Hygrothermal aging, fatigue and dynamic mechanical behavior of cellulosic particles reinforced one-component moisture curable polyurethane adhesive joints

Microcrystalline cellulose (MCC) and sawdust (SD) green fillers have great potential to act as moisture reservoirs and reactive fillers. In the present study, a one-component moisture curable polyurethane (PU) adhesive was reinforced with MCC and SD fillers. The durability of aluminum/steel joints produced using unreinforced and reinforced PU adhesives was studied using dynamic mechanical analysis (DMA), fatigue, and hygrothermal aging experiments. Lap-shear tests were conducted to evaluate the effects of aging on joints strength. Fourier-transform infrared spectroscopy (FTIR) experiments were performed on adhesive joints after hygrothermal aging to understand the changes in chemical structure due to aging, and the influence of cellulosic fillers on the aging phenomena. DMA results showed that the glass transition temperature of the reinforced PU was similar to that of the unreinforced PU. Fatigue performance of MCC and SD reinforced PU adhesive joints was found to be better than unreinforced PU joints. Further, MCC reinforced PU adhesive joints were found to be more resistant to hygrothermal aging than SD reinforced and unreinforced PU joints. Overall, MCC reinforced PU adhesive joints exhibited good fatigue and superior long-term properties.