Page 17 - Handbook of Surface Improvement and Modification

12 Scratch and Mar Resistance

Figure 2.11. Critical points of scratch damage modes of polymethylmethacrylate. [Adapted, by permission, from
An, J; Kang, B-H; Choi, B-H; Kim, H-J, Tribology Intl., 77, 32-42, 2014.]
tone surface. The depth of dimples was 2, 12 and 21 μm and the dimple density was 10, 30
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and 48%. A 2 μm thick diamond-like carbon film was deposited on the textured poly-
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etheretherketone surface. The diamond-like carbon film-coated polyetheretherketone
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with shallow dimples and a low dimple density significantly reduced wear and friction.
The automatic detection and characterisation of multiple scratches on textured poly-
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meric surfaces was developed. Images were captured by camera and analyzed by soft-
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ware which was able to distinguish scratch from textured pattern. More information on
the effect of texturing on scratch visibility and detection can be found elsewhere. 17,19
Polymethylmethacrylate is toughened by blending with elastomers including acrylic
rubbers. The addition of acrylic rubbers to polymethylmethacrylate deteriorates its scratch
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properties. Three scratch damage modes were identified including mar/plowing, whiten-
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ing, and cutting (Figure 2.11). The difference between the first critical loads (damage to
the surface) observed in flow and transverse directions was larger than that between the
second critical loads (damage to the bulk) in these directions because elongated rubber
particles affected only the material surface and the first critical load was related to the sur-
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face morphology determined by the presence of elongated rubber particles. The size of
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parabolic cracks in the flow direction was smaller than in the transverse direction. The
injection speed, holding pressure, and viscosity should be considered in the development
of a material with high scratch resistance because they control distribution and orientation
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of rubber particles.
A noticeable drop in scratch resistance was found in ASA containing 100 nm rubber
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particles when compared to ASA containing 1 μm rubber particles. Butadiene rubber
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gave better scratch resistance than butyl-acrylate rubber.
A microfibrillated cellulose and nanocrystalline cellulose were used in a waterborne
acrylate/polyurethane-based wood coatings to improve the mechanical resistance of
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coated wood surfaces. The scratch resistance improved with increasing nanocellulose
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addition. The microfibrillated cellulose was more effective than the nanocrystalline cel-