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The Effects of Environmental Conditions on the Physical and Mechanical Properties of Medium Density Fibreboard
Thesis submitted in partial fulfilment of the requirements for the degree of Bachelor of Engineering (Systems Engineering). October 1996
Two types of medium density fibreboard (MDF), one a flooring grade MDF and the other a phenol formaldehyde bonded high density board were heat treated in a conventional hot press. The samples were then exposed over saturated salt solutions to seven relative humidities (RH), and to interior and exterior weathering. Samples were then tested for moisture content (MC), thickness swelling (TS), ultimate tensile strength (UTS), flexural stress, modulus of rupture (MOR) and modulus of elasticity (MOE).
Thickness swelling and moisture content were found to increase with increasing humidity for all board types. MOE, MOR, flexural stress and UTS all decreased with increasing relative humidity.
The heat treatment decreased thickness swelling and moisture content in the low humidity ranges, but had the opposite effect in the high humidity ranges. The decrease in MC may be due to a lowering of the number of moisture accessible sites while the increase at high humidities may be associated with thermal breakdown of the adhesive. MOR, Flexural Stress and UTS all decreased as a result of the heat treatment.
Scanning electron microscopy (SEM) was used in an attempt to rationalise changes in mechanical properties that occured at different relative humidities. Results suggested that weakining of the adhesive itself rather than breakdown of the fibre-adhesive bond was responsible for the lower strengths at high moisture contents.
Powder Coating of MDF using traditional powder coating methods was attempted, but was unsuccessful.
Acknowledgements
Above all I thank my supervisors, Dr. Philip Evans from the Forestry Department and Dr. Adrian Lowe from the Engineering Department, who have made this study possible. Their interest, knowledge, patience, and especially their `open door' policies to my untimely queries were greatly appreciated. To Darius Krivanek and Peter Beutell who each devoted many hours to the technical and workshop facets of this study. To Roger Heady for his patient assistance and tuition on the electron microscope. To Dr. Ross Cunningham and Christine Donnelly for their assistance in the statistical analysis. To the staff at Powder Coating Services and Mooseheads Pub for kindly allowing the use of their resources. I thank my family, friends, housemates, workmates and fellow engineers, who in this difficult year of study have shown support and understanding.