Compositions including composites of polyvinyl chloride (PVC) and nanoparticles are disclosed. A wood-polymer composite using the PVC-nanoparticle composite as a matrix also is disclosed. The nanoparticle filler is dispersed throughout the PVC matrix by blending the nanoparticles with a mixture of PVC particles that have been pre-heated to a temperature at or above a fusion point of the PVC, thereby fusing the PVC particles prior to the addition of the nanoparticles to the matrix. Also disclosed are methods of forming the composite compositions. The composite compositions can be used to replace wood boards.