Filled polyurethane composites with lightweight fillers

A method of making a polyurethane composite comprising:

• (a) mixing
• (1) one or more isocyanates selected from the group consisting of diisocyanates, polyisocyanates, and mixtures thereof,
• (2) one or more polyols,
• (3) 35% to 75% by weight, based on the total weight of the mixture, of a particulate filler having a bulk density of 1 g/cm3 or greater, and
• (4) 4% to 20% by weight, based on the total weight of the mixture, of a lightweight filler having a bulk density of from 0.01 g/cm3 to less than 1 g/cm3 to form a mixture, wherein the lightweight filler is chosen from expanded volcanic ash, expanded perlite, pumicite, expanded vermiculite, expanded clay, foamed glass, soybean hulls, rice hulls, seeds, seed husks, chopped straw, expanded polystyrene beads, scoria, and combinations thereof;
• (b) allowing the one or more isocyanates and the one or more polyols to react in the presence of the particulate filler and the lightweight filler to form the polyurethane composite having
• (1) a density of from 2 lb/ft3 to 37 lb/ft3, and
• (2) flexural strength of 1000 psi or greater as measured by ASTM C1185-08 (2012), and
• wherein the mixture is free of a blowing or foaming agent other than water.