EFFECTS OF THERMAL AND HYDROTHERMAL TREATMENTS ON THE RESWELLING CAPABILITIES OF PULPS AND PAPERSHEETS

The water-reswelling capability of papersheets after thermal and hydro thermal treatments were evaluated as water retention values (WRVs). Wh en papersheets were subjected to heating treatments, the higher the te mperature and the higher the relative humidity, the lower the WRVs. Fu rthermore, the WRVs of handsheets prepared by drying, even at 20-degre es-C, were clearly lower than those of original pulps. This decrease i n the WRVs of the handsheets corresponds well to the decrease in the w ater accessibility of hydroxyl groups in the handsheets. Formation of stable intra- and/or inter-molecular hydrogen bonds in the non-crystal line regions of cellulose and hemicellulose is probably responsible fo r the decrease in WRVs. Hydrogen-bond formation, involving the small a mount of carboxyl groups, also seems to contribute to the decrease in WRVs. The soaking of papersheets in acid solutions (even at 20-degrees -C) resulted in decreased WRVs, probably because the carboxyl groups i n the sheets are converted from ionized form to the more hydrophobic p rotonated form.