Viscoelastic properties of wood in swelling systems

Summary

The torsion modulus and the mechanical damping were investigated on wood swollen with formamide and a series of glycols, at frequencies of 0.5 and 0.02 Hz as a function of temperature. In wood swollen with formamide to the same extent as it would swell when saturated with water, the temperature of maximum damping was about 48° and above 100°C for wood swollen with polyethylene glycols, while that of water saturated wood was 80°C. For more highly formamide swollen wood (1.2 times the swelling in water) the temperature at which maximum damping develops decreased to 30°C. With regard to the influence of swelling and temperature on the torsion modulus of wood, three regions of viscoelastic behavior were recognized in these swelling systems. They are the glassy region in non-swollen wood, where the torsion modulus decreases gradually with increasing temperature, the transition region where the torsion modulus decreases abruptly with increasing temperature and swelling, and a plateau region appearing at high temperatures for highly swollen wood where the torsion modulus remains fairly constant with temperature with a value of about one tenth the modulus for non-swollen wood.