Oxidative Degradation of Cellulosic Fibers in Historical Textiles

Introduction

In chemical terms, oxidation expresses a loss of electrons or an increase in the oxidation state by a molecule, an atom, or an ion, where the oxidized substance loses an electron from the outer orbit of its atom's nucleus, and although its reactions are often related to oxides are formed from oxygen molecules. There are specific examples that include the transfer of that electron from an oxidized substance to a reduced one, and in both cases, oxidation and reduction express a change in the oxidation state of these substances, and both are half-reactions. For a change in the oxidation state to occur, the two halves must occur together (Phillips, et al., 2000; Hudlicky, 1990).

From the foregoing, we see that oxidation in chemical reactions may take place without the presence of oxygen, and the electrons that are released during the oxidation process - as mentioned above - must be acquired by another substance, and it happens that the oxidation number of the compound that loses electrons increases, and in the old concept of oxidation, the process of iron rusting occurs for example, and atmospheric pollutants from nitrogen and sulfur are oxidized to their oxides, while in the modern one, the oxidation of hydrogen H₂ occurs by losing electrons and giving it to fluorine F₂ to form hydrogen fluoride 2HF as examples of different oxidation concepts (Schüring, et al 1999).

In another concept, the oxidation state, the oxidation stage or the number of oxidation represents the degree of oxidation of an atom in a compound, or it is the electrical charge that an atom acquires if all its bonds with other elements are of the ionic bond type by 100%, So the increase in the oxidation state of an atom during a chemical reaction called oxidation, and its decrease is known as reduction, and these reactions include the transfer of electrons, and the acquisition of an atom of electrons is considered reduction, and the opposite is oxidation, where the positive charge increases or the negative charge decreases (Hudlicky, 1990).

Concerning the oxidation of dyes, inks (Used in the Young King Tut's collection) or colorants and the oxidation of their substrates such as cellulosic objects (figure 1)- which is half of the destructive role that we previously presented and is known as corrosion (oxidation and reduction). the most famous destructive mechanisms of these materials and their cellulosic substrates in general - it is the of Oxygen-induced oxidation and catalyzed by free metallic ions in the composition of them, which will be dealt with later and in detail (Banik, 1997; Kolar et al, 2007).

Figure 1.

Faded dyes, inks, and fibers on linen and wool tunic due to oxidation

(Istvan, 2009)

Oxidation Reaction

Textile materials (figure 2). including constituent fibers, can be subjected to degradation under the influence of various factors that occur during textile use. Degradation is the process of structural changes as a result of the physical or chemical transformation that occurs in polymer materials under the influence of external factors. The most common of these factors- For textiles- are light, high temperature, environmental conditions (moisture, microorganisms, UV radiation) and during the washing process using detergents, bleachers, or organic solvents) (Machnowski and Was - Gubała, 2021, p.1).

Figure 2.

The oldest textile fragment in the world – 5000 B C, Egypt

(Best Inventions of All Time – Chronological: Part I (Prehistory-1799), n.d.)