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Effects of MDI content on properties of thermally treated oriented strand board (OSB)

Direske, Martin, Bonigut, Juergen, Wenderdel, Christoph, Scheiding, Wolfram, Krug, Detlef
European journal of wood and wood products 2018 v.76 no.3 pp. 823-831
adsorption, boiling, desorption, equations, hygroscopicity, modulus of elasticity, modulus of rupture, oriented strandboards, sorption isotherms, temperature
The paper discusses the influence of methylene diphenyl diisocyanate (MDI) content on mechanical properties of thermally post-treated single-layered oriented strand boards (OSB). The OSB differed in adhesive content (3, 4 and 5%) and the high temperature (HT) level of the thermal modification (TM) (untreated, 160, 175 °C). To characterise the mechanical behaviour of the OSB, the modulus of rupture (MOR), modulus of elasticity (MOE), and internal bond (IB) of dry and boiled specimens were determined. In addition, the adsorption and desorption isotherms were investigated. The hygroscopic sorption isotherms were calculated according to the Hailwood-Horrobin equation. It was observed that the MOR and the IB of the post-treated OSB are significantly increased with higher MDI content. An increase of the MDI content from 3% up to 5% is not sufficient to compensate the loss of strength caused by TM. However, an increase of MDI-content of about 1% compensates the significant loss of IB of dry and boiled specimens. The MOE is not influenced by TM. With increased adhesive content, thermally treated and untreated specimens show slightly higher values. The thermal post-treatment of OSB alters the wood-water-interaction. The hygroscopicity is reduced. The higher the HT level, the lower is the sorption behaviour. It was also detected that a higher MDI content does not influence the hygroscopicity.