Metodologia da secagem drástica aplicada ao desenvolvimento de programas de secagem da madeira juvenil de clones de Toona ciliata

Abstract

The Toona ciliata has been gaining ground in Brazilian forestry, aiming at the production of alternative wood for the reduction of the exploitation of native species. The study of the properties and processes that involve the wood of the species in question is necessary due to the scarse available information in relation to other exotic species implanted in Brazil. In this context, the present study aimed to evaluate the anatomical characteristics and behavior of juvenile wood from five clones of T. ciliata during drastic drying, contributing to the elaboration of the drying schedule. For the development of the study, four trees per clone of a seven year old plantation, settled in Campo Belo – MG region, were sampled at 1.30 meters of height from the ground. The trees were selected, cut and sectioned into logs. After the sawing the specimens were prepared in three radial positions of the stem, for anatomical characterization and drastic drying tests. The fiber dimensions, microfibrillar angle and basic density were evaluated. During drying at 100°C, mass loss, drying time, the presence of cracks at the top and collapse were monitored in order to obtain the drying parameters (initial temperature, final temperature and drying potential). The results obtained allowed to differentiate the clones. The average microfibril angle presented a 27% reduction in the pithbark direction, the clone MD had the highest mean of 12.27°, while the lowest recorded average was of the clone FE with 10.43°. The dimensions of the fibers presented increase in the pithbark direction. The microfibrillar angle showed reduction with increasing fiber length. Clone XB expressed greater ease in the drying process at 100°C, due to lower basic density and higher drying rates. However, the wood of the MD and FE clones showed lower drying rate, higher density and greater susceptibility to collapse. Top cracks were not observed during drying at 100°C in the wood of any of the clones studied. The wood of the clones XD, MD and FE showed similarities between the drying parameters, allowing them to be grouped in a single drying schedule. Specific drying schedules were suggested for clones XE and XB. The drying rates of clones XB and XE showed moderate relation with fiber length.