The effect of bleached pulp type on AKD internal sizing - an EuroFEX experimental paper machine study

The effect on different pulp types of internal sizing with an alkyl ketene dimer (AKD) was investigated on the EuroFEX experimental paper machine at STFI as well as by laboratory experiments. The different pulp types investigated were industrially ECF- and TCF-bleached hardwood and softwood pulps. The pulps were both dried and never dried. The EuroFEX paper machine trials were run with a Fourdrinier former and no filter was used in the experiments.

The results show that the AKD size retention and the sizing efficiency, given as the amount of AKD required to reach a specified degree of sizing, are greatly influenced by the wood species and the bleaching sequence used. Laboratory experiments support the indication from the paper machine experiments that the AKD sizing of bleached pulps is affected by a combination of physico-chemical properties of the fibers, the fines and the water phase.