The remaining chips were milled using a
knife mill (Retsch) with a 1-mm output screen and the
fraction coarser than 0.25 mm was selected for pulping.
This procedure aims to enhance the homogeneity of the
cooking. For wood chemical characterization, the wood
meal fraction was further milled to get material that passes
through a 40 mesh sieve.
Chemical composition was determined in seven selected
wood samples, aiming to cover the broad range of pulp
yield and density previously observed. Wood ash content
was determined according to TAPPI 21 [1, 22] and
extractives content was determined with ethanol:toluene
mixture (v/v, 1:3) according to TAPPI 204 [23]. lignin
(acid insoluble and soluble), neutral sugars and acetic acid
were determined following the standard biomass analytical
procedures of the National Renewable Energy Laboratory
[24].