Isocyanate-Polyol Resin as a Binder for Particleboard

In an effort to improve bond performance, a polymeric diphenylmethane diisocyanate (PMDI) was modified with various polyols as cross-linking and plasticizing agents, and the formulations were used in making particleboard. Internal bond (IB) improved 35 percent and modulus of rupture (MOR) 13.5 percent when polyethylene glycol with a molecular weight of 1000 (Peg 1000) was added to unmodified PMDI. Board properties improved most when the equivalent ratio of PMDI to Peg 1000 was 6:1 or 12:l — that is, when the formulation was 37 or 23 percent Peg 1000. Increasing the polyol molecular weight increased both board properties and resin fracture energy. When the polyol was changed from ethylene glycol (Eg) to Peg 1000 at a 12:l equivalent ratio, IB increased 30 percent and MOR 29 percent. Further increasing the polyol molecular weight by the use of Peg 1450 caused most properties to decrease slightly in comparison to those with Peg 1000; however, they were superior to those obtained with Eg. A trifunctional polyol (a triol) resulted in IB and MOR values similar to those with Peg 1000 but lower values for fracture toughness and work to maximum load, perhaps because cross-linking on the part of the triol caused a less flexible molecular structure. The triol in creased MOR 72.5 percent after a 2-hour boil, indicating that the durability of isocyanate resin might be enhanced by addition of triol.

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