Characteristics of prehydrolysis-kraft pulp fibers from Scots pine

To clarify the influence of prehydrolysis on fiber characteristics, Scots pine (Pinus sylvestris L.) wood chips were subjected to pressurized hot-water and dilute-acid prehydrolysis (0.5% H2SO4) prior to kraft pulping to partially remove hemicelluloses as hydrolyzate. After the prehydrolysis, the wood chips were submitted to kraft pulping and the pulp was fully bleached in oxygen (O), chlorine dioxide (D), alkaline extraction (E) and chlorine dioxide (D)-sequence. Measurements with an automated optical fiber analyzer showed that prehydrolysis prior to kraft pulping caused significant changes in the fiber dimensions and morphology of the final bleached pulp. Especially, a decrease in fiber width and an increase in fiber deformations were observed compared to a reference kraft pulp. The scanning electron microscopy of handsheets supported the morphology analyses and revealed alterations also in the fiber ultrastructure. The changes in both chemical and physical fiber characteristics require attention when considering the correct processing and end-use of prehydrolysis-kraft pulp fibers.