Materials and methods

To investigate the tensile properties of PLA-based biocomposites with varying nominal wood-particle contents and subsequent fungal colonization, standardized tensile specimens were fabricated using MEX AM, also referred to as 3D-printing, and experimentally characterized under uniaxial tensile loading. The investigated material combinations consisted of commercially available PLA/wood composite filaments from different manufacturers, with nominal wood-particle contents ranging from 10 to 50 wt.%. Details of the individual filament products and manufacturers are provided in Section 2.1. In a second experimental series, selected specimens were subjected to post-printing colonization using the fungus Fomes fomentarius in order to compare the mechanical response of the printed material combinations before and after fungal colonization and the associated processing conditions.

The mechanical characterization focused on the evaluation of mean Young’s modulus (E) and mean ultimate tensile strength (UTS) obtained from the engineering stress–strain curves, while fracture surfaces were qualitatively examined using representative microscopy images. To ensure comparability between all investigated material combinations, all specimens were manufactured using identical MEX AM process parameters, specimen geometry, and tensile testing conditions. Tensile tests were performed using a universal testing machine in accordance with ASTM D3039. In addition to the mechanical investigation, a supplementary screening-level Life Cycle Assessment (LCA) was conducted to compare the environmental impacts associated with the investigated PLA/wood material combinations during the MEX AM fabrication stage.

Make: raw filament materials

Commercially available PLA/wood composite filaments with nominal wood-particle contents of 10 wt.%18, 20 wt.%19, 30 wt.%20, 40 wt.%21, and 50 wt.%22 were investigated. The corresponding manufacturer technical data sheets are provided as Supplementary Material (Supplementary Material B). PLA is a bio-based thermoplastic derived from renewable feedstocks such as corn starch or sugar cane and is widely used in additive manufacturing due to its good printability and relatively high stiffness23,24. When combined with lignocellulosic fillers, e.g. wood particles, PLA can be processed into bio-based composite filaments suitable for MEX AM.

The investigated filaments were obtained as pre-compounded commercially available materials from different manufacturers and are summarised in Table 1.

Property | PLA_W10 | PLA_W20 | PLA_W30 | PLA_W40 | PLA_W50
Material | ecoPLA Light | ecoPLA Dark | R3D Wood 1 | EasyWood Pine | Wood Light Brown
Manufacturer | 3DJAKE | 3DJAKE | R3D | FormFutura | REDLINE FILAMENT
Nominal wood-particle content (wt.%) | 10 | 20 | 30 | 40 | 50
Recommended nozzle temperature (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ$$\end{document}C) | 210–230 | 210–230 | 190–210 | 200–220 | 205 ± 10
Recommended bed temperature (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ$$\end{document}C) | 35–60 | 35–60 | 45–60 | 35–60 | 0–60
Manufacturer-specified UTS (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm {N/mm^2}$$\end{document}) | 24.6 | 24.6 | 36.7 | 35 | 69.8
Manufacturer-specified strain at break (%) | 23.8 | 23.8 | 6.0 | 5–10 | 4.8
Manufacturer-specified E (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm {N/mm^2}$$\end{document}) | 370 | 370 | 3050 | 2000–3000 | 3120
Diameter (mm) | 1.75 ± 0.05 | 1.75 ± 0.05 | 1.75 ± 0.02 | 1.75 ± 0.05 | 1.75

Make: specimen fabrication

MEX AM was used to fabricate standardised tensile specimens for the mechanical investigation of the PLA/wood material combinations. MEX AM was selected due to its compatibility with commercially available PLA-based composite filaments and its widespread application in the processing of thermoplastic biocomposites25–27.

All investigated filament materials were processed using identical MEX AM process parameters to ensure comparability between the manufactured specimens. The selected process parameters were derived from preliminary printing trials and previous work reported in14,28. A nozzle diameter of 0.8 mm was used for all investigated material combinations.

Specimen fabrication was performed using a Prusa i3 MK3S+ (Prusa Research a.s., Prague, Czech Republic)29. In the applied MEX AM process, the filament material is transported into a heated extrusion system, melted, and deposited layer-wise through a nozzle onto the print bed. During printing, the print head moves along the x- and z-axes, while movement in the y-direction is realised by the print bed. A schematic representation of the MEX AM process is shown in Figure 2a.

The tensile specimens were designed according to ASTM D303930. The specimen geometry was generated using Rhinoceros 3D (Rhino) (TLM, Inc., Seattle, USA)31. The final specimen geometry consisted of a total length of 180 mm, a free (gauge) length of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$L_1 = 120$$\end{document} mm, a clamping length of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$L_2 = 30$$\end{document} mm at each end, a width of W = 15 mm, and a thickness of H = 2 mm. The geometry of the tensile specimens is illustrated in Figure 2b.

Fig. 2: Overview of the additive manufacturing process and tensile specimen geometry used in this study: (a) schematic representation of the MEX AM process28 and (b) geometry of the tensile specimen according to ASTM D303928.

All specimens were manufactured using a 0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ$$\end{document} raster orientation, in which the deposited extrusion paths were aligned parallel to the loading direction. Raster orientation is known to significantly influence the tensile properties of MEX-manufactured thermoplastics and biocomposites. Previous studies have shown that extrusion paths aligned parallel to the loading direction generally result in improved tensile strength due to more efficient load transfer along continuous filament paths32,33. The resulting layer architecture and raster orientation applied during specimen fabrication are illustrated in Fig. 3.

Fig. 3: Tensile specimen geometry and raster configuration: (a) perspective view illustrating the deposited layers and extrusion paths. The red dots indicate the extrusion path of the first (bottom) layer, while the blue dots indicate the starting edge of each deposited layer and (b) raster orientation in plan and side view.

Slicing and process parameter definition were performed using Ultimaker Cura (Version 5.2.1). An overview of the selected printing parameters is provided in Table 2. All specimens were manufactured using a layer height of 0.25 mm and a line width of 0.8 mm, resulting in eight deposited layers for the final specimen thickness of 2 mm. Each layer consisted of 19 parallel extrusion lines.

 | MEX AM Parameters
Printer | Prusa i3 MK3S+
Nozzle Diameter | 0.8 mm
 | Layer Parameters
Layer Height | 0.25 mm
Line Width | 0.8 mm
Number of Layers | 8
 | Raster Parameters
Infill Density | 100 %
Infill Pattern | Lines
Raster Orientation | 0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ$$\end{document}
 | Temperature Parameters
Printing Temperature | 190–205\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ$$\end{document}C
Bed Temperature | 65\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ$$\end{document}C
 | Printing Parameters
Print Speed | 45 mm/s
Cooling | Off

To minimise moisture-related processing effects, all filament materials were stored under dry conditions prior to printing. PLA-based materials are known to exhibit moderate hygroscopic behaviour, and absorbed moisture can lead to hydrolytic degradation during thermal processing, resulting in unstable extrusion, pore formation, reduced interlayer bonding, and decreased mechanical performance34–37. Previous studies have further shown that moisture uptake during storage can reduce tensile strength and alter the mechanical response of additively manufactured PLA components, while appropriate drying procedures improve print quality and process stability38–41. Consequently, only newly opened and pre-dried filament materials were used throughout specimen fabrication to ensure reproducible manufacturing conditions.

For each investigated material combination, 16 tensile specimens were fabricated for mechanical testing, resulting in a total of 80 specimens across all investigated material combinations. Following specimen fabrication, half of the of the manufactured specimens (40) was subjected to post-printing fungal colonisation using Fomes fomentarius.

Make: mycelium processing

Following MEX AM specimen fabrication, one half of the experimental specimens were prepared to investigate changes in the tensile properties of the additively manufactured PLA/wood material combinations following fungal colonisation and the associated processing conditions. For this purpose, 8 specimens from each of the five material combination were subjected to post-printing colonisation using the tinder fungus Fomes fomentarius (see Figure 4 and Figure 5).

The fungal strain Fomes fomentarius PaPF11 was cultivated under sterile laboratory conditions to minimise contamination by foreign microorganisms and ensure reproducible fungal growth. All cultivation procedures were performed under aseptic conditions using sterile workbenches and laminar flow cabinets. Materials and tools used during fungal cultivation were sterilised either by autoclaving or by treatment with 70 % ethanol. Colonisation was carried out in darkness at approximately 25,\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ$$\end{document}C following the cultivation procedure described by Pohl et al42. and Schmidt et al43., which is based on the methodology reported by Tacer-Caba et al44. The cultivation containers were maintained under humid conditions to support fungal growth. The relative humidity during the incubation period was not quantitatively monitored.

The cultivation procedure followed the methodology previously described in14,43 and is schematically illustrated in Figure 4. Initially, the fungal culture was propagated on agar plates (Figure 4a) and subsequently transferred onto sterilised millet grain spawn for approximately two weeks, resulting in complete mycelial overgrowth (Figure 4b). The colonised grain spawn was then used to inoculate hemp shives (Figure 4c), a lignocellulosic agricultural by-product selected due to its porous structure, lignin-rich composition, moisture retention capability, and suitability for homogeneous fungal colonisation43. During colonisation, the hemp substrate became uniformly colonised and interwoven by fungal hyphae.

Following colonisation, the mycelium-hemp substrate was shredded into smaller particles and used as embedding material for the printed tensile specimens. The shredded substrate was first distributed as a bottom layer inside the cultivation containers, after which the specimens were positioned using specimen holders to ensure reproducible spacing and orientation (Figure 4d). Subsequently, an upper layer of colonised substrate was added to fully surround the specimens. Gentle manual compaction was applied to ensure continuous contact between the substrate and specimen surfaces and to minimise hollow spaces. No quantitative compaction pressure was applied or recorded.

The assemblies were then incubated for an additional period of two weeks, during which the fungal mycelium overgrew the shredded substrate and surrounding specimen surfaces, resulting in cohesive mycelium-substrate-specimen blocks (Fig. 4e–f)14.

After completion of the colonisation process, the colonised assemblies were dried at 55,\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ$$\end{document}C in order to reduce residual moisture and terminate biological activity45–47. Subsequently, the specimens were extracted from the surrounding substrate, residual mycelium was carefully removed from the specimen surfaces, and the samples were vacuum sealed prior to mechanical testing14,43.

Fig. 4: Overview of the mycelium processing and specimen colonisation procedure adapted from14,43: (a) agar plate pure culture of Fomes fomentarius, (b) colonised millet grain spawn, (c) hemp shive substrate after fungal colonisation, (d) shredded mycelium-colonised hemp substrate used as embedding material, (e) placement of additively manufactured PLA/wood tensile specimens on a bottom layer of shredded substrate within the cultivation container, (f) formation of a fully colonised mycelium–substrate–specimen block after colonisation, (g) extraction of the specimen carrier from the colonised block, and (h) removal of residual substrate and recovery of the individual tensile specimens prior to mechanical testing.

Fig. 5: Overview of additively manufactured PLA/wood tensile specimens with different nominal wood-particle contents: (a) untreated specimens and (b) specimens after post-printing fungal colonisation using Fomes fomentarius.

Break: experimental setup and testing procedure

Mechanical characterisation of the additively manufactured tensile specimens was performed using a Universal Testing Machine (UTM), model ZwickRoell Z2.5 (ZwickRoell GmbH & Co. KG, Ulm, Germany). The testing machine provides a maximum load capacity of 2.5 kN and allows precise control of displacement and crosshead speed, making it suitable for tensile testing of PLA-based composite materials.

The tensile tests were conducted in accordance with ASTM D303930. During testing, the specimens were mounted using pneumatic grips to minimise slippage and ensure reproducible load transfer throughout the experiments. All tests were performed under displacement-controlled loading conditions until specimen failure occurred.

A constant crosshead displacement rate of 2 mm/min was applied for all tensile tests. This loading rate was selected to ensure quasi-static loading conditions and to allow direct comparison with previous investigations on additively manufactured polymer and bio-composite structures14. Similar displacement rates have also been widely employed in tensile characterisation studies of MEX-manufactured PLA-based composites and natural-fibre-reinforced polymer systems, where low crosshead speeds are recommended to minimise rate-dependent effects and to ensure stable acquisition of the elastic response9–11.

Throughout the experiments, force and displacement data were continuously recorded by the testing system. Engineering stress–strain curves were subsequently calculated from the recorded raw data, with engineering strain derived from the recorded crosshead displacement relative to the initial gauge length. Mean E and mean UTS were determined from the resulting displacement-derived engineering stress–strain curves in accordance with ASTM D303930. Young’s modulus was calculated from the initial linear elastic region of the displacement-derived stress–strain response, whereas the UTS was defined as the maximum engineering stress recorded during the tensile test. These parameters were selected because they represent the primary descriptors of tensile stiffness and load-bearing capacity for fibre- and particle-reinforced composite materials subjected to uniaxial loading30,48.

Statistical evaluation was performed separately for each investigated material combination by comparing untreated specimens with the corresponding fungal-colonised specimens possessing the same nominal wood-particle content. The resulting values of mean E and mean UTS were subsequently used for statistical analysis, as described in Section 2.5.

Figure 6 illustrates the experimental tensile testing setup and the schematic loading configuration used in this study. Visual inspection of the fractured specimens confirmed that failure occurred within the gauge section rather than in the clamping regions. Most specimens fractured approximately in the central region of the specimen, although the exact fracture location varied between individual specimens.

Fig. 6: Tensile testing configuration used in this study: (a) front view of the experimental setup using the ZwickRoell Z2.5 universal testing machine, (b) side view of a mounted PLA/wood tensile specimen during testing, and (c) schematic representation of the uniaxial tensile loading configuration indicating the loading direction and specimen orientation.

Break: statistical analysis

Statistical analyses were performed to evaluate differences in mean E and mean UTS between untreated PLA/wood material combinations and specimens subjected to fungal colonisation. For each material combination, eight specimens were tested, and the resulting values of mean E and mean UTS were used for statistical evaluation.

All statistical analyses were conducted using GraphPad Prism (Version 10.6.1)49. Mean values, standard deviations (SD), and 95 % confidence intervals were calculated for each specimen group. One-way ANOVA was performed separately for each commercial PLA/wood material combination. A two-way ANOVA was intentionally not applied because the investigated commercial filaments originated from different manufacturers and may differ not only in nominal wood-particle content but also in PLA grade, wood species, particle morphology, additives, and compounding procedures. Consequently, the investigated material combinations cannot be considered as levels of a single independent experimental factor.

To assess differences in the mean E and mean UTS of each material combination between untreated and fungal-colonised specimens, one-way Analysis Of Variance (ANOVA) followed by Tukey’s post-hoc test was performed50. Statistical significance was evaluated using the conventional significance thresholds of *p<0.05, **p<0.01, ***p<0.001, and ****p<0.0001.

The p-value represents the probability of observing a difference at least as large as that measured if no true difference exists between the compared groups (null hypothesis). Consequently, lower p-values indicate stronger statistical evidence against the null hypothesis. Differences were considered statistically significant when p<0.05, whereas results with p\ge 0.05 were considered not statistically significant (ns).

The statistical evaluation focused on pairwise comparisons between untreated PLA/wood material combinations and the corresponding fungal-colonised specimens (WM) for each investigated wood-particle content.

Simulate: life cycle assessment methodology

A supplementary screening-level Life Cycle Assessment (LCA) is conducted to compare the environmental impacts associated with the investigated PLA/wood material combinations during the printing stage of MEX AM. The assessment is structured with reference to the goal-and-scope, inventory, impact assessment, and interpretation framework of ISO 14040 and ISO 1404451,52, but it is not intended as a full ISO-compliant product LCA. The assessment builds on a previously published explainable AI-assisted environmental assessment (XAI-LCA) workflow53. The procedure specific to the present study is summarised below.

The assessment supports the comparative interpretation of the indicative environmental performance of the five investigated PLA/wood material combinations within the defined printing-stage system boundary. The foreground system is limited to MEX AM specimen fabrication, including electricity use during printing and material-combination-dependent material consumption. Upstream impacts associated with the consumed electricity and raw-material production are included through background datasets and literature-based characterization factors. The post-printing fungal colonisation process, including substrate preparation, incubation, drying, specimen extraction, and storage, is outside the system boundary of the present screening assessment. The use phase and end-of-life stage are also excluded. Three midpoint indicators are considered: Global Warming Potential (GWP), Acidification Potential (AP), and Eutrophication Potential (EP).

The declared unit is one printed tensile specimen manufactured under the defined MEX AM conditions, corresponding to one individual print job as described in the previous sections. For each material combination, the printing time is obtained from the slicing software and used to calculate the electricity consumption \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E_{\textrm{el}}$$\end{document} (kWh) through the calibrated average-power approach described in the previously published XAI–LCA workflow53. The calculated electricity consumption is modelled as an input to the foreground printing process in openLCA (v2.3.1)54. The electricity-related midpoint impacts are calculated using a German low-voltage electricity background dataset from the ELCD data package and the TRACI 2.1 midpoint method55.

The total specimen mass \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$m_{\textrm{tot}}$$\end{document} (kg) is determined using a precision digital balance. The nominal wood-particle content w (dimensionless, 0–1 by mass) is used to split the total specimen mass into PLA and wood contributions:where \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$m_{\textrm{wood}}$$\end{document} is the wood-particle mass, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$m_{\textrm{PLA}}$$\end{document} is the PLA mass, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$m_{\textrm{tot}}$$\end{document} is the measured total specimen mass, and w is the nominal wood-particle content expressed as a mass fraction.

1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\begin{aligned} m_{\textrm{PLA}} = (1-w) \cdot m_{\textrm{tot}}, \qquad m_{\textrm{wood}} = w \cdot m_{\textrm{tot}}, \end{aligned}$$\end{document}

Because suitable polymer and wood production datasets are not consistently available within the selected database, material-related impacts are calculated using literature-based cradle-to-gate characterization factors (Table 3). These factors are linearly scaled with the measured material masses:where \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$I^{\textrm{mat}}k$$\end{document} is the material-related impact for midpoint indicator k, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\textrm{CF}{k,\textrm{PLA}}$$\end{document} is the characterization factor for PLA, and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\textrm{CF}_{k,\textrm{wood}}$$\end{document} is the characterization factor for wood.

2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\begin{aligned} I^{\textrm{mat}}_k = m_{\textrm{PLA}} \cdot \textrm{CF}_{k,\textrm{PLA}} + m_{\textrm{wood}} \cdot \textrm{CF}_{k,\textrm{wood}}, \end{aligned}$$\end{document}

Material | Indicator | Unit (per kg) | Factor | Reference
PLA resin | GWP | kg CO\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document} eq/kg | 0.502 | 56
PLA resin | AP | kg SO\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document} eq/kg | 0.021 | 56
PLA resin | EP | kg N eq/kg | 0.0133 | 57
Wood flour | GWP | kg CO\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document} eq/kg | 0.14633 | 58
Wood flour | AP | kg SO\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document} eq/kg | 0.00147 | 58
Wood flour | EP | kg N eq/kg | \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$7.63\times 10^{-5}$$\end{document} | 58

It should be noted that the electricity- and material-related impact contributions are derived from different secondary data sources. The electricity-related impacts are calculated in openLCA using a German low-voltage electricity background dataset and the TRACI 2.1 midpoint method, whereas the PLA- and wood-related impact contributions are estimated using literature-based cradle-to-gate characterization factors. Although consistent units are used for each midpoint indicator, the underlying datasets may differ in terms of system boundaries, geographical and temporal representativeness, background modelling assumptions, and LCIA characterization basis. Therefore, the calculated values are intended to support the comparative interpretation of indicative trends among the investigated PLA/wood material combinations, rather than precise comparisons of absolute environmental burdens.

For each midpoint indicator k, the total printing-stage impact is obtained by combining electricity- and material-related contributions:where \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$I^{\textrm{tot}}_k$$\end{document} is the total printing-stage impact, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$I^{\textrm{elec}}_k$$\end{document} is the electricity-related impact, and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$I^{\textrm{mat}}_k$$\end{document} is the material-related impact for midpoint indicator k.

3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\begin{aligned} I^{\textrm{tot}}_k = I^{\textrm{elec}}_k + I^{\textrm{mat}}_k, \end{aligned}$$\end{document}

The resulting midpoint impacts are used to compare indicative environmental trends among the different PLA/wood material combinations and to support the subsequent interpretation of the trade-off between mechanical performance and printing-stage environmental burden under the assumptions of the present screening assessment.