The growing demand for structural composite wood panels has created an opportunity for novel cost effective binder systems. Recently, much data has been published extolling the virtues of isocyanates (PMDI) as binders for composite wood panels intended for exterior applications. To date, there are two main drawbacks which inhibit the wide spread use of PMDI as binders: 1) generally, isocyanates are more expensive than the commonly used formaldehyde binder systems and 2) isocyanates adhere strongly to the caul plate during the pressing cycle. To overcome this sticking problem, release agents are necessary which increases the overall cost of an isocyanate binder system. This study was undertaken to investigate the cost/performance of isocyanate binder systems which incorporate significant levels of low cost reactive diluents. Several binder systems were evaluated which were cost/performance effective when compared to phenol-formaldehyde (exterior) and urea-formaldehyde (interior) binders for composite wood panels.Laboratory studies have demonstrated that propylene carbonate (PC) is one such effective diluent in conjunction with isocyanates. The data indicates that acceptable composite wood panels, both exterior and interior grade, can be pro-This paper was presented at The Downloaded from 207 duced even when 30% of the isocyanate is replaced by propylene carbonate. Economical analyses indicate that the 70% PMDI/30% PC binder system offers cost advantages over 7% phenol-formaldehyde (PF) or 9% urea-formaldehyde (UF) binder systems.