WO2023099139A1

WO2023099139A1 - Fire retardant composition

Info

Publication number: WO2023099139A1
Application number: PCT/EP2022/081231
Authority: WO
Inventors: Alessandra LORENZETTI; Luca Ruggenenti
Original assignee: Velaworks S. R. O.
Priority date: 2021-11-30
Filing date: 2022-11-09
Publication date: 2023-06-08
Also published as: EP4441131A1; IT202100030218A1

Abstract

A fire retardant composition, comprising the following components: a) from 20% to 83% by weight of polyamide, characterized by a melting point lower than or equal to 275°C, b) from 7% to 45% by weight of ammonium sulfate ((NH4)2SO4), and c) from 10% to 45% by weight of a reinforcing agent, each on the total weight of the composition.

Description

FIRE RETARDANT COMPOSITION

The present invention relates to a fire retardant composition.

By virtue of basic properties such as a relatively low specific gravity, resistance to impact and wear, moderate electrical insulation, resistance to solvents, oils, greases and fuels, various polyamides and copolyamides are used in compounds for many applications such as, for example, products for the electrical/electronic sector, lighting technology products, interior and exterior furnishings, articles for construction work and packaging articles. In particular, polyamides, particularly reinforced polyamides, are commonly used in the electrical/electronic sector and in the automotive sector, where an optimum ratio between density and mechanical properties is essential in order to obtain ever lighter and higher-performing vehicles. It is also important to take into account the possible occurrence of short circuits, given the increasing importance of the electronic component in cars and the increasing development of electric or hybrid vehicles, which increase the risk of fire.

For this reason, for some applications the mechanical characteristics and the lightness of a material are not sufficient, but low flammability and flame self-extinguishing capability in the event of a fire are also required. Therefore, appropriate additives with flame retardant properties that increase these latter characteristics are necessary.

The flame retardancy (FR) of polymers is currently mandatory for many of their applications, due to strict laws and regulations in many countries. As a result, many systems have been developed to render various plastic materials fire retardant. These systems entail mixing the plastic materials with one or more additives selected from flame retardant chemical products. Most of these chemical substances are based on halogens or phosphorus and constitute, in most cases, low molecular weight compounds. They are sometimes applied in combination with synergizing co-additives, such as antimony oxide, which is added to halogenated compounds, and nitrogen compounds, which are added to phosphorus flame retardants. Halogenated additives, while providing a reasonable degree of fire safety, present several problems: they generate corrosive hydrogen halides and dense smoke during combustion and they emit highly toxic substances. In addition, it is usually necessary to use large amounts (about 25% by weight on the weight of the polymer) of halogen-based flame retardant, with consequent deterioration of the mechanical properties of the polymer.

Likewise, phosphorus derivatives are used in relatively high quantities (at least 5% by weight on the weight of the polymer). In addition, the red phosphorus that is used for polyamides may cause the emission of unwanted phosphine during and after processing. The large quantities of additives required for effective flame retardancy furthermore entail relatively high costs. In addition, the European Commission has recently added phosphatic rock, from which these flame retardants are derived, to a list of 20 critical raw materials for which supply safety is at risk and economic importance is high. Phosphatic rock is identified as non- replaceable and of great economic importance.

The use of inorganic flame retardants such as alumina trihydrate (ATH), aluminum hydroxide (A1(OH)₃) or magnesium hydroxide (Mg(OH)₂) to improve the fire performance of thermoplastic polymers is also known, but in this case also large quantities are required (up to 60% by weight on the weight of the polymer) with negative effects on the mechanical properties of the polymers. Furthermore, the use of aluminum hydroxide is incompatible with polymers such as polyamides, which are processed at temperatures above 200 °C.

Boron-based compounds (for example zinc borate) have also been used as flame retardants, but in polymers such as polyamides they are not sufficient on their own to give an adequate degree of extinguishing, characterized by a V2 or higher rating in the UL94 vertical burning test.

Nitrogen-based compounds, such as for example melamine salts such as melamine cyanurate and melamine polyphosphate, are also used to improve the flame performance of polyamides. The inclusion of these compounds in the composition results in a satisfactory flame retardancy, making it possible to obtain a VO degree of self- extinguishing in the UL94 vertical burning test up to 1.6 mm with non-reinforced polyamide (PA). By contrast, in the case of reinforced polyamides, the glass fiber acts like the wick of a candle, resulting in a downgrading of the material to V2 in the UL94 test. Moreover, the combustion of polymers containing melamine cyanurate generates toxic fumes containing hydrocyanic acid (HCN).

Some solid acids, for example silicotungstic acid, have also been proposed as flame retardants, but this is too expensive. A char sulfonic acid (CSA) has also been proposed which has shown even better effects than conventional acids. The preparation of this acid is carried out using procedures known in the literature (Wu et al. (2010) “Microwave-assisted hydrolysis of crystalline cellulose catalyzed by biomass char sulfonic acids,” Green Chem. 12, 696-700). In a typical procedure, 20 g of bamboo powder was treated with 80% sulfuric acid (100 ml) at 80°C for 3 hours in order to obtain a carbonized solid. The ground solid (10.5 g) was then immersed in 150 mL of oleum (50% by weight of SO₃) and heated to 80°C for 2 hours under N₂. After sulfonation, the suspension was filtered to yield a black precipitate. Finally, the resulting black solid was washed repeatedly with hot distilled water (>80°C, 1000 mL), until impurities such as sulfate ions were no longer detected in the washing water, then dried at 150°C for 4 hours. A disadvantage of this sulfur-based solid acid is that PA6 reacts easily with acidic substances, and the inorganic acid resulting from CSA decomposition causes the degradation of PA6, thus leading to deterioration of the mechanical performance of the materials obtained (Zhang-Yu Wang et al. “Flame Retarding Glass Fibers Reinforced Polyamide 6 by Melamine Polypho sphate/Polyurethane-Encapsulated Solid Acid”, Journal of Applied Polymer Science, Vol. 105, 3317-3322 (2007)). Given the limitations described above, the aim of the present invention is to provide a fire retardant composition that overcomes the drawbacks of the background art.

In particular, an object of the invention is to provide a fire retardant composition with a combination of flame-reaction and mechanical properties, as well as glow wire resistance properties and electrical insulation properties, that are better than the polymer compositions currently in use.

Within this aim, an object of the invention is to provide a reinforced polyamide that can be rated as V2 or higher in the UL94 vertical burning test for thicknesses equal to or greater than 0.4 mm.

Another object of the invention is to provide a reinforced polyamide that combines said flame reaction with good mechanical properties in terms of tensile modulus of elasticity and impact resistance as well as properties of glow wire resistance and electrical insulation properties.

A further object of the present invention is to provide a composition to improve the fire retardant properties of polyamides that is easily available and has a low cost.

Another object of the present invention is to provide a method for providing a fire retardant composition according to the invention that is highly reliable, relatively easy to provide and at competitive costs.

Not least an object of the invention is to provide a product comprising a fire retardant composition according to the invention.

This aim and these and other objects that will become better apparent hereinafter are achieved by a fire retardant composition comprising the following components: a) from 20% to 83% by weight of polyamide, characterized by a melting point lower than or equal to 275 °C, b) from 7% to 45% by weight of ammonium sulfate (NH^SCh), and c) from 10% to 45% by weight of a reinforcing agent, each on the total weight of the composition.

The aim and objects of the present invention are also achieved by a method for providing a fire retardant composition according to the invention, comprising the step of mixing the following components: a) from 20% to 83% by weight of polyamide in the melted state, wherein said polyamide has a melting point lower than or equal to 275°C, b) from 7% to 45% by weight of ammonium sulfate, and c) from 10% to 45% by weight of a reinforcing agent, each on the total weight of the composition.

Finally, the aim and objects of the invention are also achieved by an article comprising a fire retardant composition according to the invention.

Further characteristics and advantages of the invention will become better apparent from the following detailed description.

In a first aspect, the present invention relates to a fire retardant composition comprising the following components: a) from 20% to 83% by weight of polyamide, characterized by a melting point lower than or equal to 275 °C, b) from 7% to 45% by weight of ammonium sulfate, and c) from 10% to 45% by weight of a reinforcing agent, each on the total weight of the composition.

Within the scope of the present invention, the term “polyamide” is understood to mean a polymer characterized in that it has an amide functional group in the polymeric chain, and in particular the polyamides of the present invention are those that have a melting point lower than or equal to 275°C. Examples of polyamides are polyamide 6, polyamide 6.6, polyamide 11, and polyamide 12.

Polyamides (PA) occupy, both historically and commercially, a fundamental place in the world of polymers, and among them the most important are PA6 and PA6.6, which represent approximately 80% of the production of all polyamides. They are materials suitable for many applications by virtue of their good mechanical properties, their low density, and their modest cost.

This versatility, as well as the mechanical performance, is increased with the introduction of reinforcements such as, for example, glass fibers.

The fire retardant composition of the invention is a reinforced polyamide comprising from 10% to 45% by weight, on the total weight of the composition, of a reinforcing agent preferably selected from the group consisting of glass fiber, carbon fiber, talc, mineral fillers, nanofillers, and carbon nanotubes.

PA6 is characterized by excellent mechanical properties, good resistance to impact and to fatigue, having a low coefficient of friction and a high melting point (223°C). Furthermore, this polyamide is well suited to be transformed with conventional process technologies such as injection molding. However, PA6 has non-optimal fire retardant properties (without additives it is rated for example UL94 V2 at a thickness of 1.6 mm) and its moisture content can lead to negative consequences, such as hydrolysis, during compounding, i.e., mixing, in the melted state, the polymer with the various additives present in the composition.

Another commonly used polyamide is PA6.6, obtained via stage polymerization by mixing equimolar amounts of hexamethylene diamine and adipic acid which, by reacting, lead to the formation of the amide bonds.

PA6.6 is the aliphatic polyamide that has the best mechanical strength characteristics after PA4.6. Unlike PA6, it has greater rigidity, but lower impact resistance. It also has excellent dimensional stability, high temperature resistance and good resistance to organic solvents.

In an embodiment, the flame retardant composition according to the invention further comprises a carbonizing agent.

Carbonizing agents are additives that promote the forming of a carbon “crust” during combustion by virtue of the presence of a large number of carbon atoms. The carbon crust, once formed, protects the polymer from heat transfer and physically limits the meeting of oxygen with the combustible polymer below the crust, thus removing a reagent from the reaction. Preferably, the carbonizing agent is selected from the group consisting of pentaerythritol and oligomers thereof, polyhydroxyl alcohols, polyphenylene oxide (PPO), and polyphenylene sulfide (PPS).

Such carbonizing agent, if present, constitutes up to 20% by weight of the fire retardant composition.

In a preferred embodiment, the fire retardant composition of the invention comprises said carbonizing agent in a quantity comprised between 0.5% and 10% by weight on the total weight of the composition.

The fire retardant composition according to the invention comprises from 7% to 45%, preferably from 10% to 40%, by weight of ammonium sulfate on the total weight of the composition.

Ammonium sulfate is an ammonium salt of sulfuric acid. Its decomposition products are ammonia, which has a gas diluent effect and causes expansion of the carbon layer, and sulfuric acid, which by contrast causes dehydration of the polymer. Advantageously, ammonium sulfate, by virtue of its thermal stability, does not require a complex synthesis in order to obtain a compound adapted to be used in polyamides, since it can also be obtained as waste formed in the synthesis of caprolactam, i.e., the monomer from which polyamide 6 is then obtained.

The fire retardant composition according to the invention may further include additional additives, in particular one or more Lewis acids in quantities of up to 20% by weight, preferably between 0.1% and 10%, more preferably between 1% and 7% by weight, on the total weight of the composition. Preferably, such Lewis acids are selected from the group constituted by oxides of metals or of semimetals or salts of metals or of semimetals such as for example: (i) boron compounds, such as for example boron trifluoride and boron trichloride,

(ii) aluminum compounds, such as for example aluminum sulfate, aluminum nitrate and aluminum chloride,

(iii) zinc compounds, such as for example zinc oxide, zinc borate, zinc chloride and zinc nitrate,

(iv) silicon compounds, such as for example silicotungstic acid and silicoaluminates,

(v) zirconium compounds, such as for example zirconium oxide and zirconium sulfate, and

(vi) organic acids, such as for example oxalic acid and tartaric acid.

The fire retardant composition according to the invention may further comprise a flame retardant selected from the group constituted by flame retardants comprising phosphorous, flame retardants comprising halogens, and melamine and its derivatives. The fire retardant composition according to the invention may further comprise silica, polymers containing chain silicon such as siloxanes, copolymers based on polyolefins and containing maleic groups or acrylic groups.

In a second aspect, the present invention refers to a method for providing a fire retardant composition according to the invention, comprising the step of mixing the following components: a) from 20% to 83% by weight of polyamide in the melted state, wherein said polyamide has a melting point lower than or equal to 275°C, b) from 7% to 45% by weight of ammonium sulfate, c) from 10% to 45% by weight of a reinforcing agent, each on the total weight of the composition.

In order to improve the mechanical properties, such as for example impact resistance, ammonium sulfate is preferably ground so as to obtain a D50 lower than 150 micrometers (i.e., until a size distribution is achieved in which 50% of the ammonium sulfate particles have a diameter of 150 micrometers or less).

In a third aspect, the present invention relates to an article comprising a fire retardant composition according to the invention.

The articles according to the invention can be, for example:

- accessories for cars, trains and aircraft such as, for example, seats, armrests, headrests, dashboards, doors and interiors in general, ashtrays, battery containers, under-hood structural components, lighting components, and containers for liquids;

- accessories for agricultural use, such as containers for liquids, powders and solids, containers for chemical substances, parts of agricultural machinery, protection elements for machines and apparatuses, and containers for waste and rejects;

- industrial accessories such as for example containers for liquids, powders and solids, containers for chemical substances, parts of machines and apparatuses, protection elements for machines and apparatuses, and containers for waste and rejects;

- products for the electrical/electronic sector such as for example wall plates and their supports (for example, flush-mount boxes and fixing accessories), devices such as for example switches, selectors, shunts, pushbuttons, hole covers, outlets, actuator and sensor components, distribution panel components, components of sensors and security systems such as for example gas leak detectors, home automation, such as sensors for the automatic adjustment of lighting and intrusion prevention systems, electric charging stations: for example, electric car chargers, parts of electrical household appliances (for example, bodywork of vacuum cleaners, washing machines, coffee machines), and electronic components;

- interior and exterior furnishing elements (items and components of items) such as, for example, lamp elements (wall, ceiling, floor-mounted) manufactured for lighting technology, street furniture components and components for road signs, chairs and seats, armchairs, tables, design objects, vases and containers, trays, door or window frames, handles, door elements, door leaves, windows, and containers for household waste;

- building articles such as cable conduits, pipes for liquids, air pipes, and structural elements for doors, entrance doors, and door or window frames;

- packaging articles such as for example pallets and containers.

The invention also relates to the use of a composition according to the invention to produce an article selected from the group constituted by the articles described above.

The invention will now be described with reference to the following non-limiting example and to the associated Tables 1 and 2.

EXAMPLE: PREPARATION OF COMPOSITIONS ACCORDING TO THE INVENTION

18 formulations with variable amounts of polyamide (PA6), ammonium sulfate, glass fiber, dipentaerythritol (carbonizing agent), zinc borate (Lewis acid), melamine cyanurate, melamine polyphosphate and silica were prepared according to the proportions given in Table 1 and Table 2.

The components of the compositions were mixed using a plastograph with a chamber volume of 50 cm³. The temperature, the screw rotation rate and the mixing time were set according to the individual formulations and are given in Table 1 and Table 2. In the preparation of the material, the reinforced polymer (or the polymer and the reinforcing agent separately) was introduced into the mixing chamber, followed by all the other components of the formulation. If a twin-screw extruder is used, on the other hand, the reinforced polymer and all the other components can be inserted at the same time, at the same point of the screw, or at later times, i.e., at different points of the screw.

The test pieces for the characterizations were prepared by compression molding at a temperature of 250°C, cooled to room temperature and conditioned for 48 hours at 23°C and 50% humidity before performing the assessment of reaction to fire according to UL94-V at a thickness of 1.6 mm on the test pieces for compositions 1-11 and one or more of the following additional tests on the test pieces for compositions 12-18 as shown in Table 2:

- assessment of tensile strength properties (ISO 527-2: 2012);

- notched Izod impact strength (ISO 180: 2019);

- melt flow index at 275°C, 1.2 kg (ASTM D1238-20);

- assessment of reaction to fire according to UL94-V at a thickness of 1.6 mm;

- glow wire ignition temperature test (GWIT) (IEC 60695-2-13: 2021);

- glow wire flammability index test (GWFI) (IEC 60695-2-12: 2021);

- assessment of comparative tracking index (CTI) (IEC 60112:2020). TABLE 1

n.r. = not ratable

The data shown in Tables 1 and 2 are the average of 5 samples for each composition tested. TABLE 2

(*) For composition 14, 3 samples were found to be VO, while 2 samples were found to be V2 in the UL94 V test at 1.6 mm.

The examples show that ammonium sulfate alone makes it possible to improve reaction to fire according to UL94, making it possible to achieve up to grade VO. If ammonium sulfate is used together with dipentaerythritol or zinc borate, it is possible, for the same fire reaction grade achieved, to use a lower additive content (understood as everything that is not a polymer or glass fiber). If ammonium sulfate is used in combination with dipentaerythritol and melamine polyphosphate, the content of additives may still be reduced with respect to the use of ammonium sulfate alone. The use of dipentaerythritol together with ammonium sulfate makes it possible firstly to maintain or improve the reaction to fire with respect to the use of ammonium sulfate alone, and secondly to simultaneously improve the mechanical properties and the rheology (corresponding to a lower melt flow index). If, in addition to ammonium sulfate and dipentaerythritol, a Lewis acid, such as borate zinc, is also used, an improvement in mechanical properties (for example, tensile modulus of elasticity) and rheology (evaluated by the melt flow index at 275°C, 1.2 kg measured according to ASTM DI 238-20) is obtained with respect to the analogous formulation with ammonium sulfate alone as an additive (in addition to the reinforcement glass fiber), as well as optimum glow wire resistance, both in the glow wire ignition temperature (GWIT) test and in the glow wire flammability index (GWFI) test, and a moderate comparative tracking index (assessed by CTI). The further addition of either or both of silica and melamine cyanurate further improves the properties.

In practice it has been found that the device according to the invention fully achieves the intended aim, since ammonium sulfate is sufficient to obtain an improvement in reaction to fire, which is variable as a function of the quantities used, of the polymer and reinforcement used, and of the presence of any other additives that act as synergistic agents. The advantage of using ammonium sulfate to improve the reaction to fire of polyamides is that it is easily available, even as a waste product of other processes, cheap and with sufficient thermal stability to be usable directly in compounding without costly chemical pretreatment processes.

The fire retardant composition thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; all the details may furthermore be replaced with other technically equivalent elements.

The disclosures in Italian Patent Application No. 102021000030218 from which this application claims priority are incorporated herein by reference.

Claims

1. A fire retardant composition, comprising the following components: a) from 20% to 83% by weight of polyamide, characterized by a melting point lower than or equal to 275 °C, b) from 7% to 45% by weight of ammonium sulfate ((NH^SCL), and c) from 10% to 45% by weight of a reinforcing agent, each on the total weight of the composition.

2. The fire retardant composition according to claim 1, wherein said reinforcing agent is selected from the group consisting of glass fiber, carbon fiber, talc, mineral fillers, nanofillers, and carbon nanotubes.

3. The fire retardant composition according to claim 1 or 2, further comprising a carbonizing agent in a quantity of up to 20%, preferably between 0.5% and 10%, by weight on the total weight of the composition.

4. The fire retardant composition according to claim 3, wherein said carbonizing agent is selected from the group consisting of pentaerythritol and oligomers thereof, polyhydroxyl alcohols, polyphenylene oxide (PPO), and polyphenylene sulfide (PPS).

5. The fire retardant composition according to any one of the preceding claims, wherein the ammonium sulfate is in a quantity comprised between 15% and 40% by weight on the total weight of the composition.

6. The fire retardant composition according to any one of the preceding claims, further comprising at least one Lewis acid in a quantity of up to 20%, preferably between 0.1% and 10%, more preferably between 1% and 7% by weight, on the total weight of the composition, wherein the Lewis acid is preferably selected from the group consisting of:

(i) boron compounds, such as for example boron trifluoride and boron trichloride,

(ii) aluminum compounds, such as for example aluminum sulfate, aluminum nitrate, and aluminum chloride,

(iii) zinc compounds, such as for example zinc oxide, zinc borate, zinc chloride, and zinc nitrate,

(vi) organic acids, such as for example oxalic acid and tartaric acid.

7. The fire retardant composition according to any one of the preceding claims, further comprising at least one of: i) a flame retardant selected from the group consisting of flame retardants comprising phosphorus, flame retardants comprising halogens, and melamine and derivatives thereof, and ii) one or more of silica, siloxanes, and copolymers based on polyolefins and containing maleic groups or acrylic groups.

8. A method for providing a fire retardant composition according to the preceding claims, comprising the step of mixing the following components: a) from 20% to 83% by weight of polyamide in the melted state, wherein said polyamide has a melting point lower than or equal to 275°C, b) from 7% to 45% by weight of ammonium sulfate (NH₄SO₄), and c) from 10% to 45% of a reinforcing agent, each on the total weight of the composition.

9. The method according to claim 8, wherein said ammonium sulfate is ground so as to have a D50 of less than 150 micrometers.

10. An article comprising a fire retardant composition according to any one of claims 1 to 7.