The contribution of different types of fines to the properties of handsheets made from recycled paper

Primary and secondary fines (obtained from unrefined and refined pulps, respectively) from three different sources TMP, kraft, and recycled paper were added to unrefined and refined decrilled recycled paper stock. Results show that fines from kraft and recycled paper are quite effective, while those from TMP are ineffective in increasing handsheet density, breaking length, and burst index. In general, secondary fines are more effective than primary fines. Characteristics of different types of fines will be discussed in light of these results. what properties are responsible for the beneficial nature of secondary fines. According to Lobben (6), improved bonding is brought about by the increased specific surface of the secondary fines, which increase the relative bonded area in the sheet. According to Szwarcsztajn and Przybysz (7), primary fines from unbleached pine kraft had a specific surface of approximately 25 m /g, while secondary fines (obtained after 25 minutes of beating) had a specific surface of 140 m /g. In this sense, secondary fines act as a filler material within the bond and provide a more uniform stress distribution over a larger bonded area. The other possible role that secondary fines play in sheet bonding is described by Giertz (8) and later Molina-Mancebo and Krkoska (5). They claim that these fines increase the amount of "bound water" between surfaces so that wet web strength and eventually sheet bonding are enhanced via the Campbell effect. This increase in bound water is thought to be due to the exposed hemicelluloses on the fines surfaces.