The process parameters affecting peroxyacetic acid delignification, i.e. te
mperature, pH and chemical charge, were studied in relation to their effect
on carbohydrate depolymerization and dissolution for a softwood kraft pulp
. Carbohydrate reactions were found to follow different paths in different
pH regions. At low pH, acid hydrolysis was probably the main reason for car
bohydrate depolymerization and dissolution. At neutral pH, however, carbohy
drate depolymerization was probably caused by the decomposition products of
peroxyacetic acid. Peroxyacetic acid may also react with dissolved monosac
charides to form aldonic acids with corresponding and shorter carbon chain
lengths as well as aldoses with shorter carbon chains. These reactions were
verified through model compound studies. Because of these reactions the am
ount of carbohydrates in spent liquor is not equal to that removed from pul
p fibres during the treatment. These side reactions also consume a small am
ount of peroxyacetic acid during pulp bleaching.