The DN 30 hybrid poplar: a fiber source for high strength hardwood pulps

This study compared three hybrid poplars to aspen (Populus tremuloides) to determine their suitability for the manufacture of bleached chemithermomechanical pulp (BCTMP). The three hybrids were an 11-year-old DN 30 (P. deltoides x P. nigra), 7- and 17-year-old DN 38 (designated NE 238 by some researchers), and a 7-year-old NM 5 (P. nigra x P. maximowiczii). The 7-year-old DN 38 and NM 5 produced chemithermomechanical pulps (CTMPs) with lower strength than aspen; the 17-year-old DN 38 produced pulps with equivalent strength. Pulps produced from the 11 year-old DN 30 were much stronger than aspen pulps. The percent strain (to the point of rupture) in the tensile test and tensile energy absorption (TEA) were both ∼40% higher for the DN 30 sheets. The highest tear indices attained were ∼6.0 mN.m2/g for aspen and ∼8.0 mN.m2/g for DN 30 sheets. Kraft pulps were then produced from DN 30 grown on a different site by another organization. At an equivalent tear index to aspen kraft sheets, the TEA was 75% higher for the DN 30. This should lead to smoother paper machine operations.