It is common practice to blend a thermoplastic resin with an immiscible resin such as an elastomeric polyolefin. The mechanical properties of the blend are often better in a significant respect, e.g. in relation to impact strength, than that of the unblended thermoplastic resin. For optimum properties, the disperse phase of the polyolefin must be finely divided.. While such fine division is relatively easy to achieve during the actual blending, it is found that during subsequent processing, the particles of the finely divided disperse phase tend to agglomerate. Such agglomeration causes a change in the mechanical properties and processability and often leads to an unacceptably large and not always predictable change. Since consistency of properties of any thermoplastic resin composition is always important, such sensitivity to processing conditions constitutes an important disadvantage of known blends of thermoplastic resins having polyolefins dispersed therein. It has now been found that the morphology of such blends can be very substantially stabilized if the polyolefin blended with the thermoplastic resin is grafted with a silane compound and the silane compound is then cured by water during the blending operation. The curing brings about

cross-linking of the polyolefin and this stabilises the dispersed particles and substantially reduces or eliminates the agglomeration of the particles which, in the absence of the cross-linking, may take place during processing. The mechanical properties of the blend are substantially unaltered, or even improved, by cross-linking of the polyolefin in this way. The impact strength, in particular, is often improved.

The present invention accordingly provides a thermoplastic resin composition comprising, as continuous phase, from 65 to 90% by weight of the composition of a semicrystalline thermoplastic resin and, as disperse phase from 35 to 10* by weight of a moisture-cured silane-grafted thermoplastic or elastomeric polyolefin having a particle size in the range of 0.1 to 2.5μm.

While it has previously been proposed to produce blends of a polyolefin and a silane-grafted ethylene propylene elastomer which is cured, see British Specificatio 2116986 (Exxon Research and Engineering Co) , in the known compositions the elastomeric polymer constituted the continuous phase and there was no teaching that the cross- linking of the silane-grafted elastomer should take place during the operation of blending the elastomer with the polyolefin. According to a feature of the invention, the novel thermoplastic compositions are produced by blending together

(1) a semicrystalline thermoplastic resin and (2) a moisture- curable silane-grafted thermoplastic or elastomeric polyolefin in the presence of (3) water or a compound which releases water under the blending conditions, the conditions of blending and the proportions of the thermoplastic resin and polyolefin being such that (λ) the thermoplastic resin (1) forms the continuous phase of the blend, (B) the silane- grafted polyolefin (2) is dispersed in the blend with a particle size substantially all in the range 0.1 to 2.5 μm, and (C) the silane-grafted polyolefin (2) is cured during the blending by the water (3).

In the accompanying drawings, figures 1 and 2 show a composition comprising polypropylene as continuous phase and an ethylene/propylene elastomer as disperse phase as viewed by scanning electron microscopy before and after compression moulding respectively. Figures 3 and 4 show a similar composition in which however the ethylene/propylene elastomer has been silane-grafted in accordance with the present invention. These figures show the composition as viewed by scanning electron microscopy before and after compression moulding respectively. The compositions are described in detail in Example 1 below.

The thermoplastic resin used as continuous phase in the new compositions nay be any thermoplastic resin which can be shaped by compression or injection moulding and which is resistant to the blending conditions. The term

"semicrystalline" as used herein in relation to the thermoplastic resin means that the polymer is crystallizable, i.e. substantially non-amorphous, but may contain amorphous zones within the polymer spherulite structures. A wide variety of such resins are available. The invention is especially advantageous when applied to blends based on polypropylene or other semicrystalline linear poly-α-olefin as the continuous phase, but other thermoplastic resins may be used, e.g. linear polyamides such as polyhexamethylene adipamide or polycaprolactam, or linear polyesters such as polyethylene terephthalate or polybutylene terephthalate or other thermoplastic polymers such as polycarbonate, polystyrene, polyacrylates, polyacrylonitrile, styrene- acrylonitrile copolymer, acrylonitrile-butadiene-styrene terpolymer, polymethyl methacrylates or polyphenylene oxide. As already indicated, such thermoplastic resins are used in the proportions such that they constitute the continuous phase of the blend, and more particularly from 65 to 90%, preferably 65 to 75%, by weight of the total composition of semicrystalline thermoplastic resin and cured polyolefin.

The silane-grafted polyolefin is conveniently made by one of the two following methods. In either case the polyolefin starting material is either a thermoplastic resin such as polyethylene or an ethylene copolymer, e.g. an ethylene-vinylacetate copolymer, or an elastomeric polymer such as an ethylene-alpha ole in elastomer (such as ethylene-

propylene copolymer or ethylene-propylene-diene terpolymer) or a polyisobutene or polyisoprene elastomer.

In the first method of forming the silane-grafted polyolefin, the polyolefin is first reacted with maleic anhydride in the presence of a free radical catalyst such as an organic peroxide and the maleic anhydride grafted polyolefin so obtained is then reacted with an amino silane, e.g. a gamma-aminopropyltriethoxysilane, which reacts with the anhydride residues and thus introduces triethoxysilane radicals into the polyolefin.

In a second method, the polyolefin is reacted directly with a vinyl-silane, e.g. a vinyl-trialkoxysilane such as vinyl-trimethoxysilane, in the presence of a free radical-generating catalyst which is preferably an organic peroxide such as dibenzoyl peroxide or other peroxide which is relatively stable at ambient temperature but which decomposes at elevated temperature with production of free radicals.

With either method, and indeed with other methods which are available to those skilled in the art, the proportion of crosslinkable silane, preferably triethoxysilane, groups introduced into the polyolefin is preferably 0.2 to 0.5 per cent by weight, calculated as total silicon in the grafted polyolefin. The grafting of the silane with the polyolefin is generally carried out by a reaction extrusion or blending process (such as single or

twin screw extrusion or Brabendβr mixing) .

Whichever method of preparing the silane grafted polyolefin is used, the latter and the thermoplastic polymer resin are blended together, e . g. in a Brabender mixer or any other suitable mixing device, at an elevated temperature, e. g. 150 to 250 *C, and preferably from 180 to 200*C, until the silane-grafted polyolefin has been finely dispersed in the continuous phase of the thermoplastic polymer. During the blending and after the silane grafted polyolefin is well dispersed, water or a water-releasing agent is employed in a proportion such as to bring about crosslinking of the trialkoxysilane groups in the silane grafted polyolefin . It is greatly preferred that the dispersed silane-grafted phase becomes finely divided before crosslinking, as the impact an mechanical properties of the resultant blend depend on the particle size of the dispersed phase. Crosslinking of the dispersed phase during mixing enables good morphology control. A high intensity mixing device (such as a twin screw compounder) is preferred for making the blend. To promote this crosslinking a suitable catalyst e.g. a tin compound such as dibutyltin dilaurate , may be incorporated i the blend in a suitable proportion, e.g. 0.05 to 0.1 per cen by weight of the total of semicrystalline thermoplastic resi and silane grafted polyolefin. Crosslinking is preferably t at least 80% gel content in xylene.

Water may be used as such during preparation of the

blend, but it is also impossible to add the water in the for of a solid compound which releases water at the blending temperature. Examples of such materials include hydrated alumina, and hydrated inorganic salts such as cupric sulphate pentahydrate and magnesium sulphate heptahydrate. Such hydrated salts must be chosen so as not to have any adverse effect upon the blend; this normally presents no problem with regard to mechanical properties of the blend, but use of such salts may lead to problems of blend appearance. In whatever form the water is added, the proportion should be such as to bring about crosslinking of all the crosslinkable silane groups, e.g. trichlorosilane or trialkoxysilane residues present in the silane-grafted polyolefin. Generally about 10 to 20 per cent by weight of water based on the weight of silicon in the grafted polyolefin is appropriate, but when water is added to the blend while mixing, a large excess may need to be used to compensate for any loss due to evaporation.

The following Examples illustrate the invention. EXAMPLE 1

Vinyl tri ethoxysilane A171 of Union Carbide Company (1.5% by weight), dicumyl peroxide (0.15% by weight) and dibutyl tin dilaurate (0.05 weight per cent) were mixed with ethylene/propylene rubber (to 100%) in a Brabender mixer at 120 to 130*C. This causes the trimethoxysilane groups to become grafted to the ethylene/propylene rubber. The rubber

employed was VISTALON 504 of Exxon Chemical Company, being an amorphous EP rubber containing 53 wt % ethylene and having a Mooney viscosity M (1+8) at 100"C of 38.

Polypropylene was melted in a Brabender mixer at 200*C and 30% by weight of the silane-grafted ethylene/ propylene elastomer produced in the manner just described was then added. The polypropylene used was Vλ 8020H of Neste Oy, a homopolymer of melt flow rate at 230*C/2.16kg of 0.8, suitable for blow moulding, of density 0.902. After about 5 minutes mixing, water (5 per cent by weight) was added and the mixing was continued until the reaction was substantially complete. The blend obtained was examined by scanning electron microscopy and the crosslinked ethylene/propylene elastomer phase was found to be present in the blend in the form of 1 to 2 μm particles which were 80% insoluble as determined by xylene extraction (representing a high degree of crosslinking) . The disperse phase of crosslinked elastomer showed no tendency to agglomerate upon compression moulding, as evidenced by the results of further scanning electron microscope (SEM) analysis of the blend after it had been compression moulded at 180 ^* C/20 tonnes for 30 minutes in a Fontijne type SRB140 compression moulder. A comparison blend was prepared using the same mixing conditions as expressed above, using exactly the same additives in the mixer; however in this case the ethylene/propylene elastomer which was added to the mixer was not grafted with

vinyltrimethoxysilanβ. For this comparison blend the particle size of the dispersed phase EP increased from l-2μm to >10 μm after compression moulding at the same conditions as the silane-grafted EP/PP blend. The properties of the blends are shown in. the following Table, in which the values quoted for mechanical properties represent the average of five measurements.

Blend 1 Blend 2 (invention) polypropylene 70 70 ethylene/ propylene elastomer 30 0 silane-grafted ethylene/ propylene elastomer 0 30 impact strength (J/m) room temperature 569 563

-20'C 95 96

-40*C 66 73 E-modulus (GPa) 0.61 0.437 elongation at break (%) 604 12.5 stress at break (MPa) 18.2 12.3

For comparison, it may be stated that the polypropylene by itself has, at room temperature, an impact strength of 43.4 J/m and an E-modulus of 0.84 GPa.

The results shown in the Table demonstrate that the blend (2) of the invention has substantially the same mechanical properties as the comparison blend (1) [except for elongation at break]. However blend (2) has the advantage of

being reprocessable and exhibits an extremely stable phase morphology. This is shown in the accompanying drawings, in which Figures 1 and 2 show blend (1) as viewed by SEM before and after compression moulding, respectively; and Figures 3 and 4 show blend (2) as viewed by SEM before and after compression moulding, respectively. EXAMPLE 2

Maleic anhydride-grafted ethylene/propylene elastomer (containing 0.7 per cent by weight of maleic anhydride) was mixed at 120 ^* C in a first Brabender mixer operating at 50 revolutions per minute (rpm) , with gamma- aminopropyltriethoxysilane in a proportion of twice the stochiometric amount (i.e. in the proportion of two NH ₂ groups for each anhydride residue) . This causes the aminosilane to become grafted onto the maleated EP rubber. 70 parts by weight of polypropylene ^ras melted at 180*C in a second Brabender mixer operated at 50 rpm , and 30 parts by weight of the silane-grafted maleated EP produced in the first Brabender mixer, was added. Mixing was continued whilst raising the temperature by shear heating to 196'C, at which point water (5 parts by weight) was added while the speed of the mixer was reduced from 50 to 30 rpm. Blending was completed when the temperature reached 210*C. A rise in torque of + INm was observed, indicating that curing had occurred.

The polypropylene used was Vλ 802OH as used in

Example 1. The maleic anhydride grafted EP rubber was EXXELOR Vλ 1803 of Exxon Chemical Company, being an EP rubbe of melt index 3g/10 min (ASTM D 1238) and maleic anhydride content 0.7 wt %. The aminopropyltriethoxy silane used was A1100 of Union Carbide Company.

The experiment was repeated without the pre-reaction of amino-silane and maleated EP. In this case a physical mixture of 1.5 parts by weight amino-silane and 30 parts by weight maleated EP was added to 70 parts by weight of the polypropylene while being blended at 180*0 in a Brabender mixer. Water (5 parts by weight) was then added as in the previous experiment. The mixer was operated at 50 rpm and the rise in torque observed was 2 Nm.

In a third experiment the blending of the same ingredients was repeated except that no aminosilane was included.

Comparison of the three blends after compression moulding at 190 ^* 0/20 tonnes for 20 minutes showed that the first two blends in accordance with the invention retained their mechanical properties very well during the compression moulding operating while the third (containing no cross- linked silane residues) showed considerable agglomeration of the dispersed elastomer particles which caused substantial deterioration in the mechanical properties.