Alkanolamide as an Accelerator, Filler-dispersant and a Plasticizer in Silica-filled Natural Rubber Compounds

  

  0.5% 3 matches [52]

  0.7% 3 matches [46]

  

  0.7% 5 matches [47]

  

  0.6%

  3 matches

  [48]

  

  0.6% 2 matches [51]

  

  

  0.8% 2 matches [45]

  0.5%

  3 matches

  [53]

  

  0.5% 2 matches [55]

  

  0.4% 3 matches [57]

  

  15.4%

  Results of plagiarism analysis from 2017-12-06 08:37 UTC

  Alkanolamide as an accelerator, filler-dispersant and a plasticizer in silica-filled natural rubber compounds.pdf

  

  

  

  11 matches

   [17]

  

  2.4%

  15 matches

  [18]

  

  2.5% 12 matches [21]

  

  2.0% 11 matches [22]

  

  2.1%

  [23]

  0.9% 4 matches [39]

  

  1.8% 10 matches [25]

  

  1.3% 7 matches [30]

  

  1.2% 2 matches [31]

  

  1.2%

  4 matches

  [37]

  

  Date: 2017-12-06 08:29 UTC

  [65]

  0.2% 1 matches [84]

  

  0.3% 1 matches [78]

  

  0.3%

  2 matches

  [81]

  

  0.2%

  1 matches

  [82]

  

  

  

  0.1% 1 matches [85]

  

  0.2%

  1 matches

  [88]

  

  0.1% 1 matches [89]

  

  0.2% 1 matches [90]

  

  0.2% 1 matches

  0.3% 1 matches [77]

  [76]

  

  

  0.4% 2 matches [66]

  

  0.4% 1 matches [67]

  

  0.3%

  3 matches

  [68]

  

  0.3% 1 matches [69]

  

  0.3% 2 matches [70]

  0.2%

  2 matches

  2 matches

  [71]

  

  0.3% 1 matches [72]

  

  0.3% 2 matches [73]

  

  0.3% 2 matches [74]

  

  0.3% 2 matches [75]

  

  0.3%

  

  0.1% 1 matches [98]

  

  0.1%

  1 matches

  [99]

  

  0.1% 1 matches [101]

  

  0.1% 1 matches [102]

  

  0.1% 1 matches [103]

  

  0.1% 1 matches 9 pages, 5499 words PlagLevel: selected / overall 327 matches from 104 sources, of which 80 are online sources. Settings

  Data policy: Compare with web sources, Check against my documents, Check against my documents in the organization repository, Check against organization repository, Check against the Plagiarism Prevention Pool Sensitivity: Medium Bibliography: Consider text Citation detection: Reduce PlagLevel Whitelist: --

  Polymer Testing 32 (2013) 1313–1

  Contents lists available at ScienceDirect

  Polymer Testing

  j o u h r o n m a w e l w p a w v g . i c e e e o l : r m s . / e l o c a t e / p o l y t e s t

  Material properties Alkanolamide as an accelerator, filler-dispersant and a plasticizer in silica- lled natural rubber compounds

  fi

  a b , b

• Indra Surya , H. Ismail , A.R. Azura

  a On study leave from Department of Chemical Engineering, Engineering Faculty, University of Sumatera Utara, Medan 20155, Sumatera Utara, Indonesia b

  School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, Engineering Campus, Nibong Tebal 14300, Penang, Malaysia

a i r n t a f i b o c s l t e r a c t

Article history: A feasibility study was carried out on the utilization of Alkanolamide (ALK) on silica Received 21 May 2013 reinforcement of natural rubber (NR) by using a semi-ef cient cure system. The ALK was

  fi Accepted 25 July 2013 incorporated into the NR compound at 1.0, 3.0, 5.0, 7.0 and 9.0 phr. An investigation was carried out to examine fect of ALK on the cure characteristics and properties of NR _[17] Keywords: compounds. It was founALK gave shorter scorch and cure times for silica- lled NR _[17]

  fi Alkanolamide compounds. ALK also exhibited higher torque differences, tensile modulus, tensile

  Natural rubber _[17] strength , ha rdness and crosslink density of up to 5.0 phr of ALK loading, and then

  Filler-dispersant decreased with further ises of ALK loading. The resilience increased with increased

  Plasticizer _{[17] [37]} ALK loading. Scanning electron microscopy (SEM ) micrographs proved that 5. 0 phr of ALK Tensile properties in the silica- lled NR compound exhibited the greatest matrix tearing line and surface

  fi roughness due to higher reinforcement level of the silica , as well as better dispersion and cure enhancement.

  

Ó

2013 Elsevier Ltd. All rights reserved.

  1. Introduction black, silica does not react with sulphur, and coupling

  bonds will not be formed due to its hydrophilic silanol

  Carbon blacks and silicas of varying forms and particle- groups that are relatively incompatible with hydrocarbon sizes are very popular and have been widely utilized as rubbers , such as natural rubber [ 2] . reinforcing llers in the rubber industry. In general, the For many applications, silicas are not satisfactory alter-

  fi properties of silica-reinforced rubber vulcanisates are natives to carbon blacks because of their relatively lower usually inferior to those of carbon blacks, even when they reinforcement levels. The fundamental problem is their are of comparable size [1] . This is attributed to the apparent surface chemistry, which is more polar and hydrated than imilarity in the surface chemistry of the two materials. carbon blacks, and which cause them to be dif cult to wet,

  fi

  [30] Carbon black will react with sulphur during vulcanization disperse and interact with hydrocarbon rubbers. Numerous and form sulphur bonds that link the rubber chains, and methods have been carried out to improve the reactivity of

  [39] also tie the carbon black to the rubber . This is known as silicas with the rubber phases. One such method is the utilization of a silane-co

  filler-rubber crosslinking, another type of crosslink to the

  [ 3 [39] ]

  rubber system, and is de ned as coupling bonds [2,3]. In of the silica . The modi ed silica provide chemically active fi

  

fi

marked contrast to the hydrocarbon functionality of carbon surfaces that can participate in vulcanization, providing coupling bonds between the silane and both the silica and the rubber phases [ 4,5] . Those products show signi cant

  fi improvement in performance compared to their base

• Corresponding author.

  E-mail address: hana @eng.usm.my (H. Ismail). materials.

  fi _{Ó –} 0142-9418/$ see front matter 2013 Elsevier Ltd. All rights reserved.

  / Polymer Testing 32 (2013) 1313–1

  4 c m

  [21] according to BS 903 Part A8. The rebound resilience was calculated according to the following equation : % Resilience ¼ ½ ð1 cos 

  [ 21] q

  2 Þ=ð  1 cos q

  1 Þ  100 (1) where, q

  1 is the initial angle of displacement (45

   ), and q

  2 is the maximum rebound angle .

  2.6. Scanning electron microscopy (SEM) The tensile fractured surfaces of the compounds were examined by using a Zeiss Supra-35VP scanning electron microscope (SEM) to obtain information regarding the ller

  fi dispersion anetect the possible presence of micro-

  [70]

  defects. The fractured pieces were coated with a layer of

  gold to eliminate electrostatic charge build-up during examination.

  2.7. Fourier transform infra-red (FTIR) spectroscopy The FTIR spectra were obtained using a Perkin-Elmer 2000 series instrument. The spectrum resolution was

  1

  at 100% elongation (M100), 300% elongation (M300), and [22] elongation at break were investigated. The hardness mea- surements of the samples were performed according to ISO

  and the scanning range was from 550 to 4000 cm

  1 .

  2.8. Measurement of crosslink density Swelling tests on the rubber vulcanisates were per-

  [21]

  formed in toluene in accordance with ISO 1817. The cured

  test pieces (30 mm  5 m m  2 mm) were weighed using an electrical balance and swollen in toluene until equilib-

  [21] rium, which took 72 h at room temperature. The samples were taken out of the liquid, the toluene was removed from the sample surfaces and the weight was determined. The

  samples were then dried in the oven at 60

  

  C until constant

  Table 1 Speci cation of RBDPS.

  fi Acid value 0.30 mg KOH Free fatty acid 0.14% Iodine value

  35.3 Moisture 0.01% Colour 2.8 red/20 yellow Saturated C12:0 (lauric acid) 0.1% C14:0 (myristic acid) 1.2% C16:0 (palmitic acid) 59.1% C18:0 (stearic acid) 4.6% C20:0 (arachidic acid) 0.4% Unsaturated C18:1 (oleic acid) 28.2% C18:2 (linoleic acid) 6.3% Unknown 0.1% ^{[ 21]}

  [21] 7691-I using a Shore A type manual durometer . The resil- ience was studied using a Wallace Dunlop Tripsometer

  machine according to ISO 37. The tensile strength and stress

  Another alternative method to overcome the de ciency fi of silica is the utilization of Alkanolamide. The ingredient is synthesized from Re ned Bleached Deodorized Palm

  Sdn. Bhd., Seremban, Malaysia was used. Other com- pounding ingredients such as sulphur, zinc oxide, stearic acid, N-isopropyl-N -phenyl-p-phenylenediamine (IPPD), benzothiazolil disul de (MBTS), and precipitated silica

  fi Stearin (RBDPS), a product of crude palm oil fractionation. This article describes the preparation and utilization of the new rubber ingredient as an additive in order to improve the reinforcement level of silica to natural rubber.

  2. Experimental

  2.1. Laboratory preparation of Alkanolamide The reaction was carried out at atmospheric pressure in a 1000 ml reaction vessel tted with a stirrer. Typically,

  fi 1.0 mol of RBDPS and 3.0 mol each of diethanolamine, so- dium methoxide and methanol (as catalysts) were placed in the reaction ask. The speci s of the RBDPS are

  fl fi

  [59]

  given in Table 1. The mixture was stirred and heated ; the reaction temperature was kept constant at 70

  

  C for about five hours. The resultant mixture was extracted with diethyl ether, and washed with saturated sodium chloride solution. The crude Alkanolamide was puri ed with

  fi anhydrous sodium sulphate, and then concentrated by a rotary evaporator. The nal product, a cream-coloured,

  fi waxy, solid material, namely Alkanolamide, was used as an additive in silica- lled natural rubber compounds. The

  fi reaction procedure was as shown in Fig. 1.

  2.2. Materials Natural rubber grade SMR L obtained from Guthrie (M)

  fi (grade Vulcasil S) were supplied by Bayer Co. (M) Sdn.

  [45]

  2.3. Compounding A semi-ef cient vulcanization system was used for the

  fi compounding. The recipes for the preparation of the nat- ural rubber compounds are given in Table 2. The com- pounding was done on a two-roll mill (Model XK-160).

  Table 3 shows the designation and composition of the [94] NR-based recipes used in this study. _[ 62]

  2.4. Cure characteristics

  The cure characteristics of the silica- lled NR com- fi pounds were obtained using a Monsanto Moving Die Rheometer (MDR 2000), which was used to determine the scorch time (ts

  2 ) cure time (t

  90 ), and torque differen (M

  H dM L [62]

  ) according to ISO 3417. Samples of the respective compounds were tested at 150

   C . The compounds were

  subsequently compression moulded using a stainless steel mould at 150

  

  C with a pressure of 10 MPa using a labo- ratory hot-press based on the respective curing times.

  2.5. Tensile, hardness and resilience properties Dumbbell-shaped samples were cut from the moulded sheets. Tensile tests were performed at a cross-head speed of 500 mm/min using an Instron 3366 universal tensile

• – Bhd., Petaling Jaya, Selangor, Malaysia.

I. Surya et al. / Polymer Testing 32 (2013) 1313–1

  [84] accelerator . Increasing the ALK loading has the same [ 8] effect as increasing the amoumine in the silica- lled

  is an O H stretch of the

  

Fig. 1. Chemical reaction of the preparation of Alkanolamide.

  fi primary accelerators, through the formation of complexes which are responsible for the ssion of the sulphur mole- fi cules to form crosslinks between the linear rubber chains . It

  [18] organic substance containing nitrogen atoms promotes the curing process of ole nic rubber, comprising sulphur and

  According to Bateman , and Ismail & Ng [9] [10] , a certain

  NR compound. Hence, it can be said that the higher the ALK loading, the greater the amount of amine and the shorter the cure rate.

  fi [17]

  crease the pH of the rubber compound and, in most in- [18] stances, enhance the cure rate . Any material that makes the rubber compound more basic will enhance the cure rate since acidic materials tend trd the effect of the

  3.1. Characterization of Alkanolamide Fig. 2 shows the typical infrared spectrum of the Alka- nolamide (ALK) obtained, and shows the wave- Table 4 number of the functional groups in the ALK molecule. The strong broadband at 3370 cm

  of the ALK. Amine is an alkaline substance which will in-

  [18]

  calculate the molecular weight between two crosslinks (M c

  1

  . The spectrum clearly shows the presence of wavenumbers of the func- tional groups of ALK.

  3.2. Cure characteristics and crosslink density The effects of ALK on the cure characteristics of the silica- lled NR compound can be seen in and .

  fi Fig. 3 Table 5

  1

  3. Results and discussion

  fi cure enhancement cattributed to the amine content

  1 1 þ Q m

  ) by applying the Flory-Rehner Equation . [ 6] M c ¼

   r p

  V s

  V 1 3 = r ln 1 ð  V r Þ þ V r þ c

  V

  2 r (2)

  V r ¼

  (3)

  2M c a (4)

  where r is the rubber density ( r of NR 0. 92 g ¼

  [21]

   V s is the molar volume of the toluene (V s

  ¼ 106.4 cm [21]

  3 /mol), V r is the volume fraction of the polymer in the swollen spec- imen, Q m is the weight increase of the blends in toluene and c is the interaction parameter of the rubbtwork- solvent ( c

  [21] of NR . 393). The degree of the crosslink ¼ density is given by ; V c ¼

  1

  Fig. 3 shows that the scorch and the cure times decreased with increased ALK loading. It was observed that there was an enhancement in the cure characteristics, indicating that ALK could act as a co-curing agent or secondary accelerator in the curing process of the silica- lled NR compounds. The

• – ethanol. The C H stretches above and below 3000 cm
• – 1

  1

  e. the maximum torque minus the minimum torque. Further

  Designation Composition NR/Silica/Alkanolamide (phr) A/0.0 (Control) NR/Silica 100/30 B/1.0 /Silica/Alkanolamide 100/30/1 C/3.0 NR/Silica/Alkanolamide 100/30/3 D/5.0 NR/Silica/Alkanolamide 100/30/5 E/7.0 NR/Silica/Alkanolamide 100/30/7 F/9.0 NR/Silica/Alkanolamide 100/30/9

  Table 3 Designation and Composition of the NR-based recipes.

  1.5 a parts per hundred parts of rubber.

  MBTS

  5.0 IPPD 2. ^[72] Stearic acid 2 .

  1.5 Zinc oxide

  30.0 Sulphur

  Natural rubber (SMR L) 100.0 Alkanolamide 0.0; 1.0; 3.0; 5.0; 7.0; 9.0 Precipitated silica (Vulcasil - S)

  Ingredients Content (phr) a

  Table 2 ^{[ 17]} Composition of the rubber compounds .

  indicate saturated and unsaturated portions exist in the molecule . The umbrella mode at 1364 cm [7]

  H dM L ), i.

  means that there are more than 4 methylene atoms in a row in the molecule. The C O stretch is at 1615 cm ]

  fi [18] increased the torque difference (M

  5. 0 phr of ALK into the silica- lled rubber compound

  fi compound. resented in Table 5, the incorporation of up to

  is expected that the amine-content of the ALK would accelerate the cure and is responsible for enhancing the cure rate and the cure state of the silica- lled NR

  1

  con rms fi the presence of a methyl group (CH

  3

  ) which is attached to the carbon atom. The (CH

  2

  ) rocking band at 719 cm

  1

  , and the amide C N stretch is at 1248 cm –

I. Surya et al. / Polymer Testing 32 (2013) 1313–1

  fi inside the layers. Through this mechanism, the ability of sulphur to form a sulphide crosslink and silica to form a

  [51]

  crosslink. The ALK increased the degree of silica dispersion

  and formed the additional physical crosslinks by silica NR

  The reduction of the torque difference (M

  H dM L

  ) a fter the 5.0 phr loading, i.e. the E/7.0 NR compound, is most probably due to the softening or lubricating effect of the

  [46]

  excessive ALK, which caused a lower crosslink density. This

  can be attributed to the phenomenon of dissolving a part of the elemental sulphur and silica particles into the excessive ALK and, as a consequence, less sulphur and silica were attached to the NR chains. The ALK is a unique molecule

  which is structured by a non-polar hydrocarbon chain and polar terminal groups. The non-polar hydrocarbon chain dissolved in the non-polar NR, forming a monolayer and lubricating the NR; whereas the polar terminal groups together with other curatives and silica formed interme- diate complexes that remained insoluble. The excessive amount of ALK caused a more pronounced lubricating ef- fect, and produced boundary layers which coated and absorbed not only the curatives but also the silica ller

  [46]

  increases e ALK loading decreased the torque differ-

  physical crosslink would be less. This explanation could be

  supported by a morphological study of the tensile fractured surface of the E/7.

  0 NR compound. The fractured surface seemed smoother than that of the D/5.0 NR compound due essive ALK loading. ALK was synthesized from the

Fig. 2. The infrared spectrum of Alkanolamide.

  Table 4 The Wavenumbers of Functional Groups of Alkanolamide Molecule.

  Vibration Wavenumber (cm ^1 ) O H stretch 3370

• _– Unsaturated (C

  C) 3006 ] Saturated (CH

  3 ) 2852 C O stretch 1615

  ] CH

  C N stretch 1248 _– CH

  2 rocking 719 ^{[ 17]} Fig. 3. Scorch time ( ) and cure time ( ) of the silica- lled NR compounds t2 t90

  fi

  sulphur reaction ahanced the state of the sulphide

  the action of the ALK, not only as a secondary accelerator, but also as ller dispersant. The ALK accelerated the fi

  the silica- lled NR vulcanisates. This is clearly attributed to fi

  fi tendency to interact with each and form a ller- ller fi fi

  [53]

  ence. It is also evident that the minimum torque (M

  L ) decreased with increases in the ALK loading. It has been

  reported that M

  L

  corresponds to tler- ller inter fi

  [67]

  agglomeration [11] and is a measure of the stock viscosity

  [ 12]. The incorporation of ALK into the silica- lled NR

  fi compound reduced the viscosity of the compound and facilitated a relatively strong interaction between the ALK and the silica ller, while the silica particles had a weaker

  [18]

  [51]

  agglomeration. Consequently, the processability of the sil-

  ica dispersion in the rubber phase became easier and ied the degree of silica dispersion .

  Theoretically, the torque difference (M [18]

  H dM

  L ) repre- sents the shear dynamic modulus, which is indirectly related to the total crdensity of a rubber compound

  [18] [

  10,13–1 5 ]. The total crosslink density is contributed by the

  sulphide crosslinks and physical crosslinks [ 16,17]. The

  addition of up to 5.0 phr of ALK into the silica- lled NR fi compounds increased the torque difference (M

  H dM L

  ) f

• – attachments (which will be seen in FTIR result).

3 Umbrella mode 1364

  

I. Surya et al. / Polymer Testing 32 (2013) 1313–1

Table 5 Table 6 The Effect of Alkanolamide Loading on Torque Difference of Silica- lled NR The Value of L for Silica Dispersion in NR Phase. fi Compounds.

  Torque Property NR-based compound Torques NR-based compound A/0.0 B/1.0 C/3.0 D/5.0 E/7.0 F/9.0 A/0.0 B/1.0 C/3.0 D/5.0 E/7.0 F/9.0

  Minimum torque,

  1.23

  0.78

  0.65

  0.51

  0.24

  0.23 Maximum

  10.34

  10.29

  11.40

  11.60

  9.40 9.16 (M ), dN.m L torque, (M ), dN.m h ¼ [M /M ]

  17.50

  11.14

  9.29

  7.29

  3.43

  3.29 H r Lf Lg

  Minimum

  1.23

  0.78

  0.65

  0.51

  0.24

0.23 Maximum torque,

  10.34

  10.29

  11.40

  11.60

  9.40

  9.16 torque, (M ), dN.m (M ), dN.m L

  H Tork diff.,

  9.11

  9.51

  10.75

  11.09

  9.16 8.93 m ¼ [M /M ]

  2.12

  2.11

  2.34

  2.38

  1.93

  1.88 r Hf Hg

  (M ), dN.m h

  15.45

  9.03

  6.95

  4.91

  1.50

  1.41 H dM L L ¼ r d m r

  RBDPS, a palm oil fraction. Palm oil has the effect of plas- ticizing or lubricating rubbers [18].

  The crosslink density of the silica- lled NR vulcanisates fi was determined by the Flory Rehner approach [Eq. (2) ]. d

  Fig. 4 shows the crosslink density of the vulcanisates at

  [17]

  room temperature. The addition of up to 5. phr of ALK into

  the silica- lled rubber compound increased the crosslink fi density, and further increases in the ALK lo decreased

  [18] the crosslink density. This observation is in line with that of the torque difference (M ), which is an indirect dM

  H L measure of the crosslink density of the rubber vulcanisates.

  3.3. Silica dispersion

  Fig. 5. Modulus at 100% and 300% elongations of the silica- lled NR vul- fi

  The degree of silica dispersion in the NR phase can be canizates at various ALK loadings. determined quantitatively by equation [19,20],

  L ¼ h r  m r

  greater the available surface area for the interaction, the in which: h ¼ [M /M ], m ¼ [M /M ], where M and higher is the total crosslink density [16,17]. However, as

  r Lf Lg r Hf Hg Lf

  M are the minimum and the maximum torques of the presented in Fig. 4 , the total crosslink densities of the E/7.0

  Hf

  and M are the minimum and the filled vulcanisates; M Lg Hg and F/9.0 silica- lled NR vulcanisates were lower than

  fi maximum torques of the gum NR vulcanisates. Based on those of the B/1.0, C/3.0 and D/5.0 silica- lled NR vulcani- fi the previous study [21] (for NR gum compound vulcanized sates, and even the former vulcanisates had lower values of with the same secient formulation), M

  Lg ¼ 0.04; L. This phenomenon can be attributed to the dominant

  

  [18]

  M The lower the value of L at a particular silica ¼ 4.81. plasticizing effect of ALK. As discussed before, the excessive

  Hg

loading, the r is the silica dispersion in the rubber amount of ALK trapped the silica inside its layers, thus

  [18] phase . The value of L for the silica dispersion in the NR causing less formation of physical crosslinks. phase is presented in Table 6.

  From the data shown in Table 6, it can be seen that ALK

  [17]

  3.4. Mechanical properties caused a lowering in the value of L. The higher the ALK

  loading, the lower is the value of L. The lower value of L

  Figs. 5 8 show the effect of ALK on the tensile, hardness indicates better silica dispersion, which provides a greater

• – and resilience of the silica- lled NR vulcanisates. It can be

  fi available surface area for the silica-NR interaction. The

  

Fig. 4. Crosslink density of the silica- lled NR vulcanizates at various ALK Fig. 6. Tensile strength of the silica- lled NR vulcanizates at various ALK

fi fi

I. Surya et al. / Polymer Testing 32 (2013) 1313–1

  released by the recovery from deformation to that required to produce the deformation . According to Hofmann [ 26]

  fi Fig. 8. Elongation at break of the silica- lled NR vulcanizates at various ALK fi

  From the micrographs, it can clearly be observed that [55] the presence of ALK improved the silica dispersion. The Fig. 7. Hardness of the silica- lled NR vulcanizates at various ALK loadings.

  aE/7.0 at 300 magni cation.  fi

  fi without the addition of ALK: (A) A/0.0; (B) C/3.0; (C) D/5.0;

  10 provides the SEM micrographs of the tensile fractured surfaces of the silica- lled NR vulcanisates with and

  Scanning electron microscopy (SEM) was used to [46] determine the silica dispersion in the NR matrix . Fig.

  3.5. Scanning electron microscopy (SEM) study

  fl fi _{[ 17]}

  fi hances the total crosslink density, and as a plasticizer which improves the exibility of the lled rubber chains.

  NR compound enhanced the resilience of the silica- lled NR fi vulcanisates. Again, this can be attributed to the functions of the ALK as an accelerator and ller dispersant which en-

  fl the resilience. The incorporation of ALK into the silica- lled fi

  fl chains ; the more exible the molecular chains, the better

  [90] enhanced to some extent as the crosslink density rises, and the resilience is related to the exibility of the molecular

  [27] [24] , and Ignatz-Hoover & To , the rebound resilience is

  seen that M10rther increases in

  [17] [17] the ALK loading . The results of the tensile strength and hardness also exhibited a similar trend. According to Hertz

  [47]

  Fig. 9 shows the effect of ALK on the resilience of th

  fl the silica- lled NR vulcanisates. fi

  fl ALK loading has the same effect as an increase in free vol- ume that will enhance the exibility or the extensibility of

  fi [24], a plasticizer is a compounding material that is used not only to improve the rubber compound processing but also to modify the physical properties such as hardness, flexibility or distensibility of the rubber vulcanisates, and one of the sources from which it is made is natural oil/fat [18]. However, ALK is a waxy, solid material, and is derived from RBDPS-Crude Palm Oil, a type of natural oil. Although ALK has a smaller molecular size compared to NR, that additive could provide a monolayer in the rubber com- pound which provides free volume, thus allowing more mobility/ exibility for the rubber chains. Increasing the

  Increasing the ALK loading caused a further increase in the percentage of elongation at break. This can be attributed to the function of the ALK as an internal plasticizer to the silica- lled NR system. According to Moneypenny et al.

  As presented in Fig. 7, the addition of 1.0 phr ALK into the silica- lled NR compound resulted in the vulcanisated fi B/1.0 NR compound having a higher elongation at break.

  fi small ( 1  m m) and well dispersed in the rubber matrix. The deterioration of those properties after 5.0 phr can be attributed to the lower degree of crosslink density and the more pronounced softening effect of the excessive ALK.

  According to Hamed , in order for a ller to give sig- [25] fi ni cant reinforcement, the size of its particles must be

  [22] dispersion of silica as a result of the incorporation of ALK .

  fi micrograph of D/5. 0 exhibits a homogeneous micro

  fi explanation is in line with the data in Table 6, and the SEM micrographs of the silica- lled NR vultes. The

  The enhancement in tensile modulus, tensile strength and hardness with up to 5.0 phr ALK loading is attributed to a higher reinforcement level of silica to natural rubber due to a better degree of silica dispersion or wetting in the NR phase, as well as the cure rate and cure state enhancements phenomenon of the silica- lled NR compound. This

  [22] [23] , and Ismail & Chia , the modulus or stiffness/ hardness and tensile properties are dependent only on the degree of crosslinking. According to Ignatz-Hoover & To [24], as the crosslink density of a rubber vulcanisates in- creases, the elastic properties, such as tensile modulus, hardness and tensile strength increase, whereas viscous loss properties, such as hysteresis, decrease. Further in- creases in the crosslink density will produce a vulcanisate that tends towards brittle behaviour. Thus, at a higher crosslink density, such elastic properties as mentioned earlier begin to decrease.

  silica- lled NR vulcanisates. Resilience is the ratio of energy fi

10. SEM micrographs of the failure fracture surface of silica- lled compound at a magni cation of 300 , (a) A/0.0, (b) C/3.0, (c) D/5.0, and (d) E/7.0.

  dispersion of the ller is the least homogeneous in A/0.0, fi where large silica agglomerates can be observed. The SEM micrograph of A/0.0 also seemed relatively smooth compared to those of the others, which indicates that A/0.0 is less ductile than the othring line and

  [17] [18] surface roughness . Better silica dispersion in the D/5.

  altered the crack path, which led to increased resistance to crack propagation, and thus caused an increase in elastic properties, such as le modulus, tensile strength, and

  [73]

  hardness. The micrographs of the tensile fractured surfaces

  were in good agreement with the results obtained by Ismail [22] and Mathialagan as well as Nabil et al. which re- [ 28] [29] ported that an increase in energy was responsible for the

  Fig.

  fi fi  ^{[ 22]} / Polymer Testing 32 (2013) 1313–1

I. Surya et al. / Polymer Testing 32 (2013) 1313–1

• – – has shifted towards a lower frequency (1095 cm

  1

  According to Limper , due to its low boiling point, [32] alcohol, which is attached to the TESPT coupling agent, can be classi ed as a Volatile Organic Compound (VOC). During

  , which are attributed to the symmetric and asymmetric ing vibration of the C H

  1

  and 2848 cm

  1

  , 2916 cm

  , indicating that the vulcanisates has saturated and unsaturated portions . [7] The strong bands occurred around 2954-2956 cm

  1

  1

  fi – H stretches above and below 3000 cm

  3.6. Infrared spectroscopic study Fig. 11 shows the results of the FTIR spectroscopic study on the vulcanisates of A/0.0 and D/5.0, the control and the control with 5.0 phr. of ALK. All the gures show that the C

  indicated the more pronounced plasticizing or lubricating effect of the excessive ALK.

  roughness anmatrix tearing line of the fractured [22] surface . However, the matrix tearing line and surface roughness of E/7. 0 was smoother than those of D/5.0, which

  fi curing, the ethanol in the ALK is released, and the amine group becomes reactive and forms coupling bonds with the silanol Si O group of silicas, instead of the non-polar hy- – drocarbon of ALK interacting physically through moment dipole interaction with the long chains of NR. By this mechanism, the silica-ALK-NR bonding/interaction is formed, and the probable mechanism for such an interac- tion is presented in . Fig. 12

  ). This spectral feature indicates that there are strong interactions, not only between ALK and silica, but also between ALK and NR.

• – bonds based on CH

  1 and 1456 cm

  2 and CH

  . Also, the bands at 1538 cm

  3 [96]

  fi pounds. The results also indicated that Alkanolamide can be utilized as a plasticizer to increase the elongation at break and resilience. The incorporation of Alkanolamide also improved the reinforcement level of silica to natural rubber compounds. The tensile modulus, hardness, tensile strength and crosslink density of the silica-filled natural rubber vul- canisates were enhanced, especially up to 5.0 phr loading.

  fi poration of Alkanolamide enhanced the cure rate, and reduced the scorch time of silica- lled natural rubber com-

  4. Conclusions Alkanolamide was synthesized from RBDPS-palm oil and diethanolamine. Alkanolamide can be utilized as a new ad- ditive in silica- lled natural rubber compounds. The incor-

• – peak at 3380 cm
• – – metric stretch, and Si O Si asymmetric stretch, respec-
• – – tively. The spectrum clearly shows the presence of silica in the NR vulcanisates.

  (NO

  Acknowledgements The authors would like to thank Universiti Sains

  Malaysia for providing the research facilities for carrying

Fig. 12. The probable mechanism of coupling bond between NR and silica in the presence of Alkanolamide.

  bend), the occurrence of which are due to also observed that the Si O Si asymmetric stretching peak

  2

  (NO

  1

  (C N stretch), and – 666 cm

  2 symmetric stretch), 1279 cm 1

  (O H stretch), 1398 cm

  1 are related to the bending vibration of the methylene (CH

  1

  2 ) and methyl (CH

  3 ) groups, respectively.

  The spectra clearly show the characteristic wavenumbers of the NR vulcanisates. These characteristic wavenumbers of the NR were also reported by Wang et al. for starch/NR [30] composites, and Ooi et al. [31] for oil palm ash lled NR

  fi vulcanis

  [52]

  Fig. 11(a) shows that the presence of the O H group

  OH. In addition, two peaks are observed, i.e. at 890 cm 1

  and 1096 cm

  1

  , which can be related to the Si O Si sym-

  The IR spectrum of D/5.0 (Fig. 11b) showed similar

  [102]

  characteristic bands to that of A/0.0. In addition, new bands are observed , i.

  e. at 3830 cm

  1 is related to the presence of silanol Si–

• – 1

I. Surya et al. / Polymer Testing 32 (2013) 1313–1

  [16] .

  1803. [31] Z.X. Ooi, H. Ismail, A.A. Bakar, Synergistic effect of oil palm ash lled fi natural rubber compound at low ller loading, Polymer Testing fi (2012). [32] A. Limper, Mixing of Rubber Compounds, Carl Hanser Verlag, Munchen, 2012.

  [30] Z.-F. Wang, Z. Peng, S.-D. Li, H. Lin, K.-X. Zhang, X.-D. She, X. Fu, The impact of esteri cation on the properties of starch/natural rubber fi composite, Composites Science and Technology 69 (2009) 1797–

  fi recycled ethylene-propylene-diene-monomer ( NR/R-EPDM) blends , Polymer Testing (2012).

  [29] H. Nabil, ail, A. Azura, Compounding, mechanical and morphological properties of carbon-black- lled natural rubber/

  [27] W. Hofmann, Vulcanization and Vulcanizing Agents, Mac Laren and Sons, 1967. _[31] [28] H. Ismail, M. Mathialagan, Comparative study on the effect of partial replacement of silica or calcium carbonate by bentonite on the properties oM composites , Polymer Testing (2011). _[31]

  [24] B. Rodgers, Rubber Compounding: Chemistry and Applications, CRC, 2004. [25] G. Hamed, Engineering with Rubber How to Design Rubber Com- ponents, by AN Gent, 1992. _[37] [26] P.T. Hao, H. Ismail, A.S. Hashim, Study of two types of styrene butadiene rubber in tire tread compounds , Polymer Testing 20 (2001) 539 544 _– .

  [23] H. Ismail, H. Chia, The effects of multifunctional additive and epoxidation in silica lled natural rubber compounds, Polymer fi Testing 17 (1998) 199 210

• _– .

  Malaysia, 2002. [22] D.L. Hertz Jr., S.E. INC, Theory & practice of vulcanization, Elasto- merics (November 1984).

  [20] 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 _– . [21] I. Surya, Reinforcement of Natural Rubber and Epoxidized Natural Rubbers with Amine-treated Silica, Universiti Sains Malaysia,

  , Rubber Chemistry and Technology 52 (1979) 1019– 1029.

  [18] . F.W. Barubber Compounding: Principles, Materials, and, 1993 _[22] [19] 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

  G. Kraus, Reinforcement of Elastomers, John & Sons Inc, 1965 _[89] [17] K. Polmanteer, C. Lentz, Reinforcement studies-effect of silica structure on properties and crosslink density , Rubber Chemistry and Technology 48 (1975) 795 809 _– .

  possible, and the Division of Oleochemicals, PT. Bakri Sumatera Plantation Tbk., Medan, 20362, Sumatera Utara,

  [85]

  fi rubber compounds , Polymer Testing 21 (2002) 565 569 _– .

  [12] H. Ismail, R. Nordin, A. Noor, Cure characteristics, tensile properties and swelling behaviour of recycled rubber powder- lled natural

  [10] H. Ismail, C. Ng, Palm oil fatty acid additives (POFA s): preparation and ' application, Journal of Elastomers and Plastics 30 (1998) 308 327 _– . _[60] [11] A.K. Manna, P. De, D. Tripathy, S. De, D.G. Peiffer, Bonding between precipitated silica and epoxidized natural rubber in the presence of silane coupling agent , Journal of Applied Polymer Science 74 (1999) 389 398 _– . _[21]

  York, 1987, pp. 20 58 _– . [9] L. Bateman, P. Allen, N.R.P. Re, The Chemistry and Physics of Rubber like Substances, 1963.

  [7] B.C. Smith, Infrared Spectral Interpretation: A Systematic Approach, CRC, 1998. [8] H.L. Stephens, in: M. Morton (Ed.), The Compounding and Vulcani- zation of Rubber, Rubber Technology, Van Nostrand Reinhold, New

  Rubber Chemistry and Technology 47 (1974) 697 716 _– . [6] P.J. Flory, J. Rehner Jr., Statistical mechanics of crosslinked polymer networks II. Swelling, Journal of Chemical Physics 11 (1943) 521.

  [4] M. Ranney, C. Pagano, Silane coupling agent effects in ethylene propylene diene terpolymers, Rubber Chemistry and Technology 44 (1971) 1080 1092 _– . [5] M. Wagner, Heat generation and rubber- ller coupling bonds, fi

  [3] M. Fetterman, Precipitated silica coming of age, Rubber World 194 _– (1986) 38 40

• _– .

  [1] P.E. Pinter, C.R. Mc. Gill, Comparing rubber llers in an energy fi conscious economy, Rubber World International 177 (1978) 30 37 _– . [2] M.Q. Fetterman, The unique properties of precipitated silica in the design of high performance rubber, Elastomerics 116 (1984) 18 31

• _– .

  References

  fi Postgraduate Scholarship Program.

  (Indra Surya) is grateful to the Directorate General of Higher Education (DIKTI), Ministry of Education and Cul- ture (Kemdikbud) of the Republic of Indonesia, for the award of a scholarship under the fth batch of the Overseas

  Indonesia, for supplying the RBDPS. One of the authors

  [13] B. Boonstra, H. Cochrane, E. Dannenberg, Reinforcement of silicone rubber by particulate silica, Rubber Chemistry and Technology 48 (1975) 558 576 _– . [14] 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

• _– .
^[66] [15] P. Teh, Z. Mohd Ishak, A. Hashim, J. Karger-Kocsis, U. Ishiaku, Effects of epoxidatural rubber as a compatibilizer in melt com- pounded l rubber organoclay nanocomposites , European _– Polymer Journal 40 (2004) 2513 –2521.