Title : The compressive strength of mycelium-based composites from Namibian encroacher bush

Introduction: Namibia faces challenges of bush encroachment, affecting over 45 million hectares of rangeland and reducing biodiversity, grazing capacity, and agricultural productivity. The utilization of encroacher bush biomass is an opportunity for sustainable material innovation.

Materials and methods: The research investigated the compressive strength of mycelium-based composites (MBCs) created from two encroacher bush species, Terminalia sericea and Senegalia mellifera, using Ganoderma lucidum mycelium as a natural binder. The bush biomass was harvested through random selection from the Okondjatu district and processed into wood chips ranging from 1 to 5 mm. The substrates were supplemented with wheat bran and chalk powder, then pasteurized and inoculated with G. lucidum spawn. Mycelium-based composites were cultivated in controlled cylindrical molds for a period of 47 days and subsequently oven-dried at 99 °C. Compressive strength testing was conducted using a GCTS flat load machine, followed by data analysis through one-way ANOVA to assess the effects of substrate species and processing method.

Results: Results indicated significant variability in the compressive strength of MBCs based on substrate type and pressing condition. Composites derived from S. mellifera typically exhibited higher strength in pressed conditions, with an average of 0.76 ± 0.16 MPa, compared to non-pressed samples, which averaged 0.57 ± 0.46 MPa. This development suggested enhanced densification and mycelial bonding from pressing. Conversely, T. sericea composites displayed greater variability, with some non-pressed samples achieving compressive strength levels of up to 4.23 MPa, likely due to differences in fiber structure and porosity.

Conclusions: This study emphasizes that substrate type significantly affects the density, uniformity, and strength of mycelium-based composites. Pressing enhances composite compactness, but its impact differs based on substrate morphology. The findings suggest that Namibian encroacher bush biomass is a promising raw material for sustainable, biodegradable, non-structural construction materials. Future research should focus on optimizing substrate preparation, moisture control, and pressing conditions to improve the material consistency and mechanical performance of MBCs.

Keywords: biomass; compressive strength; encroacher bush; fungal mycelium; lignocellulosic; mycelium-based composites; saprophytic mushrooms; sustainable materials

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