Results

The mechanical behaviour of the investigated PLA/wood material combinations was evaluated by uniaxial tensile testing. The analysis focused on differences in the engineering stress–strain response, mean E, and mean UTS between the investigated material combinations and between untreated and fungal-colonised specimens.

For all investigated material combinations, mean values, standard deviations, and 95 % confidence intervals were calculated based on eight specimens per test series.

Stress–strain behaviour

Figure 7 presents the mean engineering stress–strain curves for all investigated material combinations. Solid lines represent untreated PLA/wood material combinations, whereas dashed lines correspond to specimens subjected to fungal colonisation (WM). The coloured curves indicate the different nominal wood-particle contents: black (PLA_W10), blue (PLA_W20), red (PLA_W30), green (PLA_W40), and grey (PLA_W50). The shaded regions represent the corresponding 95 % confidence intervals.

The stress–strain curves reveal clear differences between the investigated material combinations. For all material combinations, an initial approximately linear elastic region is followed by a maximum stress level corresponding to the mean UTS, after which a gradual reduction in stress is observed until specimen failure. Both the initial slope of the curves and the maximum stress values varied depending on the wood-particle content and specimen treatment condition.

Mean E was calculated from the initial linear region of the engineering stress–strain curves in accordance with ASTM D303930 and mean UTS was determined as the maximum engineering stress recorded during the tensile test. The resulting mean E and mean UTS are summarised in Table 4. All values of mean E and mean UTS are reported in \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}.

A visual comparison of the stress–strain curves indicates noticeable differences between the investigated material combinations. Among the tested commercial filaments, the PLA_W30 material combination exhibited the highest measured mean UTS.

Fig. 7: Mean engineering stress–strain curves of all investigated PLA/wood material combinations. Solid lines represent untreated specimens, whereas dashed lines indicate fungal-colonised specimens (WM). Colours correspond to the nominal wood-particle content (10–50 wt.%). Shaded regions denote the corresponding 95 % confidence intervals.

Specimen | 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}) | 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}) | Colonisation
Mean | SD | Mean | SD | Duration
PLA_W10 | 2631.74 | 18.21 | 34.29 | 0.66 | –
PLA_W20 | 2629.49 | 11.77 | 33.62 | 0.16 | –
PLA_W30 | 2685.01 | 10.23 | 37.98 | 0.16 | –
PLA_W40 | 2242.16 | 5.04 | 32.78 | 0.07 | –
PLA_W50 | 2231.05 | 20.33 | 32.86 | 0.07 | –
PLA_W10_WM | 2355.21 | 12.65 | 32.55 | 0.17 | 2 weeks
PLA_W20_WM | 2360.39 | 4.50 | 31.88 | 0.20 | 2 weeks
PLA_W30_WM | 2409.32 | 9.70 | 35.41 | 0.25 | 2 weeks
PLA_W40_WM | 2025.39 | 9.14 | 32.01 | 0.12 | 2 weeks
PLA_W50_WM | 2072.72 | 8.80 | 32.14 | 0.05 | 2 weeks

PLA/wood material combinations with 10 wt.% wood-particle content

Figure 8 summarises the mechanical response of both material combinations. Figure 8a presents the mean engineering stress–strain curves together with their 95 % confidence intervals, whereas Fig. 8b compares the resulting values of mean E and mean UTS. Both material combinations exhibited a similar overall tensile response, characterised by an initial approximately linear elastic region followed by a maximum stress level corresponding to the mean UTS. Compared with the untreated specimens, the fungal-colonised specimens exhibited a lower initial slope of the stress–strain curve and lower maximum stress values, consistent with the lower mean E and mean UTS measured for the fungal-colonised group.

Fig. 8: Mechanical characterisation of PLA_W10 and PLA_W10_WM specimens: (a) mean engineering stress–strain curves with corresponding 95 % confidence intervals and (b) comparison of mean E and mean UTS. Error bars represent standard deviations. Statistical significance was evaluated using one-way ANOVA followed by Tukey’s post-hoc test (*p<0.05, **p<0.01, ***p<0.001, ****p<0.0001).

Representative macroscopic and microscopic observations of fungal-colonised specimens are shown in Fig. 9. The highlighted regions were selected for microscopic examination after the two-week colonisation period by Fomes fomentarius. The microscopic observations reveal the presence of fungal structures on the specimen surface, confirming successful surface colonisation of the PLA/Wood specimens by Fomes fomentarius. However, the present observations do not allow conclusions regarding the extent of fungal growth within the internal specimen structure.

Fig. 9: Macroscopic overview and representative microscopy images of a fungal-colonised PLA_W10_WM specimen after two weeks of colonisation with Fomes fomentarius. The highlighted regions indicate locations selected for detailed examination. The upper micrograph shows the specimen cross-section (y–z plane), whereas the lower micrograph presents the specimen surface (x–y plane). Fungal structures are visible at the analysed locations. Scale bars correspond to 20 μm.

The untreated PLA/Wood composite containing 10 wt.% wood-particle content (PLA_W10) exhibited a mean E of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2631.74 \pm 18.21~\mathrm {N/mm^2}$$\end{document} and a mean UTS of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$34.29 \pm 0.66~\mathrm {N/mm^2}$$\end{document}. Following fungal colonisation (PLA_W10_WM), mean E decreased to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2355.21 \pm 12.65~\mathrm {N/mm^2}$$\end{document} and the mean UTS decreased to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$32.55 \pm 0.17~\mathrm {N/mm^2}$$\end{document}. These changes correspond to reductions of 10.5 % for mean E and 5.1 % for the mean UTS.

A one-way ANOVA followed by Tukey’s post-hoc test revealed statistically significant differences between PLA_W10 and PLA_W10_WM for both mean E (***p < 0.0001) and mean UTS (p < 0.05).

Overall, the PLA_W10 material combination exhibited statistically significant differences in both mean E and mean UTS between untreated and fungal-colonised specimens. The observed differences between PLA_W10 and PLA_W10_WM demonstrate that even at the lowest investigated wood-particle content, the fungal-colonised specimen group exhibited a measurably different tensile response compared with the untreated reference group. These findings are consistent with the general trend observed across all investigated PLA/wood material combinations.

PLA/Wood material combinations with 20 wt.% wood-particle content

Figure 10 summarises the mechanical response of both material combinations. Figure 10a presents the mean engineering stress–strain curves together with their 95 % confidence intervals, whereas Fig. 10b compares the resulting values of mean E and mean UTS. Both material combinations exhibited a similar overall tensile response, characterised by an initial approximately linear elastic region followed by a pronounced stress peak at a strain of approximately 0.02, corresponding to the mean UTS. Following this peak, both material combinations exhibited a noticeable reduction in stress before reaching a more gradual post-peak region. Compared with the untreated specimens, the fungal-colonised specimens exhibited a lower initial slope of the stress–strain curve and lower maximum stress values, which is consistent with the reductions observed for both mean E and mean UTS.

Fig. 10: Mechanical characterisation of PLA_W20 and PLA_W20_WM specimens: (a) mean engineering stress–strain curves with corresponding 95 % confidence intervals and (b) comparison of mean E and mean UTS. Error bars represent standard deviations. Statistical significance was evaluated using one-way ANOVA followed by Tukey’s post-hoc test (*p<0.05, **p<0.01, ***p<0.001, ****p<0.0001).

Representative macroscopic and microscopic observations of fungal-colonised specimens are shown in Fig. 11. The highlighted regions were selected for microscopic examination after the two-week colonisation period. The microscopic observations reveal the presence of fungal structures on the specimen surface, confirming successful surface colonisation of the PLA/Wood specimens by Fomes fomentarius. Similar to the observations for PLA_W10, fungal structures were primarily observed at the specimen surface. However, the present observations do not allow conclusions regarding the extent of fungal growth within the internal specimen structure.

Fig. 11: Macroscopic specimen view and microscopy analysis of PLA_W20_WM after fungal colonisation by Fomes fomentarius. Selected regions of interest are indicated in the overview image. Representative microscopic observations obtained from the cross-sectional area (y–z plane) and the outer specimen surface (x–y plane) confirm the presence of fungal structures after colonisation. Scale bars correspond to 20 μm.

For the material combination containing 20 wt.% wood-particle content (PLA_W20), the measured mean E was \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2629.49 \pm 11.77~\mathrm {N/mm^2}$$\end{document} and the mean UTS reached \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$33.62 \pm 0.16~\mathrm {N/mm^2}$$\end{document}. Following fungal colonisation (PLA_W20_WM), both properties decreased to lower values, corresponding to reductions of 10.2 % in mean E and 5.2 % in mean UTS.

A one-way ANOVA followed by Tukey’s post-hoc test revealed statistically significant differences between PLA_W20 and PLA_W20_WM for both mean E (****p < 0.0001) and mean UTS (**p < 0.01).

In summary, the fungal-colonised specimens exhibited measurable reductions in both investigated mean E and mean UTS relative to the untreated specimens. The magnitude of these changes was comparable to that observed for PLA_W10, indicating a similar response of the material to the applied colonisation and associated processing conditions.

PLA/wood material combinations with 30 wt.% wood-particle content

Figure 12 summarises the mechanical response of both material combinations. Figure 12a presents the mean engineering stress–strain curves together with their 95 % confidence intervals, whereas Fig. 12b compares the resulting values of mean E and mean UTS. Both material combinations exhibited a similar overall tensile response, characterised by an initial approximately linear elastic region followed by a maximum stress level corresponding to the mean UTS. Compared with the untreated specimens, the fungal-colonised specimens exhibited a lower initial slope of the stress–strain curve and lower maximum stress values, which is consistent with the reductions observed for both mean E and mean UTS.

Fig. 12: Mechanical characterisation of PLA_W30 and PLA_W30_WM specimens: (a) mean engineering stress–strain curves with corresponding 95 % confidence intervals and (b) comparison of mean E and mean UTS. Error bars represent standard deviations. Statistical significance was evaluated using one-way ANOVA followed by Tukey’s post-hoc test (*p<0.05, **p<0.01, ***p<0.001, ****p<0.0001).

Representative macroscopic and microscopic observations of fungal-colonised specimens are shown in Fig. 13. The highlighted regions were selected for microscopic examination after the two-week colonisation period. The microscopic observations reveal the presence of fungal structures on the specimen surface, confirming successful surface colonisation of the PLA/Wood specimens by Fomes fomentarius. Similar to the observations for PLA_W10 and PLA_W20, the present observations do not allow conclusions regarding the extent of fungal growth within the internal specimen structure.

Fig. 13: Optical microscopy observations of a fungal-colonised PLA_W30_WM specimen. The overview image identifies the investigated regions, while the detailed microscopic observations show the specimen cross-section (y–z plane) and surface region (x–y plane). Fungal structures were observed at both examination locations following the colonisation period. Scale bars correspond to 20 μm.

Among the investigated commercial filament material combinations, PLA_W30 exhibited the highest measured values of mean E and mean UTS. The untreated PLA/Wood composite containing 30 wt.% wood-particle content reached a mean E of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2685.01 \pm 10.23~\mathrm {N/mm^2}$$\end{document} and a mean UTS of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$37.98 \pm 0.16~\mathrm {N/mm^2}$$\end{document}. Following fungal colonisation (PLA_W30_WM), the mean Young’s modulus decreased to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2409.32 \pm 9.70~\mathrm {N/mm^2}$$\end{document}, while the mean UTS decreased to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$35.41 \pm 0.25~\mathrm {N/mm^2}$$\end{document}. These changes correspond to reductions of 10.3 % for mean E and 6.8 % for the mean UTS. Despite these reductions, PLA_W30_WM retained higher values of both mean E and mean UTS than all other investigated material combinations.

A one-way ANOVA followed by Tukey’s post-hoc test revealed statistically significant differences between PLA_W30 and PLA_W30_WM for both mean E (p < 0.0001) and mean UTS (p < 0.0001).

Despite the statistically significant reductions observed between the untreated and fungal-colonised specimen groups, PLA_W30_WM retained the highest measured values of both mean E and mean UTS among the investigated fungal-colonised material combinations. However, because the investigated materials originated from different commercial filaments, these results should be interpreted as material combination-specific observations rather than as evidence of an optimal wood-particle content.

PLA/Wood material combinations with 40 wt.% wood-particle content

Figure 14 summarises the mechanical response of both material combinations. Figure 14a presents the mean engineering stress–strain curves together with their 95 % confidence intervals, whereas Fig. 14b compares the resulting values of mean E and mean UTS. Both material combinations exhibited a similar overall tensile response, characterised by an initial approximately linear elastic region followed by a maximum stress level corresponding to the mean UTS. Compared with the untreated specimens, the fungal-colonised specimens exhibited a lower initial slope of the stress–strain curve and slightly lower maximum stress values, which is consistent with the reductions observed for both mean E and mean UTS.

Fig. 14: Mechanical characterisation of PLA_W40 and PLA_W40_WM specimens: (a) mean engineering stress–strain curves with corresponding 95 % confidence intervals and (b) comparison of mean E and mean UTS. Error bars represent standard deviations. Statistical significance was evaluated using one-way ANOVA followed by Tukey’s post-hoc test (*p<0.05, **p<0.01, ***p<0.001, ****p<0.0001).

Representative macroscopic and microscopic observations of fungal-colonised specimens are shown in Fig. 15. The highlighted regions were selected for microscopic examination after the two-week colonisation period by Fomes fomentarius. The microscopic observations reveal the presence of fungal structures on the specimen surface, confirming successful surface colonisation of the PLA/Wood specimens by Fomes fomentarius. Similar to the observations for the lower wood-particle contents, the present observations do not allow conclusions regarding the extent of fungal growth within the internal specimen structure.

Fig. 15: Representative microscopic examination of PLA_W40_WM specimens after two weeks of fungal colonisation. The marked positions in the macroscopic image indicate the analysed regions. The upper image depicts the cross-sectional area (y–z plane), whereas the lower image shows the specimen surface (x–y plane). Fungal structures are visible in both observation planes. Scale bars correspond to 20 μm.

A further increase in wood-particle content to 40 wt.% resulted in lower mean E and mean UTS compared with the PLA_W30 material combination. The untreated PLA/Wood composite (PLA_W40) exhibited a mean E of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2242.16 \pm 5.04~\mathrm {N/mm^2}$$\end{document} and a mean UTS of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$32.78 \pm 0.07~\mathrm {N/mm^2}$$\end{document}. Following fungal colonisation (PLA_W40_WM), mean E decreased to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2025.39 \pm 9.14~\mathrm {N/mm^2}$$\end{document}, while the mean UTS decreased to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$32.01 \pm 0.12~\mathrm {N/mm^2}$$\end{document}. These changes correspond to reductions of 9.7 % for mean E and 2.4 % for the mean UTS. Although both mean E and mean UTS decreased after fungal colonisation, the reduction in mean UTS was less pronounced than that observed for the lower wood-particle contents.

A one-way ANOVA followed by Tukey’s post-hoc test revealed statistically significant differences between PLA_W40 and PLA_W40_WM for both mean E (**p < 0.0001) and mean UTS (*p < 0.001).

The results obtained for PLA_W40 show differences in both stiffness and tensile strength between the untreated and fungal-colonised specimen groups. Compared with the values measured for PLA_W30, lower values of both mean E and mean UTS were observed for the untreated and fungal-colonised specimens. Nevertheless, the relative reduction in mean UTS remained comparatively small, suggesting that the tensile strength of this material combination was only moderately affected following the applied colonisation and associated processing conditions.

PLA/wood material combinations with 50 wt.% wood-particle content

Figure 16 summarises the mechanical response of both material combinations. Figure 16a presents the mean engineering stress–strain curves together with their 95 % confidence intervals, whereas Fig. 16b compares the resulting values of mean E and mean UTS. Both material combinations exhibited a similar overall tensile response, characterised by an initial approximately linear elastic region followed by a maximum stress level corresponding to the mean UTS. Compared with the untreated specimens, the fungal-colonised specimens exhibited a lower initial slope of the stress–strain curve and slightly lower maximum stress values, which is consistent with the reductions observed for both mean E and mean UTS.

Fig. 16: Mechanical characterisation of PLA_W50 and PLA_W50_WM specimens: (a) mean engineering stress–strain curves with corresponding 95 % confidence intervals and (b) comparison of mean E and mean UTS. Error bars represent standard deviations. Statistical significance was evaluated using one-way ANOVA followed by Tukey’s post-hoc test (*p<0.05, **p<0.01, ***p<0.001, ****p<0.0001).

Representative macroscopic and microscopic observations of fungal-colonised specimens are shown in Fig. 17. The highlighted regions were selected for microscopic examination after the two-week colonisation period by Fomes fomentarius. The microscopic observations reveal the presence of fungal structures on the specimen surface, confirming successful surface colonisation of the PLA/Wood specimens by Fomes fomentarius. Similar to the observations for all other investigated material combinations, the present observations do not allow conclusions regarding the extent of fungal growth within the internal specimen structure.

Fig. 17: Macroscopic and microscopic characterisation of a fungal-colonised PLA_W50_WM specimen. The highlighted regions were selected for microscopy after colonisation with Fomes fomentarius. Representative images from the cross-section (y–z plane) and specimen surface (x–y plane) illustrate fungal structures present on the analysed specimen. Scale bars correspond to 20 μm.

At the highest investigated wood-particle content of 50 wt.%, the untreated PLA/Wood composite (PLA_W50) exhibited a mean E of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2231.05 \pm 20.33~\mathrm {N/mm^2}$$\end{document} and a mean UTS of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$32.86 \pm 0.07~\mathrm {N/mm^2}$$\end{document}. After fungal colonisation (PLA_W50_WM), the mean Young’s modulus decreased to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2072.72 \pm 8.80~\mathrm {N/mm^2}$$\end{document}, while the mean UTS decreased to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$32.14 \pm 0.05~\mathrm {N/mm^2}$$\end{document}. These changes correspond to reductions of 7.1 % for mean E and 2.2 % for the mean UTS. Among all investigated fungal-colonised material combinations, PLA_W50_WM exhibited one of the smallest relative reductions in tensile strength.

A one-way ANOVA followed by Tukey’s post-hoc test revealed statistically significant differences between PLA_W50 and PLA_W50_WM for both mean E (p < 0.0001) and mean UTS (p < 0.0001).

For the highest investigated wood-particle content, statistically significant differences were still observed between untreated and fungal-colonised specimens for both mean E and mean UTS. However, the magnitude of the observed changes was comparatively small relative to the untreated reference specimens. Despite this, the measured tensile properties remained lower than those obtained for the PLA_W30 material combination. As discussed in Section 2.1, differences between the commercial filament systems may arise not only from nominal wood-particle content but also from manufacturer-specific material compositions and processing routes.

Statistical evaluation of mean young’s modulus and mean UTS

Figure 18 summarises the statistical comparison of mean E and mean UTS for all investigated PLA/wood material combinations before and after fungal colonisation.

The results demonstrate that statistically significant differences in mean Young’s modulus were observed between untreated and fungal-colonised specimens for all investigated wood-particle contents. Similarly, statistically significant reductions in mean UTS were observed for all material combinations, although the magnitude of the effect varied between material combinations.

Among the investigated commercial filament material combinations, PLA_W30 and PLA_W30_WM exhibited the highest measured values of both mean E and mean UTS, confirming the trends previously observed in the stress–strain analyses. Furthermore, the statistical evaluation confirms that significant differences exist between the investigated material combinations. However, because the commercial filaments originated from different manufacturers, these differences cannot be attributed exclusively to the nominal wood-particle content.

Fig. 18: Statistical comparison of mean E and mean UTS for all investigated PLA/wood material combinations before and after fungal colonisation. Grey bars represent untreated specimens, whereas brown bars represent fungal-colonised specimens (WM). Error bars indicate standard deviations. Statistical significance was evaluated using one-way ANOVA followed by Tukey’s post-hoc test (*p<0.05, **p<0.01, ***p<0.001, ****p<0.0001).

LCA results based on life cycle inventory data

Table 5 summarises the life cycle inventory data used as inputs to the supplementary screening-level printing-stage LCA for the five investigated PLA/wood material combinations (w = 0.5 to 0.1). For each material combination, the foreground inventory includes the calculated 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} and the measured 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}. The corresponding PLA and wood masses are derived from \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} according to the nominal wood-particle mass fraction.

Across the five material combinations, electricity consumption remains within a narrow range of 0.023–0.024 kWh per specimen. The total specimen mass varies from 6.030 to 6.684 g. With decreasing wood-particle content, the calculated PLA mass increases from 3.1200 to 6.0156 g, while the calculated wood mass decreases from 3.1200 to 0.6684 g.

Sample ID | w (-) | Total mass (g) | PLA mass (g) | Wood mass (g) | Electricity (kWh) | Notes
1 | 0.50 | 6.240 | 3.1200 | 3.1200 | 0.024 | 50 % wood
2 | 0.40 | 6.030 | 3.6180 | 2.4120 | 0.024 | 40 % wood
3 | 0.30 | 6.260 | 4.3820 | 1.8780 | 0.023 | 30 % wood
4 | 0.20 | 6.600 | 5.2800 | 1.3200 | 0.023 | 20 % wood
5 | 0.10 | 6.684 | 6.0156 | 0.6684 | 0.023 | 10 % wood

Figure 19 presents the contribution breakdown for GWP. The total GWP remains within a narrow range of 0.02426–0.02491 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 per specimen across the five PLA/wood material combinations. Sample 3 (w=0.30) shows the lowest total GWP, whereas Samples 2 and 5 show the highest total GWP values. In all material combinations, the electricity-related contribution forms the dominant baseline, ranging from 0.02179 to 0.02274 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 per specimen. The material-related contribution is smaller, ranging from 0.00202 to 0.00312 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 per specimen, and varies with the PLA/wood mass split.

As the nominal wood-particle content decreases from 50 % to 10 %, the PLA-related GWP contribution increases from 0.00157 to 0.00302 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, while the wood-related contribution decreases from 0.00046 to 0.00010 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. Therefore, the variation in material-related GWP is mainly associated with the increasing PLA mass fraction. However, because the electricity-related contribution is substantially larger than the material-related contribution, the total GWP values remain comparatively close across the five material combinations.

Fig. 19: Contribution breakdown for GWP for the investigated PLA/wood material combinations. The total impact is decomposed into electricity-related and material-related contributions, with the material term further split into PLA- and wood-attributed components.

The corresponding contribution breakdowns for AP and EP, together with the detailed numerical LCA results, are provided in Appendix A. These supplementary results show that AP and EP vary more clearly with decreasing wood-particle content than GWP.