Poly(Methyl Methacrylate) Coatings Containing Flame Retardant Additives from Suspensions in Water-2-Propanol

A dip-coating technique is designed for deposition of poly(methyl methacrylate) (PMMA) from water/2-propanol mixture, avoiding the use of traditional toxic solvents. Solutions of PMMA macromolecules with high molecular weight (M_W) are obtained for a water/2-propanol ratio of 0.15-0.33 and the solubilization mechanism is discussed. The ability to use concentrated PMMA solutions and high M_W of the polymer are the key factors for the successful dip coating deposition. The coating mass for 10 g L^-1 polymer solutions shows a maximum at a water/2-propanol ratio of 0.25. The deposition yield increases with the polymer concentration increase and with an increasing number of the deposited layers. PMMA deposits protect stainless steel from aqueous corrosion. The coating technique allows for the fabrication of composite coatings, containing flame-retardant materials (FRMs), such as commercial halloysite, huntite, hydrotalcite, and synthesized Al(OH)₃, in the PMMA matrix. The FRM content in the coatings is modified by variation of the FRM content in colloidal suspensions. A fundamentally new method is developed, which is based on the salting out aided dispersive extraction of Al(OH)₃ from the aqueous synthesis medium to 2-propanol. It is based on the use of hexadecylphosphonic acid molecules as extractors. The method offers advantages of reduced agglomeration.