Mechanical Properties and Water Absorption Behavior of ...

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ScienceDirect Procedia Manufacturing 2 (2015) 573 – 578

2nd International Materials, Industrial, and Manufacturing Engineering Conference, MIMEC2015, 4-6 February 2015, Bali Indonesia

Mechanical Properties and Water Absorption Behavior of Polypropylene / Ijuk Fiber Composite by Using Silane Treatment W. Z. W. Zahari1, R. N. R. L. Badri1, H. Ardyananta2, D. Kurniawan3 and F. M. Nor1* 1 2

Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, Parit Raja, Malaysia Department of Materials and Metallurgical Engineering, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia 3 Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Skudai, Malaysia

Abstract The rising concern towards environmental issues besides the need for more versatile polymer-based materials has led to increasing of interest in studying about the polymer composites filled with natural-organic fillers, which are coming from renewable sources. However, the bonds between polymeric materials and the organic fillers are not strong enough, by referring to mechanical properties. This study intends to the improvement in mechanical properties of polypropylene/ijuk fiber composite by pretreating the fiber using silane treatment. Vinyltrimethoxy silane was used for this silane treatment using immersion technique. Composites with 10wt%, 20wt%, and 30wt% fiber content were fabricated afterwards. The samples were tensile tested and the strength, modulus, and elongation were determined. The composite’s water absorption was also tested. As the result, the silane treatment helps increasing the mechanical properties and decreasing the percentage of water absorption of the composites. © by Elsevier B.V.by This is an open © 2015 2015Published The Authors. Published Elsevier B.V.access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and Peer-review under responsibility of the Scientific Committee of MIMEC2015. Selection and Peer-review under responsibility of the Scientific Committee of MIMEC2015 Keywords: Ijuk fiber; Composite; Silane treatment; Mechanical properties; Water absorption.

1. Introduction Environmental concerns have led to the interest to use green composites which are filled with natural fibers [14]. Besides the availability in large amount, low price, and biodegradability, these natural fibers are also able to impart composites certain benefits such as low density, simple fabrication processes, little health hazards, and high degree of flexibility [2]. * Corresponding author. Tel.: +607-5534853; fax: +607-5566159. E-mail address: [email protected]

2351-9789 © 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and Peer-review under responsibility of the Scientific Committee of MIMEC2015 doi:10.1016/j.promfg.2015.07.099

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Ijuk or also known as black sugar palm (Arenga Pinnata) fiber is an interesting candidate as the reinforcing natural fiber for composites. Ijuk has high tensile strength and durability since it takes very long time to biodegrade and its properties are little affected when exposed to heat, moisture, and even sea water [5,6]. Like other natural fibers, ijuk has disadvantage of being hydrophilic, which lowers the compatibility with hydrophobic polymeric matric during composite fabrication. In order to improve adhesion between natural fibers and polymer matrix, coupling or compatibilizing agents can be used. There are several chemical treatments that have been known to improve the natural fiber by modifying fiber surface properties. Alkaline treatment is among commonly used chemical treatments used on natural fibers to reinforce thermoplastic and thermoset matrices [7]. This treatment modifies the surface by disruption of hydrogen modification in the network structure [7, 8]. Silane is another commonly used chemical treatment as coupling agent for natural fibers. Silane coupling agent works by reducing the number of cellulose hydroxyl groups in fiber-matrix interfaces. In presence of water, hydrolysable alkoxy group leads to formation of silanols, which then reacts with hydroxyl group of the fibers, forming stable covalent bonds to cell wall that are chemisorbed onto the fiber surface [7]. Silane coupling agents were also found to be effective in modifying natural fiber-polymer matrix interface and increasing the interfacial strength [8,9]. This paper studies on the use of ijuk fiber that is treated using silane for use in composite with polypropylene matrix. The aim of the silane treatment is to enhance the mechanical properties and to reduce water absorption on the composites. 2. Experimental 2.1 Material For the reinforcement, ijuk was sourced from Indonesia. The fiber comes as long fibers and was cut to about 2 mm before being washed by soaking in water to remove dirt. Then, the now short fiber was dried in vacuum oven (Memmert UFE 500 from Memmert GmbH + co.kg) at 65 oC for 24 hours. The dried fiber was stored in sealed container until its use. The thermoplastic polymer as the matrix material is polypropylene (PP), provided by Lotte Chemical Titan (M) Sdn Bhd (Malaysia). For the chemical treatment, vinyltrimethoxy (C 5H12O3Si) was supplied in the form of liquid by Sigma Chemie GmbH (USA). 2.2 Silane treatment The short ijuk fiber was silane treated. Vinyltrimethoxy silane with 98% concentration was diluted in distilled water within composition 0.003l chemical in 0.997l distilled water. Magnetic-stirrer was used for 5 min to mix the solution. The fiber was then immersed for 15 min in the silane solution, followed by 2 h drying for hydrolyzing the coupling agent in vacuum oven at 100o C. The treated fibers was stored at room temperature in sealed container until next process. 2.3 Composite fabrication The composite fabrication process was carried out by using roll mill mixer PM-3000 (C.W Brabender Instruments Inc. N.J, M/no 174-6) by mixing up the treated fibers with PP at 190 oC at 10%, 20%, and 30% by weight of fibers with respect to PP. Then the compound was crushed by using plastic granulator to get pellets of composite. The pellets were then dried in vacuum oven at 65 oC for 24h. The molding composite samples was carried out by horizontal screw type injection molding (Nissei Plastic Industrial Co. Ltd, model NP7-1F). The mold was suited to make mechanical testing samples according to ASTM D 638-5. 2.4 Testing 2.4.1

Tensile test

Tensile test was conducted according to ASTM D 638-5 using Universal Testing Machine (Model AGS 10kNXD, Shimadzu). The test was performed at a crosshead speed of 1 mm/min [10].

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2.4.2

Water absorption

The water absorption tests of composites were carried out following ISO 527. To measure water uptake capacity of composite, the specimens were prepared and distilled water was the medium. From the difference of final and initial weights before and after immersion in water bath for 24 h, percentage of water uptake was calculated. In each test and type of composite, 5 specimens were tested and the average values were reported. The testing was carried out until the percentage of water uptake reach equilibrium. The calculation was based on equation 1 [11]. Mt% = Wt – Wo x 100 (1) Wo

2.4.3

Microstructural analysis

The morphology of the PP/ijuk fiber composite and the interfacial bonding between the fiber and the PP matrix was examined using analytical scanning electron microscope (SEM) model JSM-6380LA and Field Emission Scanning Electron Microscope (FESEM) model JSM-7600F JEOL Company Limited, Japan. The samples were viewed perpendicular to the fractured surface. The micrographs were taken at magnifications 350X and 1000X. All specimens were sputtered with a 5 nm thick layer of platinum coating using auto fine coating machine before inserted to the SEM [11].

3. Results and Discussion From the tensile test, the tensile strength, modulus, and elongation at yield for each composite were determined (Table 1). Table 1. Tensile test results

Material

Ijuk Fiber (wt %)

PP (wt %)

Tensile Strength (MPa)

Tensile Modulus (MPa)

Elongation at Yield (mm)

Neat PP

0

100

17.45

298.14

0.106

10

90

17.57

361.32

0.079

20

80

18.36

720.24

0.059

30

70

19.71

1052.40

0.052

10

90

20.21

1051.84

0.084

20

80

20.27

1066.30

0.065

30

70

23.00

1098.51

0.051

PP/ijuk fiber without silane treatment PP/ijuk fiber with silane treatment

3.1. Tensile Strength For composite with untreated ijuk fiber, strength remains the same (or increases slightly) at higher fiber content, almost similar to neat PP. The fact that tensile strength did not decrease at higher fiber content is a good indication of compatibility of the natural fiber to the matrix. For composite with silane treated ijuk fiber, tensile strength is higher that neat PP, and tends to increase at higher fiber content. This indicates the silane treatment works as coupling agent between the natural fiber and PP matrix, improving the interface strength [9,12].

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3.2. Tensile Modulus As expected, the Young’s modulus increases against the increasing percentage of fiber content. This comes from the high Young’s modulus of the ijuk fiber, and naturally, the more ijuk fiber content, the higher the stiffness of the composite. For composite with silane treated ijuk fiber, the Young’s modulus is already high even with only 10% fiber content. This might come from the better distribution of ijuk fiber within the PP matrix, contributed by the silane treatment [13]. 3.3. Elongation at break Contrary to results of Young’s modulus, the elongation at break for the composite decreases with increasing fiber content. This is as expected for natural fiber composites, where there is trade of between strength or stiffness and elongation at break. The values for both composites with untreated and silane treated ijuk fiber are similar, indicating that the improved interface did not contribute to improve the toughness of the composites. 3.4. Water absorption

Average Water Absorption , %

Figure 1 shows the water absorption of the neat PP and the ijuk fiber composites as a function of time. The composites’ water absorption stabilizes after 10 days of immersion in distilled water. Water absorption increases at higher fiber content. There was not much difference in water absorption between composites with untreated and silane treated ijuk fiber.

Water Absorption for Untreated (Ut) / Treated (Tr) Ijuk fiber/PP composite

1.5

0wt% - Neat PP Ut Ijuk 10wt%

1

Ut Ijuk 20wt% Ut Ijuk 30wt%

0.5

Tr Ijuk 10wt% Tr Ijuk 20wt%

0 0

5

Days

10

15

20

Tr Ijuk 30wt%

Fig.1. Water Absorption for PP/ijuk fiber composites

3.5. Morphology The effect of the surface treatment on the interface between the ijuk fiber and polypropylene was studied by referring to the fractured surface of the tensile test specimens (Fig. 2). For untreated composition, it shows there were gaps between the fiber and the matrix, indicating poor adhesion. The gaps were less apparent for composites whose ijuk fiber was silane treated. The narrower gaps between ijuk fiber and PP matrix for liane treated composites evidenced better compatibility. This was reflected by the higher mechanical properties to some extent.


Fig. 2. Image of fractured surface of composites with (a) untreated ijuk fiber at 10wt%, (b) untreated ijuk fiber at 20wt%, (c) untreated ijuk fiber at 30wt%, (d) silane treated ijuk fiber at 10wt%, (e) silane treated ijuk fiber at 20wt%, and (f) silane treated ijuk fiber at 30wt%.

4. Conclusions In the present study, silane treatment using vinyltrimethoxi silane on PP/ijuk fiber composite with fiber content of 10, 20 and 30wt% was performed. The silane treated composites showed higher strength and Young’s modulus while maintaining the elongation at break compared to untreated ones. Water absorption of the composites increases at higher fiber content, although there was not much difference in water absorption between composites with untreated and silane treated ijuk fiber. Overall, silane treatment performed in this study managed to improve adhesion between the ijuk fiber and the PP matrix.

Acknowledgements Financial supports from the Ministry of Education of Malaysia (through Fundamental Research Grant Scheme at Universiti Tun Hussein Onn Malaysia and Universiti Teknologi Malaysia no. 4F285) and from the Research and Technology and Higher Education Ministry of Indonesia are gratefully acknowledged.

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