Improving Moisture Durability of Forest Products Using Small-angle Neutron Scattering
A better understanding of how wood nanostructure swells with moisture is needed to accelerate the development of forest products with enhanced moisture durability. Despite its suitability to study nanostructures, small-angle neutron scattering (SANS) remains an underutilized tool in forest products research. Forest Service scientists investigated nanoscale moisture-induced structural changes in intact and partially cut wood cell walls using SANS and a custom-built relative humidity chamber. Water sorption caused spacing between elementary fibrils to increase with relative humidity, and this swelling accounted for more than half the transverse swelling in S2 secondary wood cell walls. Elementary fibril spacing in longitudinally cut wood cells, which were designed to mimic cells near wood-adhesive bondlines, was greater than the spacing in intact cells above 90 percent relative humidity. This suggested that some cell wall hoop constraint from the S1 and S3 cell wall layers on the S2 layer was released by cutting the cells. Furthermore, increased spacing between elementary fibrils may also create diffusion channels that are hypothesized to be responsible for the onset of fungal decay in wood. The scientists established protocols to use SANS in future research to study adhesives and protection treatments to improve moisture durability in forest products.