STUDY OF THE MECHANISM OF DYEING PROTEIN FIBERS WITH COMPOSITE DYES BASED ON MULTIVALENT METAL SALTS

УДК 621.315.614.7.677.84

Abstract

This study investigates the mechanism of dyeing protein fibers using composite dyes based on salts of polyvalent metals and organomineral components derived from local raw materials. The research aims to develop import-substituting dyeing compositions and evaluate their physicochemical properties and effectiveness in textile processing. Protein fibers such as silk, wool, and blended fabrics were treated with composite dye systems involving aromatic compounds and metal salts (Ni, Cu, Fe, Co, etc.), forming stable colored complexes within the fiber structure.

Modern analytical methods, including IR spectroscopy, thermal analysis, and physicochemical testing, were employed to assess dye–fiber interactions and color fastness properties. The results demonstrate that the developed composite dyes provide high resistance to light, washing, organic solvents, and mechanical воздействия, comparable or superior to conventional synthetic dyes. The dyeing mechanism is explained by thermodynamic affinity, diffusion processes, and the formation of covalent and coordination bonds between the dye and fiber.

The findings confirm that the use of locally sourced composite dyes based on polyvalent metal salts is a promising approach for improving textile quality, reducing dependency on imported dyes, and enhancing the durability of coloration in protein-based fabrics.

Аннотация

В данной работе исследован механизм крашения белковых волокон композиционными красителями на основе солей поливалентных металлов с использованием органоминеральных компонентов, полученных из местного сырья. Целью исследования является разработка импортозамещающих красителей и изучение их физико-химических свойств в процессе окрашивания текстильных материалов.

Объектами исследования служили белковые волокна (шелк, шерсть, смесовые ткани), которые подвергались обработке композиционными системами, содержащими ароматические соединения и соли металлов (Ni, Cu, Fe, Co и др.), образующие устойчивые окрашенные комплексы внутри структуры волокна. Для анализа использованы современные методы, включая ИК-спектроскопию, термический анализ и методы оценки прочности окраски.

Установлено, что разработанные композиционные красители обеспечивают высокую устойчивость окраски к свету, стирке, воздействию органических растворителей и трению, не уступая традиционным синтетическим красителям. Механизм крашения объясняется термодинамическим сродством, диффузией красителя в волокно и образованием ковалентных и координационных связей между красителем и субстратом.

Полученные результаты подтверждают перспективность использования композиционных красителей на основе солей поливалентных металлов из местного сырья для повышения качества текстильной продукции и снижения зависимости от импортных красителей.

Keywords: protein fibers; composite dyes; polyvalent metal salts; dyeing mechanism; textile dyeing; organomineral compounds; silk fiber; wool fiber; color fastness; coordination compounds; diffusion process; thermodynamic affinity; covalent bonding; import substitution; local raw materials; dye–fiber interaction.

Ключевые слова: белковые волокна; композиционные красители; соли поливалентных металлов; механизм крашения; текстильное окрашивание; органоминеральные соединения; шелковое волокно; шерстяное волокно; прочность окраски; координационные соединения; диффузионный процесс; термодинамическое сродство; ковалентная связь; импортозамещение; местное сырьё; взаимодействие красителя с волокном.

Introduction

Uzbekistan is a major producer of protein-based textiles. At present, one of the main tasks facing domestic textile enterprises is improving the quality of manufactured products [1].

Synthetic dyes are used to impart various colors to fabrics. In the republic, there is no production of synthetic dyes used for dyeing synthetic and natural fibers, especially protein fibers and fabrics based on them.

It should be noted that there are enterprises in the republic producing fabrics based on protein fibers, such as JSC “Atlas”, “Yodgorlik”, and others, which manufacture a wide range of fabrics based on cotton, silk, wool, and blended fibers. One of them is adras fabric, consisting of 50% cotton and 50% silk, used for clothing production.

Dyeing of these fabrics is carried out using expensive synthetic dyes imported from abroad. In this regard, the development of import-substituting composite chemical dyes based on local raw materials and the study of their physicochemical properties in the process of dyeing protein fibers, as well as the creation of a new efficient dyeing technology, is an urgent task.

The aim of this study is to investigate the mechanism of the dyeing process of protein fibers using coloring composite materials based on salts of polyvalent metals with the use of organomineral ingredients derived from local raw materials.

Objects and Research Methods

The objects of study are protein fibers such as silk, wool, cotton, as well as resorcinol, γ-aminopropyltriethoxysilane, aromatic oxy- and amino-compounds, acids, alkalis, and salts of polyvalent metals (nickel, copper, iron, cobalt, manganese, tin, chromium).

To determine the quality of the developed coloring composite materials and dyed fibers, modern physicochemical analysis methods were used, including IR spectroscopy, thermal analysis methods (DTA, TGA), complexometry, pH-metry, and other standard analytical methods, as well as methods for evaluating the physicochemical and mechanical properties of textile products.

Results and Discussion

Coloring composite materials must provide coloration resistant to various physicochemical effects during use, such as exposure to hot water, steam, active chlorine, high temperatures, light, seawater, weather conditions, washing, ironing, and friction [2].

These properties are evaluated on a five-point scale, while light fastness is assessed on an eight-point scale. The set of requirements is determined by the purpose and method of production of the dyed material. In addition to resistance to various effects, coloring composite materials are also characterized by the uniformity of dyeing and the purity of their shade [3].

These dyes are obtained through a multistage chemical synthesis process from intermediate products, which in turn are produced from aromatic and heteroaromatic compounds [4].

For a number of years, the staff of the State Unitary Enterprise “Fan va Taraqqiyot” of Tashkent State Technical University have been conducting research on the development of effective dyeing compositions based on local raw materials for coloring textile fibers and fabrics.

Protein fibers include silk, cotton, linen, and wool. Silk differs from other natural fibers (cotton, linen, wool) by the absence of a cellular structure. It shows significant similarity to artificial and synthetic fibers.

A thread separated from the mulberry silkworm cocoon consists of two adjacent fibroin filaments, coated on the outside and bonded together by a silk adhesive—sericin. Silk fiber freed from sericin has the appearance of a homogeneous, structureless filament. Through chemical and mechanical воздействия (crushing, friction), longitudinal splitting of the fiber into finer fibers—fibrils—can be achieved.

In addition to fibroin and sericin—substances of protein nature—the cocoon filament contains a small amount of compounds extractable with ether and ethyl alcohol. Silk fiber, which has a natural color (yellow, green, etc.), contains a small amount of coloring substances. After burning, a small amount of ash remains. The content of all these substances is not constant and varies widely depending on the type of silkworm, as well as feeding conditions and environment. Thus, the cocoon filament may contain 70–75% fibroin, 25–30% sericin, 0.5–0.6% ether-extractable substances, 1.5–2.5% alcohol-extractable substances, and 1–1.7% mineral substances.

Due to its amphoteric properties and ability to fix dyes through adsorption, natural silk can be dyed with dyes of many classes: acid, basic, direct, reactive, vat, and chrome dyes. The most widely used in fabric dyeing are direct, acid, and reactive dyes. The transfer of dye from the dyeing solution into the fiber during the dyeing process is explained by two phenomena [5].

First, the free energy of the dye molecule (thermodynamic potential) in the solution after fixation by active centers of the polymer is significantly higher than in the fiber. According to the laws of thermodynamics, spontaneous processes, including the dyeing of textile fibers, always proceed toward a decrease in free energy (a reduction in thermodynamic potential). Therefore, dyeing is accompanied by the accumulation of dye in the fiber and a decrease in its concentration in the dye solution. The process continues until the potentials of the dye in the fiber and in the solution are equalized (equilibrium) [6].

The higher the affinity of a given dye for the fiber, the faster the dye transfer process occurs and, as a rule, the stronger the dye–fiber bond. Affinity is a convenient comparative characteristic of different dyes with respect to a specific fiber, or of one dye relative to different fibers or dyeing conditions.

Second, the reason for dye transfer from the solution to the fiber lies in the difference in dye concentration between the fiber and the solution. Seeking to equalize concentrations in the two phases—fiber and solution—the dye crosses the phase boundary and fills the fiber until equilibrium is reached. When a dye molecule enters the fiber, it does not remain on the surface layer but tends to penetrate inside—diffusing into the substrate. Dyes diffuse either by moving through pores in the fiber filled with solution or due to segmental mobility of macromolecules of thermoplastic polymers. The concentration gradient accelerates diffusion, while affinity slows it down, since dye molecules interacting with active centers of the fiber hinder diffusion. To overcome this retardation caused by affinity, diffusion must be activated. This is achieved by changing dyeing conditions such as temperature, pH of the dye bath, and by introducing various textile auxiliaries (TAs) [7].

To study the properties of powdered dyeing composite materials based on local raw materials, laboratory experiments were conducted, the results of which are presented in Table 1. As an example, specific results obtained by us using a new method of dyeing fabrics based on protein fibers and viscose fabric are provided.

Table 1. Fastness of dyes on materials dyed with coloring composite materials

As can be seen from the table, the colorations obtained using mineral dye compositions, in comparison with those obtained using synthetic (direct) dyes, are characterized by high fastness to wet treatments (5 points), to the action of organic solvents (dry cleaning) (5 points), to rubbing (4–5 points), and to light (4–5 points).

Studies on fiber dyeing by introducing dyes into the macromolecular structure of fibrous polymers have mainly been conducted in three directions:

1. Introduction, by various methods, of aromatic amines into the composition of the fibrous polymer, capable of undergoing diazotization and coupling with azo components, resulting in the formation of color.
2. Introduction of active groups into the polymer macromolecule that are capable of interacting with the functional groups of dyes.
3. Synthesis of dyes containing atoms or groups that are reactive toward the functional groups of the fibrous polymer.

Treatment of protein-based fabrics with an aqueous solution of γ-aminopropyltriethoxysilane leads to the formation of aminated protein fabric. Subsequent treatment with an aqueous solution containing a salt of a polyvalent metal, an aromatic oxy compound, sodium nitrite, and an acid results in the formation of dinitrosoresorcinol, which readily forms colored metal complexes with cations of polyvalent metals [8].

Resorcinol, reacting with nitrous acid, forms active azo compounds, which in the presence of salts of polyvalent metals result in the formation of a dye.

At the same time, strong covalent and coordination bonds are formed between the polymer substrate and the dyeing compositions.

The fastness of coloration to various physicochemical effects depends on the nature of the dye–substrate bond. All dyes used in the dyeing of fibrous materials are retained on the fiber by intermolecular interaction forces of four types:

1. hydrogen bonds,

2. polar and nonpolar Van der Waals forces,
3. ionic forces,
4. coordination forces.

Conclusion

The conducted research demonstrates that composite dyes based on salts of polyvalent metals are effective for dyeing protein fibers and significantly improve the quality of coloration. The dyeing mechanism is governed by thermodynamic affinity, diffusion processes, and the formation of stable covalent and coordination bonds between the dye molecules and the fiber structure. These interactions ensure deep penetration of the dye into the fiber and strong fixation within the polymer matrix.

Experimental results confirm that the obtained colorations exhibit high resistance to light, washing, rubbing, and the action of organic solvents, which is mainly due to the high bond dissociation energy of covalent bonds (50–100 kcal/mol). Compared with conventional synthetic dyes, the developed composite systems provide equal or higher fastness properties.

Thus, the use of locally sourced organomineral components and polyvalent metal salts represents a promising direction for the development of efficient, environmentally and economically sustainable, import-substituting dyeing technologies for protein-based textile materials.

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