Elsevier

Materials & Design

Volume 31, Issue 10, December 2010, Pages 4960-4964
Materials & Design

Technical Report
Degradation of compressive properties of pultruded kenaf fiber reinforced composites after immersion in various solutions

https://doi.org/10.1016/j.matdes.2010.04.037Get rights and content

Abstract

In this paper, water absorption behavior of pultruded kenaf fiber reinforced unsaturated polyester composites was investigated. Residual compressive properties of the composites after immersion were also reported. Composites were prepared using pultrusion method with minimum kenaf fiber content of 70% w/w. Water absorption tests were performed at room temperature under three different solutions, i.e. distilled water, sea water and acidic solution. The diffusion coefficient of water absorption and maximum moisture content were calculated by measuring the water uptake of specimen at regular time interval. Diffusion coefficient and the highest moisture content values were recorded for composite immersed in distilled water followed by acidic solution and sea water. The water absorption of kenaf fiber reinforced unsaturated polyester composites was found to follow a Fickian’s behavior where it reach equilibrium. The compressive properties were found to decrease with the increase in the percentage of water uptake. The decay in compression properties is attributed to the plasticization of the fiber–matrix interface and swelling of the kenaf fiber.

Introduction

Natural fibers form an alternative for most widely applied synthetic fiber in composites technology and manufacturing. The interest in natural fiber was known because it is cheap and lighter in weight which provides better stiffness per weight than glass. Furthermore, natural fiber source is renewable where it considered being green and environmentally friendly. By their fairly good mechanical properties the usage of natural fiber are retained in all sort composite preparations. Unlike natural fiber, synthetic fibers like glass have been used as reinforcement in composite manufacturing via various fabrication methods. Similarly, if natural fiber reinforced composites (NFRC) were to offer an alternative fiber to the composite industry, it has to accommodate all the processing avenues of it counterpart, glass fiber.

There exist many natural fibers which have been explores such as sisal, jute, flax, hemp, etc. One of the popular natural fibers is kenaf fiber. These kenaf is an annual plant due to its rapid growth and it is an inexpensive and a renewable source plant. Kenaf fiber is obtained from the bast of stems of plants genus Hibiscus, family of Malvaceae, species of H. cannibinus and requires less water to grow because it has growing cycle of 150–180 days with average yield of 1700 kg/ha [1].

Similarly, various composite manufacturing techniques available such as, RTM, compression moulding etc. However, some of these techniques require fiber in the continuous form which is not readily available form of natural fiber. In the case of engineering composites, filament winding and pultrusion methods are most popular. Pultrusion is a unique processing technique for composite manufacturing. Pultruded composite is always associated with high strength, stiffness which particularly due to high fiber content, i.e. 70%. So, pultrusion is among a few composite processing techniques that could process composite with up to 70% fiber content in unidirectional fiber configuration. It is a continuous molding process to manufacture a composite by using continuous fiber and liquid resin. The impregnation is accomplished by guiding the reinforcement over and under rods located below the resin surface [2]. The fiber is dipped into impregnated resin bath and emerges via shape guidance before being heated in the die. Finally the composite is left to cool off before being pulled and cut into the required length.

As we know, our surrounding area is full of moisture and air. All types of polymer composites will absorb moisture to a certain extent when immersed in water or exposed to humid environment [3]. In fiber reinforced polymer (FRP), not only polymer matrix that absorb moisture but also the fiber especially the natural fiber. This particularly due to the hydrophilic nature of the natural fiber that is more sensitive towards water absorption than synthetic fiber which causing instability in the properties of the composites [4]. There are three different mechanisms that conduct the moisture penetration into composites materials namely: (1) diffusion of water molecules into the micro gaps between polymer chains, which is the main mechanism, (2) capillary transport into the gaps and flaws at the interfaces between fibers and polymer, due to incomplete wettability and impregnation, and (3) transport by micro cracks in the matrix, formed during the compounding process [4]. It has been demonstrated that the water absorption affect the performance of natural fiber reinforced composites [3], [4].

In this study, kenaf fiber reinforced polyester composites were immersed in three different solutions; distilled water, seawater and acidic solution at room temperature. The water absorption behaviors of the composites under these three different solutions were evaluated. Composite samples in the form of compression test specimen were used. Compression properties before and after immersion were analyzed and discussed.

Section snippets

Materials

Kenaf fiber was obtained from herbaceous annual plant extracted from stem provided by Malaysian Tobacco Board (LTN), Malaysia. The polyester resin used for the study was purchased from Revertex (Malaysia) Company.

Preparations of composites

Unidirectional Kenaf fiber reinforced unsaturated polyester composites were prepared using pultrusion technique. The kenaf fiber is stored in a creel stand, and was then guided into preheating chamber. Kenaf yarn was then pulled through resin bath and followed by the heated die where

Water absorption

Water absorption behavior of the composite is one of the main concerns in composites structural applications especially for natural fiber reinforced composites. For a given composite system, the water absorption characteristic depends on the content of the fiber, fiber orientation, temperature, area of the exposed surface, permeability of fibers, void content and hydrophilicity of the individual components [3], [6], [7], [8], [9]. Fig. 1 shows percentage of weight gain as a function of square

Conclusions

The effect of water absorption on the mechanical properties of pultruded KFRPC has been studied following immersion in distilled water, seawater and acidic solutions at room temperature. From the results obtained the following conclusions can be drawn:

  • (1)

    All specimens show a Fickian water absorption behavior regardless of three different solutions studied.

  • (2)

    Highest value of diffusion coefficient (D) and maximum moisture content (Mm) value was recorded for specimen immersed in distilled water then

Acknowledgements

The authors wish to thank Construction Industry Development Board of Malaysia (CIDB) and Universiti Sains Malaysia (USM) for their raw material supply and financial assistance.

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