Graduate Thesis Or Dissertation
 

The effects of diisocyanate-polyol resins on the properties of particleboard.

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1j92g938j

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  • The ability of the resin to deform plastically can be an important factor when considering the mechanical properties of particleboard. Between resin droplets there exists an unbonded region that forms the surface for a crack. When particleboard is deformed stress concentrations develop at the crack tips in the voids. A resin that deforms plastically may help to redistribute the stress. Through this process energy would be absorbed and a stronger board realized. Urea- and phenol-formaldehyde resins currently used in the particleboard industry are believed to be brittle and unable to perform in this manner. In addition, urea-bonded particleboard releases formaldehyde, which has been increasingly under attack as a health hazard, whereas, isocyanate bonded boards have no record of toxic emissions. This research is designed to utilize agents for crosslinking and plasticizing to develop diisocyanate-polyol resins of varying mechanical properties, make boards with these resins and establish relationships between the resin and board properties. The resin components used in this study include a polymeric diisocyanate (PMDI), a triol (Triol), ethylene glycol (Eg), and three polyethylene glycols with molecular weights of 1000, 1450 and 3200 (Peg 1000, Peg 1450 and Peg 3200). The PMDI was mixed in varying proportions with one or more of the polyols to make a resin to produce particleboard. The internal bond, modulus of rupture (dry and boiled), modulus of elasticity, work to maximum load, linear expansion, fracture toughness and thickness swell of the particleboard were tested. The board properties resulting from the various resins were compared to one another and to the resin fracture energy. Improvements of up to 26 percent for internal bond and nine percent for modulus of rupture were obtained when Peg 1000 was added to unmodified PMDI. The greatest increase in properties occurred when the PMDI/Peg 1000 equivalent ratio was 6/1 or 12/1. Increasing the polyol molecular weight, while maintaining a constant PMDI/polyol equivalent ratio of 12/1, increased the board properties. When the polyol was changed from Eg to Peg 1000, internal bond increased 30 percent and modulus of rupture increased 29 percent. Using Peg 1450 to further increase the polyol molecular weight caused a slight decrease in most properties in comparison to Peg 1000, however, they were superior to those obtained when Eg was used as the polyol component. The resin fracture energy increased with increasing polyol molecular weight. Combinations of three polyols, Eg, Peg 1000 and Triol, at a constant PMDI/polyol equivalent ratio of 12/1 were examined and in some cases more than one polyol as the polyol component yielded better board properties than a single polyol. Crosslinking with Triol and plasticizing with Peg 1000 generally improved the strength characteristics of the board.
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