Sulphur vulcanized elastomers reinforced with aramid-polydiene copolymers

Abstract: The present invention relates to sulfur vulcanized elastomers containing aramid-polydiene copolymers. When compounded with the elastomers, the aramid-polydiene copolymers improve the reinforcing nature of the elastomers.

Description: Manufacturers of elastomers have long been aware of the benefits from mixing materials into elastomers. Compounders use carbon black and nonblack pigments for a number of purposes, most important of which is the improvement of the mechanical properties of the elastomers. Materials which are used to increase an elastomer's strength, hardness, stiffness, etc. are known as reinforcing agents. Nonblack reinforcement agents for elastomers include hydrated silica, calcium silicate, zinc oxide, the fine particle size precipitated calcium carbonates and clay. Although physical characteristics, such as particle size and surface area are important in determining the effect a reinforcing agent has in an elastomer compound, other properties are important. For example, the adhesion between the reinforcement agent and the matrix of the elastomer is important. Whereas many of the conventional reinforcing agents have been found suitable, it is believed that these reinforcing agents do not actually form a chemical bond with the matrix of the elastomer. Therefore, it is desirable to find a reinforcing agent which is not only compatible with the matrix of the elastomer but one which is believed to form a chemical bond to the matrix of the elastomer. Takayanagi et al, Journal of Applied Polymer Science, Vol. 29, 1984, pp. 2547-2559 describe incorporation of the block copolymer of poly(p-phenylene terephthalamide) and polybutadiene into ABS. Database Chemical Abstracts, Vol. 97, No. 16, 1982, Abstract No. 128917z describes graft copolymers having an aromatic polyamide as the trunk polymer and a rubber polymer as the branch polymer. Detailed Description of the Preferred Embodiment The present invention relates to a process for reinforcing a sulfur vulcanizable elastomer, a reinforced vulcanizate and a vulcanizable rubber stock such as specified in the appended claims. The present invention relates to a process of reinforcing a sulfur vulcanizable elastomer comprising admixing with a sulfur vulcanizable elastomer from 0.5 to 70 parts per hundred parts of elastomer, of a multiblock copolymer containing an aramid block and a polybutadiene block, the multiblock copolymer of the structural formula: wherein w is an integer of from 1 to 100, y is an integer of from 10 to 500; z is an integer of from 1 to 120; X is: or mixtures thereof; B is: or mixtures thereof and wherein R is selected from the group consisting of H, Cl or CH₃ and wherein the weight percent of the aramid block ranges from 10 to 50 percent and the weight percent of the polybutadiene block ranges from 50 to 90 percent of the multiblock copolymer. The present invention also relates to a reinforced vulcanizate comprising: (a) a sulfur vulcanized elastomer; and (b) from 0.5 to 70 parts per hundred parts of elastomer, of a multiblock copolymer containing an aramid block and a polybutadiene block, the multiblock copolymer of the structural formula: wherein w is an integer of from 1 to 100; y is an integer of from 10 to 500; z is an integer of from 1 to 120; X is: or mixtures thereof; B is: or mixtures thereof; and wherein R is selected from the group consisting of H, Cl or CH₃ and wherein the weight percent of the aramid block ranges from 10 to 50 percent and the weight percent of the polybutadiene block ranges from 50 to 90 percent of the multiblock copolymer. In addition, there is disclosed a vulcanizable rubber stock comprising: (a) a sulfur vulcanizable elastomer; and (b) from 0.5 to 70 parts per hundred of elastomer, of a multiblock copolymer containing an aramid block and a polybutadiene block, the multiblock copolymer of the structural formula: wherein w is an integer of from about 1 to about 100; y is an integer of from 10 to 500; z is an integer of from 1 to 120; X is: or mixtures thereof; B is: or mixtures thereof; and wherein R is selected from the group consisting of H, Cl or CH₃. With respect to the above formula for the multiblock copolymer, w is preferably an integer of from 1 to 25; y is preferably an integer of from 70 to 90; z is preferably an integer of from 4 to 100; and X is: and B is: The aramid-polydiene copolymers for use in the present invention may have a wide range of molecular weights. Generally speaking, the number average molecular weight may range from 1,000 to 1,000,000. Preferably, the number average molecular weight ranges from 10,000 to 100,000. Specific examples of these aramid-polydiene copolymers are described in Ogata et al, Macromolecules, 18, 851 (1985); Ogata et al, Polymer Journal, 17(11) 1173 (1985) and Ogata et al, Polymer Journal, 17, (8), 935 (1985). The aramid-polydiene copolymers for use in the present invention are prepared by the direct polycondensation of liquid α,ω-polybutadienedicarboxylic acid and an amine-terminated aramid oligomer. The α,ω-polybutadienedicarboxylic acid (LPB-diacid) that is commercially available from The B. F. Goodrich Company under the designation Hycar CPB may be used to prepare the multiblock copolymers. These LPB-diacids generally have a number average molecular weight ranging from 4800 to 5200. The amine-terminated aramid oligomer is derived from the polycondensation reaction between (a) an aromatic dicarboxylic acid, and (b) an aromatic diamine. The aromatic dicarboxylic acids that may be used include those conventionally used to form polyamides such as those disclosed in Encyclopedia of Polymer Science and Engineering, Vol. 11, pp. 381-409, (1988) J. Wiley & Sons Inc. Specific examples of aromatic dicarboxylic acids include: or mixtures thereof wherein R is H, Cl or CH₃. The preferred aromatic dicarboxylic acid or chloride thereof is terephthalic acid and terephthaloyl chloride. Specific examples of aromatic diamines which may be used to prepare the amine terminated oligomer include: or mixtures thereof and wherein R is H, Cl or CH₃. Of the above, preferably the aromatic diamine is 3,4'-oxydianiline, 4,4'-oxydianiline, 1,4-p-phenylenediamine, 1,3-o-phenylenediamine or mixtures thereof. The amine-terminated aramid oligomer may be prepared by the polycondensation reaction between an aromatic dicarboxylic acid or chloride thereof and a stoichiometric excess of the aromatic amine in the presence of a condensing agent. So long as there is a molar excess, the molar ratio of the aromatic amine to the aromatic dicarboxylic acid or chloride thereof may vary. Generally speaking, the molar ratio of the aromatic amine to aromatic dicarboxylic acid ranges from 1.01 to 1.75 with a range of from 1.01 to 1.05 being preferred. The number average molecular weight of the amine-terminated oligomer may vary depending on the molar ratio of the reactants, duration of the reaction and the like. Generally speaking, the number average molecular weight of the amine-terminated oligomers range from 900 to 5100. One advantage of the present invention is that one can vary the properties of the reinforced sulfur vulcanizable or vulcanized elastomer by controlling the relative weight percentages of the aramid blocks and the polybutadiene blocks in the multiblock copolymer. If the weight percent of the aramid block is above 50 weight percent, the amount of reinforcement decreases and preparation of the multiblock copolymer becomes more difficult due to formation of free aramid (non-block). On the other hand, if the weight percent of the aramid block is below 10 weight percent, there is poor vulcanizate properties since larger amounts of the multiblock copolymer are needed to introduce the same level of aramid block. Thus, the weight percent of the aramid block ranges from 10 to 50, with the polybutadiene blocks ranging from 90 to 50 weight percent of the multiblock copolymer. A particularly preferred multiblock copolymer is when the weight percent of an aramid block ranges from 20 to 30 with the polybutadiene block ranging from 80 to 70 weight percent. The term "rubber" or "elastomer" as used herein embraces both natural rubber and all its various raw and reclaimed forms as well as various synthetic unsaturated or partially unsaturated rubbers, i.e., rubber polymers of the type which may be vulcanized with sulfur. Representative of synthetic polymers are the homopolymerization products of butadiene and its homologues and derivatives, as for example, methylbutadiene, dimethylbutadiene, pentadiene and chlorinated derivatives thereof as well as copolymers such as those formed from a butadiene or its homologues or derivatives with other unsaturated organic compounds. Among the latter are olefins, for example, ethylene, propylene or isobutylene, which copolymerizes with isoprene to form polyisobutylene also known as butyl rubber; vinyl compounds, for example, vinylchloride, acrylic acid, acrylonitrile (which polymerizes with butadiene to form NBR rubber), methacrylonitrile, methacrylic acid, methyl styrene and styrene, the latter compound polymerizing with butadiene to form SBR rubber, as well as vinyl esters and various unsaturated aldehydes, ketones and ethers, e.g., acrolein and vinylethyl ether. Also included are the various synthetic rubbers prepared from the homopolymerization of isoprene and the copolymerization of isoprene with other diolefins and various unsaturated organic compounds. Also, included are the synthetic rubbers such as 1,4-cis polybutadiene and 1,4-cis polyisoprene and similar synthetic rubbers which have been developed in recent years, such as EPDM. Such recently developed rubbers include those that have polymer bound functionality such as antioxidants and antiozonants. These polymer bound materials are known in the art and can have functionalities that provide antidegradative properties, synergism, and other properties. The preferred rubbers used in the present invention are natural rubber, polybutadiene, synthetic polyisoprene, styrene/butadiene copolymers, polychloroprene, terpolymers of acrylonitrile, butadiene and styrene and blends thereof. The present invention includes the use of various amounts of the aramid-polydiene copolymer. An advantage of the present invention is one can control the relative weight ratios of the aramid-polydiene copolymer and the sulfur vulcanizable elastomer to arrive at the desired physical properties, having taken into consideration the particular aramid-polydiene copolymer and the particular sulfur vulcanizable elastomer. The amount of the aramid-polydiene copolymer that may be added to the vulcanizable elastomer may vary but generally ranges from 0.5 to 70 parts per hundred parts of elastomer. Preferably, the amount of aramid-polydiene elastomer that is added to the vulcanizate ranges from 10 to 60 parts. The aramid-polydiene copolymer is mixed with the elastomer prior to sulfur vulcanization in a manner similar to that used for conventional reinforcing agents, such as carbon black. The methods include incorporating the aramid-polydiene copolymer in the nonproductive stock and mixing the stock in a Banbury. Use of the aramid-polydiene copolymer in a sulfur vulcanizable elastomer results in higher levels of reinforcement compared with the use of conventional fillers, e.g., carbon black. Therefore, the present invention is particularly suited for rubber stocks for use in hoses, belts and tires and in particular in the areas of the carcass, apex, chafer, bead as well as a wirecoat. Prior to vulcanization, it is believed that there is an improvement in green strength in the compounded rubber. In the compounded rubbers that have been vulcanized, there are improvements in tensile properties. With increasing amounts of the aramid-polydiene copolymer, one may reduce the amount of conventional reinforcements, such as carbon black. However, the reinforced elastomers compounded with the aramid-polydiene copolymers may further contain conventional amounts of a carbon black, silica, zinc oxide, tackifiers, methylene donors and acceptors, peptizing agents, oils, waxes, antioxidants, antiozonants, accelerators and retarders. The amount of each conventional additive will vary depending on the application, and desired application, i.e., carcass, chafer and the like, as known to those skilled in the art. The additives may be compounded with the reinforced elastomer in a manner known to those skilled in the art. Vulcanization of the reinforced elastomers containing the aramid-polydiene copolymer may be conducted at conventional, temperatures used for vulcanizable materials. For example, temperatures may range from 100°C to 200°C. Preferably, the vulcanization is conducted at temperatures ranging from 110°C to 180°C. Any of the usual vulcanization processes may be used such as heating in a press or mold, heating with superheated steam or hot air or in a salt bath. The vulcanization of the vulcanizable elastomer/aramid-polydiene copolymer mixtures is conducted in the presence of a sulfur vulcanizing agent. Examples of suitable sulfur vulcanizing agents include elemental sulfur (free sulfur) or sulfur donating vulcanizing agents, for example, an amine disulfide, polymeric polysulfide or sulfur olefin adducts. Preferably, the sulfur vulcanizing agent is elemental sulfur. Conventional amounts of the sulfur vulcanizing agents may be used in a manner known to those skilled in the art. The following examples are presented in order to illustrate but not limit the present invention. Example 1 Preparation of Aramid-Polydiene Copolymer Having 75 Percent by Weight Polybutadiene Units and 25 Percent by Weight Aramid Units In a 2 liter three-neck round bottom reaction flask was placed 4.55 grams of 1,4-p-phenylenediamine, 4.62 grams of terephthalic acid, 2.31 grams of lithium chloride, 7.07 grams of calcium chloride, 200 milliliters of pyridine and 280 milliliters of N-methyl pyrrolidone. In another flask, 29.4 grams of Hycar CTB (4200 molecular weight) was dissolved in 500 milliliters of pyridine and then added to the reaction flask. The reaction flask was purged with nitrogen and 43.4 grams of triphenyl phosphite was added. The reaction mixture was heated with stirring at 95-100°C for 16 hours. The mixture was then cooled to room temperature and poured slowly into 2 liters of methanol containing 0.5% by weight of a phenolic antioxidant. The methanol slurry was stirred for 1-2 hours after which the product was collected by filtration and washed with methanol. A yield of 36.9 grams of vacuum dried aramid-polydiene copolymer was isolated. Example 2 Preparation of Aramid-Polydiene Copolymer Having 33 Percent by Weight Polybutadiene Units and 67 Percent by Weight Aramid Units In a 2 liter three-neck round bottom reaction flask was placed 8.4 grams of Hycar CTB in 300 ml of pyridine. To this mixture was added 9.84 grams of terephthalic acid, 6.84 grams of p-phenylene diamine, 2.64 grams of LiCl, 8.08 grams of calcium chloride and 160 milliliters of N-methylpyrrolidone. The mixture was stirred and then 49.6 grams of triphenylphosphite and 100 milliliters of pyridine were added. The mixture was stirred for approximately 20 hours at a temperature of 100°C. The mixture was cooled and filtered. The solid product was combined with 1.5 liters of methanol containing 5 percent by weight of a phenolic antioxidant. The methanol slurry was stirred for 1-2 hours after which the product was collected by filtration and washed with methanol. A yield of 24.2 grams of vacuum dried aramid-polydiene copolymer was isolated. Example 3 Preparation of Aramid-Polydiene Copolymer Having 25 Percent by Weight Polybutadiene Units and 75 Percent by Weight Aramid Units The process of Example 2 was repeated except 5.25 grams of Hycar CTB was used. Example 4 Preparation of Aramid-Polydiene Copolymer Having 16 Percent by Weight Polybutadiene Units and 75 Percent by Weight Aramid Units The process of Example 2 was repeated except 3.00 grams of Hycar CTB was used. Example 5 Preparation of Polymer Having 100 Percent by Weight Aramid Units In a 250 milliliter flask were placed 1.71 grams of p-phenylenediamine, 2.46 grams terephthalic acid, 12.4 grams of triphenylphosphite, 0.66 grams of LiCl, 2.02 grams of calcium chloride, 100 milliliters of pyridine and 40 milliliters of N-methyl pyrrolidone. The mixture was stirred at 95°C for 20 hours after which the mixture was cooled and filtered. The solid product was slurried in methanol, filtered and vacuum dried to yield 3.6 grams of product. Example 6 Rubber stocks were prepared and contained medium vinyl polybutadiene, carbon black and either 100% aramid (prepared in accordance with Example 5), 16/84 PBD/aramid (Example 4), 33/67 PBD/aramid (Example 2) or 75/25 PBD/aramid (Example 3). The rubber stocks also contained conventional amounts of stearic acid, wax, antiozonant, oil, sulfur, antioxidant, zinc oxide, primary accelerator and secondary accelerator. The rubber stocks were prepared in a Brabender mixer using two separate stages of addition. The sulfur and accelerator were added to the compounds during the second stage of mixing. The aramid polymer, 75/25 PBD/aramid copolymer, 33/67 PBD/aramid copolymer, or 16/84 PBD/aramid copolymer were added to the Banbury during the first stage of mixing. Table I sets out the amounts by weight of the rubber, carbon black, and aramid or aramid-polydiene copolymer for each example. In addition, Table II lists the cure behavior and vulcanizate properties of the various rubber stocks. As can be seen from Table I, addition of free aramid (Sample 1 and 8) does result in a small increase in modulus, as expected from the addition of a filler to the compound. However, introduction of the same amount of aramid via the aramid-polybutadiene block copolymer (Samples 2-3 and 9-10) produces a significant increase in reinforcement as shown by the stress at 100% elongation (3.6 MPa vs. 2.0 MPa for the "free" aramid and 1.3 MPa for the control). It can also be seen that increasing the amount of polybutadiene in the block copolymer leads to a further increase in the reinforcement as shown by the stress at 100% elongation for the 75% polybutadiene analog (6.7 MPa for Sample 4 vs. 3.6 MPa for 33% for Sample 3 or 16% polybutadiene in Sample 2). As can be appreciated, the additional polybutadiene in the block copolymer makes incorporation easier and produces different reinforcement values. The data also indicates that with increasing levels of aramid from the block copolymer, there is an increase in the degree of reinforcement and that all increases in reinforcement values are accompanied by a drop in ultimate tensile/elongation. The data also illustrates that using aramid-polybutadiene block copolymers to replace carbon black, at these low levels, results in a modest increase in reinforcement with no change in hysteresis (tan delta values) and the higher polybutadiene content analog produced a slightly higher reinforcement in this part for part exchange. Example 7 Rubber stocks containing various amounts of natural rubber and 100% aramid or a 75/25 by weight polybutadiene/aramid copolymer were prepared in a Brabender mixer using two separate stages of addition. The compounded rubber contained conventional amounts of carbon black, silica, tackifier, methylene donor, peptizing agent, oil, antioxidant, antiozonant, sulfur, accelerator and retarder. The sulfur and accelerator were added to the stocks during the second stage of mixing. The 100% aramid or 75/25 PBD/aramid copolymer were added to the Brabender mixer during the first stage of mixing. After the rubber stocks were mixed, tensile sheets (1/10" thick) were milled and cured from the stocks. The tensile sheets were used to run Instron tensiles. Those samples designated as "a", i.e, 1a, 2a, 3a indicate that the sample was taken perpendicular to the mill direction. Those samples designated as "w", i.e, 1w, 2w, 3w indicate that the sample was taken with the mill direction. Table II sets out relative amounts of the natural rubber, 100% aramid or 75/25 polybutadiene/aramid for each sample. In addition Table II lists the cure behavior and vulcanizate properties of the various rubber stocks. As can be seen from Table II, free aramid shows a modest increase in reinforcement properties whereas bound aramid-polydiene copolymer shows a large increase in reinforcement properties.

Claims: A process for reinforcing a sulfur vulcanizable elastomer comprising admixing a sulfur vulcanizable elastomer with from 0.5 to 70 parts per hundred parts of elastomer, of a multiblock copolymer containing an aramid block and a polybutadiene block, the multiblock copolymer of the structural formula: wherein w is an integer of from 1 to 100; y is an integer of from 10 to 500; z is an integer of from 1 to 120; X is: or mixtures thereof; B is: or mixtures thereof; and wherein R is selected from the group consisting of H, Cl or CH₃ and wherein the weight percent of the aramid block ranges from 10 to 50 percent and the weight percent of the polybutadiene block ranges from 50 to 90 percent of the multiblock copolymer. The process of claim 1 wherein from 10 to 60 parts of said copolymer is used. The process of claim 1 wherein w is an integer of from 1 to 25; y is an integer of from 70 to 90; z is an integer of from 4 to 100. The process of claim 1 wherein X is: or mixtures thereof. The process of claim 1 where B is: The process of claim 1 wherein said multiblock copolymer is of the structural formula: The process of claim 1 wherein said sulfur vulcanizable elastomer is natural rubber, synthetic rubber and blends thereof. The process of claim 7 wherein said elastomer is synthetic and is selected from the group consisting of polybutadiene, polyisoprene, styrene/butadiene copolymers, EPDM, polychloroprene, terpolymers of acrylonitrile butadiene and styrene and blends thereof. A reinforced vulcanizate characterized by: (a) a sulfur vulcanized elastomer; and (b) from 0.5 to 70 parts per hundred of elastomer, of a multiblock copolymer containing an aramid block and a polybutadiene block, the multiblock copolymer of the structural formula: wherein w is an integer of from 1 to 100; y is an integer of from 10 to 500; z is an integer of from 1 to 120; X is: or mixtures thereof; B is: or mixtures thereof; and wherein R is selected from the group consisting of H, Cl or CH₃ and wherein the weight percent of the aramid block ranges from 10 to 50 percent and the weight percent of the polybutadiene block ranges from 50 to 90 percent of the multiblock copolymer. The vulcanizate of claim 9 characterized in that from 10 to 60 parts of said copolymer is used. The vulcanizate of claim 8 characterized in that w is an integer of from 1 to 25; y is an integer of from 70 to 90; and z is an integer of from 4 to 100. The vulcanizate of claim 9 characterized in that X is: or mixtures thereof. The vulcanizate of claim 12 characterized in that B is: The vulcanizate of claim 9 characterized in that said multiblock copolymer is of the structural formula: The vulcanizate of claim 9 characterized in that said elastomer is natural rubber, synthetic rubber or mixture thereof. The vulcanizate of claim 15 characterized in that said elastomer is synthetic and is selected from the group consisting of polybutadiene, polyisoprene, styrene/butadiene copolymers, EPDM, polychloroprene, terpolymers of acrylonitrile butadiene and styrene and blends thereof. A vulcanizable rubber stock characterized by: (a) a sulfur vulcanizable elastomer; and (b) from 0.5 to 70 parts per hundred of elastomer, of a multiblock copolymer containing an aramid block and a polybutadiene block, the multiblock copolymer of the structural formula: wherein w is an integer of from 1 to 100; y is an integer of from 10 to 500; z is an integer of from 1 to 120; X is: or mixtures thereof; B is: or mixtures thereof; and wherein R is selected from the group consisting of H, Cl or CH₃ and wherein the weight percent of the aramid block ranges from 10 to 50 percent and the weight percent of the polybutadiene block ranges from 50 to 90 percent of the multiblock copolymer. The vulcanizable rubber stock of claim 17 characterized in that from 10 to 60 parts of said copolymer is used. The vulcanizable rubber stock of claim 17 characterized in that w is an integer of from 1 to 25; y is an integer of from 70 to 90; and z is an integer of from 4 to 100. The vulcanizable rubber stock of claim 17 characterized in that X is: or mixtures thereof. The vulcanizable rubber stock of claim 17 characterized in that B is: The vulcanizable rubber stock of claim 17 characterized in that said multiblock copolymer is of the structural formula: The vulcanizable rubber stock of claim 17 characterized in that said elastomer is natural rubber, synthetic rubber or mixture thereof. The vulcanizable rubber stock of claim 23 characterized in that said elastomer is synthetic and is selected from the group consisting of polybutadiene, polyisoprene, styrene/butadiene copolymers, EPDM, terpolymers of acrylonitrile butadiene and styrene and blends thereof.

Inventors: BAUER RICHARD GEORGE, BURLETT DONALD JAMES, BAUER, RICHARD GEORGE, BURLETT, DONALD JAMES
Applicants: GOODYEAR TIRE & RUBBER, THE GOODYEAR TIRE & RUBBER COMPANY
Application year: 1990
Main classification: C08L21
IPC codes: C08L21, C08G69, C08L51