Insight into Degrading Effects of Two Fungi on Polyurethane Coating Failure in a Simulated Atmospheric Environment

Two different fungi, Talaromyces funiculosus (T. funiculosus) and Phanerochaete chrysosporium (P. chrysosporium), were collected from the Xishuangbanna atmospheric corrosion site and incubated on a polyurethane (PU) coating at 30 °C for two weeks under 95% relative humidity (RH). The biodegrading effects of these fungi on the coating failure were investigated from aspects of metabolism and electrochemistry. The results showed that T. funiculosus contributed more to the degradation of the PU coating failure than P. chrysosporium, and two factors played dominant roles. First, the weight of the T. funiculosus mycelium was nearly 3 times more than that of P. chrysosporium, indicating there was more substrate mycelium of T. funiculosus deep into the coatings to get more nutrition in atmospheric during colonization. Second, T. funiculosus secreted carboxylic acids, such as citric, propanoic, succinic, and tartaric acids, and accelerated the hydrolysis of the ester and urethane bonds in the PU coatings. As a result, the mycelium of T. funiculosus readily penetrated the interface of the coating and substrate resulting in a rapid proliferation. Thus, the |Z|(0.01Hz) value of the coating decreased to 5.1 × 10(4) Ω·cm(2) after 14 days of colonization by T. funiculosus while the value remained at 7.2 × 10(7) Ω·cm(2) after colonization by P. chrysosporium. These insights suggest that the biodegradation process in simulated atmospheric environments would provide theoretical guidance and directions for the design of antifungal PU coatings.