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Investigation of bio-waste natural fiber–reinforced polymer hybrid composite: effect on mechanical and tribological characteristics of biodegradable composites

  • S. SureshEmail author
  • D. Sudhakara
  • B. Vinod
Original Paper
  • 71 Downloads

Abstract

The global energy crises and environmental pollution have encouraged investigators, scientist, and engineers to develop a substitute material for the conventional material. Since the availability of the natural fibers is abundant, many researchers in the worldwide are focusing their attention on the improvement of natural fiber–reinforced composites, which act as a substitute material for the synthetic natural fibers. This work examines the study of mechanical and tribological properties of tensile, flexural, impact, wear rate, and friction coefficient of the banana/hemp hybrid composites, which are calculated with the aid of NaOH-treated composite specimens. Composites were fabricated for various wt.% of the fiber content, different length of the fiber and matrix. Surface morphology of the fractured specimen of the alkali-treated fibers composites is studied by using SEM images. The effect of water absorption behavior on the mechanical properties of banana/hemp fiber composites was also determined.

Keywords

Biodegradable Mechanical properties Surface morphology Tribology 

1 Introduction

Composite materials which are produced by high-strength synthetic fibers are widely used in many commercial applications such as in the development of the automotive component, aerospace parts, construction material, medical, marine and sporting goods. But these types of composites were imported from the foreign countries and the fabrication cost of the composite will be higher. This circumstance has led to the development of substitute materials for synthetic fibers such as carbon, glass, or aramid [1]. In a recent development, a vital amount of attention has been shown by the researcher for the potential use of natural fibers as the reinforcement material in order to replace synthetic fiber in composite materials. Even though the natural fibers are not as tough as the synthetic fibers, natural fibers are very low cost, eco-friendly, and also biodegradable material [2]. The plant fiber structures also exhibit better insulation properties against noise and heat. Most cellulose natural fibers are harvested all over the year, so the production and supply are boundless compared with the very limited supply of the synthetic fibers which are derived from the depletion of the oil resources which produce the very high price of composite material which is reinforced with synthetic fibers. At the same time, the users of industries demand the lesser price for the composite production and which also results in better quality. The natural fibers are used as an effective reinforcement material for the polymer composites because of easy availability, inexpensive, and easy production of the composite. Hemp and banana fibers are being investigated in order to have an effective substitute material to replace the synthetic fibers in many commercial applications [3]. Among the different natural fibers, hemp and banana fibers are used as an effective reinforcement material in the polymer matrix composites. Since the hemp and banana fibers are rich in cellulose content, so these fibers are planned to investigate the appropriate study of banana/hemp fibers as reinforcement in polymer matrix composites to manufacture lower-cost components for many applications. Dinh et al. [4] presented an article on recent developments in bio-composites, multiple bioplastics, and recent trends in industrial applications for natural fiber polypropylene bio-composites to provide a perspective on the possibilities and development of bio-composite materials.

Rochima et al. [5] explored the properties of nano-chitosan plastic composite materials reinforced by banana and glass fiber and exclusively tested their mechanical properties. Punyamurthy et al. [6] proposed polyester composite produced from Abaca fiber which functions as a reinforcement catalyst in which the matrix was epoxy resin. They finally concluded the composite’s mechanical properties, evaluating the specimens for tensile as well as flexural strength. It has been observed that the composite material’s tensile strength relies on the polyester strength as well as the intermolecular adhesion between reinforcement and the matrix. Prasad et al. [7] were using the combination of natural fiber and synthetic resin (polyester) to produce partially environmentally friendly sisal fiber–reinforced polyester matrix composite. Towards this end, on Sansevieria cylindrica, a dynamic mechanical assessment was performed. Fiber increased synthetic polyester matrix to research storage module, loss module, and damping factor. Finally, under transient temperature circumstances, the effects of fiber length, fiber loading, and chemical treatments were analyzed.

Venkateshwaran et al. [8] conducted a number of tests to approximate the maximum mechanical properties of the fiber size and also the weight portion. Composite specimens were generated by differing portions of fiber size (5, 10, 15, and 20 mm) and volume (8, 12, 16, and 20). In addition, sisal fibers were introduced at a various quantity proportion (25, 50, and 75%) to improve the mechanical properties of the banana/epoxy composite products. Hybridization via sisal fibers supplies mechanical properties a desirable improvement. Sharba et al. [9] developed a hybrid material that integrates all-natural and synthetic fiber, respectively, from kenaf and also glass fiber. Production was performed via a sheet molding substance process with an overall amount reinforcement of up to 30%. In order to recommend the maximum hybrid compound for structural application, mechanical properties were examined.

Prajapati et al. [10] examined the effect of coir fiber composition treatment and also noted modifications in fiber geometry and also structure. It is clear that the end results obtained from chemically refined coir fiber are a plastic scientific research reinforcement agent as well as it is appreciated doing in modern innovation as commercial material. Abdulhadi [11] assessed the result of various medicines on the mechanical properties of basalt fibers and also their polypropylene matrix bond properties. Use of maleic anhydride implanted PP has been examined to produce various fiber size and also matrix alteration. Basalt fiber mechanical properties examined with solitary filament tensile testing. Santhosh et al. [12] investigated the fiber which was treated to increase moist strength by 5% of NaOH. Both in epoxy and vinyl ester resin, banana fibers have been used as reinforcement, as well as coconut shell powder were mixed with banana fiber. This appeared to be a product of strengthening to form a synthetic hybrid.

The main objective of this research is to determine the mechanical and wear characteristics like tensile, flexural, impact, wear loss, and friction coefficient of alkali-treated natural fibers in the form of randomly oriented long banana/hemp fiber hybrid–reinforced composites. And also the identification of the optimum weight percentage of the fiber content in the composites at which the maximum mechanical properties could be obtained. The morphological behavior of the composite was studied by using the scanning electron microscope.

2 Experimental details

The output of the composites depends on the characteristics of their components and on the bonding between the matrix and the reinforcement. It is customary to test them for mechanical properties such as tensile, hardness, and flexural strength to study the performance of bio-hybrid composites. Tribological testing is performed to determine the impact of reinforcement by varying distinct loads and speeds.

2.1 Raw materials

For this experimental investigation, the banana and hemp fibers are separated and extracted from the stem of banana plants and hemp plants. These separated fibers are used as the reinforcement material. And for the matrix material, a commonly available vinyl ester resin is used. Cobalt naphthenate has used a catalyst and methyl ethyl ketones are used as the accelerator respectively [13]. Figure 1 shows the fibers used for the production of composites. The compositions and physical features of banana and hemp fibers are as shown in Tables 1 and 2.
Fig. 1

a Banana fiber; b hemp fiber

Table 1

Chemical composition of banana and hemp fiber

Reinforcement material

Cellulose (%)

Hemi cellulose (%)

Lignin (%)

Pectin (%)

Banana

57–75

6–20

5–10

2–5

Hemp

68

11

4

1

Table 2

Physical properties of banana and hemp fiber

Reinforcement material

Density (g/cc)

Specific gravity

Moisture absorption (%)

Diameter (mm)

Color

Banana

1.07

5.9

4.2

0.2–2.6

White

Hemp

1.34

6.3

11

0.8–1.2

Creamy white

2.2 Alkali treatment of banana and hemp fibers

In this research, banana and hemp fibers were immersed in 8% of NaOH solution for 2 h at 35 °C in the form of long fibers, and then they were thoroughly washed with water and then dried in an oven at 50 °C for 12 h. After this treatment, these fibers were washed completely with running water and allowed to dry at 30 °C for 24 h. To study the effect of alkali-treated fibers on the mechanical properties of standard fiber lengths of banana and hemp fibers of 20 mm, the 8% NaOH solution has been soaked at 35 °C [14]. The fibers were kept fully immersed in the alkaline solution for the different durations 3, 6, 9, and 12 h. Figure 2 shows before and after surface treatment of banana and hemp fiber.
Fig. 2

a Before treatment of banana and hemp fiber and b after treatment of banana and hemp fiber

2.3 Preparation of bio-hybrid composites plates

The process of preparation of bio-composites consists of several techniques such as hand layout process, compression molding process, and injection molding. Among them, the compression molding technique is easy to process and producing large parts that require a significant bulk of material to manufacture. In present work, compression molding technique is used to prepare hybrid composites and a rubber mold is taken as 300 × 300 × 3 mm. In order to remove the composite from mold, dies are coated with polyvinyl alcohol to ensure the surface finish. The vinyl ester resin is varied in the presence of a coupling agent in a ratio of 3:8:1 in a funnel and stirred effectively for 15 min [15]. In meantime reinforcement fibers (banana and hemp) are mixed thoroughly and added to the matrix. The manual stirring was performed to disperse fibers in the matrix and then the mixer was transferred to a compression molding machine shown in Fig. 3. In the molding process, the compressed pressure is done at 100 kgf/cm2 and the temperature is taken as 50 °C for 40 min. The weight fraction of fiber was induced and varied as 5 to 25% represented in Table 3.
Fig. 3

a Experimental set up of compression molding and b fiber samples

Table 3

Composition of composite fiber

S.No

Sample

Matrix

Reinforcement

Fiber length

1.

S1

Vinyl ester

5% banana +5% hemp

20-mm length

2.

S2

Vinyl ester

10% banana +10% hemp

20-mm length

3.

S3

Vinyl ester

15% banana +15% hemp

20-mm length

4.

S4

Vinyl ester

20% banana +20% hemp

20-mm length

5

S5

Vinyl ester

25% banana +25% hemp

20-mm length

2.4 Determination of mechanical properties

2.4.1 Microhardness

Vickers is one of several measures of the microhardness of a material. The microhardness of the bio-hybrid composites is conducted by using Vickers’s hardness testing apparatus according to ASTM E 384 standards taking a load of 80 g and a dwell time is taken as 10 s. The specimens were cut by 10 mm length and 5 mm wide to investigate Vickers microhardness. For each composition, three samples are taken and average values are reported.

2.4.2 Tensile strength

The tensile test is generally performed on flat specimens. The tests are performed as per ASTM D 3039-76 standards on a computerized Ultimate Tensile Machine (UTM) with a load of 300 kN and dwell time 15 s [16]. All samples are cut by rectangular shape with dimensions of 10 mm wide and 120 mm total gauge length, while applying a load result in gradual elongation and fracture takes place at the end.

2.4.3 Flexural strength

The short beam shear tests are conducted of all samples at room temperature to investigate flexural strength. However, a 3-point bend test was conducted to promote failure by inter-laminar shear. The flexural strength is conducted by ASTM D 59436-96 standards. All the samples were cut by the rectangular shape of 100 mm long, 25 mm wide, and 3 mm thickness [17]. Span length of 40 mm and the crosshead speed of 1 mm/min are taken in the present investigation. The temperature and humidity of this test are maintained at 22 °C and 50% respectively.

2.4.4 Impact strength

The impact resistance of the composite specimen was carried out in the production impact test machine model IT-30. The specimen was cut in accordance with ASTM D 256-10 standard [18]. All the samples of the effect were notched. Five samples were used for each mechanical examination, and the average values are recorded. The mechanical properties of alkali-treated banana/hemp fiber–reinforced composites are shown in Table 4.
Table 4

Mechanical properties of alkali-treated banana/hemp fiber–reinforced hybrid composites

Material

Tensile strength (MPa)

Flexural Strength (MPa)

Impact strength (KJ/m2)

Stiffness (GPa)

Microhardness (HV)

5% banana +5% hemp

30

34

0.54

3.05

31

10% banana +10% hemp

38

40

0.68

3.18

48

15% banana +15% hemp

42

47

0.64

3.25

65

20% banana +20% hemp

48

56

0.60

3.32

78

25% banana +25% hemp

44

51

0.58

3.27

70

It is necessary that stiffness kept to a maximum level when the desired high performance of machining would be achieved.

2.5 Water absorption test

The moisture absorption test specimens were cut from the fabricated composite plate as per the ASTM D570 [19]. Specimen edges are sealed with the resin and it is subjected to the water absorption. In an oven at 50 °C the samples were dried and then immersed in the distilled water at 30 °C for about 5 days. At the standard time interval, the test samples were taken from the water and to remove the water present in the surface of the test specimen, it was cleaned with the filter paper and weighted with digital balance. In order to perform the continuous water absorption, the test samples were re-immersed in water until the complete saturation limit was reached. Due to evaporation, an error could occur, so that the weighing of the test specimen was done within 30 s in order to avoid such kind of errors. Percent of weight change of the samples during water absorption was determined by the following Eq. (1)

$$ \mathrm{M}\%=\frac{M_t-{M}_o}{M_o}\times 100\% $$
(1)
where Mo represents the test sample dry weight and the weight at any specific time t is represented by Mt, respectively. Figure 9 indicates the effects of fiber content for all the weight percentage on the water absorption characteristics of the composite. With the increase in the fiber content in the composite, the moisture absorption gets increased for all the days. Due to the improvement of the hydrophilic character of natural fibers and the formation of the micro void in the matrix material, in the composite the fiber content increases, the saturation time will be shortened. The rate water absorption behavior was found to be same for the third, fourth, and fifth day respectively. The effect of wt.% of reinforcement on water absorption behavior is shown in Table 5.
Table 5

Effect of different wt.% of the fiber content on the water absorption behavior

Fiber content (wt.%)

Day1 water absorption (wt.%)

Day 2 water absorption (wt.%)

Day 3 water absorption (wt.%)

Day 4 water absorption (wt.%)

Day 5 Water absorption (wt.%)

5

0.68

0.73

0.78

0.8

0.81

10

0.93

0.98

1.05

1.11

1.17

15

1.82

2.16

2.3

2.48

2.5

20

2.56

2.96

3.38

3.48

3.52

25

3.22

3.7

4.43

4.55

4.58

2.6 Tribological properties

The wear test was carried out as according to the ASTM G99 standard. Cylindrical specimens having a diameter of 80 mm and a height of 20 mm were used to evaluate the wear behavior. To examine the wear under abrasive mode, the abrasive wear tests were carried out on a pin-on-disc machine. The silicon carbide-water proof emery paper (grade 100, 320, and 400) was attached to the disc [20]. Cylindrical specimens having the diameter of 80 mm and height of 20 mm were used to evaluate the wear behavior. A force transducer fixed on the loading lever arm was used to calculate the frictional force. During the experiment to calculate the linear wear, a non-contact laser displacement transducer was used. Data occurred during the calculation of linear wear and frictional forces were stored in a data acquisition system (personal computer). Normal load ranges from 20 to 40 N are used to conduct the friction test and wear test. For these varying loads, the experiments were carried out at a sliding velocity of 2 m/s and 4 m/s. Before testing of the sliding surfaces of the pins, it should be well cleaned. The initial mass and dimensions of the surface of pins were measured by using an electronic balance of accuracy 0.1 mg and digital micrometer of accuracy 1 mm. The experiment set-up was run up to a sliding distance of 500 m. After completion of the wear test, the pin was cleaned and the mass of the composite specimen was measured. For each tests condition was carried out and for further examination, the average values were calculated for wear loss and friction force. The conditions of the wear test are given in Table 6. Finally by using the scanning electron microscope, the worn out the surface in the test specimens was observed.
Table 6

Wear test conditions

S.No

Pin material

Bio-hybrid composites

1

Disc material

EN31 steel disc

2

Track radius

50–100 mm

3

Temperature

Room temperature

4

Applied loads

10–40 N

5

Sliding speeds

2–4 m/s

6

Sliding distance

300–1200 m

2.7 Characterization of bio-hybrid composites

Mechanical and tribology properties are studied, and a critical concentration of compatibilizer is found to exist in the bio-composite system. Morphology of the fracture surface was also investigated by scanning electron microscopy. The bio-composite samples were ground, etched chemically, and polished mechanically by using Kroll’s reagent (a mixture of 10 ml HF, 5 ml HNO3, and 85 ml H2O). After conducting the tribology test, each sample is examined by using SEM (SEM-ZEISS SIGMA).

3 Results and discussion

Examine the effect of natural fibers and identify mechanical properties of bio-hybrid composites. To study the behavior of each phase’s surface morphology, EDS and XRD were analyzed. Effect of sliding wear behavior was identified using different parameters (applied load, sliding distance, and sliding speed) on wear loss and coefficient of friction (C.O.F).

3.1 Microstructure analysis of initial elements

The investigation and evolution of banana and hemp with vinyl ester resin is conducted to improve mechanical and tribological properties. The search for suitable growing media in the controlled environment of growth is the basic need for experiments. Hemp is gaining popularity as developing in India and elsewhere in Europe as excellent natural biomass. The natural fiber of plant-based such as hemp has provided high strength to the composite and transfer efficiency between the matrix and the fiber. This type of fiber improves the toughness and the mechanical properties of the material [21]. The primary microstructures of banana and hemp are shown in Fig. 4. In this work 10-mm length has been taken to investigate tribology and mechanical properties at different weight fractions.
Fig. 4

Microstructure of a banana and b hemp fiber

3.2 Mechanical characterization

3.2.1 Microhardness

The microhardness is conducted for all specimens using a Shimadzu micro-hardness tester. Three measurements are made on each sample at different locations and average values are presented in Fig. 5. The microhardness is improved as compared with the matrix attributed to the addition of reinforcement particles. An increase in the hardness was also observed with increasing the weight fraction of banana/hemp fiber. The hard reinforcement particles bear the load and therefore restrict the dislocation and strength the composites. Similar behavior of increase in hardness with increasing weight fraction of hemp fiber as reinforcement particles has been reported in earlier research [22]. The microhardness of 5% banana/hemp with the vinyl ester is achieved as 30 MPa. The higher hardness was achieved to 59 MPa due to the addition of 20 wt.% (banana/hemp fiber) with vinyl ester increases compared with other investigations. Thus, increase in hardness with an increase in reaction time of fiber content lead to further refinement of fine grain structure.
Fig. 5

Graphical representation of microhardness by varying weight fraction of fiber content

3.2.2 Tensile strength

An improvement in the tensile strength was observed at the treated banana/hemp fiber–reinforced composite having the 10 wt.% of fiber content which was 19.55% when compared with the untreated banana/hemp fiber composites. While comparing the entire wt.% this level of improvement attains the maximum level in the increase in percentage. It is clear evidence that the enhancement had occurred from the 5 wt.% fiber content. Figure 6 indicates that for the banana/hemp composites the percentage of improvement in tensile strength, the ranges are higher from 15 to 20 wt.% (41.2 to 49.6%). With increasing in the higher percentage of the fiber content in the composite, it tends to decrease the tensile strength. After 20 wt.% fiber content, the percentage of tensile strength decreases. The amalgamation of fibers into thermoset matrix which leads to inadequate dispersion of fibers which is due to higher inter-fiber hydrogen bonding which holds the fibers together which has not led to the dispersion of fiber within the matrix [23]. Improper bonding of the fiber and matrix will hinder the significant augmentation of tensile strength. Thus, when the wt.% of the fiber content in the composite increases due to the dispersion of fiber and the aggregation of fibers took place and the resin could not wet the fiber properly. Hence, there is no bonding between the fiber and matrix. This commences the composite material to failure in their mechanical properties. Thus, the higher wt.% of fiber content in the composite was limited in both the circumstances whether it was treated or untreated banana/hemp fiber–reinforced composites.
Fig. 6

Effect of tensile strength by varying fiber content on different weight fraction

3.2.3 Flexural strength

Figure 7 shows the effect of alkali treatment of fibers on the flexural strength, and it clearly indicates that with an increase in the treated fiber content there is a considerable increase in the flexural strength of the composites. The composites prepared with the treated banana/hemp fiber showed maximum flexural strength at 20 wt.% of fiber content was 56.6 MPa. There is a better improvement in the flexural strength for the composite fabricated with 8% NaOH-treated fibers in all the wt.% of fiber content. After the treatment of the banana/hemp fibers, there will be the effective removal of the lignin and hemicellulose in the surface of the fiber, so the inter-fibrillar region in the fiber is likely to be less rigidity and dense [22]. This results from the fibrils themselves able to rearrange. When banana/hemp fibers are prolonged, arrangements among the fibrils in the fiber will result in better stress development in the fiber. The composites having the wt.% of the fiber content 20 wt.% was 56.6%. It clearly shows that with an increase in the treated fiber content there is a considerable increase in the flexural strength of the composites. It is due to the removal of the impurities on the surface of the fiber due to the NaOH treatment.
Fig. 7

Effect of flexural strength by varying weight fraction of fiber content

3.2.4 Impact strength and stiffness

Increasing the NaOH-treated fiber content in the composite increases the impact resistance as shown in Fig. 8. When compared with the untreated fiber composites, the impact strength values considerably increase for the treated banana/hemp fiber composites. At 20 wt.% of the fiber content, the maximum impact strength values were observed. Beyond this wt.%, the impact strength gets decreased. The enhancement in impact strength of the composite material is due to the following reason, i.e., removal of impurities from the fiber will improve the surface roughness of the fiber [24]. As a result, the mechanical interlocking between the fiber and the matrix interface is improved. The best combination mechanical properties such as flexural and tensile strength are in the range of 10 to 20 wt.% of fiber content, and the impact strength attains the maximum at 20 wt.% for the banana/hemp fiber–reinforced composites. These critical fiber contents fluctuate with the matrix, the degree of fiber-matrix adhesion, nature of the fiber, matrix, and fiber aspect ratio, etc.
Fig. 8

Effect of different weight fractions of fiber content on impact strength

The stiffness of the banana and hemp fiber with different weight fractions is presented in Table 4. The observed results are evidenced that the 20% (banana-hemp) has considerably reduced open pores and increases stiffness (3.32 Gpa) when compared with other composites. Increasing the concentration of hemp tends to improve the stiffness. The result suggests that addition of 20% (banana-hemp) is effective, due to the removal of pores and it enhances the mechanical properties of the hybrid composites. Further increasing the concentration to 25% (banana-hemp) tends to decrease the stiffness (3.27 Gpa) which is attributed to an effect of agglomeration. Therefore, A356/10%RHA-10%Fly ash hybrid composite is observed having low porosity level compared with alloy and other hybrid composites.

3.2.5 Water absorption characteristics

For the randomly oriented long banana and hemp hybrid composite, the water absorption behavior gets increased with increase in the wt.% of the fiber content. Figure 9 shows the effect of fiber content on the mechanical properties of moisture absorption on the 1st and 5th day of the composite having the fiber length of 20 mm [25].
Fig. 9

Water absorption behavior for different weight fractions of banana-hemp composite

Figure 9 shows the increases in the percentage of the moisture absorption for 20-mm fiber length of both first and fifth day at the composite having the fiber content of 10 wt.%, 15 wt.%, 20 wt.%, and 25 wt.% were 52.24%, 75.47%, 82.21%, and 87.34% respectively.

3.3 Wear characteristics

3.3.1 Effect of sliding speed on wear loss

The effect of velocity on wear loss is measured by varying sliding speeds (2–4 m/s) with a load of (20, 40 N) and a sliding distance of 500 m as shown in Fig. 10. At the initial stage, wear loss is more due to the addition of 5% banana/hemp fiber. However, it is observed that frictional heat is generated between disc and pin when increasing sliding speed results in fracture surface. Addition of 10% sisal–10% coir fiber with CFR exhibits higher wear loss at all sliding speeds attributed to a strong interface of fiber and high hardness. Ragunath et al. [26] conducted the properties of vinyl ester resin with sisal and glass fiber hybrid composite which was found with high wear resistance and improved tensile strength of 129 MPa. The banana and hemp fiber as reinforcements lead to efficient stress transfer helps to improve the mechanical properties. Similar observations are made by Johnson et al. [27]. Further addition of weight fraction of banana/hemp fiber (25%) does not show any effect on sliding speed and may result in plastic deformation. It results in tearing and scratching of material leading to the development of wear debris.
Fig. 10

Wear loss for different weight fractions at constant sliding speed of a 2 m/s and b 4 m/s

3.3.2 Effect of applied load on wear loss

The variation of wear loss on vinyl ester/5% banana–5% hemp, vinyl ester/10% banana–10% hemp, vinyl ester/15% banana–15% hemp, vinyl ester/20% banana–20% hemp, and vinyl ester/25% banana–25% hemp bio-hybrid composites plotted at different applied loads (20–40 N) with a constant sliding speed of 2 m/s and 4 m/s and a sliding distance of 500 m represented in Fig. 11. Initially, weight loss slightly increases at a load of 20 N. However, the addition of banana/hemp fiber content wear loss tends to decrease and is shown in Fig. 11b. The lower wear loss is exhibited due to a high amount of 20 wt.% banana and hemp optimum fiber content at a load of 30 N. However, increasing the applied load (40 N) tends to decrease wear resistance. A similar trend is observed in all samples due to high plowing action between pin and disc [28]. Further addition of 25% banana–25% hemp with vinyl ester leads to lower efficiency, and higher wear loss is achieved due to low hardness and high porosity. Moreover, increase in weight fraction of hybrid fiber leads to resistance of the removal of material and also improves bonding between reinforcement and matrix.
Fig. 11

Wear loss for different loads at constant sliding speed of a 2 m/s and b 4 m/s

3.3.3 Effect of sliding speed on friction

The variation of coefficient of friction of bio-hybrid composites under two sliding speeds (2, 4 m/s) with a load of (20 N, 30 N, 40 N) and a sliding distance of 500 m is presented in Fig. 12. It was observed that the C.O.F increases with increasing the sliding speed. This increase may be due to an increase in the asperities contact at the interface. A similar observation was reported by Rao and Gupta [29]. Initially, in sample 1, the C.O.F is high due to low wettability and hence friction is reduced in addition of 20% banana and hemp fiber to a vinyl ester at two sliding speeds. In further addition of 25% banana/hemp fiber (at higher speed), the solid lubrication capability of banana/hemp fiber is not retained resulting in an increase in temperature. Moreover, an increase in the temperature at the interface also leads to thermal softening of the matrix material, thereby leading to more adhesion. The SEM analysis of the worn-out samples at higher speed revealed an increase in the delamination wear, thereby leading to an increase in C.O.F.
Fig. 12

Coefficient of friction for different weight fractions at constant sliding speed of a 2 m/s and b 4 m/s

3.3.4 Effect of applied load on friction

The frictional curves corresponding to all samples are plotted at a load of 20–40 N with speed of 2 m/s and 4 m/s and a sliding distance of 500 m represented in Fig. 13. From the graph, it is observed that the C.O.F. for all composition at load 30 N shows an increasing behavior with an increase in the sliding distance. This behavior is due to an increase in the real contact area and the rise of temperature at the surface which leads to an increase in the frictional force. The sharp peaks at lower load (20 N) as seen in the curve graph may be due to the third body abrasion caused by wear debris [30]. At high load (40 N), friction is unstabilized and tends to increase the C.O.F and results in cracks on the material surface. Addition of 20% shows a low frictional coefficient due to increasing banana/hemp fiber content, and material exhibits high durability with a good blend of strength.
Fig. 13

Coefficient of friction for different loads at constant sliding speed of a 2 m/s and b 4 m/s

3.4 Surface morphology of bio-hybrid composites

A scanning electron micrograph (SEM) was taken using Carl Zeiss Sigma 300 microscope to study surface morphological appearance. The homogeneous dispersion of the banana and hemp fiber within the vinyl ester bio-hybrid composites was analyzed by SEM; the representative micrographs are presented in Fig. 14. In the hemp and banana fiber reinforced with vinyl ester, a strong interaction between the resin and the fibers can be seen in Fig. 14b, c). This is partly due to better chemical compatibility between the fibers and resin. It is also observed that the 20% banana and 20% hemp fiber dispersed well and penetrated through the vinyl ester. The hemp fiber is exfoliated within the vinyl ester resin and is shown in Fig. 14d. This is due to the good uniform distribution between the fibers [31]. It is also identified from the SEM; the banana and hemp fibers are composed of thinner platelets with a thickness of approximately between 20 and 150 nm. The addition of 25% hemp and 25% banana with vinyl ester can be seen that high agglomeration is found due to low concentrations of fiber added to the matrix. This agglomeration leads to the formation of micro-voids and cracks within the composite attributed to poor dispersion of the reinforcement in the matrix as shown in Fig. 14e. Similar morphology was observed for bio-composite specimens (on applying compression molding) by Arsyad et al. [32]. It is clear that the addition of hemp and banana fiber leads to an increase in material properties and also improves surface roughness. Therefore, the vinyl ester/20% (banana-hemp) bio-hybrid composite exhibited a smooth surface than other materials.
Fig. 14

Surface morphology of a vinyl ester/5% banana–5% hemp, b vinyl ester/10% banana–10% hemp and c vinyl ester/15% banana–15% hemp, d vinyl ester/20% banana–20% hemp and e vinyl ester/25% banana–25% hemp bio-hybrid composites

3.5 EDX analysis

The surface compositions are characterized by energy dispersive analysis of X-rays (EDX) to combine structure-property. The microscope was fitted with an energy dispersive spectrum (Zeiss EVO-50XVP) to detect the overall chemical compositions of hybrid composites. Figure 15a illustrates the C, 0, Ca, and Si mapping for sample 1 surrounded by fiber particles. The particles are sampled from a batch where fiber has been soaked in vinyl ester resin [33]. The mapping of Ca, O, and Si shows segregation of addition of 5% banana/hemp fiber to the upper and left surfaces of the (sample 2) material. The Ca and Si particles are surrounded by vinyl ester resin which can be seen in Fig. 15b, c where silica is mapped. In addition of banana/hemp fiber content up to 20% (Fig. 15d), the chemicals elements such as Ca, C, and Si are enriched in the vinyl ester resin while it forms a new layer on the surface which tends to increase the hardness of a material. Further addition of 25% banana/hemp fiber (sample 5) results in the downfall of Ca and Si elements due to poor wettability and is shown in Fig. 15e. However, it leads to fracture surface and hence reduces the material strength. Therefore, vinyl ester/20% (banana-hemp) bio-hybrid composite exhibits high calcium carbide and silica content compared with other composites. This type of material is majorly used in automotive sectors.
Fig. 15

EDX analysis of a vinyl ester/5% banana–5% hemp, b vinyl ester/10% banana–10% hemp and c vinyl ester/15% banana–15% hemp, d vinyl ester/20% banana–20% hemp and e vinyl ester/25% banana–25% hemp bio-hybrid composites

3.6 XRD analysis

In the intensity vs 2 theta diffraction curve, we see that sisal fiber is mostly amorphous in nature. Figure 16a–e shows the X-ray diffraction of bio-hybrid composites. A poor crystallinity index, as shown by the curve, implies there should be an occurrence of alkali-treated sisal fiber. It implies poor output of cellulose crystals to the fiber pivot amid treatment, showed by the lower crystalline file. The addition of hemp fiber is better situated in banana fiber with vinyl ester resin as shown in Fig. 16b, c. Addition of 10% banana and 10% hemp fiber exhibits low peaks nearly at 2θ = 11°, 18°, 21° which coincide with the JCPDS card No.89-4032 [34]. The Si and Ca phases are increased at 2θ = 26°, 28°, 32° due to the addition of 20% (banana-hemp) fiber reinforcement with vinyl ester and are shown in Fig. 16d. In further additions of 25% hemp and 25% banana fiber with vinyl ester resin, the peaks are changed and phases are a downfall due to un-uniform distribution and poor wettability as shown in Fig. 16e.
Fig. 16

XRD analysis of a vinyl ester/5% banana–5% hemp, b vinyl ester/10% banana–10% hemp and c vinyl ester/15% banana–15% hemp, d vinyl ester/20% banana–20% hemp and e vinyl ester/25% banana–25% hemp bio-hybrid composites

4 Conclusion

The requirement for the development of new products to satisfy the challenges for ingenious applications in the clinical and technological fields has become necessary in recent days. An attempt was made a novel material called “bio-hybrid composite” whose constituents to solve the need of the applications. At present, there has been rapid growth in the use of fiber-reinforced composite materials. In present work banana and hemp fiber is used as fillers in a pattern of the biodegradable composite using the vinyl ester as a matrix. This type of material was fulfilling all the conditions and the requirements such as higher strength, heat distortion temperature, and lightweight with low cost.
  • Microhardness values are much higher for the 20% (banana-hemp)–reinforced vinyl ester resin in comparison with other hybrid composites. The increased microhardness is due to a higher degree of fineness of fiber content and good wettability.

  • Tensile, flexural, and impact strength is increased (40%) for the vinyl ester/20% banana–20% hemp compared with other hybrid composites. The improvement of tensile strength is attributed to the presence of high silica and carbon content.

  • In the addition of 25% fiber, the mechanical properties of the hybrid composites were reduced due to the formation of more interfaces in the matrix and the generation of pores with voids.

  • For all applied load, sliding distances and sliding speeds were examined. The developed 20% bio-hybrid composite was exhibited low wear loss and low coefficient of friction at all sliding conditions.

  • The SEM microstructure of vinyl ester/20% (banana-hemp) bio-hybrid composite shows a pore-free compact surface. The EDS and XRD pattern confirms the formation of sisal and coir phases with their intensity of 20°,40° from the corresponding specimen.

  • Therefore, the vinyl ester/20% (banana-hemp) bio-hybrid composite exhibits improved wear resistance and hence resulting in longer material lifespan. This type of material is widely used in fishing rods, golf clubs, chairs, tables and all domestic purposes.

Notes

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Department of Mechanical EngineeringSiddartha Institute of Science and TechnologyPutturIndia
  2. 2.Department of Mechanical EngineeringPriyadarshini College of Engineering and TechnologyNelloreIndia

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