Rheology of Modified Wood by Means of Pure Solvent or Solution Treatments

Viscoelasticity of chemically modified Cedrus deodara by means of pure solvent or solution treatments has been evaluated using dynamic-mechanical analysis in bending mode at 30 °C. The samples are treated up to equilibrium conditions in solvents with different polarity (water, ethanol and acetone), and corresponding solutions with bifunctional chemicals (acyl dichloride and aliphatic-diamine). Then, in all cases the samples are air-dried and temperature equilibrated before to be characterized. Mechanical properties have been explored by means of stress–strain plots at different strain rate, creep and step-strain experiments. Dynamic-mechanical properties have been studied by frequency-strain spectra and E1, E2and tanδ have been investigated. Outcomes have been compared with those of a previous paper determined for seasoned or thermocured wood. The samples treated with the pure solvents exhibit an improvement of mechanical properties, due to the extraction of low molecular weight compounds acting as plasticizers of the lignin-based matrix: an increase of the elastic modulus, a reduction of the compliance and longer stress-relaxation time are observed. For the samples treated with the solutions of dichloride or diamine, the viscoelasticity behaviour is the resultant of plasticizers extraction and cross-linking of the polymeric matrix by means of the bifunctional reagents.