Changes induced in early- and latewood fibres by mechanical pulp refining

A study was performed to investigate how latewood and earlywood fibres were affected during TMP refining. Cross-sections of latewood and earlywood fib res were classified using a parameter Z, defined as the cross-sectional fib re wall area divided by the area of a circle with same outer perimeter. The distribution of the Z-parameter could be described as the sum of two overl apping normal distributions. Latewood fibres and earlywood fibres were foun d to behave differently during refining. Earlywood fibres were preferably s plit during refining. Most splitting occurred during Ist stage. Refining re duced fibre wall thickness more for latewood fibres than for earlywood fibr es. The changes in properties of hand sheets from the long fibre fraction w ere consistent with the changes in fibre wall structures.