Synthesis and Characterization of Polypropylene/Ramie Fiber with Hemp Fiber and Coir Fiber Natural Biopolymer Composite for Biomedical Application

Department of Mechanical Engineering, Saveetha School of Engineering, SIMATS, Chennai-, 600 125 Tamil Nadu, India Department of Mechanical Engineering, Wolaita Sodo University, Wolaita Sodo Post Box-138, Ethiopia Department of Mechanical Engineering, Aditya College of Engineering, Surampalem-, 533437 Andhra Pradesh, India Department of Mechanical Engineering, St. Peter’s Institute of Higher Education and Research, Avadi, Chennai-, 600 054 Tamil Nadu, India


Introduction
Synthetic polymer and biodegradable polymers are commonly used in bioplastic production. Biomedical applications are currently fulfilled by using natural fibers; it can be ecofriendly and offer a safe environment. The natural fibers considered for this investigation such as (a) ramie fibers, (b) hemp fibers, and (c) coir fibers were mentioned in Figure 1. Mamtaz et al. [1] give information about the composites of natural fibers through the water absorption basis with the help of various experiments. They mentioned the impact of sodium hydroxide concentration and different theoretical considerations with the number of mathematical relation equations and definitions. Van Krevelen [2] entirely explained the various details of the polymers such as natural fiber with different verities list in a clear approach. He also gives details about the fiber matrix by way of interfacial bonding. He also produced straightforward potentials summaries regarding numerous fibers mainly the hemp fiber.
Shahzad [3] studied the important and necessary characteristics such as thermal characteristics, time versus residual weight plots, temperature versus weight plots, and heat flow for the hemp fiber. They concluded that hemp fibers are good for glass fibers based on their basic characteristics except for the variability. Similarly, the matrix of biodegradable polymers, thermoset, and thermoplastic produced the greater results of the mechanical characteristics over the glass fibers. But the major disadvantage of the hemp fiber is moisture absorption which the surface treatment on the composites can reduce.
Rajak et al. [4] give the basic details of the various natural fibers like Luffa, palm, jute, banana, rice husk, kenaf, cotton, sisal, hemp, ramie, flax, and abaca also mentioned the synthetic fibers. They provide the reinforcement details and the matrix with the corresponding applications and production technique in a neat presenting method. Shahzad [5] reviewed various papers and gave details about the hemp fiber composites, and he mentioned that they could be used for automotive parts and domestic furniture. This fiber is also used as a good replacement for reinforcement of the glass fibers. The compression moulding is suitable for hemp fiber which can be used with resins like polyethylene and polypropylene. They also give recommendations for the thermoset and thermoplastic materials related to composite reinforcements.
Munde et al. [6] discussed the coir fiber, and they focused on the characteristics based on the damping and vibration. The epoxy resin, polyethylene, and polypropylene were identified as suitable for this coir fiber. The injection moulding or the extrusion methods were used to produce the components based on the structural of automobiles. Chen et al. mentioned the resins like polypropylene and polyolefin were suitable for the ramie fibers in the injection moulding method. This fiber can be used in various biomedical applications [7].
Sebe et al. [8] clearly explained the hemp fibers reinforced composites with polyester for basic mechanical properties like impact strength and flexural strength. They used the moulding method as resin transfer. The considered mechanical characteristics are improved concerning the percentage of the fiber content in the composite. Aziz and Ansell [9] investigated the polyester reinforcement of hemp fiber with Kenaf fiber composite mechanical characteristics. They used two conditions like alkali-treated and without treatment. The flexural modulus and strength reached the greatest values for the alkali-treated composites compared with the treatment condition. They also focused on the resins used for the composite preparation and concluded that polyesters had produced greater strength.
Panthapulakkal et al. [10,11] expressed that the hybridizing method is suitable for the composites of the natural fibers and synthetic fibers based on maximum mechanical characteristics. But they preferred the natural fibers because of their biodegradability. Djafar et al. [12] experimentally analysed the reinforced composites of the ramie fibers with epoxy resin and woven ramie fibers. They only focused on bending and tensile stress with SEM images and Fourier transform infrared spectroscopy analysis results. Yu et al. [13], Paiva et al. [14], and Goda et al. [15] studied and expressed ramie fiber is the suitable fiber for the reinforcement composites when compared to other fibers. It has the maximum usage in textile productions. It has the greatest tensile property from four hundred to a maximum of 1600 MPa; these values are greater than jute and flax fiber. Ramie is the preferred fiber for the research.   Srinivas et al. [16] explained natural fiber composites and mentioned the basic properties of the coir, ramie, and hemp fiber. Lakshumu Naidu et al. [17] mentioned various natural fiber basic physical properties and chemical properties. Mwaikambo [18], Ticoalu et al. [19], and Sen and Reddy [20] explained the various applications of the various natural fibers among the important applications were discussed. Hemp fiber is used in products for construction, furniture, packaging materials, textiles, etc. Similarly, coir fibers are also used for roofing sheets, casing of mirrors, ropes, brushes, paper weights, etc. Likewise, ramie fiber can be used as nets for fishing, filter cloths, materials for backing the products, sewing threads, furniture, etc.
There are many reports on the mechanical and physical properties of natural fiber reinforced polymer composites, but the effect of coir fiber and hemp fiber on the mechanical behavior of ramie fiber reinforced polymer composites is scarcely reported. The objective of this research work newly attempts to prepare the biopolymer for biomedical applications using different natural fibers. The prepared composites were tested to find the tensile strength, percentage of elongation, and Young's modulus properties. Ramie fiber considers as the base fiber. The different volume percentages of hemp fiber and coir fiber were taken. There are two sets of fiber composite fabricated for the properties comparison. One set is the composites of the ramie fiber with hemp fiber and another composite created with ramie fiber with coir fiber in various combinations of volume percentage of the fiber. The basic desirable mechanical properties were measured and compared to identify the fibers' maximum output-based volume percentage contribution.

Experimental Setup
There are two sets of composites fabricated. They are increasing hemp fiber concentration and decreasing ramie fiber concentration in total volume. In this investigation, two sets of composite fiber combinations in each set contain the ramie fiber's participation in the percentage of volume in total volume. The fiber composite of set 1 contains the ramie fiber with hemp fiber in various proportions as per Table 1. Similarly, the composite of set 2 contains the ramie fiber with the coir fiber in different proportions as per Table 2 with reducing ramie fiber volume with the incremental volume of the coir fiber volume in the total volume of the composites.
In this investigation, the two sets of composite fiber combinations in each set contain the ramie fiber's participation in the percentage of volume in total volume. There are two sets of composites fabricated. The fiber composite of  3 International Journal of Polymer Science set 1 contains the ramie fiber with hemp fiber in various proportions as per Table 1, like increasing hemp fiber concentration and decreasing Ramie fiber concentration in total volume. Similarly, the composite of set 2 contains the ramie fiber with the coir fiber in different proportions as per Table 2 with reducing ramie fiber volume with the incremental volume of the coir fiber volume in the total volume of the composites.
There are five composites created for each set of combinations. The biodegradable and bioresorbable polypropylene is used as a resin because it can be suitable for these three fibers. Hemp and coir have the individual mechanical properties higher and lower, respectively, when compared with the ramie fiber. So, the impacts of the combinations were considered for this investigation. The ancient method like compression moulding is selected to ASTM D3822 standard produce the specimens in 120 mm × 150 mm × 10 mm [21]. The two sets have similar dimensions. There are nine different specimens prepared because 100 percentage ramie fiber results can be used for both sets.
There are four different mechanical properties identified through testing. Tensile strength, percentage of elongation, and Young's modulus can be done with Figure 2 mentioned universal testing machines with the standard specifications of the specimens. Tensile test and percentage of elongation were done in the same specimen. Based on these two values, Young's modulus can be derived by the relation of the stress-strain equation-based calculations. The measuring weight comparison can identify the density of the specimens with the volume occupied relation such as unit mass per volume. Then, the corresponding values are identified for the analysis.

Results and Discussion
The experimental results were tabulated in Table 3 for set 1. They set 2 of the composite combinations, but the table mentions both coir and hemp fiber only because the ramie fiber covers the remaining percentage of the composite for both sets of composites. So the comparisons were also created with the coir and hemp fiber only, and there is also the mention for ramie fiber which is understood. Figure 3 mentioned the percentage of elongation result comparison as a bar chart. 100% of coir have the highest percentage of elongation which is the individual composite. But the combination of 25% of ramie and 75% of coir fiber composite reached the maximum elongation (15.44%) and the minimum percentage of elongation (1.982%) obtained by the composite of the composite 25% of ramie and 75% of hemp fiber. These percentage elongation variations are also represented as the contour plot in Figure 4 with various colours. The minimum and maximum percentage variations were mentioned as the various intensity in the diagram with different colours. The minimum range starts from 0 to 5%,   The tensile strength-based result was mentioned in the bar chat in Figure 5 and the contour plot in Figure 6 for clear identification. The highest tensile strength is achieved for the 100% of the hemp fiber composite specimen. There is no ramie fiber contribution. So the maximum tensile strength such as 800 MPa is obtained for the composite with 75% of hemp fiber with 25% of the ramie fiber composite [18]. Similarly, the lowest tensile strength was obtained for the 25% ramie fiber with 75% coir fiber composite. But the coir fiber-based maximum tensile strength is obtained at     International Journal of Polymer Science 455 MPa of tensile strength for the composite with 75% of ramie fiber, and the remaining 25% is coir fiber in the total volume of the composite. Figures 7 and 8 showed the experimentally measured and calculated density values variations of the composites as the graphical representation of bar chart and contour plot, respectively, with the standard deviation of 1.25 [19]. The maximum density is obtained for the individual fiber composite of the ramie fiber composite such as 1.57 g/cm 3 . Similarly, minimum density can be reached for the individual fiber specimen of the coir fiber as 1.29 g/cm 3 . But the combination-based composite of 75% ramie fiber and 25% hemp fiber reached a higher density of 1.552 g/cm 3 than the composite of the 25% coir and 75% ramie fiber-based density of 1.514 g/cm 3 . Contour plots have the two variation regions only such as 1.5 to 2.0 g/cm 3 and 1.0 to 1.5 g/cm 3 .
The outcomes of Young's modulus of set 1 and set 2 were mentioned in Figure 9 as a bar chart similar to Figure 10 as a contour plot. The highest Young's modulus (69 GPa) value is reached for 100% of the hemp fiber individual composite. Similarly, a very low Young's modulus value such as 7 GPa is reached for 100% of individual coir fiber composite [20]. But the combination of mixing-based composite has the following results. The 75% of hemp and 25% of ramie fiber composite reached the highest Young's modulus as 58.75 GPa.  Similarly, the 25% of coir fiber and 75% of ramie fiber composite produced 35.8 GPa of Young's modulus value [21]. The individual ramie fiber composite has Young's modulus of 43 GPa. The use of hemp fiber and coir fiber mixed with biodegradable and bioresorbable polypropylene/ramie fiber can produce joints and bone fixtures to alleviate pain for patients.

Conclusions
This examination of comparison of properties on ramie fiber with hemp fiber and coir fiber composites gives the following as a comparison results (i) Both the combination of set 1 and set 2 of the fiber composite can be produced (vi) The percentage of elongation of set 2 has greater results than the set 1 fiber composites such as 15.44% (vii) Here, 25% of the coir fiber with 75% of the ramie fiber produced the maximum % of elongation results (viii) Hence, the ramie fiber with hemp fiber (set 1) is suitable for the tensile strength, density, and Young's modulus-based biomedical applications. The ramie fiber with coir fiber (set 2) is suitable for elongation-based biomedical applications (ix) The use of hemp fiber and coir fiber mixed with biodegradable and bioresorbable polypropylene/ramie fiber can produce joints and bone fixtures to alleviate pain for patients

Data Availability
The data used to support the findings of this study are included in the article. Should further data or information be required, these are available from the corresponding author upon request.

Disclosure
This study was performed as a part of the Employment of Wolaita Sodo University, Wolaita Sodo, Ethiopia.