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To test this theory, 2, 1 and 0.5 mm thick R-T sections were prepared and retested. The results can be observed in Figure 65 to Figure 67. By observation, collapse shrinkage during testing is reduced with decreasing sample thickness so that no obvious collapse shrinkage is present for the 0.5 mm sample. The shrinkage intersection point (also referred to as the fibre saturation point) and total shrinkage can be calculated from the shrinkage versus MC curve by subtending the linear portion of the curve, in the bound water/shrinkage phase, until it intersects the x and y axis (Figure 63). We calculated the shrinkage at 12 %, a common published quantification of shrinkage, from the equation of the subtended line. Calculations occurred on the 1 mm thick samples for species C. citriodora, E. marginata and E. pilularis, and to avoid collapse shrinkage, on the 0.5 mm E. obliqua samples. Table 66 provides the total shrinkage, intersection point and shrinkage at 12% for each species. Published intersection point and 12% MC shrinkage values are also included, where the published intersection point data is from Budgen (1981) and the shrinkage values at 12 % MC are from Bootle (2005). No published intersection point values were available for Eucalyptus marginata or Eucalyptus obliqua. Radial and tangential shrinkage curves for all species can be observed in Figure 68 and Figure 69. Measured intersection point, total shrinkage and 12% MC shrinkage are consistent within species providing good repeatability. Published intersection point and 12% MC shrinkage values are consistent with measured data. Shrinkage values vary greatly between the tangential and radial directions as expected. Moreover, shrinkage values between species differ due to variations in physical and chemical properties. This seems particularly true for C. citriodora where the R/T shrinkage ratio at 12% MC is almost 1:1, significantly different from other species. Thus, in terms of shrinkage this species is more isotropic compared with the others tested. 10 10 88 66 44 22 E. obliqua E. pilularis E. marginata C. citriodora E. obliqua E. pilularis E. marginata C. citriodora 00 20 40 60 80 100 Moisture content (%) Figure 68. Radial shrinkage versus MC – all species 00 20 40 60 80 100 Moisture content (%) Figure 69. Tangential shrinkage versus MC – all species 104 Evaluation of super–heated steam vacuum drying viability and development of a predictive drying model for Australian hardwood species – Final report Shrinkage (%) Shrinkage (%)PDF Image | Evaluation of super-heated steam vacuum drying
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