HYGROEXPANSIVITY OF PAPER - EFFECTS OF FIBER-TO-FIBER BONDING

Effects of fibre-to-fibre bonding on the in-plane hygroexpansivity of paper have been investigated by changing wet pressing pressure and by using a debonding chemical. Increased fibre bonding, measured as an in crease in specific elastic modulus, generally increased hygroexpansivi ty, but the effect was dependent on the degree of drying restraint. Th eoretical analyses based on the micromechanics formula and the finite element analysis showed that an increase in bonded area certainly incr eases hygroexpansivity of paper but the effect is small when the fibre s are oriented in the sheet plane direction. However, when the out-of- plane configuration of the fibres exists in the bond structure, the ef fect of fibre bonding is magnified and the hygroexpansivity increases dramatically.