Page 14 - Handbook of Surface Improvement and Modification

2.1 Methods and mechanisms of protection 9

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increased from 5 to 10 wt%. Addition of nanoparticles increased hardness of coating
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resulting in a better scratch resistance.
A cryogenic treatment was used to improve adhesive strength and scratch resistance
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of fluorocarbon thin films deposited as protective coatings. The films rich in fluorine
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have low surface tension which affects their adhesion strength to substrate materials. This
may cause cracking or peeling off the film from the substrate resulting in low scratch
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resistance. The adhesion strength between silicon substrates and fluorocarbon thin films
deposited using radio frequency magnetron sputtering were improved via a remarkably
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simple, flexible and nondestructive cryogenic treatment method. The cryogenic treatment
involved keeping sample in liquid nitrogen followed by bringing it to room temperature. 9
The microstructure, hardness, adhesion strength, and scratch resistance of fluorocarbon
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thin films were significantly influenced by the cryogenic treatment. Highly crosslinked
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fluorocarbon thin films were obtained by this treatment.
An improvement in a scratch resistance was observed in ASA on annealing at 140°C
whereas a noticeable drop in scratch resistance was found in the case of ABS under the
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same condition. Significant change in surface morphology has been observed in ASA
due to possible retraction of the SAN matrix surrounding the rubber particles whereas
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ABS does show very little change (Figure 2.7).
Thermal aging had a significant effect on the scratch behavior of hydrogenated
nitrile butadiene rubber with scratch resistance of HNBR showing a dramatic decline as
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the aging process was progressing.
o
The effect of heat treatment at 85 C on microhardness and scratch resistance of
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polymethylmethacrylate has be ascertained. Microhardness (Vickers hardness) increased
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by 5, 9.5, and 14.5% with treatment duration (1, 2, 3 h) as did scratch resistance. The
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scratch width and depth decreased with the duration of treatment increase. The critical
normal load corresponding to the surface crack decrease with the increase of heat duration
o
time (from 7 to 30 days at 90 C)
in polymethylmethacrylate expo-
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sures. The longer the thermal
aging, the shorter the onset time of
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the surface crack.
Polymer blending and inter-
penetrating network formation are
common methods of improvement
of physicomechanical properties
also including surface proper-
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ties. Low-molecular-weight
polymethylmethacrylate was mis-
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cible with polycarbonate. The
components polycarbonate/
polymethylmethacrylate blend
migrated when the blend was
Figure 2.8. Relationship between poly(methyl methacrylate-co-phe-
nyl methacrylate) copolymer content in the blend with polycarbon- exposed to a temperature gradient
ate and Vickers hardness. [Adapted, by permission, from Seong, and polymethylmethacrylate was
D-W; Yeo, J-S; Hwang, S-H, J. Ind. Eng. Chem., 36, 251-4, 2016.] found on the high temperature