The Comparison of Alkanolamide and Silane Coupling Agent on the Properties of Silica-filled Natural Rubber (SMR-L) Compounds
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Polymer Testing [ 6 6 ] j o u h r o n m : a w e l w p a w g . c e e m o l / s l e o v c i a e t r e . / p o l y t e s t
[41] Material properties The comparison of alkanolamide and silane coupling agent
(SMR-L)
on the properties of silica-filled natural rubber compounds[16] a b b
,
- a Indra Surya , H. Ismail , A.R. Azura b
Department of Chemical Engineering, Engineering Faculty, University of Sumatera Utara, Medan, 20155, Sumatera Utara, Indonesia School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, Engineering Campus, Nibong Tebal , 14300, Penang, Malaysia
a e i r n t a f i b o c s l t r a c t
Article history:Alkanolamide (ALK) and Aminopropyltriethoxy Silane (APTES) were incorporated separately [14] Received 20 May 2014 into silica- lled SMR-L compounds at 1 . 0, 3.0, 5.0 and 7.0 phr. It was found that compounds
fi Accepted 6 August 2014 with both ALK and APTES exhibited cure enhancebetter ller dispersion and greater fi
Available online 27 August 2014 [34] rubber- ller interaction. Both additives also produced modulus and tensile enhancements in fi the silica- lled SMR-L compounds, especially up to a 5 . 0 phr loading. At a similar loading,
fi ES. [40]
fi Alkanolamide [28] ©
2014 Published by Elsevier Ltd . Reinforcing ef ciency fi APTES Silica-reinforcement Plasticiser
[13]
1. Introduction numerous silanol groups. The silanol groups are relatively
incompatible with hydrocarbon rubbers, such as natural
The mechanical properties such as tensile modulus, rubber and styrene butadiene rubber, therefore coupling tensile strength, tear and abrasion resistances of a rubber bonds are not formed. On the other hand, the silica parti- vulcanisate are enhanced as a result of the incorporation of cles have a strong tendency to interact with each other to reinforcing ller into the rubber compound. Carbon black form aggregates. Since the silica-hydrocarbon rubber
fi and silica are the best known reinforcing llers, and have interaction is weaker than the silica-silica interaction, the fi been widely utilised in the rubber industry. Each type of results are the formation of large agglomerates, poor reinforcing ller produces useful mechanical properties dispersion of silica and lower reinforcing ef ciency.
fi fi due to their speci c surface chemistry. Carbon black and Modulus is a well-recognised criterion of ller rein-
fi fi silica have apparently a dissimilar surface chemistry. The forcement [3] . Due to the nature of its surface chemistry, surface of carbon black is saturated with hydrocarbon silica has a low level of surface activity for rubber bonding, functional groups that react with sulphur during vulcani- resulting in small amounts of effectively immobilised rub- sation. They form sulphur bonds that link the rubber ber. Therefore, silica reinforced rubbers have
[
1 3 ] In modulus than carbon black reinforced rubbers.
chains, and also tie the carbon black to the rubber [1e2].
marked contrast to the hydrocarbon functionality of carbon In order to overcome the de ciencies of silica, coupling
fi
black, silica does not react with sulphur . The surface of agents are used for the reinforcement of hydrocarbon
silica is highly polar and hydrophilic due to the presence of rubbers. The most ef cient and presently known coupling fi agent is organosilane [4] . Organosilanes are reactive addi- tives. They are utilised to improve the silica-rubber inter-
- * Corresponding author.
action of silica- lled rubbers and, consequently, enhance fi E-mail addresses: ihana @usm.my , profhana @gmail.com (H. Ismail).
fi fi http : //dx.doi.org/10.1016/j.polymertesting.2014.08.007 © the reinforcing ef ciency . The organosilanes modify fi
[5 6] e the surface of silica . The modi ed silica provides a [7 8] e
1 is the initial angle of displacement (45
[12]
C. The com- pounds were subsequently compression-moulded using a stainless steel mould at 150
C, with a pressure of 10 MPa , based on respective curing times . [ 12]
2.4. Tensile, hardness and resilience properties
Dumbbelled samples were cut from the moulded [12] sheets . Tensile tests were performed at a cross-head speed of 50 0mm/ min using an Instron 3366 universal tensile
[17] machine, according to ISO 37 . The tensile strength (TS), stress at 100% elongation (M100 ), stress at 300% elongation (M300 ) and elongation at break (EB) were determined. The
hardness of the samples was measured according to ISO
[12]
7691-I, using a Shore A type manual durometer. The resil-
ience was studied by utilising a Wallace Dunlop Trips- [12] ometer, according to BS 903 Part A8 . The rebound resilience was calculccording to Equation . (1) % Resilience ¼ ½ ð1 cos q
[14] 2 Þ ð = 1 cos q 1 Þ 100 (1) where q
), and q
H dM L [24]
4]
2.5. Scanning electron microscopy (SEM)
The tensile fractured surfaces of the natural rubber compounds were examined by using a Zeiss Supra-35VP scanning electron microscope (SEM) to obtain informa- tion regarding the ller dispersion, and to detect the fi possible presence of micro-defects. The fractured pieces
were coated with a layer of gold to eliminate electrostatic charge build-up during examination. [
32]
2.6. Measurement of rubber ller interaction
efi The rubber- ller interaction was determined by fi swelling the cured silica- lled SMR-L compounds in
fi [15] toluene, according to ISO 1817. Test pieces with dimensions of 30mm 5
[18] ts . The initial weights were recorded prior to testing .
The test pieces were then immersed in toluene and [15] conditioned at room temre in a dark environment
[12] for 72 hours . After the conditioning period, the weights of
[15] the swollen test pieces were recorded . The swollen test
), according to ISO 3417 . Samf the respective compounds were tested at 150
90 ) and torque dif- ference (M
fi chemically active surface that can participate in vulcani- sation; providing coupling bonds between organosilane and both silica and rubber phases. There is much evidence con rming the existence of such bonds
[42] Petaling Jaya, Selangor, Malaysia . The APTES (C
fi [9e10 ]. The coupling bonds were noted to mark improvements in the mechanical properties of the rubber- lled vulcanisates
fi [].
In our previous work [ 17] , the preparation and appli- [12] [12] cation of Alkanolamide (ALK) in silica- lled natural rubber
fi compounds were reported. The incorporation of ALK
within silica- lled natural rubber compounds gave fi enhanced mechanical properties viz. tensile strength, ten- sile modulus and hardness. The enhancement of these properties was attributed to the improvement of silica dispersion in the rubber compounds, and higher crosslink density that stemmed from the incorporation of ALK. The results also indicated that ALK may function as an accel- erator and a plasticiser. In this study, the properties of silica- lled natural rubber compounds with ALK were
fi compared with those of silica- lled natural rubber com- fi pounds with Aminopropyltriethoxy Silane (APTES). APTES is a type of organosilane. Similar to ALK, APTES also con- tains amine within its molecule, and its molecular structure is shown in Fig. 1.
2. Experimental [
12]
2.1. Materials
Natural rubber grade SMR-L was obtained from Guthrie [23]
(M) Sdn . Bhd., Seremban, Malaysia. Other compounding ingredients such as sulphur, zinc oxide, stearic acid , N- isopropyl-N'-phenyl-p-phenylenediamine (IPPD), benzo- thiazolyl disul de (MBTS) and precipitated silica (grade
fi Vulcasil S) were supplied by Bayer Co. (M) Sdn. Bhd. , e
9 H
2 ), cure time (t
23 NO
3 Si) [16]
was supplied by Sigma-Aldrich. The ALK was synthesised in
our laboratory using Re ned Bleached Deodorized Palm fi
[16] Stearin (RBDPS) and diethanolamine . The reaction pro- cedures and molecular characterisations of the ALK were given in our previous report [ 17].
2.2. Compounding A semi-ef cient vulcanisation system was applied for
fi the compounding. The compounding procedure was per- formed on a two-roll mill (Model XK-160). dis- Table 1 played the compound designation and formulation of silica- lled SMR-L compounds with ALK and APTES.
fi [
17]
2.3. Cure characteristics
The cure characteristics of the silica- lled SMR-L com- fi pounds were obtained using a Monsanto Moving Die
Rheometer (MDR 2000 ), which was employed to deter- mine the scorch time (ts
[ 15] e and allowed to cool at room temperature for another 15 [12] minutes before the nal weights were recorded. The Lorenz fi
[12] and Park's equation [ 18 20]
2.0 MBTS
1.5 Sulphur
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
2.0
1.5
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0 IPPD
2.0
1.5
1.5
2.0
30.0
7.0 e e e e e e a Parts per hundred parts of rubber.
5.0
3.0
1.0
7.0 e e e e e e APTES
5.0
3.0
1.0
30.0 e ALK
30.0
30.0
1.5
30.0
30.0
30.0
30.0
30.0
1.5 Vulcasil-S
1.5
1.5
1.5
1.5
1.5
2.0
2.0
e was applied in this study. The
fi Fig. 2
[14]
Table 2 presents the torque difference (M H dM L ) of the silica- lled SMR-pounds at various ALK and APTES fi
The scorch and cure times of ALK were longer than those of APTES. This was attributed to the concentration of amine in each of the additive molecules. From the molec- ular structures of the additives, as presented in Fig. 1, i t w as seen that the mass fraction of amine in ALK was lower than that of APTES. Therefore, at a similar loading, ALK provided a lower concentration of amine than APTES.
overcome cure retardation problems in silica reinforcement [ 2,23].
creases the cure rate . Amine may also be d to [22]
[58]
addition of ALK and APTES decreased the cure and scorch times of silica- lled SMR-L compounds. Both additives may fi be considered as co-curing agents since the polar parts of these additives reacted with the silanol groups of silica to transform the hydrophilic silica into hydrophobic silica; which interacted relatively less with zinc oxide. In this manner, the performance of zinc oxide in activating the accelerator was maximised. It was seen that the higher the loading of these additives, the lower the scorch and cure times. This was attributed to the amine-content of both additives. As presented in Fig. 1, both chemicals contained accelerator activators, is an al
Consequently, zinc activity was reduced and the curing was [78] retarded . Compared to the control compound, the [ 2,21]
SMR-L compound (de ned as the control compound) cau- fi ses cure retardation. Due to its high polarity, silica inter- acted with zinc oxide during curing and formed silica d zinc, which was unable to activate the accelerator.
It is well-known that the addition of a silica ller into a fi
The effects of ALK and APTES on the scorch and cure times of silica- lled SMR-L compounds are shown in .
[14] into silica- lled SMR-L compounds produced compounds fi with a higher torque difference , compared to the control compound. The addition of up to 5.0 phr of these additives
1. Effects of ALK and APTES on cure characteristics of silica- filled SMR-L compounds
3. Results and discussion 3 .
100=Formula weight (3) [ 28]
[12] of hydrocarbon rubber (Q) was calculated based on Equa- tion . (3) Q ¼ ½ Swollen Dried weight Initial weight ½ =
fi In this study, the weight of the toluene uptake per gram
were constants. The higher the Qf/Qg value, the weaker the rller interaction became.
fi to hydrocarbon rubber in the isate ; while a and b [17]
[17] vulcanisates, respectively ; z was the ratio by weight of ller
þ b (2) where, the subscripts f and g referred to lled and fi
[17] z
swelling index was calculated according to Equation . (2) Qf Qg ae = ¼
loadings. The incorporation of 1 . 0 phr of these additives
increased the torque difference; however, it was decreased with further increase of these additives. It was also evident that the minimum torque (M
2.0
5.0
2.0
2.0
2.0
5.0 5. [26] Stearic acid 2 .
5.0
5.0
5.0
5.0
5.0
5.0
5.0
L
ZnO
fi Ingredients a Designation and composition of the SMR-L compound-based recipes Un- lled Control ALK1 ALK3 ALK5 ALK7 APTES1 APTES3 APTES5 APTES7 fi SMR-L 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
Table 1 The compound designation and formulation of silica- lled SMR-L compounds with ALK and APTES.
fi
filled SMR-L compounds reduced the ller- ller interac- fi fi tion, which led to a lower viscosity that enhanced the processability of the silica- lled SMR-L compounds.
resulting in lower viscosity of the compound . The incorporation of these additives into silica-
filler interaction became;
[48]
fi fi [13], and the value was used to measure the relative viscosity of a rubber compound . The lower the value, the weaker th- [24]
) decreased with increase of the loading of these additives. The minimum torque rep- resented the ller- ller inter agglomeration
Fig. 2. Scorch times (ts 2 ) and cure times (t 90 ) of the silica- lled SMR-L fi [8 3] e In theory, the torque difference may be used as an indication of the crosslink density of a rubber compound [ 25 28]
e . The greater the torque difference value, the higher the crosslink density. The total crosslink density was contributed by sulphide crosslinks and physical crosslinks [29 30] e
9.11
h r
Dispersion parameter Designation of the SMR-L compounds based recipes Control ALK1 ALK3 ALK5 ALK7 APTES1 APTES3 APTES5 APTES7
9.10 Table 3 The value of L for silica dispersion in SMR-L compounds.
10.94
10.21
9.48
9.16
11.09
10.75
9.51
4.81
11.14
0.33 M H eM L , dN.m
0.54
0.69
0.95
0.24
0.51
0.65
0.78
1.23
0.07
17.57
9.29
11.48
2.33
5.36
7.62
11.43
1.50
4.91
6.95
9.03
15.45
1.93 L ¼ h r em r
2.35
2.14
7.29
1.93
2.38
2.34
2.11
2.12
4.71 m r
7.71
9.86
13.57
3.43
9.43 M L , dN.m
10.90
. The addition of up to 5.0 phr of these additives into the silica- lled SMR-L compounds increased the tor- fi que difference of the SMR-L compounds. This was clearly attributed to the actions of these additives. As previously mentioned, the hydrophobic silica (due to the incorpora- tion of ALK and APTES) maintained the performance of zinc oxide in activating the MBTS, which accelerated the sulphur reaction and enhanced the state of the sulphide crosslink. The more hydrophobic silica became, the more compatible it was to SMR-L. As a consequence, the addition of these additives not only reduced the ller- ller interac-
r
Hg [30]
/M
Hf
¼ [M
r
], and m
Lg
/M
Lf
¼ [M
where: h
Lf and M Hf were the minimum and the maxtorques of the
L ¼ h r m r (4)
17,31e32].
The degree of silica dispersion, with or without the addition of ALK and APTES in the SMR-L phase, was determined quantitatively by Equation (4 ) [
3.2. Effects of ALK and APTES on the silica dispersion
The reduction of the torque difference after the 5.0 phr of ALK and APTES loading was most probably attributed to the dilution effect of excessive amounts of additives, which lowered the crosslink density. [ 30]
fi compounds.
ing to the formation of coupling bonds between the [13] additives with both silica and SMR-L . These coupling bonds were considered to be another type of crosslink , which contributed to the total crosslinks of silica- lled SMR-L
tion, but also enhanced the rubber- ller interaction; lead- fi
[13]
fi fi
]; where M
[30] filled compounds; and
10.43
with the data in Table 2. At a similar loading, the minimum torque (M
9.40
11.60
11.40
10.29
10.34
4.88
M H , dN.m
fi Cure characteristics Designation of the SMR-L compounds based recipes Un- lled Control ALK1 ALK3 ALK5 ALK7 APTES1 APTES3 APTES5 APTES7 fi
Table 2 Torque differences of silica- lled SMR-L compounds at various ALK and APTES loadings.
L ) of ALK was lower than that of APTES.
of ALK as an internal plasticiser , which caused the reduc- tion of the ller- ller interaction to lead to a better ller fi fi fi dispersion compared to APTES. This explanation was in line
M Lg and M
compound. This was attributed to the additional function
[12]
The comparison of the L value of ALK with that of APTES is presented in Table 3 Fig. 3 and . It is seen that at a similar loading, ALK caused a r L value of silica in the SMR-L
fi Consequently, silica became more compatible with SMR-L; hence improving the dispersion. The higher tding of the additives, the lower the value of L; which meant enhanced dispersion.
fi value of L. This was clearly due to the polar parts of these additive molecules that had a strong interaction with silica, which transformed the ller into a hydrophobic one.
The value of L for the silica dispersion in the SMR-L phase is presented in Table 3 Fig. 3 and . It is seen that the value of L of the silica dispersion in the rubber phase of the control compound was the highest. This was attributed to the surface of silica, which was saturated with hydrophilic silanol groups, and its relatively weak interaction with SMR-L. The silica particles also had a strong tendency to interact with each other and form large agglomerates . [33] Consequently, the dispersion of silica in the SMR-L com- pounds became poor. The addition of ALK and APTES at 1.0 phr into the silica- lled SMR-L compounds lowered the
lower the value of L at a particular silica loading , the better
¼ 4.88. The
fi compound. From Table 2, M Lg ¼ 0.07 and M Hg [22]
Hg were the minimum and the maximum torques of the un lled/gum SMR-L
2.78 e
3.3. Effects of ALK and APTES on rubber ller interactions efi The rubber- ller interaction depends on the degree of
The incorporation of up to 5.0 phr of ALK and APTES into [16] [18] the silica- lled SMR-L compounds increased the tensile fi modulus (M100 and M300 ), but modulus decreased with further increase in the loadings. The results of hardness,
RE of silica on SMR-L, due to the addition of ALK and APTES into the silica- lled SMR-L compounds, is
fi shown in . Fig.
5 As presented in Fig. 5, ALK and APTES, with various loading, increased the RE of silica on the SMR-L. This is associated with the function of the additives as surface modi ers of silica that improved its compatibility with
fi SMR-L; hence, improving the dispersion and rubber- ller
fi interaction. t a similar loading, ALK caused a higher RE of silica.
This was due to better dispersion of silica and a stronger [37] interaction of SMR-L silica in the prof ALK as e
[53] compared to APTES. This explanation is in agreement with the results in . Figs. 3 and 4
3.5. Effects of ALK and APTES on mechanical properties The effects of ALK and APTES on the M100, M300, hardness, EB, resilience and TS of silica- lled SMR-L com-
fi nds are shown in Figs. 6, 7, 8, 9, 10 and 11, respectively.
tensile strength and resilience also exhibited a similar tr
filler dispersion provided a greater surface area for rubber-
Since the tensile modulus of a rubber vulcanisate is only [13] dependent on the degree of crosslinking , the [ 34 35]
e
[13] enhancement of tensile modulus to 5 . 0 phr was attributed
[13] to a higher crosslink density due to the formation of coupling bonween the additives and both silica and
SMRe coupling bonds were another type of crosslink [ 2] , which contributed to the total crossnsity of the
[13] [13] SMR-L compounds . Therefore, with the addition of the additives , their effects were the same as an increase in crosslink density. This explanation is in line with the results
in Table 2. The silica- lled SMR-L compounds with addi- fi tives had a higher value of (M
H M L
) than the silica- lled fi vulcanisate without additives (control compound).
[14] filler interactions.
fi was infl fi uenced by the degree of ller dispersion. Enhanced
fi the ller dispersion in the rubber phase. Better ller fi fi dispersion results in stronger rubber- ller interactions. The
fi filler interaction.
fi rubber- ller interaction, with the addition of ALK and fi
APTES to the silica- lled compound (based on the Lorenz fi and Park's equation), is presented in . Fig. 4
It is shown that Qf/Qg decreased with increase of the ALK and APTES loading, up to 5.0 phr, and then increased with further increase to the loading. The decrease in Qf/Qg indicated that the SMR-L silica interactions became e stronger with the addition of ALK and APTES. This was attributed to the ability of these additives to chemically modify the surface of silica, which was then more compatible with SMR-L; hence, improving the wetting/ dispersion of silica and, consequently, img the SMR-
[53]
L silica interaction. This explanation is in agreement with e
Fig.
3. The increase of Qf/Qg after 5.0 phr loading was probably largely due to the excessive loading forming a layer in the silica- lled SMR-L system. The layer absorbed, coated and
fi trapped the silica reducing the rubber- ller interaction.
fi At a similar loading, the Qf/Qg values of ALK were lower than those of APTES. Again, this was attributed to the additional function of ALK as an internal plasticiser, which caused better ller dispersion and led to a stronger rubber-
3.4. Effects of ALK and APTES on reinforcing ef ciency of silica fi The degree of reinforcement provided by the ller was
compound High RE meant a high rubber- ller interaction, which
fi calculated through its reinforcing ef ciency (RE), which in fi its simplest form is given by Equation 5 [ 31].
RE ¼ ð M H M L f
ð M H M L g
= ðM H M L g
(5)
in which: (M H eM L ) f ¼ difference in torque value of lled compound
fi (M
H eM L
)
g ¼ difference in torque value of un lled/gum fi
The deterioration of the tensile modulus beyond 5.0 phr was attributed to the excessive loading of these additives, which caused a lower crosslink density. Presumably, the excessive amounts of these additives formed boundary layers which dissolved and coated part of the elemental curatives and silica particles, leading to decreased e e Fig.
6. Modulus at 100% of the silica- lled SMR-L compounds at various ALK fi Fig. 9. Elongation at break of the silica- lled SMR-L compounds at various fi and APTES loadings.
ALK and APTES loadings.
ALK. The ALK lowered the viscosity of the silica- lled SMR- fi
L compound, which led to better ller dispersion and fi greater rubber- ller interaction. M300 displayed the de-
fi gree of rubber- ller interactions fi [37e38]. This explanation is in line with the data in Fig. 4 , which demonstrated that the Qf/Qg values of ALK were lower than those of APTES.
As presented in Fig. 8 , hardness showed a similar behaviour as M100, which displayed the stiffness of a rubber vulcanisate [39] . Like tensile modulus, hardness also depends solely on the degree of crosslinks [34 35] . The e
[13]
enhancement of hardness up to 5. 0 phr was attributed to a
higher crosslink deand the deterioration of hardness [13] beyond 5. 0 phr was attributed to a lower crosslink density.
Fig. 7. Modulus at 300% of the silica- lled SMR-L compounds at various ALK fi
At a similar loading, the hardness of ALK was lower than and APTES loadings. that of APTES. This was due to the plasticising effect of ALK, which softened the silica- lled SMR-L vulcanisates.
fi ation of both sulphide and coupling bond crosslinks. Fig. 9 represented the effects of ALK and APTES on the
[37] Again, this explanation is in line with the data in Table 2 .
elongation at break (EB) of the silica- lled SMR-L com- fi
As presented in Figs. 6 and 7, at a similar loading, ALK pounds. As seen, APTES reduced the EB of silica- lled SMR- fi caused a decrease in M100 and an increase in M300,
L vulcanisate up to 5.0 phr of loading, and then increased compared to the silica- lled SMR-L compounds with fi slightly it as the loading further increased. EB depends
APTES. A decrease in M100 was attributed to the plasti- mostly on the degree of crosslink density [35] . Tuc-
[13]
cising effect of ALK, which modi ed the modulus/stiffness fi tion of the EB up to 5. 0 phr was simply attributed to a property. A plasticiser may be used, not only to improve the
higher crosslink density , which immobilised the SMR-L
rubber compound processing, but also to modify physical
segments from the silica surface. The increase of EB
properties (such as stiffness and exibility) of a rubber fl beyond 5.0 phr was attributed to a lower crosslink density. vulcanisate [36] .
A contrary result was obtained when ALK was utilised.
[12]
An increase in M300 was attributed to a stronger The EB increased with the increasing of ALK loadings. This rubber- ller interaction due to the plasticising effect of
fi
was attributed to the function of ALK as an internal
Fig. 8. Hardness of the silica- lled SMR-L compounds at various ALK and Fig. 10. Resilience of the silica- lled SMR-L compounds at various ALK and
fifi plasticiser, which modi ed the exibility of the silica- lled fi fl fi
SMR-L compounds. As an internal plasticiser, ALK provided a free volume that allowed increased mobility/ exibility for fl the rubber chains to move.
nsile fractured surfaces were in mutual agreement with the results in , which illustrated that the Qf/Qg values Fig.
fi was delayed until a larger strain.
3.6. Scanning electron microscopy (SEM) study The SEM micrographs in demonstrate the frac- Fig. 12 tured surfaces of silica- lled SMR-L compounds with ALK
fi and APTES at a magni cation of 200X. The micrographs fi showed the improvement of the silica dispersion due to the addition of ALK and APTES. The dispersion of the ller
fi was the least homogeneous in (a), where large silica ag- glomerates were observed (indicated by arrows in Fig. 12a). The SEM micrograph of (a) also seemed relatively smooth compared to the others, which indicated that (a)
[12]
was less ductile than the others. However, the SEM
micrograph for (c) exhibited a comparable matrix tearing [14] line and surface roughness with (f). Both (c) and (f) pre- sented the greatest matrix tearing line and surface roughness compared to the others (b, d, e and g). A greater
rubber- ller interaction in both (c) and (f) altered the fi crack path, which led to increased resistance to crack propagation that caused an increase in tensile modulus,
[63]
tensile strength and hardness. The micrographs of the
4 of ALK-5 and APTES-5 were the lowest ones. An enhancement in rupture energy, due to a greater rubber- filler interaction, was responsible for the roughness and
fi fi fi ller dispersion and greater rubber- ller interaction. Ac-
[63]
matrix tearing line of the fractured surface. The micro-
graphs of the tensile fractured surfaces were in mutual agreement with the results obtained by other researchers [ 42 43]
e who reported that an increase in rupture energy was responsible for the roughness and matrix tearing line of the fractured surface.
However, the matrix tearing lines and surfaces rough- ness of (d) and (g) were smoother than those of (c) and (f), which indicated lower crosslink densities.
4. Conclusions From this study, the following conclusions were drawn:
1. Alkanolamide and aminopropyltriethoxy silane (APTES) acted as co-curing additives in silica- lled natural rub- fi ber compounds. Both of the additives increased the cure rate and torque difference.
2. A 5.0 phr loading of alkanolamide and amino- propyltriethoxy silane (APTES) was the optimum loading to improve the properties of silica- lled al rubber
fi compounds.
3. At a similar loading, alkanolamide indicated a higher degree of silica dispersion, greater silica natural rubber e interaction and higher reinforcing ef ciency than ami-
fi
cording to Cohan [41], higher breaking elongation tends to give higher tensile strength. A higher EB meant a higher strain at break of the silica- lled SMR-L vulcanisate; which
At a similar loading, ALK produced a tensile [14] [26] strength than APTES. This may be attributed to a higher reinforcing ef ciency of ALK due, for example, to better
Fig. 10 displays the effects of ALK and APTES on the resilience of the silica- lled SMR-L compounds. It shows fi that APTES increased the resilience of silica- lled SMR-L
At a similar loading, the resiliencies of ALhigher
fi compounds up to 5.0 phr of loading, and then decreased it as the loading further increased.
Like tensile modulus and hardness, resilience also de- pends on the number of crosslinks . The enhance- [36,39] ment of resilience up to 5.0 phr was attributed to a higher crosslink density, and the deterioration of resilience beyond 5.0 phr was attributed to a lower crosslink density.
ALK presented a similar trend as APTES with loading up to 5.0 phr; however, beyond 5.0 phr, the ALK displayed a
[65]
further increase in resilience. Again, this was attributed to
the plasticising effect of the ALK, which improved the fl fi exibility of the silica- lled SMR compounds. According to
Hofmann and Ignatz-Hoover , rebound [39] &
T o [36] resilience not only depends on the degree of crosslinks, but also on the exibility of the rubber chains. The more
fl flex- ible the rubber chains, the higher the resilience. The excessive amount of ALK (7.0 phr) caused a more exible
fl silica- lled SMR chains. fi
[65]
higher the reinforcing ef ciency of the ller, and a higher fi fi tensile strength is produced.
than those of APTES. Again, this was attributed to the
plasticising effect of ALK, which caused a higher crosslink density and a higher EB (more exibility).
fl
Fig. 11 illustrates the tensile strength of silica- lled fi SMR-L compounds at various ALK and APTES loadings.
The tensile strength enhancement was attributed to the ability of ALK and APTES to improve the silica SMR-L in- e teractions. The silica surface was saturated with hydro- philic silanol groups, which were relatively incompatible with Sand its interaction with SMR-L was relatively
[41]
low. Both the silane coupling agent and ALK [ 40] [17] may chemically modify the surface of silica, and transform it into hydrophobic silica. This additive-modi ed silica was
fi more compatible with SMR-L; as a result, the improved wetting/dispersion and the improved silica SMR-L inter- e
[13]
action led to the formation of physical crosslinks. These
physical crosslinks further contributed to the total crosslink density . The greater the physical crosslink s, the [ 29 30] e
Fig. 11. Tensile strength of silica- lled SMR-L compounds at various ALK and fi APTES loadings. e
[ 60] e
Fig. 12. SEM micrographs of the failed fracture of silica- lled vulcanisate at a magni cation of 500x: (a) Control, (b) ALK3, (c) ALK5, (d) ALK7, (e) APTES3, (f) fi fi APTES5, and (g) APTES7. Acknowledgements The authors would like to thank Universiti Sains Malaysia for providing the research facilities for carrying out the experind for making this research work
[88] possible. One of the authors (Indra Surya) is grateful to the Directorate General of Higher Education (DIKTI), Ministry of Education and Culture (Kemdikbud) of the Republic of Indonesia, for the award of a scholarship under the fth
[27] H. Ismail, C. Ng, Palm oil fatty acid additives (POFA's): preparation and application, Journal of Elastomers and Plastics 30 (1998) 308 327 e . [19] [28] P. Teh, Z. Mohd Ishak, A. , J. Karger-Kocsis, U. Ishiaku, Effects of epoxidized natural rubber as a compatibilizer in melt com- pounded natural rubber oclay nanocomposites, European e Polymer Journal 40 (2004) 2513 2521 e .
[21] R. Mukhopadyay, S. De, Effect of vulcanization temperature and different llers on the properties of ef ciently vulcanized natural fi fi rubber, Rubber Chemistry and Technology 52 (1979) 263 277 e . [22] H. Long (Ed.), Basic Compounding and Processing of Rubber, Rubber Division, American Chemical Society Inc. The University of Akron,
Ohio, USA, 1985. [23] H.L. Stephens, The compounding and vulcanization of rubber, in: M. Morton (Ed.), Rubber Technology, Van Nostrand Reinhold, New
York, 1987, pp. 20 58 e . [15] [24] H. Ismail, R. Nordin, A. Noor, Cure characteristics, tensile properties and swelling behaviour of recycled rubber powder- lled natural
fi rubber compounds , Polymer Testing 21 (2002 ) 565 569 e . [23]
[25] B. Boonstra, H. Cochrane, E. Dannenberg, Reinforcement of silicone rubber by particulate silica, Rubber Chemistry and Technology 48 (1975 ) 558 576 e .
[26] H. Cochrane, C. Lin, The in uence of fumed silica properties on the fl processing, curing, and reinforcement properties of silicone rubber, Rubber Chemistry and Technology 66 (1993) 48 60 e .
[29] G. Kraus, Interactions of elastomers and reinforcing llers, Rubber fi Chemistry and Technology 38 (1965) 1070 [16] [30] K. Polmanteer, C. Lentz, Reinforcement studies-effect of silica structure on properties and crosslink density, Rubber Chemistry and Technol8 (1975) 795 809 e . [39]
fi agents in natural rubber , Journal of Polymer Science 50 (1961) 299 312 e .
[31] B. Lee, Reinforcement of uncured and cured rubber composites and its relationship to dispersive mixing-an interpretation of cure meter rheographs of carbon black loaded SBR and cis-polybutadiene compounds , Rubber Chemistry and Technology 52 (1979) 1019 1029 e .
[32] P. Pal, S. De, Effect of reinforcing silica on vulcanization, network structure, and technical properties of natural rubber, Rubber Chemistry and Technology 55 (1982) 1370 1388 e . [33] N. Hewitt, Processing technology of silica reinforced SBR, Elasto- merics, (March, 1981) 16 (1981). [34] D.L. Hertz Jr., S.E. Inc, theory practice of vulcanization, Elasto- & merics (November, 1984). [28] [35] H. Ismail, H. Chia, The effects of multifunctional additive and epoxidation lica lled natural rubber compounds , Polymer fi Testing 17 (1998) 199 210 e .
[36] B. Rodgers, Rubber Compounding: Chemistry and Applications, CRC, 2004. [37] G. Kraus, Reement of elastomers by particulate llers, Science fi and Tecgy of Rubber (1978) 387 416 e . [16] [57] [38] S. Wolff, Optimization of silane-silica OTR compounds .
Part 1: var- iations of miemperature and time during the modi cation of fi silica with bis-(3-triethoxisilylpropyl )-tetrasul de, Rubber Chemis-
fi try and Technology 55 (1982) 967 989 e .