Effects of preparation process parameters on the properties of mycelium biomass materials

Abstract: Biodegradable packaging materials have received widespread attention in recent years. The reason is that non-biodegradable packaging materials have caused serious environmental and human health issues during disposal after mass production. Fortunately, the mycelium material can be expected to serve as one of the promising biodegradable materials. In this study, the mycelium biomass material was cultivated to determine the effect of preparation process parameters on mechanical properties. Pleurotus ostreatus was selected to inoculate in a culture substrate, including the wood chips, cotton seed hulls, corn cobs, wheat bran, lime, and gypsum. The process parameters were then optimized for the properties of mycelium biomass material. After that, a three-factor and the three-level orthogonal test was carried out to investigate the three process parameters (inoculum amounts, particle size of substrate, and water addition) using the minimum cushioning coefficient and bending strength as the evaluation indexes. The maximum and minimum average diameters of mycelium were 1 641 and 520 nm, indicating the significant influence of different process parameters on the growth state of mycelium. The influencing factors were ranked in descending order of the particle size of the substrate, followed by the water addition, and inoculum amount. The bending resistance and buffering effect of mycelium material decreased as the particle size of the substrate decreased, due to the reduced internal space of substrate material. The low growth of mycelium and adherence between the substrates was attributed to the limited deformation space of material for less air circulation. The best bending resistance and buffering efficiency were achieved in the amount of water addition of 60%. As such, the bonding between the substrate inside the material depended mainly on the amount of water addition. The better mechanical properties were obtained in the relatively strong bonding, where the metabolism and growth of mycelium with suitable water was a benefit to wrapping the substrate. By contrast, the air circulation was reduced, where too much water filled the internal void in the material. The needed oxygen and metabolic carbon dioxide were not exchanged during the mycelium growth in time, leading to the low bending strength and buffering performance of the mycelium material without growth. The best bending resistance and buffering efficiency were achieved in the optimal inoculum of 10%. Once the inoculum was too low, the strains have limited contact with the substrate area, resulting in a limited area for colonization and growth. The insufficient mycelium growth reduced the bonding between substrates, leading to a decrease in the bending strength of mycelium material. A high inoculum greatly contributed to the strains competing with each other for the nutrient source, leading to the limited growth of mycelium in all strains. The optimum process parameters were optimized for the inoculum amounts of 10%, the particle size of substrate 10 mm, and water addition of 60%, corresponding to the minimum cushioning coefficient of 4.17 and the highest bending strength of 417.43 kPa of the mycelium material. Therefore, the bending strength of mycelium material was comparable to that of expanded polystyrene foam. But, the cushioning performance was less than that of expanded polystyrene foam. Three process parameters can be expected to further optimize the growth of mycelium, particularly for the better mechanical properties of the mycelium material. This finding can provide a strong reference to optimize the preparation process parameters and mechanical properties of mycelium biomass material.