GB2226035A

GB2226035A - Polymeric blends

Info

Publication number: GB2226035A
Application number: GB8900656A
Authority: GB
Inventors: John Nigel Gaitskell
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1989-01-12
Filing date: 1989-01-12
Publication date: 1990-06-20
Also published as: GB8900656D0

Abstract

Blends of polyamides such as nylons, especially nylon 6:6, and crystalline polyolefins, particularly polypropylene and including at least two and preferably three components selected from i) a polyolefin rubber, ii) a first graft copolymer derived from a crystalline polyolefin, and iii) a second graft copolymer derived from a polyolefin rubber; the graft copolymers being obtained by grafting functional groups, especially maleic anhydride residues, onto the respective polymer, the graft copolymer(s) acting to compatibilise the blend, have an improved combination of toughness, water absorption and stiffness (especially at elevated temperatures such as are used in stoving paints).

Description

POLPMERIC BLENDS This invention relates to polymeric blends and, in particular, to polyamide/polyolefin blends.

Palyamide/polyolefin blends are known valuable raw materials, both without and with additional additives and/or reinforcements, which have many applications. Owing to the inherent incompatibility between polymers in blends, it is usually necessary to prepare polyamide/polyolefin blends by adding a compatibilising agent such as an acid or anhydride graft copolymer of an olefin, for example as disclosed in UK Patent No 1403797.

Whilst the physical properties of such ternary blends enable them to be used in many applications, the low temperature impact resistance of such blends is too low for them to be considered for use in certain applications, for example motor vehicle body panels.

There is some evidence (see for example Polymer Blends, Processing, Morphology and Properties, Ed Martuscelli, Palumbo & BR< Kryszewski, Plenum Press, 1980, pages 191-200 and Polymer Blends, Processing, Morphology and Properties, Vol 2, Ed Kryszewski, Gateski & BR< Martuscelli, Plenum Press, 1984, pages 41-56) that binary systems, in which all of the polyolefin is in the form of the graft copolymer, have good impact resistance. However, in relation to applications such as body panels, such toughened polyamides have disadvantages of high cost and relative high moisture absorption properties, the latter affecting modulus and dimensional stability of the component.

Similarly, many binary polyolefin systems, eg polypropylene toughened with ethylene/propylene rubber, have insufficient stiffness to maintain dimensional stability at paint oven temperatures.

It is an object of the present invention to provide polyamide/polyolefin blends in relation to which one or more of the aforementioned disadvantages is or are reduced or obviated.

According to the present invention, a polymeric blend comprises at least one polyamide, at least one crystalline polyolefin and at least two components selected from a polyolefin rubber, a first graft copolymer derived from a crystalline polyolefin and a second graft copolymer derived from a polyolefin rubber, said graft copolymers being obtained by grafting functional groups onto the respective polymer whereby said first and/or said second graft copolymer, by interaction of said functional groups with said polyamide, compatibilises said blend.

By "crystalline polyolefin" we mean polyolefins in which at least some of the polymer chains are assembled into crystallites.

Such polyolefins give characteristic x-ray diffraction patterns and exhibit significant melting peaks in equipment such as differential scanning calorimetors.

By "polyolefin rubber" we mean polyolefins which are substantially amorphous but which may contain small amounts of a crystalline phase.

The polyamides used in blends of the invention are thermoplastic polymers obtained by polycondensation of diamines with dicarboxylic acids or by self-condensation of amino acids or lactams.

More particularly, the polyamides are linear polyamides which have fibre-forming characteristics and are usually referred to as "nylon" and includes the following polymers:polyhexamethylene adipamide (nylon 6:6) polycaprolactam (nylon 6 ) polydodecanlactam (nylon 12 ) polyhexamethylene sebacamide (nylon 6:10) polyhexamethylene isophthalamide (nylon 6:iP) polyhexamethylene terephthalamide (nylon 6:T) polymetaxylylene adipamide (nylon MXD:6) polyundecanomide (nylon 11) and copolymers therefrom. Preferred polymers are polyhexamethylene adipamide and polycaprolactam and copolymers or mixtures thereof.

The crystalline polyolefin used in blends of the invention includes one or more polymerised olefin monomers, for example polymers of ethylene or propylene and copolymers and block copolymers of those monomers with each other or with other olefin monomers. Preferred polymers are polypropylene and block copolymers of propylene and up to 25%, preferably up to 10%, by weight of ethylene.

The polyolefin rubber used in blends of the invention includes one or more polymerised olefin monomers, for example polymers of ethylene and propylene and copolymers of those monomers with each other or with other olefin monomers or other polymerisable monomers, particularly monomers having diene configurations. Preferred polymers are ethylene/propylene copolymers having an ethylene content of at least 30% by weight, preferably between 45% to 80%.

The graft copolymers used in blends of the invention are preferably obtained by grafting an unsaturated dicarboxylic acid or the anhydride thereof onto the respective polymer. The unsaturated acid or anhydride may be any acid or anhydride which reacts with the respective polymer to form the respective graft copolymer having the required compatibilising properties. Preferred compounds are maleic acid, itaconic acid or, particularly, maleic anhydride.

Preferred graft copolymers used in blend of the invention are grafted using maleic anhydride. The first graft copolymer preferably has both a grafted anhydride content and a residual free anhydride content of between 0.5t to 5%, more particularly 1% to 2%, preferably 1.4% to 1.6%, by weight. The second graft copolymer preferably has a grafted anhydride content of 0.5% to 5%, more particularly 0.8% to 1% by weight and a residual free anhydride content of up to 2%, more particularly up to 0.5% by weight.

Preferably, the graft copolymers are obtained by grafting the functional groups onto polymers of the same olefins as the crystalline polyolefin and the polyolefin rubber, respectively. Although the polymers used in the grafting process need not be identical to the other polyolefins, they are preferably of the same general type.

Preferably, the first graft copolymer is derived from polypropylene or block copolymers of propylene and up to 25, preferably up to 10%, by weight of ethylene. Preferably, the second graft copolymer is derived from ethylene/propylene copolymers having an ethylene content of at least 30% by weight, preferably between 45% to 80%.

In preferred blends according to the invention, the proportions of the components, if present, are within the following prefeTred percentage (by weight) ranges:polyamide: 205 to 80%, preferably 30% to 40Z; crystalline polyolefin: 20% to 80%, preferably 30% to 50%; polyolefin rubber: ~ 0t to 25, preferably 5% to 205; first graft copolymer: 0% to 10%, preferably 3% to 7%; and second graft copolymer : 0% to 25%, preferably 3% to 15%.

Preferably, the total amount of graft copolymer in the blend is between 1% to 20%, preferably between 3% and 15%, and more particularly between 7% and 11%.

Although four component blends, eg containing polyamide and crystalline polyolefin together with two out of three of the components polyolefin rubber and first and second graft copolymers, are within the scope of the invention, preferred blends according to the invention comprise all five components.

Thus, in a particularly preferred embodiment of the invention, a polymeric blend comprises 30% to 40% by weight of a polyamide, 30% to 50t by weight of a propylene polymer or block copolymer thereof with up to 25% by weight of ethylene, 10% to 20% by weight of a copolymer of ethylene and propylene containing at least 50% by weight of ethylene, 3% to 7% by weight of said first graft copolymer and 3% to 15% of said second graft copolymer.

Preferably, at least a proportion of said polyamide has a number average molecular weight of at least 20,000 and, more particularly, at least 23,000.

The polymeric blends of the invention can contain various stabilisers, lubricants and other additives as is well known in the art. The blends may also contain fillers and/or reinforcements such as powdered minerals and glass, carbon or organic fibres or combinations thereof.

The invention is illustrated by reference to the following Example.

Example A number of blends (see Tables 1 to 3) were made.

In each case, the appropriate granular or powdered components were tumbled-mixed together to form a substantially homogeneous dry blend. The dry blend was then metered into the feed pocket of a corotating twin-screw compounding extruder (Werner & Pfleider ZSK-30).

the extruder bad an approximate length to diameter ratio for each screw of 32 , with a barrel length of 10 sections. The feed pocket was situated in barrel section 1 and the extrusion die was attached to barrel section 10. Vent ports were situated at barrel sections 4 and 9, vacuum being applied to the latter vent port. The vent port at section 4 was either left open to atmosphere or closed, either condition being satisfactory.

The co-rotating, intermeshing screws of the extruder each consisted of a similar series of Werner & Pfleider conveying or kneading components (of two start or twin lobe type) arranged to provide a conveying, melting and intimate mixing action on the blend components, decompression zones at barrel sections 4 and 9 and extrusion pressure at the extrusion die. Two different configurations of the conveyingXkneading components were used (designated screw profile 1 or 2 in Table 4), both adequately fulfilling the requirements.

Extrusion conditions are given in Table 4, the melt temperatu quoted being measured near the extrusion die.

The extruded laces were water-bath quenched, superficially dr and cut into pellets. The pellets were vacuum oven dried under reduced pressure at about 900C for 18 hours. The pellets were then moulded into the required test pieces using conventional screw preplasticising injection moulding machines. Typically, the set barrel temperatures ranged from about 260"C at the hopper end to about 2700C or 2800C at the nozzle end. For blends 14 to 19, the temperature profile was reversed to give about 2700C at the hopper end to about 2550C at the nozzle end. In all cases, the moulds were water heated to about 700C to 80 C. Other moulding machine settings were chosen to give good quality test pieces.

The Applicants found it was important to add the components to the extruder during a single extrusion operation, because tests involving blends in which the polyamide and the second graft copolymer were added as a preformed component appeared to give inferior results.

However, the compositions of the invention could also be prepared by adding various components at different openings in an extruder barrel during the same extrusion operation.

In Table 1, blends 1 and 2 are three component blends, for example similar to the blends disclosed in GB 1403797, which have been included for comparison with blends 3 to 20 which are blends according to the inventiç In Table 1, the tests have been determined as follows: FLEZURAL MODULUS: was determined using the method of ISO 178-i975.

Test pieces were the parallel-sided central portions of injectionmoulded tensile bars (as for ISO 527-1966(E), type 1 test specimen) about lOmm wide x 3.2mm thick. A span of 50mm was used and the test machine crosshead speed was 10mm/ min except for blends 7, 8 and 9 when it was 2mm/ min.

NOTCHED IZOD: was determined using the method of ISO 180-1982(E), method designation ISO 180/4A. The notches were moulded into the test pieces for all blends except 20, the test pieces for blend 20 having a notch of standard dimensions machined therein.

DROP WEIGHT IMPACT:was measured using an apparatus in which a loaded striker having a hemispherical lower end falls vertically to impact a test piece resting horizontally and unclamped on an annular support ring. The striker is guided to fall under gravity along the axis passing through the centre of the support ring normal to the plane thereof.

Although the specific apparatus used is proprietory to ICI, the test configuration is generally as described in draft international standard ISO/DIS6603-2. The test parameters used were: - mass of loaded striker 10.0 kg diameter of hemispherical end 12.7 mm internal diameter of support ring 5G mm height through which striker falls to hit the test piece 190C mm A rapid-response, transducer is located near to the hemispherical end of the striker.

The output from the transducer is fed to a computer which measures force as a function of time during a test and, knowing the terminal speed of the shaft at impact, is able to calculate a total energy absorption figure (in joules) for the impact on the specimen. The impact values quoted in Table 1 are the mean values of five tests for each blend.

The test specimens were 3 mm to 3.2 mm thick and were either in the form of 115 mm diameter discs (blends 7, 8 and 10 to 20) or 80 mm squares (blends 1 to 6 and 9). The discs were made by injection moulding into side-gated moulds. The squares were quarter portions of 160 mm squares which were moulded by gating along one edge from a coathanger-shaped runner which gave a substantially uniform advancing melt front during moulding.

CONDITIONING: all test specimens were left in containers of dry air for at least five days before testing. The specimens were tested dry and as moulded at the temperatures stated in Table 1. For the -300C tests, the specimens were equilibriated to that temperature immediately prior to the test.

In Table 1, the components are as follows: A is the polyamide; B is the crystalline polyolefin; C is the polyolefin rubber; D is the first graft copolymer and is a maleinised block copolymer of propylene and up to 10% ethylene containing about 1.5% by weight of grafted maleic anhydride and about 1.5% by weight of free anhydride. A typical preparation of such a polymer is described in GB1403797. The same copolymer was used in all of the blends in powdered form having been cryogenically ground; and E is the second graft copolymer and is a maleinised copolymer of ethylene (about 805 by weight) and propylene containing about 1.0t by weight of grafted maleic anhydride and less than 0.5% by weight of free maleic anhydride. The preparation of the copolymer is similar to that of the first graft copolymer, but it was used in pellet form. The same copolymer was used in all of the blends except blend 20 in which was used EXXELOR VA1801 (trade name of Exxon Corp). EXXELOR VA1801 is an ethylene/propylene graft copolymer having a total maleic anydride content of approximately 0.7% by weight.

Table 2 identifies the specific components used in the blends by trade name or code and Table 3 identifies the compositions A to C represented by the trade name or code.

TABLE 1

BLEND COMPONENT (% BY WEIGHT) FLEXURAL NOTCHED IZOD DROP WEIGHT NO MODULUS (kJ/m) IMPACT (J) A B C D E (GPa) AT23 C AT -30 C AT 23 C AT -30 C 1 40 56 - 4 - 1.6 11 6.7 3.7 2.2 2 40 56 - 4 - 1.6 6.9 6.4 4.8 1.2 3 40 44 - 4 12 0.9 21 8.7 7.5 3.3 4 40 44 - 4 12 0.9 45 8.0 20 3.1 5 40 44 12 4 - 1.3 13 10 12 4.4 6 30 54 12 4 - 1.1 8.7 6.1 25 9.1 7 30 54 12 4 - 1.1 16 9.5 24 4.0 8 36 44 11 - 9 0.8 38 15 13 5.4 9 36 42 9 4 9 0.8 64 32 25 8.2 10 36 44 11 4 5 1.0 84 20 27 5.6 11 36 44 11 4 5 0.9 88 14 32 14 12 36 44 11 4 5 1.0 87 15 32 16 13 36 38 17 4 5 1.0 96 21 32 13 14 35 45 11 4 5 0.9 63 22 27 17 15 35 45 11 4 5 0.9 38 16 21 17 16 35 45 11 4 5 0.9 41 15 24 12 17 35 45 11 4 5 1.0 53 17 28 19 18 35 39 17 4 5 1.0 62 21 28 26 19 35 39 17 4 5 0.9 29 17 17 12 20 35 39 17 4 5 1.0 54 10 28 11 TABLE 2

BLEND COMPONENT (TRADE NAME OR CODE)* NO (For covenience, in many instances the full trade name is given in Table 3 only) A B C 1 A117 PROPATHENE GWN 213 2 A117 GXM 214 3 A117 GXM 214 4 A117 GWM 213 5 A146 GWM 213 EXXELOR V808 6 A146 GWM 213 EXXELOR V808 7 A146 GWM 213 EXXELOR V808 8 A146 GWM 213 EXXELOR V808 9 A117 GWM 213 EXXELOR V808 10 A144 GWM 213 EXXELOR V808 11 A146 GWM 213 EXXELOR V808 12 A148 GWM 213 EXXELOR V808 13 A146 GWM 213 EXXELOR VM23 14 A146 GWM 213 EXXELOR V808 15 A146 GWM 213(22.5%)/GXM 214(22.5%) EXXELOR V808 16 A117(5%)/A146(30%) GWM 213(22.5%)/GXM 214(22.5%) EXXELOR V808 17 B300(5%)/A146(30%) GWM 213(22.5%)/GXM 214(22.5%) EXXELOR VM23 18 A146 GWM 213 EXXELOR VM22 19 A146 GX 214 EXXELOR VM23 20 A146 GWM 213 EXXELOR VM23 *Unless otherwise indicated, all of the trade names or codes belong to Imperial Chemical Industries plc.

EXXELOR is the trade name of Exxon Corp.

TABLE 3

TRADE NAME COMPOSITION OR CODE MARANYL A117 Nylon 6:6 generally having a number average molecular weight of 16500-18000 MARANYL A144 Nylon 6:6 generally having a number average molecular weight of 18500-23000 MARANYL A146 Nylon 6:6 generally having a number average molecular weight of 23000-28000 MARANYL A148 Nylon 6::6 generally having a number average molecular weight of 28000-32000 MARANYL B300 Nylon 6 generally having a number average molecular weight of 17000-19000 PROPATHENE GWM 213 Polypropylene PROPATHENE GXM 214 Polypropylene EXXELOR V808 Ethylene (approx (approx 75% by weight)/propylene rubber EXXELOR VM22 Ethylene/propylene rubber (60% by weight/polypropylene (40% by weight) blend EXXELOR VM23 Ethylene/propylene rubber (60% by weight/polypropylene (40% by weight) blend TABLE 4 BLEND NO PROFILE SCREW SPEED FEED RATE *MEASURED MELT (REV/MIN) (kg/hour) TEMP (oC) 1 1 275 20 294 2 1 275 20 289 3 2 275 20 297 4 1 275 20 296 5 1 275 20 296 6 1 275 20 293 7 2- 275 25 289 8 2 275 25 293 9 1 275 20 295 10 2 275 25 292 11 2 275 25 292 12 2 275 25 291 13 2 275 25 293 14 2 275 25 286 15 2 275 25 287 16 2 275 25 286 17 2 275 25 286 18 2 275 25 287 19 2 275 25 284 20 2 275 25 298 * All barrel zones were set to 280"C for each blending operation.

The reduced pressure measured during each blending operation at the vent port in barrel section 9 was less than ambient atmospheric pressure by about 685 mm to 710 mm (27 to 28 inches) of mercury.

Claims

Claims

1. A polymeric blend comprising at least one polyamide, at least one crystalline polyolefin and at least two components selected from a polyolefin rubber, a first graft copolymer derived from a crystalline polyolefin and a second graft copolymer derived from a polyolefin rubber, said graft copolymers being obtained by grafting functional groups onto the respective polymer whereby said first and/or said second graft copolymer, by interaction of said functional groups with said polyamide, compatibilises said blend.

2. A blend according to claim 1, in which said polyamide is polyhexamethylene adipamide, polycaprolactam, polydodecamlactam, polyhexamethylene sebacamide, polyhexamethylene isopthalamide, polyhexamethylene terephthalamide, polymetaxylylene adipamide or polyundecanomide or copolymers therefrom or mixtures thereof.

3. A blend according to claim 1 or claim 2, in which at least a portion of said polyamide has a number average molecular weight of at least 20,000.

4. A blend according to any one of the preceding claims, in which said polyamide comprises 20% to 80% by weight of the blend.

5. A blend according to any one of the preceding claims, in which said polyamide comprises 30% to 405 by weight of the blend.

6. A blend according to any one of the preceding claims, in which said crystalline polyolefin is polypropylene or a block copolymer of propylene with up to 25% by weight of ethylene.

7. A blend according to any one of the preceding claims, in which said crystalline polyolefin comprises 20% to 80% by weight of the blend.

8. A blend according to any one of the preceding claims, in which said crystalline polyolefin comprises 30% to 50% by weight of the blend.

9. A blend according to any one of the preceding claims, in which said polyolefin rubber is an ethylene and propylene copolymer having an ethylene content of at least 305.

P. A blend accordng to claim 9, in which the ethylene content of the covcR-çmer is between 45% to 80%.

il. A blend according to anyone of the preceding claims, in which said polyolefin rubber comprises 0% to 25% by weight of the blend.

12. A blend according to anyone of the preceding claims in which said polyolefin rubber comprises 5% to 20% by weight of the blend.

13. A blend according to any one of the preceding claims, in which said functional groups are derived from maleic acid, itaconic acid or maleic anhydride.

14. A blend according to any one of claims 1 to 13, in which said functional groups are derived from maleic anhydride and in which said grafted copolymers have both a grafted anhydride content and a residual free anhydride content of between 0.5% and 5% by weight.

15. A blend according to any one of the preceding claims, in which the polymer from which said first graft copolymer is derived is polypropylene or a block copolymer of propylene with up to 25% by weight of ethylene.

16. A blend according to any one of the preceding claims, in which the polymer from which said second graft copolymer is derived is an ethylene and propylene copolymer having an ethylene content of at least 30%.

17. A blend according to claim 16, in which the ethylene content of the copolymer is between 45% to 80%.

18. A blend according to any one of the preceding claims, in which said first graft copolymer comprises up to 10% by weight of the blend.

19. A blend according to any one of the preceding claims, in which said first graft copolymer comprises up to 5% by weight of the blend.

20. A blend according to any one of the preceding claims, in which said second graft copolymer comprises up to 25% by weight of the blend.

21. A blend according to any one of the preceding claims, in which said second graft cooplymer comprises between 3% and 15% by weight of the blend.

22. A blend according to any one of the preceding claims, in which the total amount of graft copolymer in the blend is between 1% and 20% by weight.

23. A blend according to any one of the preceding claims, in which the total amount of graft copolymer in the blend is between 3, and 15% by weight.

24. A blend according to any one of the preceding claims, in which the total amount of graft copolymer in the blend is between 7% and 11Z by weight.

25. A blend according to any one of the preceding claims, comprises said polyamide, said crystalline polyolefin and two out of three of said polyolefin rubber and said first and second graft copolymers.

26. A blend according to any one of claims 1 to 24, comprises said polyamide, said crystalline polyolefin, said polyolefin rubber and said first and second graft copolymers.

27. A blend according to any one of the preceding claims, which optionally includes stabilisers, lubricants, fillers and/or reinforcements.

28. A process for the production of a blend as claimed in any one of the preceding claims, in which the components are blended together during a single extrusion operation.

29. A blend according to claim 1 substantially as hereinbefore described with reference to the Example.