Dimensional stability and irreversible thickness swell of thermally treated oriented strandboards (OSB)

Abstract

This paper discusses thickness swell and irreversible thickness swell properties after immersion in water for 24, 48, 96 and 168 h, changes in equilibrium moisture content (EMC) and determination of dimensional changes associated with changes in relative humidity of laboratory-made methylene diphenyl diisocyanate (MDI)-bonded oriented strandboards (OSB). It was observed that thermal post-treatment of said OSB had a positive effect on the above mentioned properties. As far as thickness swell and irreversible thickness swell are concerned, it could be shown that the thermally modified variants generally performed better, i.e. lower values than the respective untreated ones for all four immersion periods and MDI dosages of 3.0, 4.0 und 5.0 %. It was furthermore noticeable that the swelling potential was not exhausted after immersion for 24 h and a prolonged immersion period led to significant increases in respective thickness swelling values. The EMC was decreased and the determination of dimensional changes associated with changes in relative humidity showed that thermally post-treated OSB displayed lower thickness changes when “drying“(from 65 to 30 % relative humidity; RH) as well as when “moistening“(from 65 to 85 % RH) than the untreated controls. For all of the above mentioned properties it can be concluded that the influence of the post-treatment temperature proved to be greater than the reduction of the hydrophobing agent from 1.0 to 0 %.