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Similar plots resulted for all species, except original 1 mm thick micro-samples of E. obliqua, which showed abnormal shrinkage occurring at high MC due to cell collapse during free water removal (Figure 64). E obliqua is a renowned collapse prone species (Bootle, 2004). The radial and tangential shrinkage begins very soon after drying commences and increases abnormally down to 20-40 % MC. At this point the collapse shrinkage slows down as the sample reaches the bound water domain. In the domain of bound water, normal shrinkage takes place (< 20 % MC). Only this part of the shrinkage is recovered when the sample re-absorbs water. The E. obliqua collapse results observed are consistent with results observed by Perré (2007b) for E. gundal (E. gunnii x dalrympleana). This author theorised that it may be possible to avoid collapse shrinkage during shrinkage tests for this species by cutting thinner R-T sections in the longitudinal direction. Dadswell (1972), observed the range of fibre length of E. obliqua is between 1.04-1.27 mm Thus, by reducing the dimension of samples to less than 0.6 mm thickness, the majority of wood fibres will be severed. A cut fibre will not collapse as tension of the cell wall will not be set up if the ends of the fibres are not whole (Redman, 2001). 20 15 10 5 0 0 20 40 60 80 100 120 140 12 8 4 00 20 40 60 80 100 120 140 160 Moisture Content (%) Figure 66. Tangential and radial shrinkage versus MC – E. obliqua 1 mm thick sample 10 8 6 4 2 00 20 40 60 80 100 120 140 160 Moisture Content (%) Figure 67. Tangential and radial shrinkage versus MC – E. 0.5 mm thick sample 103 Tangential Radial Collapse Radial Tangential Moisture Content (%) Figure 64. Excessive shrinkage caused by collapse Tangential and radial shrinkage versus MC – E. obliqua original 1 mm thick sample 12 8 4 00 20 40 60 80 100 120 140 160 Moisture Content (%) Figure 65. Tangential and radial shrinkage versus MC – E. obliqua 2 mm thick sample Tangential Radial Tangential Radial Evaluation of super–heated steam vacuum drying viability and development of a predictive drying model for Australian hardwood species – Final report Shrinkage (%) Shrinkage (%) Shrinkage (%) Shrinkage (%)PDF Image | Evaluation of super-heated steam vacuum drying
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