Thermorheological Complexity and Fragility in Plasticized Lignocellulose

It is demonstrated that plasticized lignocellulose fails to satisfy classic criteria normally required to validate time/temperature superposition (TTS) in dynamic mechanical analysis (DMA). However, insightful relaxation behavior is available and dismissing it would be a mistake. TTS was applied to Liriodendron tulipifera wood using parallel plate compressive-torsion DMA with specimens immersed in different organic liquids, ranging from weak to strong swelling power. While all storage moduli shifted smoothly, thermorheological complexity was detected in loss modulus shift failures, which themselves must reflect unknown structural features. Storage modulus shift factors clearly distinguished solvent specific relaxation behavior and interpretations through the WLF model or through fragility (cooperativity) analysis are useful. However, it is demonstrated that fragility analysis is preferred and solvents of different swelling power are compared. Coupled with other methods, TTS and fragility analysis warrant further development as a means to improve the understanding of structure/property relationships in plasticized lignocellulose.