Scholarly article on topic 'Evaluation of Mechanical Properties of Epoxy/Nanoclay/Multi-Walled Carbon Nanotube Nanocomposites using Taguchi Method'

Evaluation of Mechanical Properties of Epoxy/Nanoclay/Multi-Walled Carbon Nanotube Nanocomposites using Taguchi Method Academic research paper on "Materials engineering"

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Abstract of research paper on Materials engineering, author of scientific article — K.Z.K. Ahmad, S.Hj. Ahmad, M.A. Tarawneh, P.R. Apte

Abstract This paper reports the improvement of the mechanical properties of epoxy/nanoclay/multi-walled carbon nanotube (MWNT) nanocomposites prepared by the solution casting method for a range of pre-cure temperatures (room temperature, 50, and 70°C), cure temperature (120, 130, and 140°C), nanoclay content (0.5, 1.0, 1.5 wt%) and content of MWNT (0.2, 0.6, 1.0 wt%) for three levels. The influence of these parameters on the mechanical properties of epoxy/nanoclay/MWNT has been investigated using Taguchi's experimental design. The output measured responses are the tensile properties (tensile modulus, tensile strength and strain at break), impact strength and fracture toughness. From the Analysis of Mean (ANOM) and Analysis of Variance (ANOVA), MWNT content, pre-cure temperature and cure temperature had the most significant effects for the impact strength with contribution percentages of 38%, 28% and 23% respectively. However, for the fracture toughness and strain at break, the enhancements of properties come from the nanoclay content (59%), MWNT content (18%) and pre-cure temperature (23%). While the improvement in tensile strength was influenced by nanoclay and MWNT content, the cure temperature has a stronger effect on the tensile modulus. In this respect, Taguchi method points to the Taguchi method, in this way, points to the dominant parameters and gives the optimum parameter settings for each mechanical property. Confirmation experiments were performed with the optimum parameter settings and the mechanical properties were measured compared with the predicted results.

Academic research paper on topic "Evaluation of Mechanical Properties of Epoxy/Nanoclay/Multi-Walled Carbon Nanotube Nanocomposites using Taguchi Method"

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Procedía Chemistry 4 (2012) 80 - 86

Evaluation of Mechanical Properties of Epoxy/Nanoclay/Multi-Walled Carbon Nanotube Nanocomposites using Taguchi Method

K.Z.K. Ahmad3'*, S.Hj. Ahmad3, M.A.Tarawneha, P.R. Apteb

aMaterials Science Programme, School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Malaysia bDepartment of Electrical Engineering, Indian Institute of Technology Bombay, India

Abstract

This paper reports the improvement of the mechanical properties of epoxy/nanoclay/multi-walled carbon nanotube (MWNT) nanocomposites prepared by the solution casting method for a range of pre-cure temperatures (room temperature, 50, and 70 °C), cure temperature (120, 130, and 140 °C), nanoclay content (0.5, 1.0, 1.5 wt%) and content of MWNT (0.2, 0.6, 1.0 wt%) for three levels. The influence of these parameters on the mechanical properties of epoxy/nanoclay/MWNT has been investigated using Taguchi's experimental design. The output measured responses are the tensile properties (tensile modulus, tensile strength and strain at break), impact strength and fracture toughness. From the Analysis of Mean (ANOM) and Analysis of Variance (ANOVA), MWNT content, pre-cure temperature and cure temperature had the most significant effects for the impact strength with contribution percentages of 38%, 28% and 23% respectively. However, for the fracture toughness and strain at break, the enhancements of properties come from the nanoclay content (59%), MWNT content (18%) and pre-cure temperature (23%). While the improvement in tensile strength was influenced by nanoclay and MWNT content, the cure temperature has a stronger effect on the tensile modulus. In this respect, Taguchi method points to the Taguchi method, in this way, points to the dominant parameters and gives the optimum parameter settings for each mechanical property. Confirmation experiments were performed with the optimum parameter settings and the mechanical properties were measured compared with the predicted results.

© 2012 Published by Elsevier Ltd.

Keywords: Carbon nanotube; nanoclay; Taguchi method.

* Corresponding author. Tel.:+60-12-2050652 Email address: kuzarina@upnm.edu.my

1876-6196 © 2012 Published by Elsevier Ltd. doi:10.1016/j.proche.2012.06.012

1. Introduction

For decades epoxies have attracted remarkable attention from science as well as industry. Due to their unique mechanical, electrical, and thermal properties, the applications of epoxies vary from adhesives, protective coatings in appliances, and encapsulation to high performance applications, including aircraft components, filaments, pipes, tanks, pressure vessels and tools [1]. Due to their unique mechanical, electrical and thermal properties, the application of epoxies vary from adhesives, protective coatings in appliances, and encapsulation to high performance applications including the addition of nanomaterials in epoxy structures leads to a dramatic change in the properties. The development of new properties is possible due to the unexpected hybrid properties derived from at least two different forms and shapes of materials. The inclusion of nanomaterials brings impressive results in respect of efficient reinforcement without sacrificing the ductility, impact strength, heat stability or other important characteristics. Most structural applications require a balance between stiffness and impact, which has been achieved by using nanoclays or nanosilicates at loadings of less than 10%. This inclusion improves the mechanical, thermal, dimensional and barrier properties. In most of the epoxy/clay nanocomposites research, clay minerals have been fully used because of the low cost and availability compared to other layered materials [2-4]. The unique structure of these materials allows the modification of the crystal lattice and allows the modification of the crystal lattice and allow the existence of exfoliated structures in most of the polymers. Among all types of nanoparticles, carbon nanotubes have become the preferred choice as they contribute the most to the fracture toughness and tensile strength. Many researchers have also studied the effect and influence of carbon nanotube on the mechanical properties of nanocomposites [5,6]. Since carbon nanotubes are unique and novel nanoparticles, the study and exploitation of these potential fillers are far from being complete. Furthermore, the implementation of this filler in processing has faced a major challenge in achieving the homogeneous dispersion of the nanotubes in the polymer matrices and thus limited the application of recovered materials. As cited above, the effect of the parameters on one or more properties has been individually studied on epoxy/clay or epoxy/MWNT in the literature, the effect of the parameters on one or more properties has been individually studied on epoxy/clay or epoxy/MWNT in the literature, while the other factors were kept unchanged. However, to our knowledge there is no available report on the epoxy/nanoclay/MWNT nanocomposites regarding their parameter effect on the mechanical properties using the Design of Experiment (DoE) method. In this study, all experiments were designed using the Taguchi Method in order to obtain the optimized value in tensile strength, tensile modulus, strain at break, fracture toughness and impact strength by varying the nanoclay and MWNT content, pre cure temperature and cure temperature.

2. Experiment

2.1. Materials

The epoxy used in this study was Morcote BJC 39, which contains epoxy resin and hardener amines supplied by Vistec Technology Sdn Bhd. MMT Na+ is an untreated montmorillonite which is a natural montmorillonite from Southern Clay Products. To avoid moisture absorption, the clay powder was dried in the oven for 24 h prior to processing and preparation of the samples. The MWNTs were produced by catalytic chemical vapor deposition (CCVD) and manufactured by Arkema (Graphistrength™ C100). The specifications of MWNTs are as follows: purity > 90%, length 0.1-10 ^m, diameter 10-15 nm.

2.2. Experimental design by Taguchi method

The design of experiments (DOE) technique executes fewer experiments compared to factorial experiments. This method also uses the analysis of variance and mean to analyze the result and interaction between factor effects. This method also screens the significant factors affecting the response from those with less significance and gives the optimum parameter to obtain the maximum performance. Furthermore, the Taguchi method is the only method that encourages noisy inputs during experimentation. In this study, the most appropriate orthogonal array to be used is a 9-trial experimental (L9). In this design, four factors have been chosen: composition of clay and MWNT, pre cure temperature and cure temperature. All independent factors were considered for three levels (Table 1). In order to select the factors and levels, a literature review was conducted on other reference publications [7-10]. The practical aspects and some screening experimental work have been considered. The responding variables can be optimized using the Analysis of Mean (ANOM) and the Analysis of Variance (ANOVA).

Table 1: Parameters and their variation levels

Parameter and symbol -

Pre-cure temperature Room temperature 50 °C 70 °C

Cure temperature 120 °C 130 °C 140 °C

Nanoclay content (wt %) 0.5 1.0 1.5

MWNT content (wt %) 0.2 0.6 1.0

2.3. Sample preparation and characterization

Table 2. Taguchi orthogonal array of designed experiments based on the coded levels

Trial Sample code Pre-cure Cure Nanoclay MWCNT content

temperature temperature content (wt%) (wt%)

1 EH1 RT 120 °C 0.5 0.2

2 EH2 RT 130 °C 1.0 0.6

3 EH3 RT 140 °C 1.5 1.0

4 EH4 50 °C 120 °C 1.0 1.0

5 EH5 50 °C 130 °C 1.5 0.2

6 EH6 50 °C 140 °C 0.5 0.6

7 EH7 70 °C 120 °C 1.5 0.6

8 EH8 70 °C 130 °C 0.5 1.0

9 EH9 70 °C 140 °C 1.0 0.2

First, nanoclay and carbon nanotube were ground appropriately in an agate mortar and pestle. Aluminum foil was used to cover the mortar to ensure a thorough mixing and clean surface during the process. The clay-MWNT hybrids were prepared according to an L9 array (Table 2). After mixing, clay-MWNT was dispersed in the mixture of methanol and Liquid Epoxidized Natural Rubber (LENR) and sonicated using an ultrasonic bath (70 Watts, 42 KHz). LENR was prepared by a photochemical degradation technique [11]. The solution was then introduced into the epoxy resin and sonicated for 3 h. To remove additional bubbles during the process, the mixture was then degassed. Later, the hardener with ratio 1:3 and degassing agent (Defoamer 722) were added with gentle mixing and degassed again. The

mixture was then poured into a steel mold for the pre-curing and curing process. The tensile test was performed at room temperature according to ASTM D638-91. A gauge length of 100 mm was employed with a cross-head speed of 5mm/min using Testometric 350 model M350-10CT. The Izod impact strength was determined using the Ray Ran pendulum Impact System according to ASTM D256-88. The fracture toughness was executed at room temperature according to ASTM D5045 using testing machine Testometric 350 model M350-10CT.

3. Results and Discussion

3.1. Pareto ANOVA

By using ANOVA and ANOM analysis, significant factors and interactions of factors can be easily detected in this study. The determination of these criteria is based on the cumulative contribution ratio (expressed in %) to be about 90%. The analysis was performed for each mechanical properties involved in this study and the ANOVA diagrams are depicted in Figure 1.

Fig. 1. ANOVA diagram analysis for the contribution factors of mechanical properties of nanocomposites

Based on Figure 1a, to obtain the maximum tensile strength, nanoclay and MWNT content have dominant effects contributing 42% and 33%, respectively. Both factors were also marked on the diagram to improve the strain at break (Figure 1c) while the pre-cure temperature is the other significant factor.

Pareto ANOVA diagram for tensile modulus is demonstated in Figure 1b. The enhancement of tensile modulus mainly relies on cure temperature, nanoclay content and pre-cure temperature. The ANOVA diagram for fracture toughness is depicted in Figure 1d, which displays a similar pattern with Figures 1a and 1c with cure temperature being an insignificant factor. The nanoclay content has higher effects on strain at break and fracture toughness than on tensile strength and tensile modulus with a 59%

contribution. However, cure temperature seems more dominant for the tensile modulus enhancement with a contribution of 41% compared to 30% for nanoclay content.

A different trend is shown in Figure 1e for the impact strength as the MWNT content is the major contributor followed by pre-cure temperature and cure temperature. The nanoclay content exhibits a lesser role in promoting the impact property in contrast to the other evaluated properties.

3.2. Determination of optimum conditions

The best possible levels of mix proportions were investigated based on the S/N chart for optimizing the mechanical properties using the Taguchi method. In order to optimize the mechanical properties, "the larger the better" objective function was used to evaluate the statistical data. The effects of each parameter on the tensile strength, impact strength and fracture toughness are shown on Figures 2 and 3. For this study, as the hybrid with the optimum parameter is not included in the L9 orthogonal array, it was prepared and exposed to all mechanical tests. The optimum parameter to attain an epoxy/clay/MWCNT hybrid nanocomposite with maximum properties can be determined by maximum points in the main-effects plots in Figures 2 and 3. According to Figures 2 and 3, the optimum parameters of the target properties are tabulated in Table 3.

•9 S.O ai

Î « g 3.0

1 1.0 §0.0

Factor Effect Plot strain at break

Vv ' — V - 7------1— Ou Mean

goo O O O U 1.0 ■ 1.5 ■ 0.2 ' 0.6 ■ 1.0 ' On-..:

Control Factor Levels

Fig. 2. Main effect for (a) tensile strength (b) Tensile modulus and (c) strain at break

Fig. 3. Main effect for (a) fracture toughness and (b) impact strength

In order to verify the optimum parameter using ANOM and ANOVA analysis, laboratory experiments were executed to verify whether the mechanical properties (tensile strength, Young's Modulus, strain at break, fracture toughness and impact strength) can be maximized by the proposed condition (Table 3). The predicted mechanical properties and experimentals result are shown in Table 4. These results show that there is good concurrence between the experimental results and the results obtained by Taguchi's approach.

Table 3. Optimum parameter for mechanical properties of epoxy/nanoclay/MWNT nanocomposites

Optimum Pre-cure Cure Nanoclay MWNT

Parameter temperature temperature content (wt%) content (wt%)

Tensile strength RT 140 °C 1.5 0.6

Young's Modulus RT 140 °C 0.5 0.6

Strain at break RT 140 °C 0.5 0.6

Fracture toughness 70 °C 130 °C 1.0 0.6

Impact strength 50 °C 130 °C 0.5 0.2

Table 4. Optimum mechanical properties of epoxy/nanoclay/MWNT nanocomposites from fine tuning experiments

Mechanical properties

Predicted result Experimental result

Tensile strength (MPa) Young's Modulus (MPa) Strain at break (%) Fracture toughness (MPam1/2) Impact strength (kJ/m2)

48.8 to 49.7 2310 to 2360

1.97 to 3.5 0.595 to 0.953 2.4 to 2.45

43.4 to 49.0 2381 to 2597 1.03 to 1.66 2.396 to 4.308 1.805 to 2.778

4. Conclusion

In this study, the Taguchi method was used as an alternative approach to plan experimental work on the effect of factors affecting the mechanical properties of epoxy/nanoclay/ multi-walled carbon nanotube nanocomposites. This method was found to be an effective technique to optimize the tensile strength, tensile modulus, fracture toughness and impact strength. The MWNT content plays an important role in respect of the impact strength properties followed by pre-cure temperature and cure temperature. However, for the fracture toughness and strain at break, the enhancements of properties comes from the nanoclay content while the MWNT content and pre-cure temperature were the other significant factors.

Although the improvement in tensile strength was influenced by the nanoclay and MWNT content, the cure temperature has a stronger effect on the tensile modulus

Acknowledgement

This work was supported under grant UKM-OUP-NBT-29-142/2011.The authors are grateful to the Universiti Kebangsaan Malaysia for supporting this research.

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