Suitability of Cow Horn as Filler in an Epoxy Composite

: This study focuses on assessment of cow horn as filler in an epoxy composite. A particle-reinforced composite was developed using horn particles (HP) and epoxy resin with filler of varying percentage weight (5%, 10%, 15%, 20%. 25%, 30%, 35%, 40 %) at particle sizes of 100 and 150 μ m. The composites were developed by hand lay-up technique with varying process parameters. The properties of the developed composites were examined through tensile, flexural and impact tests. The results showed that the tensile properties of the polymers reduced with the incorporation of the cow horn as filler. But at higher curing temperature, a better strength was achieved. Meanwhile, the flexural and impact properties of the polymers increased with the incorporation of the fiber in no particular order. The composite materials with particle size of 100 µm with curing temperature of 80 o C exhibited higher tensile (37.58 MPa) and impact properties (74 J) than the lower particles. Generally, the cow horn was found to be a good potential filler in the composite if prepared using higher curing temperature as exhibited through its mechanical properties.

Failure of materials in service and its consequences have been major concerns amongst Engineers leading to emergent of modern materials for different engineering applications. Modern engineering materials include metals, polymers, ceramics and composites. Ceramics, although are strong in compression, but generally weak in tension. Meanwhile, metals tend to have equal strengths both in tension and compression; composites have been developed to overcome the deficiencies of members of a particular class of materials (John, 1992). With extensive applications of polymers and its composites, due to their excellent mechanical properties, the demands for the materials are increasing (Fang et al., 2017). There are different composites that have been considered over time in lieu with optimizing materials to achieve good mechanical properties. Natural fibers are being considered as an alternative reinforcement in polymer composite due to their advantages over conventional glass and carbon (Saheb and Jog, 1999). These advantages include low cost, comparable specific tensile properties, renewability, recyclability, biodegradability, less health risk, non-irritation to skin, and non-abrasive to the equipment (Malkapuram et al., 2009). Generally, polymers are classified as thermoplastics and thermosetting. Thermoplastic materials currently dominate as matrices for bio-fibres (Malkapuram et al., 2009). The most commonly used thermoplastics for structural applications are polypropylene, polyethylene, and poly vinyl chloride (PVC); while phenolic, epoxy and polyester resins are the most commonly used thermosetting matrices (Malkapuram et al., 2009). Most plastics possess low impact strength in their natural forms (American Chemistry Council, 2019); hence there is need for reinforcement which enhances the mechanical properties. Reinforced polymer composite has found its applications in variety of places such as the automobile industry like the car bumper, among others. Although, this bumper has been produced to possess good mechanical properties, but has tendency to break when subjected to little or no impact forces, which has become a problem to Engineers (Mazumbar, 2001). Meanwhile, studies revealed that the manufacturers were able to meet automotive requirements of cost, appearance and performance utilizing composites (Mazumbar, 2001). Currently, composite body panels have a successful track record in all categories from exotic sports cars to passenger cars to small, medium, and heavy truck applications. In 2000, the automotive industry used 318 million pounds of composites. Because the automotive market is very cost-sensitive, carbon fiber composites are not yet accepted due to their higher material costs.
Epoxy resins are thermosetting polymers with good chemical resistance, high mechanical properties and thermal stability, high adhesive strength as well as high electrical insulation (Agarwal et al., 2017). For high performance applications in aerospace and marine structures, epoxy resins are used. This is as a result of its ease processing, hot and wet strength in conjunction with excellent mechanical properties in composites (Mukhopadhway, 2005). According to Mukhopadhway (2005), superior mechanical properties and better resistance to degradation made the performance of epoxy to be similar to that of polyester. Reinforcement could be either fiber reinforced, particle reinforced, flat flakes reinforced or filler reinforced. Fillers are added to a polymer formulation to reduce the costs and improve the properties. Fillers can either be solid, liquid or gas. They occupy space and replace the expensive resin with less expensive compounds without modifying other characteristics.
In this study, cow horn is being considered as the filler in an epoxy composite, being a material containing fibrous protein material called keratin (McKittrick et al., 2012). It has been regarded as a viable reinforcing material. It is a tough, resilent, very ductile material that possesses highly resistant to impact with its reasonable amount of carbon present (Kumar & Boopathy, 2014;McKittrick et al., 2012). This study therefore aims at testing cow horn as a suitable composite reinforcing material (filler) and imperative to produce composite with excellent mechanical properties which are also quite affordable as well as possess vast applications.

MATERIALS AND METHODS
The materials used in this study include cow horns; epoxy resin and catalyst which were respectively obtained at Sobi-Ilorin abattoir (Kwara State, Nigeria) and from a local vendor at Ojota, Lagos State, Nigeria. The cow horn was thoroughly washed and air dried to remove debris on it. Subsequently, the air-dried cow horn samples were oven dried using a conventional oven at 100 o C for 126 hours to completely remove moisture in the horn. Figure 1 shows the cow horn samples in the oven for drying. The dried cow horn samples were crushed using a SNE FOURE Hammer Mill and then transferred to a "Broyeur-clero" ball mill ( Figure 2). The milling operation was carried out for 22 hours. The milled cow horn was then sieved manually, using 100 microns and 150 microns sieves, to segregate two different sizes of horn particles. Production of Epoxy Composite: The epoxy and each of 100 and 150 μm cow horn (were separately measured using an electronic measuring scale in different ratios as presented in Table 1 and kept separately in different containers ( Figure 3a). In activating the resin, it was gradually mixed with the catalyst (hardener). A lot of care was taken at this stage, since rapid mixing might allow air bubbles to get trapped into the mixture. The weighted cow horn samples were then added to this mixture and mixed for about 5 minutes till homogeneity was attained. The Mixture of cow horn and resin is shown in Figure 3b.
The cow horn and epoxy were then poured into the wooden mould ( Figure 4a) and allowed to cool. The moulds were left, after proper marking, for natural curing at room temperature for 72 hours (Figure 4b).
To reduce the negative effects of polymerization shrinkage and increase hardness and wear resistance of the lightly cured resin composite samples ( Figure  4c), post curing (heat treatment) of the specimens was done in a conventional oven at varying curing temperatures of 60 and 80 o C.
This process was also to further harden, set the cast epoxy resin composites and to increase its mechanical properties. This process was in line with the practice of earlier researchers (Irawan et al., 2011;Khondker et al., 2005;Bello et al., 2015).

Determination of the Corn Horn Elemental Chemical
Composition: The external cover of the horn (hoofs) were removed and soaked in water to make them free of blood and dirty materials. Subsequently, the cleaned horn was cut into smaller chips and rewashed in hot water and later sun-dried for 15 days. The elemental chemical composition of the corn horn sample was carried out using Shimadzu 720 XRF Analyzer (Maker: Shimadzu Cooperation, Japan).    Figure 6) . The thickness of each of the samples was measured at three different positions along the length of the specimen and the average thickness was used for calibration. The test speed used was 5.0 mm/min with the gauge length fixed at 57.00 mm. Eight samples were tested for each test type. The flexural samples were prepared and the test was carried using ASTM D790-03 as a guide. The flexural test was evaluated using three-point bending flexural test, as recommended in ASTM D790-03 (Pham et al. 2014;Irawan et al., 2011;Kumar and Sankar, 2019). Figure 7 (a and b) shows the pictorial flexural test sample dimensions as stipulated in ASTM standards and the impact machined used for the test respectively. The samples for the impact test were prepared as presented in Figure 8 and the test was carried out in accordance with the guidelines in ASTM D256-04 standard at Department of Mechanical Engineering, University of Ilorin, Nigeria.

RESULTS AND DISCUSSION
The results of the elemental chemical composition of the corn horn sample are presented in Table 2. The major component was Sulphur (78.23 %), while calcium (8.10 %) and Molybdenum (5.80 %) constitute another significant element in the material. The values of the elemental composition of the corn horn were within the range values earlier discovered by Abdullahi and Salihi (2007).  horn. This might be as a result of poor compatibility between the matrix and cow horn particle. According to (Kumar et al. (2017), effective load transfer between the matrix and the particles serves as the base for the tensile strength of a particle-reinforced polymer matrix composite. Addition of cow horn as filler decreased the tensile strength of the composite in no particular order. Considering specimen c40, the tensile strength of the composite was found to be 8.  Duraisamy et al. (2017), horse particles in the composite create weakness in the adhesive force between the resin and the filler (horse particle) because horse particle acts as stress concentration points. Thus, the strength of the virgin epoxy composites decreases.   & 10), it is obvious that the specimens of 100μm particle size had better tensile strength values than specimens of 150μm particle size. According to Fu et al. (2008) particle size, good bonding strength between fibre particles and resins, and particle loading are parts of factors that affect the strength.  At specimen c40, the flexure strength of the composite was found to be 41.34 MPa for sample with curing temperature of 80 0 C, but recorded a low flexural strength value for sample with curing temperature of 60 0 C (5.398 MPa). Considering specimen c35, the flexural strength of sample with curing temperature of 80 0 C and that sample with curing temperature of 60 0 C were little or no difference in values of 30.21 MPa and 30.74Mpa respectively. This might be as a result of a good compatibility between the horn particles and the epoxy at that composition (Kumar et al. 2017). For specimen c30, there was a drastic drop in the flexural strength to 5.06 MPa for sample with curing temperature of 80 0 C and a value of 18.47 MPa for sample with curing temperature of 60 0 C. Low flexural strength values were recorded for specimens' c25 and c20 in an ascending order. Specimen c10 also exhibited a high flexural strength for sample with curing temperature of 80 0 C (33.05 MPa). At specimen c5, the flexural strength value was 7.09 MPa for sample with curing temperature of 80 0 C and 5.31 MPa for sample with curing temperature of 60 0 C. The results revealed that the post curing temperature has a noticeable effect on the flexural strength of the composite. From the obtained results, the highest flexural strength was obtainable with sample c5, 100 μm particle sizes with curing temperature of 80 0 C. Figure 12 shows the flexural strength variation of the various specimens at 150 μm. Generally, the specimens' flexural strengths were between 5. The results revealed an increase in the flexural strength values of specimen p100 with addition of cow horn. Also, addition of cow horn of particle size 150μm as filler in the composite increased the flexural strength of the composite in no particular order. In Figure 13, the impact energy variations for the various specimens at 60 0 C are presented. In general, the specimens' impact values ranged between 69 and 74 J for samples of 100 μm particle size, and between 69 and 72 J for samples of 100 μm particle size. The results indicate that the impact energy of p100 was 68 AMBALI, IO; SHUAIB-BABATA, YL; ALASI, TO; AREMU, IN; IBRAHIM, HK; ELAKHAME, ZU; ABDULRAMAN, SO J. Specimen c40 has impact energy of 72 J at 100 μm particle size and impact energy of 68 J at particle size of 150 μm. Specimen c30 has the same impact value of 71 J at both size variations. Specimen c25 recorded the highest the impact energy of 74 J at 100 μm. Specimen c20 has an impact energy value of 70 J and 69 J at particle sizes of 100 μm and 150 μm respectively. Specimen c15 also recorded an impact value of 69 J and 70 J at 100 μm and 150 μm respectively. Specimen c10 has impact energy of 71 J at 100 μm particle size, while at 150μm particle size impact energy of 69 J was recorded. Specimen c5 also has the same impact energy at both size variations (100 μm and150 μm particle sizes) with a value of 69 J. From the results obtained, specimen c25 has the highest impact energy (74 J) with particle size of 100 μm. Though, c40 recorded very close impact energy value of 72 J with particle size of 150 μm. The increase in the impact strength of the new composite is an indication of good bonding strength of the specimens.
Conclusions: At higher curing temperature, better flexural, impact and tensile properties were achieved in the polymers with the incorporation of the cow horn as filler. Also, the composite materials with particle size of 100 µm with curing temperature of 80 o C exhibited higher tensile and impact properties. Therefore, the cow horn was found to be a good potential filler in the composite if prepared using higher curing temperature as exhibited through its mechanical properties. A composite prepared at 150µm mixture is highly recommended for an impact application of the composited especially for material engineering to be subjected to impact application. Further research works on the use of cow horn as filler in epoxy composite and also the effect of alkali treatment on the compatibility of the cow horn particles and epoxy are recommended