Molecular origin of mechano-sorptive creep in cellulosic fibres

Mechano-sorptive creep, i.e. the increased rate of creep that occurs during changing relative humidity, when loading paper or wood, is a phenomenon still not fully understood. This phenomenon was here investigated by examining the changes occurring at the molecular level utilising FTIR spectroscopy. By subjecting the paper to deuterated water, the changes involving both the crystalline hydroxyls as well as those in accessible regions could be examined. During loading, the cellulose molecular chains are stretched taking the load. In addition, during mechano-sorptive creep a further exchange from OH to OD groups occurred. This was interpreted as caused by slippage between cellulose fibrils allowing previously non-accessible hydroxyls to become available for deuterium exchange. Thus, the loosening of the structure, during the changing moisture conditions, is interpreted as what has led to the increased creep and the possibility for new areas of cellulose fibril/fibril aggregates to be exposed to the deuterium exchange.