METHOD FOR THE CONTINUOUS PREPARATION OF FORMULATED POLYAMIDE PREPOLYMERS

Abstract

A method for continuously preparing a formulated polyamide prepolymer, of which the solution viscosity is from 0.25 dL/g to 0.70 dL/g, as measured according to ISO 307:2007 in m-cresol at 20 C., the method including a step of polycondensation on the basis of one or more polyamide precursor monomers, said polycondensation step being carried out in an extruder comprising at least two co-rotating conveying screws, the at least one monomer being previously fed therein in solid or liquid form without being dissolved in a solvent or in water, and said polycondensation step being carried out without extraction of the water formed during said polycondensation step and comprising the addition of at least one additive during said polycondensation step in the extruder.

Claims

1. A method for the continuous preparation of a formulated polyamide prepolymer, the viscosity in solution of which is comprised from 0.25 dL/g to 0.70 dL/g, as measured according to ISO 307:2007 in m-cresol at 20 C., said formulated polyamide prepolymer having a weight average molecular weight (Mn) is less than 10,000 g/mol as determined by calculation from the level of terminal functions determined by potentiometric titration in solution and the functionality of said prepolymers or by NMR assay or by size exclusion chromatography, wherein it comprises a step of polycondensation from one or several polyamide precursor monomers, said polycondensation step being carried out in a single extruder comprising at least two co-rotating conveying screws, said monomer(s) being previously added in solid or liquid form without dissolving in a solvent or in water, and said polycondensation step being carried out without extraction of the by-products formed, and comprising the addition of at least one additive during said polycondensation step in the extruder, said extruder not having any degassing devices, or any device for removing the polycondensation by-product(s) formed, and the water formed, consisting of an outlet on the outside at atmospheric pressure, or of an outlet connected to a device making it possible to create a low-pressure zone in the extruder, such as a vacuum pump during the reaction.

2. The method according to claim 1, wherein the average degree of polymerization (DPn) of the resulting polyamide is less than 50, as determined from the number average molecular weight (Mn) of the polyamide according to the following formula:
DPn=Mn/M.sub.0[Formula 1] with Mn, the number average molecular weight of the polyamide, and M.sub.0 the number average molecular weight of the monomers.

3. The method according to claim 1, wherein the polyamide is an aliphatic polyamide.

4. The method according to claim 3, wherein the monomer(s) is (are) at least one C6 to C18.

5. The method according to claim 3, wherein the monomer(s) is (are) at least one C6 to C18.

6. The method according to claim 3, wherein the monomer(s) is (are) at least one C6 to C18.

7. The method according to claim 1, wherein the extruder is a twin-screw extruder with two co-rotating conveying screws.

8. The method according to claim 7, wherein it is carried out at a temperature comprised from 220 to 340 C.

9. The method according to claim 8, wherein the residence time of the material in the extruder at the temperature comprised from 220 to 340 C. makes it possible to execute the polycondensation reaction so as to arrive at the desired average degree of polymerization, said residence time being greater than or equal to 1 minute.

10. The method according to claim 1, wherein the extruder is an annular multi-screw extruder comprising at least 6 screws.

11. The method according to claim 10, wherein the residence time of the material in the extruder at the temperature comprised from 220 to 340 C. makes it possible to execute the polycondensation reaction so as to arrive at the desired average degree of polymerization, said residence time being greater than or equal to 1 minute.

12. The method according to claim 7, wherein the residence time of the material in the extruder is greater than or equal to 1 minute.

13. The method according to claim 1, wherein said at least one additive is selected from catalysts, fillers, dyes, stabilizers, plasticizers, surfactants, nucleating agents, pigments, whiteners, antioxidants, lubricants, flame retardants, natural waxes, and mixtures thereof.

14. The method according to claim 1, wherein said at least one additive is added to said single extruder in the main hopper.

15. The method according to claim 1, wherein said at least one additive is added to said single extruder after the main hopper.

Description

EXAMPLES

Example 1 (Comparative)

[0113] Representative example of the preparation of a formulated aliphatic polyamide

[0114] A PA11 prepolymer formulated with H.sub.3PO.sub.2 was prepared in two steps:

[0115] a first step per batch process for the preparation of the prepolymer:

[0116] To a 14 liter autoclave reactor, 5 kg of the following raw materials are added: [0117] 500 g water, [0118] the diamine and the dicarboxylic acid and/or the amino acid, [0119] 0.1 g of a WACKER AK1000 antifoam agent (from Wacker Silicones).

[0120] The closed reactor is purged of its residual oxygen then heated to a material temperature of 230 C. After 30 minutes of stirring under these conditions, the pressurized vapor that formed in the reactor is relaxed progressively over 60 minutes, while progressively adjusting the temperature of the material such that it stabilizes at Tf+10 C. at atmospheric pressure.

[0121] The oligomer (prepolymer) is then emptied through the bottom valve then cooled in a water bath then milled.

[0122] A PA11 prepolymer of Mn=3000 and viscosity 0.40 was prepared,

[0123] without the use of diamine or dicarboxylic acid, from 11-aminoundecanoic acid (CAS 2432-99-7), according to this procedure with a residence time much longer (more than one hour) than that of the method described in examples 2 and 3 of the invention (between 1 and 5 minutes),

[0124] then a second compounding step with the H.sub.3PO.sub.2 additive in aqueous solution (8000 ppm of H.sub.3PO.sub.2) in an Evolum32HT twin-screw extruder (EV32 Clextral) with a diameter D=32 mm (length=40D)

Example 2 (Invention)

[0125] A formulated PA11 prepolymer was prepared from solid state 11-aminoundecanoic acid (CAS 2432-99-7) on an EV32 twin-screw extruder (Clextral) with a diameter D=32 mm (length=40D) without extraction of the by-products formed during the polycondensation, and addition of H.sub.3PO.sub.2 in aqueous solution (8,000 ppm of H.sub.3PO.sub.2) in the main hopper or after the main hopper (Tables 1 and 2).

TABLE-US-00001 TABLE 1 Formulation PA11 + H.sub.3PO.sub.2 8,000 ppm in 8,000 ppm after H.sub.3PO.sub.2 main hopper main hopper Flow rate (kg/h) 12 12 9 Screw speed (rpm) 300 300 225 Temperature 290 280 300 280 300 Viscosity in solution ISO 307: 2007 0.41 0.27 0.38 0.35 0.53 (m-cresol at 20 C.)

TABLE-US-00002 TABLE 2 Temperature Profile 280 = 20/150/250/280/280/280/280/280/280/280-260 290 = 20/150/250/290/290/290/290/290/290/290-260 300 = 20/100/200/300/300/300/300/300/300/300-260

Example 3 (Invention)

[0126] A formulated PA11 prepolymer was prepared from solid state 11-aminoundecanoic acid (CAS 2432-99-7) on an EV32 twin-screw extruder (Clextral) with a diameter D=32 mm (length=40D) without extraction of the by-products formed during the polycondensation, and addition of H.sub.3PO.sub.4 in aqueous solution (5,300 ppm of H.sub.3PO.sub.4) in the main hopper or after the main hopper (Tables 3 and 4).

TABLE-US-00003 TABLE 3 Formulation PA11 + H.sub.3PO.sub.4 5,300 ppm in 5,300 ppm after H.sub.3PO.sub.4 main hopper main hopper Flow rate (kg/h) 12 12 9 Screw speed 300 300 225 (rpm) Temperature 280 280 290 300 280 Visco 0.42 0.40 0.57 0.66 0.52

TABLE-US-00004 TABLE 4 Temperature Profile 280 = 20/150/250/280/280/280/280/280/280/280-260 290 = 20/150/250/290/290/290/290/290/290/290-260 300 = 20/100/200/300/300/300/300/300/300/300-260

[0127] Examples 2 and 3 show that a formulated PA11 may be obtained in a single step by the continuous method of the invention with the required viscosity characteristics.

[0128] Furthermore, the formulated products resulting from the method of the invention are comparable to those resulting from the batch process with regard to several points such as viscosity in solution, grinding ability, shaping and mechanical properties of the resulting product.