Analysis of processes operative within plywood during hot pressing Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/v692t813b

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  • In plywood manufacture, the interaction of wood with resin during hot pressing is responsible for the development of glue bond strength and hence panel quality. In this study, temperature and vapor pressure distributions and compaction of laminates were measured during pressing. Analysis of these factors emphasized boards formed under conventional (standard) conditions. However, some laminates were also studied with modified veneer moisture contents and platen pressures. By analysing data generated from laminates during pressing in the laboratory, the nature of interdepencence between heat transfer, vapor pressure accumulation and board compaction and how they are affected by veneer moisture content and platen pressure were considered. Complementary to the above work, the rate of strength development of phenol-formaldehyde resin forming a bond between wood wafers was determined. Bonds were formed under a range of steady-state temperatures and immediately tested in shear mode. Curves of bond strength versus pressing time were derived for each of the eight temperatures used. The relationship between rate of bond strength development, temperature and pressing time was quantified. At elevated temperatures very rapid resin curing was observed compared to that at lower temperatures. Open assembly time, resin pot life and wood wafer characteristics did not have a significant effects on the rate of curing of the resin under the range of conditions used in this project. The data generated from both experiments were combined to derive a model for predicting glue bond strength development at various locations in the laminate during hot pressing. The principle for the construction of the model is described as well as factors which should be accounted for in future refinements. Quantitive analysis of the interaction of these variables will aid in optimising the manufacture of plywood. The use of high MC veneers and selection of appropriate pressing variables depends upon such analysis. The development of new materials and evaluation of new adhesive systems are longer term goals.
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