*Bending Strength and Modulus of Elasticity after Exposure to Coniophora Puteana*

The test results of the specimens' mechanical properties show that in the initial state, the composites reinforced with oat and millet husk had a bending strength of 44 MPa and 31 MPa, respectively, while the specimens' modulus of elasticity was 3790 MPa and 2870 MPa, respectively (Figure 4). It can be noticed that the properties of the composite with oat husks are more useful than those of the composite with millet husks in the initial state. The reason for this may be the influence of the shape and wetting degree of the filler. Oat fillers have an elongated shape, which is advantageous for their mechanical properties. In general, millet fillers have irregular shapes [20]. In addition, fillers naturally have different moisture absorption capacities.

**Figure 4.** Test results of (**a**) bending strength and (**b**) modulus of elasticity of oat and millet huskreinforced composites after exposure to *Coniophora puteana* and manual mycelium removal with a soft brush (B) and with water under pressure (W). Test results of reference specimens in initial state (R) have been also presented. The results are expressed in MPa.

The test results of the composites obtained after 14 days of soaking in water, followed by 4 months of exposure to fungi at 22 ◦C and at 70% humidity, show that these conditions reduce their flexural strength and modulus of elasticity, compared to the reference material. This was also reported in other papers [8]. The method of cleaning had a small effect on the oat husk composite. After exposure to fungus and cleaning with a brush, the oat husk composite had a bending strength of 40 MPa and a modulus of elasticity of 2460 MPa, while after water cleaning, the bending strength of this composite was 38 MPa and a modulus of elasticity was 2340 MPa (Figure 4).

On the other hand, the effect of the mycelium removal method on the composite with millet filler was significant in comparison to the oat filler composite. After exposure to *Coniophora puteana* and cleaning with a brush, the composite had a bending strength of 21 MPa and a modulus of elasticity of 1050 MPa, while the composite cleaned with water had a bending strength of 27 MPa and a modulus of elasticity of 1530 MPa (Figure 4). In relation to the mass loss test of the composite with millet husks, the reason for the difference may be the lack of fillers in the pores, as well as the higher efficiency of the mycelium removal method with water.

### **5. Conclusions**

Based on the results of the oat husk-reinforced composite tests, the following conclusions can be drawn:


• The method of mycelium removal does not significantly affect the physical and mechanical properties of the oat filler composite.

The conclusions based on the results of the millet husk-reinforced composite are as follows:


It was concluded that the effects of mycelium removal methods depend on the type of filler. It is still difficult to determine which was the most effective method of cleaning the specimens due to the constrained conditions and few composite fillers used. Further research including extended parameters that affect the mechanical and physical properties of the natural filler-reinforced composites is planned.

**Author Contributions:** Conceptualisation, M.G.; methodology, M.G.; formal analysis, E.S.; investigation, M.G.; writing—original draft preparation, M.G.; writing—review and editing, E.S.; visualization, M.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Ministry of Education and Science as part of the project LN-002.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** The publication cost of this paper was covered with funds provided by the Polish National Agency for Academic Exchange (NAWA) ("MATBUD'2023—Developing international scientific cooperation in the field of building materials engineering" BPI/WTP/2021/1/00002, MATBUD'2023).

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the study's design, in the collection, analyses, or interpretation of data, in the writing of the manuscript, or in the decision to publish the results.
