Influence of impulse drying on the retention and sizing of paper with alkyl ketene dimer.

Impulse drying has a negative effect on AKD retention and sizing, but PAE and PEI may offer a solution.

Impulse drying has been used in the paper machine press section to enhance the dewatering of the paper web through an intense temperature and peak pressure impact. In this work, the researchers studied the effects of impulse drying on AKD retention and on the efficiency of sizing. Impulse-pressed handsheets beaten to 25[degrees]SR or 40[degrees]SR were prepared. The sizing efficiency and AKD retention were characterized by the Hercules sizing test and by gas chromatography.

When pressing temperature was increased, both the AKD retention and the sizing of the impulse-pressed handsheets were affected negatively. The mechanisms of dewatering in impulse drying are thought to be responsible for this negative effect.

In evaluating the effects of wet pressing time on AKD sizing and retention, the researchers found that longer pressing times reduce paper sizing considerably. Apparently, the longer duration lowered the total AKD retained and the amounts of reacted AKD.

The addition of PAE and PEI promoted AKD retention under conventional pressing conditions. Therefore, the use of these polymers may be a viable way to increase the AKD retention and sizing on papers submitted to impulse drying.

Mendes and Costa are with LEPAE--Dept. of Chemical Engineering, Faculty of Engineering, University of Porto, Portugal, Xiao is with the Dept. of Chemical Engineering, University of New Brunswick, Fredericton, NB E3B 5A3, Canada; Belgacem is with Ecole Francaise de Papeterie et des Industrie Graphiques, INPG, Laboratoire de Genie des Procedes Papetiers, Grenoble, France; and Roberts is with the Dept. of Paper Science, UMIST, Manchester, England. Email Xiao at [e-mail].