DIMENSIONAL STABILITY OF MODIFIED COMPOSITE PANELS
Keywords:Water resistance, accelerated weathering, heat-treatment, chemical impregnation
Dimensional stability of wood-based composites with changing moisture content remains an important challenge in the industry for many applications. Wood identification technologies have shown significant promise to improve dimensional stability. The main objective of this research project was to study the effectiveness of impregnation and heat treatments on wood composites when exposed to selected moisture environments. Moisture exposure conditions included one-sided water spray, one-sided liquid water contact, constant high RH, and cyclic exposure to high and low RH. Commercial moisture-resistant medium-density fiberboard (MDF) and birch plywood panels, as well as laboratory manufactured birch plywood panels, were modified by impregnation with phenol-formaldehyde (PF) resin, 1,3-dimethylol-4,5-dihydroxyethylenurea (DMDHEU) resin, or subjected to heat treatment at 205oC for 2 h to improve dimensional stability. All treatments improved moisture resistance. Plywood impregnated with PF or DMDHEU resin showed the lowest thickness swelling values, with maximum values not higher than 5% after 192 h of exposure. Heat-treated MDF and heat-treated plywood samples resulted in 11% and 6% thickness swell after water spray exposure, respectively. The heat-treated plywood resulted in lower linear expansion (LE) than untreated plywood, with an average reduction of 54%; whereas the heat-treated MDF material did not show improvement of LE relative to control MDF samples.
The copyright of an article published in Wood and Fiber Science is transferred to the Society of Wood Science and Technology (for U. S. Government employees: to the extent transferable), effective if and when the article is accepted for publication. This transfer grants the Society of Wood Science and Technology permission to republish all or any part of the article in any form, e.g., reprints for sale, microfiche, proceedings, etc. However, the authors reserve the following as set forth in the Copyright Law:
1. All proprietary rights other than copyright, such as patent rights.
2. The right to grant or refuse permission to third parties to republish all or part of the article or translations thereof. In the case of whole articles, such third parties must obtain Society of Wood Science and Technology written permission as well. However, the Society may grant rights with respect to Journal issues as a whole.
3. The right to use all or part of this article in future works of their own, such as lectures, press releases, reviews, text books, or reprint books.