Effect of Kenaf Core Fibre (Hibiscus cannabinus) as one of the Dispersing Phases in Brake Pad Composite Production

Brakes are essential parts of all means of transportation. Their function is to slow or stop a vehicle by friction. Asbestos has been widely used in the production of brake pads. However, its application poses adverse effects on human health and the environment. The aim of this study was to determine the effect of kenaf core fibers as one of the dispersing phases in brake pad composite production. The materials and methods employed in the study, followed procedures in established standards and literatures. The materials were grounded into fine powder and sieved into grade sizes of 100 µm and 200 µm. They were weighed on a digital scale according to a specified composition and mixed thoroughly for about five (5) minutes to obtain homogeneity of the mixture. Afterwards, the mixed compositions were placed inside a 5 cm × 3 cm × 2 cm cylindrical mould. These mixtures were then compacted on a hydraulic press and allowed to dry at an ambient temperature of 37°C. A series of physio-mechanical tests such as porosity, ash content, density, compressive strength, hardness and wear rate were conducted on the developed brake pad samples as well as the control samples. The results showed that the average values for porosity, ash content and density of the developed samples enhanced with kenaf core fibres were 0.813%, 57.25% and 1.389 kg/m3 respectively. These values compare well with that of the control samples. Also, the hardness, wear rate and compressive strength of the samples enhanced with kenaf fibers gave average values of 121.25 BHN, 10.121×10-2 g/km and 105.75 MPa respectively. These values also compare well with that of the control samples. From the results gotten and all the properties determined, the study showed that kenaf core fibres has good potentials as dispersing phases for brake pad composite production.


INTRODUCTION
Brakes are important parts of any means of transportation. They help to slow or stop a vehicle by friction, converting kinetic energy to heat energy which is then dissipated. In the past asbestos and some semi metallic materials were used to manufacture brake pads. Asbestos became progressively more popular among brake pad manufacturers because of its sound absorption, average tensile strength, and resistance to heat, electrical and chemical damage. However, studies have shown that they are carcinogenic. They release tiny particles suspension to the atmosphere as the pads wear out in service. When inhaled, these dusts can cause certain health issues including a number of lung and brain diseases [1]. There is a paradigm shift from the use of asbestos in the manufacturing industry as many researchers are continually carrying out various research works to evaluate other materials that can serve as a preferred alternative to asbestos [2]. Semi-metallic brake pads in the other hand produce much noise and dust. This no doubt, encourages noise and air pollution, needless to talk about the attendant respiratory diseases the dust could cause [3]. This is why researchers are continually seeking to develop other materials that could offer competitive performance like the asbestos and semi-metallic brake pads. worked on the evaluation of palm kernel fibers (PKFs) for production of asbestos-free automotive brake pads. The results were compared with commercial asbestos based brake pads. Results showed that PKF can be suitable for replacement of asbestos brake pads with epoxy resin as a binder. The samples however, exhibited a relatively high wear rate which is not desirable for a brake lining material. Akuet al., (2012) studied the use of periwinkle shell as a potential material for asbestos free brake pad using spectroscopic and wear analysis [5]. They found out that periwinkle shell could be used for the production of non-asbestos brake pad. Thermal decomposition was observed in terms of global mass loss by using a DTA/TGA thermo-gravimetric analyzer. Fourier transform infrared spectrometry (FTIR) was also carried out on the periwinkle shell particles [6]. The result of these tests showed a lower density than that of the asbestos brake pad. The various results obtained were compared with asbestos which confirmed that periwinkle shell can be used as a material for brake pad production [7]. Although, all these researchers have carried out various research works on the related study but none of them have used Kenaf core fibre as a dispersing phase as a possible mix in a typical palm kernel-based brake pad composite [8]. Hence, considering the various challenges connected to brake pad formulation and utilization, the aim of this study was to determine the Effect of Kenaf Core Fibre (Hibbiscus cannabinus) as one of the Dispersing Phases in Brake pad composite production [9]. Kenaf plants are natural occurring plant fibres that grow rapidly in any type of soil [10]. They reach 12-18 feet in 150 days and are readily available. Studies have also shown that Kenaf fibres have good mechanical properties ranging from high hardness to high compressive strength [11].

METHODOLOGY
The methods used to achieve the stated objectives followed established standards and published journals. The study was purely experimental. The methods are classified into the following: • Kenaf core fibre extraction and preparation • Brake pad sample production • Physio-mechanical properties determination • 2.1 Kenaf core fibre extraction and preparation: A Kenaf core fibre was extracted from the kenaf stem using water retting process. This process ensured the degradation of the pectic materials, hemicellulose and lignin and also improved the quality of the fibre. The fibre was placed in water for 14-24 days and the bast was separated from the core. 2.2 Brake pad sample production: In order to assist fibre dispersion, the composite materials were grounded into fine powder & sieved into grade sizes of 100μm and 200μm. The components were mixed using the composition shown in the

6.
Resin 20 20 20 20 The mixtures were then placed inside a cylindrical mould with of 5cm height x 3cm radius. These mixtures were then compacted on a Hydraulic press. Thereafter the moulded materials were removed and allowed to dry at ambient temperature of 37 o C.

Physio-Mechanical Properties Determination
i. Porosity Test: This was evaluated from the formula as stated by [12].
(3.1) D = density of water; M2 = the mass of test sample after absorbing water (g); M1 = mass of test sample before absorbing water (g); v = Volume of test sample (cm 3 ).

ii. Ash Content Determination
About 1.20g of the samples were weighed in a cooled crucible which was oven dried by heating in a furnace to 550°C for about 1 hour. Then the samples were charred. The samples were then cooled in a desiccator and weighed. The ash content formula is in line with that of Bala (2017) and was calculated according to the formula below: Where ܹ0= weight of empty crucible; ܹ1 = weight of crucible + sample; ܹ2 = weight of crucible and residue i.e. after cooling.

iii. Density Test
A clean sample was weighed accurately in air using an electronic pocket scale and then suspended in water. The weight of the sample when suspended in water was determined and the volume of the sample was determined from the effect of displacement by water. The formula below was then used to calculate the sample density: Density (ȡ (3.3) Where m = the mass of test sample (g) and v = the measuring volume of test piece (cm 3 ) by liquid displacement method iv.

Brinell Hardness Test
This was determined by a Brinell hardness tester with 10 mm steel ball indenter and applied force of 2 KN. The samples were placed on anvils acting as support for the test samples. A minor force was applied to the test sample in a controlled manner then the major force was applied. The reading was taken when the large pointer came to rest and dwelled for about 4s. The load was then removed by returning the crank handle to the latched position and the hardness values was noted from the digital scale. v.
Wear Rate Test The sample was tested by using pin on wear tester. The sample weight was taken before and after test using a digital measuring scale. The weight difference of each sample indicated the loss in weight. The tester provided a friction temperature range of 110°C which was adjusted. The sample was fixed in the tester which rotated with a speed of 1000 rpm for 5 minutes. The disc diameter was 200 mm. The wear rate was then calculated using the formula (Madeswaran 2016)     Table 3.1 shows the results of the porosity values for the developed brake pad composite samples and that of the control. It can be seen that as the percentage of Kenaf core fibre increases for each sample, the porosity values decrease [13,20]. Also, as the particle sizes increases for each sample, the porosity values of the sample increases. This was attributed to the fact that as the sieve size increases, an increase in the number and size of pores in the samples will allow more water molecules to seep in. The YDOXHV REWDLQHG IRU WKH ȝP VDPSOH UDQJHV IURP -0.84% while WKH YDOXHV REWDLQHG IRU WKH ȝP VDPSOHV KDV KLJKHU SRURVLW\ RI -0.90% for samples A to D [14]. It can also be seen that the average porosity of the sieve grade samples as the percentage of kenaf core fibre increased were found to be 0.813% and 0.853% respectively [21][22][23][24]. The average porosity value for each percentage increase in kenaf were compared to that of asbestos brake pad (0.9 %) and they are within the range of a standard brake pad [24,26]. Table 3.2 shows the results of the ash content values for the developed brake pad composite samples and that of the control [26,32]. It can be seen that as the percentage of kenaf increases, the ash content increases for each sample. Also, the ash content decreases as the particle size increases for each sample [32,34] 7KH ȝP VLHYH JUDGH VDPSOHV JDYH UHVXOWV ZLWKLQ WKH UDQJH of 45 -IRU VDPSOHV $ WR ' ZKLOH WKH VDPSOHV ZLWK ȝP JDYH YDOXHV EHWZHHQ -69%. The average ash content value for percentage increase in kenaf compare well to that of asbestos brake pad (56%). This value also compares well with the research carried out by [19]. Table 3.3 shows the results of the density values for the developed brake pad composite samples and that of the control. It can be seen that the density values generally decreased as the percentage composition of Kenaf increased from sample A to D. This is due to the fact that the density of Kenaf being an organic material is less dense hence, as more of it is added, the density of the sample reduces [34,35]. It can also be observed that as the particle sizes increased, the density YDOXHV LQFUHDVHG 7KH ȝP VLHYH JUDGH VDPSOH JDYH UHVXOWV UDQJLQJ IURP kg/m 3 -1.511 kg/m 3 for VDPSOHV $ WR ' ZKLOH WKH VDPSOHV RI WKH ȝP JDYH YDOXHV EHWZHHQ kg/m 3 -1.621 kg/m 3 . The average density value for each sieve size were compared to that of asbestos brake  [36][37][38][39]. These values compare well with that of Idris (2013) who worked on eco-friendly asbestos free brake-pad using banana peels. Figure 3.1 shows the results of the hardness values for the developed brake pad composite samples and that of the control [40,41]. It can be seen that as the percentage of Kenaf fibres increases for each sample, the hardness values of each sample increases [42,44]. Also, as the particle sizes increases for each sample, the hardness values of each sample decreases. It was observed that the EULQHOO KDUGQHVV YDOXHV REWDLQHG IRU WKH ȝP VDPSOH UDQJHV IURP -146 BHN while the YDOXHV REWDLQHG IRU WKH ȝP VDPSOHs had values ranging from 106 -132 BHN for samples A to D [45,46]. The average hardness obtained from the hardness test for this material (129.5 BHN) compares with that of the control (standard brake pad hardness value of 101 BHN) and was seen to be within the range. This value is also in line with what [47] reported in his work. Figure 3.2 shows the results of the wear rates for the developed brake pad composite samples and that of the control. As the percentage composition of Kenaf fibres increased, the wear rate decreased [48][49][50]. Also, it was seen that the wear rates increased as the particle sizes increased. 7KH ZHDU UDWHV RI WKH ȝP VDPSOH JDYH UHVXOWV UDQJLQJ IURP -4.162(×10 -2 ) (g/km) while WKH ȝP VDPSOH JDYH YDOXHV IURP -5.379 (×10 -2 ) (g/km). The values also compare well with that reported by [51,54]. Figure 3.3 shows the result of the compressive strength of the produced samples with percentage increase in kenaf core fibre [55,56]. It can be observed that the compressive strength of each sample increased gradually as the percentage of Kenaf increased. Also, the compressive strength decreased as the particle size increased [57]. This can be attributed to the fact that the surface area and pore packaging capability of the filler in the resin are decreasing with increasing particle size. 7KH ȝP VLHYH JUDGH VDmples gave the higher compressive strengths of 99 -126 MPa for VDPSOHV $ WR ' ZKLOH WKH VDPSOHV RI ȝP JDYH YDOXHV EHWZHHQ -102 MPa. It can also be seen that the average compressive strengths of the samples are 107.75 MPa and 98.5 MPa respectively [58]. The average compressive strength for each particle size with increasing kenaf also compares well to that of asbestos brake pad (110 MPa) and showed better properties [31].

CONCLUSION
The research was carried out with as much waste and eco-friendly material as possible and these materials can be sourced locally. Four test samples of brake pad composite enhanced with kenaf core fibers were made with two different particle sieve sizes, 100 ȝm and 200 ȝm. These samples were then tested for hardness, compressive strength, ash content, porosity, density and wear rate [32]. The results were compared with brake pad composites produced from asbestos, as the control. The following conclusions can be drawn from the study: x The 100 ȝm particle size samples of Kenaf gave the best brake pad sample properties in all. The porosity, density and wear rate of the produced samples decreased in value as percentage of kenaf core fibre increased, while the ash content, hardness and compressive strength increased as percentage of kenaf increased [59,61].
x As the particle size increased, ash content, hardness and compressive strength of the produced samples decreased in value, while the density, porosity rate and wear rate increased as particle size increased. Based on the above test results of these brake pads composite, Kenaf core fibre can be used as a dispersing phase for brake pad composites, because the derived properties are within the range of that of the standard commercial brake pads.

Recommendation
More research should be encouraged in the production of brake pads from organic and locally available materials. The government should empower more universities with proper testing laboratories so as to ease stress and economies of testing.