Enhanced lignin-dominated relaxation strength under water-swollen conditions revealed by archived DMS data from naturally aged hinoki wood

Abstract

Long-term natural aging may alter molecular mobility in lignocellulosic cell walls, but relaxation magnitude and kinetics need not change in parallel. Archived 2007 dynamic mechanical spectroscopy (DMS) data were reanalyzed for water-swollen hinoki ( Chamaecyparis obtusa ), comprising five naturally aged materials and one modern reference. The archived series is specimen-resolved rather than population-replicated. First-heating tan δ profiles were evaluated separately for loss-feature magnitude, breadth, and apparent kinetics. Across all five naturally aged materials, the lignin-dominated loss feature was larger than in the modern reference, whereas peak breadth and apparent activation energy remained material dependent. Separate analysis of the second heating showed that the larger loss magnitude persisted after a common preceding heating-cooling cycle, while peak-temperature responses were heterogeneous among materials. These results identify enhanced lignin-dominated relaxation magnitude as the most consistent observation in this historical series, while limiting inference to the characterized specimens rather than a population-level aging effect.