Transient moisture effects in materials

The paper reviews transient moisture effects in various materials with emphasis on their viscoelastic properties and durability. The first part of the review is dedicated to the phenomenological aspects of the effects in materials such as whole wood, plywood, particleboard, fibreboard, paper, natural and synthetic fibres and composite materials. Creep, creep recovery, dynamic response and failure as influenced by various transient moisture conditions are discussed in relation to the materials system, the extent and rate of moisture change, loading modes, temperature levels, specimen sizes, type of solvent and preventive measures. The second part is devoted to the discussion of mechanistic models. Explanations of the phenomenon from a molecular and materials standpoint are assessed, compared and discussed in depth so that one can gain deeper insight into the phenomenon as discussed in the first part. The main mechanisms discussed include: (i) hydrogen bonding, (ii) slip planes and (iii) crystallite slippage and rotation.