Thermoplastic deformation of poplar wood plasticized by ionic liquids measured by a nonisothermal compression technique

The in situ thermoplasticization of poplar wood with ionic liquids (ILs) has been investigated. The thermoplastic deformation of wood samples treated with four types of ILs at various concentrations was determined through nonisothermal compression tests by means of a rotational rheometer. Results show that increasing the concentration of ILs reduced softening temperature and increased deformation compared to the untreated control. Scanning electron microscopy revealed that plastic deformation of wood cells from the applied compression stress varied, depending on cell type, and occurred without cell wall fracture. X-ray diffraction analysis of compressed wood showed that wood treated with ILs exhibits a greater crystallinity index than the untreated control. The recovered strain in compressed samples decreased with increasing temperature and concentration of ILs to 18% weight percent gain (WPG) and then decreased slightly to 36% WPG. In treated samples, the combined wood/IL blends demonstrated less thermal stability than wood and ILs alone. Results also show that plastic deformation of IL-treated wood resulted in viscous buckling of unfractured cell walls. This deformation mode likely resulted from the disintegration of intermolecular and intramolecular hydrogen bonding between cell wall polymers through the combined effect of ILs, pressure, and high temperature.