WO2025093295A1

WO2025093295A1 - Use of fatty acid esters or alkoxylates as color stabilizers in flame-retardant polymer compositions

Info

Publication number: WO2025093295A1
Application number: PCT/EP2024/079183
Authority: WO
Inventors: Eva Maria Leuschner; Sebastian Hoerold
Original assignee: Clariant International Ltd
Current assignee: Clariant International Ltd
Priority date: 2023-10-30
Filing date: 2024-10-16
Publication date: 2025-05-08
Anticipated expiration: 2026-04-30
Also published as: WO2025093296A1

Abstract

The invention concerns the use of a fatty acid ester or its alkoxylate as color stabilizer in a flame-retardant polyamide composition, wherein the fatty acid ester is formed from esterification of a monoglycerol and at least two C8-C32 saturated or unsaturated fatty acids. This invention is particularly useful in applications where both flame retardancy and color stability of polyamide materials are critical.

Description

Use of Fatty Acid Esters or Alkoxylates as Color Stabilizers in Flame-Retardant Polymer Compositions

The present invention pertains to a flame retardant composition that uses a fatty ester or alkoxylate thereof to impart enhanced discoloration stability to polyamide materials. This invention also encompasses a flame-resistant polyamide composition characterized by superior discoloration resistance. Among its diverse applications, this composition is particularly suitable for use as a molding compound.

To comply with the stringent flame retardancy standards imposed by plastics processors and industrial regulatory bodies, the incorporation of flame retardants to polyamide composition is usually deemed necessary. There are various flame retardants and synergists available for this purpose. In recent years, nonhalogenated flame retardant systems have become popular due to their ability to generate low smoke density and less toxic smoke composition during combustion, in addition to other environmental benefits.

Among the nonhalogenated flame retardants, the salts of phosphinic acids (also known as phosphinates) have demonstrated exceptional effectiveness as flame retardants and particularly for thermoplastic polymers (DE-A-2252258 and DE-A- 2447727).

However, due to the need for relatively high dosages of phosphinate flame retardants in thermoplastic polymers to achieve adequate flame resistance, the reactivity of these retardants during high-temperature processing in the polymer melt can negatively impact the stability of the flame-retardant polymer. For instance, the phosphinate flame retardant could cause discoloration of a polyamide composition immediately after melt processing, especially at temperatures close to or above 300°C.

DE-A-196 14 424 describes phosphinates in combination with nitrogen-containing synergists in polyesters and polyamides. DE-A-199 33 901 describes phosphinates in combination with melamine polyphosphate as another flame retardant synergist for polyesters and polyamides. However, the use of these synergists with phosphinates in a polyamide molding compound could lead to partial polymer degradation and thereby causing polymer discoloration, especially at processing temperatures close to or above 300°C. WO-A-2004/022640 has described a means to mitigate such flame-retardant polymer discoloration occurred during the high- temperature melt processing, by the addition of basic or amphoteric oxides, hydroxides, carbonates, silicates, borates, stannates, mixed oxide hydroxides, oxide hydroxide carbonates, hydroxide silicates or hydroxide, and/or borates to phosphinate flame retardants or their synergistic mixtures.

Nevertheless, discoloration of a flame-retardant polyamide material can also occur after prolonged exposure to a water medium, long after being produced by melt processing. It has been observed in WO-A-2019/076688 that, prolonged storage of a phosphinate flame-retardant containing black polyamide material in a water medium can result in the material fading to gray. Such discoloration phenomenal was observed in both reinforced and unreinforced black polyamide test samples after storage in water at room temperature for one to seven days. The discoloration instability observed for flame-retardant polyamide material can pose a significant problem in various applications, particularly in the automotive industry where the resistance of polymer molding compounds to various substances, such as windshield wiper fluid, is crucial. To mitigate this discoloration issue in flameretardant polyamide material, WO-A-2019/076688 provided a solution which relies on the addition of at least one polyester to the polyamide composition.

However, the incorporation of an alternative polymer into polyamide material may impede its applicability for specific use cases where polyamide serves as the primary polymer component to attain the desired mechanical attributes, specifically with regards to tensile strength and elongation at break, as suggested by the examples presented in WO-A-2019/076688. Additionally, it has been observed by the inventor that when exposed to elevated environmental temperatures, specifically 40°C or above, discoloration of polyamides is significantly intensified. The prior art, WO-A-2019/076688, does not address or provide a remedy for this high- temperature induced discoloration of polyamides. Thus, it is an object of the present invention to provide a new technical solution to solve the color instability issue of flame-retardant polyamide material when exposed to water, at room temperature or higher, without compromising its flame retardancy and mechanical properties.

This object is achieved by using a fatty acid ester or alkoxylate thereof as color stabilizer in a flame-retardant polyamide composition, wherein the fatty acid ester is formed from esterification of a monoglycerol and at least two C8-C32 saturated or unsaturated fatty acids, and wherein the flame-retardant polyamide composition comprises: as component A), one or more thermoplastic polyamides; and a flame retardant composition comprising as component B) a dialkylphosphinic salt of the formula (I)

in which

R¹ and R² are the same or different and are C1-C18 alkyl in linear, branched or cyclic form, Ce-C aryl, C7-C18 arylalkyl, and/or C7-C18 alkylaryl,

M is Mg, Ca, Al, Sb, Sn, Ge, Ti, Zn, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na, K, and/or a protonated nitrogen base; m is 1 to 4; and as component C) the fatty acid ester, or alkoxylate thereof.

In formula (I) of component B), R¹, R² are the same or different and preferably selected from a group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, tertbutyl, n-pentyl, hexyl, and phenyl; M is preferably selected from a group consisting of Al and Zn, more preferably Al; and m denotes the valence of M and is preferably A particularly preferred example of component B) is diethyl phosphinic salt of Al.

Other examples of component B) include ethylbutylphosphinic salt, dibutylphosphinic salt, ethylhexylphosphinic salt, butylhexylphosphinic salt, ethyloctylphosphinic salt, sec-butylethylphosphinic salt, (1- ethylbutyl)butylphosphinic salt, ethyl(1 -methylpentyl)phosphinic salt, di-sec- butylphosphinic salt (di-1 -methylpropylphosphinic salt), propyl(hexyl)phosphinic salt, dihexylphosphinic salt, hexyl(nonyl)phosphinic salt, and dinonylphosphinic salt.

Component B) usually takes up 50% to 99% by weight of the flame retardant composition, preferably 60% to 95% by weight.

The flame retardant composition according to the present invention further comprises, as component C), a fatty acid ester formed from esterification of a monoglycerol and at least two C8-C32 saturated or unsaturated fatty acids, or alkoxylate thereof.

The term “monoglycerol”, as used herein, is also known as glycerol, glycerin or glycerine in the art and refers to a simple polyhydric alcohol compound with the chemical formula C3H8O3. It consists of a three-carbon backbone, each carbon atom of which is bonded to a hydroxyl group (-OH). Monoglycerol is a colorless, odorless, and viscous liquid that is highly soluble in water.

Preferred examples of C8-C32 saturated or unsaturated fatty acid may be selected from a group consisting of caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, palmitic acid, stearic acid, oleic acid, arachidic acid, eicosenoic acid, behenic acid, docosenoic acid, lignoceric acid, cerotic acid, montanic acid, lacceroic acid, hexatriacontanoic acid, and a mixture thereof.

Alternatively, the component C) in the flame retardant composition according to the present invention can be an alkoxylate of a fatty acid ester as described above. An alkoxylate of a fatty acid ester, as in the present invention, refers to a compound that is derived from a fatty acid ester by the addition of one or more alkoxy groups, for example ethylene oxide groups (-CH2CH2O-), propylene oxide groups (- CH2CH2CH2O-) or butylene oxide groups (-CH2CH2CH2CH2O-), preferably ethylene oxide groups (-CH2CH2O-). For the purpose of the present invention, the number of alkoxy groups in an alkoxylate compound C) is preferably from 1 to 10, and more preferably from 3 to 8.

Component C) usually takes up 1 % to 40% by weight of the flame retardant composition, preferably 5% to 35% by weight.

In a preferred embodiment of the present invention, the component C) is a fatty acid ester formed from esterification of a monoglycerol and at least two C12-C32 saturated or unsaturated fatty acids. More preferably, said C12-C32 saturated or unsaturated fatty acid is selected from a group consisting of oleic acid, cerotic acid, montanic acid, lacceroic acid, hexatriacontanoic acid and a mixture thereof.

The flame retardant composition according to the present invention may further comprise, as component E), a salt of phosphorous acid of the formula (II)

[HP(=O)O₂]²-M’ ⁿ⁺ (II) in which

M’ is Mg, Ca, Al, Sb, Sn, Ge, Ti, Zn, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na, and/or K, and is preferably Al; n is 1 to 4 and preferably 3.

Component E) is preferably an aluminum salt of phosphorous acid, which may be selected from a group consisting of aluminum hydrogen phosphite [AI(H2PO3)3], secondary aluminum phosphite [Al2(HPO3)3], basic aluminum phosphite [AI(OH)(H2PO3)2*2H2O], aluminum phosphite tetrahydrate [Al2(HPO3)3*4H2O], aluminum phosphonate, AI?(HPO3)9(OH)6(1 ,6-hexanediamine)i.5*12H2O, AI₂(HPO3)³*xAI₂O3*nH₂O where x = 1 -2.27 and n = 1-50, AI₄H₆Pi60i₈, and aluminum phosphites of the formulas (III), (IV), and/or (V) below:

AI₂(HPO₃)3 *(H₂O)_q (HI) wherein q is 0 to 4;

Al2.00M_z(HPO3)y(OH)v *(H₂O)W (IV) wherein

M represents alkali metal ions, z is 0.01 to 1 .5, y is 2.63 to 3.5, v is 0 to 2, and w is 0 to 4;

AI₂.oo(HP03)u(H₂P03)t *(H₂0)S (V) wherein u is 2 to 2.99 and t is 2 to 0.01 , and s is 0 to 4.

Preferred component E) may also be selected from mixtures of aluminum phosphite of the formula (III) with sparingly soluble aluminum salts and nitrogen-free extraneous ions, mixtures of aluminum phosphite of the formula (Illi) with aluminum salts, mixtures of aluminum phosphite of the formulas (III) to (V) with aluminum hydrogen phosphite [AI(H₂PO3)3], with secondary aluminum phosphite [AI₂(HPO3)3], with basic aluminum phosphite [AI(OH)(H₂PO3)2*2H₂O], with aluminum phosphite tetrahydrate [AI₂(HPO3)3*4H₂O], with aluminum phosphonate, with AI₇(HPO₃)9(OH)₆(1 ,6-hexanediamine)i.₅*12H₂O, with AI₂(HPO3)3*xAI₂O3*nH₂O where x = 1-2.27 and n = 1-50, and/or with AhHeP Ois.

If present, component E) usually takes up 5% to 40% by weight of the flame retardant composition, preferably 10% to 30% by weight. The flame retardant composition according to the present invention may further comprise, as component F), one or more condensation products of melamine and/or reaction products of melamine with phosphoric acids and/or melamine cyanurate; and as component G), a zinc salt selected from a group consisting of zinc oxide, zinc borate, and zinc stannate.

Component F) is preferably selected from a group consisting of melem, melam, melon, dimelamine pyrophosphate, melamine polyphosphate, melem polyphosphate, melam polyphosphate, melon polyphosphate and mixed polysalts thereof, and nitrogen-containing phosphates of the formula (NH4)yH3-_yPO4 or (NH4PO3)Z, where y is 1 to 3 and z is 1 to 10 000. More preferably, component F) is selected from melem, melam and melamine polyphosphate.

A particularly preferred zinc salt component G) is zinc borate.

If present, component F) usually takes up 5% to 40% by weight of the flame retardant composition, preferably from 20% to 35% by weight.

If present, component G) usually takes up 1 to 10% by weight of the flame retardant composition, preferably from 3% to 7% by weight.

According to the present invention, the one or more thermoplastic polyamides as component A) in the flame-retardant polyamide composition may be selected from a group consisting of aliphatic polyamides, semiaromatic polyamides, aromatic polyamides, elastomeric polyamides, and mixtures thereof.

Preferably, the one or more thermoplastic polyamides comprise at least one aliphatic polyamide, wherein the aliphatic polyamide can be selected from a group consisting of nylon-2/12, nylon-4, nylon-4/6, nylon-6, nylon-6, 6, a copolymer of nylon-6 and nylon-6, 6, nylon-6/9, nylon-6/10, nylon-6/12, nylon-6/66, nylon-7, nylon- 7/7, nylon-8, nylon-8/8, nylon-9, nylon-9/9, nylon-10, nylon-10/9, nylon-10/10, nylon- 11 , nylon-12, and nylon-6, 10, and is preferably nylon-6, nylon-6, 6, or mixture thereof. More preferably, the one or more thermoplastic polyamides comprise at least one aliphatic polyamide and at least one semi-aromatic polyamide, wherein the at least one aliphatic polyamide may be selected from nylon-6, nylon-6, 6, and a copolymer of nylon-6 and nylon-6, 6; and wherein the at least one semi-aromatic polyamide may be selected from polyphthalamide (PPA), polyamide-imide (PAI), polyamideether (PAE) and polyamide-triazine (PAT), preferably PPA.

It has been discovered by the inventor that, when a flame-retardant polyamide composition according to the present invention comprises a mixture of at least one aliphatic polyamide and at least one semi-aromatic polyamide, further improvement of discoloration stability can be achieved, at room temperature or higher temperatures.

One particularly preferred example of component A) is a mixture of nylon-6, 6 and PPA.

Component A) usually takes up 30% to 95% by weight of the flame-retardant polyamide composition, preferably 40% to 90% by weight.

The flame-retardant polyamide composition according to the present invention may further comprise, as component D), a filler or reinforcer. The component D) may be selected from a group consisting of glass fibers, glass beads, and mineral fillers.

If present, component D) usually takes up 10% to 40% by weight of the flameretardant polyamide composition, preferably 15% to 35% by weight.

The flame-retardant polyamide composition according to the present invention may further comprise, as component H), a pigment or a dye. The pigment can be any pigment used in polyamide application, including but not limited to carbon black, titanium dioxide, ultramarine blue (a blue pigment made from a complex sodium- silicate-sulfur compound), iron oxide pigment, phthalocyanine pigment, and various ranges of yellow/red/green pigments commonly used in nylon applications. In a preferred embodiment of the invention the polyamide compounds are dark in color, such as black or dark blue.

The dye can be any dye used for coloring polyamide, including but not limited to acid dye, metal complex dye, disperse sulfur dye and vat dye.

If present, component H) usually takes up 1 % to 5% by weight of the flame-retardant polyamide composition, preferably 1 % to 3% by weight.

The flame-retardant polyamide composition according to the present invention optionally comprises further additives, wherein the further additives are selected from the group consisting of antioxidants, UV stabilizers, gamma-ray stabilizers, hydrolysis stabilizers, co-stabilizers for antioxidants, antistatics, emulsifiers, nucleating agents, plasticizers, processing auxiliaries, impact modifiers, and/or further flame retardant other than component B). Examples of suitable further flame retardants are aryl phosphates, phosphonates, phosphazenes, salts of hypophosphorous acid, and red phosphorus.

The flame-retardant polyamide composition according to the invention preferably comprises,

30% to 95% by weight of component A), 5% to 25% by weight of component B), 0.5% to 5% by weight of component C),

0% to 40% by weight of component D),

0% to 15% by weight of component E),

0% to 15% by weight of component F),

0% to 2% by weight of component G), and

0% to 5% by weight of component H), wherein the sum total of the components is always 100% by weight.

In one embodiment of the present invention, the flame-retardant polyamide composition comprises,

30% to 90% and preferably 35 to 85% by weight of component A), 5% to 25% and preferably 8% to 20% by weight of component B), 0.5% to 5% and preferably 1 % to 4% by weight of component C), 10% to 40% and preferably 15% to 35% by weight of component D), 0% to 15% and preferably 1 % to 10% by weight of component E), 0% to 15% and preferably 1 % to 10% by weight of component F), 0% to 2% by weight of component G), and

In another embodiment of the present invention, the flame-retardant polyamide composition comprises,

35% to 85% and preferably 40 to 80% by weight of component A),

5% to 25% and preferably 8% to 18% by weight of component B),

0.5% to 5% and preferably 1 % to 3% by weight of component C),

10% to 40% and preferably 15% to 35% by weight of component D),

3% to 10% and preferably 3% to 8% by weight of component E),

0% to 10% by weight of component F),

0% to 2% by weight of component G), and

In yet another embodiment of the present invention, the flame-retardant polyamide composition comprises,

35% to 60% and preferably 40 to 60% by weight of component A), 5% to 25% and preferably 8% to 18% by weight of component B), 0.5% to 5% and preferably 1 % to 3% by weight of component C), 10% to 40% and preferably 15% to 35% by weight of component D), 0% to 10% by weight of component E),

3% to 10% by weight of component F),

0.5% to 2% by weight of component G), and

0% to 5% by weight of component H), wherein the sum total of the components is always 100% by weight. The invention further relates to the use of a flame-retardant polyamide composition as above-described in the electricals and electronics sector, in or for plug connectors, current-bearing components in power distributors (residual current protection), circuit boards, potting compounds, power connectors, circuit breakers, lamp housings (LED housings), capacitor housings, coil elements, and ventilators for grounding contacts, plugs, in/on printed circuit boards, housings for plugs, cables, flexible circuit boards, charging cables for mobile phones, motor covers, textile coatings, and other products.

In the abovementioned uses, the polyamides are preferably in the form of shaped bodies, films, filaments, foils, and/or fibers.

Finally, the invention also relates to a three-dimensional article comprising the invented flame-retardant polyamide composition, wherein said article is a shaped body, injection molding, extrusion compound, and/or extrudate.

Examples

Hereinafter, the present invention is described in more detail and specifically with reference to the Examples, which however are not intended to limit the present invention.

1. Components used

Polyamide (Component A1)

A1 : Ultramid® A27, Nylon-6, 6 pellets (from BASF AG, Germany)

Flame retardant (Component B)

Exolit® OP 1230, Aluminum salt of diethylphosphinic acid, hereinafter referred to as Depal (from Clariant, Switzerland).

C8-C32 fatty acid esters of monoglycerol (Component C)

C1 : Palmester 4010, glycerol trioleate, CAS 122-32-7 (from KLK OLEO Germany) C2: Licolub® WE 4, Glycerides, montan-wax, CAS 68476-38-0 (from Clariant, Switzerland)

Different fatty acid ester in comparison examples (named as Component FE)

FE1 : Licowax® E, glycol montanite, esters of montan wax acid based on glycol (from Clariant, Switzerland)

FE2: Ligastar® NA R/D, Sodiumstearate, CAS: 822-16-2 (from Peter Greven)

FE3: Glucopure® DEG M0500, Lauroyl Methyl Glucamide (from Clariant)

Glass fiber (Component D)

ChopVantage® HP 3610 EC 10 4.5 mm glass fiber (from PPG Ind. Fiber Glass, the Netherlands)

Aluminum salt of phosphorous acid (Component E)

Or aluminum phosphite, hereinafter referred to as Phopal

Melamine polyphosphate (Component F)

Melapur® 200/70 (from BASF, Germany), hereinafter referred to as MPP

Zinc salt (Component G)

Zink borate

Pigment (Component H)

Carbon black masterbatch 30% in polymer carrier

2. Production, processing, and testing of flame-retardant polymer molding compounds

Flame retardant or a flame retardant composition was mixed with a fatty acid ester (component C or FE) in the ratio specified in the table and incorporated via the side intake of a twin-screw extruder (Leistritz ZSE 27/44D) into the polymer component A1 (PA 6,6) at temperatures of 260 to 310°C, or at 300-340°C when PPA (Component A2) was present. The glass fibers (component D) were added via a second side intake. The homogenized polymer strand was drawn off, cooled in a water bath, and then pelletized.

After sufficient drying, the molding compounds were processed into test specimens on an injection-molding machine (Arburg 320 C Allrounder) at melt temperatures of 250 to 340°C and tested and classified for flame retardancy using the UL 94 test (Underwriter Laboratories). For the color tests component H was directly added to the granulates during injection molding.

The UL 94 fire classifications are as follows:

V-0: Afterflame time never longer than 10 sec, total of afterflame times for 10 flame applications not more than 50 sec, no flaming drops, no complete consumption of the specimen, afterglow time for specimens never longer than 30 sec after end of flame application.

V-1 : Afterflame time never longer than 30 sec after end of flame application, total of afterflame times for 10 flame applications not more than 250 sec, afterglow time for specimens never longer than 60 sec after end of flame application, remaining criteria as for V-0.

V-2: Cotton indicator ignited by flaming drops, remaining criteria as for V-1

Not classifiable (ncl): Does not conform to fire classification V-2.

The fire classification of the polymer samples was determined based on the average afterburning time of two flame treatments (10 seconds each) of 5 test samples each. (Test specimen thickness - 1 .6 mm)

Tensile strength (N/mm²), elongation at break, and tear strength were measured according to DIN EN ISO 527 (%); impact resistance [kJ/m²], and notched impact strength [kJ/m²] were measured according to DIN EN ISO 179, and immediately after the molding compounds were processed into test specimens, as listed in the tables below.

The change in color in polymer compositions after water storage was determined by storing 3 mm thick plates semi-immersed in water for seven days at different temperatures (23°C and 50°C). The color (Lab values) was then measured in accordance with DIN 6174 using a CM 3600d spectrophotometer with white and black standards and measuring apertures, and the results were evaluated using SpectraMagic NX software (from Minolta Europe GmbH, Germany). The plate color difference after 7-day storage in water was represented by the AE*ab value based on JIS Z 8730.

For comparability, all tests in the respective series, unless otherwise stated, were performed under identical conditions (temperature programs, screw geometry, injection molding parameters, etc.).

All amounts are reported as % by weight and are based on the polymer molding compound including the flame retardant combination and additives.

Table 1 shows discoloration stability of flame-retardant polymer molding compounds that contain pigment and optionally a further fatty acid ester additive. Without said further fatty acid ester additive, polymer composition R1 has demonstrated poor discoloration stability. This is indicated by the significant color change that was observed in the sample after seven days of storage in water, as indicated by the AE*ab value.

Table 1

Comparative Example C1 contains 2wt% of Licowax® E (component FE1 ), which is a fatty acid ester based on glycol. This additive did not provide a notable improvement on the discoloration stability of the reference polymer composition, at 23°C or 50°C. In contrast, the addition of a fatty acid ester formed from esterification of a monoglycerol and at least two C8-C32 saturated or unsaturated fatty acids (component C1 -C2) was found to enhance the discoloration stability of the reference flame-retardant polymer during water storage for 7 days at 23°C or 50°C, as indicated by the visual color observation and largely reduced AE*ab value at both temperatures. In Table 2, the stability of discoloration, flame retardancy, and mechanical properties of various glass fiber reinforced polymer molding compounds are compared. These molding compounds contain black pigment (H) for the discoloration test and can also include a flame retardant composition (B, F, G) and fatty acid ester additives (C or FE). Table 2

Example R2 shows that glass fiber-reinforced polyamide composition without flame retardant did not undergo notable color change during water storage period. When a flame retardant composition (B, F and G) was added to a similar polyamide composition, the discoloration has emerged as a concern, evidenced by the visual color change and associated AE*ab value in Example C2, measured at 23°C or 50°C. Comparative Examples C3 and C4 further include an additive of fatty acid ester not based on glycerol (component FE2 or FE3), and this additive did not bring any improvement on the discoloration stability, at 23°C or 50°C. In contrast, the addition of similar amount of a fatty acid ester formed from esterification of a monoglycerol and at least two C8-C32 saturated or unsaturated fatty acids in inventive Example I3 significantly reduced or essentially eliminated the polymer color change during water storage, while still maintaining high levels of mechanical values and a UL 94 V-0 fire classification of C2.

Another observed finding is that the inventive Example I3 exhibited lower water uptake compared to the comparative Examples C2-C4 after 2 days of immersion in water, indicating an enhanced dimensional stability of the inventive polymer composition examples.

In Table 3, the discoloration stability, flame retardancy, and mechanical properties of various glass fiber reinforced polymer molding compounds are compared. These molding compounds contain black pigment (H) for the discoloration test and can also include a flame retardant composition (B, E) and fatty acid ester additives (C or FE).

Table 3

Example R2 is again placed in Table 3, which shows that a glass fiber-reinforced polyamide composition without flame retardant did not undergo notable color change during water storage. When a flame retardant composition (B and E) was added to such a polyamide composition, the discoloration has emerged as a concern, evidenced by the visual color change and associated AE*ab value in Example C5 measured at 23°C or 50°C. Comparative Example C6 further includes an additive of fatty acid ester not based on glycerol (component FE3), which did not bring any improvement on the polymer discoloration stability.

In contrast, the addition of similar amount of a fatty acid ester formed from esterification of a monoglycerol and at least two C8-C32 saturated or unsaturated fatty acids in inventive Examples I4-I5 significantly reduced or essentially eliminated the polymer color change during water storage period measured at 23°C or 50°C, while still maintaining high levels of mechanical values and a UL 94 V-0 fire classification of C5.

From Tables 1 -3, one could observe that the undesired polymer discoloration in all flame-retardant polymer compositions has been largely reduced or essentially eliminated by the small addition of a fatty acid ester formed from esterification of a monoglycerol and at least two C8-C32 saturated or unsaturated fatty acids, but not by other fatty acid esters tested.

Claims

1. Use of a fatty acid ester or alkoxylate thereof as color stabilizer in a flameretardant polyamide composition, wherein the fatty acid ester is formed from esterification of a monoglycerol and at least two C8-C32 saturated or unsaturated fatty acids, and wherein the flame-retardant polyamide composition comprises: as component A), one or more thermoplastic polyamides; and a flame retardant composition comprising as component B) a dialkylphosphinic salt of the formula (I)

in which

R¹ and R² are the same or different and are C1-C18 alkyl in linear, branched or cyclic form, C6-C18 aryl, C7-C18 arylalkyl, and/or C7-C18 alkylaryl,

M is Mg, Ca, Al, Sb, Sn, Ge, Ti, Zn, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na, K, and/or a protonated nitrogen base; m is 1 to 4; and as component C) the fatty acid ester or alkoxylate thereof.

2. The use of claim 1 , wherein the flame retardant composition comprises,

50% to 99% and preferably 60 to 95 % by weight of component B), and

1 % to 40% and preferably 5% to 35% by weight of component C), each based on the total weight of the flame retardant composition.

3. The use of any of claims 1 or 2, wherein said C8-C32 saturated or unsaturated fatty acid is selected from a group consisting of caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, palmitic acid, stearic acid, oleic acid, arachidic acid, eicosenoic acid, behenic acid, docosenoic acid, lignoceric acid, cerotic acid, montanic acid, lacceroic acid, hexatriacontanoic acid, and a mixture thereof.

4. The use of any of claims 1-3, wherein the component C) is an alkoxylate and has 1 to 10 alkoxy groups.

5. The use of any of claims 1 -3, wherein component C) is a fatty acid ester formed from esterification of a monoglycerol and at least two C12-C32 saturated or unsaturated fatty acids.

6. The use of claim 5, wherein said C12-C32 saturated or unsaturated fatty acid is selected from a group consisting of oleic acid, cerotic acid, montanic acid, lacceroic acid, hexatriacontanoic acid and a mixture thereof.

7. The use of any of claims 1-6, wherein said flame retardant composition further comprises as compound E), a salt of phosphorous acid of the formula (II)

[HP(=O)O₂]²-M’ ⁿ⁺ (II) in which

8. The use of any of claims 1-7, wherein said flame retardant composition further comprises as component F), one or more condensation products of melamine and/or reaction products of melamine with phosphoric acids and/or melamine cyanurate; and as component G), a zinc salt selected from a group consisting of zinc oxide, zinc borate, and zinc stannate.

9. The use of claim 1 , wherein the one or more thermoplastic polyamides comprise an aliphatic polyamide and a semi-aromatic polyamide.

10. The use of any of claims 1-9, wherein said flame-retardant polyamide composition further comprises as component D), a filler or reinforcer.

11. The use of any of claims 1-10, wherein said flame-retardant polyamide composition further comprises as compound H) a pigment or a dye.

12. The use of claim 11 , wherein said flame-retardant polyamide composition comprises,

0% to 40% by weight of component D),

0% to 15% by weight of component E),

0% to 15 % by weight of component F),

0% to 2% by weight of component G), and

13. The use of claim 11 , wherein said flame-retardant polyamide composition comprises,

30% to 90% and preferably 35 to 85% by weight of component A),

5% to 25% and preferably 8% to 20% by weight of component B),

0.5% to 5% and preferably 1 % to 4% by weight of component C),

10% to 40% and preferably 15% to 35% by weight of component D),

0% to 15% and preferably 1 % to 10% by weight of component E),

0% to 15% and preferably 1 % to 10% by weight of component F),

0% to 2% by weight of component G), and