Tread Stocks Research Articles

Synergistic enhancement of magic triangle properties of PC tread stocks modified by amine-capped trans-1,4-poly (butadiene-co-isoprene)

The development of high-performance “green tires” with synergistically improved “magic triangle” properties like lower rolling resistance, higher wet-skid resistance and higher abrasion resistance has always been a hot issue. In this work, an effective strategy for developing high-performance “green tires” with simultaneously improved “magic triangle” properties of solution-polymerized styrene-butadiene rubber (SSBR)/cis-1,4-polybutadiene rubber (BR) nanocomposites modified by amine-capped trans-1,4-poly(butadiene-co-isoprene) copolymers (F-TBIR) was proposed. A series of F-TBIR with 10–60 mol% amine-capped efficiency (CE) and 30-90 × 104 weight-average molecular weight (Mw) were synthesized by using heterogeneous TiCl4/MgCl2–Al(i-Bu)3 Ziegler-Natta catalyst with dicyclohexylamine (DCHA) as chain transfer agent (CTA). With the increase in CE of F-TBIR, the silica-filled SSBR/BR/F-TBIR compounds exhibited improved green strength, modulus at 100 % elongation and bound rubber, and their vulcanizates showed synergistically improved “magic triangle” properties like obviously reduced rolling resistance and abrasion loss, and increased wet-skid resistance. It was found that the incorporation of 10 phr F-TBIR3 with CE of 60 mol% and Mw of 32 × 104 resulted in highly expected properties of the SSBR/BR/F-TBIR3 nanocomposite. The contribution mechanism of F-TBIR3 was discussed based on the improvements of polymer network structures and filler network structures. This work is expected to provide an effective strategy to construct the desired network structures for high-performance rubber composites.

Influences of crosslinkable crystalline copolymer on the polymer network and filler dispersion of NR/ESBR/CB nanocomposites

Considering that the short service life and frequent replacement of the off-the-road tires (OTR) have raised critical environmental problems, the development of long service life OTR with low rolling resistance, high resistance to abrasion and fatigue holds great potential in resolving both environmental and resource issues. Herein, crystalline trans-1, 4-poly (butadiene-co-isoprene) (TBIR) is introduced into the traditional formula of the OTR tire tread stocks (natural rubber (NR)/emulsion polymerized styrene-butadiene rubber (ESBR)). The effects of TBIR on polymer aggregation structures, crosslinking networks, filler-rubber interactions and filler dispersion are examined and discussed in detail. It has been revealed that the TBIR-incorporated nanocomposites present reduced heat build-up and rolling resistance, outstanding abrasion and fatigue resistance. The study is expected to propose effective strategy to develop “green” OTR tire tread stocks with excellent performances like low rolling resistance and prolonged service life.

Synthesis and Characterization of trans-1,4-Poly(butadiene-co-isoprene) Rubbers (TBIR) with Different Fraction and Chain Sequence Distribution and Its Influence on the Properties of Natural Rubber/TBIR/Carbon Black Composites

Higher performance tire tread stocks with lower rolling resistance, higher abrasion, and fatigue resistance are urgent needs considering environmental protection, resource saving, and personal safe...

Rubber Nanocomposites with Nano-Scale Phase Structures and Kinetically Inhibited Filler Flocculation for Enhanced Integrated Performances via Reactive Multiblock Copolymer Incorporation

Solution-polymerized styrene–butadiene rubber (SSBR) is commonly used as rubber tread stock for high wet-skid resistance, but SSBR suffers from shortcomings including high rolling resistance, unsatisfied abrasion resistance, and fatigue resistance, which triggers great research efforts in pursuing tread stock with balanced performances. Herein, a facile strategy was proposed through introducing novel trans-1,4-poly(butadiene-co-isoprene) rubber (TBIR) into silica-filled SSBR composites. The filler networks and rubber phase structures of SSBR/TBIR blends were investigated in detail. It was found out that TBIR was responsible for the depression of filler flocculation during annealing and vulcanization processes, which will contribute to the improvements of filler dispersion status in SSBR/TBIR vulcanizates. The covulcanization and compatibility of the two domains in SSBR/TBIR blends were also investigated. Consequently, the resultant SSBR/TBIR vulcanizates exhibit excellent integrated properties. Furthermor...

Elastomer nanocomposites with superior dynamic mechanical properties via trans-1, 4-poly (butadiene-co-isoprene) incorporation

A new strategy for high performance tire tread stocks is proposed by incorporating novel synthetic crystalline trans-1, 4-poly (butadiene-co-isoprene) rubber (TBIR) into the traditional amorphous SSBR/BR blends. The silica filled SSBR/BR/TBIR composites after chemical crosslinking exhibited significantly improved dynamical properties compared with filled SSBR/BR composites, such as 2–3 times higher tensile fatigue resistance, improved wet-skid resistance and abrasion resistance, lower rolling resistance and heat built-up, etc. Further discussions revealed that crystalline TBIR components improved silica dispersion by increasing the strength and modulus of SSBR/BR/TBIR rubber matrix, and modulated network structures of the rubber matrix in the form of TBIR lamellar fibrils, both of which were expected to contribute to the greatly improved tensile fatigue resistance and other properties. The incorporation of TBIR in tire tread stocks will provide a solution for high performance tire production without changing the present processing technology and formulations.

Modification of SSBR/BR with Trans-1,4-Polyisoprene Alloy Rubber for High Performance Passenger Car Radical Tire Tread Stock†

Modification of SSBR/BR with Trans-1,4-Polyisoprene Alloy Rubber for High Performance Passenger Car Radical Tire Tread Stock†

Nanocomposites from styrene-butadiene rubber (SBR) and multiwall carbon nanotubes (MWCNT) part 1: Morphology and rheology

Because of the exceptionally high modulus and aspect ratios of multiwall carbon nanotubes (MWCNT), there has been much interest in using them as reinforcing agents for polymer composites. However, the commercial implementation of such nanocomposites has generally met with very limited success owing to poor dispersion of the MWCNT in the polymer matrix. A strategy that overcomes many of these difficulties is described here with a view towards incorporating MWCNT with carbon black or silica for improved elastomer performance in such applications as tires. Key issues are control of the MWCNT surface functionality for proper individual tube dispersion, their aspect ratio for a balance of mechanical performance versus melt processability and an appropriate masterbatch concentration for ease of further formulation by rubber goods manufacturers. Styrene-butadiene rubber (SBR), commonly used as a tread stock for tires, is employed here as the matrix for creation of a masterbatch with oxidized MWCNT (12.3–15 wt.%). Masterbatch rheology is necessary to understand how to achieve good dispersion and conformation of the MWCNT in the final product. Rheological characterization of the masterbatch nanocomposites and their dilutions over shear rate ranges relevant for processing will be described. Scanning transmission electron microscopy (STEM) investigations have revealed that this process produces good dispersion of the MWCNT's in the SBR matrix. The distribution of diameters, contour lengths, and end-to-end distances of the MWCNT in these formulations has also been determined. Effective tube aspect ratios for the nanocomposites with various MWCNT loadings were estimated by analysis of the rheological data for uncured specimens and the dynamic mechanical properties of cured composites using the Guth–Gold–Smallwood theory. These materials do not show a high level of electrical conductivity as might be expected from a percolation concept, signifying excellent tube dispersion and formation of a bound rubber layer on the discrete MWCNT.

Temperature-magnitude superposition of the dynamic mechanical response of tire stocks

The frequency and temperature dependence of shear compliance and modulus for two tire tread stocks resembles very closely the corresponding results for a sample of carbon black in process oil (FITZGERALD, 1982); in particular, as for the carbon black in oil, superposition of compliance or modulus vs frequency curves at different temperatures is not possible by horizontal shifts along the frequency axis. Good superposition of elastic compliance or modulus curves to a common reference temperature is obtained, however, by vertical, magnitude shifts.

Elastomer Blend Properties—Influence of Carbon Black Type and Location

Abstract Criteria for minimizing hysteresis in carbon-black-filled elastomer blends are: (1) large black unit size, wide distribution, and low structure; (2) higher black loading in the discrete polymer phase (large zones); and (3) polymer of lower hysteresis as the continuous phase (low black loading). Of the different strength properties that were evaluated, tear and fatigue resistance showed the greatest dependence on black location in NR-BR and NR-SBR blends. Both properties were markedly higher for NR-BR, with most of the black in the NR phase. In NR-SBR, tear strength was higher with high loadings of black in the SBR. Fatigue life showed a reverse pattern, but the variations were not as great in this system. Criteria for maximizing tear resistance are: (1) small black unit size, low structure; (2) higher loading of carbon black in the continuous polymer phase ; and (3) the polymer of higher strength as the continuous phase. There may also be optimum levels of polymer zone size and black size distribution which affect tear strength. Optimized performance in a 50:50 NR-BR radial truck tire tread stock was obtained with a wide-distribution N-375 (50:50 N-351-N-110 blend) black with 75% location in the NR phase. This black gave 5–6°C lower heat buildup, equivalent modulus, 35% higher tear strength, and almost double the fatigue life of a conventionally mixed N-220 at essentially equivalent tread wear resistance (−4%). Optimized performance in 50:50 NR-SBR was indicated for a wide-distribution N-231 type (50:50 blend of N-351-N-119) with 75% of the black in the SBR phase. In comparison to conventionally mixed N-234 and N-220, this black gave about 8–10°C lower heat buildup, about 15% lower modulus, and essentially equal tensile, tear, and fatigue properties. Alternatively, a standard N-231 type with 75% location in the NR phase showed about 5–6°C lower heat buildup, about 20% lower modulus, equivalent tensile strength, 60% higher tear resistance, and 75–120% higher fatigue life.

Synthesis and Elastomeric Properties of Copolymers of Butadiene and 1,3-Pentadiene

Abstract Random copolymers of all trans structure have been prepared from butadiene and 1,3-pentadiene, in the presence of vanadium compounds and alkyl aluminum halides composed catalyst systems. Copolymers of butadiene and pentadiene, in the composition range of 30-45 weight per cent of pentadiene, are amorphous at room temperature at rest but crystallize upon stretching. Cured tread stocks show improved technological properties with respect to other synthetic diene-based elastomers. Very good processing and extrusion behavior, high tack, tear strength, and abrasion resistance are outstanding properties of the BP copolymers in the field of general purpose rubbers.

Rubber Stocks for Improved Performance of Polyester Cord Tires

Abstract Carcass stocks were developed with acceptable properties and good adhesion to polyester tire cords after severe heat aging in laboratory tests. These stocks contained vulcanization accelerators that did not liberate amines and were based either on synthetic poly (isoprene) (IR)/butadiene/styrene (SBR) elastomer blends, as recommended in previous work, or natural rubber/SBR compounds containing an additive to inhibit the deleterious effects of amines present as impurities in NR. Standard SBR/poly (butadiene) (BR) tread stocks containing amine-free accelerators were developed to match the exceptionally long scorch time and good physical properties attained with sulfenamide accelerators normally used in such stocks. Large batches (˜400 pounds) of amine-free tread stock were processed without any scorch problems on a commercial Banbury mixer and tread extruder. With these tread stocks, containing amine-free accelerators, it is possible to build completely amine-free polyester cord tires. In a variety of wheel tests designed to assess durability under extreme conditions, 2-ply tires with cords of Dacron polyester containing amine-free tread and carcass stocks showed highly improved durability (180-440 per cent) compared to control tires made with stocks containing amines. In a wheel test simulating the running of a tire underinflated for an extended period (low pressure endurance test), tire durability increased with decreasing amine content of the rubber stocks used. In a special high temperature tire fatigue test to produce break-above-bead failures, tires combining an experimental Dacron polyester with low carboxyl content and in amine-free stocks ran 350 per cent longer than tires of standard T-68 Dacron in amine containing stocks. These tests clearly illustrated the additive benefits of combining an improved polyester with stocks having reduced amine content.

Improvement of Tire Traction with Chlorobutyl Rubber

Abstract The skid resistance of tires can be improved with tread compounds which have high hysteresis losses. Chlorobutyl rubber is a chlorinated isobutylene-isoprene copolymer of interest in tread compounds because of its high damping (low resilience) characteristics. The traction of tread stocks containing blends of Chlorobutyl and SBR has been evaluated in laboratory and tire tests. In the laboratory, traction performance is estimated using the Portable Skid Resistance Tester as well as the classical rebound tests. Typical results are summarized. The influence of compounding parameters, namely, composition of the polymer blend and carbon black loading, on the skid properties of the tread compound is also discussed. Tire traction performance is determined with an automated vehicle designed to measure both peak and sliding skid resistance. Overall, significant improvements in traction performance have been found for radial tires with Chlorobutyl-containing tire treads; the level of improvement is directly proportional to the Chlorobutyl content of the polymer blend. Some loss in treadwear appears unavoidable, however.

Lubricated Friction of Rubber. VII. Notes on a Standard Tire and Procedure for Skid Testing

Abstract In an effort to achieve uniformity in testing and reporting skid resistance as a necessary preliminary to attempts to make improvements in roads on a rational basis, cooperative efforts have been underway over the past several years to standardize apparatus and equipment. One part of this effort has been the designation of a standard tire (ASTM E249-64T) for skid resistance testing. At the time this standard was set up important factors in skid resistance were not fully known and a composition was chosen on the basis that it was representative of actual tread stocks which have been used and had skid resistance shown by experience to be satisfactory. We have recently described evidence that the skid resistance of tires on real roads can be described absolutely in terms of properties of the tread stock which can be measured readily in the laboratory. In the course of this work we have further found evidence that the proposed standard tire is not as sensitive to variation in properties of the road as others which might be used. We have also shown that important properties of the road surface can be measured without a priori knowledge of the character of the road by the use of more than one rubber composition at the same location. Finally, we have observed that speed sensitivity of friction on road surfaces can be determined by low speed measurements. This report is therefore written to suggest that consideration be given to revision of procedures currently in view to take advantage of advances in our present state of knowledge. Since the recommendations constitute a substantial departure, they are not set forth here in specific detail, but their basis presented for consideration.

Accelerated Oxidations of Polyisoprene. IV. Effects of Sulfinic Acids on Bulk Natural Rubber

Abstract This paper shows that benzene and toluene sulfinic acids cause rapid disintegration of a cured tread stock in the presence of air at 30° C, a slower reaction in the absence of oxygen. The sulfinic acids also cause rapid solution of smoked sheet in o-dichlorobenzene at 30° C in the absence of oxygen to give mobile solutions.

Solution Masterbatching Studies

Abstract Hydrosolution masterbatching (HSMB) imparts excellent dispersion and improved pigment-to-polymer adhesion to carbon and oil masterbatches of poly-butadiene, SBR and blends of these rubbers. Tire tests show HSMB stocks to resist wear slightly better than like stocks mixed in a conventional manner. The HSMB process can be used to produce fully compounded vulcanizable tread stocks in which the stock is discharged continuously from a drying extruder. The dispersion and adhesion advantages of HSMB stocks are also noted in complete masterbatches. HSMB oil, black, and polymer masterbatches usually have higher viscosity, tensile strength, hardness, and dynamic modulus but lower resilience and reduced scorch safety, in comparison with conventionally mixed stock. Carbon black dispersion as revealed by light and electron microscope analysis is excellent. Experiments characterizing carbon gel and development of carbon black dispersion on HSMB stocks (vacuum dried), indicate the total effective molecular contact between elastomer and pigment to be increased, so that, in effect, surface area is increased.

Laboratory Testing of Tread-Stock Abrasion Resistance at Constant Transmitted Power II. A New Laboratory Abrasion Instrument

Abstract The first paper in this series described the results of laboratory measurements and road evaluation tests on a series of tread stocks over a wide range of severities, and indicated the various advantages and limitations involved in the laboratory and road measurements. It is the purpose of the present paper to describe in greater detail the abrasion instrument used in these studies. The laboratory measurement of abrasion resistance was reviewed by Buist in 1950. The paper describes 21 laboratory abraders. Developments in abrasion instruments and methods which have since appeared in the literature have been primarily concerned with modifications and refinements on these basic types. A novel type of instrument described by Newton, Grinter and Sears, uses stationary knife blades to scrape a rotating rubber disc. The research group at the Emeryville Shell Development laboratories investigating characterization of elastomeric properties some years ago decided that its requirements in laboratory abrasion testing could best be satisfied by an abrader of the Dunlop-Lambourn type because of its versatility in providing control of angular velocity, load, slip, energy transfer, and temperature. Also, in the Lambourn abrader, the motor-driven vulcanizate wheel driving a braked abrasive wheel resembles the action of a driven tire rolling on a pavement. A given section of the tire tread surface is subjected to stressing and abrasion only during the portion of the cycle when in direct contact with the abrading surface. Cooling and relaxation occur during the portion of the cycle when the section is not in contact with the surface. Viscoelastic and abrasion mechanisms can operate in the laboratory at frequency levels approximating those encountered in road tests.

An electron microscopic reinforcement criteria for carbon black masterbatches

A study was made to establish and define reinforcement criteria for the evaluation of the incorporation of carbon black in black masterbatch. Using replica electron microscopy, examination of the fractured surfaces of black masterbatches indicated that three terms were needed to correlate the quality of this black incorporation with the physical properties of the masterbatch. These are, in order of increasing effect on vulcanizate properties: dispersion, grinding, and bonding. Using these reinforcement criteria the performance characteristics of a tread stock made with such masterbatches can be predicted with good reliability.

Metal Halides in Vinylpyridine Rubber (PBR)

Abstract It has been found that PBR is made stronger by the addition of certain metal halides. A kind of cross-linking results, probably by coordination of pyridine nitrogens. This crosslinking can be used as a supplement to that produced by curing with sulfur. The result is improved physical properties in vulcanized products. Gum stocks show higher tensile strength. Filled stocks show higher tensile strength and elongation at 100° C and greater resistance to abrasion and to cut-growth. The system also has the capacity to develop high modulus. Because of this, lesser amounts of filler may be used. The result is a compound which has hysteresis properties like a carcass stock and abrasion resistance like a tread stock. This is an interesting combination of properties, which should fine useful applications.

High speed measurements of dry adhesion as related to the friction and abrasion of elastomers

AbstractStudies of friction and abrasion of elastomers have indicated that static friction or adhesion may be one of the important parameters in the traction and wear obtained with automobile tires. In this case static friction is considered to exist where a point of contact, adhesive attachment, or an interlocking is made between the rolling tire and the road which is strong enough to hold and transfer energy from one surface to the other. To investigate the magnitude of adhesion between tire tread rubber and the road, a test was developed that would measure the dry adhesion of rubber to other materials at break‐away speeds above the recovery rate of the rubber. By using clean dry surfaces and break‐away speeds of 2000 in./min., adhesive values in the order of 100 psi were measured with butyl tread stocks against impact styrene or against a rough stone surface. Much lower values were obtained for SBR and natural rubber. The influence of surface contamination, break‐away velocity, and hysteresis was also studied. The equipment used and the procedures for these tests are described in this paper.

An Electron Microscope Reinforcement Criterion for Carbon Black Masterbatches

Abstract With the advent of wet masterbatching methods, which provide a preliminary dispersion of carbon black in latex, techniques for the microscopic evaluation of the quality of this incorporation proved inadequate. Three reinforcement criteria were developed for such evaluations: dispersion, grinding, and bonding. Using these criteria the performance characteristics of a tread stock made with such masterbatches can be predicted with good reliability. The correlation of reinforcement criteria and the raw Mooney of the masterbatch reveals the striking effect of improved carbon black incorporation on this property. Using this correlation it should be possible to evaluate masterbatch production on a continuous basis.