Curing characteristics, mechanical, morphological, and swelling assessment of liquid epoxidized natural rubber coated oil palm ash reinforced natural rubber composites

Accepted Manuscript Curing Characteristics, Mechanical, Morphological, and Swelling Assessment of Liquid Epoxidized Natural Rubber Coated Oil Palm Ash Reinforced Natural Rubber Composites Zhong Xian Ooi, Hanafi Ismail, Azhar Abu Bakar PII:

S0142-9418(13)00235-3

DOI:

10.1016/j.polymertesting.2013.11.007

Reference:

POTE 4156

To appear in:

Polymer Testing

Received Date: 23 September 2013 Accepted Date: 14 November 2013

Please cite this article as: Z.X. Ooi, H. Ismail , A.A. Bakar, Curing Characteristics, Mechanical, Morphological, and Swelling Assessment of Liquid Epoxidized Natural Rubber Coated Oil Palm Ash Reinforced Natural Rubber Composites, Polymer Testing (2013), doi: 10.1016/ j.polymertesting.2013.11.007. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Material Properties Curing Characteristics, Mechanical, Morphological, and Swelling Assessment of Liquid Epoxidized Natural Rubber Coated Oil Palm Ash Reinforced Natural

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Rubber Composites

Zhong Xian Ooi, Hanafi Ismail*, Azhar Abu Bakar

Division of Polymer Engineering, School of Materials and Mineral Resources

Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal,

ABSTRACT

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Penang, Malaysia

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This paper studies the effectiveness of the surface treatment of Oil Palm Ash (OPA) by Liquid Epoxidized Natural Rubber (LENR) and its effect on the properties of Natural Rubber (NR) composites. Curing characteristics, mechanical properties, morphology and swelling were studied. Two series of OPA filled NR composites, raw OPA and LENR-coated OPA, were used alternately to compare the improvement of mechanical properties, degree of swelling and curing characteristics. The LENRcoated OPA filled NR composites showed shorter scorch and cure times than those of

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raw OPA. The addition of LENR-coated OPA reduced the torque variation, tensile modulus and hardness of the filled NR composites, due to the rigidity of OPA being reduced after the LENR coating process. LENR-coated OPA increased the rubber phase volume in the OPA filled NR composites and, therefore, reduced the swelling

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resistance and retarded the crosslink density of the OPA filled NR composites. However, an improvement of tensile strength and elongation at break was obtained for

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the LENR-coated OPA filled NR composites when compared to the raw OPA samples. The tensile fractured surface of the LENR-coated OPA filled NR composites clearly showed the penetration of the rubber chains into the porous-structured OPA and supported the tensile strength results obtained. Keywords: Liquid epoxidized natural rubber; Oil palm ash; Natural rubber; Curing characteristics; Mechanical properties

* To whom correspondence should be addressed Email address: [email protected] Tel.: +604 5996113

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Fax: +604 5941011 1. Introduction

There are various types of fillers, either organic or inorganic, that have been

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studied and reported in previous literature [1,2]. Some, such as carbon black, silica,

calcium carbonate, talc and clay, have been very widely used. By-products, such as fly ash [3], rice husk ash [4], oil palm ash [5], paper sludge [6], etc., have also been

utilized to address cost and environmental issues. However, the incorporation of those

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fillers in rubber compounds to transform them into valuable products is restricted owing to the reduction of properties, such as tensile strength and elongation at break. According to the previous report by Ooi et al. [7], a very low Oil Palm Ash (OPA)

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loading in a natural rubber compound simultaneously improved the tensile strength and elongation at break. The work also proved that porous-structured OPA could form a better interaction with the natural rubber matrix. However, it was believed that the optimum tensile strength of natural rubber composites could be further enhanced by applying surface treatment to the OPA particles.

In this study, a surface treatment is investigated by pre-treating the oil palm ash

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with Liquid Epoxidized Natural Rubber (LENR). The LENR was coated onto the surface of the OPA particles prior to compounding with natural rubber. LENR was deemed preferable, due to its chemical structure of isoprene units with regular oxirane groups, whilst the liquid phase of Epoxidized Natural Rubber (ENR) could penetrate

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more easily into the porous-structured OPA and wet the outer-layer more effectively. The cure characteristics, mechanical properties and degree of swelling of LENRcoated OPA filled NR composites were investigated. The morphology of the tensile

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fractured surface of LENR-coated OPA filled NR composites was also studied.

2. Experimental

2.1. Materials

SMR L grade Natural rubber, purchased from Zarm Scientific & Supplies (M) Sdn. Bhd., was used as the matrix. The Oil Palm Ash (OPA) filler was collected from United Oil Palm Mill, Penang, Malaysia. Prior to modification, raw OPA particles

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were sieved to a 75 µm mesh size and dried in a vacuum oven at 80ºC for 24 hours to expel moisture. Other curing ingredients, including zinc oxide, stearic acid, NIsopropyl-N'-phenyl-p-phenylenediamine

(IPPD),

N-cyclohexyl-2-benzothiazole

sulfenamide (CBS) and sulphur, were provided by Bayer (M) Ltd. and used as

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received.

2.1. ENR coating

A 10% wt/v ENR solution (LENR) was prepared by stirring the ENR-50 (supplied

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by Zarm Scientific & Supplies (M) Sdn. Bhd.) in toluene (purchased from Sigma

Aldrich (M) Sdn. Bhd.) until the ENR-50 was fully dissolved. The raw OPA particles

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were mixed and stirred using a mechanical stirrer for one hour at room temperature and then transferred to an Elma ultrasonic vibrator (model Transsonic Digital S) for another 30 minutes to ensure that the OPA particles were optimally coated by ENR. The LENR-coated OPA was filtered and dried in an oven at 60ºC until constant weight was obtained.

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2.2. Characterization of LENR-coated OPA

Fourier Transform Infrared spectroscopy (FTIR) was used to obtain qualitative information on the functional groups and chemical characteristics of the raw OPA and the LENR-coated OPA. Before being subjected to FTIR, potassium bromide (KBr)

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and OPA were ground to form a pellet, which was then used to obtain the infrared spectra of OPA; where KBr is an inert, infrared transparent material, and acts as a

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support for the OPA. FTIR spectra were obtained and recorded in transmission mode using a Perkin Elmer Spectrometer (Massachusetts, USA) in the range of 450cm-1 to 4000cm-1 at a resolution of 4 cm-1. For each spectrum, 16 scans were co-added. The LENR-coated OPA was characterised in the same manner as the raw OPA.

2.3. Composite preparation

The OPA loading levels used in this study were 0.5, 1, 3, 7, and 9 phr. The detailed formulations are shown in Table 1. Mixing of raw materials was done using a conventional laboratory sized two-roll mill (model XK 160). A total mixing time of

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about 20 minutes avoided premature vulcanisation due to excessive heat generated during compounding. The mixing sequences were kept constant for all mixes. Curing characteristics, such as scorch time (ts2), cure time (tc90) and maximum torque (MH), of OPA filled NR composites were determined using a Monsanto Moving Die

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Rheometer (model MDR 2000); according to ISO 3417, at 150ºC, followed by compression moulding at 150ºC according to their respective tc90 values. The moulded sheets were conditioned in desiccators for 24 hours prior to further testing. The

LENR-coated OPA was designated as LOPA and compounded in the same manner as

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raw OPA filled NR composites (control).

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2.4. Mechanical tests

Tensile testing of five dumbbell shaped specimens cut from moulded sheet with a thickness of about 2mm was conducted according to ISO 37, using a universal tensile testing machine (model Instron 3366) at a crosshead speed of 500mm/min. The tensile strength, elongation at break, and tensile modulus (M100 and M300) were evaluated from stress-strain determinations and the averages of the five repeated tests for each compound were recorded. Hardness test measurement was conducted using a Shore A

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type durometer under conditions according to ISO 7619.

2.5. Morphological studies

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The raw OPA and LENR-coated OPA particles were mounted on aluminium stubs and sputter-coated with a thin layer of gold in order to avoid electrostatic charge and

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poor resolution during examination. This was followed by scanning with an electron microscope (FESEM: model Zeiss Supra 35 VP). Tensile fractured surfaces of raw OPA and LENR-coated OPA filled NR composites were scanned in the same manner as the OPA particles. The tensile fractured surfaces observed were used to study the mode of fracture and support the changes in tensile properties.

2.6. Assessment of swelling percentages

The swelling test was carried out according to ISO 1817. The cured specimens, with dimensions of 30mm x 5mm x 2mm, were weighed using an electric balance,

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followed by immersion in a toluene for 72 hours at room temperature (25⁰C) in a dark environment. After the conditioning period, the swollen specimens were taken out and weighed again. The specimens were then dried in an oven at 70ºC until constant weight was obtained. The crosslink density was measured by applying the Flory

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Rehner equation [8,9] as given in Equations (3)-(5) below: (1)

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(2)

(3)

where, Mc is the molecular weight between crosslinks, ρp is the density of the NR

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(0.92 g cm-3), Vs is the molar volume of the toluene (106.4 cm3/mol), Vr is the volume fraction of the swollen rubber, Qm is the swelling mass of the OPA filled NR vulcanizates in the toluene, χ is the interaction parameter between the rubber network and the toluene (χ = 0.393) and Vc is the degree of crosslink density.

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3. Results and discussion

3.1. LOPA characterization

The FTIR spectra of raw OPA particles and LENR-coated OPA particles are shown in Figure 1. The characteristic vibration bands for the raw OPA have already

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been noted in a previous report [10] where the existence of Si-O, Al-O or Si-O-Al and also calcite was confirmed. However, with the LENR coating, the FTIR analysis in

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the 450-4000 cm-1 indicated that the OPA functional group was changing. The new peak observed within 2800-3000 cm-1 was assigned to the stretching vibration of CH2 and CH3 modes from the isoprene unit of ENR itself. Also, the bands from 850-1300 cm-1 tended to broaden compared to the FTIR spectra of raw OPA. It is suggested that there was a combination or physical interactions between the functional group (Si-O) of OPA with the oxirane groups from the LENR during the coating process. The surface morphologies of raw OPA and LENR-coated OPA were studied and are compared in Figure 2. The raw OPA typically showed irregular shapes with a rough surface and a porous structure. The surface of the ash is capable of absorption,

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and thus the LENR would penetrate into the porous structure of the OPA during the coating process and form a coating layer. This LENR layer was believed to form an interphase within OPA and NR, thereby improving the compatibility between OPA and NR matrices. Unfortunately, the LENR coating method used may lead to an

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agglomeration of OPA (as shown in Figure 2b), which may cause difficulties in the compounding process.

3.2. Curing characteristics

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Figures 3 to 5 show the curing characteristics i.e., scorch time (ts2), cure time (tc90)

and torque variation (MH – ML) of LENR-coated OPA filled NR composites, and

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compares them to the raw OPA filled NR composites (control). The ts2 and tc90 of the OPA filled NR composites showed a decrease whilst the torque variation increased when the OPA loading was increased for both raw OPA and LENR-coated OPAs. At the same filler loading, the curing characteristics of LENR-coated OPA filled NR composites were found to be lower than that of raw OPA filled NR composites. This may be attributed to the adjacent double bond by the oxirane group from ENR, which was accelerated in the vulcanization reaction [11,12]. Even although the addition of a

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compatibilizer was expected to improve the torque variation of composites; the LENR coating showed a contrasting effect by lowering the torque variation of the OPA filled NR composites. This was mainly caused by softening of the composites due to the ratio of the rubber phase volume to raw filler being increased when LENR-coated

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OPA was added. This is clearly shown in Figure 2, where the surface morphology of the raw OPA changed after LENR coating. The outer phase of the OPA (LENR) was

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able to behave as a plasticizer imparting toughness to the OPA and, consequently, reducing its rigidity. In addition, the LENR coating may have changed the crosslink density of the natural rubber composites, as torque variation is an indirect measure of crosslink density [13]. This could be due to an increase of rubber phase volume (with respect to the active curing agent remaining constant); thus, the distance between potential crosslinking sites became longer and increased the mobility of the composite’s macromolecular chains.

3.3. Mechanical properties

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Table 2 presents the tensile properties and hardness of the raw OPA and LENRcoated OPA filled NR composites. From the results shown, the tensile strength and elongation at break increased when a very low OPA loading was added, but tended to reduce beyond 1 phr loading of the OPA. The same trend was observed for the

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LENR-treated OPA filled NR composites. Furthermore, the LENR-coated OPA filled NR composites showed a higher value than that of the raw OPA at a similar filler

loading. It is deduced that the coating layer of LENR had a positive contribution to better adhesion by wetting the OPA more effectively and reducing the micro-void

within the raw OPA and the NR matrix. As already noted, the LENR was able to

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penetrate into the porous structure of the OPA, whilst the isoprene units were cross-

linked to the natural rubber chains (as shown in Figure 6). The interphase LENR chain

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that cross-linked to the natural rubber chain could act as a chain extender when the external stress was applied, thus resulting in an improvement in the elongation at break of OPA filled NR composites. This may be attributed to the ability of ENR to strain crystallize like natural rubber [14]. Rattanasom et al. [15] also demonstrated that strain induced crystallization could be responsible for strength increases in rubber composites. Another more prominent fact that accounts for the strength improvement is that the ENR chain penetrated into the porous structure of the OPA during the

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coating process and wetted the outer layer of the OPA particles. It was, therefore, able to absorb and transfer stress more effectively, thus leading to improved tensile strength.

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Tensile modulus at 100% (M100) and 300% (M300) elongation at break and hardness of OPA filled NR composites, with and without LENR coating, are shown in Table 2.

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Both tensile moduli (M100 and M300) of the NR composites increased as the OPA loading increased. However, the LENR-coated OPA filled NR composites showed a lower tensile modulus than that of the corresponding raw OPA filled NR composites. As modulus is a measure of the stiffness [16], the same trend was observed for the hardness of the LENR-coated OPA filled NR composites, as compared to the raw OPA ones. This finding was attributed to the softening of the LENR-coated OPA particles (as discussed earlier). Riley et al. [17] and Ismail and Mathialagan [18] reported that filler modulus and filler loading do affect the tensile modulus of composites. This explains why the tensile modulus of LENR-coated OPA filled NR

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composites increased with increasing LENR-coated OPA loading, but showed a lower value than that of the raw OPA filled NR composites.

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3.4. Morphological studies

The SEM micrographs of the tensile fractured surface of raw OPA filled NR

composites and LENR-coated OPA filled NR composites are shown in Figure 7. It

can be clearly seen that the LENR-coated OPA (Figures 7b and 7d) was well-

embedded in the natural rubber matrix, compared to the raw OPA filled NR

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composites (Figures 7a and 7c). It was interesting to note that the bridging rubber

chain that penetrated the OPA could be observed in the LENR-coated OPA filled NR

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composites at 1 phr and even at 7 phr LENR-coated OPA loading. This indicates why higher tensile strength and elongation at break was observed when LENR-coated OPA was added into the NR matrix.

3.5. Swelling assessment

Figure 8 shows the swelling of the raw OPA and LENR-coated OPA filled NR

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composites. As reported in our previous study [7], the addition of OPA could restrict the toluene solvent from penetrating into the NR composites. However, in this study, the LENR-coated OPA filled NR composites exhibited higher degrees of swelling than the corresponding loading of raw OPA filled NR composites. The higher

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absorption of toluene solvent was mainly because the rubber phase volume was increased in the LENR-coated OPA/NR system. The crosslink density was evaluated

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according to the Flory Rehner equation [8] (as shown in Figure 8b). It was found that the crosslink density of the OPA filled NR composites increased when the raw OPA or LENR-coated OPA loading was increased. However, the LENR-coated OPA filled NR composites indicated a lower crosslink density than that of the raw OPA filled NR composites. This observation was in line with the torque variation results discussed earlier. The same reason may be used to account for the molecular weight between crosslink points in the rubber phase becoming longer; and, consequently, inducing a more flexible chain in the rubber network to allow a higher toluene uptake.

4. Conclusions

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The following conclusions can be drawn for the effectiveness of using liquid epoxidized natural rubber-coated OPA in natural rubber composites, instead of raw OPA. The FTIR results show the changes in the peaks of OPA spectra after LENR

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coating. The scorch and cure times were reduced with the addition of LENR-coated OPA, more than with the raw OPA. The torque variation, tensile modulus, hardness

and crosslink density of LENR-coated OPA filled NR composites showed lower values than those of raw OPA. Increases of tensile strength and elongation at break

were observed due to the formation of a LENR interphase between OPA and NR

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matrixes, which helped penetration into the porous-structured OPA in order to make a stronger interfacial adhesion, whilst at the same time imparting a more flexible chain.

demonstrated by SEM observation.

Acknowledgement

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The better physical interaction between LENR-coated OPA and the NR matrix was

This work was financially supported by the Ministry of Science, Technology and Innovation (MOSTI) science fund (Project no. 305/PBAHAN/6013380) and MyPhD

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(Z.X. Ooi).

References

N. Nugay, B. Erman. Property optimization in nitrile rubber composites via

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[1]

hybrid filler systems. J. Appl. Polym. Sci. 2001; 79: 366-374. Z.X. Ooi, H. Ismail, A. Abu Bakar. Optimisation of oil palm ash as

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[2]

reinforcement in natural rubber vulcanisation: A comparison between silica and carbon black fillers. Polym. Test. 2013; 32(4): 625-630.

[3]

N. Sombatsompop, S. Thongsang, T. Markpin, E. Wimolmala. Fly Ash Particles and Precipitated Silica as Fillers in Rubbers. I. Untreated Fillers in Natural Rubber and Styrene–Butadiene Rubber Compounds. J. Appl. Polym. Sci. 2004; 93: 2119-2130.

[4]

W. Arayapranee, N. Na-Ranong, G.L. Rempel. Application of Rice Husk Ash as Fillers in the Natural Rubber Industry. J. Appl. Polym. Sci. 2005; 98: 34-41.

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[5]

H. Ismail, F.S. Haw. Curing Characteristics and Mechanical Properties of Hybrid Palm Ash/Silica/Natural Rubber Composites. J. Reinf. Plast. Compos. 2010; 29(1): 105-111.

[6]

H. Ismail, A. Rusli, A.A. Rashid. Maleated natural rubber as a coupling agent

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for paper sludge filled natural rubber composites. Polym. Test. 2005; 24(7): 856-862. [7]

Z.X. Ooi, H. Ismail, A. Abu Bakar. Synergistic effect of oil palm ash filled

P.J. Flory, J. Rehner. Statistical Mechanics of Cross‐Linked Polymer Networks

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[8]

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natural rubber compound at low filler loading. Polym. Test. 2013; 32(1): 38-44.

II. Swelling. J. Chem. Phys. 1943; 11(11): 521-526. [9]

P. Pasbakhsh, H. Ismail, M.N. Ahmad Fauzi, A. Abu Bakar. EPDM/modified halloysite nanocomposites. Applied Clay Science 2010; 48(3): 405-413.

[10] Z.X. Ooi, H. Ismail, A. Abu Bakar. Characterization of oil palm ash (OPA) and thermal properties of OPA filled natural rubber compounds. J. Elastomers Plast.

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2013; Accepted and In-Press. Doi: 10.1177/0095244313489901. [11] H. Ismail, H.C. Leong. Curing characteristics and mechanical properties of natural rubber/chloroprene rubber and epoxidized natural rubber/chloroprene rubber blends. Polym. Test. 2001; 20(5): 509-516.

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[12] P.L. Teh, Z.A. Mohd Ishak, A.S. Hashim, J. Karger-Kocsis, U.S. Ishiaku. Effects of epoxidized natural rubber as a compatibilizer in melt compounded

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natural rubber–organoclay nanocomposites. Eur. Polym. J. 2004; 40(11), 25132521.

[13] H.M. Da Costa, L.L.Y. Visconte, R.C.R. Nunes, C.R.G. Furtado. Rice husk ash filled natural rubber. III. Role of metal oxides in kinetics of sulphur vulcanization. J. Appl. Polym. Sci. 2003; 90(6), 1519-1531.

[14] I.R. Gelling. Epoxidized natural rubber. Journal of Natural Rubber Research 1991, 6(3): 184-205. [15] N. Rattanasom, S. Prasertsri, T. Ruangritnumchai. Comparison of the mechanical properties at similar hardness level of natural rubber filled with various reinforcing-fillers. Polym. Test. 2009; 28(1), 8-12.

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[16] A. Mousa, J. Karger-Kocsis. Rheological and thermodynamic behaviour of styrene/butadiene rubber-organoclay nanocomposites. Macromol. Mater. Eng. 2001; 286(4), 260-266. [17] A.M. Riley, C.D. Paynter, P.M. McGenity, J.M. Adams. Factors affecting the

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impact properties of mineral filled polypropylene. Plast. Rub. Proc. Appl. 1990; 14(2): 85-93.

[18] H. Ismail, M. Mathialagan. Curing Characteristics, Morphological, Tensile and Thermal Properties of Bentonite-Filled Ethylene-Propylene-Diene Monomer

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M AN U

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(EPDM) Composites. Polym-Plast Technol. Eng. 2011; 50(14): 1421-1428.

List of tables

Table

Table caption

Table 1

Formulation of Oil Palm Ash (OPA) filled natural rubber composites

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Table 2

Mechanical properties of raw OPA and LENR-coated OPA

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(LOPA) filled NR composites

List of figures

Figure

Figure caption

Figure 1

FTIR spectra of (a) raw OPA particles, (b) LENR-coated OPA particles Surface morphologies of (a) raw OPA particles, (b) LENR-coated

Figure 2

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OPA particles Figure 3

Scorch times (ts2) of raw OPA and LENR-coated OPA filled NR composites

Figure 4

Cure times (tc90) of raw OPA and LENR-coated OPA filled NR

Figure 5

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composites Torque variations of raw OPA and LENR-coated OPA filled NR composites Figure 6

Proposed schematic diagram between LENR-coated OPA and natural rubber chain

SEM images of (a) 1 phr raw OPA, (b) 1 phr LENR-coated OPA,

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Figure 7

(c) 7 phr raw OPA, (d) 7 phr LENR-coated OPA filled NR

Figure 8

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composites

Raw OPA and LENR-coated OPA filled NR composite’s (a)

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swelling percentages and (b) crosslink densities

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Table 1: Formulation of Oil Palm Ash (OPA) filled natural rubber composites Compound (phra)

NR (SMR L)

100

Zinc oxide

1.5

Stearic acid

1.5

IPPD

2.0

CBS

1.9

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Sulphur

1.6

OPA

0, 0.5, 1, 3, 7, 9

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b

Parts per hundred parts of rubber

b

Same phr loading for raw OPA and LOPA-coated OPA

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a

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Materials

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NR composites

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Table 2: Mechanical properties of raw OPA and LENR-coated OPA (LOPA) filled

Elongation at

M100

M300

Hardness

(MPa)

break (%)

(MPa)

(MPa)

(Shore A)

Gum NR

21.8

1049

0.66

1.56

39.0

NR/OPA0.5

21.9

1054

0.68

1.64

40.6

NR/OPA1

25.2

1127

0.69

1.66

40.7

NR/OPA3

23.9

1114

0.70

1.70

41.7

NR/OPA7

23.2

1086

0.75

1.81

43.3

NR/OPA9

23.1

1069

0.76

1.82

44.1

NR/LOPA0.5

24.5

1089

0.65

1.58

40.3

NR/LOPA1

26.6

1145

0.66

1.59

40.6

NR/LOPA3

25.1

1123

0.66

1.60

41.7

NR/LOPA7

24.7

1107

0.69

1.69

42.7

NR/LOPA9

23.4

0.70

1.69

43.6

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Tensile strength

Sample Code

1097

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