Development of a bilayer coating to improve the adhesion between stainless steel and in situ-polymerized poly(methyl methacrylate)

Abstract

A bilayer coating was developed that may be applied over a stainless steel surface to enhance the adhesive strength with in situ-polymerized poly(methyl methacrylate). The first layer was an epoxy based on diglycidyl ether of bisphenol A (DGEBA) crosslinked with N-(2-aminoethyl)-3- aminopropyltrimethoxysilane (AEAPS). A prereaction and a fast cure were needed to avoid phase separation after the dip coating process. The second layer constituted of an organic-inorganic hybrid formulation synthesized by a sol-gel process. It was based on 2-hydroxyethylmethacrylate (HEMA), 3- methacryloxypropyltrimethoxysilane (MPMS), and tetraethoxysilane (TEPS). This layer provided silanol groups to react with the methoxysilane groups of the first layer and methacrylate groups to produce covalent bonds during the methyl methacrylate polymerization. Stainless steel plaques were successively coated with both layers (about 700 nm per layer), using a dip coating process. Both coated and uncoated plaques were bonded with a 0.55-mm thickness of a two-parts PMMA cement, using the standard geometry to perform single lap-shear strength tests. The average lap-shear strength increased from 3.4 ±1.5 MPa for the uncoated metals to 9.7 ±1.5 MPa for the plaques coated with the bilayer system.