Some Studies of Sawdust-Synthetic Resin Combinations for Hardboard Manufacture

The development of an experimental technique for the laboratory production of small test specimens of sawdust-synthetic resin boards using untreated sawdust and dry synthetic resin powders is described and the results of exploratory tests showing the effect of a number of factors on the quality of the final product are given. The examination of the exploratory test samples made the importance of certain factors clear, particularly the requirement of high pressing temperatures to obtain stability. Indications were that temperatures of 430?F. to 440?F. at 500 psi and 10 percent resin content approached the practical maximum if a tendency to the development of burns in the board is to be avoided. There were also strong indications that extension of the heating time beyond that necessary to cure, the resin was needed to obtain high stability, and 15 minutes pressing appeared to be the minimum effective period. The most favorable resin content for the medium grade of sawdust used was in the vicinity of 10 percent, and little improvement in properties occurred with higher resin content when the moisture content was 10 percent or higher. Pressing at 500 psi at 400?F, or more caused a considerable increase in density as compared with the original wood, and at the same time insured intimate contact between particles and effective use of the resin. Moisture content appeared most important in its effect on plasticity, and at 500 psi moisture contents significantly lower than 10 percent were apparently insufficient to ensure good contact between sawdust particles, and specimens were lower in density and strength. It was found that particle size of the solid resin was very important and results generally were strongly in favor of a resin particle size passing a 72-mesh sieve, which was the minimum grade tested.

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