GB1599164A - Plastics-elastomer compositions - Google Patents

Description

(54) PLASTICS-ELASTOMER COMPOSITIONS (71) We, EXXON RESEARCH AND ENGINEERING COMPANY, a Corporation duly Organised and existing under the laws of the State of Delaware, United States of America, of Linden, New Jersey, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to blends of stiff polyalkylene plastics and elastomers.

The plastics industry is using extensively synthetic elastomers to extend the operating capabilities of thermoplastics polyalkylene polymers. This is particularly so for polypropylene where impact strength, toughness, melt strength and capacity for filler loading is improved by incorporation of an elastomer such as ethylene-propylene rubber (EPR) or ethylene-propylene-diene terpolymer rubber (EPDM).

Currently blend preparation is usually performed in high shear equipment, for example internal mixers, continuous mixers or mixing extruders such as Werner-Pfleiderer Twin-Screws. Polymer bales and high shear equipment is always required for mixing the preliminary concentrate in order to disperse intimately the elastomer into the polyolefin matrix. This is because it is not possible to blend in one step elastomer crumbs or pellets with the polyolefin in a plastics type extruder since (1) elastomer pellets or crumbs would agglomerate on storage (EP impact grades being low in ethylene content are sticky) and (2) shear is not intensive enough in order to disperse intimately the EP in polyolefin. The preliminary concentrate is then pelletized and diluted with additional polyolefin to reach the final blend composition, generally in a non-intensive mixer such as a plastics type extruder.The cost of preparing such concentrates by such methods is comparatively high.

We have now devised a method of preparing blends of stiff polyethylene plastics and elastomers which is simpler and cheaper than those methods in current use.

According to this invention a polyalkylene plastics/elastomer blend is made by a process which comprises mixing together a blend of a solution of a polyalkylene plastics of hardness, Shore D (ASTM D2240) greater than 40 and having a flexural modulus (ASTM D790) greater than 150 mega pascals with a solution of an elastomer to form a homogeneous solution and precipitating the blend of polyalkylene plastics and elastomer from the homogeneous solution and if precipitating by means of steam stripping, drying the precipitated blend.

Preferred polyalkylenes are polyethylene or polypropylene. The polyalkylene is usually thermoplastic. Particulaly suitable is low pressure isotactic polypropylene which usually has a density of from 0.86 to 0.91 glcc and a molecular weight of from 50,000 to 500,000 as determined by the intrinsic viscosity method and preferably of melt flow rates of 0.5, 5 or 12 g/10 min at 230"C. Thus one can use Esso grade isotactic polypropylene 151 which has a hardness, Shore D, 5 sec of 71 (ASTM D2240) and a flexural modulus of 1430 mega pascals (ASTM D790). Also suitable is isotactic polypropylene which has a hardness, Shore D of 70 to 80 and a flexurual modulus of 1100-1800 mega pascals.Another suitable polyalkylene is low pressure polyethylene (high density polyethylene) which usually has a density of from 0.94 to 0.96 g/cc, a molecular weight of from 30,000 to 500,000 a melt index of from 0.3 to 30 g/10 min. at 1900C, a hardness, Shore D of about 60 and a flexurual modulus of about 1000 mega pascals. These low pressure polyalkylenes may be made by the well-known polymerization method using a Ziegler catalyst (e.g. AlCl3 and TiCl4). Also one may use low density polyethylene (LDPE) of melt index 0.8 to 30 g/10 min. at 1900C, a hardness, Shore D of above 40 to 52 and flexurual modulus of 150-230 mega pascals.

The elastomer can be for example butyl rubber, halogenated butyl rubber, EPR, EPDM, polyisobutene (Vistanex (Registered Trade Mark)), SBR (styrene-butadiene rubber), IR (Isoprene rubber), NR (natural rubber) or NBR (nitrile rubber), polybutadiene, polychloroprene, polysulphides and Hypalon (chlorosulphonated polyethylene (Registered Trade Mark).

Butyl rubber comprises a copolymer of a major proportion, e.g. 85 - 99 wt.%, preferably 95-99 wt.%, of a C4 to C8 isoolefin, such as isobutene, with a minor proportion, e.g. 0.1 to 15 wt.%, preferably 0.5 to 5 wt.%, of a C4 to C14 multiolefin, such as butadiene, piperylene or isoprene. Halogenated butyl rubber is produced by halogenating unmodified, unvulcanised butyl rubber, e.g. chlorination or bromination, so that the rubber contains at least 0.5 wit.% and preferably at least 1.0 wt. % of combined halogen, but not more than one atom of chlorine and three atoms of bromine contained in the polymer per molecule of multiolefin present therein.

Ethylene-propylene copolymers and ethylene-propylene-diene terpolymers are usually prepared by contacting a feed stream containing the monomers (i.e. ethylene and propylene; and ethylene, propylene and a diene respectively) with a Ziegler catalyst in the presence of an inert saturated C5 to C8 hydrocarbon diluent, e.g. an alkane or cyclo alkane such as n-pentane, isopentane, n-hexane, isohexane or n-octane. The copolymerization is usually carried out at a pressure of 1 to 5 atmospheres. The diolefin used in making EPDM is usually a C6 to C16 non-conjugated diolefin, e.g. 1, 4-hexadiene, 1,5 - octadiene or a 2-alkyl norbornad.

Styrene-butadiene rubber is usually made by the co-polymerization of about 3 parts by weight of butadiene with 1 part by weight of styrene, the monomers being suspended in finely divided emulsion form in a large proportion of water in the presence of a detergent.

The polyalkylene plastics and elastomer are mixed together in the form of a solution. The plastics is dissolved in a suitable solvent, for polypropylene suitable solvents at temperatures above llO"C include aliphatic or cycloaliphatic hydrocarbons, for example en tane, hexane or heptane or halogenated hydrocarbons e.g. chlorohexane or aromatic hydrocarbons, for example benzene, toluene, xylene, higher aliphatic esters and ketones or di n-amyl ether. For LDPE the same solvents are suitable but should be used at temperatures 20C to 30"C lower depending on the degree of branching of the LDPE. It may be necessary to heat the plastics and solvent to obtain a solution.Thus, a suitable solution is one of polypropylene dissolved in hexane toluene or xylene heated to a temperature of at least 110 C for fast dissolution rate.

Likewise the elastomer is dissolved in a solvent, the nature of which can vary according to the particular elastomer which is being used. For EPR and EPDM suitable solvents include hydrocarbons, for example pentane hexane or heptane. Another suitable solvent for EPR and EPDM is an oil or lubricant compatible therewith. Particularly suitable are mineral oils, for example paraffinic types of viscosity gravity constant 0.79 to 0.82, naphthenic types of viscosity gravity constant 0.82 to 0.90 or aromatic types of viscosity gravity constant 0.90 to 1.10. If desired or if necessary the elastomer and solvent are heated to ensure the formation of a solution.

The two solutions are mixed to form a homogeneous solution. Usually "in-line" mixing will be quite sufficient. If the solutions are rather viscous it may be desirable to use mixers such as Statco contactors or centrifugal pumps. When this homogeneous solution has been formed the solution is then treated so as to precipitate therefrom a blend of the plastics and elastomer. This may be achieved by for example vapour stripping or precipitation by the use of a precipitant.

Vapour stripping is usually steam stripping and the procedure is as follows: The polymer blend solution is contacted with medium pressure steam in an underwater or above water stubby nozzle in a flash tank in order to remove the solvent. The temperature of the water is maintained at about 100"C. The polymer crumbs which are formed are dispersed in hot water. To this slurry (temperature range ] 00-120 C and polymer concentrations 2 to 6 wt.%) it is sometimes necessary to add dispersants (e.g. metal stearate) in order to prevent polymer crumbs from sticking together and to add inhibitors of phenolic or amine type to prevent degradation due to heat. Additional stripping can take place in a steam stripper, the steam being either co-current or contracurrent to the polymer flow.

Precipitation with a precipitant involves treating the solution with a non-solvent for the plastics and elastomer. Examples of such non-solvents for blends of polypropylene and EPR or EPDM are alcohols, for example methanol. ethanol or isopropanol or ketones, for example acetone, diethyl ketone or methyl ethyl ketone.

After precipitating the polymer it is necessary either to filter the solvent or separate the polymer from the solvent/non solvent by techniques such as centrifugation.

After the plastics and elastomer have precipitated from the solution they must be dried if steam stripping has been used. Precipitation by other techniques may if desired be followed by drying. This drying is conveniently achieved by the use of a finishing extruder whereupon the finished product will be non-agglomerated pellets or crumbs.

Other methods of drying the precipitated blend of plastics and elastomer include spray drying to obtain powdered polymer blend or evaporating the solvent on a film evaporator (e.g. LUWA thin film evaporator).

Although the process of this invention is applicable to any blend of plastics and elastomer in all proportions it is preferable if the elastomer is a minor proportion by weight of the blend, preferably 10 to 50% by weight, basedon the total weight of plastics and elastomer.

If desired when the blend of the solutions of plastics and elastomer are formed, before precipitation takes place, some grafting of the elastomer onto the plastics may be effected.

This may be effected by mechano chemical degradation, e.g. cavitational ultrasonic irradiation of polymer solution (gives block copolymer), shaking high speed stirring and forcing the polymer blend solution through microorifices, discharging of high voltages through polymer solution, addition to polymer solution of a cross linking agent or free radical donor (e.g. azo diisobutyronitrile or peroxides), addition of oxygen, comastication of polymer solution, ultrasonic degradation of the polymerization solution and submitting polymer solution to radiation.

The process of this invention results in pellets or crumbs of the blend of plastics and elastomer. This particulated blend may if desired be diluted with further plastics, e.g.

polyolefin, in a plastics type injection moulding machine. Thus, masterbatch crumbs or pellets (pellets being prepared using simple screw extruders) can be used to prepare modified polypropylene with excellent impact properties by letting down (diluting) the masterbatch i.e. blend of elastomer and polypropylene) in non-intensive mixing equipment, e.g. a single screw extruder or directly in the hopper of an injection moulding machine.

Using the process of this invention it is possible to prepare directly elastomer/polyolefin masterbatches of excellent dispersion at a polymer plant site, for instance at an EPDM plant. This avoids the expensive and tedious mixing of elastomer and polyolefin using high shear equipment. Masterbatch crumbs or pellets of excellent impact properties and with a tendency not to agglomerate are also obtained. Furthermore, the blends prepared by the process of the invention do not lead to degradation as mixing is performed in solution and hence there is no shearing.

Another advantage of the invention is its ability to obtain non-sticky crumbs of EPR or EPDM of low Mooney and/or ethylene content. These crumbs which are normally sticky may be made non-sticky by adding polypropylene in accordance with the process of this invention.

The advantages of this invention are shown in the following Examples.

Example 1 Masterbatch 1 was prepared by blending (a) Exxon grade isotactic polypropylene 151 (powder -hardness, Shore D, 5 sec 71 and flexural modulus 1430 mega pascals: 2 wt.% solution in xylene at 125"C with (b) a 5 wt.% Vistalon 404 'cement', i.e. a 5 wt.% Vistalon 404 solution in hexane withdrawn from a Vistalon plant before steam stripping. Vistalon 404 is an Exxon EPR grade of Mooney viscosity ML (1+8) @ 100"C = 40.

The solution (b) was added to solution (a) in a stirred vessel in such a way that solution temperature was maintained above 90"C.

The polymer blend solution of the following composition: propylene 151/Visatalon 404 = 30/70 by weight was clear and no polymer precipitation occurred above 80"C.

The polymer blend was precipitated by pouring the above solution into an excess of acetone at ambient temperature. The precipitation polymer blend was dried in a mill (roll temperature 1300C), extruded using a single screw extruder at 200"C, calendered into a sheet which was cooled down and then granulated at ambient temperature.

Masterbatch 2 was prepared by blending Exxon grade polypropylene 151 pellets (or powder) and Vistalon 404 in a Banbury internal mixer (conventional process) using the following procedure: sufficient polypropylene and elastomer amount were charged to give a good ram action at flux (high rotor speed, high ram pressure, water off). Once the mixture reached flux temperature (160"C), mixing was continued for 3 minutes. The blend was then dumped. The final blend composition was polypropylene 151/Vistalon 404 = 30/70 by weight. The polymer blend was extruded using the same single screw extruder at 200 as for masterbatch 1, calendered into a sheet which was cooled down and then granulated at ambient temperature.

Masterbatch 3 was prepared by blending Vistalon 404 with polypropylene 151 powder on a mill (roll temperature 1300C), extruded using the same single screw extruder at 200"C, calendered into a sheet which was cooled down and then granulated at ambient temperature. The composition was polypropylene 151/Vistalon 404 = 30/70 by weight.

Although the polymer blend seemed homogeneous after extruding it at 2000C in a single screw extruder (200"C is above the polypropylene flux temperature) and although the masterbatch 3 granules were non sticky (which is of practical interest) it will be shown later that the polymer dispersion was not good enough for imparting good impact strength to the final blend.

Masterbatch 1 granules were then tumble blended with polypropylene 151 pellets and fed to an injection moulding machine for moulding 2 mm. thick test pieces of the composition: polypropylene 151/Vistalon (Registered Trade Mark) 404 = 80/20 by weight (final blend 1).

The same treatment was applied to masterbatches 2 and 3 (final blends 2 and 3).

The final blend properties were as follows: Final blend properties Property ASTM Test Polypropylene Blend 1 Blend 2 Blend 3 151 Melt flow rate g/10 mm (230"C. D1238 12 10.2 9.2 9.0 21.6N) Secant flexural D790 1470 940 890 960 modulus, MPa Impact, 2 Kg falling weight BS2782,306B Impact brittle brittle brittle brittle Energy, J at modified height at less than at 12 at 12 at 5 minus 20"C one joule The properties of blend 1 (object of the invention) are slightly superior to those of blend 2 (conventional process) i.e. slightly higher melt flow rate and rigidity at equivalent impact strength.

Blend 3 impact properties are poor, indicating poor dispersion of Vistalon 404 in polypropylene.

Example 2 Masterbatch 4 was prepared by blending (a) Exxon grade polypropylene 151 powder (same as Example 1): 2 wt.% solution in xylene at 1250C with (b) a 5 wt. % Vistalon (Registered Trade Mark) 5600 'cement' (as in Example 1) Vistalon 5600 in an Exxon EPDM grade of Mooney viscosity ML (1 + 8) @ 1270C = 70.

The solution (b) was added to solution (a) in a stirred vessel in such a way that the solution temperature was maintained above 90"C.

The polymer blend solution of the following composition: polypropylene 151/Vistalon 5600 = 30/70 by weight was clear and no polymer precipitation occurred above 80C.

The polymer blend was precipitated from the solution using steam stripping at 100"C in order to remove hexane and xylene. The polymer blend was dried on a mill (roll temperature 1300C), extruded using a single screw extruder at 2000C, calendered into sheet which was cooled down and then granulated at ambient temperature.

Masterbatch 5 was prepared by blending Exxon grade polypropylene 151 powder and Vistalon 5600 in a Banbury internal mixer using the same procedure as described for masterbatch 2 in the Example 1. The final blend composition for masterbatch 5 was polypropylene 151/Vistalon 5600 = 30/70 by weight. The polymer blend was extruded using a single screw extruder at 2000C, calendered under the form of a sheet which was cooled down and then granulated at ambient temperature.

Masterbatch 4 granules were then tumble blended with polypropylene 151 pellets and fed to an injection moulding machine for moulding 2 mm. thick test pieces of the composition: polypropylene 151/Vistalon 5600 = 75/25 by weight (final blend 4). The same treatment was applied to masterbatch 4 (final blend 5).

The final blend properties were as follows: Final blend properties Property ASTM Test Blend 4 Blend 5 Melt flow rate g/10 mn (230"C, 21.6N) D1238 4.9 4.8 Secant flexurual modulus, MPa D790 1050 1040 Impact, 2 K falling weight BS 2782,306B brittle at brittle at Energy, J. ( -30 C (modified height) 12 10 The properties of blend 4 (object of the invention) were at least as good as the properties of blend 5 (conventional process).

WHAT WE CLAIM IS: 1. A process of making a polyalkylene plastics/elastomer blend which comprises mixing together a solution of a polyalkylene plastics of hardness, Shore D greater than 40 and having a flexurual modulus (ASTM D790) greater than 150 mega pascals with a solution of an elastomer to form a homogeneous solution and precipitating the blend of polyalkylene plastics and elastomer from the homogeneous solution and if precipitating by means of steam stripping, drying the precipitated blend, 2. A process according to claim 1 wherein the polyalkylene is polypropylene.

3. A process according to any one of the preceding claims wherein the elastomer is butyl rubber.

4. A process according to either claims 1 or 2 wherein the elastomer is an ethylene-propylene copolymer or an ethylene-propylene-diene terpolymer.

5. A process according to any one of the preceding claims wherein the polyalkylene plastics is dissolved in an aliphatic, aromatic or cycloaliphatic hydrocarbon or a halogenated hydrocarbon.

6. A process according to claim 5 wherein polypropylene is dissolved in hexane, toluene or xylene heated to a temperature of at least 110 C.

7. A process according to any one of claims 4 to 6 wherein the elastomer is dissolved in a hydrocarbon solvent.

8. A process according to any one of the preceding claims wherein the blend of polyalkylene plastics and elastomer is precipitated from the homogeneous solution by steam stripping.

9. A process according to any one of claims 1 to 7 wherein the blend of polyalkylene plastics and elastomer is precipitated from the homogeneous solution by using a precipitant.

10. A process according to claim 9 wherein the polyalkyleneplastics is polypropylene and the rubber is EPR or EPDM and an alcohol or ketone is used as precipitant.

11. A process according to either of claims 9 and 10 wherein the precipitated blend of polyalkylene plastics and elastomer is dried.

12. A process according to any one of the preceding claims wherein the amount of elastomer is 10 to 50% by weight of the total weight of the blend of polyalkylene plastics and elastomer.

13. A process according to claim 1 substantially as hereinbefore described with reference to either of the Examples.

14. A polyalkylene plastics/elastomer blend whenever made by the process according to any one of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (14)

**WARNING** start of CLMS field may overlap end of DESC **. The final blend properties were as follows: Final blend properties Property ASTM Test Blend 4 Blend 5 Melt flow rate g/10 mn (230"C, 21.6N) D1238 4.9 4.8 Secant flexurual modulus, MPa D790 1050 1040 Impact, 2 K falling weight BS 2782,306B brittle at brittle at Energy, J. ( -30 C (modified height) 12 10 The properties of blend 4 (object of the invention) were at least as good as the properties of blend 5 (conventional process). WHAT WE CLAIM IS:

1. A process of making a polyalkylene plastics/elastomer blend which comprises mixing together a solution of a polyalkylene plastics of hardness, Shore D greater than 40 and having a flexurual modulus (ASTM D790) greater than 150 mega pascals with a solution of an elastomer to form a homogeneous solution and precipitating the blend of polyalkylene plastics and elastomer from the homogeneous solution and if precipitating by means of steam stripping, drying the precipitated blend,

2. A process according to claim 1 wherein the polyalkylene is polypropylene.

3. A process according to any one of the preceding claims wherein the elastomer is butyl rubber.

4. A process according to either claims 1 or 2 wherein the elastomer is an ethylene-propylene copolymer or an ethylene-propylene-diene terpolymer.

5. A process according to any one of the preceding claims wherein the polyalkylene plastics is dissolved in an aliphatic, aromatic or cycloaliphatic hydrocarbon or a halogenated hydrocarbon.

6. A process according to claim 5 wherein polypropylene is dissolved in hexane, toluene or xylene heated to a temperature of at least 110 C.

7. A process according to any one of claims 4 to 6 wherein the elastomer is dissolved in a hydrocarbon solvent.

8. A process according to any one of the preceding claims wherein the blend of polyalkylene plastics and elastomer is precipitated from the homogeneous solution by steam stripping.

9. A process according to any one of claims 1 to 7 wherein the blend of polyalkylene plastics and elastomer is precipitated from the homogeneous solution by using a precipitant.

10. A process according to claim 9 wherein the polyalkyleneplastics is polypropylene and the rubber is EPR or EPDM and an alcohol or ketone is used as precipitant.

11. A process according to either of claims 9 and 10 wherein the precipitated blend of polyalkylene plastics and elastomer is dried.

12. A process according to any one of the preceding claims wherein the amount of elastomer is 10 to 50% by weight of the total weight of the blend of polyalkylene plastics and elastomer.

13. A process according to claim 1 substantially as hereinbefore described with reference to either of the Examples.

14. A polyalkylene plastics/elastomer blend whenever made by the process according to any one of the preceding claims.