Page 126 - Handbook of Surface Improvement and Modification

8

Easy Surface Cleaning and

Stain Inhibition

8.1 METHODS AND MECHANISMS OF SURFACE CLEANING

Several important topics are discussed in this section, including
• cleanliness evaluation and better cleaning methods
• self-cleaning systems
• stain-resistant materials
• anti-graffiti coatings and graffiti removal
Presence of organic contaminants on various surfaces has a large impact on proper-
1
ties of materials and joints in aerospace, electronics, construction, etc. Wettability mea-
surements provide a convenient and rapid method for probing the outermost surface of a
1
material. High surface energy materials, such as metals, glass, and ceramics, are fre-
quently coated with a layer of organic molecules which reduce their surface free energy
and make their surfaces hydrophobic (contaminated material had a contact angle of 80 o
1
o
which was reduced to 30 after degreasing). The contact angle measurement is an easy
and sensitive technique to evaluate cleanliness. It should be taken into consideration that
the results of contact angle measurements will contradict achievements in the discussed
below stain-resistant and self-cleaning materials because their goals are reached by
1
obtaining hydrophobic surface. This shows that the definition of cleanliness depends on
circumstances − if related to degreasing (or cleaning), the removed surface contaminants
1
are likely be hydrophobic.
Industry involved in cleaning produced a large number of products which are used at
home, in public places, and industrial applications. Their common feature is that they have
to be discarded after they have done the job, which obviously results in environmental pol-
lution on a large scale and scores of methods to clean this pollution. The topic of this book
is not related to this subject but it is worth mentioning the contribution which aims at deal-
ing with contaminants right where they are formed. Rather than to dispose of contami-
nated cleaner, its regeneration process is performed in this contribution by adsorption-
2
coagulation and flocculation in place of formation. A treatment process was tested on
2
multiple recycling of acid and basic cleaning solutions. The microbiological analyses
using a resistant bacterial strain (Bacillus subtilis spores) showed that solutions regener-
ated up to 20 times maintained the same bactericidal efficiency as the original cleaning
2
2
solutions. The regenerated solutions allowed better surface wettability. This contribution
is cited as more valuable approach than discarding dirty cleaners to the waste stream
2
which is then subjected to the general cleaning methods.