Mechanical and thermal characterization of additive manufactured fish scale powder reinforced PLA biocomposites

This research work is aimed to convert fish scale wastes as an effective reinforcement in polylactic acid (PLA) as a new bio-composite filament for fused deposition-based 3D printing applications. Various concentrations of fish scale particles (0, 10, 20, and 30%) were used to make the filaments. The performance of the developed filaments was assessed by printing the filament into various test specimens to perform tensile, flexural, impact, hardness, and water absorption experiments as per the ASTM standards. The outcomes of the results show that the PLA/fish scale powder (20%) composite has performed well than the remaining composites. Furthermore, the adding 20% fish scale powder increased the tensile strength and flexural strength of the 3D printed PLA composite by 15% and 39.78% respectively. This is evident that the novel bio-composite exhibited better properties than the pure polymer making it a potential replacement as bone-grafting material and scaffolds for bio-engineering applications.


Introduction
About 10-20 million seafood wastes are created every year and the significant wastes are comprised of sea shells, crab shells, fish scales, fish bones, shrimp wastes and lobsters, which are thrown out and dumped around the landscapes of the aqua medium. The dumped-in waste products pose harmful effects on the environment in terms of creating unpleasant odors, aqua medium pollution. Moreover, these polluted landscapes might be a potential insect breeding arena [1]. While it costs more to properly dispose of these wastes, employing them as sustainable reinforcement material in the development of composites would support the circular economy. From the 5 R's (Refuse, Reduce, Reuse, Repurpose, Recycle) principle, reuse and recycling are significant concerns for converting solid waste into resources instead of refuse and reduction. If properly recycled and collected, these marine wastes can be used as biocomponents for the creation of biodegradable polymers, bone grafts, and bio-scaffolds, among other things. This method will promote sustainable growth and open the door to a circular economy [2].
According to research from the World Food Organization (WFO), the world produced about 200 million tonnes of fish scales in 2016, of which 150 million tonnes came from the maritime environment [3]. Fish scales are a type of seafood that cannot be avoided. They are full of nutrients and proteins. Only 40 percent of the different nutrients are edible, and the other parts, like fish scales, are considered biowaste [4]. Every year, 8-10 million tonnes of fish scales are thrown away worldwide [5]. Chitin, protein, and minerals like calcium, zinc, Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. iron, and copper make up the fish scale. Researchers are trying to dig up the sea shell waste and get the chitin out. Various researchers directly crushed the fish scales and utilized them as value-added materials in different ways, like as adsorbents, and flocculants [6], in the production of electronic [7], medicinal [8], and polymer composite products.
Making polymer composites using bio-reinforcements is becoming a growing area of study. Bioreinforcement materials are good for the environment because they are made from the materials available in nature. It can be utilized as reinforcement in polymer composites made from organic or inorganic materials [9]. The problem with organic materials is that they tend to absorb water, which can lower the mechanical characterization of the polymer composites. To overcome researchers extended their interest to work in inorganic bio-reinforcements made from biowastes like crab shells, corals, seashells, fish, and chicken bones [10]. Researchers nowadays are exploring the use of agro waste fillers such as corncob [11], citrus limetta peel, millet husk [12], tamarind nut [13][14][15][16], banana peel [17,18], coconut shell [19], spent coffee bean [20][21][22], tea leaf [23,24], egg shell [25][26][27], corn husk [28], lima bean shell and mung bean shell [29]. Several other researchers also discussed the utilization of organic and inorganic fillers for composite applications [30][31][32].
The footprint of carbon is the main reason to think about using this biowaste to reinforce polymer composites. However, if the sustainable processing route isn't considered, the end products won't be of good quality or cost-effectively made [33]. In the 4th industrial revolution, additive manufacturing is a big part of making intelligent materials for the aerospace, cars, and medical industries. Additive manufacturing makes it possible to cut costs and use less energy during product development. This is because additive manufacturing doesn't require special tools like fixtures and moulds to make the parts [34]. Therefore, it saves more energy regarding materials and time when making parts, and the parts made at the end are more accurate. The fused deposition modelling process is the best of the additive manufacturing methods because it requires less money upfront, works faster, and can be used with more complicated designs [35]. PLA is a potential material with better biodegradable and biocompatible properties, making them suitable for developing biomaterials [36]. Bioactive glass, Ca 3 Po 4 , carbon-based particles, Ti, and Mg were reinforced to the PLA matrix to enhance its important properties of both mechanical and thermal. The reinforcement material and polymers were thoroughly mixed and then an extrusion process was carried out to produce composite filaments that can be used in 3D printing. Before using the filament by adopting polymeric 3D printing, the filament's quality needs to be checked and improved. More scientists are trying to improve the function of filaments made from polymeric composite through the extrusion process by adding different organic and inorganic reinforcements [37].
Marton et al used waste from an Australian royal palm to reinforce acrylonitrile butadiene styrene filaments for 3Dimensional printing. Different amounts of fibre loading (5, 10, 15, and 20 wt%) are used to pull out the filaments. The results showed that it is possible to make a filament by reinforcing it with wood particles that are 50 μm in size, and the 15% Australian palm fibre composition works better than the other compositions [38]. Jingjing Liao et al used PLA with accelyted tannin filler; the PLA with 20% accelerated tannin did not impact the end product tensile qualities. For safe processing, a temperature under 250°C is advised for 3D printing. When printing with PLA and AT, one can prevent the printing flaws of phase separation and acetylated tannin aggregation by using temperatures lower than 220°C [39]. Salonika et al reported that PLA/Diatomaceous Earth (DE) filament, with the addition of 10 wt% DE, the yield point reduced by 3% to 35.02 MPa. With the addition of 15 wt% diatomaceous Earth, it can accept significant declines in all parameters except for young's modulus. The degradation of material characteristics results from the PLA/DE composition. Young's modulus and yield stress levels can significantly increase when adding diatomite [40]. Yogeshwaran et al investigated the preparation of biocomposites polymer-fish scale waste to improve the mechanical properties of tensile (108 MPa), flexural (8.15 MPa), and impact (7.5 J) [41]. Rajasekaran et al investigate the effects of different volume fractions of fish scale reinforced fiber with epoxy resin on the mechanical properties. The composite exhibited the following strengths: Tensile strength of 40% was 24.2 N mm −2 , Flexural strength of 30% was 63.6 N mm −2 , and Impact strength of 25% was 5.5 J. Similar trends were observed in the analysis of hardness properties. However, the addition of more fish-scale fiber led to a decrease in mechanical characteristics due to the uneven distribution of the fiber within the epoxy matrix [42].
Different reinforcing particles of cellulosic and non-cellulosic were utilized to develop PLA-based polymeric bio-composites. By means of fused deposition modelling & 3D printing pens, the extruded filaments were used as a precursor to making polymer composites. Using the FDM method, more studies are focusing on developing PLA-based bio-composites [43]. However, from the available literature, works in reinforcing fish scale waste in PLA matrix to create 3D printable filaments are scarce. Further, comprehensive studies on the effects of fish scale waste inclusion in the mechanical behavior of the PLA matrix need further advancement. With the aforementioned gaps in mind, the work has been performed to produce PLA-reinforced fish scale powder filament for 3D printing. Three distinct combinations (10%, 20%, and 30%) of fish scale powders were chosen. The developed novel filament has been used to print various test specimens based on fused deposition modelling. FTIR, TGA, and XRD characterizations were done on the newly developed composites. Mechanical characterizations like tensile, bending, hardness, impact, and water absorption tests were performed on the 3Dprinted test specimen. Scanning electron microscope studies reveals the fractured morphological surface of the tested sample.

Materials
INGEO 3D850 extrusion-grade polylactic acid pellets were purchased from Kare 3D printing technologies. Asreceived spherical shape PLA pellets with pale white color, were the properties of 1.24 g/c.c. specific gravity, melt flow index of 7 g min −1 [according to ISO 1133-A at 190°C/2.16 kg], melting temperature of 180°C [Tm], and temperature of glass-transition [Tg] of 60°C. Fish scales were collected from the local fish markets in and around the Kumbakonam region of Tamilnadu. The collected fish scales were milled to powder at Aquaculture Specialists Ltd., Chennai. A large quantity of cutla fish scales (0.1 mm-0.2 mm thick and 10-15 mm long) was collected from the Kumbakonam fish market shown in figure 1; fish scales were initially cleaned in doubledistilled water and then dried for 24 h at 80°C in an air oven. After removing the scales (160-300 g) and washing any surface pollutants away with clean aqua, the fish scales were submerged for two days in 6 L of deionized aqua. The collagen, protein, and limiting fish scale layer were mostly removed from fish scales by stirring it at 500 rpm for roughly 2 h at room temperature in 1000 ml of 0.25 M HCl. Deionized water and 0.5 M NaOH were used to wash the fish scales until the pH was about 7.0. Finally, the washed fish scales were placed in the furnace for three hours at 900°C to produce a crude product, which was then ground and strained through the fabric to make the final FS powder shown in figure 1, which has a particle size of 30 to 45 μm in range.

Extrusion of filaments and its characterization
The composite precursors were used to create three different mass ratios of PLA: FSP (90:10, 80:20, and 70:30). The raw materials of PLA and FSP were stirred for 2 min at 180 to 195°C and 200 revolutions per minute (rpm) using twin screw extruder. After mixing the composites, membranes were squeezed from the material using a hot press and dried. Standard sample sizes were carved out of these paper-thin plates for subsequent analysis.
The 3D printing filaments were extruded (as per the parameters listed in table 1) under 220°C temperature with a rotational velocity of 50 rpm of the screw. The extruded filament diameter is maintained at 1.75 ± 0.05 mm by regulating the coil speed during extrusion. The compounding procedure, filament synthesis, and 3D printing uses are all depicted. The samples were made using a 3D printer that extrudes material at a temperature of 190°C temperature and a speed of rotation at 6 rpm. Printing of Single-layer (about thickness 0.05 mm), the x and z-axis speeds were set to 150 and 23 mm s −1 . The original filament did not have any gaps in the diagram. They were stacking the filaments to create the final 3D-printed item, resulting in a gap between the tapes. After stacking, the result is porous because of the 0.5-50 μm width and 80-130 μm length gaps between the filaments.
The variations in surface chemical composition caused by the bio-filler chemical treatments were studied using FTIR. The Spectra 100 FTIR spectrometer of Perkin Elmer was utilized. scanning was done with a resolution of 4 cm −1 over a range of 400-4000 cm −1 at a scanning speed of 2 mm s −1 . X-ray diffraction (XRD) study employing an X-ray diffractometer was utilized to examine the synthesized fish scales' crystalline structure and phase morphology (Rigaku MiniFlex 600). Radiation Cu K (λ = 0.154 nm) was used to do the analysis, with the operating conditions of current and voltage set at 40 mV & 40 kV respectively, over a 2θ range of 10°−80°.

Mechanical testing
PLA: FSP were produced at different proportions (90:10, 80:20, and 70:30) and subjected to measure the tensile strength, flexibility, impact resistance, water absorption, and hardness. According to ASTM: D-638 standard, the tensile test was conducted in the printed specimen in a universal mechanical testing machine with a ram speed and load cell capacity of 10 mm s −1 & 10 kN. Three samples were examined for each specimen for conforming repeatability, and tests were taken at room temperature. As a result, the maximum tensile strength, elasticity modulus, and percentage elongation were determined.
As per the standard of ASTM: D-790, conducted the flexural test in a three-point flexural configuration. The model bends and cracks when a weight is put in the center of it. Therefore, it is a 3-point bend test, favoring inter-laminar shear failure in most cases.
As per the ASTM: D-256 standard, conducted an impact test using a Charpy impact rig. The test apparatus must be loaded with the sample before allowing it to swing till it breaks or fractures. The energy required to break the material is calculated using the impact test.
Vickers hardness tests were conducted by utilizing test forces in the 1 to 1000 gf range, following ASTM: E-384 standard. A diamond with an apical angle of 136°is used for the Vickers hardness test. SEM Hitachi S4100 equipment was used to analyze the morphology of the fractured 3D-printed specimens. The samples were placed in a sputter coater chamber after being arranged together on aluminium stubs (Polaron E 5000). Specimens were sputtered through an Au/Pd target at 12 mA for 2 min to eliminate the electrostatic charge.

Water absorption test
The printed specimen in a water absorption specimen underwent the water absorption test following ASTM: D-570 standard. The filament's capacity to absorb water was used to determine how hydrophobic they were. An individual filament was printed to a length of 70 ± 1 mm, and it was then immersed for regular intervals of 10, 20, and 30 days at ambient temperature in 50 ml of distilled aqua in a beaker. The tested filaments were dried at vacuum conditions for 6 h at 80°C, and the dry weight of the filaments was then determined (W 0 ). The samples were removed from the water in regular intervals of 10, 20, and 30 days and cleaned with filter paper W1 denotes the weight, and the following equation was used to compute the water acceptance of PLA/FSP-filled filaments: Where, W 0 = Weight of printed material before immersion and W 1 = Weight of printed material 30 days after immersion.

Thermogravimetric analysis
Thermogravimetric analysis (TGA) was carried out to examine the heat degradation behaviour of the FSP-filled PLA in a nitrogen atmosphere. The 50 ml min −1 gas flow rate was maintained from 30°C to 600°C. Each sample weighed 5 mg, and the heating rate was regulated at 10°C min −1 .         figure 8. Pictures of 3 Dimensional printed specimens display the filaments and the filling of the voids between the layers. Material failure is caused by breakage in the filament, filler pullout, and poor adhesion between layers, voids, and cracks. The fractured PLA/FSP20 composite sample displays a smooth brittle fracture during tensile loading, indicating rapid crack propagation in neat PLA samples. However, SEM images of the fractured PLA/FSP composite show a ductile mode of fracture with slow crack propagation, indicated by the blur and rough surface detected. This ductility enhancement is attributed to the added fish scale particles, which are uniformly distributed in the PLA matrix and exhibit better adhesion. The SEM image also reveals particle pull-out and attachment, further confirming the uniform distribution and improved adhesion. The alkali treatment has improved interfacial adhesion and unvarying particle distribution, potentially leading to increased tensile strength in the composite.

Flexural test
The flexural properties of produced composites were evaluated using a 3-point bending test, and the findings are shown in figure 9. The results reveal that the PLA/FSP20 sample flexural strength and modulus is improved due

Impact test
The value of impact strength was attained to 0.2, 0.12, 0.25, and 0.14 J for 0% of weight, 10% of weight, 20% of weight, and 30% of the weight of fish scale particle content in the PLA-based matrix compositions, respectively. Adding fish scale powder at a 20 wt% concentration leads to a better impact-bearing tendency of the printed specimen, as shown in figure 10. The better impact resistance behaviour in polymeric composites is attributed to the energy dissipation in the zone getting damaged and the deflection of fracture around the stiffer filler particles.

Hardness test
The hardness tests performed on the produced composites are shown in figure 11. It was found that the hardness increased and maintained between 34.45 and 39.793 HV by adding fish scale particles to the PLA matrix. The   hardness of PLA was increased at 15.5% with the inclusion of 20 wt% of fish scale powder, with the highest value being 39.793 HV. Hard fish scale powder increases the composite resistance to local plastic deformation due to indentation, which is responsible for enhanced hardness value.

Water absorption test
The result indicates that there was lower absorption of water in the PLA/FSP20 composite at 1.05% shown in figure 12. On the other hand, compared with neat PLA, PLA/FSP10, and PLA/FSP30 exhibits higher water absorption value of 1.28, 1.59, and 1.41%. The inclusion of inorganic particles in the extruded filaments may result in increased porosity, leading to the observation results in micro-void development during the printing of the polymer composites. However, a better filler matrix interface in the PLA/FSP 20 specimen leads to fewer voids in the specimen surface.

Thermogravimetric analysis (TGA)
The TGA results (figure 13) can be analyzed in different phases to recognize the degradation behavior of the composite materials. Initially, the weight loss observed below 285 0 C corresponds to the thermal decomposition of the polymer chains in pure PLA, where random scission of ester bonds occurs, resulting in the release of low molecular weight fragments. At approximately 350 0 C, a significant weight loss of 24% indicates a secondary degradation stage, involving the further breakdown of residual fragments and the elimination of volatile species like carbon dioxide, water, and small organic molecules. The presence of FSP particles in the PLA-FSP composites influences the thermal behavior. FSP acts as a heat sink, dissipating heat and delaying the degradation process. It also hinders the mobility and diffusion of volatile degradation products, resulting in a slower weight loss rate. The addition of FSP at different concentrations (10%, 20%, and 30%) to PLA leads to moderately corresponding degradation temperatures around 386°C. This suggests that FSP reinforces PLA by creating a physical barrier that restricts the movement of polymer chains, enhancing thermal stability and increasing the degradation temperature. Overall, the TGA results demonstrate that the observed weight loss in the analysis reflects the degradation of the composite materials. PLA exhibits distinct degradation phases, while the presence of FSP effects the degradation behavior of the PLA-FSP composites.

Conclusions
In conclusion, the addition of FSP in the PLA matrix leading to a bio-composite has shown significant improvements in various mechanical and physical properties. Comparing the different weight percentages of FSP, the PLA/FSP20 composite consistently performed better than the other compositions. Regarding tensile properties, the tensile strength of the neat PLA composite was 35 ± 1.2 MPa. However, the addition of up to 20 wt% FSP improved the tensile strength compared to other filler loadings. This improvement in tensile strength can be qualified to the development of rigid surfaces within the composite matrix when micron-sized additives with high stiffness, such as fish scale powder, are added. The PLA/FSP20 composite exhibited the highest tensile modulus of 3.23 ± 0.2 GPa among the different compositions studied. The elongation at break, which represents the flexibility and ductility of the material, was also enhanced by the addition of FSP. The PLA/ FSP10, PLA/FSP20, and PLA/FSP30 composites showed improvements of 17.28%, 19%, and 19%, respectively, compared to the neat PLA sample. In relation to flexural properties, the PLA/FSP20 composite demonstrated the highest flexural strength (822.53 ± 1.8 MPa) and flexural modulus (61.411 ± 0.4 GPa) among the studied compositions. The inclusion of fish scale particles at 20 wt% resulted in improved flexural properties, indicating the exceptional engagement of the PLA composite with inorganic fillers.
Furthermore, the impact resistance of the printed PLA/FSP composites was found to be better with the addition of 20 wt% FSP. This improvement in impact strength can be qualified to the energy dissipation in the damaged zone and the deflection of fracture around the stiffer filler particles. The hardness values of the PLA/ FSP composites increased and remained between 34.45 and 39.793 HV with the addition of fish scale particles. The highest hardness value was obtained with the PLA/FSP20 composite, which exhibited a 15.5% increase compared to neat PLA. In terms of water absorption, the PLA/FSP20 composite showed the lowest absorption rate (1.05%), while PLA/FSP10 and PLA/FSP30 exhibited higher values. The presence of inorganic particles in the composites may have led to increased porosity, resulting in higher water absorption values. However, the PLA/FSP20 specimen showed a better filler-matrix interface, resulting in fewer voids on the surface. Thermogravimetric analysis (TGA) revealed that the PLA/FSP composites exhibited thermal stability within the expected range. The degradation temperatures of the composites were comparable to commercially available data for PLA and reinforced PLA, further supporting their suitability for temperature-dependent applications.
Overall, the results demonstrate that the incorporation of fish scale powder as a filler in PLA composite enhances mechanical properties such as tensile strength, tensile modulus, flexural strength, and flexural modulus. The composites also exhibit improved elongation at break, impact resistance, hardness, and thermal stability. The PLA/FSP20 composite consistently outperformed the other compositions in most of the studied properties, highlighting its potential as a promising material for various applications.