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UBC Theses and Dissertations

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UBC Theses and Dissertations

Relating pressure response profile during hot pressing to property development in flakeboard Feng, Yan

Abstract

The pressure response profile of a flakeboard during hot pressing was exclusively studied using variables of flake species (aspen and lodgepole pine), flake types (small-size flakes and large-size flakes), resin contents (0 and 8 percent), moisture contents (2 and 6 percent), and press closing times (30, 60 and 90 seconds). This pressure response profile was found to reflect the panel's overall rheological behaviour in relation to each of the variables. Pressure response was related to the development of the panel properties such as vertical density gradient, modulus of rupture, modulus of elasticity, internal bond and dimensional stability, as well as the development of in situ adhesive cure. The development of a panel vertical density gradient was found to depend on the panel overall rheological behaviour during hot pressing and could be well determined either by mat pressure response or by mat displacement response. The development of the panel modulus of rupture, modulus of elasticity, and internal bond, on the other hand, depended not only on the development of the vertical density gradient, but the adhesive cure as well. The in situ adhesive cure could be determined by mat displacement response for a panel with limited rheological response during hot pressing. With large rheological response, the mat displacement was not sensitive to adhesive cure. By monitoring system temperature, mat pressure and displacement response, the developments of panel properties and in situ adhesive cure could be satisfactorily explained. The feasibility of altering panel properties by pressure manipulation was also studied. The introduction of a pressure breathing stage during hot pressing was found to improve properties only in panels with 2 percent moisture content. With 6 percent moisture content, panel properties were adversely affected.

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