**1. Introduction**

Our everyday human life has been transformed by plastic playing an important part in many aspects of life. Global plastic production from petrochemical sources is increasing rapidly, owing to its extraordinary mechanical, versatility, and barrier properties [1]. As a raw material, around 4% of the total extracted fossil fuels are consumed for the production of these bio-composites. Increasing future demand suggests that by the year 2050, 20% of total fossil fuel extracted internationally may be consumed to produce plastic [2]. The production of these plastics is creating a big challenge, as very few of them are recycled or reused [3,4]. These plastics can remain in the environment for a long period of time, even 1000 years. Moreover, the harmful effect of this waste on the environment is very high. A significant amount of carbon dioxide and other toxic gases are released from this waste, which is harmful to human health and nature [5]. Because of these effects on human health and the environment, finding an alternative has become inevitable.

Bio-composite can be a suitable alternative to petrochemical plastic. Significant development is being made in bio-composite, to make it usable. The production of these

**Citation:** Hossain, N.; Chowdhury, M.A.; Noman, T.I.; Rana, M.M.; Ali, M.H.; Alruwais, R.S.; Alam, M.S.; Alamry, K.A.; Aljabri, M.D.; Rahman, M.M. Synthesis and Characterization of Eco-Friendly Bio-Composite from Fenugreek as a Natural Resource. *Polymers* **2022**, *14*, 5141. https:// doi.org/10.3390/polym14235141

Academic Editors: Edina Rusen and Sergio Torres-Giner

Received: 19 September 2022 Accepted: 10 November 2022 Published: 25 November 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

plastics has also significantly increased, although the production of bio-composites is only 0.59% of total plastic production [6,7]. The data suggest that more research is necessary to replace harmful plastics completely in any kind of application. One big drawback of bio-composite is its high price compared to conventional plastic, which makes it uncompetitive in the market and limits its use. One alternative to reduce the cost can be the use of waste or by-products of the agri-food industry, which are produced every day in huge quantities [8]. This low-cost waste and by-products are rich in protein, making them competitive candidates to be used as raw material to synthesize bio-composite [9].

The materials of bio-composite that need to biodegrade quickly should have antibacterial properties to kill harmful viruses and bacteria produced from food, but should not have harmful effects on human health and the environment, in order to be used as biodegradable food packaging. Many researchers have synthesized composite bio-composite to improve physio-chemical properties, but such a type of bio-composite contains harmful additives, such as sulfuric acid or titanium dioxide [10–14]. Thus, it is necessary to focus on the research of synthesizing biodegradable bio-secured plastic that is not harmful to human beings and the environment, is not expensive, has antibacterial properties, is available in nature, and represents properties allowing it to be used as a true alternative to petrochemical plastic.

Starch is an available, biodegradable, and low-cost material used as a renewable polymer in wide number of applications. The production of biodegradable films using starch shows promising results, although shortcomings are still there in mechanical properties, dimensional stability, hydrophilicity, and light permissibility. A nonstructured and plasticized version of starch is known as thermoplastic starch, prepared by adding plasticizers to the mixture of starch. Plasticizers can penetrate starch molecules and form hydrogen bonds, which are necessary to increase the durability of the bio-composite [14]. Thermoplastic starch materials are cost-effective, biodegradable, abundant in nature, and renewable. However, humidity causes recrystallization problems in these materials, which drastically decreases their mechanical properties [15]. The other shortcomings of these materials are their hydrophilic character and lower thermal stability [16,17].

Throughout human history, it has been known that Fenugreek is consumed as a food and used as medicine. Its seeds are used in spices, to increase the taste of food. Numerous medicinal properties such as hypocholesterolemic, gastric stimulant, antidiabetic agent, hepatoprotective effect, lactation aid, anticancer, galactagogue, and antibacterial, are available in the seeds of fenugreek. Some of these effects are attributed to the intrinsic dietary fiber constituent. The texture of food is changed by the dietary fiber, which is almost 25% of the seeds. It is also used as a food stabilizer, emulsifying agent, and adhesive, because of its high fiber, gum, and protein content. The protein is more soluble in an alkaline solution. It helps us with digestion, and it can modify food [18,19]. Fenugreek contains up to 60% starch. Different industrial products such as polysaccharides, kernel powder, gum, starch, and oil are produced (Table 1) from fenugreek [20–22].

**Table 1.** Percentages of chemical compounds present in fenugreek seed.


Tamarind is a commercially valuable plant that grows in different parts of Asia, Africa, and America. It is an evergreen plant belonging to the Fabaceae family and Caesalpinioideae subfamily. Different parts of the tree, including leaves, seed, shell, and fiber are used in pharmaceutical, food, electrochemical, biofuel, composite, water, and textile industries [23]. Around 55% pulp, 34% seed, and 11% shell and fiber are available in a typical tamarind pod. Tartaric acid, reducing sugar, and minerals including calcium, phosphorus, and potassium are available in the pulp of tamarind seeds [24]. The pulp has antimicrobial properties and can be used as a preservative. Tamarind seeds contain Zn, Fe, Mg, P, Na, K and Ca as minerals [25]. Tamarind seeds contain polysaccharides that are naturally biodegradable and biocompatible. A typical tamarind fruit fiber contains cellulose, hemicelluloses, lignin, wax, and moisture. The tamarind shell which covers the pulp contains carbohydrates, free tartaric acid, and protein [26]. The leaves of tamarind are composed of lipids, vitamins, fatty acids, and flavonoids [27]. Table 2 shows the percentages of chemical compounds present in the tamarind seed [28].

**Table 2.** Percentages of chemical compounds present in tamarind seed.


In the current situation of increased pollution worldwide because of synthetic petrochemical plastic, biodegradable composite can be a good source that will help to minimize environmental pollution. Both tamarind and fenugreek are abundant in the local area, and can be grown in vast quantities because of the good quality of the soil. Therefore, it can be said that both tamarind and fenugreek can be used as raw materials to manufacture bio-composite as an alternative source.

The current research work shows the synthesis and characterization of biodegradability properties of bio-composites synthesized from naturally available and cheap sources, which can be used as an alternative to synthetic plastic. The purpose of this work is to show the usability of naturally cheap sources of a biodegradable composite material that can kill bacteria, so that the material can be used for food-packaging applications. The bio-composite in this research work was synthesized from naturally available fenugreek seeds. The synthesized bio-composites were characterized by biodegradable, mechanical, FTIR, SEM, XRD, thermal and antimicrobial tests.

#### **2. Materials and Methodology**

#### *2.1. Materials*

The bio-composites were synthesized by tamarind, fenugreek, distilled water, vinegar, and glycerin. After collecting the tamarind seeds from the local market of the Gazipur district, Bangladesh, they were washed properly with deionized water, boiled for 30 min, and blended to make the extract of starch. Fenugreek was also collected from the local market of the Gazipur district of Bangladesh. The collected fenugreek was also washed properly with deionized water, boiled for 30 min, and blended, and thus starch was obtained. The environmental lab of IUBAT within the department of civil engineering supplied the necessary distilled water for the experiments. Glycerin and white vinegar were also collected from the local market of the Gazipur District of Bangladesh.

### *2.2. Production of Bio-Composite*

Table 3 shows the synthesized bio-composites at different percentages of fenugreek. Initially, with the help of a precise electronic scale, all the ingredients were carefully and precisely weighted. After measuring, the mixing of the ingredients was performed using a magnetic stirrer shown in Figure 1, followed by blending. Clumping was avoided by stirring for seven minutes. Heat was applied to the process at 100 ◦C temperature. A thick and translucent mixture was obtained after some time. Aluminum foil was used for pouring the mixture, and bubbles were removed if found. The desired bio-composites were obtained after six hours of natural cooling. The thickness of the obtained bio-composite was 1 mm, and it was opaque and chocolate-colored. The obtained bio-composite samples were then taken for characterization. All the samples were made in a dry environment.


**Table 3.** The used constituents with their percentages.

**Figure 1.** Bio-composite preparation from the natural sources.

### *2.3. Characterization*

#### 2.3.1. Biodegradation Test

The synthesized bio-composites were subjected to different characterization processes. For the biodegradability test, each sample was cut to a size of 50 mm × 20 mm × 1 mm. The average weight of each sample was 10 gm. The samples were buried at 2 cm depth. The pH value of the soil was 6. Weight loss was measured by burying the bio-composite samples in soil for 7, 15, and 30 days, in aerobic conditions. Before burying the bio-composite samples under the soil, the weight of each sample was measured carefully, using a precise electronic balance. After the test, each sample was removed from the soil, cleaned with water, dried, and the weight was taken again (Table 3). The biodegradability was measured using the following formula:

$$\text{Biodegradability} \left( \% \right) = \frac{W1 - W2}{W1} \times 100$$

Here, *W*1 = the weight of the bio-composite sample before the biodegradable test. *W*2 = the weight of the bio-composite sample after the biodegradable test [29–34].

#### 2.3.2. Mechanical Test

After production, the bio-composite samples were taken for mechanical testing. A universal testing machine controlled by a computer called CMT-10 was employed to evaluate the tensile properties of the bio-composite samples. All the tests were conducted maintaining the ASTM D638-77 standard method. The samples were cut with a dimension

of 100 mm × 30 mm, in a dry environment. Then the samples were hung on a ring, using a thread at the bottom part of the samples with an attached hook, to place the loads. Maintaining a 2 mm/min strain rate, the force–distance data was measured at room temperature, and the loads were applied until the samples failed. The total length of the failure samples was measured carefully, and recorded. The total applied loads were recorded as well. Elongation and tensile strength were measured with the help of a stress–strain curve. For the same condition, 5 experiments were done for each sample, and the average value was considered.

### 2.3.3. Scanning Electron Microscopy Test

The surface microstructure of the synthesized bio-composites was analyzed by a Hitachi brand scanning electron microscope, model number S-4800. For analyzing the surface of these bio-composite samples, the bio-composites were submerged in liquid nitrogen and cut into 0.5 cm2-sized samples. Then, cryo-fracturing was performed. The cryo-fractured samples were fixed onto the support using adhesive tape and mounted on aluminum stubs. Coating of the bio-composite samples was performed with goldpalladium, to observe the microstructure.
