poly-1-butene/clay nanocomposite effect of compatibilizers on thermal and fire retardant properties

Polymers for Advanced Technologies 2006, 17(4), 246-254. DOI:10.1002/pat.688

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Poly-1-Butene/Clay Nanocomposite Effect of Compatibilisers on

Thermal and Fire Retardant Properties

Sergio Bocchinia1

, Alberto Frachea, Giovanni Camino

a, Enrico Costantini

b,

Giuseppe Ferrarab and Fabiana Fatinel

b

a) Centro di Cultura per l’Ingegneria delle Materie Plastiche, Politecnico di Torino sede

di Alessandria, INSTM Research Unit, V. Teresa Michel 5 15100 Alessandria, Italy

b) Centro Ricerche "G. Natta"- Basell poliolefine Italia, P.le L. Donegani 44100

Ferrara, Italy

ABSTRACT: Isotactic poly-1-butene was melt blended with montmorillonite modified

with di-methyl di-hydrogentallow ammonium ion. Maleic anhydride grafted

polypropylene or polyethylene-vinyl-acetate were used as compatibilisers. Thermal and

fire retardant behaviour of the polymer matrix were enhanced by the attitude of clay to

form a thermally stable protecting physical barrier on the surface of the decomposing

polymer material.

Keywords: Clay, Flame retardance, Compatibilisation, Polybutene, Cone calorimeter,

Thermal stability, Nanocomposite

e-mail: [email protected]

mailto:[email protected]


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INTRODUCTION

Polymer nanocomposites are emerging as a new class of industrially important

materials. At loading levels of 2-3 wt% of inorganic they offer similar performance to

conventional polymeric composites with 30-50 % wt of reinforcing fillers1,2,3,4

The clay containing polymer nanocomposites, which are the most developed so far,

offer several advantages over the polymer matrix or classical composites. The main

improvements are in: modulus, heat resistance, dimensional stability, barrier properties

and flame retardancy.

Clay polymer nanocomposites have been proposed as a new approach for fire retardance

of polymers, shifting fire retardant action from gas phase as in the case of most

traditional systems, to the condensed phase. Indeed recent results obtained in polymer

materials combining inorganic and organic structures at nanoscale level show that

ablation of the organic structure occurs on combustion with formation of a protective

surface layer composed by a thermally stable combination of char and inorganic

material.5,6,7,8

Nowadays the strategy of polymer nanocomposites preparation is based on primary

intercalation of onium ions between the clay layers by cation exchange to render them

organophilic (organoclay). Most of the work existing in literature and industrial

applications concern melt blending of organoclays with polyamides and other polar

matrices whereas clay-polyolefin nanocomposites are in the early stage of development

because of difficulty to diffuse these non-polar, non-reactive polymers even into the

organophilic environment of modified organoclay interlamellar galleries. In these cases

a compatibiliser e.g. maleic anhydride grafted polypropylene is introduced in melt

compounding with the matrix polyolefin9,10,11

To best of our knowledge there are a few published papers which concern melt blending

of organophilic clays with poly-1-butene.12,13

The work is focalised on mechanical

properties of the obtained intercalated nanocomposite but also an increase of

temperature thermal degradation temperature in presence of air is claimed.

In the present work poly-1-butene is melt-blended with clay using two different

compatibilisers: maleic anhydride grafted polypropylene and poly (ethylene-co-


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vinylacetate). The effect of type of compatibiliser on morphologies, thermal properties

and fire resistance is studied.

EXPERIMENTAL

Materials:

Poly-1-butene highly isotactic, semi-crystalline, nucleated homopolymer, PB 0110

(PB1) supplied by Basell s.p.a. was used. Compatibilisers are poly-propylene

functionalized with 1.2 wt% of maleic anhydride POLYBOND 3200 (PB) supplied by

Uniroyal Chemical and poly(ethylene-co-vinylacetate) 9% wt of vinyl acetate Elvax 750

(El9) supplied by duPont. All polymers were used as supplied.

The filler used is a natural montmorillonite modified by ion-exchange with di-methyl

di-hydrogentallow ammonium salt (95 meq/100 g clay) Cloisite 20A (Cl) supplied by

Southern Clay products Inc. which was dried 4 hours at 100°C under vacuum before

processing. The materials used are listed in Table 1.

Table 1: Composition of melt-blended samples and abbreviations of the materials

Sample PB 0110 Compatibiliser Cloisite 20A

% Type % wt. % wt.

PB1 100.0 - - -

PB1Cl 95.0 - - 5.0

PB1El9 97.9 Elvax 750 2.1 -

PB1El9Cl 93.0 Elvax 750 2.0 5.0

PB1PB 94.7 POLYBOND 3200 5.3 -

PB1PBCl 90.0 POLYBOND 3200 5.0 5.0

Melt processing:

The composites were prepared via melt-processing using a LEISTRITZ 27 co-rotating

twin screw extruder (d=27 mm, l/d=40) using a low shear stress screw profile (Figure

1). Thermal profile 160-170-170-170-165-165-165-165-165-170, throughput 6 kg/h,

speed 100 rpm were used. The residence time was about 70 s. Three samples of PB1


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with 5% wt of clay (side-feeding 14 d) respectively without compatibiliser, with 5 wt%

PB and 2 wt% El9 were prepared (Table 1). Blank samples were prepared by processing

without clay the PB1 with the same amount of compatibilisers. Specimens for cone

calorimeter and X-ray diffraction were prepared using a hydraulic press with the two

heated plates at 160 °C using a pressure of 25 Bar for 5 minutes.

Figure 1: LEISTRITZ 27 co-rotating twin screw extruder (d=27 mm, l/d=40) profile

Characterization

X ray diffraction (XRD)

XRD-analyses were performed on compression-moulded 30x30x0.5 mm samples with a

Thermo ARL diffractometer X-tra 48 using Cu-Kα X-ray source (λ = 1.540562 Å),

step-size 0.02° at 2°min-1

scanning rate.

SEM analysis

SEM analyses were performed with a LEO 1450 VP using the backscattered modality

on surface of fragile fracture from injection-moulded samples fractured after cooling by

immersion in liquid nitrogen.

20D 40D 36D

Vacuum

32D 28D 24D

Side Feeder

16D 12

D 8D

Polymer

4D


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TEM analysis

TEM specimens were stained with RuO4 before microtoming, then microtomed at room

temperature with an Ultramicrotome Leica UCT, thickness was about 90 nm. The grid

was 50 mesh, coated with pioloform. The analyses were performed with a Philips CM

120.

Thermogravimetric analysis (TGA)

Thermogravimetric analyses were carried out in a TA instruments Q500 thermo-balance

using a platinum pan. The measures were performed respectively under nitrogen and air

(purge flow 60 cm3 min

-1). Heating rate of 10 °C min

-1 and temperature range between

50 °C and 800 °C were applied.

Thermal degradations in air at constant temperature were performed with an initial

heating rate of 10 °C min-1

between 50 °C and 300 °C, followed by a plateau of 8 h at

300 °C. A final ramp in nitrogen was performed with heating rate of 10°C min-1

between 300 °C and 800 °C.

The experiments were preformed at list two times in order to confirm the data. The

experimental error is ± 1% by weight.

Oxygen consumption calorimetry (Cone Calorimeter)

The cone calorimeter tests were performed according to the ISO 5660-1 standard using

a Fire Testing Technology Standard Cone Calorimeter; the samples (50x50x3 mm) were

irradiated with a 50 kW m-2

heat flux and the ignition of the flame was obtained by a

spark.

The combustion behaviour is evaluated by: time to ignition (TTI), heat release rate

(HRR), peak of heat release rate (pkHRR), fire performance index FPI (defined as

pkHRR/TTI), total heat release (THR), smoke factor (SF), total evolution of CO (TCO)

and CO2 (TCO2). To analyse fire spread, analogously to “Single Burning Item”, a

FIGRA (FIre Growth RAte) index is defined as maximum of the ratio of HRR respect to

time and reported. The measures were repeated at least 3 times. The experimental error

is ± 10 %.


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FT-IR analysis

IR analyses were performed using a Perkin Elmer Spectrum GX Infrared Spectrometer.

The samples were prepared with the KBr disc techniques using a finely ground mixture

of 1 mg of sample and 100 mg of KBr pressed at 4 Mbar.

RESULT and DISCUSSION

Morphology analysis

X-ray diffraction is the main method used to asses dispersion of clays in a polymeric

matrix. From XRD d001, the commonly named “interlayer-spacing”, is calculated using

the Bragg’s law. Results of XRD are shown in Figure 2 and summarized in Table 2.

2 4 6 8

0

2000

4000

Cloisite 20A

PB1Cl

PB1El9Cl

PB1PBCl

c.p

.s.

2(deg)

2.43 nm

2.58 nm

3.11 nm

Figure 2: X-ray diffraction of Melt blended samples


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The organoclay Cloisite 20A presents a diffraction peak at 2θ 3.62 ° equivalent to

d001=2.43 nm. On dispersion in PB1, intercalation of the polymer between the layers of

the organoclay takes place. However, the sample without compatibiliser or

compatibilised with maleic anhydride grafted polypropylene (PB1PBCl) show a

d001=2.58 nm indicating that a very limited intercalation occurs with an increase of

interlayer of 0.15 nm. Whereas the sample compatibilised with EVA (PB1El9Cl) shows

a d001=3.11 with an expansion of the clay layer of 0.68 nm, indicating that extensive

intercalation for PB1El9Cl is obtained.

Table 2: d001 X-ray diffraction peak of melt-blended samples

Sample 2θ d001

degree nm

Cloisite 20A 3.62 2.43

PB1Cl 3.42 2.58

PB1PBCl 3.42 2.58

PB1El9Cl 2.84 3.11

SEM analysis of the non-compatibilised samples shows the presence of two types of

structure: irregular 10-20 μm spherical aggregates and smaller platelets-like aggregates

(Figure 3 a-b). The poor adhesion of clay is evidenced by the separation between

polymer and clays and presence of holes platelets-like-shaped. The compatibiliser

presence enhances dispersion and adhesion (Figure 3 c-f), platelets-like aggregates are

smaller and polymer adheres on them, especially for PB1PBCl (Figure 3 e-f) where the

small platelets are barely recognisable.

TEM images of the three samples are similar (figure 4 a-c) showing dark areas

corresponding to the aggregates seen in the SEM images of figure 3.

Summarising, the morphology of the poly-1-butene samples is complex comprising

aggregates in which intercalation of the polymer between the clay layers occurs

depending on the type of compatibiliser.


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a) b)

c) d)

e) f)

Figure 3: SEM analyses of melt blended samples, a-b) poly-1-butene / Cloisite 20A

(PB1Cl) magnification a=1000 b=5000 c-d) poly-1-butene / Elvax750 / Cloisite 20A

magnification c=1000 d=5000 e-f) poly-1-butene / POLYBOND3200 / Cloisite 20A

magnification a=1000 f=5000

Holes


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a) b)

c)

Figure 4: TEM analyses of melt blended samples, a) poly-1-butene / Cloisite 20A

(PB1Cl) b) poly-1-butene / Elvax750 / Cloisite 20A c) poly-1-butene /

POLYBOND3200 / Cloisite 20A

Thermal decomposition

The thermal stability of materials and blank samples was evaluated by TGA. The

temperature at which 10% and 50% of volatilisation occur (respectively T10% and T50%),

the derivative TGA curve peak (Tmax) and the residual weight at 600 °C (wtres) are

reported in Tables 3 and 4.


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Table 3: Thermogravimetic analysis of materials containing clay and blank samples in

nitrogen. Heating rate 10 °C min-1

, temperature range 50 °C-800 °C, purge gas:

nitrogen; 60 cm3 min

-1

Sample T10% T50% Tmax wtres (600 °C)

(°C) (°C) (°C) %

PB1 425 450 455 0.0

PB1Cl 430 443 445 2.4

PB1El9 403 446 454 0.7

PB1El9Cl 431 446 449 3.6

PB1PB 396 444 454 0.6

PB1PBCl 433 448 450 3.7

Table 4: Thermogravimetic analysis of materials containing clay and blank samples in

air. Heating rate 10 °C min-1

, temperature range 50 °C-800 °C, purge gas: nitrogen; 60

cm3 min

-1

Sample T10% T50% Tmax wtres (600 °C)

(°C) (°C) (°C) %

PB1 301 346 351 0.2

PB1Cl 336 389 401 2.4

PB1El9 305 349 355 0.0

PB1El9Cl 344 397 414 4.1

PB1PB 302 345 345 0.1

PB1PBCl 361 417 435 3.8

The thermal degradation in nitrogen (Table 3, Figure 5) occurs for all materials in a

single step. The T10% of pure PB1 is 425 °C, whereas it is 403 and 396 °C for the

compatibiliser containing blank samples PB1El9 and PB1PB respectively. This

decrease of stability is due to the presence in the blank of the less stable polymers El9

and PB which have a T10% in nitrogen around 400 °C when heated alone. All the

materials containing organoclay show a similar behaviour with a T10% of around 430 °C,


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higher than both PB1 (+5 °C) and the compatibilised, clay-free two blank samples

(+30/37 °C). Whereas the organoclay destabilises the polymer matrix as the degradation

proceeds as shown by decrease of 5-10 °C of Tmax in the case of the composites as

compared to the corresponding blank samples. A clear picture of the thermal

degradation is provided by the derivative curves of Figure 5. The rate of weight loss at

Tmax for PB1 increases from 2.9 %°C-1

to 8.8 %°C-1

in the presence of the organoclay

(Figure 5). Similar results were found for compatibilised materials. This behaviour was

already observed for polypropylene blended with cloisite 20A.14,15

The initial delay in

volatilization is explained by the clay layers acting as a diffusion barrier for

volatilization of chain fragments formed by thermal degradation. Whereas the increase

of volatilisation rate is due to the well known catalytic degradation activity of zeolitic

structure (such as that exhibited by the clays) on hydrocarbon moieties which

overcomes the barrier effect at the temperature at which extensive degradation

occurs16,17,18

. The residue for materials containing organoclay does not exceed 3.7 % in

weight which is in agreement with the clay inorganic part content of the composites.

200 300 400 500 600

0

20

40

60

80

100

0

-2

-4

-6

-8

-10

PB1

PB1Cl

We

igh

t (%

)

Temperature (°C)

457 °C

447 °C

We

igh

t L

oss d

eri

va

tive

(%

°C-1)

Figure 5: a) Thermal degradation in nitrogen 10 °C min-1

of Poly-1-butene (PB1) Poly-

1-butene/cloisite 20A 5 wt% (PB1Cl)


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Thermal gravimetric analyses in air demonstrate that in thermal oxidative processes

(Table 4) stability is largely improved by presence of clay. Degradation in air for PB1

(Figure 6) occurs still in a single step, as for degradation in nitrogen, but there is a

diminution of about 100 °C for T10%, T50% and Tmax, (Table 4) as already known for

polyolefins15

.

300 400 500

0

20

40

60

80

100

0,0

-0,5

-1,0

-1,5

-2,0

-2,5

-3,0

-3,5

-4,0

435 °C

414 °C

PB1

PB1Cl

PB1El9Cl

PB1PBCl

351 °CWeig

ht (%

)

Temperature (°C)

401 °C

De

riva

tive

We

igh

t (%

°C

-1)

Figure 6: Thermal oxidative degradation in air 10 °C min-1

of Poly-1-butene (PB1)

Poly-1-butene/ cloisite 20A 5 wt% (PB1Cl), Poly-1-butene/Elvax 750/cloisite 20A 5

wt% (PB1El9Cl), Poly-1-butene/POLYBOND 3200/ cloisite 20A 5 wt% (PB1PBCl)

Indeed in nitrogen, the pure thermal volatilisation of PB1 begins at about 380 °C in

Figure 5 at which temperature the carbon-carbon bonds of the polymer chain begin to

break at a measurable rate giving chain end carbon macro-radicals (I) and (II) (Scheme

1, Reaction a) which propagate the radical chain volatilisation process19

. A complex

mixture of saturated and unsaturated hydrocarbons is formed which volatilise, when

they become small enough as a result of chain fragmentation to reach a vapour pressure

high enough for evaporation. Whereas in the presence of oxygen, volatilisation begins

and ends in the Figure 6 in a range of temperature (250-400 °C) in which the rate of

Reaction a, is negligible. This is because in the presence of air, the initiation of the

chain volatilisation process is due to hydrogen abstraction by molecular oxygen well

known to behave as a bi-radical because of its two impaired electrons in the ground


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state (Scheme I, Reaction b). Once the on-chain macromolecular carbon radical (III) is

formed; it can either undergo β-scission (Scheme I, Reactions c and d) or react with

oxygen (Scheme I Reactions e and f).

CHCH

2

CH2

CH3

N2

O2

CH2

CH3

CH2

C CH

2CH

CH3

CH2

CH2

CH2

CH

CH3 CH

3

CH2

CH CH

2

CH2

CH3

CH2

CCH

2CH

CH3

CH2

OO

CH2

CH2 CH

CH3

CH3

CH2

CCH

O2

OH O

H2O

2

CH2

CH3

CH2

CCH

2CH

CH3

CH2

OOH

O2

CH2

CH

CH3

CH3

CH2

CCH

2CH

2

CH2

CH

CH3

CH2

CH2

CH2

C

CH3

CH4

a

b

I II

c

O2H

Fragmentation

chain-trasfer

volatilisation

III

IV

< 250 °C

VI

+

d

PB1

+ PB1

f

Thermolysis

Oxidised Products

Volatilisation

III+ III +

+

> 250 °C

e

+ PB1

g

.c

d

i

II

PB1

+ III

h

Scheme 1: Thermal and thermo-oxidative volatilisation of Poly-1-butene (PB1) on

heating at 10 °C min-1

Reaction c gives two fragments, one being radical II and the other an unsaturated chain

end-fragment of PB1, whereas reaction d gives a methyl radical and a double bond on

the polymer chain. Both reactions can initiate radical chain formation of volatiles


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respectively through fragmentation of radical (II) or hydrogen abstraction with

formation of methane and radical (III) (Scheme 1 Reaction g).

Reaction with oxygen through route e is favoured below 250 °C being a combination

reaction of the macro-radical with an unpaired electron of oxygen. The resulting peroxy

radical (IV) extracts hydrogen from PB1 (Scheme I Reaction h) giving radical (III) and

a hydroperoxide group which undergoes thermolysis with formation of oxidised groups

on PB1 and chain scission to chain fragments which can eventually volatilise19

. The

combination of reactions e and h constitutes the propagation step of the well known

chain radical peroxidation process involved in the low temperature oxidation of

polymers whereas the thermolysis of the hydroperoxides is responsible for the

branching character of polymer oxidation processes19

. The contribution of reaction e

and h to volatilisation is limited by the low diffusion rate of oxygen in the polymer as

compared to the monomolecular scission of radical (III). Above 250 °C, the stabilisation

of radical (III) through hydrogen abstraction by the biradical O2 with formation of a

carbon-carbon double bond, and a hydroperoxide radical (Scheme 1, Reaction f)

becomes dominant over oxygen addition20

. The peroxy radical abstracts hydrogen from

PB1 giving hydrogen peroxide and radical (III) (Scheme 1, Reaction i). Combination of

this process with reaction f represents the propagation step of an oxygen assisted

dehydrogenation chain radical process which competes effectively with the peroxidation

above 250 °C20

.

The rate of hydrogen abstraction from PB1 (Scheme 1, Reaction b) is high enough to

initiate the volatilisation (Scheme 1, Reactions c and d) which becomes essentially an

oxygen initiated pyrolitic process with very low formation of oxidised volatile species.

Whereas, in the heating conditions of the TGA the reaction rate of radicals (III) with

oxygen is too low to compete with chain scission through path c and d (Scheme 1) due

to relatively high heating rate (10 °C min-1

) and low diffusion coefficient of oxygen into

the polymer. In clay containing samples, the volatilisation of the polymer matrix leaves

behind the clay which creates a surface ceramic layer acting as a barrier for oxygen

diffusion which slows down the rate of initiation of the volatilisation. This protective

effect depends on the type of compatibiliser. Whereas intercalation and/or exfoliation of

the clay is expected to increase the barrier effectiveness, the results of figure 6 show that

intercalation as measured by X-ray does not correspond to the degree of the protection


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provided to the polymer matrix from the action of oxygen. Indeed, the sample showing

the highest intercalation degree (PB1El9Cl) shows an increase of Tmax (60 °C) which is

comparable to that of one of the samples characterised by a slight intercalation which

does not contain any compatibiliser (PB1Cl).

a)

100 200 300 400 500

20

40

60

80

100

PB1

PB1El9

PB1PB

PB1Cl

PB1El9Cl

PB1PBCl

wt (%

)

Time (min)

b)

400 500 600 700 800

10

20

30

PB1

PB1El9

PB1PB

PB1Cl

PB1El9Cl

PB1PBCl

wt (%

)

Temperature (°C)

Figure 7: a) Isothermal degradation in air (300 °C) of poly-1-butene/Cloisite samples b)

Final ramp in nitrogen heating rate of 10°C min-1

between 300 °C and 800 °C


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On the other hand, the highest protection (Tmax increases 116 °C) is supplied by the

other sample, also characterised by a slight intercalation, which is compatibilised by PB

(PB1PBCl).

The unsaturated groups formed by oxidative dehydrogenation (Scheme 1, Reaction f)

tend to dehydrogenate further to an aromatised char as shown for example in

polypropylene15

. In PB1, charring in thermal oxidation is not observed on heating at 10

°C min-1

. However on isothermal heating at 300 °C, PB1 gives 10 % of a charred

residue which decreases at around 8% in the presence of the compatibiliser PB (Figure

7a). In the case of the composites the weight loss rate follows the same order as in the

programmed heating experiments of the Figure 6 as expected. Whereas a substantial

char yeld increase (30%) is found PB1El9Cl, which shows the highest intercalation, and

for the material which shows the highest resistance to thermal oxidation in Figure 6

(PB1PBCl). The thermal stability of the charred material produced by isothermal

oxidation at 300 °C is quite limited, breaking down to volatiles at 350-450 °c under

nitrogen (Figure 7b).

Both the oxygen physical shielding and chemical charring effect observed for the

nanocomposites in thermal oxidative conditions is bound to depend on the degree of

clay dispersion in the polymer matrix. However, the observed order in oxygen shielding

and charring yield: PB1Cl<PB1El9Cl<PB1PBCl is in contrast with the degree of

intercalation as measured by XRD: PB1Cl ≈ PB1PBCl < PB1El9Cl. This could be

explained assuming that the thermal oxidation behaviour of the nanocomposites could

be affected by increasing of clay dispersion promoted by heating. Indeed, heat induces

polymer chain scission producing mobile chain fragments in the polymer melt which

can diffuse between the clay layers more easily than the original chains. Furthermore,

the polymer molecules become polar on heating in air owing the peroxidation reaction e

and h of Scheme 1. This attributes a degree of hydrophilicity to the shortened mobile

polymer chain fragments which further promotes intercalation-exfoliation of the matrix

within the organoclay layers.

Thus, on heating in air, the combination of molecular weight reduction of the polymer

and its increased polarity is likely to lead to a progressive build up of a new

intercalated-exfoliated morphology. Thermal oxidation behaviour indicates that the


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thermal morphology rearrangement leads to a better dispersion when the compatibiliser

is the maleic anhydride grafted polypropylene (PB).

A temperature promoted modification of the room temperature clay dispersion in EVA

was previously demonstrated by an X-ray “in-situ” examination of the nanocomposite

morphology evolution on heating.21

Fire behaviour under forced flame conditions

Cone-calorimeter analyses permit to evaluate the behaviour of materials simulating

different fire condition. PB1 exposed to 50 kW m-2

radiant heat from the cone heater

(well developed fire) begins to burn after melting. The combustion parameters of table 5

for the blank samples are comparable to those of PB1 if experimental errors (± 10%) are

taken into account. Time to pkHRR is however larger in figure 8 for PB1 and PB1PB

(c.a. 100 sec) as compared to PB1El9 (ca. 90 sec.)

Clay presence changes the charring of the nanocomposites behaviour in cone

calorimeter. The material PB1Cl containing only cloisite without compatibiliser shows

formation of small compact char platelets while chars formed from PB1El9Cl and

PB1PBCl result spongy. The pkHRR (Table 5, Figure 8) is reduced in function of

volume of char formed and qualitatively follows the order found for the thermal

oxidative degradation (Figure 6) PB1PBCl > PB1El9Cl ~ PB1Cl. Owing to decrease of

TTI for PB1Cl and PB1El9Cl, a significant decrease of the fire performance index is

found only for PB1PBCl (from 59 to 42). FIGRA index confirms the other data,

PB1PBCl has the lowest value and is the only one significantly different from blank

samples meaning that for this sample there is a diminution of fire spreads in a

hypothetic fire.


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0 50 100 150 200

0

500

1000

1500

2000 PB1

PB1El9

PB1PB

PB1Cl

PB1El9Cl

PB1PBCl

He

at re

lea

se

ra

te k

W m

-2

Time (s)

Figure 8: a) Heat release rate for poly-1-butene (PB1), poly-1-butene/Cloisite 20A

(PB1Cl), poly-1-butene / Elvax 750 (PB1El9), poly-1-butene / Elvax 750 / Cloisite 20A

(PB1El9Cl), poly-1-butene / POLYBOND 3200 (PB1PB), poly-1-butene /

POLYBOND 3200 / Cloiste 20A (PB1PBCl)

It is interesting to note that the THR does not change while TCO and TCO2 increase.

Smoke Factor instead decreases for the presence of clay. This behaviour could be

related to that metal hydroxide fillers usually used as smoke suppressor such as

magnesium dihydroxide and aluminium trihydroxide22,23

because of their ability to form

Lewis acids sites that are able to change aromatic molecules into adsorbed positive

radicals hence decreasing the concentration of aromatic smoke precursor. The Lewis

acid sites, electron attractors, have also an oxidizing character enhancing production of

carbon dioxide and carbon monoxide.


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4000 3500 3000 2500 2000 1500 1000 500

1640 cm-1

C=C

2923, 2851 cm-1

CH2

1046 cm-1

Si-O-Si Cl

PB1PBClA

bs

orb

an

ce

Wave number (cm-1)

3648 cm-1

Si-OH 1469 cm-1

C-H

Figure 9: FT-IR of cone calorimeter ashes, KBr pellets of Poly-1-butene / POLYBOND

3200 / Cloisite 20A (PB1PBCl) compared with Cloisite 20A (Cl)

FT-IR analyses on the cone residues show similar chemical composition with the bands

typical of phyllosilicates (Figure 9)24

. Spectral band at 3648 cm-1

is typical OH

stretching of montmorillonite with high amount of Al in the octahedral sites. The strong

bands at 1046 cm-1

, typical of Si-O-Si stretching of tetrahedral ions in the layered

structure, confirm the presence of non degraded montmorillonite; eventual formation of

an amorphous tri-dimensional phase for silica would have shifted at 1100 cm-1

the band.

N+

R

R

H

N+

R

HRH

+elimination

-

decomposition

-

Acid site

N(CH3)2CH2CH2

Clay surfaceClay surfaceClay surface

Scheme 2: Hoffman degradation of hydrogen tallow cation bond to montmorillonite

and formation of acid sites:

All these bands are analogous to initial Cloisite 20A (Figure 9) however there is no

trace of bands due to hydrogen tallow of onium cation (Figure 9) substantially CH2


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stretching (2923, 2851 cm-1

) and bending (1469 cm-1

) so, during combustion, Cloisite

20A lost the organic part with a mechanism already known25

that involves Hoffman

degradation of ammines (Scheme 2) to form acidic montmorillonite.

The weak band around 1640 cm-1

that appears in the 3 ashes is probably due to carbon

double bond stretching of aromatic products present in the ashes in small quantities.

Table 5: Cone calorimeter of melt-blended samples: time to ignition (TTI), peak of heat

release rate (pkHRR), total heat release (THR), total carbon monoxide (TCO), total

carbon dioxide (TCO2), Smoke Factor (S.F.), Fire Performance Index (FPI), FIre

Growth Rate (FIGRA) index

Cone Calorimeter PB1 PB1Cl PB1El9 PB1El9Cl PB1PB PB1PBCl

TTI S 34 32 30 31 32 34

pkHRR kW m-2 2011 1714 2169 1677 1917 1412

THR MJ m-2 108 107 107 104 107 104

TCO kg/kg 4.08 4.77 4.85 6.29 4.39 5.25

TCO2 kg/kg 443 506 472 613 415 537

SF MJm-2 3465 3075 3549 2974 3253 2538

FPI kWm-2

s-1 59 54 71 54 61 42

FIGRA kWm-2

s-1

22 22 25 22 21 16

X-rays analyses (Figure 10) confirm IR-results: there is no trace of amorphous band due

to montmorillonite degradation to amorphous silica. Interlayer space is reduced to 0.96

nm a measure comparable with anhydrous sodium montmorillonite confirming the loss

of onium cations and the formation of acidic montmorillonite. The other peaks (d100 at

about 20°and d040 at about 35°) typical of layered structure of montmorillonite do not

change letting suppose that the structural order of montmorillonite layers are not

changed during the process of burning.

Cone calorimeter results agree with TGA analyses, as the capacity of nanocomposites to

form a thermally stable protecting physical barrier on the surface is the key of poly-1-

butene stabilisation during thermal degradation as well as in combustion. Clay

dispersion should play a key-role in the ablative assembling of the protective layer. The


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more dispersed is the clay, the faster is re-assembling during volatilization of polymer

in thermo-oxidation or burning tests.

0 5 10 15 20 25 30 35 40 45

1000

d001

=2.43 nm

d001

= 0.96 nm d030

= 0.25 nm

PB1PBCl

Inte

nsity

2(deg)

d100

= 0.44 nm

Closite 20A

Figure 10: X-ray analyses of initial clay and cone calorimeter ashes, Cloisite 20A and

Poly-1-butene / POLYBOND 3200 Cloisite 20A (PB1PBCl)

CONCLUSIONS

X-ray, SEM and TEM analyses give evidence that melt blending of poly-1-butene with

the organoclay Cloisite 20A gives intercalated nanocomposites which morphology

depends on type of compatibiliser used. With EVA extensive intercalation takes place

as shown by XRD whereas thermal oxidation and combustion behaviour indicate that a

morphology rearrangement may occur on heating leading to a better clay dispersion

with maleic anhydride grafted polypropylene.

The thermal oxidation and combustion behaviour of the poly-1-butene/clay

nanocomposite depend on a dual physical and chemical action of the finely dispersed

clay layers.

The physical protective action of the nanoscopically dispersed clay towards oxidation

and combustion depends on re-assembling of the clay layers back to the

montmorillonite structure while thermal ablation of the polymer matrix occurs, as


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shown by X-rays and infrared of combustion residues. A thermally stable inorganic skin

is thus provided by the clay which insulates the material from oxygen and heat, slowing

down the thermal decomposition and combustion of the polymer matrix.

The chemical catalytic effect of the clay layers is shown either by thermal

destabilisation of poly-1-butene in inert atmosphere or by charring in the presence of

oxygen on heating in air or in combustion which reduces combustible volatiles evolved

by thermal oxidation of the polymer.

AKNOLEDGMENT

The authors thank Dr. Thomas Frenchen Dr. Thomas Frechen of GKP/P, BASF

Aktiengesellschaft for TEM analyses.

Symbols and Abbreviation

Cl Cloisite 20A

EL9 ELVAX 750

FIGRA Fire growth rate

FPI Fire performance index

HRR Heat release rate

PB POLYBOND 3200

PB1 Poly-1-butene

pkHRR Peak of heat release rate

SEM Scanning electron microscopy

SF Smoke factor

TEM Transmission electron microscopy

TCO Total evolution of CO

TCO2 Total evolution of CO2

TGA Thermal gravimetric analysis

THR Total heat release

TTI Time to ignition

XRD X ray diffraction


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poly-1-butene/clay nanocomposite effect of compatibilizers on thermal and fire retardant properties

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