WO1994013740A1

WO1994013740A1 - Extrusion or blow-moulding of polyamide compositions

Info

Publication number: WO1994013740A1
Application number: PCT/CA1993/000503
Authority: WO
Inventors: Shailesh Ratilal Doshi; Tom-Axel Baltus; Margaret Louise Mcintosh
Original assignee: Dupont Canada Inc.
Priority date: 1992-12-10
Filing date: 1993-11-24
Publication date: 1994-06-23
Also published as: AU5556794A; GB9225811D0; CA2130476A1

Abstract

A blow moulding process in which a parison is formed from a polyamide composition and an extrusion process in which a profile is extruded from a polyamide compositon are disclosed. The polyamide composition comprises (a) 55-90 % by weight of a polyamide selected from the group consisting of (i) polyamides having a weight average molecular weight of greater than 25 000, and (ii) polyamides that are soluble in formic acid and which have an RV measured in formic acid of at least 40; and (b) 10-45 % by weight of a polymer selected from the group consisting of grafted polymer and mixtures of grafted polymer and ungrafted polymer. Each of the grafted polymer and ungrafted polymer are independently selected from the polyolefins having a melt index of less than 10 dg/min. The polyolefin of the grafted polymer is grafted with 0.1-5.0 % by weight of an ethylenically unsaturated carboxylic acid or anhydride. The grafted polymer is 25-100 % by weight of the polymer of (b). The composition exhibits a relative increase in melt viscosity at low shear stress compared to the polyamide of (a). The compositons may be used in the blow moulding of for example bottles, containers and hollow under-the-hood automotive components and in the extrusion of for example rods, tubing, cable jacketing and other profiles.

Description

EXTRUSION OR BLOW-MOULDING OF POLYAMIDE COMPOSITIONS

The present invention relates to extrusion and blow-moulding processes using polyamide compositions and to such compositions, and especially to improvements therein. In particular, the invention relates to extrusion and blow-moulding processes in which the polyamide compositions have increased melt viscosity at low stress levels to impart melt sag resistance and moderately low viscosity at high stress levels, to impart improved extrudabi1ity.

Polyamides may be fabricated into a wide variety of products. The compositions used must have melt viscosity characteristics that are appropriate to the process being used, as discussed in published European patent application 0 295 906 of D.S. Dykes and K.D. Kuhnemann, published 1988 December 21. The use of compositions of polyamides and epoxides in extrusion processes is disclosed therein. Polyamide compositions for blow moulding are disclosed in U.S. Patent 5 122 570 of P.M.

Subramanian, issued 1992 June 16, such compositions being semi-crystalline polyamide, selected toughening agent and an anhydride-rich ethylene copolymer.

Blow moulding and extrusion are important processing operations used in the manufacture of finished articles from polymeric compositions. Blow moulding is the process normally used for the manufacture of hollow articles for example bottles, jugs and the like, from thermoplastic polymers e.g. polyethylene, polypropylene and polyvinyl chloride. Blow moulding processes are finding increasing use in the manufacture of engineering and structural components, for example automotive under- the-hood components e.g. fluid reservoirs, resonators and the like, which have to be manufactured from so-called engineering polymers e.g. polyamides. Extrusion processes are used for making continuous profiles for example pipe, tubing or other profiles of a specific cross-sectional shape. For automotive and other critical end-use applications, such extrusion processes utilize engineering polymers.

Both blow moulding and extrusion processes require polymer compositions with unique rheological characteristics for commercially acceptable operation. In blow moulding processes, molten polymer is extruded vertically from an annular die into a cavity between two halves of a mould, in the form of a tube known as a parison. The mould is then closed, capturing the parison between the halves of the mould. Air is blown into the parison to force the molten polymer into contact with and to the shape of the walls of the mould. The melt is cooled by circulation of a cooling fluid through channels within the walls of the mould, after which the moulded part is removed. During extrusion and until it is captured by the halves of the mould, the parison undergoes deformation characterized by extension or stretching of the parison under the influence of its own weight; as the only influence on the parison is its weight, the deformation occurs under low levels of stress. For successful operation of the process, the polymer must exhibit sufficiently high melt viscosity under low stress that the parison is able to support itself without extensive drawing, sagging or thinning in localized areas.

In an extrusion process, polymer melt is extruded from a die in the form of a continuous profile which then enters a cooling chamber for solidification. The travel of the extrudate from the die to the cooling chamber is usually free from any surface, and in order to preserve the desired cross-sectional shape the extrudate needs to be able to support itself without undergoing excessive sagging. As with blow moulding processes, this also requires a polymer that has a sufficiently high melt viscosity under low levels of stress.

While high melt viscosity at low stress levels is required for the above processes, a moderately low melt viscosity is required under high levels of stress, and correspondingly high rates of flow, encountered in the extruder and die. A melt viscosity that is too high under these conditions leads to excessive pressure build- up and requires high torques for extrusion, which ultimately limits the rate of throughput obtainable from the extruder. Very high melt viscosity under these conditions may also lead to a phenomenon known as melt fracture where the surface of the extrudate becomes rough and wavy making the process difficult to operate and the resultant parts unacceptable.

The stress acting on a melt parison in a blow moulding process or on melt exudate during its travel from the die to the cooling chamber in an extrusion process is extensional in nature. However, it is extremely difficult to characterize melt viscosity of a polymer over a wide range of extensional stress, and melt viscosity measurements are commonly carried out over a wide range of shear stress. Polyamides are characterized by low melt viscosity under both high and low shear stress i.e. they tend to have poor melt sag resistance. Techniques that increase the melt viscosity under low shear stress also tend to increase the melt viscosity under high shear stress, with the result that the resultant polyamide compositions tend to be unacceptable for blow moulding or extrusion processes. Preferred characteristics for blow moulding and extrusion are high viscosity at low shear stress and moderately low melt viscosity under high shear stress levels. Polyamide compositions suitable for blow moulding and extrusion processes have how been found.

Accordingly, the present invention provides a blow moulding process in which a parison is formed from a polyamide composition, characterized in that said composition comprises:

(a) 55-90% by weight of a polyamide selected from the group consisting of (i) polyamides having a weight average molecular weight of greater than 25 000, and (ii) polyamides that are soluble in formic acid and which have an RV measured in formic acid of at least 40; and

(b) 10-45% by weight of a polymer selected from the group consisting of grafted polymer and mixtures of grafted polymer and ungrafted polymer, each of said grafted polymer and ungrafted polymer being independently selected from polyolefins having a melt index of less than 10 dg/min, the polyolefin of said grafted polymer having been grafted with 0.1-5.0% by weight of an ethylenically unsaturated carboxylic acid or anhydride, the grafted polymer being 25-100% by weight of the polymer of (b) ; and said composition exhibiting a relative increase in melt viscosity at low shear stress compared to the polyamide of (a) . The present invention also provides an extrusion process in which a profile is extruded from a polyamide composition, characterized in that said composition comprises:

(b) 10-45% by weight of a polymer selected from the group consisting of grafted polymer and mixtures of grafted polymer and ungrafted polymer, each of said grafted polymer and ungrafted polymer being independently selected from polyolefins having a melt index of less than 10 dg/ in, the polyolefin of said grafted polymer having been grafted with 0.1-5.0% by weight of an ethylenically unsaturated carboxylie acid or anhydride, the grafted polymer being 25-100% by weight of the polymer of (b) ; and said composition exhibiting a relative increase in melt viscosity at low shear stress compared to the polyamide of (a) .

In preferred embodiments of the processes of the invention, the polyamide has an amine end group content of at least 30 equivalents/10⁶ grams of polymer. The present invention also provides a polyamide composition comprising:

(b) 10-45% by weight of a polymer selected from the group consisting of grafted polymer and mixtures of grafted polymer and ungrafted polymer, each of said grafted polymer and ungrafted polymer being independently selected from polyolefins having a melt index of less than 10 dg/min, the polyolefin of said grafted polymer having been grafted with 0.1-5.0% by weight of an ethylenically unsaturated carboxylic acid or anhydride, the grafted polymer being 25-100% by weight of the polymer of (b) ; and said composition exhibiting a relative increase in melt viscosity at low shear stress compared to the polyamide of (a) . In a preferred embodiment of the composition of the invention, the polyamide has an amine end group content of at least 30 equivalents/10⁶ grams of polymer.

In the drawing. Fig. 1 illustrates melt viscosity-shear stress data for a number of compositions of Example I.

The invention relates to polyamide compositions and their use in certain processes viz. blow moulding and extrusion processes. The polyamide is a condensation polymer, commonly known as "nylon", having recurring units of aliphatic and/or aromatic amide groups in the molecular chain. Examples of aliphatic polyamides are nylon 6, nylon 66, nylon 610, nylon 612, and their related copolymers e.g. nylon 6/66. Aromatic polyamides may be formed from aromatic acids e.g. terephthalic and/or isophthalic acids, especially in which the diamine is hexamethylene diamine, 2-methyl pentamethylene diamine, dodecamethylene diamine and/or other related branched and unbranched dia ines. The polyamide forms 55-90% by weight of the composition, especially 60-85% of the composition.

In one embodiment of the invention, the polyamides used in the composition have a weight average molecular weight of greater than 25 000. Polyamides with a weight average molecular weight of less than 25 000 generally will not exhibit an acceptable melt viscosity at low shear rates. Preferably, the weight average molecular weight is less than 100 000, especially less than 50 000 for acceptable melt viscosity under high shear i.e. during extrusion. In another embodiment, the polyamides are soluble in formic acid, and the molecular weight of the polymers may be characterized in terms of relative viscosity (RV) , which is defined as the ratio of the viscosity of an 8.4% solution of the polymer (by weight) in 90% formic acid solvent to the viscosity of the formic acid solvent at room temperature. In this embodiment, the polyamides used in the compositions have an RV of at least about 40; such polymers are commercially available e.g. as injection moulding grade nylon polymers. Polymers with an RV of less than 40 will generally not exhibit an acceptable melt viscosity at low shear rates. The RV should be less than 200, preferably less than 100, for acceptable melt viscosity under high shear e.g. during extrusion. The polyamide preferably has an amine end group content of at least 30 equivalents/10⁶ grams of polymer, especially at least 35 equivalents/10⁶ grams of polymer, for acceptable compatibilization of the polyamide and polyolefin phases of the composition by the acid or anhydride-grafted polymers. At lower amine end group contents, the compatibilization of the nylon and polyolefin phases may be inadequate; this can manifest itself as, for example, insufficient enhancement of low shear viscosity or poor pinch-off strength in the blow moulded parts. Poor pinch-off strength occurs when two parts e.g. the two halves, of a finished blow moulded article are not bonded together with adequate strength, and the two halves may be readily pulled apart.

The polyolefins used in the present invention may be polyethylene, polypropylene, copolymers of two or more of ethylene, propylene, butene, hexene, octene, butadiene, hexadiene and related monomers, or olefinic thermoplastic elastomers. The polyolefins preferably have a low melt index i.e. a high melt viscosity; melt index is measured by the procedure of ASTM D-1238, at temperatures appropriate to the particular polymer. The melt index of the polyolefin should be less than about 10 dg/min, preferably less than about 2 dg/min. It is preferred to use a polyolefin with a density of less than about 0.94 g/cm³, especially less than about 0.935 g/cm³, to improve modification of the rheology of the composition and increase toughness of the fabricated articles. In especially preferred embodiments, at least part of the polyolefin is a low modulus elastomeric polymer e.g. ethylene/propylene/diene (EPDM) thermoplastic elastomer, to improve modification of the rheology of the composition and increase toughness.

The compatibilization between the nylon and polyolefin phases is achieved by the use of functionalized or grafted polymers that are reactive and/or comparative with both the nylon and polyolefin phases. The grafted polymers are polyolefins, as defined above, that have been grafted with acid and/or anhydride group-containing monomers. Examples of the acids and anhydrides, which may be mono-, di or polycarboxylic acids, are acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, itaconic anhydride, maleic anhydride, and substituted maleic anhydride e.g. dimethyl maleic anhydride or citraconic anhydride, nadic anhydride, nadic methyl anhydride and tetrahydric phthalic anhydride. Examples of the derivatives of the unsaturated acids are salts, amides, imides and esters e.g. mono- and disodium maleate, acrylamide, maleimide, glycidyl methacrylate and diethyl fu arate. The preferred grafting monomer is maleic anhydride. Such polymers should also have high viscosity, as characterized by low melt index which has to be measured at a temperature appropriate to the particular polymer. A melt index of less than about 10 dg/min is acceptable for the grafted polyolefins, with melt indices of less than 2 dg/min being preferred. The acid and/or anhydride graft level should be in the range of about 0.1%-5%, especially 0.3-4%, by weight. A method for the grafting of ethylenically unsaturated carboxylic acids or anhydrides onto polyolefins is described in U.S. Patent 4 612 155 of R.A. Zelonka and C.S. Wong, issued 1986 September 16. It is preferred to use grafted polymer with a density of less than 0.94 g/cm³, especially less than about 0.935 g/cm³, to improve modification of the rheology of the composition and increase toughness of the fabricated article. It is especially preferred that at least part of the grafted polymer is a grafted low moldulus elastomeric polymer e.g. ethylene-propylene- diene (EPDM) thermoplastic elastomer grafted with acid and/or anhydride group-containing monomers, to improve modification of the rheology of the composition and to increase toughness.

The polyolefins and grafted polymer are used in amount such that the ratio is in the range of about 0:1 to 3:1, by weight, especially 0.2 to 2.5:1.[start] Fillers and reinforcements used for improving physical mechanical properties of thermoplastic polymers may also.be incorporated into the compositions. Examples of such reinforcements and fillers are glass fibres, glass flakes, glass spheres, particulate minerals e.g. calcium carbonate, talc, mica, wollastonite, clay, silica and the like, minerals synthetic fibres e.g. calcium sulphate fibres, aramid fibres etc. The fillers and reinforcements, generally tend to increase the melt viscosity at low shear rates to higher values than for the equivalent unfilled or unreinforced compositions, and thus provide even greater resistance to melt sagging. [end]

The compositions may be prepared using conventional apparatus for the mixing and blending of polymer compositions, examples of which are single and multiple screw extruders, internal batch and continuous mixers, roll mills, kneaders and the like. Alternatively, the compositions may be prepared by dry mixing the components together, and melt fabricating the resulting mixtures directly into articles using blow moulding or extrusion processes.

The compositions may be used in blow moulding and extrusion processes e.g. in the manufacture of bottles, containers, hollow under-the-hood automotive components and other blow moulded articles, and in the manufacture of rods, tubing, cable jackets and other extruded profiles.

The invention is illustrated by the following examples.

Example I The shear rate - melt viscosity curves were determined for the polymer compositions listed below, at temperatures appropriate to the polymers in the compositions and using a Kayness capillary viscometer. Further details and the shear rate-melt viscosity data are tabulated in Table I.

The.composition were: Composition (a) is a comparative composition that is an injection moulding grade nylon 6 having a relative viscosity (RV) of 51;

Composition (b) is a comparative composition that is an injection moulding grade nylon 66 having an RV of 52; Composition (c) is a comparative composition that is an extrusion grade nylon 6 with an RV of 140;

Composition (d) is a comparative composition that is an extrusion grade nylon 6 with an RV of 253; Composition (e) is a comparative composition that is an extrusion grade nylon 6 with an RV of 285; Composition (f) is a blend, on a weight basis, of (i)

59.75% Nylon 66 having an RV of 52 and an amine end level of 55 equivalent/10⁶ g , (ii) 25% polyethylene having a melt index of 0.6 dg/min and a density of 0.919 g/cm³, (iii) 15% of a grafted polyethylene having a melt index of about 2 dg/min, a density of 0.92 g/cm³ and containing approximately 1% grafted maleic anhydride, and (iv) 0.25% of thermal stabilizers;

Composition (g) is a blend, on a weight basis, of (i) 59.75% nylon 6 having an RV of 46 and amine end level of 23 equivalents/10⁶ gm, (ii) 25% polyethylene having a melt index of 1.4 dg/min and a density of 0.92 g/cm³, (iii) 10% grafted polyethylene having a melt index of about 2 dg/min, a density of 0.92 g/cm³ and containing approximately 1% grafted maleic anhydride, (iv) 5% grafted ethylene-propylene-diene thermoplastic elastomer containing approximately 1.7% grafted fumaric acid, and (v) 0.25% of thermal stabilizers; Composition (h) is a blend, on a weight basis, of (i)69.75% nylon 6 having an RV of 48 and amine end level of 37 equivalents/10⁶ gm, (ii) 13% polyethylene having a melt index of 1.4 dg/min and a density of 0.92 g/cm², (iii) 6.5% grafted polyethylene with a melt index of about 2 dg/min, a density of about 0.92 g/cm³ and containing approximately 1% grafted maleic anhydride, (iv) 6.5% grafted ethylene-propylene-diene thermoplastic elastomer containing approximately 1.7% grafted fumaric acid, (v) 4.4% black pigment concentrate, and (vi) 0.25% of thermal stabilizers; Composition (i) is a blend, on a weight basis, of (i) 69.75% nylon 6 having an RV of 67 and amine end level of 51 equivalents/10⁶ gm, (ii) 13% polyethylene with a melt index of 1.4 dg/min and a density of 0.92 g/cm³, (iii) 6.5% grafted polyethylene with a melt index of about 2 dg/min, a density of about 0.92 g/cm³ and containing approximately 1% grafted maleic anhydride, (iv) 6.5% grafted ethylene-propylene-diene thermoplastic elastomer with approximately 1.7% grafted fumaric acid, (v) 4,4% black pigment concentrate, and (vi) 0.25% of thermal stabilizers; Composition (j) is a blend, on a weight basis, of (i) 69.75% nylon 6 having an RV of 140 and amine end level of 36 equivalents/10^ό gm, (ii) 13% polyethylene having a melt index of 1.4 dg/min and a density of 0.92 g/cm³, (iii) 6.5% grafted polyethylene having a melt index of about 2 dg/min, a density of about 0.92 g/cm³ and containing approximately 1% grafted maleic anhydride, (iv) 6.5% grafted ethylene-propylene-diene thermoplastic elastomer having approximately 1.7% grafted fumaric acid, (v) 4.4% black pigment concentrate, and (vi) 0.25% of thermal stabilizers;

Composition (k) is a blend, on a weight basis, of (i) 69.75% nylon 6 having an RV of 78 and amine end level of 14 equivalents/10⁶ gm, (ii) 13% polyethylene having a melt index of 1.4 dg/min and a density of 0.92 g/cm³, (iii)

6.5% grafted polyethylene having a melt index of about 2 dg/min, a density of about 0.92 g/cm³ and containing approximately 1% grafted maleic anhydride, (iv) 6.5% grafted ethylene-propylene-diene thermoplastic elastomer with approximately 1.7% grafted fumaric acid, (v) 4.4% black pigment concentrate, and (vi) 0.25% of thermal stabilizers; and

Composition (1) is a blend, on a weight basis, of (i) 69.75% nylon 6 having an RV an amine end level of 23 equivalents/10⁶ gm, (ii) 13% polyethylene having a melt index of 1.4 dg/min and a density of 0.92 g/cm³, (iii) 6.5% grafted polyethylene having a melt index of about 2 dg/min, a density of about 0.92 g/cm³ and containing approximately 1% grafted maleic anhydride, (iv) 6.5% grafted ethylene-propylene-diene thermoplastic elastomer having approximately 1.7% grafted fumaric acid, (v) 4.4% black pigment concentrate, and (vi) 0.25% thermal stabilizers.

In the above compositions, the polyethylene was an ethylene/butene-l copolymer containing 6.7% butene-1. The same type of polymer was used for the grafted polymer. The EPDM elastomer contained 70% by weight of ethylene, 26% by weight of propylene and 4% by weight of hexadiene.

The above compositions were prepared by dry mixing the components of the composition, and then melt blending the resultant mixture in a Werner & Pfleiderer 53 mm twin screw extruder at 250 rpm. For compositions based on nylon 6, a temperature profile of 210^βC in the feed section, 230-235^βC in the barrel section and 235°C at the die was used. For compositions based on nylon 66, a temperature profile of 240°C in the feed section, 270-280^βC in the barrel section and 280^βC at the die was used. The resulting polymer melt was pelletized to obtain the composition in the form of pellets.

Compositions were evaluated in blow moulding and extrusion processes. Blow moulding evaluation was carried out using a blow moulding apparatus with an accumulator head of 1.4 kg capacity and a representative mould for an automotive plenum chamber. Extrusion evaluation was carried out by making nominally 6 mm diameter tubing. A melt temperature of about 228^βC was used for nylon 6 compositions, and a melt temperature of about 265°C was used for nylon 66 compositions.

Compositions (a) and (b) are comparative examples of low RV nylon 6 and nylon 66 compositions that are intended for use in injection moulding apparatus. The melt viscosities are extremely low, compared with compositions required for blow moulding and extrusion.

Thus, these compositions are unsuitable for blow moulding and extrusion process.

Compositions (c) , (d) and (e) are comparative examples of nylon 6 compositions having higher RV values than Compositions (a) and (b) , and were evaluated in blow moulding processes. Compositions (c) and (d) were difficult to blow mould because the melt viscosities of these compositions at low levels of stress were not sufficiently high to prevent excessive sagging of the melt parison. Compositions (e) exhibited extremely high melt viscosity, which made the composition difficult to extrude into a parison at acceptable rates; however, the parison exhibited excellent resistance to sagging under its own weight. Compositions (f) , (g) , (h) and (i) illustrate the present invention. Compositions (f) and (g) were evaluated in small diameter tubing extrusion process. Both compositions were processed successfully into tubing with nominal diameter of about 6 mm. Compositions (h) and (i) were evaluated in the blow moulding operation, and compared against high RV nylon 6 compositions (c) , (d) and (e) . In a blow moulding operation involving the same size of parison, the stress acting on the parison due to the weight of the parison will be the same for all compositions, thereby providing a comparison at common levels of stress.

In a blow moulding process. Compositions (h) and (i) exhibited excellent resistance to melt sagging, and yet were easy to extrude at high throughput. It took less than half the time to extrude sufficient melt to make the blow moulded parts, as compared with the time required for Composition (e) . Composition (i) exhibited even greater resistance to sagging than (h) , due to the higher RV of the nylon 6 composition. Composition (j) is similar to Composition (h) , except that it is based on nylon 6 with a substantially higher RV. This composition exhibited extremely high melt viscosity ,at high shear stress, and was extremely difficult to extrude into parisons. Composition (i) is also similar to Composition (h) , except that it is based on nylon 6 with higher RV but a lower level of amine ends. Blow moulding evaluation of this composition showed that although it has sufficiently high viscosity at low stress levels to exhibit good resistance to melt parison sagging, it lacked so-called pinch-off strength, which is defined as the stress necessary to pull apart two halves of the moulded article bonded by pinch-off in the mould cavity, after the article has been moulded. Composition (1) is similar to (h) , being based on nylon 6 with a low level of amine ends. While t is possible to blow mould this composition, its resistance to sagging of the parison was not as great as that of either of Compositions (h) or (i) . Figure 1 illustrates melt viscosity - shear stress relationships for Compositions (c) , (d) , (e) , (h) and (i) . In the case of the high RV nylon 6 compositions (c) , (d) and (e) , the melt viscosity curve flattens out towards the low shear stress end, and the viscosity does not show a rapid rise as the shear stress is reduced; consequently, any attempt to increase the melt viscosity at low stress by increasing the molecular weight i.e. increasing RV, also increases the melt viscosity under high shear stress levels thereby making the composition difficult to extrude. In contrast, Compositions (h) and (i) exhibit a completely different behaviour, characterized by a steep viscosity curve with the melt viscosity rising sharply as the shear stress is reduced. Such high viscosity at low shear stress levels provides excellent resistance to melt sagging or drawing of the parison during a blow moulding operation. On the other hand, the melt viscosity drops to low values at high shear stress, below that of Compositions (c) , (d) or (e) , which allows for relatively easy extrusion of material. Thus, the present invention provides a way of modifying rheology of relatively low molecular weight polyamides such that the resistance to melt sagging is improved without comprising the ease of extrusion.

TABLE I Shear Rate - Viscosity Relationships

Comp. Temp.< Shear Rate (1/s)—

(°C) 0.087 0.174 0.26 0.347 0.52

Shear Rate - Viscosity Relationships (cont.)

Comp. Temp. < Shear Rate (1/s)

CO 25 100 350 830 1200 (b) 280 250 270 230 190 170

Note: Data for Composition (e) is representative data, as melt viscosity data was changing during measurement.

MF « melt fracture occurred.

Viscosity is reported in Pa.s

The samples of the compositions were dried at 80°C for two hours in a dehumidified drier to moisture levels below 0.05% by weight prior to measurements being conducted.

The data represent apparent viscosity and shear stress; Bagley and Robinowitch corrections were not applied.

Example II

Short glass fibre reinforced compositions were prepared by melt blending and uniformly dispersing various levels of short glass fibres into Composition (h) of Example I. On a weight basis, these compositions were nominally as follows: Composition (m) . 87% Composition (h) 13% short of Example 1 glass fibres

Composition (n) 80% Composition (h) 20% short of Example 1 glass fibres Composition (o) 75% Composition (h) 25% short of Example 1 glass fibres Composition (p) 70% Composition (h) 30% short of Example 1 glass fibres

The melt blending and glass dispersion was carried out in a 53 mm,Werner and Pfleiderer twin screw extruder running at 200 rpm using a temperature profile of 210°C in the feed section, 230-235^βC in the barrel section and 235 -C at the die. In each case, the resulting melt was pelletized to obtain the composition in the form of pellets.

The shear rate-viscosity relationships for these compositions were determined using a Kayness capillary viscometer at 240°C. The data are tabulated in Table II.

TABLE II

Shear Rate - Viscosity Relationships

Viscosity is reported in units of Pa.s The samples of the compositions were dried at 80°C for two hours in a dehumidified drier to moisture levels below 0.05% by weight prior to measurements being conducted.

The data represent apparent viscosity and shear stress; Bagley and Robinowitch corrections were not applied. Compositions were evaluated in the blow moulding process of Example I. The mould used was designed to produce hollow rectangular plaques measuring roughly 42 x 10 x 5 cm. It had inserts to produce either textured sections or two square draw pockets measuring approximately 3.8 x 3.8 x 0.6 cm and 1.9 x 1.9 x 0.6 cm on one side of the blow moulded parts. The draw pockets provide a measure of the ability of the composition to be drawn into features representing sharp changes in geometry. A melt temperature of about 235°C was used for blow moulding evaluation of all of the compositions. All of the compositions exhibited excellent resistance to melt sagging. Compared to the unreinforced composition (h) of Example 1, the above composition exhibited significantly lower die swell in the thickness and diameter of the parison. All the compositions were able to produce good blow moulded parts when the textured insert was used in the mould. When the insert with square draw pockets was used, compositions (m) and (n) produced good parts. In case of compositions (o) and (p) , the draw pockets were not sharply defined and had thin rounded corners. This indicates a reduced drawability of the melt at higher glass loadings.

Claims

CLAIMS :

1. A blow moulding process in which a parison is formed from a polyamide composition, characterized in that said composition comprises:

(b) 10-45% by weight of a polymer selected from the group consisting of grafted polymer and mixtures of grafted polymer and ungrafted polymer, each of said grafted polymer and ungrafted polymer being independently selected from the polyolefins having a melt index of less than 10 dg/min, the polyolefin of said grafted polymer having been grafted with 0.1-5.0% by weight of an ethylenically unsaturated carboxylic acid or anhydride, the grafted polymer being 25-100% by weight of the polymer of (b) ; and said composition exhibiting a relative increase in melt viscosity at low shear stress compared to the polyamide of (a) .

2. An extrusion process in which a profile is extruded from a polyamide composition, characterized in that said composition comprises:

(b) 10-45% by weight of polymer selected from the group consisting of grafted polymer and mixtures of grafted polymer and ungrafted polymer, each of said grafted polymer and ungrafted polymer being independently selected from polyolefins having a melt index of less than 10 dg/min, the polyolefin of said grafted polymer having been grafted with 0.1-5.0% by weight of an ethylenically unsaturated carboxylic acid or anhydride, the grafted polymer being 25-100% by weight of the polymer of (b) ; and said composition exhibiting a relative increase in melt viscosity at low shear stress compared to the polyamide of (a) .

3. The process of Claim 1 or Claim 2 in which the polyamide has an amine end group content of at least 30 equivalents/10⁶ grams of polymer.

4. The process of any one of Claims 1-3 in which the weight average molecular weight of any polyamide of (a) (i) is less than 100 000 and the RV of any polyamide of (a) (ii) is less than 200.

5. The process of any one of Claims 1-4 in which the polyamide is a polyamide of (a) (i) .

6. The process of any one of Claims 1-4 in which the polyamide is a polyamide of (a) (ii) .

7. The process of any one of Claims 1-6 in which the polyamide is an aliphatic polyamide.

8. The process of any one of Claims 1-7 in which the polyolefin is grafted with maleic anhydride.

9. A polyamide composition comprising:

(a) 55-90% by weight of a polyamide selected from the group consisting of (i) polya dies having a weight average molecular weight of greater than 25 000, and (ii) polyamides that are soluble in formic acid and which have an RV measured in formic acid of at lest 40; and

(b) 10-45% by weight of a polymer selected from the group consisting of grafted polymer and mixtures of grafted polymer and ungrafted polymer, each of said grafted polymer and ungrafted polymer being independently selected from polyolefins having a melt index of less than 10 dg/min, the polyolefin of said grafted polymer having been grafted with 0.1-5.0% by weight of an ethylenically unsaturated carboxylic acid or anhydride, the grafted polymer being 25-100% by weight of the polymer of (b) ; and said composition exhibiting a relative increase in melt viscosity at low shear stress compared to the polyamide of (a) .

10. The composition of Claim 9 in which the polyamide has an amine end group content of at least 30 equivalents/10⁶ grams of polymer.

11. The compositions of Claim 9 or Claim 10 in which the weight average molecular weight of any polyamide of (a) (i) is less than 100 000 and the RV of any polyamide of (a) (ii) is less than 200.

12. The composition of any one of Claims 9-11 in which the polyamide is a polyamide of (a) (i) .

13. The composition of any one of Claims 9-11 in which the polyamide is a polyamide of (a) (ii) .

14. The composition of any one of Claims 9-13 in which the polyolefin is grafted with maleic anhydride.