Abstract
The electrical properties of chicken feather fiber (CFF) and kenaf fiber (KF) unsaturated polyester (UP) composites have been studied with reference to fiber loading and frequency. Tests were carried out to compare the suitability of the two different composites as a dielectric material. The chicken feather fiber unsaturated polyester composite exhibited an overall lower dielectric constant, dissipation factor, and loss factor compared to the kenaf fiber unsaturated polyester composites. The values were high for the composites with fiber contents at 40%. The dielectric value increments were high at low frequencies, and they gradually reached significantly lower values at higher frequencies. Based on the results it was judged that chicken feather fiber composites would be suitable for application as high speed printed circuit board (PCB) material with good frequency stability at 1 MHz. Finally, an attempt was made to correlate the experimental values with theoretical calculations.
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Comparative Study of Dielectric Properties of Chicken Feather/Kenaf Fiber Reinforced Unsaturated Polyester Composites
Kwong Siong Kiew, Sinin Hamdan, and Md. Rezaur Rahman *
The electrical properties of chicken feather fiber (CFF) and kenaf fiber (KF) unsaturated polyester (UP) composites have been studied with reference to fiber loading and frequency. Tests were carried out to compare the suitability of the two different composites as a dielectric material. The chicken feather fiber unsaturated polyester composite exhibited an overall lower dielectric constant, dissipation factor, and loss factor compared to the kenaf fiber unsaturated polyester composites. The values were high for the composites with fiber contents at 40%. The dielectric value increments were high at low frequencies, and they gradually reached significantly lower values at higher frequencies. Based on the results it was judged that chicken feather fiber composites would be suitable for application as high speed printed circuit board (PCB) material with good frequency stability at 1 MHz. Finally, an attempt was made to correlate the experimental values with theoretical calculations.
Keywords: Chicken feather fiber; Dielectric properties; Unsaturated polyester; Kenaf fiber; Biocomposite; Permittivity; Dielectric constant; Dissipation factor; Loss factor
Contact information: Faculty of Engineering, University Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia; *Corresponding author: mdrezaurr@gmail.com
INTRODUCTION
There has been an acceleration of research studies focusing on organic bio-composites obtained from agricultural reserves, prompted by concern about depletion of natural resources, or the unsustainability of inorganic fiber. Biocomposites are defined as composite materials containing at least one biological phase (Zhan et al. 2011). In the United States alone, approximately 2×109 kg of chicken feathers are generated every year (Parkinson 1998). The disposal of the feathers is carried out, in most cases, by burial, whereas an improved, more effective, and expectantly beneficial utilization of chicken feather waste is desirable (Cheng et al. 2009).
Feathers are composed primarily of keratin protein, with the three basic parts of the feather identified as the quill, the barbs, and the barbules (Huda and Yang 2009). Keratin is relatively hydrophobic. It has a similar strength to that of nylon, but a diameter smaller than that of wool (Cheng et al. 2009).
It is anticipated that chicken feathers, as part of the organic fiber family, will not suffer from the wear of the polymer processing equipment and size reduction during processing, both of which may occur with the use of inorganic fibers or fillers (Barone and Schmidt 2005). Moreover, organic fibers such as chicken feathers may offer the possibility of covalently bonding the matrix polymer to the fiber either directly or through a similar type of chemical coupling, such that chemical processing can be carried out more easily, as compared to inorganic fiber (e.g. glass fibers) (Barone and Schmidt 2005).
Kenaf and jute are warm-season annual row crops having a single, often straight, and unbranched stem. Kenaf and jute fibers have been used for rope, canvas, and sacking due to the easy availability, lightweight, low-cost, and other attractive features (Rashdi et al. 2009; Rahman et. al. 2008, 2010).
Zhan et al. (2011) demonstrated the use of chicken feather fibers with epoxy resin to produce composite samples and proposed their potential application for printed circuit boards (PCBs). An investigation of using soybean resins and chicken feather fibers was conducted by Zhan and Wool (2010) to evaluate feasibility for possible applications in electronic devices such as printed circuit boards (PCBs). In recent studies, the need to produce materials with improved electrical properties versus the standard epoxy offerings is crucial to the development of the PCB industry. In particular, improvements in the dielectric constant (permittivity) and dissipation factor (loss tangent) are the properties of interest, as materials with the lower values of these properties are needed for circuits to operate at high frequencies (Kelley 2007). Consumer printed circuit boards (PCBs) intended for applications such as mobile phones or computers typically require low values of dielectric constant and loss (Kelley 2007). Various dielectric studies have been conducted by researchers utilizing different kinds of fibers and matrices (Sreekumar et al. 2012; Kulshrestha and Sastry 2006; Rahman et. al. 2009; Bose et al. 2012; He et al. 2008; Sosa-Morales et al. 2010; Nuriel et al. 2000; Chand and Jain 2005; Zhou et al. 2012; Bhat et al. 2012; Barreto et al. 2010), but none have coupled the use of unsaturated polyester with chicken feather fibers or kenaf fibers yet.
The use of unsaturated polyester as the matrix for the composite has become increasingly popular with fiber reinforcements such as sisal fibers, flax fibers, hemp fibers, alfa fibers, and so on (Santhong et al. 2009; Haq et al. 2009a; Marais et al. 2005; Bessadok et al. 2009; Sawpan et al. 2012; Haq et al. 2009b). However, there have been few trials using a composite with chicken feather fibers or kenaf fibers.
In the present research, composites were fabricated using unsaturated polyester (UP) as a matrix material and chicken feather fibers (CFF) or kenaf fibers (KF) as the reinforcements. A dielectric study was undertaken for both composites to determine the suitability of each type of composite relative to its utilization as a dielectric material.
EXPERIMENTAL
Materials
The matrix material used in this study was based on the unsaturated polyester resin with the trade name ”Reversol P9509” supplied by Revertex (Malaysia) Sdn. Bhd. Company. This type of unsaturated polyester resin has a rigid, low reactivity, and thixotropic general purpose othophthalic characteristics. For curing, the matrix needs to be mixed with a curing catalyst, namely methyl ethyl ketone peroxide (MEKP) at a concentration of 1% by weight ratio of the matrix. For reinforcements, kenaf fibers and chicken feather fibers were used to complete the composite materials.
Fiber Preparation
The kenaf fibers obtained were drenched in hot water at 100˚C. The kenaf fibers were left to soak, washed in a water-soluble ethanol, and sun-dried for 7 h. To make sure that the fibers were completely dried, the fibers were left in an oven at 80ºC for 24 h. The kenaf fibers were processed using a round vibratory sieves machine to remove the chunks of fiber. The kenaf fiber lengths after the separation were 3 to 6 mm.
The chicken feather fibers were obtained from a local poultry farm as raw chicken feather materials. The chicken feathers were left to soak, washed in a water-soluble ethanol, and sun-dried for 7 to 8 h. To make sure that the materials were completely dried, the chicken feathers were left in furnace at 80ºC for 24 h. The raw chicken feathers obtained after the furnace were cut into sizes of 3 to 6 mm.
Specimen Preparation Method
All of the fiber matrix materials were degassed in a vacuum for a minimum of 5 min to remove the air bubbles before curing. The unsaturated polyester composites were cured with MEKP at a 1% weight ratio of the unsaturated polyester matrix. The mold was compressed using a cold-press and left for 24 h. Each mold trial was comprised of three fiber composite samples. The dimensions presented for each fiber composite was disc-shaped with a diameter of 500 mm and a thickness of 5 mm. A schematic of the mold press is shown in Fig. 1.
Fig. 1. Dielectric mold
Composite Testing
The HP 16451B dielectric test fixture with an HP LCR impedance analyzer was utilized to obtain the dielectric properties of unsaturated polyester chicken feather fiber and kenaf fiber composites. The samples were analyzed using a contacting electrode method, which uses a rigid metal electrode. The samples fabricated have flat surfaces and low compressibility. Hence, by using this method, it can raise the accuracy of the measurement. The tests were done in the frequency range of 60 Hz, 1 KHz, 10 KHz, 100 KHz, and 1 MHz. The sample studies were disc-shaped with a diameter of 500 mm and a thickness of 5 mm. The average value was recorded by the HP impedance analyzer after the samples had been tested 15 times at a given frequency.
The dielectric constant (r) of the testing materials can be calculated from the capacitance using the equation,
(1)
where t is the thickness, C is the capacitance, r is the radius of the test specimen, and is the dielectric constant of the free space.
The loss tangent (tan δ) can be obtained directly from the HP impedance analyzer. Table 1 shows the fiber ration and actual fiber content (%) in composites.
Table 1. Fiber Content (%) in Composites
RESULTS AND DISCUSSION
Permittivity Measurement
The dielectric constant of a material is defined as the ratio of the capacitance of a condenser containing the material to that of the same condenser under vacuum (Sreekumar et al. 2012). Figures 2 and 3 represent the dielectric constant of unsaturated polyester CFF composites and KF composites as a function of the fiber content and the frequency at room temperature, respectively. As observed from both Figs. 2 and 3, the dielectric constant of the unsaturated polyester CFF and the unsaturated polyester KF increased over the range of frequencies at the given orders of UP>CFF10>CFF20> CFF30>CFF40 and UP>KF15.8>KF21.83>KF37.25>KF43.5. The increase of the value is mainly contributed by the interfacial, orientation, atomic, and electron polarizations in the material (Kulshrestha and Sastry 2006). The polarization of the matrix and fillet contribute to interfacial polarization. An increase in the fiber loading of the CFF leads to increased orientation and interfacial polarization, which results from the polar groups’ presence in the cellulose fibers (Sreekumar et al. 2012).
Other work has shown that unsaturated polyester has low dielectric constant values over the range of frequencies considered; this is because it only has induced atomic and electronic polarizations to account for (Kelley 2007). As shown from a single fiber loading trend, the dielectric constant is always highest at the lowest frequency due to the increase in orientation polarization at lower frequencies (Sosa-Morales et al. 2010). The process of complete orientation polarization is achievable only at lower frequencies, and this formulates the decrease in the dielectric constant as the frequency increases. The term is called “lag in orientation of polarization” (Sosa-Morales et al. 2010). Figure 4 compares the dielectric constants of the KF composites and the CFF composites at 20% fiber loading and 40% fiber loading, respectively. It can be seen that the KF composites exhibited high values at low frequencies and low values at high frequencies. In comparison with the KF composites, the CFF composites showed a better frequency stability at all ranges of frequencies. This is largely due to the physical attributes of the CFF, which is lightweight and in comparison to the kenaf fiber, the amount of fiber loading does not contribute to the same volume attributes. The CFF has a greater volume of fiber than the KF when comparing with the same mass amount of fiber loading. The greater volume of fiber contributes to more orientation and interfacial polarization in the CFF composites than the KF composites. Furthermore, the hollow structure of the chicken feathers incorporates air (dielectric constant = 1.0), which also contributes to the fact that the dielectric constant decreases with the increasing fiber contents (Zhan et. al. 2011).
Fig. 2. Dielectric constant of CFF/UP composites as a function of fiber content and frequency at room temperature