Characterizing hydro-thermal compression behavior of aspen wood strands

Abstract

This study evaluates the microscopic changes of paulownia solid wood panels subjected to thermal compression via characterizing the changes in wood microstructure. The panels, with dimensions of 500 mm × 100 mm × 20 mm, were hot-pressed in a tangential direction by using a laboratory-type hot press at a temperature of either 150 °C or 170 °C and a pressure of 2 MPa for 45 min. Microscopic investigations conducted by light microscopy showed that slightly more damage occurred in the samples compressed at 170 °C and 2 MPa than at 150 °C and 2 MPa, and that the distribution of deformation in the panels was not uniform in the growth rings of the two treatment groups. The cell collapse was not observed in the microstructure of paulownia wood after the thermal compression. Cell shapes and their arrangement in the growth ring alongside loading direction were interpreted as effective factors governing the non-uniform distribution of damage and the lack of cell collapse in the microstructure.

Hybrid oriented strand boards made from Moso bamboo (Phyllostachys pubescens Mazel) and Aspen (Populus tremuloides Michx.): species-separated three-layer boards

“…One reason aspen is used for OSB is that the material is very low in density-285 to 410 kg/m 3 , but mostly between 300 and 350 kg/m 3 (Peters et al 2002, with a high compaction ratio. The board surface layers in particular are very effectively densified during hot pressing to give a composite of small elements and fissures that is similar in strength properties to undamaged solid parent material (Zhou et al 2009(Zhou et al , 2011. Semple et al (2007) compared the performance of clonal aspen wood of different density (from 328 to 408 kg/m 3 ) in OSB and found that mat compaction and densification was greater for lower density wood strands leading to superior board properties.…”

Hybrid Oriented Strand Boards made from Moso bamboo (Phyllostachys pubescens Mazel) and Aspen (Populus tremuloides Michx.): uniformly mixed single layer uni-directional boards

“…To obtain the required IB, strength and stiffness properties of OSB using low density, low strength aspen logs, the density of core (for IB), and even more so the surface layers (for flexural properties) must be increased much above that of the parent wood (Spelter et al 1996), and the strands plasticise and deform sufficiently to form intimate wood-adhesive-wood contact (Wolcott et al 1990). High degrees of layer densification and associated thickness swelling problems have been studied extensively during development of industrial OSB building products (Xu and Winistorfer 1995;Andrews 1998;Andrews et al 2001;Dai et al 2002;Winistorfer 2000, 2001;Zhou et al 2009). Blomberg and Persson (2004) and Blomberg et al (2006) clearly demonstrated how artificially densified aspen wood swells and largely regains its original shape after 24 h soaking in water.…”

Modeling vertical density profile formation for strand-based wood composites during hot pressing: Part 2. Experimental investigations and model validation

“…Based on the predicted temperature and MC distributions from the heat and mass transfer model, the strand compression modulus at a given time during the press cycle can be determined [2]. Then according to the stress-strain relationship for strand columns in compression, the layer deformation and hence the layer density can be obtained with the above-mentioned iterative method.…”

“…On the other hand, the function for compression modulus itself was empirically determined by experimental work [2], which also could introduce some uncertainties to the VDP model. If the surface layer densities are overestimated in the model, at a given target panel density, this will unavoidably result in the underestimated core layer densities.…”