Investigation of fungal self-healing in nano-particulate glass fibre reinforced polymer composites

The idea is inspired by the common biological anti-damaging mechanism: a natural self-healing process, which happens after damage has occurred to allow the material to regain its load-bearing capacity. Those materials have some potential benefits over traditional fibre reinforced composites: lighter structures and better structural optimization, longer life spans, and lower maintenance. This work attempts to study how a self-healing mechanism is possible in glass fibre reinforced epoxy (GFRP) composites by adopting a fungal growth followed by a bioinspired strategy for the internal healing of microcracks. Compatibility of fungal strains with glass fibres and the incorporation of selected strains (#20 Cmbaney and #1088 Amstitway) in an epoxy matrix, with and without a nanoclay coating (Cloisite 30B, 1 wt%) were evaluated. Standard tensile and flexural tests were carried out and hygrothermal ageing tests were undertaken by the storage of the samples in water and in NaOH solutions at a temperature of 45°C until 30 days had lapsed. The presence of fungi was further confirmed and the structural stability of fungus in the composite material analyzed using a Scanning Electron Microscopy (SEM) and optical microscopy. Unique strain specific mechanical characteristics were found from the experimental results. Incorporation of #20 Cmbaney strain also led to about 88% decrease in tensile strength, which suggests that this strain is detrimental and if it exists inside the composite structure, it would act as a weak phase. The composite containing the #1088 Amstitway strain and nanoclay coating, on the other hand, had a tensile strength of 27.37 kg when compared to the unmodified composite, which is a 6.56% increase. The SEM micrographs verified the structural integrity of the fungal trammel inside the epoxy, thereby conforming to the crack-bridging hypothesis. Significant degradation of flexural and tensile properties was noticed due to hygrothermal aging; the most significant degradation was seen with composites with nanoclay coating in NaOH aging medium with flexural strength reducing up to 43.9% after 30 days. The tensile strength was decreased by 51.87% in composite containing uncoated nanoclay in NaOH and 35.30% in water based composite containing nanoclay coated by nanolubricants during 22 day period. The results show that the fungal network itself experiences degradation in harsh service conditions, thus rendering the fungus' healing potential limited. The present work demonstrates the feasibility of fungal integration as a bioinspired technique for passive self-healing, and also reveals the need to explore additional active biological repair approaches and the durability of the environment.