Deterioration of vulcanized natural rubber sheets is associated with removal of calcium carbonate filler by wood-decay fungi Trichaptum abietinum and Trichaptum biforme

Wood-decay fungi may show potential in the degradation of rubber products in a natural and environmentally friendly process. Therefore, this study investigated the degradation of vulcanized natural rubber sheets by wood-decay fungi Trichaptum abietinum and Trichaptum biforme and the action of these fungi on the internal and external morphology, chemical composition, and physical properties of the rubber sheets. Scanning electron microscopy-energy dispersive X-ray spectroscopy analysis demonstrated that T. abietinum and T. biforme caused significant changes in the morphology of whole rubber. Crystals including calcium elements were formed on the rubber sheet after fungal treatment. Thermogravimetric analysis revealed a decrease in ash ingredient content corresponding to calcium carbonate in rubber treated with T. biforme for 3 months. These results suggest that the removal of the calcium carbonate filler from the rubber was associated with the deterioration of vulcanized natural rubber sheets by fungi. Furthermore, physical characteristics, durometer hardness, and tensile strength at the breakage point in rubber sheets were clearly altered after fungal treatment, although weight loss was not remarkable. We herein report for the first time that T. abietinum and T. biforme deteriorate vulcanized rubber sheets accompanied by transformation and translocation of calcium carbonate in vulcanized rubber.