POLYAMIDE MIXTURE HAVING IMPROVED FLUIDITY

Abstract

The invention relates to a thermoplastic composition having improved fluidity in the molten state, comprising at least: (a) a polyamide that has a melt viscosity greater than or equal to 50 Pa.Math.s, and (b) a non-evolutive polyamide having a melt viscosity lower than the melt viscosity of said polyamide (a), above 0.8 Pa.Math.s, and having a number-average molecular weight Mn lower than that of said polyamide (a), said composition having a melt viscosity that is stabilized at a value below the melt viscosity of said polyamide (a), said polyamide (b) having: a concentration of amine end groups (AEG) and/or of carboxyl end groups (CEG) less than or equal to 20 meq/kg, or a concentration of amine end groups (AEG) greater than or equal to 25 meq/kg; a concentration of acid end groups (CEG) greater than or equal to 25 meq/kg; and a concentration of blocked end groups (BEG) greater than or equal to 25 meq/kg.

Claims

1. A thermoplastic composition having improved fluidity in the molten state, comprising at least: (a) a polyamide that has a melt viscosity greater than or equal to 50 Pa.Math.s, and (b) a non-evolutive polyamide having a melt viscosity lower than the melt viscosity of said polyamide (a), above 0.8 Pa.Math.s, and having a number-average molecular weight Mn lower than that of said polyamide (a), said composition having a melt viscosity that is stabilized at a value below the melt viscosity of said polyamide (a), said polyamide (b) having: a concentration of amine end groups (AEG) and/or of carboxyl end groups (CEG) less than or equal to 20 meq/kg, or a concentration of amine end groups (AEG) greater than or equal to 25 meq/kg; a concentration of acid end groups (CEG) greater than or equal to 25 meq/kg; and a concentration of blocked end groups (BEG) greater than or equal to 25 meq/kg.

2. The composition as claimed in claim 1, in which the content of polyamide (b) is from 5 wt % to 50 wt % relative to the total weight of the composition.

3. The composition as claimed in claim 2, in which the content of polyamide (b) is from 5 to 20 wt % relative to the total weight of the composition.

4. The composition as claimed in claim 3, in which the content of polyamide (b) is from 5 to 12 wt % relative to the total weight of the composition.

5. The composition as claimed in claim 1, in which polyamides (a) and (b) are structurally similar to one another, or are derived from the same polyamide, and the melting point of polyamide (b) being less than or equal to that of polyamide (a).

6. The composition as claimed in claim 1, having a melt viscosity below 50% of the melt viscosity of said polyamide (a).

7. The composition as claimed in claim 1, having a melt viscosity that increases, at most by 25%, relative to its initial value for a time of at least 15 minutes, at constant temperature and pressure under an inert atmosphere.

8. The composition as claimed in claim 1, said polyamide (b) having a melt viscosity below 50 Pa.Math.s.

9. The composition as claimed in claim 1, in which said polyamide (b) has a concentration of amine end groups (AEG) and/or of carboxyl end groups (CEG) less than or equal to 15 meq/kg.

10. The composition as claimed in claim 1, said polyamide (b) having a number-average molecular weight Mn between 5000 and 8500 g/mol.

11. The composition as claimed in claim 1, said polyamide (a) having a melt viscosity ranging from 50 to 2000 Pa.Math.s.

12. The composition as claimed in claim 1, said polyamide (a) having a number-average molecular weight Mn between 8000 and 40000 g/mol.

13. The composition as claimed in claim 1, in which said polyamides (a) and (b) are selected independently of one another from the polyamides resulting from the polycondensation of at least one aliphatic dicarboxylic acid with an aliphatic or cyclic diamine, the polyamides resulting from polycondensation of at least one aromatic dicarboxylic acid and an aliphatic or aromatic diamine, the polyamides obtained by polycondensation of at least one amino acid or lactam with itself, or mixtures thereof and (co)polyamides.

14. The composition as claimed in claim 1, said polyamides (a) and (b) being selected independently of one another from the group consisting of: PA 66, PA 6.10, PA 6.12, PA 12.12, PA 4.6, MXD 6, PA 6, PA 7, PA 9T, PA 10T, PA 11, PA 12, PA 6T/6I, PA 6T/6I/66, the copolyamides derived therefrom, and mixtures thereof.

15. The composition as claimed in claim 1, said polyamides (a) and (b) comprising, independently of one another, hydroxyaromatic units bound chemically to the chain of the polyamide.

16. A method for manufacturing a composite comprising at least one step of impregnation of a reinforcing fabric with a composition as claimed in claim 1 in the molten state.

17. A composite article obtained by the method as claimed in claim 16.

18. (canceled)

Description

EXAMPLES

[0188] Protocols and Methods

[0189] The melt viscosities of the polyamides employed were measured using a Rheometrics RDA3 rheometer (a rheometer comprising a 25-mm cone-and-plate device) according to the aforementioned measurement protocol, at a temperature of 280° C.

[0190] The molecular weights of the polyamides were found by measurement by gel permeation chromatography (GPC), also called size exclusion chromatography (SEC). The GPC measurements of PA66s are carried out in dichloromethane (solvent and eluent), after chemical modification of the polyamide to solubilize it. A UV detector is used, as the chemically modified polyamide has a UV chromophore. The molecular weight distribution and the average molecular weights Mn and Mw are calculated in polystyrene equivalents, after calibration with commercially available standards. Measurements based on absolute molecular weights are carried out by viscosimetric detection. Mn and Mw may be calculated from the overall distribution or after truncation of the low molecular weights if we do not wish to take into account the contribution from the cyclic oligomers.

Example 1: Thermoplastic Compositions Based on PA66

[0191] Compositions according to the invention or comparative compositions based either on a polyamide of type PA66 STABAMID® 22FE1 or a polyamide of type PA66 STABAMID® 26AE1, both marketed by SOLVAY, as polyamide (a), whose viscosity we aim to reduce, are prepared.

[0192] Polyamide PA66 STABAMID® 22FE1, considered alone in control composition 1, has a melting point of 260° C., a melt viscosity of about 68 Pa.Math.s, and a number-average molecular weight Mn of 8500 g/mol.

[0193] Polyamide PA66 STABAMID® 26AE1, considered alone in control composition 2, has a melting point of 262° C., a melt viscosity of about 500 Pa.Math.s, and a number-average molecular weight Mn of 20400 g/mol.

[0194] Compositions 1 to 9 were each supplemented with an ancillary compound intended to improve their fluidity in the molten state.

[0195] These compounds are: [0196] either a plasticizer, namely cyclized poly(butylene terephthalate) (CBT 100 marketed by CYCLICS CORPORATION) (comparative compositions 1, 2 and 7); [0197] or a non-evolutive polyamide PA66, so-called “low mass”, designated SHF51 (compositions 5, 6 and 9); [0198] or polyphenylene ether PPE (grade SA120 from Sabic, having a molecular weight Mn of 2300 g/mol) (comparative compositions 3, 4 and 8);
in the contents by weight given in Table 1 below.

[0199] The “low mass” polyamide PA66 SHF51 has a melting point of 262° C., a number-average molecular weight Mn of 8650 g/mol (truncation 300 g/mol), a weight-average molecular weight Mw of 14600 g/mol, a melt viscosity of about 6 Pa.Math.s and a viscosity index VI of 52.5 mL/g (determined in formic acid according to ISO 307).

[0200] It is obtained by adding acetic acid during polymerization, and has an AEG content equal to 64.5 meq/kg, a CEG content equal to 62 meq/kg, and a BEG content equal to 198 meq/kg.

[0201] Polyamide PA66 SHF51 is synthesized according to a standard method for synthesis of polyamide 66 followed by a finishing step for 15 minutes. The molten product is then extruded via the pouring valve and collected on a metal plate, on which it crystallizes. The crystallized polyamide is ground and then dried, finally obtaining a powder that is ready to use.

[0202] The compositions in the following Table 1 are obtained by mixing the various constituents in the molten state by batch extrusion using a twin-screw Microcompounder (DSM): speed 100 rpm, residence time 4 minutes, at 280° C., under a stream of nitrogen.

[0203] The viscosity of the compositions is measured according to the same protocol as for the polyamides.

[0204] The results obtained are shown in Table 1 below.

TABLE-US-00001 TABLE 1 PA66 PA66 PA66 22FE1 26AE1 CBT 100 SHF51 PPE Viscosity (in wt %) (in wt %) (in wt %) (in wt %) (in wt %) (in Pa .Math. s) Control 1 100 0 0 0 0 68 Composition 1 96 0 4 0 0 30 (not according to the invention) Composition 2 80 0 20 0 0 45 (not according to the invention) Composition 3 95 0 0 0 5 70 (not according to the invention) Composition 4 90 0 0 0 10 70 (not according to the invention) Composition 5 90 0 0 10 0 22 (according to the invention) Composition 6 95 0 0 5 0 28 (according to the invention) Control 2 0 100 0 0 0 500 Composition 7 0 96 4 0 0 500 (not according to the invention) Composition 8 0 90 0 0 10 700 (not according to the invention) Composition 9 0 90 0 10 0 200 (according to the invention)

[0205] These results clearly show that the use of a non-evolutive polymer (b) that is compatible with a polyamide (a) allows significant reduction in the viscosity of the latter.

[0206] In fact, the above table shows that the presence of 5 to 10 wt % of polyamide PA66 SHF51 makes it possible to reduce the viscosity of polyamide PA66 22FE1 or of polyamide PA66 26AE1 by about 60 to 70% (see compositions 5, 6 and 9). It should also be noted that the viscosity of these compositions comprising polyamide PA66 SHF51 remains stable even after holding in the molten state for at least 15 minutes, or even at least 30 minutes (under nitrogen), which proves absence of reaction (condensation) between the two polymers.

[0207] In contrast, adding a polymer such as the low-mass thermoplastic polymer PPE does not lower the viscosity of a polyamide of this kind (see compositions 1 to 4, 7 and 8). Plasticizer CBT100 makes it possible to lower the viscosity of the composition appreciably, but in an unstable manner (increase in the level of viscosity over time).

Example 2: Effect of the Mixing Conditions on the Behavior of the Thermoplastic Composition with Improved Fluidity

[0208] Tests were carried out by mixing by extrusion with different residence times in the molten state, in order to confirm the improved fluidity of thermoplastic compositions comprising at least one mixture of polyamide of different molecular weight.

[0209] The tests were carried out using a Leistritz ZSE 18 MAAX twin-screw extruder (screw diameter 18 mm, length 44D). The conditions of material flow rate (kg/h) and rotary speed of the screws (rpm) were defined in order to obtain a residence time varying between 30 seconds and 105 seconds. An average residence time for manufacture of formulated polymer (compound) is typically of the order of 1 minute.

[0210] The polymers used are PA66 26AE2 and PA66 SHF51 (described above).

[0211] The PA66 STABAMID® 26AE2 polyamide marketed by SOLVAY, considered alone has, before extrusion, a melting point of 261° C., a melt viscosity of about 425 Pa.Math.s (T=280° C. and 10 rad/s), and a number-average molecular weight Mn of 18255 g/mol (truncation 5000 g/mol).

[0212] The tests that were undertaken considered a single composition based on a mixture of 80% 26AE2+20% SHF51 (wt %) with different residence times RT in the range from 30 seconds to 105 seconds depending on the material flow rate Q (kg/h) and the rotary speed of the extruder n (rpm). The polymers are used in the form of granules, in the dry state (drying for 12 h, 100° C. under vacuum).

[0213] The viscosity of the compositions is measured at 280° C. using an ARES rheometer with frequency scanning from high to low frequencies. The viscosity value is obtained at 10 rad/s after vacuum drying at 110° C.

[0214] The results obtained are shown in Table 2 below.

TABLE-US-00002 TABLE 2 Effect of mixing conditions (thermoplastic compositions based on PA66) Flow rate Q Speed n Residence Viscosity CEG AEG VI (kg/h) (rpm) Q/n time RT (s) (Pa .Math. s) meq/kg meq/kg mL/g Control 1 6 700 0.009 45 420 — — 135 (26AE2) (control) Control 2 6 700 0.009 45 5 — — 51 (SHF51) (control) Test 1 3 300 0.01 105 175 73.7 41.8 116.4 Test 2 3 700 0.004 90 177 72.1 41.5 114.7 Test 3 3 1100 0.003 75 155 70.3 44.2 112.8 Test 4 6 300 0.02 50 150 74.3 42.7 115.0 Test 5 6 700 0.009 45 153 74.5 42.8 114.0 Test 6 6 1100 0.005 40 135 73.3 44.3 110.5 Test 7 9 300 0.003 30 138 75.4 42.3 113.6 Test 8 9 700 0.013 30 140 79.0 45.0 115.3 Test 9 9 1100 0.008 30 200 75.7 42.3 112.5

[0215] These results show that the use of a reduced-mass non-evolutive polymer (b) with a polyamide (a) of higher mass allows a significant reduction in the viscosity of the latter; the viscosity level obtained is very slightly dependent on the residence time in the extruder.

[0216] It should be noted, moreover, that the viscosities of the composition comprising polyamide PA66 SHF51 remain stable even after holding in the molten state in the rheometer for 15 minutes (under nitrogen).

[0217] In addition, determinations of amino and acid end groups of the polyamide were carried out on the compositions obtained.

[0218] The measurement is performed by potentiometric back-determination of the amino and carboxylic end groups of the polyamide. All the functions are alkalized by adding 8 ml of 0.05N tetrabutylammonium hydroxide, followed by determination with 0.05N hydrochloric acid in methanol. The dissolution solvent is based on a mixture of 77% TFE (Solvay) and 23% chloroform (Normapur).

[0219] The potentiometric chain is validated on a control (aminocaproic acid 7470<CEG, and AEG<7650 in meq/kg). The measurements are performed on a Metrohm potentiometric setup.

[0220] The measurements carried out on the samples from tests 1 to 9 (Table 2) show that the sum of the GT is relatively stable with the residence time RT (taking into account the precision for the measurements).

[0221] Measurements of viscosity index VI (according to standard ISO 307) were also carried out: the results obtained show that the VI is relatively stable with the residence time RT (taking into account the precision of the measurements).

Example 3: Mechanical Properties of a Composition Based on a Polyamide Mixture—Fracture Toughness K1c

[0222] A composition based on polyamide PA66 22FE1 (described above) and PA66 SHF51 (described above) was prepared by mixing in a twin-screw extruder: mixture 65% 22FE1+35% SHF51 (wt %).

[0223] Bars were injected using the granules obtained with the extruder, in order to obtain test specimens for mechanical testing.

[0224] A critical property with respect to the molecular weights of the polymers is resistance to cracking, called fracture toughness. In opening mode (mode I), the resistance to cracking or toughness is represented by the critical factor of stress intensity K1c (or energy G1c).

[0225] The measurements are performed according to standard ISO 13586: notching of the test specimens, then mechanical tests of the 3-point bending type in the dry state (RH=0) (drying for 12 h, 100° C. under vacuum).

[0226] The values obtained are presented in Table 3 below.

TABLE-US-00003 TABLE 3 Mechanical properties (thermoplastic compositions based on PA66) Toughness K1c Viscosity (Pa .Math. s) Modulus E (GPa) (MPa .Math. m½) Control 1 70 3.8 3.5 (22FE1) Control 2 5 3.75 1.6 (SHF51) Composition 20 3.8 3.5 65/35

[0227] These results show that although the use of a non-evolutive “low mass” polymer compatible with a “high mass” polyamide allows a significant reduction in the viscosity of the latter, it does not alter certain properties in the solid state such as the elastic modulus E or the fracture toughness (K1c, or Gc). The presence of a “low mass” polymer in a reduced proportion makes it possible to obtain a greatly improved fluidity while maintaining good mechanical performance, which is provided essentially by the “high mass” polymer. It is thus possible to obtain a good compromise between fluidity and fracture toughness (Gc).

Example 4: Wetting Behavior of a Composition Based on a Polyamide Mixture—Polymer/Class Interface

[0228] A composition based on polyamide PA66 22FE1 (described above) and PA66 SHF51 (described above) was prepared by mixing in a twin-screw extruder: mixture of 70% 22FE1+30% SHF51 (wt %).

[0229] The granules obtained were dried for 12 h at 100° C. under vacuum.

[0230] The wetting in the molten state was measured for PA66 22FE1, PA66 SHF51 and the 70/30 composition. Glass plates were prepared: surface cleaning/degreasing by alcohol/acetone treatment and then activation of the surface (silanols SiOH) by treatment with H.sub.2O.sub.2 (30%)/H.sub.2SO.sub.4 (70%) solution.

[0231] The wetting of the polymer in the molten state is measured from the angle θ obtained for granules deposited on a glass plate and heated to 290° C. The measurements were obtained at temperature with a Kruss DSA100 tensiometer, under argon.

[0232] The values obtained after a stabilization time of 150 seconds are presented in Table 4 below.

TABLE-US-00004 TABLE 4 Wetting, hot (thermoplastic compositions based on PA66) Viscosity (Pa .Math. s) Angle θ (°) Control 1 70 72 (22FE1) Control 2 5 64 (SHF51) Composition 70/30 22 51

[0233] These results show that although the use of a non-evolutive “low mass” polymer compatible with a “high mass” polyamide allows a significant reduction in the viscosity of the latter, it also gives a notable improvement of wetting with respect to a glass surface. It is thus possible to obtain interfaces of good quality with these compositions.

Example 5: Preparation of a Composite with Equilibrated Fabric (Satin)

[0234] Thermoplastic composition 5 from example 1 (Table 1) is used in this example for preparing a composite.

[0235] The reinforcing fabric used is a glass fiber fabric with satin of 8 having a weight of 500 g/m.sup.2.

[0236] The thermoplastic composition in question is used in the form of powder. The powders are obtained by cryogenic grinding, either in dry ice, or in liquid nitrogen.

[0237] The composite components are produced using a Schwabenthan temperature-controlled double platen hydraulic press (Polystat 300A): heating plates (heating resistances), and cooled plates (water circulation). A metal mold with a cavity with the dimensions 150 mm×150 mm or 200 mm×300 mm is used.

[0238] To make a composite containing 60 vol % of glass fibers with the fabric with a weight of 500 g/m.sup.2, a metal frame is inserted between the platens, in which a preform is placed consisting of an alternating stack comprising 6 sheets of glass cloth, powder uniformly distributed between each, the two outer layers being sheets of glass cloth.

[0239] The temperature of the platens of the press is first raised to 275° C. (in the case of PA66) before inserting the preform. At this temperature, pressure is applied between 1 and 20 bar and maintained at this value; rapid degassing may optionally be carried out. The whole is maintained at the same temperature and pressure, without degassing, for a time sufficient for good impregnation (stabilization of the pressure and of the distance between platens). The mold is then transferred to the cooled plate device and held at a pressure between 1 and 5 bar for a time of less than 5 minutes.

[0240] The cycle time is above 10 minutes for viscosities above 250 Pa.Math.s; it is reduced to about 10 minutes for viscosities between 250 and 70 Pa.Math.s; finally, for low viscosities (below 50 Pa.Math.s) the cycle time is less than 5 minutes.

[0241] The composite components thus obtained have dimensions of 150 mm×150 mm or 200 mm×300 mm and a thickness of about 2 mm.

[0242] The presence of a small proportion of low mass' polymer makes it possible to obtain greatly improved fluidity while maintaining good mechanical performance, which is provided essentially by the polymer of higher mass. It is thus possible to obtain a good compromise between fluidity and fracture toughness (Gc).

[0243] Moreover, the presence of low-mass polymer gives the composition excellent hot wettability on fabric (hot fabric). This contributes to securing a good level of interfacial cohesion between the polymer and the reinforcing fibers.

[0244] The very low viscosity of the thermoplastic compositions according to the invention thus allows excellent consolidation (void percentage: 0.1%), for a volume percentage of fibers of 60% and a short cycle time (under 5 minutes).

[0245] The void percentage is measured by weighing (standard ASTM D2734-94), and optionally checked by observation with a scanning electron microscope (SEM) for low levels.

[0246] The cycle time corresponds to the total time between heating the mold to temperature and cooling under pressure.

Example 6: Preparation of a Composite with Unidirectional Woven Reinforcement

[0247] A mixture of polymer based on PA66 STABAMID 22FE1 polyamide (described above) and “low mass” PA66 SHF51 (described above) was produced using a Leistritz ZSE 18 MAAX twin-screw extruder (screw diameter 18 mm, length 44D), and conditions of material flow rate (kg/h) and rotary speed of the screws (rpm) leading to a residence time of less than 1 min. The ratio used is 70% PA66 22FE1 and 30% PA66 SHF51.

[0248] The thermoplastic composition thus obtained is used in this example for preparing a composite (stratified) plate.

[0249] The reinforcing fabric used is a glass fiber fabric of the unidirectional woven type with high modulus, consisting of roving at 0° (warp: 1200 tex), a warp spacer thread (136 tex) and a thread at 90° (weft: 70 tex) with a distance between weft thread of 5 mm, and having an overall weight of 520 g/m.sup.2.

[0250] The thermoplastic composition in question is used in the form of powder. The powders are obtained by cryogenic grinding, either in dry ice, or in liquid nitrogen, and then drying (RH=0).

[0251] The composite components are produced using a Pinette Emidecau hydraulic press with temperature-controlled platens (PEI Lab 600 kN): controlled platen heating (heating resistances)/cooling (air-water circulation). A metal mold with a cavity with the dimensions 450 mm×500 mm is used.

[0252] To make a composite containing 55 vol % of glass fibers with the fabric with a weight of 500 g/m.sup.2, a metal frame is inserted between the platens, in which a preform is placed consisting of an alternating stack comprising 8 plies of glass cloth, with powder uniformly distributed between each. The number of plies is adjusted so as to vary the proportion of fibers: 45, 50 and 55 vol %.

[0253] The temperature of the platens of the press is first raised to 265° C. before inserting the preform. At this temperature, pressure is applied progressively in a controlled manner between 1 and 3.5 bar and held at this value while the temperature is raised in a controlled manner to 280° C. The whole is kept at the same temperature and pressure, without degassing, for 2.5 min to ensure good impregnation (stabilization of the pressure and of the distance between platens). The assembly under pressure is then cooled at 5° C./min and then 20° C./min to a temperature of 80° C. for mold release.

[0254] The composite components thus obtained have dimensions of 500×450 mm and a thickness of about 3.4 mm.

[0255] The very low viscosity of the thermoplastic composition according to the invention makes it possible to obtain excellent consolidation (void percentage: 0.1%), for a volume percentage of fibers of 55% and a short cycle time (under 4 minutes).

[0256] For comparison (Control), composite plates were produced with the same protocol using PA66 22FE1 polymer.

[0257] The mechanical properties are measured on specimens cut from the plates, with the 0° axis corresponding to the direction of the warp rovings of the unidirectional woven fabrics HM, according to standard NF EN ISO 5274. The void percentage (density) is measured according to standard ASTM D2734-94.

[0258] The effective level of fiber was measured by calcination: it is 54 vol % for intended 55%, 48 vol % for intended 50% and 43 vol % for intended 45%.

[0259] The values obtained are presented in Table 5 below.

TABLE-US-00005 TABLE 5 Mechanical performance of stratified composites based on thermoplastic compositions (PA66) Level of fibers: Level of fibers: Level of fibers: 43 vol %. 48 vol %. 54 vol %. Breaking Breaking Breaking Modulus stress Modulus stress Modulus stress E (GPa) (MPa) E (GPa) (MPa) E (GPa) (MPa) Composite 32.5 515 38 580 42 635 Control (base 22FE1) Composite 33.5 620 39.1 650 42.9 705 according to the invention (base Composition 70/30)

[0260] These results show that the use of a non-evolutive “low mass” polymer compatible with a “high mass” polyamide makes it possible to improve the properties of stratified composites considerably relative to the use of the “high mass” polyamide alone. This gain in performance is connected with better impregnation of the reinforcement and a better interface quality.