Simulated MCC (Modified Continuous Cooking) pulping of radiata pine in
the laboratory produced pulps of about 20% higher strength potential
than the corresponding conventional kraft pulps at the same Kappa numb
er. To provide information on the higher selectivity of the MCC proces
s, lignins from laboratory simulated MCC pulping were compared to thos
e formed during conventional kraft pulping. Analysis by thioacidolysis
showed that, compared to conventional kraft pulps of equivalent ligni
n content, laboratory MCC pulps contained similar levels of uncondense
d P-ethers. However significant enol ether formation was found in the
initial phase and beginning of the bulk phase of delignification durin
g laboratory MCC pulping, suggesting a deficiency of sulfide in the fi
bre in these parts of the cook This sulfide deficiency cannot explain
the improved pulping selectivity. Thioacidolysis products from higher
yield MCC pulps showed similar molecular mass profiles to those of cor
responding kraft pulps, indicating that the lignins from the two proce
sses had similar degrees of condensation. Lignins isolated from conven
tional and MCC pulps at two similar Kappa numbers were compared by ele
mental analysis, methoxyl determination and quantitative C-13 NMR spec
troscopy. These results showed no significant difference between the c
onventional and modified pulp lignins. Overall this study provided no
evidence to indicate that the greater selectivity of the MCC process w
as due to changes in the behaviour of the lignin during pulping.