Scratch behavior of nanoparticle Al₂O₃‐filled gelatin films

Abstract Nanoscale alumina/protein gel composite films with 10–50 wt% filler were subjected to scratch testing and compared to micron‐scale alumina/protein gel composites. Atomic force microscopy (AFM) was employed to examine the width, depth, and morphology of the as‐produced scratches. The results show that the scratch depth in gelatin films and the tearing within the scratch decrease dramatically with the addition of the nanoscale (average particle size, 13 nm) alumina fillers. It was found that refining the particle size distribution of the Al₂O₃ powder (average particle size, 10 nm, with no particles larger than 70 nm) further reduced the scratch depth and width, while improving the dimensional integrity and surface roughness of the nanocomposites. Aging of the gelatin films improved the intrinsic scratch resistance of both filled and unfilled gelatin films. In comparison, micron‐size Al₂O₃ filler not only increased the scratch width, but also resulted in poor particle dispersion and low transparency of the films. The optical clarity of the nanofilled composites was much higher than that of the composites with micron‐size filler.