Mechanical Properties of Glass Fiber Reinforced Polyester ZnO NanoComposites

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ScienceDirect Materials Today: Proceedings 2 (2015) 2817 – 2825

4th International Conference on Materials Processing and Characterization

Mechanical Properties of Glass Fiber Reinforced Polyester ZnO NanoComposites a

Naga Raju Ba* , Ramji Kb , Prasad V.S.R.Kc Department of Mechanical Engineering, Anil Neerukonda Institute of Technology and Sciences, Visakhapatnam 531162, India b Department of Mechanical Engineering, Andhra University, Visakhapatnam - 530003, India c Principal, Anil Neerukonda Institute of Technology and Sciences, Visakhapatnam - 531162, India.

Abstract The Mechanical properties of Glass Fiber Reinforced Polyester-ZnO nanocomposite (GFRP-ZnO nanocomposite) were studied. The synthesized ZnO nanoparticles are functionalized with γ-aminopropyltriethoxysilane and are mixed with polyester resin through ultra-sonication for in different weight fractions as 1%, 2%, 4%, and 6%. Glass fiber such as Woven Roving(WR) is considered in different wt fractions such as 70/30wt%, 60/40wt%, 50/50wt% for preparing GFRP-ZnO nanocomposite. The influence of ZnO nanoparticles on the mechanical properties like tensile strength and hardness were investigated. The comparison of different weight fractions of WR is also studied. These properties were found to improve for GFRP-ZnO nanocomposites for the reinforcements upto 2wt% and also observed that 50/50wt% gives better results. © 2014 The Authors. Elsevier Ltd. All rights reserved.

© 2015 Elsevier Ltd. All rights reserved. Selectionand andpeer-review peer-review under responsibility the conference committee the 4th International conference Selection under responsibility of theof conference committee membersmembers of the 4th of International conference on Materials on Materials and Processing and Characterization. Processing Characterization. Keywords: ZnO nanoparticles; Ultrasonication;polymer nanocomposites;Mechanical properties;

Corresponding author: +91 9849820049 (Mobile) Fax No. 08933-226395, E-mail: [email protected]

2214-7853 © 2015 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the conference committee members of the 4th International conference on Materials Processing and Characterization. doi:10.1016/j.matpr.2015.07.294

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Introduction

Unsaturated Polyester (UP) resins have been widely used in the automotive field, building construction, water pipes, boat hulls, architectural panels, panels in aircraft and stackable chairs due to their easy processing ability, high chemical resistance, and relatively low price [1, 2]. Glass fiber-reinforced polymer composites are one of the most widely used composite materials [3]. The addition of fibers to the polymer matrix dramatically increases the overall mechanical strength of the composite material as compared to the neat polymer. The boundary where these components meet is thus inherent to such materials and is greatly called interface and the region near this interface is generally referred to as ‘interphase’. The interphase is a very small region over which the mechanical and physical properties change from the bulk properties of one component (glass) to the bulk properties of the other component (polymer). In the context of Glass Fiber Reinforced Polyester (GFRP) composites the interphase region is very important as the load transfer from the matrix to the fibers occurs through this region. Now research is going on nanocomposites to get superior properties when compared to conventional composites. Nanocomposites are a class of composites derived from ultra fine inorganic particles with sizes on the order of nanometers that are homogeneously dispersed in a polymer matrix. Because of their nanometer size, nanocomposites possess properties that are superior to those of conventional composites and because of interfacial adhesion being maximized. [4-8] With the addition of nanosized inorganic particles into polymer matrices the new composites material exhibit attractive mechanical, thermal, optical and electrical properties which greatly differ from that of conventional composites [9, 10]. The unprecedented mechanical properties of nylon 6-clay nano composite synthesized by in-situ polymerization were first demonstrated by researchers at the Toyota Central Research Laboratories. Such nanocomposites exhibited significant improvement in strength and modulus, namely, 40% in tensile strength, 60% in flexural strength, 68% in tensile modulus, and 126% in flexural modulus [11]. ZnO is a key technological material and finds use in a large gamut of applications like interconnects in nanoelectronics, piezoelectric devices, optoelectronics, chemical sensors and AFM tips. ZnO has three specific advantages, (i) it is a semiconductor, with a direct wide band gap of 3.37 eV and a large excitation binding energy (60 meV). (ii) Due to its non central symmetry (wurtzite structure), ZnO is highly piezoelectric, which is a key property in building electromechanically coupled sensors and transducers. (iii) ZnO is a bio-safe and biocompatible material, and can be used for biomedical applications [12].Mechanical, electrical, electromechanically coupling, optical and chemical properties of ZnO bulk crystals, ZnO thin films and ZnO nanostructures have been extensively discussed in several review articles [12-16]. ZnO nano particles have been studied as fillers of a series of polymers such as polyacrilonitrile [17, 18], polystyrene [19], polystyrenebutycrylate [20], polyphenylene sulfide [21] and PTFE [22]. However, the extent of property modification depends on the base polymer and on the size, distribution and dispersion of the nanoparticles and on the adhesion at the filler matrix interface. No significant work has been reported about the study of mechanical properties of GFRP-ZnO nanocomposite in different weight fractions. Glass reinforcement such as woven roving (WR) in different weight fractions are considered for investigation in the present work. Studies are carried out on synthesis and characterization of ZnO nanoparticles and mechanical properties of GFRP-ZnO nanocomposite) in different weight fractions. In this study ZnO nanoparticles were synthesized by a simple carbonate route, and functionalized with γaminopropyltriethoxysilane (APS) to improve the bonding and uniform dispersion between ZnO nanoparticles and polyester matrix to study the influence of ZnO nanoparticles on the Mechanical properties such as Tensile strength and Hardness were influenced by the content of ZnO nanoparticles. 2.

Experimentation

2.1 Materials Required for Fabrication of GFRP-ZnO Nanocomposites ¾ Zinc oxide nano powder synthesized by Carbonate Route and Average size of particle is determined as 34nm, by the same authors [23]. It is organically modified with a γ-aminopropyltriethoxysilane (APS) by sonication process. ¾ Resin: Unsaturated polyester has been a popular thermo set used as a polymer matrix in composites [24 and 25]. In the present work, unsaturated polyester resin is used. It is pre-promoted for ambient temperature cure with addition of Methyl Ethyl Ketone Peroxide (MEKP) as catalyst. It is convenient for hand lay-up

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applications and easy air release. Unsaturated polyester possesses many advantages compared to other thermosetting resins including room temperature cure capability, good mechanical properties and transparency, low pressure moulding capabilities which make it particularly valuable for large component manufacture at relatively low cost [26]. In contrast to other thermosetting resins, no by-product is formed during the curing reaction. Hence resins can be cast, moulded at low pressure and temperature. [24]. ¾ Woven roving (WR) is taken from saint-gobain-vertrotex India ltd. 2.2. Functionalization of ZnO Nanoparticles Improvements in mechanical properties are dependent upon the nature of interactions between the matrix and filler. A γ-aminopropyltriethoxysilane (APS) is used to disperse/exfoliate the ZnO nanoparticles in polyester matrix making use of an ultra sonicator. The compounding process was carried out with varying ZnO contents (1wt%, 2wt%, 4wt% and 6wt %) and the technique was found highly efficient and environment friendly. 2.3. Synthesis of GFRP-ZnO Nanocomposites The glass fiber reinforcement such as woven roving (WR) is to be considered and treated ZnO nano polyester as a thermosetting resin material for the synthesis of GFRP-ZnO nano composites. The orthophalic polyester pre-promoted for ambient temperature with addition of MEPK) as catalyst.

Fig.2.1 (a) and Fig.2.1 (b). Synthesis of GFRP-ZnO Nanocomposites by Hand- layup technique

A hand-layup technique was adapted to fabricate the GFRP-ZnO nano composites [27]. For fabricating these composites, a smooth wooden mould was placed horizontally and coated with light layer of liquid polyvinyl acetate (PVA) as a release agent as shown in Fig. 2.1(a) & 2.1(b). A plain roller soaked with treated nano ZnO polyester resin rolled over the mould surface to make the first layer of nano ZnO-polyester resin, followed by a layer of woven roving (WR) laid over the first layer of nano ZnO- polyester resin. Entrapped air between the layers was squeezed out during build up process, using a smooth steel roller, which also ensured that the polyester resin layers distributed uniformly over the surfaces. Then another layer of nano ZnO-polyester resin was applied over the glass fiber sheet. Repeating the same steps, GFRP-ZnO nanocomposites were built up to thickness of 4mm and consisted of three layers of woven roving (WR) glass fibers. Then the material was cured under room temperature condition for 24hrs. The above process is carried in different weight fractions such as 70/30wt%(70% polyester resin and 30% glass reinforced material as WR),60/40wt%, 50/50 wt% fraction and different wt %s of treated ZnO nano particles such as 1wt%, 2wt%,4wt%, 6wt% to study the influence of ZnO nanoparticles. 2.4. Experimentation for Mechanical Properties of GFRP-ZnO Nanocomposites 2.4.1Tensile Strength Tensile test was conducted for different wt percents of polymer/glass fiber such as 70/30 wt. %, 60/40 wt. %, and 50/50 wt. % for the WR as glass reinforcements, by introducing ZnO nanoparticles in various percentages as 1%, 2%, 4%, and 6% by wt. using a DAK - UTM at the cross head speed of 1mm/min according to ASTM D 638 IV

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as shown in Fig.2.2. For each nanocomposite, five specimens were tested and the average value was taken. The tensile strength is obtained from stress-strain curves. The model tensile specimens after conducting tensile test are represented in Fig.2.3

Fig.2.2 ASTM D638 Type IV standard specimen

Fig.2.3 tensile test specimens after fracture

2.4.2 Hardness Hardness tests were carried out using Barcoll Hardness testing machine and testing specimens were prepared as per ASTM D-2583. The specimen was placed under the indentor of the Barcol hardness tester and a uniform pressure was applied to the specimen until the dial indicator reached a maximum. The depth of the penetration was converted into absolute Barcol numbers. For each nanocomposite, 10 specimens were tested and the average value was taken. These tests were carried out for different wt.% fractions such as 70/30 wt.%, 60/40 wt.% and 50/50 wt.% and by introducing ZnO nanoparticles in various percentages as 1%, 2%, 4%, and 6% by wt. to study the Hardness of GFRP - ZnO nanocomposites. 3.

Results and Discussion

3.1. Tensile properties for GFRP-ZnO Nanocomposites for Different wt.% of Polymer and WR as Reinforcement The three graphs plotted in Figs. 3.1, 3.2 and 3.3 shows the variation of Tensile strength and the influence of ZnO nanoparticles, when WR is used as reinforcement with three different weight percentages of polymers. From Fig.3.1 it is observed that Tensile strength for Pure GFRP composite (70/30 wt.% of polymer and Woven Roving as reinforcement) has a value of 73.82MPa. When reinforced with 1 wt.% ZnO nanoparticles, Tensile strength is improved from 73.82 MPa to 97 MPa. It is then observed that Tensile strength reaches a maximum value of 102.36 MPa at 2 wt.%, thus showing an improvement in Tensile strength of upto 38%. Later the Tensile strength is found to decrease by further reinforcement with ZnO nanoparticles beyond 2 wt.% and it reaches a value of 75.23 MPa by increasing the nano ZnO to 6 wt.%.

Fig. 3.1 Variation of Tensile strength at different % nano ZnO for 70/30 wt.% of polymer and Woven Roving as reinforcement

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From Fig.3.2 it is observed that Tensile strength for Pure GFRP composite (60/40 wt.% of polymer and Woven Roving as reinforcement) has a value of 95.42 MPa With reinforcement of ZnO nanoparticles. The Tensile strength is improved from 95.42 MPa to 121.46 MPa by reinforcing with nano ZnO upto 1 wt.% and reaches a maximum value of 135.06 MPa (41% improvement) at 2 wt.% of nano ZnO. Thus, a gradual decrease is observed by addition of ZnO nanoparticles beyond 2 wt.%, and it falls to 92.86 MPa at the 6 wt.% nano ZnO. This is similar to the trend shown in Fig.3.1 for 70/30 wt.% of GFRP - ZnO nanocomposites.

Fig. 3.2 Variation of Tensile strength at different % nano ZnO for 60/40 wt.% of polymer and Woven Roving as reinforcement

Tensile Strength(MPa)

Fig.3.3 explains a similar version of variation of Tensile strength for 50/50 wt.% GFRP - ZnO nanocomposite and the trend for the strength variation at different wt percents of ZnO nanoparticles is observed to be similar to the trends discussed in the above. This also confirms that the wt.% of synthesis of the materials vary their Tensile strengths, though they exhibit similar change in qualitative trend of Tensile strength with addition of nano ZnO particles. 180 160 140 120 100 80 60 40 20 0

165.45

149.44 120.2

117.42 90.24

0

1

2

3

4

5

6

%Nano ZnO Fig. 3.3 Variation of Tensile strength at different % nano ZnO for 50/50 wt.% of polymer and Woven Roving as reinforcement

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Fig3.4. SEM image of 2 wt.% nano ZnO filled GFRP nanocomposites

The comparative study of the above three graphs with different wt. percents of polymer and glass reinforcements show that the 50/50 wt.% yields higher Tensile strength at 2 wt.% due to good fiber matrix adhesion which is confirmed by the SEM image shown in Fig.3.4. The Fig.3.5 illustrates the synchronization of the graphical representations and the conclusions are drawn.

Fig.3.5 Comparison of different wt. percentages between tensile strength and % nano ZnO and WR as reinforcement

3.2. Hardness of GFRP-ZnO Nanocomposites 3.2.1 Hardness of GFRP - ZnO nanocomposites for different wt. percentages of polymer and Woven Roving as reinforcement Experimental results showed that the Hardness is improved from 30.4 to 38.3 by reinforcing by 1% wt. nano ZnO and to 39.6 by reinforcing 2% by wt. nano ZnO. Thus there is an improvement of 29.8% by reinforcing with 1 wt.% nano ZnO and there is an improvement of 30.2% by reinforcing 2 wt.% nano ZnO. It is evident that, there is not much difference in improvement of Hardness by reinforcing 1% and 2% by wt. of nano ZnO and also that there is a decrease in Hardness values after 2 wt.%. Graphs plotted for Hardness Vs wt.% nano ZnO in case of Polymer/WR (70/30 wt.%) in Fig.3.6 confirms this, along with the plots drawn for 60/40 wt.% and 50/50 wt.% GFRP - ZnO nanocomposites in which WR is used as reinforcement in Fig.s 3.7 and 3.8. This can also confirm that the wt.% of synthesis of the materials vary their Hardness, though they exhibit similar trend of path change in Hardness with addition of nano ZnO particles.

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Fig. 3.6 Variation of Hardness at different % nano ZnO for 70/30 wt.% of polymer and WR as reinforcemen t

Fig. 3.7 Variation of Hardness at different % nano ZnO for 60/40 wt.% of polymer and WR as reinforcement

Fig.3.8 Variation of Hardness at different % nano ZnO for 50/50 wt.% of polymer and WR as reinforcement

It is also observed from the comparative study of different weight percents of polymer and glass

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reinforcements that the 50/50 wt.% yields higher Hardness values as shown in Fig.3.9.

Fig. 3.9 Comparison of different wt. percentages between Hardness and % nano ZnO and WR as reinforcement

From the above Analysis, we observe that, the tensile strength and hardness increases with increase of nano ZnO particles initially and then decreases with further increase of nano ZnO particles as already discussed. It can be arrived that the optimal nano ZnO content for tensile strength is obtained at 2.0 wt% and the properties are decreased with higher filler content. The improvement of tensile properties by the addition of ZnO nano particles is due to the enhancement of fiber-matrix adhesion. Nano particles have high specific surface area and high surface energy to their small scales. Thus, they can react with macro molecular chains chemically and physically to enhance the interactions between fiber and matrix interfaces. The decrease of the tensile strength of the composites with more than 2 wt% ZnO nano particles may be attributed to the aggregation of excess filler in glass fiber polyester matrix. Furthmore, the aggregation behavior increased with increasing of ZnO nano particles content, indicating an increase in the incompatibility of the GFRP-ZnO nano composites with excess of ZnO content. 4.Conclusion The GFRP nanocomposites are synthesized with different wt.% of polymer with glass reinforcement of WR. These composites are reinforced with different wt.% of nano ZnO particle and conducted various tests to determine the Tensile strength and Hardness conducted on these composites. The analysis of experimental data has brought the following conclusions. 1. The ZnO nanopartcles showed an intense effect on the mechanical properties of the composites. The tensile strength and hardness of composites increased significantly by adding ZnO nanoparticles upto 2 wt% and further adding of ZnO nanoparticles decrease both Tensile strength and Hardness. The improvement of these properties by the addition of ZnO nanoparticles is due to the enhancement of fiber-matrix adhesion. The Decrease of both tensile strength and Hardness is due to agglomerates of ZnO nanoparticles. The agglomerates of ZnO nanoparticles can be the points of stress to damage the structure of the polymeric matrix, which results in decreasing of mechanical properties 2.

Reinforcements of GFRP-ZnO nanocomposites with low weight percentages loading of ZnO nanoparticles yielded enhanced tensile strengths and hardness compared to neat Glass reinforced polyester composites.

3.

In comparision with different weight percentages of polymer and Glass fibers, 50/50 weight percentage gives enhaced mechanical properties when compared to 60/40 wt%, 70/70 weight percentages.

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