Cut Growth Resistance Research Articles

Influence of oligomeric resins on natural rubber-carbon black-silica composites for tire tread application

The investigation aims to understand the impact of different resins on properties of natural rubber (NR) based tire tread composites, providing valuable insights for the optimization of tire performance. In current research six different types of resins, namely rosin modified dicyclopentadiene(DCPD), gum rosin, C5 aliphatic resin, alpha methyl styrene (AMS) resin, koresin and terpene phenol resin, were selected for assessing structural influence of resins on cure characteristics, reinforcement, abrasion resistance, cut-tear resistance, heat-build-up, viscoelastic properties of carbon black-silica loaded NR composites. During mixing of rubber composites, condensation reaction between hydroxyl groups of silica with phenolic groups of koresin and terpene phenol resin, leading to elimination of water molecules was confirmed by Fourier transform infrared spectroscopy. The addition of resins led to a reduction in crosslink density, maximum torque and delta torque. The compounds with gum rosin and rosin modified DCPD showed lower crosslink densities translating into lower tensile strength, lower stress at 100%, 200%, 300% strain, and higher elongation at break among the resins. Rosin modified DCPD based composite exhibited the highest cut growth resistance and tear strength. Rolling resistance indicator (tanδ@70 °C) of resin-based composites followed the order: gum rosin > rosin modified DCPD > koresin > C5 resin > terpene phenol resin > AMS resin. The snow traction (tanδ@-15 °C), the order was: AMS = C5 > gum rosin > terpene phenol = koresin > rosin modified DCPD. The dynamic stiffness (É) of the gum rosin-based compound was significantly increased at low strain (0.1%) and low temperatures (-80–20 °C) compared to other resins. Furthermore, atomic force microscopy was employed to analyze surface topography and roughness of the resin-based NR composites, providing valuable insights into interfacial characteristics.

Effect of pre‐mastication on dispersion of nanoclay in presence of carbon black in an inner liner compound: Studies on physicomechanical and functional properties

AbstractThe present study demonstrates the use of “pre‐mastication” technique for getting higher dispersion of organoclay, Cloisite 15A, in an inner liner compound based on 70:30 bromobutyl and natural rubber blend, in presence of higher concentration of carbon black (60 phr) for the improvement of functional properties like fatigue cut growth and air permeability resistance. Studies have showed that the organoclay was almost equally distributed within the blend both in absence as well as in presence of carbon black. The vulcanization curve showed a marked increase in cure acceleration as well as a significant rise in the maximum torque value because of higher crosslinking aided by the participation of the quaternary amine present in Cloisite 15A; however, in the carbon black loaded compound, the cure acceleration was not so pronounced because of engaging interaction between amine and functional groups of carbon black. The microscopic study revealed a good dispersion of Cloisite 15A within the elastomer blend‐ in presence of carbon black. The anisotropic platelets of Cloisite 15A and carbon black particles jointly formed “nano units”, which occluded a portion of elastomer segments vis‐a‐vis partial intercalation within the clay gallery. Such a reinforcing model was instrumental in improving the physicomechanical and functional properties under static and dynamic conditions. The organoclay displayed a much‐improved properties at 2 and 4 phr doses in presence of 60 phr carbon black because of formation of enough “nano units” while deterioration was observed at 6 phr dose due to clay aggregation. Based on the results obtained on functional properties it was concluded that the 4 phr of organoclay compounded in “pre‐mastication” mode delivered the best improvement and thus it was recommended for future up‐scaling study.

Admicellar polymerization modified silica via a continuous stirred-tank reactor system: Comparative properties of rubber compounding

Abstract Fillers such as silica are often added to rubber to improve performance in commercial applications. The use of silica in rubber compounds improves important compound properties such as tensile strength and cut growth resistance. A difficulty with using silica as a filler is the high energy of mixing due to both poor rubber–filler and strong filler–filler interactions. Improved compatibility between the silica and rubber can be achieved using admicellar polymerization to modify the silica surface. Previously, this process had been performed only in batch reactors, which are usually not appropriate for industrial applications, especially for providing a consistent product. In this work, a continuous stirred-tank reactor (CSTR) for admicellar polymerization was developed. The feed was comprised of precipitated silica, cetyltrimethylammonium bromide (CTAB) cationic surfactant, styrene and isoprene comonomers, and 2,2′-azobisisobutyronitrile initiator. The results showed that the modified silica reduced T90 cure times and improved modulus, abrasion resistance, and compression set. The optimum conditions for surface modification of silica by the admicellar polymerization process were 5 g comonomer loading per kg silica and a 30-min reaction time. In comparison with the modified silica using a batch process, the modified silica obtained from the CSTR process was found to be superior in the performance of rubber compound.

Effect of Carbon Black Concentration on Cut Growth in NR Vulcanizates

Abstract Dumbbell specimens containing edge razor-cuts of various depths, c, have been prepared from sulfur-vulcanized natural rubber compositions containing 0–75 phr of N115 black. Normal tensile strengths (c=0) of the gum and all black-filled samples are similar. However, cut growth resistance (CGR) relative to the gum, depends strongly on black content and cut depth. With about 6–15 phr of black, filled specimens are weaker than the gum and fracture occurs by simple forward growth of the original cut tip, i.e., a single crack develops and propagates laterally. At about 18 phr of black, filled specimens become stronger than the gum and cracking becomes complex. Prior to catastrophic rupture, crack splitting occurs near the original cut tip - forming at least two slowly-growing, longitudinal cracks. These reduce the stress concentration caused by the cut, thereby delaying rupture, and marking the onset of “reinforcement”. All pre-cut specimens containing 18–75 phr of black are stronger than the gum and they exhibit crack splitting. Specimens containing 50 phr of black have the highest strength - being about ten times as strong as the gum when cuts are large. The decrease in CGR at low levels of black and increase at high levels is attributed to competing effects upon the addition of carbon black to NR.

Use of Nonblack Fillers in Tire Compounds

Abstract A variety of nonblack fillers are used in the rubber components of tires. Calcium carbonate, clay, precipitated silica, talc and titanium dioxide are used in white sidewall compounds to impart desired physical properties and appearance. Precipitated silica can be used in black sidewall compounds, including nonstaining EPDM black sidewalls, to significantly improve tear strength, cut-growth resistance and resistance to ozone aging. Precipitated silica is used extensively in wire coat compounds in conjunction with resorcinol and methylene donating resins, and can be used with organocobalt salts to improve adhesive properties, tear strength and cut-growth resistance. Calcium carbonate, clay, mica and talc are found in innerliner compounds, and precipitated silica can be used. Precipitated silica is used in the treads of off-the-road tires such as earthmover tires, in order to improve tear strength and cut-growth resistance. Clay and talc can be used in tire treads. Precipitated silica is also used in the treads of tires of vehicles used for highway driving, such as passenger cars and trucks, in order to reduce the rolling resistance and increase the wet traction of the tire. It is necessary to modify the surface of precipitated silica with a bifunctional organosilane coupling agent in order to maintain tire treadwear for highway vehicles. Figures 16 and 17 are pictorial summaries of the use of nonblack fillers and the benefits of using precipitated silica in the various components of tire compounds, respectively.

Polar copolymer-surface-modified precipitated silica

To improve the performance of rubber compounds using precipitated silica as a reinforcing filler, the silica surface was directly modified by (1) adsorption of a surfactant onto the surface, (2) adsolubilization of an organic monomer, (3) in situ polymerization of the monomer in the surfactant bilayer, and (4) partial surfactant removal. Silica was thus modified using copolymers of isoprene or 1,3-butadiene with vinyl acetate, acrylonitrile, 4-methoxystyrene, 4-chlorostyrene, and methyl methacrylate on the silica surface. 4-Methoxystyrene/butadiene modification afforded the most promising candidate based on evaluation in a silica-filled, natural/styrene-butadiene rubber shoe sole compound that also has been used as a model tire compound. Physical testing showed that cure times were decreased, and break strength, tear energy, elongation to break, and cut growth resistance were increased. Thus, surface modification of silica by the in situ polymerization of organic monomers has been shown to be a flexible process capable of producing unique materials useful in improving rubber cure properties and the cured compound physical properties. © 1996 John Wiley & Sons, Inc.

Organic polymer‐surface modified precipitated silica

AbstractTo improve the performance of rubber compounds using precipitated silica as a reinforcing filler, the silica surface was directly modified by (1) adsorption of a surfactant, (2) adsolubilization of an organic monomer, (3) in situ polymerization of the monomer in the surfactant bilayer, and (4) partial surfactant removal. Silica was thus surface modified with polymerized styrene, isoprene, butadiene, and copolymers. Styrene–butadiene modification afforded the most promising candidate based on evaluation in a silica‐filled model tire compound. Compound physical testing showed that cure times were decreased, and break strength, tear energy, elongation to break, and cut growth resistance were increased. Thus, surface modification of silica by the in situ polymerization of organic monomers affords unique materials useful in improving rubber cure properties and cured compound physical properties. © 1995 John Wiley & Sons, Inc.

Silica Properties/Rubber Performance Correlation. Carbon Black-Filled Rubber Compounds

Abstract The effectiveness of predicting rubber performance based on measured silica physical properties in silica- and carbon black-filled compounds is presented for three rubber formulations: an off-the-road tire tread, a wire coat stock and a V-belt. Correlation and regression analyses were performed using SAS software for sixteen physical properties of thirteen precipitated silicas, and sixteen rubber compound performance characteristics of the three compounds. Silica physical properties studied include various measurements of surface area and structure, particle size, pH and impurities. Rubber performance characteristics studied include cure properties and physical properties such as stress/strain, tear strength, cut growth resistance, abrasion resistance and heat build-up. The present study confirms that silica surface area is the single best predictor of the effect that varying silica physical properties have on the physical performance of cured, carbon black-filled rubber compounds containing precipitated silica. Silica structure, as measured by DBP absorption and nitrogen or mercury pore volume, is a secondary predictor of certain rubber physical properties. The confidence limits of the predictions is dependent upon the concentration of precipitated silica used in the carbon black-filled rubber compound.

Fatigue Cut Growth of Thermoplastic Polyurethanes

A fatigue cut growth evaluation for thermoplastic polyurethanes is pre sented. The results from an experimental design study that included four different polyol types, the effect of the molecular weight of the polyol and three different urethane contents are discussed. The polycarbonate polyol showed the lowest fatigue cut growth resistance. The molecular weight of the TPUs is of key importance for dynamic fatigue applications. The crack length as a function of the number of cycles and the cut growth rate as a function of the tearing energy for selected TPUs are also shown.

Carbon Black Distribution in NR/Polybutadiene Blends

Abstract The distribution of carbon black between the phases of a NR/cis-1,4-polybutatdiene (BR) blend was studied. An N550 carbon black was added to the blend using different mixing techniques. The carbon-black distribution was determined using a variety of analytical techniques. The crystallization temperature of the BR was measured by differential scanning calorimetry. This temperature is related to the carbon-black level in the BR phase. Samples were dissolved in toluene to separate the bound and soluble rubber portions and the fractions were analysed for polymer type and amount by solid stale 13C MAS nuclear magnetic resonance. Results indicated that the N550 black has no preference for either the NH or the BR. In phase mixed samples, the majority of the black remains in tho polymer to which it is initially udded. When black and polymers are mixed simultaneously, the black tends to distribute itself uniformly between the polymers. Physical test results on a typical sidewall compound indicated that the location of the carbon black has a significant effect on physical properties, especially cut-growth resistance.

Anisotropy of Ultimate Properties in Vulcanizates of EPDM/High-Diene-Rubber Blends

Abstract It can be concluded from this work that the ultimate mechanical properties of NR/EPDM blends are indeed anisotropic, but that the tendency towards anisotropy (and, thus, the tendency towards weakness in certain directions, e.g., a tendency to tear with the processing-flow direction or grain) is greatly reduced when one uses the dynamic vulcanization technique. This technique improves cut-growth resistance (in the grain direction), peel strength, and interply adhesion. Also, because of the modification of the EPDM to give reactive sites (pendent succinic-anhydride groups) for vulcanization to occur by a means other than sulfur, the cure-rate incompatibility problem is greatly ameliorated. Thus, improvements in permanent set, hysteresis, and rebound are obtained by using the techniques of this report.

Effect of molecular weight distribution of poly(oxytetramethylene)glycol on cut growth resistance of polyurethane

A new method is proposed to improve the cut growth resistance of polyether-based polyurethane elastomers, i.e., polyethers used in this method are characterized by a double-humped distribution of molecular weight (DHDM), prepared by blending low-molecular-weight components and high-molecular-weight ones. The measurements of stress–strain curves, viscoelastic properties, and DSC thermograms of polyurethane elastomers before and after fatigue tests indicate that the destruction of the super molecular structure because of fatigue is smaller in the elastomer by our method, while in the conventional elastomer it is greatly destructed to change into fibrous structure. Further, the broad line NMR measurements show that the molecular motion of DHDM-type elastomers is more active, which is considered to contribute to the improved cut growth resistance of the elastomers.

Effect of Heterogeneous Carbon Black Distribution on the Properties of Polymer Blends

Abstract The results of this work support earlier findings regarding the transfer of carbon black in blends of BR with SBR, NR, and CIIR. Compared to conventionally-mixed compounds, in most cases vulcanizates with a heterogeneous carbon black distribution have superior hysteresis properties, presumably due to the presence of the unloaded layer mitigating the generally observed deleterious effects of carbon black upon these properties. The effect of unloaded SBR or BR layers on stress-strain values is quite small in SBR/BR blends where the zone size of the elastomer phases is small, but significant in SBR/NR and BR/NR where the zone size of the elastomer phases is larger. Superior cut growth resistance is seen for NR/BR and SBR/BR blends containing unloaded BR. The properties of SBR/BR and NR/BR blends in which most of the black is in the BR phase suggest that they may find utility in applications where superior hysteresis properties are required; e.g., in radial-tire sidewalls. Compounds with a heterogeneous carbon black distribution may also find utility in wire and cable applications, due to their superior insulating properties.

Mechanical Properties of High Density Cellular Urethanes

The use of cellular polyurethanes either as microporous foams in shoe upper materials (poromerics) or in closed cell form as soling materials has increased rapidly during the last few years in the footwear industry. Compared with vulcanised rubbers, these materials have high strength over an extended temperature range, high set and good resistance to cut growth. The research now presented.has been concerned with determining the reasons for these mechanical properties of polyurethane as compared with compounded conventional vulcanised rubbers. The supplementary contribution to the thesis presents a review of earlier work on the strength and reinforcement of crystalline, amorphous and filled vulcanised rubbers and includes a short section on the effect of crosslinking on ultimate failure properties of natural rubber. This study has been extended by the author into the effect of chain branching in polyurethane elastomers on the failure properties. The viscoelastic properties of natural and artificial leathers are also discussed in order to demonstrate similarities between the different materials and show how a cellular polyurethane sheet has hysteresial properties similar to those of a natural material of fibrous structure. It is shown that a cubical lattice model can be applied to explain the differences between such mechanical properties as modulus, tensile and tear strength of a cellular polyurethane and the corresponding solid material of the same polymer. This model, which has previously been applied to the mechanical properties of a natural rubber latex foam, indicates that the strength of cellular polyurethanes is due to the very high strength of the solid material. An extensive investigation into the effect of time and temperature on the tensile properties of cellular and solid polyurethanes is presented in order to show that polyurethanes of the type used in poromerics have a very broad relaxation spectrum extending over 18 decades of time. Because of this response to deformation, the failure properties remain fairly constant over the temperature range from 21 – 160°c. Above 160°c, the tensile properties fall quite markedly. Stress softening in these polyurethanes is very high and can only be reversed by heating to temperatures above 160°c. The cut growth and fatigue properties of cellular and solid polyurethanes are considered. Following a brief review of the investigation on cut growth and fatigue of vulcanised rubbers involving the use of tearing energy theory, it is shown that cut growth and hysteresis properties of vulcanised .rubbers can be correlated. The lower limit of tearing energy (To) below which no cut growth takes place in the absence of chemical effects is found to be higher for polyurethanes than for vulcanised rubbers. Fatigue failure of cellular polyurethanes is found to be due to cut growth from the largest pore in the sample. These data are also compared with measurements on other two phase elastomer systems such as styrene butadiene copolymer vulcanisates with high styrene content and polystyrene-polybutadiene thermoplastic rubbers. From an extensive review of the literature on the structure of polyurethane elastomers, it is deduced that polyurethanes of the type used in poromerics consist of a segmented structure of long polyester chains connected to very minute (25A) hard urethane segments. The cohesion of the hard segments is primarily due to hydrogen bonding and other physical forces. It is concluded that the high strength, good cut growth resistance and broad relaxation spectrum of polyurethanes are due to the reinforcement given by the hard urethane segments which act as well dispersed minute filler particles in the polyester rubber matrix. The hydrogen bonding between the hard segments dissociates at approximately 170°c so giving a degree of thermoplasticity which produces a very high permanent set. An appendix discusses some of the practical applications in the footwear industry of the work presented, such as forming of poromerics, tearing from stitch-holes and flex cracking of solings

Carboxylic Rubbers. I. Synthesis and Structures

Abstract It is well known that the high strength of unfilled (pure gum) natural rubber and some synthetic rubber compounds can be explained by the homogeneity of the polymer chain which determines its ability to crystallize or to orient on stretching. The character of the vulcanization network as well as the structure of the main chain is of importance. This has been verified by the use of polyethylene polyamines and other chemical compounds as vulcanization accelerators for butadiene-styrene rubber (SKS-30A) to produce high strength (up to 200 kg/cm2) gum rubber compounds. In certain cases, only the structure of the vulcanization network obtained with carboxyl-containing rubber compounds can account for obtaining the same effects as are obtained with natural or other synthetic rubber compounds as a result of homogeneity of polymer chain. The first work done by us on carboxyl-containing (carboxylic) rubbers was done in 1954\2-1955. In this work it was shown that polymers of isoprene and of butadiene, copolymers of butadiene with styrene, butadiene with acrylonitrile, and others, which contain small quantities of methacrylic acid (1\2-2 mole %) in the chain, can be vulcanized with oxides of divalent metals to give pure gum and lightly filled compounds characterized by high strength and elasticity, good resistance to heat aging and good cut growth resistance.

Carboxylic Rubbers. II. Properties of Cured Stocks

Abstract The experimental evidence shows that the mechanical and elastic properties of the carboxylic rubber compounds far exceed those of the synthetic rubber type compounds. Important qualities of gum and lightly filled carboxylic rubber compounds are: good mechanical and elastic properties, high cut growth resistance and good resistance to heat aging. The disadvantage is the tendency of the carboxylic rubber mixtures to scorch. Carboxylic rubbers are of considerable interest for the preparation of general and special purpose rubber compounds.

Factors Affecting Laboratory Cut-Growth Resistance of Cold SBR Tread Stocks

Abstract By using an existing cut-growth test in a new way it has been possible not only to increase the reproducibility of the results, but also to show important relations between cut-growth resistance and modulus, or the elongation at break of cold SBR tread stocks. The logarithm of the cut-growth resistance of cold SBR vulcanizates as measured on a modified De Mattia machine, is shown to be a linear function of the 300 per cent modulus, except for certain undercured stocks. The slope of the curve is dependent on the type and the amount of black, but is relatively independent of the type of curing system, amount of antioxidant, and time of Geer aging. An equation has been found which relates cut-growth resistance at 150° F with the elongation at break of the vulcanizate. Except for stocks having black loadings in excess of about 55 phr and having in addition modulus values less than 800 psi, this relation appears to be nearly independent of black loading, type of black, curing system, time or temperature of cure, antioxidant concentration, and extent of Geer aging. The elongation at break of an SBR tread stock thus appears to be a primary factor governing its groove-cracking behavior. The relation between cut-growth resistance and modulus is of secondary significance and evidently depends upon the interrelation between the modulus and breaking elongation of these formulations. The breaking elongation, however, cannot be the sole factor governing the groove-cracking behavior; otherwise there would be no restrictions on the validity of the breaking elongation equation.

Chemigum SL—An Elastomeric Polyester-Urethane

Abstract A great deal of interest has been aroused in recent years in isocyanate chemistry by the announcement of new elastomers based on diisocyanate modification of polyesters. Early du Pont patent literature described diisocyanate modified alkyds, and Vulcaprene A, an elastomeric diisocyanate modified polyesteramide, has been offered to the rubber trade by Imperial Chemical Industries, Ltd., England. Several articles also have been published on Vulcollan by Bayer and associates on work done in the laboratories of Fabenfabriken Bayer Co., Leverkusen, Germany. More recently a new elastomeric polyester-urethane, Chemigum SL, was described by the Goodyear Tire and Rubber Co. These rubbers are first made in the form of processible and storable raw gums, having many of the characteristics of pale crepe natural rubber. They can then be mixed on the mill or in the Banbury with additional curatives, such as diisocyanates and other compounding agents, and cured in standard rubber molds. The cured physical properties of Chemigum SL are very similar to Vulcollan; both exhibit unusual toughness. Tensile strength is very high, as is resistance to cutting and chipping. Since the polyester-urethanes are saturated, cut-growth resistance is excellent. Even when cuts are initiated by sharp objects, there is no tendency to grow, even under stress. In this respect a vast superiority is shown over natural rubber or GR-S.

Gel as a Definitive Property in GR-S Technology

Abstract 1. Of the gel fraction that may occur in GR-S, only that portion which has low swelling volume in benzene—tight (B) gel—markedly affects processing behavior and quality of product. 2. As the proportion of tight (B) gel increases, mixing operations become more difficult, and the quality of the final vulcanizate is lowered; specifically, decreased tensile strength, increased modulus, and decreased cut-growth resistance result. Where maximum quality is desired, processing conditions which favor the formation of tight gel should be avoided. 3. Conversely, appreciable amounts of tight (B) gel aid the processing operations of calendering and extrusion by reducing shrinkage and roughness. Where ease of processing is paramount and quality defects can be tolerated, heat-plasticization cycles which favor gel formation may be used to advantage. 4. To account for the observed effects of tight gel, the theory is advanced that fillers cannot enter this gel portion. This explanation is supported by a limited amount of direct evidence. 5. Heat-plasticization studies of GR-S at 320° F in the presence and absence of carbon black indicate that the black reduces the tendency to gel formation. For short heat treatments, common to many factory processes, the effect has no significance. For extended heat plasticization, incorporation of the black first may be either advantageous or detrimental, depending on whether maximum quality or ease of processing is the end objective.

Gel as a Definitive Property in GR-S Technology

Abstract 1. Of the gel fraction that may occur in GR-S, only that portion which has low swelling volume in benzene—tight (B) gel—markedly affects processing behavior and quality of product. 2. As the proportion of tight (B) gel increases, mixing operations become more difficult, and the quality of the final vulcanizate is lowered; specifically, decreased tensile strength, increased modulus, and decreased cut-growth resistance result. Where maximum quality is desired, processing conditions which favor the formation of tight gel should be avoided. 3. Conversely, appreciable amounts of tight (B) gel aid the processing operations of calendering and extrusion by reducing shrinkage and roughness. Where ease of processing is paramount and quality defects can be tolerated, heat-plasticization cycles which favor gel formation may be used to advantage. 4. To account for the observed effects of tight gel, the theory is advanced that fillers cannot enter this gel portion. This explanation is supported by a limited am...