epoxidized natural rubber sepiolite epoxidized natural ......chemical modification [9]. commercial...

ELASTOMERE UND KUNSTSTOFFE ELASTOMERS AND PLASTICS

18 KGK · 07-8 2017 www.kgk-rubberpoint.de

Epoxidized Natural Rubber Sepiolite Silane Coupling Agent Composites

Sepiolite reinforced Epoxidized Natural Rubber (ENR) composites were prepa-red by incorporation different loadings of sepiolite. Curing characteristics and mechanical properties were improved. These findings are corresponding to the greater rubber-filler interaction bet-ween the hydroxyl and siloxane groups available on the structure of sepiolite and respective epoxy segment of ENR matrix. Attempt to further improve these properties was done through the use of silane coupling agent, that is N-(3-(Trimethoxysilyl)propyl) ethylene diamine. The rubber-filler interaction between the sepiolite and ENR matrix was enhanced. The presence of silane coupling agent gave shorter curing time and enhanced mechanical proper-ties. The mechanical properties shown are in good agreement to the SEM mi-crographs.

Epoxidierter Naturkautschuk – Modifiziert mit Sepiolite KompositenEpoxidierter Naturkautschuk Sepiolite Silankopplungsagens Komposite

Sepiolite verstärkte epoxidierte Natur-kautschuk (ENR)–Komposite wurden durch die Einarbeitung unterschied- licher Konzentrationen von Sepiolite hergestellt. Die Vulkanisation und die mechanischen Eigenschaften wurden verbessert. Diese Resultate korrespon-dieren mit höherer Kautschuk-Füllstoff- Wechselwirkungen zwischen den Hydroxyl- und Siloxangruppen, die durch die Sepiolite-Struktur und insbe-sondere durch die Epoxi-Segmente der ENR-Matrix zur Verfügung stehen. Eine weitere Verbesserung der Eigenschaf-ten wurde durch das Silankopplungs-agens N-(3-(Trimethoxysilyl)propyl)-ethylendiamin erreicht. Die Kautschuk-Füllstoff-Wechselwirkung zwischen Sepiolite und der ENR-Matrix wurden verbessert. Das Silan führt zu kürzeren Vulkanisationszeiten und verbesserten mechanischen Eigenschaften. Diese stimmen gut mit REM-Aufnahmen überein.

Figures and Tables:By a kind approval of the authors.

1. Introduction One of the most important phenomena in material science is the reinforcement of rubber by rigid particles, such as car-bon black, silica, clays, and calcium car-bonate, to name a few [1-3]. It is a well-known fact that the addition of rigid fil-ler particles, even in small amounts, to a rubber, strongly influences its mechani-cal behavior. Polymer matrices (e.g., ther-mosets, thermoplastics, elastomers) re-inforced by nanofillers have attracted considerable attention in recent times due to their higher mechanical, thermal and physical properties [4-6].

Sepiolite is a microcrystalline hydra-ted magnesium silicate with Si12Mg8O30(OH,F)4.(H2O)4·8H2O as the unit cell formula [7], showing a microfibrous morphology with particle size in the ran-ge of 2 – 10 in length. Sepiolite has three main characteristics. Firstly, it has unique needle-like fibrous structure that loose rapidly when dispersed in water or other polar solvent, forming a monomer fiber or small fiber bundles. Secondly, it has a tunnel-like micro-pore channel structure (see Figure 1). Sepiolite shows an alter-nation of blocks and tunnels that grow in the direction of the fibre. Each structural block is composed of two tetrahedral sili-ca sheets sandwiching a central sheet of magnesium oxide-hydroxide. This struc-ture provides infinite channels along the fibre axis with a cross section of about 1 × 0.4 nm2. Finally, the strong adsorption capability of sepiolite, it has very high specific surface area. Such relatively high surface area is from the fibrous morpho-logy and intra-crystalline tunnels of the sepiolite. Due to the great surface area and the existence of siloxane surface and silanol group of the sepiolite, the deve-lopment of the new composites based on the sepiolite and modified natural rubber is a potent challenge.

Epoxidized natural rubber (ENR) is a derivative of natural rubber produced by chemical modification [9]. Commercial grade ENR comes in two grades, ENR 25 and ENR 50 where the unsaturated back-bone has been replaced to an epoxide group at 25 mol% and 50 mol% respec-tively. Epoxy groups are randomly distri-buted along the polymer chain of ENR. It shows better oil resistance, damping and

low gas permeability compared to natu-ral rubber. The increment in polarity also increased the compatibility with polar rubbers and/or polar fillers.

The idea of this work is to use the se-piolite in ENR matrix. This is to gain the properties enhancement arising from the unique structures of sepiolite in as-sociation with the molecular sequence of ENR rubber. It is believe to give the com-posite with higher compatibility, physical and thermal stability to the composites. A further aim of this study was also car-ried out through the use of silane coup-ling agent where a reinforcement me-chanism and possible interactions among two components are proposed. To the best of our knowledge, no att-empts have been made so far to investi-gate the potential of sepiolite filled ENR composites. In this article, cure characte-ristics, mechanical properties, fractured surfaces and their corresponding rubber-filler interaction have been investigated.

2. Experimental Details

2.1 MaterialsThe formulation used for compounding is presented in Table 1. Epoxidized natu-ral rubber with 25% epoxy content (EP-OXYPRENE 25) was used as a matrix which was obtained from Guthrie Group Sdn. Bhd. Malaysia. Sepiolite was obtai-ned from Hebei Dfl Minmet refractories

Epoxidized Natural Rubber/ Modified Sepiolite Composites

AuthorsNabil Hayeemasae, Pattani, Thailand, Nor Hidayah Zakaria, Hanafi Ismail, Penang, Malaysia

Corresponding author:Dr. Nabil Hayeemasae, Tel: +6673-312-213 Fax: +6673-331-099 E-Mail: [email protected] of Rubber Technol-ogy and Polymer Science, Facul-ty of Science and Technology, Prince of Songkla University, Pattani Campus, 94000, Pattani, Thailand


19KGK · 07-8 2017www.kgk-rubberpoint.de

Corporation. China. The main constitu-ents of Sepiolite are SiO2 (45 – 58%), Al2O3 (0.2 – 0.4%), MgO (21 – 28%), Fe2O3 (0.1 – 0.3%), CaO (33 – 35%), H2O (9 – 15%) and loss on ignition with 27 – 28%. Silane coupling agent namely N-(3-(Trimethoxysilyl) propyl) ethylenediami-ne was obtained from Dow Corning Sili-cones Malaysia Sdn Bhd with the trade’s name of Dow Corning® Z-6032 Silane. The physical properties of the sepiolite were shown in Table 2. Sepiolite is in needle structure (see Figure 2) which in-dicates high reinforcing structure and suitable to use as reinforcing filler in rubber compounds. Zinc oxide, stearic acid and sulphur were supplied by Zarm & Chemical Supplier Sdn Bhd. N-isopro-pyl-N’-phenyl-p-phenylenediamine (IPPD), Tetramethylthiuram disulfide (TMTD) and N-cyclohexyl-2-benzothiazo-lesulphenamide (CBS) were obtained from LANXESS Corporation.

2.2 Preparation of compositesSimultaneous incorporation of ENR 25, silane coupling agent and the entire amount of additives were mixed on a la-boratory-sized two-roll-mill (model XK-160) at ambient temperature. The total mixing time was kept to a minimum to avoid sticking of the rubber compound on the mill rolls. The compounds without the silane coupling agent were also pre-pared as reference. For the discussion here, the composites with and without silane coupling agent will be designated as US for the untreated and TS for the si-lane-treated sepiolites.

The resulting compounds were later tested for its curing characteristics using a Monsanto Moving Die Rheometer (MDR 2000). The compounds were subsequent-ly compression-molded using a stainless steel mould at 150°C with a pressure of 10 MPa using a laboratory hot-press based on respectively curing times.

2.3 Curing characteristicsCuring Characteristics such as torques, scorch time and cure time of sepiolite filled ENR composites was determined by using a Monsanto Moving Die Rheo-meter (model MDR 2000) according to ISO 3417:2008, at 150˚C and test time was set for 30 minutes with range of the torque at 25 dNm.

2.4 Measurement of tensile propertiesDumbbell-shaped samples were cut from the moulded sheets according to ISO 37:2011. Tensile tests were perfor-

med at a cross-head speed of 500 mm/min. Tensile tests were carried out with a universal tensile machine Instron 3366 to determine the tensile properties in terms of tensile strength, stress at 100% elongation (M100), stress at 300% elon-gation (M300) and elongation at break.

2.5 Measurement of tear behaviourTear strength of the vulcanizates were determined using Instron Universal Tes-ting Machine according to ISO 34-1:2015 with cross-head speed of 100 mm/min and the two “trouser legs” were fixed to the jaws of the tensile machine. The tear strength was evaluated from the aver-ages of the five repeated tests for each compound.

Fig. 1: Schematic model representing the sepiolite structure [8].

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2.6 Assessment of rubber-filler interactionCure test pieces of dimension 30 × 5 × 2 mm3 were swollen in toluene until equi-librium, which took 72 h at room tempe-rature. The samples were taken out from the liquid, the toluene was removed from the samples’ surface and the weight was determined. The samples were then dried in the oven at 60°C until the constant weights were obtained.

The Lorenz and Parks equation was used to study the rubber-filler interac-tion (Qf/Qg).

(1)

1 The formulation used for preparing the ENR/Sepiolite composites.Material Formulation (phr)ENR 25 100Sulphur 1.6Zinc oxide 2.6Stearic acid 1.5CBS 1.9TMTD 0.9IPPD 2.0Silane 2.0Sepiolite 0, 1.0, 2.5, 5.0, 7.5, 10.0N-cyclohexyl-2-benzothiazolesulphenamide, Tetramethylthiuram disulphide, N-isopropyl-N-phenylenediamine.

2 Properties of sepiolite.Colour Light-creamForm PowderSize 325 mesh/ 44 micronsBulk density 0.86g/ml (Typically 600 – 1200kg/m3)Expanded volume 9 – 10ml /gImpurity 5 – 9%Moisture 0.5 – 2%pH 7 – 9Melting point 1550°C



(2)

(3)

Q is defined as grams of solvent per

gram of rubber hydrocarbon, the subscripts f and g in equation refer to filled and gum vulcanizates, respectively. The higher the Qf/Qg values, the lower the rubber-filler interaction.

2.6 Scanning electron microscopyThe fractured specimens were collected and the fractured surface was observed using Field Emission Scanning Electron Microscope (FESEM) ZEISS SUPRA 35VP. The fractured pieces were coated with layer of gold palladium with BIO-RAD Polaron Division SEM to eliminate elect-rostatic charge build-up during examina-tion.

3. Results and Discussion

3.1 Curing characteristicsThe curing characteristics of the US and TS filled ENR composites are listed in Table 1. Maximum torque (MH) is a measure of stiffness or shear modulus of the com-pletely vulcanized test specimens at the curing temperature. The MH was found to increase consistently with increasing sepi-olite loading. It is known that sepiolite used is a hard solid powder, thus, increas-ing of sepiolite loading gives rise to a re-duction in the deformable rubber portion in the compounds, which is known as the dilution effect [10]. The addition of filler restricts the flow of rubber compounds resulting an increase in viscosity. Accord-ing to Mittal et al. [11], the maximum torque (MH) was generally correlated with the durometer hardness and modu-lus. This also indicated that the incorpora-tion of sepiolite increases the stiffness of the rubber. Similar observations were also

made for torque difference (MH-ML), which is a measure of the difference be-tween stiffness or shear modulus of the fully vulcanized and unvulcanized test specimens taken at the lower point of the vulcanizing curve. The MH-ML value is in-directly related to the physical and chemi-cal crosslinking. Therefore, it can be con-cluded that the incorporation of sepiolite has contributed to the better interaction between sepiolite and ENR matrix. As for the TS, the MH and MH - ML of TS filled ENR composites were slightly higher than that of US filled ENR composites. This was attributed to the higher degree of rubber-filler interaction, arising from the silane coupling agent. As a result, the chemical linkages between the silane and the sepi-olite together with the ENR-25 matrix are formed.

Scorch time (ts2) was an important parameter to the rubber processor, as a short ts2 may lead to fasten the prematu-re vulcanization. As can be seen in Table 3, the control sample had the highest ts2 which was 0.91 min. Then, the ts2 slowly decreased with increasing sepiolite loa-ding. The decrement of ts2 can be associ-ated to the filler related parameters such as surface area, moisture content, and metal oxide content. In particular, the magnesium oxide contents in the sepio-lite itself. As widely accepted that, the magnesium oxide is usually used as cure activator for the rubber compounds [12], it is able to act as a cation at the double bond to activate the crosslinking process. This probable reason also influenced the cure time (tc90) of the composites. The optimum (tc90) had reduced when sepio-lite was added to the rubber compounds.

Another reasonable explaination might be due to the ENR itself. In general, ENR has a tendency to stick on the surface of mill. This makes the rubber remained a period of time on the mill during mixing. As sepiolite loading increases and conse-quently, generates more heat due to addi-tional friction. It is interesting to be high-lighted that the epoxidation plays an im-portant role in the curing process of the compounds. Gelling and Morrison [13] have reported that the epoxide groups of ENR can also activate the adjoining doub-le bonds. As a result, fastern cure rate is observed for ENR compounds.

At similar sepiolite loading, the pre-sence of a silane coupling agent has de-creased the ts2 and tc90 of the ENR com-posites. This was due to the better dis-persion of the TS in the ENR matrix as compared to untreated sepiolite. De et

Fig. 2: SEM micrograph of raw Sepiolite.

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3 Curing characteristics of untreated (US) and treated (TS) sepilotes filled ENR composites.Sepiolite loading (phr)

MH (dN.m) MH - ML (dN.m) Scorch time, ts2 (min)

Cure time, tc90 (min)

Control 5.83 5.73 0.91 1.22US 1 6.01 5.88 0.84 1.19US 2.5 6.49 6.40 0.80 1.16US 5 6.58 6.46 0.76 1.10US 7.5 6.76 6.64 0.74 1.09US 10 6.80 6.67 0.71 1.07TS 1 6.40 6.25 0.79 1.11TS 2.5 6.63 6.48 0.76 1.08TS 5 6.69 6.62 0.74 1.06TS 7.5 6.89 6.80 0.71 1.03TS 10 7.11 7.02 0.68 1.01



al., [14] stated that the silane coupling agent generally favors the curing process of the rubber compounds. Well-dispersed filler would induce heat during the shea-ring force between rubber matrix and filler. As a result, the ts2 and tc90 eventu-ally reduced.

Mechanical propertiesThe effect of sepiolite loading on the stress at 100% elongation (M100) and at 300% elongation (M300) of US and TS filled ENR composites are shown in Table 4. It can be seen that the M100 and M300 increased gradually with an increase of sepiolite loading. As more sepiolite parti-cles get into the rubber, the elasticity of the rubber is reduced, resulting in more rigid, stiffer, and harder vulcanizates. Fur-thermore, the increment of tensile modu-lus with increasing sepiolite loading may be due to the effect of strain amplifica-tion, resulting from the fact that the sepiolite is in the rigid phase at tested temperature, which cannot be deformed. As a consequence, the intrinsic strain of the polymer matrix is higher than the external strain yielding a strain indepen-dent contribution to the modulus which is well-known as hydrodynamic effect [15]. This result is corresponding to the maximum torque (MH) observed in the preceding section. Ishak et al. [16] men-tioned that three factors affected the composites modulus were filler modulus, filler loading and aspect ratio. High stiff-ness composite required filler particle of high modulus and high aspect ratio and preferably at higher filler loading.

As expected, the tensile modulus of TS filled ENR composites showed higher tensile modulus than untreated compo-sites. This result is distinctively different for the stress at 300% elongation. Fu et al. [17] have noted that the three main factors affecting the composites’ modu-lus were filler modulus, filler loading, and filler aspect ratio. High stiffness composite requires filler particles of high modulus and high aspect ratio (the ratio of the major to the minor dimension of a particle), and preferably at high filler loading. Since all of those factors have been kept more or less constant in the present study, it can be inferred that the presence of coupling agents have led to a significant improvement in the filler–matrix interfacial bonding. This will obvi-ously results in an increase in the effici-ency of stress transfer from the matrix to the filler, which consequently gives rise to higher modulus.

Fig. 3: Tensile strength of untreated (US) and silane-treated (TS) sepilotes filled ENR composites.

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Fig. 4: Proposed model of interac-tions and bon-ding between se-piolite and ENR molecule.

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4 Tensile modulus of untreated sepiolite (US) and treated sepilote (TS) filled ENR composites.Sepiolite loading (phr) M100 (MPa) M300 (MPa)Control 0.85 ± 0.05 2.03 ± 0.06US 1 0.86 ± 0.04 2.12 ± 0.03US 2.5 0.94 ± 0.03 2.35 ± 0.03US 5 1.05 ± 0.09 2.45 ± 0.06US 7.5 1.07 ± 0.07 2.54 ± 0.05US 10 1.15 ± 0.04 2.65 ± 0.05TS 1 0.97 ± 0.06 2.45 ± 0.08TS 2.5 1.02 ± 0.03 2.60 ± 0.04TS 5 1.07 ± 0.07 2.78 ± 0.02TS 7.5 1.11 ± 0.02 2.85 ± 0.04TS 10 1.20 ± 0.01 3.11 ± 0.03

Figure 3 shows tensile strength of US and TS filled ENR composites. It shows that the tensile strength increases with more sepiolite loading. The tensile strength however decreases after 5 phr

and 2.5 phr of the US and TS filled compo-sites respectively. The small particle size of sepiolite generates a large surface area that can interact with the rubber and di-minish particle-to-particle distance. The



surface area is one of the important cha-racteristics in reinforcing fillers because the particles with larger surface areas in-crease the properties of the polymer [18-19]. Stronger bonding occurs with more contact area available to react with the polymer matrix. Apart from that, the hig-her rubber-filler interaction of sepiolite and ENR matrix play an important role on the properties enhancement. This can again be attributed to interactions bet-ween the hydroxyl and siloxane groups available on the sepiolite and epoxide groups of ENR through hydrogen bonding and/or chemical bonding that occur after possible ring opening of the epoxy ring either during mixing or compression mol-ding, as previously proposed by Manna et al. [20] and Rocha et al. [21]. A possible mechanism for bonding between the ENR and sepiolite is proposed in Figure 4. The enhancement of this interaction improves

the wetting and adhesion of the polymer to the filler and consequently allows bet-ter stress transfer in the composites.

Comparing the tensile strength of US and TS filled ENR composites; the TS pro-vides significant improvement to the tensile strength of the composites. As can be seen from the result, it is obvious-ly observed that only 2.5 phr of TS is adequate to give the highest tensile strength to the ENR composites. This shows that the treatment of 2.5 phr of sepiolite gives rise to shear strength at the filler interface and forms strong ad-hesion between treated sepiolite and rubber matrix. As a consequence, such shear stress was comparatively transfer-red from the matrix to filler, allowing the filler fully interacted to the ENR matrix and improved rubber-fller interaction at the event of lower amount sepiolite in comparison to that untreated one.

From the amount of silane’s point of view, it can be concluded that the use of 2 phr of silane with 2.5 phr of sepiolite is sufficient to give the composites grea-test tensile strength. This shows that the efficiency of silane in coupling with sepi-olite is significantly superior in compari-son to other loadings. When silane is used, there are two reaction mechanisms competitively taking place during com-pound mixing or during compression moulding. These mechanisms are all temperature dependent: (1) the silane-to-sepiolite or silanization/hydrophoba-tion reaction and (2) the silane-to-rubber or coupling reaction as shown in Figure 5.

The reduction in tensile strength with loading beyond 5 phr of sepiolite loading is simply due to the dilution effect [10]. When more sepiolite particles are integ-rated into the ENR matrix, the sepiolite particles tend to interact with each other, known as filler–filler interaction or ag-glomeration. Nielsen and Landel [22] and Jordhamo et al., [23] reported that the filler-polymer interphase discontinuity is created in the particulate filled composi-tes due to poor stress transfer which ge-nerates weak structure. Agglomeration of the filler particles and de-wetting of the polymer at the interphase aggravate the situation by creating stress concent-ration points which account for the wea-kness in the composite.

The elongation at break of the US and TS filled ENR composites is shown in Fig-ure 6. Increasing sepiolite loading results in an increase in the flexibility of ENR composites. The larger surface area and the softer characteristic of sepiolite load-ed material lead to better interfacial in-teractions between sepiolite and ENR. The homogenous dispersion of sepiolite inside the ENR is responsible for the high-er ductility of the composites. It is inter-esting to highlight that the elongation at break of the composites are improved by the addition of silane coupling agent. This is clearly attributed to the improved interfacial interaction between sepiolite and ENR matrix. However, with the pres-ence of highly contained sepiolite in the ENR composites, it resulted in decrease of the elongation at break. The flexibility of the composites decreases due the ag-glomeration occurs, creating the partially separated micro spaces between the filler and the matrix and finally leading to in-crease the ruptures. When considering the amount of sepiolite use, it was found that the decreasing trend of TS filled ENR composites was found earlier than those

Fig. 5: Proposed model of interactions and bonding between sepio-lite and ENR molecule with the presence of silane coupling agent.

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Fig. 6: Elon-gation at break of un-treated (US) and silane-treated (TS) sepilotes filled ENR composites.

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of US counterparts. This is clearly due to the less efficiency of silane coupling agent at higher filler loading as discussed earlier in term of tensile strength.

The tear strength of US and TS filled ENR composites is shown in Figure 7. It can be seen that the addition of sepiolite had successfully increased the tear strength. The particle size of the sepiolite is small enough to gain higher contact area to the ENR matrix, which results in a better interaction between the ENR mat-rix and the sepiolite. In addition to that, strong rubber-filler interaction obtained from ENR and sepiolite is also responsib-le to the higher energy required to cause the tearing failure. Therefore, the tear strength is improved upon the use of se-piolite. The decreasing trend of tear strength when the sepiolite is over 5 phr is simply due to the agglomeration of sepolite which caused to poorer rubber-filler interaction. The increment of tear strength of treated sepiolite filled ENR in comparison to the untreated one is due to the formation of hydrogen bonding and improvement in the interfacial inter-actions between sepiolite and ENR mat-rix. This enhancement in the tear strength is corresponding to the tear strength and elongation at break obser-ved in the previous section.

3.3 Rubber-filler interactionThe reinforcement of a rubber by filler was associated with a strong interaction between the filler surface and the rubber [24]. Thus, swelling test was important testing for the rubber processor to deter-mine the rubber-filler interaction of the rubber composites. As the rubber compos-ites were immersed in toluene, toluene was penetrated into the free volume be-tween crosslink causing swelling of rub-ber composites. The weight of test speci-men was keep increasing up to a maxi-mum point in which the space between crosslink points had been fully filled by toluene. Figure 9 shows the rubber-filler interaction of US and TS filled ENR com-posites. It is well accepted that the lower the Qf/Qg value, the higher the rubber-filler interaction. Increasing sepiolite load-ing resulted in a strong interaction be-tween sepiolite and the ENR matrix. From the Qf/Qg values, it is evidently shown that it is correspondence to the tensile strength, elongation at break and tear strength observed in the previous study, indicating that strong rubber-filler inter-action is observed at the certain amount of sepiolite and after using the silane

Fig. 7: Tear strength of untreated (US) and si-lane-treated (TS) sepilo-tes filled ENR compo-sites.

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Fig. 8: Rub-ber-filler in-teraction (Qf/Qg) of untreated (US) and silane-trea-ted (TS) sepilotes filled ENR composites.

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coupling agent. The higher rubber-filler interaction observed is simply because of high surface activity and, consequently, high affinity of sepiolite to interact to rub-ber as proposed in Figures 4 and 5.

3.4 Tensile and tear fractured surfacesFigure 9 illustrates the SEM micrographs of tensile fractured surfaces of US and TS filled ENR composites at 100x magnifica-tion. Figure 9A shows the fractured sur-faces of gum vulcanizate. Smooth and soft surfaces were observed because no rigid filler was incorporated into the ma-trix. Figures 9B, 9C, and 9D show the fractured surfaces of US filled ENR com-posites at 2.5, 5, and 10 phr of sepiolite respectively. The roughness and frequen-cy of tearing in US filled ENR composites were visible when sepiolite was added into the matrix. This indicates that more energy is needed to break the sample. A

slight increment in the matrix’s rough-ness with increased levels of US is in ag-reement with the tensile results obser-ved. However, when US is incorporated beyond 5 phr, the US tends to agglome-rate, due to the strong filler–filler inter-action as well as the detachment of sepi-olite. This is shown in Figure 9D, indica-ting that less energy is required to cause failure in the materials. The high filler–filler interaction of sepiolite in ENR mat-rix causes a reduction of tensile strength.

The tensile fractured surfaces of the TS filled ENR composites are also illus-trated in Figures 9E, 9F and 9G. With the addition of TS in concentrations up to 2.5 phr, an augmentation in surface roughness occurs as well as compared to the fractured surface with loading at 5 phr of US (see Figure 9C) and materials with gum vulcanizate (see Figure 9A), which shows less tearing lines leading to



lower ultimate tensile value. Better ho-mogeneity in TS filled ENR composites indicates a coherence of the TS and the ENR phases. The uniform dispersion of TS in the ENR matrix alters the crack path, which leads to resistance from crack propagation and hence results in higher tensile strengths and improved mechanical properties.

Figure 10 displays the tear fractured surfaces of US and TS filled ENR composi-tes at 100x magnification. With the addi-tion of US in concentrations up to 5 phr (see Figures 10A, 10B and 10C), the failure surfaces show feature of well-developed interfacial interaction and low pull-out of US on the fracture surface was seen. An augmentation in surface roughness and a homogeneous pattern are more pro-nounced for the TS filled ENR composites (see Figures 10E, 10F and 10G), indicating a coherence of the TS particles and the ENR phases. However, for the 10.0 phr of US and TS were added (see Figures 10D and 10G), it can be seen that there were a lot of voids on the fracture surface. This showed that it was easily pulled out sepi-olite when amount of the filler was ex-ceed optimum amount which cause filler agglomeration happened.

4. ConclusionsThe following conclusion can be presented:1. SEM image of sepiolite particles clear-ly showed that sepiolite particles are in needle structure, indicating that high contact area and reinforcement can be attained by incorporating sepiolite.2. The addition of sepiolite resulted in faster scorch (ts2) and curing times (tc90) where MH increased consistently with the increase of sepiolite loading due to the highly restricted molecular motion of macromolecules when sepiolite was in-corporated.3. The tensile strength of sepiolites filled ENR composites shown optimum value at 5 phr and 2.5 phr for the US and TS respec-tively. SEM images exhibited more surface roughness for the composites at 5 phr se-piolite loading. As a result, higher energy is needed to cause a failure to the sample.4. The rubber-filler interaction between the sepiolite and ENR matrix was enhan-ced by the addition of silane coupling agent where two major factors are concer-ned i.e., the hydrogen bonding between the hydroxyl available on the sepiolite and epoxide groups of ENR through and/or chemical bonding that occur after possible ring opening of the epoxy ring either du-ring mixing or compression molding.

Fig. 9: Tensile fractured surfaces obtained from SEM of untreated (US) and silane-treated (TS) sepilotes filled ENR composites at 100x magnification: Control (A), US2.5 (B), US5 (C), US10 (D), TS2.5 (E), TS5 (F) and TS10 (G).

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Fig. 10: Tear fractured surfaces obtained from SEM of untreated (US) and silane-treated (TS) sepilotes filled ENR composites at 100x magnification: Control (A), US2.5 (B), US5 (C), US10 (D), TS2.5 (E), TS5 (F) and TS10 (G).

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epoxidized natural rubber sepiolite epoxidized natural ......chemical modification [9]. commercial...

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