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CHAPTER 2
LITERATURE REVIEW
This chapter consists of information which related to the study such as the theory and
method that had been used by the others in order to investigate the corrosion
behavior of tool steel in tannic acids. This information is important because it will
lead to this study applicability until complete. In this research, it also the best way to
guide and face the problem encountered during the completion of this study.
2.1 Definition of Tannins
The term “tannins” is no longer strange in chemistry field. It is comes from the
ancient Celtic word for oak which is a typical source of tannins for leather making
(Bisanda et al., 2003). According to Khanbabaee and Van Ree (2001), the name
“tannin” is derived from the French word „Tanin‟ which means a tanning substance
that used for a range of natural polyphenols. The ancient society had been using
tannins to convert animal skin to form leather which are able to interact and
precipitate proteins including the protein found in animal skin (Hagerman, 2002). In
nature, the tannins are found worldwide in many different families of the higher
plants such as in chestnut, pine and oak wood.
Tannins are secondary metabolites that widely found in plant kingdom and it produce
by condensation of simple phenolics (Chavan et al., 2001). Although tannins
themselves are secondary phenolic metabolites, their chemical reactivities and
biological activities have distinguished them from other plant of secondary phenolics
(Hagerman, 2002).
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