GB2562167A

GB2562167A - Fire retardant natural rubber based compositions

Info

Publication number: GB2562167A
Application number: GB1806256.2A
Authority: GB
Inventors: Fernando Marina
Original assignee: LEMBAGA GETAH MALAYSIA; Tun Abdul Razak Research Centre
Current assignee: LEMBAGA GETAH MALAYSIA; Tun Abdul Razak Research Centre
Priority date: 2017-05-02
Filing date: 2018-04-17
Publication date: 2018-11-07
Also published as: GB201806256D0; MY182405A

Abstract

A flame retardant rubber composition comprises a rubber compound containing epoxidised natural rubber (ENR), inorganic filler, and a flame retarding additive. Typically, the inorganic filler is present in an amount of 40-65 wt.% and may be aluminium hydroxide, magnesium hydroxide, zinc borate, zinc hydroxyl stannate, or silica. The flame retarding additive may be an intumescent additive and may be an organic phosphorus-nitrogen-containing compound, such as ethylene diamine phosphate. The rubber compound may contain 25 mol.% or 50 mol.% epoxidised natural rubber. A flame retarding composition comprising epoxidised natural rubber, inorganic filler, and an additive is also disclosed. A further halogen-free flame retarding composition comprising epoxidised natural rubber, inorganic filler, and an organic phosphorus-nitrogen-containing additive is claimed.

Description

(71) Applicant(s):

Lembaga Getah Malaysia

15th Floor 148 Jalan Ampang, Kuala Lumpur 50450, Malaysia

Tun Abdul Razak Research Centre (Incorporated in the United Kingdom) BRICKENDONBURY, Hertfordshire, SG13 8NL, United Kingdom (51) INT CL:

C08K5/00 (2006.01) C08K3/10 (2018.01) C08K 5/521 (2006.01) C08L 7/00 (2006.01) (56) Documents Cited:

EP 1361249 A2 CN 106317519 A CN 105860506 A (58) Field of Search:

INT CL C08K, C08L Other: WPI, EPODOC

C08K 3/013 (2018.01) C08K 5/17 (2006.01) C08K 13/02 (2006.01) C08L 15/00 (2006.01)

CN 106479007 A CN 105860510 A CN 105754171 A (72) Inventor(s):

Marina Fernando (74) Agent and/or Address for Service:

Williams Powell

Staple Inn, LONDON, WC1V 7QH, United Kingdom (54) Title of the Invention: Fire retardant natural rubber based compositions Abstract Title: Fire retardant rubber composition (57) Aflame retardant rubber composition comprises a rubber compound containing epoxidised natural rubber (ENR), inorganic filler, and a flame retarding additive. Typically, the inorganic filler is present in an amount of 40-65 wt.% and may be aluminium hydroxide, magnesium hydroxide, zinc borate, zinc hydroxyl stannate, or silica. The flame retarding additive may be an intumescent additive and may be an organic phosphorus-nitrogen-containing compound, such as ethylene diamine phosphate. The rubber compound may contain 25 mol.% or 50 mol.% epoxidised natural rubber. Aflame retarding composition comprising epoxidised natural rubber, inorganic filler, and an additive is also disclosed. A further halogen-free flame retarding composition comprising epoxidised natural rubber, inorganic filler, and an organic phosphorus-nitrogen-containing additive is claimed.

1/4

	IR	NR(SMR 10)	DPNR	ENR50
max. % weight loss rate, (%wt. loss/sec)	0.82	0.88	0.82	0.72
Temperature at maximum wt. loss, (°C)	389	383	389	412

FIGURE 1

2/4

	Standard	Requirement	Measurement on
			ENR 50 based, Natural-FR compound
Smoke density,	EN5659-2;25kW/m²	<150	97 (9mm)
Ds max
Smoke toxicity, CITg	EN5659-2;25kW/m²	<0.75	0.22 (9mm)
Flame Spread,CHF	EN ISO 9239-1, kW/m²	>8	>10.8 (9mm)
Flammability	BS EN ISO 4589- 2:1999	>32	54.3 (6mm) 48.3(4mm)

FIGURE 2

3/4

	SMR 10	ENR50
max. % weight loss rate, (%wt. loss/sec)	0.19	0.16
Temperature at maximum wt.loss, (°C)	382	412

FIGURE 3

4/4

	ENR50	EPDM/EVA
max. % weight loss rate, (%wt. loss/sec)	0.06	0.07
Temperature at maximum wt.loss, (°C)	419	370

FIGURE 4

FIRE RETARDANT NATURAL RUBBER BASED COMPOSITIONS

Field of Invention

The present invention relates to fire retardant natural rubber compositions, and more particularly to halogen-free fire retardant compositions based on epoxidized natural rubber (ENR).

Background of the Invention

In the industrial rubber products sector, new requirements for reaction to fire tests on materials are in place, such as in the construction and transportation industries. Fire statistics clearly indicate that more lives are lost by smoke density, which impedes escape and is toxic by inhalation. Legislation on the use of materials exists in several industrial sectors worldwide to improve the safety of the public and safeguard structures. One such example is the requirements in the rail sector where stringent testing is needed as part of a product acceptance phase. For example, in the rail sector in Europe the new harmonized EU standard Railway applications-Fire protection on railway vehicles, Part 2: Requirements for fire behaviour of materials and components - EN45545-2 (2013) lists requirements for flame resistance of materials used in rolling stock. In this standard hazard level categories are indicated, based on a matrix which consider the train design and the operating environment. The defined material tests, consider many aspects of fire development and growth such as, the heat released from a burning material, the extent of flame spread once initiated, the ease of ignition as well as the smoke density and toxicity. Current use halogen free, low smoke, low toxic emission rubbers are based on synthetic elastomers, and do not contribute to a low carbon economy, thus the present invention provides a greener route to achieving material flammability resistance.

EP 2196492B1 discloses a method of protecting an elastomeric body with fire retardant coating. The fire retardant coating has been successfully commercialized and is in use to protect rubber springs in the rail bogie. The fire retardant coating is halogen-free and comprises a fire retardant substance and a binder material. The fire retardant coating can be adapted to include at least one material from the group zinc borate, aluminium trihydrate, expandable graphite, ammonium polyphosphate, magnesium hydroxide, montmorillonite clay and red phosphorous. Similarly, it is claimed that the binder material can be selected from the group consisting of NR, EPDM ENR, SBR, PU, NBR and HNBR.

WO 2014019008 discloses a polymeric composition suitable for use as a coating containing a vinyl-acetate containing thermoplastic polymer and an unsaturated elastomer vulcanized with sulphur and a method of application of the coating thereof is claimed.

The above coatings approach is not based on natural resource derived polymers and accordingly there is a commercial need for the provision of halogen-free natural rubber based fire retardant compositions. These will have potential applications as an outer layer in rubber to metal-bonded products as well as to be used directly on its own and not as an outer layer, in other suitable applications such as flooring.

Summary of the Invention

An aspect of the present invention provides a halogen-free flame retarding composition comprising an epoxidized natural rubber, inorganic fillers in range of 40 to 65 in weight percentage; and an organic nitrogen-phosphorous containing additive .

Another aspect of the present invention provides a flame retarding rubber composition having hardness of 90 IRHD, 50 mol % epoxidized natural rubber and suitable for entrance matting in public or private establishments.

A further aspect of the present invention provides a flame retarding rubber composition having hardness of 85 IRHD, 50 mol % epoxidized natural rubber and suitable for coloured floor tiles in public areas.

A further aspect of the present invention provides a flame retarding rubber composition having hardness of 78 IRHD, 25 mol % epoxidized natural rubber and suitable for use as an outer fire retardant layer in anti-vibration components.

Brief Description of the Drawings

Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a table illustrating TGA/DTG data for raw rubbers in air at 30°C/min, according to an embodiment herein;

Figure 2 shows a table illustrating fire test data on ENR 50 based fire retardant entrance matting compound (Natural-FR) , according to an embodiment herein;

Figure 3 shows a table illustrating TGA/DTG data on typical fire retardant compounds used in entrance matting and a SMR 10 compound based on the same formulation as the ENR 50 compound measured in air at a rate of 30°C/min, according to an embodiment herein; and

Figure 4 shows a table illustrating TGA/DTG data on current fire retardant compounds used in entrance matting and the ENR 50 compound measured in air at a rate of 10°C/min

Detailed Description of the Preferred Embodiments

The teachings herein relate generally to flame-retardant rubber compositions to produce rubber articles in industrial applications, which needs to meet current requirements for fire safe materials. The flame-retardant rubber compositions as described can be used in making articles that can be used at public places wherein flame resistance is required to prevent fire initiation and spread.

The preferred embodiments provide a halogen-free fire retardant composition that comprises epoxidised natural rubber with varying degrees of epoxidation, inorganic fillers in the range 40% - 65% by weight, and an organic nitrogenphosphorous containing additive with possible synergism with epoxidised natural rubber.

The preferred flame/fire retardant rubber composition described herein is made using natural rubber based compound and more specifically an epoxidized natural rubber. The natural rubber based compound advantageously consists of an epoxidized natural rubber (ENR). Since no synthetic rubber derived from petroleum resources is used, it is possible to reduce the amount of use of materials derived from petroleum resources .

Thermal decomposition data on the raw ENR 50 rubber using thermogravimetric analysis and differential thermogravimetric analysis (TGA/DTG) when compared with other natural rubbers demonstrates its superior performance as shown in Figure 1. The maximum rate of weight loss for ENR is 12% lower than synthetic polyisoprene (IR) and deproteinised natural rubber (DPNR) and 18% lower than field grade natural rubber (NR), SMR 10. Similarly, the temperature at which the maximum decomposition occurs is also higher for ENR 50 by 23°C and 29°C compared with IR and NR (SMR 10).

The epoxidized natural rubber (ENR) is a modified natural rubber, in which unsaturated double bonds of a natural rubber (NR) are epoxidized. Epoxidation increases the glass transition temperature by approximately 1° for each mole percent epoxidation, the resulting polymer as compared with NR has improved damping, better oil resistance, reduced gas permeability, improved interaction with polar fillers such as silica resulting in improved wet grip. The ability to strain crystallize is however retained up to 75% epoxidation and epoxidation reduces the storage hardening. Unlike NR, premastication of ENR is not generally required as the breakdown on a mill or in an internal mixer is rapid. ENR is normally compounded with either semi-EV and EV cure. A base is added to ENR recipes to improve the ageing behaviour of ENR based compounds.

With respect to the epoxidized natural rubber (ENR), those commercially available may be used such as Ekoprena™ as manufactured by FGV in Malaysia, or those formed by epoxidizing a natural rubber (NR) may be used. With respect to the method for epoxidizing the natural rubber (NR), not particularly limited, for example, a chlorohydrin method, a direct oxidizing method, a hydrogen peroxide method, an alkyl hydroperoxide method and a peroxide method may be used. With respect to the peroxide method, for example, a method may be used in which, for example, an emulsion of a natural rubber is allowed to react with an organic peroxy acid, such as acetic peroxy acid and formic peroxy acid, serving as an epoxidizing agent.

The epoxidation ratio of the epoxidized natural rubber (ENR) is preferably set to 5 mol % or more, preferably, to 10 mol % or more. In the present specification, the epoxidation ratio refers to a ratio of the number of epoxidized double bonds among all the number of double bonds in a natural rubber prior to the epoxidization, and this ratio is found by using, for example, a titration analysis and a nuclear magnetic resonance (NMR) analysis. With respect to the epoxidized natural rubber (ENR), typically, an epoxidized natural rubber having an epoxidation ratio of 25 mol %, or an epoxidized natural rubber having an epoxidation ratio of 50 mol %, may be used in fire retardant formulations

Fire retardant rubber compound based on epoxidised natural rubber thus provides a fully compliant rubber compound that can meet current reaction to fire tests specifications on materials for a number of rubber products. Data showing the compliance of an entrance matting compound based on epoxidized natural rubber is shown in Figure 2.

The rubber composition according to the preferred embodiment of the present invention comprises one or more inorganic fillers. The inorganic filler is preferably blended in a range from 40 to 65 parts by weight relative to the total weight of the compound. The compounding amount of the inorganic filler is preferably set to 40 parts by weight or more, preferably to 50 parts by mass or more, and is also preferably set to 65 parts by mass or less.

The inorganic filler consists of at least one material selected from the group consisting of, aluminium hydroxide, magnesium hydroxide, zinc borate, zinc hydroxy stannate and silica .

In the preferred embodiments, in addition to inorganic fillers, organic phosphorus-nitrogen compound, ethylene diamine phosphate (commercially available from Polymer Tailoring, UK) are used as an additive in the epoxidized natural rubber to confer the required flame retardancy to composition. These types of fire retardants can be active either in the condensed or the vapour-phase or both. Phosphorus has very good flame retarding properties and it is believed that the evolution of ammonia from the decomposition of the nitrogen-phosphorus additive, a non-flammable gas, dilutes the fire gases. The decomposition of the nitrogenphosphorus additive results also in phosphoric acid which encourages char formation.

In the preferred embodiments, the range of fillers and fire retardant additives specified, when used in combination were found to act with epoxidised natural rubber in a manner to give enhanced fire retardant activity. The addition of fire retardant additives delays the thermal decomposition of the epoxidised natural rubber based compound when compared with a similar compound based on fire retardant natural rubber as shown in Figure 3. This is illustrated by data showing that the maximum rate of weight loss is significantly reduced by the addition of FR additives (comparing values in Figure 1 and Figure 3) but that the ENR 50 based compound has a lower maximum rate of weight loss as compared with the NR based compound. The maximum temperature at which the maximum weight loss rate occurs, is higher for the ENR 50 compound than the NR based compound indicating the delayed thermal decomposition of the ENR 50 compound.

The preferred embodiments comprising epoxidised natural rubber with varying degrees of epoxidation, inorganic fillers in the range 40% - 65% by weight, and an organic phosphorousnitrogen containing additive are believed to deliver enhanced fire retardant properties through synergistic interactions between the various fillers, fire retardant additives and the epoxidised natural rubber.

According to an embodiment of the present invention a flame retarding rubber composition having hardness of 90 IRHD comprising an epoxidized natural rubber, an inorganic filler in range of 40 to 65 in weight percentage and an organic phosphorous-nitrogen containing additive is suitable for suitable for entrance matting in metro stations and other areas where fire retardant material requirements are present. Figure 4 shows thermal decomposition data (TGA/DTG) on a fire retardant compound in current use in entrance matting manufacture made from an ENR 50 based compound and a comparison with a fire compliant EPDM/EVA compound also used currently in entrance matting manufacture. The ENR 50 based compound shows improved decomposition characteristics as compared with the EPDM/EVA compound. Furthermore, the ENR 50 compound meets all requirements in reaction to fire tests

in place specified	for materials used as in BS EN 45545-2:2013.	flooring	for	railways	as
According	to an embodiment of the present	invention flame
retarding	rubber composition has	hardness	of	85 IRHD	and

includes an epoxidized natural rubber, an inorganic filler in range of 40 to 65 in weight percentage or by mass, and an organic phosphorous-nitrogen containing additives, such as ethylene diamine phosphate, ammonium polyphosphate, melamine phosphate, melamine polyphosphate or their mixtures, are suitable for coloured floor tiles in public areas.

According to an embodiment of the present invention flame retarding rubber composition having hardness of 78 IRHD comprising an epoxidized natural rubber, an inorganic filler in range of 40 to 65 in weight percentage and an organic phosphorous-nitrogen containing one additive is suitable for use as an outer fire retardant layer in anti-vibration components .

A Typical FR formulation based on ENR 50 formulation consists of the following:

Ingredient	% w/w
ENR 50 (Ekoprena™ 50)	20 - 30
Carbon Black (or silica)	0-10 (or 0 - 20)

Inorganic FR fillers	40 - 65
Organic phosphorous-nitrogen	0-10
additive
Antidegradants,	activators,	0.5 - 5.0
base, colorant
Cure System
Sulphur		0.25 - 0.5
Sulfenamide		0.25-0.5
PVI		0 - 0.1

While various embodiments are disclosed herein, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail may be made therein without departing from the spirit and scope of the methods and systems disclosed herein. Thus, the breadth and scope of the claims should not be limited by any of the example embodiments disclosed herein.

Claims

1. A flame retarding rubber composition comprising:

a rubber compound containing an epoxidized natural rubber;

inorganic fillers in range of 40 to 65 parts by mass; and a flame retarding additive.

2. The flame retarding composition of claim 1, wherein said additive is a phosphorous-nitrogen containing additive.

3. The flame retarding composition of claim 1, wherein the flame retarding additive is an organic phosphorousnitrogen containing compound.

4. The flame retarding composition of claim 1, 2 or 3, where in the flame retarding rubber composition has a hardness of 90 IRHD.

5. The flame retarding composition of claim 4, wherein the rubber compound has 50 mol % epoxidized natural rubber.

6. The flame retarding composition of claim 1, 2, or 3, where in the flame retarding rubber composition has hardness of 85 IRHD.

7. The flame retarding composition of claim 6, wherein the rubber compound has 50 mol % epoxidized natural rubber.

8. The flame retarding composition of claim 1, 2 or 3, where in the flame retarding rubber composition has hardness of 78 IRHD.

9. The flame retarding composition of claim 8, wherein the rubber compound has 25 mol % epoxidized natural rubber.

10. The flame retarding composition of any preceding claim, wherein the flame retarding additive is an intumescent flame retardant additive.

11. The flame retarding composition of any preceding claim, wherein the inorganic filler is selected from at least aluminium hydroxide, magnesium hydroxide, zinc borate, zinc hydroxyl stannate and silica.

12. A flame retarding composition comprising:

a natural rubber compound consisting of an epoxidized natural rubber;

an inorganic filler in range of 40 to 65 parts by mass; and an additive.

13. A halogen free flame retarding composition comprising:

an epoxidized natural rubber;

an inorganic filler in range of 40 to 65 parts by mass; and an organic phosphorous-nitrogen containing additive .

14. The flame retarding composition of claim 13, where in the flame retarding rubber composition having hardness of 90 IRHD.

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Application No: GB 1806256.2 Examiner: Dr Paul Minton