Abstract: A three stages process for the preparation of solid thermoplastic compositions based on polyvinyl alcohol comprising the mixing in a mixer of a first charge, comprising the polyvinyl alcohol and solid plasticizers, with a second charge constituted by one or more hydroxylated organic compounds selected from glycols, glycol ethers and alkanolamines and at least a salt of an alkaline and/or alkaline earth metal, and a third charge containing at least one or more solid polyhydroxylated alcohols, glycols and glycolic ethers, liquid alkanolamines, organic or inorganic mineral acids, hydrated inorganic salts, polymers having a low molecular weight, stabilizers and possible mineral charges, is described.