nr-csm-biogenic silica rubber blend composites

7/29/2019 NR-CSM-Biogenic Silica Rubber Blend Composites

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NR/CSM/biogenic silica rubber blend composites

Gordana Markovic a, Milena Marinovic-Cincovic b, Vojislav Jovanovic c, Suzana Samarzija-Jovanovic c,,Jaroslava Budinski-Simendic d

a Tigar, Nikole Paica 213, 18300 Pirot, Serbiab University of Belgrade, Institute of Nuclear Science Vinca, Mike Petrovica Alasa 12-14, 11000 Belgrade, Serbiac Faculty of Natural Science and Mathematics, University of Pritina, Lole Ribara 29, 38220 Kosovska Mitrovica, Serbiad University of Novi Sad, Faculty of Technology, Bulevar cara Lazara 1, 21000 Novi Sad, Serbia

a r t i c l e i n f o

Article history:

Received 9 April 2013

Received in revised form 20 May 2013

Accepted 22 June 2013

Available online 10 July 2013

Keywords:

A. Particle-reinforcement

B. Mechanical properties

D. Thermal analysis

Biogenic silica

a b s t r a c t

Biogenic silica (BSi) was added at different ratios to some polymer blends of polyisoprene rubber (NR)

and chlorosulphonated polyethylene rubber (CSM) cured by conventional sulfur system. The reinforcing

performance of the filler was investigated using rheometric, mechanical and swelling measurements, dif-

ferential scanning calorimetry (DSC), thermogravimetric (TGA) and scanning electron microscopy (SEM)

analysis. There was a remarkable decrease in the optimum cure time ( tc90) and the scorch time (ts2),

which was associated with an increase in the cure rate index (CRI), with filler loading up to 30 phr in

the different blend ratios. The tensile strength and hardness was 45 Sh-A higher in the case for the dif-

ferent blend compositions, while the resistance to swelling in toluene became higher. SEM photographs

show that the filler is located at the interface between the different polymers which induces compatibi-

lization in the immiscible blends. DSC scans of the filled blends showed shifts in the glass transition tem-

peratures Tg which can be attributed to the improve interfacial bonding between filler and NR/CSM

matrix. A higher thermal stability of NR/CSM/BSi composites was detected.

2013 Elsevier Ltd. All rights reserved.

1. Introduction

Synthetic rubbers are now commonly used, especially for tire

industry after blending with other rubbers and silica as an effective

reinforcing agent [1]. Elastomeric materials based on polyisoprene

rubber (NR) have a high strength, quite good crack resistance, wet

grip and weather resistance. Chlorosulphonated polyethylene rub-

ber (CSM) exhibits excellent ultraviolet and oxygen stability. In

addition to applications for box gloves, this rubber has additional

uses such as in lining and sheath materials, coatings, and adhesives

[2].

The use of blends of rubber is widespread, the purpose being to

obtain a balance of properties, including cost, which one elastomeralone cannot supply. Synthetic rubbers may, therefore, be added to

each other as binary mixtures to improve the inferior properties of

one of the components [3]. It is known that incorporation filler into

a binary polymer immiscible blend can affect the phase separation

due to the interaction of the individual components of the blend

with the solid surface [4]. Many researchers reported the use of fill-

ers of inorganic nature for the purpose of compatibilization. The

use of a mineral filler like silica served as compatibilizer for an

immiscible mixture of polyolefin with polyacrylates and polymeth-

acrylates [5].

Also, for polymethylmethacrylate/polyvinyl acetate blend the

efficiency of biogenic silica (BSi) as compatibilizer [6] is confirmed

and indicated that the rate of phase separation of the filled blends

became lower. Other authors [7] mentioned that the introduction

of a filler surface compatible with the polymer mixture can change

the position and shape of the curve of the phase separation. Expla-

nations were put for understanding the compatibilizing effect of

inorganic matter when incorporated into immiscible blends; one

of these explanations is attributed to the diminished molecular

mobility which prevents the phase separation of the components

[6,7]. Another mechanism is proposed [8] by which large aspect ra-tio fillers, with at least one dimension in the nanometer range, can

form in situ grafts by adsorbing large amounts of polymer, which

in turn are very effective at reducing the interfacial tension and

inducing compatibilization in highly immiscible blends. This phe-

nomenon appears to be mostly a function of the aspect ratio and

hence widely applicable to most polymers blends irrespective of

the chemical nature of the filler.

The main interest was related on the effect of biogenic silica

(BSi) as a filler on the deformation mechanisms and mechanical

properties of composites based on the polymer matrix. Diatoma-

ceous comes as a biogenic silica (BSi) from the word diatom,

which is the single celled aquatic plant. Diatoms are living

1359-8368/$ - see front matter 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.compositesb.2013.06.045

Corresponding author. Tel.: +381 607300105.

E-mail address: [email protected] (S. Samarzija-Jovanovic).

Composites: Part B 55 (2013) 368373

Contents lists available at SciVerse ScienceDirect

Composites: Part B

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o m p o s i t e s b
http://dx.doi.org/10.1016/j.compositesb.2013.06.045mailto:[email protected]://dx.doi.org/10.1016/j.compositesb.2013.06.045http://www.sciencedirect.com/science/journal/13598368http://www.elsevier.com/locate/compositesbhttp://www.elsevier.com/locate/compositesbhttp://www.sciencedirect.com/science/journal/13598368http://dx.doi.org/10.1016/j.compositesb.2013.06.045mailto:[email protected]://dx.doi.org/10.1016/j.compositesb.2013.06.045http://crossmark.dyndns.org/dialog/?doi=10.1016/j.compositesb.2013.06.045&domain=pdf


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phytoplanktons which form an important part of marine and fresh-

water. The silicate shell, termed frustule supports a fleshy body.

The fossil beds are skeletons sunk to the bed of lake or sea after as

the body died and formed deposits there. Diatoms are found in a

great variety of forms [9]. The skeletal remains of diatoms with

sub-micron-sized hole are described as indescribable particle

shape far from any simple classification [10].

The specific diatom morphology and chemical resistance could

be the base of using this material as filler in composites. There is

little in the literature on this subject. Adhesion between matrix

and filler phases in composites is important in crack propagation

and composite failure. The study of the deformation and failure

process, their relation to the structure of composite and the

strength of interactions between the polymer matrix and filler

phases may provide useful information for the development the

new composite materials with diatoms.

In the present work, biogenic silica (BSi), was incorporated into

some binary mixtures of polyisoprene/chlorosulphonated polyeth-

ylene (NR/CSM) rubber blends to investigate reinforcing effect of

the filler.

2. Experimental

2.1. Materials

Polyisoprene rubber, NR, produced by Indian Standard Natural

Rubber, grade 5 (ISNR-5) Chlorosulphonated polyethylene, CSM,

Hypalon-40, with 35% chlorine and 1% sulfur by weight was ob-

tained from E. I. Du Pont de Nemours and Co., Inc., USA, 1.18 g/

cm3, Mw 5.52x105 Mw/Mn 1.97); Filler: diatomaceous earth as a

biogenic silica (BSi), (DBP absorption 130 cm3/100 g) with the

average size of primary particle 28 lm. The content of filler was

0, 10, 20, 30 and 40 phr.

2.2. Compounding and torque measurements

The rubber compounds were prepared at different ratios of NR/

CSM, 100/0, 75/25, 50/50, 25/75 and 0/100 by using a laboratory-

size two-roll mill maintained at 40 5 C. The roller speed ratio

was n1/n2 = 28/22. The mixing time was 20 min. Then the filler

was added in different amounts, 10, 20, 30 and 40 parts per hun-

dred rubbers (phr), and mixed with each of the blends at room

temperature. Finally, magnesium oxide (Anscor P), tetrame-

thylthiuramdisulfide (TMTD), and slow accelerator N-cyclohexyl-

2-benzothiazole sulfonamide (Vulcanite CZ) as curing agent were

loaded. For efficient vulcanization (EV) system, the amounts of

TMTD and S were 2.5 and 0.75 phr (parts per hundred), respec-

tively. The physical and chemical characteristics of diatomaceous

earth are presented in Table 1.

2.3. Characterization

2.3.1. Cure characteristics

The sheeted rubber compound was conditioned at 23 2 C for

24 h prior to cure assessment on a Monsanto Moving Die Rheom-

eter (model 100S, USA) at 160 C. The compound formulations (Ta-

ble 2) expressed in part per hundred parts of rubber, phr. All test

specimens were compression molded at 160 C during the respec-

tive optimum cure time (tc90) determined from the Monsanto Rhe-

ometer. The scorch time, ts2 is the timeto 2 units of torque increase

above minimum torque, and optimum cure time, tc90 is the time to

90% of maximum torque development calculated from the follow-

ing expression:

Mc90 Mh Ml 0:9 Ml 1

where Mh is the maximum torque, and Mc90 a new torque reading

corresponding to 90% cure in the rubber were determined from

the cure traces generated at 160 2 C by oscillating disc rheometer

curemeter at an angular displacement of 3 and a frequency of

1.7 Hz [11].

The cure rate index (CRI) is the measure of rate of vulcanization

based on the difference between optimum cure time of vulcaniza-

tion tc90

and the scorch time ts2

. It can be calculated from the rela-

tion [12]:

CRI 1

tc90 ts2 100 2

2.3.2. Mechanical properties

The sheets were cut, marked according to the time and temper-

ature determined from the oscillating disc rheometer and vulca-

nized in clean polished molds in a press at 160 C. The

vulcanized sheets were cut into dumbbell-shaped specimens (five

replicates from each sample) for the evaluation of the mechanical

properties [13] using an electronic tensile testing machine (Zwick

1425, Germany) at speed of 500 mm/min. Samples of at least

0.12 mm in thickness with flat surface were cut for hardness test.The measurement was carried out according to ASTM D 2240 using

durometer of model 306L type. The unit of hardness is expressed in

(Shore A).

2.3.3. Swelling measurements

The swelling degree was determined on the basis of equilibrium

solventswelling measurements in toluene. The samples (about

0.10.2 g) were submerged in the toluene and after the swelling

equilibrium was reached, that means, no change in the weight of

the swollen sample was observed, the mass of toluene was deter-

mined according to the ASTM D 471. The swollen samples were

weighed and then dried in an oven to a constant weight. The last

weight was taken as the correct weight of the sample free from dis-

solved matter. The swelling percentage (Q) of the samples was cal-culated as follows [14]:

Qms m0

m0 100 3

where ms and mo represent the weights of the samples after swell-

ing and free from dissolved matter respectively. All these tests were

Table 1

The physical and chemical characteristics of biogenic silica (BSi) (diatomaceous

earth).

Physical properties Chemical properties

Specification grade SiO2 P90.1%

Appearance White fine

powder

Al2O3 64%

Description Flux-calcined Fe2O3 61.5%

Specific gravity 2.3 g /cm3 CaO 60.6%

Moisture 61.0% MgO 60.5%

Loss on ignition 63.8% Others 60.8%

PH 810 Pb, mg/kg


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performed at room temperature (25 C) for 24 h, and the reported

results were averaged from a minimum of five specimens.

2.3.4. Thermogravimetric analysis

The measurements were made at a heating rate 10 C min1, at

a temperature range 0800 C, using Perkin Elmer TGS-2 Thermo

gravimetric system. The experiments were done in nitrogen atmo-sphere. About 58 mg of the sample was used for the analysis.

2.3.5. Differential scanning calorimetry (DSC)

The differential scanning calorimetry (DSC) was performed on a

DSC 2910 (DuPont instrument) for the determination of the glass

transition temperatures.

2.3.6. Scanning electron microscopy (SEM)

The scanning electron microscopy images of the rubber blends

fractured surfaces were taken by a JEOL JSM-5400 model of the

microscope. The samples were sputter coated with gold for 3 min

under high vacuum with image magnifications of 2000 and

7500X, respectively.

3. Results and discussion

3.1. Cure characteristics

In the case of biogenic silica, however, strong filler/ filler inter-

actions resulting from polar surface functional groups such as

siloxane [15] are believed to be primarily responsible for the in-

creases recorded. It is interesting that measured the Mooney vis-

cosities of some silica filled rubber compounds, and likewise

observed large increases, particularly at high loading of the filler,

with some of their results. These workers ascribed the increases

to strong filler/filler interaction of silica.

The cure characteristics of the different blends are shown in Ta-

ble 2. The minimum torque, Ml was slightly affected with increaseof the biogenic silica (BSi) loading for the different blend composi-

tions, however, a significant increase in the maximum torque, Mh,

resulted from increasing the biogenic silica (BSi) to 30 phr and

started to decrease upon further increase in the filler loading

(30 phr). The difference between Mh and Ml is a rough measure

of the crosslink density of the samples and usually known as

DM. It can be seen that, DMincreases with increasing biogenic sil-

ica concentrations except for (30 phr silica) there is a slightly de-

crease in DM due to the highly increase of the fillerfiller inter-

agglomeration formation of biogenic silica remarked with the high

value of Ml.

The table also shows that the incorporation of the biogenic sil-

ica (BSi) significantly decreases the optimum cure time (tc90) and

increases the scorch time (ts2), while the cure rate index (CRI) is

nearly constant may be due to strong interfacial rubberfiller

interaction.

The changes in rheometric torque with filler loading can be

used to characterize the filler-matrix interaction or reinforcement.

The reinforcement factor af can calculated from the rheographs

[16] and is given by:

af DMfilled DMunfilled

DMunfilled4

where DMfilled andDMunfilled are the changes in max torque during

vulcanization for the filled and unfilled compounds respectively.

From af values listed in Table 2 it is clear that the values ofaf for

NR/CSM/BSi are continuously increasing with the addition of bio-

genic silica including the pure NR and CSM, which indicates affinity

of the biogenic silica (BSi) for both phases. 30 phr seems to be the

optimum loading of the biogenic silica (BSi), further increase

(40 phr) was associated with a re-increase in the tc90 and scorch

time ts2 or a decrease in the CRI, which can be explained by the

agglomeration of the filler particles.

3.2. Mechanical properties

It is well known that the smaller particle size filler has a larger

surface area and thus there is greater interaction between filler andpolymer matrix. The degree of reinforcement depends on the ex-

tent of polymer and filler interaction. Generally, mechanical prop-

erties increase is a result of the additional reinforcement of the

polymer phase. Also, the mechanical properties of the pure NR

and CSM components are weak in the absence of reinforcing filler,

and consequently the mechanical properties of their blends are

also inferior and this originates principally from the incompatibil-

ity of both components with each other in view of the fact that NR

has less polarity than the CSM.

Tensile strength is mainly related to the stress distribution

within rubber and the effective increase in the rupture path. From

the Table 3, tensile modulus is improvement as a filler loading in-

crease up to 30 phr. With further increase in the loading of the fil-

ler, the tensile strength reduced. The lowest tensile strengthobserved is due to large mean agglomerate particles size of bio-

genic silica and weak interaction between filler and polymer ma-

trix. It is well known that interaction between filler and filler is

dominant in the case of silica filled polymer blends. These observa-

tions indicate that the mean agglomerate particles size play an

important role in affecting the mechanical properties of NR/CSM

blends. However, they were still much better in comparison with

the equivalent blends without filler, particularly in the case of ten-

sile strength (45 MPa). It is worthy to note that the tensile

strength was also enhanced, especially in the case of NR/CSM,

(50/50) and (25/75) blends, which indicate the lubricating effect

of the diatomaceous earth and the lack of weak spots or inhomoge-

neities in the filled blends [17].

The surface activity is an important factor, indicating the extentof polymer-filler interaction. With good polymerfiller interaction,

Table 2

Effect of biogenic silica (BSi) content on the cure characteristic of NR/CSM rubber

blends.

NR/CSM BSi Ml Mh DM ts2 tc90 CRI af(phr) (phr) (dNm) (dNm) (dNm) (min) (min) (min1)

100/0 0 5 25 20 7 10 33

10 6 26 20 8 9 100 0

20 6 26 20 8 9 100 0

30 6 27 21 8 9 100 0.0540 6 28 22 7 8 100 0.1

75/25 0 7 27 20 8 12 25

10 7 27 20 9 11 50 0

20 7 28 21 10 11 100 0.05

30 7 28 22 9 10 100 0.1

40 7 29 22 8 9 100 0.1

50/50 0 7 28 21 7 15 12.5

10 7 28 21 8 14 16.7 0

20 7 28 21 8 14 16.7 0

30 7 29 22 7 13 16.7 0.05

40 7 29 22 6 13 14.3 0.05

25/75 0 8 28 20 8 16 12.5

10 8 28 20 9 16 14.3 0

20 8 28 20 9 15 16.7 0

30 9 30 21 8 15 14.3 0.05

40 9 29 20 7 14 14.3 0

0/100 0 9 29 20 10 19 11.1

10 9 30 21 8 18 10 0.05

20 9 30 21 8 18 10 0.05

30 9 32 22 8 17 11.1 0.1

40 9 32 22 7 17 10 0.1

370 G. Markovic et al. / Composites: Part B 55 (2013) 368373


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there would be increases in modulus as well as mechanical proper-

ties. Based on this concept, biogenic silica has very high surface

activity, which is provide greater reinforcement. The probability

for the formation of a filler network enhanced with further in-

crease in loading which is caused by a closer distance between

aggregates in the rubber system and a better filler filler interac-tion [18]. The further loaded biogenic silica could stiffen rubber

by replacing the polymer with rigid and non deformable particles,

which yielded higher modulus which is noticed clearly from

Table 3.

In the Table 3 the effect of filler loading on elongation-at-break

are shown. It indicates that elongation-at break (%) decreases

gradually with increasing filler loading. The reduction of elonga-

tion-at-break is due to stiffening of the polymer matrix by the fil-

ler. Further increase in filler loading causes the molecular mobility

decrease due to extensive formation of physical bond between the

filler particles and the polymer chain that stiffen the matrix [19].

When the biogenic silica is filler increase, the polymer matrix pro-

gressively is becoming reinforced and hence lowering elongation-

at-break at any filler loading.The hardness which depends on the distribution of the rigid fil-

ler in the host matrix is increased with increasing the filler content.

It is well known that incorporation of the filler particles in the soft

matrix reduces the elasticity of the polymer chains resulting in

more rigid composites [20]. From Table 3 one can see that the addi-

tion of the biogenic silica showed a marked increase in hardness,

which reflects an improved stiffness for the rubberfiller compos-

ites. This result is expected because as more filler is incorporated in

the rubber matrix, the plasticity of the rubber chain is reduced

resulting in more rigid composites [21].

The hardness is increased because the filler particles have rela-

tively higher modulus than that of rubber matrix. It is well known

that the addition of the filler in rubber compounding leads to a lin-

ear increase in materials hardness; moreover the internationalrubber hardness degree is correlated with the elastic modulus

[22]. Presence of these stiff fillers and entanglement of polymer

chains renders the rubber composites harder than the respective

unfilled polymer [23]. These results are well agreed with the

encountered increase in the cross-link density.

3.3. Swelling properties

Table 3 shows the effect of blend compositions on the swelling

degree of NR/CSM/BSi rubber blends composites. CSM rubber has

excellent resistance to most chemicals and this explains why per-

centage of swelling of BSi filled NR/CSM rubber blend matrix is

low. The swellingratio Q is gradually decreased with increasing sil-

ica. This is a result for the formation of more cross-links in the

vicinity of the fillers owing to the chain segments and facilitates

the cross-link formation [24] consequently an increase in the fil-

lerrubber interaction will be constructed.

Incorporating the filler into the blend caused a decrease in the

equilibrium swelling in toluene. The decrease reached 58% in the

case of NR/CSM (100/0) blend filled with 30 phr, while in the case

of NR/CSM (0/100) blend with the same filler loading the ratio rise

to 45%. This proves that the filler increased the polarity of the over-

all system due to the presence of hydroxyl groups on its surface

and this lowers the interactions with toluene. Additional evidence

for this explanation is the re-increase in the equilibrium swelling

in toluene above 30 phr loading which means agglomeration of

the filler particles due to the interaction of the hydroxyl groups

with each other. It was expected that these interactions at 30 phr

should be shifted to higher or lower concentrations of the filler

with varying the composition of the blend, however, this was not

the case.

3.4. Thermogravimetric analysis

The thermal stability of the NR/CSM/BSi rubber blend compos-

ites as a function of blend compositions was investigated using

thermo-gravimetric analysis. (Table 4 and Fig. 1a and b). One re-

gion of NR/CSM/BSi rubber blends degradation is observed. Thedegradation occurs in the temperature region 350400 C. The

degradation started at 60 C and was completed at 800 C. The deg-

radation is due to the elimination of chlorine from the CSM chain is

due to the main chain scission. The total mass loss observed at

814.5 C was 70.4%. It has been reported that the thermal stability

of polymer blend can be improved by the incorporation of biogenic

silica (BSi). In the case of NR/CSM/BSi rubber blends, the degrada-

tion starts at a higher temperature than that for NR/CSM rubber

blend and NR and CSM rubber alone and unfilled.

T0.5 indicates the initial decomposition temperature (IDT) (5%

mass loss) whereas T10 and T30 show the higher degradation rate

of the polymer blends composites. It can be seen that according

to the IDT biogenic silica filled NR/CSM compounds are more stable

than unfilled compounds. In the next step (at 10% mass loss) with30 phr of biogenic silica filled NR/CSM rubber composites have

higher temperature values (309.1 C) than other samples. At 30%

mass loss, the NR/CSM rubber blends filled with 30 phr biogenic

silica are the most stability (394 C) also, than other compounds.

As shown in Fig. 1a and b, the incorporation of the filler resulted

in all samples improvement of thermal stability. Ash residue con-

tent increased with higher filler loading. The higher content of

ash residue in degradation process depends on the initial CSM plus

added experimentally. The large flexible polysulfidic linkages un-

dergo chain scission and convert into monosulfidic and disulfidic

linkages [25]. Synthetic rubber decomposes by random-chain scis-

sion with intramolecular hydrogen transfer. The shift of values of

the DTG peaks to a high temperature indicating increased thermal

stability with 30 phr content of biogenic silica filled rubber blendcomposites.

Table 3

Effect of biogenic silica (BSi) content on the mechanical and swelling properties of NR/

CSM rubber blends.

NR/

CSM

BSi Tensile

strength

Elongation at

break

Hardness Equilibrium

swelling

(phr) (phr) (MPa) (%) (Sh-A) (%)

100/0 0 10 350 40 68

10 12 340 42 64

20 13 330 44 6230 14 300 45 58

40 14 370 45 58

75/25 0 11 340 45 64

10 13 330 46 60

20 14 330 47 59

30 14 320 48 57

40 15 310 48 56

50/50 0 12 330 47 55

10 12 320 48 51

20 14 300 49 40

30 17 280 54 38

40 15 270 50 37

25/75 0 14 340 48 50

10 15 330 49 48

20 16 320 49 47

30 17 320 50 4540 17 320 52 40

0/100 0 15 320 51 48

10 16 300 53 47

20 16 290 54 46

30 17 250 54 45

40 17 230 54 45

G. Markovic et al. / Composites: Part B 55 (2013) 368373 371
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3.5. DSC measurement

DSC scans for the individual components NR and CSM rubber,

unfilled NR/CSM rubber blend (50/50) and 30 phr biogenic silica

filled NR /CSM/BSi (50/50/30) rubber blend are represented in

Fig. 2. The Tg of the individual components of the blends were

found to be 76 and 49 C for NR and CSM, respectively. For

the unfilled blends, the Tg is shifted to high temperature for 54

and33 C and this was explained [26], as due to interactions be-

tween the different phases at the boundaries forming a third phase,whose presence causes the polymer chains to draw aside resulting

in a small increase of their segmental mobility. The presence of

biogenic silica, change Tg of rubber blend (Fig. 2) due to the restric-

tion on the segmental motion of the polymeric chain by the addi-tion of cross-linking. The separation of polymer macromolecules

under the influence of this biogenic silica is compensated in this

case by the polymerfiller interactions.

3.6. Morphological study

According to Sadhu and Bhowmick [27], SEM is an important

tool for observing the surface morphology of crack initiation and

Table 4

The temperature values of 0.5%,mass loss (T0.5), 10% mass loss (T10) and 30% mass loss

(T30) and the final decomposition temperature of NR, CSM, NR/CSM (50/50) and NR/

CSM/BSi (50/50/30) rubber blend composites.

NR CSM NR/CSM NR/CSM/BSi

DTG peak (C) 283.3 354.5 319.6 405.6

444.8 452.2

Mass loss (%) 31.9 26.3 25.3 34.3

50.1 53Total mass loss (%) 71.8 70.9 68.2 70.4

Temperature values for selected mass loss

T0.5% (C) 59.9 127.2 19.9 63.9

T10% (C) 226.8 303.6 255.2 309.1

T30%(C) 279.4 361.7 333.3 394

Tend(C) 800.7 803 718.5 814.5

Fig. 1. TG (a) and DTG (b) curve of NR/CSM (100/0), NR/CSM (0/100), NR/CSM (50/

50) and NR/CSM/BSi (50/50/30) rubber blend composites.

Fig. 2. DSC scans of NR/CSM (100/0), NR/CSM (0/100), NR/CSM (50/50) and NR/

CSM/BSi (50/50/30) rubber blend composites.

Fig. 3. SEM of unfilled NR/CSM (50/50) (a) and biogenic silica filled NR/CSM (50/50/30) rubber blends (b).

372 G. Markovic et al. / Composites: Part B 55 (2013) 368373


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the failure process in composite materials. Figs. 3 show the SEM

photograph of the fracture surfaces of tensile test specimen of

the composites studied. The fracture surface of NR/CSM rubber

blend composite without biogenic silica (BSi) (composite A) in

Fig. 3a exhibits brittle fracture. However, the presence of BSi

changes the failure pattern which indicates the presence of bonded

BSi as a result of filler-rubber interaction and adhesion. The stron-

ger BSi/rubber adhesion in Fig. 3a and b causes low breakage in the

rubber matrix leading to the reduction of tensile properties as ten-

sile strength and elongation at break. This observation is supported

by the swelling measurement data shown in Table 3. Since the

lower the Q, values, the higher will be the extent of interaction be-

tween the filler and the rubber matrix [27], it can be concluded

that the higher BSi/rubber adhesion in the composites obtained.

4. Conclusions

Biogenic silica (BSi) was used as a reinforcing filler at different

ratios in polyisoprene/chlorosulphonated polyethylene (NR/CSM)

rubber blends. A decrease in the optimum cure time (tc90) and

scorch time (ts2) was observed and this was associated with an in-

crease in the cure rate index (CRI) with filler loading up to 30 phr.

The tensile strength for 45 MPa higher in the case of the filled

blends; also the toughness increased with the use of the filler

which indicates the lubricating effect of the filler. Furthermore,

the resistance to swelling in toluene became higher. Induced com-

patibilization can be obtained from the location of the filler at the

interface between the immiscible blends as can be evidenced from

the SEM pictures. The Tg of filled rubber blends is shifted to high

temperature. Also, thermal stability increase with filler content in-

creases. Biogenic silica (BSi) has a potential to be used as ecological

filler in the rubber industry.

Acknowledgements

Financial support for this study was granted by the Ministry of

Science and Technological Development of the Republic of Serbia(Projects Numbers 45022 and 45020).

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