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

Abstract

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 × 104 Ω·cm2 after 14 days of colonization by T. funiculosus while the value remained at 7.2 × 107 Ω·cm2 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.

Investigating Different Local Polyurethane Coatings Degradation Effects and Corrosion Behaivors by Talaromyces funiculosus via Wire Beam Electrodes

“…According to the previous work from our group, the ester bond hydrolysis that occurs in the PU structure can be accelerated because of the carboxylic acids secreted by T. funiculosus . Moreover, along with the hydrolysis of the ester and urethane bonds, carbon chains and ring structures were also broken by T. funiculosus [ 27 ].…”

“…An irregular micro-crack located at the upper-right of the edge of the huge blister ( Figure 11 d) may act as a channel for the transfer of electrolytes to metal substrates and lead to the formation of this blister. This may be caused by the attack of mycelium and the coating degradation caused by secretions of T. funiculosus [ 27 ]. In Figure 11 e, the coating on the #18 electrode surface was basically smooth, with some corrugated areas near the colonized individual spores of T. funiculosus .…”

“…In our previous work, the biodegradation effect of Talaromyces funiculosus ( T. funiculosus ), which was isolated from the atmospheric environment of the rainforest in Xishuang-banna (southern China), was studied in humid and hot atmospheric environments. Because of the organic acid secreted by T. funiculosus and its mycelium attacking, the PU coatings exhibited local damage and contributed to the presence of wrinkles, blisters, and even micro-holes [ 27 ]. However, we did not distinguish the barrier properties of these different areas.…”