Nylon 11/silica nanocomposite coatings applied by the HVOF process. II. Mechanical and barrier properties

Nylon 11 coatings filled with nominal 0-15 vol % of nanosized silica or car bon black were produced using the high velocity oxy-fuel combustion spray p rocess. The scratch and sliding wear resistance, mechanical, and barrier pr operties of nanocomposite coatings were measured. The effect of powder init ial size, filler content, filler chemistry, coating microstructure, and mor phology were evaluated. Improvements of up to 35% in scratch and 67% in wea r resistance were obtained for coatings with nominal 15 vol % contents of h ydrophobic silica or carbon black, respectively, relative to unfilled coati ngs. This increase appeared to be primarily attributable to filler addition and increased matrix crystallinity. Particle surface chemistry, distributi on, and dispersion also contributed to the differences in coating scratch a nd wear performance. Reinforcement of the polymer matrix resulted in increa ses of up to 205% in the glass storage modulus of nanocomposite coatings. T his increase was shown to be a function of both the surface chemistry and a mount of reinforcement. The storage modulus of nanocomposite coatings at te mperatures above the glass transition temperature was higher than that of u nfilled coatings by up to 195%, depending primarily on the particle size of the starting polymer powder. Results also showed that the water vapor tran smission rate through nanoreinforced coatings decreased by up to 50% compar ed with pure polymer coatings. The aqueous permeability of coatings produce d from smaller particle size polymers (D-30) was lower than the permeabilit y of coatings produced from larger particles because of the lower porositie s and higher densities achieved in D-30 coatings. (C) 2000 John Wiley & Son s, Inc.