Cell wall fracture properties in relation to lignin distribution and cell dimensions among three genetic groups of radiata pine

Summary

The position of fracture within the cell wall on split tangential longitudinal surfaces of air dry wood was quantified for three genetic groups of Pinus radiata D. Don. Differences in the position of fracture within the cell wall among these groups of trees were compared with lignin distribution and cell wall dimensions. In the control trees equivalent to typical New Zealand grown radiata pine, fracture occurred predominantly between the middle lamella and S1 layers as well as within the S1 layer, producing large numbers of fines on the fracture surface. In the open pollinated NZ850–55 group, fracture occurred predominantly between the S1 and S2 layers as well as within the S1 layer, producing fewer fines on the surface. In the NZ850–55 x Guadalupe group, fracture occurred in a similar fashion to the open pollinated group except for a greater number of transwall fractures exposing the cell lumen on the fracture surface. The differences in fracture behaviour between the control and genetically select groups are attributed to reduced lignification at the S1/S2 boundary in the genetically select trees. Observed differences in both the type of fracture and its location were unrelated to cell dimensions. These observations are discussed in relation to the observed differences in thermomechanical pulping properties exhibited by these groups of trees.