A binder comprising isocyanate droplets in water, wherein the isocyanate droplets have an average droplet size of 500 microns or less, and the isocyanate droplets have shells comprising a biopolymer or a reaction product of a biopolymer and isocyanate. The biopolymer may be a biopolymer nanoparticle or cooked and chemically modified starch. Optionally, the binder may also include urea. The substrate for the binder may be wood, another lignocellulosic material, or synthetic or natural fibers. In particular examples, the binder is used to make no added formaldehyde wood composites including particle board and MDF.