Adhesion of RFL-coated aramid fibres to elastomers: The role of elastomer–latex compatibility

The performance of fibre-reinforced composites is strongly dependent on the nature and the strength of the fibre–matrix interface. Good interfacial bonding is required to ensure load transfer from matrix to reinforcing fibres. For rubber-reinforced composites, resorcinol formaldehyde latex (RFL) is known as a fibre surface coating which is able to provide good adhesion between rubber and fibres. In the present study, aramid fibres are investigated, because of their significantly higher modulus and strength, compared to other commercial fibres. Their adhesion after being coated with RFL, in compounds based on natural rubber (NR) and in NR blended with a small amount of styrene butadiene rubber (SBR) is investigated. It is shown that though having very similar tensile properties, the latter compound has much better adhesion to RFL which is also less sensitive to RFL ageing, compared to the pure NR compound. It is argued that an interphase region is formed between RFL and the elastomer, which is stronger for the compound containing SBR due to its enhanced compatibility with the latex part of the RFL.     

Structure and adhesive properties of the RFL‐coated continuous basalt fiber cord/rubber interface

The relationships between the structure of the resorcinol‐formaldehyde‐latex (RFL) layer, static adhesion, and interfacial fatigue properties between the RFL‐coated continuous basalt fiber (CBF) cord and a rubber matrix were studied using films prepared from RFL systems with various formulas and H samples prepared with RFL‐coated CBF cord and NR/SBR matrix. Thermomechanical analysis and tensile testing of the RFL films were carried out using a dynamic mechanical analyzer (DMA). The H pull‐out force and fatigue properties were tested using a universal testing machine and an MTS, respectively. The interfacial fatigue life of the RFL‐coated CBF cord/rubber samples exhibited different variation regularity from the variation of the H pull‐out force as F/R and L/RF changed. The static adhesion reflected the connection strength between the cord and the rubber matrix, whereas the characteristics and the properties of the RFL layer played a decisive role in determining the damage rate of the adhesion. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44353.     

Effects of ozone and UV on tire cord adhesion

Ozone exposure of resorcinol-formaldehyde-latex (RFL) dipped tire cords reduces adhesion because ozone attacks the double bonds in the butadiene component of the rubber latex in RFL and impairs its cocuring with the solid rubber compound. This mechanism also explains: (a) the ineffectiveness of chemical antiozonants or chloroprene latex as RFL additives, (b) the increased ozone sensitivity of RFL adhesion with progressive curing of RFL dip, and (c) the insensitivity to ozone of adhesion with RF-EPDM adhesives. A major reduction in the rate of adhesion loss in either ozone (50 pphm, 50% RH) or UV (carbon arc, 4 hr) was demonstrated when small amounts of waxes (3% solids basis) were added to the RFL dip. The waxes protect the RFL adhesive by blooming to the surface of the adhesive treated cord.     

Factors influencing resorcinol–formaldehyde–latex‐coated continuous basalt fiber cord/rubber interfacial fatigue behavior: Loading direction and RFL formula

In this study, samples were prepared with resorcinol–formaldehyde–latex (RFL)‐coated continuous basalt fiber (CBF) cords and a natural rubber (NR)/styrene–butadiene rubber (SBR) matrix for interfacial fatigue tests under periodic radial loading conducted using a De Mattia Rubber Flexometer. The effects of the RFL formula on the interfacial fatigue behavior, including the fatigue life and the evolution of residual adhesion strength, were the focus of this work. The fatigue behavior was compared with that under axial loading. The results showed that under radial loading, the residual adhesion strength of the samples remained higher than that under axial loading, and the evolution of adhesion was divided into three stages. The adhesion improvement in the second stage was due to further cocrosslinking between the rubber matrix and the latex in the RFL layer, and the duration of the second stage was determined by the amount of reactive latex in the RFL layer. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46619.     

Thermo-oxidative stability of rubber magnetic composites cured with sulfur,peroxide and mixed curing systems

Rubber magnetic composites were prepared by incorporation of strontium ferrite into rubber matrices based on natural rubber (NR) and acrylonitrile butadiene rubber. The sulphur, peroxide and mixed sulphur/peroxide curing systems were applied for cross-linking of rubber compounds. The main goal of the work was to investigate the influence of the curing system composition on the physical–mechanical and magnetic properties of prepared composites. The thermo-oxidative stability of the composite materials was assessed by evaluation of thermogravimetric analysis and ageing test. The results showed that the composition of curing system influences the physical–mechanical properties of composites, but in strong dependence on the type of rubber matrix. After exposure of test sample to the conditions of thermo-oxidative ageing, the changes in composite properties were also recorded. The influence of thermo-oxidative degradation was more pronounced in the case of composites based on NR, where the sample cured only with peroxide system was almost completely degraded in the given conditions of ageing. On the other hand, the magnetic characteristics of composites seem to be influenced neither by curing system composition nor by ageing.     

Improving adhesion between polyester cord and rubber by using glycidyl-POSS

Poly(ethylene terephthalate) (PET) cords are usually coated with epoxy and/or isocyanate solutions (like methylene diphenyl diisocyanate [MDI]) before resorcinol-formaldehyde-latex (RFL) to increase the adhesion efficiency of RFL. In this article, the addition of glycidyl polyhedral oligomeric silsesquioxane (GPOSS) as an adhesion promoter to PET cord was investigated for reinforcing PET cord/rubber interfacial adhesion. Therefore, GPOSS treated PET cords (GPOSS + MDI + RFL) were prepared in different process conditions like different GPOSS ratios and oven curing times and then vulcanized with rubber. RFL, GPOSS + RFL, MDI + RFL, and commercial epoxies treated PET cord samples were also prepared for comparison with GPOSS+MDI + RFL treated PET cord. The thermal, mechanical, and morphological properties of the treated PET yarn and their composites with rubber were investigated. It was seen that in the GPOSS coated PET yarns increased the stiffness and no change was observed in the tensile strength of the PET yarns. It was determined that the utilization of GPOSS in the PET cord improved the adhesion of the cord to rubber when compared with other treated PET cords via H-adhesion and strip peel adhesion tests. Especially, since adhesion values give better results than commercially used epoxies, GPOSS as an adhesion promoter can be recommended in the rubber industry.     

Effects of Disturbing Parameters on the Stability of Latex and Resorcinol Formaldehyde Latex Based Adhesives

Synthetic cords may be coated with resorcinol formaldehyde latex (RFL)-based adhesives to adhere the cord to the rubber in industrial goods such as tires and conveyor belts. The stability of the adhesive and the stability of its component latex are crucial, both for ideal adhesion and for the homogeneity of the cord surface. Latex is a colloidal polymeric dispersion, which may lose its stability upon mechanical stress or upon interaction with some chemicals that lead to the formation of coagulated polymeric particles. This article reports on the influences of both external mechanical stresses and chemical interactions on RFL adhesives and latex stability, adhesion, and viscosity. High speed mixing, treatment with excess RF, and temperature variations were applied as disrupting parameters.     

Adhesion between poly(ethylene terephthalate) silk and chlorohydrin rubber for aerial film

The surface adhesion activation of poly(ethylene terephthalate) silk (PET silk) was accomplished through dipping in a reaction product of a water‐soluble modified epoxide resin (SJR‐2) and a precondensed resorcinol‐formaldehyde (SJR‐1), and by partial curing of the dip. Then, the adhesion activated sample was coated with a single resorcinol‐formaldehyde latex (RFL) dip prepared from SJR‐1. The effects of heat treatment conditions and formulation of impregnation solution as well as RFL prepared with water‐soluble SJR‐1 resin on the adhesion between PET silk and chlorohydrin rubber for aerial film were studied. High adhesion between PET silk and chlorohydrin rubber was obtained by using optimized RFL formulation and heat treatment condition, and the high levels of adhesion were maintained after oil impregnating test, dynamic fatigue and storage stability test. The PET silk possessed good adhesion to natural rubber (NR), chloroprene rubber (CR), hydrogenated nitrile rubber (HNBR), acrylonitrile‐butadiene and rubber (NBR), and chlorohydrin rubber (CHR). RFL filled with diffused carbon black improved the fatigue endurance and oil resistance of adhesion. The adhesion activator is nontoxic. This method of adhesion activation and RFL preparation for adhesion treatment of poly(ethylene terephthalate) silk is a practical technique with excellent technological, economical, and safety effects. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2097–2099, 2003     

A moisture absorption and adhesion study of the process of blending film using p‐alkylphenol‐resorcinol‐formaldehyde and rubber latex

p‐alkylphenol‐resorcinol‐formaldehyde‐latex (ARFL) films were prepared by co‐condensation of p‐alkylphenols and resorcinol with formaldehyde to generate modified phenolic resins, followed by blending with rubber latex, aging, and finally curing. The weight‐gain of the ARFL films and the tensile force of the coated fiberglass were studied under different temperatures and various humidities. The surfaces of the ARFL films were further analyzed by measuring the static contact angle and the findings were confirmed by Fourier Transform Infrared Spectroscopy (FTIR) and X‐ray photoelectron spectroscopy (XPS) analysis. The adhesion between the coated fiberglass and neoprene rubber was evaluated using the H‐adhesion technique. The best hydrophobicity and the largest water contact angle were displayed on the surface of the p‐nonylphenol‐resorcinol‐formaldehyde‐latex (NRFL) film, with a weight‐gain percent that was 40.0% (wt %) lower and a static contact angle that was 22.6° more than that of the resorcinol‐formaldehyde‐latex (RFL) film. The NRFL‐coated fiberglass had a higher tensile force and H‐adhesion force than the RFL‐coated fiberglass. The shelf life of NRFL‐coated fiberglass can be raised significantly at 40°C and under 98% humidity. The mechanism of the dramatic drop in the tensile force of the coated fiberglass is also discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Some plasma treatment of PET fibres and adhesion testing to rubber

Polyethylene terephthalate fibre cords were modified with oxygen, water or hydrogen peroxide cold plasmas or coated with acrylic acid, butadiene and hydrogen sulfide cold plasmas. Treated surfaces were studied in terms of their surface energies by contact angle measurement and morphology by scanning electron microscopy. Plasma treated cords were coated with a resorcinol-formaldehyde latex and tested as rubber reinforcing materials. Oxygen plasma treatment leads to the greatest increase in adhesion but hydrogen sulfide also yielded promising results.     

Studies on rubber‐to‐nylon tire cord bonding

Nylon tire cord (1680/2) was dipped in different adhesives based on resorcinol formaldehyde resin and latex (RFL) and was bonded to natural rubber‐based compounds. The resin‐rubber ratio in the RFL adhesive was optimized. The variation of pull‐through load was studied by varying the drying and curing temperature of the dipped nylon tire cord. RFL adhesive based on vinylpyridine latex was found to have better rubber‐to‐nylon tire cord bonding, compared with the one based on natural rubber latex. Addition of a formaldehyde donor into the RFL adhesive/rubber compound improves adhesion. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1197–1202, 1999     

Estimation of dynamic adhesion from static test results in the model cord–RFL–rubber system

Generally, nylon and polyester cords are used to reinforce rubber compounds. These composites are used in many sectors, such as tire and belt manufacturing. To increase adhesion performance a resorcinol–formaldehyde–latex (RFL) adhesive is applied on the cord, which bonds chemically to both cord and rubber and, thus, it improves both the thermodynamic work of adhesion and the loss function at the cord/rubber interface. Adhesion strength between the cord and rubber determines the performance of the system. So to study the performance of the cord–rubber system, adhesion strength must be evaluated. Cord–rubber adhesion strength can be evaluated in static and dynamic modes. The H-Pull (H-adhesion) test method is a static and relatively simple method that is usually employed to control raw material quality. Fatigue test is one of dynamic adhesion test methods that are used to determine the performance of cord–rubber interface. Some important factors such as cyclic stress and heat buildup are involved in this test procedure. To investigate the accuracy of the H-Pull test results, the cord–rubber samples were prepared using poly(ethylene terephthalate) (PET) cord and NR/SBR rubber. Then H-adhesion was determined at elevated temperatures. The adhesion strength was also evaluated in dynamic (fatigue) mode at different temperatures. Authors have proposed an equation to estimate dynamic adhesion from H-Pull test results.     

Effects of heat and moisture on characteristics,tensile properties of RFL‐coated rayon cords,and their adhesion with NR/SBR matrix

The objective of this study was to evaluate the effects of heat and moisture on the characteristics and tensile properties of resorcinol‐formaldehyde‐latex (RFL)‐coated rayon cords and their adhesion to the natural rubber (NR)/styrene‐butadiene rubber (SBR) matrix. The water absorption ratio, shrinking percentage, breaking force, and elongation at break of the cords, which were treated under various temperature‐humidity conditions, were tested, and an attenuated total reflection (ATR)‐Fourier transform infrared (FTIR) spectroscopy was used to investigate the chemical changes of the outer RFL layer. The static adhesion was investigated by an H pull‐out test, and the evolution of the adhesive properties of the RFL‐coated rayon cord/rubber matrix was tracked by an elastomer testing system. A scanning electron microscope (SEM) was employed to observe the interfacial fracture caused by both H pull out and fatigue. The results of this investigation show that the moisture absorption significantly affects the characteristics and the mechanical properties of rayon cords. The chemical state of the RFL layer and the static adhesion of the cord/rubber matrix were not obviously affected, but the interfacial fatigue life was extended due to the decrease of the load in the second of three fatigue stages, which was caused by a reduction in the modulus of the rayon cords. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45559.     

Curing characteristics and mechanical properties of alkali‐treated grass‐fiber‐filled natural rubber composites and effects of bonding agent

To improve adhesion between fiber and matrix, natural rubber was reinforced with a special type of alkali‐treated grass fiber (Cyperus Tegetum Rox b). The cure characteristics and mechanical properties of grass‐fiber‐filled natural rubber composites with different mesh sizes were studied with various fiber loadings. Increasing the amount of fibers resulted in the composites having reduced tensile strength but increased modulus. The better mechanical properties of the 400‐mesh grass‐fiber‐filled natural rubber composite showed that the rubber/fiber interface was improved by the addition of resorcinol formaldehyde latex (RFL) as bonding agent for this particular formulation. The optimum cure time decreased with increases in fiber loading, but there was no appreciable change in scorch time. Although the optimum cure time of vulcanizates having RFL‐treated fibers was higher than that of the other vulcanizates, it decreased with fiber loading in the presence of RFL as the bonding agent. But this value was lower than that of the rubber composite without RFL. Investigation of equilibrium swelling in a hydrocarbon solvent was also carried out. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3151–3160, 2006     

Adhesion behavior of nylon tire cord/adhesive/rubber systems

In static and dynamic adhesion tests, the behavior of nylon tire cord/resorcinol-formaldehyde–latex (RFL) adhesive/rubber systems was shown to be strongly influenced by the dipping and curing conditions, cord size, and the thickness of rubber layer adjacent to cords. The nature and extent of these effects were different in three types of adhesion tests which differed in stress concentrations they induced at the cord–rubber interface. The influence of stress concentration due to increased cord size was clearly seen in dynamic adhesion tests where the peel strengths of two-ply cord/rubber samples were measured after flexing them under tension over a pulley for predetermined periods at 230°F. In these tests, the adhesion of samples with large cords weakened more rapidly than that of small cords. The static adhesion level attained with nylons 6 and 66 and other polyamide fibers was strongly dependent on the conditions (time, temperature) under which the RFL adhesive was applied and cured. At any given exposure, adhesion initially increased rapidly with the RFL curing temperature and attained a maximum above a temperature which is characteristic of the polyamide. For nylon 66, optimum adhesion was attained with different combinations of RFL curing temperatures (390–460°F) and times (20–120 sec). Finally the adhesion of nylons 6 and 66 is discussed from thermodynamic considerations based on entropy change.     

芳纶平纹布表面预处理及其与天然橡胶的界面粘合性能

研究了自制芳纶表面改性剂A和胶粘剂类型对芳纶布/天然橡胶复合材料界面粘合性能的影响,并利用SEM分析了芳纶纤维改性前后的表面形貌和复合材料剥离界面形貌。结果表明,使用改性剂A处理的芳纶布、开姆洛克胶粘剂和天然橡胶制成的复合材料粘合强度达到了13.9kN/m,与未处理芳纶布相比提高了162%,较间苯二酚/甲醛/胶乳胶粘剂(RFL)的提高了61%;复合材料剥离界面微观形貌为橡胶撕裂和芳纶纤维劈裂共存;改性剂A对芳纶表面浸润良好,二者有一定程度的化学反应。     

Tire cord adhesion—A TEM study

Tire 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.     

Adhesion of kevlar aramid cords to rubber

Adhesion development to Kevlar aramid yarn is discussed in relation to polymer characteristics and parameters of molecular structure that determine specific or entropic interactions with adhesives. The effects of rubber compounding variables on adhesion of Kevlar tire cords treated with epoxy/RFL adhesives were determined using the single-cord pull-out and 2-ply peel adhesion tests, which differ in sensitivity to physical properties (stiffness) of the rubber compound. Kevlar adhesion was unaffected by changes in the curing system (e.g., sulfur level, type of sulfenamide accelerator) used in a high-modulus tire belt compound. Methylene donor/acceptor-type bonding agents in the compound improved the adhesion initially and after exposure of dipped cords to ozone. RFL modifications (e.g., use of preformed versus in situ RF resins) improved adhesion. Effects of rubber compounds and adhesive on adhesion are discussed in relation to their chemical and physical characteristics. Lastly, two types of adhesive systems were developed for bonding Kevlar to high-modulus nitrile and neoprene compounds used in hoses. The simple system involves curing an aqueous epoxy dip and then applying an air-drying, solvent-based cement (polyisocyanate). The other consists of curing two aqueous dips (epoxy/RFL with latex modification).     

Adhesion improvement of tire cord induced by gas plasma

The adhesion of poly(ethylene terephthalate) (PET) to rubber in tire composites was significantly improved by exposure of the PET to “low-temperature” gas plasmas. Rubber composites built using a single-dip resorcinol–formaldehyde–latex (RFL) adhesive and plasma-treated PET reinforcement were studied. The effects of treatment conditions on this adhesion improvement were examined. The improvement was insensitive to nature of the gas, exposure time, power level, and pressure within the operating limits of the plasma generator. Fiber finish on filaments being treated was detrimental to the adhesion improvement; however, an overcoating of treated filaments with finish was not detrimental. The effects of tire building operations on this adhesion improvement of treated PET were examined. The improvement was found over a wide range of adhesives, adhesive-curing conditions, rubber compositions, and bonding testing conditions.     

Mechanical properties of natural rubber/grafted cellulose fibre composites

Mechanical properties of natural rubber/allyl acrylate and allyl methacrylate grafted cellulose fibre composites are presented. Stress/strain measurements and dynamic mechanical measurements indicate that the adhesion between grafted fibres and matrix is better than that in samples containing untreated cellulose fibres. This makes it possible to vary the composite properties by varying the fibre type and/or fibre amount.