Collapsed and re-swollen archaeological wood: efficiency and effects on the chemical and viscoelastic characteristics of wood

The efficiency of different swelling agents in recovering the shape of collapsed archaeological wood (where the original object figure is lost) was evaluated. Furthermore, the effect of these treatments on the chemical and viscoelastic characteristics of wood was assessed by dynamical mechanical analysis (DMA). In preliminary trials, carried out on both alder (Alnus spp) and a highly decayed ash wood (Fraxinus excelsior L.), the efficiency of various organic solvents (dimethylsulfoxide, ethylene diamine, ethylene glycol, ethylene glycol mono butyl ether, N,N-dimethylacetamide) and active alkali urea (an experimental treatment previously proposed for collapsed wood) was considered in relation to three working temperatures. Following, medium decayed Scots pine (Pinus sylvestris L.), highly decayed maritime pine (Pinus pinaster Aiton), and two differently decayed oak woods (Quercus spp) were used to investigate the effects of the three best agents on the viscoelastic properties of wood and, again, their efficiency. Tests demonstrated that in most decayed samples, although high swelling was obtained, lignin was lost and a substantial weight decrease was observed. However, in least decayed samples a loss of cellulose crystallinity was detected. These occurrences reflected on both samples stiffness (that strongly reduced after treatments) and dissipative behaviour (an increase of damping factors could be observed after treatments in alkaline conditions). Thus, swelling agents, although satisfactory in the shape recovery of collapsed wood, should be used only in cases of real injury imputable to collapse (a specific consolidation treatment should be considered in addition).