Transient moisture effects on wood creep

• Published in: Wood science and technology Vol. 36; no. 6; pp. 447 - 462
• Main Authors: NAVI, P, PITTET, V, PLUMMER, C. J. G
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01.12.2002; Springer Nature B.V
• Subjects: Applied sciences; Cellulose; Cellulose fibers; Coupling (molecular); Creep (materials); Crystal structure; Crystalline cellulose; Crystallinity; Divergence; Exact sciences and technology; Fibrils; Humidity; Hydrogen bonding; Load distribution; Mechanical properties; Moisture effects; Polymer industry, paints, wood; Polymers; Properties and testing; Shrinkage; Viscoelasticity; Wood; Wood. Paper. Non wovens; Deformation; Water sorption; Wood; Creep; Molecular structure; Cellulose; Cyclic test; Water content; Mechanical properties; Crystallinity; Experimental study; Rheological properties
• ISSN: 0043-7719; 1432-5225
• DOI: 10.1007/s00226-002-0157-1

To gain insight into the physical nature of the coupling between mechanical stress and humidity variations, the behaviour of thin wood strips was studied using specially developed apparatus for creep/recovery and relaxation/blotting-out tests in a controlled humidity environment. The load time and the rate of viscoelastic creep were found to have little influence on mechano-sorptive creep. Moreover, creep trajectory curves for specimens with continuous and interrupted humidity cycles indicated divergence from simple creep-limit behaviour. The effect of transient moisture was also modelled numerically at the molecular level using an idealized cellulose-based composite. Preliminary results suggest that: (i) during free shrinkage, the cellulose chains in elementary fibrils may bend perpendicular to the planes of the hydrogen bonded sheets which form the crystalline lattice; (ii) transient hydrogen bonding between the crystalline cellulose and amorphous polymer owing to the introduction or removal of water may accelerate shear slip between the two phases in the presence of an external load.