Experimental Investigation of Aloe Vera-Treated False Banana (Ensete Ventricosum) Fibre-Reinforced Polypropylene Composite

Abstract

This research work investigates the effects of the concentration and treatment of chopped false banana (Ensete ventricosum) fibres on the mechanical properties of a polypropylene matrix. The chopped false banana fibres (FBFs) were modified using Aloe Vera gel following treatment with 5% NaOH for 12 h at room temperature, with 1% acetic acid used to neutralise the remaining NaOH. FBF-reinforced polypropylene composite plates were then manufactured with 10, 20, 30, and 40 wt.% of chopped FBF. The mechanical properties were investigated using the compressive, impact, and three-point bending tests. Regarding the mechanical properties of the FBF-reinforced polypropylene composites, it was found that they have a maximum average compressive strength of 17.2 MPa. A maximum bending strength of 12.109 MPa was found for the Aloe Vera gel-treated composite with 30 wt.% of FBF. The maximum average compressive strength for this composite was 17.19 MPa. A maximum bending strength of 9.97 MPa for untreated composites was recorded for the composite with 10 wt.% of FBF. Finally, Aloe Vera-treated FBF-reinforced composites have better mechanical properties than untreated ones. The mechanical properties of Aloe Vera-treated FBF-reinforced polypropylene composites, as determined via impact, compressive and flexural tests, were superior for composites with 30 wt.% of FBF.

1. Introduction

A composite is a material consisting of two or more phases on a macroscopic scale whose performance and properties are designed to be higher than those of the component materials acting autonomously. In many cases, especially for the composite materials used in structural engineering, the geometric arrangement of one phase is continuous and serves to hold the other component(s) together. This component is referred to as the matrix material. The other component(s), often referred to as inclusion(s) and/or reinforcement(s), are materials that can be either continuous or discontinuous and are held together by the matrix. The reinforcing phase provides strength and stiffness. In most cases, the reinforcement is harder, stronger, and stiffer than the matrix. There may also be interface materials, or interphases, between the matrix and the inclusion [1,2]. There are three general types of the matrix material. Metal matrix composites (MMCs), ceramic matrix composite (CMCs), and polymer matrix composite (PMCs) are the three matrixes that are used in the composite [3], automotive, and aircraft industries [4,5]. Polypropylene (PP) is the most popular plastic resin; it is one of the most frequently consumed propylene derivatives in the industry and is categorised as a thermoplastic. Approximately 50 million tons of PP are manufactured and used per annum in the world [6].

Natural composite materials are widespread in nature in the forms of plants or bones. Wood, due to its polymer components in the form of cellulose, which is an organic compound connecting the cell walls of wood, and lignin, a substance in plants that binds cellulose, can be considered a natural composite [7]. Biocomposites are considered next-generation materials because they can be manufactured using naturally sourced ingredients, ensuring sustainability, reducing the use of petroleum-based components, and supporting green chemistry [8]. Materials derived from renewable resources are sought to replace not only the reinforcing phase but also the matrix of composite materials, which solves some of the recycling problems of synthetic-based composites. Biocomposites are composite materials containing one or more phases of organic origin. The reinforcement material can be a vegetable fibre such as hemp, flax, cotton, bamboo, agave, sisal, kapok, jute, and the like. In recent years, there has been a renewed interest in composites based on natural components due to increased environmental and health concerns and the desire for more sustainable production methods and reductions in energy consumption.

Currently, worldwide environmental and economic interests stimulate research on designing new materials, a substantial portion of which is based on natural renewable resources to avoid the further degradation of the environment by petroleum-based materials [9]. Fibres from false bananas are among the widely used natural fibres [10]. Enset (or false banana) is the vernacular name used in the Amharic language for Enset ventricosum, which is a staple food crop and part of a successful and sustainable indigenous farming system in the south and southwestern parts of Ethiopia [11,12]. Depending on the type of clone, environmental conditions, and management practices, Enset plants attain heights of 4 to 11 m and pseudo-stem heights of 2 to 5 m, with circumferences of 1.5 to 3.0 m. At maturity, the corm is 0.7 to 1.8 m long and 1.5 to 2.5 m in circumference. As shown in Figure 1a, the Enset plant is a source of food, mainly containing carbohydrates. About 21 million Ethiopians are Enset growers and consumers, with the number of Enset growers estimated to be 9.8 million. Figure 1b shows the sheath of the Enset plant, and the pulverised corms, after fermentation in a pit, result in the production of kocho. Kocho is the main product for making a pancake-like food.

Bulla is another important food product from Enset. It is produced from a solidified liquid after dehydrating a fresh mixture of scraped leaf sheath and pulverised corms. Bulla is consumed mainly in porridge and gruel, and in a crumbled form. The corms of some clones are cooked and consumed similarly to the roots and tubers of other crops [10,11]. The Enset plant has great potential as a source of natural fibres. False banana fibres (FBFs) are cellular clusters with diameters ranging from 100 to 400 μm [13]. Gairola et al. [14] and Mizera et al. [9,15,16] found that the creep properties and tensile behaviour of FBFs relates to their industrial application as a reinforcement in composite materials. The microstructure of natural fibres can be modified through physical and chemical treatments [17].

In general, natural fibres have the advantages of low density, low cost, and biodegradability. However, the main disadvantages of natural fibres in composites are poor compatibility between the fibre and the matrix and a relatively high degree of moisture sorption. Therefore, chemical treatments are considered for modifying the fibre surface properties [18]. Several natural fibres such as jute [19], coir [20], bagasse [21], sisal [22], FBF [14], flax, and Luffa cylindrica fibres [23] have been studied as reinforcements and fillers in polymer composites. Those studies were performed to improve mechanical properties such as tensile strength, impact strength, flexural modulus, compressive strength, etc. Natural-fibre-reinforced polymers can exhibit very different mechanical performances and environmental ageing resistances, depending on their interphase properties [12]. The principal function of the interface is to facilitate the transfer of stress from fibre to fibre across the matrix. The interfacial bond between the reinforcing fibres and the resin matrix is an important element in assuring the mechanical properties of the composites. Insufficient interface quality between the fibres and the polymer matrix is the first and most important problem in natural-fibre-reinforced composites [24].

The surface modification of fibres via chemical treatments is one of the largest areas of current research, and it could be achieved via biological treatment by using Aloe Vera after treating the fibre with NaOH. Further treatment with Aloe Vera gels could enhance the fibre’s mechanical properties by reducing fibre breakdown or increasing its strength. Aloe Vera gel is extracted from the Aloe Vera plant. Aloe Vera is a multi-functional perennial with or without a woody trunk. It is extensively distributed in sub-Saharan Africa, Madagascar, and other islands of southern Africa. Forty-six Aloe species have been recognised in Ethiopia, 24 of which are endemic [25]. Barbosa et al. [26] reported that the ascorbic acid found in Aloe Vera acts as a strong antibacterial agent that inhibits enzymatic activity and interferes with the bacterial genetic mechanism. Aloe Vera fibre-reinforced biocomposites are characterised by improved compressive, flexural, and tensile properties compared to raw-fibre-reinforced biocomposites [27,28]. Moreover, the Aloe Vera gel exerts a positive influence on the physico-chemical properties of composite alginate–Aloe Vera films [29]. The commercial and industrial applications of fibre-reinforced polymer composites and Aloe Vera-fibre-reinforced biocomposites are highly varied, with the major structural application areas including th4 aircraft and the space, automotive, sporting goods, marine, and infrastructure industries. Fibre-reinforced polymer composites are also used in electronics. For example, the applications of fibre-reinforced polymer composites in the automotive industry can be classified into three groups: body components, chassis components, and engine components. Exterior body components, such as the bonnet or door panels, require high degrees of stiffness and damage tolerance [3].

In this paper, the effect of the concentration of chopped false banana (Ensete ventricosum) fibres treated with Aloe Vera gel on the mechanical properties of polypropylene composites was studied. Four weight concentrations of FBFs, 10, 20, 30 and 40 wt.%, were considered. The mechanical properties of the manufactured biocomposites were tested using a compression test, three-point bending test, and impact test in accordance with the ASTM D695-15, ASTM D256-10, and ASTM D7264-15 standards, respectively.

2. Material and Methods

2.1. Test Material

In the present investigation, chopped FBFs were used as a reinforcement and granular polypropylene resin was used as the matrix material. FBFs were extracted mechanically from the Enset ventricusom plant by scraping the layers on inclined, flat wood, and the polypropylene matrix was collected from a local plastic bag manufacturer in Bahir Dar (Ethiopia).

The FBFs were immersed in an aqueous solution of 5% NaOH at room temperature for 12 h to enhance their surface roughness, which increases the integrity of the fibres and the matrixes. After 12 h, the FBFs were squeezed to remove any remaining liquid. The FBFs were returned to a plastic beaker filled with distilled water for 4 h with occasional stirring. The water was again changed, and the above-described process was repeated twice more. The FBFs were removed from the water after the third rinse. They were then squeezed well to remove any remaining water, and the fibres were neutralised to eliminate the remaining NaOH using acetic acid (CH₃COOH) at room temperature for 12 h. After neutralisation, the FBFs were treated using 1% Aloe Vera gel at room temperature for 12 h. The FBFs were then dried completely. After treatment, the raw FBFs had lost about 20% of their weight due to a reduction in moisture because of the dehumidification property of Aloe Vera gel.

2.2. Experimental Design

The experiment was designed by considering the FBF concentration and fibre treatment. Weight fractions of 10–40% of FBFs were used as reinforcements, and polypropylene was used as the matrix. In this study, chopped FBF-reinforced PP composites with 10, 20, 30 and 40 wt.% of FBFs were used to investigate their impact, compressive, and three-point bending properties. Aloe Vera gel-treated and untreated composites were tested. The Aloe Vera treatment was conducted after customisation and neutralisation.

Table 1. Concentration of FBF with PP during the manufacturing of both Aloe Vera-treated and untreated samples.

Specimen Type	Content, wt.%
	PP	FBF
10FBF	90	10
20FBF	80	20
30FBF	70	30
40FBF	60	40

shows the composition of the fibres and the matrix of the composites tested.

2.3. Preparation of Composite Plates

The four composite plate materials designed for this study were prepared using the conventional hand lay-up method and compression-moulding technique for the fabrication of composite plates. Composite plates were manufactured for each fibre weight for treatment with Aloe Vera and without treatment. Figure 2 presents the samples prepared.

2.4. Mechanical Testing

The FBF-reinforced PP (FBFRPP) composite specimens were tested using the compressive, impact, and three-point bending tests. The behaviour of the samples under a compressive load was assessed according to the ASTM D695-15 [30] standard, which covers the testing of the mechanical properties of unreinforced and reinforced plastics, including high-modulus composites, under compressive loading. During the test, the samples were placed in the holders of a universal testing machine, and an axial compressive load was applied. Samples with standard dimensions of 3.2 mm × 19 mm × 79.4 mm were tested. The following parameters were measured: minimum compressive force (Fpc), maximum compressive force (Fbc), minimum compressive stress (Rpc); and maximum compressive stress (Rbc).

The impact energy of the FBF-based composites was determined by using the Izod method, according to the ASTM D256-10 standard. The impact energy was calculated using a dial gauge that was fitted on the testing machine. The Izod impact test method uses a pendulum system to apply force to an un-notched specimen. This impact test allows for the strength, ductility, and notch sensitivity of composites and other polymeric materials to be determined.

The three-point bending test, according to the ASTM D7264-15 standard, was used to determine the strength properties and flexural stiffness of the composites [31]. Bars of a rectangular cross section with dimensions of 4 mm × 13 mm × 128 mm were supported on a beam and deflected at a constant rate. The support span length was 102.4 mm, and the support span to depth ratio was 32:1. The following parameters were considered: minimum bending force (Fpb), maximum bending force (Fbb), minimum bending strength (Rpb), and maximum bending strength (Rbb).

In each test, five samples were tested for each specimen type, and the average values of the mechanical parameters were determined.

3. Results and Discussion

In this section, the results and a discussion of the impact, compressive, and flexural tests are presented.

3.1. Impact Test

The impact test for the un-notched specimens was carried out by keeping in mind that the notches may induce a concentration of stress in their vicinity and the impact strength of the FBFRPP composite may be further reduced.

Figure 3 shows the effects of Aloe Vera and fibre content on the strength of the manufactured samples. As can be seen, when the fibre content increases from 10% to 40% FBF, the results show an increase in impact energy. However, the maximum impact energy was recorded at 30 wt.% of FBF for the Aloe Vera-treated FBFs (Figure 3a) due to good interfacial bonding between the false banana fibre and the polypropylene matrix. For the reinforcement of natural fibres in the matrix, several problems occur along the interface due to the presence of hydrophilic hydroxyl groups. This hinders the effective reaction with the matrix. In addition to this, pectin and waxy substances cover the reactive functional groups of the fibre and act as barriers to interlocking with the matrix [32,33]. To overcome this, early treatment, especially with NaOH, plays a vital role in making the surfaces irregular, and Aloe Vera is very crucial in increasing the mechanical strength by maintaining the hydrophilic properties. A good result was recorded for the Aloe Vera-treated FBF-reinforced PP composite. This was 60.58 J of impact energy, achieved at 30 wt.% of FBF in the PP composite, and beyond this fibre content, it was observed that the impact strength results decreased.

For the non-Aloe Vera-treated (only NaOH and acetic acid) FBF, the maximum impact energy was found in the composite consisting of 20 wt.% of FBF. Comparing these two results, which have the same fibre content but different treatments, the Aloe Vera-treated FBF-reinforced PP composites have much superior properties, with a difference of 57.15% greater than the non-Aloe Vera-treated (only NaOH and acetic acid) PP composites.

Generally, the impact strength values of the Aloe Vera-treated composites consisting of 30 wt.% of FBF are higher compared with the impact strength values of the 10 wt.%, FBF, 20 wt.% FBF, and 40 wt.% of FBF, as shown in

Table 2. Comparison of the impact energy values of Aloe Vera-treated and untreated FBF-reinforced PP composites.

Specimen Type	Average Impact Energy, J		Advantage of Aloe Vera Treatment over Non-Treatment with Respect to the Increase in Impact Energy
	Aloe Vera-Treated FBF	FBF Treated Only with NaOH and Acetic Acid
10FBF	40.34	28.01	44% greater
20FBF	53.59	34.10	57.15% greater
30FBF	60.58	31.59	91.77% greater
40FBF	52.58	21.97	142.5% grater

. This is due to good interfacial bonding between the FBF and the polypropylene matrix. This result indicates that it is important to chemically treat the FBF when using it to manufacture a composite. Alkali treatment of a natural fibre is a common method for producing high-quality fibres [34]. This shows that early alkali treatment of FBF plays an incredibly vital role in making the fibre surface irregular, and Aloe Vera plays a role in maintaining the hydrophilic nature of the FBF.

3.2. Compression Test

Figure 4 shows the effect of fibre concentration on Aloe Vera-treated FBFRPP composites with respect to the stress and force responses of the materials tested. The maximum compressive strength (Rbc) of 17.19 MPa was recorded for a 30 wt.% of FBF composite. The minimum compressive strength (Rpc) of 16.62 MPa was recorded for the composite consisting of 40 wt.% of FBF. It can be seen again from Figure 4 that the fibre content affects the compressive strength of the material, and when the fibre content increases, the compressive strength also increases up to a FBF content of 30 wt.%, and beyond 30 wt.%, the material strength decreases. Similar conclusions can be drawn for the impact of FBF content on FBFRPP composites in relation to compressive forces. The maximum compressive forces (Fbc) were found for the Aloe Vera-treated FBFRPP composite consisting of 30 wt.% of FBF, while the minimum compressive force (Fpc) was found for the 10 wt.% of FBF.

Figure 5 presents the compressive strengths for different contents of chopped FBF-reinforced polypropylene composites treated only with NaOH and acetic acid, and it can be seen that the maximum compressive strength was recorded for a 10 wt.% of FBF (12.16 MPa). When we compare only this fibre content, the Aloe Vera-treated FBFRPP composites have an advantage of 38.2% over the untreated ones, which directly implies that Aloe Vera treatment can play a significant role in enhancing the mechanical properties of FBFs.

Generally, a promising result was recorded for 30 wt.% of FBF for the Aloe Vera-treated chopped FBF-reinforced PP composite, and this is because the bonding between the fibres and the matrix is good. The maximum compressive strength of the non-Aloe Vera-treated specimens was 12.16 MPa, which was recorded for 10 wt.% of FBF. No non-Aloe Vera-treated chopped FBF-reinforced PP composite had a higher result than the Aloe Vera-treated specimens. The fibre content truly affected the mechanical properties, and the minimum results were recorded at a content of 40 wt.% of chopped FBF in the composite.

3.3. Three-Point Bending Test

The flexural test measures the force required to bend a beam under three-point loading conditions. The data are often used to select elements for parts that will support loads without variation [35]. Figure 6 shows the bending strengths of the Aloe Vera-treated FBFRPP composites. It can be seen that the bending strength is highly affected by the fibre content, and when the FBF content increases, the values of the bending strength also increase until 30 wt.% content of chopped FBF is reached in the composite, and for contents higher than this, the bending strength decreases slightly. It can be emphasised that the bonding between the fibre and matrix decreases when the fibre content increases. If there is poor adhesion across the phase boundary, then a relatively weak dispersion of force occurs, resulting in poor mechanical properties [36]. The maximum bending strength (Rbb) was recorded at 12.109 MPa for the Aloe Vera-treated chopped FBF-reinforced PP composite consisting of 30 wt.% of FBF, and minimum bending strength (Rpb) was recorded for the 40% composition. The maximum and minimum bending forces are presented as Fbb and Fpb in the figure, respectively.

Figure 7 shows the bending strength of the non-Aloe Vera-treated chopped FBF-reinforced PP composites. It can be seen that the highest bending strength was recorded for the 10 wt.% chopped FBF composite, which is 9.97 MPa. When we compare the bending strength for the Aloe Vera-treated and non-Aloe Vera-treated (only NaOH and acetic acid) chopped FBF-reinforced PP composites, the Aloe Vera-treated chopped FBFRPP composites have an advantage of 21.4% over the non-Aloe Vera-treated ones. However, comparing the bending strength for the same content of chopped FBF, for example, at 10 wt.% of FBF, the maximum bending strength was obtained for the Aloe Vera-treated samples. The Aloe Vera-treated chopped FBF-reinforced PP composites have an 8.5% superior bending strength compared to the untreated composites.

4. Conclusions

In this paper, composite plates were manufactured from chopped false banana fibres and PP matrix via two types of treatment. The first treatment used NaOH, acetic acid, and Aloe Vera gel, and the second treatment only used NaOH and acetic acid. The mechanical properties, such as compressive, impact, and three-point bending strengths, were investigated based on the ASTM standards. This was carried out to clearly understand the effects of Aloe Vera on the mechanical properties of chopped FBF-reinforced PP composites for weight contents of FBF between 10 and 40%. Based on the findings of this investigation, the following conclusions can be drawn:

• The mechanical properties of chopped FBF-reinforced PP composites were enhanced by the Aloe Vera treatment.
• The maximum bending strength was recorded at about 12.1 MPa for the Aloe Vera-treated chopped FBF-reinforced PP composite with 30 wt.% of FBF. The maximum bending strength of about 9.9 MPa for untreated composites was recorded for the composite with 10 wt.% of FBF.
• The maximum impact energy (about 60.6 J) was recorded for the Aloe Vera-treated composite containing 30 wt.% of FBF. For the non-Aloe Vera-treated composite with the same FBF content, the impact energy was about twice as low (31.59 J).
• The maximum average compressive strength (about 17.19 MPa) was found for specimen of Aloe Vera gel-treated composite containing 30 wt.% of FBF.
• When the FBF content increases, the mechanical properties of the Aloe Vera-treated FBFRPP composites increase until a chopped FBF content of 30 wt.% is reached, but beyond an FBF content of 30 wt.%, the mechanical properties decrease. This implies that the fibre weight fraction truly affects the mechanical properties of the composites tested.