GB2147589A - Preparing fibre-reinforcing rubbery polymers - Google Patents

Abstract

Fibre-reinforced rubbery polymers are prepared by mixing polymeric para-phenylene terephthalamide fibre with a solution of a rubbery polymer in a hydrocarbon solvent, and recovering the product by removing the solvent, in which either the fibre is subjected to fluffing prior to mixing, or the mixture is subjected to shearing agitation.

Description

SPECIFICATION Preparing fibre-reinforced rubbery polymers It is well known to reinforce rubbery polymers, and various fibres or fibrous materials have been used for such reinforcement. C.A. 90 (1 979) 40010t discloses the use of short aramid fibres as a reinforcing agent for nitrile rubber. US-A-4263184 discloses a homogeneous pre-dispersed fibre composition prepared by mixing a latex of a polymer with fibrous material, and mixing a coagulant with the resultant wetted fibre mixture. The difficulty of producing a uniform dispersion of fibres in a rubber matrix is well known, especially when the fibres are added to the rubber under conventional mixing conditions.

In the present invention, a rubbery polymer is reinforced using polymeric para-phenylene terephthalamide fibres having an average length of from 1 to 5 mm and a BET surface area of at least 1 m2/g.

According to a first aspect of the present invention, a process for preparing a fibre-reinforced rubbery polymer comprises subjecting the fibres to agitation, e.g. in a containment vessel, and thereby fluffing the fibres; mixing from 1 to 20 parts by weight (on a dry fibre basis) of the fluffed fibres with a solution of 100 parts by weight of the rubbery polymer in a hydrocarbon solvent; and removing the solvent.

According to a second aspect of the present invention, a process for preparing a fibrereinforced rubbery polymer comprises mixing from 1 to 20 parts by weight of the fibres with a solution of 100 parts by weight of the rubbery polymer in a hydrocarbon solvent; subjecting the mixture to shearing agitation; and removing the solvent.

Polymers which may be used in the present invention are the synthetic rubbery polymers which may readily be put into or are available in solution in hydrocarbon solvents. Such synthetic rubbery polymers include polybutadiene, polyisoprene, isobutylene-isoprene (butyl) polymers, bromobutyl, polymers, chlorobutyl polymers, styrene-butadiene polymers, ethylenepropylene polymers and ethylene-propylene-non-conjugated diene polymers. Such polymers are generally solid materials, usually having Mooney viscosities (ML 1 + 8 at 100 C or 1 25 C) of from 30 to 80.Suitable hydrocarbon solvents include aliphatic alkanes such as hexane, heptane and octane, aromatic hydrocarbons such as benzene, toluene and xylene, cyclic hydrocarbons such as cyclopentane and cyclohexane, and mixtures of such solvents, optionally in admixture with other hydrocarbons such as pentane, 1-butene and 2-butene. The polymer may be put into solution in the hydrocarbon solvent by the known dissolving methods or may be formed in the hydrocarbon solvent as by polymerization. When the polymer is formed in the hydrocarbon solvent as by polymerization, such as for polybutadiene, polyisoprene, ethylene-propylene polymers and ethylene-propylene-non-conjugated diene polymers, the solution may contain part or all of the other materials used in the polymerization process such as residual monomers, polymerization modifiers, residual catalyst and the like.Generally, the solution from the polymerization system will contain a polymerization stopper such as one or more alcohol.

The polymeric paraphenylene terephthalamide fibre is a known commercial product sold as Kevlar and belongs to the class of fibres known as aramids. Preferred aramid fibres are those in the form known as wet pulp, having a fibre length of from about 1 to about 5 mm, a BET surface area of greater than 1 m2/g and preferably from about 7 to about 1 2 m2/g and contain from about 40 to about 60 weight per cent of water. Examples of wet pulp have been described by Du Pont as merge 4t6F 104 and #F 205 and as having Canadian Standard Freeness, respectively, of 450 to 575 and 300 to 425. Such fibres may be used as purchased or may be dried to remove at least part of the water present. Preferably, the fibres are used as purchased.

In one embodiment of the invention, the fibres are fluffed before mixing with the polymer solution in order to largely separate the fibres from one another, said fluffing comprising subjecting the fibres to agitation, such as with an impeller, in a containment vessel. Such a containment vessel preferably is large enough to allow the fibres to be largely separable from one another. Because these aramid fibres contain numerous fine diameter fibrils attached to the main fibre and these fibrils tend to become entangled with one another, it is not possible to readily separate each fibre completely from each other fibre; however, the fluffing process does provide a degree of separation adequate for the present process.In a second embodiment of the invention, the fibres are largely separated from one another while in admixture with the polymer in solution by subjecting the mixture containing the fibres and the polymer solution to shearing agitation.

The solution of the polymer and the aramid fibres are mixed together by adding the fibres to the solution of the polymer or by adding the solution of the polymer to the fibre with agitation of the mixture in order to disperse the fibres throughout the polymer solution. Preferably, the agitation will provide adequate mixing to avoid local agglomerations of fibre throughout the polymer solution. When the fibre has been fluffed before mixing with the polymer solution such agitation is adequate to obtain the desired dispersion of the fibre. When the fibre has not been fluffed before mixing with the polymer solution it is necessary for the mixture to be subjected to shearing agitation to obtain the desired dispersion of the fibre.The presence in the polymer solution of the fibres does cause the viscosity to increase--in order to maintain the viscosity of the mixture in a reasonable range, it is preferred that the concentration of polymer in the hydrocarbon solution be not more than about 1 5 weight per cent (15 parts by weight of polymer per 100 parts by weight of polymer plus solvent) and most preferably not more than about 1 2 weight per cent.

The amount of aramid fibre that may be added is on a dry fibre basis from at least 1 to about 20 parts by weight per 100 parts by weight of polymer. Above about 20 parts of fibre, it has been found to be very difficult to produce a reasonably uniform dispersion of the fibre in the polymer. Preferably, the amount of fibre added is from about 2 to about 1 2 parts by weight per 100 parts by weight of polymer.

It is surprising that the aramid fibre can be mixed with the polymer solution by such relatively simple means. The fibre cannot be readily dispersed in the bulk polymer because of entanglement of the fibres. The fibre is not soluble in readily available hydrocarbon solvents.

The solvent can be removed from the fibre-solution mixture by conventional means such as vaporization under vacuum at slightly elevated temperature, contact with hot water and steam and subsequent drying of the water wet product and by contact of the fibre-solution mixture with a non-solvent, such as an alcohol, to precipitate the fibre reinforced polymer which may then be dried to remove residual materials.

The fibre reinforced rubbery polymers of this invention may be used in conventional applications for the polymers but especially where improved green strength and improved tear resistance are required. The fibre reinforced rubbery polymers will generally be used by compounding in the normal manner with other reinforcing agents such as the carbon blacks, plasticizers, tackifiers, stabilizers and cure active agents, the compounded polymer being vulcanized, such as by heating at elevated temperatures.

In the following examples, all parts are parts by weight unless expressed otherwise and the compound and vulcanizate tests are ASTM procedures. "Kevlar" and "Taktene" may be registered Trade Marks.

EXAMPLE 1 Samples of polybutadiene were prepared by polymerization and used as the polymer solution to which was added the aramid fibre. Polymer was prepared in three bottles using the conditions shown in Table I. After 60 minutes polymerization, the bottles were short-stopped by the addition of 5 ml of an ethanol/isopropanol mixture, antioxidant was added and the contents of each bottle were transferred to a 23 litre can containing the amount of Kevlar fibre shown in Table I. The Kevlar fibre was a Wet Pulp having an average length of about 4 mm, merge number 6F 104, Canadian Standard Freeness of 450 to 575 and BET surface area of about 10 m2/g and contained about 53 weight per cent of water. The fibre had been fluffed by putting into a high speed blender and shearing for about 1 5 minutes. The polymer solution and fibre was agitated for up to 45 minutes. Samples of the polymer solution and fibre were inspected and found to contain a uniform distribution of the fibre with few, if any, fibre agglomerates.

TABLE I Experiment A B C Polymerization Details Cyclohexane g 234 234 234 Butene-l 8 100 100 100 Butadiene g 100 100 100 Water millimoles 0.393 0.393 0.393 Cobalt octoate millimoles 0.0095 0.0095 0.0095 Di-ethyl aluminum chloride millimoles 0.981 0.981 0.981 1,5-Cyclooctadiene millimoles 3.53 3.53 3.53 Temperature OC 26 26 26 Time hrs. 1 1 1 Assumed polymer formed g 70 70 70 Fibre added 8 8 5 5.4 EXAMPLE 2 Samples of polybutadiene were dissolved in cyclohexane to form polymer solutions. The polybutadiene used was Taktene 1203, having a cis-1,4 content of about 98 per cent and a Mooney (ML 1 + 4 at 100"C) of 41, 120 g of polybutadiene was dissolved in 600 g of cyclohexane by shaking until the polymer dissolved. The fibre used was the Kevlar as described in Example 1 and was fluffed as described therein.The fibre was added to the polymer solution which was then mixed with an air-driven stirrer for about 40 minutes. During the mixing, an additional 300 g of cyclohexane was added at about 20 minutes. The reinforced polymer was recovered by removing the solvent under vacuum at a temperature of about 60"C for 24 hours.

The recovered reinforced polymer was compounded on a two-roll rubber mill with the addition of, based on polymer content, 50 parts of Industrial Reference #4 carbon black, 3 parts of zinc oxide, 2 parts of stearic acid, 1.5 parts of sulphur and 0.9 parts of N-tert-butyl-2-benzothiazole sulphenamide. The compounded stock was formed into sheets and vulcanized for 25 minutes at 160"C. Test results on the vulcanizates are provided in Table il, together with the green strength data for the compounded sheets.

TABLE II Experiment # A B C D E F Polybutadiene g 120 120 120 120 120 120 Fibre (dry) g 0 3.6 7.2 10.8 14.4 21.6 Cbl pound green strength Tensile strength (W) MPa 0.3 0.46 1.37 2.38 3.86 4.23 (A) MPa 0.26 0.29 0.57 0.57 1.04 1.19 Elongation (W) so 920 270 185 90 65 50 (A) % > 1000 630 320 310 205 165 lcsnizate properties Tensile (W) MPa 24.5 19.6 17.9 15.9 14.2 10.9 (A) MPa 20.2 20.1 17.4 14.2 12.6 10.2 100:: Modulus (W) MPa 1.9 2.1 4.3 6.6 10.0 9.1 (A) MPa 1.8 2.7 2.6 2.7 3.8 4.3 300"X, modulus (W) MPa 11.3 11.4 12.2 11.8 12.1 (A) MPa 11.4 11.5 10.4 9.5 10.6 9.7 Elongation (W) z 460 420 400 370 330 270 (A) X 420 420 410 400 350 300 Tensile set (w) 4, 5 5 6 5 13 13 (A)% 4 4 5 6 9 9 Trouser tear (W)kN/m 34 35.3 40.5 30.1 19.2 18.2 (A)kN/m 35 36.7 23.7 13.2 14 15.3 W means with the grain A means across the grain EXAMPLE 3 Samples of EPDM and butyl polymers were dissolved in cyclohexane.The EPDM contained about 60 weight per cent of bound ethylene and about 5 weight per cent of bound ethylidene norbornene and had a Mooney viscosity (ML 1 + 8 at 100"C) of about 30. The butyl polymer contained about 1.6 mole per cent of bound isprene, the balance being isobutylene, and had a Mooney viscosity (ML 1 + 12 at 125"C) of about 50. The solutions contained, based on polymer and solvent, about 14.3 weight per cent of polymer. 400 ml of cyclohexane was added to a lab blender, about one-third of the polymer solution was added and the agitation at slow speed was initiated. Kevlar fibre in the amounts shown in Table Ill was added over a period of about five minutes following which the remaining polymer solution was slowly added over a period of about thirty minutes, the agitation being at a slightly higher speed.On completing the addition of the remaining polymer solution, the agitation was increased to the highest speed for about 2 minutes and then discontinued. The contents of the blender were transferred to a dish and dried under vacuum for about 16 hours at 70"C to remove the cyclohexane.

The polymer-fibre blends were compounded in the recipes shown in Table Ill, vulcanized at 160QC and tested with the results as shown, where W means with the grain and A means against the grain and MBT is mercaptobenzothiazole and TMTD is tetramethylthiuram disulphide.

TABLE III Experiment # A B C D Wt. of butyl 8 - - - - Wt. of EPDM g 100 100 100 100 Wt. of fibre (dry) 8 0 5 10 15 Compounding recipe Polymer + fibre 100 105 110 115 Carbon black (N-330) 50 50 50 50 Paraffinic oil 10 10 10 10 Zinc oxide 5 5 5 5 Stearic acid 1 1 1 1 Sulphur 1.5 1.5 1.5 1.5 MBT 0.5 0.5 0.5 0.5 TMTD 1 1 1 1 Green strength Tensile - W MPa 0.68 2.0 3.07 3.47 - A MPa 0.68 0.93 1.0 1.14 Elongation - W Z 125 60 60 20 - A % 120 60 65 65 Vulc. time mins 13.5 12 12 13.5 Tensile - W MPa 23.5 18.6 15.4 11.3 - A MPa 18.6 15.9 13.2 11.6 100% Modulus - W MPa 4.1 7.3 10.2 - A MPa 4.1 5.0 6.1 7.0 300% Modulus - W MPa 17.3 17.5 17.1 - A MPa 17.8 - - Elongation - W Z 380 320 290 60 - A Z 310 290 250 250 Trouser tear - W kN/m 5.0 13.2 17.8 20.5 - A kN/m 3.7 18.3 17.6 29.2 Hardness Shore A 79 89 92 94 TABLE III (Cont'd) Experiment # E F G H Wt. of butyl g 100 100 100 100 Wt. of EPDM 8 - - - - Wt. of fibre (dry) g 0 5 10 15 Compounding recipe Polymer + fibre 100 105 110 115 Carbon black (N-330) 50 50 50 50 Paraffinic oil 10 10 10 10 Zinc oxide 3 3 3 3 Stearic acid 1 1 1 1 Sulphur 1.5 1.5 1.5 1.5 MBT 0.5 0.5 0.5 0.5 TMTD 1 1 1 1 Green strength Tensile - W MPa 0.36 1.53 4.28 5.57 -oA MPa 0.37 0.53 0.66 0.98 Elongation - W % > 1500 595 170 130 - A % > 1500 340 460 505 Vulc. time mins 28 15.5 15.5 18 Tensile - W MPa 18.1 14.0 10.4 13.3 - A MPa 16.8 12.4 9.9 8.7 100% Modulus - W MPa 1.57 4.54 7.68 - A MPa 1.5 1.47 2.27 2.73 300% Modulus - W MPa 7.2 6.2 8.1 - A MPa 7.6 5.0 5.6 5.9 Elongation - W % 570 550 430 80 - A % 540 550 500 450 Trouser tear - W kN/m 55.1 51.8 53.1 26.8 - A kN/m 18.1 37.1 38.9 28 Hardness Shore A 66 74 77 84

Claims (7)

1. A process for preparing a fibre-reinforced rubbery polymer, which comprises subjecting polymeric para-phenylene terephthalamide fibres having an average length of from 1 to 5 mm and a BET surface area of at least 1 m2/g to agitation in a containment vessel, and thereby fluffing the fibres; mixing from 1 to 20 parts by weight (on a dry fibre basis) of the fluffed fibres with a solution of 100 parts by weight of a rubbery polymer in a hydrocarbon solvent; and removing the solvent.

2. A process for preparing a fibre-reinforced rubbery polymer, which comprises mixing from 1 to 20 parts by weight of polymeric para-phenylene terephthalamide fibre as defined in claim 1 with a solution of 100 parts by weight of a rubbery polymer in a hydrocarbon solvent; subjecting the mixture to shearing agitation; and removing the solvent.

3. A process according to claim 1 or claim 2, in which the rubbery polymer is a synthetic rubbery polymer selected from polybutadiene, polyisoprene, isobutylene-isoprene polymers, bromobutyl polymers, chlorobutyl polymers, styrene-butadiene polymers, ethylene-propylene polymers and ethylene-propylene-non-conjugated diene polymers.

4. A process according to any preceding claim, in which the polymeric para-phenylene terephthalamide fibre has a BET surface area of from 7 to 1 2 m2/g.

5. A process according to any preceding claim, in which the solution contains not more than 1 5 parts by weight polymer per 100 parts by weight polymer plus solvent.

6. A process according to any preceding claim, in which there are from 2 to 12 parts by weight fibre per 100 parts by weight polymer.

7. A process according to claim 1 or claim 2, as herein described in any of the Examples.