auger electron spectroscopy (AES) showed a stabilized adhesion interphase by BAE incorporation, resulting in the enhancement of the adhesion retention.

Influence of Cure Conditions on the Adhesion of Rubber Compound to Brass-plated Steel Cord. Part II. Cure Time

The effect of the cure time of a rubber compound on the adhesion with brass-plated steel cord was investigated. The formation, growth and degradation of the adhesion interphase formed between the rubber compound and brass-plated steel cord was also observed as well as the formation of a weak boundary layer in the rubber near the adhesion interphase. With increase in the cure time from a fourth to four times of t 90, the pull-out force after vulcanization increased significantly up to one-half of t 90 followed by a slight increase to t 90, and then decreased slowly with further increase in cure time. This decrease in pull-out force upon prolonged vulcanization may be explained by the severe degradation of rubber compound attached to the adhesion interphase. Also, upon prolonged vulcanization, the adhesion interphase with a rich ZnS layer may act as a barrier to copper diffusion which is required to form the adhesion interphase of copper sulfide. After thermal aging of the adhesion samples, the pull-out force decreased in comparison with that of the unaged. The decrease of pull-out force after thermal aging stemmed mainly from the decline of tensile properties after thermal aging. The adhesion after humidity aging was different from that after thermal aging. Upon increasing the cure time to one-half of t 90, the pull-out force increased. But a further increase in the cure time caused a decline in pull-out force. This phenomenon can be explained by the degradation of the adhesion interphase. At longer cure time, a severe growth of copper sulfide and a large amount of dezincification were observed in the adhesion interphase. At shorter cure time, a significant growth of copper sulfide in the adhesion interphase does not occur, whereas the formation a of a ZnS layer appeared after humidity aging. With increasing cure time, the formation of a weak boundary layer in the rubber near the adhesion interphase increased, resulting in the cohesive failure of the rubber layer. The proper formation of the adhesion interphase and the good physical properties of the rubber compound at optimum cure time can lead to the high retention of adhesion.

Influence of Cure Conditions on the Adhesion of Rubber Compound to Brass-plated Steel Cord. Part I. Cure Temperature

The effect of the cure temperature of rubber compound on the adhesion with brass-plated steel cord was investigated in conjunction with the formation, growth and degradation of the adhesion interphase formed between the rubber compound and brass-plated steel cord. With increasing cure temperature from 130°C to 190°C, the pull-out force after cure decreased linearly. This decrease in adhesion force at higher temperature may be explained by the limitation of the mass transfer of vulcanizing agents into the adhesion interphase and/or rubber compound near the adhesion interphase, resulting in a deficiency of sulfur due to the fast cure of the rubber compound which significantly retards the diffusion of vulcanizing chemicals. Also, at a high temperature, an adhesion interphase with a ZnS-rich layer, which may act as a barrier to copper diffusion for the formation of the adhesion interphase of copper sulfide, was formed. After thermal aging of the adhesion samples, the pull-out force decreased in comparison with that of the unaged. The decrease of pull-out force after thermal aging stemmed mainly from the decline of the tensile properties after thermal aging. The adhesion property after humidity aging was completely different from that after thermal aging. With increase in the cure temperature to 160°C, the pull-out force increased. But further increase in the cure temperature caused a decline in pull-out force. This phenomenon can be explained by the degradation of the adhesion interphase. At lower cure temperatures, a severe growth of copper sulfide and a large extent of dezincification were observed in the adhesion interphase. At higher cure temperatures, a significant growth of copper sulfide in the adhesion interphase appeared. The proper formation of the adhesion interphase and good physical properties of the rubber compound at a moderate cure temperature can result in high retention of adhesion properties.

P-Hydroxy-benzoic acid as an adhesion promoter for rubber compounds to a brass-plated steel cord

The adhesion between a p-hydroxy-benzoic acid (POB) containing rubber compounds and a brass-plated steel cord was investigated to understand the role of POB as an adhesion promoter. The cure rate slowed down when POB was added to the rubber compound, but changes in the physical properties were not significant. An improvement in adhesion was seen with a low loading of POB in the range of 0.5-1 phr, while an adverse effect was observed only with a high loading at 4 phr and a long aging time of 15 days. The adhesion interphase between a rubber compound and a thin brass film studied using AES showed an acceleration of the copper sulfide formation by POB incorporation, resulting in an enhancement of the adhesion. However, a higher POB loading as well as a longer aging time leads to a large increase in the migration of copper into the rubber and excessive growth of the zinc oxide layer, resulting in a decreased adhesion property.

Promotion effect of a chlorotriazine derivative on the adhesion between rubber compounds and a brass-plated steel cord

The adhesion between chlorotriazine derivative (TZ)-loaded rubber compounds and a brass-plated steel cord was studied to understand how TZ acted as an adhesion promoter. With the loading of the rubber compound with TZ, the cure rate became slow, but changes in the physical properties were not significant. An improvement in adhesion was obvious at a low TZ loading ranging from 0.5 to 2.0 phr. An adverse effect was observed with high loadings up to 8 phr and aging treatments for 15 days. Since the concentration of sulfur in the interphase of the rubber compound/ brass film adhesion samples after humidity aging was high for the rubber compound with high loadings of TZ, the acceleration of sulfide formation by TZ loading was confirmed. Lack of oxygen in the interphase indicated the conversion of zinc oxide to zinc sulfide in the rubber compound containing TZ. The control of zinc oxide formation in the adhesion interphase by TZ is suggested to be the reason for the adhesion promotion by TZ.

The adhesion properties of stearic acid-loaded rubber compounds to brass-plated steel cords

The effect of stearic acid loading in rubber on the adhesion between rubber compounds and brass-plated steel cords was examined in respect to aging treatments and cure conditions. The adhesion interphase of a thin brass film/rubber compound containing stearic acid was investigated using an Auger electron spectrometer. The loading of stearic acid to rubber was not effective in the improvement of adhesion of rubber stock cured under optimum conditions, whereas it improved the adhesion property of premature cured samples by enhancing the physical property. High loading of stearic acid severely deteriorated the adhesion property, even at an unaged state due to the excessive formation of zinc sulfide. The loading of stearic acid did not affect the sensitivity of the rubber compound to humidity and thermal aging, but amplified the deterioration of adhesion when the rubber compound was subjected to salt solution aging, resulting in extremely poor adhesion. The effects of other ingredients and the aging treatment were also thoroughly examined.

Effect of ZnO contents at the surface of brass-plated steel cord on the adhesion property to rubber compound

An effect of ZnO concentration at the surface of brass-plated steel cord on the adhesion property between a rubber compound and a brass-plated steel cord was investigated. Cord composition was determined by an Auger microscope with Ar ion sputtering. Two different steel cords were prepared; one (cord A) had higher ZnO concentration at the cord surface compared to the other (cord B). Pull-out force of unaged adhesion sample of cord A was lower than that of cord B. But the adhesion durability of the humidity-aged adhesion sample of cord A was better than the latter. Rubber coverage of the pull out cord for the unaged adhesion samples of cord A was poor, indicating insufficient formation of an adhesion layer. Pull-out force of the thermal-aged adhesion samples decreased with increasing aging time and that of cord A was lower than that of cord B. The enhancement of rubber coverage during initial aging period could be explained by an additional formation of copper sulfide at the adhesion interphase and an increase of modulus of rubber compound adjacent to the adhesion layer. With further increases of aging time, adhesion interphase grew excessively and the physical property of rubber compound deteriorated significantly, such that rubber coverage of adhesion samples decreased markedly with increasing aging time.