Fabrication and Performance Investigation of Natural-Glass Fiber Hybrid Laminated Composites at Different Stacking Orientations

ABSTRACT As the resources are declining globally, researchers are constantly looking for the development of new materials. The composite materials using natural fibers are one of the best solutions nowadays in this regard. In third-world countries, jute is produced abundantly. Moreover, banana is widely available due to their reproduction ability from an existing plant. This study involves the use of jute-glass fiber laminas and banana-glass fiber laminas with epoxy resin, individually, to produce hybrid laminated composites. Different Stacking orientations such as [0°/G/G/0°], [0°/G/G/30°], and [30°/G/G/30°] have been utilized for both jute and banana fibers to find the best hybrid laminated composite. The mechanical properties such as tensile, flexural, impact, hardness, and heat reversion properties along with some physical properties like density, specific gravity, and water absorption of these hybrid laminated composites have been tested according to the ASTM standards. The fracture surface has been examined using scanning electron microscopy (SEM) for microscopic visualization. It has been found from the experimental results that the jute-glass fiber composite shows better mechanical and physical properties, and among all the stacking orientations, [0°/G/G/0°] orientation provides higher tensile strength, flexural strength, and physical properties, whereas [0°/G/G/30°] orientation shows the better impact and hardness properties.


Introduction
For a long time, specialists and researchers have been persistently trying to identify more novel materials that may accelerate the pace of advancement. Furthermore, nature consciousness is 370%. Similarly, sisal/glass hybrid composites showed an increasing trend for tensile strength with the increasing glass volume fraction (Arumugam et al. 2020). Natural fibers are mostly hybridized with glass fibers for application in numerous field because glass fibers offer a low-cost solution than carbon, aramid, etc. fibers as well as has compatible properties with natural fibers which ensure better hybridization (Shahzad and Ullah Nasir 2017;Vigneshwaran et al. 2020). Furthermore, different orientations of fibers or different plies and different volume fractions of the fibers are responsible for the variation in mechanical properties (Shahzad 2019). (Sujon, Habib, and Abedin Sujon, Ahsan Habib, and Zoynal Abedin 2020) experimented on the jute fiber at a constant volume fraction (25%) with different stacking orientations to evaluate the variation in tensile strength. Subsequently, the thickness also plays a vital role along with orientations according to (Banakar, Shivananda, and Niranjan 2012) as they evaluated the impact of thickness and fiber orientations on the glass/epoxy resin composite. They took three different orientations for each of the 2 mm and 3 mm thicknesses, and it has been observed that the tensile strength decreases with the increasing thickness. In addition, similar to the tensile strength, the orientation also affects the flexural strength (Sandeep et al. 2014). (Shuvescha, Parvin, and Rafiquzzaman 2017) analyzed the coconut midrib epoxy composite at different fiber orientations to identify the variation in hardness and impact strength along with flexural variation. In addition to the fiber orientations, different fiber contents or volume fractions of fibers may have effects on the mechanical properties of the hybrid composites (Kaleemulla and Siddeswarappa 2010). (Ramesh, Palanikumar, and Reddy Ramesh, Palanikumar, and Hemachandra Reddy 2016) worked on the jute-sisal-glass hybrid composite with volume of 40:0:60,0:40:60 and 20:20:60 to evaluate the mechanical properties like tensile, flexural, impact, etc. with two different orientations by modulating the volume fraction. It has been found that the 0 � oriented hybrid composite provides better mechanical properties than the 90 � oriented composite, and Jute-sisal-glass hybrid composite with a volume ratio of 0:40:60 provides the lowest strength where jute was absent. Following these, (Shuib et al. 2019) made a compression plate for the healing purpose of tibia fracture by maintaining the same stacking sequences between the bamboo fiber and glass fiber where only the orientation played a variable role. They analyzed different fiber orientations of the bamboo fiber to find out better tensile and flexural strength. Due to the fiber length variation, the mechanical properties of the banana-glass fiber composites change with the variation of fiber loading or volume fraction (Joseph et al. 2002).
Though researchers put great attention on hybrid composites with different stacking sequences using Jute/Glass and Banana/Glass individually, no work done regarding Jute/Glass or Banana/ Glass where the different orientation of natural fibers (jute or Banana) plays a significant role in a constant stacking sequence. This novel work consists of 4 layers of hybrid composites fabrication following [0°J/G/G/0°J], [0°J/G/G/30°J], [30°J/G/G/30°J], [0°B/G/G/0°B], [0°B/G/G/30°B], and [30°B/G/G/30°B] arrangements and characterization of mechanical and physical properties to determine the best-oriented material as well comparing the hybridization effect of Jute and Banana fibers individually within identical arrangements. Consequently, composites were tested to evaluate their mechanical properties (e.g., tensile, flexural, impact, heat reversion, and hardness properties) and physical properties (e.g., density, specific gravity, and water absorption properties). The fracture surfaces were also investigated using scanning electron microscopy (SEM).

Materials collection
For preparing the jute-glass fiber and banana-glass fiber hybrid composites, the natural jute fiber was collected from a local jute mill situated in Khulna, Bangladesh. The natural banana fiber was collected from the "Eco-banana fiber extraction plant" in Shivganj, Bogura, Bangladesh. Bi-directional E-Glass fibers were obtained from local suppliers "Real Fibre Glass Industries," Dhaka, Bangladesh. For binding purposes, the epoxy ly556 and hy951 were used and purchased from "Herenba Instruments and Engineering" located in Chennai, India. A handloom was utilized for unidirectional fiber-making purposes. The handloom bar was made from an ebonite material cutting shop in Khulna, Bangladesh. The mechanical and physical properties of the usable materials are listed in Table 1.

Materials preparation and fabrication process
In order to fabricate Jute-Glass and Banana-Glass hybrid composites, first assignment was unidirectional mat preparation using Jute and Banana individually. For that reason, a handloom was used to incorporate the fibers in straight direction for ensuring 0° parallel fibers. Figure 1 illustrates the unidirectional fiber materials and utilized handloom structure.
After completing the mat preparation, the unidirectional jute and banana fiber materials were cut into 19 cm × 25 cm size, weighted, and mixed with resin and hardener following 30:70 constant volume fraction shown in Table 2. Again, according to stoichiometric consideration, 11:1 ratio between epoxy resin and hardener was maintained. hand lay up technique was followed to fabricate the hybrid laminated composites. For both jute and banana fiber composites, the stacking sequences were the same. Figure 2 shows that the woven glass fiber was fixed between jute fiber or banana fiber materials. Here, three stacking sequences were common for both jute and banana fiber hybrid composites.

Tensile testing
A dog-bone-shaped specimens were used for the tensile tests. To perform the tensile test, the ASTM D3039 was followed along with the dimension of the specimen was taken as 150 mm × 30 mm. Moreover, 300KN Shimadzu AGS-X universal testing machine (UTM) was used with 10 mm/min crosshead speed. The workpiece was exposed to an axial load while it was clamped on both sides of the jaws of the testing machine. Before the load was applied, a gauge length 30 mm was selected according to the composite material standard for the strain calculation. Furthermore, the ultimate force was recorded depending on the gauge length variation.

SEM analysis
The tensile strength difference between the jute-glass fiber and banana-glass fiber hybrid composite was illustrated utilizing the morphological view of their fracture surface by using the ZEISS EVO/18 Research Scanning Electron Microscope, Germany. Each sample was cut 10 mm above the fractured zone after the tensile test. The fractured surface was viewed at 50x, 100x, 150x, 250x, and 500x magnifications.

Flexural testing
The flexural properties of the hybrid composites were tested by a three-point loading framework, where the distance between the two static points was 110 mm, and the loading point applied force on the center of the specimen length. 135 mm × 20 mm dimension was maintained for each type of specimen according to the ASTM D790. A computerized INSTRON universal testing machine was used for the three-point bending test. A 10 KN load cell with a 2 mm/min cross-head speed was used to ensure continuous loading. Furthermore, the span length of the specimens was 80% of their original length following the ASTM instruction.

Impact testing
The impact strength of the jute-glass fiber and banana-glass fiber hybrid composites was tested using the "Semi-Automatic Digital ASTM Charpy Impact Testing Machine, Model: TFIT (ASTM)." For the impact test, the ASTM-A370 was followed. The specimen was gripped in an impact tester horizontally so that the pendulum strikes at the specimen's v-nose with sufficient kinetic energy. The capacity of the Charpy impact tester was 400J.

Hardness testing
Rockwell hardness tests were carried out. In the Rockwell testing machine, a minor or primary force was delivered to the specimen using a ball indenter. But the Rockwell hardness value was derived from the initial and final depth conditions. The Rockwell hardness technique determines the permanent depth of the surface created by the ball indenter. For the Rockwell hardness method, the ASTM E-18 was followed. The specimen size was 10 mm × 10 mm.

Heat reversion testing
The heat reversion method is usually applied to determine the thermal resistance of a material against a high temperature. An electric oven was used for heating the composite materials and heat reversion (%) was calculated following equation (1). Before putting into the oven, the composite specimen was marked at two points at a distance of 40 mm between them. Then the specimen was submerged into the diesel oil that had a flashing point of 85°C. After 15 minutes of heating, the specimen was removed from the oven, and the length between the marked points was measured.
Where, ΔL j j = L 0 -L; L is the distance between marked points after test and L 0 is the distance between marked points before test.

Density testing
For the determination of density, the dry weight of all specimens was measured using a 4-digit weight balance machine. Besides, the thickness of all specimens was measured by using digital slide calipers. Then the mass of each specimen was divided by its volume to find the density. It is noted that the density of the specimen means the apparent density of the specimen as the internal void was not considered.

Specific gravity testing
For the specific gravity measurement, the dry weight of each specimen was measured by a 4-digit weight balance machine. A 250 mL beaker full of water was employed, where each type of specimen was immersed with a fixed thread. Moreover, the weight of the specimen was determined cautiously so that the specimen was not in contact with the beaker's sidewall. The following formula was followed for determining the specific gravity of all specimens: Specific gravity ¼ Dry weight Water weight after immersion À Water weight before immersion

Water absorption testing
The water absorption test was carried out to determine the exact moisture affinity of the jute-glass fiber and banana-glass fiber hybrid composites. A 120 mm × 20 mm sized rectangle specimen was used according to the ASTM-570. The dry weight of all specimens was measured by a 4-digit weight machine before immersing them into normal water. After a week, the weight gain of the submerged specimen was determined by percentage using the following equation: Where, w 1 is the dry weight of the specimen, and w 2 is the weight of the specimen after immersion.

Tensile properties
The results of the tensile test for all hybrid laminates are recorded in Table 3. From the tensile test results, it was apparent that the jute-glass fibers-oriented hybrid composites possessed higher tensile strength than the banana-glass fiber-oriented hybrid composites for the same orientation. The comparative stress vs strain curves developed from the UTM for all types of hybrid laminates are exhibited in Figure 3 The modulus of elasticity of all specimens was determined utilizing the linear portion of the stress-strain graph. When a specimen arrived at its yield quality, it began to act as a fragile material and started to break. Figure 4 illustrates the comparisons between all types of hybrid-oriented composites. It was observed that the [0°J/G/G/0°J] orientation provided the highest tensile strength of 106.50 MPa, whereas the [30°J/G/G/ 30°J] orientation delivered 80.21 MPa tensile strength only. The huge difference between these two tensile strengths was because of the different fiber orientations. For both jute and banana fibers, the 0 � fibers at both upper and lower surfaces provided the highest tensile strength. But when the 0 � fiber was replaced by 30 � fiber, the tensile strength declined, and the strength was lowest when both of the upper and lower surface fibers were replaced by 30 � fibers. As a result, the [0°J/G/G/0°J] orientation showed 106.5 MPa tensile strength but in the case of [0°J/G/G/30°J] and [30°J/G/G/30°J] orientations, the strength reduced by 13.33% and 24.67%, respectively. Similarly, this decreasing trend was followed by banana-glass fiber composite. The [0°B/G/G/0°B] orientation provided 84.82 MPa tensile strength, whereas the strength deteriorated by 19.02% and 48.96% for the [0°B/G/G/30°B] and [30°B/G/G/30°B] orientations, respectively. It was also noted that [0°B/G/G/0°B] orientation had higher tensile strength than the [30°J/G/G/30°J] orientation. The modulus of elasticity of the fiber was also affected by fiber orientation as the [0°J/G/G/0°J] orientation provided 12.22 GPa Young's modulus but the [30°J/G/G/30°J] orientation delivered only 4.07 GPa. The banana-glass fiber composite also maintained this diminishing trend. Though normally, banana fiber shows very less but higher strength than the jute fiber. However, in this study jute-glass fiber composite shows higher strength than the banana-glass fiber composite. Similar to the tensile strength, the jute-glass fibersoriented hybrid composites exhibited a superior modulus of elasticity compared to the banana-glass fiberoriented hybrid composites for the same orientation. Stress (N/mm2)

SEM observation
The fractured surfaces were investigated extensively by Scanning Electron Microscope (SEM) to determine and characterize the microscopic mode of fractures as shown in Figures 5-8. Generally, up to the elastic limit, the bonding between the matrix phase and fibers remains very strong. However, after the elastic limit, the adhesion characteristics become very weak. That's why the matrix phase starts to crack with the increasing load. Usually, the fibers show higher strength than the matrix phase, which is the reason behind the cracking of the matrix phase before the fibers (Furtos et al. 2013;Jacob et al. 2005).
There are many factors for reducing strength, such as air voids, fiber orientations, adhesion or bonding, agglomeration, etc. It was observed that the matrix phase-fibers bonding started to loosen due to the applied load that affected the cracking of the banana fibers. At the high strength, the glass fibers initiated to break after ensuring the banana fibers pull-out due to the uneven transfer of stress between the fibers. This was the result of agglomeration that happened due to the fibers compacting together in the matrix phase. By comparing Figures 5 and 6, it could be concluded that, as the matrix phase broke drastically in the [30°B/G/G/30°B] orientation, its fibers pull-out occurred at a lower strength than the [0°B/G/G/0°B] orientation. Concurrently, the 30° banana fibers were not sufficiently strong to hold against the crack propagation because the load-bearing fibers were too weak compared to the 0° banana fibers. Furthermore, the matrix and fibers delamination were a big issue for the fracture before a considerable load. But the [0°B/G/G/ 0°B] orientation delivered a great tensile strength because of its availability of high load-carrying fibers, even after its matrix phase got broken after debonding. (Braga and Magalhaes 2015) observed the microstructure of Jute-Glass hybrid composites using SEM and saw a few voids between matrix and jute fibers because of having random fibers pullout. Similarly, we observed the pull-out of jute fibers and glass fibers occurred at the rear side as shown in Figures 5 and 6 respectively. Nevertheless, adequate interfacial bonding between matrix phase and fibers can reduce the possibility of earlier cracking as matrix can transfer stress toward high load carrying fibers (Furtos et al. 2012). It was clearly observed from Figure 7 that the pull-out of jute fibers and glass fibers occurred at the rear side in the [0°J/G/G/0°J] orientation. The matrix-phase bonded with the fibers comparatively better than other combinations. As the strong fibers were capable to carry a high-scale load, the 0 � fibers were able to withstand the increasing load. But Figure 8 shows that the [30 � J/G/G/30 � J] orientation had high delamination and pull-out of fibers. On its upper surface, some debris was visible, which influenced the reduction of its strength. Besides, more delamination had been found in the 30 � jute fibers compared to the 0° jute fibers. As high stress acted on the small concentrated surface of [30 � J/G/G/30 � J] orientation, the high-scale delamination happened. Therefore, its weak fibers were unable to carry high loads.

Flexural properties
The flexural properties of the six different types of hybrid laminates were estimated with the UTM. The flexural test results are summed up in Table 4. The results revealed that similar to the tensile strength, the jute-glass fiber hybrid composites showed superior flexural strength than the banana-glass fiber hybrid composites for the same orientation.  Before the load reaches its capacity it is distributed evenly between the fibers and matrix in the laminates. The crack starts where the fiber-matrix adhesion is poor and begins to spread over the entire length of the laminate section. The density of all specimens was between 990 and 1350 kg/m 3, but the jute-glass hybrid composite had higher density than the banana-glass hybrid composite for the same orientation.    comparative stress vs strain curves developed from the UTM for all types of hybrid laminates are illustrated in Figure 9.

Impact properties
The impact test was carried out for the six different hybrid laminates, where the energy loss was detected by the Charpy impact tester. It was observed that the impact test result was different from the previous flexural and tensile tests in terms of orientation. The diverse stacking sequences can alter the distinctive strength parameters such as the dissipation energy, initiation energy, and total energy (Pothan, Thomas, and George 1999). Due to the pendulum tip's striking on the composite, the crack initiated to propagate; but before cracking, some amount of energy got absorbed in the fiber. The crack could not propagate linearly as the resin acted as a matrix phase in between the fibers. In order to compare the impact values of jute-glass fiber and banana-glass fiber hybrid composites, Figure 11 has been developed. It was observed that the [0°J/G/G/30°J] orientation had a higher impact strength than the [0°J/G/G/0°J] orientation. Because when the 0° fiber of the lower surface was replaced by 30° fibers, the crack experienced different types of surfaces on the upper and lower surfaces of the specimen. Therefore, the crack covered more specimen surface area and took more time to propagate, thus enhancing the energy absorption (Navaneethakrishnan et al. 2019). When the thickness and fiber volume fraction amplify, the adjusted fibers require high energy to break down (Jiyas, Kumar, and John 2016). It is apparent that the banana-glass hybrid composite always had a slightly higher thickness than the jute-glass hybrid composite, even though the same volume fraction was maintained for both of them. Therefore, all banana-glass fiber hybrid composite orientations showed higher impact energy than the jute-glass fiber hybrid composite because of their difference in thickness only.

Hardness properties
The comparison among their average hardness numbers is shown in Figure 12. The experimental results showed that the jute-glass fiber hybrid composite exhibited a higher hardness value than the banana-glass fiber hybrid composite for the same orientation. The [0°J/G/G/0°J] orientation had an average hardness number of 96.5 HRB, whereas the [0°B/G/G/0°B] orientation showed only 77.166 HRB. Similarly, the [0°J/G/G/30°J] and [30°J/G/G/30°J] orientations had larger HRB values than the [0°B/G/G/30°B] and [30°B/G/G/30°B] orientations, respectively. So, the jute-glass fiber hybrid composite was harder than the banana-glass fiber hybrid composite. Moreover, the fiber orientation greatly influenced the hardness of the composite surface. The [0°J/G/G/30°J] orientation had higher hardness than the [0°J/G/G/0°J] and [30°J/G/G/30°J] orientations. Similarly, the [0°B/G/G/30°B] orientation was harder than the [0°B/G/G/0°B] and [30°B/G/G/30°B] orientations. So, similar to the impact strength, the dissimilarly oriented fibers on the upper and lower surfaces of the composites exhibited higher hardness than the similarly oriented fibers. Although the value of HRB greatly fluctuated among the banana-glass fiber hybrid composite orientations, the various orientations of jute-glass fiber hybrid composite showed slight differences.

Heat reversion properties
For determining the ability of the composites to withstand heat, the heat reversion test was carried out at 60°C, 80°C, 100°C, 120°C, 140°C, and 150°C temperatures. When the temperature goes down to room temperature residual stress formed on composites structures which has significant impact on materials properties. But the level of residual stress mostly depends on the temperature difference between heated specimen and exposed room temperature, expansion or shrinkage thermal co-efficient, volume fraction and elastic co-efficient of materials inside fibers (Parlevliet, Bersee, and Beukers 2007). Consequently, Figure 12. Variation of hardness numbers for different orientations of hybrid composites. (Butylina, Martikka, and Kärki 2013) conducted the heat reversion analysis on wood reinforced composites and found that with the increasing volume fraction of fibers, linear thermal expansion/ shrinkage decreased. Again, heat reversion value of different volume fractioned composites showed an abrupt change without any clear trend. Though in our experiment, we kept a constant volume fraction for all considerations, two different fibers stacked with matrix at different orientation. Where gap between oriented fibers, dissimilar orientation in [0 � B/G/G/30°B], [0 � J/G/G/30°J] combinations and elastic and thermal co-efficient difference between fibers might have great influence on heat reversion results shown in Figure 13. It was obvious that the temperature effect on the jute-glass fiber and banana fiber hybrid composites was very low. Up to 100°C, all the specimens had constant length. The [30 � J/G/ G/30 � J] orientation showed no fluctuation in length due to the temperature variation, whereas the [0 � B/ G/G/0°B] orientation showed higher sensibity i.g. 3.75% heat reversion up to 140°C but it again reduced to 1.25% at 150°C shown in Table 5. Similarly when the temperature was modulated from 140°C to 150°C, [0 � B/G/G/30 � B] composite showed 2.5% contraction characteristics, whereas the jute-glass fiber composite orientations remained unaltered in length. Among all the orientations, the [30 � J/G/G/30°J] and [0 � B/G/G/30°B] orientations showed slightly better resistance against the thermal change.

Density properties
Generally, density of a composite depends on the relative proportion of matrix and reinforcing materials and this is one of the most important factors determining the properties of the composites. The densities obtained for all hybrid composites are presented in Table 6. The density of all specimens was between 990 kg/m 3 and 1350 kg/m 3, but the jute-glass hybrid composite had a higher density than the banana-glass hybrid composite for the same orientation. For both jute-glass fiber and banana-glass

Specific gravity properties
The specific gravity was evaluated for all hybrid laminated composites as listed in Table 7. Though the difference was marginal for different orientations, the jute-glass fiber hybrid composite had higher specific gravity than the banana-glass fiber hybrid composite. The [0°J/G/G/30°J] orientation had the highest specific gravity, whereas the [0°B/G/G/30°B] orientation had the least specific gravity.

Water absorption properties
The water absorption behavior of the different orientations of hybrid composites was examined against the periodical time-frame. It could be easily concluded that the banana-glass fiber hybrid composite exhibited better water absorption capability than the jute-glass fiber hybrid composite at any orientation. The water absorption ability can be significantly affected due to the compatibility between the fibers, and the absorption of the polymer composite improves due to the voids and flaws of the fibers (Kulkarni et al. 2008). In Figure 14, the water absorption percentage vs immersion time has been shown to explore the water affinity behavior of different orientations of composites. The highest absorption for the [0°J/G/G/0°J] orientation was 10.218% at the end of 11 th week, whereas the percentage of absorption by the [0°B/G/G/0°B] orientation was 18.268% at the same time period. After 11 th week, both hybrid composites began to lose their moisture contents. But there was a distinction between the [0°J/G/G/30°J] and [0°B/G/G/30°B] orientations. After 11 th week, the [0°J/G/G/30°J] orientation started to release water but even then, the [0°B/G/G/30°B] orientation continued to absorb water until 12 th week. After that, it started to release water. Here, the fiber orientations played a great role in water absorption. After 4 weeks, the [0°J/G/G/0°J] orientation absorbed 6.289% water. When both upper and lower surfaces had 0° fibers, the water permeability was the same on both sides. But when one of the surfaces was substituted by a 30° fiber, e.g., the [0°J/G/G/30°J] orientation, the water entering path got reduced because the two sides provided different characteristics paths for water. So, the absorption percentage got reduced to 1.763% only. Again, when the 0° fibers of the both surfaces of Furthermore, along with the water absorption, the thickness of the hybrid composites got altered. The variation of thickness with the immersion time has been presented in Figure 15. The thickness showed a proportional relationship with the water absorption. When the moisture content increased, the thickness of all specimens gradually enhanced. Similarly, the releasing of the moisture content lowered their thickness.

Conclusion
This paper evaluated the physical and mechanical properties of the jute-glass fiber and banana-glass fiber hybrid composites by employing the appropriate standard testing methods. The specimen size was precisely maintained for all experiments. For all orientations, the same volume fraction of the fibers and resin was effectively maintained for ensuring less void fraction. The experimental results showed that the orientation played a vital role in determining the physical properties. The [0°J/G/G/0° J] and [0°B/G/G/0°B] orientations showed higher tensile and flexural strength compared to the other orientations of the same hybrid composite. In addition, the decreasing characteristics were shown by both jute-glass fiber and banana-glass fiber hybrid composites when the 0° fibers got replaced by 30° fibers. However, in the impact and hardness tests, the [0°J/G/G/30°J] and [0°B/G/G/30°B] orientations provided higher strength than the other orientations due to their crack propagation mechanism. But by SEM fracture mode analysis and from the physical performance tests, we concluded that the [0°J/G/ G/0°J] and [0°B/G/G/0°B] orientations had remarkable properties and internal structures.

Highlights
• A novel natural fiber composite which is sustainable and possesses excellent mechanical properties • High fracture strength as well as other mechanical properties such as tensile, flexural and impact • Fiber orientation has a significant effect on physical and mechanical properties

Acknowledgments
We thank all the staff of the Solid Mechanics Laboratory, Department of Mechanical Engineering at Khulna University of Engineering and Technology for their assistance in completing the mission.

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Funding
The author(s) reported there is no funding associated with the work featured in this article.

Data availability statement
The data required to reproduce these findings can be shared upon request.

Ethical approval
There are no human subjects in this article and informed consent is not applicable.

Ethical statement
This is the original work of the authors and has never been published anywhere else. The paper is not being looked at for publication anywhere else at the moment. Previous works are cited in the text and references are maintained appropriately.