Eggshell‑Derived Powder as Reinforcement for Structures Manufactured by Digital Light Processing

Vol.:(0123456789) International Journal of Precision Engineering and Manufacturing-Green Technology (2025) 12:1737–1748 https://doi.org/10.1007/s40684-025-00724-1 1 3 REGULAR PAPER Online ISSN 2198-0810 Print ISSN 2288-6206 Eggshell‑Derived Powder asReinforcement forStructures Manufactured byDigital Light Processing TeresaCarranza1· IraiaOsquila1· PedroGuerrero1,2,3· KorodelaCaba1,2 · AitorTejo‑Otero1,4 Received: 22 October 2024 / Revised: 14 February 2025 / Accepted: 17 February 2025 / Published online: 14 March 2025 © The Author(s) 2025 Abstract The global warming is a current challenge that demands innovative solutions in waste management. Eggshells, a common waste product, present an opportunity within the circular economy. This material, when combined with resins, can be transformed into a valuable resource as a reinforcement. In this study, eggshells-derived calcium acetate was combined with a resin and used to create a viscous printable material, allowing for the manufacture of samples with small pores and enhancing structural integrity. Additionally, X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) confirmed the successful integration and uniform distribution of calcium acetate. Furthermore, increasing relative density from 50 to 75% led to an increase of hardness from 2.33 to 8.58 N, highlighting the relevance of the structure design to tailor the mechanical performance of the resulting structure, with cohesiveness values of 1, indicating total shape recovery after deformation. This approach not only demonstrates the versatility of eggshells but also highlights the effectiveness of DLP technology to produce structures with complex geometries. This research opens new avenues for reusing discarded materials, promoting sustainable practices and reducing the environmental impact of our consumption habits. Keywords Bio-based· Eggshell· 3D printing· Digital light processing 1 Introduction The increasing global population is generating a rising volume of waste, much of which is discarded without being repurposed. To tackle these challenges and promote sustainable development, it is crucial to explore innovative recycling and reuse methods. One promising area of research is the utilization of agricultural and food industry by-products, which are bio-based products and typically discarded as waste. In particular, around 8.6 million tons of eggshell are produced every day, ranking it as the 15th most polluting waste product [1]. Eggshells are primarily composed of calcium carbonate (CaCO3), around a 96%, 1% MgCO3, 1% Ca3(PO4)2, and organic matter [2]. The eggshells possess notable mechanical properties and are biodegradable, making them an attractive material for various applications, such as biomedical applications [3]. However, eggshell cannot be used as it is because it must undergo through a process that includes the collection, cleaning, grinding and sieving of eggshells in order to produce a fine powder. After that, combining eggshell powder with other materials offers advantages, such as the improvement of mechanical properties [4]. For example, Ashok etal. [5] produced PLA films containing 1, 2, 3, 4, and 5 wt % eggshell particles having a size of 25μm. The addition of filler improved the tensile strength by 5.4, 25.6, 51.8, 82.1, and 33.9%, respectively, while the modulus increased by 1.7, 24.3, 53.4, 70.5, and 20.6%, respectively. Additionally, the valorization of eggshell contributes to waste reduction and promotes a circular economy [6]. In this regard, Flores etal. [7] investigated a novel method to obtain bio-based hydroxyapatite from a residue of eggshells. Despite the advantages shown, the * Koro dela Caba k[email protected] 1 BIOMAT Research Group, Escuela de Ingeniería de Gipuzkoa, University oftheBasque Country (UPV/EHU), 20018Donostia-SanSebastián, Spain 2 Basque Center forMaterials (BCMaterials), Applications andNanostructures, UPV/EHU Science Park, 48940Leioa, Spain 3 Proteinmat Materials SL, Avenida de Tolosa 72, 20018Donostia-SanSebastián, Spain 4 Department ofGraphic Design andEngineering Projects, Faculty ofEngineering inBilbao, University oftheBasque Country (UPV/EHU), 48013Bilbao, Spain 1738 International Journal of Precision Engineering and Manufacturing-Green Technology (2025) 12:1737–1748 1 3 research carried out in polymers containing eggshell particle is limited. The relevance of this this work lies not only in the valorization of eggshells, but also in its transformation into calcium acetate, which is soluble, facilitating its incorporation into the resin to enhance the functional properties of the final product. Regarding the processing of bio-based materials, 3D printing is a field that has rapidly grown during the last years in different sectors such as aeronautics, automotive or medical. This technology is based on the development of complex 3D printed objects layer-upon-layer. Among the different additive manufacturing (AM) technologies, there are seven categories according to ISO/ASTM 52900 Standard [8]: Vat Photopolymerization, including Digital Light Processing (DLP), Stereolithography (SLA), LaserInduced Forward Transfer (LIFT), Liquid–Crystal Display (LCD), Two-Photon Polymerization (2PP), and Volumetric 3D Printing (V3DP); Material Extrusion, which includes Fused Filament Fabrication (FFF) and Direct Ink Writing (DIW); Material Jetting (MJ); Binder Jetting (BJ); Powder Bed Fusion (PBF), which includes Selective Laser Sintering (SLS) and Selective Laser Melting (SLM); Directed Energy Deposition (DED); and Sheet Lamination. The incorporation of fine powder for 3D printable samples has been carried out using mainly FFF and DIW techniques. For example, Gang etal. [9] combined five natural biominerals, including eggshell, with L-polylactic acid (PLLA) ink. Samples were 3D printed by means of FFF and showed that the particle size was mainly around 500–900nm and, therefore, no block would happen since the nozzle is 410µm. Sankaravel etal. [10] combined eggshell with PLA to manufacture 3D printed samples, concluding that an increase of eggshell showed an improvement in the mechanical properties. On the other hand, Gezek etal. [11] used DIW to develop 3D printed samples based on polycaprolactone (PCL) with eggshell microparticles, concluding that the increase in the microparticle content led to a less crystalline structure. Hembrick-Holloman etal. [12] also developed 3D printed samples with the combination of the previous material with eggshell and concluded with similar results to those of Gezek etal. [11]. Using another AM technology, SLA, Yavuz etal. [13] developed samples with eggshell at different concentrations: 1%, 3% and 5%. The best results were obtained with 1% of eggshell due to an enhancement in the elastic modulus, tensile strength, and hardness of the 3D printed composite specimens. Regarding other types of particles, Lalegani Dezaki etal. [14] demonstrated that incorporating mussel and wheat particles into PLA enhances the mechanical performance of 3D printed samples. Additionally, the combination of wheat with PLA revealed a high shape recovery ratio. In the same line, Rezayat etal. [15] incorporated iron into PLA, improving the mechanical properties of the 3D printed samples. Taking all of this into account, previous research highlights gaps in the current state-of-the-art. Although eggshellderived particles have been incorporated into materials and used to fabricate samples by means of AM technologies, the focus has been limited to FFF and DIW methods, leaving other 3D printing techniques to a side. For example, light-based 3D printing emerged as a powerful toolbox for hierarchical and complex structures as they offer superior resolution and freedom of design compared to nozzlebased methods [16]. Additionally, to the best of the authors’ knowledge, there are no published papers on the use of calcium acetate, material to be used in the present paper, in the development of 3D printed prototypes. In this regard, calcium acetate can be obtained from eggshells, which are primarily composed of calcium carbonate. By reacting eggshell-derived calcium carbonate with acetic acid, calcium acetate is obtained. This process leverages waste eggshells as a resource for developing chemical compounds. The main novelty of this work is that explores the potential of light-based 3D printing to fabricate complex structures with enhanced mechanical properties by synthesizing calcium acetate from eggshells and its incorporating into a bio-based resin. The integration of calcium acetate into the resin improves printability and mechanical performance, demonstrating its viability as a reinforcement material. Additionally, this research provides a comprehensive characterization of the material, including rheological behavior, and mechanical performance of the 3D printed structures, highlighting the potential of eggshell-derived calcium acetate as valorized additive for 3D printing manufacture. Therefore, the aim of this paper is to show that eggshellderived powder can be used as reinforcement for bio-based materials prepared via digital light processing. For that, firstly, an initial analysis of the material printability is carried out. Additionally, a physicochemical analysis of the material with and without calcium acetate is performed. After that, the macroand microstructure of the 3D printed samples is assessed. Finally, the mechanical properties of the 3D printed samples are measured using texture profile analysis and compression tests assays. 2 Materials andMethods 2.1 Materials The resin used in this study, Bioflex A10 MF Monomer Free (BFA10MF), was supplied by 3Dresyns (Barcelona, Spain). This monomer free resin is non-toxic and biocompatible and, thus, suitable for biomedical applications. Eggshells were used to prepare the resin reinforcement. For that, eggshell powder was dissolved in acetic acid 1M, stirring at 200rpm for 2h to convert it into calcium acetate. After that, the 1739International Journal of Precision Engineering and Manufacturing-Green Technology (2025) 12:1737–1748 1 3 solution was left to dry at room temperature and calcium acetate (CaAc) powder was obtained. 2.2 Preparation ofMixtures After preparing the calcium acetate, the resin was mixed with 1% of calcium acetate. This amount was selected based on preliminary assays that show that higher amounts led to agglomerations. The mixture was left stirring overnight to ensure a good dispersion of the calcium acetate, preventing any residue from settling at the bottom of the flask. 2.3 Rheological Analysis The rheological assessments were conducted using a Thermo Scientific Haake Rheostress1 Rheometer (IFI S.L., Spain). A stainless-steel measuring plate P35 (ø 35mm) was used for all tests, with a 1mm gap between the stationary and rotating plates. The temperature was maintained at 21°C, corresponding to the printing temperature. Shear rate sweeps ranging from 0.003 to 1000 s−1 were performed to analyze the apparent viscosity of the resin, both with and without calcium acetate. In addition, photorheology tests were carried out with Ares G2 rheometer (Ta Instruments, USA) to measure the rapid changes in mechanical properties during the photopolymerization of photo-crosslinkable materials. The assays were performed at 21°C using 20mm diameter plate and 0.3mm gap at 1Hz frequency and 1% deformation. The moduli crossover time, where the storage modulus (G′) equals the loss modulus (G″), was also obtained applying the 405nm light with 10 mW/cm2 intensity. Storage modulus (G′) is a measure of the elasticity of a material [17] or stored energy during deformation, representing its ability to recover its original shape when the applied stress is removed. It indicates the stiffness of the material in a viscoelastic system, with higher values signifying more solid-like behaviour. On the other hand, the loss modulus (G″) quantifies the energy dissipated in a viscoelastic material during deformation, representing its viscous behaviour [17]. It indicates how much the material flows under stress, with higher values signifying greater energy loss and damping properties. The reading of the samples was started without light until both modules stabilised and 30s after the start of the reading the UV light was applied. This parameter is crucial for assessing the transition of the material from a liquid to a solid state during photocrosslinking. 2.4 Optimization of3D Printing Procedure In this study, the 3D printed samples were fabricated using the Anycubic Photon D2 printer (Anycubic, China). This printer employs the digital light processing (DLP) technique (Fig.1A), which is vat polymerization process where a light source (generally UV light) cures a photopolymer resin. This method employs a digital micromirror device (DMD) containing thousands of tiny, pivoting mirrors to accurately direct UV light onto specific areas of the resin. Additionally, DLP is faster and more efficient than an SLA 3D printer, but also allow using wide range of wavelengths. Before 3D printing the samples, it is essential to perform a curing depth assay. Cure depth is a crucial parameter in light-based 3D printing technologies, as it determines the exposure time required for curing a specific layer thickness. The procedure involved exposing the resin to various exposure times to observe the resulting layer thickness. Figure1B illustrates the curing depth assay results, showing that longer exposure times produce thicker layers. Additionally, as the cure time increases, less UV light can penetrate the resin mixture, reducing the energy absorbed by the uncured resin during photopolymerization. The 3D models were designed using MS Lattice, an open-source software capable of generating uniform and graded lattices based on triply periodic minimal surfaces (TPMS) [18]. Figure1C shows the 3D models with 50% (GYR50) and 75% (GYR75) densities, each having a diameter of 12mm and a height of 6mm. These relative densities were selected to evaluate the influence of porosity on the structural and mechanical properties of the 3D printed samples. A 50% relative density provides a peanut morphology for GYR50, while a 75% relative density offers a denser configuration, with a smaller circular morphology for GYR75. The 3D model has the form of a gyroid, which is an infinitely connected periodic minimal surface containing no straight lines. This structure is complex and, therefore, achieving its manufacture shows the efficacy of not only the 3D printable material and its optimization, but also the efficacy of the technique. The digital models were then transferred to Anycubic Photon Workshop to apply the necessary 3D printing settings: a layer thickness of 0.1mm (ensuring high quality and excellent resolution) and an exposure time of 10s per layer. Additionally, the first five layers were overcured with an exposure time of 80s to ensure a strong adhesion. Twelve 3D printed samples could be manufactured at the same time (Fig.1D) in order to show one of the advantages of this technology: 3D printing optimization by printing several samples at a time. After printing, the samples were washed with isopropyl alcohol (IPA) and cured for 15min. In sum, 4 types of samples were analyzed: BFA10MF-GYR50 (without calcium acetate and 50% relative density), BFA10MFGYR575 (without calcium acetate and 75% relative density), BFA10MF-CaAc-GYR50 (with calcium acetate and 50% relative density), and BFA10MF-CaAc-GYR75 (with calcium acetate and 75% relative density). 1740 International Journal of Precision Engineering and Manufacturing-Green Technology (2025) 12:1737–1748 1 3 2.5 X‑Ray Diffraction (XRD) X-ray diffraction (XRD) analysis, a powerful analytical technique used to determine the crystallographic structure, was carried out using a diffraction unit (PANalyticXpert PRO). The radiation was generated from a Cu-Kα (λ = 1.5418Å) source at 40kV and 40mA. Data were collected from 2θ values from 2° to 50°, where θ is the incidence angle of the X-ray beam on the 3D-printed products. 2.6 Differential Scanning Calorimetry (DSC) Differential scanning calorimetry (DSC) was performed using a DSC 822 (Mettler Toledo S.A.E.). About 3.0 ± 0.2mg of sample were weighed and sealed in aluminium pans, which were heated from -50°C to 300°C at 10°C/min under nitrogen atmosphere (10mL N2/min). Fig. 1 A Preparation of calcium acetate from eggshell. B Digital light processing 3D printing process scheme. C Exposure time vs thickness plot. D Twelve 3D printed samples manufacture at the same time. E Visual comparison of the 3D printed samples with the digital model 1741International Journal of Precision Engineering and Manufacturing-Green Technology (2025) 12:1737–1748 1 3 2.7 Elemental Analysis (EA) andEnergy Dispersive Spectroscopy (EDS) Elemental analysis (EA) was performed using a Euro EA Elemental Analyser. Carbon (C), oxygen (O) and calcium content was determined by doing a ratio between all the elements of the mixture. Then, using the EDS is possible to do an elemental mapping to check the distribution of the particles throughout the material. This was carried out with the resin as control and the resin with the calcium acetate. The main elements that were analyzed were carbon (C), oxygen (O) and calcium (Ca), with their corresponding percentage in the resins. 2.8 Optical Microscopy Optimal images were taken using a Nikon Eclipse E600 optical microscope with digital camera (Izasa Scientific,) equipped with 10 × objective and 10 × eyepieces. These images were analyzed with Image J software in order to check the pores pattern and size. 2.9 Scanning Electron Microscopy (SEM) The surface morphology and the cross-section of the 3D printed samples were evaluated by scanning electron microscopy (SEM) using a Hitachi S-4800 (Madrid, Spain) with an acceleration voltage of 5.0kV. Prior to observation, samples were mounted on a metal stub with double-sided adhesive tape and coated under vacuum with gold (JFC-1100) in an argon atmosphere. 2.10 Mechanical Properties A TA.XT.Plus C Texture Analyzer (Aname, Madrid, Spain) with a 5kg load cell was used to obtain texture profile analysis (TPA). Data were collected using compression tests at 1mm/s speed, 20% strain, 5s between compression assays (for the texture profile analysis) and 5g trigger force with a 50mm aluminum cylinder (P/50). Data were collected and assessed using Exponent Connect 8.0.16.0 Lite software (Stable Micro Systems, Godalming, UK). Hardness and cohesiveness were determined for the texture profile analysis. 2.11 Statistical Analysis The significance of differences among the samples was determined by analysis of variance (ANOVA). The analysis was done with an SPSS computer program (SPSS Statistic 28.0) and Tukey’s test was used for multiple comparisons. Differences were statistically significant at the p < 0.05 level. 3 Results andDiscussion 3.1 Rheological Properties oftheInks One of the most critical parameters for determining the printability of a material is its rheological performance because a low viscosity could lead to polymer shrinkage and too high viscosity could lead to agglomeration [19]. In this study, the addition of calcium acetate is examined for its impact on the viscosity behavior of the resin. As noted by Leite de Camargo [20], highly loaded resin suspensions exhibit non-linear behavior due to particulate scattering. Another study carried out by Cai etal. [21] investigated the effect of the silica content in the viscosity of the resin and showed that the higher is the silica content in the resin, the higher is the viscosity. This means that the 3D printing process becomes more difficult. Therefore, it is necessary to assess whether the addition of 1 wt % calcium acetate affects the resin’s viscosity. As shown in Fig.3A, the resin, with and without calcium acetate, exhibit shear-thinning behavior, since viscosity decreases with increasing shear rate. According to Luo etal. [22] and Kuhnt etal. [23], the resin viscosity for polymeric resins should be below 10Pa·s. In the present study, both materials demonstrate excellent rheological properties suitable for light-based 3D printing: at a shear rate of 1 s−1, the viscosity is around 0.5Pa·s, dropping to 0.3Pa·s at a shear rate of 100 s−1. The viscosity of the resin used in the present work align with Komissarenko etal. [24], which synthesized a mono-/tri-acrylate-based slurry with 75 wt % of zirconia, which has a viscosity of 1.6Pa·s at 30 s−1. Regarding photorheology, with the addition of calcium acetate, the crossover modulus increases from 32 to 120Pa and the crossover time from 60 to 62s. The incorporation of calcium acetate affects the crosslinking process, delaying the transition from liquid to solid. This observation is consistent with the findings of Yared etal. [25], who demonstrated that a higher solid content in the composition results in slower photocuring. In terms of G′ and G″ values up to the crossover point, Fig.2B and C show that both samples display similar photorheological behavior, with G″ higher than G′. This signifies that both formulations exhibit a more fluid-like behavior until the crossover. Beyond this point, the resins exhibit a more solid-like behavior, as G′ is over G″. 3.2 Evaluation oftheCrystallinity on3D Printed Samples Figure3A shows the crystallinity of the resin with and without calcium acetate. A higher peak intensity indicates a higher degree of crystallinity demonstrating that the calcium 1742 International Journal of Precision Engineering and Manufacturing-Green Technology (2025) 12:1737–1748 1 3 acetate is integrated in the resin matrix. The XRD pattern consisted on a peak of both 3D printed structures at 2θ = 20°. Regarding thermal properties, Fig.3B depicts that both samples show similar thermal behavior up to 200°C, where the sample without acetate shows a sharp decrease at 250°C, while the sample with acetate shows a less pronounced decrease that stabilized at 250°C. Similar findings were reported in various studies [26, 27]. For example, Barreto etal. [26] carried out different DSC curves showing that a higher concentration of calcium attributes a thermal stability. Figure3C shows the energy-dispersive X-ray spectroscopy (EDS) mapping, illustrating the distribution patterns Fig. 2 Rheological properties. A Viscosity–shear rate curves. B Storage (G′) and loss (G″) modulus for BFA10MF. C Storage (G′) and loss (G″) modulus for BFA10MF-CaAc Fig. 3 A XRD patterns, B DSC curves, And C EDS mapping of BFA10MF and BFA10MF-CaAc 1743International Journal of Precision Engineering and Manufacturing-Green Technology (2025) 12:1737–1748 1 3 of carbon (C), nitrogen (N), and calcium (Ca). This confirms the presence of calcium acetate in the 3D printed samples. Despite the presence of some clusters in certain areas, EDS elemental mapping analysis demonstrates a uniform distribution of calcium throughout the 3D printed sample. Table1 details the proportion of each element in the 3D printed samples. Wu etal. [27] also reinforced their samples with mineral compounds containing calcium, which contributed to improve the material thermal properties. 3.3 Characterization ofthe3D Printed Samples 3.3.1 Shape Fidelity Figure4 shows that both the digital models and the 3D printed samples show similar patterns in terms of the pores size and distribution. On the one hand, both 3D printed BFA10MF-GYR50 and BFA10MF-CaAc-GYR50 samples show the peanut morphology. On the other hand, both BFA10MF-GYR75 and BFA10MF-CaAc-GYR75 samples show smaller pores throughout the surface. As GYR50 samples have bigger pores, their 3D printing quality is better than that of GYR75 samples since there is less chance of overcuring between layers. Furthermore, it was observed that the addition of calcium acetate did not affect the morphology and thus the shape fidelity of the samples, confirming the data obtained in the rheological assessment where the viscosity, curing time and final moduli (G′ and G″) were not significantly different between the system with and without calcium acetate. The morphology shown in Figs.4 and 5 indicates the surface roughness, common for 3D printed samples that do not undergo over a post-processing [28]. According to Sasany etal. [29], the higher the layer height, the rougher the surface; additionally 3D printing time also affects roughness. Therefore, both layer thickness and 3D printing time can be varied to modify the surface morphology. 3.3.2 Inner Structure Figure5 shows the cross-sectional SEM images of the 3D printed samples. The inner structure shows the different cavities, but also the difference between both densities (GYR50 and GYR75 samples). The higher density led to smaller pores and, therefore, more clogging was obtained. On the other hand, the pore shows their entire path through GYR50 samples. 3.4 Texture Analysis of3D Printed Samples 3D printed samples with and without calcium acetate were analyzed using textural profile analysis, which consisted of two repetitions of uniaxial compression at a 20% strain value with a recovery time between them. Figure6 shows the texture analysis of the different 3D printed samples regarding porosity and calcium acetate addition. The first and the second peaks in the TPA curve represent key mechanical properties of a material under a certain deformation. The first peak corresponds to the force required to compress the material during initial deformation, which is a direct measure of its hardness or resistance to deformation. The second peak arises during the recompression phase and reflects the ability of the material to recover its shape after deformation. Table 1 Elemental composition of BFA10MF and BFA10MF-CaAc Sample C O Ca BFA10MF 57.22 ± 0.91 42.78 ± 0.91 – BFA10MF-CaAc 57.4 ± 0.91 42.38 ± 1.03 0.22 ± 0.16 Fig. 4 Surface morphology images for comparing the pore size and distribution of the 3D printed samples as a function of density (GYR50 and GYR75 samples). Scale bar is 250µm 1744 International Journal of Precision Engineering and Manufacturing-Green Technology (2025) 12:1737–1748 1 3 The ratio of the area under the second peak to the area under the first peak, known as cohesiveness, indicates the capacity of the material to recover its original form. A cohesiveness value close to one suggests that the material nearly fully recovers its shape, demonstrating elastic or resilient behavior, while lower values indicate partial recovery or plastic deformation. Firstly, the addition of calcium acetate causes an increase in the hardness. As expected, the higher the density, the lower the porosity and, hence, the hardness also increases. Regarding the cohesiveness, all 3D printed samples show a total recovery after the second cycle. The values of hardness and cohesiveness of the 3D printed samples can be found in Table2. 3.5 Mechanical Properties of3D Printed Samples The mechanical behavior of the 3D printed samples was analyzed by carrying out compression tests until a 20% strain. Figure7 shows the mechanical properties of the 3D printed samples (BFA10MF and BFA10MF Ca-Ac) for GYR50 and GYR 75. On the one hand, the higher the density, the higher the strength, since there are less pores. This is in concordance with other studies [30–32]. For example, RoohaniEsfahani etal. [30] 3D printed samples with different pore size and printing design leading to approximate porosities showing that the higher the porosity, the softer the material. On the other hand, Fig.7B and D show that the addition of the calcium acetate leads to an improvement in the strength of the 3D printed samples. For instance, Lyu etal. [33] studied the impact of calcium acetate and showed an improvement on the mechanical properties in the range of 0–2% of calcium acetate. This is in line with Wang etal. [34] that studied the influence of calcium acetate at ratios between 0 and 20%. The mechanical properties were improved until a 5% of calcium acetate; however, a decrease in the compressive strength was achieved with values over 5%. 4 Conclusions This paper presents the successful development of a composite material combining a resin core with calcium acetate derived from eggshells, enabling the 3D printing of samples via digital light processing (DLP). Rheological analysis demonstrated that the composite viscosity was suitable for light-based 3D printing, with values in the range of 0.3–0.5Pa·s at shear rates from 1 to 100 s−1, with the addition of calcium acetate having no detrimental impact on its flow properties. X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) mapping confirmed the successful integration of calcium acetate into the resin matrix. The 3D printed samples, manufactured with complex geometries, highlighted the potential of this technology for creating intricate structures that would be difficult to achieve with conventional methods. Further analysis of the outer and inner structures of the 3D printed samples revealed the presence of pores. In terms of mechanical properties, the study showed a Fig. 5 Cross-sectional SEM images of the 3D printed samples as a function of density rates (GYR50 and GYR75 samples). Scale bar is 1mm 1745International Journal of Precision Engineering and Manufacturing-Green Technology (2025) 12:1737–1748 1 3 clear correlation between increased relative densities, from 50 to 75%, and enhanced mechanical performance, from 2.33 to 8.58 N for hardness values, with cohesiveness values of 1 and, thus, a total shape recovery after deformation. Therefore, the novelty of this work lies in the valorization and modification of discarded materials to facilitate the processing of bio-based materials by sustainable practices, with the aim of enhancing the material properties as well as contributing to reducing the environmental impact. Fig. 6 Texture profile analysis of the 3D printed samples of A BFA10MF-GYR50, B BFA10MF Ca-Ac-GYR50, C BFA10MF-GYR75 and D BFA10MF Ca-Ac-GYR75 Table 2 Hardness and cohesiveness values obtained by texture profile analysis a , bTwo means followed by the same letter in the same column are not significantly (p > 0.05) different through the Tukey’s multiple range test Density Sample Hardness [N] Cohesiveness GYR50 BFA10MF 1.92 ± 0.44a0.99 ± 0.01a BFA10MF Ca-Ac 2.33 ± 1.11a1.02 ± 0.02a GYR75 BFA10MF 7.58 ± 1.10b1.00 ± 0.02a BFA10MF Ca-Ac 8.58 ± 1.61b1.01 ± 0.01a