PROCESS FOR CHEMICALLY MODIFYING A POLYMERIC PART IN ORDER TO IMPART FLAME-RETARDANT PROPERTIES THERETO OR TO IMPROVE SAID PROPERTIES INVOLVING A COVALENT REACTION WITH AT LEAST ONE COMPOUND BEARING AN ISOCYANATE GROUP

Abstract

A process for chemically modifying a polymeric part in order to impart flame-retardant properties thereto or to improve the properties, the process comprising the following steps: a step of reacting a polymeric part comprising at least one polymer comprising, as reactive groups, amine groups and/or hydroxyl groups, with a functional compound, referred to as first compound, comprising at least one isocyanate group and at least one vinyl type polymerisable group, the isocyanate groups reacting, covalently with all or some of the amine groups and/or hydroxyl groups of the polymer(s), resulting in a polymeric part bonded, covalently, to residues of the functional compound; using the vinyl type polymerisable groups of the residues of the functional compound, a step of polymerising a second compound comprising at least one vinyl type polymerisable group and at least one group comprising at least one phosphorus atom, the reaction step and said polymerisation step being carried out in the presence of at least one supercritical fluid.

Claims

1.-14. (canceled)

15. Process for chemically modifying a polymeric part in order to impart flame-retardant properties thereto or to improve said properties, said process comprising the following steps: a step of reacting a polymeric part comprising at least one polymer comprising, as reactive groups, amine groups and/or hydroxyl groups, with a functional compound, referred to as first compound, comprising at least one isocyanate group and at least one vinyl type polymerisable group, the isocyanate groups reacting, covalently with all or some of the amine groups and/or hydroxyl groups of the polymer(s), resulting in a polymeric part bonded, covalently, to residues of the functional compound; using the vinyl type polymerisable groups of the residues of the functional compound, a step of polymerising a second compound comprising at least one vinyl type polymerisable group and at least one group comprising at least one phosphorus atom, said reaction step and said polymerisation step being carried out in the presence of at least one supercritical fluid.

16. Process according to claim 15, wherein the supercritical fluid is supercritical CO.sub.2.

17. Process according to claim 15, wherein the polymeric part is a part comprising one or more polyamides.

18. Process according to claim 15, wherein the polymeric part is a part made of polyamide-12.

19. Process according to claim 15, wherein the polymeric part is a part made of polyamide-12, which has a density less than or equal to 960 kg/m.sup.3, preferably less than or equal to 900 kg/m.sup.3.

20. Process according to claim 19, wherein the density is less than or equal to 960 kg/m.sup.3.

21. Process according to claim 19, wherein the density is less than or equal to 900 kg/m.sup.3.

22. Process according to claim 15, wherein the functional compound is a non-polymeric compound.

23. Process according to claim 15, wherein the functional compound is a compound comprising an isocyanate group, at least one vinyl type polymerisable group and at least one group comprising at least one phosphorus atom.

24. Process according to claim 15, wherein the functional compound complies with the following formula: ##STR00007##

25. Process according to claim 15, wherein the step of reacting a polymetric part is carried out in the presence of at least one cosolvent and/or at least one catalyst.

26. Process according to claim 15, wherein the step of reacting the polymeric part includes the following operations: an operation of placing, in a reactor, the polymeric part, the functional compound, optionally at least one cosolvent and optionally at least one catalyst; an operation of introducing CO.sub.2 into the reactor; an operation of pressurising and heating the reactor to a temperature greater than the critical temperature of CO.sub.2 and to a pressure greater than the critical pressure of CO.sub.2, this temperature and this pressure being maintained until the completion of the reaction.

27. Process according to claim 15, wherein the polymerisation step is carried out in the presence of at least one supercritical fluid, identical to that used during the reaction step with the functional compound.

28. Process according to claim 15, wherein the second compound comprises, as groups(s) comprising at least one phosphorus atom, at least one phosphate group.

29. Process according to claim 15, wherein the second compound is bis[2-(methacryloyloxy)ethyl]phosphate.

30. Process according to claim 15, wherein the polymerisation step is carried out in the presence of a free radical initiator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] FIG. 1 is an infrared spectrum with a y-axis representing the absorbance (A) and an x-axis representing the wave number N (in cm.sup.−1), the curve a) corresponding to the compound OP alone, the curve b) to the untreated part and curve c) to the functionalised part.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Example 1

[0066] This example illustrates the implementation of a specific embodiment of the chemical modification process according to the invention consisting of a chemical modification of a part made of polyamide-12, so as to improve the flame-retardant properties thereof.

[0067] For this purpose, an organophosphorus compound, bis[2-(methacryloyloxy)ethyl]phosphate (hereinafter referred to as “OP”), was chosen and three phases, which will be developed in more detail hereinafter, were carried out:

[0068] a) a liquid-phase synthesis phase of an intermediate compound (hereinafter referred to as intermediate isocyanate/OP compound) by reacting hexamethyldiisocyanate with bis[2-(methacryloyloxy)ethyl]phosphate, this step being capable of being illustrated with the following reaction diagram:

##STR00004##

[0069] b) a step of grafting, in supercritical CO.sub.2, the intermediate isocyanate/OP compound with polyamide-12, this step being capable of being illustrated by the following reaction diagram:

##STR00005##

n corresponding to the repeat number of the repeat unit between brackets.

[0070] c) a phase of polymerising the organophosphorus compound OP, this step being capable of being illustrated by the following reaction diagram:

##STR00006##

[0071] n corresponding to the repeat number of the repeat unit of the polyamide and p corresponding to the repeat number of the repeat unit between brackets.

[0072] 1) Synthesis of the Intermediate Isocyanate/OP Compound

[0073] The table below illustrates, in order, the steps for accessing synthesis of the intermediate isocyanate/OP compound.

TABLE-US-00001 Step 1 Introduction of 1.2 g of 1,4-diazabicyclo[2.2.2]octane (DABCO) (11 mmol), as a catalyst, into a glass container Step 2 Purging of the container with argon Step 3 Addition of 10 mL of anhydrous acetone Step 4 Stirring of the mixture under argon bubbling until the DABCO has completely dissolved Step 5 Addition of 3.4 g of OP previously dissolved in 5 mL of anhydrous acetone Step 6 Stirring of the mixture under argon bubbling Step 7 Addition of 1.8 g of hexamethyldiisocyanate (11 mmol) Step 8 Stirring of the mixture under argon bubbling until the reagents have completely dissolved Step 9 Obtaining the intermediate isocyanate/OP compound

[0074] 2) Grafting of the Intermediate Compound onto a Part Made of Polyamide-12 and Polymerisation of the Organophosphorus Compound

[0075] The initial part made of polyamide-12 is a parallelepipedal test specimen having a length of 127 mm, a width of 12.7 mm, a thickness of 5 mm and a mass between 7 and 8 g.

[0076] The aforementioned part undergoes the following successive steps: [0077] a step of impregnation/grafting of the intermediate compound (referred to as “Step 1” below); [0078] a step of impregnation with a free radical initiator (azobisisobutyronitrile AiBN) and OP compound (referred to as “Step 2a” below); [0079] a step of polymerising the organophosphorus compound OP (referred to as “Step 2b” below);

[0080] These three steps are conducted in supercritical CO.sub.2 in a “batch” type reactor. More specifically, the reactor is a 600 mL “batch” type stainless steel reactor equipped with an external heating system. CO.sub.2 is introduced into the reactor with a dual-piston pump in which the heads are cooled to a temperature less than 5° C. to obtain a liquid-phase CO.sub.2 at this stage prior to the reaction. It is equipped, at the bottom thereof, with a 60 mL capacity crystalliser intended to receive the reagents, the optional catalyst and the optional cosolvent. The part made of polyamide-12 is suspended over the crystalliser to prevent any contact therewith. The experiments commence at ambient temperature. The reactor is then pressurised to a target pressure and then heated to the desired temperature. The part is kept under the treatment conditions for a necessary time until the completion of the reaction in question. The heating of the reactor is then switched off inducing a slow depressurisation. The residual pressure is evacuated with the various valves located on the cover of the reactor.

[0081] More specifically, the operating conditions of the steps mentioned above are listed in the table below.

TABLE-US-00002 Step 1 Introduction of the intermediate isocyanate/OP compound previously synthesised and the part made of polyamide-12 in the reactor and reaction in supercritical CO.sub.2 (300 bar, 100° C.) for 4 hours Step 2a Introduction of 0.5 g of AiBN and introduction of 3 g of OP compound into the reactor in supercritical CO.sub.2 (100 bar, 60° C.) for 1 hour enabling the impregnation and decomposition of AiBN Step 2b Increase in the pressure (300 bar) and temperature (100° C.) and holding for 2 hours for the polymerisation of OP compound

[0082] The part obtained following these steps is homogeneous and has a black colour.

[0083] It is analysed by infrared spectroscopy in comparison to OP compound alone and a similar but untreated part.

[0084] The infrared spectrum obtained is illustrated in FIG. 1, the y-axis representing the absorbance (A) and the x-axis the wave number N (in cm.sup.−1), the curve a) corresponding to OP compound alone, the curve b) to the untreated part and curve c) to the functionalised part.

[0085] The peak 3290 cm.sup.−1 corresponds to the N—H group and only belongs to the untreated polyamide-12. The two peaks at 1715 cm.sup.−1 and 1162 cm.sup.−1, for their part, are only characteristics of the commercial organophosphorus compound.

[0086] The spectrum obtained with the functionalised polyamide-12 part therefore confirms the presence of the phosphate group on the treated part and thus validates the chemical synthesis.

[0087] The evaluation of the flame-retardant behaviour of the parts (one functionalised part and one non-functionalised part) is also carried out according to the UL94V standard. For this, a flame is applied on the vertically positioned part for 10 seconds. The residual combustion and incandescence times and the flow of ignited drops from the sample are then evaluated. Two ignitions are applied for this test.

[0088] The results of the test are listed in the table below.

TABLE-US-00003 Non-functionalised Functionalised Evaluation criteria part part Combustion time during 5 seconds 0 seconds application of first flame Combustion time during 5 seconds 2 seconds application of second flame Incandescent polyamide Yes No flow

[0089] While the untreated parts exhibit ignited drop flows on each ignition, no combustion, or incandescence, or ignited drop flow were observed for the functionalised part, which demonstrates the effectiveness of the flame-retardant property.

[0090] Furthermore, under the effect of the flammability test, the non-functionalised parts display a molten effect, whereas for the functionalised part, the formation of a crust under the effect of the flame makes it possible to prevent any ignition or ignited flows (which proves the effectiveness of the flame-retardant properties).