1 Introduction

Biocomposite materials are stronger, lighter, easily degradable, and extensively used in many technical applications. Biocomposites have recently been used in automobile, aerospace and industries [1]. Also, in the automobile sector, composite materials are mainly used to reduce the weight of the parts. To satisfy the need for biocomposites, different bio-composite materials, which are renewable and bioeconomic, have been emerging over the past decade. Scientists worldwide developed innovative biomaterials using natural fiber and additive materials [2, 3]. Research is being done worldwide on how biocomposites can be produced with excellent mechanical properties, how cheap they can be made and how much money can be saved in producing biocomposites. This results in the finding of novel fiber-reinforced material. The various fibers extracted from the plant are bagasse, Jute, coir, pineapple, banana, sisal, opuntia cladode, areca, and bamboo, which are studied [4]. The cellulose content and the density of the opuntia fiber are the same as that of abaca which is conventional fiber. The density of the opuntia fiber is 1.54 g/cm3, and the conventional fiber, like abaca, is 1.5 g/cm3. The Jute sisal also exhibited the same fiber density of 1.3 and 1.5 g/cm3 [5, 6]. The opuntia cladodes have a hierarchical reticular hexagonal structure due to the formation of networks of tiny fibers. To make the composite, epoxy is the standard resin used in many research. The research is similar to the opuntia fiber in cactus fiber [7, 8]. It was found that the vibration testing of the cactus showed resistance, and also, there is an improved mechanical, thermal and load-bearing capacity. The property of the material is improved due to the silane process. The aqueous 3-aminopropyltrimethoxysilane is the most commonly used silane solution. The result from the research showed that the silane-treated fiber shows silane-treated bio silica, and the 30% opuntia fiber-reinforced composite enhances the mechanical properties of the composites [9].

Many research has been developed to make novel eco-friendly bio fillers for refining the material properties for household and industrial usage in many research. For example, industrial waste products, buildings and biowaste can be used as a reinforcement [10, 11]. Research on the economic particle fillers for particular applications is very much necessary. Much research has been done on reinforcing the composites taking the cost-effective end-product as a primary objective [12, 13]. Biochar is one of the low-cost, eco-friendly reinforcement materials obtained from waste products from the home and industry. Biochar is more readily available, cheap and economical [14, 15]. Using bio-fillers enhances the electrical properties, thermal conductivity and optical characteristics, making them remarkable in many industrial applications. The impact of carbon from the end product of the pyrolysis process as an additive for the composite reinforcement is studied. The outcome shows that the electrical resistance of the developed material is reduced after the addition of the carbon particles. Also, using Biochar produces the EMI shielding property in one investigation. Also, the electrical resistance of Biochar can be varied by the process of annealing between temperatures of 950 to 1400 °C [16, 17]. Several research studies have proven that mechanical characteristics like flexural, tensile, impact strength, and the material’s hardness are improved with the increase in the percentage of the biochar material.

Hence, from the various literature, it can be seen that the usage of Biochar on composites in various forms for particular applications is investigated. Biochar can be produced using various methods, and its properties can be changed according to the processing technique used for particular applications. However, not much research has been done on Palm flower biochar. The various minerals and the carbon in the Biochar from the palm flower are higher. Also, the Opuntia cladode fiber composites and the palm flower Biochar has been investigated in detail. Based on this, this research aims to develop the composite from the Opuntia cladode fiber and the palm flower Biochar at various percentages and their properties are studied in this research. The silane process is used as a surface treatment of the fiber, and the hand layup technique is used to produce the different composite mixtures. Epoxy is used as a base medium in preparing the composites. The research showed that the composite obtained from the epoxy showed a perfect application in the automotive defence, sports and manufacturing sectors.

2 Materials and methods

This research uses Araldite LY 556 epoxy resin, which has a 1.09 g/cm³ of density and 190 g/mol of molecular weight. The hardener and the epoxy resin are obtained from HUNTSMAN India Pvt. Ltd. The surface modifier chemical used in this research is Aminopropyltriethoxysilane, obtained from Sigma Aldrich. The other secondary chemicals needed for this research are obtained from Coimbatore, India.

2.1 Fiber extraction

Opuntia cladode is the most commonly available plant in India. The plant can grow to a 6 to 7 m height, and its pads have thorns. First, the thorns are carefully removed from the plant, and the pads are rinsed in water before further processing. For three days, the pads are soaked, and then they are dried in the sun. The mechanical shear method separates the fiber from the cladodes without causing any damage. The properties of the extracted Opuntia cladode are shown in Table 1. The fiber contains a very good quantity of cellulose; hence, it can reinforce plastics. The various process involved in the preparation of fiber is shown in Fig. 1.

Fig. 1
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Various steps in preparation of composites

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Table 1 Various parameters of processed Opuntia cladode fiber [12, 13]
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2.2 Preparation of biochar

The waste of palm flowers is collected from the agricultural fields of Madurai city, India. The obtained palm flower is dried completely in a hot air oven. The torrefaction procedure is carried out for 2 h at 200 °C. From the literature, it is seen that the conversion of biomass into Biochar takes place at a temperature of 300 °C. This temperature is not maintained in this research. The reason is that an increase in the temperature beyond a certain range results in biomass conversion into ash. Thus, the temperature is maintained at 250 °C for this research. After the Biochar is obtained, the product is completely washed in distilled water, and the pH of the solution is maintained neutral. The wet Biochar is then dried by placing it in a hot air oven, and then it is finely powdered for the particular application as a replacement for cement.

2.3 Silane process and preparation of the composite laminate

The extracted Opuntia cladode fiber is treated with an aqueous solution of Aminopropyltriethoxysilane. This solution contains 5% water and 95% ethanol. The pH of the solution is maintained at 4.5 to 5.6 for hydrolysis. Drop by drop and with stirring action, the silane solution is added to create a uniform solution. Then, the obtained natural fibers are dipped in an ethanol-water solution for 10 min and dried in a preheated oven at 120 °C. The composites are prepared using the hand lay-up technique. Table 1 shows different percentages of biochar particles are added to the silane. The curing agent is added to the solution in a 1:10 ratio. The preheated pre-blended resin and the hardener are transferred to the rubber mold. Before the process, the rubber mold is cleaned with acetone, and the wax is applied carefully by hand. From the literature, it is found that the optimal combination for mixing the fiber in the composites is 30%, so the composites are developed with 40% of the short fiber shown in Table 2. To maintain the uniform thickness of the composites, excess glue is removed, and air bubbles trapped in the composites are eliminated using a cotton roller [18]. Curing and post-curing are done under atmospheric conditions for 24 and 48 h.

Table 2 Designations of the prepared composites
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3 Result and discussion

3.1 Mechanical properties

Table 3 shows the mechanical properties of the prepared composites. The various properties evaluated in this research are flexural strength, tensile strength, hardness, and impact toughness of the various composites. The composites with the designation C have lower mechanical characteristics, with 112 MPa of flexural strength, 64 MPa of tensile strength, 0.32 J of impact toughness, and 86 Shore-D hardness [19]. The composite exhibits a brittle nature, resulting in lower mechanical characteristics. This brittleness indicates that composite C has a very low load-bearing capacity. In the case of composite C with the designation C1, there is an increase in mechanical properties [20]. The flexural strength improves to 162 MPa, tensile strength to 102 MPa, impact energy to 4.5 J, and hardness to 88. The hexagonal reticular hierarchical structure of the prepared composites increases their load-bearing capacity, leading to improved mechanical properties.

Table 3 Properties of the prepared composites
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SEM fractography in Fig. 2 confirms that the prepared fiber adheres well to the resin, indicating good adhesion. This strong adhesion is due to the silane surface treatment process, where the large amount of OH group in the resin reacts with NH2 in the silane-treated fiber, enhancing the adhesion of the prepared composites [21]. With the addition of 2% and 3% biochar, the results are highly beneficial as the mechanical properties of the prepared composites increase. Composite C3 exhibits a flexural strength of 217 MPa, tensile strength of 178 MPa, impact strength of 7.2 J, and hardness up to 92 Shore-D on the hardness scale. The porous property of the Biochar permits the resin to form a strong bond, resulting in increased mechanical properties of the prepared composites [22]. However, at 5% volume of Biochar, there is a slight reduction in mechanical properties compared to composite designation C3. This is because the large accumulation of Biochar in a particular area results in stress-intensity development, leading to interfacial cracking and larger river marks. Hence, the optimal addition of Biochar into the fiber and resin mixture is 3% volume, which provides the best mechanical performance for the prepared composites.

Fig. 2
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SEM fractography of the mechanical test specimen

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3.2 Wear properties

Table 4 shows the wear properties of the various composites. The COF and specific wear rate of the composite with the designation C1 are 0.8 and 0.025 mm3/Nm, respectively. The brittle nature of the epoxy resin increases the chances of abrasion wear, resulting in a higher specific wear rate for pure epoxy composites [23]. However, on adding 40% volume of Opuntia cladode fiber, the COF of the composite reduces to 0.58, and the specific wear rate decreases to 0.018 mm3/Nm. The wear resistance improves mainly due to the presence of fiber, enhancing sliding forces and resulting in less wear debris [23]. Furthermore, with the addition of Biochar, the wear resistance of the material further improves [24]. The Biochar acts as a solid lubricant between the composite and the rotational disc, made of EN24 material for the wear experiment [25]. The improved COF value is mainly due to the reduction in cross-linking density caused by the presence of Biochar. Composite designation C5 shows a COF of 0.41 and a wear rate of 0.0049 mm3/Nm, indicating that adding palm flower biochar enhances the wear resistance of the alloy.

Table 4 Wear properties of the composites
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3.3 Thermal conductivity

Figure 3 shows the thermal conductivity of the different composites designated from C to C5. The lowest thermal conductivity of 0.245 W/mK is observed for the pure resin. This lower thermal conductivity is due to the epoxy molecules’ poor vibration and intermolecular tightness [26]. However, with the addition of 40% fiber and Biochar, the thermal conductivity of the material improves. The composite with designation C1 exhibits a thermal conductivity of 0.36 W/mK. Similarly, with the addition of Biochar, the thermal conductivity is further enhanced [27,28,29,30]. For composites C2, C3, C4, and C5, the thermal conductivity values are 0.42 W/mK, 0.43 W/mK, 0.48 W/mK, and 0.49 W/mK, respectively. The presence of Biochar in the material effectively conducts heat [24]. It has been found that as the volume percentage of biochar decreases, the heat conductivity also decreases. A smaller quantity of palm biochar results in inadequate network development, whereas a higher amount improves the heat transmission rate [31]. Thus, increasing the palm biochar in the composites enhances the thermal conduction of the material.

Fig. 3
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Thermal conductivity of the prepared composites

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3.4 Water absorption

The water absorption property of the epoxy and its composites is shown in Fig. 4. The percentage of water absorption for the pure epoxy after immersion is 0.086. The molecular structure of the pure epoxy molecule has extremely low permeability to water due to a higher amount of OH molecules, which repel water and act as a resistance to water absorption; however, with the addition of 40% of Opuntia cladode fiber, the water absorption percentage increases [32]. Composite C1 shows a water absorption of 0.134, attributed to water-absorbing pores in the fiber that enhance water intake. Moreover, adding palm biochar further increases the water absorption capacity to 0.138, 0.145, and 0.147 for composites C3, C4, and C5, respectively. The silane surface treatment process regulates the water absorption capacity of the fiber [33]. The difference in water absorption capacity for each fiber is minimal, as the silane treatment of the composites prevents excessive moisture absorption and results in lower absorption percentages [34].

Fig. 4
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Water absorption properties

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4 Conclusion

In this research the bio composite is prepared using the Opuntia cladode fiber and palm flower Biochar and its mechanical properties, thermal and water absorption characteristics are analysed. The five different composites are prepared using the hand layup techniques and are tested as per the ASTM standard. From the investigations the following conclusions are made.

  • Composites containing 40% opuntia cladode short fibers exhibit improved mechanical parameters, such as flexural strength, tensile strength, impact toughness, hardness, and adhesion strength. Composite C3 demonstrates impressive mechanical qualities, including a flexural strength of 217 MPa, a tensile strength of 178 MPa, an impact strength of 7.2 J, and a hardness of up to 92 Shore-D on the hardness scale. However, adding 5% Biochar slightly reduces the mechanical characteristics compared to composite designation C3. This decline can be attributed to Biochar deposition in specific areas, causing increased stress intensity, interfacial cracking, and greater river markings. Hence, the appropriate Biochar quantity in the fiber and resin mixture to enhance mechanical performance is 3% volume, achieving the optimal balance between reinforcement and potential disadvantages, ensuring that the created composites display exceptional mechanical properties. It is also observed that an increased amount of fiber and palm charcoal improves the wear characteristics.

  • The thermal conductivities of the composites are as follows: C1–0.36 W/mK, C2–0.42 W/mK, C3–0.43 W/mK, C4–0.48 W/mK, and C5–0.49 W/mK. Biochar increases heat conduction while decreasing biochar volume decreases thermal conductivity. Increasing the concentration of palm charcoal enhances heat transmission and, consequently, thermal conductivity.

  • Due to the limited permeability induced by OH molecules, pure epoxy has a water absorption rate of 0.086. Using 40% Opuntia Cladode Fibre improves water absorption, resulting in Composite C1’s water absorption rate of 0.134. Adding palm charcoal further improves water absorption, yielding values of 0.138, 0.145, and 0.147 for composites C3, C4, and C5, respectively. Silane treatment reduces water absorption in all composites, resulting in lower percentages.