The present invention relates to a process for chemically modifying a specific polymeric part in order to impart flame retardant properties thereto or to improve these properties, said process involving a covalent reaction with at least one flame retardant compound.
Conventionally, the flame retardant properties of a polymeric part can be modified or improved in different manners, such as for example:
In view of the above, the authors of the present invention have proposed to develop a process for modifying a polymeric part in order to impart flame retardant properties thereto or to improve these properties which does not have the limitations of the processes mentioned below.
Thus, the invention relates to a process for chemically modifying a polymeric part in order to impart flame retardant properties thereto or to improve these properties, said process comprising a step of reacting a polymeric part comprising at least one polymer comprising, as reactive groups, amine groups and/or hydroxyl groups, with a flame retardant compound comprising at least one group reacting, by nucleophilic substitution or nucleophilic addition, with some or all of the amine groups and/or hydroxyl groups of the polymer(s), the reaction being implemented with said compound in gaseous form.
By polymeric part, it is specified that it is, conventionally, a part made of a material comprising at least one polymer comprising, as reactive groups, amine groups and/or hydroxyl groups, said polymer(s) being in the form of the part, for example, by a shaping technique, such as the 3D printing technique, the extrusion/injection technique, the additive manufacturing technique, the process of the invention can thus be part of the manufacturing cycle of a part at the “post-process” stage (that is to say the finishing stage of the part after its shaping).
The term “flame retardant compound” means a compound capable of imparting flame retardant properties.
Thanks to the reaction involving a flame retardant compound in gaseous form to chemically modify the polymeric part, the following advantages have been identified:
Moreover, the process of the invention can have the following advantages:
As mentioned above, the process of the invention comprises a step of reacting a polymeric part comprising at least one polymer comprising, as reactive groups, amine groups and/or hydroxyl groups, with a flame retardant compound comprising at least one group reacting, by nucleophilic substitution or nucleophilic addition, with some or all of the amine groups and/or hydroxyl groups of the polymer(s), said compound being in gaseous form under the reaction conditions.
The polymeric part intended to be treated in accordance with the process of the invention is a part comprising (or even consisting exclusively of) at least one polymer comprising, as reactive groups, amine groups and/or hydroxyl groups, the amine and/or hydroxyl groups reacting, covalently, by nucleophilic substitution or nucleophilic addition with the flame retardant compound(s).
In particular, the polymeric part intended to be treated in accordance with the process of the invention may be a part comprising (or even consisting exclusively of) one or more polyamides and, even more specifically, the polymeric part can be a polyamide-12 part, the reactive groups being, in this case, amine groups. More specifically, the part can be made of porous or partially porous polyamide-12 and, even more specifically, a polyamide-12 having a density which is less than or equal to 960 kg/m3, for example ranging from 650 kg/m3 to 960 kg/m3, preferably less than or equal to 900 kg/m3, for example ranging from 700 kg/m3 to 900 kg/m3.
The flame retardant compound(s) comprise at least one group reacting, by nucleophilic substitution or nucleophilic addition, with some or all of the amine groups and/or hydroxyl groups of the polymer(s), this or these groups can be:
it being understood that the amine groups and/or the hydroxyl groups constitute nucleophilic groups reacting with nucleofuge groups, in the case of a nucleophilic substitution reaction, or reacting with the electrophilic groups, in the case of a nucleophilic addition reaction.
The flame retardant compound(s) advantageously comprise at least one group comprising at least one phosphorus atom, at least one sulphur atom and/or at least one silicon atom, which constitutes the functional group of interest since it is capable of imparting flame retardant properties to the polymeric part.
More specifically, when the reaction step is a nucleophilic substitution reaction step, the flame retardant compound(s) can be selected from the following compounds:
The chloride compounds comprising at least one —SO2— group can further comprise a group comprising at least one heteroatom selected from N, O, Si or P, such as the following specific compounds: trimethylsilyl chlorosulfonate, (2-trimethylsilyl)ethanesulfonyl chloride.
The chloride compounds comprising at least one —PO— group can further comprise a hydrocarbon, aliphatic or aromatic group and/or a group comprising at least one heteroatom selected from N, O, Si or P.
Specific compounds comprising at least one —PO— group can be selected from:
The chloride compounds comprising at least one —PS— group can further comprise a hydrocarbon, aliphatic or aromatic group and/or a group comprising at least one heteroatom selected from N, O, Si or P, such as O,O′-diethyl methylphosphonothioate (CAS number: 6996-81-2).
More specifically, when the reaction step is a nucleophilic addition reaction step, the flame retardant compound(s) can be selected from:
Among the conventional siloxane compounds, mention may be made of hexamethylcyclotrisiloxane.
The flame retardant compound(s) react in the gaseous state with the polymeric part, which means that they are capable of existing in this gaseous state under the reaction conditions. More specifically, the flame retardant compound(s) may have a boiling point that can be reached under the following temperature and pressure conditions: a temperature which is less than or equal to 145° C. and a pressure which is greater than or equal to 10 mbar.
In particular, when the flame retardant compound(s) are chloride compounds comprising at least one —PO— group, such as diphosphoryl chloride, the reaction step can be carried out at a temperature ranging from 140 to 145° C. and a pressure ranging from 40 to 45 mbar.
When the flame retardant compound(s) are chloride compounds comprising at least one —SO2— group, such as trimethylsilyl chlorosulfonate, the reaction step can be carried out at a temperature ranging from 115 to 120° C. and a pressure ranging from 30 to 35 mbar.
The reaction step is advantageously carried out exclusively in the presence of the polymeric part and the flame retardant compound(s) and, in particular, in the absence of organic solvent(s).
The reaction step is carried out at a temperature and a pressure necessary to maintain the flame retardant compound(s) in the gaseous state and to the reaction between the flame retardant compound(s) and the polymer(s) of the polymeric part.
More specifically, the reaction step can include the following operations:
At the end of the reaction step, the polymeric parts are thus chemically modified and are covalently bonded to (or covalently grafted by) residues of the flame retardant compound(s) (the residues being what remains after it(they) has(have) reacted with the amine groups and/or hydroxyl groups of the polymer(s) of the polymeric part).
The reaction step can be implemented in a reactor, for example, of the autoclave type, comprising an enclosure intended to receive the polymeric part and the flame retardant compound(s), means for regulating the pressure of said enclosure for creating a vacuum therein (for example, via a vacuum pump communicating with the enclosure) and heating means.
After the reaction step, the polymeric part thus modified can, advantageously, then be subjected to a drying, for example, by heating or under vacuum and more specifically, to a heat treatment step which can be qualified as a heat treatment step of finishing the part, which allows homogenising the surface functionalisation of the part and thus imparting optimal fire retardant properties thereto.
In particular, the heat treatment step can comprise the following operations:
It is understood that the temperature and the duration will be selected so as not to alter the polymeric part.
Other advantages and features of the invention will appear in the nonlimiting detailed description below.
This example illustrates the implementation of a specific mode of the chemical modification process of the invention consisting of a chemical modification of a polyamide-12 part, so as to improve the flame retardant properties thereof by a flame retardant compound: diphosphoryl chloride of formula (Cl2P(O)OP(O)Cl2).
This flame retardant compound was selected because it has vaporisation conditions in line with the properties of polyamide-12, in particular relative to its melting temperature. Indeed, the boiling temperature of diphosphoryl chloride is 214° C. at 1 bar, i.e. 140° C. for an absolute pressure of 130 mbar.
The reaction of polyamide-12 with the flame retardant compound mentioned above can be represented by the following reaction scheme:
the other chlorine atoms can also be involved in a nucleophilic substitution
reaction with other —NH groups of the polyamide-12.
The process has been implemented in a device schematically illustrated in the appended
The polyamide-12 sample to be treated (reference 1) is suspended in the deposition reactor 3, sealed and with magnetic stirring, previously heated to the treatment temperature then the latter is pressurised by vacuum drawing up to 40 mbar thanks to the vacuum pump 5 by opening the valve 7. Once the desired pressure has been obtained, the valve 7 is closed in order to maintain the deposition reactor 3 under vacuum and isolated.
In an adjacent reactor 9 which is connected to the deposition reactor 3, a known amount of flame retardant compound 11 is injected, at a temperature such that the latter is preheated or even in the gaseous state in order to facilitate its vaporisation.
When the temperature and pressure conditions allow maintaining the flame retardant compound in its vapour form, then the valve 13 between the deposition reactor 3 and the adjacent reactor 9 is opened. This is followed by the vaporisation of the compound in the conduit 15 inserted into deposition reactor 3 and thanks to the pressure difference between the two reactors 3 and 9.
The flame retardant compound is then inserted into the deposition reactor 3 via an injection nozzle 17 connected to the pipe 15. A plate 19 forming a physical barrier is located above the injection nozzle 17 to prevent any liquid projection of the flame retardant compound on the sample to be treated. The reaction (possibly its condensation) between the flame retardant compound and the sample to be treated thus takes place.
At the end of the duration of the process (from 1 to 30 minutes), purge cycles are performed in the reactor in order to recover the excess of the flame retardant compound which has not reacted. The pressure is released, then the treated sample is removed and placed in the oven (5 minutes to 1 hour), in order to completely eliminate the flame retardant compound which has not reacted.
More specifically, three tests were carried out with the operating conditions listed in the table below.
For accuracy, the loading rate (in mg) corresponds to the amount of flame retardant compound deposited on the sample, while the loading rate loading rate (in mass %) corresponds to the mass ratio of the amount of flame retardant compound deposited on the total mass of the sample after treatment.
For these different tests, characterisation by spectroscopic analysis (XPS and ToF SIMS) of the treated samples has allowed highlighting and confirming the formation of covalent bonds between the polymer and the flame retardant compound. Indeed, there is a modification of the XPS spectrum of the element N obtained on the treated polyamide-12. The complementary ToF-SIMS analyses confirmed the formation of —NP(O)— groups.
Consequently, these characterisations confirm that this post-treatment does not constitute a simple surface deposition. This is truly a covalent chemical grafting of the flame retardant compound onto the PA-12. This feature then makes the deposition much more robust. Its adherence relative to PA-12 is then very strong.
For these different tests, flame tests were also carried out to determine whether the samples originating from these tests (having a length of 125 mm, a width of 13 mm and a thickness of 5 mm) belong to the fire classes V-0, V-1, V-2 according to a representative test of the UL94V standard. Under multiple ignition, both the residual combustion and afterglow time and the casting of ignited drops from the sample are evaluated for this purpose.
The results obtained correspond to a V-0, namely the results:
Moreover, a comparative fire test was carried out with:
On observation, it appears that, unlike the untreated part, the treated part reveals very low ignition times (or even zero) during the 2 ignitions. In addition, no glowing drop likely to ignite the cotton was observed with the treated part.
This example illustrates the implementation of a specific mode of the chemical modification process of the invention consisting of a chemical modification of a polyamide-12 part, so as to improve the flame retardant properties thereof by a flame retardant compound: trimethylsilyl chlorosulfonate.
This flame retardant compound was selected because it has vaporisation conditions in line with the properties of polyamide-12, in particular relative to its melting temperature. Indeed, its vaporisation conditions are 80° C. at 50 mbar, 95° C. at 100 mbar or even 120° C. at 250 mbar.
The reaction of polyamide-12 with the flame retardant compound mentioned above can be represented by the following reaction scheme:
Thus, the trimethylsilyl chlorosulfonate is grafted onto the surface of the PA-12 part by forming covalent bonds. This reaction is accompanied by the formation of HCI.
More specifically, seven tests were carried out according to a process similar to that set out in Example 1, with the specific operating conditions listed in the table below.
For accuracy, the loading rate (in mg) corresponds to the amount of flame retardant compound deposited on the sample, while the loading rate (in mass %) corresponds to the mass ratio of the amount of flame retardant compound deposited on the total mass of the sample after treatment.
The flame tests described in Example 1 and performed (test representative of the UL94V standard) on the polyamide-12 parts treated with trimethylsilyl chlorosulfonate revealed that the grade VO was obtained according to the UL94V standard.
Moreover, the test was carried out on a sample having a loading rate of 85 mg i.e. 1.1 m%. It then appears that even with a low loading rate, the ignition times are zero and no glowing drop is formed.
Number | Date | Country | Kind |
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2008402 | Aug 2020 | FR | national |
Filing Document | Filing Date | Country | Kind |
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PCT/FR2021/051442 | 8/5/2021 | WO |