iDECON 2012 – International Conference on Design and Concurrent Engineering Universiti Teknikal Malaysia Melaka (UTeM) 15-16 October 2012
Fabrication and Characterization of Epoxidized Natural Rubber Reinforced Single-Walled Carbon Nanotubes Nanocomposite Elyas Talib, Noraiham Mohamad, Mohd Warikh Abd Rashid, Mohd Asyadi Azam Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka, Durian Tunggal, 76100 Melaka, Malaysia Phone: +606-3316972, Fax: +606-3316411, Email:
[email protected],
[email protected]
Abstract The use of single-walled carbon nanotubes (SWCNTs) as a reinforcement in rubber nanocomposites nowadays attracts a great deal of attention. The rubber used in this study was epoxidized natural rubber (ENR) with SWCNTs as nanofiller. The influence of nanofillers on the mechanical and thermal properties of the produced nanocomposite was studied. SWCNT/ENR nanocomposite with 1 wt% of CNTs achieved maximum tensile strength at 13.64 MPa, which is 58 % higher than that of unmixed. With the addition of SWCNTs, the strength and elongation at break of the ENR decreased, and simultaneously, the strength modulus, tear resistance and hardness increased. Moreover, from the differential scanning calorimetry (DSC) analysis, the increase of Tm, Tc, and ΔHc were also confirmed.
Keywords: epoxidized natural rubber; single-walled carbon nanotubes; nanocomposite; mechanical properties; differential scanning calorimetry .
I.
INTRODUCTION
Nanocomposites can be defined as composites filled with nanofillers such as nanoparticles, and recently are gaining significant attention from scientists and engineers. It is well-known that nanocomposites have superior physical properties, because of the high surface-to-volume ratio of nanometer scale reinforcing fillers embedded in the matrix, compared to the conventional fiber or particle reinforced composites. Despite single-walled carbon nanotubes (SWCNTs) have been widely used with different kinds of polymers, yet, very little work involving one of the natural resource- rubbers. Usually, elastomeric materials reinforced with carbon black or silica, although the full effects of these fillers are diminished due to their agglomeration [1-3]. It finds a key to incorporate well-blended nanofiller into rubber to obtain beneficial mechanical and physical properties. Further, the advantages of SWCNTs as nanofiller is because it has many remarkable properties such as electrical conductivity; six orders of magnitude higher than the copper [4], high current carrying capacity [5], excellent field emitter [6], high aspect ratio, and small tip radius of curvature are ideal for field emission. For advanced applications, SWCNTs have been used in many types of devices such as
batteries, electrochemical capacitors [7, 8] and field-effect transistors [9]. The concept of nano-sized filler-reinforced material was recently demonstrated by the incorporation of nanoparticles in a rubbery polymer matrix such as clay into natural rubber and SWCNTs into silicone rubber [10]. As known, rubber is a thermal and electrical insulator. Thus, incorporation of conductive fillers into this material could produce composite material with electrical conductivity. Rubber nanocomposites may suit various industrial applications such as tire component, electrical sensors, vibration-proof, shock dampener, and electrical shielding [11-14]. Differences in mechanical properties and applications can be considered to ensure that the objectives of learning are successful. It correlates to the aspects of toughness [15], hardness [15-17], elastic [16], and electrical conductivity [18-20]. As a pilot study of rarely-explored studies, epoxidized natural rubber (ENR) with SWCNT reinforcement was prepared with a filler content of only 1% by weight. The present study focused on the preparation of two samples; unmixed ENR and SWCNT/ENR nanocomposite. The results to be discussed are not only for characterizing the mechanical properties (Universal Testing Machine (UTM); Instron), but also analyzing the melting temperature and crystalline temperature of the as-prepared nanocomposites by using Differential Scanning Calorimetry (DSC). II.
METHODOLOGY
Two sets of ENR based samples were prepared; namely unmixed ENR (no SWCNT addition) and SWCNT/ENR nanocomposite. The fabrication process of SWCNT/ENR is shown in Figure 1. For the SWCNT/ENR, SWCNTs (0.46 g) and ENR (46.24 g) were blended together in the Internal Mixer. The time taken is shown in Figure 2. The temperature and rotation of rotor used in this process were 150 °C and 60 rpm, respectively. Curative agents were then added into the SWCNT/ENR and blended again for 4 min. The composition of ENR used in the work is given in Table 1. The SWCNTs were purchased from Sigma-Aldrich (0.7 - 1.3 nm), ENR rubber used in this work was supplied by Mentari Equipment & Project Sdn. Bhd.
Blend
Process
Crush
Vulcanization
Equipment Internal Mixer
Crusher
Hot Press
Sample
Fig.1. Fabrication process of SWCNT/ENR nanocomposite.
Internal Mixer Processing
The vulcanization was carried out at 150 °C for 20 min by using a hot press machine. The pressure for the hot press was adjusted 300 kPa to obtain the thickness (200 ~ 300-µm) of rubber composite sheet. The SWCNT nanocomposite were black and unmixed was yellow. Epoxidized natural rubber nanocomposites thin sheets with SWCNTs reinforcement were prepared with filler content of 1% by weight. Sample stips were prepared by cutting the sheets to 3 mm x 10 mm x 0.3 mm size for testing.
Time Taken (min)
Loading of ENR
0
Rotor Started
1
Addition of Filler
4
Addition of Curatives
8
III. Dump
Fig. 2. A flow chart of the blend process using internal mixer. Table 1. Rubber compound formulation. Ingredients ENR Zinc Oxide Sulfur Stearic Acid SWCNT
RESULTS AND DISCUSSION
12
Parts per hundred 100 3.75 1.5 1.88 1.0
(phr)
First, the result for the tensile strength is shown in Figure 3. The testing is to identify the differential between unmixed ENR and SWCNT/ENR to get which one is stronger and tough. From Figure 3, the SWCNT/ENR and unmixed ENR are 13.64 MPa and 9.84 MPa respectively. Thus, the calculated difference is 3.60 MPa, a 58.09 % increase. This shows that the SWCNT/ENR nanocomposite is stronger and tougher than the unmixed ENR. This observation suggests that SWCNTs acted as very good reinforcement agent consequently contributing to the increase in hardness of the blends. And, this is consistent with the hardness test that has been done for both samples. By the addition of SWCNTs, the hardness increased of up to 17.33, 52.18 % from the unmixed ENR (Figure 4).
15
3000
10
DSC (uw)
Tensile Strength (MPa)
intercalated/exfoliated polymer chains with the nanofillers, thereby enhance the Tc, Tm, and ΔHc for SWCNT/ENR nanocomposite.
5
2000 1000 0 60
0 0
0.2
0.4
0.6
0.8
1
1.2
65
70
SWCNTs Content (wt%)
75
80
85
90
95
100
Temperature (°C)
Fig. 3. Comparison of tensile strength between SWCNT/ENR and unmixed ENR. The data obtained from mechanical testing using UTM
1 wt% SWCNTs
0 wt% SWCNTs
Fig. 5. The endothermic curves of SWCNT/ENR nanocomposite. Table 2. Melting and crystallinity characteristics of SWCNT/ENR nanocomposite.
Shore Hardness
17.5
Sample
17 16.5 16 15.5 15 0
0.2
0.4
0.6
0.8
1
ENR
SWCNTs content (wt%)
Tm (°C)
Tc (°C)
ΔHc (J/g)
Xc (%)
0
67.23
78.6
4.25
12.11
1
67.42
87.1
9.10
25.93
1.2
SWCNTs Content (wt%)
Fig. 4. Comparison of shore hardness between SWCNT/ENR and unmixed ENR. The heating and cooling scan of Differential Scanning Calorimetry (DSC) were used to determine the melting temperature (Tm), crystalline temperature (Tc), and crystalline level from the heat of crystallization of SWCNT/ENR nanocomposites. The plots of DSC analysis at varied SWCNT/ENR content are shown in Figure 5. The endothermic melting peak displayed the melting temperature, whereas, the exothermic curves of the samples displayed the crystallization temperature. The area under the curves indicates the heat of crystallization (ΔHc) values which depend on the crystallinity of the material. The degree of the crystallinity of these samples can be calculated as the ratio of ΔHc of the samples with ΔHc of unmixed. The data on DSC analysis were listed in Table 2. From the table, it was confirmed that Tc, Tm, and ΔHc for SWCNT/ENR nanocomposite were increased with the addition of SWCNTs. In the case of polymer nanocomposites, the DSC measurement is useful for the identification of the extent of intercalation/exfoliation of the nanoparticles in the polymer matrix [21]. The segmental mobility of the polymer matrix are greatly affected by the interactions of the
In the present study, DSC measurements were performed at a temperature range of 40 °C to 120 °C. The Tm and Tc were observed to increase from 67.23 °C and 78.6 °C for control unmixed blends to 67.42 °C and 87.1 °C for 1wt% of SWCNTs respectively. Moreover, ΔHc of the sample also increased with 4.25 J/g for control to 9.10 J/g for 1wt% of SWCNTs. The increments in Tc, Tm, and ΔHc of samples might be due to the well dispersed SWCNTs on the free volume of polymer blends as well as the confinement of the intercalated/exfoliated polymer chains within the SWCNTs galleries, which resists the segmental motion of the polymer chains [22].
IV CONCLUSIONS Nanocomposite of epoxidized natural rubber reinforced with single-walled carbon nanotubes were synthesized and blend processed using internal mixer. It was found that the tensile strength and hardness of the nanocomposites was enhanced by incorporating of SWCNT nanofiller, even at low 1% filler content. SWCNT/ENR nanocomposite showed an increase in initial modulus with increasing filler content. According to the DSC also showed the increase of Tc, Tm, and ΔHc with increasing filler content. Further studies are required for better understanding of structural properties and
morphology of the nanocomposite and consequently its future usage from the viewpoint of industrial applications.
ACKNOWLEDGEMENT The Ministry of Higher Education is thanked for the financial support (MyPhD). The authors are also grateful to technicians of Polymer Lab and Engineering Materials Lab, UTeM for the experimental support. REFERENCES [1]
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