CHANGES IN FIBER LIGNIN DURING LABORATORY MCC PULPING

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.