Poplar breeding for superior papermaking fibers

The papermaking properties of twenty-two pure and hybrid poplars are being evaluated in an on-going investigation. Twenty of the poplars were harvested after 7.5 years from three different sites in the Midwestern and North Central US. The other 2 poplars survived at only two of three sites (64 total samples). Although additional results are presented, we focus on only two of the poplars from Year 1 of the study. The Crandon hybrid had the highest growth rate (tonnes ha^-1y^-1) and wood density (both averaged across the 3 sites). This poplar had a high cellulose content (compared to the average), a low lignin content and produced bleached kraft fibers at a high yield (wt. % on wood chips). Further, this poplar responded very well to kraft pulping and oxygen delignification and bleached to the highest final brightness ever observed in our laboratory (94.5% Elrepho). It also produced an 18 kappa number unbleached pulp with <0.5% rejects in only two-thirds the time required for sugar maple (Acer saccharum). The second poplar is clone 220-5 that had the highest area-weighted average microfibril angle (MFA) and excellent tensile properties. Eleven of the 22 poplars were selected for investigation in Year 2 and 31 total samples were harvested from the three sites after 8.5 years of growth. There was an increase of ∼0.05mm in average fiber length (AFL) and tear index increased by 0.5 -1.0 mN-m²/g for most of the poplars. The lignin in four of the eleven poplars was quite reactive in kraft and soda/AQ pulping and in O₂ delignification. Some of these lignins were analyzed and found to have a high syringyl to guaiacyl ratio by nitrobenzene oxidation and permanganate oxidation.