Polymer Degradation and Stability 86 (2004) 69e73

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The effect of decabromodiphenyl oxide andantimony trioxide on the flame retardation of

ethyleneepropyleneediene copolymer/polypropylene blends

Li Yua, Wenjun Wangb, Weidong Xiaoa,)

aFaculty of Chemistry and Material Science, Hubei University, Wuhan 430062, ChinabSchool of Life Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, China

Received 21 October 2003; received in revised form 31 December 2003; accepted 3 January 2004

Abstract

The flammability of ethyleneepropyleneediene copolymer/polypropylene (EPDM/PP) filled with decabromodiphenyl oxide(FR-10) and antimony trioxide (Sb2O3) is discussed. Limiting oxygen index (LOI), tensile strength and thermo-gravimetric analysis(TGA) were used. The results showed that FR-10 and Sb2O3 had little flame retardation effect on EPDM/PP. FR-10/Sb2O3 had very

good flame retardation and could display synergism in EPDM/PP. The addition of flame retardant could deteriorate the tensilestrength and elongation at break of EPDM/PP. FR-10 and FR-10/Sb2O3 lowered the initial decomposition temperature of EPDM/PP, which did not affect their application.

� 2004 Elsevier Ltd. All rights reserved.

Keywords: EPDM/PP; Flame retardation; Decabromodiphenyl oxide; Antimony trioxide; Synergism

1. Introduction

Thermoplastic elastomers (TPEs) are materials withthe processing behaviour of thermoplastics but havingmechanical properties and elastic recovery similar to theordinary thermosets or vulcanised rubbers [1]. Amongdifferent sorts of TPEs, those prepared by physical meltmixing of a polyolefin and an elastomer have gainedsignificant attention due to the ease of tailoring therequired properties and also the simple preparationmethod [2].

Polypropylene (PP) is one of the major commoditypolymers, having excellent physical properties such ashigh stiffness and tensile strength. However, due toa relatively high glass transition temperature (about0 (C [3]), PP shows brittle behaviour at low temper-atures, which limits its applications. In order to improvethe impact strength at low temperatures, PP has beenmixed with different elastomers. Among these elasto-mers, ethyleneepropyleneediene copolymer (EPDM) is

) Corresponding author.

E-mail address: yuli75w@sohu.com (L. Yu).

0141-3910/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.polymdegradstab.2004.01.015

the most widely used [4,5]. EPDM/PP is extensively usedin many fields, for example, cars, electric casings, in-terior decoration, insulation, and so on. However, thelimiting oxygen index of untreated EPDM/PP is only 18.This drawback restricts the range of its application.However, little literature has been found on the flameretardation of EPDM/PP. Therefore, it should be animportant task to study its flame retardation.

Flame retardation is a technology by which the nor-mal degradation or combustion of polymers is alteredby addition of certain chemicals. Some polymers areinherently, to a relative degree, fire retardant or smokeretardant and their fire performance is acceptable forcertain applications. However, for many polymers, it isnecessary to improve their fire performance by in-corporating commercially available flame retardant [6].Traditionally, the halogenated organic compounds werewell known flame retardant additives for the hostpolymers. They were generally used in incorporationwith antimony trioxide compounds to enhance theirflame retardant efficiency (halogen-antimony synergisticeffect) [7]. On the whole, flame retardant systems basedon halogenated organic compounds frequently had a

70 L. Yu et al. / Polymer Degradation and Stability 86 (2004) 69e73

negative effect on mechanical properties of the poly-mers. The presence of antimony trioxide acting insynergy with the halogenated organic compoundscreated interfaces with the host polymers, which maylead to a deterioration of tensile strength and elongationat break [8].

In this study, we appraised the properties of EPDM/PP flame-retarded by decabromodiphenyl oxide (FR-10)and antimony trioxide (Sb2O3). Then the fire behaviourof the formulations was investigated by limiting oxygenindex (LOI) and the mechanical properties were testedthrough the tensile strength; finally the thermal behav-iour was investigated with the thermo-gravimetricanalysis (TGA).

2. Experimental

2.1. Raw materials

EPDM used in this work was a commercial polymerEPDM3080, manufactured by Jilin Chemical Ltd(China). PP was also a commercial polymer PP401 andwas supplied by Langang Petrochemical Ltd (Gansu,China). Phenolic resin (Type 2402) was supplied byZaoyang Chemical Ltd (Hubei, China) and used asvulcanising agent. Stannous chloride (SnCl2�2H2O) wasa commercial product from Haiguang Chemical Phar-macy Industry (Tianjin, China) and used as cureaccelerator. FR-10 was produced by Hangu salt Industry(Changlu, Tianjin, China). Antimony trioxide was pro-duced by Yiyang antimony Industry (Hunan, China).The size of antimony trioxide is 0.5e1.0 mm.

2.2. Preparation of the samples

A typical recipe is given in Table 1. EPDM and PPwere mixed in a twin screw compounder (Type SK-160B, made in Shanghai, China) at 170 (C for 5 min.For the formulation with a cross-linking system, phe-nolic resin and stannous chloride were added into themixer and the mixing was carried out for about 5 min.Flame retardant, including FR-10, Sb2O3 and FR-10/Sb2O3, was added into the mixer and the mixing wascontinued for about 5 min. The temperature and rollerspeed remained unchanged in these experiments for allthe blends. Test samples were prepared in a PressVulcaniser (Type XL-B4004002, made in Wujin Rubber

Table 1

Typical recipe for preparation of the samples

Ingredient Amount ( g)

EPDM 60

PP 40

Phenolic resin 3

Stannous chloride 0.6

Machine Manufactory, Changzhou, China), first hotpressing at 10 MPa, 180 (C for 10 min and then coolingto 100 (C.

2.3. Measurements of the samples

2.3.1. Limiting oxygen index (LOI)The minimum oxygen concentration required to

sustain burning was measured. Samples were held ver-tically in an oxygen index system instrument (Type HC-2, made in Jiangning Analysis Instrument Factory,Nanjing, China). All the tests were carried out accordingto the standard oxygen index test ISO 4589-1984.

2.3.2. Mechanical propertiesThe tensile strength and elongation at break were

measured at room temperature with a Material TestSystem (Model AG-10KNA, made in Shimadzu Cor-poration Kyoto, Japan) according to the standard GB/T16421-1996 (China). The elongation rate was set at100 mm/min.

2.3.3. Thermo-gravimetric analysis (TGA)The decomposition temperature of flame-retarded

EPDM/PP was observed using a PerkineElmer thermo-gravimetric analyser under nitrogen atmosphere, withsample masses of about 5.5 mg and a heating rate of20 (C/min. The range of temperature was 30e600 (C.

3. Results and discussion

3.1. Limiting oxygen index (LOI)

The limiting oxygen indexes of flame-retardedEPDM/PP are listed in Table 2. The results showed thatuntreated EPDM/PP had low resistance to combustion.After addition of FR-10, LOI value increased slightly.

Table 2

LOI value and mechanical properties of untreated and treated EPDM/

PP

FR-10

(phr)

Sb2O3

(phr)

Tensile

strength (MPa)

Elongation

at break (%)

LOI

0 0 19.2 382 18.0

10 0 21.0 424 18.4

15 0 20.6 416 19.3

20 0 20.0 382 19.7

25 0 19.2 356 20.2

0 3 18.7 347 19.3

0 5 17.9 322 19.7

0 7 17.2 289 19.7

0 10 16.5 257 20.2

20 3 16.6 319 23.2

20 5 16.6 310 24.1

20 7 16.4 299 25.4

20 10 16.2 212 25.4

71L. Yu et al. / Polymer Degradation and Stability 86 (2004) 69e73

With increasing amounts of FR-10 the value was raisedfrom 18.0 to 20.2. The results indicate that FR-10 aloneis not a very effective flame retardant towards EPDM/PP. The presence of a small amount of Sb2O3 couldincrease the LOI value of EPDM/PP, as the value wasraised from 18.0 to 19.3, but the LOI value had littlesignificant variation from 3 to 10 phr. Therefore, theflame retardation of Sb2O3 towards EPDM/PP also wasnot very good. There were higher LOI values as Sb2O3

was incorporated with FR-10 because of synergism.Antimony trioxide acted as a synergist with halogens,

particularly with bromine, while it was almost totallyineffective when used without halogen. Synergism occur-red through a series of reactions; the basic reaction inthe case of brominated flame retardant was [9]:

Sb2O3C6HBr52SbBr3C3H2O

where the HBr was produced resulting from the decom-position of brominated flame retardant. Antimony tri-bromide formed a dense white smoke that snuffed theflame by excluding oxygen from the front of the flame.

In order to determine properly if two kinds of flameretardant have synergism, we can compare LAB withLACB. LAB is the LOI value when two kinds of flameretardant are commonly used. LACB ¼ LACLB � LP,LA or LB is the LOI value when flame retardant is usedalone, LP is the LOI value of polymer matrix [10]. WhenLAB > LACB, two kinds of flame retardant havesynergism. When LAB ¼ LACB, two kinds of flame re-tardant have additional role. When LAB !LACB, twokinds of flame retardant have opposite role.

The DLOI (DLOI ¼ LAB � LACB) values of Sb2O3

incorporated with FR-10 are listed in Table 3. Theresults showed that DLOI > 0, so FR-10 incorporatedwith Sb2O3 had synergism. The stronger the synergism,the bigger the DLOI value was. When we added 20 phrFR-10 and 7 phr Sb2O3, DLOI value was biggest.

3.2. Mechanical properties

In general, flame retardant caused a decrease in themechanical properties. In order to assess the effect of the

Table 3

The DLOI value of EPDM/PP containing FR-10 and Sb2O3

FR-10

(phr)

Sb2O3

(phr)

LF LS LP LFCS LFS DLOI

20 3 19.7 19.3 18.0 21.0 23.2 2.2

20 5 19.7 19.7 18.0 21.4 24.1 2.7

20 7 19.7 19.7 18.0 21.4 25.4 4.0

20 10 19.7 20.2 18.0 21.9 25.4 3.5

LF, LS, LFS are the LOI values of EPDM/PP, respectively, flame-

retarded by FR-10, Sb2O3, FR-10/Sb2O3.

LP is the LOI value of untreated EPDM/PP.

LFCS ¼ LFCLS � LP.

DLOI value is the difference of LOI value between LFS and LFCS.

flame retardant on mechanical properties of EPDM/PP,the tensile strength and elongation at break were mea-sured. The data are presented in Table 2. It was evidentthat the addition of FR-10 could increase the mechan-ical properties of EPDM/PP, as the tensile strength wasraised from 19.2 to 21.0 MPa and the elongation atbreak was raised from 382 to 424%. But the moreFR-10 was added, the less were the tensile strength andelongation at break. When we added 25 phr FR-10 toEPDM/PP, the tensile strength and elongation at break,respectively, dropped to 19.2 MPa and 356%. AddingSb2O3 sharply decreased the mechanical properties, asthe tensile strength was reduced from 18.7 to 16.5 MPaand the elongation at break dropped from 347 to 257%.Sb2O3 is a mineral and can create interfaces withEPDM/PP, which may lead to a deterioration of tensilestrength and elongation at break. Adding FR-10/Sb2O3

resulted in a reduction of the elongation at break from319 to 212%, but the tensile strength changed little.When we added 20 phr FR-10 and 10 phr Sb2O3, theelongation at break dropped to 212%, which is notadequate for the application of EPDM/PP. In order toobtain a better combination of mechanical propertiesand flame retardation, the combination of 20 phr FR-10and 7 phr Sb2O3 seemed to be a suitable solution.

3.3. Thermo-gravimetric analysis (TGA)

When the so-called flame retardant elements areincorporated into polymeric materials, the weight losspattern of the polymers is altered. Fig. 1 shows someTGA thermograms of EPDM/PP investigated in thisstudy. Thermal stability and degradation data ofEPDM/PP from TGA thermograms are listed in Table 4.

The difference in degradation behaviour of theEPDM/PP containing various flame retardant elementscould be clearly seen from the differential thermo-gravimetric (DTG) thermograms. Based on the numbersof peaks in the DTG thermograms, the weight lossprocesses of EPDM/PPwere considered as several stages.Owing to the action of the flame retardant elements, verydifferent degradation behaviour was observed anddifferent numbers of weight loss stages were found [11].The temperatures at the maximumweight loss rate (Tmax)and the value of the maximum weight loss rate (Rmax) forevery stage of weight loss were read from the peak valuesof the DTG thermograms (Table 4).

In nitrogen, the untreated EPDM/PP showed a massloss stage (assigned as stage 2 weight loss) at temper-ature about 430 (C. Introducing FR-10 into EPDM/PPcaused a second stage mass loss (assigned as stage 1weight loss). Introducing FR-10 into EPDM/PP wouldreduce the initial decomposition temperature of EPDM/PP. The depressed initial decomposition temperatureof the FR-10-containing EPDM/PP might possiblyresult from the decomposition of CeBr bonds or the

72 L. Yu et al. / Polymer Degradation and Stability 86 (2004) 69e73

100

1# 2#

3# 4#

80

60

40

Wei

ght

20

030 100 200 300 400

Temperature(°C)

Temperature(°C) Temperature(°C)

Temperature(°C)

500 600–60

–40

–20

0 100

80

60

40

20

030 100 200 300 400 500 600

–60

–40

–20

0

100

80

60

40

20

030 100 200 300 400 500 600

–60

–40

–20

0100

80

60

40

20

030 100 200 300 400 500 600

–60

–40

–20

0

Wei

ght

Wei

ght

Wei

ght

Der

ivat

ive

Wei

ght

/m

in)

Der

ivat

ive

Wei

ght

/m

in)

Der

ivat

ive

Wei

ght

/m

in)

Der

ivat

ive

Wei

ght

/m

in)

Fig. 1. Some typical TGA thermograms of EPDM/PP: (1#) the untreated EPDM/PP; (2#) the add-on of 20 phr FR-10; (3#) the add-on of 7 phr

Sb2O3; (4#) the add-on of 20 phr FR-10 and 7 phr Sb2O3.

evaporation of FR-10. However, the weight loss of theFR-10-containing EPDM/PP at high temperatures re-gion (see R2

max in Table 4) was less than that of un-treated EPDM/PP. This was due to the fact that thedecomposition of CeBr bonds or the evaporation ofFR-10 at relatively lower temperature protected theresidues from heat. The percentage of totally relativemass loss in stage 1 of FR-10-containing EPDM/PP,which was the difference between W1 (see Table 4) andthe percentage of total mass loss of untreated EPDM/PPin the temperature, was proportional to the addition ofFR-10. FR-10 mostly decomposed or evaporated instage 1, and that is why FR-10 was not an effective flameretardant towards EPDM/PP.

The thermogram of the Sb2O3-containing EPDM/PPwas the same as that of untreated EPDM/PP except forthe char ratio at 600 (C. The char ratio at 600 (C ofthe Sb2O3-containing EPDM/PP was 4.3 wt% and wasnearly proportional to the addition of Sb2O3 whichmostly did not evaporate on heating. So Sb2O3 wasnot an effective flame retardant towards EPDM/PP.From the results of limiting oxygen index and thermo-gravimetric analysis, Sb2O3 mostly played a filling rolein EPDM/PP.

If we introduced FR-10 and Sb2O3 into EPDM/PP,much more complicated mass loss behaviours wereobserved. The char ratio at 600 (C was 1.8 wt%, whichwas higher than those of untreated EPDM/PP and the

Table 4

Thermal stability and degradation data of EPDM/PP from TGA thermograms: (1#) the untreated EPDM/PP; (2#) the add-on of 20 phr FR-10; (3#)

the add-on of 7 phr Sb2O3; (4#) the add-on of 20 phr FR-10 and 7 phr Sb2O3

T5%

((C)Tmax

1

((C)Rmax

1

(%/(C)W1

(wt%)

Tmax2

((C)Rmax

2

(%/(C)Tmax

3

((C)Rmax

3

(%/(C)Tf

((C)Char ratio at

600 (C (wt%)

1# 437 0.6 489 52.3 502 0

2# 369 416 6.7 21.4 497 36.7 506 0.5

3# 443 487 52.9 504 4.3

4# 361 374 13.5 19.3 476 30.0 542 2.9 552 1.8

T5% represents the onset decomposition temperature of 5% weight loss.

Tmax represents the temperature of maximum weight loss rate in the n-stage decomposition.

Rmax represents the maximum weight loss rate in the n-stage decomposition.

Tf represents the final decomposition temperature.

W represents the percentage of total mass loss in the stage 1 decomposition.

73L. Yu et al. / Polymer Degradation and Stability 86 (2004) 69e73

FR-10-containing EPDM/PP. As mentioned previously,Sb2O3 had converted SbBr3. From a promotion ofcharring after the main stage of weight loss, we can inferthat SbBr3 had both flame chemistry and a condensedphase effect. It was also found that 4# showed relativelyhigher Rmax

1 than 2#, which could account for central-ization of flame retardant decomposition. That is to say,the add-on of Sb2O3 could accelerate the decompositionof FR-10.

4. Conclusions

According to the analysis of the results of experi-ments, it was evident that untreated EPDM/PP had lowresistance to combustion. FR-10 and Sb2O3 when usedalone produced little improvement in the flame re-tardation. The combination of FR-10 and Sb2O3

showed more effective flame retardation than theindividual components. The maximum LOI value was25.4, which was obtained from EPDM/PP containing25 phr FR-10 and 7 phr Sb2O3. But, if too much flameretardant was added in the compound, the tensilestrength and elongation at break decreased rapidly.The thermal behaviour of EPDM/PP, such as the

degradation patterns, temperatures and rates of maxi-mum mass loss was altered by these flame retardants.FR-10 and FR-10/Sb2O3 lowered the initial decompo-sition temperature of EPDM/PP, but not sufficiently toaffect their application.

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